GEORGETOWN UNIVERSITY (THE)
Aberrant norepinephrine [NE] neurotransmission in the human brain is linked to mood disorders, depression, drug addiction and neurodegenerative diseases. ? -synuclein [? -Syn], a member of the synuclein family of proteins, is expressed in monoaminergic neurons, but its function in the brain is not known. We have shown that ?.-Syn can modulate the function and trafficking of the NE transporter [NET], through interactions with the microtubule [MT] cytoskeleton. We show here that ? -Syn can also regulate these NET activities. Such modulation by ? -Syn is unique to NET. In a rat model of depression, there is overexpression of ? -Syn, causing NET function and trafficking to be dysregulated and unresponsive to the effects of nocodazole [a MT destabilizing agent], probably due to tight binding of the ? -Syn/NET complex to the MT cytoskeleton. Chronic treatment of these animals with desipramine [a NET blocker] reduces ? -Syn protein expression, while increasing ?.-Syn levels, permitting NET to be appropriately regulated by ?.-Syn, with full restoration of nocodazole sensitivity. In postmortem brains from patients with depression, we also show that ? -Syn is overexpressed, adding clinical relevance for a role for ? -Syn in the genesis and maintenance of depression in humans. We hypothesize that ? -Syn acts as a prodepressant, and that imbalances in ? -Syn/?.-Syn expression levels is central to the genesis of depression. When overexpressed, ? -Syn overrides the normative regulation of NET by ?.-Syn. Therefore, targeting ? -Syn expression levels may be key to controlling depression in humans. We will investigate here in detail the cellular and molecular mechanisms by which desipramine reduces ? -Syn levels in both in vitro and in vivo models, which express either ? -Syn alone or both ? -Syn and NET, in the presence or absence of ?.-Syn. We will also analyze the mechanisms by which other NET antidepressants decrease ? -Syn expression in in vitro models. Finally, we will measure neurochemical and behavioral responses to NET antidepressants in ?.-Syn overexpressing transgenic mice, as well as in ?.-Syn knock-out mice. From these studies we will be able to assess the mechanisms by which ? -Syn expression is regulated as well as ascertain the physiopathological relevance of sucrtain if DMI affects ? -Syn promoter thereby altering its expression levels, we will conduct nuclear run-on assays, using isolated nuclei.