Extracellular visfatin activates gluconeogenesis in HepG2 cells through the classical PKA/CREB-dependent pathway.

Abstract

Adipokines reportedly affect hepatic gluconeogenesis, and the adipokine visfatin

is known to be related to insulin resistance and type 2 diabetes. However,

whether visfatin contributes to hepatic gluconeogenesis remains unclear.

Visfatin, also known as nicotinamide phosphoribosyltransferase (NAMPT), modulates

sirtuin1 (SIRT1) through the regulation of nicotinamide adenine dinucleotide

(NAD). Therefore, we investigated the effect of extracellular visfatin on glucose

production in HepG2 cells, and evaluated whether extracellular visfatin affects

hepatic gluconeogenesis via an NAD+-SIRT1-dependent pathway. Treatment with

visfatin significantly increased glucose production and the mRNA expression and

protein levels of phosphoenolpyruvate carboxykinase (PEPCK) and

glucose-6-phosphatase (G6Pase) in HepG2 cells in a time- and

concentration-dependent manner. Knockdown of SIRT1 had no remarkable effect on

the induction of gluconeogenesis by visfatin. Subsequently, we evaluated if

extracellular visfatin stimulates the production of gluconeogenic enzymes through

the classical protein kinase A (PKA)/cyclic AMP-responsive element (CRE)-binding

protein (CREB)-dependent process. The phosphorylation of CREB and PKA increased

significantly in HepG2 cells treated with visfatin. Additionally, knockdown of

CREB and PKA inhibited visfatin-induced gluconeogenesis in HepG2 cells. In

summary, extracellular visfatin modulates glucose production in HepG2 cells

through the PKA/CREB pathway, rather than via SIRT1 signaling.