CD200 Inhibits Inflammatory Response by Promoting KATP Channel Opening in Microglia Cells in Parkinson's Disease

BACKGROUND As the second most common neurodegenerative disorder after Alzheimer's disease (AD), Parkinson's disease (PD) principally impacts the motor system in approximately 7 million patients worldwide. The present study aimed to explore the effects of cluster of differentiation (CD200) on adenosine triphosphate-sensitive potassium (KATP) channels and inflammatory response in PD mice. MATERIAL AND METHODS We created an in vivo PD model by intraperitoneal injection of 30 mg/kg/day 1-Methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine hydrochloride (MPTP. HCL) for 5 consecutive days, and we created an in vitro PD model by injection of 100 μM 1-methyl-4-phenylpyridinium ion (MPP+) in primary microglia cells. Expression level of CD200/CD200R, inwardly rectifying potassium (Kir6.1/6.2), and sulfonylurea receptor (Sur1/2) were detected by Western blot (WB). Immunohistochemistry (IHC) was utilized to assess CD11b (microglia marker) and tyrosine hydroxylase (TH, a marker reveals dopamine level in neurons) expression levels. An in vitro PD model was applied to detect the influence of CD200 on ATP and inflammatory factors released from microglia. Interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-1β mRNA levels were explored by realtime quantitative polymerase chain reaction (RT-QPCR), and their protein levels were identified by enzyme-linked immunosorbent assay (ELISA). RESULTS WB exhibited time-dependent down-regulation of CD200/CD200R in cerebra of PD mice compared to control mice, with Kir 6.1 and SUR 2 expressed mainly in microglia. IHC showed that CD11b reached a peak at the 1st day after MPTP treatment, followed by time-dependent reduction, and TH decreased noticeably after MPTP induction. RT-QPCR demonstrated that compared with controls, IFN-γ, TNF-α, and IL-1β mRNA levels were significantly elevated at MPTP-1d, was reduced at MPTP-3d, and then returned to baseline at MPTP-7d. IHC showed that MPP+ significantly elevated microglia release of ATP. Similar to the effect of pinacidil (K+ channel opener), CD200 remarkably depressed MPP+-induced ATP release. ELISA showed that MPP+ significantly increased IFN-γ, TNF-α, and IL-1β release, and CD200 and pinacidil remarkably suppressed this elevation. CONCLUSIONS Our results show a novel role of CD200 in promoting opening of the KATP channel, inhibiting microglia activation and release of ATP, as well as inflammatory factors, thus protecting dopaminergic (DA) neurons against damage and alleviating PD.