Sirtuin 3 regulates mitochondrial protein acetylation and metabolism in tubular epithelial cells during renal fibrosis

Proximal tubular epithelial cells (TECs) demand high energy and rely on mitochondrial oxidative phosphorylation as the main energy source. However, this is disturbed in renal fibrosis. Acetylation is an important post-translational modification for mitochondrial metabolism. The mitochondrial protein NAD(+)-dependent deacetylase sirtuin 3 (SIRT3) regulates mitochondrial metabolic function. Therefore, we aimed to identify the changes in the acetylome in tubules from fibrotic kidneys and determine their association with mitochondria. We found that decreased SIRT3 expression was accompanied by increased acetylation in mitochondria that have separated from TECs during the early phase of renal fibrosis. Sirt3 knockout mice were susceptible to hyper-acetylated mitochondrial proteins and to severe renal fibrosis. The activation of SIRT3 by honokiol ameliorated acetylation and prevented renal fibrosis. Analysis of the acetylome in separated tubules using LC-MS/MS showed that most kidney proteins were hyper-acetylated after unilateral ureteral obstruction. The increased acetylated proteins with 26.76% were mitochondrial proteins which were mapped to a broad range of mitochondrial pathways including fatty acid beta-oxidation, the tricarboxylic acid cycle (TCA cycle), and oxidative phosphorylation. Pyruvate dehydrogenase E1 alpha (PDHE1 alpha), which is the primary link between glycolysis and the TCA cycle, was hyper-acetylated at lysine 385 in TECs after TGF-beta 1 stimulation and was regulated by SIRT3. Our findings showed that mitochondrial proteins involved in regulating energy metabolism were acetylated and targeted by SIRT3 in TECs. The deacetylation of PDHE1 alpha by SIRT3 at lysine 385 plays a key role in metabolic reprogramming associated with renal fibrosis.

Automated summary

Proximal tubular epithelial cells (TECs) require high energy and rely on mitochondrial oxidative phosphorylation as their main energy source. However, in renal fibrosis, this process is disrupted. Sirtuin 3 (SIRT3), a mitochondrial protein, regulates mitochondrial metabolic function through deacetylation. Decreased SIRT3 expression in TECs during early renal fibrosis leads to increased acetylation in mitochondria, contributing to the development of severe renal fibrosis.Activation of SIRT3 can prevent renal fibrosis by reducing acetylation levels in mitochondrial proteins.