Repair, Degradation, and Calcium Regulation in Aging Muscle
Sponsor: Program Project P01 AG12993 (Reactive Oxygen Species in Aging) PI :Elias K. Michaelis
Contact: Diana Bigelow
The long-term goal of this project is to understand cellular processes responsible for the accumulation of oxidized calcium regulatory proteins and the concomitant prolongation of the calcium transient in senescent muscle. Our focus is on both the SR Ca-ATPase and the ryanodine receptor (RyR) calcium release channel, two calcium regulatory proteins that play a major role in eliciting intracellular calcium transients. The RyR releases intracellular calcium to initiate muscle contraction while the SR Ca-ATPase mediates the rate-limiting re-sequestration of calcium back into the SR lumen both allowing muscle relaxation and resetting of the cellular calcium gradient for the next calcium release and contraction.
Previous work here has established the highly abundant and specific accumulation of 3-nitro-tyrosine modification of the SERCA2a (slow-twitch/cardiac) isoform of the Ca-ATPase in slow-twitch skeletal muscle with corresponding loss of function. We also observe nitrotyrosine modification (nitration) of SERCA2a expressed in the heart, but to a more modest extent, suggesting different cellular environments in these different myocytes. Thus we hypothesize that age-related accumulation of oxidized proteins results from alterations in ratios of concentrations of reactive oxygen species (ROS) relative to efficiencies of processes for the repair and degradation of modified proteins. Therefore, the first specific aim of this project is to elucidate cellular pathways responsible for degradation of nitrotyrosine-modified SERCA2a. In addition, the nitrotyrosine modification implies the presence of several ROS (ONOO--, NO•, and O2-•) which, in turn, have functional implications for the RyR and its major regulators, particularly, calmodulin. Thus, our second specific aim involves (2) characterization of the altered regulation of the RyR with oxidized calmodulin (CaM) and other regulatory molecules in senescent muscle.