Abstract
BackgroundThe non-cancerous functions of Akt in the airway are understudied. In some tissues, Akt phosphorylates and activates endothelial nitric oxide synthase (eNOS) to produce nitric oxide (NO) that has anti-inflammatory effects. NO production has antibacterial and antiviral effects in the airway, and increasing NO may be a useful anti-pathogen strategy. Akt also stimulates the nuclear factor erythroid 2–related factor 2 (Nrf-2) transcription factor, which transcribes antioxidant genes. Therefore, we hypothesized that activation of the Akt/eNOS pathway, which also activates Nrf-2, may have protective effects in human airway cells against injury.MethodsTo directly test the effects of Akt signaling in the airway, we treated A549 and 16HBE cells as well as primary bronchial, nasal, and type II alveolar epithelial cells with small molecule Akt activator SC79. We examined the effects of SC79 on eNOS activation, NO production, Nrf-2 target levels, and interleukin-8 (IL-8) transcription during exposure to TNF-α or Pseudomonas flagellin (TLR5 agonist). Additionally, air–liquid interface bronchial cultures were treated with cadmium, an oxidative stressor that causes airway barrier breakdown.ResultsSC79 induced a ~ twofold induction of p-eNOS and Nrf-2 protein levels blocked by PI3K inhibitor LY294002. Live cell imaging revealed SC79 increased acute NO production. Quantitative RT-PCR showed a ~ twofold increase in Nrf-2 target gene transcription. TNF-α or flagellin-induced IL-8 levels were also significantly reduced with SC79 treatment. Moreover, the transepithelial electrical resistance decrease observed with cadmium was ameliorated by SC79, likely by an acute increase in tight junction protein ZO-1 levels.ConclusionsTogether, the data presented here demonstrate SC79 activation of Akt induces potentially anti-pathogenic NO production, antioxidant gene transcription, reduces IL-8 transcription, and may protect against oxidative barrier dysfunction in a wide range of airway epithelial cells.
Highlights
The non-cancerous functions of Protein kinase B (Akt) in the airway are understudied
We previously showed that acute nitric oxide (NO) production via endothelial nitric oxide synthase (eNOS) can markedly enhance the phagocytic activity of macrophages [14], a major cell type involved in airway epithelial innate immunity
We demonstrated that SC79 activation of Akt has two downstream targets important for innate defense in airway epithelial cells: phosphorylation of eNOS and upregulation of nuclear factor erythroid 2–related factor 2 (Nrf-2) (Fig. 7), which likely have beneficial effects against inflammation and oxidative stress
Summary
Akt phosphorylates and activates endothelial nitric oxide synthase (eNOS) to produce nitric oxide (NO) that has anti-inflammatory effects. NO production has antibacterial and antiviral effects in the airway, and increasing NO may be a useful antipathogen strategy. We hypothesized that activation of the Akt/eNOS pathway, which activates Nrf-2, may have protective effects in human airway cells against injury. There is a need for new therapeutic strategies to reduce inflammation and restore barrier function in diseases such as asthma, chronic rhinosinusitis (CRS), cystic fibrosis (CF), and chronic obstructive pulmonary diseases (COPD). Because Akt is activated downstream of inflammatory receptors like toll-like receptors (TLRs) among many other kinases (described in the discussion), the specific positive or negative contributions of Akt to inflammation in airway epithelial cells has been unclear and required empirical testing
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
