Hepcidin from the Chinese Spiny Frog (Quasipaa spinosa) Integrates Membrane-Disruptive Antibacterial Activity with Macrophage-Mediated Protection Against Elizabethkingia miricola

Abstract

Background/Objectives: Hepcidin is a cysteine-rich antimicrobial peptide that links iron homeostasis and innate immunity in vertebrates, but its functions in amphibians remain poorly understood. The Chinese spiny frog (Quasipaa spinosa) is an economically important species that suffers serious losses from bacterial diseases. This study aimed to identify and functionally characterize a hepcidin homolog (QsHep) from Q. spinosa, focusing on its antibacterial activity, immunomodulatory effects on primary macrophages, and protective efficacy against Elizabethkingia miricola infection. Methods: The QsHep gene was cloned and analyzed, its tissue distribution and inducible expression were examined by qRT-PCR, and the synthetic peptide was tested for antimicrobial, membrane-disruptive, and immunomodulatory activities in vitro, as well as for in vivo protection in an E. miricola infection model. Results: QsHep encodes a typical preprohepcidin with a signal peptide, prodomain, and a conserved mature peptide containing eight cysteine residues. QsHep was widely expressed, with the highest levels in liver, and was significantly upregulated in liver and spleen following bacterial challenge. Synthetic QsHep displayed broad-spectrum antibacterial activity, including strong inhibition of E. miricola, and induced dose-dependent membrane damage in E. miricola. QsHep showed no obvious cytotoxicity but significantly enhanced chemotaxis, phagocytic activity, and respiratory burst in primary macrophages. In vivo, QsHep treatment markedly improved the survival of E. miricola-infected frogs in a dose-dependent manner. Conclusions: QsHep is an amphibian hepcidin that combines membrane-disruptive antibacterial activity with the activation of macrophage effector functions and confers significant protection against bacterial infection in vivo. These findings expand our understanding of hepcidin-mediated innate immunity in amphibians and highlight QsHep as a promising peptide candidate for controlling bacterial diseases in frog aquaculture.