Differential carnitine/acylcarnitine translocase expression defines distinct metabolic signatures in skeletal muscle cells

Abstract Import of acylcarnitine into mitochondrial matrix through carnitine/acylcarnitine‐translocase (CACT) is fundamental for lipid catabolism. To probe the effect of CACT down‐expression on lipid metabolism in muscle, human myocytes were stably transfected with CACT‐antisense construct. In presence of low concentration of palmitate, transfected cells showed decreased palmitate oxidation and acetyl‐carnitine content, increased palmitoyl‐carnitine level, and reduced insulin‐dependent decrease of fatty acylcarnitine‐to‐fatty acyl‐CoA ratio. The augmented palmitoyl‐carnitine synthesis, also in the presence of insulin, could be related to an altered regulation of carnitine‐palmitoyl‐transferase 1 (CPT 1) by malonyl‐CoA, whose synthesis is dependent by the availability of cytosolic acetyl‐groups. Indeed, all the described effects were completely overcome by CACT neo‐expression by recombinant adenovirus vector or by addition of acetyl‐carnitine to cultures. Acetyl‐carnitine effect was related to an increase of malonyl‐CoA and was abolished by down‐expression, via antisense RNA strategy, of acetyl‐CoA carboxylase‐β, the mitochondrial membrane enzyme involved in the direct CPT 1 inhibition via malonyl‐CoA synthesis. Thus, in our experimental model the modulation of CACT expression has consequences for CPT 1 activity, while the biologic effects of acetyl‐carnitine are not associated with a generic supply of energy compounds but to the anaplerotic property of the molecule. © 2004 Wiley‐Liss, Inc.