ACSS2 gene variants determine kidney disease risk by controlling de novo lipogenesis in kidney tubules.

Worldwide, over 800 million people are affected by kidney disease, yet its pathogenesis remains elusive, hindering the development of novel therapeutics. In this study, we used kidney-specific expression of quantitative traits and single-nucleus open chromatin analysis to show that genetic variants linked to kidney dysfunction on chromosome 20 target the acyl-CoA synthetase short-chain family 2 (ACSS2). By generating ACSS2-KO mice, we demonstrated their protection from kidney fibrosis in multiple disease models. Our analysis of primary tubular cells revealed that ACSS2 regulated de novo lipogenesis (DNL), causing NADPH depletion and increasing ROS levels, ultimately leading to NLRP3-dependent pyroptosis. Additionally, we discovered that pharmacological inhibition or genetic ablation of fatty acid synthase safeguarded kidney cells against profibrotic gene expression and prevented kidney disease in mice. Lipid accumulation and the expression of genes related to DNL were elevated in the kidneys of patients with fibrosis. Our findings pinpoint ACSS2 as a critical kidney disease gene and reveal the role of DNL in kidney disease.

Metformin prevents hypoxia-induced podocyte injury by regulating the ZEB2/TG2 axis.

AIM: Podocytes, a vital component of the glomerular filtration barrier, are vulnerable to various noxious stimuli, including Hypoxic. HIF1α that transduces hypoxic adaptations induces Transglutaminase 2 (TG2), which catalyses cross-linking of extracellular matrix proteins. In this study, we investigated the mechanism of regulation of TG2 by HIF1α. METHODS: HIF1α was induced in podocytes by treating with FG4592 (Roxadustat) or hypoxia (1% oxygen) and in mice by treating with FG4592. Gene expression and protein analysis of ZEB2, TRPC6 and TG2 were performed in both experimental models. Histological and kidney function analyses were performed in mice. RESULTS: Data mining revealed co-expression of HIF1α, ZEB2, TRPC6 and TG2 in the chronic kidney diseases (CKD)-validated dataset. We observed elevated expression of ZEB2, TRPC6 and TG2 in FG4592-treated podocytes. Ectopic expression of ZEB2 resulted in high TRPC6 expression, elevated intracellular calcium levels and increased TG2 activity. Blocking the TRPC6 channel or inhibiting its expression partially attenuated FG4592-induced TG2 activity, whereas suppression of ZEB2 expression significantly abolished TG2 activity. Furthermore, we noticed the induction of the ZEB2/TRPC6/TG2 axis in podocytes in mice administered with FG-4592. Metformin ameliorated the HIF1α-induced podocyte injury and proteinuria in mice administered with FG-4592. CONCLUSION: This study demonstrates that HIF1α stimulates both TG2 expression and activity via ZEB2/TRPC6 axis, whereas abrogation of HIF1α by metformin prevented hypoxia-induced glomerular injury. Metformin could be explored to treat proteinuric diseases such as CKD, sleep apnea and renal Ischemia-reperfusion-injury, where hypoxia is considered a risk factor.

Growth hormone induces transforming growth factor-ß1 in podocytes: Implications in podocytopathy and proteinuria.

Pituitary growth hormone (GH) is essential for growth, metabolism, and renal function. Overactive GH signaling is associated with impaired kidney function. Glomerular podocytes, a key kidney cell type, play an indispensable role in the renal filtration and express GH receptors (GHR), suggesting the direct action of GH on these cells. However, the precise mechanism and the downstream signaling events by which GH leads to diabetic nephropathy remain to be elucidated. Here we performed proteome analysis of the condition media from human podocytes and confirmed that GH-induces TGF-ß1. Inhibition of GH/GHR stimulated-JAK2 signaling abrogates GH-induced TGF-ß1 secretion. Mice administered with GH showed glomerular manifestations concomitant with proteinuria. Pharmacological inhibition of TGF-ßR1 in mice prevented GH-induced TGF-ß dependent SMAD signaling and proteinuria. Conditional deletion of GHR in podocytes protected mice from streptozotocin-induced diabetic nephropathy. GH and TGF-ß1 signaling components expression was elevated in the kidneys of human diabetic nephropathy patients. Our study identifies that GH induces TGF-ß1 in podocytes, contributing to diabetic nephropathy.

Detrimental effects of hypoxia on glomerular podocytes.

Hypoxia-inducible factor1 (HIF1) plays a pivotal role in ensuring cells adapt to low-oxygen conditions. Depletion of oxygen, a co-substrate during hydroxylation of prolyl (P402 and P564) residues of HIF1⍺, evades HIF1⍺ ubiquitination and enables its dimerization with HIF1ß to mediate global transcriptional response to hypoxia. Though HIF1 is largely considered eliciting a protective role during physiological or pathological hypoxia or ischemia, elevated HIF1 during chronic hypoxia contributes to glomerular diseases' pathology and proteinuria. The glomerulus is responsible for renal permselectivity and excretion of ultra-filtrated urine. Podocytes are the glomerulus' major cell types and are instrumental for glomerular filtration, permselectivity, and glomerular basement membrane maintenance. Podocyte injury is expected to impair the efficiency of glomerular filtration and manifestation of glomerulosclerosis and proteinuria. Accumulated evidence suggests that podocytes are susceptible to various insults during chronic hypoxia, including podocyte EMT, slit-diaphragm dysfunction, foot process effacement, and cytoskeletal derangement due to accumulation of HIF1. This review discusses how hypoxia/HIF1 signaling regulates various features and function of podocytes during exposure to chronic hypoxia or inducing HIF1 by various chemical modulators.

Cerebral ischemia induces TRPC6 via HIF1α/ZEB2 axis in the glomerular podocytes and contributes to proteinuria.

Podocytes are specialized cells of the glomerulus and key component of the glomerular filtration apparatus (GFA). GFA regulates the permselectivity and ultrafiltration of blood. The mechanism by which the integrity of the GFA is compromised and manifest in proteinuria during ischemic stroke remains enigmatic. We investigated the mechanism of ischemic hypoxia-induced proteinuria in a middle cerebral artery occlusion (MCAO) model. Ischemic hypoxia resulted in the accumulation of HIF1α in the podocytes that resulted in the increased expression of ZEB2 (Zinc finger E-box-binding homeobox 2). ZEB2, in turn, induced TRPC6 (transient receptor potential cation channel, subfamily C, member 6), which has increased selectivity for calcium. Elevated expression of TRPC6 elicited increased calcium influx and aberrant activation of focal adhesion kinase (FAK) in podocytes. FAK activation resulted in the stress fibers reorganization and podocyte foot process effacement. Our study suggests overactive HIF1α/ZEB2 axis during ischemic-hypoxia raises intracellular calcium levels via TRPC6 and consequently altered podocyte structure and function thus contributes to proteinuria.