943 Gastric Bypass Surgery for Morbid Obesity Disrupts Entero-Pancreatic Physiology

Abstract

G A A b st ra ct s synthesis, and third in terms of fatty acid synthesis (behind adipose and liver). Although the role of Insigs in regulating hepatic lipid metabolism is known, their role in the intestine is unknown. AIM: To study the role of Insig proteins on the regulation of lipid synthesis in the small intestine. METHODS: Mice with germline disruption of Insig2 and Villin-Cre mediated disruption of Insig1 in the intestine were generated (designated Vil-Insig mice). Tissues and plasma were harvested. Enterocytes were isolated and fractionated for immunoblotting, which was quantified by densitometry. mRNAs were quantified by qPCR. Plasma lipids were measured using a Vitros 250 chemistry analyzer. Jejuna were cryosectioned and stained with oil red O. RESULTS: The deletion of Insigs in intestine resulted in a loss of the normal feedback inhibition of SREBP processing and of HMGR proteolysis. Enterocyte nuclear SREBP-1 and SREBP-2 levels were increased in the Vil-Insig mice by 5-fold and 8fold, respectively. HMGR protein levels were increased by 18-fold. mRNA levels of SREBP lipogenic target genes were all increased; the greatest of which was stearoyl-CoA desaturase1 mRNA, which was increased 195-fold. As a consequence of this loss of SREBP-feedback inhibition, plasma cholesterol levels in the Vil-Insig mice were increased by 55% (123+/9 mg/dL vs 191+/-6 mg/dL, p,0.0001). Neutral lipid levels were increased in the jejunal crypts of the Vil-Insig mice as evidenced by oil red O staining. CONCLUSION: These studies indicate that the essential elements of the regulatory pathway for lipid synthesis function in the enterocyte as they do in the hepatocyte. Insig proteins provide essential negative feedback regulation on lipid biosynthesis in the intestine, and this regulation is required to maintain normal plasma cholesterol levels. Insigs mediate these effects by negatively regulating SREBPs and HMGR, to affect both cholesterol and fatty acid synthesis. Further studies will be required to determine if the increase in plasma cholesterol seen in the Vil-insig mice is related to changes in chylomicron synthesis/metabolism, and if Insig proteins affect enterocyte development, given the unique finding of lipid accumulation in the intestinal crypts.