Upregulation of cholesterol absorption as a mechanism for cholecystokinin-induced hypercholesterolemia [Gene Regulation]

April 1st, 2014 by Zhou, L., Yang, H., Okoro, E. E., Guo, Z.

Excessive absorption of intestinal cholesterol is a risk factor for atherosclerosis. This report examines the effect of cholecystokinin (CCK) on plasma cholesterol levels and intestinal cholesterol absorption using the in vivo models of C57BL/6 wild-type and low-density lipoprotein receptor knockout (LDLR-/-) mice. The findings are supported by in vitro studies involving mouse primary intestinal epithelial cells (MPIECs) and human Caco-2 cells; both express CCK receptor-1 and -2 (CCK1R; CCK2R). We found that intravenous injection of [Thr28, Nle31]-CCK increased plasma cholesterol levels and intestinal cholesterol absorption in both wild-type and LDLR-/- mice. Treatment of MPIECs with CCK increased cholesterol absorption, while selective inhibition of CCK1R and CCK2R with antagonists attenuated CCK-induced cholesterol absorption. In Caco-2 cells, CCK enhanced CCK1R/CCK2R hetero-dimerization. Knockdown of both CCK1R and CCK2 or either one of them alone diminished CCK-induced cholesterol absorption to the same extent. CCK also increased cell surface-associated Niemann-Pick C1 Like 1 (NPC1L1) but did not alter its total protein expression. Inhibition or knockdown of NPC1L1 attenuated CCK-induced cholesterol absorption. CCK enhanced phosphatidylinositide 3-kinase (PI3K) and Akt phosphorylation and augmented the interaction between NPC1L1 and Rab-GTPase-11a (Rab11a), while knockdown of CCK receptors or inhibition of G protein &beta&gamma dimers (G&beta&gamma) diminished CCK-induced PI3K and Akt phosphorylation. Inhibition of PI3K and Akt or knockdown of PI3K also diminished CCK-induced NPC1L1-Rab11a interactions and cholesterol absorption. Knockdown of Rab11a suppressed CCK-induced NPC1L1 translocation and cholesterol absorption. These data imply that CCK enhances cholesterol absorption by activation of a pathway involving CCK1R/CCK2R, Gβγ, PI3K, Akt, Rab11a and NPC1L1.