Nonmuscle myosin heavy chain-B expression in balloon-dilated and stented arteries: A study in the atherosclerotic Yucatan micropig

Background. Restenosis after balloon angioplasty is in part due to remodelling, whereas restenosis after stenting is entirely due to neointima formation. Nonmuscle myosin heavy chain-B (NMMHC-B) is expressed by vascular smooth muscle cells and because of its overexpression in restenotic lesions after balloon angioplasty, NMMHC-B is proposed as a potential therapeutic target. Because the mechanisms underlying restenosis after balloon angioplasty or after stenting are different we hypothesised that the expression of NMMHC-B would differ in balloon-dilated versus stented arteries. Methods. To study the localisation and time course of expression of NMMHC-B, we performed stenting or balloon dilation in peripheral arteries of 16 atherosclerotic Yucatan micropigs and used serial intravascular ultrasound (IVUS) and angiography to measure geometric dimensions following balloon angioplasty or stenting. In situ hybridisation techniques were used to detect NMMHC-B mRNA. 5'-bromo-2'- deoxyuridine (BrdU) was administered to detect proliferating cells. By counting the number of silver grains in the different layers of the artery, we could compare the amount of expression at the different time points between the groups. Results. In intima and media, NMMHC-B expression increased after balloon dilation and stenting and peaked at 7 days. In stented arteries, the expression of NMMHC-B remained high for up to 42 days after injury, whereas in balloon-dilated arteries it had normalised. In the adventitia of balloon-dilated arteries, but not of stented arteries, NMMHC-B expression peaked at 7 days. NMMHC-B expression was not limited to proliferating cells. Conclusion. NMMHC-B is expressed near sites of active repair after arterial injury, but not limited to proliferating cells. The different pattern of NMMHC-B expression after balloon dilation compared with stenting may be related to arterial remodelling, because stented arteries that do not remodel lack this conspicuous adventitial expression at 7 days.