Regulation of 3-hydroxy-3-methylglutaryl CoA reductase by analogs of cholesterol and bile acids in cultured intestinal mucosa

The role of enterocyte cholesterol metabolism in intestinal cell growth and differentiation

Cholesterol is an essential constituent of all mammalian cell membranes, and its availability is therefore a prerequisite for cellular growth and other functions. To define further the role of cholesterol metabolism in the intestine both in vitro and in vivo, studies were performed. Several lines of evidence based on these studies suggest that the main purpose of local cholesterol synthesis in the gut is the support of rapid enterocyte proliferation: 1) growth was inhibited during pharmacologic suppression of cholesterol synthesis in intestinal organ or cell culture; 2) the endocrine regulation of intestinal growth was in most but not all instances accompanied by appropriate changes in cholesterol synthesis; 3) most of cholesterol synthesis and lipoprotein uptake was localized predominantly in the crypt and lower villus region; and 4) very little of the sterol synthesized by the intestinal mucosa was exported into lymph but seems rather to be incorporated into cell membranes.

Lipid esterification and secretion by the mouse intestine in organ culture

Explants of adult mouse jejunum were cultured for different time periods and incubated in presence of a lipid diet emulsified by sodium taurocholate or complexed with albumin. The esterification of fatty acids and the secretion of triglycerides and phospholipids were measured and compared to the lipid absorption observed in vivo after the perfusion of the same diet. The results show that, in vitro, the enterocytes esterify the fatty acids present in the medium and secrete them with a yield improving during the culture and even better than the absorption observed in the in vivo experiments.

Bile acid induced interconversion of 3-hydroxy-3-methylglutaryl Coenzyme A reductase in cultured intestine

The effect of bile acids and bile acid/cholesterol micelles on 3-hydroxy-3-methylglutaryl coenzyme A reductase, the key enzyme of cholesterol synthesis, was investigated in cultured intestine. Glycocholic and glycodeoxycholic acid both suppressed total (fully activated) reductase activity after 3 h culture. The portion of expressed reductase, determined in the presence of NaF, was unaffected at 3 h, but decreased after 24 h of bile acid treatment. In contrast, total enzyme activity was stimulated up to 2.5-fold at 24 h; this bile acid effect was blocked by additional cholesterol. These results suggest that bile acids modulate both total reductase activity and the activation state of the enzyme in cultured intestine.