mRNA stability as a function of striated muscle oxidative capacity

A change in mRNA stability alters the abundance of mRNA available for translation and is emerging as a critical pathway influencing gene expression. Variations in the stability of functional and regulatory mitochondrial proteins may contribute to the divergent mitochondrial densities observed in striated muscle. Thus we hypothesized that the stability of mRNAs encoding for regulatory nuclear and mitochondrial transcription factors would be inversely proportional to muscle oxidative capacity and would be facilitated by the activity of RNA binding proteins (RBPs). The stability of mitochondrial transcription factor A (Tfam), peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), and nuclear respiratory factor 2α (NRF-2α) mRNA was assessed in striated muscles with distinct oxidative capacities using in vitro decay assays. All three mitochondrial regulators were rapidly degraded in cardiac and slow-twitch red (STR) muscle, resulting in a ∼60-65% lower (P < 0.05) mRNA half-life (t(1/2)) compared with fast-twitch white (FTW) fibers. This accelerated rate of Tfam mRNA decay was matched by a 2.5-fold increase in Tfam transcription in slow- compared with fast-twitch muscle (P = 0.05). Protein expression of four unique RBPs [AU-rich binding factor 1 (AUF1), human antigen R (HuR), KH-homology splicing regulatory protein (KSRP), and CUG binding protein 1 (CUGBP1)] believed to modulate mRNA stability was elevated in cardiac and STR muscles (P < 0.05) and was moderately associated with the decay of Tfam, PGC-1α, and NRF-2α mRNA. Variable rates of transcript degradation were apparent when comparing all transcripts within the same muscle type. Thus the distribution of RBPs appears to follow a fiber-type specific pattern and subsequently functions to alter the stability of specific mitochondrial regulators in a transcript- and tissue-specific fashion.