Apoptosis of retinal ganglion cells in glaucoma: an update of the molecular pathways involved in cell death.

Apoptosis is a genetically controlled form of cell death that ganglion cells undergo during normal development of the retina and in diseases affecting the optic nerve, such as glaucoma. This mechanism of cell death is controlled by specific genes and their products that are activated in the dying cell. To date, the mechanism of ganglion cell apoptosis is poorly understood, but research on cell death in other areas has provided a blueprint for the study of dying ganglion cells in animal models. Extensive research of the genetic pathways of apoptosis of neurons, in general, has yielded new information about the principal genes that are involved in this process. This review is meant to survey the major genetic players that are active in neuronal cell death and discuss their possible roles in retinal ganglion cells. One of the primary regulatory steps is the activation of the tumor-suppressor protein, p53. This protein functions as a transcription factor that can up-regulate the expression of the proapoptotic gene bax and down-regulate the expression of the antiapoptotic gene brl-2. Changes in the concentrations of these gene products can further stimulate apoptotic events, including changes in mitochondria that ultimately lead to the activation of a family of cysteine proteases called caspases that digest the dying cell from within. An understanding of the genetic pathways of apoptosis may lead to the design of new treatments that could prevent its activation or arrest the process when started.