Adenosine A(2A) receptor antagonism reverses inflammation-induced impairment of microglial process extension in a model of Parkinson's disease

Microglia, the immune cells of the central nervous system, constantly survey the parenchyma in the healthy brain to maintain homeostasis. When a disturbance, such as cell death, results in ATP release in vivo, microglial processes respond by utilizing P2Y12 purinergic receptors to trigger extension toward the site of damage. Processes ultimately surround the injury site, preventing the spread of harmful cellular constituents and assisting with tissue repair. In contrast to the healthy brain, many neurodegenerative diseases, including Parkinson’s disease, are characterized by the presence of neuroinflammation. Yet, the ability of microglia to respond to tissue damage under pro-inflammatory conditions has not been well studied. To assess the ability of microglia to respond to tissue injury and localized cell death in the context of Parkinson’s disease, we performed confocal imaging of acute brain slices from mice with microglia-specific green fluorescent protein expression. Microglia in coronal slices containing the substantia nigra extend processes toward a mechanical injury in a P2Y12 receptor-dependent manner. However, microglia in mice treated for 5 days with 20 mg/kg/day 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) show significantly reduced process displacement toward the injury compared to microglia © 2014 Elsevier Inc. All rights reserved. Corresponding author: Stefka Gyoneva, Department of Pharmacology, Rollins Research Center Rm 5062, 1510 Clifton Rd. NE, Atlanta, GA 30322; Tel. : (404) 727-1375, Fax: (404) 727-0365; stefka.gyoneva@gmail.com. 1Present address: Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 2Present address: RFS Pharma LLC. , Tucker, GA 30084 Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Conflict of interest: The authors declare no competing financial interests. NIH Public Access Author Manuscript Neurobiol Dis. Author manuscript; available in PMC 2015 July 01. Published in final edited form as: Neurobiol Dis. 2014 July ; 67: 191–202. doi:10.1016/j.nbd. 2014.03. 004. N IH -P A A uhor M anscript N IH -P A A uhor M anscript N IH -P A A uhor M anscript in control animals. Pre-treatment of slices from MPTP-injected mice with the A2A receptorselective antagonist preladenant restores the ability of activated microglia to respond to tissue damage. These data support the hypothesis that chronic inflammation impedes microglial motility in response to further injury, such as cell death, and suggest that some aspects of the neuroprotection observed with adenosine A2A receptor antagonists may involve direct or indirect actions at microglia.