Current treatments for chronic obstructive pulmonary disease (COPD) attempt to ameliorate symptoms and prevent exacerbations. Studies have identified an insertion (I)/deletion (D) polymorphism in an intron of the angiotensin converting enzyme (ACE) gene. D/D homozygotes (~25% of the population) exhibit more severe COPD but the mechanism is unclear. Our major goal is to investigate and target the role of ACE in the development of COPD. Patients with COPD are plagued by chronic inflammation, leading to increased lung compliance. Alveolar macrophages (AMs) are critical to the local inflammatory response in COPD. ACE is expressed on the surface of AMs and its abundance regulates levels of angiotensin II (ANGII), which in turn binds the ANGII type I (AT1) receptor on AMs. Inflammation in COPD causes bronchospasm, which can result in hypoxia. Hypoxia, in turn, causes an increase in ANGII, a key inflammatory mediator, creating a vicious cycle. Our preliminary data show that AMs generate an inflammatory response to hypoxia that is blocked by the AT1 receptor blocker, losartan. We also found increased pulmonary ACE and ANGII in subjects with the ACE D/D genotype. Our data suggest that the intronic sequence encodes microRNAs (miRNAs), small RNAs that can regulate protein abundance. Our overarching hypothesis is that the ACE D/D genotype increases translation of ACE protein, leading to an exaggerated ANGII response during hypoxia, increasing the severity of COPD.
Aim 1 will test the hypothesis that the ACE D/D polymorphism is associated with elevated ACE activity and lung inflammation compared to I/I subjects. In parallel, we will determine if these levels predict differences in lung compliance, as quantified by magnetic resonance elastography (MRE).
In Aim 2, we will test the hypothesis that hypoxia causes a dose-dependent increase in ACE and ANGII that is exaggerated in AMs from D/D versus I/I subjects. Our preliminary data suggest the expression of ACE-specific miRNAs from the intronic sequence.
Aim 3 will test the hypothesis that reduced expression of these miRNAs in D/D subjects causes an increase in ACE translation compared to I/I subjects. This will foster discovery of previously unrecognized targets that could decrease ACE activity in the lung. The iTarget COBRE will facilitate these studies by providing strong mentorship for career development and a multidisciplinary environment to promote scientific growth. The Visualizing Molecular Interactions Core will facilitate our MRE imaging analysis, while the Molecular Tools Core will provide constructs for modulating cellular levels of miRNAs. Our protein translation studies will benefit from enhanced scientific interactions with the Kettenbach Laboratory. Drs. McLellan and Grigoryan will offer expertise in protein design and protein biochemistry. These studies will determine novel anti-inflammatory strategies to target COPD, including the potential repurposing of the AT1 receptor blocker losartan. Our studies will simultaneously uncover additional targets regulating ACE, leading to the development of novel therapeutics for inflammatory lung diseases.
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