PI 3-kinase isoform p110α mediated FOXO1 inactivation protects against aortic aneurysm formation

Aims: Abdominal aortic aneurysms (AAAs) are characterized by loss of contractile smooth muscle cells (SMCs). Regenerative approaches for AAAs should therefore aim at enriching aortic SMC content. We explored the role of PI 3-kinase isoform p110, a crucial regulator of cellular proliferation, survival and phenotype, for vascular integrity and AAA disease. Methods and results: Mice lacking p110 or FOXO1 in SMCs (sm-p110-/-, sm-FOXO1-/-) were exposed to the porcine pancreatic elastase (PPE) AAA model. Phenotypic alterations were examined by ultrasound, (immuno)histochemistry, transmission electron microscopy, functional and cellular assays, and single cell RNA-sequencing (scRNA-seq) in tamoxifen-inducible ism-p110-/--eYFP lineage tracing mice. PPE treatment of sm-p110-/- mice yielded aggravated AAA formation compared to wild-type controls. AAA onset in sm-p110-/- aortae was facilitated by a subtle preexisting basal phenotype displaying smaller media area, impaired aortic wall structure, and diminished responsiveness to vasodilators. During AAA progression, PPE treated sm-p110-/- aortae were characterized by impaired vascular remodeling, reduced SMC content and medial cell proliferation, and increased elastic fiber breaks and ECM degradation. scRNA-seq revealed decreased content of proliferative and reparative SMC clusters and increased inflamed SMCs in ism-p110-/--eYFP mice. p110 deficient SMCs displayed impaired SMC proliferation, and production of elastin fibers. This phenotype was rescued by FOXO1 inactivation in p110-/- SMCs. FOXO1 deficiency in SMCs protected against AAA in PPE-treated sm-FOXO1-/- mice. Pharmacological activation of p110 ameliorated AAA in wild type mice but not in sm-FOXO1-/- mice. Relevance of p110/FOXO1 signaling in human AAA disease was indicated in patient samples. Conclusions: p110-mediated inactivation of FOXO1 in SMCs protects against AAA disease and contributes to maintaining aortic wall homoeostasis. p110 signaling promotes transition into proliferating and reparative SMC phenotypes while attenuating de-differentiation into inflammatory SMC subtypes. Our findings identify (pharmacological) activation of p110 signaling in SMCs as a new therapeutic strategy to promote prevention and regeneration of AAA disease.