Apolipoprotein A-IV Reduces Hepatic Gluconeogenesis through Nuclear Receptor NR1D1

Xiaoming Li,Min Xu,Fei Wang,Alison B Kohan,Michael K Haas,Qing Yang,Danwen Lou,Silvana Obici,W Sean Davidson,Patrick Tso

doi:10.1074/jbc.m113.511766

Abstract

We showed recently that apoA-IV improves glucose homeostasis by enhancing pancreatic insulin secretion in the presence of elevated levels of glucose. Therefore, examined whether apolipoprotein A-IV (apoA-IV) also regulates glucose metabolism through the suppression of hepatic gluconeogenesis. The ability of apoA-IV to lower gluconeogenic gene expression and glucose production was measured in apoA-IV(-/-) and wild-type mice and primary mouse hepatocytes. The transcriptional regulation of Glc-6-Pase and phosphoenolpyruvate carboxykinase (PEPCK) by apoA-IV was determined by luciferase activity assay. Using bacterial two-hybrid library screening, NR1D1 was identified as a putative apoA-IV-binding protein. The colocalization and interaction between apoA-IV and NR1D1 were confirmed by immunofluorescence, in situ proximity ligation assay, and coimmunoprecipitation. Enhanced recruitment of NR1D1 and activity by apoA-IV to Glc-6-Pase promoter was verified with ChIP and a luciferase assay. Down-regulation of apoA-IV on gluconeogenic genes is mediated through NR1D1, as illustrated in cells with NR1D1 knockdown by siRNA. We found that apoA-IV suppresses the expression of PEPCK and Glc-6-Pase in hepatocytes; decreases hepatic glucose production; binds and activates nuclear receptor NR1D1 and stimulates NR1D1 expression; in cells lacking NR1D1, fails to inhibit PEPCK and Glc-6-Pase gene expression; and stimulates higher hepatic glucose production and higher gluconeogenic gene expression in apoA-IV(-/-) mice. We conclude that apoA-IV inhibits hepatic gluconeogenesis by decreasing Glc-6-Pase and PEPCK gene expression through NR1D1. This novel regulatory pathway connects an influx of energy as fat from the gut (and subsequent apoA-IV secretion) with inhibition of hepatic glucose production.

Highlights

The role of apolipoprotein A-IV (apoA-IV) in hepatic gluconeogenesis is unknown
The plasma insulin level was unaffected. This reduction of glucose by apoA-IV lasted from 2– 4 h in fed animals and from 4 – 6 h in 5-h fasted mice. To determine whether this effect of apoA-IV on blood glucose is a result of alterations in hepatic gluconeogenesis, 2 h after treatment with exogenous apoA-IV, hepatic gluconeogenic gene expression was determined
We observed the presence of apoA-IV and NR1D1 in the immunoprecipitated complex isolated by anti-GFP antibodies (Fig. 5A). These results demonstrate that apoA-IV binds to NR1D1 located in the nucleus

Summary

Background

The role of apoA-IV in hepatic gluconeogenesis is unknown. Results: ApoA-IV interacts with NR1D1and stimulates its expression and decreases hepatic Glc-6-Pase and PEPCK expression and glucose production. We determined that apoA-IV acts to reduce hepatic gluconeogenesis, mediated through the nuclear receptor subfamily 1, group D, member 1 (NR1D1), known as REVERB␣ It is an important transcription factor regulating glucose metabolism by suppressing the expression of gluconeogenic genes [15,16,17]. ApoA-IV Regulates Gluconeogenesis via NR1D1 presses the expression of the gluconeogenic genes PEPCK2 and Glc-6-Pase and, hepatic glucose production through the NR1D1 pathway. This is a novel and important finding, regarding this important role of apoA-IV in glucose metabolism and linking lipid and glucose metabolism

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION