Molecular correlates for maximal oxygen uptake and type 1 fibers

Maximal oxygen uptake (V̇O_2max) and the amount of type 1 fibers are interrelated, but the underlying unifying molecular mechanisms are poorly understood. To explore these mechanisms, we related gene expression profiles in skeletal muscle biopsies of 43 age-matched men from published datasets with V̇O_2max and the amount of type 1 fibers and replicated some of the findings in muscle biopsies from 154 young and elderly individuals using real-time PCR. We identified 66 probe sets (genes or expressed sequence tags) positively and 83 probe sets inversely correlated with V̇O_2maxand 171 probe sets positively and 217 probe sets inversely correlated with percentage of type 1 fibers in human skeletal muscle. Genes involved in oxidative phosphorylation (OXPHOS) showed high expression in individuals with high V̇O_2max, whereas the opposite was not the case in individuals with low V̇O_2max. Instead, genes such as AHNAK and BCL6 were associated with low V̇O_2max. Also, expression of the OXPHOS genes NDUFB5 and ATP5C1 increased with exercise training and decreased with aging. In contrast, expression of AHNAK in skeletal muscle decreased with exercise training and increased with aging. Eleven genes (NDUFB4, COX5A, UQCRB, ATP5C1, ATP5G3, ETHE1, FABP3, ISCA1, MYST4, C9orf3, and PKIA) were positively correlated with both V̇O_2max and the percentage of type 1 fibers. V̇O_2max closely reflects expression of OXPHOS genes, particularly that of NDUFB5 and ATP5C1, in skeletal muscle, suggesting good muscle fitness. In contrast, a high expression of AHNAK was associated with a low V̇O_2max and poor muscle fitness.