Rare coding variants in CTSO, a potential new actor of arterial remodeling, are associated to familial intracranial aneurysm

Background Intracranial aneurysm (IA) is a common cerebrovascular abnormality characterized by localized dilation and wall thinning in intracranial arteries, that frequently leads to fatal vascular rupture. The mechanisms underlying IA formation, growth and rupture are mostly unknown, and while increasing evidence suggest a genetic component of IA, identification of specific genes or causal molecular pathways remains largely inconclusive and only a small fraction of the risk attributable to genetics for IA in the general population. Methods: Here, we combined whole exome sequencing and identity-by -descent analyses with functional investigations to identify rare IA predisposing variants in familial forms of IA and understand their contribution to the pathophysiology of IA. Results We identified two rare missense variants in the CTSO gene shared by all the affected relatives in two large pedigrees with multiple IA-affected relative. CTSO encodes for the cysteine-type papain-like cathepsin CTSO. Functional analyses revealed that CTSO acts as an extracellular protease controlling vascular smooth muscle cell migration and adhesion to the extracellular matrix. CTSO depletion, as well as expression of the two CTSO variants, which were poorly secreted, led to increase the amount of fibronectin. This effect is associated with a marked increase in VSMC stiffness which was rescued by exogenous CTSO. Conclusions This report identifies rare CTSO variants in familial IA patients and suggests that the increased susceptibility to IA induced by these variants is likely related to their primary effects on the vascular tissue, and more particularly on the media layer of the wall of cerebral arteries. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was funded by the French national research agency (ANR) (Programme d Investissements d Avenir ANR6-16-IDEX-0007 [NeXT Initiative], ANR-15-CE17-0008-01 [to GL], ANR-21-CE17-0006 [to RBo] and ANR-21-CE14-0016 [to A-CV]), the French Ministry of Health (clinical trial [NCT02848495][1] to RBo), Fondation pour la Recherche Médicale (R22131NN-RAD22168NNA to GL), Institut de France-Académie des Sciences (Lamonica Award to GL, supporting M-AM) and the local fund Genavie (to MF and RR). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Institutional Review Boards (Comité consultatif sur le traitement de l information en matière de recherche dans le domaine de la santé, Commission Nationale de l Informatique et des Libertés), the Ethics Committees of Nantes, the French Ministry of Research (n. DC-2011-1399) and by the Comité de Protection des Personnes gave ethical approval for this work (Clinical Trial [NCT02712892][2]). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT02848495&atom=%2Fmedrxiv%2Fearly%2F2023%2F02%2F02%2F2023.01.31.23285168.atom [2]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT02712892&atom=%2Fmedrxiv%2Fearly%2F2023%2F02%2F02%2F2023.01.31.23285168.atom