The goals of this project are to investigate the role of altered ion homeostasis and ion signaling in cell injury and protective adaptation. We previously demonstrated that an increase in cytosolic free [Ca2+] (Cai) is causally involved in necrotic cell injury, and that reducing the rise in Cai is protective. One series of studies are investigating the mechanisms involved in protective adaptation (preconditioning). Brief intermittent periods of stress (ischemia, H2O2, osmotic stress, LPS etc.), termed preconditioning (PC), provide protection against injury during a subsequent longer period of stress. Our previous studies have shown that preconditioning reduces the rise in Cai. Current studies involve elucidating the signaling pathways that are responsible for this reduced rise in Cai. We have shown the following. 1. Protein kinase C (PKC) is involved in PC. Activators of PKC mimic preconditioning and inhibitors of PKC block PC. 2. Phosphoinositide-3- kinase (PI3-kinase) is upstream of PKC. Wortmannin, an inhibitor of PI3-kinase blocks the protective effects of preconditioning, but does not block the protection induced by DOG, a direct activator of PKC. 3. 12-lipoxygenase (12-LO) metabolites are involved in PC. PC causes an increase in 12-LO metabolites, inhibitors of 12-LO metabolism block preconditioning, and addition of a 12-LO metabolite mimics preconditioning. Also, mice which are null for 12-lipoxygenase are not protected by PC. 4. 12-LO is downstream of PKC. In an attempt to order PKC and 12-LO metabolites in PC, we find that PKC activators increase 12-LO metabolism and inhibitors of PKC block the preconditioning induced increase in 12-LO metabolism. Inhibitors of 12-LO also block the protection induced by activators of PKC. 5. A 5-hydroxydecanoate (5-HD) inhibitable K-channel is downstream of 12-LO. We find that 5HD blocks the protective effects of preconditioning as well as the protective effects of 12-HpETE (the 12-lipoxygenase metabolite that mimics preconditioning). A second series of studies are investigating the basis of gender differences in the response to cell injury. Studies using mice that overexpress the plasma membrane Na/Ca exchanger have shown that perfused hearts from male, but not female Na/Ca overexpressor mice have poor recovery of function following stress, most likely due to an increase in Cai, because of increased Na/Ca exchange. The functional recovery of hearts from bilateral ovariectomized female transgenic mice was significantly worse than that of non-ovariectomized female transgenics and similar to that of male transgenic mice, suggesting that estrogen counters the effects of overexpression of the Na/Ca exchanger. Interestingly we also find that in mice that overexpress the beta2-adrenergic receptor (beta2AR), there is increased injury in male vs. female hearts. The increased injury in the beta2AR overexpressor mice is due to coupling to Gs rather than Gi (beta2AR signal through both Gs and Gi) since pertussis toxin, an inhibitor of Gi, exacerbates the injury. - Calcium, lipoxygenase metabolism, protein kinase C, nuclear magnetic resonance, sarcoplasmic reticulum
Showing the most recent 10 out of 44 publications
