Background Pulmonary arterial hypertension (PAH) is prominent as a vascular involvement in systemic sclerosis (SSc), which remains a leading cause of death in spite of current best treatments. As the pulmonary vascular disease (PVD) can be well compensated for, more than a half of the pulmonary circulation is impaired before early PAH is detected. Although recent studies focused on molecular basis of the PVD, the underlying mechanisms have not been fully elucidated, especially at the early stage of the disease.
Objectives To detect the subclinical PVD, and to explore the changes in transcriptome of peripheral blood at the early stage of SSc associated PAH.
Methods Total of 74 cases without PAH symptoms (NYHA I) with either Raynaud phenomenon (RP: n=61), skin sclerosis (n=43) or SSc-related autoantibody (anti-RNP: n=10, centromere: n=36, topoisomerase-1: n=2, RNA polymerase III: n=2) were enrolled. To detect the latent PAH, exercise Doppler echocardiography (DE) with Master's two-step stress was carried out. Systolic PAP (sPAP) was determined by maximum velocities of tricuspid regurgitation jets, and exercise induced pulmonary hypertension (exPH) group was segregated from normal response group (exN) with using the definition of a sPAP greater than 40 mm Hg during exercise, or a exercise increase in sPAP by greater than 20 mm Hg1). For transcriptome analysis, total RNAs from whole peripheral blood cells were extracted with using PAXgene miRNA kit. After constructing single-stranded, strand-specific libraries, multiplex sequencing was done. After quantifying the expressions of transcripts, differentially expressed genes (DEGs) between exPH and exN group were selected by paired T-test (P<0.05). And then, hierarchical clustering analysis and pathway enrichment analysis (PathVisio) were performed.
Results There were no significant differences between exPH and exN group in the result of total skin score, serum BNP, tests of pulmonary function and thermography after 0°C-stress. Positive SSc-related autoantibody was a risk factor for exPH (odds ratio, 1.41); especially, positive anti-RNP seemed to be prominent (odds ratio, 3.21). Based on the 817 DEGs between exPH and exN group, the hierarchical clustering showed major 4 clusters, and one of them consisted of only cases in exPH group. When we focused on 117 genes reported to be directly implicated in the development of PAH2), it is noteworthy that 4 of them including TGF-β induced protein were differentially expressed. Pathway analysis of transcriptome revealed that 22 pathways, such as hypertrophy model, lung fibrosis and Wnt/B-catenin signaling, were differently enriched between exPH and exN group.
Conclusions The paradigm of SSc-PAH management should ideally be aimed at detecting early PVD and starting treatment prior to fulfilling the criteria for PAH. Although detection of early PVD in SSc patients remains a major challenge, exercise DE seemed to be a good, non-invasive method for screening. It is noteworthy that expression changes in some of known PAH-related genes were detected from peripheral blood of exPH patients. It shows the possibility that the therapeutic intervention at early stage of the disease may alter the clinical course.
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Parikh VN et al., Circulation 125, 1520–1532 (2012).
Disclosure of Interest None declared