Relationship between autophagy and apoptosis in Paracentrotus lividus embryos cadmium exposed

Abstract

Sea urchin embryo is a developmental model that offers an excellent opportunity to investigate the possible adaptive response of cells exposed to different stress during differentiation. We previously demonstrated that cadmium treatment triggers the accumulation of metal in embryonic cells and the activation of defense systems depending on concentration and exposure time, through the synthesis of heat shock proteins and/ or the initiation of apoptosis. Using several techniques to detect autophagy (neutral red, acridine orange and LC3-detection) we demonstrated that Cd-exposed P. lividus embryos adopt this process as an additional stratagem to safeguard the developmental program. In particular we observed that embryos treated at subletal Cd concentration activate a massive autophagic response after 18 h, which decreases between 21 and 24 h, in the opposite of apoptotic process. In order to investigate a possible temporal relationship between autophagy and apoptosis, we tested apoptotic signals by TUNEL and immunofluorescence in situ assays of cleaved caspase-3. Quantitative analysis has shown that embryos activate a massive apoptosis after 24 h of Cd-exposure. erefore a functional relationship between autophagy and apoptosis was estimated evaluating apoptotic signals in Cd-exposed embryos, upon treatment with the autophagic inhibitor 3-methyladenine. We found that the inhibition of autophagy produced a contemporaneous reduction of apoptotic signals, suggesting that the two phenomena are functionally related. In effect using methylpyruvate, a cell-permeable substrate for ATP production, apoptotic signals were substantially restored. ese data could be explained considering that autophagy could energetically contribute to apoptotic execution through its catabolic role.