Spamprin4-23, a novel mud crab peptide, protects against Vibrio alginolyticus infection via immunomodulation

The aquaculture industry faces significant challenges from Vibrio species, particularly Vibrio alginolyticus, which are major pathogens of farmed aquatic animals. The widespread issue of antibiotic resistance and the limited availability of effective therapeutic drugs necessitate the discovery of novel antibacterial strategies. Marine organisms, like the mud crab Scylla paramamosain, are rich sources of unique antimicrobial peptides (AMPs) that offer promising alternatives to conventional antibiotics, often acting through distinct mechanisms such as immunomodulation.

Researchers identified a previously uncharacterized functional gene, Spamprin, in Scylla paramamosain, noting its tissue-specific distribution and upregulation after LPS stimulation. Through bioinformatics, a truncated peptide, Spamprin4-23, was derived. This peptide was then evaluated for its antimicrobial activity in vitro against a range of microorganisms. Its mechanism of action was investigated by assessing bacterial membrane permeability and morphological changes. Cytotoxicity was tested on crab hemocytes and mammalian HEK293T cells. Finally, the protective effects of Spamprin4-23 were assessed in vivo in Vibrio alginolyticus-challenged mud crabs, measuring bacterial burden, survival rates, and immune-related gene expression.

Spamprin4-23 demonstrated potent antimicrobial activity against a wide range of microorganisms in vitro. Mechanistically, the peptide significantly increased bacterial membrane permeability and induced distinct morphological changes in target microorganisms. Importantly, Spamprin4-23 exhibited no cytotoxic effects against crab hemocytes or mammalian HEK293T cells, suggesting a favorable safety profile. While Spamprin4-23 showed no direct bactericidal activity against V. alginolyticus in vitro, it conferred significant protection in vivo.

Spamprin4-23 reduced bacterial burden in host tissues and led to improved survival of V. alginolyticus-challenged mud crabs. This protective effect was primarily associated with the peptide's immunomodulatory activity, evidenced by the modulation of immune-related gene expression within the host.