Autophagy is related to apoptosis in sea urchin embryos exposed to cadmium

Abstract

The sea urchin embryo is a suitable model system that offers an excellent opportunity to investigate different defense strategies activated in stress conditions. We previously showed that cadmium treatment provokes the accumulation of metal in dose-time dependent manner in embryonic cells and the activation of defense systems, such as the synthesis of HSPs and/or the initiation of apoptosis. Analyzing 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 with subletal Cd concentration activate massive autophagic response after 18h of treatment. In addition, autophagy decreases between 21h and 24h, in the opposite of apoptotic process (1-2). In order to investigate a possible temporal relationship between autophagy and apoptosis , we tested apoptosis by immunodetection in situ of cleaved caspase-3 and TUNEL assays we showed that embryos activate a massive apoptosis after 24h of Cd-treatment. In addition, a functional relationship between autophagy and apoptosis was estimated evaluating apoptosis in Cd-exposed embryos with inhibited autophagy, by treatment with 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. Considering the catabolic role, an energetic hypothesis to explain this relationship was evaluated; in this case autophagy could contribute to apoptotic process providing ATP, necessary for execution of the apoptotic program. In effect, using Methylpyruvate (MP), a substrate for ATP production, in embryos with inhibited autophagy, apoptosis was substantially restored. In this context, autophagy could play a crucial role in stress response of this suitable model system (3). References (1) Klionsky, DJ et al. (2012). Autophagy. 8, 445-544. (2) Chiarelli et al. (2011). Autophagy. 7, 1028-1034. (3) Chiarelli et al. (2012). Cells. 1, 597-616.