Blockade of TGF-β (Transforming Growth Factor Beta) Signaling by Deletion of in Smooth Muscle Cells of 11-Month-Old Mice Alters Aortic Structure and Causes Vasomotor Dysfunction-Brief Report.

BACKGROUND

To test the hypothesis that smooth muscle cell (SMC) TGF-β (transforming growth factor beta) signaling contributes to maintenance of aortic structure and function beyond the early postnatal period.

METHODS

We deleted the TBR2 (type 2 TGF-β receptor) in SMC of 11-month-old mice (genotype -CreER, termed TBR2) and compared their ascending aorta structure and vasomotor function to controls (-CreER, termed TBR2).

RESULTS

We confirmed loss of aortic SMC TBR2 by immunoblotting. Four weeks after SMC TBR2 loss, TBR2 mice did not have aortic rupture, ulceration, dissection, dilation, or evidence of medial hemorrhage. However, aortic medial area of TBR2 mice was increased by 27% (0.14±0.01 versus 0.11±0.01 mm; =0.01) and medial thickness was increased by 23% (40±1.9 versus 33±1.3 μm; =0.004) compared with littermate controls. Wire myography performed on ascending aortic rings showed hypercontractility of TBR2 aortas to phenylephrine (E, 15.9±1.2 versus 10.8±0.7 mN; =0.0003) and reduced relaxation and sensitivity to acetylcholine (E, 64±14% versus 96±2%; =0.001; -logEC, 6.9±0.1 versus 7.7±0.1; =0.0001). Neither maximal relaxation nor sensitivity to sodium nitroprusside differed (E, 102±0.3% versus 101±0.3%; -logEC, 8.0±0.04 versus 7.9±0.08; >0.4 for both).

CONCLUSIONS

Loss of TGF-β signaling in aortic SMC of 1-year-old mice does not cause early severe aortopathy or death; however, it causes mild structural and substantial physiological abnormalities. SMC TGF-β signaling plays an important role in maintaining aortic homeostasis in older mice. This role should be considered in the design of clinical studies that aim to prevent aortopathy by blocking SMC TGF-β signaling.