Signal Transduction Of Mitochondrial Apoptotic Pathway During The Autolysis Of Sea Cucumber (Stichopus Japonicus)

Sea cucumber body wall melting occurs under certain circumstances,such as expose to high temperature,nutrient deficiency and exposure to sunlight or UV irradiation.This phenomenon is a major concern for sea cucumber production,particularly during cultivation,transportation,handling and processing.Thus,understanding the sea cucumber melting mechanism could contribute to the sea cucumber cultivation and processing industry.The early data of research has shown that apoptosis plays a critical role in the initial stage.However,it is still unclear how apoptosis is triggered in this process.Based on sea cucumber(Stichopus japonicus),we examined the reactive oxygen species(ROS)and the depolarization of mitochondria transmembrane potential by inversion fluorescence microscope.Furthermore,the activity of SOD and the change of calcium ion concentration in coelomic fluid cells during autolysis were also detected.The levels of B-cell lymphoma-2(Bcl-2),Bcl-2 Associated X Protein(Bax)and pro-caspase-3 were examined by western blotting during the sea cucumber melting induced by ultraviolet exposure.We also investigated the contribution of caspase-3 and caspase-9 in this process by injecting pan-caspase inhibitor,and the changes of the expression of caspase-3 was determined.The results showed that ultraviolet exposure stimulates the ROS production,and consumed a large amount of SOD,resulting in the decrease of SOD content in the cells.At the same time,the content of calcium ions in sea cucumber coelomic fluid cells was increased,along with the decrease of mitochondrial membrane potential.We found a decrease of Bcl-2 and increase of Bax in the mitochondria after ultraviolet exposure.We also demonstrated that these changes are associated with the elevated activity of caspase-9 and-3.Meanwhile,the expression level of pro-caspase-3 decreased gradually,while the expression level of caspse-3 mRNA was up-regulated.Finally,our data showed that inhibition of caspase-9 and-3 using inhibitor suppresses the ultraviolet induced sea cucumber melting.These results suggest that the apoptosis during sea cucumber melting is mediated through the mitochondria dysfunction and following activation of caspase signaling pathway.This study presents a novel insight into the mechanism of sea cucumber melting.