Bovine and human cathelicidin cationic host defense peptides similarly suppress transcriptional responses to bacterial lipopolysaccharide

Neeloffer Mookherjee^*^,1, Heather L. Wilson^,1, Silvana Doria^*, Yurij Popowych, Reza Falsafi^*, Jie (Jessie) Yu^*, YueXin Li^*, Sarah Veatch^*, Fiona M. Roche, Kelly L. Brown^*, Fiona S. L. Brinkman, Karsten Hokamp, Andy Potter, Lorne A. Babiuk, Philip J. Griebel and Robert E. W. Hancock^*^,2

^* Centre for Microbial Diseases and Immunity Research, Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada;
Vaccine and Infectious Disease Organization, University of Saskatchewan, Saskatoon, Canada; and
Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada

² Correspondence: Centre for Microbial Diseases and Immunity Research, Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC, Canada. E-mail: bob{at}cmdr.ubc.ca

Genomic approaches can be exploited to expose the complexitiesand conservation of biological systems such as the immune networkacross various mammalian species. In this study, temporal transcriptionalexpression profiles were analyzed in human and bovine monocyticcells in response to the TLR-4 agonist, LPS, in the presenceor absence of their respective host defense peptides. The cathelicidinpeptides, human LL-37 and bovine myeloid antimicrobial peptide-27(BMAP-27), are homologs, yet they have diverged notably in termsof sequence similarity. In spite of their low sequence similarities,both of these cathelicidin peptides demonstrated potent, antiendotoxinactivity in monocytic cells at low, physiologically relevantconcentrations. Microarray studies indicated that 10 ng/ml LPSled to the up-regulation of 125 genes in human monocytes, 106of which were suppressed in the presence of 5 µg/ml ofthe human peptide LL-37. To confirm and extend these data, temporaltranscriptional responses to LPS were assessed in the presenceor absence of the species-specific host defense peptides byquantitative real-time PCR. The transcriptional trends of 20LPS-induced genes were analyzed in bovine and human monocyticcells. These studies demonstrated conserved trends of gene responsesin that both peptides were able to profoundly suppress manyLPS-induced genes. Consistent with this, the human and bovinepeptides suppressed LPS-induced translocation of NF- ${kappa}$ B subunitsp50 and p65 into the nucleus of monocytic cells. However, therewere also distinct differences in responses to LPS and the peptides;for example, treatment with 5 µg/ml BMAP-27 alone tendedto influence gene expression (RELA, TNF- ${alpha}$ -induced protein 2,MAPK phosphatase 1/dual specificity phosphatase 1, I ${kappa}$ B ${kappa}$ B, NF ${kappa}$ BIL1,TNF receptor-associated factor 2) to a greater extent than didthe same amount of human LL-37. We hypothesize that the immunomodulatoryeffects of the species-specific host defense peptides play acritical role in regulating inflammation and represent an evolutionarilyconserved mechanism for maintaining homeostasis, although thesequence divergence of these peptides is substantial.

Key Words: endotoxin • inflammation