PACAP ACTS AS AN ANTIMICROBIAL PEPTIDE AND IMMUNOSTIMULANT DURING FLAVOBACTERIUM PSYCHROPHILUM INFECTIONS IN RTS11 MACROPHAGES
Shawna Semple, University of Waterloo
Shawna L. Semple1, Tania Rodríguez-Ramos1, Yamila Carpio2, John S. Lumsden3, Mario P. Estrada2 and Brian Dixon1
1Department of Biology, University of Waterloo, Waterloo, ON, Canada 2Center for Genetic Engineering and Biotechnology, Havana, Cuba 3Department of Pathobiology, University of Guelph, Guelph, ON, Canada
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide capable of performing roles as a neurotransmitter, neuromodulator and vasodilator. This polypeptide belongs to the glucagon/secretin superfamily, of which some members have been shown to act as antimicrobial peptides in both mammalian and aquatic organisms. In teleosts, PACAP has been demonstrated to have direct antimicrobial activity against several aquatic pathogens, yet this phenomenon has never been studied throughout a live bacterial infection. The present study focuses on the influence of PACAP on the rainbow trout monocyte/macrophage- like cell line, RTS11, when exposed to the coldwater bacterial pathogen Flavobacterium psychrophilum. PACAP was shown to have direct antimicrobial activity on F. psychrophilum when grown in both cytophaga broth and cell culture media. Further, the ability of teleostean PACAP to permeabilize the membrane of an aquatic pathogen, F. psychrophilum, was revealed for the first time. Interestingly, when RTS11 was pre-treated with PACAP for 24 hours before experiencing exposure to live F. psychrophilum, growth of the pathogen was severely inhibited in a dose-dependent manner. Relative expression of pro-inflammatory cytokines and PACAP receptors was also observed in RTS11 following PACAP exposure alone and in conjunction with live F. psychrophilum challenge. The results of this study provide evidence that PACAP has immunostimulatory activity on rainbow trout macrophages as well as direct antimicrobial activity against an aquatic bacterial pathogen. As there are numerous pathogens that impact the aquaculture industry, PACAP may stimulate the teleost immune system while also providing an efficacious alternative to antibiotic use.