BMPRII deficiency impairs apoptosis via the BMPRII-ALK1-BclX-mediated pathway in pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a devastating cardiovascular disorder characterized by the remodelling of pre-capillary pulmonary arteries. The vascular remodelling observed in PAH patients results from excessive proliferation and apoptosis resistance of pulmonary arterial smooth muscle cells (PASMCs) and pulmonary arterial endothelial cells (PAECs). We have previously demonstrated that mutations in the type II receptor for bone morphogenetic protein (BMPRII) underlie the majority of the familial and inherited forms of the disease. We have further demonstrated that BMPRII deficiency promotes excessive proliferation and attenuates apoptosis in PASMCs, but the underlying mechanisms remain unclear. The major objective of this study is to investigate how BMPRII deficiency impairs apoptosis in PAH. Using multidisciplinary approaches, we demonstrate that deficiency in the expression of BMPRII impairs apoptosis by modulating the alternative splicing of the apoptotic regulator, B-cell lymphoma X (Bcl-x) transcripts: a finding observed in circulating leukocytes and lungs of PAH subjects, hypoxia-induced PAH rat lungs as well as in PASMCs and PAECs. BMPRII deficiency elicits cell specific effects: promoting the expression of Bcl-xL transcripts in PASMCs while inhibiting it in ECs, thus exerting differential apoptotic effects in these cells. The pro-survival effect of BMPRII receptor is mediated through the activin receptor-like kinase 1 (ALK1) but not the ALK3 receptor. Finally, we show that BMPRII interacts with the ALK1 receptor and pathogenic mutations in the BMPR2 gene abolish this interaction. Taken together, dysfunctional BMPRII responsiveness impairs apoptosis via the BMPRII-ALK1-Bcl-xL pathway in PAH. We suggest Bcl-xL as a potential biomarker and druggable target.

Aminoglycoside-mediated promotion of translation readthrough occurs through a non-stochastic mechanism that competes with translation termination.

Attempts have been made to treat nonsense-associated genetic disorders by chemical agents and hence an improved mechanistic insight into the decoding of readthrough signals is essential for the identification and characterisation of factors for the treatment of these disorders. To identify either novel compounds or genes that modulate translation readthrough, we have employed dual reporter-based high-throughput screens that use enzymatic and fluorescence activities and screened bioactive National Institute of Neurological Disease Syndrome (NINDS) compounds (n = 1000) and siRNA (n = 288) libraries. Whilst siRNAs targeting kinases such as CSNK1G3 and NME3 negatively regulate readthrough, neither the bioactive NINDS compounds nor PTC124 promote readthrough. Of note, PTC124 has previously been shown to promote readthrough. Furthermore, the impacts of G418 on the components of eukaryotic selenocysteine incorporation machinery have also been investigated. The selenocysteine machinery decodes the stop codon UGA specifying selenocysteine in natural selenoprotein genes. We have found that the eukaryotic SelC gene promotes the selenocysteine insertion sequence (SECIS)-mediated readthrough but inhibits the readthrough activity induced by G418. We have previously reported that SECIS-mediated readthrough at UGA codons follows a non-processive mechanism. Here, we show that G418-mediated promotion of readthrough also occurs through a non-processive mechanism which competes with translation termination. Based on our observations, we suggest that proteins generated through a non-processive mechanism may be therapeutically beneficial for the resolution of nonsense-associated genetic disorders.