Nmr Studies Of The Mechanisms Of Cell Injury

Environmental Health Sciences

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Abstract

We have shown that protective mechanisms attenuate the ionic alterations associated with cell injury. Our recent studies have focused on understanding the signaling pathways involved in a stress induced protection known as preconditioning (PC) and the protective effect of female hormones. We have found that brief intermittent periods of stress, termed preconditioning (PC) provides protection during a subsequent sustained period of stress (e.g. ischemia). Thus following ischemia, PC hearts have less necrosis (cell death) and improved post-ischemic function (measured as improved recovery of left ventricular developed pressure (LVDP). We have elucidated many of the signaling pathways involved in PC. Preconditioning leads to release of agonists such as adenosine, bradykinin and opioids which bind to G-protein coupled receptors and activate a signaling cascade that result in cardioprotection. PC acting results in the activation of phosphatidylinositol-3-kinase (PI3K) which leads to phosphorylation of a number of downstream signaling molecules such as AKT, protein kinase C (PKC), glycogen synthase kinase-3? (GSK-3?), endothelial nitric oxide synthase (eNOS), ERK and the mitochondrial KATP channel. We also find that activation of PI3K is important for endosomal receptor signaling which is important for cardioprotection. The mitochndria play an important role in cardioprotection and we find that Bcl-2 association with the voltage dependent anion channel (VDAC) plays a crucial role in reducing myocardial cell death. We have tested the ability of drugs such as erythropoetin to initiate cardioprotection. In addition to stress induced protection, we have found that under conditions of Ca2+ overload, females have reduced cell injury. In hearts from three different transgenic mouse models (Na+-Ca2+ overexpressor, ?2-adrenergic receptor (?2AR) overexpressor, phospholamban KO), which all would be expected to have an increase in sarcoplasmic reticulum (SR) calcium, we find that males but not females have poorer recovery of function following stress. Although we do not typically observe gender differences in response to injury in wild type (WT) hearts, such differences become apparent if we raise extracellular calcium or treat hearts with isoproterenol, conditions that increase cell Ca2+. Nitric oxide is involved in mediating this protection in females, as inhibitors of nitric oxide synthase block the protection in females, and the protection is not observed in mice lacking eNOS or nNOS. We have also shown that females have less a rise in Na+ during ischemia. We have also made the novel observation that the cardioprotection observed in females involved S-nitrosylation of the L-type Ca2+ channel which reduces Ca2+ entry into the heart thereby reducing Ca2+ overload and thereby resulting in cardioprotection. We have also demonstrated that cardioprotection in females is mediated by the beta estrogen receptor. Lastly we have demonstrated that females subjected to pressure overload develop less hypertrophy and that this effect is mediated by estrogen receptor beta.