A Cellular Stress Model for the Sequestration of Redox‐Active Glial Iron in the Aging and Degenerating Nervous System

Abstract

The mechanisms responsible for the accumulation of redox‐active brain iron in normal senescence and in Parkinson's disease remain poorly understood. The aminothiol compound cysteamine (CSH) induces the appearance of autofluorescent, iron‐rich cytoplasmic granules in cultured astroglia that are identical to glial inclusions that progressively accumulate in the aging periventricular brain. Both in situ and in culture, these glial inclusions appear to arise in the context of a generalized cellular stress (heat shock) response. Several laboratories have previously concluded that porphyrins and heme ferrous iron are responsible, respectively, for red‐orange autofluorescence and nonenzymatic peroxidase activity in the glial inclusions. In the present study we found that, contrary to hypothesis, CSH suppresses the incorporation of the heme precursors δ‐amino[14C]levulinic acid and [14C]glycine into astroglial porphyrin and heme in primary culture. Similar results were obtained when the cells were preloaded with radiolabeled heme precursors for 24 h before CSH treatment, suggesting that the latter directly inhibits porphyrin‐heme biosynthesis rather than limiting precursor uptake by these cells. We also demonstrated that CSH exposure results in the sequestration of iron‐59 by astroglial mitochondria (granule precursors). The results of this study suggest that stress‐related trapping of nonheme iron by astroglial mitochondria may be an important mechanism underlying the pathological accumulation of redox‐active iron in the basal ganglia of subjects with Parkinson's disease. CSH‐treated astrocytes provide a useful model to investigate the role of stress‐related dysregulation of neuroglial iron metabolism in the aging and degenerating nervous system.

Mitochondrial Iron Sequestration in Dopamine‐Challenged Astroglia: Role of Heme Oxygenase‐1 and the Permeability Transition Pore

“…The effect of CSH on mitochondrial iron sequestration was demonstrable only when inorganic s9FeC1,, but not 59Fe-labeled diferric transferrin, served as the metal donor (Wang et al, 1995). This latter observation is consistent with previous reports that intracellular transport of low molecular weight inorganic iron may be far more efficient than that of transferrin-bound iron in certain tissues (Richardson and Ponka, 1997) and is commensurate with reports that transferrin binding sites are enigmatically deficient in PD-affected neural tissues exhibiting iron overload (Mash et al, 1991;Gelman, 1995;Faucheux et al, 1997).…”

“…Submicromolar doses of D A (0.1 p M ) induced weak glial HO-1 expression and mitochondrial uptake of non-transferrin-derived iron in some trials, but the effects were inconsistent. As in the case of CSH (Wang et al, 1995), (data not shown), or mitochondrial compartments (Fig. 1 D).…”

“…To assess the purity of the mitochondrial and lysosomal fractions, the cell sonicates were assayed for cytochrome c oxidase activity and P-galactosidase activity, respectively, as previously described (Wang et al, 1995). The mitochondria] purity was increased 65-fold and the lysosomal purity was increased 60-fold relative to whole-cell preparations.…”

“…We previously demonstrated that the sulfhydryl compound cysteamine (CSH) inhibits porphyrin heme biosynthesis in cultured astroglia and significantly augments the incorporation of s9Fe (or "Fe) into astroglial mitochondria without affecting transfer of the metal into whole-cell and lysosomal compartments (Wang et al, 1995). The effect of CSH on mitochondrial iron sequestration was demonstrable only when inorganic s9FeC1,, but not 59Fe-labeled diferric transferrin, served as the metal donor (Wang et al, 1995).…”

Hohenheim Consensus Workshop: Copper

“…The consequence is a disturbed iron distribution. Either iron deficiency (Wang et al, 1995) or iron excess were observed, leading to neurodegenerative sequels in certain areas of the brain (Gittlin, 1998). In addition, ceruloplasmin has antioxidative functions as it reduces Fe 2þ -dependent oxidative stress (Gutteridge, 1980).…”