Subcellular compartmentalisation of copper, iron, manganese, and zinc in the Parkinson's disease brain

Abstract

Elevated iron and decreased copper levels are cardinal features of the degenerating substantia nigra pars compacta in the Parkinson's disease brain. Both of these redox-active metals, and fellow transition metals manganese and zinc, are found at high concentrations within the midbrain and participate in a range of unique biological reactions. We examined the total metal content and cellular compartmentalisation of manganese, iron, copper and zinc in the degenerating substantia nigra, disease-affected but non-degenerating fusiform gyrus, and unaffected occipital cortex in the post mortem Parkinson's disease brain compared with age-matched controls. An expected increase in iron and a decrease in copper concentration was isolated to the soluble cellular fraction, encompassing both interstitial and cytosolic metals and metal-binding proteins, rather than the membrane-associated or insoluble fractions. Manganese and zinc levels did not differ between experimental groups. Altered Fe and Cu levels were unrelated to Braak pathological staging in our cases of late-stage (Braak stage V and VI) disease. The data supports our hypothesis that regional alterations in Fe and Cu, and in proteins that utilise these metals, contribute to the regional selectively of neuronal vulnerability in this disorder.

Fig. 1

Biometal distribution in the occipital cortex (OCx) fusiform gyrus (FUS) and substantia nigra (SN) of healthy aged controls and Parkinson’s disease. (a) The concentration of Cu in control tissue was highest in the SN, though in the Parkinson’s disease brain Cu concentrations decreased to levels equivalent to that in the control SN. (b) In control brains, the concentration of Fe in the SN was also significantly higher than the FUS and OCx regions. Iron concentrations were further elevated in the Parkinson’s disease SN. (c) Zinc concentrations were lowest in the OCx, and (d) Mn was highest within the SN. Neither Zn or Mn were altered in the Parkinson’s disease OCx, FUS or SN. * p < 0.05, ** p < 0.01, *** p < 0.001 (vs control regions); # p < 0.05, ### p < 0.001 (control vs Parkinson’s disease SN). All concentrations are μg g⁻¹ wet weight of tissue.

Fig. 2

Within both the Parkinson’s disease and control SN, the majority of (a) Cu, (b) Fe, and (c) Zn was present in the soluble fraction, followed by the membrane and insoluble fractions, respectively. (d) For Mn, equivalent amounts were distributed between the soluble and membrane-bound fractions. In the Parkinson’s disease SN, the observed reduction in total Cu and increase in total Fe are confined to the soluble fraction, and a decrease in Zn within the membrane-associated fraction was also observed, although total Zn levels were not altered. ## p < 0.01, (control vs Parkinson’s disease). All concentrations are μg g⁻¹ wet weight of tissue.

Fig. 3

Concentration of (a) Cu, (b) Fe, (c) Zn, (d) and Mn in cellular fractions according to Braak staging in the Parkinson’s disease OCx, FUS and SN. Only Fe shows any significant change in concentration between Braak stage V and VI, with a decrease in the soluble fraction of OCx and increase in the membrane-bound fraction in the SN in stage VI. # p < 0.05; ## p < 0.01. I = insoluble, M = membrane, S = soluble.