Cysteamine pretreatment of the astroglial substratum (mitochondrial iron sequestration) enhances PC12 cell vulnerability to oxidative injury

Much of the excess iron reported in the substantia nigra of subjects with P arkinson's disease (PD) implicates nonneuronal (glial) cellular compartment s. Pet, the significance of these glial iron deposits vis-a-vis toxicity to indigent nigrostriatal dopaminergic neurons remains unclear. Cysteamine (C SH) induces the appearance of iron-rich (peroxidase-positive cytoplasmic in clusions in cultured rat astroglia, which are identical to glial inclusions that progressively accumulate in substantia nigra and other subcortical br ain regions with advancing age. Ne previously demonstrated that the iron-me diated peroxidase activity in these cells oxidizes dopamine and other catec hols to potentially neurotoxic semiquinone radicals. In the present study, we cocultured catecholamine-secreting PC12 cells (as low-density dispersed cells or high-density colonies) atop monolayers of either CSH-pretreated (i ron-enriched) or control rat astroglial substrata In some experiments, the PC12 cells were differentiated with nerve growth factor (NGF). The nature o f the glial substratum did not appreciably affect the growth characteristic s of the PC12 cells. However, undifferentiated PC12 cells grown atop CSH-pr etreated astrocytes (a senescent glial phenotype) were far more susceptible to dopamine(1 mu M)-H2O2(1 mu M)-related killing than PC12 cells cultured on control astroglia. Differentiated PC12 cells behaved similarly although the fraction killed was about half that seen with the undifferentiated PC12 cells. In the latter experiments, PC12 cell death was abrogated by coadmin istration of the antioxidants, ascorbate (200 mu M), melatonin (100 mu M), or resveratrol (50 mu M) or the iron chelator, deferoxamine (400 mu M), att esting to the role of oxidative stress and catalytic iron in the mechanism of PC12 cell death in this system. The aging-associated accumulation of red ox-active iron in subcortical astrocytes may facilitate the bioactivation o f dopamine to neuronotoxic free radical intermediates and thereby predispos e the senescent nervous system to PD and other neurodegenerative disorders. (C) 1999 Academic Press.