Abstract 201: Increased Susceptibility to Bleomycin-induced Pulmonary Injury in Mice Carrying a Mutant Type 2 Bone Morphogenetic Protein Receptor Gene
Heterozygous mutations in the gene encoding the type 2 bone morphogenetic protein receptor (BMPR2) gene are associated with familial and sporadic primary pulmonary hypertension (PPH). Importantly, only a minority of patients carrying the mutation develop the disorder suggesting that an additional stimulus is required for susceptible individuals to develop PPH. Using mice which were heterozygous for a BMPR2 allele lacking exons 4 and 5 (BMPR2+/−), we tested the hypothesis that BMPR2 mutations increase susceptibility to pulmonary injury. Wild-type (WT) and BMPR2+/− mice (10 -12 weeks old) received bleomycin (0.002U/g·BW) intratracheally. Two weeks later, mice were anesthetized and systemic arterial pressure (SAP) and right ventricular systolic pressure (RVSP) were measured. Thereafter, lung specimens were harvested for histology and measurement of gene expression. Bleomycin induced peribronchiolar and parenchymal fibrosis in both genotypes, but fibrosis was much more prominent in BMPR2+/− mice. Similarly, Sirius Red staining revealed that bleomycin caused greater pulmonary collagen deposition in BMPR+/− than WT mice. Bleomycin increased pulmonary PAI-1 and collagen 1 gene expression in both genotypes as measured using quantitative RT-PCR, but induction of both genes was greater in BMPR+/− than WT mice (PAI-1: 24±3- vs 12±4-fold. collagen 1: 7±1- vs 3±1-fold. P<0.05 vs WT for both). Bleomycin increased TNFα mRNA levels in BMPR2+/- mice but not in WT mice (2.9±0.4-fold, p<0.001 vs BMPR2+/− without bleomycin). RVSP was greater in BMPR2+/− than in WT mice (28±1 and 26±1, respectively, P<0.05) at baseline. Bleomycin increased RVSP in BMPR2+/− but not WT mice (32±4 and 26±2, respectively, P<0.005 vs WT with bleomycin), whereas bleomycin did not alter SAP in either genotype. These findings suggest that BMPR2 heterozygosity increases susceptibility to pulmonary injury induced by bleomycin associated with the progression of pulmonary arterial hypertension.