Unveiling the interactions among BMPR-2, ALK-1 and 5-HTT genes in the pathophysiology of HAPE.

CONTEXT: Few potential candidate genes coding for type I and II receptors of transforming growth factor beta signaling pathway and the serotonin transporter have been associated with pulmonary hypertension (PH). The latter being a phenotype for high altitude pulmonary edema (HAPE), these genes are hypothesized to be crucial markers to investigate under the hypobaric hypoxic environment of high altitude.

AIMS: We hence aimed to investigate bone-morphogenetic protein-2 (BMP2), bone morphogenetic protein receptor type-II (BMPR-2), activin receptor-like kinase-1 (ALK-1), serotonin transporter (5-HTT) and serotonin (5-HT) for their contribution, individually/epistatically, to clinical endpoints by altering downstream signaling molecules.

METHODS AND MATERIALS: In a case-control design, interactions between/among polymorphisms of BMPR-2, ALK-1 and 5-HTT were screened in 200 HAPE-patients (HAPE-p) and 200 HAPE-free sojourners (HAPE-f). Plasma biomarker BMP-2 and 5-HT were estimated. The relative gene expression was also witnessed in 20 humans/10 rats followed by correlation analyses.

RESULTS: The genotype/allele models revealed the prevalence of BMPR-2 rs6717924A-rs4303700A-rs1048829A; ALK-1 rs11169953T-rs3759178C-rs706816C and 5-HTT rs6354C in HAPE (P≤0.05). Multifactor dimensionality reduction for interactions among genes revealed a 4-locus model of BMPR-2 rs6717924G/A; ALK-1 rs11169953C/T-rs706816T/C and 5-HTT rs6354A/C as the best disease predicting (P≤0.001); whereas HapEvolution analysis confirmed the alleles rs6717924A, rs4303700A and rs6354C as the best interacting (P≤0.01). Plasma levels of BMP-2 and 5-HT were elevated in HAPE (P≤0.0001). The expression of BMP-2, ALK-1, 5-HT, 5-HTT was elevated and of BMPR-2 decreased in humans and rats (P≤0.05). The risk alleles BMPR-2 rs6717924A-rs4303700G-rs1048829A; ALK-1 rs11169953T-rs706816C and 5-HTT rs6354C correlated inversely with arterial oxygen saturation (SaO2) and positively with mean arterial pressure (MAP), BMP-2 and 5-HT in HAPE. Likewise, haplotypes BMPR-2 GGGCGAAAA, AAATAGGGA and ALK-1 CCTCAAAG, CCTTAAAG correlated with clinical markers and biomarkers (P≤0.01). BMP-2 and 5-HT correlated positively with MAP and negatively with SaO2 (P≤0.01).

CONCLUSIONS: The genetic-interactions among BMPR-2, ALK-1, and 5-HTT polymorphisms, elevated BMP-2 and 5-HT levels and differential gene expression substantiated the strong genetic contribution in HAPE pathophysiology.