CHARACTERIZATION OF THE VASCULAR PATHOLOGY IN THE ACTA2 R258C MOUSE MODEL AND CEREBROVASCULAR CHARACTERIZATION OF THE ACTA2 NULL MOUSE
Date of Graduation
Masters of Science (MS)
Dianna Milewicz MD PhD
Ananth Annapragada PhD
Jaroslaw Aronowski PhD
Siddharth Prakash MD PhD
Yang Xia MD PhD
Mutations in ACTA2, the gene encoding for smooth muscle α-actin, predispose patients to a wide range of vascular diseases and is most commonly associated with thoracic aortic aneurysms (TAAD) and dissections (TAAD) and strokes. TAAD in patients is characterized by aortic media degeneration and loss in contractile force generation followed by aortic enlargement and subsequent rupture. Most stroke cases associated with ACTA2 are described as moyamoya-like cerebrovascular incidents characterized by distal occlusion of the internal carotid artery, stenosis of arteries in the Circle of Willis, and straightening of cerebral arteries. Patient samples are scarcely available for analysis, and the few obtained are from end stages of the disease. For these reason, we decided to study the causative mechanisms of vascular disease using the Acta2R258C transgenic and Acta2-/- mouse models.
The aortic phenotype was studied using the transgenic mouse model bred with Acta2-/- mice to decrease the ACTA2 wildtype to mutant ratio. Acta2+/+ R258C TGmice have decreased aortic contractility and mild medial wall degeneration but no evidence of aortic enlargement was observed. However, Acta2+/- R258C TG mice showed severe aortic wall degeneration, elastic fiber rupture and proteoglycan accumulation along with significant aortic dilation. After carotid artery ligation, Acta2+/- R258C TG mice presented with an excessive proliferative response to injury, leading to increased inflammatory response, unresolved thrombi and severe occlusion of the lumen.
Cerebral imaging and histology were studied in WT, Acta2+/-, Acta-/- mouse mode. Straightening of the cerebrovascular arteries was observed in Acta2+/- and Acta2-/- mice when compared with WT mice. Narrowing and/or obstruction of arteries were also present in the Acta2 mutant mice, in particular in the internal carotid arteries. Histopathologic analysis showed thickening of the medial layer in both large and small arteries throughout the vasculature with decreased cell density in the large arteries.
We were able to recapitulate significant characteristics of the aortic and cerebrovascular pathology seen in patients with ACTA2 mutations in our Acta2 mouse models, proving to be a valuable tool to study the underlying mechanisms of vascular disease. Furthermore, both aneurysm formation and SMC proliferative response were exacerbated by decreasing the amount of endogenous Acta2 in our transgenic model. The severity of the cerebrovascular pathology did not vary between Acta2+/- and Acta-/-, suggesting a dose dependent effect in these mice. Meanwhile, the Acta2 R258C mutation appears to have a dominant negative effect, as its effects are inversely correlated to the amount of endogenous actin in an organism.
ACTA2, Aneurysm, Dissection, Aorta, Stroke, Cerebrovascular, Mouse Model