Pulmonary expression of the hepatocyte growth factor receptor c-Met shifts from medial to intimal layer after cavopulmonary anastomosis

Abstract

Objective Pulmonary arteriovenous malformations occur in up to 60% of patients after cavopulmonary anastomosis. We compared the effects of cavopulmonary anastomosis and pulmonary artery banding on lung gene expression in an ovine model to study the abnormal pulmonary vascular remodeling after the exclusion of inferior vena caval blood independent of reduced pulmonary blood flow. We previously demonstrated by contrast echocardiography that pulmonary arteriovenous malformations develop by 8 weeks after cavopulmonary anastomosis but not after pulmonary artery banding. Hepatocyte growth factor, a pleiotropic factor with morphogenic, mitogenic, and angiogenic activities, signals via its specific receptor c-Met to induce the antiapoptotic factor Bcl-2. In this study, we examined pulmonary artery expression of these factors and their potential role in pulmonary artery remodeling after cavopulmonary anastomosis and pulmonary artery banding. Methods Eighteen lambs aged 35 to 45 days were placed into 3 groups: cavopulmonary anastomosis, pulmonary artery banding, and control (n = 6/group). In the cavopulmonary anastomosis group, the superior vena cava was anastomosed to the right pulmonary artery in an end-to-end fashion. In the pulmonary artery banding group, the left pulmonary artery was banded to reduce blood flow to 20% of control. The control group had a simple right pulmonary artery clamp for 30 minutes. Lung was harvested for Western blot, reverse transcriptase–polymerase chain reaction, and immunostaining at 2 weeks (n = 3/group) and 5 weeks (n = 3/group) after surgery. Results The expression of c-Met mRNA after cavopulmonary anastomosis was increased by twofold compared with the control or pulmonary artery banding group. The total lung expression of c-Met by Western blot was also up regulated at 2 weeks ( P < .05). However, total lung expression of hepatocyte growth factor and Bcl-2 by Western and reverse transcriptase–polymerase chain reaction was not different from the control and pulmonary artery banding groups at both 2 and 5 weeks after surgery. Immunohistochemical analysis revealed that c-Met expression was localized to the intimal layer of the pulmonary artery in the cavopulmonary anastomosis, while its expression in the control and pulmonary artery banding lungs was localized to the medial layer. Localization of Bcl-2 on the intimal layer in lambs with cavopulmonary anastomosis followed the same pattern as c-Met. Conclusions After cavopulmonary anastomosis, pulmonary artery expression of the hepatocyte growth factor receptor c-Met and one of its downstream effectors, Bcl-2, had increased in the intimal layer and decreased in the medial layer. Because the hepatocyte growth factor signaling promotes increased endothelial cell survival, it may have a role in pulmonary artery remodeling following cavopulmonary anastomosis. In addition, the change of c-Met expression in the medial layer after cavopulmonary anastomosis suggests a possible mechanism for the smooth muscle cell alteration related to abnormal angiogenesis.