GYY4137 Regulates Extracellular Matrix Turnover in the Diabetic Kidney by Modulating Retinoid X Receptor Signaling

Diabetic kidney is associated with an accumulation of extracellular matrix (ECM) leading to renal fibrosis. Dysregulation of retinoic acid metabolism involving retinoic acid receptors (RARs) and retinoid X receptors (RXRs) has been shown to play a crucial role in diabetic nephropathy (DN). Furthermore, RARs and peroxisome proliferator-activated receptor γ (PPARγ) are known to control the RXR-mediated transcriptional regulation of several target genes involved in DN. Recently, RAR and RXR have been shown to upregulate plasminogen activator inhibitor-1 (PAI-1), a major player involved in ECM accumulation and renal fibrosis during DN. Interestingly, hydrogen sulfide (H2S) has been shown to ameliorate adverse renal remodeling in DN. We investigated the role of RXR signaling in the ECM turnover in diabetic kidney, and whether H2S can mitigate ECM accumulation by modulating PPAR/RAR-mediated RXR signaling. We used wild-type (C57BL/6J), diabetic (C57BL/6-Ins2Akita/J) mice and mouse mesangial cells (MCs) as experimental models. GYY4137 was used as a H2S donor. Results showed that in diabetic kidney, the expression of PPARγ was decreased, whereas upregulations of RXRα, RXRβ, and RARγ1 expression were observed. The changes were associated with elevated PAI-1, MMP-9 and MMP-13. In addition, the expressions of collagen IV, fibronectin and laminin were increased, whereas elastin expression was decreased in the diabetic kidney. Excessive collagen deposition was observed predominantly in the peri-glomerular and glomerular regions of the diabetic kidney. Immunohistochemical localization revealed elevated expression of fibronectin and laminin in the glomeruli of the diabetic kidney. GYY4137 reversed the pathological changes. Similar results were observed in in vitro experiments. In conclusion, our data suggest that RXR signaling plays a significant role in ECM turnover, and GYY4137 modulates PPAR/RAR-mediated RXR signaling to ameliorate PAI-1-dependent adverse ECM turnover in DN.

P0719SRC KINASES AGGRAVATE DIABETIC KIDNEY INJURY THROUGH ACTIVATION OF ENDOPLASMIC RETICULUM STRESS

Background and Aims Diabetic kidney disease (DKD) is the major cause of end-stage kidney disease which is characterized by prominent kidney fibrosis. Src family kinases (SFKs), a family of proto-oncogenes, has been acknowledged to mediate the development of kidney fibrosis. While, several studies in liver and skeletal muscle suggested the role of Src kinases in activating endoplasmic reticulum (ER) stress. The present study aimed to investigate the mechanism of Src kinases-ER stress in mediating the progression of DKD. Method Type 1 diabetes was induced by a single 60 mg/kg i.p injection of streptozotocin (STZ) in 7-week-old male, Sprague-Dawley rats. Diabetic rats received 8-week-treatment of either KF-1607 (30 mg/kg/day), a pharmacological inhibitor of SFKs, or losartan (1 mg/kg/day), a standard treatment for patients with DKD. Results Among SFKs, Fyn and Lyn kinases were particularly increased in the diabetic kidney. Inhibition of Src kinases by KF-1607 improved kidney function and inhibited tubular injury, presented by decreased serum creatinine, albuminuria, and urinary KIM-1 excretion. Pathological changes in the kidney, such as enhanced glomerular volume, tuft area, and fractional mesangial area, were ameliorated in KF-treated rats. Highly-accumulated collagen network as well as increased TGF-β and α-SMA mRNA levels in the diabetic kidney were also significantly reduced in response to KF treatment. Furthermore, it consistently attenuated kidney inflammation and oxidative stress. The renoprotective effects of KF were interestingly similar to those of losartan. We showed increases in protein levels of phosphorylated IRE-1α, ATF6, GRP78 as well as CHOP indicating an exacerbated ER stress in the diabetic kidney. These ER stress markers were significantly decreased in KF treated mice. Conclusion Altogether, Src kinases through activation of ER stress aggravates kidney injury in STZ-induced diabetic rats.

Role of Impaired Nutrient and Oxygen Deprivation Signaling and Deficient Autophagic Flux in Diabetic CKD Development: Implications for Understanding the Effects of Sodium-Glucose Cotransporter 2-Inhibitors

Growing evidence indicates that oxidative and endoplasmic reticular stress, which trigger changes in ion channels and inflammatory pathways that may undermine cellular homeostasis and survival, are critical determinants of injury in the diabetic kidney. Cells are normally able to mitigate these cellular stresses by maintaining high levels of autophagy, an intracellular lysosome-dependent degradative pathway that clears the cytoplasm of dysfunctional organelles. However, the capacity for autophagy in both podocytes and renal tubular cells is markedly impaired in type 2 diabetes, and this deficiency contributes importantly to the intensity of renal injury. The primary drivers of autophagy in states of nutrient and oxygen deprivation—sirtuin-1 (SIRT1), AMP-activated protein kinase (AMPK), and hypoxia-inducible factors (HIF-1α and HIF-2α)—can exert renoprotective effects by promoting autophagic flux and by exerting direct effects on sodium transport and inflammasome activation. Type 2 diabetes is characterized by marked suppression of SIRT1 and AMPK, leading to a diminution in autophagic flux in glomerular podocytes and renal tubules and markedly increasing their susceptibility to renal injury. Importantly, because insulin acts to depress autophagic flux, these derangements in nutrient deprivation signaling are not ameliorated by antihyperglycemic drugs that enhance insulin secretion or signaling. Metformin is an established AMPK agonist that can promote autophagy, but its effects on the course of CKD have been demonstrated only in the experimental setting. In contrast, the effects of sodium-glucose cotransporter–2 (SGLT2) inhibitors may be related primarily to enhanced SIRT1 and HIF-2α signaling; this can explain the effects of SGLT2 inhibitors to promote ketonemia and erythrocytosis and potentially underlies their actions to increase autophagy and mute inflammation in the diabetic kidney. These distinctions may contribute importantly to the consistent benefit of SGLT2 inhibitors to slow the deterioration in glomerular function and reduce the risk of ESKD in large-scale randomized clinical trials of patients with type 2 diabetes.