Pharmacological activation of PI 3-kinase isoform p110α ameliorates abdominal aortic aneurysm formation
M Vantler, E M Berghausen, M Schorscher, M Zierden, L Gnatzy-Feik, S Baldus, S RosenkranzAbstract
Background
Abdominal aortic aneurysms (AAA) are characterized by the loss of contractile smooth muscle cells (SMCs) due to cell death and de-differentiation. Therefore, pharmacological interventions should aim to increase the number of SMCs in the diseased aortic wall. The catalytic class IA PI 3-kinase isoform p110α is a key regulator of cell proliferation and survival. Herein, we tested the hypothesis that activation of p110α increases aortic SMC content and protects from AAA development and progression.
Methods
To investigate the impact of p110α on AAA formation and progression, AAA was induced by application of porcine pancreatic elastase (PPE) in mice lacking p110α in SMCs (sm-p110α-/-) or in wild-type animals stimulated with the pharmacological p110α activator UCL-TRO-1938. Phenotypic changes in aortae were examined by ultrasound, immunohistochemistry, and histochemistry. The effects of UCL-TRO-1938 and the specific Forkhead-box O1 (FOXO1) inhibitor AS1842856 on SMC proliferation and migration were investigated by standard techniques. Downstream signaling pathways were analyzed by Western blotting.
Results
PPE treatment of sm-p110α-/- mice resulted in a significantly increased abdominal aortic diameter compared to wild-type controls after 28 days (70.2±32.5% versus 42.4±18.9%, n=9-10, p<0.05). p110α was involved in the regeneration processes during AAA progression. Vascular remodeling, SMC content, and medial cell proliferation were increased in PPE treated wild-type mice, while these processes were diminished in sm-p110α-/- aortae. In addition, elastic fibers in sm-p110α-/- aortae were characterized by more frequent breaks. Preliminary results suggest that p110α activation with UCL-TRO-1938 protected wild mice from AAA formation (40.9±15.3% versus 67.8±38.0%, n=5, respectively). UCL-TRO-1938 (10µM) induced proliferation (2.91±0.84-fold increase, p<0.05) and migration (1.81±0.17 fold increase, p<0.05) of wild-type SMCs, but not p110α-/- SMCs (1.11±0.34 (proliferation) and 1.29±0.25 (migration)). Western blot analyses of downstream signaling events revealed that UCL-TRO-1938 induces phosphorylation/activation of AKT and phosphorylation/inactivation of the transcription factor FOXO1. Inactivation of FOXO1 is essential for p110α-mediated SMC proliferation as the wild type phenotype could be completely rescued in p110α-deficient SMCs by specific inhibition of FOXO1.
Conclusions
p110α activity in SMCs protects against the development and progression of AAA by increasing SMC content in the aortic wall. The novel p110α activator UCL-TRO-1938 stimulates proliferation and migration of SMCs in vitro and ameliorates AAA formation in vivo. It therefore represents a potential pharmacological agent for stabilizing the aortic wall during AAA development and progression.