Our previous study reported that
thyroid-stimulating hormone (TSH) promotes
cholesterol synthesis via the cyclic
adenosine monophosphate/
protein kinase A/cAMP regulatory
element-
binding protein (cAMP/PKA/CREB) pathway after binding to
TSH receptors (TSHR) in the liver. The hepatic cAMP/PKA/CREB pathway also plays an important role in maintaining fasting
glucose homeostasis. These findings implied a possible role for TSH in hepatic
glucose metabolism. In this study, we used
TSH receptor knockout mice (Tshr-ko mice) to clarify the effect of Tshr deletion on hepatic
glucose metabolism, and investigated whether the effects of TSH directly regulate hepatic gluconeogenesis in HepG2 cells. Tshr-ko mice exhibited decreased fasting
blood glucose levels, increased
insulin sensitivity but normal level of fasting plasma
insulin. Tshr deletion impaired hepatic
glucose production by down-regulating the expression of
glucose-6-phosphatase (G6P) and
phosphoenolpyruvate pyruvate carboxylase (PEPCK)
mRNA, two rate-limiting
enzymes in hepatic gluconeogenesis, and enhancing the abundance of hepatic
glucokinase (GK), the first
enzyme regulating
glycogen synthesis. Moreover, Tshr deletion inhibited the
protein expression of hepatic phospho-CREB and increased the
protein expression of hepatic phospho-
AMP-activated protein kinase (p-AMPK), two up-stream regulators of PEPCK and G6P
mRNA. In HepG2 cells, TSH increased the expression of G6P and PEPCK at
mRNA level. These results indicated the simulative effects of TSH on hepatic
glucose production in vivo and in vitro, suggesting a novel role for TSH in hepatic
glucose metabolism.