Insulin induces the translocation of the fatty acid transporter FAT/CD36 to the plasma membrane

Abstract

-It is well known that muscle contraction and insulin can independently translocate GLUT-4 from an intracellular depot to the plasma membrane. Recently, we have shown that the fatty acid transporter FAT/CD36 is translocated from an intracellular depot to the plasma membrane by muscle contraction (Ͻ30 min) (Bonen et al. J Biol Chem 275: 14501-14508, 2000). In the present study, we examined whether insulin also induced the translocation of FAT/CD36 in rat skeletal muscle. In studies in perfused rat hindlimb muscles, we observed that insulin increased fatty acid uptake by ϩ51%. Insulin increased the rate of palmitate incorporation into triacylglycerols, diacylglycerols, and phospholipids (P Ͻ 0.05) while reducing muscle palmitate oxidation (P Ͻ 0.05). Perfusing rat hindlimb muscles with insulin increased plasma membrane FAT/CD36 by ϩ48% (P Ͻ 0.05), whereas concomitantly the intracellular FAT/CD36 depot was reduced by 68% (P Ͻ 0.05). These insulin-induced effects on FAT/CD36 translocation were inhibited by the phosphatidylinositol 3-kinase inhibitor LY-294002. Thus these studies have shown for the first time that insulin can induce the translocation of FAT/CD36 from an intracellular depot to the plasma membrane.This reveals a previously unknown level of regulation of fatty acid transport by insulin and may well have important consequences in furthering our understanding of the relation between fatty acid metabolism and insulin resistance.

Insulin stimulates fatty acid transport by regulating expression of FAT/CD36 but not FABPpm

“…For these purposes we 1) subfractionated cardiac myocytes to examine the effects of insulin on the subcellular distribution of FAT/CD36, 2) determined the plasmalemmal content of FAT/CD36 in giant vesicles, into which 3) we had examined the rates of palmitate transport. In agreement with our previous work (18,19), insulin induced the translocation of FAT/CD36 from an intracellular depot to the plasma membrane within 30 min, before any changes in FAT/CD36 expression had occurred (data not shown). With more prolonged exposure to insulin (2 h) there were two effects: 1) FAT/CD36 expression was increased, and 2) the plasmalemmal FAT/CD36 was also further increased whereas the intracellular depot was decreased.…”

“…Giant sarcolemmal vesicles were prepared as we have previously reported (18,20). Briefly, perfused ventricles were scored into strips with a scalpel and incubated for 1 h at 34°C in KCl-MOPS supplemented with 0.142 mg/ml PMSF, 10 mg/ml aprotinin, and 150 U/ml type II collagenase.…”

“…LCFA transport was performed as we have previously reported (18,20 1%BSA-KCl-MOPS) was added and the sample immediately centrifuged (12,000 g, 2 min). The supernatant fraction was aspirated, and the bottom of the tube containing the pellet was cut off and placed in a scintillation vial.…”

“…In recent years, it has been shown that rates of LCFA transport can be regulated acutely and chronically. In heart and skeletal muscle exposed briefly to insulin (15 min) and in contracting muscle (Ͻ30 min), rates of LCFA transport are increased due to the translocation of FAT/CD36 from an intracellular depot to the plasma membrane (4,18,19). Expression of FAT/CD36 mRNA is upregulated by LCFAs in neonatal cardiac myocytes (30), although the functional metabolic consequences of these changes on LCFA transport and metabolism have not been determined.…”

Intramyocellular lipid accumulation is associated with permanent relocation ex vivo and in vitro of fatty acid translocase (FAT)/CD36 in obese patients

“…Permanent sarcolemmal FAT/CD36 relocation is dependent on obesity or type 2 diabetes Translocation of FAT/CD36 from intracellular depots to the sarcolemmal membrane of the muscle fibre is an important regulator of fatty acid transport and utilisation in muscle [31,32]. We monitored total FAT/CD36 levels by western blot on muscle tissue extracts from the four groups of donors (Fig.…”