Aging results in copper accumulations in glial fibrillary acidic protein-positive cells in the subventricular zone

Age-dependent increase of brain copper levels and expressions of copper regulatory proteins in the subventricular zone and choroid plexus

Our recent data suggest a high accumulation of copper (Cu) in the subventricular zone (SVZ) along the wall of brain ventricles. Anatomically, SVZ is in direct contact with cerebrospinal fluid (CSF), which is secreted by a neighboring tissue choroid plexus (CP). Changes in Cu regulatory gene expressions in the SVZ and CP as the function of aging may determine Cu levels in the CSF and SVZ. This study was designed to investigate the associations between age, Cu levels, and Cu regulatory genes in SVZ and plexus. The SVZ and CP were dissected from brains of 3-week, 10-week, or 9-month old male rats. Analyses by atomic absorption spectroscopy revealed that the SVZ of adult and old animals contained the highest Cu level compared with other tested brain regions. Significantly positive correlations between age and Cu levels in SVZ and plexus were observed; the SVZ Cu level of old animals was 7.5- and 5.8-fold higher than those of young and adult rats (p < 0.01), respectively. Quantitation by qPCR of the transcriptional expressions of Cu regulatory proteins showed that the SVZ expressed the highest level of Cu storage protein metallothioneins (MTs), while the CP expressed the high level of Cu transporter protein Ctr1. Noticeably, Cu levels in the SVZ were positively associated with type B slow proliferating cell marker Gfap (p < 0.05), but inversely associated with type A proliferating neuroblast marker Dcx (p < 0.05) and type C transit amplifying progenitor marker Nestin (p < 0.01). Dmt1 had significant positive correlations with age and Cu levels in the plexus (p < 0.01). These findings suggest that Cu levels in all tested brain regions are increased as the function of age. The SVZ shows a different expression pattern of Cu-regulatory genes from the CP. The age-related increase of MTs and decrease of Ctr1 may contribute to the high Cu level in this neurogenesis active brain region.

Elevated adult neurogenesis in brain subventricular zone following in vivo manganese exposure: roles of copper and DMT1

The brain subventricular zone (SVZ) is a source of neural precursor cells; these cells travel along the rostral migratory stream (RMS) to destination areas in the process of adult neurogenesis. Recent x-ray fluorescence (XRF) studies reveal an extensive accumulation of copper (Cu) in the SVZ. Earlier human and animal studies also suggest an altered Cu homeostasis after manganese (Mn) exposure. This study was designed to test the hypothesis that Mn exposure by acting on the divalent metal transporter-1 (DMT1) altered Cu levels in SVZ and RMS, thereby affecting adult neurogenesis. Adult rats received intraperitoneal (i.p.) injections of 6 mg Mn/kg as MnCl2 once daily for 4 weeks with concomitant injections of bromodeoxyuridine (BrdU) for 5 days in the last week. In control rats, Cu levels were significantly higher in the SVZ than other brain regions examined. Mn exposure significantly reduced Cu concentrations in the SVZ (P < 0.01). Immunohistochemical data showed that in vivo Mn exposure significantly increased numbers of BrdU(+) cells, which were accompanied with increased GFAP(+) astrocytic stem cells and DCX(+) neuroblasts in SVZ and RMS. Quantitative RT-PCR and Western blot confirmed the increased expression of DMT1 in SVZ following in vivo Mn exposure, which contributed to Mn accumulation in the neurogenesis pathway. Taken together, these results indicate a clear disruptive effect of Mn on adult neurogenesis; the effect appears due partly to Mn induction of DMT1 and its interference with cellular Cu regulation in SVZ and RMS. The future research directions based on these observations are also discussed.

Quantitation and localization of intracellular redox active metals by X-ray fluorescence microscopy in cortical neurons derived from APP and APLP2 knockout tissue

The amyloid precursor protein (APP) gene family includes APP and the amyloid precursor-like proteins, APLP1 and APLP2. These proteins contain metal binding sites for copper, zinc and iron and are known to have physiological roles in modulating the metal homeostasis in brain cells. Here we report the application of X-ray fluorescence microscopy (XFM) to investigate the subcellular distribution patterns of the metal ions Cu, Zn, Fe, and Ca in individual neurons derived from APP and APLP2 knockout mice brains to further define their role in metal homeostasis. These studies add to the growing body of data that the APP family of proteins are metalloproteins that have shared as well as distinct effects on metals. As we continue to delineate the cellular effects of the APP family of proteins it is important to consider how metals are involved in their actions.

Biological metals and metal-targeting compounds in major neurodegenerative diseases

Metals are functionally essential, but redistribute in neurodegenerative disease where they induce protein aggregates, catalyze radical formation, and lose bioavailability.

X-ray fluorescence imaging of the hippocampal formation after manganese exposure

Manganese (Mn) intoxication results in neurological conditions similar, but not identical, to idiopathic Parkinson's disease. While the mechanism(s) by which Mn exposure leads to neurotoxic effects remains unclear, studies by magnetic resonance imaging demonstrate a high Mn accumulation in the hippocampal formation (HPCf) of the brain. Metal quantification using this method is not possible. Using X-ray fluorescence imaging, we measured the distribution of Mn in the HPCf for a rodent model of chronic Mn exposure and quantitatively compared it with distributions of other biologically relevant metals. We found considerable increases in average Mn concentrations in all analyzed areas and we identified the dentate gyrus (DG) and the cornus ammonis 3 (CA3) layer as areas accumulating the highest Mn content (∼1.2 μg Mn per g tissue). The DG is significantly enriched with iron (Fe), while the CA3 layer has high zinc (Zn) content. Additionally, significant spatial correlations were found for Mn-Zn concentrations across the HPCf substructures and for Mn-Fe concentrations in the DG. Combined results support that at least two mechanisms may be responsible for Mn transport and/or storage in the brain, associated with either Fe or Zn. Subcellular resolution images of metal distribution in cells of the CA3 show diffuse Mn distributions consistent with Mn localization in both the cytoplasm and nucleus. Mn was not increased in localized intracellular Fe or copper accumulations. A consistent Mn-Zn correlation both at the tissue (40 μm × 40 μm) and cellular (0.3 μm × 0.3 μm) levels suggests that a Zn transport/storage mechanism in the HPCf is likely associated with Mn accumulation.