title: Effect of age on the processing and import of matrix-destined mitochondrial proteins in skeletal muscle.
abstract: Deregulation of muscle mitochondrial biogenesis may explain the altered mitochondrial properties associated with aging. Maintenance of the mitochondrial network requires the continuous incorporation of nascent proteins into their subcompartments via the protein import pathway. We examined whether this pathway was impaired in muscle of aged animals, focusing on the subsarcolemmal and intermyofibrillar mitochondrial populations. Our results indicate that the import of proteins into the mitochondrial matrix was unaltered with age. Interestingly, import assays supplemented with the cytosolic fraction illustrated an attenuation of protein import, and this effect was similar between age groups. We observed a 2.5-fold increase in protein degradation in the presence of the cytosolic fraction obtained from aged animals. Thus, the reduction of mitochondrial content and/or function observed with aging may not rely on altered activity of the import pathway but rather on the availability of preproteins that are susceptible to elevated rates of degradation by cytosolic factors.
authors.affiliation: School of Kinesiology & Health Science, York University, 4700 Keele Street, Toronto, Ontario, Canada.
authors.forename: Julianna H
authors.initials: JH
authors.lastname: Huang
authors.forename: Anna-Maria
authors.initials: AM
authors.lastname: Joseph
authors.forename: Vladimir
authors.initials: V
authors.lastname: Ljubicic
authors.forename: Sobia
authors.initials: S
authors.lastname: Iqbal
authors.forename: David A
authors.initials: DA
authors.lastname: Hood
mesh_terms: D000375:Aging / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D001835:Body Weight; D003600:Cytosol / Q000737:chemistry; D008297:Male; D008931:Mitochondria, Muscle / Q000648:ultrastructure; D024101:Mitochondrial Proteins / Q000378:metabolism*; D018832:Molecular Chaperones / Q000032:analysis; D018482:Muscle, Skeletal / Q000378:metabolism*; D009954:Ornithine Carbamoyltransferase / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley
chemical_list: D024101:Mitochondrial Proteins; D018832:Molecular Chaperones; D011498:Protein Precursors; D009954:Ornithine Carbamoyltransferase