The ALK-1/SMAD/ATOH8 axis attenuates hypoxic responses and protects against the development of pulmonary arterial hypertension

Abstract

Dysregulated bone morphogenetic protein (BMP) signaling in endothelial cells (ECs) is implicated in vascular diseases such as pulmonary arterial hypertension (PAH). Here, we showed that the transcription factor ATOH8 was a direct target of SMAD1/5 and was induced in a manner dependent on BMP but independent of Notch, another critical signaling pathway in ECs. In zebrafish and mice, inactivation of Atoh8 did not cause an arteriovenous malformation–like phenotype, which may arise because of dysregulated Notch signaling. In contrast, Atoh8-deficient mice exhibited a phenotype mimicking PAH, which included increased pulmonary arterial pressure and right ventricular hypertrophy. Moreover, ATOH8 expression was decreased in PAH patient lungs. We showed that in cells, ATOH8 interacted with hypoxia-inducible factor 2α (HIF-2α) and decreased its abundance, leading to reduced induction of HIF-2α target genes in response to hypoxia. Together, these findings suggest that the BMP receptor type II/ALK-1/SMAD/ATOH8 axis may attenuate hypoxic responses in ECs in the pulmonary circulation and may help prevent the development of PAH.

BMP-induced Atoh8 attenuates osteoclastogenesis by suppressing Runx2 transcriptional activity and reducing the Rankl/Opg expression ratio in osteoblasts

“…Recently, we generated a constitutive Atoh8-KO mouse (Atoh8 LacZ(ex1) ) by replacing a large part of exon 1 with a LacZ-reporter cassette. 32 We confirmed that Atoh8 mRNA expression was absent in KO bone ( Fig. 2c, lower panel).…”

“…1g); both regions are well conserved from zebrafish to humans. 32 In primary osteoblasts purified from newborn mouse calvariae or MC3T3-E1 osteoblasts, the anti-Smad1 antibody immunoprecipitated fragments of SBR1 and SBR2; while SBR2 signals were predominant, both SBRs were further enriched upon BMP-6 treatment ( Fig. 1h, i).…”

“…We recently found that the half-life of exogenously expressed ATOH8 protein is~30 min, while the ATOH8 mutant lacking the bHLH region (ATOH8 Δ231-286) is more stable than the full-length protein. 32 Indeed, the Atoh8-Runx2 interaction is more evident in the presence of MG132 (Fig. 8b).…”

“…1h, i). To evaluate the potential of SBRs as transcriptional enhancers in osteoblasts, we used luciferase reporter constructs of SBR1 or SBR2 32 and performed luciferase assays. BMP-6 enhanced SBR1 activity in both MC3T3-E1 and ST-2 cells, while it only faintly enhanced SBR2 (Fig.…”

“…The Atoh8 gene encodes a basic helix-loop-helix (bHLH) protein. 40 To further confirm the specificity of this interaction, we used deletion mutant constructs of human ATOH8 32 (Fig. 8c).…”