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 aneurysmand 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.

TGF-β Family Signaling in Connective Tissue and Skeletal Diseases

“…However, although the role of enhanced TGF-b signaling is well established in MFS, the mechanisms by which LDS mutations cause disease and a tissue signature for increased TGF-b signaling during aneurysm progression remain unclear. In vitro experiments consistently show that mutant receptors are expressed, traffic to the cell surface, and bind ligand but fail to phosphorylate Smad2 in response to exogenous TGF-b (Mizuguchi et al 2004;Horbelt et al 2010;Gallo et al 2014). However, histological and biochemical assessment of aortic tissue derived from patients affected by LDS, or mouse models, show a paradoxical signature of high TGF-b signaling (van de Laar et al 2011;Lindsay et al 2012;Gallo et al 2014).…”

“…In vitro experiments consistently show that mutant receptors are expressed, traffic to the cell surface, and bind ligand but fail to phosphorylate Smad2 in response to exogenous TGF-b (Mizuguchi et al 2004;Horbelt et al 2010;Gallo et al 2014). However, histological and biochemical assessment of aortic tissue derived from patients affected by LDS, or mouse models, show a paradoxical signature of high TGF-b signaling (van de Laar et al 2011;Lindsay et al 2012;Gallo et al 2014). These contrasting observations have generated controversy in the field regarding the specific role of TGF-b in the initiation and progression of aneurysm (Lavoie et al 2005;Dietz 2010;Mallat and Daugherty 2015).…”

“…However, none of these mechanisms has been validated to date. A possible paracrine mechanism is suggested by the observation that expression of TGF-b1 is increased in tissues derived from LDS-3 and LDS-4 patients and in LDS mouse models (van de Laar et al 2011;Lindsay et al 2012;Gallo et al 2014), and that treatment of LDS mouse models with losartan, which normalizes aortic root growth and aortic wall architecture in these animals, is associated with reduction of excessive TGF-b1 expression and Smad2 and Erk MAPK activation in LDS mice (Gallo et al 2014).…”

Cytochrome P450 1B1 Contributes to the Development of Angiotensin II–Induced Aortic Aneurysm in Male Apoe−/− Mice

“…Quantification of elastin fiber breaks per high-power field (Â40) per replicate (three sections per slide) of each treatment group of (n Z 5) in control and treatment groups of mice (n Z 5) was performed manually. 20 …”

Insights into ascending aortic aneurysm pathogenesis using in vivo and ex vivo imaging systems in angiotensin II-infused mice

“…Although there are multiple genetic disruptions that lead to ascending aortic aneurysms and dissection, these diseases can be mimicked by manipulations in animal models. It is worth noting that angiotensin II (Ang II) and its type 1 (AT1) receptor activation contribute to the development and progression of ascending aortic pathologies in all of these animal models (2)(3)(4)(5)(6)(7). Ascending aortic aneurysms are one risk factor for aortic dissection.…”