Our proposal aims to study a novel compensatory cell survival signaling pathway mediated by PKCd- PKD1 during the early stages of oxidative damage in the nigrostriatal dopaminergic system. Although oxidative stress, apoptosis are known to be important in the degenerative process in dopaminergic neurons in Parkinson's disease (PD), the apoptotic signaling mechanisms downstream of caspase-3 that contribute to the degeneration of dopaminergic neurons are poorly understood. We have identified that PKCd, a member of the novel PKC isoform family, is highly expressed in nigral dopaminergic neurons, and the kinase is persistently activated via a novel mechanism by which caspase-3 proteolytically cleaves to permanently dissociate the catalytic subunit from the regulatory subunit of PKCd. We demonstrated that PKCd proteolytic activation contributes to apoptotic cell death of dopaminergic neurons during oxidative damage. While dissecting the oxidative signaling pathway in cell culture models of PD, we also unexpectedly identified that protein kinase D1 (PKD1) is activated by a PKCd dependent mechanism to protect dopaminergic neurons from the early stages of oxidative insult. Therefore, we propose to systematically characterize the PKCd-PKD1 oxidative signaling in nigral degenerative processes using cell culture and animal models of PD as well as human postmortem PD brains. This will be accomplished by pursuing the following specific aims: (i) To determine the mechanism of PKD1 activation in dopaminergic neurons during oxidative stress using cell culture models of PD, (ii) To examine PKD1 and PKCd activation mechanisms resulting from mitochondrial defects in a new transgenic 'MitoPark' PD mouse model, in a PKCd knockout (PKCd-/-) mouse model and in human postmortem PD brains, iii) o demonstrate the anti-apoptotic compensatory function of PKD1 against nigral dopaminergic degeneration using an inducible PKD1 kinase-dead (PKD1-KD) transgenic mouse model and constitutively active PKD1over-expressing model. Cellular, molecular and neurochemical approaches will be used to delineate these specific aims. Together, the proposed PKCd-PKD1 signaling will provide comprehensive information about signaling pathways associated with compensatory protective responses at the early stages of oxidative stress, as well as the cell signaling mechanisms that override the protective responses during prolonged oxidative insult in nigral dopaminergic neurons. The proposed work has translational potential, as neuroprotective strategies targeting the proposed signaling pathway may prove to be effective against PD.
Parkinson's disease (PD) is a major neurodegenerative disorder affecting over a million Americans with an associated annual cost of several billion dollars. Current treatment approaches available for PD are symptomatic and fail to prevent the progression of the neurodegenerative process. The present drugs are limited in their effectiveness to either slow or stop the progressive neurodegenerative processes in PD, largely due to the lack of mechanistic insights into the selective dopaminergic degenerative process. We propose to characterize a previously unexplored oxidative signaling pathway in nigral dopaminergic degeneration, and this signaling pathway could provide a novel target for the development of an effective therapeutic agent.
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