A New Treatment for Heritable Pulmonary Artery Hypertension Caused by Nonsense Mutations
Abstract
Topic Area: Respiratory Health Background: Heritable pulmonary artery hypertension (hPAH) is a lethal disease of the blood vessels through the lungs that secondarily causes heart failure and increasing difficulty pumping blood through those blood vessels. hPAH is characterized by progressively increasing pressures in the pulmonary arteries, and corresponding right heart failure as the heart eventually fails to pump blood against an increasing pressure that opposes this. There are no effective treatments available to treat hPAH. The fundamental cause of hPAH in many cases is a specific type of mutation called a nonsense mutation in the Bmpr2 gene. This nonsense mutation fails to induce synthesis of the BMPR2 (bone morphogenetic protein receptor type 2) protein, which is a key receptor in the bone morphogenetic protein signaling pathway that influences lung development, among other things. Nonsense mutations cause disease because they mistakenly encode a premature termination codon (PTC), rather than a codon specifying an amino acid in the protein. Hence, translation at the ribosomes is stopped prematurely, and the truncated protein synthesized usually doesn’t function (called a loss of function mutation). Certain antibiotic compounds have been known to effect read-through, which can occur by specific effects at the ribosomes that cause them to insert a random amino acid in place of the PTC that is encoded by the mutant mRNA. However, because of excessive toxicity when used long term, these compounds are unacceptable as treatments for hPAH. We therefore created several alternative compounds that also produce read-through, and one of these — GJ103 — subsequently became our candidate compound, and will be tested in this proposal. How exactly read-through phenomena occur is still poorly understood. In addition to directly reading through the PTC, there are alternative pathways that can have a major impact on translational yield, specifically, a process called nonsense mediated decay (NMD). NMD is a cellular quality control mechanism that detects and quickly clears mutant mRNA from the cell. There appears to be a significant relationship between compounds that elicit read-through and the NMD pathways. Specifically, NMD may be activated by read-through compounds, which would be expected to decrease read-through because of the unavailability of significant quantities of mRNA. Hence, read-through yield might well decrease significantly. Here, we propose that combining read-through with suppression of NMD might together elicit substantial read-through yield. This can occur because suppressing NMD improves the availability and stability of mRNA transcripts containing a PTC, which can then be read through with improved yield. We propose two aims. Studies in Aim 1 will test the ability of GJ103 by itself to induce read-through. Our preliminary data show that up to 65% of wild-type BMPR2 protein can be synthesized in the pulmonary arteries of mice that have Bmpr2 nonsense mutations by GJ103 alone, but we do not yet know the impact of GJ103 on NMD. Because we suspect that GJ103 might activate NMD, studies proposed in Aim 2 will combine pharmacologic inhibition of NMD (using compounds called NMDI-1 [for nonsense mediated decay inhibitor-1] and NMDI-14) with treatment using GJ103 to try to prevent development of hPAH in mice prone to develop hPAH (specifically, Bmpr2+/R899X and Bmpr2+/R584X mice). We will measure NMD (using quantitative PCR) and development of hPAH pathology (using microechocardiography and measurement of right heart and pulmonary arterial pressures) as a result. We will also measure expression of proteins in the BMP signaling pathway that should increase as a result of activation of this pathway (Smads, phospho-Smads, Id-1, VE-cadherin). We anticipate that combining NMD suppression using NMDI-1 or NMDI-14 with read-through using GJ103 will collectively enhance production of BMPR2 protein
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 10, 2021
- Source ID
- W81XWH2010181
Entities
People
- Virender Rehan
Organizations
- Harbor–UCLA Medical Center
- United States Army