CircRNA254 functions as the miR-375 sponge to inhibit coelomocyte apoptosis via targeting BAG2 in V. splendidus-challenged Apostichopus japonicus

Abstract

Circular RNAs (circRNAs) function as immune regulators in many biological processes in mammals, while their function and underlying mechanisms in invertebrates are largely unexplored. In this study, the competing endogenous RNA (ceRNA) mechanism of circRNA that sponges miR-375 and thus regulates AjBAG2-mediated coelomocyte apoptosis was evaluated in Apostichopus japonicus. The results showed that circRNA254 (circ254) was significantly down-regulated in the intestines and coelomocytes after Vibrio splendidus challenge or Lipopolysaccharide exposure, which matched the RNA-seq results in A. japonicus within skin ulceration syndrome. Dual-luciferase and RNA FISH assays indicated that circ254 could directly combine with miR-375, in which circ254 possesses three binding sites of miR-375. Moreover, circ254 knockdown significantly promoted the coelomocyte apoptosis levels upon pathogen infection in vivo and in vitro. Furthermore, circ254 silencing could also down-regulate AjBAG2 expression and thereby promoting the levels of coelomocyte apoptosis levels and the expression of caspase 3, which the phenomenon could be reversed by treatment with miR-375 inhibitors. Taken together, our results confirmed that circ254 functions as a ceRNA of AjBAG2 by sponging miR-375, resulting in the inhibition of coelomocyte apoptosis in A. japonicus.