Baicalin regulates SirT1/STAT3 pathway and restrains excessive hepatic glucose production.

ABSTRACT

Sirtuin 1 (SirT1) and signal transducer and activator of transcription 3 (STAT3) oppositely regulate hepatic gluconeogenic genes and the association remains to be elucidated. Baicalin is a natural flavonoid with beneficial effects on glucose and lipid metabolism. This study aims to investigate the effect of baicalin on hepatic gluconeogenesis with focus on the regulation of fatty acid mobilization and SirT1/STAT3 pathway. In HFD feeding or fasting state, hepatic gluconeogenesis and fatty acid oxidation induced SirT1 expression due to the increased nicotinamide adenine dinucleotide+ (NAD+) contents. Baicalin reduces endogenous glucose production via suppression of hepatic gluconeogenesis and decreased SirT1 induction via reducing NAD+ accumulation in an energy-sensing way. Fasting increased SirT1 protein in STAT3 immunoprecipitation products and less in the liver of baicalin-treated mice, indicating that baicalin blocked the binding of SirT1 to STAT3 and thus preserved STAT3 acetylation. SirT1 knockdown enhanced the protective effect of baicalin on pyruvate-induced STAT3 phosphorylation and acetylation, these results further indicated that the regulation of STAT3 activity by baicalin was dependent on SirT1. Moreover, HFD feeding increased gene expression for PGC-1α in the liver, but the transcriptional regulation was inhibited by baicalin treatment. SirT1 overexpression and STAT3 inhibition enhanced pyruvate-mediated PGC-1α gene expression, suggesting that deacetylation of STAT3 by SirT1 is required for PGC-1α activity on hepatic gluconeogenesis. Taken together, these results showed that baicalin restrained HGP via inhibiting SirT1 activity coupled with STAT3 acetylation and subsequent PGC-1α suppression, suggesting that hepatic SirT1 and STAT3 pathway may provide therapeutic advantages for the control of hyperglycemia.