Although mesenchymal stromal (stem) cell (MSC) administration attenuates sepsis-induced lung injury in pre-clinical models, the mechanism(s) of action and host immune system contributions to its therapeutic effects, remain elusive. We show that treatment with MSCs decreased expression of host-derived microRNA (miR)-193b-5p and increased expression of its target gene, the tight junctional protein occludin (Ocln), in lungs from septic mice. Mutating the Ocln 3′ UTR miR-193b-5p binding sequence impaired binding to Ocln mRNA. Inhibition of miR-193b-5p in human primary pulmonary microvascular endothelial cells (HPMECs) prevents tumor necrosis factor (TNF)-induced decrease in Ocln gene and protein expression and loss of barrier function. MSC conditioned media mitigated TNF-induced miR-193b-5p upregulation and Ocln downregulation in vitro. When administered in vivo, MSC conditioned media recapitulated the effects of MSC administration on pulmonary miR-193b-5p and Ocln expression. MiR-193b deficient mice were resistant to pulmonary inflammation and injury induced by LPS instillation. Silencing of Ocln in miR-193b deficient mice partially recovered the susceptibility to LPS-induced lung injury. In vivo inhibition of miR-193b-5p protected mice from endotoxin-induced lung injury. Finally, the clinical significance of these results was supported by the finding of increased miR-193b-5p expression levels in lung autopsy samples from Acute Respiratory Distress Syndrome patients who died with diffuse alveolar damage.
Apolipoprotein-E-deficient mice exhibit an increased susceptibility to disseminated candidiasis
