TGFb-Dependent Cell-Matrix Interactions in Thoracic Aortopathy

Yale University, New Haven CT

Investigators

Abstract

PROJECT SUMMARY – PROJECT 2 Thoracic aortic disease (TAD), including aneurysms, dissection, and rupture, are responsible for significant morbidity and mortality afflicting both sexes, young and old alike. Findings over many years show that aberrant activity of transforming growth factor-beta (TGFβ) plays an important role in TAD, yet controversy remains regarding the precise mechanisms. A prevailing paradigm invokes increased TGFβ signaling as causing TAD, however a collection of pathologic variants in genes encoding TGFβ receptors, ligands, and effectors that are associated with hereditary TAD, called Loeys-Dietz syndrome, are characterized as loss-of-function. Whether paradoxical TGFβ overactivity in advanced aortic lesions of Loeys-Dietz syndrome is secondary, and either pathological vs. compensatory, is unknown and mechanisms driving increased signaling in the context of heterozygous, functionally null alleles have not been defined. This lack of understanding continues to hinder the identification of improved therapeutic approaches. We, and others, have proposed an alternative hypothesis that decreased TGFβ signaling predisposes to early development of TAD. In previous work, we showed that disruption of TGFβ signaling in the immature aorta of mice impairs vessel wall homeostasis. We have extended our investigations to the mature aorta. Preliminary experiments demonstrate the unexpected findings of a vulnerable aortic phenotype within days of disrupting TGFβ signaling. Increased blood pressure or intense exercise for 30 minutes cause hemorrhagic lesions of the thoracic aorta. Characterization of these lesions prior to time-dependent responses to injury provides an unparalleled appreciation of initial mechanisms causing aortic dissection. Whole transcriptome RNA sequencing has identified rapid downregulation of numerous transcripts for proteins linking extracellular matrix to transmembrane receptors to adaptor molecules to cytoskeleton required for mechanotransduction. The overall goal of this project is to understand how and when changes induced by altered TGFβ signaling and altered expression of TGFβ-dependent proteins result in TAD. We hypothesize that (i) decreased TGFβ signaling precedes and exacerbates aortopathy, (ii) disruption of TGFβ signaling impairs mechanotransduction, and (iii) TGFβ-dependent impairment of medial cell-matrix interactions increases aortic vulnerability with each of these mechanisms being perturbed by maladaptive or compensatory responses to altered wall stresses from aortic dilatation. To test these hypotheses, we will use a combination of genetically modified mouse models, clinically relevant triggers of increased blood pressure and cardiac inotropy, and human specimens. The work will link mechanisms of TAD from altered TGFβ signaling to that of other genetic etiologies affecting the ECM (Project 3) and the actomyosin apparatus (Project 1) and leverage rapid candidate gene screening in humanized zebrafish (Project 5) and integrative computational modeling (Project 4). Successful completion of Project 2 will advance our understanding of how and when TGFβ signaling governs medial integrity and how this understanding can identify new therapeutic targets.