Lysine Methyltransferases SMYD2 and SMYD3: Emerging Targets in Kidney Diseases

Abstract

Background

The SET and MYND domain-containing (SMYD) protein family is a group of lysine methyltransferases with SET and MYND domains and plays a critical role in regulating gene expression through the methylation of histone and non-histone proteins.

Summary

Studies have linked mutations or overexpression of SMYD2 and SMYD3 to various cancers, including renal carcinoma. Recent research also demonstrates that the expression levels and activity of SMYD2 and SMYD3 are increased in animal models of renal diseases such as autosomal dominant polycystic kidney disease, renal fibrosis, and diabetic nephropathy. Inhibiting either SMYD2 or SMYD3 pharmacologically or genetically can effectively suppress renal tumorigenesis and cystic formation while improving outcomes in renal fibrosis and diabetic nephropathy. Additionally, SMYD2 and SMYD3 are involved in the pathogenesis of acute kidney injury.

Key Messages

This review summarizes the roles of these two lysine methyltransferases in renal diseases, highlights their mechanisms, and emphasizes their potential as therapeutic targets for kidney disorders.

Introduction

Aberrant epigenetic modifications are critically involved in the pathogenesis of kidney diseases, with histone methylation being a key research focus. Histone methylation modification enzymes regulate various cellular functions, including heterochromatin formation, X chromosome inactivation, transcriptional regulation, and stem cell maintenance and differentiation [1]. Increasing evidence suggests that the dysregulation or aberrant expression of these enzymes contributes significantly to kidney disease progression by disrupting gene expression programs and altering protein functions, ultimately impairing renal cellular metabolism and homeostasis [2, 3].

The SMYD (SET and MYND domain-containing) family of lysine methyltransferases – comprising SMYD1 through SMYD5 – has attracted growing interest. While initially characterized for their roles in embryogenesis, cardiac and skeletal muscle development, and tumorigenesis [4–6], members of the SMYD family also play essential roles in renal physiology and pathology. Through histone and non-histone methylation, SMYD proteins modulate key signaling pathways and gene expression networks in renal cells, thereby influencing cellular characteristics and disease-related processes [7–10]. For example, SMYD2 has been shown to promote the development and progression of both acute kidney injury (AKI) and chronic kidney disease (CKD) by regulating pathological mechanisms such as cell proliferation, apoptosis, inflammation, and fibrosis [10–12]. Given these multifaceted roles, the SMYD family is increasingly recognized as a potential therapeutic target in kidney disease research.

Among the SMYD family members, only SMYD2 and SMYD3 exhibit notable expression in renal tissues. This review focuses on the biological functions and regulatory mechanisms of SMYD2 and SMYD3 in kidney cells and across various experimental models of renal diseases. Specifically, we examine their roles in renal tumors, autosomal dominant polycystic kidney disease (ADPKD), AKI, renal fibrosis, and diabetic nephropathy (Table 1). In addition, we discuss the therapeutic potential of targeting SMYD2 and SMYD3 in these pathological conditions.

Table 1.

SMYD2 and SMYD3 inhibition on kidney diseases in various in vitro and in vivo models

Inhibitors or KO mice	Models in vitro	Models in vivo	Effects and mechanisms	References
SMYD2 siRNA, AZ505	HK-2 cells, HEK293T cells, OSRC-2 cells, 786-O cells	Tumor orthotopic xenograft in nude mice, tumor subcutaneous xenograft in nude mice, lung metastasis mice model	Inhibit ccRCC cell growth, migration, and invasion by blocking SMYD2/miR-125b/DKK3 pathway, enhance the synergistic effect with anticancer drugs	[13]
SMYD2 siRNA, AZ505	MEK cells, PH2 cells, PN24 cells, mIMCD3 cells	Ksp-Cre Pkd1-knockout mice model, tamoxifen-induced conditional Pkd1-knockout mice model	Delay renal cyst formation and growth, inhibit STAT3 and NF-κB-p65 activation	[10]
SMYD2 siRNA, AZ505	NRK-49F cells, NIH3T3 fibroblasts	Ksp-Cre Pkd1-knockout mice model, tamoxifen-induced conditional Pkd1-knockout mice model	Ameliorate renal fibrosis, suppress the TGF-β-induced expression of fibrotic genes, activation of renal fibroblasts, and the formation of stress fibers	[9]
SMYD2 siRNA, AZ505	NRK-49F cells	Mouse model of unilateral ureteral obstruction	Attenuate fibrosis, reduce the activation of renal interstitial fibroblasts, inhibit TGF-β1-induced EMT	[14]
SMYD2 siRNA, LV-SMYD2, AZ505, LLY507	NRK-52E cells, HK2 cells	Cisplatin-induced CKD mouse model	Attenuate renal fibrosis, inflammation and apoptosis, inhibit cisplatin-induced EMT	[11, 15]
SMYD2 siRNA	HK2 cells	Glyoxylate-induced CaOx stones mouse model	Inhibit CaOx-induced glycolysis, apoptosis, inflammation, and EMT	[16]
AZ505	NRK-49F cells	Streptozotocin (STZ)-induced DN	Attenuate renal fibrosis, inhibit activation of rat renal fibroblasts	[17]
AZ505, RTT extract	/	Streptozotocin (STZ)-induced DN	Attenuate renal fibrosis and inflammation	[18]
SMYD2 siRNA, AZ505	MTEC cells	Cisplatin-induced AKI mouse model	Reduce renal dysfunction and renal tubular cell death, prevent renal tubular injury	[12]
SMYD3 shRNA	TK10 cells, KRC/Y cells, A498 cells, 786-O cells	Tumor xenograft in nude mice	Inhibit survival, invasion, and growth of RCC cells with VHL mutation	[8]
SMYD3 shRNA	mIMCD3 cells, HEK293T cells, NIH3T3 fibroblasts	Ksp-Cre Pkd1-knockout mice model, tamoxifen-induced conditional Pkd1-knockout mice model	Delayed renal cyst growth and improve kidney function, reduced genomic instability, and primary cilia	[7]
SMYD3 siRNA, BCI-121	MTEC cells	I/R-induced AKI mouse model	Aggravate I/R injury and apoptosis, inhibit EGF-induced proliferation and dedifferentiation	[19]

SMYD Family

Structure and Function of the SMYD Family

The SMYD (SET and MYND domain-containing) family of proteins is located on chromosome 1q32.3 of the human genome [20] and is characterized by broad yet spatiotemporally regulated expression across mammalian tissues and organs. Despite their functional diversity, SMYD proteins share a structurally conserved architecture consisting of several key domains (Fig. 1). These include the following: (1) SET domain – comprising three subdomains: N-SET (N-terminal), I-SET (insertion), and C-SET (core), this domain is responsible for catalyzing methylation reactions on both histone and non-histone substrates; (2) MYND domain – a zinc finger structure composed of seven cysteine residues and one histidine, primarily involved in mediating protein-protein interactions; (3) CTD – formed by anti-parallel α-helices, the CTD interacts with the I-SET and post-SET domains to create a deep and narrow substrate-binding pocket [6]. The CTD also contributes to enzymatic activation by facilitating the binding of SMYD proteins to substrates or molecular chaperones such as heat shock protein 90 (HSP90) [21].

Fig. 1.

Domain architecture of SMYD family proteins. SMYD (SET and MYND domain-containing) family proteins share a conserved structural organization composed of the following key domains arranged sequentially: N-SET domain (N-terminal portion of the SET domain); MYND domain, which contains a zinc finger motif critical for protein-protein interactions; I-SET domain (intervening SET subdomain); C-SET domain (C-terminal portion of the SET domain); post-SET domain, involved in substrate recognition and catalysis; C-terminal domain (CTD), which may contribute to substrate specificity and subcellular localization.

The biochemical activity of SMYD proteins arises from their ability to methylate a broad spectrum of histone and non-histone targets through a substrate-dependent mechanism. Notably, multiple SMYD family members can methylate the same substrate, potentially modifying it simultaneously or in a coordinated fashion. Subcellular localization studies have shown that SMYD family members function in both the nucleus and cytoplasm. Nuclear-localized SMYD proteins influence gene expression and chromatin remodeling, whereas cytoplasmic forms regulate diverse cellular signaling pathways and other biological processes. Collectively, the multifaceted roles of SMYD proteins highlight their importance not only in normal development but also in the pathogenesis of various diseases.

SMYD2

SMYD2 is one of the most extensively studied members of the SMYD family and is distinguished by its unique structural and functional properties. Binding of cofactors induces conformational changes in its CTD, expanding its protein interaction network and enhancing its enzymatic activity [22]. SMYD2 is highly expressed in various tissues, including the heart, brain, liver, kidney, thymus, and ovaries, and is localized to both the nucleus and cytoplasm [20].

Functionally, SMYD2 catalyzes the methylation of histone substrates – specifically H3K4 and H3K36 – as well as a range of non-histone proteins, such as p53 [23], heat shock protein 90 (HSP90) [24], and poly(ADP-ribosyl)transferase 1 [25]. Through these modifications, SMYD2 promotes gene transcription and regulates essential cellular processes including proliferation, differentiation, apoptosis, angiogenesis, and cancer cell invasion and metastasis. It also plays important roles in brain development and the maturation of skeletal muscle and cardiomyocytes, while contributing to the pathogenesis of various cancers, including gastric, bladder, colorectal, and breast cancer [7, 26–28]. For example, SMYD2 has been shown to promote breast cancer progression by enhancing the expression of the melanoma cell adhesion molecule through H3K36me2 methylation at its promoter region, thereby facilitating tumor growth and maintaining stem-like properties [29]. In cardiomyocytes, SMYD2 suppresses the intrinsic apoptotic pathway by methylating lysine 370 of the p53 transcription factor, thus inhibiting p53-mediated cell death [30].

SMYD3

The MYND domain of SMYD3 is structurally distinctive, positioned near the substrate-binding pocket and characterized by a positively charged surface that enables direct DNA interaction. This unique feature enhances its histone methyltransferase activity by facilitating substrate recognition and chromatin association [31]. SMYD3 exhibits spatiotemporally regulated expression across various organs, including the heart, skeletal muscle, testis, thymus, brain, kidney, and ovary. Notably, its nuclear accumulation is particularly prominent during the S and G2-M phases of the cell cycle, reflecting its involvement in cell proliferation [32].

SMYD3 methylates a broad range of substrates, including histones – such as H3K4 [33], H4K5 [34], and H4K20 [35] – as well as non-histone proteins like vascular endothelial growth factor receptor 1 [36], mitogen-activated protein kinase kinase kinase 2 [37], AKT1 [38], human epidermal growth factor receptor 2 [39], and enhancer of zeste homolog 2 [40]. Through H3K4 methylation in particular, SMYD3 modulates chromatin structure and transcriptional activity [41]. This epigenetic regulation plays a crucial role in controlling the expression of genes involved in cell cycle progression, differentiation, and signal transduction, including the activation of several oncogenes. Furthermore, SMYD3 is implicated in skeletal muscle development and various malignancies [41, 42]. For example, SMYD3 has been shown to upregulate matrix metalloproteinase-9 expression in diverse cancer cell types – including leukemic, fibrosarcoma, and breast cancer cells – by catalyzing H3K4 methylation at the matrix metalloproteinase-9 promoter region [5].

SMYD2 and SMYD3 in Kidney Diseases

A growing body of evidence indicates that SMYD2 and SMYD3 play pivotal roles in the onset and progression of a wide range of kidney diseases, including renal cell carcinoma (RCC), autosomal dominant polycystic kidney disease (ADPKD), renal fibrosis, diabetic nephropathy, and AKI. Notably, the majority of these findings have been derived from studies using animal models.

Role of SMYD2 in Kidney Diseases

SMYD2 exerts its biological functions primarily through the methylation of both histone and non-histone target proteins. In the cardiovascular system, SMYD2 preserves sarcomere integrity by methylating HSP90 and the HSP90-titin complex, which is essential for maintaining myofibrillar structure and function [24]. In Hirschsprung’s disease, SMYD2 promotes cellular proliferation and migration by modulating METTL3 expression and enhancing m⁶A RNA methylation [43]. In the context of kidney disease, SMYD2 regulates critical pathological processes – including cell proliferation, apoptosis, inflammation, and fibrosis – through the methylation of histone substrates (e.g., H3K36me3) and non-histone proteins such as NF-κB, STAT3, and phosphatase and tensin homolog (PTEN). Its renal specificity is attributed to two major factors: (1) pathway-specific targeting in renal disease – SMYD2 coordinates the regulation of multiple disease-relevant pathways, including carcinogenesis (via the miR-125b/DKK3 axis), cystogenesis (via the STAT3/NF-κB feedback loop), fibrogenesis (through TGF-β/Smad3 signaling), and AKI (through p53-dependent apoptosis); (2) kidney-specific microenvironmental cues – conditions such as high glucose and hypoxia characteristic of diseased renal tissue aberrantly activate SMYD2. This leads to enhanced methylation of renal substrates such as STAT3 at lysine 685 in ADPKD, and PTEN at lysine 313 in renal fibrosis. These context-dependent modifications underscore SMYD2’s critical involvement in kidney disease pathogenesis and highlight its potential as a therapeutic target.

SMYD2 and RCC

SMYD2 plays a pivotal role in promoting the development, metastasis, and multidrug resistance of RCC. It is significantly overexpressed in RCC patient tissues and xenograft tumors, and its elevated expression correlates with poor clinical outcomes – including reduced overall and disease-free survival – in patients with clear cell RCC (ccRCC) [13, 44, 45]. The histological similarity between benign eosinophilic tumors and RCC often complicates diagnosis [46]. However, SMYD2 transcript levels have diagnostic utility: they can distinguish papillary RCC (chRCC) from eosinophilic tumors with a sensitivity of 71.0% and specificity of 73.3%, underscoring its potential as both a diagnostic and prognostic biomarker for RCC aggressiveness [44, 45]. Mechanistically, chromatin immunoprecipitation studies have demonstrated that the SMYD2 inhibitor AZ505 blocks SMYD2 binding to the miR-125b promoter, thereby inhibiting the SMYD2/miR-125b/DKK3 oncogenic axis. This suppression leads to reduced proliferation, migration, and invasion of ccRCC cells. In addition, SMYD2 inhibition downregulates the expression of P-glycoprotein (P-gP), a key effector of chemoresistance, thereby enhancing the chemosensitivity of RCC cells [13].

SMYD2 and ADPKD

SMYD2 has emerged as a novel epigenetic regulator of cyst growth in ADPKD [47] (Fig. 2). It is significantly upregulated in renal epithelial cells from PKD1-mutant mice and ADPKD patient samples. Loss of SMYD2 delays cyst formation and progression in PKD1-mutant kidneys. Mechanistically, SMYD2 methylates STAT3 at lysine 685 and NF-κB p65 at lysine 310, thereby modulating their phosphorylation status and promoting proliferation and apoptosis in cystic epithelial cells. Moreover, SMYD2 orchestrates pro-inflammatory cytokine networks through two independent but synergistic positive feedback loops: the SMYD2-STAT3-IL-6-SMYD2 axis and the SMYD2-NF-κB p65-TNFα-SMYD2 axis, which collectively drive cyst growth in ADPKD [10]. In parallel, SMYD2 directly binds to promoters of transforming growth factor-beta (TGF-β) and fibrosis-related genes, regulating their transcription and activating fibroblasts. This establishes a SMYD2-TGF-β-Smad3-SMYD2 feedback loop that exacerbates renal fibrosis associated with ADPKD [9].

Fig. 2.

SMYD2-mediated pathways in PKD1-mutant renal epithelial cells and kidneys. In PKD1-mutant renal epithelial cells and kidneys, upregulated SMYD2 contributes to cyst growth and fibrosis through multiple signaling mechanisms. SMYD2 methylates the p65 subunit of NF-κB and STAT3, enhancing their activation. It modulates cytokine networks through two independent positive feedback loops: the SMYD2-STAT3-IL-6-SMYD2 axis and the SMYD2-NF-κB p65-TNFα-SMYD2 axis, thereby amplifying pro-inflammatory and proliferative signaling to promote cystogenesis. Additionally, TGF-β/Smad3 signaling upregulates SMYD2 transcription. In turn, SMYD2 enhances fibrotic gene expression via histone methylation, establishing a SMYD2-TGF-β-Smad3-SMYD2-positive feedback loop that drives renal fibrosis. Key downstream targets include fibronectin (Fn), collagen I (Col1a1), and alpha-smooth muscle actin (α-SMA).

SMYD2 and AKI

SMYD2 plays a significant role in AKI. Both SMYD2 and its histone methylation mark, H3K36me3, are upregulated in murine kidneys following ischemia/reperfusion (I/R) injury, coinciding with increased levels of cleaved caspase-3, p53, and phosphorylated p53 in proximal tubules, as well as activation of JNK-STAT3 signaling pathways [48]. Caspase-3 and p53 mediate apoptotic cell death, while STAT3 contributes to inflammatory responses [49].

Pharmacological inhibition of SMYD2 by AZ505 confers protection against cisplatin-induced AKI. AZ505 treatment reduces histopathological kidney damage, suppresses tubular apoptosis, decreases the release of inflammatory cytokines, and promotes tubular regeneration. Mechanistically, AZ505 inhibits cleaved caspase-3, BAX expression, and p53 phosphorylation, while enhancing the expression of cell cycle proteins and suppressing STAT3 and NF-κB phosphorylation. These effects collectively promote tubular cell proliferation and mitigate inflammation [12, 15].

Although these findings position SMYD2 as a promising therapeutic target in AKI, current evidence largely stems from cisplatin-induced injury models. Further research is required to elucidate SMYD2’s role across diverse AKI etiologies.

SMYD2 and Renal Fibrosis

SMYD2 drives the progression of renal fibrosis (Fig. 3). Both SMYD2 and its associated histone mark H3K36me3 are upregulated in chronically injured kidneys. Inhibition of SMYD2 effectively attenuates fibrosis by suppressing G2/M phase epithelial cell cycle arrest, inhibiting renal interstitial fibroblast activation and proliferation, and modulating inflammatory responses and signaling pathways [14].

Fig. 3.

SMYD2-mediated pathways in chronic kidney disease (CKD). SMYD2 drives fibrosis through multiple context-specific mechanisms in CKD. In calcium oxalate (CaOx)-induced nephropathy, SMYD2 methylates PTEN, resulting in the activation of the AKT/mTOR pathway. This promotes glycolytic reprogramming in renal tubular cells, enhancing fibrotic progression. In unilateral ureteral obstruction (UUO) and cisplatin-induced CKD models, upregulated SMYD2 contributes to fibrosis by inducing G2/M cell cycle arrest, renal fibroblast activation, epithelial-to-mesenchymal transition (EMT), and by activating TGF-β/Smad3, ERK, AKT, NF-κB, and STAT3 pathways. In diabetic kidney disease (DKD), SMYD2 is upregulated in response to high glucose (HG) or streptozotocin (STZ) exposure. It promotes NF-κB p65 phosphorylation, nuclear translocation, and transcriptional activation of fibrotic genes via histone methylation, exacerbating renal inflammation and fibrosis.

In human and animal models of calcium oxalate (CaOx) kidney stones, SMYD2 and glycolytic enzymes are elevated. SMYD2 promotes tubular glycolysis and metabolic reprogramming by activating the AKT/mTOR pathway through methylation of PTEN, contributing to tubular injury and fibrosis [16]. In unilateral ureteral obstruction-induced CKD models, treatment with the SMYD2 inhibitor AZ505 suppresses Snail and Twist expression, inhibiting epithelial-to-mesenchymal transition and reducing ERK1/2, STAT3, and NF-κB activation. This leads to decreased extracellular matrix deposition and fibrosis [14]. Additionally, both SMYD2 inhibitors AZ505 and LLY507 ameliorate cisplatin-induced CKD by blocking TGF-β1/Smad3-mediated fibroblast activation, as well as inhibiting NF-κB activation and apoptosis [11, 15].

SMYD2 and Diabetic Kidney Disease

Diabetic kidney disease (DKD), a major complication of diabetes, is characterized by glomerular hypertrophy, proteinuria, reduced glomerular filtration rate, and progressive fibrosis, ultimately leading to renal failure. Pathological features include mesangial hyperplasia, thickening of the glomerular basement membrane, capillary occlusion, podocyte injury, and fibroblast activation [50]. Hyperglycemia promotes fibroblast transdifferentiation into myofibroblasts, which secretes excessive extracellular matrix, driving extensive fibrosis [51, 52]. Nuclear factor kappa B (NF-κB) plays a key role in regulating this phenotypic transition of fibroblasts [53].

SMYD2 contributes to DKD pathogenesis by activating renal fibroblasts under hyperglycemic conditions. SMYD2 expression is upregulated in the kidneys of streptozotocin-induced diabetic mice [54]. Both Ranunculus ternatus extracts and the SMYD2 inhibitor AZ505 reduce SMYD2 levels, H3K36me3 histone methylation, and NF-κB p65 phosphorylation, exerting anti-inflammatory and anti-fibrotic effects in diabetic nephropathy models [17, 18]. In NRK49F fibroblast cells, high glucose induces nuclear co-localization of phosphorylated NF-κB p65 (p-p65) and SMYD2. Treatment with AZ505 blocks p-p65 nuclear translocation and expression, thereby inhibiting hyperglycemia-induced fibroblast activation [17].

Role of SMYD3 in Kidney Disease

Current research highlights that SMYD3 regulates cell fate decisions through epigenetic reprogramming of target gene transcription, a fundamental mechanism conserved across various organ diseases. In cancer, SMYD3 promotes tumor progression by activating kinases and facilitating degradation of tumor suppressors [41]. During skeletal muscle development, SMYD3 modulates differentiation by targeting the myogenic regulator myogenin [55]. In vascular remodeling, SMYD3 enhances vascular smooth muscle cell proliferation and migration by increasing H3K4me3 marks at specific gene promoters [56]. In kidney disease (Fig. 4), SMYD3 epigenetically contributes to the progression of RCC and ADPKD, while also facilitating repair processes in AKI. It displays three kidney-specific features: (1) an oncogenic mechanism dependent on a von Hippel-Lindau (VHL)-deficient microenvironment; (2) regulation of ciliary function via α-tubulin methylation; and (3) a context-dependent protective role during AKI regeneration.

Fig. 4.

SMYD3-associated pathways across kidney disease models. SMYD3 exerts distinct roles across different renal pathologies via epigenetic regulation: (1) ischemia/reperfusion (I/R)-induced acute kidney injury (AKI): SMYD3 enhances H3K4me3 enrichment at the EGFR promoter, promoting its transcription. This upregulates EGFR/AKT signaling, supporting tubular cell survival, dedifferentiation, and proliferation, thereby facilitating post-injury renal repair. (2) Renal cell carcinoma (RCC): SMYD3 is recruited by lncRNA CDKN2B-AS1 and CBP to the NUF2 promoter, increasing H3K4me3 and H3K27ac to drive NUF2 expression and tumor progression. In parallel, the VHL/HIF-2α/SMYD3 cascade directs SMYD3 to the EGFR promoter, enhancing H3K4me3 deposition and EGFR transcription, further promoting RCC malignancy. (3) Autosomal dominant polycystic kidney disease (ADPKD): SMYD3 modulates key PKD-associated signaling pathways (e.g., NF-κB p65, STAT3, ERK1/2, and cyclin D1) that regulate cell proliferation, apoptosis, and the cell cycle. Additionally, SMYD3 methylates α-tubulin-K40, disrupting mitotic integrity and ciliary function, contributing to genomic instability and cystogenesis.

SMYD3 and RCC

SMYD3 expression is markedly elevated in RCC tumors and is associated with advanced disease stage, aggressive histological subtypes, high nuclear grade, and poorer patient survival outcomes [8, 57]. Mechanistically, the long noncoding RNA CDKN2B-AS1 recruits SMYD3 along with the histone acetyltransferase CREB-binding protein to the promoter region of NUF2, promoting enrichment of H3K4me3 and H3K27ac marks, thereby enhancing NUF2 transcription and facilitating ccRCC progression [58]. Additionally, SMYD3 knockdown significantly impairs RCC cell proliferation, reduces colony formation, diminishes tumorigenic potential, and induces apoptosis [8]. Through the VHL/HIF-2α/SMYD3 signaling axis, SMYD3 catalyzes H3K4me2 and H3K4me3 modifications at the epidermal growth factor receptor (EGFR) promoter, increasing SP1 transcription factor binding and upregulating EGFR expression, thereby driving RCC progression [8].

SMYD3 and ADPKD

In ADPKD, loss of polycystin-1 (encoded by PKD1) and disruption of primary cilia are critical drivers of cyst growth [59]. Chromosomal instability contributes to clonal heterogeneity, further accelerating cyst progression, a hallmark of ADPKD [60]. SMYD3 is upregulated in PKD1-mutant mice and human ADPKD kidneys, where it enhances transcriptional activity through increased H3K4me3 deposition. Notably, SMYD3 knockout delays cyst development and improves renal function in PKD1-mutant mice [7]. Mechanistically, SMYD3 influences key PKD-related signaling pathways – such as NF-κB p65, STAT3, ERK1/2, CDK4, CDK6, and cyclin D1 – regulating cell proliferation, apoptosis, and cell cycle progression. Moreover, SMYD3 modulates primary cilia assembly by localizing to centrosomes and promotes genomic instability by methylating α-tubulin at lysine 40 (K40), thereby exacerbating cyst growth [7].

SMYD3 and AKI

Our recent studies demonstrated that SMYD3 is upregulated in murine kidneys following I/R injury. Pharmacological inhibition of SMYD3 using the selective inhibitor BCI-121 worsened tubular injury, increased apoptosis, and impaired renal function in this model [19]. Further investigations revealed that BCI-121 also suppressed renal epithelial cell differentiation and proliferation. Mechanistically, SMYD3 promotes EGFR expression and activates EGFR/AKT signaling by mediating H3K4me3 enrichment at the EGFR promoter. Considering the pivotal role of EGFR in tubular cell survival and regeneration after AKI [61], SMYD3-mediated activation of the EGFR pathway likely plays a critical protective role in renal recovery.

SMYD3 and Renal Fibrosis

Although SMYD3’s role in renal fibrosis remains to be fully elucidated, it has been shown to regulate renal fibroblast proliferation. Recent studies using iTRAQ technology identified elevated SMYD3 and H3K4me3 levels in renal tissues from rats with fetal growth restriction [62]. Moreover, SMYD3 expression strongly correlates with proliferation and reprogramming efficiency in porcine fibroblasts. SMYD3 upregulation enhances fibroblast proliferation and improves developmental potential in nuclear transfer embryos [63]. Similarly, overexpression of SMYD3 promotes proliferation and increases the efficiency of induced pluripotent stem cell generation in bovine embryonic fibroblasts [64]. Given that renal fibroblast activation and proliferation are key drivers of CKD progression, it is plausible that SMYD3 plays an important role in renal fibrosis and CKD pathogenesis. This hypothesis warrants further investigation.

Distinct Roles of SMYD2 and SMYD3 in Kidney Diseases

While SMYD2 and SMYD3 share pathogenic roles in promoting renal tumors, ADPKD, fibrosis, and diabetic nephropathy, their functional roles and underlying mechanisms diverge in AKI. SMYD2 exacerbates tubular damage by activating p53-dependent apoptosis, cleaved caspase 3, and JNK-STAT3 inflammatory pathways in a murine model of cisplatin-induced AKI [12]. In contrast, SMYD3 exerts a protective effect on the renal epithelium by sustaining EGFR/AKT-mediated cell survival and regeneration in a murine model of I/R-induced AKI [19]. The reasons behind this dichotomy remain unclear but may relate to the specific AKI model employed. Further studies are warranted to comprehensively assess the distinct functional roles of SMYD2 and SMYD3 across diverse AKI models.

SMYD2 and SMYD3 as Potential Therapeutic Targets for Kidney Diseases

SMYD2

SMYD2 is upregulated in renal tumors, AKI, and CKD, with its expression closely correlating with disease onset and progression. Thus, SMYD2 represents a promising therapeutic target for treating renal tumors as well as acute and CKDs.

SMYD2 inhibitors are categorized into five structural classes: benzoxazinones (e.g., AZ505), diphenylpiperazines (e.g., LLY-507), aminopyrazolone (e.g., BAY-598), noncompetitive inhibitors (EPZ series), and SAM-competitive inhibitors (e.g., PFI-5) [65]. Among these, BAY-598 and EPZ compounds demonstrate favorable oral bioavailability but exhibit limited cellular activity [66, 67]. AZ505 is the most extensively studied in kidney disease models, showing therapeutic efficacy against fibrosis, ADPKD, and AKI; however, long-term safety and human data remain lacking. Notably, 6-month administration of AZ505 (10 mg/kg, i.p.) significantly delayed cyst formation in mice with good tolerability and no observed weight loss [14]. LLY-507 offers superior pharmacokinetics, high selectivity, and low cytotoxicity [68] and effectively attenuated fibrosis in cisplatin-induced CKD models with efficacy comparable to AZ505 and without weight loss [11].

Significant progress has been made in elucidating SMYD2’s role in cancer progression. SMYD2 is frequently upregulated across multiple cancers, where its expression correlates with enhanced proliferation, metastasis, immune evasion, and drug resistance. The SMYD2 inhibitor AZ505 suppresses triple-negative breast cancer growth by inhibiting methylation mediated by STAT3, NF-κB p65, and protein tyrosine phosphatase non-receptor type 13 (PTPN13) [27]. Additionally, AZ505 reduces proliferation in human renal cancer primary cells and xenograft models, while also enhancing chemosensitivity in RCC [13]. Given cisplatin’s widespread use as a chemotherapeutic agent and AZ505’s protective effects against cisplatin-induced kidney injury, dual targeting of SMYD2 could both potentiate cisplatin’s antitumor efficacy and confer renal protection. Therefore, AZ505 holds promise as a chemotherapeutic adjuvant in RCC and as a novel therapeutic agent for CKDs such as ADPKD, potentially improving overall patient outcomes.

SMYD3

SMYD3 is overexpressed in RCC, correlating with tumor progression and poor patient prognosis. Silencing SMYD3 markedly inhibits RCC growth and invasiveness, making it a promising therapeutic target. Several high-selectivity SMYD3 inhibitors have been developed, including BCI-121, nano-EM127, BAY-6035, EPZ031686, EPZ030456, and GSK2807 [69]. Among these, EM127 and BAY-6035 show significantly higher binding affinity compared to the micromolar-potency inhibitor BCI-121 [70–72]. EM127 inhibits SMYD3 through covalent binding to Cys186, while BAY-6035 is highly selective and inactive against 34 other methyltransferases. In contrast, BCI-121’s lower potency raises concerns about off-target effects. However, EM127, BAY-6035, and related compounds exhibit poor membrane permeability – likely due to nitrogenous heterocycles – and pose risks of CYP450-mediated drug-drug interactions, necessitating careful metabolite toxicity evaluation [70–72]. EPZ031686 improves lipophilicity by blocking hydrogen-bond donors, showing strong cellular activity, excellent oral bioavailability, and metabolic stability [73], making it a promising candidate for targeted kidney disease therapy. Both BCI-121 (administered at 50 mg/kg thrice weekly for 6 weeks) and nano-EM127 effectively inhibit SMYD3 in vivo [74, 75]. Key challenges remain: EM127’s low permeability and potential toxicity linked to irreversible inhibition, and BCI-121’s off-target risks. Notably, EM127’s sustained inhibition may benefit chronic diseases like ADPKD and cancer.

Despite promising preclinical results with SMYD2/3 inhibitors such as AZ505 in kidney disease models, clinical translation faces several hurdles: (1) tissue-specific paradoxes – SMYD2 is cardioprotective [30] but exacerbates apoptosis in AKI [12], so systemic administration could cause unpredictable off-target effects. SMYD3 is oncogenic in RCC but promotes renal tubular regeneration in AKI, meaning its inhibition might impair tissue repair. (2) Lack of human pharmacokinetic/pharmacodynamic data – no clinical trials have been reported for these inhibitors. Although AZ505 and LLY-507 appear safe in animal studies, their long-term human safety remains uncharacterized. (3) Model limitations – most SMYD2 research in AKI uses cisplatin-induced models; studies in ischemia/reperfusion or sepsis models are needed. Similarly, the role of SMYD3 in renal fibrosis is mostly inferred from fibroblast data, requiring direct evidence from CKD models.

Conclusions and Perspectives

The SMYD family regulates transcription and diverse cellular processes, including proliferation, differentiation, and apoptosis [69, 76]. Among its five members, SMYD2 and SMYD3 have emerged as key epigenetic regulators in kidney diseases, modulating cystogenesis, fibrosis, diabetic nephropathy, and AKI through methylation of both histone and non-histone substrates [7, 9, 10, 12, 14, 18, 77]. While SMYD2 has been extensively studied in renal tumors [13, 45], ADPKD [9, 10], fibrosis [11, 14, 16], and AKI [12], research on SMYD3 remains nascent, primarily focusing on RCC and ADPKD [7, 8]. Despite accumulating evidence implicating both enzymes in diverse renal pathologies, the precise molecular mechanisms remain incompletely understood. Both SMYD2 and SMYD3 engage multiple signaling pathways, such as TGF-β and STAT3, and methylate various substrates, complicating mechanistic delineation [9, 14, 69, 76]. Notably, SMYD2 displays context-dependent functions – promoting fibrosis in ADPKD while exacerbating inflammation during AKI [10, 12]. Thus, systemic inhibition risks unintended off-target effects. Addressing inhibitor specificity and pathway complexity is essential for therapeutic translation. Future research should prioritize comprehensive mapping of non-histone substrates and context-dependent interactions. Moreover, it is critical to evaluate the efficacy and mechanisms of various SMYD2/3 inhibitors across diverse animal models of kidney disease and to employ combinatorial approaches for deeper mechanistic insights – foundational steps toward realizing their full therapeutic potential.

Conflict of Interest Statement

Shougang Zhuang was a member of the journal’s Editorial Board at the time of submission. The other authors declared no competing interest in this work.

Funding Sources

This study was supported by grants from the National Natural Science Foundation of China (82370698 and 82070700 to S.Z.) and US National Institutes of Health (1R56DK135540-01 to S.Z.).

Author Contributions

Xinyu Du and Liyuan Yao are responsible for collecting literature and drafting the review. Shougang Zhuang revised the manuscript. All authors read and approved the final manuscript.

Funding Statement

This study was supported by grants from the National Natural Science Foundation of China (82370698 and 82070700 to S.Z.) and US National Institutes of Health (1R56DK135540-01 to S.Z.).