Relationship between autophagy and apoptosis in Paracentrotus lividus embryos cadmium exposed

Cadmium is a strong toxicant for living organism since it does not have biological roles and can cause several cellular damages comprising genotoxicity, oxidative stress, and other biochemical dysfunctions. Marine invertebrate embryos represent a suitable model system where to investigate the effects of many stressors on development and cell viability. Here we investigated the toxic effect of cadmium on sea urchin Paracentrotus lividus embryos focusing our attention on metal-inducead autophagy and the possible temporal and functional relationship with 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 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. Quantitative analysis has shown 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. 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. These data could be explained considering that autophagy could energetically contribute to apoptotic execution through its catabolic role.