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New roles for alpha B-crystallin in protecting the myocardium from ischemia/reperfusion injury


Expression of [alpha]BC in the heart has been implicated in providing protection from acute stresses, such as ischemia and reperfusion, by binding to specific target proteins. This dissertation explores two new mechanisms by which [alpha]BC can protect the heart from I/R. First, the role of [alpha]BC in maintaining mitochondrial integrity and function during I/R is examined. Previous work has demonstrated that [alpha]BC associates with and protects mitochondria during I/R. This work expands upon these studies by examining the kinetics of [alpha]BC translocation and phosphorylation of [alpha]BC, an event that is required for [alpha]BC to provide maximal protection against stress. This study shows that, in response to ischemia, [alpha]BC reaches maximal accumulation at the mitochondria following 20 minutes of ischemia. Furthermore, there is an accumulation of phospho -[alpha]BC-S59, the most protective form of [alpha]BC, at the mitochondria. This study goes further to demonstrate that the presence of a phospho-[alpha]BC-S59 mimic, at the mitochondria, provides protection against H₂O₂-induced cytochrome c release. Moreover, this study demonstrates that [alpha]BC physically interacts with VDAC, a possible mechanism by which [alpha]BC prevents cytochrome c release. The second study explores a role for [alpha]BC in regulating the ceullar redox environment. Hearts from mice harboring deletions of both [alpha]BC and HSPB2 were found to have significantly lower levels of glutathione compared to controls. Consistent with this finding, glutathione reductase (GR) activity was significantly impaired in the knockout mice. HeLa cells were used as a model to further examine a role for [alpha]BC in glutathione recycling since, like the knockout mice, they lack both [alpha]BC and HSPB2. Expression of [alpha]BC in HeLa cells was found to enhance glutathione levels during H₂O₂ treatment, enhance GR activity, and prevent apoptosis. Moreover, [alpha]BC was shown to directly interact with GR and enhance its activity. The third study of this dissertation examines the use of protein transduction domains to facilitate the delivery of [alpha]BC proteins across cell membranes. This study introduces a novel system that could be used as a research or a therapeutic platform for delivering proteins, nucleic acids or small molecules

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