Expression analysis of extracellular microRNA in bronchoalveolar lavage fluid from patients with pulmonary sarcoidosis

Background and objective: MicroRNA (miRNA) are transcriptional regulators implicated in pulmonary sarcoidosis and packaged in extracellular vesicles (EV) during cellular communication. We characterized EV and investigated miRNA expression in bronchoalveolar lavage (BAL) fluid from sarcoidosis patients.

Methods: EV were characterized for size(s) using dynamic light scattering and transmission electron microscopy (TEM) analysis and protein markers by immunoblotting. Twelve extracellular and 5 cellular miRNA were investigated in BAL from 16 chest X-ray stage-I (CXR-I) and 17 CXR stage-II (CXR-II) sarcoidosis patients. Associations between miRNA and disease characteristics (extrapulmonary involvement, pulmonary function and BAL cell profile) were statistically analysed.

Results: BAL from sarcoidosis patients contained exosomes and microvesicles (MV) as EV. In these EV, expression of miR-146a (P = 0.007), miR-150 (P = 0.003) and BAL cellular miR-21 (P = 0.01) was increased in CXR-II compared with CXR-I. Other detected EV (miR-21 and miR-26a) and cellular (miR-31, miR-129-3p, miR-146a and miR-452) miRNA were not differentially expressed. The investigated miRNA did not reflect extrapulmonary involvement, but EV miR-146a and miR-150 were negatively correlated with pulmonary function (miR-146a with vital capacity (VC; Spearman's correlation coefficient (r_s ), P = -0.657, 0.007), percent predicted forced expiratory volume in 1 s (FEV₁ ; -0.662, 0.006) and FEV₁ /forced vital capacity (FVC) ratio (-0.649, 0.008); miR-150 correlated negatively with VC (-0.584, 0.019) and FEV₁ /FVC ratio (-0.746, 0.001) in CXR-II cases).

Conclusion: Our data provide evidence that exosomes and microvesicles as extracellular vesicles are present in the bronchoalveolar space of sarcoidosis patients and they differentially express EV miRNA (miR-146a and miR-150), the expression of which correlates negatively with pulmonary function indices. The significance of these findings for disease pathophysiology and clinical course require further investigation.