Secretion of miRNA-containing extracellular vesicles (EV) by bronchial epithelial cells in allergic airway inflammation

Background: miRNAs (miR) are critical regulators of the immune system. Recently they have been shown to be secreted into EVs for inter-cell communication (Valadi et al., Nat Cell Biol, 2007). We previously identified an up-regulation of miR-17 and -21 in murine lung homogenate in Ovalbumin (OVA) induced allergic airway inflammation (AAI).

Objective: We now asked if mir-17 and miR-21 are produced by the human bronchial epithelium and released into EVs in AAI.

Methods: Primary normal human bronchial epithelial (NHBE) cells were cultured at the air-liquid interface and treated with Interleukin (IL) 13 to model a T-helper 2 environment. EVs were isolated by Exoquick-TC or qEV columns and quantified by bead-based flow cytometry for CD63. miRNA levels were assessed by qRT-PCR.

Results: CD63+ EVs were present in both the apical as well as the basal cell compartment with different secretion patterns upon IL13 treatment. Upon IL13 treatment EV miR-17 and -21 levels increased first in the basal cell compartment and later in the apical. In two murine models for AAI, OVA and house-dust mite, miR-17 and -21 were significantly up-regulated in EVs from broncho-alveolar lavage fluid (BALF) while CD63+ EV amounts were similar.

Conclusion: EV are secreted in vitro upon IL13 treatment of primary NHBE cells and are present in BALF of murine AAI and we have first hints for altered miRNA levels in “asthmatic EVs”. Currently, we are investigating if a distribution of miRNA via EVs can perpetuate an asthmatic response and expand it to other cell types such as immune cells, or vice versa have a regenerative effect on the airway epithelium.