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 4

Defective TGF-β receptor signaling in LDS VSMCs in response to exogenous ligand but not under normal culture conditions.

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Defective TGF-β receptor signaling in LDS VSMCs in response to exogenous...
(A) Aortic VSMCs derived from wild-type and Tgfbr2G357W/+ mice were starved for 24 hours in 2% serum and then exposed to 10 or 1 ng/ml TGF-β1 for 1 hour. Signaling events were assayed by Western blot (the black line indicates lanes that were run on the same gel but were noncontiguous) (n = 3). (B) Western blot analysis of wild-type and Tgfbr2+/– VSMCs stimulated as in A (n = 3). (C) Western blot analysis of wild-type and 2x Tg-Tgfbr2GW VSMCs stimulated as in A (n = 3). (D) Levels of pSmad2 in unstimulated control and Tgfbr2G357W/+ VSMCs grown in 5% serum to approximately 80% confluence prior to analysis (n = 4). (E) Analysis of Tgfb1, Tgfb2, and Tgfb3 expression in control and Tgfbr2G357W/+ VSMCs cultured as in D (n = 4). 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. *P < 0.05.