FAT/CD36 is located on the outer mitochondrial membrane, upstream of long-chain acyl-CoA synthetase, and regulates palmitate oxidation

Abstract

FAT/CD36 (fatty acid translocase/Cluster of Differentiation 36), a plasma membrane fatty-acid transport protein, has been found on mitochondrial membranes; however, it remains unclear where FAT/CD36 resides on this organelle or its functional role within mitochondria. In the present study, we demonstrate, using several different approaches, that in skeletal muscle FAT/CD36 resides on the OMM (outer mitochondrial membrane). To determine the functional role of mitochondrial FAT/CD36 in this tissue, we determined oxygen consumption rates in permeabilized muscle fibres in WT (wild-type) and FAT/CD36-KO (knockout) mice using a variety of substrates. Despite comparable muscle mitochondrial content, as assessed by unaltered mtDNA (mitochondrial DNA), citrate synthase, β-hydroxyacyl-CoA dehydrogenase, cytochrome c oxidase complex IV and respiratory capacities [maximal OXPHOS (oxidative phosphorylation) respiration] in WT and KO mice, palmitate-supported respiration was 34% lower in KO animals. In contrast, palmitoyl-CoA-supported respiration was unchanged. These results indicate that FAT/CD36 is key for palmitate-supported respiration. Therefore we propose a working model of mitochondrial fatty-acid transport, in which FAT/CD36 is positioned on the OMM, upstream of long-chain acyl-CoA synthetase, thereby contributing to the regulation of mitochondrial fatty-acid transport. We further support this model by providing evidence that FAT/CD36 is not located in mitochondrial contact sites, and therefore does not directly interact with carnitine palmitoyltransferase-I as original proposed.

High-Fat Diet–Induced Mitochondrial Biogenesis Is Regulated by Mitochondrial-Derived Reactive Oxygen Species Activation of CaMKII

“…Mitochondrial DNA (mtDNA) copy number was determined in the red gastrocnemius muscle using real-time PCR as previously reported (13). Maximal sacro(endo)plasmic reticulum Ca 2+ -ATPase (SERCA) activity and Ca 2+ uptake were determined in red tibialis anterior homogenates as previously reported (14).…”

“…Western blotting in red gastrocnemius muscles using commercially available antibodies was performed as previously reported (13,16,18). CaMKII was detected at ;55-60 kDa, representing the d/g isoform.…”

Ca2+ Binding/Permeation via Calcium Channel, CaV1.1, Regulates the Intracellular Distribution of the Fatty Acid Transport Protein, CD36, and Fatty Acid Metabolism

“…In skeletal muscle, CD36 has been shown to bind to the outer mitochondrial membrane (36). Continuous cycling of CD36 between cell surface and intracellular compartments has been reported (48).…”

“…Yoshida et al (12) showed that CD36 deficiency decreases ␤-oxidation in the absence of changes in mitochondrial number and enzyme content and proposed that CD36 is a key component in fuel selection both at rest and during exercise. Smith et al (36) found that CD36 deficiency decreased palmitate-supported mitochondrial respiration by 34%, but did not alter palmitoyl-CoA-supported respiration, demonstrating that CD36 functions upstream of acylCoA synthetase. Mice lacking CD36 have similarities to the EK mice, including reduced FA oxidation in muscle and increased respiratory exchange ratio (47).…”

Parkin reinvents itself to regulate fatty acid metabolism by tagging CD36

“…Identified first in Drosophila, where it was reported that Parkin-null flies cannot climb or fly and exhibit reduced body mass (19), it was later shown in various mammalian cell types that under stressful conditions, Parkin selectively translocates to damaged mitochondria to ubiquitinate mitochondrial proteins and induce mitophagy (8). It is worth noting that the Parkin substrate CD36 has been identified in isolated mitochondrial preparations, especially under states of high-energy demand such as exercise, where it would facilitate FA access to metabolizing enzymes (20).…”