Experimental Ischemic Stroke-Induced Alpha-Synuclein Pathology Enhances Endothelial Inflammatory Response and Impairs Angiogenesis.

Background: α-Syn (alpha-synuclein) increases and oligomerization contributes to ischemic brain damage. Nevertheless, the exact mechanisms of ischemia-induced α-Syn pathology after stroke are understudied. In this exploratory and hypothesis-testing study, we specifically investigated how ischemia-induced α-Syn pathology impacts vascular inflammation and angiogenesis.

Methods: Transient focal cerebral ischemia was induced in C57BL/6J wild-type and C57BL/6S mice with spontaneous deletion of α-Syn. In total, 72 mice were randomized to receive sham (12) or ischemia (60), with 1:1 allocation to genotype. Ischemic mice were included if presenting ≥3 intraischemic focal deficits. Experimental end points were 48 hours (acute phase) and 7 days (subacute phase) of reperfusion. Sensorimotor assessment, elevated plus maze, and survival analysis were stroke outcome readouts. Brain samples were collected for quantitative real-time polymerase chain reaction, Western blot, and immunohistochemistry. In vitro ischemia in brain microvascular endothelial cells was used to investigate the direct effect of extracellular α-Syn.

Results: In vivo, cerebral ischemia induced α-Syn 2.5-fold change gene expression, 2.7- to 3.2-fold-change protein oligomerization with apparent localization around cortical ischemic vessels. Improved subacute functional recovery linked to better survival was observed in C57BL/6S α-Syn null (87% to end point) versus C57BL/6J (45%) ischemic mice. The α-Syn null mice had reduced expression of ICAM-1, MMP-9, and vascular permeability factors, associated with less infiltrating leukocytes and juxta-vascular microglia in the acute phase. In the subacute phase, they showed upregulated proangiogenic factors (VEGF-A, VEGFR-2, Angpt-2, and IL-6) and angiogenic vessels. In vitro, brain microvascular endothelial cells upregulated ICAM-1, IL-6, and VEGFR-2 expression when exposed to recombinant α-Syn at the beginning of ischemia and to a larger extent when α-Syn was preconditioned for 18 hours in hypoxia.

Conclusions: These findings indicate that ischemia-triggered pathological α-Syn leads to worse outcome in stroke mice by promoting endothelial inflammatory response and immune cell infiltration during the acute phase and by limiting angiogenesis in the subacute phase.