Angiotensin II–dependent TGF-β signaling contributes to Loeys-Dietz syndrome vascular pathogenesis
Elena M. Gallo, … , David L. Huso, Harry C. Dietz
Elena M. Gallo, … , David L. Huso, Harry C. Dietz
Published December 20, 2013
Citation Information: J Clin Invest. 2014;124(1):448-460. https://doi.org/10.1172/JCI69666.
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Research Article

Angiotensin II–dependent TGF-β signaling contributes to Loeys-Dietz syndrome vascular pathogenesis

Abstract

Loeys-Dietz syndrome (LDS) is a connective tissue disorder that is characterized by a high risk for aneurysm and dissection throughout the arterial tree and phenotypically resembles Marfan syndrome. LDS is caused by heterozygous missense mutations in either TGF-β receptor gene (TGFBR1 or TGFBR2), which are predicted to result in diminished TGF-β signaling; however, aortic surgical samples from patients show evidence of paradoxically increased TGF-β signaling. We generated 2 knockin mouse strains with LDS mutations in either Tgfbr1 or Tgfbr2 and a transgenic mouse overexpressing mutant Tgfbr2. Knockin and transgenic mice, but not haploinsufficient animals, recapitulated the LDS phenotype. While heterozygous mutant cells had diminished signaling in response to exogenous TGF-β in vitro, they maintained normal levels of Smad2 phosphorylation under steady-state culture conditions, suggesting a chronic compensation. Analysis of TGF-β signaling in the aortic wall in vivo revealed progressive upregulation of Smad2 phosphorylation and TGF-β target gene output, which paralleled worsening of aneurysm pathology and coincided with upregulation of TGF-β1 ligand expression. Importantly, suppression of Smad2 phosphorylation and TGF-β1 expression correlated with the therapeutic efficacy of the angiotensin II type 1 receptor antagonist losartan. Together, these data suggest that increased TGF-β signaling contributes to postnatal aneurysm progression in LDS.

Authors

Elena M. Gallo, David C. Loch, Jennifer P. Habashi, Juan F. Calderon, Yichun Chen, Djahida Bedja, Christel van Erp, Elizabeth E. Gerber, Sarah J. Parker, Kimberly Sauls, Daniel P. Judge, Sara K. Cooke, Mark E. Lindsay, Rosanne Rouf, Loretha Myers, Colette M. ap Rhys, Kathleen C. Kent, Russell A. Norris, David L. Huso, Harry C. Dietz

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Figure 3

Transgenic mice overexpressing the Tgfbr2G357W mutant allele recapitulate vascular LDS phenotypes.

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Transgenic mice overexpressing the Tgfbr2G357W mutant allele recapitulat...
(A) Schematic representation of control (1x Tg-Tgfbr2) and mutant (1x Tg-Tgfbr2GW) transgenic constructs, both under the control of the Rosa26 promoter. (B) Expression of endogenous and transgenic cDNA in aortic tissue of 1x Tg-Tgfbr2, 1x Tg-Tgfbr2GW, and control mice, as evaluated by RT-PCR and indicated underneath the blots. After digestion with the restriction enzyme MfeI, which cuts the transgenic (both control and mutant) but not the endogenous cDNA, the PCR product was incubated with a radioactive probe specific for the Tgfbr2 cDNA (the black lines indicate lanes that were run on the same gel but were noncontiguous). (C) Aortic root diameter of 24-week-old mice, as measured by echocardiography (n ≥ 6). (D) Quantification of elastin fiber breaks per high-power field in control and mutant transgenic mice (n ≥ 6) and representative VVG-stained aortic root sections from 24-week-old wild-type and transgenic mice. (C and D) The upper and lower margins of the box define the 75th and 25th percentiles, respectively; the internal line defines the median, and the whiskers define the range. Scale bar: 40 μm. (E) Representative images of vascular anatomy in control and transgenic mouse models. (F) Kaplan-Meier survival curve showing reduced life span for 2x Tg-Tgfbr2GW mice but not for 1x Tg-Tgfbr2 and 1x Tg-Tgfbr2GW mice (wild-type, n = 25; 1x Tg-Tgfbr2, n = 23; 1x Tg-Tgfbr2GW, n = 26; 2x Tg-Tgfbr2GW, n = 30). *P < 0.05, ††P < 0.00005.