Altered lipid homeostasis and increased whole body fat are hallmarks of obesity which has become a national epidemic. In turn, mammalian intestinal absorption of lipids is dependent on bile acids. Bile acids themselves are reabsorbed in the distal ileum via the intestinal apical sodium-dependent bile acid co-transporter (ASBT, SC10A2) localized at the brush border membrane (BBM) of absorptive villus cells. ASBT is the sole bile acid absorptive mechanism in the human intestine. While increased lipid absorption is known in obesity, how ASBT mediated intestinal bile acid absorption may be regulate in obesity is not known. Preliminary studies in well- established in-vivo models of obesity, specifically in Obese Zucker rats and TALLYHO mice, suggest that ASBT is increased in villus cells. This is not secondary to altered Na-extruding capacity of the cell as Na-K- ATPase levels were not increased but decreased in these cells. Similar observations were seen in obese humans. Given these translationally relevant novel observations, the overall hypothesis of this proposal is that enhanced lipid absorption of obesity mediated by bile acids is facilitated by stimulation of ASBT during obesity. Therefore, the overall aim of this proposal is to determine the molecular and intracellular mechanisms of regulation of ASBT in obesity.
Three specific aims will complementarily and comprehensively address this novel hypothesis:
Aim 1. Determine the broad applicability of stimulation of ASBT in villus cells during obesity Aim 2. Delineate the specific transcriptional mechanism of stimulation of ASBT in villus cells.
Aim 3. Determine the specific post-transcriptional mechanism of stimulation of ASBT in villus cells. The results of these studies will provide new and important knowledge of the regulation of the ASBT in obesity which may allow for the design of ASBT inhibitors that would reduce lipid absorption and decrease obesity. The novel observations of this proposal about the regulation of ASBT during obesity will provide the basis for a future R01 application, which will focus on the intracellular mechanism of regulation of ASBT stimulation as well as the alterations in ASBT in human obesity. Ultimately, better understanding of ASBT regulation in obesity will result in better treatment modalities for the obesity epidemic in this country.