Perinatal hypoxia aggravates occlusive pulmonary vasculopathy in SU5416/hypoxia-treated rats later in life.

Pulmonary arterial hypertension (PAH) is a fatal disease, which is characterized by occlusive pulmonary vascular disease (PVD) in small pulmonary arteries. It remains unknown whether perinatal insults aggravate occlusive PVD later in life. We tested the hypothesis that perinatal hypoxia aggravates PVD and survival in rats. PVD was induced in rats with/without perinatal hypoxia (embryonic day 14 to postnatal day 3) by injecting SU5416 at 7 wk of age and subsequent exposure to hypoxia for 3 wk (SU5416/hypoxia). Hemodynamic and morphological analyses were performed in rats with/without perinatal hypoxia at 7 wk of age (baseline rats, n = 12) and at 15 wk of age in 4 groups of rats: SU5416/hypoxia or control rats with/without perinatal hypoxia (n = 40). Pulmonary artery smooth muscle cells (PASMCs) from the baseline rats with/without perinatal hypoxia were used to assess cell proliferation, inflammation, and genomic DNA methylation profile. Although perinatal hypoxia alone did not affect survival, physiological, or pathological parameters at baseline or at the end of the experimental period in controls, perinatal hypoxia decreased weight gain and survival rate and increased right ventricular systolic pressure, right ventricular hypertrophy, and indices of PVD in SU5416/hypoxia rats. Perinatal hypoxia alone accelerated the proliferation and inflammation of cultured PASMCs from baseline rats, which was associated with DNA methylation. In conclusion, we established the first fatal animal model of PAH with worsening hemodynamics and occlusive PVD elicited by perinatal hypoxia, which was associated with hyperproliferative, proinflammatory, and epigenetic changes in cultured PASMCs. These findings provide insights into the treatment and prevention of occlusive PVD.

CRISPR-mediated Bmpr2 point mutation exacerbates late pulmonary vasculopathy and reduces survival in rats with experimental pulmonary hypertension.

BACKGROUND: Patients with pulmonary arterial hypertension (PAH) carrying bone morphogenetic protein receptor type 2 (Bmpr2) mutations present earlier with severe hemodynamic compromise and have poorer survival outcomes than those without mutation. The mechanism underlying the worsening clinical phenotype of PAH with Bmpr2 mutations has been largely unaddressed in rat models of pulmonary hypertension (PH) because of the difficulty in reproducing progressive PH in mice and genetic modification in rats. We tested whether a clinically-relevant Bmpr2 mutation affects the progressive features of monocrotaline (MCT) induced-PH in rats. METHODS: A monoallelic single nucleotide insertion in exon 1 of Bmpr2 (+/44insG) was generated in rats using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9, then PH, pulmonary vascular disease (PVD) and survival after MCT injection with or without a phosphodiesterase type 5 inhibitor, tadalafil, administration were assessed. RESULTS: The +/44insG rats had reduced BMPR2 signalling in the lungs compared with wild-type. PH and PVD assessed at 3-weeks after MCT injection were similar in wild-type and +/44insG rats. However, survival at 4-weeks after MCT injection was significantly reduced in +/44insG rats. Among the rats surviving at 4-weeks after MCT administration, +/44insG rats had increased weight ratio of right ventricle to left ventricle plus septum (RV/[LV + S]) and % medial wall thickness (MWT) in pulmonary arteries (PAs). Immunohistochemical analysis showed increased vessels with Ki67-positive cells in the lungs, decreased mature and increased immature smooth muscle cell phenotype markers in the PAs in +/44insG rats compared with wild-type at 3-weeks after MCT injection. Contraction of PA in response to prostaglandin-F2α and endothelin-1 were significantly reduced in the +/44insG rats. The +/44insG rats that had received tadalafil had a worse survival with a significant increase in RV/(LV + S), %MWT in distal PAs and RV myocardial fibrosis compared with wild-type. CONCLUSIONS: The present study demonstrates that the Bmpr2 mutation promotes dedifferentiation of PA smooth muscle cells, late PVD and RV myocardial fibrosis and adversely impacts both the natural and post-treatment courses of MCT-PH in rats with significant effects only in the late stages and warrants preclinical studies using this new genetic model to optimize treatment outcomes of heritable PAH.