Orexin B Reduces Cerebral Aneurysms by Inhibiting SP-1 via OX2R Activation

Cerebral aneurysms (CAs) are dangerous dilations of intracranial arteries with a high rupture risk, leading to devastating outcomes. Current treatments often involve invasive procedures, and the underlying molecular mechanisms driving CA formation remain poorly understood, limiting pharmacological prevention strategies. The Orexin B/OX2R system, primarily known for its roles in arousal and metabolism, has recently been implicated in vascular pathology, presenting a novel avenue for investigation into CA pathogenesis and potential therapeutic targets.

Researchers measured serum Orexin A and B levels in 38 CA patients and 43 healthy controls. A murine CA model was established using elastase-induced aneurysms in wild-type (WT) and OX2R knockout (OX2R-/-) mice. WT mice received Orexin B 30 μg/kg/day for 7 weeks, with controls receiving vehicle. Aneurysm size, inflammatory markers (IL-6, MMP-9, MCP-1, E-selectin), macrophage infiltration (CD68), and SP-1 expression were assessed. In vitro studies used human brain microvascular endothelial cells (HBMVECs) to examine Ang II-induced OX2R suppression, monocyte adhesion, and SP-1-mediated signaling.

CA patients exhibited significantly reduced serum Orexin B levels (3.21 ± 0.52 pg/mL) compared to healthy controls (8.56 ± 1.23 pg/mL, p < 0.01), with no change in Orexin A. OX2R expression was downregulated in the circle of Willis of CA mice. Orexin B administration attenuated aneurysm formation in WT mice, reducing aneurysm size from 3.72 ± 0.469 mm to 1.93 ± 0.252 mm (p < 0.01). This protective effect was entirely absent in OX2R-/- mice. Orexin B suppressed the expression of inflammatory mediators (IL-6, MMP-9, MCP-1, E-selectin), reduced CD68+ macrophage infiltration, and decreased SP-1 levels in WT but not OX2R-/- mice. In HBMVECs, Ang II dose-dependently reduced OX2R expression.

Orexin B inhibited Ang II-induced monocyte adhesion and SP-1-mediated pro-inflammatory signaling, effects that were abolished by OX2R siRNA or SP-1 overexpression, confirming the OX2R/SP-1 axis.