Differential association of adipophilin and TIP47 proteins with cytoplasmic lipid droplets in mouse enterocytes during dietary fat absorption.

Recently, we found that enterocytes dynamically store triglycerides (TGs) in cytoplasmic lipid droplets (CLDs) during dietary fat absorption. A dynamic pool of TG in the form of CLDs which expands and depletes relative to time post dietary fat challenge is present in the absorptive cells of the small intestine, enterocytes. To identify cellular factors which may play a role in the regulation of this dynamic process we investigated the expression and localization of a lipid droplet associated protein family, PAT proteins, in enterocytes of mice chronically and acutely challenged by dietary fat. We found that adipophilin and Tip47 are the only PAT genes present in mouse intestinal mucosa and both genes are present at higher levels after high-fat challenges. We found TIP47 protein present in the intestine from chow and high-fat challenged mice; however, adipophilin protein was only present after high-fat challenges. In addition, TIP47 protein level was higher after an acute than a chronic high-fat challenge whereas adipophilin protein level was higher after a chronic than an acute high-fat challenge. We co-imaged TG in CLDs using CARS microscopy and TIP47 or adipophilin using immunocytochemistry in isolated enterocytes from mice challenged chronically and acutely by high levels of dietary fat. TIP47, but not adipophilin, coats CLDs in enterocytes after an acute high-fat challenge suggesting that TIP47 plays a role in the synthesis of CLDs from newly synthesized TG at the beginning of the process of dietary fat absorption in enterocytes. Adipophilin, on the other hand, coats CLDs only in enterocytes of chronic high-fat fed mice suggesting that adipophilin may play a role in the stabilization of TG stored in CLDs in longer term. These results suggest distinct roles for TIP47 and adipophilin in dietary fat absorption.