Right ventricular cyclic nucleotide signaling is decreased in hyperoxia-induced pulmonary hypertension in neonatal mice

Abstract

Pulmonary hypertension (PH) and right ventricular hypertrophy (RVH) affect 25-35% of premature infants with significant bronchopulmonary dysplasia (BPD), increasing morbidity and mortality. We sought to determine the role of phosphodiesterase 5 (PDE5) in the right ventricle (RV) and left ventricle (LV) in a hyperoxia-induced neonatal mouse model of PH and RVH. After birth, C57BL/6 mice were placed in room air (RA) or 75% O2 (CH) for 14 days to induce PH and RVH. Mice were euthanized at 14 days or recovered in RA for 14 days or 42 days prior to euthanasia at 28 or 56 days of age. Some pups received sildenafil or vehicle (3 mg·kg(-1)·dose(-1) sc) every other day from P0. RVH was assessed by Fulton's index [RV wt/(LV + septum) wt]. PDE5 protein expression was analyzed via Western blot, PDE5 activity was measured by commercially available assay, and cGMP was measured by enzyme-linked immunoassay. Hyperoxia induced RVH in mice after 14 days, and RVH did not resolve until 56 days of age. Hyperoxia increased PDE5 expression and activity in RV, but not LV + S, after 14 days. PDE5 expression normalized by 28 days of age, but PDE5 activity did not normalize until 56 days of age. Sildenafil given during hyperoxia prevented RVH, decreased RV PDE5 activity, and increased RV cGMP levels. Mice with cardiac-specific overexpression of PDE5 had increased RVH in RA. These findings suggest normal RV PDE5 function is disrupted by hyperoxia, and elevated PDE5 contributes to RVH and remodeling. Therefore, in addition to impacting the pulmonary vasculature, sildenafil also targets PDE5 in the neonatal mouse RV and decreases RVH.

Aberrant cGMP signaling persists during recovery in mice with oxygen-induced pulmonary hypertension

“…Similarly, exposure of newborn rodents to high levels of oxygen results in an arrest of alveolar development, leading to alveolar simplification [ 7 , 31 ]. In agreement with other published reports demonstrating the persistence of alveolar simplification in adult rats and mice exposed to hyperoxia during the neonatal period [ 8 , 26 – 29 , 32 ], we demonstrate that this impairment in alveolarization persists in our model, showing no significant recovery after a 1 week period of room air recovery (Figs 1 and 2 ). One group has demonstrated in mice that septal thickness is unchanged after 14d of exposure to 85% O 2 , but is modestly increased after 14d of room air recovery [ 21 ], whereas another group using >90% O 2 , showed an increase in septal thickness after 10d of exposure [ 33 ].…”

“…We demonstrate that exposure of neonatal mice to high levels of oxygen during the first two weeks of life leads to persistent pulmonary and cardiovascular anomalies as well as disruptions in pulmonary vascular NO-cGMP signaling that are still apparent at one month of life. This is consistent with other recent studies suggesting that hyperoxia-mediated lung and cardiovascular injury can last up to 8 weeks of age in mice [ 8 , 26 – 28 ]. However, to date, no one has investigated potential therapeutic options in established disease, which is where data is desperately needed clinically.…”

“…Despite no observable benefit of sildenafil on remodeling of small PAs and lack of effects on vessel density, there were clear improvements in hyperoxia-induced RVH ( Fig 9A ). Combined with recently published studies from our lab demonstrating positive effects of sildenafil on right ventricular PDE5 activity and cGMP levels [ 26 ], these findings suggest that sildenafil has direct and distinct effects on the myocardium both during hyperoxia and during room air recovery, independent of its effects on the pulmonary vascular bed.…”

“…Here we demonstrate that both RVH and vessel numbers continue to be significantly affected at 21d such that the right ventricle remains hypertrophied, and there are fewer small vessels in the lungs ( Fig 3 ). We have recently published that the RVH is not completely resolved until 8 weeks of age in mice exposed to hyperoxia during the neonatal period [ 26 ]. Medial wall thickness, a marker of pulmonary vascular remodeling, remains elevated in 21d mice ( Fig 4 ).…”

Dose-dependent effects of glucocorticoids on pulmonary vascular development in a murine model of hyperoxic lung injury

“…PDE5 is the primary phosphodiesterase in the lung vasculature and contributes to vasoconstriction by degrading cGMP. Our lab has previously demonstrated increased PDE5 activity in the murine model of hyperoxic lung injury ( 10 , 38 ). We also demonstrated that hyperoxia-induced RVH and PA remodeling can be partially reversed with PDE5 inhibitor, sildenafil, underscoring the importance of aberrant cGMP signaling in the development of PH in this model ( 10 ).…”