A pilot study assessing the effect of air pollution on extracellular vesicles in systemic sclerosis

Introduction: The identification of specific diagnostic and prognostic biomarkers remains an unmet need in Systemic Sclerosis (SSc). Over the past few years, it has been suggested that extracellular vescicles (EVs) and environmental toxicants, such as particulate matter (PM), may have an important role in the pathogenesis of autoimmune diseases. At present, no data are available on the impact of PM exposure on EVs from patients with SSc. Our aim was to evaluate the effects of PM with aerodynamic diameter less than 10 µm (PM10) and 2.5 µm (PM2.5) on EVs in SSc and osteoarthritis (OA). Material and Methods: Plasma EVs were analyzed by Nanosight and flow cytometry after labeling with the following markers: CD14 (monocyte), CD61 (platelet), CD25 (T-reg), human endogenous retrovirus w (HERV-w) and human leukocyte antigen G (HLA-G). Demographic and clinical data were collected for each patient. Plasma EV concentrations were measured in SSc and OA patients and were analyzed by generalized linear regression models. Daily PM concentrations, estimated by the Regional Environmental Protection Agency at municipality resolution, were used to assign short-term exposure (mean of the 7 days preceding the evaluation) to each study subject. Results: 12 consecutive limited cutaneous SSc (11 female, median age 66.8 yrs, median disease duration 12.3 yrs, median mRSS 3.5) and 12 patients with OA (8 female, median age 67.1 yrs, median disease duration 9.3 yrs) were enrolled. In the table below, EV count and MV subtypes are reported with respect to PM2.5 and PM10 exposure both in SSc and OA patients. The increase of PM2.5 led to a decrease of HERV-w+ microvesicles (MV) in both SSc (β =-0.10; p=0.01) and OA (β =-0.09; p=0.01) and of HLA-G+ (β =-0.11; p<0. 01) only in SSc. Similar results were observed analyzing PM10 exposure. Analysis of EV concentration according to their dimensions showed a negative association in the size range of exosomes (63-92nm) in SSc compared to OA (p<0. 05) and in the range of MV (230-510 nm). A positive association between HLA-G+ with ESR (β =0.34; p<0.01). Conclusions: In our study, limited cutaneous SSc showed different EV concentrations from controls: SSc tends to have less exosomes and more MV than OA. Moreover, environmental stimuli are confirmed to be able to influence HERV-w+ MV release both in SSc and controls. Finally, in SSc patients PM exposure could significantly alter the release of HLA-G+ MV that has been correlated to the process of self-tolerance maintenance.