SERCA overexpression reduces hydroxyl radical injury in murine myocardium

Hydroxyl radicals (center dot OH) are involved in the pathogenesis of ischemia-reperfusion injury and are observed in clinical situations, including acute heart failure, stroke, and myocardial infarction. Acute transient exposure to center dot OH causes an intracellular Ca2+ overload and leads to impaired contractility. We investigated whether upregulation of sarcoplasmic reticulum Ca2+-ATPase function (SERCA) can attenuate center dot OH-induced dysfunction. Small, contracting right ventricular papillary muscles from wild-type (WT) SERCA1a-overexpressing (transgenic, TG) and SERCA2a heterogeneous knockout ( HET) mice were directly exposed to center dot OH. This brief 2-min exposure led to a transient elevation of diastolic force (F-dia) and depression of developed force (F-dev). In WT mice, Fdia increased to 485 +/- 49% and Fdev decreased to 11 +/- 3%. In sharp contrast, in TG mice Fdia increased only to 241 +/- 17%, whereas Fdev decreased only to 51 +/- 5% (P < 0.05 vs. WT). In HET mice, Fdia rose more than WT (to 597 +/- 20%, P < 0.05), whereas Fdev was reduced in a similar amount. After similar to 45 min after center dot OH exposure, a new steady state was reached: Fdev returned to 37 +/- 6% and 32 +/- 6%, whereas Fdia came back to 238 +/- 28% and 292 +/- 17% in WT and HET mice, respectively. In contrast, the sustained dysfunction was significantly less in TG mice: Fdia and Fdev returned to 144 +/- 20% and 67 +/- 6%, respectively. Before exposure to center dot OH, there is decrease in phospholamban (PLB) phosphorylation at Ser16 (pPLBSer16) and PLB phosphorylation at Thr17 (pPLBThr17) in TG mice and an increase in pPLBSer16 and pPLBThr17 in HET mice versus WT. After exposure to center dot OH there is decrease in pPLBSer16 in WT, TG, and HET mice but no significant change in the level of pPLBThr17 in any group. The results indicate that SERCA overexpression can reduce the center dot OH-induced contractile dysfunction in murine myocardium, whereas a reduced SR Ca2+-ATPase activity aggravates this injury. Loss of pPLB levels at Ser16 likely amplifies the differences observed in injury response.