The origin and composition of peroxidase-positive granules in cysteamine-treated astrocytes in culture

A Review on the Antimutagenic and Anticancer Effects of Cysteamine

Cancer is one of the leading causes of death worldwide. First-line treatments usually include surgery, radiotherapy, and/or systemic therapy. These methods can be associated with serious adverse events and can be toxic to healthy cells. Despite the new advances in cancer therapies, there is still a continuous need for safe and effective therapeutic agents. Cysteamine is an aminothiol endogenously synthetized by human cells during the degradation of coenzyme-A. It has been safely used in humans for the treatment of several pathologies including cystinosis and neurodegenerative diseases. Cysteamine has been shown to be a potent antimutagenic, anticarcinogenic, and antimelanoma in various in vitro and in vivo studies, but a review on these aspects of cysteamine's use in medicine is lacking in the current literature. The efficacy of cysteamine has been shown in vitro and in vivo for the treatment of different types of cancer, such as gastrointestinal cancer, pancreatic cancer, sarcomas, hepatocellular carcinoma, and melanoma, leading to the significant reduction of lesions and/or the increase of survival time. Although the mechanisms of action are not fully understood, possible explanations are (i) free radical scavenging, (ii) alteration of the tumor cell proliferation by affecting nucleic acid and protein synthesis or inhibition of DNA synthesis, and (iii) hormone regulation. In conclusion, regarding the high safety profile of cysteamine and the current literature data presented in this article, cysteamine might be considered as an interesting molecule for the prevention and the treatment of cancer. Further clinical studies should be performed to support these data in humans.

FABP7 upregulation induces a neurotoxic phenotype in astrocytes

Fatty acid binding proteins (FABPs) are key regulators of lipid metabolism, energy homeostasis, and inflammation. They participate in fatty acid metabolism by regulating their uptake, transport, and availability of ligands to nuclear receptors. In the adult brain, FABP7 is especially abundant in astrocytes that are rich in cytoplasmic granules originated from damaged mitochondria. Mitochondrial dysfunction and oxidative stress have been implicated in the neurodegenerative process observed in amyotrophic lateral sclerosis (ALS), either as a primary cause or as a secondary component of the pathogenic process. Here we investigated the expression of FABP7 in animal models of human superoxide dismutase 1 (hSOD1)-linked ALS. In the spinal cord of symptomatic mutant hSOD1-expressing mice, FABP7 is upregulated in gray matter astrocytes. Using a coculture model, we examined the effect of increased FABP7 expression in astrocyte-motor neuron interaction. Our data show that FABP7 overexpression directly promotes an NF-κB-driven pro-inflammatory response in nontransgenic astrocytes that ultimately is detrimental for motor neuron survival. Addition of trophic factors, capable of supporting motor neuron survival in pure cultures, did not prevent motor neuron loss in cocultures with FABP7 overexpressing astrocytes. In addition, astrocyte cultures obtained from symptomatic hSOD1-expressing mice display upregulated FABP7 expression. Silencing endogenous FABP7 in these cultures decreases the expression of inflammatory markers and their toxicity toward cocultured motor neurons. Our results identify a key role of FABP7 in the regulation of the inflammatory response in astrocytes and identify FABP7 as a potential therapeutic target to prevent astrocyte-mediated motor neuron toxicity in ALS.

On the nature of the Cu-rich aggregates in brain astrocytes

Fulfilling a bevy of biological roles, copper is an essential metal for healthy brain function. Cu dyshomeostasis has been demonstrated to be involved in some neurological conditions including Menkes and Alzheimer's diseases. We have previously reported localized Cu-rich aggregates in astrocytes of the subventricular zone (SVZ) in rodent brains with Cu concentrations in the hundreds of millimolar. Metallothionein, a cysteine-rich protein critical to metal homeostasis and known to participate in a variety of neuroprotective and neuroregenerative processes, was proposed as a binding protein. Here, we present an analysis of metallothionein(1,2) knockout (MTKO) mice and age-matched controls using X-ray fluorescence microscopy. In large structures such as the corpus callosum, cortex, and striatum, there is no significant difference in Cu, Fe, or Zn concentrations in MTKO mice compared to age-matched controls. In the astrocyte-rich subventricular zone where Cu-rich aggregates reside, approximately 1/3 as many Cu-rich aggregates persist in MTKO mice resulting in a decrease in periventricular Cu concentration. Aggregates in both wild-type and MTKO mice show XANES spectra characteristic of CuxSy multimetallic clusters and have similar [S]/[Cu] ratios. Consistent with assignment as a CuxSy multimetallic cluster, the astrocyte-rich SVZ of both MTKO and wild-type mice exhibit autofluorescent bodies, though MTKO mice exhibit fewer. Furthermore, XRF imaging of Au-labeled lysosomes and ubiquitin demonstrates a lack of co-localization with Cu-rich aggregates suggesting they are not involved in a degradation pathway. Overall, these data suggest that Cu in aggregates is bound by either metallothionein-3 or a yet unknown protein similar to metallothionein.

Copper accumulation in rodent brain astrocytes: A species difference

Changes in Cu homeostasis have been implicated in multiple neurodegenerative diseases. Factors controlling and regulating the distribution of Cu in the brain remain largely unknown. We have previously reported that a sub-set of astrocytes in the subventricular zone (SVZ) contain Cu-rich aggregates. Here we expand previous studies with detailed X-ray fluorescent imaging (XRF) analysis of the additional brain areas of hippocampus (HP) and rostral migratory stream (RMS). We also use conventional DAB (3,3'-diaminobenzidine) staining which accesses both peroxidase and pseudo-peroxidase activities. Both the HP and RMS support neurogenesis while the latter also serves as a migratory pathway for neuronal precursors. Some variations in neurogenic activities have been noticed between species (such as mice and rats). We report here that in rats, the HP, rostral migratory stream (RMS) and third ventricle contain glia which stain positively for DAB and contain copper-rich aggregates as measured by XRF. In contrast, mice hippocampi and RMS display neither DAB+ aggregates nor Cu-rich accumulations via XRF. DAB+ aggregates were not induced in the HP of mice transgenic for human amyloid precursor protein (APP) and presenilin, suggesting that accumulations positively stained for DAB are not directly caused by APP. These observed critical differences suggest different properties of the astrocytes in two species. Results suggest that the rat model may have important advantages over the mouse model for the study of hippocampal aging and neurodegeneration.

Neurotherapeutic effects of novel HO-1 inhibitors in vitro and in a transgenic mouse model of Alzheimer's disease

Heme oxygenase-1 (HO-1) encoded by the HMOX1 gene is a 32-kDa stress protein that catabolizes heme to biliverdin, free iron, and carbon monoxide (CO). Glial HO-1 is over-expressed in the CNS of subjects with Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). The HMOX1 gene is exquisitely sensitive to oxidative stress and is induced in brain and other tissues in various models of disease and trauma. Induction of the glial HMOX1 gene may lead to pathological brain iron deposition, intracellular oxidative damage, and bioenergetic failure in AD and other human CNS disorders such as PD and MS. Therefore, targeted suppression of glial HO-1 hyperactivity may prove to be a rational and effective therapeutic intervention in AD and related neurodegenerative disorders. In this study, we report the effects of QC-47, QC-56, and OB-28, novel azole-based competitive and reversible inhibitors of HO-1, on oxidative damage to whole-cell and mitochondrial compartments in rat astrocytes transfected with the HMOX1 gene. We also report the effect of OB-28 on the behavior and neuropathology of APP(swe)/PS1(∆E9) mice. OB-28 was found to reduce oxidative damage to whole-cell and mitochondrial compartments in rat astrocytes transfected with the HMOX1 gene. Moreover, OB-28 was found to significantly counter behavioral deficits and neuropathological alterations in APP(swe)/PS1(∆E9) mice. Attenuation of AD-associated behavioral deficits and neuropathological changes suggests that HO-1 may be a promising target for neuroprotective intervention in AD and other neurodegenerative diseases. We propose that the targeted suppression of glial heme oxygenase-1 (HO-1) hyperactivity may prove to be a rational and effective therapeutic intervention in Alzheimer's disease (AD) and related neurodegenerative disorders. We report attenuation by a selective HO-1 inhibitor of oxidative damage to whole-cell and mitochondrial compartments in astrocytes in vitro and amelioration of behavioral anomalies in a transgenic mouse model of AD.

Astroglial heme oxygenase-1 and the origin of corpora amylacea in aging and degenerating neural tissues

BACKGROUND

Corpora amylacea (CA) are glycoproteinaceous (predominantly glial and extracellular) inclusions that accumulate in normal aging brain and, to a greater extent, in Alzheimer disease (AD). Previous pharmacological evidence suggested that up-regulation of endogenous heme oxygenase-1 (HO-1) in astrocytes promotes transformation of normal mitochondria to CA-like inclusions. Here, we determined whether 1) HMOX1 transfection fosters the accumulation of CA-like inclusions in cultured rat astroglia; 2) the HMOX1 transgene promotes CA formation in the brains of aging GFAP.HMOX1 mice; and 3) brain mitochondrial damage and CA biogenesis are augmented in persons with mild cognitive impairment (MCI), a harbinger of AD.

METHODS

CA were ascertained in (i) neonatal rat astroglia transfected with flag-tagged human HO-1 cDNA, (ii) brain sections derived from 19month-old GFAP.HMOX1 and wild-type (WT) mice, and (iii) post-mortem hippocampal sections from individuals with mild (MCI) and no cognitive impairment (NCI) after staining with PAS or antisera against HO-1, ubiquitin (Ub), manganese superoxide dismutase (MnSOD), and α-synuclein or tyrosine hydroxylase (TH).

RESULTS

HMOX1 transfection induced cytoplasmic vacuolation and the accumulation of PAS+ inclusions in cultured astroglia. Numerous CA-like inclusions stained with PAS and immunoreactive for HO-1, Ub and MnSOD were observed in the brains of GFAP.HMOX1 mice, but were rarely encountered in age-matched, WT controls. Numbers of HO-1-positive CA were significantly increased in certain hippocampal strata of MCI subjects relative to NCI preparations. MnSOD and Ub proteins co-localized to CA in both the control and MCI specimens.

CONCLUSIONS

HO-1 promotes mitochondrial damage and CA biogenesis in astrocyte cultures and in the intact aging brain. CA formation is enhanced in the MCI hippocampus and thus occurs relatively early in the pathogenesis of AD. Glial HO-1 suppression may attenuate bioenergetic failure and slow disease progression in AD and other neurodegenerative conditions featuring accelerated accumulation of CA.

Cysteamine: an old drug with new potential

Cysteamine is an amino thiol with the chemical formula HSCH2CH2NH2. Endogenously, cysteamine is derived from coenzyme A degradation, although its plasma concentrations are low. Most experience with cysteamine as a drug originates from the field of the orphan disease cystinosis, in which cysteamine is prescribed to decrease intralysosomal cystine accumulation. However, over the years, the drug has been used for several other applications both in vitro and in vivo. In this article, we review the different applications of cysteamine, ending with an overview of ongoing clinical trials for new indications, such as neurodegenerative disorders and nonalcoholic fatty liver disease (NAFLD). The recent development of an enteric-coated cysteamine formulation makes cysteamine more patient friendly and will extend its applicability for both old and new indications.

Autophagy-mediated chemosensitization by cysteamine in cancer cells

Cysteamine (CS) has many biomedical and clinical applications because of its excellent water solubility, low cytotoxicity and good biocompatibility. A previous study by Brawer et al. reported the occurrence of many Gomori inclusion bodies in CS-treated astrocytes, which would suggest the induction of autophagy. Here we provided a comprehensive line of evidence demonstrating that CS caused autophagosome accumulation in cancer cells. CS exerted a biphasic effect on the autophagy process, increasing the formation of autophagosomes in the early phase and blocking the autophagic degradation in a later phase. Furthermore, we showed that CS sensitized doxorubicin-elicited chemotherapeutic killing in HeLa, B16 melanoma and doxorubicin-resistant MCF-7 cells and also enhanced chemotherapeutic efficacy of doxorubicin in a mouse melanoma model. Finally, we demonstrated that the chemosensitizing effect of CS was at least partly dependent on its ability to modulate autophagy. Our results revealed a novel biological function for CS in enhancing the chemotherapeutic effect of doxorubicin through autophagy modulation and pointed to the potential use of CS in adjunct cancer chemotherapy.

In utero exposure to tributyltin chloride differentially alters male and female fetal gonad morphology and gene expression profiles in the Sprague–Dawley rat

Tributyltin (TBT) is an environmental contaminant commonly used in anti-fouling agents for boats, as well as a by-product from several industrial processes. It has been shown to accumulate in organisms living in areas with heavy maritime traffic thereby entering the food chain. Here, we determined the consequences of in utero exposure to TBT on the developing fetal gonads in the Sprague-Dawley rat. Timed pregnant rats were gavaged either with vehicle or TBT (0.25, 2.5, 10 or 20 mg/kg) from days 0 to 19 or 8 to 19 of gestation. On gestational day 20, dams were sacrificed; fetal testes and ovaries were processed for light (LM) or electron microscopic (EM) evaluation and RNA was prepared for gene expression profiling. At the highest doses of TBT the number of Sertoli cells and gonocytes was reduced, there were large intracellular spaces between Sertoli cells and gonocytes and there was an increased abundance of lipid droplets in the Sertoli cells; EM studies revealed abnormally dilated endoplasmic reticulum in Sertoli cells and gonocytes. In the intertubular region between adjacent interstitial cells, immunostaining for the gap junctional protein connexin 43 was strong in controls, whereas it was reduced or completely absent in treated rats. In the ovaries, TBT (20 mg/kg, days 0-19; 10 mg/kg, days 8-19) reduced the number of germ cells by 44% and 46%, respectively. On examining gene expression profiles in the testis, 40 genes out of 1176 tested were upregulated more than two-fold over control. While no genes were upregulated in the TBT exposed fetal ovary, eight genes were downregulated. In conclusion, in utero exposure to TBT resulted in gender-specific alterations in gonadal development and gene expression profiles suggesting that there may be different adaptive changes to toxicity in developing male and female rats.

Distribution and quantitation of the anti-trypanosomal diamidine 2,5-bis(4-amidinophenyl)furan (DB75) and its N-methoxy prodrug DB289 in murine brain tissue

The current epidemic of sleeping sickness, also known as human African trypanosomiasis in sub-Saharan Africa places nearly 60 million people at risk for developing this life threatening infection. Although effective treatments for early-stage sleeping sickness exist, these drugs usually require extended dosing schedules and intravenous administration. New treatments are also needed for cerebral (late) stage trypanosomiasis. 2,5-Bis(4-amidinophenyl)furan (DB75), a pentamidine analog, has potent in vitro and in vivo anti-trypanosomal activity. However, DB75 does not exhibit significant oral bioavailability and has proved to be ineffective against mouse models of late-stage sleeping sickness regardless of administration route. To circumvent the limited oral bioavailability of DB75, an N-methoxy prodrug 2,5-bis(4-amidinophenyl)furan-bis-O-methylamidoxime (DB289) was designed and developed initially as a compound to treat AIDS-related Pneumocystis carinii pneumonia (PCP). Despite excellent oral activity against early-stage sleeping sickness, oral administration of DB289 exhibited limited efficacy in mouse models of late-stage disease. DB289 has recently entered Phase II(b) clinical trials to treat primary-stage sleeping sickness in Central Africa. The current study takes advantage of the innate fluorescence of DB75 and DB289 along with specific and sensitive quantitative analyses to examine plasma and brain distribution of these compounds. Animals were dosed with intravenous DB75, oral DB289, and intravenous DB289. Following intravenous administration, DB75 was readily detectable in whole brain extracts and persisted for long periods. Fluorescence microscopy revealed that DB75 did not penetrate into brain parenchyma, however, but was sequestered within cells lining the blood-brain and blood-cerebrospinal fluid barriers. In contrast, brain tissue of mice treated with oral DB289 exhibited diffuse fluorescence within the brain parenchyma, suggesting that the prodrug was not trapped within blood-brain barrier cells (BBB). However, maximal brain concentrations of the active compound DB75 were very low (13 nmol/mg of tissue at 24 h). Intravenous administration of DB289 resulted in a qualitatively similar fluorescence pattern to oral DB289, indicating again that DB289 and DB75 were present within brain parenchyma, not only in barrier regions. Furthermore, peak DB75 tissue levels were higher (61 nmol/mg of tissue at 24 h) than with oral prodrug. The near five-fold increase in brain levels of DB289 combined with parenchymal localization of compound fluorescence after intravenous administration suggest that the unaltered prodrug penetrates the blood-brain barrier, and may be subject to in situ biotransformation. Intravenous administration of DB289 should be evaluated in mouse models of late-stage sleeping sickness.

Brain iron deposition and the free radical-mitochondrial theory of ageing

The central hypothesis of this paper states that oxidative stress, augmented iron deposition, and mitochondrial insufficiency in the ageing and degenerating CNS constitute a single neuropathological 'lesion', and that the advent of one component of this triad obligates the appearance of the others. Evidence in support of this unifying perspective is adduced from human neuropathological studies, experimental paradigms of ageing-associated neurological disorders, and a comprehensive model of astroglial senescence. A pivotal role for the enzyme, heme oxygenase-1 (HO-1) in consolidating this tripartite lesion in the ageing and diseased CNS is emphasized. The data are discussed in the context of a revised 'free radical-mitochondrial-metal' theory of brain ageing, and some scientific and clinical implications of the latter are considered.

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 Parkinson's disease (PD) implicates nonneuronal (glial) cellular compartments. Yet, the significance of these glial iron deposits vis-a-vis toxicity to indigent nigrostriatal dopaminergic neurons remains unclear. Cysteamine (CSH) induces the appearance of iron-rich (peroxidase-positive) cytoplasmic inclusions in cultured rat astroglia, which are identical to glial inclusions that progressively accumulate in substantia nigra and other subcortical brain regions with advancing age. We previously demonstrated that the iron-mediated peroxidase activity in these cells oxidizes dopamine and other catechols 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 (iron-enriched) or control rat astroglial substrata. In some experiments, the PC12 cells were differentiated with nerve growth factor (NGF). The nature of the glial substratum did not appreciably affect the growth characteristics of the PC12 cells. However, undifferentiated PC12 cells grown atop CSH-pretreated astrocytes (a senescent glial phenotype) were far more susceptible to dopamine(1 microM)-H2O2(1 microM)-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 coadministration of the antioxidants, ascorbate (200 microM), melatonin (100 microM), or resveratrol (50 microM) or the iron chelator, deferoxamine (400 microM), attesting to the role of oxidative stress and catalytic iron in the mechanism of PC12 cell death in this system. The aging-associated accumulation of redox-active iron in subcortical astrocytes may facilitate the bioactivation of dopamine to neuronotoxic free radical intermediates and thereby predispose the senescent nervous system to PD and other neurodegenerative disorders.

Corpora-amylacea and the family of polyglucosan diseases

The history, characters, composition and topography of corpora amylacea (CA) in man and the analogous polyglucosan bodies (PGB) in other species are documented, noting particularly the wide variation in the numbers found with age and in neurological disease. Their origins from both neurons and glia and their probable migrations and ultimate fate are discussed. Their presence is also noted in other organs, particularly in the heart. The occurrence in isolated cases of occasional 'massive' usually focal accumulations of similar polyglucosan bodies in association with certain chronic neurological diseases is noted and the specific conditions Adult Polyglucosan body disease and type IV glycogenosis where they are found throughout the nervous system in great excess is discussed. The distinctive differences of CA from the PGB of Lafora body disease and Bielschowsky body disease are emphasised. When considering their functional roles, a parallel is briefly drawn on the one hand between normal CA and the bodies in the polyglucosan disorders and on the other with the lysosomal system and its associated storage diseases. It is suggested that these two systems are complementary ways by which large, metabolically active cells such as neurons, astrocytes, cardiac myocytes and probably many other cell types, dispose of the products of stressful metabolic events throughout life and the continuing underlying process of aging and degradation of long lived cellular proteins. Each debris disposal system must be regulated in its own way and must inevitably, a priori, be heir to metabolic defects that give rise in each to its own set of metabolic disorders.

Acceleration of ageing-related gliopathic changes and hippocampal dysfunction following intracerebroventricular infusion of cysteamine in adult rats

The sulphydryl agent, cysteamine, accelerates the ageing-related accumulation of peroxidase-positive (iron-rich) cytoplasmic inclusions in rat subcortical astroglia and induces their appearance in primary neuroglial cultures. In the present study, infusion of cysteamine into the lateral ventricle of young, adult rats (1 mg/day for three weeks followed by a one-month drug "washout" period) significantly increased numbers of peroxidase-positive astrocytic granules in the stratum oriens of the CA1 hippocampus relative to saline-infused controls. In contrast to the gliopathic changes, no evidence of neuronal or myelin damage was observed in the cysteamine-exposed rats. The cysteamine-treated animals exhibited significant impairment in spatial learning as determined using a three-panel runway task. The working memory deficits were more robust at the end of the drug washout period than immediately following cessation of the cysteamine infusion. Thus, the cysteamine-related memory deficits are of long duration and are not due to any acute neuroactive properties of the drug itself. Using hippocampal slices prepared after the drug washout period, we observed attenuated paired-pulse depression, with no significant effects on basal excitatory synaptic transmission or induction of long-term potentiation, in the cysteamine-infused animals relative to controls. We propose that, in cysteamine-treated rats and in the course of normal ageing, hippocampal dysfunction and associated cognitive deficits may be secondary to fundamental pathological processes originating within the astroglial compartment.

Experimental induction of corpora amylacea in adult rat brain

Corpora amylacea (CA) are glycoproteinaceous inclusions that accumulate in astroglia and other brain cells as a function of advancing age and, to an even greater extent, in several human neurodegenerative conditions. The mechanisms responsible for their biogenesis and their subcellular origin(s) remain unclear. We previously demonstrated that the sulfhydryl agent, cysteamine (CSH), promotes the accumulation of CA-like inclusions in cultured rat astroglia. In the present study, we show that subcutaneous administration of CSH to adult rats (150 mg/kg for 6 weeks followed by a 5-week drug-washout period) elicits the accumulation of CA in many cortical and subcortical brain regions. As in the aging human brain and in CSH-treated rat astrocyte cultures, the inclusions are periodic acid-Schiff -positive and are consistently immunostained with antibodies directed against mitochondrial epitopes and ubiquitin. Our findings support our contention that mitochondria are important structural precursors of CA, and that CSH accelerates aging-like processes in rat astroglia both in vitro and in the intact brain.

Astrocyte mitochondria: a substrate for iron deposition in the aging rat substantia nigra

Little is currently known concerning the cellular substrates for, and the mechanisms mediating the pathological deposition of, redox-active brain iron in Parkinson's disease. In various subcortical brain regions, populations of astroglia progressively accumulate peroxidase-positive cytoplasmic inclusions derived from effete, iron-laden mitochondria. In the present study, histochemical, ultrastructural, and elemental microanalytical techniques were used to demonstrate the existence of peroxidase-positive astroglia in the substantia nigra of adult rats. At 4 months of age and earlier, few GFAP-positive nigral astroglia contained small, electron-dense cytoplasmic inclusions which exhibited faint endogenous peroxidase activity (diaminobenzidine reaction product) and no detectable iron by microprobe analysis. In contrast, by 14-18 months of age, there was a significant, fourfold increase in numbers of peroxidase-positive astrocyte inclusions in the substantia nigra. The nigral gliosomes in the older animals were heterogeneously electron dense, immunoreactive for ubiquitin and a mitochondrial epitope, and often exhibited X-ray emission peaks for iron. Copper peaks were also detected in a minority of nigral gliosomes. Previous in vitro work indicated that the iron-mediated peroxidase activity in these cells promotes the bioactivation of dopamine and other catechols to neurotoxic free radical intermediates. Thus, mitochondrial sequestration of redox-active iron in aging nigral astroglia may be one factor predisposing the senescent nervous system to parkinsonism and other neurodegenerative disorders.

Age-related congophilic inclusions in the brains of apolipoprotein E-deficient mice

The hippocampal region of apolipoprotein E-deficient mice of varying ages was examined for any morphological changes by light and electron microscopy. Unusual periodic acid-Schiff-positive granules were seen in the hippocampal area of these animals as early as the fourth week of life and their numbers increased gradually with age. These granules were never found in control C57BL/6J (B6) mice before six months-of-age and their numbers were invariable low. They were strongly congophilic when stained with a modified Congo Red technique and reacted with a monoclonal antibody specific to amino acids 17-24 and 35-43 of the beta-amyloid peptide. The immunostaining of these granules with the beta-amyloid peptide was lost after specific adsorption with the appropriate synthetic peptide. These granules were identified ultrastructurally as non-membrane-bound fibrillogranular material in the cytoplasm of protoplasmic astrocytes. The data indicate that an amyloid-like protein accumulates in the protoplasmic astrocytes of the hippocampus of apolipoprotein E-deficient mice, especially in the brains of old animals.

A cellular stress model for the differential expression of glial lysosomal cathepsins in the aging nervous system

Activation of the endosomal-lysosomal system and altered expression of various lysosomal hydrolases have been implicated in several senescence-dependent neurodegenerative disorders and occurs, to a lesser extent, in the course of normal brain aging. The progressive accumulation of autofluorescent, peroxidase-positive astrocytic granules represents a highly consistent biomarker of aging in the vertebrate CNS. The sulfhydryl agent cysteamine greatly accelerates the accumulation of these glial inclusions in situ and in primary brain cell cultures. We previously determined that these glial inclusions are derived from abnormal mitochondria which undergo fusion with lysosomal elements in a complex autophagic process. In the present study, we demonstrate that cysteamine suppresses cathepsin B mRNA levels and immunoreactive protein in cultured astroglia, whereas cathepsin D mRNA and protein levels are significantly augmented by CSH exposure in these cells. Moreover, cathepsin D (but not cathepsin B) exhibits robust colocalization to the red autofluorescent inclusions. Concordant with our in vitro observations, cathepsin B immunoreactivity is prominent in the hypothalamic ventromedial nucleus which accumulates few autofluorescent glial inclusions during aging and is relatively inapparent in the heavily granulated hypothalamic arcuate nucleus. Conversely, cathepsin D is prominent in the aging arcuate nucleus where it colocalizes to the autofluorescent inclusions and exhibits scant immunoreactivity in the adjacent ventromedial nuclear complex. In senescent astroglia, oxidative stress may down-regulate the cathepsin B gene as part of a concerted cellular stress (heat shock) response. Glial cathepsin D, on the other hand, resists stress-related inhibition and may play an important role in disposing of oxidatively modified mitochondria in the aging and degenerating nervous system.

Long-term effects of cysteamine on cognitive and locomotor behavior in rats: relationship to hippocampal glial pathology and somatostatin levels

Peroxidase-positive astrocytic inclusions, derived from effete, iron-laden mitochondria, accumulate in the rat hippocampus, striatum and other subcortical brain regions as a function of advancing age. The sulfhydryl agent, cysteamine (CSH), accelerates the appearance of this senescent glial phenotype both in primary astrocyte cultures and in the aging subcortical brain in situ. Earlier experiments have shown that short-term administration of CSH results in reversible depletion of brain somatostatin (SS) levels, cognitive deficits and decreases in locomotor activity. In the present study, we tested spatial learning/memory and motor functioning in rats at 4-5 weeks following cessation of chronic (6 week) CSH treatment to determine whether behavioral deficits may be associated with gliopathic changes within the dorsal hippocampus distinct from the behavioral abnormalities accruing to the immediate effects of the drug. CSH-treated rats displayed significantly impaired performance in the Morris water maze 4-5 weeks following termination of prolonged CSH treatment. In contrast, locomotor activity was not affected in this experimental paradigm. CSH-treated animals exhibited significantly higher numbers of peroxidase-positive astrocyte granules as well as total numbers of GFAP-positive astrocytes in the CA1 sector of the dorsal hippocampus relative to saline-treated controls. In the hilus of the dentate gyrus, numbers of both peroxidase-positive glial inclusions and astrocytes were unaffected by CSH exposure. At 5 weeks following cessation of CSH treatment, SS levels in the hippocampus and hypothalamus (but not cerebral cortex) were elevated relative to those of saline-treated controls. Our results indicate that chronic CSH exposure induces senescence-like changes in CA1 astrocytes which are associated with deficits in cognitive, but not locomotor, behavior and elevated levels of hippocampal and hypothalamic SS. Pathological glial-neuronal interactions within the hippocampus and other subcortical brain regions may play an important role in the cognitive decline observed during normal senescence and in aging-related neurodegenerative disorders.

Sequestration of mitotic (M-phase) chromosomes in autophagosomes: mitotic programmed cell death in human Chang liver cells induced by an OH* burst from vanadyl(4)

BACKGROUND

Fragmentation of genomic DNA in apoptosis/programmed cell death (PCD) is a characteristic hallmark in which both 2N and 4N DNA from G1, S, and G2/M cell cycle phases were seen degraded to the sub-2N Ao level in PCD such as from serum deprivation, glucocorticoid treatment, and gamma-radiation. However M-phase (mitotic) cells are said to perish only via non-programmed or necrotic cell death unless they were allowed to complete cytokinesis and re-enter interphase. The morphological criteria of PCD refer only to interphase cells with intact nuclear membranes, none seems applied to mitotic cells. We show here autophagic sequestration of mitotic chromosomes in a typical PCD response where G1, S, and G2/M DNA were replaced by a sub-2N Ao peak, suggesting that mitotic cells may yet have the option of PCD or suicide. Autophagy is absent in necrosis.

METHODS

Mitotic human Chang liver cells in normal monolayer culture were compared with apoptotic counterparts initiated by a burst of hydroxyl free radicals (OH*) generated from vanadium internalized by an NH4Cl prepulse containing vanadyl(4) ions. Total (free and bound) vanadium uptake was quantitated by elemental spectral analysis of single cells using a) Particle-Induced X-ray Emission (PIXE) profiling, and b) Scanning Transmission Ion Microscopy (STIM) in the nuclear microscope. The Coulter EPICS PROFILE II flow cytometer was used for a) the cell cycle analysis using propidium iodide-DNA binding, b) intracellular pH (pHi) evaluation in the acidification-and-recovery cycle, using ratiometric 2',7'-bis(2-carboxyethyl)-5 (and-6)-carboxyfluorescein (BCECF) fluorescence quantitation. Transmission electron microscopy examined the morphological changes. Vanadyl(4)- generated hydroxyl free radicals (OH*) were evaluated by measuring OH*-benzoic adduct fluorescence at 304/413 nm using the SPEX Fluoromax photon counting spectrofluorometer.

RESULTS

Nuclear microscopy showed that a 30 min acidification prepulse containing 4mM vanadyl(4) ions, V(4), had increased the total (free and bound) vanadium concentration of human Chang liver cells from normal ultratrace levels to 56,992 ppm of dry wt (1.1174 Eq per kg dry wt). After the prepulse, cells realkalinized in DMEM growth medium, recovering to the physiological pHi level in 30 min. At the physiological pH 7 level, V(4) generated a burst of OH* free radicals in the order of 15,000 folds above the prepulse (pH 4.5) level. In these conditions, spectrofluorometric evaluation showed loss of DNA intercalation with propidium iodide (PI-DNA binding) indicating DNA degradation. Cell-by-cell evaluation of the PI-DNA binding by flow cytometry showed abolition of G1, S, and G2/M phases and their replacement by a sub-2N Ao peak of fragmented DNA, emulating serum deprivation PCD in these cells. Immediately upon initiating an OH* burst ultrastructural profiles showed mitotic chromosomes (M-phase chromatin) being surrounded by rough endoplasmic reticulum (RER) and small vesicles, indicating their sequestration in autophagosomes. Autophagy was also seen to be a prominent feature in serum deprivation PCD.

CONCLUSION

Sequestration of mitotic chromosomes by autophagosomes in a typical PCD response showed a well-defined morphological pathway for direct degradation of M-phase chromatin without first completing cytokinesis. Mitotic cells could commit suicide via autophagy directed at its own chromatin. Autophagic sequestration of chromatin in PCD is novel.

Redox perturbations in cysteamine-stressed astroglia: implications for inclusion formation and gliosis in the aging brain

The aminothiol compound, cysteamine (CSH), induces astrocyte hypertrophy (gliosis) and the appearance of autofluorescent, peroxidase-positive cytoplasmic granules in these cells akin to changes that occur spontaneously in astroglia of the aging periventricular brain. Paradoxically, CSH damages astroglial mitochondria (granule precursors) while protecting these cells from subsequent H2O2 and mechanoenzymatic stress. In this study, in vitro CSH administration significantly increased manganese superoxide dismutase (MnSOD) activity in cultured astroglia. Immunoblot and Northern analyses indicated that MnSOD protein and mRNA levels were increased in cultured astrocytes after 3-6 days of CSH treatment. Systemic administration of CSH also significantly augmented MnSOD activity in the intact diencephalon. CSH caused a pronounced (6-fold), but transient, increase in the level of reduced glutathione (GSH) in cultured astrocytes. In contrast, catalase and glutathione reductase (GR) activities were suppressed, whereas copper-zinc superoxide dismutase (CuZnSOD) activity remained unchanged both in cultured astroglia and in the intact diencephalon following CSH treatment. Glutathione peroxidase (GP) activity was increased after 3 and 48 h of CSH treatment and then declined below control levels in cultured astrocytes. CSH inhibited the formation of thiobarbituric acid-reactive products (TBAR) in whole astrocyte monolayers, although it promoted TBAR formation in suspensions of isolated astroglial mitochondria. CSH-related oxidative stress may accelerate aging-related changes in astroglial mitochondria while conferring cytoprotection to these cells by stimulating the upregulation of various heat shock proteins and MnSOD. These cytoprotective responses may facilitate astrocyte survival and the development of reactive gliosis in the face of concomitant neuronal degeneration. CSH-treated astrocytes may serve as a model for the (dys)regulation of neuroglial MnSOD and other antioxidant enzymes in the aging and degenerating nervous system.

Estrogen induction of glial heat shock proteins: implications for hypothalamic aging

In the aging mammalian hypothalamus, a unique subpopulation of glial cells accumulates peroxidase-positive cytoplasmic inclusions distinct from lipofuscin. In adult rodents, this senescence-dependent glial granulation is accelerated by administration of estradiol valerate. In the present study, brain sections derived from male rats given 3 monthly intramuscular injections of estradiol valerate (0.2 mg or 2.0 mg) were immunostained for heat shock proteins and glial fibrillary acidic protein to determine whether a glial stress response is implicated in estrogen-induced granulation. Our findings indicate that estrogen elicits a heat shock response and subsequent granulation in astrocytes residing in estradiol receptor-rich brain regions including the arcuate nucleus and the wall surrounding the third ventricle but not in estradiol receptor-deficient regions such as the striatum and corpus callosum. The heat shock proteins induced by estrogen, namely, the 27, 72, and 90 kDa stress proteins, are upregulated in astrocytes in response to oxidative challenge supporting our hypothesis that estrogen mediates senescent changes in the rodent hypothalamus through oxidative mechanisms.

Experimental induction of corpora amylacea-like inclusions in rat astroglia

Corpora amylacea (CA) are glycoproteinaceous inclusions that accumulate in the human central nervous system during normal ageing, and to an even greater extent in Alzheimer's disease and other neurodegenerative disorders. They are particularly prominent in subpial and subependymal regions, and are most commonly located within astrocytes and their processes. We previously demonstrated that human CA share many tinctorial and histochemical properties in common with Gomori-positive cytoplasmic granules which accumulate in periventricular astrocytes of the ageing vertebrate brain and in rat astroglial cultures exposed to the sulphydryl agent, cysteamine (CSH). In the present study, long-term exposure of neonatal rat astrocyte cultures to CSH resulted in the formation of large spherical, PAS-positive cytoplasmic inclusions which are highly reminiscent of, if not identical to, human CA. As in the case of human CA and Gomori-positive astrocyte granules, the CSH-induced CA-like inclusions exhibit non-enzymatic peroxidase activity and consistent immunolabelling with antibodies directed against the mitochondrial protein, sulphite oxidase. Taken together, our findings suggest that progressive mitochondrial damage and macroautophagy play an important role in the biogenesis of CA (and Gomori-positive granules) in astrocytes of the ageing periventricular brain.

Differential effects of cysteamine on heat shock protein induction and cytoplasmic granulation in astrocytes and glioma cells

The sulfhydryl agent, cysteamine (CSH), promotes the accumulation of autofluorescent, peroxidase-positive cytoplasmic granules in cultured astroglia akin to those which naturally accumulate in astrocytes of the aging periventricular brain. Both in vitro and in situ, CSH rapidly induces various heat shock proteins (HSP) in astrocytes long before granulation occurs. In the present study, we determined that CSH treatment resulted in an increase in HSP 27, HSP 90 and heme oxygenase (HO-1) at both the protein and mRNA level. We also showed that C6 glioma cells, unlike primary astrocytes, constitutively express HSP 27, HSP 90 and HO-1 at low levels. Moreover, CSH is incapable of eliciting further HSP expression or inducing granulation in the glioma cells. Our results support the hypothesis that the biogenesis of redox-active astrocytic inclusions in CSH-treated glial cultures and in the aging periventricular brain is dependent on an antecedent cellular stress response.

Mitochondrial constituents of corpora amylacea and autofluorescent astrocytic inclusions in senescent human brain

Corpora amylacea (CA) are cytoplasmic inclusions that accumulate in human brain in the course of normal aging, and to an even greater extent, in Alzheimer's disease and other neurodegenerative conditions. In senescent and Alzheimer-diseased human brains, astrocytes in limbic and periventricular regions exhibit red autofluorescent inclusions, homologous to Gomori-positive astrocyte granules previously described in the brains of aging rodents and other vertebrates. We have shown that Gomori inclusions in situ and in culture are derived from autophagocytosed mitochondria exhibiting iron-mediated peroxidase activity. In the human brain, the autofluorescent inclusions share many properties with CA. Both types of inclusion progressively accumulate in periventricular regions with advancing age, are largely astrocytic in origin, and contain various heat shock proteins and ubiquitin. Using histochemistry in conjunction with cofocal microscopy, we demonstrated that both CA and the red autofluorescent granules exhibit non-enzymatic peroxidase activity and an affinity for CAH and PAS. The only major divergent histochemical feature between the Gomori-positive astrocyte granules and CA is the presence of orange-red autofluorescence in the former and the absence of endogenous fluorescence in the latter. On the basis of numerous shared topographic and histochemical features, we hypothesized that CA are largely derived from autofluorescent (Gomori-positive) astrocyte granules which reside in periventricular regions of the senescent CNS. Immunofluorescent labeling and laser scanning confocal microscopy demonstrated consistent colocalization of the mitochondrial proteins, sulfite oxidase, and heat shock protein 60, to both CA and the autofluorescent astroglial inclusions. In addition, both CA and the autofluorescent astrocyte granules exhibit staining for DNA which colocalizes to mitochondrial antigens and therefore likely represents mitochondrial nucleic acid in dual-labeled preparations. These observations suggest that a) Gomori-positive astrocyte granules in human brain are homologous to those described in rodents, b) Gomori-positive granules may be structural precursors of CA in senescent human brain, and c) in the aging human brain, degenerate mitochondria within periventricular astrocytes give rise to autofluorescent cytoplasmic granules and corpora amylacea.

Composition of Gomori-positive inclusions in astrocytes of the hypothalamic arcuate nucleus

BACKGROUND

Astrocytes within the hypothalamic arcuate nucleus contain Gomori-positive inclusions that exhibit a nonenzymatic peroxidase activity. The source and composition of these Gomori-positive inclusions are currently unknown. Recent evidence, derived from cultured astrocytes, suggests that Gomori-positive inclusions may consist of autophagocytized accumulations of altered mitochondria and that the peroxidase activity is generated by iron or other metals which accumulate in these mitochondria.

METHODS

The present study applies electron microscopy, energy dispersive X-ray microanalysis, and immunocytochemistry in conjunction with confocal microscopy to determine the structure and composition of Gomori-positive inclusions in vivo.

RESULTS

The results indicate that Gomori-positive inclusions are heterogeneous structures often associated with microtubules and that they contain conspicuous mitochondrial components. Gomori-positive inclusions exhibit X-ray emission peaks for copper and, less often, chromium, either of which could account for the peroxidase activity.

CONCLUSIONS

These results support the hypothesis that Gomori-positive inclusions are autophagosomes in which mitochondria are prominent.

The 21-aminosteroid antioxidant, U74389F, prevents estradiol-induced depletion of hypothalamic beta-endorphin in adult female rats

A single intramuscular injection of 2 mg estradiol valerate (EV) results in neuronal degeneration and beta-endorphin depletion in the hypothalamic arcuate nucleus of adult female rats. We have hypothesized that peroxidase-positive astrocytes in this brain region oxidize estrogens and catecholestrogens to semiquinone radicals which mediate oxidative neuronal injury. In the present study, dietary administration of the potent antioxidant 21-aminosteroid, U-74389F, completely blocked EV-induced beta-endorphin depletion in the hypothalami of adult female rats. Neither EV nor 21-aminosteroid treatment had any effect on hypothalamic concentrations of neuropeptide Y and Met-enkephalin, confirming that the estradiol lesion is fairly selective for the beta-endorphin cell population. The present findings support the hypothesis that the toxic effect of estradiol on hypothalamic beta-endorphin neurons is mediated by free radicals.