Roles of mitochondrial sirtuins in mitochondrial function, redox homeostasis, insulin resistance and type 2 diabetes

Mitochondria are the metabolic hubs that process a number of reactions including tricarboxylic acid cycle, β-oxidation of fatty acids and part of the urea cycle and pyrimidine nucleotide biosynthesis. Mitochondrial dysfunction impairs redox homeostasis and metabolic adaptation, leading to aging and metabolic disorders like insulin resistance and type 2 diabetes. SIRT3, SIRT4 and SIRT5 belong to the sirtuin family proteins and are located at mitochondria and also known as mitochondrial sirtuins. They catalyze NAD⁺-dependent deacylation (deacetylation, demalonylation and desuccinylation) and ADP-ribosylation and modulate the function of mitochondrial targets to regulate the metabolic status in mammalian cells. Emerging evidence has revealed that mitochondrial sirtuins coordinate the regulation of gene expression and activities of a wide spectrum of enzymes to orchestrate oxidative metabolism and stress responses. Mitochondrial sirtuins act in synergistic or antagonistic manners to promote respiratory function, antioxidant defense, insulin response and adipogenesis to protect individuals from aging and aging-related metabolic abnormalities. In this review, we focus on the molecular mechanisms by which mitochondrial sirtuins regulate oxidative metabolism and antioxidant defense and discuss the roles of their deficiency in the impairment of mitochondrial function and pathogenesis of insulin resistance and type 2 diabetes.