Effect of maternal administration of betamethasone on peripheral arterial development in fetal rabbit lungs

Objectives: Glucocorticoids promote lung maturation and reduce the incidence of respiratory distress syndrome in premature newborns. We hypothesized that betamethasone (BM), which is known to induce thinning of the alveolar walls, would also thin the arterial media and adventitia of intra-parenchymatic vessels in developing rabbit lungs. Study Design: 112 fetuses from 21 time-mated, pregnant, giant white rabbits received maternal injections of BM at either 0.05 or 0.1 mg/kg/day on days 25-26 of gestational age. Controls received either saline (10 does, 56 fetuses) or no injection (10 does, 59 fetuses). Fetuses were harvested from day 27 onwards until term (day 31). 44 additional fetuses (8 does) were harvested between days 23 and 26. Endpoints were wet lung-to-body weight ratio, vascular morphometric indices and immunohistochemistry staining for α-smooth muscle actin, Flk-1, vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS). ANOVA (Tukey's test) and independent t test (p < 0.05) were used for comparison between BM and saline groups. Results: Maternal BM injected on days 25-26 to pregnant rabbits induced a significant decrease in fetal body and lung weight and the lung-to-body weight ratio in the preterm pups shortly after injection. BM led to a dose-dependent thinning of the arterial media and adventitia (pulmonary arteries with an external diameter (ED) of <100 μm), to an increase in the percentage of non-muscularized peripheral vessels (ED <60 μm), in eNOS and VEGF immunoreactivity of the endothelial and smooth muscle cells in the pulmonary vessels and to an increase in Flk-1-positive pulmonary epithelial cell density. Conclusions: Maternal administration of BM caused thinning of the arterial wall of pulmonary vessels (ED <100 μm) and a decrease in muscularization in peripheral vessels (ED <60 μm). This coincided with increased expression of Flk-1 in the endothelium and smooth muscle cells of the pulmonary arteries. All the effects studied were dose-dependent. Copyrigh

HSPB1, HSPB6, HSPB7 and HSPB8 Protect against RhoA GTPase-Induced Remodeling in Tachypaced Atrial Myocytes

BACKGROUND: We previously demonstrated the small heat shock protein, HSPB1, to prevent tachycardia remodeling in in vitro and in vivo models for Atrial Fibrillation (AF). To gain insight into its mechanism of action, we examined the protective effect of all 10 members of the HSPB family on tachycardia remodeling. Furthermore, modulating effects of HSPB on RhoA GTPase activity and F-actin stress fiber formation were examined, as this pathway was found of prime importance in tachycardia remodeling events and the initiation of AF. METHODS AND RESULTS: Tachypacing (4 Hz) of HL-1 atrial myocytes significantly and progressively reduced the amplitude of Ca²⁺ transients (CaT). In addition to HSPB1, also overexpression of HSPB6, HSPB7 and HSPB8 protected against tachypacing-induced CaT reduction. The protective effect was independent of HSPB1. Moreover, tachypacing induced RhoA GTPase activity and caused F-actin stress fiber formation. The ROCK inhibitor Y27632 significantly prevented tachypacing-induced F-actin formation and CaT reductions, showing that RhoA activation is required for remodeling. Although all protective HSPB members prevented the formation of F-actin stress fibers, their mode of action differs. Whilst HSPB1, HSPB6 and HSPB7 acted via direct prevention of F-actin formation, HSPB8-protection was mediated via inhibition of RhoA GTPase activity. CONCLUSION: Overexpression of HSPB1, as well as HSPB6, HSPB7 and HSPB8 independently protect against tachycardia remodeling by attenuation of the RhoA GTPase pathway at different levels. The cardioprotective role for multiple HSPB members indicate a possible therapeutic benefit of compounds able to boost the expression of single or multiple members of the HSPB family