Intertissue regulation of carnitine palmitoyltransferase I (CPTI): Mitochondrial membrane properties and gene expression in rainbow trout (Oncorhynchus mykiss)

Abstract

Carnitine palmitoyltransferase (CPT) I is regulated by several genetic and non-genetic factors including allosteric inhibition, mitochondrial membrane composition and/or fluidity and transcriptional regulation of enzyme content. To determine the intrinsic differences in these regulating factors that may result in differences between tissues in fatty acid oxidation ability, mitochondria were isolated from red, white and heart muscles and liver tissue from rainbow trout. Maximal activity (V(max)) for beta-oxidation enzymes and citrate synthase per mg tissue protein as well as CPT I in isolated mitochondria followed a pattern across tissues of red muscle>heart>white muscle>liver suggesting both quantitative and qualitative differences in mitochondria. CPT I inhibition showed a similar pattern with the highest malonyl-CoA concentration to inhibit activity by 50% (IC(50)) found in red muscle while liver had the lowest. Tissue malonyl-CoA content was highest in white muscle with no differences between the other tissues. Interestingly, the gene expression profiles did not follow the same pattern as the tissue enzyme activity. CPT I mRNA expression was greatest in heart>red muscle>white muscle>liver. In contrast, PPARalpha mRNA was greatest in the liver>red muscle>heart>white muscle. There were no significant differences in the mRNA expression of PPARbeta between tissues. As well, no significant differences were found in the mitochondrial membrane composition between tissues, however, there was a tendency for red muscle to exhibit higher proportions of PUFAs as well as a decreased PC:PE ratio, both of which would indicate increased membrane fluidity. In fact, there were significant correlations between IC(50) of CPT I for malonyl-CoA and indicators of membrane fluidity across tissues. This supports the notion that sensitivity of CPT I to its allosteric regulator could be modulated by changes in mitochondrial membrane composition and/or fluidity.

Molecular characterization of a gilthead sea bream (Sparus aurata) muscle tissue cDNA for carnitine palmitoyltransferase 1B (CPT1B)

“…These results are very similar to those reported for the mRNA expression of a trout CPT1 (Morash et al, 2008). Therefore, we conclude that the identified cDNA encodes for a muscle-specific isoform of CPT1 and is therefore orthologous to the mammalian CPT1B.…”

“…In an early study of a trout CPT1 cDNA it was suggested that a single CPT1 gene is present in trout, due to the ubiquitous presence of its transcripts in the tissues of the fish (Gutières et al, 2003). However, more recent evidence, including the catalytic examination of CPT1 activity in trout tissues, has indicated the presence of multiple CPT1 proteins (Morash et al, 2008). The sequence data available now supports the presence of multiple CPT1 genes in trout and several other studies have reported the measurement of various trout CPT1 mRNAs (Kolditz et al, 2008;Lansard et al, 2009;Morash et al, 2009;Plagnes-Juan et al, 2008;Polakof et al, 2010).…”

“…the species in which a CPT1 encoding sequence was first identified (Gutières et al, 2003). Although it was originally proposed that trout expressed a single CPT1 gene corresponding to the mammalian liver isoform (Gutières et al, 2003), further studies of CPT1 sensitivity for malonyl-CoA, coupled to determination of relative mRNA expression levels, in the tissues of thefish suggested the presence of additional isoform(s) (Morash et al,2008). Indeed, another three CPT1-like sequences have recently been identified in trout, and their expression has subsequently been studied in response to nutritional and hormonal stimuli, and in relation to the expression of other genes encoding enzymes involved in fatty acid metabolism, including two trout PPAR isotypes (Kolditz et al, 2008;Lansard et al, 2009;Morash et al, 2009;Plagnes-Juan et al, 2008;Polakof et al, 2010).…”

Regulation of Carnitine Palmitoyltransferase (CPT) I during Fasting in Rainbow Trout (Oncorhynchus mykiss) Promotes Increased Mitochondrial Fatty Acid Oxidation

“…Previously, there was thought to be only one CPT I gene in fish (Gutieres et al 2003). However, our recent research has demonstrated that CPT I in liver and muscle are differentially sensitive to malonyl-CoA, though unlike in CPT I in mammals, CPT I in trout liver is more sensitive to malonyl-CoA than CPT I in trout muscle is (Morash et al 2008). Recently we have shown that these taxa-specific differences may be the result of genome duplications in bony fishes giving rise to five distinct CPT I isoforms in trout with tissuespecific expression patterns (Morash et al 2010).…”

“…Regulation of mitochondrial fat oxidation involves both genetic and nongenetic regulation of CPT I activity (McClelland 2004;Morash et al 2008). CPT I isoforms are encoded by two different genes, CPT Ia and CPT Ib, expressed in the liver and muscle, respectively (Britton et al 1997).…”