Hypoxia and reoxygenation create havoc in cells. This havoc if unrepaired will ultimately lead to cell dysfunction and death in diseases such as myocardial infarction and stroke, the number one causes of death and disability in the US. Unfortunately, no effective therapy for hypoxic injury, short of restoring oxygenation, has been approved, suggesting that an unrecognized aspect of hypoxic injury is not being effectively treated by previous strategies. Mitochondria have long been recognized as central to hypoxic injury. Mitochondria are the primary utilizer of oxygen in cells, converting oxygen to the chemical potential energy required for the survival of cells and the organism. Mitochondria also are central to cell death processes ? in particular apoptosis and forms of calcium-mediated death including necrosis. Both necrosis and apoptosis are thought to be the most prevalent mechanisms of death after hypoxic injury. However, a full understanding of how hypoxia injures mitochondria leading to cell death is lacking. We have recently reported a novel type of hypoxia- induced mitochondrial pathology ? mitochondrial protein misfolding. Our published data show that mitochondrial protein misfolding occurs early in the hypoxic injury cascade, prior to any evidence of cell death. This suggests the hypothesis that mitochondrial protein misfolding may be both a consequence of hypoxia and a cause of hypoxic cell injury and death. Consistent with this hypothesis, genetic or pharmacologic manipulations in the nematode C. elegans that activate the mitochondrial unfolded protein response (mitoUPR), an intracellular homeostatic response to mitochondrial misfolded proteins, protects from hypoxic injury and improves animal survival. Since this publication, we have developed new fluorescent mitochondrial protein reporter tools in C. elegans in order to study protein misfolding directly and have preliminary evidence that mitochondrial proteins not only misfold but aggregate after hypoxia. The goals of this project are to develop a fundamental understanding of hypoxia-induced mitochondrial protein misfolding and aggregation, to identify ways to mitigate disruption of mitochondrial proteostasis, and to determine if similar disruption can be detected and mitigated in mouse models of human disease. Our general strategy is to take advantage of the speed, low cost, and specialized cell biological tools of C. elegans for fundamental discovery and to apply where possible our discoveries to mammalian models of hypoxic disease.
Our specific aims are as follows:
Aim 1. Determine the identity of the misfolded and aggregated mitochondrial proteins and the kinetics, determinants, and consequences of aggregation.
Aim 2. Identify genetic and pharmacological manipulations that ameliorate mitochondrial protein misfolding in C. elegans.
Aim 3. Determine whether mitochondrial protein misfolding/aggregation occur in mouse models of disease. Completion of these aims will increase our understanding of a novel hypoxic pathology of the mitochondria and will potentially identify ways to mitigate it.
Hypoxic cell death in the form of stroke and myocardial infarction is the number one cause of mortality in the US. Through the research aims proposed here, new mechanisms of damage to mitochondria, the powerhouse of the cell, will be discovered and understood. Through a better understanding of mitochondrial injury, new strategies to treat stroke and myocardial infarction may emerge.
| Kaufman, Daniel M; Wu, Xia; Scott, Barbara A et al. (2017) Ageing and hypoxia cause protein aggregation in mitochondria. Cell Death Differ 24:1730-1738 |
