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

Abstract

Because insulin has been shown to stimulate long-chain fatty acid (LCFA) esterification in skeletal muscle and cardiac myocytes, we investigated whether insulin increased the rate of LCFA transport by altering the expression and the subcellular distribution of the fatty acid transporters FAT/CD36 and FABPpm. In cardiac myocytes, insulin very rapidly increased the expression of FAT/CD36 protein in a time-and dose-dependent manner. During a 2-h period, insulin (10 nM) increased cardiac myocyte FAT/CD36 protein by 25% after 60 min and attained a maximum after 90 -120 min (ϩ40 -50%). There was a dose-dependent relationship between insulin (10 Ϫ12 to 10 Ϫ7 M) and FAT/CD36 expression. The half-maximal increase in FAT/CD36 protein occurred at 0.5 ϫ 10 Ϫ9 M insulin, and the maximal increase occurred at 10 Ϫ9 to 10 Ϫ8 M insulin (ϩ40 -50%). There were similar insulin-induced increments in FAT/CD36 protein in cardiac myocytes (ϩ43%) and in Langendorff-perfused hearts (ϩ32%). In contrast to FAT/CD36, insulin did not alter the expression of FABPpm protein in either cardiac myocytes or the perfused heart. By use of specific inhibitors of insulin-signaling pathways, it was shown that insulin-induced expression of FAT/CD36 occurred via the PI 3-kinase/Akt insulin-signaling pathway. Subcellular fractionation of cardiac myocytes revealed that insulin not only increased the expression of FAT/CD36, but this hormone also targeted some of the FAT/CD36 to the plasma membrane while concomitantly lowering the intracellular depot of FAT/ CD36. At the functional level, the insulin-induced increase in FAT/ CD36 protein resulted in an increased rate of palmitate transport into giant vesicles (ϩ34%), which paralleled the increase in plasmalemmal FAT/CD36 (ϩ29%). The present studies have shown that insulin regulates protein expression of FAT/CD36, but not FABPpm, via the PI 3-kinase/Akt insulin-signaling pathway. fatty acid translocase; plasma membrane-associated fatty acid-binding protein; cardiac myocytes; transport; plasma membrane; low-density microsomes; perfusion; heart LONG-CHAIN FATTY ACIDS (LCFAs) are taken up into cells by passive diffusion and by protein-mediated mechanisms involving a number of fatty acid-binding proteins (12,25). Overexpression of fatty acid transporters, including fatty acid translocase (FAT/CD36) and plasma membrane-associated fatty acid-binding protein (FABPpm), increase LCFA uptake (13,14). 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. In more detailed studies, FAT/CD36 mRNA and protein expression and plasma...

CD36: Implications in cardiovascular disease

“…Thiazolidinediones, a major new class of drugs to treat diabetes, up regulate CD36 in monocytes/macrophages, adipose and muscle (Wilmsen, Ciaraldi, Carter, Reehman, Mudaliar, & Henry, 2003, Kolak, et al, 2006, Hirakata, Tozawa, Imura, & Sugiyama, 2004,Llaverias, et al, 2006, and may therefore contribute to the insulin-sensitizing effects of these drugs as a result of plasma fatty acid clearance, but also potentially to atherosclerosis and obesity in these patients. Interestingly, glucose/insulin appears to increase CD36 expression (Sampson, Davies, Braschi, Ivory, & Hughes, 2003,Griffin, et al, 2001,Chabowski, et al, 2004,Chen, Yang, Loux, Georgeson, & Harmon, 2006, and because CD36 is expressed on tissues important in fatty acid metabolism (heart, skeletal muscle, fat, and in pathological states, liver) this may imply an important role for CD36 in insulin resistance (see later). Regulation of CD36 expression can be mediated both pre-and post-transcription.…”

“…In skeletal muscle, CD36 is important for fatty acid uptake, and its expression is regulated by both the environmental and cellular milieu (Chabowski, Gorski, Calles-Escandon, Tandon, & Bonen, 2006,Chabowski, et al, 2004,Chabowski, et al, 2005,Benton, Han, Febbraio, Graham, & Bonen, 2006,Cameron-Smith, et al, 2003. Studies in isolated cardiac muscle cells, using a specific CD36 inhibitor, sulfo-N-succinimidyl oleate, also showed that CD36 is likely the major membrane protein involved in fatty acid uptake (Koonen, et al, 2005).…”

The fatty acid transporter FAT/CD36 is upregulated in subcutaneous and visceral adipose tissues in human obesity and type 2 diabetes

“…9 In addition, we have recently shown that insulin rapidly induces the expression of FAT/CD36 in cardiac myocytes and in the heart. 26 In humans, FAT/CD36 mRNA is increased in muscle during a hyperinsulinemic-euglycemic clamp, 27 and FAT/CD36 mRNA and insulin are correlated. 25 Thus, a circumstantial case can be made implicating increased concentrations of insulin in upregulating the expression of adipose tissue FAT/CD36.…”

Effects of leptin on the expression of fatty acid-binding proteins in human placental cell cultures

“…Altered FAT/CD36 expression is genetically linked with situations where insulin resistance and abnormal lipid metabolism occur in rats and humans (11,12). In humans, FAT/ CD36 is considered to be a significant factor in metabolic adaptation in diet and in susceptibility to certain abnormal situations related to diet (4,13,14).…”

“…For example, in situations where lipid uptake is increased, such as in pre-adipocyte to adipocyte differentiation, during perinatal and postnatal heart development, in the skeletal muscle of diabetic experimental animals and in the heart of animals under fat-rich diet (7). Insulin and leptin regulate the expression of proteins associated with fatty acid binding and transportation (namely FAT, FABPpm, FATP and cytosolic FABPs) in various tissues through PPAR (peroxisome proliferator-activated receptors) (11,12,15).…”