Fellowship for Naga: Role of cyclophilin D in the vulnerability of neuronal and synaptic mitochondria to undergo permeability transition.

Mitochondria are important regulators of cellular Ca2+ homeostasis, producers of adenosine triphosphate (ATP) via oxidative phosphorylation, and regulators of cell death pathways. We previously observed that synaptic mitochondria take up lower amounts of calcium before undergoing mitochondrial permeability transition (mPT) than do non-synaptic mitochondria(Brown et aI., 2006). Further we also observed a higher content of cyclophilin D (one of the components of permeability transition pore) in synaptic mitochondria. Synaptic mitochondria are predominantly neuronal in origin, whereas non-synaptic mitochondria are obtained from neurons, glia, and other cells. Therefore here we propose to determine the mechanism underlying the different Ca2+ uptake capacities of synaptic vs. non-synaptic mitochondria, and also whether this differences in Ca2+ uptake capacity applies to neurons in general or is specific to presynaptic neuronal mitochondria. SPECIFIC AIM 1: To examine the hypothesis that contrasting levels of Cyp D in synaptic and non-synaptic mitochondria underlie the different Ca2+ uptake capacity of these mitochondrial populations. The goal of this specific aim is to understand whether contrasting levels of Cyp D are responsible for different calcium uptake capacities of synaptic and non-synaptic mitochondria. SPECIFIC AIM 2: To examine the hypothesis that the Cyp D levels in synaptic vs. non-synaptic mitochondria reflect the relative proportion of neuronal vs. glial mitochondria in these two mitochondrial fractions. This specific aim is to determine whether the observed variation in Cyp D levels and calcium buffering abilities between synaptic and non-synaptic mitochondria exists between neuronal and glial mitochondria. SPECIFIC AIM 3: To examine the hypothesis that neuronal synaptic vs. neuronal non-synaptic mitochondria have differing Ca2+ uptake capacities. This specific aim focuses on synaptic and non-synaptic mitochondria specifically of neurons. The data obtained in this proposal will help in understanding the role of Cyp D in Ca2+ uptake and sensitivity of synapses to Ca2+overload. These experiments have important implications and suggest that much higher concentrations of CsA may be necessary to protect neurons against calcium induced toxicity in CNS than were previously recognized.