CD36 Is Important for Fatty Acid and Cholesterol Uptake by the Proximal but Not Distal Intestine

Abstract

CD36, a membrane protein that facilitates fatty acid uptake, is highly expressed in the intestine on the luminal surface of enterocytes. Cd36 null (Cd36 ؊/؊ ) mice exhibit impaired chylomicron secretion but no overall lipid absorption defect. Because chylomicron production is most efficient proximally we examined whether CD36 function is important for proximal lipid absorption. CD36 levels followed a steep decreasing gradient along three equal-length, proximal to distal intestinal segments (S1-S3). Enterocytes isolated from the small intestines of Cd36 ؊/؊ mice, when compared with wild type counterparts, exhibited reduced uptake of fatty acid (50%) and cholesterol (60%) in S1. The high affinity fatty acid uptake component was missing in Cd36 ؊/؊ cells. Fatty acid incorporation into triglyceride and triglyceride secretion were also reduced in Cd36 ؊/؊ S1 enterocytes. In vivo, proximal absorption was monitored using mass spectrometry from oleic acid enrichment of S1 lipids, 90 min (active absorption) and 5 h (steady state) after intragastric olive oil (70% triolein). Oleate enrichment was 50% reduced at 90 min in Cd36 ؊/؊ tissue consistent with defective uptake whereas no differences were measured at 5 h. In Cd36 ؊/؊ S1, mRNA for L-fabp, Dgat1, and apoA-IV was reduced. Protein levels for FATP4, SR-BI, and NPC1L1 were similar, whereas those for apoB48 and apoA-IV were significantly lower. A large increase in NPC1L1 was observed in Cd36 ؊/؊ S2 and S3. The findings support the role of CD36 in proximal absorption of dietary fatty acid and cholesterol for optimal chylomicron formation, whereas CD36-independent mechanisms predominate in distal segments. CD36 or fatty acid translocase (FAT)3 is an 88-kDa transmembrane protein with broad specificity. Its ligands include long-chain fatty acids, native and oxidized lipoproteins, thrombospondin-1, collagen, amyloid ␤, and malaria-infected erythrocytes, recently reviewed in Ref. 1. CD36 has been shown to bind long-chain fatty acids (2, 3) and to facilitate their transfer into the cell (4, 5). Deficiency or overexpression of the protein is associated with alterations in uptake and metabolism of longchain fatty acids in rodents (4, 6, 7). In humans, Cd36 deficiency (8) and polymorphisms in the Cd36 gene (9) are associated with abnormalities in FA clearance (10, 11), insulin responsiveness (11, 12), and lipoprotein metabolism (13, 14). As a result CD36 has been implicated in the etiology of diabetes and atherosclerosis (14, 15).Consistent with its role in FA uptake CD36 is very abundant in the heart, skeletal muscle, adipose tissue (16), and the capillary endothelium (17). The protein is also highly expressed in the small intestine (16,18,19) and localizes to the apical membrane of villi enterocytes (19). Expression levels and localization strongly suggest a function in lipid absorption but this could not be documented in previous studies by us and others (20 -22). Administration of a lipid load to Cd36-deficient mice did not identify alterations in the blood appearance of intes...

CD36 Mediates Both Cellular Uptake of Very Long Chain Fatty Acids and Their Intestinal Absorption in Mice

“…We utilized this technique to further show that the net absorption of long chain FAs in mice maintained on a high-fat diet is also normal. These data appear to contrast our recent finding that the intestinal absorption of 18:1 is delayed (but not reduced) in CD36-deficient mice following an acute, intragastric bolus of triacylglycerols enriched in triolein (21). The shorter time period (90 min) used in this triolein study versus 24 h for the fecal dual isotope recovery used in the present work is the primary difference likely leading to the disparate results.…”

“…We and others (8,21,27) have previously reported that the net absorption of long chain FAs is normal in CD36-deficient mice. Here, we confirm these data using the fecal dual isotope recovery method that is more precise than the indirect methods used previously.…”

“…Niemann-Pick C1 Like 1 (NPC1L1) is a protein required for the efficient absorption of dietary cholesterol in the intestine (19) and may act in a complex with other proteins such as SR-BI (20). In addition, NPC1L1 protein levels are dramatically elevated in the intestine of CD36-deficient mice (21). To determine if NPC1L1 may also be required for CD36-mediated VLCFA absorption, WT mice were treated with an oral dose of ezetimibe (10 mg/kg body weight), a specific inhibitor of NPC1L1-mediated cholesterol absorption (22), and E 24:0 measured as described above.…”

Small Intestine but Not Liver Lysophosphatidylcholine Acyltransferase 3 (Lpcat3) Deficiency Has a Dominant Effect on Plasma Lipid Metabolism

“…The former mediates cholesterol uptake, and the latter mediates excretion of excessive cholesterol into the intestinal lumen (22,23). CD36 also participates in cholesterol uptake at the brush border of enterocytes (24,25). Three proteins, namely CD36 (25), plasma membrane-associated fatty acidbinding protein (26), and FATP4 (27), are involved in free fatty acid uptake by enterocytes.…”

Targeted enhancement of oleoylethanolamide production in proximal small intestine induces across-meal satiety in rats

“…Both exogenous OEA administration (18) and endogenous OEA overproduction (present results) stimulate expression of the PPAR-␣-regulated protein CD36. This multifunctional cell-membrane glycoprotein is highly expressed in the small intestine and has been implicated in the transport of fatty acids across the enterocyte membrane (7,12), confirming the suggestion that OEA signaling at PPAR-␣ regulates lipid absorption along with food intake (25). A final consideration is the time course of the anorexic effects of OEA overproduction.…”