The hypothesis to be tested here is that interventions following trauma that increase the glycosylation of nucleocytoplasmic proteins in cardiomyocytes decrease the cellular damage that would otherwise contribute to hypovolemic circulatory collapse. Our preliminary data demonstrate that in a rat model of hypovolemic stress, the infusion of glucosamine leads to a striking improvement in post-trauma function. We also demonstrate that glucosamine is protective in isolated heart models of ischemia/reperfusion and calcium overload. We propose that this protection results from an amplification of a natural, stress-activated, pro-survival pathway triggered by increased flux through the hexosamine biosynthesis pathway (HBP). The capacity to transduce an increase in the HBP's primary product, UDP-GIcNAc, into complex cellular responses comes about because O-GIcNAc transferase (OGT) is activated and recognizes distinct proteins as levels of UDP-GIcNAc increase. The identification of heat shock protein (HSP)-70 as an HBP-induced protein substrate for the OGT and the finding that HSP's associate with other proteins in part based on their ability to bind O-GIcNAc position this pathway at the center of a primary cellular response to stress. In support of this central role for O-GIcNAc in cellular protection, it is now clear that various stresses lead to increases in levels of both UDP-GIcNAc and protein-associated O-GIcNAc. We suggest that interventions that amplify and/or accelerate increases in O-GIcNAc greatly decrease the damage resulting from stress, particularly hypovolemic stress.
Our Specific Aims are: to optimize recovery in the rat model of hypovolemic stress through interventions that increase UDP-GIcNAc and to test the efficacy of these interventions in swine; to test the hypothesis that the mechanism by which increased UDP-GIcNAc leads to its ameliorating effects is because of an increase in O-GIcNAc on nuclear and cytoplasmic proteins; to document and identify the nucleocytoplasmic proteins in the heart that are preferentially derivatized with O-GIcNAc when protection is optimized in the hypovolemic rat model; to investigate the decrease in calcium influx seen with increased UDP-GIcNAc in mediating improved recoveries.
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