ANGPTL6 variant induces cerebral vascular dysfunction and predisposes to intracranial aneurysm in mice

Background Intracranial aneurysm (IA) is a common cerebrovascular abnormality characterized by localized dilation and wall thinning in intracranial arteries, that frequently leads to fatal sub-arachnoid hemorrhage. Pathophysiological mechanisms responsible for AI remains largely unknown, but increasing evidence suggest that genetic susceptibility plays a predominant role. We recently identified a rare nonsense variant in ANGPTL6 gene that prevented angiopoietin-like 6 (ANGPTL6) secretion and predisposed to IA. The aim of this study is now to understand why the ANGPTL6 variant predisposes to IA. Methods Angptl6 -knock in mice were generated by homologous recombination. Cerebral arteries of the circle of Willis have been analyzed under basal and hemodynamic overload conditions. Functional properties of cerebral arteries have been analyzed by pressure arteriography. Effect of recombinant ANGPTL6 have been assessed on vascular smooth muscle cells and ANGPTL6 partners have been analyzed by surface plasmon resonance. Results Angptl6 -knock in mice display endothelial dysfunction expressed by reduced NO production in response to flow in cerebral arteries. They present exaggerated dilatation of cerebral arteries under hypertensive stress, and aggravated wall damage and aneurysmal remodeling of the intima and media at arterial bifurcations of the circle of Willis under hemodynamic overload. Matrix bound ANGPTL6 decreased VSMC migration and increased adhesion and FAK signaling activation, without affecting VSMC phenotype. Surface plasmon resonance analyses identified αvβ5 integrin as a new ANPTL6 receptor. Conclusions Angptl6 -knock in mice mimicked the main features of IA in humans. ANGPTL6 appears to be an extracellular matrix component regulating vascular cell function, which may be involved in mechanosensing and generating adapted vascular cell responses to hemodynamic stress. Non-secreted ANGPTL6 variants would result in the loss of this function, thus favoring IA under conditions of hemodynamic overload.