IP(3)R-Grp75-VDAC1-MCU calcium regulation axis antagonists protect podocytes from apoptosis and decrease proteinuria in an Adriamycin nephropathy rat model

BACKGROUND: The mechanism of podocyte apoptosis is not fully understood. In addition, the role of the inositol 1,4,5-triphosphate receptor (IP(3)R)/glucose-regulated protein 75 (Grp75)/voltage-dependent anion channel 1 (VDAC1)/mitochondrial calcium uniporter (MCU) calcium regulation axis, which is located at sites of endoplasmic reticulum (ER) mitochondria coupling, in the mechanism of podocyte apoptosis is unclear. This study aimed to understand the roles of this axis in podocyte apoptosis and explore potential targets for podocyte protection. METHODS: The expression of IP(3)R, Grp75, VDAC1, and MCU and mitochondrial Ca(2+) were analyzed during Adriamycin- or angiotensin II-induced apoptosis in cultured mouse podocytes. The interaction between IP(3)R, Grp75, and VDAC1 was investigated using co-immunoprecipitation experiments. The effects of IP(3)R, Grp75, and MCU agonists and antagonists on mitochondrial Ca(2+) and apoptosis were investigated in cultured podocytes. The podocyte-protective effects of an MCU inhibitor were further investigated in rats with Adriamycin-induced nephropathy. RESULTS: Increased expression of IP(3)R, Grp75, VDAC1 and MCU, enhanced interaction among the IP(3)R-Grp75-VDAC1 complex, mitochondrial Ca(2+) overload, and increased active caspase-3 levels were confirmed during Adriamycin- or angiotensin II-induced mouse podocyte apoptosis. Agonists of this axis facilitated mitochondrial Ca(2+) overload and podocyte apoptosis, whereas specific antagonists against IP(3)R, Grp75, or MCU prevented mitochondrial Ca(2+) overload and podocyte apoptosis. A specific MCU inhibitor prevented Adriamycin-induced proteinuria and podocyte foot process effacement in rats. CONCLUSIONS: This study identified a novel pathway in which the IP(3)R-Grp75-VDAC1-MCU calcium regulation axis mediated podocyte apoptosis by facilitating mitochondrial Ca(2+) overload. Antagonists that inhibit Ca(2+) transfer from ER to mitochondria protected mouse podocytes from apoptosis. An MCU inhibitor protected podocytes and decreased proteinuria in rats with Adriamycin-induced nephropathy. Therefore, antagonists to this pathway have promise as novel podocyte-protective drugs.