The Role Of PLZF In Hepatic Gluconeogenesis And Its Molecular Mechanism

Diabetes mellitus is one of the most serious metabolic diseases in the world,characterized by the feature of hyperglycemia. Hepatic gluconeogenesis plays a key role in maintaining blood glucose homeostasis, and its over-activation contributes importantly to the pathogenesis of diabetes. Therefore, study on the mechanism underlying the regulation of hepatic gluconeogenesis will be informative to the prevention and treatment of diabetes or other disorders associated with gluconeogenesis. On the other hand, the promyelocytic leukemia zinc finger (PLZF) protein is a zinc finger protein involved in major biological processes. Interestingly, a growing evidences reveals that PLZF is implicated in the regulation of glucose and lipid metabolism. However, its precise role in the metabolic regulation remains unknown. In the present study, we aimed to explore the molecular mechanisms through which PLZF regulates hepatic gluconeogenesis.To address this question, we used the gain- and loss-of-function strategy to manipulate PLZF expression levels both in vivo and in vitro through adenoviral transduction and siRNA delivery. We first examined the effects of nutritional signals on hepatic PLZF expression. Next, glucose and pyruvate tolerance and insulin sensitivity were determined in response to PLZF manipulation by using glucose tolerance test(GTT), pyruvate tolerance test (PTT) and insulin tolerance test (ITT), respectively. At the molecular level, real-time quantitative PCR and Western blot analyses were performed to quantify the expression levels of PLZF and gluconeogenic genes PEPCK and G6Pase in the liver. The activation of insulin/Akt signal pathway was also determined. In addition,luciferase reporter and chromatin immunoprecipitation (ChIP) assays were used to investigate the coordination of peroxisome prol iferator-acti vated receptor-y coactivator-la (PGC-la) and the glucocorticoid receptor (GR) in regulating plzf transcription.We found that in the livers of fasted mice and diabetic mice, the expression levels of PLZF were up-regulated. Glucocorticoids, such as dexamethasone (Dex), also increased the expression of PLZF in mouse liver cell line AML-12 and mouse primary hepatocytes,these suggesting that gluconeogenic signals induce PLZF expression. Overexpression of PLZF in mouse liver increased the expression of gluconeogenetic genes, increased hepatic glucose output, leading to hyperglycemia. In contrast, PLZF knockdown in liver resulted in the opposite phenotypes. Similarly, PLZF increased the expression of PEPCK and G6Pase in vitro. More importantly, in the pathological settings such as type 2 diabetes, PLZF knockdown in liver decreased the expression of G6Pase and PEPCK.Blood glucose levels were also significantly lower in mice with liver-specific PLZF knockdown. Correspondingly, these mice showed improved glucose and pyruvate tolerance and insulin sensitivity. Mechanistically, PLZF reduced the expression levels of phosphorylated Akt both in vivo and in vitro. On the other hand, PGC-1?, activated the transcriptional activity of the plzf promoter with the glucocorticoid receptor (GR). ChIP assays showed that PGC-la was recruited to the GR binding sites of the plzf promoter and altered the local chromatin environment from a repressive to an active state.In summary, our results strongly suggest that PLZF activates gluconeogenesis and increases glucose output under the control of the PGC-la/GR complex. To the best of our knowledge, this is the first time to explore the relationship between PLZF and hepatic glucose metabolism. Based on our findings, PLZF may serve as a pharmaceutical target to treat metabolic diseases with over-activated gluconeogenesis.