The Immunomodulation Effects And Mechanisms Of Cathelicidin-related Antimicrobial Peptide(CRAMP)in Mouse Models Of Intestinal Colitis And Asthma

Cathelicidin is a bioactive polypeptide family widely found in vertebrates, and its cathelin domain is highly conserved in different species. Only a single cathelicidin gene exists in human and mouse, and the related antimicrobial peptide named LL-37 in human and CRAMP in mice respectively. LL37 and CRAMP are very similar in structure, function and tissue distribution. Thus, studying the pathophysiology of CRAMP in murine models of human diseases will facilitate understanding of the roles and pathophysiological mechanisms of LL-37 in clinical disorders. The earliest studies of LL-37/CRAMP were mainly focused on its broad-spectrum anti-microbial activity. An increasing number of research data in recent years shows that Cathelicidin also plays an important role on regulating the immune responses as a key molecule. It is involved in immunopathogenesis of inflammatory diseases, autoimmune diseases and cancers. However, the functions of LL-37/CRAMP are multiple, and it can either promote or suppress inflammation under various immunopathological mechanisms, which may attribute to the specific pathological microenvironment in different disease conditions.This study aims to investigate the possible roles of CRAMP in mouse models of asthma and inflammatory bowel diseases, reveal its regulatory mechanism under different pathological microenvironment, and assess the potential applications of targeting CRAMP for a therapeutic purpose in inflammatory diseases. This study mainly include:1. Using macrophage cell line RAW264.7 to show that synthetic peptide CRAMP suppress LPS stimulated expression of inflammatory cytokine TNF, and intranasal administration of CRAMP induced inflammatory cells infiltration and proinflammatory cytokine accumulation in airway; 2. Intranasal intervention with exogenous CRAMP exacerbated OVA-induced inflammatory cells infiltration and proinflammatory cytokine accumulation in airway, OVA-IgE elevation in serum, and lung tissue inflammation and airway goblet cells hyperplasia; 3. Employing TNBS or Oxazolone to induce mouse models of Crohn’s diseases (CD) and ulcerative colitis (UC), revealing that CRAMP and its receptor were highly expressed in Oxazolone-induced UC mice rather than TNBS-induced CD mice; 4. Intrarectally administration with exogenous CRAMP reduced significantly inflammatory cells and inflammatory cytokines accumulation and intestinal epithelial damage, and increased the expression of tissue repair related genes, but had no effects on Th and Treg immune response, showing a therapeutic effect; 5. Intraperitoneal administration with CRAMP reduced inflammatory cytokine level in Oxazolone-induced colitis, but it decreased the level of tissue repair related genes expression and exacerbated mouse death and bodyweight loss; 6. Based on HBcAg VLPs, anti-CRAMP vaccines were constructed, and CRAMP antiserum were prepared by immunizing mice with the vaccines. Passive immunization with antiserum to neutralize abnormally increased CRAMP in oxazolone-induced colitis showed that there were no influences on mouse death, bodyweight loss, intestinal inflammation, and T cell responses, indicating that CRAMP mainly affect the innate immunity and epithelial repair and not adaptive immunity to function in Oxazolone-induced colitis.The results demonstrated that CRAMP exacerbated significantly allergen-induced acute airway inflammatory responses, and local administration of CRAMP significantly suppressed inflammatory responses in oxazolone-induced intestinal colitis. These results suggest that targeting CRAMP signaling pathway for a therapeutic purpose need careful consideration the detailed disease conditions and immunopathological mechanisms, moreover, local administration of exogenous CRAMP is a possible and promising therapeutic approach in the treatment of inflammatory bowel diseases.