Caveolin-1 Is Not Required for Murine Intestinal Cholesterol Transport

Abstract

Caveolin-1 (CAV1) is the structural protein of the filamentous coat that decorates the cytoplasmic surface of each caveola. Cell culture studies have implicated CAV1 in playing an important role in intracellular cholesterol trafficking. In addition, it has been reported that CAV1 forms a detergent-resistant protein complex with Annexin-2 in enterocytes that can be disrupted by the cholesterol absorption inhibitor ezetimibe, suggesting a possible role for CAV1 in cholesterol absorption. In this report, we have evaluated cholesterol homeostasis in Cav1 knock-out mice. Deletion of CAV1 does not result in either a compensatory increase of CAV2 or CAV3 in intestine. In addition, Cav1 knock-out mice display normal mRNA and protein levels of Annexin-2 or the putative cholesterol transport protein Niemann-Pick C1-like 1 (NPC1L1) in proximal intestinal mucosa. Fractional cholesterol absorption and fecal neutral sterol excretion are statistically similar in Cav1 knock-out mice and their wild-type littermates. Moreover, oral administration of ezetimibe is equally effective in decreasing cholesterol absorption in Cav1 null mice and wild-type controls. The mRNA expression levels of genes sensitive to intracellular cholesterol concentration (ATP-binding cassette transporters ABCA1 and ABCG5, hydroxymethylglutaryl-CoA synthase and the LDL receptor) are similarly altered in the proximal intestinal mucosa of Cav1 null and wild-type mice following ezetimibe treatment. These results demonstrate that CAV1 is not required for cholesterol absorption or ezetimibe sensitivity in the mouse.

Fenofibrate reduces intestinal cholesterol absorption via PPARα-dependent modulation of NPC1L1 expression in mouse

“…5A, ezetimibe potently decreases cholesterol absorption relative to vehicle controls (?92% decrease, 45% to 4%; P , 0.05). This magnitude of decrease matches several other reports showing that ezetimibe decreases cholesterol absorption by .90% in various mouse models (8,18,38,39). Fenofibrate moderately decreases fractional cholesterol absorption (42% decrease, 45% to 26%; P , 0.05), similar to other mouse studies presented here (Figs.…”

“…Not only should knockout animals (lacking the putative transporter) have markedly reduced cholesterol absorption, they might also be insensitive to ezetimibe. Along these lines, Sr-bI-and Cav1-knockout mice have similar cholesterol absorption as wild-type mice and are fully sensitive to ezetimibe (8,18), suggesting that these proteins are not critical for the net movement of cholesterol across the intestinal epithelium. In contrast, mice lacking Npc1l1 have markedly decreased fractional cholesterol absorption (9,19) and are insensitive to ezetimibe (9).…”

“…The housekeeping gene, cyclophilin, did not differ between treatment groups (data not shown). In situ hybridization was carried out on transverse and longitudinal sections of segments of jejunum (13-18 cm from the pyloric sphincter) using an antisense RNA probe directed at the 3 ¶ untranslated region of NPC1L1 mRNA determined previously to be specific to NPC1L1 (without cross-reacting with NPC1) by Northern analysis (18). As shown in Fig.…”

“…Total protein obtained from whole-cell lysates of the proximal third of the small intestine were size-fractionated on 6% SDS-polyacrylamide gels (40 mg/lane), transferred electrophoretically to nitrocellulose membranes, and incubated with either polyclonal antisera for actin (sc-1616; Santa Cruz Biotechnology, Inc.) or NPC1L1 (provided by Helen Hobbs, University of Texas Southwestern Medical Center) (18). Proteins were visualized by exposure to film after sequential treatment with specific primary antibodies, appropriate HRP-conjugated secondary antibodies, and a standard ECL kit (Amersham).…”

Diosgenin stimulation of fecal cholesterol excretion in mice is not NPC1L1 dependent

“…2); 2) presumably due to less cholesterol uptake by enterocytes, feedback upregulation of cholesterol synthetic gene expression in the small intestine occurred in ezetimibe-treated mice and L1KO mice (17, 34) but not in diosgenin-treated mice (Fig. 3C); 3) probably because of less cholesterol available to activate the nuclear receptor liver X receptor (34), the intestinal expression of ABCA1 was dramatically reduced in ezetimibe-treated mice and L1KO mice (17,34,35) but not in diosgenin-treated mice (Fig. 3B); and 4) diosgenin treatment neither affected NPC1L1 expression in the intestine (Fig.…”