Molecular Basis for Dysregulated Activation of NKX2‐5 in the Vascular Remodeling of Systemic Sclerosis

OBJECTIVE: NKX2‐5 is a homeobox transcription factor that is required for the formation of the heart and vessels during development, with significant postnatal down‐regulation and reactivation in disease states, characterized by vascular remodeling. The purpose of this study was to investigate mechanisms that activate NKX2‐5 expression in diseased vessels, such as systemic sclerosis (scleroderma; SSc)–associated pulmonary hypertension (PH), and to identify genetic variability that potentially underlies susceptibility to specific vascular complications. METHODS: We explored NKX2‐5 expression in biopsy samples from patients with SSc‐associated PH and in pulmonary artery smooth muscle cells (PASMCs) from patients with scleroderma. Disease‐associated putative functional single‐nucleotide polymorphisms (SNPs) at the NKX2-5 locus were cloned and studied in reporter gene assays. SNP function was further examined through protein–DNA binding assays, chromatin immunoprecipitation assays, and RNA silencing analyses. RESULTS: Increased NKX2‐5 expression in biopsy samples from patients with SSc‐associated PH was localized to remodeled vessels and PASMCs. Meta‐analysis of 2 independent scleroderma cohorts revealed an association of rs3131917 with scleroderma (P = 0.029). We demonstrated that disease‐associated SNPs are located in a novel functional enhancer, which increases NKX2-5 transcriptional activity through the binding of GATA‐6, c‐Jun, and myocyte‐specific enhancer factor 2C. We also characterized an activator/coactivator transcription‐enhancer factor domain 1 (TEAD1)/Yes‐associated protein 1 (YAP1) complex, which was bound at rs3095870, another functional SNP, with TEAD1 binding the risk allele and activating the transcription of NKX2-5. CONCLUSION: NKX2-5 is genetically associated with scleroderma, pulmonary hypertension, and fibrosis. Functional evidence revealed a regulatory mechanism that results in NKX2-5 transcriptional activation in PASMCs through the interaction of an upstream promoter and a novel downstream enhancer. This mechanism can act as a model for NKX2‐5 activation in cardiovascular disease characterized by vascular remodeling.