Long-chain acyl-CoA profiles in cultured fibroblasts from patients with defects in fatty acid oxidation

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

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-beta, 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.

Involvement of fatty acid synthase in axonal development in mouse embryos

BACKGROUND

Dynamic protein palmitoylation of signalling proteins is thought to be an important step in the regulation of signal transduction in eukaryotic cells. The enzyme responsible for protein palmitoylation in vertebrates, however, has not been identified. I have previously reported that p260/270, which is expressed in embryos of the silkworm Bombyx mori, has protein palmitoylase activity.

RESULTS

A homologue of Bombyx p260/270, mouse fatty-acid synthase (FAS), was shown to be expressed specifically throughout most of the central and peripheral nervous system in mouse embryos. Mouse FAS was expressed specifically in cultured primary neurones in which growth-associated protein (GAP)-43 was expressed. GAP-43, by protein palmitoylation, regulates Go signal transduction and neural axonal growth. In a cell-free system, purified FAS from mouse embryos transferred palmitate to GAP-43 through cysteine residues. Furthermore, cerulenin, an inhibitor of FAS, reduced axonal growth and in vivo palmitoylation of GAP-43 in cultured neurones.

CONCLUSIONS

Mouse FAS was hypothesized to be responsible for the palmitoylation of GAP-43 and subsequent regulation of axonal growth in mouse embryos.