Apoptotic Bodies in Kidney Disease

Abstract

Apoptotic bodies are membrane-bound vesicles generated during the terminal stages of programmed cell death and are traditionally viewed as inert cellular debris. Emerging evidence, however, positions apoptotic bodies as dynamic mediators of intercellular communication with critical roles in kidney physiology and pathology. In the healthy kidney, efficient efferocytosis of apoptotic bodies maintains tissue homeostasis by ensuring immunologically silent clearance of apoptotic remnants. In AKI, extensive tubular epithelial apoptosis generates a high burden of apoptotic bodies that can amplify inflammation, endothelial dysfunction, and adaptive immune activation when clearance is impaired, yet promote resolution and epithelial repair when efficiently removed. In CKD, persistent low-grade apoptosis combined with defective efferocytosis leads to progressive accumulation of apoptotic bodies in the interstitium, where their bioactive cargo—including damage-associated molecular patterns, cytokines, growth factors, and profibrotic microRNAs—drives fibroblast activation, extracellular matrix expansion, and fibrosis. In the vasculature, apoptotic bodies derived from vascular smooth muscle cells act as nucleation sites for calcium-phosphate crystal deposition, linking apoptosis to the development of medial vascular calcification in CKD. Together, these findings highlight apoptotic bodies as active regulators of injury, inflammation, fibrosis, regeneration, and vascular pathology. Understanding the determinants of their pathogenic versus reparative effects could yield new biomarkers and therapeutic strategies, including modulation of efferocytosis, targeting apoptotic body–derived signaling pathways, and engineering apoptotic bodies–based delivery systems.

Introduction

Apoptosis, or programmed cell death, plays a crucial role in maintaining renal homeostasis by eliminating damaged, dysfunctional, or excess cells in a controlled manner. This finely regulated process ensures the integrity of the kidney, preventing unwanted immune activation and contributing to tissue remodeling and regeneration. One of the hallmark features of apoptosis is the formation of apoptotic bodies, membrane-bound vesicular structures that package nuclear and cytoplasmic material from the dying cell. The apoptotic bodies are subsequently recognized and engulfed by professional phagocytes, such as macrophages, or neighboring epithelial cells, facilitating the safe and immunologically silent clearance of apoptosis-derived remnant vesicles.¹

Historically, apoptotic bodies were regarded as passive byproducts of cell death; however, recent research revealed that apoptotic bodies are dynamic and bioactive entities. They are now understood to participate actively in intercellular communication by delivering a variety of signaling molecules, including proteins, lipids, and nucleic acids to recipient cells.² These vesicles can exert diverse effects, modulating immune responses, promoting inflammation, triggering fibrotic pathways, or even supporting tissue repair and regeneration.³ This emerging understanding has positioned apoptotic bodies as critical mediators in the pathophysiology of numerous diseases.

In the context of kidney disease, the role of apoptotic bodies remains an underexplored yet highly promising area of study. Their involvement in modulating inflammation, influencing fibrotic responses, and potentially contributing to tissue regeneration suggests that they may serve as both biomarkers and therapeutic targets in kidney pathology. As such, further investigation into the production, composition, and functional impact of apoptotic bodies in various forms of kidney injury and disease could yield valuable insights with significant translational implications for diagnosis, prognosis, and treatment. Of particular interest is also the involvement of apoptotic bodies in medial calcification pathogenetic process because arterial stiffness is one of the main contributors of the development of cardiovascular comorbidities in patients with CKD.

Biogenesis, Molecular Composition, and Function

Apoptotic bodies are membrane-bound vesicles that arise during the terminal stages of apoptosis, the tightly regulated process of programmed cell death. Apoptosis is executed by two different pathways, the extrinsic and the intrinsic, converging with the activation of the executioner caspases.^4,5 The extrinsic pathway is characterized by the binding of ligands to death receptors and the recruitment of adapter proteins through the death domains.⁶ In the intrinsic pathway, different types of triggers act by either inducing an augmentation in the expression of proapoptotic members of the B-cell lymphoma 2 (Bcl-2) family or their activation such as Bcl-2–associated X protein/Bcl-2 homologous antagonist/killer proteins. The result is an increase of the outer mitochondrial membrane permeability with the release of mitochondrial intermembrane content to the cytosol and activation of the effector caspases.⁷

The apoptotic cells undergo a process of disintegration culminating in the formation of apoptotic bodies. Typically ranging in size from 500 to 5000 nm in diameter, apoptotic body formation involves a complex process of cellular disassembly in which the dying cell fragments into smaller vesicles, each encapsulated by a lipid bilayer. Apoptotic bodies differ from exosomes and microvesicles in markers, cellular components cargo, and in size since exosomes are 30–100 nm in diameter and microvesicles 50–100 nm.⁸ Apoptotic body formation is a finely regulated process of vesiculation that can be divided into three different phases: blebbing, protrusion, and fragmentation. In the blebbing phase, the apoptotic cell shrinks because of an imbalance of the intra-extracellular hydrostatic pressure and because of a decrease of apoptotic cell volume.⁹ Moreover, an actin-myosin contraction leads to cytoskeletal reorganization with nuclear membrane rupture and membrane blebbing.^10,11 The membrane protrusion phase can be different for different cell types with three major protrusion patterns being microtubule spikes, string-like protrusion called apoptopodia, or beaded apoptopodia.^3,12 In the fragmentation phase, the base of each apoptotic vesicles tightens up to the release of a multitude of vesicles that based on the diameter can be termed either apoptotic bodies, apoptotic microvesicles, or apoptotic exosomes. Besides size, apoptotic bodies differentiate from other apoptotic vesicles because they contain a variable number of micro and macro nuclei because of chromatin condensation and nuclear slitting.¹³

A distinguishing feature of apoptotic bodies is the externalization of specific find-me and eat-me signals on their surface to be recognized by phagocytic cells such as macrophages. Find-me molecules are secreted to create a chemotactic gradient to attract macrophages, such as chemokines, nucleotides, ATP, and lipids.^14,15 Specific eat-me signals act to induce apoptotic bodies phagocytosis, most notably phosphatidylserine.¹⁶ Under normal physiologic conditions, phosphatidylserine is confined to the inner leaflet of the plasma membrane. However, during apoptosis, it is translocated to the outer leaflet, serving as a key recognition signal for phagocytes. In addition to phagocytic cells, also fibroblast, endothelial, and stem cells may remove apoptotic bodies.¹⁷ The elimination mechanism can be receptor-mediated, and the differences between professional and nonprofessional phagocytes may lay in the different type of receptor.¹⁶ Interestingly, some of these receptors may be involved in apoptotic bodies clearance by fusion as phosphatidyl choline receptor brain-specific angiogenesis inhibitor 1.¹⁸ Apoptotic bodies are not merely cellular debris; they encapsulate a diverse array of biomolecules reflective of their cellular origin (Table 1). Their contents typically include nuclear fragments, such as fragmented DNA and associated histone proteins, representing the breakdown of the cell genetic material^19,20; ribosomal RNA and microRNA, which may participate in gene regulatory processes in recipient cells upon transfer^21,22; mitochondrial DNA and proteins, many of which may retain biological activity²⁰ triggering inflammation in kidney disease^23,24; cytosolic proteins, such as damage-associated molecular patterns (DAMPs), including high-mobility group box 1 (HMGB1) protein²⁵ and IL-1α,²⁶ which can act as immune stimulators or Gas6 that can act as regulator of cell migration when released into the extracellular space²⁷; cytokines, chemokine, and regulatory molecules, such as IL-8, monocyte chemoattractant protein-1, and C-X-C motif chemokine ligand 1; and adhesion molecules such as intercellular adhesion molecule-1 and E-selectin and antigen presentation machinery such as transporter associated with antigen processing 1, human leukocyte antigen class I B, and human leukocyte antigen-F, which may modulate innate and adaptative immune processes.^28,29

Table 1.

Characteristics of apoptotic bodies

Feature	Description
Formation	Occurs during the terminal phase of apoptosis; results from cellular fragmentation
Size	500–5000 nm in diameter
Membrane features	Displays find-me and eat-me signals such as phosphatidylserine, facilitating recognition and clearance by phagocytes
Typical contents	Nuclear fragments (DNA, histones) Ribosomal RNA and microRNA Mitochondrial DNA and proteins Cytosolic proteins Cytokines, chemokine, and regulatory molecules

Every day, 200–300 billion cells in the body become apoptotic, producing apoptotic bodies that are cleared by phagocytic cells, a process named efferocytosis.^30,31 Generally, efferocytosis causes anti-inflammatory responses or is immunologically silent.³² Nevertheless, apoptotic bodies removal could be defective during disease triggering and participating in disease development. As a result, apoptotic bodies may shift from being immunologically silent to proinflammatory agents, contributing to the pathogenesis of chronic inflammatory and fibrotic conditions.³³

Apoptotic bodies can also be involved in autoimmunity. In fact, they are enriched in histone H3, and the presence of antihistone H3 antibodies in SLE demonstrated their involvement in the disease pathogenesis.³⁴ Apoptotic bodies can be the means by which viruses spread during disease as for influenza A–infected monocyte¹² or for hepatitis C–infected hepatocytes³⁵ or HIV-1 in tubular renal cells.³⁶

Apoptotic Bodies in AKI

AKI is characterized by a rapid decline in kidney function, typically defined by an abrupt reduction in GFR and/or a rise in serum creatinine and/or reduction in urine output.^37,38 The etiologies are diverse but most commonly include ischemia-reperfusion injury (as occurs with shock, surgery, or vascular occlusion) and exposure to nephrotoxic agents, such as certain drugs (e.g., cisplatin, aminoglycosides), toxins, sepsis, or contrast media.^39–41 Within the kidney, the tubular epithelium, and specifically the proximal tubules, are among the most vulnerable compartments. The proximal tubular epithelial cells have high mitochondrial content, high metabolic/ATP demand, and limited glycolytic reserve and are therefore especially susceptible to hypoxia, oxidative stress, and toxic insults.⁴² As a result, insults such as ischemia-reperfusion or nephrotoxic exposures frequently result in apoptotic cell death of proximal tubular epithelia.⁴³

Interestingly, the apoptotic response in tubular epithelial cells during AKI has been documented in both experimental animal models and human biopsy samples.^42,43 Mechanistically, tubular epithelial apoptosis in AKI is mediated via both the intrinsic pathway—involving Bcl-2–associated X protein/Bcl-2 homologous antagonist/killer, cytochrome c release, caspase-9 activation—and via the extrinsic pathway—involving Fas/FasL, TNF-α receptor engagement, and caspase-8 activation.⁴³ In the context of AKI, large numbers of proximal tubule epithelial cells undergoing apoptosis generate a significant load of apoptotic bodies in the tubular lumen, the interstitial compartment, and the peritubular capillary/tubular interface.⁴⁴

Apoptotic bodies may carry or release DAMPs—such as HMGB1, mitochondrial DNA, histones, and oxidized mitochondrial proteins—which bind to and activate pattern recognition receptors (e.g., Toll-like receptor 2/Toll-like receptor 4) on resident renal cells or infiltrating immune cells.^45,46 Activation of Toll-like receptor/pattern recognition receptor signaling stimulates production of proinflammatory cytokines (IL-1β, IL-6, TNF-α) and chemokines (monocyte chemoattractant protein-1/C-C motif chemokine ligand 2), driving recruitment of neutrophils, monocytes/macrophages, and T cells into the injured kidney parenchyma.^47,48 In the tubular and peritubular microenvironment, such influx of inflammatory cells further injures the tubules via reactive oxygen species production, protease release, and microvascular disruption. In addition, the recruited leukocytes and their adherence to the endothelium contribute to endothelial activation, leukocyte–endothelial adhesion, increased permeability, and microvascular obstruction.⁴⁹

The release of mitochondrial-derived components, reactive oxygen species, and pro-oxidant molecules from apoptotic bodies can directly injure peritubular capillary endothelial cells. Endothelial activation (with increased expression of adhesion molecules, prothrombotic phenotype) leads to increased vascular permeability and leukocyte recruitment. Injury to the microcirculation results in reduced perfusion and peritubular capillary rarefaction,⁴⁴ which interrupts oxygen delivery to the metabolically demanding tubules.^50,51 Loss of peritubular capillaries is increasingly recognized as a pivotal mechanism linking AKI to CKD.^52,53

Apoptotic bodies may also carry intracellular antigens—such as nuclear antigens, mitochondrial peptides, or oxidized proteins—that can be taken up by dendritic cells or macrophages in the interstitium. These antigen-bearing phagocytes can then process and present antigen to T cells, potentially driving adaptive immune responses.⁴⁴ Although apoptosis is classically considered immunologically silent, when clearance of apoptotic bodies is delayed or inefficient (leading to secondary necrosis), the released intracellular contents and intact antigen structures can become immunogenic.^50,51 In the kidney, prolonged exposure of antigens and DAMPs in the context of apoptotic bodies may support sustained inflammation or even autoimmunity, thereby delaying repair.

The process of efferocytosis by macrophages or surviving tubular epithelial cells triggers anti-inflammatory signals. For example, engulfment of apoptotic bodies via receptors such as kidney injury molecule-1 on surviving proximal tubule epithelial cells or macrophages leads to downstream signaling that suppresses NF-κB activation and reduces expression of proinflammatory Toll-like receptor 4, thereby helping dampen the local immune response.⁵⁴ Engulfment also promotes macrophage polarization toward an M2-like phenotype, associated with release of anti-inflammatory cytokines such as IL-10 and TGF-β, which support resolution of inflammation and matrix remodeling.⁵³

Importantly, efferocytosis of apoptotic neutrophils actively reprograms macrophages toward an anti-inflammatory phenotype. In ischemic AKI, defective efferocytosis delays functional recovery, whereas efficient clearance of neutrophil apoptotic bodies promotes epithelial repair. Therefore, neutrophil apoptosis and efferocytosis have a role in the recovery from ischemic AKI.^55,56

The phagocytosis of apoptotic bodies under immunoregulatory conditions can also support the recruitment or differentiation of regulatory T cells (Tregs), a subset of T cells known for immunosuppressive and tissue-protective functions. Tregs limit effector T-cell activation, suppress autoimmunity, and support tissue repair following injury.⁴⁵ In kidney injury models, strategies that enhance Treg numbers have been associated with better outcomes and decreased progression to fibrosis. Thus, in the kidney after AKI, efficient clearance of apoptotic bodies may shift the milieu toward a regulatory immune environment conducive to regeneration.

In summary, during AKI, the wave of proximal tubular cell apoptosis generates a high burden of apoptotic bodies which—depending on the efficiency of their clearance and the context of the surrounding microenvironment—have roles: on one side, propagating inflammation, endothelial injury, and adaptive immune activation; on the other side, when handled optimally, promoting resolution, immunoregulation, and tissue repair. Understanding how to steer the response toward the reparative side (e.g., by enhancing efferocytosis or modulating DAMP signaling) may offer promising strategies to prevent the transition from AKI to CKD. Importantly, a critical determinant of long-term kidney outcome after AKI is the balance between maladaptive inflammation and effective tissue repair, targeting offering a promising avenue to interrupt the pathological continuum from AKI to CKD and improve long-term kidney outcomes.

Together, these findings underscore the context-dependent effects of apoptotic bodies in AKI (Figure 1). Their accumulation and exposure to immune cells can aggravate tissue injury, whereas their effective clearance helps restore homeostasis and limit chronic damage. Understanding and manipulating these pathways may open new therapeutic avenues for mitigating AKI and improving recovery outcomes.⁵⁷

Figure 1.

Role of apoptotic bodies derived from proximal tubular epithelial cell apoptosis during AKI. Left panel (harmful effects): During AKI, apoptosis of proximal tubular epithelial cells leads to the generation and release of apoptotic bodies and other DAMPs. These signals promote inflammatory signaling, recruitment of neutrophils and T cells, amplification of inflammation, and microvascular rarefaction, thereby contributing to ongoing tissue injury and progression to CKD. Right panel (reparative effects): In contrast, efficient clearance of apoptotic bodies by surviving tubular epithelial cells and macrophages through KIM-1–mediated efferocytosis promotes anti-inflammatory signaling. Polarization toward M2 macrophages and the release of anti-inflammatory cytokines such as IL-10 and TGF-β facilitate resolution of inflammation and support tissue repair and recovery following AKI. Figure was created with the help of ChatGPT. DAMP, damage-associated molecular pattern; KIM-1, kidney injury molecule-1.

Apoptotic Bodies in CKD and Fibrosis

In CKD, persistent metabolic, oxidative, and inflammatory stress induces sustained injury of tubular epithelial cells and interstitial cells, resulting in ongoing low-grade apoptosis rather than acute, high-intensity cell death.⁵⁸ Chronic apoptotic activity is particularly prominent in proximal tubular epithelial cells, where mitochondrial dysfunction, proteinuria-induced stress, and cytokine signaling (e.g., TGF-β and TNF-α) maintain apoptotic pathways.⁵⁹ Unlike AKI, in which apoptotic cells are efficiently cleared by professional phagocytes, CKD is frequently characterized by defective efferocytosis, leading to impaired recognition and removal of apoptotic cells and their vesicular remnants.^60,61 This inefficiency results in the progressive accumulation of apoptotic bodies within the kidney interstitium, where they perpetuate inflammation and fibrogenesis.^62,63

These accumulated apoptotic bodies are not inert by-products of cellular turnover but exert potent biological effects that actively drive fibrogenesis (Figure 2). Mechanistically, they influence the fibrotic microenvironment through several interconnected processes.

Figure 2.

Role of apoptotic bodies in CKD progression and fibrosis. Sustained cellular stress, inflammation, and injury in the kidney promote ongoing apoptosis of renal cells, leading to increased generation of apoptotic bodies. Defective or insufficient efferocytosis results in the accumulation of apoptotic bodies and persistent low-grade apoptosis, perpetuating a proinflammatory and profibrotic microenvironment. Apoptotic bodies interact with resident interstitial cells, promoting fibroblast-to-myofibroblast transition and activation. The resulting expansion of myofibroblasts enhances excessive extracellular matrix deposition, driving tubulointerstitial fibrosis and contributing to progressive structural damage and functional decline in CKD. Figure was created with the help of ChatGPT.

Importantly, the profibrotic effects of apoptic bodies should be related to TGF-β signaling, the central orchestrator of fibroblast activation, whereas chronic hypoxia, metabolic stress, and oxidative injury maintain myofibroblast survival.^64,65 Apoptic bodies can lower activation thresholds, prolong fibroblast responsiveness, and reinforce signaling loops synergizing with them.⁶⁶

Apoptotic bodies released from dying tubular epithelial cells contain bioactive cargo, including latent TGF-β, PDGF, and microRNAs such as micro RNA (miR)-21.⁴⁴ In addition, uptake of these vesicles by resident interstitial fibroblasts triggers signaling cascades that promote their activation and differentiation into α-smooth muscle actin–positive myofibroblasts, which display enhanced contractility and high secretory activity.⁶⁷ This process represents a critical driver of interstitial fibrosis, as myofibroblasts are the principal effector cells responsible for extracellular matrix (ECM) expansion.^65,68

Activated myofibroblasts stimulated by apoptotic body–derived signals secrete excessive amounts of fibronectin and collagens I and III, leading to disorganization of the tubular basement membrane and distortion of normal nephron architecture.^69,70 This maladaptive ECM accumulation narrows interstitial spaces, reduces capillary density, and promotes tissue hypoxia, creating a vicious cycle that further amplifies fibrogenesis.^71,72 Furthermore, accumulation of uncleared apoptotic debris may reinforce this process by sustaining proinflammatory and profibrotic signaling within the interstitium.

Apoptotic bodies and apoptotic cell–derived extracellular vesicles are enriched in profibrotic microRNAs (e.g., miR-21, miR-199a-5p) and cytokines such as TGF-β and IL-1β, which propagate fibrogenic signaling through paracrine communication. These vesicles can be internalized by neighboring fibroblasts, macrophages, and endothelial cells, amplifying the local activation of SMAD- and phosphoinositide 3-kinase/protein kinase B–dependent pathways.⁷³ For instance, miR-21 represses SMAD7 and phosphatase and tensin homolog, thereby sustaining TGF-β–driven fibroblast activation and ECM synthesis.⁷⁴

Interestingly, the pathologic role of apoptotic body accumulation is particularly evident in diabetic nephropathy and lupus nephritis, where increased apoptotic burden and defective efferocytosis correlate with severe interstitial fibrosis, macrophage infiltration, and faster decline in eGFR.^75–77 In these diseases, apoptotic bodies contribute not only to immune dysregulation but also to irreversible structural remodeling, reinforcing the concept that unresolved apoptotic cell clearance represents a critical, active driver of CKD progression.⁷⁸

Collectively, these findings support a mechanistic model in which persistent apoptosis and defective efferocytosis lead to apoptotic body accumulation, perpetuating interstitial inflammation, fibroblast activation, and maladaptive ECM deposition. This self-sustaining cycle converts adaptive repair into progressive fibrosis, culminating in tubular atrophy, nephron loss, and irreversible decline in kidney function.⁷⁹

Taken together, this evidence suggests that in CKD, especially in its fibrotic forms, apoptotic bodies represent more than just a consequence of cell death—they are active mediators of disease progression.

Apoptotic Bodies in Repair and Regeneration

Apoptotic bodies may play a beneficial role in tissue regeneration under certain physiologic and pathologic conditions. Although typically associated with the clearance of dying cells and immune modulation, emerging evidence suggests that apoptotic bodies can actively contribute to the repair and regeneration processes in damaged tissues through several mechanisms (Figure 3).

Figure 3.

Regenerative roles of apoptotic body–derived vesicles in tissue repair. Apoptotic body–derived vesicles released from apoptotic cells serve as bioactive mediators that promote tissue regeneration. These vesicles deliver regenerative microRNAs and other molecular cargo to progenitor and stem cells, modulating gene expression and activating prosurvival signaling pathways. Apoptotic body–associated signals also enhance endothelial cell function and stimulate angiogenesis through the induction of growth factors. In parallel, they modulate macrophage phenotype toward anti-inflammatory and prorepair states, increasing the production of anti-inflammatory cytokines. Collectively, these coordinated effects support renal tubular cell recovery and tissue repair. In murine kidney injury models, apoptotic body–derived vesicles accelerate epithelial regeneration, highlighting their therapeutic potential in postinjury repair. Figure was created with the help of ChatGPT.

Delivery of Regenerative MicroRNAs to Progenitor Cells

Apoptotic bodies can encapsulate and transport specific microRNAs that have regenerative properties. When these microRNAs are transferred to nearby or distant cells, they can influence gene expression patterns that promote cell proliferation, differentiation, and tissue regeneration. Zernecke and coworkers demonstrated that endothelial cell–derived apoptotic bodies have a protective vascular effect limiting atherosclerosis and stabilizing the plaque by delivering miR-126 to recipient vascular smooth muscle cell (VSMC), through the induction of C-X-C motif chemokine ligand 12 production.⁸⁰

Promotion of Angiogenesis and Endothelial Cell Survival

Supporting endothelial cell survival and proliferation, apoptotic bodies help restore vascular networks. In angiogenesis, apoptotic bodies may have a dual role: directly, endothelial apoptotic bodies can increase endothelial cell progenitor number and induce differentiation,⁸¹ stimulating angiogenesis by transferring mRNA⁸²; indirectly, when engulfed by phagocytes, apoptotic bodies can trigger the release of vascular endothelial growth factor.⁸³

Modulation of Macrophages toward Prorepair Phenotypes

Macrophages play a pivotal role in tissue healing by adopting different functional phenotypes. Apoptotic bodies can influence macrophage polarization, shifting them from a proinflammatory state (M1) to a prorepair or anti-inflammatory phenotype (M2). This switch promotes resolution of inflammation, facilitating tissue regeneration. In a model of osteoarthritis in mice, M2 macrophage-derived apoptotic bodies can reverse inflammatory response caused by M1 macrophage, probably through enrichment in miR-21-5p, thus preventing articular cartilage damage.⁸⁴

Recently, the modulatory properties of apoptotic body membrane proteins on inflammation and the capacity to induce regenerative responses have been leveraged to produce engineered microparticles to promote healing processes. Apoptotic bodies from adipose tissue stem cells have been encapsulated in microspheres and proposed for diabetic wound healing and for vascular injury repairing.^85,86

Moreover, in an animal study on a mouse model of AKI, the group of Hou et al. demonstrated that nanoparticles encapsulated with membrane of apoptotic renal tubular epithelial cells enhanced the clearance of damaged mitochondria, thereby reducing inflammation and improving ischemia-reperfusion injury.⁸⁷

Apoptotic Bodies and Vascular Calcification in CKD

The calcification process is a finely regulated physiologic process fundamental for mineralization, but in pathologic conditions, it can occur in soft tissue, indicated as ectopic calcification.⁸⁸ Vascular calcification, defined as the pathologic deposition of calcium phosphate crystals in the vessel wall, occurs in atherosclerotic plaque and in tunica media. In patients with CKD, vascular calcification is a major cardiovascular complication and contributes significantly to their morbidity and mortality.⁸⁹ Calcification in CKD mainly affects the media layer, with VSMCs as the principal cell type involved.⁹⁰ The mechanisms underlying vascular calcification are several, with a role of abnormal Ca-Pi homeostasis, decrease of calcification inhibitors, inflammation, VSMC osteoblastic differentiation, and apoptosis.⁹¹ Inappropriate apoptosis may have a role in the ectopic calcification development,^92,93 and a link between apoptosis and medial calcification^94,95 has been demonstrated by Proudfoot in spontaneously calcifying human aortic VSMCs in vitro.⁹⁶ In this study, the authors demonstrated that apoptosis precedes calcium deposition and its induction by a combination of anti-Fas IgM and cycloheximide exacerbated calcified nodule formation, whereas apoptosis prevention by the caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone.fmk decreased calcification. In the same study, a role for apoptotic bodies was supposed because proapoptotic stimuli generated abundant apoptotic bodies, which concentrate calcium in the form of calcium carbonate. Also in the calcification process of the atherosclerotic plaque, it has demonstrated an accumulation of apoptotic bodies due probably to an insufficient removal by less efficient phagocytes.^97,98 Thus, apoptotic bodies originating from VSMCs have an exacerbating role in medial calcification acting as nucleation sites for calcification and as the machinery to deposit calcium crystal in the vessel wall.⁹⁹

If the role of medial calcification in the onset of kidney disease cardiovascular comorbidities has been extensively elucidated, the role of endothelium in the calcification process is less clear. Recently, a study demonstrated that human aortic endothelial cells can calcify in vitro, and that in arteries from dialysis patients, endothelial cells accumulate fine intracytoplasmic calcium crystals.¹⁰⁰ Endothelial dysfunction and apoptosis are also involved in arterial calcification observed in the early stages of atherosclerosis.¹⁰¹ It has been hypothesized a role for apoptotic bodies derived from endothelial cells in endothelial repair, nevertheless, the relevancy of endothelial calcification and apoptosis to the medial calcification is a field that needs to be investigated.

In summary, there is evidence that apoptotic bodies from VSMC may be involved in the exacerbation of medial calcification, whereas the role of apoptotic bodies from endothelium needs to be elucidated.

Clinical Implications

Quantification of apoptotic bodies in plasma or urine may reflect injury severity. Proteomic or RNA profiling of apoptotic body content could offer insights into ongoing pathophysiology.⁵⁷ Therapeutic strategies that modulate apoptotic bodies biology are increasingly compelling. For example, enhancing efferocytosis to accelerate the clearance of apoptotic bodies may prevent the accumulation of secondary necrosis and resultant inflammatory trigger release, a scenario implicated in chronic disease pathogenesis.¹⁰² Concomitantly, blockade of profibrotic signaling cascades downstream of apoptotic body exposure—such as inhibition of TGF-β– or HMGB1-mediated activation of fibroblasts—represents a viable antiremodeling approach to mitigate fibrosis driven by apoptotic body cargo. Finally, engineered apoptotic bodies or apoptotic body-mimetics present a novel vector platform: For instance, apoptotic bodies derived from endothelial cells carrying miR-126 have been shown to modulate vascular progenitor recruitment and lesion stability in atherosclerosis models.⁸⁰ Translating this concept, apoptotic bodies deliberately loaded with miRs or anti-inflammatory payloads could provide targeted delivery to phagocytes or stromal cells, serving as Trojan horses to reprogram the microenvironment (as recently demonstrated in tumor immunotherapy platforms using apoptotic bodies laden with stimulator of interferon genes agonists).¹⁰³ Collectively, these avenues emphasize the necessity of robust translational biomarkers to track apoptotic body kinetics, composition, and downstream signaling in clinical contexts, alongside the development of agents with favorable safety margins and well-defined pharmacodynamics.

One potential therapeutic approach is the inhibition of apoptosis to limit the formation of apoptotic bodies, thus attenuating DAMP release, dampening inflammatory amplification, and favoring a reparative microenvironment that limits progression from AKI to CKD.

Vascular calcification is a major determinant of cardiovascular risk CKD. Growing evidence implies apoptotic bodies as active contributors to this process. During VSMC apoptosis, apoptotic bodies expose phosphatidylserine and other anionic phospholipids that serve as nucleation sites for calcium-phosphate deposition, initiating microcalcification. In the uremic milieu, altered apoptotic body generation and impaired clearance may accelerate this process, linking disordered mineral metabolism to vascular injury.¹⁰⁴

Clinically, apoptotic bodies may serve as biomarkers and therapeutic targets in CKD-associated vascular calcification. The abundance, composition, and calcific potential of circulating or tissue-derived apoptotic bodies could help identify patients at a higher risk of cardiovascular events. Moreover, therapeutic approaches that enhance efferocytosis or modulate apoptotic body membrane composition may mitigate vesicle-mediated mineral deposition and slow calcific progression.

Despite the promising evidence, the methods for separation and purification of apoptotic bodies are still in their infancy. The current methods, reviewed by Zhou et al.,¹⁰⁵ rely on some specific features such as size, DNA, RNA, mitochondrial cargo, and some characteristic membrane markers. Nevertheless, the main challenges are the overlap with other vesicles population and the lack of reliable specific markers. In kidney disease, the isolation from urine may represent an interesting alternative and integrating approach.

Conclusions

Apoptotic bodies have emerged as far more than passive byproducts of programmed cell death; they are active biologic entities with profound influence on kidney health and disease. In AKI, an excessive burden of uncleared apoptotic bodies can amplify tubular and endothelial injury, whereas in CKD, their chronic accumulation fuels fibroblast activation and maladaptive ECM deposition, promoting progressive nephron loss. Moreover, apoptotic body–mediated nucleation of calcium-phosphate crystals provides a mechanistic link between apoptosis and vascular calcification, a major contributor to cardiovascular morbidity in CKD. At the same time, the regenerative potential of apoptotic bodies—through delivery of reparative microRNAs, support of angiogenesis, and induction of prohealing macrophage phenotypes—underscores their dualistic nature.

Collectively, these insights position apoptotic bodies as central regulators of kidney injury and repair, as well as promising biomarkers and therapeutic targets. Future work should clarify the molecular determinants that dictate whether apoptotic bodies exert protective or pathogenic actions and explore strategies to modulate their formation, clearance, and signaling. Leveraging these pathways may open new avenues to mitigate kidney injury, limit fibrosis, reduce vascular calcification, and ultimately improve outcomes for patients with either acute or chronic kidney diseases.

Disclosures

Disclosure forms, as provided by each author, are available with the online version of the article at http://links.lww.com/JSN/F727.

Author Contributions

Conceptualization: Paola Ciceri, Mario Cozzolino.

Supervision: Mario Cozzolino.

Writing – original draft: Paola Ciceri, Mario Cozzolino.

Writing – review & editing: Paola Ciceri, Mario Cozzolino.

Funding

None.