Fatty acids increase glucose uptake and metabolism in C₂C₁₂myoblasts stably transfected with human lipoprotein lipase

Abstract

Capell WH, Schlaepfer IR, Wolfe P, Watson PA, Bessesen DH, Pagliassotti MJ, Eckel RH. Fatty acids increase glucose uptake and metabolism in C2C12 myoblasts stably transfected with human lipoprotein lipase. Am J Physiol Endocrinol Metab 299: E576 -E583, 2010. First published July 13, 2010; doi:10.1152/ajpendo.00618.2009.-Cellular effects of FFA might differ from those of lipoprotein triglyceride (TG)-derived fatty acids (TGFA). The aim of the current study was to examine the relationship between lipoprotein lipase (LPL) expression, TGFA, or FFA availability and glucose metabolism in the absence of insulin in C 2C12 myoblasts. Control myoblasts or myoblasts stably transfected with human lipoprotein lipase (C2/LPL; 15-fold greater LPL activity) were incubated for 12 h in fetal bovine serum-free medium in the absence or presence of Intralipid-20. Intracellular retention of labeled medium glucose was assessed in a subset of experiments. In the presence of Intralipid, medium glucose disappearance was increased in C2/LPL cells but not in control cells. In both cell types, glucose label retention in cellular TG was increased in the presence of Intralipid; incubation with albumin-bound oleate produced similar results. In the presence of Intralipid, the LPL hydrolytic inhibitor tetrahydrolipstatin blocked excess glucose retention in cellular TG but did not significantly decrease glucose disappearance in C2/LPL cells. Changes in glucose transport or hexokinase II did not explain the altered glucose disappearance in C2/LPL cells. Our results suggest that LPL overexpression in these cells leads to chronic metabolic adaptations that alter glucose uptake and retention. in vitro; intracellular lipid; Akt; AMP-activated protein kinase; glucose transporter FATTY ACIDS AND GLUCOSE CAN COMPETE as oxidative fuels within muscle [for review, see Randle (37)]. Additionally, increased triglyceride (TG) content has been associated with insulin resistance in various insulin-sensitive tissues (21,24,29,31,41,43), and accumulation of lipid species within cells might directly affect cell insulin signaling (42). Therefore, examining cellular interactions between lipid and glucose may be valuable in understanding cell metabolism and the pathogenesis of insulin resistance.Studies of the cellular effects of lipids typically focus on free fatty acids (FFA) and have only rarely examined lipoprotein TG-derived fatty acids (TGFA). Circulating within lipoproteins, TGFA have the potential for unique cellular interactions that are distinct from FFA. Specifically, TGFA enter skeletal muscle cells and adipocytes following hydrolytic release, requiring the hydrolytic enzyme lipoprotein lipase (LPL) (14). Additionally, the binding of lipoproteins to LPL at the endothelial surface allows lipoproteins to interact with cell receptors and promotes whole particle uptake (6,13,28,38). Most studies to date utilizing TG emulsions have coinfused heparin, which releases LPL from its endothelial-bound position and disrupts these potential bridging functions. Because ...