The crosstalk between glomerular endothelial cells and podocytes controls their responses to metabolic stimuli in diabetic nephropathy

USP22 promotes angiotensin II-induced podocyte injury by deubiquitinating and stabilizing HMGB1

BACKGROUND

Chronic kidney disease (CKD) remains a significant global health burden, with hypertensive nephropathy (HN) as one of its primary causes. Podocyte injury is a key factor in the progression of CKD. However, the molecular mechanisms underlying angiotensin II-induced podocyte injury remain incompletely understood. Ubiquitin-specific protease 22 (USP22) has been reported to facilitate a range of cellular processes, including cell proliferation and apoptosis. However, the role of USP22 in HN pathogenesis is unclear.

METHODS

The expression of USP22 was assessed in kidney samples from hypertensive nephropathy patients, angiotensin II-induced hypertensive nephropathy mouse models, and cultured podocytes treated with angiotensin II. Podocyte-specific USP22 knockout mice were used to investigate the effects of USP22 deletion on podocyte injury and inflammation.

RESULTS

USP22 expression was significantly upregulated in kidneys of HN patients, angiotensin II-induced mouse models, and cultured podocytes. Podocyte-specific deletion of USP22 markedly reduced angiotensin II-induced podocyte injury and inflammatory responses. Furthermore, we identified high-mobility group box protein 1 (HMGB1) as a protein that interacts with USP22. USP22 deubiquitinated and stabilized HMGB1 through K48-linked ubiquitination. Downregulation of USP22 expression improved kidney function and pathological changes in HN by promoting HMGB1 degradation.

CONCLUSION

This study identifies USP22 as a key regulator of angiotensin II-induced podocyte injury and inflammation through its interaction with HMGB1. Our findings revealed that following glomerular injury, damage and shedding of tubular cells also occurred. Targeting the USP22-HMGB1 axis offers a promising therapeutic strategy for treating hypertensive nephropathy and other types of CKD.

Targeting senescence to prevent diabetic kidney disease: Exploring molecular mechanisms and potential therapeutic targets for disease management

BACKGROUND/AIMS

As a microvascular complication, diabetic kidney disease is the leading cause of chronic kidney disease and end-stage renal disease worldwide. While the underlying pathophysiology driving transition of diabetic kidney disease to renal failure is yet to be fully understood, recent studies suggest that cellular senescence is central in disease development and progression. Consequently, understanding the molecular mechanisms which initiate and drive senescence in response to the diabetic milieu is crucial in developing targeted therapies that halt progression of renal disease.

METHODS

To understand the mechanistic pathways underpinning cellular senescence in the context of diabetic kidney disease, we reviewed the literature using PubMed for English language articles that contained key words related to senescence, inflammation, fibrosis, senescence-associated secretory phenotype (SASP), autophagy, and diabetes.

RESULTS

Aberrant accumulation of metabolically active senescent cells is a notable event in the progression of diabetic kidney disease. Through autocrine- and paracrine-mediated mechanisms, resident senescent cells potentiate inflammation and fibrosis through increased expression and secretion of pro-inflammatory cytokines, chemoattractants, recruitment of immune cells, myofibroblast activation, and extracellular matrix remodelling. Compounds that eliminate senescent cells and/or target the SASP - including senolytic and senomorphics drugs - demonstrate promising results in reducing the senescent cell burden and associated pro-inflammatory effect.

CONCLUSIONS

Here we evidence the link between senescence and diabetic kidney disease and highlight underlying molecular mechanisms and potential therapeutic targets that could be exploited to delay disease progression and improve outcomes for individuals with the disease. Trials are now required to translate their therapeutic potential to a clinical setting.

Cellular cross-talk drives mesenchymal transdifferentiation in diabetic kidney disease

While changes in glomerular function and structure may herald diabetic kidney disease (DKD), many studies have underscored the significance of tubule-interstitial changes in the progression of DKD. Indeed, tubule-interstitial fibrosis may be the most important determinant of progression of DKD as in many forms of chronic glomerulopathies. The mechanisms underlying the effects of tubular changes on glomerular function in DKD have intrigued many investigators, and therefore, the signaling mechanisms underlying the cross-talk between tubular cells and glomerular cells have been the focus of investigation in many recent studies. Additionally, the observations of slowing of glomerular filtration rate (GFR) decline and reduction of proteinuria by recent drugs such as SGLT-2 blockers, whose primary mechanism of action is on proximal tubules, further strengthen the concept of cross-talk between the tubular and glomerular cells. Recently, the focus of research on the pathogenesis of DKD has primarily centered around exploring the cross-talk between various signaling pathways in the diabetic kidney as well as cross-talk between tubular and glomerular endothelial cells and podocytes with special relevance to epithelial-to-mesenchymal transition (EMT) and endothelial-to-mesenchymal transition (EndoMT). The focus of this review is to provide a general description of cell-to-cell cross-talk in the diabetic kidney and to highlight these concepts with evidence in relation to the physiology and pathophysiology of DKD.

Genetic deletion of calcium-independent phospholipase A2γ protects mice from diabetic nephropathy

Calcium-independent phospholipase A2γ (iPLA2γ) is localized in glomerular epithelial cells (GECs)/podocytes at the mitochondria and endoplasmic reticulum, and can mediate release of arachidonic acid and prostanoids. Global knockout (KO) of iPLA2γ in mice did not cause albuminuria, but resulted in mitochondrial structural abnormalities and enhanced autophagy in podocytes. In acute glomerulonephritis, deletion of iPLA2γ exacerbated albuminuria and podocyte injury. This study addresses the role of iPLA2γ in diabetic nephropathy. Hyperglycemia was induced in male mice with streptozotocin (STZ). STZ induced progressive albuminuria in control mice (over 21 weeks), while albuminuria did not increase in iPLA2γ KO mice, remaining comparable to untreated groups. Despite similar exposure to STZ, the STZ-treated iPLA2γ KO mice developed a lower level of hyperglycemia compared to STZ-treated control. However, there was no significant correlation between the degree of hyperglycemia and albuminuria, and even iPLA2γ KO mice with greatest hyperglycemia did not develop significant albuminuria. Mortality at 21 weeks was greatest in diabetic control mice. Sclerotic glomeruli and enlarged glomerular capillary loops were increased significantly in diabetic control compared to diabetic iPLA2γ KO mice. Glomerular matrix was expanded in diabetic mice, with control exceeding iPLA2γ KO. Glomerular autophagy (increased LC3-II and decreased p62) was enhanced in diabetic iPLA2γ KO mice compared to control. Treatment of cultured GECs with H2O2 resulted in increased cell death in control GECs compared to iPLA2γ KO, and the increase was slightly greater in medium with high glucose compared to low glucose. H2O2-induced cell death was not affected by inhibition of prostanoid production with indomethacin. In conclusion, mice with global deletion of iPLA2γ are protected from developing chronic glomerular injury in diabetic nephropathy. This is associated with increased glomerular autophagy.

Deletion of IRE1α in podocytes exacerbates diabetic nephropathy in mice

Protein misfolding in the endoplasmic reticulum (ER) of podocytes contributes to the pathogenesis of glomerular diseases. Protein misfolding activates the unfolded protein response (UPR), a compensatory signaling network. We address the role of the UPR and the UPR transducer, inositol-requiring enzyme 1α (IRE1α), in streptozotocin-induced diabetic nephropathy in mice. Diabetes caused progressive albuminuria in control mice that was exacerbated in podocyte-specific IRE1α knockout (KO) mice. Compared to diabetic controls, diabetic IRE1α KO mice showed reductions in podocyte number and synaptopodin. Glomerular ultrastructure was altered only in diabetic IRE1α KO mice; the major changes included widening of podocyte foot processes and glomerular basement membrane. Activation of the UPR and autophagy was evident in diabetic control, but not diabetic IRE1α KO mice. Analysis of human glomerular gene expression in the JuCKD-Glom database demonstrated induction of genes associated with the ER, UPR and autophagy in diabetic nephropathy. Thus, mice with podocyte-specific deletion of IRE1α demonstrate more severe diabetic nephropathy and attenuation of the glomerular UPR and autophagy, implying a protective effect of IRE1α. These results are consistent with data in human diabetic nephropathy and highlight the potential for therapeutically targeting these pathways.

Crosstalk among podocytes, glomerular endothelial cells and mesangial cells in diabetic kidney disease: an updated review

Diabetic kidney disease (DKD) is a long-term and serious complication of diabetes that affects millions of people worldwide. It is characterized by proteinuria, glomerular damage, and renal fibrosis, leading to end-stage renal disease, and the pathogenesis is complex and involves multiple cellular and molecular mechanisms. Among three kinds of intraglomerular cells including podocytes, glomerular endothelial cells (GECs) and mesangial cells (MCs), the alterations in one cell type can produce changes in the others. The cell-to-cell crosstalk plays a crucial role in maintaining the glomerular filtration barrier (GFB) and homeostasis. In this review, we summarized the recent advances in understanding the pathological changes and interactions of these three types of cells in DKD and then focused on the signaling pathways and factors that mediate the crosstalk, such as angiopoietins, vascular endothelial growth factors, transforming growth factor-β, Krüppel-like factors, retinoic acid receptor response protein 1 and exosomes, etc. Furthermore, we also simply introduce the application of the latest technologies in studying cell interactions within glomerular cells and new promising mediators for cell crosstalk in DKD. In conclusion, this review provides a comprehensive and updated overview of the glomerular crosstalk in DKD and highlights its importance for the development of novel intervention approaches.