Bone Morphogenetic Protein Receptor Mutation and Heritable Pulmonary Arterial Hypertension
Frump, Andrea Lee
More than 200 heterozygous mutations in the type 2 BMP receptor gene, BMPR2, have been identified in patients with Heritable Pulmonary Arterial Hypertension (HPAH). Two recent studies have grouped patients with BMPR2 mutations by susceptibility to nonsense-mediated mRNA decay (NMD) to determine if this affects clinical outcome, and have reported conflicting results. One study reported more severe clinical outcomes occur in patients with BMPR2 mutations by-passing NMD (NMD negative mutations). These comprise 40% of HPAH mutations and are predicted to express BMPR2 mutant products. A second study reported no difference between NMD negative BMPR2 mutations and BMPR2 mutations susceptible to NMD (NMD positive mutations). Here, we address Bmpr2 mutation type and severity of experimental pulmonary hypertension (PH) in vivo and in vitro using an NMD negative Bmpr2 mutant mouse model (Bmpr2 Δ Ex2/+) and an NMD positive Bmpr2 mutant mouse model (Bmpr2+/-). We report differences in basal signaling pathways and right ventricular systolic pressure in the Bmpr2 Δ Ex2/+ mice and increased formation of vascular obstructive lesions in a SUGEN5416 and hypoxia model of PH. These findings indicate significant differences between Bmpr2 mutation types that likely account for more severe PH in NMD negative mutations. Next, we characterize the expression and trafficking of an HPAH-associated NMD negative BMPR2 mutation, an in-frame deletion of BMPR2 EXON2 (BMPR2 Δ Ex2), in HPAH patient-derived lymphocytes and in pulmonary endothelial cells (PECs) from Bmpr2 Δ Ex2/+ mice. The endogenous BMPR2 Δ Ex2 mutant product does not reach the cell surface and is retained in the endoplasmic reticulum. We show that Bmpr2 Δ Ex2/+ PECs have defects in the BMP-induced signaling, and addition of chemical chaperones restores trafficking of the mutant product to the cell surface and signaling function. Finally, we report the generation of induced pluripotent stem cell lines from HPAH patients with NMD positive and NMD negative BMPR2 mutations. Together, these data provide evidence of significant differences between Bmpr2 mutation type and susceptibility to experimental PH, and further show that these differences could be due to expression of an endogenous, mis-trafficked NMD negative protein.