Date Published: January 31, 2019
Publisher: Public Library of Science
Author(s): Ayako Chida-Nagai, Masaki Shintani, Hiroki Sato, Tomotaka Nakayama, Masaki Nii, Hiroyuki Akagawa, Toru Furukawa, Amer Rana, Yoshiyuki Furutani, Kei Inai, Shigeaki Nonoyama, Toshio Nakanishi, Yoshihiro Fukumoto.
Although mutations in several genes have been reported in pulmonary arterial hypertension (PAH), most of PAH cases do not carry these mutations. This study aimed to identify a novel cause of PAH. To determine the disease-causing variants, direct sequencing and multiplex ligation-dependent probe amplification were performed to analyze 18 families with multiple affected family members with PAH. In one of the 18 families with PAH, no disease-causing variants were found in any of BMPR2, ACVRL1, ENG, SMAD1/4/8, BMPR1B, NOTCH3, CAV1, or KCNK3. In this family, a female proband and her paternal aunt developed PAH in their childhood. Whole-exome next-generation sequencing was performed in the 2 PAH patients and the proband’s healthy mother, and a BRCA1-associated protein (BRAP) gene variant, p.Arg554Leu, was identified in the 2 family members with PAH, but not in the proband’s mother without PAH. Functional analyses were performed using human pulmonary arterial smooth muscle cells (hPASMCs). Knockdown of BRAP via small interfering RNA in hPASMCs induced p53 signaling pathway activation and decreased cell proliferation. Overexpression of either wild-type BRAP or p.Arg554Leu-BRAP cDNA constructs caused cell death confounding these studies, however we observed higher levels of p53 signaling inactivation and hPASMC proliferation in cells expressing p.Arg554Leu-BRAP compared to wild-type BRAP. In addition, p.Arg554Leu-BRAP induced decreased apoptosis of hPASMCs compared with wild-type BRAP. In conclusion, we have identified a novel variant of BRAP in a Japanese family with PAH and our results suggest it could have a gain-of-function. This study sheds light on new mechanism of PAH pathogenesis.
Pulmonary arterial hypertension (PAH) is a progressive, potentially fatal disease. Based on the Nice Classification in 2013, idiopathic PAH (IPAH) is a sporadic disease in which there is neither a family history of PAH nor an identified risk factor. Heritable PAH (HPAH) is inherited in an autosomal dominant fashion with 10–20% penetrance.
The study participants included 18 families with multiple affected family members with PAH (Fig 1).
A BRAP variant (NM_006768.4, c.1661 G>T p.Arg554Leu) was identified in the 2 family members with PAH, which was absent in the proband’s mother without PAH (Fig 2A and 2B). The variant was not found in dbSNP, the 1000 genomes databases, the EVS, or the HGVD. It was regarded as “Probably damaging (0.998)” in the Polyphen-2 and “Damaging (0.01)” in the SIFT Human Protein. The CADD score was 35. In addition, it was absent in 152 Japanese healthy controls and 300 Caucasian healthy controls. Moreover, pathogenic variant of BRAP including p.Arg554Leu was absent in 109 IPAH patients who had no known disease-causing gene mutations.
This is the first study to report on a BRAP variant in a family with multiple PAH patients. In addition, we also described originally that BRAP could affect the growth and apoptosis of hPASMCs through p53 signaling pathway.