Cells of NG2 lineage increase in glomeruli of mice following podocyte depletion

Progression of albuminuria and podocyte injury in focal segmental glomerulosclerosis inhibited by enhanced glycosphingolipid GM3 via valproic acid

Focal segmental glomerulosclerosis, characterized by decreased numbers of podocytes in glomeruli, is a common cause of refractory nephrotic syndrome. Recently, we showed that enhanced glycosphingolipid GM3 expression after administration of valproic acid, an upregulator of ST3GAL5/St3gal5, was effective in preventing albuminuria and podocyte injury. We also revealed the molecular mechanism for this preventive effect, which involves GM3 directly binding nephrin that then act together in glycolipid-enriched membrane (GEM) fractions under normal conditions and in non-GEM fractions under nephrin injury conditions. Kidney disease is frequently referred to as a "silent killer" because it is often difficult to detect subjective symptoms. Thus, primary treatment for these diseases is initiated after the onset of disease progression. Consequently, the efficacy of enhanced levels of GM3 induced by valproic acid needs to be evaluated after the onset of the disease with severe albuminuria such as focal segmental glomerulosclerosis. Here, we report the therapeutic effect of enhanced GM3 expression induced via administration of valproic acid on albuminuria and podocyte injury after the onset focal segmental glomerulosclerosis in anti-nephrin antibody treated mice. Our findings suggest elevated levels of GM3 following treatment with valproic acid has therapeutic utility for kidney disease associated with severe albuminuria and podocyte injury.

Ion channels and channelopathies in glomeruli

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.

Glycosphingolipid GM3 prevents albuminuria and podocytopathy induced by anti-nephrin antibody

Podocytopathy, which is characterized by injury to podocytes, frequently causes proteinuria or nephrotic syndrome. There is currently a paucity of effective therapeutic drugs to treat proteinuric kidney disease. Recent research suggests the possibility that glycosphingolipid GM3 maintains podocyte function by acting on various molecules including nephrin, but its mechanism of action remains unknown. Here, various analyses were performed to examine the potential relationship between GM3 and nephrin, and the function of GM3 in podocytes using podocytopathy mice, GM3 synthase gene knockout mice, and nephrin injury cells. Reduced amounts of GM3 and nephrin were observed in podocytopathy mice. Intriguingly, this reduction of GM3 and nephrin, as well as albuminuria, were inhibited by administration of valproic acid. However, when the same experiment was performed using GM3 synthase gene knockout mice, valproic acid administration did not inhibit albuminuria. Equivalent results were obtained in model cells. These findings indicate that GM3 acts with nephrin in a collaborative manner in the cell membrane. Taken together, elevated levels of GM3 stabilize nephrin, which is a key molecule of the slit diaphragm, by enhancing the environment of the cell membrane and preventing albuminuria. This study provides novel insight into new drug discovery, which may offer a new therapy for kidney disease with albuminuria.

Protective effects of budesonide on LPS‑induced podocyte injury by modulating macrophage M1/M2 polarization: Evidence from in vitro and in silico studies

Budesonide (Bud), one of the most widely used lung medicines, is currently used as a repurposing medicine for immunoglobulin A nephropathy (IgAN) treatment. The progression of IgAN is related to inflammation involving macrophages and podocytes. The present study aimed to explore the effects of Bud on classically activated (M1)/alternatively activated (M2) macrophage polarization and podocyte injury under lipopolysaccharide (LPS)-induced inflammatory stress in vitro. Anti-inflammatory bioinformation of Bud was identified based on the Gene Expression Omnibus database. RAW264.7 cells were treated with normal medium, LPS, curcumin (Cur, positive control), or Bud 5, 10, or 20 µM. The expression levels of inducible nitric oxide synthase (iNOS), TNF-α, mannose receptor (CD206) and arginase (Arg)-1 were quantified by western blotting. The collected supernatants from macrophages were termed (Nor)MS, (LPS)MS, (Cur)MS and (Bud)MS. The TNF-α, IL-1β and nitric oxide (NO) levels in the supernatants were evaluated by ELISA and Griess assay. The podocytes were cultured in different supernatants and their survival rates were assessed by bromodeoxyuridine assay. TNF signaling is an important pathway by which Bud exerts anti-inflammatory activities. Compared with the LPS group, 5, 10 and 20 µM Bud significantly increased Arg-1 and decreased iNOS expression (Six: P<0.05) and 20 µM Bud significantly increased Arg-1 and CD206 and decreased iNOS and TNF-α expression (Four: P<0.05). Cur significantly decreased iNOS and TNF-α expression (Two: P<0.05). Compared with LPS, 5, 10 and 20 µM Bud and Cur significantly decreased TNF-α, IL-1β and NO levels (All: P<0.05). The podocyte survival rates of (Bud)MS and (Cur)MS were significantly higher than those of (LPS)MS (Four: P<0.05). The protective effect of Bud on podocyte injury is related to its modulation of M1/M2 polarization.

Kidney repair and regeneration: perspectives of the NIDDK (Re)Building a Kidney consortium

Acute kidney injury impacts ∼13.3 million individuals and causes ∼1.7 million deaths per year globally. Numerous injury pathways contribute to acute kidney injury, including cell cycle arrest, senescence, inflammation, mitochondrial dysfunction, and endothelial injury and dysfunction, and can lead to chronic inflammation and fibrosis. However, factors enabling productive repair versus nonproductive, persistent injury states remain less understood. The (Re)Building a Kidney (RBK) consortium is a National Institute of Diabetes and Digestive and Kidney Diseases consortium focused on both endogenous kidney repair mechanisms and the generation of new kidney tissue. This short review provides an update on RBK studies of endogenous nephron repair, addressing the following questions: (i) What is productive nephron repair? (ii) What are the cellular sources and drivers of repair? and (iii) How do RBK studies promote development of therapeutics? Also, we provide a guide to RBK's open access data hub for accessing, downloading, and further analyzing data sets.

Global transcriptomic changes occur in aged mouse podocytes

Glomerular podocytes undergo structural and functional changes with advanced age, that increase susceptibility of aging kidneys to worse outcomes following superimposed glomerular diseases. To delineate transcriptional changes in podocytes in aged mice, RNA-seq was performed on isolated populations of reporter-labeled (tdTomato) podocytes from multiple young (two to three months) and advanced aged mice (22 to 24 months, equivalent to 70 plus year old humans). Of the 2,494 differentially expressed genes, 1,219 were higher and 1,275 were lower in aged podocytes. Pathway enrichment showed that major biological processes increased in aged podocytes included immune responses, non-coding RNA metabolism, gene silencing and MAP kinase signaling. Conversely, aged podocytes showed downregulation of developmental, morphogenesis and metabolic processes. Canonical podocyte marker gene expression decreased in aged podocytes, with increases in apoptotic and senescence genes providing a mechanism for the progressive loss of podocytes seen with aging. In addition, we revealed aberrations in the podocyte autocrine signaling network, identified the top transcription factors perturbed in aged podocytes, and uncovered candidate gene modulations that might promote healthy aging in podocytes. The transcriptional signature of aging is distinct from other kidney diseases. Thus, our study provides insights into biomarker discovery and molecular targeting of the aging process itself within podocytes.

Inhibition of Renal Stellate Cell Activation Reduces Renal Fibrosis

Interstitial fibrosis is a common feature of chronic kidney disease, and platelet-derived growth factor receptor-β (PDGFR-β)-positive mesenchymal cells are reportedly the major source of scar-producing myofibroblasts. We had previously demonstrated that albumin and its derivative R-III (a retinol-binding protein-albumin domain III fusion protein) inhibited the transdifferentiation/activation of hepatic stellate cells (HSCs) to myofibroblasts and that R-III administration reduced liver fibrosis. In this study, we isolated cells (referred to as renal stellate cells, RSCs) from rat kidney tissues using the HSC isolation protocol and compared their morphological and biochemical characteristics with those of HSCs. RSCs shared many characteristics with HSCs, such as storage of vitamin A-containing lipid droplets and expression of HSC markers as well as pericyte markers. RSCs underwent spontaneous transdifferentiation into myofibroblasts in in vitro culture, which was inhibited by albumin expression or R-III treatment. We also evaluated the therapeutic effects of R-III in unilateral ureteral obstruction (UUO)-induced renal fibrosis in mice. Injected R-III localized predominantly in cytoglobin/stellate cell activation-associated protein (Cygb/STAP)-positive cells in the kidney and reduced renal fibrosis. These findings suggest that RSCs can be recognized as the renal counterparts of HSCs and that RSCs represent an attractive therapeutic target for anti-fibrotic therapy.