Astragaloside IV inhibits palmitic acid-induced apoptosis through regulation of calcium homeostasis in mice podocytes

Loss of podocytes is a hallmark of diabetic nephropathy, and a growing body of evidence indicates that podocytes are susceptible to palmitic acid (PA). We have previously shown that AS-IV inhibited PA-induced podocyte apoptosis by activating sarcoendoplasmic reticulum Ca²⁺ ATPase (SERCA), which indicate calcium regulation may involve in the process. Immunofluorescence staining, Western blot and flow cytometry were used to measure the protective efficacy of AS-IV to ameliorate PA-induced ER stress and podocyte apoptosis. Meanwhile, AS-IV inhibited cytochrome c release, decreased mitochondrial membrane potential, accompany with the depletion of endoplasmic reticulum Ca²⁺ and elevation of cytosolic and mitochondrial Ca²⁺. Sequestration of cytosolic calcium with BAPTA-AM limited the response of podocyte apoptosis, while during the process the effect of AS-IV was also restrained. In contrast, elevation of cytosolic calcium with calcium ionophore ionomycin was depressed by AS-IV addition. Furthermore, inhibiting TRPC6 expression with SKF96365 or TRPC6 siRNA counteracted the beneficial effect of AS-IV. Our study provides further evidence to conclude the inhibitory effect of AS-IV to podocyte apoptosis is Ca²⁺-dependent. And the efficacy correlates with inhibiting TRPC6-mediated Ca²⁺ influx, and then cellular Ca²⁺ disturbance was coordinated.