FAT/CD36 is localized in sarcolemma and in vesicle-like structures in subsarcolemma regions but not in mitochondria

Abstract

This article is available online at http://www.jlr.org structures in subsarcolemma regions, but not in mitochondria. J. Lipid Res . 2010. 51: 1504-1512. Supplementary key words skeletal muscle • isolated mitochondria • immunocytochemistry • human • Zucker ratsRecent fi ndings in rodent and human skeletal muscle suggest that the plasma membrane protein fatty acid translocase CD36 (FAT/CD36) is located in the mitochondrial outer membrane ( 1-6 ). These fi ndings lead to the idea that FAT/CD36 could be important in regulating longchain fatty acid (LCFA) transport into mitochondria ( 7 ). Elucidating the possible role of mitochondrial FAT/CD36 content could be of great importance, because decreased mitochondrial membrane FAT/CD36 content could reduce mitochondrial LCFA uptake and oxidation, leading to accumulation of LCFA derivatives, which have been linked to the development of insulin resistance by inhibition of key regulatory signaling molecules in the insulin signaling cascade ( 8-10 ). Initially, it was suggested that FAT/CD36 interacted with carnitine palmitoyltransferase 1 (CPT 1), the mitochondrial enzyme that catalyzes the fi rst step in ␤ -oxidation of LCFA, in regulation of LCFA entry into mitochondria. This was based on the observation that the addition of sulfo-N-succinimidyl esters (SSO), a FAT/CD36 inhibitor ( 11, 12 ), reduced CPT 1 activity by ‫ف‬ 50% ( 1 ). However, other studies have shown a ‫ف‬ 90% Abstract The primary aim of the present study was to investigate in which cellular compartments fatty acid translocase CD36 ( FAT/CD36) is localized. Intact and fully functional skeletal muscle mitochondria were isolated from lean and obese female Zucker rats and from 10 healthy male individuals. FAT/CD36 could not be detected in the isolated mitochondria, whereas the mitochondrial marker F 1 ATPase-␤ was clearly detected using immunoblotting. Lack of markers for other membrane structures indicated that the mitochondria were not contaminated with membranes known to contain FAT/CD36. In addition, fl uorescence immunocytochemistry was performed on single muscle fi bers dissected from soleus muscle of lean and obese Zucker rats and from the vastus lateralis muscle from humans. Costaining against FAT/CD36 and MitoNEET clearly show that FAT/CD36 is highly present in sarcolemma and it also associates with some vesicle-like intracellular compartments. However, FAT/CD36 protein was not detected in mitochondrial membranes, supporting the biochemical fi ndings. Based on the presented data, FAT/CD36 seems to be abundantly expressed in sarcolemma and in vesicle-like structures throughout the muscle cell. However, FAT/CD36 is not present in mitochondria in rat or human skeletal muscle. Thus, the functional role of FAT/CD36 in lipid transport seems primarily to be allocated to the plasma membrane in skeletal muscle. -Jeppesen, J., M. Morgensen, C. Prats, K. Sahlin, K. Madsen, and B. Kiens. Abbreviations: CPT 1, carnitine palmitoyltransferase 1; CS, citrate synthase; FABPc, cytosolic fatty acid binding protein; FAT/C...

Metabolic Syndrome and Insulin Resistance: Underlying Causes and Modification by Exercise Training

“…Bezaire and colleagues put forth the notion that fatty acid transporters FAT/CD and FATP1 are involved in the transfer of FAs into the mitochondria possibly by direct binding to the mitochondrial membrane (66, 96). This work is recently disputed by Jeppesen et al (315). Regardless of whether these proteins bind directly to mitochondria, at least in the case of FATP, skeletal muscle-specific overexpression in mice promoted increased skeletal muscle fatty acid uptake and oxidation specifically, but did not predispose animals to diet-induced insulin resistance (274).…”

AMPKα2deficiency uncovers time dependency in the regulation of contraction-induced palmitate and glucose uptake in mouse muscle

“…Because we could not isolate mitochondrial membrane fractions on top of nuclear fractions from the small amount of hindlimb muscles that we had, we could not determine whether CD36 protein content was altered in mitochondrial membranes. Indeed, it has been suggested by some (18,19), but not others (23), that mitochondrial membrane CD36 content is an important factor in the regulation of FA oxidation. Because of the methodological limitations described above, we cannot contribute data to this debate.…”

CD36 actions in the heart: Lipids, calcium, inflammation, repair and more?

“…In addition increased mitochondrial CD36 content paralleled upregulation of FA oxidation [70-72]. Association of CD36 with mitochondria could not be observed in one study that used both biochemical fractionation and imaging and tested co-localization of CD36 with the mitochondrial protein MitoNeet [73]. This discrepancy might reflect the possibility that CD36 association with the mitochondria is dynamically regulated and could reflect a CD36 pool in mitochondria-associated membranes.…”