Alterations in TGF-β1 expression in lambs with increased pulmonary blood flow and pulmonary hypertension

The mechanisms responsible for pulmonary vascular remodeling in congenital heart disease with increased pulmonary blood flow remain unclear. We developed a lamb model of congenital heart disease and increased pulmonary blood flow utilizing an in utero placed aortopulmonary vascular graft (shunted lambs). Morphometric analysis of barium-injected pulmonary arteries indicated that by 4 wk of age, shunts had twice the pulmonary arterial density of controls (P < 0.05), and their pulmonary vessels showed increased muscularization and medial thickness at both 4 and 8 wk of age (P < 0.05). To determine the potential role of TGF-β1 in this vascular remodeling, we investigated vascular changes in expression and localization of TGF-β1 and its receptors TβRI, ALK-1, and TβRII in lungs of shunted and control lambs at 1 day and 1, 4, and 8 wk of life. Western blots demonstrated that TGF-β1 and ALK-1 expression was elevated in shunts compared with control at 1 and 4 wk of age (P < 0.05). In contrast, the antiangiogenic signaling receptor TβRI was decreased at 4 wk of age (P < 0.05). Immunohistochemistry demonstrated shunts had increased TGF-β1 and TβRI expression in smooth muscle layer and increased TGF-β1 and ALK-1 in endothelium of small pulmonary arteries at 1 and 4 wk of age. Moreover, TβRI expression was significantly reduced in endothelium of pulmonary arteries in the shunt at 1 and 4 wk. Our data suggest that increased pulmonary blood flow dysregulates TGF-β1 signaling, producing imbalance between pro- and antiangiogenic signaling that may be important in vascular remodeling in shunted lambs.