Abstract 106: Young Tgfbr2 G357W/+ Mice Have Decreased Expression of TGF-β Ligands and Receptors in the Proximal Aorta, Aortic Root Dilation, and Aortic Elongation

Introduction: Tgfbr2 G357W/+ mice have a loss-of-function Tgfbr2 allele ( G357W ) that is orthologous to an allele found in humans with Loeys-Dietz syndrome (LDS). Tgfbr2 G357W/+ mice have kyphosis, aortic dilation and elongation, and die suddenly from aortic rupture. Elevations of mRNA encoding TGF-β ligands in cultured vascular smooth muscle cells from Tgfbr2 G357W/+ mice and LDS patients—as well as increased expression of Tgfb1 and Col1a1 and elevation of both P-Smad2 and P-ERK1/2 in aortic roots of older (24-36-week) Tgfbr2 G357W/+ mice—suggest that paradoxically increased TGF-β signaling might be responsible for aortic pathology in LDS. Hypothesis: We hypothesized that downregulation of TGF-β signaling components accompanies the development of aortic pathology in young Tgfbr2 G357W/+ mice. Methods: We performed anatomic and gene-expression studies on 8- and 12-wk-old Tgfbr2 G357W/+ mice and wild type (WT) littermates. For anatomic studies, mice were perfusion-fixed with formalin, and aortic length was measured in situ. Aortic roots as well as ascending (ASA), descending thoracic (DTA) and abdominal aortas (AA) were then embedded in OCT. Frozen sections were stained with H & E. External and internal elastic lamina lengths, aortic wall thickness and medial areas were measured. For gene expression studies, mice were saline-perfused, and the aortic root, ASA, and arch were snap frozen en bloc. RNA was extracted and TGF-β ligand and receptor mRNA were measured. Results: LDS mice (12 wk old; n = 7-9 vs 12 WT) had elongated ASA, arch, and DTA (~20%; P≤0.02), their aortic roots were dilated (20%; P<0.001), and their DTA wall thickness and medial areas were decreased (15%; P<0.01). No aortic wall hematomas were observed, and Prussian Blue staining was absent in aortic sections. mRNA encoding Tgfb1 , Tgfb2, Tgfbr1, Tgfbr3, Serpine1 , and LoxL1 were decreased in LDS mouse aortas (20-34%; P<0.05 for all; n=9-10). LDS mice (8 wk old; n = 10 vs 12 WT) had only borderline decreased aortic Tgfbr1 mRNA. Conclusions: In Tgfbr2 G357W/+ mice, development of aortic pathology is accompanied by decreased expression of several TGF-β signaling pathway components. These data suggest that the G357W loss-of-function allele causes aortopathy via an early reduction of aortic TGF-β signaling.