Sweet Sixteenth for ChREBP: Established Roles and Future Goals.

With the identification of ChREBP in 2001, our interest in understanding the molecular control of carbohydrate sensing has surged. While ChREBP was initially studied as a master regulator of lipogenesis in liver and fat tissue, it is now clear that ChREBP functions as a central metabolic coordinator in a variety of cell types in response to environmental and hormonal signals, with wide implications in health and disease. Celebrating its sweet sixteenth birthday, we review here the current knowledge about the function and regulation of ChREBP throughout usual and less explored tissues, to recapitulate ChREBP's role as a whole-body glucose sensor.

The suppression of hepatic glucose production improves metabolism and insulin sensitivity in subcutaneous adipose tissue in mice.

AIMS/HYPOTHESIS: Despite the strong correlation between non-alcoholic fatty liver disease and insulin resistance, hepatic steatosis is associated with greater whole-body insulin sensitivity in several models. We previously reported that the inhibition of hepatic glucose production (HGP) protects against the development of obesity and diabetes despite severe steatosis, thanks to the secretion of specific hepatokines such as fibroblast growth factor 21 (FGF21) and angiopoietin-related growth factor. In this work, we focused on adipose tissue to assess whether liver metabolic fluxes might, by interorgan communication, control insulin signalling in lean animals. METHODS: Insulin signalling was studied in the adipose tissue of mice lacking the catalytic subunit of glucose 6-phosphatase, the key enzyme in endogenous glucose production, in the liver (L-G6pc -/- mice). Morphological and metabolic changes in the adipose tissues were characterised by histological analyses, gene expression and protein content. RESULTS: Mice lacking HGP exhibited improved insulin sensitivity of the phosphoinositide 3-kinase/Akt pathway in the subcutaneous adipose tissue associated with a browning of adipocytes. The suppression of HGP increased FGF21 levels in lean animals, and increased FGF21 was responsible for the metabolic changes in the subcutaneous adipose tissue but not for its greater insulin sensitivity. The latter might be linked to an increase in the ratio of monounsaturated to saturated fatty acids released by the liver. CONCLUSIONS: Our work provides evidence that HGP controls subcutaneous adipose tissue browning and insulin sensitivity through two pathways: the release of beneficial hepatokines and changes in hepatic fatty acids profile.

A link between hepatic glucose production and peripheral energy metabolism via hepatokines.

Type 2 diabetes is characterized by a deterioration of glucose tolerance, which associates insulin resistance of glucose uptake by peripheral tissues and increased endogenous glucose production. Here we report that the specific suppression of hepatic glucose production positively modulates whole-body glucose and energy metabolism. We used mice deficient in liver glucose-6 phosphatase that is mandatory for endogenous glucose production. When they were fed a high fat/high sucrose diet, they resisted the development of diabetes and obesity due to the activation of peripheral glucose metabolism and thermogenesis. This was linked to the secretion of hepatic hormones like fibroblast growth factor 21 and angiopoietin-like factor 6. Interestingly, the deletion of hepatic glucose-6 phosphatase in previously obese and insulin-resistant mice resulted in the rapid restoration of glucose and body weight controls. Therefore, hepatic glucose production is an essential lever for the control of whole-body energy metabolism during the development of obesity and diabetes.

Control of blood glucose in the absence of hepatic glucose production during prolonged fasting in mice: induction of renal and intestinal gluconeogenesis by glucagon.

OBJECTIVE: Since the pioneering work of Claude Bernard, the scientific community has considered the liver to be the major source of endogenous glucose production in all postabsorptive situations. Nevertheless, the kidneys and intestine can also produce glucose in blood, particularly during fasting and under protein feeding. The aim of this study was to better define the importance of the three gluconeogenic organs in glucose homeostasis. RESEARCH DESIGN AND METHODS: We investigated blood glucose regulation during fasting in a mouse model of inducible liver-specific deletion of the glucose-6-phosphatase gene (L-G6pc(-/-) mice), encoding a mandatory enzyme for glucose production. Furthermore, we characterized molecular mechanisms underlying expression changes of gluconeogenic genes (G6pc, Pck1, and glutaminase) in both the kidneys and intestine. RESULTS: We show that the absence of hepatic glucose release had no major effect on the control of fasting plasma glucose concentration. Instead, compensatory induction of gluconeogenesis occurred in the kidneys and intestine, driven by glucagon, glucocorticoids, and acidosis. Moreover, the extrahepatic action of glucagon took place in wild-type mice. CONCLUSIONS: Our study provides a definitive quantitative estimate of the capacity of extrahepatic gluconeogenesis to sustain fasting endogenous glucose production under the control of glucagon, regardless of the contribution of the liver. Thus, the current dogma relating to the respective role of the liver and of extrahepatic gluconeogenic organs in glucose homeostasis requires re-examination.

Targeted deletion of liver glucose-6 phosphatase mimics glycogen storage disease type 1a including development of multiple adenomas.

BACKGROUND AND AIMS: Glycogen storage disease type 1a (GSD1a) is an inherited disease caused by a deficiency in the catalytic subunit of the glucose-6 phosphatase enzyme (G6Pase). GSD1a is characterized by hypoglycaemia, hyperlipidemia, and lactic acidosis with associated hepatic (including hepatocellular adenomas), renal, and intestinal disorders. A total G6pc (catalytic subunit of G6Pase) knock-out mouse model has been generated that mimics the human pathology. However, these mice rarely live longer than 3 months and long-term liver pathogenesis cannot be evaluated. Herein, we report the long-term characterization of a liver-specific G6pc knock-out mouse model (L-G6pc(-/-)). METHODS: We generated L-G6pc(-/-) mice using an inducible CRE-lox strategy and followed up the development of hepatic tumours using magnetic resonance imaging. RESULTS: L-G6pc(-/-) mice are viable and exhibit normoglycemia in the fed state. They develop hyperlipidemia, lactic acidosis, and uricemia during the first month after gene deletion. However, these plasmatic parameters improved after 6 months. L-G6pc(-/-) mice develop hepatomegaly with glycogen accumulation and hepatic steatosis. Using an MRI approach, we could detect hepatic nodules with diameters of less than 1 mm, 9 months after induction of deficiency. Hepatic nodules (1 mm) were detected in 30-40% of L-G6pc(-/-) mice at 12 months. After 18 months, all L-G6pc(-/-) mice developed multiple hepatocellular adenomas of 1-10 mm diameter. CONCLUSIONS: This is the first report of a viable animal model of the hepatic pathology of GSD1a, including the late development of hepatocellular adenomas.