The development of motor and cognitive dysfunction during aging may be, in part associated with perturbations of central dopamine (DA) neurotransmission. At the molecular level, DA signaling is dynamically regulated by a diverse set of macromolecules including biosynthetic enzymes, degradative enzymes, secretory proteins, ion channels, pre- and post synaptic receptors and transporters. Various abnormalities in DA function have been postulated as causes of various types of neurodegenerative diseases, psychopathology and drug addiction. Several neuronal factors such as neurotrophic factors support development and neuroplasticity of DA neurons. Alterations or any compromised expression and regulation of these molecules may leads to age-related vulnerability of DA neurons. The plasma membrane dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2) are essential for normal DA neurotransmission. DAT terminates the action of DA and maintain the extracellular levels of DA, whereas VMAT2 loads cytoplasmic DA into to vesicles and subsequent vesicular DA release as well as maintain intracellular cytoplasmic DA levels. High concentrations of DA and/or DA-metabolites in either intracellular cytoplasmic or elevated extracellular DA are documented to be toxic to striatal presynaptic dopaminergic terminals. Thus perturbation of the tightly regulated balance of these two transporters function may predispose the neurons to damage by variety of insults, such as growth factor deficiency or exposure to environmental toxins at different levels of life-span. While changes in DAT mRNAs and binding sites have been implicated in aging and Parkinson's disease, there are no studies investigating relevant alterations in transporter function, regulation and sub-cellular distribution in pre-synaptic DA terminals that are associated with normal aging. The central goal of this project is to comprehend the neuroadaptive changes in DAT and VMAT2 functional regulation during aging and test the hypothesis that the expression of DAT and VMAT2 can predict the selective vulnerability of DA terminals. Combining state-of art biochemical and molecular approaches with the animal model outlined in animal core, this project proposes to determine systematically (a) the progression of changes in the expression and regulation DAT and VMAT2 associated with normal aging and (b) age-related alterations in the expression and regulation of DAT and VMAT2 under the conditions of environmental insults such as exposure to methamphetamine, and (c) the early adaptive changes in the expression and regulation of DAT and VMAT2 under growth factor deficiency (GDNF, and BDNF heterozygous transgenic animals) and the relationship to DA neuron vulnerability during aging processes. To accomplish this a number of dependent variables related to transporter function will be quantified, including 1) expression, transporter activity, sub-cellular distribution and 2) phosphorylation state of transporter, PP2Ac/alpha-synuclein -DAT association. These studies will aid in our understanding the compensatory changes occurring in DA neurons during normal aging process and could identify novel molecular targets for pharmacological intervention in age related neurodegenerative diseases.
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