A UFMylation-COPII axis orchestrates lipid transport in intestinal enterocytes and regulates systemic lipid balance

BACKGROUND: Intestinal lipid absorption and chylomicron secretion are essential for systemic lipid homeostasis, yet the regulatory mechanisms coordinating lipoprotein assembly and ER export remain poorly understood. UFMylation is a newly identified ubiquitin-like modification pathway that plays critical roles in endoplasmic reticulum (ER)-related cellular activities such as protein quality control, ER-associated degradation (ERAD) and ER-phagy. However, its role in intestinal lipid transport and systemic lipid homeostasis is completely unclear. METHODS: To elucidate the role of UFMylation in intestinal lipid metabolism, we generated intestinal epithelial cell (IEC)-specific knockout mouse model of Ufbp1, a key component of the UFMylation pathway, and a double knockout model of Ufbp1 and IRE1α, one of the three signaling branches of Unfolded Protein response (UPR). After observing lipid droplet accumulation in the intestinal tissue of Ufbp1 and IRE1α double knockout mice, we further examined lipid metabolism in Ufbp1 knockout mice under high-fat diet. Finally, we used C2BBe1, a subclone of Caco-2 cell, as a cell model to investigate the role of UFMylation in Coat Protein Complex II (COPII)-mediated lipid transport in enterocytes. RESULTS: We serendipitously found that the combination of Ufbp1 and IRE1α deficiencies led to dramatic accumulation of lipid droplets in the enterocytes, thereby impairing enterocyte function and causing significant growth retardation. Furthermore, we found that Ufbp1 IEC-specific knockout mice were highly resistant to high-fat diet-induced hyperlipidemia. On the molecular level, we found that the components of the UFMylation pathway interacted with COPII complex and regulates the recruitment of COPII coat to ER-located lipoprotein. CONCLUSIONS: Our findings have established that the UFMylation pathway is a novel mediator of enterocyte lipid transport and a key partner of COPII-mediated trafficking.