Podocytes are key structural components of the glomerular filtration barrier and are essential for maintaining selective protein filtration. Podocyte dysfunction is closely associated with proteinuria and the progression of glomerulosclerosis, constituting the common pathological basis of various chronic kidney diseases such as diabetic nephropathy and focal segmental glomerulosclerosis. While histone post-translational modifications have been extensively studied in podocyte biology, recent attention has shifted toward the regulatory roles of nonhistone post-translational modifications. By modulating protein stability, activity, localization, and interactions, these modifications participate in core biological processes such as apoptosis, cytoskeletal remodeling, inflammatory signaling, and metabolic reprogramming. Nevertheless, the strength of evidence is not uniform across post-translational modification categories. While some mechanisms have been directly demonstrated in podocytes, others are inferred mainly from broader kidney injury models or from studies in non-podocyte cell types. Accordingly, not all reported post-translational modification changes should be interpreted as equally well-established causal drivers of podocyte injury. This review focuses on the molecular regulatory networks and pathophysiological significance of major nonhistone post-translational modifications, including acetylation, phosphorylation, methylation, lactylation, ubiquitination, and SUMOylation. We further propose a hypothesis-generating and integrative conceptual model of podocyte deterioration, linking initiating pathological stimuli to stress transduction and downstream effector decompensation that may culminate in structural collapse. Importantly, this proposed cascade is not intended to represent a universally validated linear sequence or a definitive disease mechanism. Rather, it provides an organizing framework to generate testable hypotheses. We further highlight the therapeutic promise of targeting nonhistone post-translational modification pathways while acknowledging the considerable translational challenges that remain. By synthesizing the mechanistic landscape of nonhistone post-translational modifications, this review provides an integrated framework for advancing our understanding of podocytopathy pathogenesis and fostering the development of precision-targeted therapies.

To examine the co-development of vasculature and renal epithelial tissue, we employed a human pluripotent stem cell-derived kidney organoid system. We found that cooperative signaling through the glucocorticoid receptor and mineralocorticoid receptor via hydrocortisone enabled rich endothelial cell differentiation and vessel formation. Bulk RNA sequencing analysis revealed that hydrocortisone perturbs an angiogenic transcriptional program early in development and promotes instead a pro-endothelial survival transcriptional program, with upregulation of angiopoietin 1 at both the mRNA and protein level. Additionally, we saw that hydrocortisone does not seem to significantly affect gene expression of canonical nephrogenic genes compared to our controls, suggesting its effect is largely restricted to endothelial cell differentiation. Our results show that kidney organoids offer a unique platform to study developmental signals that drive endothelial cell differentiation and vessel formation. ### Competing Interest Statement The authors have declared no competing interest. National Institute of General Medical Sciences, https://ror.org/04q48ey07, P30GM154610, P20GM203423, 1P20GM144265-01A1 Scott R. Mackenzie Foundation U.S. National Science Foundation, 2243416, OIA-1849227

Dectin-1, a pattern recognition receptor predominantly expressed on myeloid cells, is required for maintaining immune homeostasis. However, the role of Dectin-1 in chronic kidney disease (CKD) remains unknown. Here we reported that Dectin-1 was markedly upregulated in the fibrotic kidneys of CKD patients, primarily in macrophages, and its expression correlated with fibrosis severity and renal dysfunction. Genetic deletion of Dectin-1 attenuated renal fibrosis induced by unilateral ureteral obstruction (UUO) or ischemia-reperfusion (IR), a finding confirmed in bone marrow chimeric mice. Macrophage-specific Dectin-1 deletion similarly protected against renal fibrosis, demonstrating its cell-autonomous role. Mechanistically, Dectin-1 promoted macrophage infiltration via Syk/NF-κB/CCL2-CCR2 axis, while facilitating macrophage-to-myofibroblast transition (MMT) by activating TGF-β/Smad signaling. Pre-clinically, pharmacological inhibition of Dectin-1 with Laminarin significantly reduced renal fibrosis in UUO and IR models, highlighting its therapeutic potential for CKD.

BACKGROUND:Vessel-lining endothelial cells (ECs) rely on heparan sulfate (HS) proteoglycans to regulate vascular permeability and to maintain vascular homeostasis. Hpa2 (heparanase 2) is a little-known, nonenzymatic, HS-binding protein. We hypothesized major functions and thus characterized the role of endogenous Hpa2 in the vertebrate vascular system. METHODS:We use zebrafish larvae as our primary animal model. Hpa2 loss-of-function (LOF) was induced by CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated 9) and morpholino antisense strategies. We assessed vascular permeability, blood vessel architecture, and EC morphology using transgenic zebrafish and transmission electron microscopy. rHpa2 (recombinant heparanase 2) was generated to study the functionality of Hpa2 in endothelial tissue cultures, zebrafish, and mice. RESULTS:We detected Hpa2 expression in hepatic tissue and localized Hpa2 protein in the vasculature of zebrafish and mammals. Hpa2 LOF increased zebrafish vascular permeability and altered EC and extracellular matrix morphology. rHpa2 rescued the Hpa2 LOF phenotype. Hpa2 LOF reduced HS levels and caused EC gene expression changes involved in signal transduction. rHpa2 competed with growth factors FGF2 (fibroblast growth factor-2) and VEGFA165 (vascular endothelial growth factor A165) for binding on the EC surface and consequently reduced the signal response these factors elicit. rHpa2 prevented VEGFA165-induced vascular permeability in murine ex vivo kidneys. Pharmacological inhibition of FGF2/VEGFR (VEGF receptor) signaling alleviated the Hpa2 LOF phenotype in zebrafish. CONCLUSIONS:We suggest that Hpa2 is a circulating molecule that maintains vascular integrity by regulating vascular HS-dependent growth factor signaling. Our model outlines Hpa2-related vascular function and could indicate therapeutic utilities.

INTRODUCTION:Aging is associated with progressive loss of kidney function and vascular structure, with and without chronic kidney disease. However, the mechanisms driving kidney vascular aging and potential therapeutic interventions remain poorly understood. METHODS:African turquoise killifish (Nothobranchius furzeri), a naturally short-lived vertebrate, were used to investigate the natural course of kidney aging. We inhibited the sodium-glucose co-transporter 2 using dapagliflozin (SGLT2i) to test a potential therapeutic intervention. Histological, immunofluorescent, and 3D vascular imaging were used to evaluate glomerular, tubular, vascular and functional changes. Single nuclei transcriptomic profiling was performed on whole kidneys to identify age, sex and treatment-associated molecular signatures. RESULTS:Aged killifish kidneys exhibited hallmark features of kidney aging, including glomerulosclerosis, tubular atrophy, and vascular rarefaction. Functional changes included increased proteinuria and altered tubular transporter function. Transcriptomic profiling revealed a metabolic shift from oxidative phosphorylation to glycolysis and upregulation of pro-inflammatory pathways. Aged vasculature displayed a marked reduction in tight junctions and cell-cell contacts. SGLT2i attenuated age-related vascular rarefaction, preserved functional capillary networks, reduced albuminuria, preserved a youthful transcriptional profile and enhanced key intercellular signaling pathways. CONCLUSIONS:Our study establishes the killifish as a translational model for investigating kidney vascular aging. SGLT2i preserves kidney microvascular structure and function, reduces proteinuria, and maintains a more youthful transcriptome. These results support a vascular-protective role of SGLT2i in mitigating age-related kidney deterioration.

Introduction:Aging is associated with progressive loss of renal function and vascular structure, with and without chronic kidney disease. However, the mechanisms driving renal vascular aging and potential therapeutic interventions remain poorly understood. Methods:To model this state-of-affairs, we used African turquoise killifish (Nothobranchius furzeri), a naturally short-lived vertebrate. We then inhibited the sodium-glucose co-transporter 2 using dapagliflozin (SGLT2i) to test a potential therapeutic intervention. Histological, immunofluorescent, and 3D vascular imaging were used to evaluate glomerular, tubular, vascular and functional changes. Single-nuclei transcriptomic profiling was performed on whole kidneys to identify age- and treatment-associated molecular signatures. Results:Aged killifish kidneys exhibited hallmark features of renal aging, including glomerulosclerosis, tubular fibrosis, and vascular rarefaction. Functional changes included increased proteinuria and altered tubular transporter function. Transcriptomic profiling revealed a metabolic shift from oxidative phosphorylation to glycolysis and upregulation of pro-inflammatory pathways. Aged vasculature also displayed a marked reduction in tight junctions and cell-cell contacts. SGLT2i attenuated age-related vascular rarefaction, preserved functional capillary networks, reduced albuminuria, restored a youthful transcriptional profile and enhanced intercellular signaling. However, killifish lifespan was not extended. Conclusion:This study establishes the killifish as a translational model for investigating renal vascular aging. We show that SGLT2i preserves renal microvascular structure and function, reduces proteinuria, and reprograms the aged transcriptome. These results support a vascular-protective role of SGLT2i in mitigating age-related renal deterioration.

Some 25 years after its founding as a marine laboratory in 1898 by Tufts University, The Mt. Desert Island Biological Laboratory (MDIBL) became a center for advances in renal physiology for the next 90 years. Populated by summer investigators from major US and international universities, who used marine species as model systems, the MDIBL has been the site for foundational discoveries ranging from whole-animal urinary excretion protocols that delineated proximal tubule secretion and glomerular filtration to the use of isolated kidney tubules to dissect solute transport steps. By the end of the 20th Century, MDIBL investigators had adopted modern molecular techniques to isolate and purify, then visualize, renal proteins, and clone their relevant genes. More recently, they have used a transgenic fish model to study the molecular control of glomerular filtration. Thus, much of what is presently accepted as models for the function of the vertebrate/mammalian kidney is due to the unique, collaborative research, by basic scientists and clinicians, at a cold-water marine laboratory in Maine.

Diabetic microvascular complications (DmVCs) and chronic venous disease (CVD) share common risk factors and pathophysiological features. However, they are often assessed and managed as separate conditions. The study objective was to map the available clinical evidence of venoactive drugs (VADs), beyond their demonstrated effects on sign and symptoms of CVD, in the management of patients with diabetic retinopathy (DR), diabetic nephropathy (DN) and diabetic peripheral neuropathy (DPN). We conducted a Scoping Review to map the clinical evidence on VADs recommended for treating CVD in the management of DR, DN and DPN to address VADs choices in clinics. PubMed and Cochrane Library databases were searched, studies in any language were included with no restriction on publication date. In total, 393 records were identified. Most included studies (N.=42) assessed clinical outcomes in DR (N.=33), followed by DN (N.=7) and DPN (N.=2). The median (range) publication date of the included studies was 2001 (1970-2022). Most studies were randomized trials (57%), followed by case series (17%), and case-control studies/systematic reviews (both 10%). Calcium dobesilate (CaD), was the most assessed VAD in DR (85%), DN (86%), and DPN (50%). CaD has shown significant improvements in DR and DN based on systematic-review data. Our findings suggest that VADs, in particular CaD, may represent a promising therapeutic option for the treatment of patients with both CVD and DmVC. Medical recommendations for VADs prescription should consider patients' microvascular status, evidence about VADs, as well as the multi-modal treatment approach.

Heparan sulfate (HS) proteoglycans are life-supporting proteins comprising a core protein to which one or more HS glycan chains are covalently bound. HS proteoglycans act as binding sites for circulating cells and molecules, allow gradient formation, and provide local storage capacities. They act as coreceptors, fine-tuning growth factor receptors and activating intracellular signaling pathways. HS glycan chains are cleaved and regulated by heparanase 1 (Hpa1). Heparanase 2 (Hpa2) is a close homolog of Hpa1. Unlike Hpa1, Hpa2 lacks enzymatic activity but nonetheless binds HS with high affinity, thus modulating HS-mediated biological processes. Only a few functions of Hpa2 have been unraveled. Under disease conditions that include the Mendelian urofacial syndrome, Hpa2 expression is markedly down-regulated, most compellingly demonstrated in several cancers. Hpa2 also circulates in the bloodstream, potentially originating from secretory organs such as liver and pancreas. The Hpa2 promotor is inducible by cellular stressors including cytotoxic, proteostatic, and endoplasmic reticulum stress. Activating transcription factor 3 (ATF3) induces Hpa2 gene expression. We summarize Hpa2 regulation in the framework of health and disease to foster research into its function. The underlying mystery remains: ‘How does this “heparanase,” which is actually a non-heparanase, work, and what are the ramifications?

Managing tryptophan (TRP) availability is important for cell homeostasis, and a dynamic balance between dietary intake and its catabolism is crucial. The enzymes of the kynurenine pathway (KP) mediate the main catabolic route for TRP. Its intermediary products, collectively known as kynurenines, are considered metabolically active and highly pleiotropic. Some progress has been made in the description of the biological function of the kynurenines, and despite the growing number of studies that show an association between TRP metabolism and kidney function, not much is known about the cellular mechanisms involved. To assess if the kynurenines play a role in glomerular dysfunction, we carried out a series of experiments aimed at describing the effect of changes in the relative abundance of the kynurenines on cells of the glomerulus, both in vivo and in vitro. We used a transgenic zebrafish line as a model to show that systemic changes in the KP either by morpholino knockdown, enzymatic inhibition, or kynurenine supplementation, lead to pericardial effusion, yolk sac edema, and excretion of high molecular weight proteins, all signs of impaired glomerular filtration. Cultured podocytes incubated with a KP inhibitor show changes in cell size, morphology and focal adhesions, leading to a higher detachment rate. Additionally, there is a change in the polarization status of the mitochondria, showing a loss of membrane potential and an alteration of bioenergetics parameters. Taken together, our results highlight the importance of kynurenine metabolite levels in the maintenance of a functioning filtration barrier.

The genetic predisposition to high glucose-induced peritoneal membrane (PM) injury during peritoneal dialysis (PD) and its mechanisms are of substantial clinical interest. We compared PD-induced peritoneal injury between two closely related mouse substrains, C57BL/6J and C57BL/6N, which differ in the function of the mitochondrial enzyme nicotinamide nucleotide transhydrogenase (NNT). Nnt(+/+) C57BL/6N mice exhibited significantly greater susceptibility, as indicated by mesothelial cell loss, fibrosis, neoangiogenesis, inflammation, M1 macrophage infiltration, and reduced ultrafiltration. To further investigate NNT's role, we silenced NNT in vitro. Knockdown prevented mitochondrial ROS accumulation, reduced pro-inflammatory mediator release in mesothelial cells, inhibited M1 polarization in macrophages, and impaired fibroblast proliferation under high glucose. We also observed a reverse NNT reaction in fibroblasts, contributing to glucose-induced ROS. Our findings indicate reduced genetic susceptibility of Nnt(-/-) C57BL/6J mice to PD-induced PM damage and identify NNT as a potential therapeutic target for PD-associated peritoneal injury.

Human induced pluripotent stem cell (iPSC) - derived kidney organoids are powerful models of kidney development and disease but lack mature vasculature. Here, we show that co-culture with human monocyte-derived macrophages (MDM) induces robust endothelial and stromal differentiation in iPSC-derived kidney organoids. MDM promoted the formation of lumenized capillary networks, an effect reproduced by iPSC-derived macrophages and the THP-1 monocyte line. In contrast, organoids without MDM displayed only transient endothelial differentiation that coincided with transient VEGFA upregulation and that regressed during maturation. MDM counteracted this transient phase by releasing soluble Neuropilin-1 (sNRP1), which sequestered VEGFA and stabilized late endothelial development, evidenced by sustained CD31 promoter activity. Transcriptomic profiling revealed that MDM redirected mesodermal fate suppressing lateral plate and cardiac mesoderm while promoting paraxial and intermediate mesoderm and the generation of FoxD1⁺ stromal progenitors via CXCL5 (ENA-78) secretion. These stromal cells supported late endothelial maturation and enhanced overall organoid differentiation. Our findings uncover a macrophage-driven mechanism coupling stromal and vascular development, providing a strategy to achieve functional vascularization in kidney organoids and improving their physiological relevance for research applications. ### Competing Interest Statement The authors have declared no competing interest. Deutsche Forschungsgemeinschaft, EXC 2155 RESIST; project number 390874280, LA 3680/9-1, LA 3680/10-1, KA 5549/2-1 Niedersächsisches Ministerium für Wissenschaft und Kultur, ZN3340 European Research Council, 101100859, 101158172 zukunft.niedersachsen, R2N.Micro-Replace-Systems German Center of Lung Research (DZL) and the Federal Ministry of Research, Technology and Space, SMARTibone project Fraunhofer Internal Programs, Attract 40-01696

Recipients’ age has emerged as a key factor that impacts on acute renal allograft rejection and graft survival. Age-related functional and structural changes in the immune system have been observed, yet the precise influence of aged immunity on kidney transplant remains unclear. In an initial retrospective analysis of clinical data gathered from two major centers in China and Germany, we found a correlation between aging and mitigated rejection outcomes in kidney recipients. To study the mechanism, we performed kidney transplantation on mice and observed attenuated allograft rejection in senescent recipients. Single-cell transcriptome analysis of allograft kidneys indicated a protective role of p21high macrophages in aged mice. Supernatant collected from p21high macrophage primary culture inhibited the cytotoxic function and proliferation of CD8+ T cells. Zfp36 is highly expressed in senescent p21high macrophages. To determine its role in renal allograft rejection, we studied mice with Zfp36 conditionally deleted in macrophages (Zfp36-cKO). These mice developed exacerbated allograft rejection with enhanced IL-27 production and CD8+ T cell hyperactivation. Inhibition of IL-27 with neutralizing antibody or deletion of IL-27 receptor on CD8+ T cells reversed acute renal allograft rejection in Zfp36-cKO mice. Moreover, in vitro silencing Zfp36 with siRNA led to impaired degradation of IL-27 p28 mRNA and a subsequent increase of IL-27 in p21high macrophages. In conclusion, senescent macrophages protect renal allograft rejection by suppressing CD8+ T cells via a Zfp36/IL-27-dependent mechanism. These findings may provide innovative therapeutic strategies for addressing kidney allograft rejection.

Postischemic acute kidney injury (AKI) is a common clinical complication and often fatal, with no effective treatment available. Little is known about the role of leukocytes trapped in renal vessels during ischemia-reperfusion injury (IRI) in the postischemic AKI. We designed a new animal model in rats with preforming renal artery lavage prior to IRI to investigate the effect of diminishing the residual circulating leukocytes on kidney damage and inflammation. Moreover, the functional changes of macrophages in hypoxia reoxygenation condition were also analyzed. We found pre-ischemic renal lavage significantly decreased the serum creatinine and blood urea nitrogen levels, and downregulated the mRNA and protein expressions in kidneys and urinary secretion of kidney injury molecule-1 of rats after IRI. The renal pathological damage caused by IRI was also ameliorated by pre-ischemic renal lavage, as evidenced by fewer cast formation, diminished morphological signs of AKI in the tissue at 24 hours after IRI. Pre-ischemic renal lavage reduced the numbers of infiltrating CD68(+)macrophages and MPO(+)neutrophils. The mRNA expression of pro-inflammatory mediator in IRI kidneys and the levels of pro-inflammatory cytokines in circulatory system and urine were also reduced due to pre-ischemic lavage. Compared with nontreated rats with IRI, pre-ischemic renal lavage significantly reduced the phosphorylation levels of ERK and p65 subunit of NF-kappa B in the kidney after IRI. In addition, we found hypoxia/reoxygenation could promote the expression of pro-inflammatory mediators and inhibit the expression of anti-inflammatory factors by regulating ERK/NF-kappa B signaling pathway. Thus, pre-ischemic renal lavage could clearly reduce the renal damage after IRI by attenuating inflammation, and macrophages trapped in renal vessels during IRI could be important pathogenic factors driving tissue injury.