Mechanisms of Smooth Muscle Cell Differentiation Are Distinctly Altered in Thoracic Aortic Aneurysms Associated with Bicuspid or Tricuspid Aortic Valves

Abstract

Cellular and molecular mechanisms of thoracic aortic aneurysm are not clear and therapeutic approaches are mostly absent. Thoracic aortic aneurysm is associated with defective differentiation of smooth muscle cells (SMC) of aortic wall. Bicuspid aortic valve (BAV) comparing to tricuspid aortic valve (TAV) significantly predisposes to a risk of thoracic aortic aneurysms. It has been suggested recently that BAV-associated aortopathies represent a separate pathology comparing to TAV-associated dilations. The only proven candidate gene that has been associated with BAV remains NOTCH1. In this study we tested the hypothesis that Notch-dependent and related TGF-β and BMP differentiation pathways are differently altered in aortic SMC of BAV- vs. TAV-associated aortic aneurysms. SMC were isolated from aortic tissues of the patients with BAV- or TAV-associated aortic aneurysms and from healthy donors used as controls. Gene expression was verified by qPCR and Western blotting. For TGF-β induced differentiation SMC were treated with the medium containing TGF-β1. To induce proosteogenic signaling we cultured SMC in the presence of specific osteogenic factors. Notch-dependent differentiation was induced via lentiviral transduction of SMC with activated Notch1 domain. MYOCD expression, a master gene of SMC differentiation, was down regulated in SMC of both BAV and TAV patients. Discriminant analysis of gene expression patterns included a set of contractile genes specific for SMC, Notch-related genes and proosteogenic genes and revealed that control cells form a separate cluster from both BAV and TAV group, while BAV- and TAV-derived SMC are partially distinct with some overlapping. In differentiation experiments TGF-β caused similar patterns of target gene expression for BAV- and TAV derived cells while the induction was higher in the diseased cells than in control ones. Osteogenic induction caused significant change in RUNX2 expression exclusively in BAV group. Notch activation induced significant ACTA2 expression also exclusively in BAV group. We show that Notch acts synergistically with proosteogenic factors to induce ACTA2 transcription and osteogenic differentiation. In conclusion we have found differences in responsiveness of SMC to Notch and to proosteogenic induction between BAV- and TAV-associated aortic aneurysms.

Enlightening the Association between Bicuspid Aortic Valve and Aortopathy

“…Osteogenic induction caused elevated RUNX2 expression in BAV patients, enhancing calcification in BAV-derived SMCs. In addition, NOTCH activation was identified to significantly increase ACTA2 expression specifically in BAV patients, leading to increased osteogenic differentiation in SMCs [ 48 ]. Finally, decreased expression of Bcl-2, a mediator of apoptosis, has been identified in BAV aortas and may be involved in SMC apoptosis [ 49 ].…”

Non‐coding RNAs in aortic dissection: From biomarkers to therapeutic targets

“…During AD pathogenesis, the dysfunctional VSMCs are considered to be one of the most important factors, mainly including apoptosis and phenotype switching. 29 VSMC phenotypic transformation is a biological process which is characterized by the transformation of a contractile (differentiated) phenotype into a synthetic (dedifferentiated) phenotype that could occur under the influence of the environment including signal transduction, gene transcription and epigenetic modification. 30 Several molecular mechanisms are involved in this process, such as serum response factor (SRF), Krüppel-like factor 4 (KLF4), forkhead box O 4 (FOXO4), microRNAs, ten-eleven-translocation 2 (TET2), Rho-actin and transforming growth factor-β (TGF-β).…”

Role of calcification in aortic degeneration

“…При исследовании уровня экспрессии генов в культурах гладкомышечных клеток пациентов с аневризмой грудной аорты нами было показано, что уровень транскрипции маркера остеогенной дифференцировки BMP2 повышен в ГМК при аневризме, ассоциированной с бикуспидальным аортальным клапаном. Повышение BMP2 при аневризме аорты у пациентов с бикуспидальным аортальным клапаном может означать, что сигнальные пути, отвечающие за кальцификацию, вносят вклад в развитие аневризмы [71]. Согласно данным другого нашего исследования, в эндотелиальных клетках BMP2 также был повышен при аневризме.…”

“…Но каким образом мутации в гене NOTCH1 или изменения в активности сигнального пути Notch влияют на этот процесс, остается неизвестным. В наших исследованиях мы также показали, что при аневризме грудной аорты происходят изменения активности сигнального пути Notch и BMP даже в отсутствии мутаций в генах Notch, и эти нарушения, по нашему мнению, вносят свой вклад в развитие заболевания [70,71].…”