zed: 1) Substance P exacerbates neurotoxins-induced nigral dopaminergic neurodegeneration through activation of microglial NADPH oxidase Dysregulation of substance P (SP), a major endogenous neuropeptide present in the striatonigral projecting pathway, has been linked with Parkinsons disease (PD). However, roles of SP in regulating long-term survival of dopaminergic neurons in the substantia nigra (SN) remain unstudied. Here, we demonstrate that SP exacerbates dopaminergic neurodegeneration in rodent PD models through augmenting microglia-mediated neuroinflammation. Two in vivo rodent PD models were employed: 1) a single dose of LPS or 2) repeated MPTP regimen in SP-deficient (TAC1-/-), neurokinin-1 receptor (conventional G-proteincouple receptor for SP) knockout (NK-1R-/-) or wild type (WT) mice. We found that lack of endogenous SP significantly decreased LPS- or MPTP-induced dopaminergic neurotoxicity in both SN and striatum and brain neuroinflammation. Surprisingly, no difference of the above-mentioned changes were observed between NK-1R-/- and WT mice, suggesting that these synergistic effects of SP and neurotoxins are not mediated through the conventional NK-1R. In midbrain neuron-glia cultures, SP enhanced both LPS- and MPP+-induced dopaminergic neurodegeneration and neuroinflammation with an interesting bimodal dose-response curve: effective in nanomolar (10-810-7M) and subpicomolar (10-1410-13 M) concentrations, but not in between. Further studies revealed that subpicomolar SP, which is released from terminals of the striatal-nigral neurons, diffused out synaptic junction and acted on the surrounding microglia. We identified NADPH oxidase, an important superoxide-producing enzyme in microglia, was a novel NK1R-independent target responsible for the synergistic effects of SP and neurotoxins. Additional mechanistic studies showed that SP directly bound to gp91phox, the membrane subunit of NADPH oxidase, through C-terminal PHE-GLY-LEU-MET domain and then either alone or with LPS induced membrane translocation of cytosolic subunits p47phox and p67phox, resulting in NADPH oxidase activation. Signaling studies further showed that SP was capable of enhancing production of TNF by potentiating LPS-induced activation of MAPK and NF-B pathway through NADPH oxidase-dependent manner. Altogether, we have demonstrated a GPCR-independent novel mechanism whereby SP displays its pro-inflammatory effect by directly binding to the gp91phox and increasing superoxide production, which is critically linked with synergistic neurotoxic effects between SP and neurotoxins in PD. 2) Development of novel therapeutic drug for treatementof Parkinson's disease The purpose of this study was to determine whether targeting microglial NADPH oxidase (NOX2) could serve as a novel strategy for Parkinsons disease (PD) therapy. Mice received a single injection of lipopolysaccharide (LPS), which displayed progressive motor deficits and loss of nigral dopaminergic neurons, were post-treated at 3, 6 and 10 months with a NOX2 inhibitor diphenyliodonium (DPI, 10 ng/kg/day) for two weeks. Seven months after DPI post-treatment, LPS-elicited motor deficits, loss of dopaminergic neurons and enhanced microglial proinflammatory factor production were attenuated in DPI-treated mice. These effects of DPI are linked with NOX2 inhibition, since in vitro studies showed that NOX2 deficiency abolished the DPI-afforded neuroprotection. Furthermore, low dose DPI specifically inhibited activation of NOX2, but not other cytochrome enzymes. Thus, post-treatment with DPI in extremely low concentrations is capable of slowing the disease progression and suggest that targeting NOX2 can be a novel disease-modifying strategy for PD therapy.
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