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Doctorat en Sciences médicales / info:eu-repo/semantics/nonPublished

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

The population of adolescent and adults with congenital heart disease (CHD) has grown rapidly. Right ventricular (RV) dysfunction remains an important issue of concern in the long-term follow up of these patients. While circulating biomarkers have shown promise in the assessment and monitoring of adult patients with left heart diseases, little is known of the role of biomarkers in reflecting RV performance in CHD patients. Emerging circulating biomarkers that reflect underlying pathophysiologic processes have gained increasing attention. These include inflammatory cytokines namely tumour necrosis factor (TNF)-α, a biomarker of apoptosis annexin A5 (AnxA5), carboxy-terminal propeptide of type I procollagen (PICP) and amino-terminal propeptide of type III procollagen (PIIINP) that reflects collagen synthesis and turnover, low circulating levels of cardiac troponin T as detected by highly sensitive assay (hs-cTnT) that may reflect subclinical myocardial injury, and microRNAs found to be involved in cardiac remodeling. The studies in this thesis aimed to test the hypothesis that circulating biomarkers may be altered in patients with volume-overloaded right ventricles after repair of tetralogy (TOF) and pressure-overloaded right ventricles after atrial switch operation for complete transposition of the great arteries (TGA), and are related to indices of RV function. In patients after TOF repair, increased circulating PICP and PIIINP levels were associated with worse subpulmonary RV and left ventricular (LV) function. In particular, these propeptides correlated positively with LV mechanical dyssynchrony, implicating a possible role of increased collagen synthesis in its pathogenesis. Increased plasma levels of hs-cTnT were further found in 30% of female, but not male patients. Female patients with elevated hs-cTnT levels compared to those without had greater RV volumes and LV mechanical dyssynchrony. Independent correlates of hs-cTnT in patients as determined from multivariate analysis were sex and RV ejection fraction. MicroRNA profiling following validation confirmed alteration of circulating levels of miR-99b and miR-766 in repaired TOF patients, a pattern distinct from that reported for left heart diseases. The miRNA expression was, however, not related to the cardiac functional indices. Patients after atrial repair for TGA had significantly higher circulating AnxA5 and TNF-αlevels, but similar PICP, PIIINP levels, compared with controls. Elevated AnxA5 level was associated with impaired systemic RV myocardial deformation, increased subpulmonary ventricular eccentricity, and increased TNF-αlevel. Elevation of hs-cTnT is found in 39% of the patients. The positive correlation between hs-cTnT level and systemic RV volume may suggest a role of hs-cTnT in reflecting RV remodeling. Circulating microRNA expression profiling and further validation identified 11 upregulated microRNAs (miR-16, miR-106a, miR-144*, miR-18a, miR-25, miR-451, miR-486-3p, miR-486-5p, miR-505*, let-7e and miR-93). Among them, miR-18a and miR-486-5p correlated negatively with systemic ventricular myocardial acceleration during isovolumic contraction, a relatively-load independent measure of systemic RV contractility. To conclude, these biomarkers reflect in varying extent the structural, functional, biological alteration of the subpulmonary and systemic right ventricles of the CHD patients late after surgical repair. These data may provide new perspectives in the understanding of progressive RV dysfunction in the adult CHD population and hopefully shed more lights on novel therapeutic interventions. / published_or_final_version / Paediatrics and Adolescent Medicine / Doctoral / Doctor of Philosophy

Chapitre 1. Introduction<p><p>\ / Doctorat en sciences médicales / info:eu-repo/semantics/nonPublished

Indiana University-Purdue University Indianapolis (IUPUI) / 17-β estradiol (E2) exerts protective effects in hypoxia-induced pulmonary hypertension (HPH) via endothelial cell estrogen receptor (ER)-dependent mechanisms. However, the effects of hypoxia on ER expression in the pulmonary-right ventricle (RV) axis remain unknown. Based on previous data suggesting a role of ER-β in mediating E2 protection, we hypothesized that hypoxia selectively up-regulates ER-β in the lung and pulmonary endothelial cells. In our Male Sprague-Dawley rat model, chronic hypoxia exposure (10% FiO2) resulted in a robust HPH phenotype associated with significant increases in ER- β but not ER-α protein in the lung via western blotting. More importantly, this hypoxia-induced ER-β increase was not replicated in the RV, left ventricle (LV) or in the liver. Hence, hypoxia-induced ER-β up-regulation appears to be lung-specific. Ex vivo, hypoxia exposure time-dependently up-regulated ER-β but not ER-α in cultured primary rat pulmonary artery endothelial cells (RPAECs) exposed to hypoxia (1% O2) for 4, 24 or 72h. Furthermore, the hypoxia induced ER-β protein abundance, while not accompanied by increases in its own transcript, was associated with ER-β nuclear translocation, suggesting increase in activity as well as post-transcriptional up-regulation of ER-β. Indeed, the requirement for ER-β activation was indicated in hypoxic ER-βKO mice where administration of E2 failed to inhibit hypoxia-induced pro-proliferative ERK1/2 signaling. Interestingly, HIF-1α accumulation was noted in lung tissue of hypoxic ER-βKO mice; consistent with previously reported negative feedback of ER-β on HIF-1α protein and transcriptional activation. In RAPECs, HIF-1 stabilization and overexpression did not replicate the effects of ER- β up-regulation seen in gas hypoxia; suggestive that HIF-1α is not sufficient for ER-β up- regulation. Similarly, HIF-1 inhibition with chetomin did not result in ER-β down-regulation. HIF-1α knockdown in RPAECs in hypoxic conditions is currently being investigated. Hypoxia increases ER- β, but not ER-α in the lung and lung vascular cells. Interpreted in context of beneficial effects of E2 on hypoxic PA and RV remodeling, our data suggest a protective role for ER-β in HPH. The mechanisms by which hypoxia increases ER-β appears to be post-transcriptional and HIF-1α independent. Elucidating hypoxia-related ER-β signaling pathways in PAECs may reveal novel therapeutic targets in HPH.