Lineage-specific events underlie aortic root aneurysm pathogenesis in Loeys-Dietz syndrome
Elena Gallo MacFarlane, Sarah J. Parker, Joseph Y. Shin, Benjamin E. Kang, Shira G. Ziegler, Tyler J. Creamer, Rustam Bagirzadeh, Djahida Bedja, Yichun Chen, Juan F. Calderon, Katherine Weissler, Pamela A. Frischmeyer-Guerrerio, Mark E. Lindsay, Jennifer P. Habashi, Harry C. Dietz
Elena Gallo MacFarlane, Sarah J. Parker, Joseph Y. Shin, Benjamin E. Kang, Shira G. Ziegler, Tyler J. Creamer, Rustam Bagirzadeh, Djahida Bedja, Yichun Chen, Juan F. Calderon, Katherine Weissler, Pamela A. Frischmeyer-Guerrerio, Mark E. Lindsay, Jennifer P. Habashi, Harry C. Dietz
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Research Article Vascular biology

Lineage-specific events underlie aortic root aneurysm pathogenesis in Loeys-Dietz syndrome

Abstract

The aortic root is the predominant site for development of aneurysm caused by heterozygous loss-of-function mutations in positive effectors of the transforming growth factor-β (TGF-β) pathway. Using a mouse model of Loeys-Dietz syndrome (LDS) that carries a heterozygous kinase-inactivating mutation in TGF-β receptor I, we found that the effects of this mutation depend on the lineage of origin of vascular smooth muscle cells (VSMCs). Secondary heart field–derived (SHF-derived), but not neighboring cardiac neural crest–derived (CNC-derived), VSMCs showed impaired Smad2/3 activation in response to TGF-β, increased expression of angiotensin II (AngII) type 1 receptor (Agtr1a), enhanced responsiveness to AngII, and higher expression of TGF-β ligands. The preserved TGF-β signaling potential in CNC-derived VSMCs associated, in vivo, with increased Smad2/3 phosphorylation. CNC-, but not SHF-specific, deletion of Smad2 preserved aortic wall architecture and reduced aortic dilation in this mouse model of LDS. Taken together, these data suggest that aortic root aneurysm predisposition in this LDS mouse model depends both on defective Smad signaling in SHF-derived VSMCs and excessive Smad signaling in CNC-derived VSMCs. This work highlights the importance of considering the regional microenvironment and specifically lineage-dependent variation in the vulnerability to mutations in the development and testing of pathogenic models for aortic aneurysm.

Authors

Elena Gallo MacFarlane, Sarah J. Parker, Joseph Y. Shin, Benjamin E. Kang, Shira G. Ziegler, Tyler J. Creamer, Rustam Bagirzadeh, Djahida Bedja, Yichun Chen, Juan F. Calderon, Katherine Weissler, Pamela A. Frischmeyer-Guerrerio, Mark E. Lindsay, Jennifer P. Habashi, Harry C. Dietz

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Figure 1

Tbr1MR/+ mice develop dilation of the aortic root in association with localized increase in Smad2/3 phosphorylation.

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Tbr1MR/+ mice develop dilation of the aortic root in association with l...
(A) Masson’s trichrome staining of the proximal aorta of control (Tbr1+/+) and mutant (Tbr1MR/+) mice at 20 weeks of age. Scale bars: 1,000 μm. The dashed rectangles indicate the areas used for in situ analyses. (B) Aortic diameters of mice of the indicated genotypes at 16 weeks of age. F, females (n = 13 for Tbr1+/+ and n = 10 for Tbr1MR/+); M, males (n = 12 for Tbr1+/+; n = 6 for Tbr1MR/+). No sex-specific differences were observed within any experimental group. P values refer to Kruskal-Wallis test with FDR-based multiple comparison correction. (C) Representative parasternal long-axis echocardiographic view showing the boundaries from which measurements were taken for aortic root (yellow arrows) and ascending aorta (blue arrows). (D) Representative immunofluorescence (IF) images of the aortic root of 16-week-old mice of the indicated genotypes probed with an anti–p-Smad2 or an unrelated anti–p-Smad2/3 antibody. Scale bars: 50 μm. Image enhancement for visual display was applied uniformly to all panels. Experiment was conducted at least 3 times. (E) Representative IF images of the aortic root and ascending aorta of 12-week-old mice probed with an anti–p-Smad2 antibody. Scale bars: 50 μm. Image enhancement for visual display was applied uniformly to all panels. Experiment was conducted at least 3 times. (F) Immunoblot of protein lysates from the aortic root and ascending aorta of mice of the indicated genotypes at 24 and 32 weeks of age after probing with antibodies that recognize p-Smad2 and β-actin (n = 3). Quantification of p-Smad2 after normalization to β-actin is shown on the right. P values refer to 1-way ANOVA followed by Holm-Sidak’s multiple comparisons test. Numerical data are presented as scatter dot-plots with boxes, with the box denoting the mean; error bars identify the 95% confidence interval.