LL-37 Inhibits Nthi-dna-induced IFN-β Expression And Alleviates Lung Inflammatory Injury In Infected Mice

Objective: To investigate the role of LL-37/CRAMP on NTHi-DNAinduced-IFN-β and lung inflammatory injury in NTHi-infected COPD mice,and explore the regulatory mechanism.Background: Chronic obstructive pulmonary disease(COPD)is the third most common chronic disease in China after hypertension and diabetes.Non-typeable Haemophilus influenzae(NTHi)infection is one of the leading causes of acute exacerbation of COPD(AECOPD).To study the mechanism of interaction between host and NTHi may provide new ideas and methods for the prevention and treatment of COPD caused by NTHi infection.In our previous experiments,we found that NTHi-DNA can enhance the inflammatory response by promoting IFN-β secretion,which is not conducive to the prognosis of COPD.However,we wonder whether there is a molecule that can regulate NTHi-DNA-mediated immune response during COPD.It was found in clinical samples that the expression level of antibacterial peptide LL-37 is closely related to the progression of COPD disease.LL-37 is the only cathelicidin family of antimicrobial peptides in human,which plays an indispensable role in the host immune response.Cathelicidin-related antimicrobial peptide(CRAMP)is the homologue of LL-37 in mice.It was also confirmed in our preliminary study when RAW264.7 cells were stimulated by NTHi-DNA,the expression of LL-37/CRAMP will be up-regulated.It suggests that LL-37/CRAMP may be involved in NTHi-DNA-mediated immune response and play an important role in COPD disease.Therefore,we will explore the relationship between NTHi-DNA and LL-37/CRAMP,and elucidated its interaction mechanism in NTHi-infected COPD.Methods and Results:1.The treatment of NTHi-DNA or NTHi can promote the expression of LL-37/CRAMP in RAW264.7 cells.Although exogenous LL-37/CRAMP does not affect the phagocytosis of RAW264.7 cells on NTHi,it can significantly promote the killing ability of macrophages.2.LL-37/CRAMP can reduce the NTHi-DNA or NTHi-induced expression of IFN-β,inflammatory factors IL-1β,IL-6,ISG15 and the proinflammatory marker NOS2 in vitro.The regulation effect of LL-37/CRAMP on NTHi-DNA-mediated immune response may be related to STING/p38 MAPK signaling pathway.3.In NTHi-infected COPD mice,LL-37/CRAMP can inhibit the expression of IFN-β and inflammatory factors IL-1β,IL-6,and ISG15.In addition,LL-37/CRAMP can partially recover the weight loss and alleviate lung inflammatory damage caused by NTHi infection.Conclusions: In this study,we confirmed that LL-37/CRAMP can decrease the over-expression of NTHi-DNA mediated IFN-β and IFN-β-related inflammatory cytokine,further reduce lung inflammatory injury in NTHi-infected COPD mice.Moreover,we demonstrated that LL-37/CRAMP exerts its immune regulation on NTHi-DNA through the STING/p38 MAPK signaling pathway.In summary,our finding elucidated the relationship between NTHi-DNA immune stimulation and antimicrobial peptide LL-37/CRAMP in macrophages,revealed the regulatory role of LL-37/CRAMP in the prevention of bacterial infection in COPD disease,which provides a new insight into the prevention and treatment of COPD with NTHi infection.