Abstract WP306: Endothelial CD200 Signaling Protects Brain Against Ischemic Damage

Abstract

Background: Stroke is currently the leading cause of death and long-term disability in the US. Ischemic stroke induced inflammatory responses contribute to neuronal damage and stroke outcomes. CD200 and its receptor, CD200R, constitute an endogenous inhibitory signaling that is being increasingly recognized in studies of neuroinflammation in various central nervous system disorders. CD200 is a type 1 membrane glycoprotein that is broadly expressed by endothelia and neurons in the brain. We have previously reported the role of neuronal CD200 in stroke; in the present study, we examined the role of endothelial CD200 signaling in acute ischemic stroke. Hypothesis: Endothelial CD200 signaling is neuroprotective in acute ischemic stroke. Methods: Endothelial CD200 conditional knock out (CKO) mice were generated by breeding CD200 gene floxed mice with Cdh5 Cre mice. The mice were subjected to a 60-min transient middle cerebral artery occlusion (MCAO). Flow cytometry, Immunohistochemical staining, and western blotting were performed to assess the post-stroke inflammation; stroke outcomes (infarct volume and neurobehavioral deficits) were evaluated at 24 h or 72 h days after MCAO. Results: Flow cytometry results found CD200R was near null expressed on microglia at 24h and 72h after stoke and endothelial CKO of CD200 had no impact on peripheral immune cell development. Immunohistochemical staining confirmed CD200 was expressed on CD200 floxed but not on CD200 CKO endothelia. Western blot results showed CKO of CD200 from endothelia did not change BBB protein expression. CD200 CKO mice exhibited larger infarct size, worse neurological deficit scores (NDS), and more deficits in the tape adhesive/removal test than control mice 72h after MCAO (Fig. 1). Conclusions: Endothelial CD200 signaling protects brains against ischemic injury through a mechanism not directly related to microglial activation; instead, CD200R + circulating immune cells may be involved.