Abstract
Chylomicron metabolism is critical for determining plasma levels of triacylglycerols (TAGs) and cholesterol, both of which are risk factors for CVD. The rates of chylomicron secretion and remnant clearance are controlled by intracellular and extracellular factors, including apoC-III. We have previously shown that human apoC-III overexpression in mice (apoC-IIITg mice) decreases the rate of chylomicron secretion into lymph, as well as the TAG composition in chylomicrons. We now find that this decrease in chylomicron secretion is not due to the intracellular effects of apoC-III, but instead that primary murine enteroids are capable of taking up TAG from TAG-rich lipoproteins (TRLs) on their basolateral surface; and via Seahorse analyses, we find that mitochondrial respiration is induced by basolateral TRLs. Furthermore, TAG uptake into the enterocyte is inhibited when excess apoC-III is present on TRLs. In vivo, we find that dietary TAG is diverted from the cytosolic lipid droplets and driven toward mitochondrial FA oxidation when plasma apoC-III is high (or when basolateral substrates are absent). We propose that this pathway of basolateral lipid substrate transport (BLST) plays a physiologically relevant role in the maintenance of dietary lipid absorption and chylomicron secretion. Further, when apoC-III is in excess, it inhibits BLST and chylomicron secretion.
Highlights
Chylomicron metabolism is critical for determining plasma levels of triacylglycerols (TAGs) and cholesterol, both of which are risk factors for CVD
We show that enterocytes take up triacylglycerol-rich lipoprotein (TRL) on their basolateral surface, and that excess apoC-III on TRLs inhibits this uptake in a dose-dependent manner
We show that delivery of TRLs to the basolateral face of enterocytes stimulates enterocyte mitochondrial respiration, which suggests that TRLs may be a source of lipid substrates for enterocyte FA oxidation (FAO)
Summary
Chylomicron metabolism is critical for determining plasma levels of triacylglycerols (TAGs) and cholesterol, both of which are risk factors for CVD. We find that dietary TAG is diverted from the cytosolic lipid droplets and driven toward mitochondrial FA oxidation when plasma apoC-III is high (or when basolateral substrates are absent) We propose that this pathway of basolateral lipid substrate transport (BLST) plays a physiologically relevant role in the maintenance of dietary lipid absorption and chylomicron secretion. Intestinal basolateral lipid substrate transport is linked to chylomicron secretion and is regulated by apoC-III. The regulation of chylomicron synthesis and secretion (including the transport of FFAs across the apical membrane, the enzymatic TAG reesterification pathway, and the construction and maturation of apoB-48-containing chylomicrons in the ER and Golgi) is driven by the presence of dietary fat in the small intestinal lumen. CLD metabolism is driven by proteins located on the organelle’s membrane, including perilipins (PLINs) (PLIN2 and PLIN3), TAG lipases (ATGL and HSL), and structural proteins (CIDEB) [6, 7]
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