Intestinal Reg4 deficiency confers susceptibility to high-fat diet-induced liver steatosis by increasing intestinal fat absorption in mice

Abstract

Regenerating gene family member 4 (REG4) is a novel marker for enteroendocrine cells and is selectively expressed in specialised enteroendocrine cells of the small intestine. However, the exact roles of REG4 are largely unknown. In this study we investigate the effects of REG4 on the development of dietary fat-dependent liver steatosis and the mechanisms involved. Mice with intestinal-specific Reg4 deficiency (Reg4 ΔIEC ) and Reg4-floxed alleles (Reg4 fl/fl ) were generated to investigate the effects of Reg4 on diet-induced obesity and liver steatosis. Serum levels of REG4 were also measured in children with obesity using ELISA. Reg4 ΔIEC mice fed a high-fat diet demonstrated significantly increased intestinal fat absorption and were prone to obesity and hepatic steatosis. Importantly, Reg4 ΔIEC mice exhibit enhanced activation of adenosine monophosphate-activated protein kinase (AMPK) signalling and increased protein abundance of the intestinal fat transporters, as well as enzymes involved in triglyceride synthesis and packaging at the proximal small intestine. Moreover, REG4 administration reduced fat absorption, and decreased the expression of intestinal fat absorption-related proteins in cultured intestinal cells possibly via the CaMKK2-AMPK pathway. Serum REG4 levels were markedly lower in children with obesity with advanced liver steatosis (p <0.05). Serum REG4 levels were inversely correlated with levels of liver enzymes, homeostasis model assessment of insulin resistance, low-density lipoprotein cholesterol, and triglycerides. Our findings directly link Reg4 deficiency with increased fat absorption and obesity-related liver steatosis, and suggest that REG4 may provide a potential target for prevention and treatment of liver steatosis in children. Hepatic steatosis is a key histological feature of non-alcoholic fatty liver disease, which is the leading chronic liver disease in children leading to the development of metabolic diseases; however, little is known about mechanisms induced by dietary fat. Intestinal REG4 acts as a novel enteroendocrine hormone reducing high-fat-diet-induced liver steatosis with decreasing intestinal fat absorption. REG4 may be a novel target for treatment of paediatric liver steatosis from the perspective of crosstalk between intestine and liver.