PNNL

Abstract

In the aging heart, decreased rates of calcium transport mediated by the SERCA2a isoform of the sarcoplasmic reticulum (SR) Ca-ATPase are responsible for the slower sequestration of cytosolic calcium and consequent prolonged muscle relaxation times. We report a 60% decrease in Ca-ATPase activity in the senescent Fischer 344 rat heart relative to that of young adult hearts; this functional decrease can be attributed, in part, to the 18% lower abundance of SERCA2a protein. Here, we show here that the additional loss of activity is a result of increased 3-nitrotyrosine modification of the Ca-ATPase. Age-dependent increases in nitration of cardiac SERCA2a are identified using multiple analytical methods. In the young (adult) heart one molar equivalent of nitrotyrosine is distributed over at least five tyrosines within the Ca-ATPase, identified as Tyr122, Tyr130, Tyr497, Tyr586 and Tyr990. In the senescent heart, the stoichiometry of nitration increases by more than two nitrotyrosines per Ca-ATPase, coinciding with the appearance of nitrated Tyr294, Tyr295, and Tyr753. The abundant recovery of native analogs for each of the nitrated peptides indicates partial modification of multiple tyrosines within cardiac SERCA2a. In contrast, within skeletal muscle SERCA2a a homogeneous pattern of nitration appears, with full site (1 mol/mol) nitration of Tyr753, in young, with additional nitration of Tyr294 and Tyr295, in senescent muscle. The nitration of these latter vicinal sites correlates with diminished transport function in both striated muscle types. Thus the enhanced function of the Ca-ATPase during aging in the heart in comparison with that in slow-twitch skeletal muscle is consistent with different endogenous degradation or repair activities that function to minimize the accumulation of Ca-ATPase with reduced activity.