AB0208 UP-REGULATION OF TMEM176A AND TMEM176B IN PERIPHERAL BLOOD CELLS, A POSSIBLE BIOMARKER FOR THE DEVELOPMENT OF EARLY PULMONARY VASCULAR DISEASE IN SYSTEMIC SCLEROSIS
Authors: Yoshinobu Koyama, Soichiro Fuke, Yoshiharu Sato, Akemi Senoh, Toshie Higuchi
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> Pulmonary arterial hypertension (PAH) is prominent as a vascular involvement of 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 2/3 of the pulmonary circulation is impaired by the time of diagnosis. However, there were few studies focusing on the molecular mechanisms of PVD at the subclinical stage of PAH in SSc patients. <h3>Objectives</h3> To detect candidate genes involved in the development of PVD before diagnosis of PAH in SSc patients. <h3>Methods</h3> Total of 88 patients who had not met PAH criteria with Raynaud phenomenon (n=75), skin sclerosis (n=58) or SSc-related autoantibody (n=59) was enrolled. To detect the early PVD, exercise Doppler echocardiography (exDE) was carried out. The exercise induced pulmonary arterial hypertension (exPAH) group was segregated from normal response group (exN) with using the reported definition<sup>1)</sup>. The exDE was followed every 6 or 12 months for up to 3 years. For gene expression analysis, total RNAs from whole peripheral blood cells were extracted by PAXgene system and multiplex sequencing was done. To identify candidate genes involved in the pathogenesis of the early PVD, the differentially expressed genes (DEGs) between exPAH and exN group were visualized by volcano plots, a scatter plots calculated to show fold-changes and p-values of DEGs. After identifying the candidate genes, weighted gene co-expression network analysis (WGCNA) was performed to find the co-expressed gene cluster. And then, enrichment analysis using gene ontology (GO) terms were performed to investigate roles of the gene cluster in pathogenesis of PVD. <h3>Results</h3> Patients were fall into exPAH group (n=14) and exN group (n=74) at the baseline. After gene expression analysis, 1204 DEGs between exPAH and exN group were identified. Volcano plots indicated that expressions of TMEM176A and TMEM176B were prominent (log<sub>2</sub> fold-change &gt;1.25 and –log<sub>10</sub>p-value &gt;3.5) in exPAH patients. We also found that the expressions of these genes were highly correlated with each other (R<sup>2</sup>=0.9724, p&lt;0.01). 11 out of 74 patients (14.9%) in exN group progressed to exPAH group during follow-up period (24.8±11.3 months). The expressions of TMEM176A/B at the baseline were significantly up-regulated in the group of clinical progression as compare with others (log<sub>2</sub> fold-change from the average: TMEM176A: 0.78±1.31 vs. -0.35±1.65; p=0.022, TMEM176B: 0.71±1.38 vs. -0.38±1.78; p=0.034). By WGCNA and GO enrichment analysis, the terms, such as related to "apoptosis", "Toll-like receptor signaling" and "dendritic cell differentiation" were found in the co-expressed gene cluster of TMEM176A/B. <h3>Conclusion</h3> Although elucidating the mechanisms for progression of early PVD in SSc remains a major challenge, (1) we found up-regulation of TMEM176A/B was prominent in exPAH group; (2) TMEM176A/B was significantly up-regulated at the baseline in the patients progressed from exN to exPAH group during the follow-up period; (3) the co-expressed gene cluster of TMEM176A/B includes genes related to "apoptosis", "Toll-like receptor signaling" and "dendritic cell differentiation". TMEM176A/B was found initially to be a regulator for DC maturation in mice<sup>2)</sup> but functions of human ortholog of these genes remain still unclear. However, our findings suggest that the up-regulation of TMEM176A/B in peripheral blood cells is possible to be a biomarker for the development of early PVD in SSc. <h3>Reference</h3> [1] R. Naeije, et al., Am J resp and critical care med 187, 576-583 (2013). 2) Condamine, T.et al., J of leuko biol88, 507-515 (2010). <h3>Disclosure of Interests</h3> Yoshinobu Koyama Paid instructor for: Asahi Kasei Pharma, Speakers bureau: BMS, Chugai, Ayumi and Eli Lilly, Soichiro Fuke: None declared, Yoshiharu Sato: None declared, Akemi Senoh: None declared, Toshie Higuchi: None declared