There is mounting evidence that a core mechanism of programmed cell death, regardless of organism or cell type, is an event in mitochondria termed """"""""PT"""""""" characterized by a catastrophic loss of mitochondrial outer member an permeability, which is medicated by a proteinaceous pore composed of the inner mitochondrial membrane ADP/ATP translocae (ANT). Other proteins that either comprise that PT pore, or regulate it, are several mitochondrial outer membrane proteins: the PBR 18 kDa proteins, porin (VDAC), and the Bc12 family of proteins. There are many cellular perturbations that trigger PT, and cell death, including oxidative stress, perturbations of cellular calcium homeostasis, growth factor withdrawal, ceramide, FAS ligand, glucocorticoids, and others. In all cases, PT is associated with efflux of calcium from mitochondria, and there is also evidence that calcium efflux is the primary trigger of PT, rather that merely the result of PT. Significantly, there is also evidence that the ADP/ATP transclocases (ANT proteins) are an important route for calcium efflux from mitochondria a. The possibility that the PBR regulates PT, as a result of its association with both porin (VDAC) and ANT proteins, is of special significance for this project, because evidence already exists that PBR levels are elevated in brain microglial cells after brain injury, and are a marker for brain inflammation. There is a well developed pharmacology for both PBR and ANT, which provides the potential to modulate inflammatory reactions and/or brain cell death rates via administration of drugs. To elucidate the specific functions of ANT proteins and PBR in programmed cell death, our specific aims are to: (1) study the express of three mitochondrial ANT isoforms in human brain samples, in order to determine which isoform is preferentially expressed and whether their expression is regulated with aging or in response to pathologic conditions associated with Alzheimer's of epilepsy; (2) determine if PBR expression is elevated in activated human microglia, as is the case in animal models, whether PBR ligands activate or modulate the activation of microglia in cell culture, and whether PBR ligands effect susceptibility of glial cells to cell death; and 3) study the effects of each of the human ANT genes on mitochondrial calcium homeostasis. This will be done initially in yeast model system in which the endogenous ANT genes are deleted, and a single human ANT gene is expressed.
