The role of microRNA in the development of pulmonary arterial hypertension: studies in cell culture and animal models.

Grant, Jennifer Sarah (2014) The role of microRNA in the development of pulmonary arterial hypertension: studies in cell culture and animal models. PhD thesis, University of Glasgow.

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Pulmonary arterial hypertension (PAH) is a complex disease characterised by narrowing and remodelling of the small pulmonary arteries. This process involves all cell types within the vessel wall and results in an increase in pulmonary artery pressure, right heart failure and can eventually lead to premature death. Diagnosis of PAH occurs late in disease progression with patients already displaying severe hemodynamic compromise and mortality rates remain unacceptably high despite current treatment. Therefore the development of new therapies is required to manage the symptoms and treat the underlying causes of this multifaceted disease. Recent studies have highlighted a role for microRNAs (miRNAs) in the initiation, development and progression of PAH. MiRNAs are small non-coding RNA molecules ~22 nucleotides long that negatively regulate gene expression. Previous work from our laboratory has shown that miRNAs are dysregulated within the lung during the development of experimental pulmonary hypertension (PH). Consequently, the aim of this study was to assess the involvement of specific miRNAs in the development of PAH using cell culture and experimental models of PH.

The first miRNA focused on was miR-451 which is up-regulated in the lungs from animal models of PH. In human pulmonary artery smooth muscle cells (hPASMCs), miR-451 over-expression promoted migration in the absence of serum but had no effect on cellular proliferation. Silencing of miR-451 was performed in vivo using antimiR-451 and miR-451 knockout mice. Indices of PAH were assessed after exposure to hypoxia via measurement of right ventricular pressure (RVP), right ventricular hypertrophy (RVH) and pulmonary vascular remodelling. There was a reduction in systolic RVP in hypoxic rats pre-treated with antimiR-451 compared to control antimiR (47.7 ± 1.36 mmHg and 56.0 ± 2.03 mmHg respectively, p<0.01). MiR-451 knockout mice exposed to chronic hypoxia displayed no significant differences for PAH indices compared to wild type hypoxic mice. Thus illustrating that transient inhibition of miR-451 attenuates the development of PH in hypoxic rats however, genetic deletion of miR-451 has no beneficial effect on the development of PH. This may be due to compensatory mechanisms present in the miR-451 knockout mice.

Previous work has also shown that miR-145 is up-regulated in the lungs and pulmonary arteries from animal models of PH as well as PAH patients. Therefore miR-145 expression was modulated in rats using antimiR-145 both prior to and post exposure to hypoxia and SU5416 administration. Prophylactic silencing of miR-145 in the hypoxia/SU5416 model of PH showed no beneficial effect on the development of PH compared to control antimiR treated rats exposed to hypoxia. Therapeutic modulation of miR-145 also demonstrated no protective effect on RVP, RVH or muscularisation of pulmonary arteries in the rat hypoxia/SU5416 model. There was however a significant reduction in the number of occluded vessels in rats with established PH treated with antimiR-145. This reduction in occluded vessel count is interesting as it was not observed in the prevention study. Further work is required to pinpoint the exact mechanisms through which antimiR-145 is producing this positive effect on pulmonary vessels with therapeutic silencing of miR-145.

The role of miR-145 on PAH development was further investigated with the use of miR-145 knockout mice. Recent studies show that genetic ablation of miR-145 protects female mice from developing hypoxia-induced PH. We therefore sought to establish whether this beneficial response was also observed in male miR-145 knockout mice. Hypoxic male miR-145 knockout mice showed similar indices of PAH as hypoxic miR-145 wild type mice, with increased RVP and RVH compared with normoxic mice. Pulmonary vascular remodelling analysis indicates that miR-145 knockout mice exposed to hypoxia may have a reduction in remodelling compared to wild type hypoxic mice however this does not reach significance. Thus it appears from this study that male miR-145 knockout mice are not protected against developing PAH as the female knockout mice are. The results from this study on male miR-145 knockout mice demonstrate that the effects of silencing miR-145 in vivo are indeed gender specific.

As well as affecting the pulmonary arteries, PAH also induces changes within the right ventricle culminating in right ventricular dysfunction and failure. Therefore a miRNA profile was established for the PAH diseased right ventricle. MiR-27a and miR-27b were up-regulated within the right ventricle of hypoxia/SU5416 mice and rats, respectively. This response appears to be cardiac specific and may help to establish therapies to maintain and stabilise RV function.

In summary of these findings, we have confirmed that miRNAs are dysregulated within the lung and right ventricle during PH development. Results suggest that there are complex mechanisms regulating miRNA processing within the lung during the development of PAH and that these pathways may be gender specific. Further work is required to understand the genes targeted, and therefore the pathways modulated, by miRNAs during PAH development to enhance our understanding of the intricate systems involved in disease progression. MiRNAs represent a potential therapeutic target for the treatment of PAH with further work required to pinpoint the exact mechanistic pathways through which they exert their effects.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: pulmonary arterial hypertension, microRNA, miR-145, miR-451.
Subjects: Q Science > Q Science (General)
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cardiovascular & Metabolic Health > Cardiovascular & Metabolic Health
Supervisor's Name: Baker, Professor Andrew, MacLean, Professor Margaret and Thomas, Dr. Matthew
Date of Award: 2014
Depositing User: Mrs Jennifer Grant
Unique ID: glathesis:2014-5261
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 24 Jun 2014 10:35
Last Modified: 23 Jun 2017 12:09

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