Human skeletal muscle fibre type variations correlate with PPARα, PPARδ and PGC-1α mRNA

Aims: Studies from genetically modified animals have been instrumental in highlighting genes and their products involved in the regulation of muscle fibre type and oxidative phenotypes; however, evidence in humans is limited. Our aim was therefore to investigate expression of those genes implicated in the regulation of oxidative fibre phenotypes in humans. Methods: Using quantitative polymerase chain reaction we determined mRNA expression of selected genes in skeletal muscle from three different groups, displaying physiological and pathological variations in muscle fibre type, activity and skeletal muscle metabolism respectively: (i) elite athletes (cyclists), with an increased proportion of type I slow twitch, oxidative fibres, (ii) normally active subjects with an average fibre type distribution, and (iii) spinal cord-injured subjects with a low proportion of type I fibres. Results: Skeletal muscle mRNA expression of calcineurin A alpha and A beta, peroxisome proliferator-activated receptor (PPAR)-alpha and -delta, and PPAR gamma coactivator (PGC)-1 alpha and -1 beta was determined. Calcineurin A alpha and calcineurin A beta mRNA expression was similar between groups. In contrast, mRNA expression of PPAR alpha, PPAR delta, PGC-1 alpha and -1 beta was increased in athletes, when compared with normally active subjects. Furthermore, mRNA expression of PPAR alpha, PPAR delta, PGC-1 alpha and -1 beta was reduced in spinal cord-injured subjects. Additionally, PPAR alpha, PPAR delta and PGC-1 alpha correlated with oxidative fibre content. Conclusion: Skeletal muscle mRNA expression of PPAR alpha, PPAR delta, PGC-1 alpha and -1 beta reflects differences in type I muscle fibres associated with pathologically and physiologically induced skeletal muscle fibre type differences.