ANTIMICROBIAL PEPTIDES IN AMPHIBIAN SKIN SECRETIONS

Mangoni, M.L.(1), Miele, R.(1), Mignogna, G.(1), Borro, M.(1), Fiocco, D.(1), Simmaco, M.(1), Barra, D.(1)

(1)Dipartimento di Scienze Biochimiche A. Rossi Fanelli, Università La Sapienza, Piazzale Aldo Moro 5, 00185, Roma

Amphibian skin secretions contain many biologically active compounds, among which a number of antimicrobial peptides has been isolated and characterized in our laboratory. These peptides are synthesized by ribosomes as inactive precursors and proteolytically processed in several steps to the active forms, which are then stored in the granular glands of the skin. Some of these molecules contain, as result of a post-translational modification, a D-amino acid in their sequence. Antimicrobial peptides are considered the effector molecules of innate immunity, acting as a first line of defense against bacterial infections. We have studied the biological activity of purified peptides and their analogues against Gram-positive and Gram-negative bacteria as well as fungi. We have also used frogs as model systems for the study of factors controlling both natural infections and the natural flora. We have demonstrated that glucocorticoids (GC), known to suppress immune functions in mammalian cell cultures, influence the peptide-mediated innate immunity in amphibia. In particular, GC-treatment of Rana esculenta results in the almost complete inhibition of the de novo synthesis of the antimicrobial peptides normally present in the skin secretion, as monitored by both HPLC and Northern blot analyses. In addition, immunoblot analysis of skin proteins shows a clear rise of IB. These results suggest that frogs in vivo regulate their peptide antibiotic synthesis by an NF-B/IB-like mechanism. The determination of the structure of a number of genes coding for antimicrobial peptides in Bombina orientalis has actually shown that their promoter regions contain recognition sites for nuclear factors. Experiments performed in vivo demonstrate for the first time the inducibility of defence peptides in a vertebrate and that the absence of natural flora prevents the production of antimicrobial peptides in skin secretion.

CORRESPONDENCE TO:

Donatella Barra, Dipartimento di Scienze Biochimiche ‘A. Rossi Fanelli’, Università La Sapienza ,Piazzale Aldo Moro 5, 00185 Roma, Email: donatella.barra@uniroma1.it