Hydrogen peroxide induces apoptotic-like cell death in coelomocytes of Themiste petricola (Sipuncula).

Apoptosis is an active form of cell death that plays a critical role in physiological and pathological conditions of multicellular organisms. These conditions include development, organogenesis, and elimination of infected, mutated, or damaged cells. Sipunculan cells may respond to changes in environmental exposure to oxidative stress by induction of apoptotic cell death. In coelomocytes of the sipunculan worm Themiste petricola, we evaluated morphological and biochemical changes that were induced by hydrogen peroxide (H2O2) and that could be compatible with an apoptotic-like phenotype. At an exposure of 100 mM H2O2, coelomocytes exhibited several morphological hallmarks of apoptosis such as chromatin condensation, nuclear segmentation, cell volume decrease, membrane blebbing, and formation of apoptotic bodies. Biochemical evidences of apoptotic-like cell death included exposure of phosphatidylserine (PS) in the outer leaflet of the plasma membrane and oligonucleosomal DNA fragmentation. In addition, exposure of coelomocytes to H2O2 induced a rapid massive loss of mitochondrial membrane potential and of the acidic pH of lysosomes. Overall, our results showed that, in sipunculan coelomocytes, H2O2 can induce changes compatible with an apoptotic-like phenotype. The finding of an oxidative-stress-induced apoptotic-like phenotype in a sipunculan worm may indicate that this kind of cell death process participates in regulation of cell number during physiological and pathological situations, including immune responses.