Ca2+-SpVAMP2 pathway promotes exosome secretion to resist the infection of Vibrio parahaemolyticus in mud crab (Scylla paramamosain)

Exosomes play an important role in the innate immune system. Many types of cells can secrete exosomes in both normal and abnormal status. However, the mechanism of exosome secretion in invertebrates has not been reported. In this study, the mechanism of the secretion of exosomes regulated by the Ca²⁺ signaling pathway in the hemocytes of mud crabs (Scylla paramamosain) under infection with Vibrio parahaemolyticus was investigated. The results showed that the increase of exosome secretion in mud crabs infected with V. parahaemolyticus was caused by the increase in intracellular Ca²⁺ level. In addition, transcriptome sequencing and differential expression analysis revealed that SpVAMP2, a vesicle-associated membrane protein 2, was found to be involved in the exosome secretion regulated by Ca²⁺ signaling. Further research revealed that SpVAMP2 can inhibit MVB from entering the lysosome for degradation and promote the release of exosomes. Additionally, the secretion of exosomes upregulated the expression of anti-lipopolysaccharide factors and enhanced the survival rate of mud crabs after V. parahaemolyticus infection. This study clarified the exosome secretion regulated by the Ca²⁺-SpVAMP2 pathway, which, in turn, increased the innate immune response in mud crabs to resist the invasion of V. parahaemolyticus.