Postnatal Deletion of Fat Storage-inducing Transmembrane Protein 2 (FIT2/FITM2) Causes Lethal Enteropathy

Vera J Goh,Jolene S.Y Tan,Bryan C Tan,Colin Seow,Wei-Yi Ong,Yen Ching Lim,Lei Sun,Sujoy Ghosh,David L Silver

doi:10.1074/jbc.m115.676700

Abstract

Lipid droplets (LDs) are phylogenetically conserved cytoplasmic organelles that store neutral lipids within a phospholipid monolayer. LDs compartmentalize lipids and may help to prevent cellular damage caused by their excess or bioactive forms. FIT2 is a ubiquitously expressed transmembrane endoplasmic reticulum (ER) membrane protein that has previously been implicated in LD formation in mammalian cells and tissue. Recent data indicate that FIT2 plays an essential role in fat storage in an in vivo constitutive adipose FIT2 knock-out mouse model, but the physiological effects of postnatal whole body FIT2 depletion have never been studied. Here, we show that tamoxifen-induced FIT2 deletion using a whole body ROSA26CreER(T2)-driven FIT2 knock-out (iF2KO) mouse model leads to lethal intestinal pathology, including villus blunting and death of intestinal crypts, and loss of lipid absorption. iF2KO mice lose weight and die within 2 weeks after the first tamoxifen dose. At the cellular level, LDs failed to form in iF2KO enterocytes after acute oil challenge and instead accumulated within the ER. Intestinal bile acid transporters were transcriptionally dysregulated in iF2KO mice, leading to the buildup of bile acids within enterocytes. These data support the conclusion that FIT2 plays an essential role in regulating intestinal health and survival postnatally.

Highlights

FIT2 is an endoplasmic reticulum (ER) protein implicated in regulating cytosolic Lipid droplets (LDs) formation in mammals
These data indicate that cytosolic LDs are not required for chylomicron assembly and secretion but that FIT2 is essential for maintaining neutral lipid and BA homeostasis within enterocytes, which is in turn important for small intestinal health and function
We previously deleted FIT2 in an adipose tissue knock-out mouse model, leading to defects in LD storage of fat in white adipose tissue (WAT), infiltration of WAT with inflammatory macrophages, death of adipocytes, and metabolic dysfunction typical of lipodystrophies, which was significantly exacerbated by high fat feeding [11]

Summary

Background

FIT2 is an ER protein implicated in regulating cytosolic LD formation in mammals. Results: FIT2 deficiency in an inducible whole body knock-out mouse model leads to lethal enteropathy. 2 The abbreviations used are: LD, lipid droplet; BA, bile acid; ER, endoplasmic reticulum; TG, triglyceride; WAT, white adipose tissue; OST, organic solute transporter; FAS, fatty-acid synthase; EdU, 5-ethynyl-2Ј-deoxyuridine DPBS, Dulbecco’s phosphate-buffered saline; MTP, microsomal triglyceride transfer protein; ASBT, apical sodium-dependent bile acid transporter These changes were accompanied by a disruption of de novo cytosolic LD formation in the small intestine upon acute fat challenge, leading to a shift in the distribution of neutral lipid into the ER, but without changes in chylomicron synthesis upon acute fat challenge These data indicate that cytosolic LDs are not required for chylomicron assembly and secretion but that FIT2 is essential for maintaining neutral lipid and BA homeostasis within enterocytes, which is in turn important for small intestinal health and function

Experimental Procedures

Results

Discussion