Strange though it may seem, each day billions of cells in the human body kill themselves. Indeed its fundamental to our health: failure of cells to die can lead to problems like cancer, among other things. Even in the fetus, programmed cell death plays a critical role, helping to shape the developing body. For years biologists have assumed that cell suicide occurs by way of a singular process dubbed apoptosis. But in a report published today in the Proceedings of the National Academy of Sciences, researchers announced that they have uncovered a second cell death program, which they are calling paraptosis. Unlike apoptosis--in which cell death is characterized by fragmentation of the cell, its nucleus and its DNA--paraptosis occurs when empty pockets known as vacuoles form in the cells cytoplasm, and the cells energy-producing organelles, or mitochondria, swell. Further differentiating the two programs, drugs used to block apoptosis are ineffective against paraptosis.
Of interest, scientists have also observed paraptosis-like characteristics in lower organisms whose emergence predates the evolution of apoptosis. Paraptosis may therefore be the older cell death program. "Understanding the biochemical pathway(s) for non-apoptotic programmed cell death has potential implications for the understanding of neurodegeneration, cancer therapeutics, development, and evolutionary aspects of cell death programs," the team concludes. "We are fascinated by paraptosis because it appears to occur during the development of the nervous system, as well as in some cases of neurodegeneration," team member Dale Bredesen of the Buck Institute for Age Research comments. "Therefore, although it may be the road less traveled in dying cancer cells, it appears to be a well-worn path in brain cells, and therefore a potentially important therapeutic target."