Pulmonary Artery (PA) Smooth Muscle (SM) Proteins in Postnatal Sheep with High Flow Pulmonary Hypertension (PH). ♦ 146

Abstract

Placement of an aortopulmonary shunt in fetal sheep results in increased pulmonary blood flow, PH, and PA remodeling postnatally much like that seen in children with congenital heart disease and left-to-right shunts. In fetal sheep with PH due to ductal ligation, where PA blood flow is normal but PA remodeling also occurs, we reported altered PA SM expression of myosin heavy chain isoforms (MHCI), in particular, increases in MHC-B (a 200kD nonmuscle or fetal MHCI) and decreases in adult MHCI, SM1 (204kD) and SM2 (200kD). Thus, the normal conversion in PA SM from a “synthetic” to a“contractile” phenotype is impaired. This has not been examined in the high flow model of PH. Thus we obtained 3rd-4th generation PA and femoral arteries from ≈30d postnatal sheep with (n=8) and without (n=7) aortopulmonary shunts and measured contents of total and soluble protein, actin/myosin, filamin and desmin (cytoskeletal proteins), and MHCI by SDS-PAGE with 3-20% and 4% gels, respectively. 200kD MHCI were separated by westem analysis. While PA total protein was unaltered with PH, soluble protein contents and the soluble/total protein ratio were decreased 35%* and 25%*, respectively. Myosin contents were also lower with PH (3.08±0.2[SE] vs 6.54±0.8* μg/mg wet weight), while actin was unchanged, thus actin/myosin ratios were greater, 3.08±0.2 vs 1.95±0.1*. Desmin contents were unaltered by PH, but filamin was 63%* lower. Contents of 200(1.05±0.1 vs 1.90±0.3* μg/mg wet weight) and 204(2.18±0.3 vs 4.64±0.6* μg/mg wet weight) kD MHCI also were lower with PH. Furthermore, PA MHC-B expression, determined by western analysis, was greater with PH. Femoral artery SM protein contents were unaffected by PH. PA contractile and cytoskeletal proteins are significantly decreased in the presence of PH, in particular myosin, SM1, SM2 and filamin, while nonmuscle MHC-B is increased, consistent with SM growth and/or remodeling. These changes with high flow PH resemble those seen in the ductal ligation model of PH, which has normal flow, suggesting that in fetal-newborn sheep the PA either maintains or develops a synthetic SM phenotype in response to elevations in PA pressure independent of flow. *P<0.04.