MiRNA-34a deficiency impairs endothelial function and stimulates its proliferation-the impact on angiotensin II-induced abdominal aortic aneurysm

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): This work was supported by National Science Center grant SONATA BIS No. 2016/22/E/NZ3/00405 (AGP) and the project for PhD students and Young Scientists FBBB N19/MNW/000005 (AK). Background Abdominal aortic aneurysm (AAA) is a permanent dilatation of the abdominal aorta, which bears a high risk of rupture and sudden death of the patient. The pathogenic mechanisms of AAA remain elusive and surgical intervention represents the only treatment option. The involvement of endothelial cells (ECs) in the formation of aneurysms is still a matter of debate. Purpose As AAA is an age-related cardiovascular disease, we aimed to investigate the role of age-related miRNA-34a in ECs in pathogenesis of AAA. The deficiency of this miRNA has been so far proved preventive in several cardiovascular disease settings; however, the detailed mechanisms of protection have not been elucidated and the impact on EC function has not been addressed. Methods In vitro experiments were performed on primary human aortic ECs with RNA interference-mediated depletion of miRNA-34a. Animal studies were done on tamoxifen-induced EC-specific knockout of miRNA-34a or Rainbow mice. For aneurysm studies, we used an angiotensin II (AngII)-based model. Aortas and ECs were characterised using intravital microscopy, atomic force microscopy, fluorescent stainings, EPR, blood pressure measurements and Doppler flowmetry. Results Deficiency of miRNA-34a in vivo led to age-dependent EC dysfunction, as evidenced by a decreased length and coverage of glycocalyx and reduced NO production, with a concomitant increase in arterial stiffness, leukocyte adhesion and prothrombotic phenotype. However, despite detrimental effects of miRNA-34a deficiency on EC function, it did not result in a higher aneurysm incidence in young mice in AngII model. Quite surprisingly, the formation of the aneurysm was abrogated in older miRNA-34aEC-KO animals. Changes in expression of AngII receptors, proinflammatory molecules or blood pressure could not account for these anti-AAA effects of miRNA deficiency. Instead, we found significantly enhanced proliferation of intimal ECs upon AngII in young and old miRNA-34aEC-KO mice. The results were further corroborated in vitro, where we demonstrated loss of endothelial markers, with a concomitant increase in proliferation and preserved angiogenic function of miRNA-34aEC-KO. Additionally, we used multicolour EC lineage tracing to address the significance of endothelial proliferation during aneurysm formation. In stable aneurysms, we observed a polyclonal expansion of ECs in the intimal layer and, particularly, in the aneurysmal area. Of note, we did not detect any EC proliferation in the ruptured AAA. Conclusions miRNA-34a deficiency impairs EC function and stimulate EC proliferation, the latter presumably determined protection against Ang-II AAA in older mice. Therefore, we postulate that EC proliferation plays a more significant role than the preservation of EC function in protection against AAA. The fine-tuning of ECs proliferation may have a therapeutical role in the treatment of aneurysms.