Exploring adventitial pericyte dysfunction and MEK/ERK signalling as therapeutic targets in thoracic aortic aneurysm

Abstract Background Thoracic aortic aneurysm (TAA) is a life-threatening condition characterized by progressive aortic dilation and structural weakening, often culminating in dissection or rupture. Despite advancements in imaging and surgical techniques, effective pharmacological interventions remain lacking, leaving a significant clinical gap. Recent studies highlight the adventitia and its vascular network, the vasa vasorum (VV), as key contributors to TAA pathology. The role of adventitial pericytes (APCs) in maintaining VV integrity and aortic wall homeostasis, and their potential dysfunction in TAA, is poorly understood. Purpose This study investigates APC involvement in VV remodelling during TAA progression and explores the therapeutic potential of targeting the MEK/ERK pathway to restore APC function and mitigate aneurysm development. Methods Human aortic adventitia samples from TAA patients (n=9) and controls (n=6) were analysed via histology and immunohistochemistry to assess VV remodelling and APC coverage. APCs were isolated, cultured, and characterized through immunocytochemistry, proliferation assays, migration assays, angiogenic tube formation assays, gelatinase assays, ELISA, RT-qPCR, and Western blotting. Finally, TAA-APCs subjected to in-vitro treatment using PD0325901 (n=6) in a dose of 250nM every 48h or DMSO (vehicle, n=6) for ten days, followed by functional and molecular analyses. Results Histological analysis revealed significant VV remodelling in TAA samples, with decreased VV density (p<0.01), increased luminal diameter (p<0.01) and wall thickness (p<0.01) compared to controls. APC coverage of VV was markedly reduced in TAA (p<0.01), correlating with increased VV size, and associated with increased APCs detachment (p<0.01). Compared to controls, isolated TAA-APCs showed higher expression of P-ERK (p<0.05), and exhibited increased proliferation (p<0.0001), migration (p<0.05), and impaired angiogenic support (p<0.05) associated with increased anti-angiogenic factors ANGPT-2 and TSP-1 (p<0.01), alongside increased secretion of inflammatory cytokines IL-6 and MCP-1 (p<0.05), MMP-9 activity and gene expression with dysregulated fibronectin/collagen formation (p<0.05). In-vitro, MEK-inhibition by PD0325901 restored APCs contractile phenotype, regulated proliferation (p<0.01), migration (p<0.0001), and enhanced angiogenic capacity (p<0.0001) while inhibiting ANGPT-2 (p<0.05), IL-6, MCP-1 (p<0.01), fibronectin secretion (p<0.01), and MMP-2/MMP-9 activity (p<0.05) and increased gene expression of TIMP-2 (p<0.05) with no effect on cell viability. Conclusion This study identifies APC dysfunction as a key driver of VV remodelling in TAA, with MEK/ERK hyperactivation playing a crucial role. Targeting this pathway with selective MEK inhibitor restores APC function and offers a promising therapeutic strategy to prevent aneurysm progression, addressing the urgent need for pharmacological interventions in TAA management.