Translationally Controlled Tumour Protein as a Novel Therapeutic Target in Pulmonary Arterial Hypertension

Title: Translationally Controlled Tumour Protein as a Novel Therapeutic Target in Pulmonary Arterial Hypertension
Authors: Foster, William Swinburne
Date: 2016
Abstract: Background: Pulmonary arterial hypertension (PAH) is a multifaceted disease characterized by elevated pulmonary arterial pressure, right ventricular hypertrophy, and a poor prognosis. Pathological hallmarks of PAH include pulmonary vascular remodelling, pre-capillary arterial obliteration, and plexiform lesions. Over the past 15 years, pulmonary endothelial cell (EC) apoptosis has been repeatedly implicated as a key trigger of occlusive arterial remodelling in PAH. While it has been hypothesized that pulmonary EC apoptosis gives rise to the emergence of growth-dysregulated, apoptosis- resistant ECs involved in arterial remodelling, the molecular mechanisms linking these two events has not yet been fully elucidated. Recently, our lab identified translationally controlled tumour protein (TCTP) as one of several significantly dysregulated proteins in culture-derived blood-outgrowth endothelial cells (BOECs) isolated from hereditable PAH (HPAH) patients harbouring mutations in the gene encoding for bone morphogenetic protein receptor type 2. Immunohistological analyses indicated that TCTP expression was associated with intra-luminal pulmonary ECs and inflammatory cells in the remodelled vessels of both human PAH patients and SU5416 rats. Furthermore, TCTP silencing abrogated excessive HPAH BOEC proliferation and promoted apoptosis in vitro. Hypothesis: We hypothesized that TCTP represents a central molecular mechanism linking pulmonary arterial EC damage and apoptosis to the emergence of growth- dysregulated lung vascular cells and complex arterial remodelling in PAH.Purpose: The purpose of the present thesis was to examine the effects TCTP inhibition on EC survival and TCTP abundance in vitro as well as on pulmonary hemodynamic changes and arterial remodelling in vivo using a well-validated rat model of severe PAH. Methods: Inhibition of TCTP was accomplished using two TCTP small molecule inhibitors, sertraline and thioridazine. In vitro, rat lung microvascular ECs (RLMVECs) were exposed to thioridazine and assayed for TCTP abundance, survival, and markers of apoptosis. In vivo, PAH was induced in male Sprague Dawley rats using SU5416 combined with 3 weeks of chronic hypoxia (SU/CH). After 4 weeks, right ventricle systolic pressure (RVSP) was measured by direct catheterization and osmotic pumps containing either thioridazine or sertraline were implanted subcutaneously. Following 3 weeks of small molecule delivery, RVSP was re-evaluated, cardiac function/structure was determined using transthoracic echocardiography, and histological analyses of vascular remodelling and inflammation were performed. Results: Our in vitro experiments demonstrated that thioridazine was able to significantly down-regulate TCTP levels and induce an apoptotic phenotype in RLMVECs. In the SU/CH rat model of severe PAH, both thioridazine and sertraline failed to have any effect on pulmonary hemodynamics, right ventricle structure/function, or vascular remodelling. Moreover, neither small molecule was able to detectably down-regulate TCTP levels in the lungs of SU/CH rats. Immunofluorescence staining revealed that TCTP expression occasionally corresponded with the expression of macrophage/monocyte marker CD68 in the lungs of SU/CH rats, consistent with its expression by inflammatory cells; however, no significant differences were found in adventitial cell clearance in the presence or absence of the inhibitors. Conclusions: Our findings support previous reports that thioridazine is able to significantly down-regulate TCTP and induce apoptosis in vitro. In contrast, both small molecule inhibitors failed to down-regulate lung TCTP levels or have any beneficial effects on the progression of PAH in SU/CH rats.
CollectionThèses, 2011 - // Theses, 2011 -