AIM: We previously showed that increased PI3K activity was associated with impaired IFN-β responses to influenza infection in the primary bronchial epithelial cells (pBECs) from people with chronic obstructive pulmonary disease (COPD). In this study we aim to determine the pathway that led to increased PI3K activity and subsequent reduction in IFN-β in COPD.

METHODS: pBECs from healthy controls and subjects with COPD were infected with human influenza A/H1N1 at MOI of 5. SHP-1, pAkt, IRF3/pIRF3, and IFN-β was measured by immunoblotting. Viral replication was measured by plaque assay. miR-155 and Akt mRNA was measured by qPCR. SHP-1- or Akt-siRNA, or miR-155 inhibitor was added 24hr before infection.

RESULTS: Increased PI3K activity (pAkt-S473) in COPD pBECs was the result of reduced level of negative regulator SHP-1. Treatment with SHP-1 siRNA led to increased pAKt and decreased IFN-β induction. miR-155 has been shown to directly target SHP-1, and its level was significantly enhanced in COPD pBECs. Inhibition of miR-155 restored SHP-1 level and decreased PI3K activation. Moreover inhibition of Akt or SHP-1 by siRNA also reduced pIRF3 and IFN-β response in both healthy and COPD pBECs. miR-155 inhibition resulted in increased pIRF3 activation and IFN-β response in COPD pBECs. This increase in antiviral responses then led to reduced viral replication.

CONCLUSION: Enhanced PI3K activity was the result of decreased SHP-1 and increased miR-155 level. Elevated PI3K activity led to decreased IFN-β response to influenza infection in COPD pBECs, resulting in enhanced viral replication. By using miR-155 inhibitor the level of PI3K activity was reduced, which led to increased antiviral responses to influenza infection in both healthy and COPD pBECs.