Dritsoula, A; (2017) Regulation of NKX2-5 in blood vessels. Doctoral thesis , UCL (University College London).

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Abstract

NKX2-5 is a transcription factor required for the formation of the heart and vessels during development. Postnatal expression is significantly downregulated, and then re-activated in diseased conditions characterised by vascular remodelling. However, the mechanisms regulating NKX2-5 activation in diseased vessels remain unknown. The aim of this thesis is to identify these mechanisms and provide information on how the gene contributes to cardiovascular pathologies, such as sclerodermaassociated pulmonary hypertension. A case-control genetic association study was performed in two independent cohorts of scleroderma patients. Associated SNPs located in the NKX2-5 genomic region were cloned into reporter vectors, and transcriptional activity was assessed by reporter-gene assays. Associated SNPs were further evaluated through proteinDNA binding assays, chromatin immunoprecipitation and RNA silencing. Signalling mechanisms activating NKX2-5 expression were investigated in vascular endothelial and smooth muscle cells using a panel of selective inhibitors. Meta-analysis across the two independent cohorts revealed that rs3131917 was associated with scleroderma. Rs3132139, downstream of NKX2-5, was significantly associated with pulmonary hypertension in both cohorts. The region containing rs3132139 and rs3131917 was shown to be a novel functional enhancer, which increased NKX2-5 transcriptional activity through the binding of GATA6, c-JUN, and MEF-2c. An activator TEAD/YAP1 complex was shown to bind at rs3095870, another functional SNP upstream of NKX2-5 transcription start site, which showed marginal association with scleroderma. Signalling mechanisms, involving TGF-β, ERK5, AKT and hypoxia, stimulated NKX2-5 expression during phenotypic modulation of vascular endothelial and smooth muscle cells. Overall, the data showed that NKX2-5 is genetically associated with scleroderma and pulmonary hypertension. Functional evidence revealed a regulatory mechanism, activated by TGF-β, which results in NKX2-5 transcription in human vascular smooth muscle cells through the interaction of an upstream promoter and a novel downstream enhancer. These regulatory mechanisms can act as a model for NKX2-5 activation in cardiovascular disease characterised by vascular remodelling

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