Bcl-2 mediates coelomocytes apoptosis by suppressing cytochrome c release in Vibrio splendidus challenged Apostichopus japonicus.

Apoptosis is an evolutionarily conserved immune response and plays a fundamental role in many physiological processes. In this study, the important apoptosis regulator of Bcl-2 homolog from economic marine animal Apostichopus japonicus (AjBcl-2) was cloned and its roles in V. splendidus infection explored. The AjBcl-2 gene contains 3263 nucleotides, with a 5' UTR of 519 bp, an ORF of 660 bp encoding 219 aa sequences, and a 3' UTR of 2084 bp. The AjBcl-2 protein shared a conserved Bcl domain and three Bcl-2 homology domains by SMART program. In healthy sea cucumbers, AjBcl-2 mRNA was expressed in all examined tissues with the peak expression in coelomocytes. The mRNA and protein levels of AjBcl-2 in coelomocytes were depressed at 12 h and 24 h, and induced at 48 h post V. splendidus challenge. In the same conditions, coelomocytes apoptosis rates were significantly increased at 24 h and decreased at 48 h. Moreover, siRNA-mediated AjBcl-2 knockdown significantly increased the coelomocytes apoptosis rates, which could be partially recovered by recombinant AjBcl-2 administration. Furthermore, there was an increase in the AjCyt c protein expression coupled with the downregulation expression of AjBcl-2 post AjBcl-2 silencing. Our results suggested that AjBcl-2 suppressed apoptosis by preventing the AjCyt c release in coelomocytes, and thus mediating V. splendidus infection in sea cucumbers.