Astragaloside IV attenuates proteinuria in streptozotocin-induced diabetic nephropathy via the inhibition of endoplasmic reticulum stress

Background: Diabetic nephropathy (DN) is a major cause of Chronic Kidney Disease and End-Stage Renal Disease throughout the world; however, the reversibility of diabetic nephropathy remains controversial. Endoplasmic reticulum (ER) stress plays an important role in the pathogenesis of DN. Astragaloside IV (AS-IV) is derived from Astragalus membranaceus (Fisch) Bge, a widely used traditional herbal medicine in China, and has diverse pharmacological activities including the attenuation of podocyte injury and amelioration of proteinuria in idiopathic nephrotic syndrome. The present study aimed to investigate the effect and mechanism of AS-IV on proteinuria in the rat streptozotocin (STZ)-induced model of diabetes. Methods: Male Sprague-Dawley (SD) rats were randomly divided into four groups: normal control (Normal group), diabetic nephropathy (Model group), diabetic nephropathy plus AS-IV treatment (AS-IV group) and diabetic nephropathy plus 4-phenyl butyric acid treatment (PBA group). ER stress was induced in cultured human podocytes, pretreated with or without AS-IV, with tunicamycin (TM). At the end of 8 weeks, serum creatinine (Scr), blood urea nitrogen (BUN) and 24-hour urinary protein excretion rate (UAER) were determined. Renal morphology was examined after periodic acid-Schiff staining of kidney sections. Apoptosis of podocytes was measured by flow cytometry. The total expression and phosphorylation of eIF2a, PERK and JNK, and the expression of CHOP and cleaved caspase-3 were determined by western blotting. The expression of glucose-regulated protein 78 (GRP78) and 150 kDa oxygen-regulated protein (ORP150) mRNA and protein was determined by real-time PCR and western blotting respectively. Results: AS-IV treatment significantly reduced urinary albumin excretion, plasma creatinine and blood urea nitrogen levels, and prevented the mesangial matrix expansion and increase in mean mesangial induced by STZ. AS-IV also prevented the phosphorylation of eIF2a, PERK and JNK, and inhibited the expression of GRP78 and ORP150 markedly, both in vivo and in vitro. AS-IV inhibited the TM-induced apoptosis of podocytes, concomitant with decreased CHOP expression and cleaved caspase-3. Conclusions: This study supports the hypothesis that AS-IV reduces proteinuria and attenuates diabetes, which is associated with decreased ER stress. This might be an important mechanism in the renoprotective function of AS-IV in the pathogenesis of DN.