The cellular response to nutritional and environmental stress has been associated with the pathology of many diseases. Major contributors to cell fate decisions in response to stress are: (i) cell-type specific factors, (ii) time and (iii) intensity of stress. Chronic and high intensity stress conditions attenuate survival signals and favor apoptotic signals. This proposal will explore the molecular mechanisms of cell fate decisions during hypertonic stress. Hypertonic stress causes loss of intracellular water, cell shrinkage and macromolecular crowding. Disease-related examples are hyperglycemia in diabetes (HHS, Hyperglycemic Hyperosmolar State), macrophage cell death in inflammatory sites, dehydration of the ocular surface in dry eye syndrome and increased susceptibility to infections and retinal cell apoptosis in diabetic retinopathy. During the previous grant cycle we were the first to identify a novel pathway that promotes cell death during hypertonic stress. We showed that a specific signaling pathway (eIF21-P), the master regulator of survival and apoptotic signals in all stress responses, mediates the cytoplasmic localization of a nuclear protein that represses synthesis of proteins that promote cell survival. This cellular response shifts the balance to cell death (apoptosis) by weakening the survival mechanisms of the stressed cells. Regulation of the subcellular localization of nuclear proteins by extracellular signaling is an understudied and emerging area of research. We propose to identify some of the critical factors which are involved in the switch of balance from survival to apoptosis during hypertonic stress. We will determine (i) the signaling pathways that affect translation of mRNAs coding for proteins that determine cell fate during hypertonic stress. (ii) specific signaling molecules (cleaved tRNAs) involved in inhibition of protein synthesis during hypertonic stress and (iii) the effect of inflammation in hypertonic stress-induced cell death in a model of human disease. These studies will increase our understanding of stress-induced human diseases and generate biological markers that can be used for drug development.
A recently recognized pathology is the increased extracellular osmolarity at sites of inflammation. Increased extracellular osmolarity causes osmotic stress, which leads to loss of intracellular water, cell shrinkage, macromolecular crowding and death. Diseases such as diabetic retinopathy, Hyperglycemic Hyperosmolar State (HHS) in diabetes, macrophage cell death at inflammatory sites, and dehydration of the ocular surface in dry eye syndrome are some examples that involve increased systemic or local extracellular osmolarity. The studies in this proposal will bring new insights into the molecular events that determine cell fate when osmolarities increase above normal and will assist in the development of drugs to attenuate undesirable apoptosis of healthy cells.
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