(879.1) Dysregulated Mitochondrial Respiration Occurs With Aging

Poster Board Number: E260

Roberto Leija (University of California), Ashley Tovar (University of California), Casey Curl (University of California), Adam Osmond (University of California), Jose Arevalo (University of California), Justin Duong (University of California), George Brooks (University of California)

Numerous metabolic changes occur in skeletal muscle with aging. At the crossroads of these changes lies the cellular energy highway, the mitochondrial reticulum. Aging is associated with altered patterns of mitochondrial dynamics and morphology, which are thought to be primarily driven by mitochondrial fragmentation. This fragmentation phenomenon may also lead to altered mitochondrial respiration with aging. We used a mouse model and measured parameters of respiration in muscle mitochondrial preparations to evaluate the hypothesis of aging-related effects on metabolism and energy substrate partitioning. Mixed skeletal muscle of C57/Bl6 mice (n=32) was excised from single hind-limbs of young males (YM) (n=8), old males (OM) (n=8), young females (YF) (n=8) and old females (OF) (n=8). Tissues were homogenized in an isotonic solution supplemented with 0.15% protease inhibitor. Mitochondria were isolated by differential centrifugation and their concentrations were determined by BCA analysis. Isolated mitochondria (0.1mg of mitochondria/mL of respiration medium) were then respired using a Clarke-Type Electrode at 25°C with 100 nM of ADP and either 10 mM Pyruvate+ 2.5 mM Malate (P+M) or 40 uM Palmitoyl-L-Carnitine+ 1 mM Malate (PC+M) as substrates. Respiratory Control Ratios (RCR) were calculated as the quotient of State 3 (ADP-stimulated respiration) and State 4 (recovery rate post ATP synthesis) respiratory rates (State 3/State 4) and compared between substrate and age. ADP to oxygen ratios (P:O) were calculated by dividing the amount of ADP added to the respiratory chamber by the oxygen consumption rate (nmol of O2/mg of mitochondria/minute) of state 3 respiration. RCR in both P+M and PC+M significantly decreased with aging [P+M (plt;0.05): YM (4.1±0.9) vs. OM (2.7±1.1); YF (5.1±1.4 ) vs. OF (3.2±2)] [PC+M (plt;0.05): YM (4.2±0.9) vs. OM (2.4±0.7); YF (3.4.±0.5 ) vs. OF (2.2±0.9)]. P:O in both P+M and PC+M did not significantly change with aging [P+M: (p=0.69): YM (2.9±0.3) vs. OM (2.9±0.2); YF: (p=0.07): (3±0.1) vs. OF (2.9±0.1)] [PC+M:(p=0.65); YM (2.9±0.4) vs. OM (2.9±0.3); (p=0.22): YF (2.9±0.2) vs. OF (2.7±0.3)]. While there were no significant changes in the P:O the age related decreases in the RCR were characterized by a lower capacity to respire derivatives of both CHO and FA. Decreased State 3 respiration and RCR typically corresponds to loss of respiratory capacity and loosening of coupling efficiency. Because exercise increases mitochondrial function and biogenesis it may be prudent to study older animals after exercise training. We plan to further investigate the structural changes in the mitochondrial reticulum and proteome that may be altering mitochondrial function in aging.

Support or Funding Information

This study was supported by NIH 1 R01 AG059715-01