MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF THE RESPONSE OF DIFFERENTIATED PC12 CELLS TO CALCIUM STRESS

The mechanisms that lead ultimately to neuronal death in pathological ageing of the brain remain mostly unknown as in the case of Parkinson' s disease where there is a progressive and selective loss of dopaminer gic neurons within the substantia nigra. Dopamine-expressing PC12 cell s that were neuronally differentiated by nerve growth factor treatment were chosen as a culture model in which to study some of the changes that may occur during the course of the degenerative process. They wer e exposed to the calcium ionophore A23187 in order to produce a sustai ned rise in cytoplasmic calcium, a phenomenon related to various patho logical conditions. The degenerative effects of the ionophore were dos e- and time-dependent. They were characterized by early fragmentation of the neurites followed ultimately by a loss in cell viability. Bioch emical changes, such as a decrease in [H-3]dopamine uptake and modulat ions of the tyrosine hydroxylase gene, were detected before macroscopi c evidence of cell suffering (e.g. neurite fragmentation) could be obs erved. Although an ongoing degenerative process was occurring in cell somata, PC12 cells were able to recover upon ionophore withdrawal. Cha racteristics of apoptosis such as chromatin condensation and DNA fragm entation were detectable in a small population of dying cells. DNA fra gmentation could be prevented by the endonuclease inhibitor aurintrica rboxylic acid. New protein synthesis was not required, as cycloheximid e failed to prevent degeneration. Taken together, these results sugges t that differentiated PC12 cells react to calcium stress through a seq uence of regulatory processes which appears to be independent of the a poptotic pathway.