Sirt6 deficiency contributes to mitochondrial fission and oxidative damage in podocytes via ROCK1‐Drp1 signalling pathway

Abstract

Objectives: Increasing evidence suggests that mitochondrial dysfunction is the key driver of angiotensin II (Ang II)-induced kidney injury. This study was designed to investigate whether Sirtuin 6 (Sirt6) could affect Ang II-induced mitochondrial damage and the potential mechanisms.Materials and Methods: Podocyte-specific Sirt6 knockout mice were infused with Ang II and cultured podocytes were stimulated with Ang II to evaluate the effects of Sirt6 on mitochondrial structure and function in podocytes. Immunofluorescence staining was used to detect protein expression and mitochondrial morphology in vitro. Electron microscopy was used to assess mitochondrial morphology in mice.Western blotting was used to quantify protein expression.Results: Mitochondrial fission and decreased Sirt6 expression were observed in podocytes from Ang II-infused mice. In Sirt6-deficient mice, Ang II infusion induced increased apoptosis and mitochondrial fragmentation in podocytes than that in Ang II-infused wild-type mice. In cultured human podocytes, Sirt6 knockdown exacerbated Ang II-induced mitochondrial fission, whereas Sirt6 overexpression ameliorated the Ang II-induced changes in the balance between mitochondrial fusion and fission.Functional studies revealed that Sirt6 deficiency exacerbated mitochondrial fission by promoting dynamin-related protein 1 (Drp1) phosphorylation. Furthermore, Sirt6 mediated Drp1 phosphorylation by promoting Rho-associated coiled coil-containing protein kinase 1 (ROCK1) expression. Conclusion:Our study has identified Sirt6 as a vital factor that protects against Ang II-induced mitochondrial fission and apoptosis in podocytes via the ROCK1-Drp1 signalling pathway. | INTRODUCTIONThe renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in the occurrence and progression of chronic kidney diseases (CKD). 1 Zhaowei Chen and Wei Liang contributed equally to this work.

Epigenetic regulation of mitochondrial‐endoplasmic reticulum dynamics in kidney diseases

“…Similar to Sirt3, Sirt6 is also located in mitochondria and decreases AKI's progression by suppressing Drp1 (Chen et al, 2022). In Sirt6 knockout mice, after infusion of angiotensin II, increased mitochondrial fission and fragmentation in podocytes was observed that provoked cell apoptosis and, ultimately AKI.…”

“…Similarly, another study found that silybin increases the Sirt3 expression in renal tubular cells in the kidney, through which silybin improves mitochondrial dynamics and mitochondrial activity in cisplatin‐induced AKI rats (Li et al, 2017). Similar to Sirt3, Sirt6 is also located in mitochondria and decreases AKI's progression by suppressing Drp1 (Chen et al, 2022). In Sirt6 knockout mice, after infusion of angiotensin II, increased mitochondrial fission and fragmentation in podocytes was observed that provoked cell apoptosis and, ultimately AKI.…”

“…In Sirt6 knockout mice, after infusion of angiotensin II, increased mitochondrial fission and fragmentation in podocytes was observed that provoked cell apoptosis and, ultimately AKI. Furthermore, an increase in the phosphorylation of Drp‐1 was observed, which was decreased by the action of Sirt6 through the activation of Rho‐associated coiled coil‐containing protein kinase 1 (ROCK1) in mitochondria of podocytes (Chen et al, 2022) (Table 1).…”

Sirtuins in kidney diseases: potential mechanism and therapeutic targets

“…In DKD mice, Sirt6 expression is reduced, and AMPK is dephosphorylated with abnormal mitochondrial function, whereas, Sirt6 overexpression increases AMPK phosphorylation levels, suggesting that Sirt6 inhibits mitochondrial dysfunction in DKD by regulating AMPK [ 60 ]. In addition, Sirt6 overexpression also ameliorated the Ang II-induced changes in the balance between mitochondrial fusion and fission [ 61 ]. Progressive EMT in the kidneys of db/db mice is associated with Sirt6 downregulation, and reduced Sirt6 levels lead to progressive renal injury, such as tubular injury.…”

“…ROS levels and cytochrome c release exacerbate mitochondrial dysfunction [ 137 ]. Sirt6 knockdown exacerbated HG-induced reduction of mitochondrial numbers, increased mitochondrial superoxide production, and decreased mitochondrial membrane potential, which exacerbated mitochondrial division through DRP1 phosphorylation, whereas Sirt6 overexpression increased AMPK phosphorylation, attenuated HG-induced apoptosis of podocytes and oxidative stress, and improved Ang II-induced changes in the balance between mitochondrial fusion and division [ 60 , 61 ]. In addition, Sirt1 protects podocytes by deacetylating cortactin, thereby maintaining actin cytoskeleton integrity [ 32 ].…”