Rationale:
Sirtuins are
NAD+-dependent
protein deacylases known to have protective effects against age-related diseases such as diabetes,
cancer, and
neurodegenerative disease.
SIRT2 is the only primarily cytoplasmic
isoform and its overall role in
glucose homeostasis remains uncertain. Methods: SIRT2-knockout (KO) rats were constructed to evaluate the role of
SIRT2 in
glucose homeostasis. The effect of
SIRT2 on β-cell function was detected by investigating the morphology, insulin secretion, and metabolomic state of islets. The deacetylation and stabilization of GKRP in β-cells by
SIRT2 were determined by western blot, adenoviral
infection, and immunoprecipitation. Results: SIRT2-KO rats exhibited
impaired glucose tolerance and
glucose-stimulated insulin secretion (GSIS), without change in
insulin sensitivity.
SIRT2 deficiency or inhibition by AGK2 decreased GSIS in isolated rat islets, with lowered oxygen consumption rate. Adenovirus-mediated overexpression of
SIRT2 enhanced insulin secretion from rat islets. Metabolomics analysis revealed a decrease in metabolites of glycolysis and tricarboxylic acid cycle in SIRT2-KO islets compared with control islets. Our study further demonstrated that
glucokinase regulatory protein (GKRP), an endogenous inhibitor of
glucokinase (GCK), was expressed in rat islets.
SIRT2 overexpression deacetylated GKRP in INS-1 β-cells.
SIRT2 knockout or inhibition elevated GKRP protein stability in islet β-cells, leading to an increase in the interaction of GKRP and GCK. On the contrary,
SIRT2 inhibition promoted the protein degradation of ALDOA, a glycolytic
enzyme. Conclusions:
SIRT2 ablation inhibits GSIS through blocking GKRP protein degradation and promoting ALDOA protein degradation, resulting in a decrease in glycolytic flux.