Apoptosis, ROS and Calcium Signaling in Human Spermatozoa: Relationship to Infertility

Apoptosis or programmed cell death is a physiological process involving a finely regulated cascade of biochemical events. The main features of this pathway are the activation of specific proteases such as caspases, the release of pro-apoptotic mitochondrial factors, and finally changes in nuclear morphology and DNA fragmentation. Throughout the apoptotic process, one of the responsible signals for initiating the process of programmed cell death is a sustained and manteined increase in intracellular calcium levels ([Ca2+]i). Experimental evidence suggests that an increase in [Ca2+]i could be associated with the apoptotic signal. In fact, an overload of [Ca2+]i due to depletion of intracellular stores or calcium influx from the extracellular medium has been suggested to be a signal that precedes the apoptotic process. Additionally, apoptosis also can be stimulated by oxidizing agents such as hydrogen peroxide and menadione, and inhibited by antioxidants.