Second Heart Field-derived Cells Contribute to Angiotensin II-mediated Ascending Aortopathies
Authors: Sawada Hisashi , Katsumata Yuriko , Higashi Hideyuki , Zhang Chen , Li Yanming , Morgan Stephanie , Lee Lang H. , Singh Sasha A. , Chen Jeff Z. , Franklin Michael K. , Moorleghen Jessica J. , Howatt Deborah A. , Rateri Debra L. , Shen Ying H. , LeMaire Scott A. , Aikawa Masanori , Majesky Mark W. , Lu Hong S. , Daugherty Alan 
Published: February 2020

Background

The ascending aorta is a common location for aneurysm and dissection. This aortic region is populated by a mosaic of medial and adventitial cells that are embryonically derived from either the second heart field (SHF) or the cardiac neural crest. SHF-derived cells populate areas that coincide with the spatial specificity of thoracic aortopathies. The purpose of this study was to determine whether and how SHF-derived cells contribute to ascending aortopathies.

Methods

Ascending aortic pathologies were examined in patients with sporadic thoracic aortopathies and angiotensin II (AngII)-infused mice. Ascending aortas without overt pathology from AngII-infused mice were subjected to mass spectrometry assisted proteomics, and molecular features of SHF-derived cells were determined by single cell transcriptomic analyses. Genetic deletion of either low-density lipoprotein receptor-related protein 1 (Lrp1) or transforming growth factor-β receptor 2 (Tgfbr2) in SHF- derived cells was conducted to examine the impact of SHF-derived cells on vascular integrity.

Results

Pathologies in human ascending aortic aneurysmal tissues were predominant in outer medial layers and adventitia. This gradient was mimicked in mouse aortas following AngII infusion that was coincident with the distribution of SHF-derived cells. Proteomics indicated that brief AngII infusion, prior to overt pathology, evoked downregulation of SMC proteins and differential expression of extracellular matrix proteins, including several LRP1 ligands. LRP1 deletion in SHF-derived cells augmented AngII-induced ascending aortic aneurysm and rupture. Single cell transcriptomic analysis revealed that brief AngII infusion decreasedLrp1andTgfbr2mRNA abundance in SHF-derived cells and induced a unique fibroblast population with low abundance ofTgfbr2mRNA. SHF-specificTgfbr2deletion led to embryonic lethality at E12.5 with dilatation of the outflow tract and retroperitoneal hemorrhage. Integration of proteomic and single cell transcriptomics results identified plasminogen activator inhibitor 1 (PAI1) as the most increased protein in SHF-derived SMCs and fibroblasts during AngII infusion. Immunostaining revealed a transmural gradient of PAI1 in both ascending aortas of AngII-infused mice and human ascending aneurysmal aortas that mimicked the gradient of medial and adventitial pathologies.

Conclusion

SHF-derived cells exert a critical role in maintaining vascular integrity through LRP1 and TGF-β signaling associated with increases of aortic PAI1.

Abstract Figure

Clinical Perspective

What is new?

-

SHF-derived SMCs and fibroblasts associate with AngII-induced aortic pathologies.

-

AngII induces a distinct fibroblast sub-cluster that is less abundant for mRNAs related to major extracellular components and TGFβ ligands and receptors, but more abundant for proliferative genes.

-

TGFBR2 deletion in SHF-derived cells are embryonic lethal with significant dilatation of the outflow tract in mice.

-

SHF-specific deletion of LRP1 leads to aortic pathologies in mice, supporting the importance of SHF-derived cells in maintaining ascending aortic wall integrity.

What are the clinical implications?

-

Heterogeneity of the embryonic origins of SMCs and fibroblasts contributes to complex mechanisms of vasculopathy formation, which should be considered when investigating the pathogenesis of thoracic aortopathies.