Autophagy is related to apoptosis in Paracentrotus lividus embryos cadmium exposed

Abstract

P. lividus embryo offers an excellent opportunity to investigate the adaptive response of cells exposed to different stress. We previously demonstrated that cadmium treatment triggers the accumulation of metal in embryonic cells and the activation of defense system depending on concentration and exposure time, through the synthesis of HSPs and/or the initiation of apoptosis. Analysing autophagy, by neutral red, acridine orange and LC3-detection, we demonstrated that Cd-exposed embryos adopt this process as an additional stratagem to safeguard the developmental program. We observed that embryos treated at subletal Cd concentration activate a massive autophagic response after 18h, which decreases between 21 and 24h, 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. We showed that embryos activate a massive apoptosis after 24h of Cd-exposure. Therefore a functional relationship between autophagy and apoptosis was estimated evaluating apoptotic signals in Cd-exposed embryos, upon treatment with the autophagic inhibitor 3-methyladenine (3-MA). We found that the inhibition of autophagy produced a reduction of apoptotic signals, suggesting that the two phenomena are functionally related. In effect using methylpyruvate (MP), a substrate for ATP production, apoptosis was substantially restored. This suggests that autophagy could energetically contribute to apoptotic execution through its catabolic role.