Systemic sclerosis
Figure 1 Heatmap depicting the differential expression of the 53 candidate biomarkers identified in the discovery cohort: standardised expression values of the 53 differentially expressed proteins in the discovery cohort. Red values indicate overexpression and blue values underexpression compared with the mean expression level.
suggested chemerin to be a more promising pathophysiological lead, we chose to focus our investigations on this latter protein.
additional details, see also online supplemental table 1). We iden- tified 53 proteins differentially expressed between the 2 groups (figure 1). Among them, two analytes showed a significant correlation with PVR in cases: chemerin ( ρ =0.62, p=0.01), an adipokine (figure 2); and SET nuclear protooncogene ( ρ =0.62, p=0.01). Similar results were found when removing an outlier patient with markedly high PVR value from the analysis. In a second step, to confirm these results, serum levels of chem- erin and SET were then measured by ELISA in 24 cases and 17 controls from an independent validation cohort (table 1; online supplemental table 1). Consistently, serum levels of chemerin were significantly higher (p=0.01) and correlated significantly with PVR levels ( ρ =0.42, p=0.04) in cases (figure 2). Serum SET levels were undetectable in both cases and controls when measured by ELISA, consistent with its intracellular nature. In a third step, in order to determine if other SSc manifes- tations influenced biomarker concentrations, chemerin serum levels from our discovery cases and controls were compared with other patient groups included in the SOMAscan dataset: patients with dcSSc, no extensive ILD and no PAH (n=11); patients with lcSSc, extensive ILD and no PAH (n=10); and healthy controls (n=11). Circulating concentrations of chemerin were only increased in the PAH group, and similar to healthy controls in all others (figure 3). Overall, these results could suggest that chemerin seems a potential surrogate biomarker for PVR in SSc-PAH. Since results with SET were not reproduced, and since literature data
Expression of chemerin receptor CMKLR1 is increased on PA- SMCs from SSc-PAH patients Because the binding of chemerin to its receptor CMKLR1 stim- ulates the proliferation and migration of PA-SMCs, 26 we first performed a single cell RNA-sequencing (scRNAseq) analysis in lungs from four SSc-PAH and four non-SSc controls to obtain a global view of chemerin and CMKLR1 expression patterns. Our scRNAseq data indicate that CMKLR1 was predominantly expressed by a subpopulation of cells expressing α -SMA and clustering with PA-SMCs/pericytes and myofibroblasts; as well as by endothelial cells and macrophages (figure 4). However, no significant difference between SSc-PAH patients and non-SSc controls was observed in CMKLR1 mRNA expression levels in these different cell populations. In addition, our scRNAseq data indicated that chemerin is mostly expressed by fibroblasts, PA-SMCs/pericytes and mesothelial cells, with a significant increase in SSc-PAH patients as compared with non-SSc controls for this last cell population (figure 4). To confirm our scRNAseq data, confocal microscopic anal- yses were next performed on lung specimens dually labelled with CMLKR1 and a specific PA-SMC marker, α -SMA. Examination of CMLKR1 protein expression patterns showed CMLKR1 staining to be more pronounced in the smooth muscle layer in
Sanges S, et al . Ann Rheum Dis 2023; 82 :365–373. doi:10.1136/ard-2022-223237
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