Comparison of expression of contractile proteins and myosin heavy chain isoforms (MHCI) in ovine aorta (Ao) and bladder from early fetal through late neonatal periods

Smooth muscle (SM₁ and SM₂) and nonmuscle (MHC-B) MHCI in Ao and bladder are developmentally regulated. However, their patterns of expression are not fully described, and it is unclear if changes occur with hormonal or functional alterations prior to or at birth. Thus we quantified MHCI and contractile proteins over a prolonged developmental period using Ao and bladder from female fetal (n= 19, 72 to 140d; term- 143d) and newborn (n=25; 1 to 120d) sheep. Tissues were analyzed for total and soluble protein contents (μg/mg wet weight), actin, MHC and MHCf contents (μg/mg wet weight) by SDS-PAOE, using 3-20% gradient and 4% gels, and 200 kDa MHCI by Western Analysis with SM₂ and MHC-B specific antisera. Ao proteins gradually rose between ≤ 100d gestation (n=6) and ≥3 mos after birth (n=9): total protein from 65±6 [SEM] to 92±8 (R=0.40, p=0.007), soluble protein 37±3 to 58±5 (R=0.48, p=0.001), actin 3.9±0.9 to 16±2 (R=0.62, p<0.001), and MHC 2.1±0.2 to 4.5±0.5 (R=0.52, p<0.001). Actin/MHC ratios also rose 2.4-fold(R=0.62, p<0.001). In contrast, bladder proteins generally increased (p<0.001, ANOVA) before birth and remained unchanged thereafter: total protein from 46±7 (≤100d gestation, n=6) to 78±4 (130-140d gestation, n=8) to 81±6 (≥3 mos after birth, n=9); soluble protein 38±5 to 58±5 to 69±5, and actin 4.4±0.3 to 12±2 to 19±1; MHC, however, gradually rose from 2.6±0.2 to 6.5±0.6 (R=0.62, p<0.001). 204 kDa MHCI content in Ao and bladder increased 4.3-fold (R=0.68) and 1.5-fold (R=0.58; p<0.001), respectively, by ≥3 mos. Although 200 kDa MHCI content in Ao was unchanged, averaging 1.4±0.1 throughout development, expression of SM₂ increased 80% while MHC-B fell proportionally. In contrast, bladder 200 kDa MHCI content rose throughout development, increasing 3-fold by ≥3 mos after birth (R=0.64, p<0.001); however, only SM₂ was expressed. Whereas Ao proteins and MHCI gradually rise throughout development, demonstrating no association with known prenatal events, most bladder proteins increase significantly during the last 3 wks of gestation and the only 200 kDa MHCI expressed was SM₂. These differences in the patterns of smooth muscle protein expression and ontogeny could be due to differing function of these two smooth muscle types during development.