Innovative strategies to enhance MSCs efficacy in acute kidney injury (Review)

Abstract

Acute kidney injury (AKI) remains a significant clinical challenge, characterized by rapid kidney dysfunction with potential progression to chronic kidney disease. Mesenchymal stem cells (MSCs) offer promising therapeutic potential due to their regenerative, immunomodulatory and anti-inflammatory capabilities. Despite these advantages, clinical translation is hampered by low MSCs retention, limited cell survival and suboptimal secretion of therapeutic factors in injured renal tissues. Recent research efforts have introduced innovative strategies to optimize MSCs effectiveness, including various preconditioning approaches (hypoxia, chemical/drug-based and biological cytokines), advanced three-dimensional cell culture methods (hydrogels and spheroids), genetic modification techniques and improved delivery routes. The present review summarizes current advancements, underlying mechanisms and therapeutic outcomes associated with these novel strategies to enhance MSCs efficacy in AKI, highlighting their clinical potential and guiding future translational research directions.

1. Introduction

Acute kidney injury (AKI) is a prevalent clinical condition characterized by a rapid elevation in serum creatinine levels and/or reduced urine output, resulting from various factors such as renal ischemia, sepsis, or drug toxicity (1,2). Global data suggests ~13.3 million individuals experience AKI annually, with a rising trend (3). In neonates, AKI is observed in one-third of infants and associated with increased risk of mortality (4). Besides its acute effects, AKI can advance to chronic kidney disease (CKD) and end-stage kidney disease, necessitating kidney transplantation or replacement therapy (5-9). These outcomes not only diminish patients' quality of life but also impose substantial financial strain on families and strain public healthcare systems. Currently, AKI management primarily involves supportive and preventive measures, lacking targeted pharmacological treatments (10,11). Moreover, due to AKI often co-occurring with conditions such as heart failure, hypoxic ischemic encephalopathy and sepsis, patients commonly receive multiple medications concurrently, heightening the risk of adverse drug interactions. Therefore, there is a critical demand for developing safer and more efficient approaches to manage and impede AKI progression.

Mesenchymal stem cells (MSCs) have garnered considerable attention for their potential in treating AKI due to their multipotency, robust self-renewal and ability to differentiate into various cell types (12,13). Derived from sources such as bone marrow, adipose tissue and umbilical cord blood, MSCs secrete a diverse array of bioactive molecules, including cytokines, chemokines, growth factors and microvesicles, which collectively promote cell proliferation, inhibit apoptosis, enhance angiogenesis, facilitate tissue repair, modulate immune responses and prevent fibrosis (14-18). In addition to these paracrine effects, MSC-derived extracellular vesicles serve as promising carriers for drug delivery, further expanding their therapeutic utility (19,20). Previous studies have also uncovered a novel mechanism whereby MSCs transfer healthy mitochondria to injured cells via tunneling nanotubes (21-23), thereby boosting cellular energy metabolism and contributing to tissue repair (24,25). The present review summarized the methods by which MSCs repair damaged cells in AKI (Fig. 1). Despite these promising attributes, clinical applications of MSCs in AKI are challenged by issues such as low cell retention, limited survival and suboptimal secretion of bioactive factors (26,27). Consequently, researchers are investigating innovative strategies, such as preconditioning techniques, optimized cell culture protocols, improved delivery methods, to overcome these limitations and enhance the efficacy of MSC-based therapies for AKI (28,29). The present review summarized these novel strategies and their underlying mechanisms in treating AKI.

Figure 1.

Mechanisms underlying MSC-mediated renal repair in AKI. MSCs derived from various sources and facilitate renal repair through multiple intercellular communication pathways. These include (1) mitochondrial transfer via TNTs, (2) direct cell fusion, (3) secretion of extracellular vesicles such as exosomes and microvesicles containing miRNA, cytokines, mitochondria and therapeutic drugs and (4) gap junction-mediated transfer of signaling molecules via connexins. These mechanisms collectively contribute to promoting renal progenitor/stem cell activation, reducing apoptosis of tubular epithelial cells, shifting macrophage polarization from the pro-inflammatory M1 to anti-inflammatory M2 phenotype and inhibiting T-cell and dendritic cell-mediated immune responses. Consequently, MSCs markedly enhance renal regeneration, facilitating the repair and functional recovery of injured kidneys in AKI. MSCs, mesenchymal stem cells; AKI, acute kidney injury; TNTs, tunneling nanotubes; BMSCs, bone mesenchymal stem cells; ADMSCs, adipose-derived mesenchymal stem cells; hpMSCs, human placenta-derived mesenchymal stem cells; WJMSCs, Wharton's jelly-derived mesenchymal stem cells; UCMSCs, umbilical cord mesenchymal stem cells.

2. Strategies to optimize the therapeutic potential of MSCs

Recent advances in MSCs biology and bioengineering have led to new strategies to overcome limitations of MSC-based therapies. As shown in Fig. 2, both extracellular and intracellular strategies have been employed to enhance the therapeutic potential of MSCs. Extracellular approaches include physical preconditioning (such as hypoxic culture and mechanical stimulation), chemical or drug-based preconditioning, biological stimulation with cytokines or hormones and cell-to-cell co-culture. Interestingly, 3D culture (hydrogels and spheroid formation) help recreate a more physiologically relevant microenvironment. On the intracellular level, genetic modification can further optimize MSCs functionality. Moreover, optimizing MSCs administration and selecting the suitable source of MSCs are also efficacies strategies.

Figure 2.

Different preconditioned MSCs strategies. This figure summarizes the current preconditioned methods for MSCs. These strategies include changing the culture environment, drugs treatment, chemical stimulation, biological compounds preconditioning, cell-to-cell coculture and genetic modification, all aimed at enhancing their biological characteristics and therapeutic effects. MSCs, mesenchymal stem cells.

Extracellular strategies

Physical preconditioning

Hypoxia

Unlike the standard cell culture environment with regular oxygen levels (21%), transplanted MSCs face a hypoxic microenvironment in injured tissues. Culturing MSCs under hypoxic conditions enhance the function of MSCs by increasing proliferation, survival, homing, differentiation and paracrine activities (30-33), which may enhance their therapeutic potential in treatment of AKI.

Hypoxic preconditioning of MSCs has shown promising results in the treatment of AKI. Various oxygen concentrations have been tested for preconditioning MSCs, with different sources of MSCs and animal models. MSCs preconditioned under low oxygen conditions (1% O₂, 5% O₂ and CoCl₂) contribute markedly to kidney function restoration; 1% O₂-preconditioned human adipose-derived MSCs (hADMSCs) in rats with ischemia-reperfusion injury (IRI) showed improvements in apoptosis, enhanced anti-oxidative capacity and increased vascularization, leading to overall renal function improvement (34). Furthermore, 1% O₂-preconditioned hADMSCs showed enhanced immunomodulatory effects, improved angiogenesis and reduced oxidative stress, leading to improved renal preservation (35). Additionally, 1% O₂-preconditioned human bone marrow MSCs led to a marked renal function restoration in IRI rat models (36).

Notably, higher oxygen concentrations, such as 5% O₂, also provided beneficial effects. A study reported that hypoxic preconditioning of human umbilical cord MSCs (hUCMSCs) with 5% O₂ in a gentamicin-induced acute renal failure rat model led to increased expression of hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), integrins and stromal-derived factor-1, all of which ameliorated renal function (37). Moreover, a study showed that 5% O₂-preconditioned AD-MSCs in mice with IRI demonstrated an increase in EVs particle number and protein concentrations, which reduced oxidative reactions and protected kidney function (38). Similarly, rat BMSCs exposed to CoCl₂, which mimics the hypoxic environment, showed enhanced hypoxia-inducible factor 1 (HIF-1) and C-X-C chemokine receptor type 4 (CXCR4) expression, improved migration and prolonged retention, contributing to improved kidney preservation in IRI (39).

These findings highlight that hypoxic preconditioning is a potent strategy for optimizing MSCs-based therapies in AKI. The enhancement of key pathways such as angiogenesis, anti-oxidative mechanisms and immunomodulatory effects, along with improved cellular retention and migration, makes hypoxia preconditioned MSCs a promising candidate for clinical applications in AKI treatment. However, it is important to note that prolonged or excessive exposure to hypoxia may have a negative impact on cellular metabolism and proliferation, leading to unstable cell function or inducing apoptosis. The present review summarized the role of hypoxia pretreated MSCs in the preclinical model of AKI (Table I) (34-41).

Table I.

The role of hypoxia pretreated MSCs in preclinical AKI models.

Authors, year	Source of MSCs	Oxygen concentration	Animal	Model	Outcome	(Refs.)
Zhang et al, 2014	hADMSCs	1% O2	SD rats	IRI-AKI	Improvement in apoptosis, enhanced anti-oxidative capacity, increased vascularization and improved histological injury; overall renal function improvement	(34)
Collino et al, 2019	hADMSCs	1% O2	Wistar rats	IRI-AKI	Enhanced immunomodulatory effects with increased intracellular ATP recovery, improved angiogenesis and decreased ROS, leading to improved renal preservation	(35)
Jang et al, 2018	hBMSCs	1% O2	SD, rats	IRI-AKI	High-dose hypoxia-preconditioned MSCs contributed to renal function restoration	(36)
Putra et al, 2019	hUCMSCs	5% O2	Wistar rats	Gentamicin-ARF	Elevated expression of VEGF, HGF, integrin α4, integrin β1 (forming VLA-4) and stromal-derived factor-1, leading to amelioration of renal function in ARF	(37)
Yuan et al, 2025	ADMSCs	5% O2	SD rats	IRI-AKI	Increase in EV particle number and protein concentrations, reduce oxidative reactions and protect kidney function	(38)
Overath et al, 2016 2025	ADMSCs	0.5%O2	C57BL/6 mice	Cisplatin-AKI	Served as an effective source of inductive signals (e.g., VEGF, HIF-1, MMP-12) to restore kidney function	(39)
Yu et al, 2013	Rat BMSCs	CoCl2	SD rats	IRI-AKI	Enhanced expression of HIF-1 and CXCR4, improved migration, longer retention and increased secretory capability	(40)
Tseng et al, 2021	BMSCs	1% O2	SD rats	IRI-AKI	Increased renal tubular autophagy; however, noted renal function impairment, interstitial inflammation and tubular mortality were observed	(41)

MSCs, mesenchymal stem cells; hADMSCs, human adipose-derived mesenchymal stem cells; SD, Sprague-Dawley; IRI, ischemia-reperfusion injury; hBMSC, human bone mesenchymal stem cells; hUCMSCs, human umbilical cord mesenchymal stem cells; ARF, acute renal failure; EV, extracellular vesicle; ATP, adenosine triphosphate; ROS, reactive oxygen species; VEGF, vascular endothelial growth factor; HGF, hepatocyte growth factor; HIF-1, hypoxia inducible factor-1; MMP-12, matrix metalloproteinase-12; CXCR4, C-X-C chemokine receptor type 4; O₂, Oxygen; Cis, cisplatin.

Chemical and drugs preconditioning

To identify effective strategies for optimizing MSCs, researchers have explored chemical preconditioning approaches. These agents are primarily characterized by strong antioxidant, anti-inflammatory and tissue-repair properties. The aim is to protect the cellular membrane structure, improve the microenvironment of MSCs and enhance their stability within this environment. Recent studies which reported on drugs and chemical preconditioned MSCs in AKI models were summarized in Table II (42-46).

Table II.

Chemical and drugs preconditioning MSCs in preclinical AKI models.

Authors, year	Source of MSCs	Drug	Animal	Disease model	Outcome	(Refs.)
Deng et al, 2020	hUCMSCs	Chlorzoxane	Wistar rats	Thy1.1-AKI	Reduced inflammatory infiltration and tissue damage	(44)
Cai et al, 2014	Rat BMSCs	Atorvastatin	SD rats	IRI-AKI	Improved survival rate; decreased oxidative stress and cytokine levels	(45)
Altun et al, 2012	Rat BMSCs	Darbepoetin	SD rats	IRI-AKI	Improved renal function; kidney tissue recovery; renoprotection	(46)
Liu et al, 2013	Rat BMSCs	Vitamin E	Wistar rats	Gentamicin-AKI	Kidney tissue recovery	(42)
Guo et al, 2018	Mice UCMSCs	Vitamin E	Wistar mice	IRI-AKI	Reduced renal inflammation by controlling inflammatory cytokines in the AKI-related microenvironment	(43)

MSCs, mesenchymal stem cells; AKI, acute kidney injury; hUCMSCs, human umbilical cord mesenchymal stem cells; BMSCs, bone mesenchymal stem cells; UCMSCs, umbilical cord mesenchymal stem cells; IRI, ischemia-reperfusion injury; AKI, acute kidney injury.

Chlorzoxane (CZ)

CZ is a powerful muscle relaxant (47). As an FDA-approved drug, CZ has been shown to enhance the expression of anti-inflammatory cytokines, chemokines and critical immunoregulatory enzymes indoleamine 2,3-dioxygenase by promoting Forkhead box protein O3 phosphorylation. This process induces MSCs to adopt an anti-inflammatory phenotype, thereby strengthening their immunosuppressive capacity without increasing immunogenicity (44). In vitro, CZ markedly reduces T-cell activation and proliferation, substantially boosting the immunosuppressive function of hUCMSCs. In Thy1.1 antibody-induced AKI animal models, CZ-pretreated hUCMSCs effectively attenuated renal inflammation and decreased fibrinoid necrosis of the glomeruli, indicating a superior protective effect against kidney injury (44).

Atorvastatin (Ator)

Ator has been shown to possess anti-apoptotic, antioxidant and anti-inflammatory properties (48). Ator improves the microenvironment not only by synergistically enhancing the inherent effects of BMSCs but also by introducing additional therapeutic benefits to BMSCs transplantation (49). Cai et al (45) proposed a combined therapeutic strategy for IRI in a rat model. Rats were administered Ator (lipitor; 5 mg/kg/day by gavage) starting 3 days before MSCs transplantation and continuing until sacrifice. Immediately following IRI, BMSCs were delivered via the left carotid artery. The results indicated that the Ator + MSCs combination therapy could synergistically promote post-ischemic renal functional and morphological recovery. These benefits may stem from the statin-mediated suppression of oxidative stress and inflammation in the injured kidney by inhibiting TLR4 signaling, thereby creating a more favorable environment for engrafted MSCs (45).

Darbepoetin (DPO)

The erythropoietin receptor (EpoR) is not only expressed on hematopoietic cells but has also been reported in specific renal cell types, including tubular epithelial cells and mesangial cells (50). Growing evidence from animal studies indicates that erythropoietin (EPO) directly acts on these renal cells to mitigate AKI, a protective effect attributed to its antiapoptotic, antioxidative, anti-inflammatory properties and angiogenesis (51). DPO, a genetically modified EPO analog, exhibits a prolonged half-life and enhanced stability, enabling reduced dosing frequency while retaining biological activity comparable to native EPO (52). Altun et al (46), rats treated ischemia reperfusion injury (IRI)-induced AKI with either DPO, MSCs, or both (MSCs and DPO concomitantly). The results demonstrated that the combined administration of MSCs and DPO provided superior renoprotection and mitigated tissue damage, although the underlying mechanisms require further investigation.

Vitamin E

Vitamin E, a fat-soluble vitamin with antioxidant properties, can reduce reactive oxygen species (ROS) and prevent cell death, thus benefiting AKI therapy pathways (53-55). The therapeutic effects of combining BMSCs with Vitamin E in a gentamicin-induced AKI model have been shown to involve promoting tubular cell proliferation, inhibiting apoptosis and improving both renal function and pathological abnormalities (42). Another study (43) confirmed that co-administration of UCMSCs and Vitamin E markedly suppressed renal inflammation by modulating inflammatory cytokines [interleukin (IL)-lβ, tumor necrosis factor (TNF)-α and IL-10] in the AKI microenvironment, thereby reducing kidney injury. Moreover, this combined treatment achieved more favorable outcomes than using UCMSCs or Vitamin E alone.

Others

Research has shown that ADMSCs from patients with stage 5 CKD, pretreated with metformin, can slow down the aging of CKD-MSCs (56). Subsequently, the study showed that metformin pretreated ADMSCs markedly attenuate renal inflammation and fibrosis in a CKD mouse model induced by unilateral ureteral obstruction (UUO). This finding suggests that even MSCs derived from CKD patients, can be functionally optimized through agents such as metformin and developed as patient-derived, autologous MSC-based therapeutic products for CKD, offering a novel approach to personalized stem cell therapy (56). Hu et al (57) demonstrated that CA-pretreated BMSCs from mice could alleviate renal fibrosis by inhibiting the TGF-β1/TNF-α/TNFR1 pathway. However, there have been no published studies combining these two drugs with MSCs for the treatment of AKI and further research is needed.

Overall, multiple studies have confirmed that chemical drug preconditioning effectively enhances the antioxidative and anti-inflammatory abilities of MSCs. However, these drugs may have certain effects on the kidneys or other organs. Therefore, the potential side effects and long-term impacts of drug preconditioning need to be further evaluated through additional research.

Biological compounds preconditioning

MSCs typically exhibit low immunogenicity, thereby rarely triggering strong rejection responses in allogeneic transplantation (58,59). Moreover, research has demonstrated that the immunomodulatory and immunosuppressive capacities of MSCs can be further activated when exposed to inflammatory stimuli or residing within an inflammatory microenvironment (60-62). Numerous studies have shown that both exogenous and endogenous pro-inflammatory stimuli, such as interferon gamma (IFN-γ) (63), TNF-α (64,65), IL-17 (66), IL-1β (67), Toll-like receptor (TLR) (68) and TLR ligands (69), can activate or precondition MSCs, enhancing their secretion of immunoregulatory factors and their therapeutic potential. Current preconditioning studies targeting AKI have primarily focused on IFN-γ, IL-17 and IL-1β. While several reports indicate that TNF-α and TLR4 ligand-preconditioned MSCs can boost therapeutic efficacy in other disease models (65,70-72), there is relatively little published literature regarding the efficacy of TNF-α or TLR4-induced MSCs preconditioning in improving AKI outcomes. Additionally, the combined administration of MSCs with low doses of hormones has demonstrated significant renoprotective effects in various animal models (73,74). Biological compound preconditioning MSCs may offer novel insights into enhancing their therapeutic applications in AKI via hormones and cytokines. The recent findings were summarized in Table III (75-81).

Table III.

Biological Compounds preconditioning MSCs in preclinical AKI models.

Authors, year	Source of MSCs	Cytokines/hormones	Animal/cells	Disease model	Cytokines/hormones	Outcome	(Refs.)
Aussel et al, 2021	Rat BMSCs	IL-1β	SD rats	HS-AKI	IL-1β	Lower serum levels of creatinine, urea and cystatin; high secretion of immunomodulatory molecules	(75)
Bai et al, 2017	Mice BMSCs	IL-17A	C57BL/6 mice	IRI-AKI	IL-17A	Improved MSC efficacy in alleviating inflammation; upregulation of COX2 and increased secretion of PGE2; high Treg percentage	(76)
Chen et al, 2014	Rat ADMSCs	Melatonin	SD rats	Sepsis-AKI	Melatonin	Reduced kidney injury and inflammation; suppressed ROS generation and oxidative stress; decreased fibrosis and apoptosis	(77)
Kanai et al, 2021	Rat BMSCs	IFNγ	SD rats	IRI-AKI	IFNγ	Increased production of PGE2; enhanced generation of immunosup pressive macrophages; reduced inflammation	(78)
Mias et al, 2008	Rat BMSCs	Melatonin	SD rats	IRI-AKI	Melatonin	Upregulation and overexpression of antioxidant enzymes; protection against oxidative stress; improved proangiogenic and antiapoptotic properties	(79)
Zhao et al, 2015	hADMSCs	Melatonin	HK-2 cells	Cis-AKI	Melatonin	Enhanced proliferation, increased expression of survival proteins and antioxidative enzymes	(80)
Zhou et al, 2020	Rat BMSCs	EPO	SD rats	IRI-AKI	EPO	Reduced blood urea nitrogen, improved pathological scores and decreased serum creatinine	(81)

MSCs, mesenchymal stem cells; AKI, acute kidney injury; BMSCs, bone mesenchymal stem cells; ADMSCs, adipose-derived mesenchymal stem cells; HS, hemorrhagic shock; EPO, erythropoietin.

Cytokines

IL-17A

IL-17A modulates MSCs immunoregulatory functions without affecting MHC expression (66,82,83), has been shown to enhance the therapeutic potential of BMSCs in mouse models of AKI (76). Mechanistically, IL-17A induces the expansion of regulatory T cells (Tregs), thereby reinforcing immunosuppression and repairing renal function. Conversely, the absence of Tregs diminishes T-cell suppression and negates the beneficial effects of IL-17A preconditioning (76).

IFN-γ

IFN-γ has been employed to pretreat MSCs (63,84). IFN-γ-preconditioned BMSCs administered via the abdominal aorta in rat models of IRI and UUO exhibited marked reductions in immune cell infiltration and renal fibrosis (78). In mechanism, IFN-γ-preconditioned BMSCs upregulated PGE₂ related responses, which induced the polarization of immunosuppressive CD163⁺CD206⁺ macrophages in the local renal microenvironment. This immunomodulatory shift markedly attenuated inflammatory cell infiltration, restored immune homeostasis and ultimately protected against IRI-induced AKI (78).

IL-1β

IL-1β has been used to pretreat MSCs and has been shown to enhance MSCs immune regulation functions. Intravenous injection of IL-1β pretreated MSCs in hemorrhagic shock rats resulted in decreased plasma creatinine, urea nitrogen, cystatin C and kidney injury molecule kidney injury molecule 1 levels on renal tissue sections. In vitro experiments demonstrated that IL-1β-pretreated MSCs reduced systemic cytokines (IL-1α, IL-6 and IL-10) of monocytes and granulocytes, as well as CD80 and CD86, inhibiting activation of PD-1/PDL-1 axis. This suggests that IL-1β enhances MSCs efficiency by promoting its immunomodulatory activity (75).

Hormones

Melatonin

Melatonin, a neurohormone primarily secreted by the pineal gland, plays a crucial role in regulating circadian rhythms (85-89). It is recognized as an effective free radical scavenger with protective effects on various dysfunctional organs, including the kidney (73,74). Given that inflammation and oxidative stress are key contributors to the impaired function of transplanted MSCs in disease environments, preconditioning MSCs with melatonin may prove beneficial (73,90,91). Animal studies in models of lung injury and cerebral and limb ischemia have demonstrated that melatonin preconditioning enhances the therapeutic outcomes of MSCs (92-96). Notably, melatonin not only exerts potent antioxidant effects by reducing free radical production, but also its receptors, MT1 and MT2, widely expressed on MSCs, may also modulate cell fate via receptor-dependent mechanisms (97-99). AKI caused by sepsis is a particularly severe subtype with high morbidity and mortality. Chen et al (77). compared melatonin-preconditioned ADMSCs with ADMSCs alone in a cecal ligation and puncture model, finding that the combined therapy produced superior anti-inflammatory, antioxidant, anti-apoptotic and anti-fibrotic responses, as well as lower serum creatinine levels and reduced renal damage on histological examination. In vitro, melatonin preconditioning markedly enhances ADMSCs proliferation and upregulates key survival and antioxidant proteins such as phosphorylated Erk1/2, Akt, SOD-1 and heme oxygenase-1 (HO-1) (77). The conditioned medium from these cells further promoted proliferation, migration and anti-apoptotic effects in cisplatin-exposed human renal epithelial cells (80). Moreover, Saberi et al (100) demonstrated that pretreatment of BMSCs with melatonin enhanced their homing to the injured kidney, reduced renal cell apoptosis, decreased the expression of TNF-α, α-SMA and TGF-β1 and increased E-cadherin levels in UUO. Ultimately, this approach improved the integrity of the tubular basement membrane, ameliorated tissue architecture and effectively mitigated renal fibrosis.

Erythropoietin (EPO)

EPO is an endogenous hormone primarily secreted by the kidney that regulates red blood cell production (101). It stimulates the proliferation and differentiation of hematopoietic stem cells (HSCs) in the bone marrow through signaling via the EpoR (102). Notably, both BMSCs and HSCs express homologous EpoR. EPO has shown therapeutic potential in various conditions such as myocardial infarction (103), cerebral ischemia (104), chronic heart failure (105) and kidney injury (101,106) through its anti-inflammatory and antioxidant effects. Zhou et al (107). demonstrated that 48-h EPO pretreatment markedly enhances the proliferation rate, cytoskeletal reorganization, migration capacity and expression of the chemokine receptor CXCR4 in BMSCs, thereby improving their homing ability and cellular functionality in vitro. Subsequently, compared with untreated BMSCs, EPO-preconditioned BMSCs not only more effectively restored renal function but also markedly reduced interstitial lymphocyte infiltration, tubular swelling, necrosis and interstitial fibrosis in a cyclosporine A-induced nephrotoxicity rat model (107). Zhou et al (81) further reported that EPO pretreatment upregulated the expression of SIRT1 and the anti-apoptotic protein Bcl-2 while downregulating the pro-apoptotic protein p53 in BMSCs, thereby enhancing their survival rate and anti-apoptotic capacity. The authors observed that in a rat AKI model, GFP-labeled BMSCs infused after 24 h primarily accumulated in the lungs, whereas EPO pretreatment reduced pulmonary retention and increased their distribution to the injured kidneys. Moreover, AKI rats treated with EPO-preconditioned BMSCs exhibited markedly lower serum levels of IL-1β and TNF-α, along with elevated IL-10 levels and demonstrated more pronounced improvements in renal function (81). These findings indicate that EPO pretreatment not only enhances the survival and anti-apoptotic capabilities of BMSCs but also improves their homing and distribution in vivo, thereby markedly augmenting their therapeutic efficacy in AKI.

Relaxin

Relaxin is primarily secreted by the corpus luteum during pregnancy, with minor expression in the brain, heart and kidneys (108). It plays a key role in mediating adaptive hemodynamic changes, including increased cardiac output, enhanced renal blood flow and improved arterial compliance (109-113). Several investigations have explored relaxin preconditioning of MSCs (114,115). Although direct evidence of relaxin preconditioned MSCs protecting against AKI is currently lacking, combined therapy has been shown to mitigate fibrosis progression in a UUO model in normotensive mice (116,117). Badawi et al (117) developed a novel combinatorial approach for CKD patients using synthetic relaxin (Serelaxin) with BMSCs to restore and enhance endothelial progenitor cell populations. While BMSCs alone have demonstrated blood pressure reduction and anti-fibrotic effects comparable to perindopril, serelaxin monotherapy markedly decreases tubular injury and moderately reduces renal fibrosis (114). These findings suggest that further research is needed to fully elucidate the renoprotective potential of relaxin preconditioned MSCs in the setting of AKI.

In summarily, biological preconditioning strategies enhance the therapeutic effects in AKI by activating the immunomodulatory function of MSCs through cytokines or hormones. However, its main drawback is the potential risk of overstimulation, leading to unwanted side effects, such as excessive inflammation or immune modulation, which could complicate therapeutic use.

Three-dimensional (3D) culture

Conventionally, cell cultures are primarily performed on flat, two-dimensional substrates. Nevertheless, in a two-dimensional setup, the interplay among cells and between cells and the extracellular matrix (ECM) is not entirely consistent with that in vivo. In order to more closely mimic the in vivo microenvironment and improve cellular function as well as the physiological relevance of experimental data, MSCs 3D cell culture methods have been developed and applied in the study of AKI (Table IV) (118-125).

Table IV.

3D culture MSCs in preclinical AKI models.

Authors, year	Source of MSCs	Culture materials	Animal	Disease model	Outcome	(Refs.)
Feng et al, 2016	Mice ADMSCs	IGF-1 C domain-modified hydrogel	C57BL/6 mice	IRI-AKI	Enhanced anti-inflammatory effects; improved angiogenesis; promoted MSC survival and retention	(118)
Fu et al, 2022	BMSCs	Enzyme-crosslinked gelatin hydrogel	C57BL/6 mice	Glycerol-AKI	Renal function improvement; reduction of tubular fibrosis and damage	(119)
Geng et al, 2017	Mouse BMSCs	Biological membrane	C57BL/6 mice	Glycerol-AKI	Improved renal tubular lesions; decreased apoptosis; maintained renal function	(120)
Han et al, 2023	MSCs	HA hydrogels	BalbC mice	IRI-AKI	Significant reduction in fibrosis-related markers; decreased inflammatory cytokines; lower urine NGAL levels	(121)
Huang et al, 2017	hADMSCs	Co-gels of collagen and decellularized vascular matrix	SD rats	IRI-AKI	Increased MSC survival and paracrine activity; improved renal function; enhanced vascularization; reduced tissue injury and apoptosis	(122)
Najafiet al, 2022	WJMSCs	Integrin receptor-binding nanofibrous peptide hydrogel	BALB/c mice	IRI-AKI	Increased MSC proliferation; enhanced recovery of renal injury; reduction in kidney injury-related biomarkers	(123)
Xu et al, 2016	hADMSCs	3D spheroid culture	SD rats	IRI-AKI	Higher levels of extracellular matrix protein; production increased paracrine secretion of cytokines; reduced tissue damage	(124)
Wang et al, 2020	hpMSCs	Hybrid β-Sheet peptide hydrogel consisting of IGF-1C domain and D-Form peptide	C57BL/6 mice	IRI-AKI	Enhanced cell engraftment; decreased renal fibrosis; facilitated angiogenesis; recovery of renal function	(125)

MSCs, mesenchymal stem cells; AKI, acute kidney injury; IRI, ischemia-reperfusion injury; HA, hyaluronic acid; BMSCs, bone mesenchymal stem cells; hpMSCs, human placenta-derived mesenchymal stem cells; ADMSCs, adipose-derived mesenchymal stem cells; WJMSCs, wharton's jelly-derived mesenchymal stem cells.

Hydrogel-focused

Hydrogels are regarded as one of the most promising options for MSCs 3D culture and delivery (126,127). Hydrogels, formed through chemical or physical crosslinking, are 3D porous polymer networks with high water content and tunable chemical and physical attributes (126,128). Owing to their substantial water content and porous structure, hydrogels facilitate the diffusion of nutrients and metabolites within the network (129). In this way, hydrogels can serve as an artificial ECM around the cells, providing the necessary conditions for cell-to-matrix and cell-to-cell interactions, thus influencing MSCs behavior and function (130). At present, hydrogels have been explored to replicate the native microenvironment of cells in vivo and they are categorized by source or fabrication approach into natural hydrogels, synthetic hydrogels and hybrid hydrogels (130). Notably, the effectiveness of hydrogels as scaffolds to support cellular growth and function has been confirmed in various preclinical AKI models (119,121,131).

Natural hydrogels

Hydrogels made from natural materials have gained significant interest in recent years because of their excellent biocompatibility, biodegradability and eco-friendly nature (132). Common natural polymers utilized are agarose, alginate, chitosan, collagen, hyaluronic acid, gelatin and fibrin (133-136). These materials can be categorized as either polysaccharide-based or protein-based hydrogels (137).

Alginate

Alginate, a linear hydrophilic polysaccharide from brown algae and specific bacteria, comprises β-d-mannuronic acid and α-l-guluronic acid (135). This biopolymer, soluble and cost-effective, with high biocompatibility and appropriate rheological properties, is widely used in 3D bioprinting (138). Before its bioink application, alginate was extensively researched in regenerative medicine and tissue engineering for MSCs culture and delivery (139-141). It further facilitates the regulated secretion of paracrine factors derived from MSCs (142,143). Nonetheless, the limited biodegradability and cell-adhesive characteristics of alginate restrict its potential uses (138,139). Efforts are ongoing to address these constraints. A recent study proposed that an alginate-hyaluronic acid hydrogel blend could be a promising option for AKI treatment (121).

Chitosan

Chitosan is a naturally occurring linear polysaccharide, is derived from crustacean exoskeletons and fungal cell walls (134,139). Beyond its structural resemblance to glycosaminoglycans in the ECM, it exhibits biocompatibility, biodegradability, antimicrobial properties, non-toxicity and affordability (144). These hydrogels demonstrate notable responsiveness to changes in pH and temperature (145), enhancing their adaptability for diverse applications. In vivo research has shown that chitosan hydrogels improve MSCs retention, viability and therapeutic efficacy in AKI (118,146). However, their weak mechanical properties and limited solubility in physiological environments restrict biomedical utility. Combining chitosan with peptides or alternative hydrogels offers a potential solution to these limitations (137,145).

Collagen

Collagen is a fibrous structure, constitutes the predominant structural component in mammalian extracellular matrices (147). Owing to properties such as biodegradability, biocompatibility, elasticity and resemblance to natural tissue structures, collagen-based hydrogels are widely utilized as biomimetic scaffolds for 3D culture applications (139). Evidence indicates that scaffolds constructed from collagen effectively promote MSCs retention, proliferation, functional performance and phenotypic stability, consequently augmenting their therapeutic potential in treating AKI (122,139,148). A decellularized vascular matrix combined with collagen (co-gel) and MSCs were jointly transplanted into the kidneys of rats with IRI-induced AKI, the survival rate of MSCs and their paracrine effects in the injured kidneys were improved (122). More importantly, the co-gel markedly augmented the therapeutic efficacy of MSCs in AKI, including reducing cell death and tissue damage and improving angiogenesis and renal function (149). Duragen is an absorbable collagen-based artificial matrix that was used as a biological membrane to encapsulate MSCs transplanted into AKI mouse kidneys, preventing MSCs escape, prolonging their survival in vivo, improving renal function, ameliorating tubular lesions and reducing apoptosis. The authors also demonstrated in cell-based experiments that duragen-encapsulated MSCs protected renal cells from myoglobin-induced apoptosis. Thus, this confirms the potential of duragen-encapsulated MSCs as a new therapeutic strategy for AKI (150).

Gelatin

Gelatin, a biocompatible polypeptide obtained from bovine or porcine collagen, comprises 18 distinct amino acids (139,151) and possesses lower antigenicity relative to collagen (151). Due to its advantageous properties, such as affordability, commercial accessibility, water solubility, good adhesion and straightforward processing, gelatin has become widely adopted in biomedical applications (152). Research involving AKI models demonstrates that gelatin-based hydrogels combined with MSCs effectively promote MSC survival, thus facilitating tissue repair (119). However, challenges of gelatin hydrogels include low mechanical strength, quick enzymatic breakdown and poor thermal stability (153). Pure gelatin undergoes a sol-gel shift close to body temperature, allowing it to be injected as a thin liquid at 37°C, but it does not solidify into a stable hydrogel in vivo (154). Modifications are necessary to enhance the overall properties of natural gelatin.

ECM

Kidney ECM hydrogels have attracted significant interest as biomaterials for regenerative medicine (155). By selectively removing cellular components while preserving the native proteins, glycosaminoglycans and growth factors, these hydrogels maintain essential bioactive properties, biocompatibility and minimal immunogenic responses (156,157). Compared with hydrogels derived from individual ECM components, kidney ECM hydrogels uniquely preserve the complete biochemical profile of renal tissue and do not include proteins obtained from tumorigenic sources as does Matrigel (158). Kidney ECM hydrogels are currently being explored as injectable scaffolds to facilitate renal regeneration and tissue repair, showing promising outcomes (159). In a related investigation, embedding ADMSCs within kidney ECM hydrogels markedly enhanced cell retention and survival after transplantation into ischemic rat kidneys. Moreover, ECM hydrogels promoted growth factor secretion while reducing oxidative damage and apoptosis, suggesting therapeutic promise for AKI treatment (160). However, due to inherent variability associated with natural biomaterials, the characteristics of kidney ECM hydrogels and their specific influences on cellular behavior require further elucidation (158). Additional studies should further clarify these issues to provide deeper insights into AKI management.

Hyaluronic acid (HA)

HA is extensively found within mammalian tissues, including connective tissues, synovial fluid and vitreous humor (61,78). HA exhibits distinctive properties, including inherent bioactivity, excellent hydrophilicity, biodegradability and low cellular adhesiveness, making it a promising biomaterial candidate (145). These advantages make HA-based hydrogels increasingly suitable for numerous biomedical applications. As a crucial ECM constituent, HA markedly contributes to various biological processes, such as cellular proliferation, angiogenesis, embryogenesis, wound repair, stromal structuring and morphogenetic events (126). Implanting stem cells in HA hydrogels influences the release of cytokines/chemokines, counteracts pro-inflammatory mediators secreted by immune cells, thereby modulating immune responses and improving AKI (161). A previous investigation demonstrated that injecting MSCs encapsulated within HA hydrogels directly into kidneys subjected to IRI effectively attenuated ECM remodeling at one month post injury in mice (162). Notably, the highly thermoreversible nature of HA hydrogels provides favorable conditions for their use as injectable scaffolds for MSCs culture and delivery, or as implantable materials for soft and hard tissue repair and reconstruction (163). However, due to insufficient stability at body temperature and limited controlled-release capacity for bioactive molecules, chemical modifications and covalent crosslinking are required to improve the performance of HA hydrogels (164). Anyway, the aforementioned research proved that HA hydrogels have the potential to alleviate AKI.

Others

Agarose (129), Matrigel (165) and fibrin (166)-based hydrogels have also been employed to culture and deliver MSCs and serve as viable scaffolds for MSCs cultivation, but research on their application in AKI remains limited and warrants further investigation.

Synthetic hydrogels

Synthetic hydrogels are artificially engineered, 3D polymer networks that can absorb and retain large amounts of water, mimicking the properties of the natural ECM. They are widely used in biomedical applications such as tissue engineering, drug delivery and wound healing. Fu et al (119) discovered a novel therapeutic strategy for rhabdomyolysis. The authors used 3D modeling and printing to create an elastic sac that mimicked the kidney's dimensions and shape. This sac was applied as an outer coating for the kidney along with MSC-laden hydrogel (119). This innovative technology not only offers a versatile solution for organ restoration but also presents a promising option for AKI treatment. In another study, a new β-sheet supramolecular self-assembling peptide hydrogel was developed by combining insulin-like growth factor-1C (IGF-1C) with a D-assembling motif Nap-DFDFG, along with human placenta-derived mesenchymal stem cells for AKI. The results demonstrated that this hydrogel enhanced cell engraftment, ameliorated renal function, stimulated angiogenesis and reduced renal fibrosis in a mouse model of IRI induced AKI (125). Furthermore, an injectable nitric oxide (NO)-releasing hydrogel was created through physical crosslinking using short aromatic dipeptides. This hydrogel (Fmoc-diphenylalanine S-nitroso-N-acetylpenicillamine; Fmoc-FFSNAP) enabled localized and sustained NO release, leading to enhanced regeneration post-IRI and improved renal function (167). A recent study compared the therapeutic efficacy of Fmoc-FF + Fmoc-RGD-MSCs with free MSCs and Fmoc-FF + Fmoc-RGD-SNAP-MSCs in a renal IRI injury model. The hydrogel was combined with Wharton's jelly-derived MSCs and administered via intrarenal injection at three sites in IRI mice. Results demonstrated that the hydrogel treatment markedly enhanced renal function biomarkers, decreased reactive oxygen species production, improved histopathological changes and promoted the recovery and endothelial regeneration of the injured kidney (123).

Hybrid hydrogels

Feng et al (118) demonstrated that a bioactive hydrogel, formed by immobilizing the C domain peptide of IGF-1C on chitosan, provided an artificial microenvironment for adipose-derived ADMSCs, which enhanced cell viability through paracrine effects and protected against IRI.

Spheroid culture

An alternative approach to 3D cell culture involves spheroid formation. This scaffold-free method enables MSCs and their ECM to self-assemble into tissue-like structures. Various techniques facilitate spheroid production, including liquid overlay, rotary culture, magnetic levitation, microparticle culture and the hanging drop method (168,169). Research suggests therapeutic applications for MSCs spheroids in kidney disorders. For example, Xu et al (124) demonstrated the enhanced therapeutic effects of human ADMSCs spheroids in AKI models. Compared with traditional monolayer cultures, these 3D aggregates showed increased secretion of ECM components (collagen I, fibronectin and laminin) along with superior antioxidative and anti-apoptotic capabilities.

Additionally, MSCs cultured with 3D spheroids exhibit enhanced secretion of paracrine cytokines such as VEGF and bFGF (angiogenic factors), EGF and HGF (anti-apoptotic factors), IGF (antioxidant) and TSG-6 (anti-inflammatory). These spheroids display greater in vivo survival and sustained paracrine effects, aligning with in vitro observations. In rat models of IRI-induced AKI, intrarenal injection of 3D spheroids provides superior renal protection compared to 2D-cultured cells, mitigating apoptosis, tissue injury and enhancing angiogenesis and functional recovery (124). Hybrid 3D spheroids composed of MSCs, vascular endothelial cells and podocytes can mimic glomerular microenvironments. Transplantation of these constructs into the renal cortex of hypertensive nephropathy mice improves kidney function, suggesting that engineered hybrid spheroids could markedly enhance podocyte replacement strategies and therapeutic outcomes (170).

3D culture of MSCs offers significant advantages in enhancing cell function and therapeutic effects, but it may also pose certain risks. First, the technical complexity and controllability of 3D culture systems are relatively low, which may lead to abnormalities in cell growth and differentiation. Second, hypoxia may occur in the center of the cells, affecting their survival and function. In addition, the therapeutic effects of 3D culture may vary due to inconsistencies in culture conditions and it may trigger immune rejection responses. Finally, the long-term effects and safety are not yet clear, particularly in clinical applications and further optimization and evaluation are needed.

Intracellular strategies (genetic modification)

To enhance MSCs therapeutic potential in AKI, intracellular engineering methods such as genetic and epigenetic modifications have been extensively studied. Genetic modification involves changing MSCs' DNA sequence to regulate the expression of important genes. For example, boosting HO-1 and VEGF, genes crucial for antioxidant defense and angiogenesis, has been found to notably enhance MSCs migration, vascular targeting, anti-inflammatory abilities and viability, ultimately improving renal healing (171). These protective impacts are mainly mediated through activating signaling pathways such as PI3K/Akt and MEK/ERK (172,173).

Gene modification currently used include viral vector-based systems such as lentiviruses, retroviruses, adenoviruses and adeno-associated viruses, as well as non-viral systems such as plasmid DNA, RNA and protein-RNA complexes (171,174). In AKI preclinical models, these approaches have been used to boost the regenerative and immunomodulatory capabilities of MSCs, enhancing their proliferation, influencing differentiation potential and enhancing their anti-inflammatory and antioxidative functions (Table V) (175-182). Despite encouraging outcomes, the clinical application of these methods is restricted. Genetic modification might unintentionally affect genomic regions outside the target, leading to potential risks of genotoxicity, cytotoxicity, or tumorigenesis (183). Furthermore, ethical and safety issues associated with gene editing technologies are impeding their broad clinical implementation. Therefore, although genetic manipulation is a potent tool for refining MSC-based therapies for AKI, further optimization and thorough safety assessment are crucial before clinical adoption.

Table V.

Gene-modified MSC-based therapy in AKI animal models.

Authors, year	Source of MSCs	Modified gene	Animal	Disease model	Outcome	(Refs.)
Zhang et al, 2021	UCMSCs	HGF	SD rats	IRI-AKI	Promoted renal cell regeneration, inhibited apoptosis and inflammation	(174)
Chen et al, 2011	BMSCs	Kallikrein	Wistar rats	IRI-AKI	Inhibited apoptosis and inflammation	(175)
Hagiwara et al, 2008	BMSCs	CXCR4	C57BL/6J mice	IRI-AKI	Increased homing of BMSCs and increased release of cytokines	(176)
Liu et al, 2013	BMSCs	CXCR4	C57BL/6 mice	IRI-AKI	Enhanced migration of MSCs and improved renal function	(177)
Liu et al, 2013	BMSCs	HO-1	SD rats	IRI-AKI	Enhanced proliferation and differentiation of BMSCs	(178)
Liu et al, 2018	BMSCs	HO-1	SD rats	IRI-AKI	Alleviated apoptosis of BMSCs and antioxidant effects	(179)
Liu et al, 2015	AFSCs	VEGF	SD rats	IRI-AKI	Enhanced therapeutic effect by mitogen, angiogenesis and anti-inflammatory action	(180)
Da Cunha et al, 2017	BMSCs	Survivin	C57BL/6 mice	IRI-AKI	Improved MSC survival, increased protective cytokines	(181)

MSCs, mesenchymal stem cells; AKI, acute kidney injury; SD, Sprague-Dawley; BMSCs, bone mesenchymal stem cells; UCMSCs, umbilical cord mesenchymal stem cells; AFSCs, amniotic fluid stem cell; VEGF, vascular endothelial growth factor; HO-1, heme oxygenase-1; HGF, hepatocyte growth factor; IRI, ischemia-reperfusion injury.

The mechanisms by which preconditioning strategies enhance MSCs function can be briefly summarized as follows: Physical preconditioning (such as hypoxic culture) enhances MSCs function by promoting proliferation, survival, homing, differentiation and paracrine activity, thereby improving renal function recovery. Chemical preconditioning primarily enhances MSCs stability by protecting cell membrane structures and improving the MSCs microenvironment through antioxidant, anti-inflammatory and tissue repair properties. Biological preconditioning activates MSC's immunomodulatory functions through cytokines or hormones, further enhancing their therapeutic effects. In addition, genetic modification optimizes MSC therapy for AKI by altering gene expression to enhance MSCs migration, vascular targeting and anti-inflammatory abilities. Further mechanisms specific pathways are still being explored.

Although these strategies have their advantages, they also present some challenges. Physical preconditioning and 3D culture methods are relatively simple, but there may be variability in cell growth and differentiation consistency. Chemical and biological preconditioning methods are comparatively simple and have high reproducibility, but more research may be needed to evaluate their long-term effects and potential side effects. Genetic modification strategies can markedly enhance MSCs functionality, but their safety and ethical concerns still need further evaluation. A combination of these strategies may be the best approach for treating AKI in the future, but further research and optimization are still required.

Improvement in administration routes

To fully leverage the diverse therapeutic capabilities of MSCs, it is crucial to ensure the adequate delivery of cells to the site of injury, which is a fundamental requirement for the efficacy of MSC-based therapy. The selection of the administration route markedly influences therapeutic results, with no consensus on the most effective approach to date (148). Systemic and local injections are currently the main methods used in preclinical and clinical studies, while innovative strategies such as encapsulated delivery of biomaterials and pulsed focused ultrasound (pFUS) guidance are gaining attention (184) (Fig. 3).

Figure 3.

Delivery routes and adjuvant strategies for MSC-based therapy in AKI models. Multiple administration routes have been explored to enhance the therapeutic efficacy of MSCs in AKI. Systemic injection methods include IV, IP and (IA) delivery, allowing widespread cell distribution. Local injection approaches, such as SC, IR and RA routes, facilitate direct cell delivery to the injured kidney, improving targeting efficiency. Adjuvant methods, including PFUS, biomaterials and cell sheet engineering, are employed to enhance MSCs retention, viability and therapeutic function at the injury site. These strategies aim to overcome challenges such as poor engraftment, limited homing and transient efficacy of transplanted MSCs in AKI. MSCs, mesenchymal stem cells; AKI, acute kidney injury; IV, intravenous; IP, intraperitoneal; IA, intra-arterial; SC, subcapsular; IR, intrarenal; RA, renal arterial; PFUS, pulsed focused ultrasound.

Systemic administration included intransient (IV), intra-arterial (IA), intraperitoneal (IP), accounting for 74% of MSCs injected. IV is commonly used for systemic delivery of bone marrow MSCs because it is simple and minimally invasive, with tail vein injection being the most dominant mode. However, an important drawback is the 'lung first-pass effect', which causes MSCs to become trapped in the lungs (185,186). In addition, MSCs tend to accumulate in the liver after intravenous injection, thereby reducing their concentration to reach the kidneys (187). Although administering higher numbers of MSCs could mitigate this problem, it potentially elevates the likelihood of complications, including thrombotic events and pulmonary embolism (188-190). By contrast, IA has shown higher efficacy by bypassing lung filters, improving MSCs homing and increasing cell delivery to target tissues, despite the risk of cell embolism and higher invasiveness (191,192). Whether intraperitoneally administered MSCs can enter the systemic circulation has not been reported, although they have the ability to reach the renal parenchyma.

Topical administration accounts for ~40% of MSCs injection, including intra-renal, subcapsular, renal-arterial. The MSC sheet transplantation has emerged in recent years as a novel localized delivery strategy for MSCs. Like above topical administration, this approach enables direct and precise renal implantation, enhancing cellular engraftment and therapeutic efficacy while circumventing pulmonary entrapment and reducing pulmonary complication risks (193). Notably, MSC sheet transplantation uniquely maintains high local cell concentrations at target sites, thereby promoting renal tissue regeneration (193). Various topical administration methods have been evaluated in AKI models showing good results, with intra-renal injections being extensively studied for their ease of use. Other methods, such as hydrogel, microgel and biomaterials aforementioned, simulate the interaction between cells in vivo and improve the viability of MSCs. In addition, pFUS-guided delivery of MSCs was reported to improve microenvironment, up-regulate adhesion factors and guide MSCs homing and viability (184). Due to the small number of published reports, more studies are needed to confirm its safety and effectiveness.

3. Clinical translation and perspectives

Although preclinical studies have demonstrated the therapeutic potential of MSCs and preconditioned MSCs in AKI, their clinical translation remains a crucial step in validating efficacy and safety in human patients. A review of current clinical trials (Table VI; https://clinicaltrials.gov/) reveals multiple studies exploring MSC-based therapies for AKI, including autologous or allogeneic MSCs derived from sources such as umbilical cord (UCMSCs), bone marrow (BMSCs) and adipose tissue (ADMSCs). These trials aim to evaluate parameters such as renal function recovery, inflammatory marker modulation and long-term safety, with results confirming the safety of MSC infusion for AKI treatment. Preconditioning strategies (such as hypoxia, cytokine priming, or pharmacological agents such as melatonin) have been employed to enhance MSCs survival and reparative function. However, challenges such as optimizing dosage, administration routes and quality control of MSCs products must still be addressed to ensure reproducible therapeutic outcomes. Future research should focus on biomarker-guided patient stratification and combination therapies (such as MSC-derived exosomes) to maximize treatment efficacy.

Table VI.

Clinical trials of MSCs therapy in AKI.

Number	Estimated enrollment	Phase	MSCs source	Status	Sponsor	Clinical trial ID
1	80	I/II	UCMSCs	Not recruiting	Chinese PLA General Hospital, China	NCT04194671
2	15	I	ADMSCs	Recruiting	Tambi Jarmi, USA	NCT04388761
3	15	I	BMMSCs	Completed	AlloCure Inc., USA	NCT00733876
4	24	I/II	MSCs	Not recruiting	Sentien Biotechnologies, Inc.	NCT03015623
5	50	II	HUCMSCs	Recruiting	Chinese PLA General Hospital, China	NCT06954740
6	70	I/II	ADMSCs	Not recruiting	Hope Biosciences	NCT06654193

MSCs, mesenchymal stem cells; AKI, acute kidney injury; UCMSCs: umbilical cord mesenchymal stem cells; ADMSCs: adipose-derived mesenchymal stem cells; BMMSCs: bone marrow mesenchymal stem cells.

4. Conclusion

In summary, MSCs show promise for treating AKI. However, clinical outcomes have not matched preclinical findings, indicating challenges for translation to clinical practice. Researchers have investigated strategies including pretreatment, changing cell culture environment, alternative delivery routes to address these hurdles. Moreover, due to patient heterogeneity, treatment approaches should be personalized based on factors such as age, genetics and overall health. Further research is warranted to enhance MSC-based therapies for effective clinical application in AKI treatment.

Abbreviations

AKI

acute kidney injury

CKD

chronic kidney disease

MSCs

mesenchymal stem cells

hAD-MSCs

human adipose-derived MSCs

hUC-MSCs

human umbilical cord MSCs

EVs

extracellular vesicles

CZ

Chlorzoxane

Ator

Atorvastatin

DPO

darbepoetin

EpoR

erythropoietin receptor

EPO

erythropoietin

ROS

reactive oxygen species

UUO

unilateral ureteral obstruction

Tregs

regulatory T cells

IRI

ischemia reperfusion injury

ADMSCs

adipose-derived MSCs

HSCs

hematopoietic stem cells

3D

three-dimensional

ECM

extracellular matrix

HA

hyaluronic acid

GAG

glycosaminoglycan

IGF-1C

insulin-like growth factor-1C

WJ-MSCs

Wharton's jelly-derived MSCs

pFUS

pulsed focused ultrasound

IV

intransient

IA

intra-arterial

IP

intraperitoneal

HO-1

heme oxygenase-1

VEGF

vascular endothelial growth factor

Funding Statement

The present review was supported by National Natural Science Foundation (grant no. 82200830); Sichuan Science and Technology Program (grant no. 2025ZNSFSC0617); The Project of Southwest Medical University Affiliated Traditional Medicine Hospital (grant no. 2022-CXTD-03) and Southwest Medical University Technology Program (grant no. 2023ZYYQ01).

Availability of data and materials

Not applicable.

Authors' contributions

ND was responsible for writing, reviewing and editing, supervision and project administration. LW was responsible for conceptualization, writing, reviewing and editing, supervision and funding acquisition. JK was responsible for supervision and project administration. YZ, JD and JF were responsible for writing, reviewing and editing, writing the original draft, visualization, software, methodology, investigation, formal analysis, data curation and conceptualization. MY and HW were responsible for writing, reviewing and editing, supervision and funding acquisition. Data authentication is not applicable. All authors read and approved the final manuscript.

Ethics approval and consent to participate

Not applicable.

Patient consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Authors' information

Professor Li Wang ORCID:0000000338813149 Professor Nathupakorn Dechsupa ORCID: 0000-0002-0412-9659.