Abstract P772: Complement C3a Receptor Deletion is Neuroprotective in a Murine Model of Vascular Cognitive Impairment

Abstract

Background: Chronic cerebral hypoperfusion (CCH) leads to vascular contributions to cognitive impairment and dementia (VCID). We and others have reported that either the genetic deficiency of complement C3a receptor (C3aR) or its pharmacological inhibition in rodents protect against cerebral ischemia. Hypothesis: CCH augments VCID via overactivation of C3aR in brain. Methods: Male C3aR knockout (C3aR -/- ) and wild-type (C3aR +/+ ) mice (Age:12 weeks; N=8-10/gp) were subjected to either VCID with bilateral common carotid artery stenosis (BCAS) or sham surgery. At 4-mo post-BCAS, changes in cerebral blood flow (CBF), hippocampal atrophy (HA), white matter degeneration (WMD) and ventricular size were determined with laser speckle contrast analysis and magnetic resonance imaging. Behavioral outcomes were evaluated using Morris water maze (MWM) and novel object recognition (NOR). Histopathology with Luxol-Fast Blue (LFB) staining, and protein biochemistry with Western blotting were also performed. Results: BCAS resulted in reduced CBF, inducing HA, WMD and ventricle enlargement in both groups compared to their sham controls. These deleterious findings were attenuated in C3aR -/- compared to C3aR +/+ mice. Moreover, the C3aR -/- -BCAS group performed significantly better than C3aR +/+ -BCAS group in MWM and NOR tests; however, mice subjected to BCAS never outperformed their sham-groups. WMD demonstrated by LFB-staining and reduced expression of myelin basic protein and tight junction proteins (ZO-1 and Occludin) in mice subjected to BCAS was mitigated in C3aR -/- as compared to C3aR +/+ mice. C3aR +/+ -BCAS also showed significantly higher expression of C3a in plasma and C3aR in brain lysates compared to their sham-controls. Conclusion: CCH augments C3aR activation leading to poor outcomes in VCID. Therefore, future studies in cell-specific mutant mice are warranted to understand the pathological role of C3aR in VCID.