α-MSH is partially involved in the immunomodulation of Nile tilapia (Oreochromis niloticus) antibacterial immunity

Abstract

α-Melanocyte-stimulating hormone (α-MSH) is a well-studied neuropeptide controlling skin and hair color. Besides, numerous immunomodulation roles of α-MSH were recorded in humans and mice. However, the regulatory effects of α-MSH in teleost immunity haven't been well elucidated. In this study, several precursor molecules of α-MSH (POMCs) and its receptors (MCRs) in Nile tilapia (Oreochromis niloticus) were characterized, and their expression characteristics and specific functions on antibacterial immunity were determined. Overall, POMCs and MCRs were principally detected in the brain, skin, and liver, and were remarkably promoted post Streptococcus agalactiae infection. However, tiny POMCs and MCRs were observed in tilapia immune organs (head kidney and spleen) or lymphocytes, and no evident immunomodulation effect was detected in vitro. Moreover, the in vivo challenge experiments revealed that α-MSH protects tilapia from bacterial infection by regulating responses in the brain and intestine. This study lays theoretical data for a deeper comprehension of the immunomodulation mechanisms of teleost α-MSH and the evolutional process of the vertebrate melanocortin system.