Programmed cell death: does it play a role in Parkinson's disease?

In recent years, the possibility that programmed cell death (PCD), which is mediated by genetic programs intrinsic to the cell, may underlie the degeneration of neurons that occurs in Parkinson's disease (PD) and allied disorders has become an important hypothesis. Although PCD was originally identified in tissues as a normal developmental phenomenon, there is no question that it can also occur in neurologic disease and models thereof. The possibility that PCD could occur in dopamine neurons in degenerative disease is made plausible by the observations that natural cell death, with the morphology of apoptosis, does occur in these neurons and that this event is regulated by developmental target interactions. In addition, it has been shown that apoptotic death can be induced in these neurons in some animal models of parkinsonism. We have shown, for example, that apoptosis can be induced during development by intrastriatal injection of the neurotoxin 6-hydroxydopamine. Other investigators have shown that apoptosis can be induced in a chronic model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyride toxicity. However, investigations in human PD brains have yielded mixed results thus far, with some investigators identifying evidence of apoptotic death but others not. Further investigation of human postmortem tissue will benefit from a more complete understanding of the molecular basis of PCD in dopamine neurons, such that its molecular features can be investigated, rather than strictly relying on the morphologic markers presently available.