Mitochondrial protein import in muscle of p53 wildtype (WT) and knockout (KO) mice

Mitochondrial biogenesis requires the coordinated interplay of the nuclear and mitochondrial genomes. Nuclear‐encoded mitochondrial proteins are imported into the organelle by the protein import machinery (PIM). Thus, we sought to elucidate whether the reduced mitochondrial content in p53 deficient animals could be attributed to defects in the import pathway. Subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria were isolated from muscle of p53 WT and KO mice. The PIM proteins Tom20 and Tim23 were decreased by 28% and 36% (p<0.05) respectively in SS mitochondria of KO mice. The mitochondrial heat shock protein70 (mtHSP70), crucial for import of proteins into the mitochondria, was reduced by ~51% in SS mitochondria from KO mice, compared to WT counterparts. In contrast, other mitochondrial chaperones such as mtHSP60 and cpn10 were not different between the two genotypes. To evaluate protein import, isolated SS and IMF mitochondria from p53 WT and KO mice were incubated with radiolabelled, matrix‐destined precursor protein. No changes were observed in the rate of protein import between the two genotypes. These data suggest that absence of p53 results in lower levels of important PIM components, however this was not reflected by a functional deficit as measured by matrix protein import. Whether import into other compartments, such as the outer or inner membranes, is defective, remains to be determined.