An Myh11 single lysine deletion causes aortic dissection by reducing aortic structural integrity and contractility

Pathogenic variants in myosin heavy chain (Myh11) cause familial thoracic aortic aneurysms and dissections (FTAAD). However, the underlying pathological mechanisms remain unclear because of a lack of animal models. In this study, we established a mouse model with Myh11 K1256del, the pathogenic variant we found previously in two FTAAD families. The Myh11(∆K/∆K) aorta showed increased wall thickness and ultrastructural abnormalities, including weakened cell adhesion. Notably, the Myh11(∆K/+) mice developed aortic dissections and intramural haematomas when stimulated with angiotensin II. Mechanistically, integrin subunit alpha2 (Itga2) was downregulated in the Myh11(∆K/∆K) aortas, and the smooth muscle cell lineage cells that differentiated from Myh11(∆K/∆K) induced pluripotent stem cells. The contractility of the Myh11(∆K/∆K) aortas in response to phenylephrine was also reduced. These results imply that the suboptimal cell adhesion indicated by Itga2 downregulation causes a defect in the contraction of the aorta. Consequently, the defective contraction may increase the haemodynamic stress underlying the aortic dissections.