Intestinal caveolin-1 is important for dietary fatty acid absorption

Abstract

SUMMARY How dietary fatty acids are absorbed into the enterocyte and transported to the ER is not established. We tested the possibility that caveolin-1 containing lipid rafts and endocytic vesicles were involved. Apical brush border membranes took up 15% of albumin bound 3H-oleate whereas brush border membranes from caveolin-1 KO mice took up only 1%. In brush border membranes, the 3H-oleate was in the detergent resistant fraction of an OptiPrep gradient. On OptiPrep gradients of intestinal cytosol, we also found the 3H-oleate in the detergent resistant fraction, separate from OptiPrep gradients spiked with 3H-oleate or 3H-triacylglycerol. Caveolin-1 immuno-depletion of cytosol removed 91% of absorbed 3H-oleate whereas immuno-depletion using IgG, or anti-caveolin-2 or −3 or anti-clathrin antibodies removed 20%. Electron microscopy showed the presence of caveolin-1 containing vesicles in WT mouse cytosol that were 4 fold increased by feeding intestinal sacs 1 mM oleate. No vesicles were seen in caveolin-1 KO mouse cytosol. Caveolin-1 KO mice gained less weight on a 23% fat diet and had increased fat in their stool compared to WT mice. We conclude that dietary fatty acids are absorbed by caveolae in enterocyte brush border membranes, are endocytosed, and transported in cytosol in caveolin-1 containing endocytic vesicles.

Dietary and biliary phosphatidylcholine activates PKCζ in rat intestine

“…Similarly treated lyso-PC standards were used for cytosol did not affect the mechanism of FA absorption. Absorbed FA enters the cytosol on a CEV and appears in the detergent resistant membrane (DRM) fraction of an OptiPrep gradient ( 16 ). Despite the wide variation in the PC intake (0-9 µmol/h), the FA tracer, [ 3 H]oleate, remained in the DRM in cytosol, consistent with our prior observations ( Fig.…”

“…Despite the wide variation in the PC intake (0-9 µmol/h), the FA tracer, [ 3 H]oleate, remained in the DRM in cytosol, consistent with our prior observations ( Fig. 1A -E ( 16 ).…”

“…10 ). This theory would suggest that dietary FAs (MAG) enter the apical membrane of enterocytes via caveolae and are endocytosed as CEVs in proportion to the quantity of absorbed FAs ( 16 ). We propose that the CEVs are targeted to the ER where they unload their FA and MAG (not shown to be present in CEV) cargo.…”

“…TAG radioactivity was determined by liquid scintillation as described ( 16 ). Phospholipids were similarly measured.…”

“…Caveolin-1-containing endocytic vesicles (CEVs) were isolated as described previously ( 16 ). In brief, cytosol (1 mg protein) was treated with 1% Triton X-100.…”