- Boortz KA, Syring KE, Dai C, Pound LD, Oeser JK, Jacobson DA, Wang JC, McGuinness OP, Powers AC, O'Brien RM. G6PC2 Modulates Fasting Blood Glucose In Male Mice in Response to Stress. Endocrinology. 2016 Jun 14. en20161245. PMID: 27300767 [PubMed].
G6PC2 encodes an islet-specific glucose-6-phosphatase catalytic subunit. Genome wide association studies have shown that single nucleotide polymorphisms (SNPs) in the G6PC2 gene are associated with variations in fasting blood glucose (FBG) but not fasting plasma insulin (FPI). Molecular analyses examining the functional effects of these SNPs demonstrate that elevated G6PC2 expression is associated with elevated FBG. Studies in mice complement these GWAS data and show that deletion of the G6pc2 gene lowers FBG without affecting FPI. This suggests that, together with glucokinase, G6PC2 forms a substrate cycle that determines the glucose sensitivity of insulin secretion. Because GWAS and mouse studies demonstrate that elevated G6PC2 expression raises FBG and because chronically elevated FBG is detrimental to human health, increasing the risk of type 2 diabetes, it is unclear why G6PC2 evolved. We show here that the synthetic glucocorticoid dexamethasone strongly induces human G6PC2 promoter activity and endogenous G6PC2 expression in isolated human islets. Acute treatment with dexamethasone selectively induces endogenous G6pc2 expression in 129SvEv but not C57BL/6J mouse pancreas and isolated islets. The difference is due to a SNP in the C57BL/6J G6pc2 promoter that abolishes glucocorticoid receptor binding. In 6 hr fasted, non-stressed 129SvEv mice, deletion of G6pc2 lowers FBG. In response to the stress of repeated physical restraint, which is associated with elevated plasma glucocorticoid levels, G6pc2 gene expression is induced and the difference in FBG between WT and KO mice is enhanced. These data suggest that G6PC2 may have evolved to modulate FBG in response to stress.