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Postnatal Deletion of the Type II Transforming Growth Factor-&bgr; Receptor in Smooth Muscle Cells Causes Severe Aortopathy in Mice

Objective—Prenatal deletion of the type II transforming growth factor-&bgr; (TGF-&bgr;) receptor (TBRII) prevents normal vascular morphogenesis and smooth muscle cell (SMC) differentiation, causing embryonic death. The role of TBRII in adult SMC is less well studied. Clarification of this role has important clinical implications because TBRII deletion should ablate TGF-&bgr; signaling, and blockade of TGF-&bgr; signaling is envisioned as a treatment for human aortopathies. We hypothesized that postnatal loss of SMC TBRII would cause aortopathy. Approach and Results—We generated mice with either of 2 tamoxifen-inducible SMC-specific Cre (SMC-CreERT2) alleles and homozygous floxed Tgfbr2 alleles. Mice were injected with tamoxifen, and their aortas examined 4 and 14 weeks later. Both SMC-CreERT2 alleles efficiently and specifically rearranged a floxed reporter gene and efficiently rearranged a floxed Tgfbr2 allele, resulting in loss of aortic medial TBRII protein. Loss of SMC TBRII caused severe aortopathy, including hemorrhage, ulceration, dissection, dilation, accumulation of macrophage markers, elastolysis, abnormal proteoglycan accumulation, and aberrant SMC gene expression. All areas of the aorta were affected, with the most severe pathology in the ascending aorta. Cre-mediated loss of SMC TBRII in vitro ablated both canonical and noncanonical TGF-&bgr; signaling and reproduced some of the gene expression abnormalities detected in vivo. Conclusions—SMC TBRII plays a critical role in maintaining postnatal aortic homeostasis. Loss of SMC TBRII disrupts TGF-&bgr; signaling, acutely alters SMC gene expression, and rapidly results in severe and durable aortopathy. These results suggest that pharmacological blockade of TGF-&bgr; signaling in humans could cause aortic disease rather than prevent it.