Airway epithelial cells secrete altered exosomal microRNAs in murine experimental and human paediatric asthma
Background: miRNAs (miR) are critical regulators of the immune system. Recently they have been shown to be secreted into exosomes for inter-cell communication (Valadi et al., Nat Cell Biol, 2007). We previously identified an up-regulation of miR-17, -144 and -21 in murine lung homogenate in Ovalbumin (OVA) induced allergic airway inflammation (AAI) and in nasal epithelial cells of children with allergic asthma.
Objective: We now aimed to decipher the role of the bronchial epithelium in the production and secretion of miRNAs in asthma.
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. Exosomes were isolated by Exoquick-TC from cell culture, broncho-alveolar lavage fluid (BALF) of mice and human nasal washes and quantified by flow cytometry or ELISA for CD63. miRNA levels were assessed by qRT-PCR.
Results: Exosomal miR-17 and -21 levels were initially increased upon IL-13 treatment in the basal cell compartment and later on the apical. In murine BALF of OVA-induced AAI miR-17 and -21 were significantly up-regulated while exosome amounts were similar. These finding were consolidated in house dust mite induced AAI. All miRNAs could be detected in exosomes of human nasal washes.
Conclusion: miR-17 and -21 levels in exosomes were increased upon in vitro IL-13 treatment of primary NHBE cells and in biofluids of murine AAI and human paediatric asthma. A distribution of miRNAs via exosomes could perpetuate an asthmatic response and expand it to other cell types such as immune cells.