Abstract
BackgroundThe mechanism of podocyte apoptosis is not fully understood. In addition, the role of the inositol 1,4,5-triphosphate receptor (IP3R)/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.MethodsThe expression of IP3R, Grp75, VDAC1, and MCU and mitochondrial Ca2+ were analyzed during Adriamycin- or angiotensin II-induced apoptosis in cultured mouse podocytes. The interaction between IP3R, Grp75, and VDAC1 was investigated using co-immunoprecipitation experiments. The effects of IP3R, Grp75, and MCU agonists and antagonists on mitochondrial Ca2+ and apoptosis were investigated in cultured podocytes. The podocyte-protective effects of an MCU inhibitor were further investigated in rats with Adriamycin-induced nephropathy.ResultsIncreased expression of IP3R, Grp75, VDAC1 and MCU, enhanced interaction among the IP3R-Grp75-VDAC1 complex, mitochondrial Ca2+ overload, and increased active caspase-3 levels were confirmed during Adriamycin- or angiotensin II-induced mouse podocyte apoptosis. Agonists of this axis facilitated mitochondrial Ca2+ overload and podocyte apoptosis, whereas specific antagonists against IP3R, Grp75, or MCU prevented mitochondrial Ca2+ overload and podocyte apoptosis. A specific MCU inhibitor prevented Adriamycin-induced proteinuria and podocyte foot process effacement in rats.ConclusionsThis study identified a novel pathway in which the IP3R-Grp75-VDAC1-MCU calcium regulation axis mediated podocyte apoptosis by facilitating mitochondrial Ca2+ overload. Antagonists that inhibit Ca2+ 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.
Highlights
The mechanism of podocyte apoptosis is not fully understood
Enhanced expression and interaction of the Inositol 1 (IP3R)-Grp75VDAC1-mitochondrial calcium uniporter (MCU) calcium regulation axis mediated podocyte apoptosis by facilitating mitochondrial Ca2+ overload Compared with normal Ctl podocytes, the apoptosis rate revealed by flow cytometry in mouse podocytes treated with ADR (13.02% ± 0.93% vs. 2.56% ± 0.49%, P = 0.000, n = 3) or Ang Angiotensin II (II) (10.58% ± 1.38% vs. 2.40% ± 0.85%, P = 0.001, n = 3) increased significantly (Fig. 1a), active caspase-3 level revealed by western blotting in mouse podocytes treated with ADR (P = 0.006, n = 4) or angiotensin II (Ang II) (P = 0.021, n = 4) increased significantly (Fig. 1b)
Compared with the podocytes treated with ADR only (P = 0.124, n = 12) or Ang II only (P = 0.083, n = 12), the increase in mitochondrial Ca2+ induced by ADR or Ang II was not prevented by additional treatment with EDTA (Fig. 1c)
Summary
The role of the inositol 1,4,5-triphosphate receptor (IP3R)/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. Methods: The expression of IP3R, Grp, VDAC1, and MCU and mitochondrial Ca2+ were analyzed during Adriamycin- or angiotensin II-induced apoptosis in cultured mouse podocytes. The effects of IP3R, Grp, and MCU agonists and antagonists on mitochondrial Ca2+ and apoptosis were investigated in cultured podocytes. Podocyte apoptosis play a key role in the development of focal segmental glomerulosclerosis. Different mechanisms could mediate podocyte apoptosis, such as cytosolic Ca2+ overload [2], mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and oxidative stress [3]. Ca2+ transfer from the ER to the mitochondria is required for mitochondrial
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