Reduction of calbindin-28k mRNA levels in Alzheimer as compared to Huntington hippocampus

Vitamin D and Its Analogues Decrease Amyloid-β (Aβ) Formation and Increase Aβ-Degradation

Alzheimer's disease (AD) is characterized by extracellular plaques in the brain, mainly consisting of amyloid-β (Aβ), as derived from sequential cleavage of the amyloid precursor protein. Epidemiological studies suggest a tight link between hypovitaminosis of the secosteroid vitamin D and AD. Besides decreased vitamin D level in AD patients, an effect of vitamin D on Aβ-homeostasis is discussed. However, the exact underlying mechanisms remain to be elucidated and nothing is known about the potential effect of vitamin D analogues. Here we systematically investigate the effect of vitamin D and therapeutically used analogues (maxacalcitol, calcipotriol, alfacalcidol, paricalcitol, doxercalciferol) on AD-relevant mechanisms. D₂ and D₃ analogues decreased Aβ-production and increased Aβ-degradation in neuroblastoma cells or vitamin D deficient mouse brains. Effects were mediated by affecting the Aβ-producing enzymes BACE1 and γ-secretase. A reduced secretase activity was accompanied by a decreased BACE1 protein level and nicastrin expression, an essential component of the γ-secretase. Vitamin D and analogues decreased β-secretase activity, not only in mouse brains with mild vitamin D hypovitaminosis, but also in non-deficient mouse brains. Our results further strengthen the link between AD and vitamin D, suggesting that supplementation of vitamin D or vitamin D analogues might have beneficial effects in AD prevention.

Pretreatment with apoaequorin protects hippocampal CA1 neurons from oxygen-glucose deprivation

Ischemic stroke affects ∼795,000 people each year in the U.S., which results in an estimated annual cost of $73.7 billion. Calcium is pivotal in a variety of neuronal signaling cascades, however, during ischemia, excess calcium influx can trigger excitotoxic cell death. Calcium binding proteins help neurons regulate/buffer intracellular calcium levels during ischemia. Aequorin is a calcium binding protein isolated from the jellyfish Aequorea victoria, and has been used for years as a calcium indicator, but little is known about its neuroprotective properties. The present study used an in vitro rat brain slice preparation to test the hypothesis that an intra-hippocampal infusion of apoaequorin (the calcium binding component of aequorin) protects neurons from ischemic cell death. Bilaterally cannulated rats received an apoaequorin infusion in one hemisphere and vehicle control in the other. Hippocampal slices were then prepared and subjected to 5 minutes of oxygen-glucose deprivation (OGD), and cell death was assayed by trypan blue exclusion. Apoaequorin dose-dependently protected neurons from OGD--doses of 1% and 4% (but not 0.4%) significantly decreased the number of trypan blue-labeled neurons. This effect was also time dependent, lasting up to 48 hours. This time dependent effect was paralleled by changes in cytokine and chemokine expression, indicating that apoaequorin may protect neurons via a neuroimmunomodulatory mechanism. These data support the hypothesis that pretreatment with apoaequorin protects neurons against ischemic cell death, and may be an effective neurotherapeutic.

Phenotypic changes in calbindin D28K immunoreactivity in the hippocampus of Fmr1 knockout mice

Fragile X syndrome (FXS), the most prevalent form of inherited mental retardation, is caused by the lack of FMRP (fragile mental retardation protein) as a result of the transcriptional silencing of the FMR1 gene. Here we analyze the immunohistochemical expression of the calbindin D28K protein in the hippocampus of Fmr1 knockout (KO) mice and compare it with that of their wildtype (WT) littermates. The spatial distribution pattern of calbindin-immunoreactive cells in the hippocampus was similar in WT and KO mice but for each age studied (ranging from 3.5-8 months) the dentate gyrus of Fmr1-KO mice showed a significant reduction in calbindin-immunoreactive granule cells. Also, the number of calbindin-immunoreactive cells was reduced in the CA1 pyramidal layer in KO mice compared to their WT littermates. In addition, Frm1-KO mice showed a group of calbindin-immunoreactive cells located only in the left CA3b subregion that was only sometimes observed in WT mice. Overall, the absence of FMRP results in a dysregulation of the calbindin protein expression in the hippocampus. This dysregulation is cell type- and time-dependent and as a consequence key elements of the hippocampal trisynaptic circuitry may lack calbindin in critical periods for normal memory/learning abilities to be achieved and may explain some of the FXS symptoms observed in the Fmr1-KO mouse model.

Investigation of annexin A5 as a biomarker for Alzheimer's disease using neuronal cell culture and mouse model

Alzheimer's disease (AD) differs from other forms of dementia in its relation to amyloid beta peptide (Abeta). Abeta, a proteolytic product of amyloid precursor proteins (APP), has a toxic effect on neuronal cells, which involves perturbation of their Ca(2+) homeostasis. This effect implies that changes of protein expression in neuronal cells with calcium stress should provide a molecular marker for this disease. In the present study, we used the supernatant from a neuronal cell culture after incubation with or without Abeta and isolated a Ca(2+)-dependent acidic phospholipid binding fraction to perform a proteomic study. Several unique proteins were identified after incubation with Abeta. We focused on annexin A5, among these proteins, because it binds both Ca(2+) and lipids likely to be involved in calcium homeostasis. Tg2576 transgenic mice (AD model) overexpressing mutant human APP showed a significant increase of annexin A5 in the brain cortex but not in other organs, including liver, kidney, lung, and intestine. In human plasma samples, the level of annexin A5 was significantly increased in a proportion of AD patients compared with a control group (P < 0.0001 in the logistic regression analysis). From the receiver operating characteristic (ROC) curve with plasma annexin A5 concentrations, the mean area under the curve (AUC 0.898) suggests that annexin A5 is a favorable marker for AD.

Sex differences in the cerebellum and frontal cortex: roles of estrogen receptor alpha and sex chromosome genes

Most neurobehavioral diseases are sexually dimorphic in their incidence, and sex differences in the brain may be key for understanding and treating these diseases. Calbindin (Calb) D28K is used as a biomarker for the well-studied sexually dimorphic nucleus, a hypothalamic structure that is larger in males than in females. In the current study weanling C56BL/6J mice were used to examine sex differences in the Calb protein and message focusing on regions outside of the hypothalamus. A robust sex difference was found in Calb in the frontal cortex (FC) and cerebellum (CB; specifically in Purkinje cells); mRNA and protein were higher in females than in males. Using 2 mouse lines, i.e. one with a complete deletion of estrogen receptor alpha (ERα) and the other with uncoupled gonads and sex chromosomes, we probed the mechanisms that underlie sexual dimorphisms. In the FC, deletion of ERα reduced Calb1 mRNA in females compared to males. In addition, females with XY sex chromosomes had levels of Calb1 equal to those of males. Thus, both ERα and the sex chromosome complement regulate Calb1 in the FC. In the CB, ERα knockout mice of both sexes had reduced Calb1 mRNA, yet sex differences were retained. However, the sex chromosome complement, regardless of gonadal sex, dictated Calb1 mRNA levels. Mice with XX chromosomes had significantly greater Calb1 than did XY mice. This is the first study demonstrating that sex chromosome genes are a driving force producing sex differences in the CB and FC, which are neuoranatomical regions involved in many normal functions and in neurobehavioral diseases.

Effects of long-term memantine on memory and neuropathology in Ts65Dn mice, a model for Down syndrome

Memantine is a partial NMDA receptor antagonist that has been shown to improve learning and memory in several animal models, and is approved for the treatment of Alzheimer's disease (AD). Chronic treatments using memantine in animal models of Alzheimer's disease show disease-modifying effects and suggest a potential neuroprotective function. The present study assessed the effects of both short- and long-term memantine treatment in a mouse model of Down syndrome (DS), the Ts65Dn mouse. The Ts65Dn mouse contains a partial trisomy of murine chromosome 16, and exhibits hippocampal-dependent memory deficits, as well as progressive degeneration of basal forebrain cholinergic neurons (BCFNs). Ts65Dn mice were treated with memantine for a period of 6 months, beginning at 4 months of age. At the end of treatment the mice underwent memory testing using novel object recognition and water radial arm maze tasks, and then histologically analyzed for markers of neurodegeneration. Memantine treatment improved spatial and recognition memory performance in the Ts65Dn mice, though not to the level of normosomic littermate controls. Despite these memory improvements, histological analysis found no morphological signs of neuroprotection of basal forebrain cholinergic or locus coeruleus neurons in memantine-treated Ts65Dn mice. However, memantine treatment of Ts65Dn mice gave rise to elevated brain-derived neurotrophic factor expression in the hippocampus and frontal cortex, suggesting a mechanism of behavioral modification. Thus, our findings provide further evidence for memory facilitation of memantine, but suggest pharmacological rather than neuroprotective effects of memantine both after acute and chronic treatment in this mouse model.

Cholinergic degeneration and memory loss delayed by vitamin E in a Down syndrome mouse model

Down syndrome (DS) individuals develop several neuropathological hallmarks seen in Alzheimer's disease, including cognitive decline and the early loss of cholinergic markers in the basal forebrain. These deficits are replicated in the Ts65Dn mouse, which contains a partial trisomy of murine chromosome 16, the orthologous genetic segment to human chromosome 21. Oxidative stress levels are elevated early in DS, and may contribute to the neurodegeneration seen in these individuals. We evaluated oxidative stress in Ts65Dn mice, and assessed the efficacy of long-term antioxidant supplementation on memory and basal forebrain pathology. We report that oxidative stress was elevated in the adult Ts65Dn brain, and that supplementation with the antioxidant vitamin E effectively reduced these markers. Also, Ts65Dn mice receiving vitamin E exhibited improved performance on a spatial working memory task and showed an attenuation of cholinergic neuron pathology in the basal forebrain. This study provides evidence that vitamin E delays onset of cognitive and morphological abnormalities in a mouse model of DS, and may represent a safe and effective treatment early in the progression of DS neuropathology.

Purinergic receptor-stimulated IP3-mediated Ca2+ release enhances neuroprotection by increasing astrocyte mitochondrial metabolism during aging

Astrocytes play an essential role in the maintenance and protection of the brain, which we reported was diminished with age. Here, we demonstrate that activation of a purinergic receptor (P2Y-R) signaling pathway, in astrocytes, significantly increases the resistance of astrocytes and neurons to oxidative stress. Interestingly, P2Y-R activation in old astrocytes increased their resistance to oxidative stress to levels that were comparable with stimulated young astrocytes. P2Y-R enhanced neuroprotection was blocked by oligomycin and by Xestospongin C, inhibitors of the ATP synthase and of inositol (1,4,5) triphosphate (IP3) binding to the IP3 receptor, respectively. Treatment of astrocytes with a membrane permeant analog of IP3 also protected astrocytes against oxidative stress. These data indicate that P2Y-R enhanced astrocyte neuroprotection is mediated by a Ca2+-dependent increase in mitochondrial metabolism. These data also reveal a signaling pathway that can rapidly respond to central energy needs throughout the aging process.

Calbindin D-28k immunoreactivity increases in the hippocampus after long-term treatment of soy isoflavones in middle-aged ovariectomized and male rats

This article investigates the long-term effects of soybean isoflavones (ISO) on the changes of calbindin D-28k (CB) immunoreactivity in the hippocampus in middle-aged ovariectomized female rats as well as middle-aged control female and male rats to identify any correlation between calcium and phytoestrogens. In the CA1 region, CB immunoreactivity in the ovariectomized females was similar to that of the control females, whereas CB immunoreactivity in the males was significantly lower than that of the control females. In the dentate gyrus, CB immunoreactivity in the ovariectomized females and males was significantly lower than that of the control females. CB immunoreactivity in all groups was increased dose-dependently after ISO treatment in the CA1 region and dentate gyrus. This result suggests that ISO treatment enhances the expression of CB immunoreactivity in the hippocampus in the middle-aged rats.

Is vitamin D hypothesis for schizophrenia valid? Independent segregation of psychosis in a family with vitamin-D-dependent rickets type IIA

The vitamin D hypothesis of schizophrenia is a recent concept bringing together old observations on environmental risk factors and new findings on the neurodevelopmental effects of vitamin D. Candidate genes related to the vitamin D endocrine system have not yet been fully explored for this purpose. The coexistence of vitamin-D-dependent-rickets type II with alopecia (VDDR IIA) and different forms of psychosis in the same inbred family has provided us with an opportunity to investigate the presumed relationship between vitamin D deficiency and psychosis. Psychiatric examination and molecular genetic studies were performed in this family overloaded with psychotic disorders and VDDR IIA. Forty members were evaluated in order to describe their phenotypic features. The family was tested for a linkage to the chromosome 12q12-q14 region where the vitamin D receptor (VDR) gene is located. Psychosis was the common phenotype in the 18 psychiatrically affected members. Pedigree analysis did not show a cosegregation of psychosis and rickets. Lod scores were not significant to prove a linkage between psychosis and VDR locus. The authors concluded that (1) the neurodevelopmental consequences of vitamin D deficiency do not play a causative role in psychotic disorders, (2) these two syndromes are inherited independently, and (3) vitamin D deficiency does not act as a risk factor in subjects susceptible to psychosis.

Locally reduced levels of acidic FGF lead to decreased expression of 28-kda calbindin and contribute to the selective vulnerability of the neurons in the entorhinal cortex in Alzheimer's disease

Recent studies demonstrate that a disturbed calcium-homeostasis leading to increased susceptibility to excitotoxic triggers plays a major role in the neurodegenerative process initiating in layer 2 of the entorhinal cortex (EC2) during Alzheimer's disease (AD). Thus, proteins binding free Ca++ (i.e. calbindin) and factors regulating these proteins are of great importance for the neuroprotective-neurotoxic balance in the affected brain regions. In the present combined human and in vitro study evidence is provided that altered levels of the acidic fibroblast growth factor (aFGF) and calbindin expression are concomitantly present in EC2 neurons and have interactive effects. A dramatic loss of aFGF- and calbindin-labeled EC2 neurons was found. Further analysis of the surviving EC2 neurons revealed a strong immunoreactivity to calbindin and aFGF. In vitro experiments show that aFGF regulates calbindin expression, because treatment of differentiating neurons with recombinant aFGF increases calbindin expression in a time-dependent fashion. The data imply that a reduced expression of aFGF in EC2 neurons of AD brains leads to lower levels of calbindin resulting in decreased neuroprotective capacity.

Evidence of functional vitamin D receptors in rat hippocampus

The steroid hormone vitamin D has important biological roles in calcium transport, cell growth, and cell differentiation. Its cellular activities are mediated by high affinity interaction with the vitamin D receptor. In brain, autoradiographic, immunohistologic, and messenger RNA expression studies implicate a number of neuronal systems, including the hippocampus, as potential targets of vitamin D. However, cellular distribution and protein expression, and binding of the receptor to vitamin D response elements have yet to be established in hippocampus. This investigation was undertaken to characterize the vitamin D receptor in rat hippocampus with western blot, immunocytochemistry, and gel shift analyses. The presence of the receptor protein in hippocampus extracts was revealed with western blotting using an anti-rat vitamin D receptor antiserum. In vivo and in vitro immunocytochemical results confirmed the presence of vitamin D receptor in neuronal and glial cells. In the hippocampus, the receptor was localized in pyramidal and granule cell layers, CA1, CA2, and CA3 subfields and in the dentate gyrus. Double labeling for the vitamin D receptor and glial fibrillary acidic protein revealed that glia also expressed the receptor protein. Gel shift analyses evaluated with the murine osteopontin vitamin D response element indicated a specific, bound receptor-containing complex from hippocampal extracts. Altogether, these findings clearly document the localization of vitamin D receptor in rat hippocampus and that hippocampus contains vitamin D receptors capable of specifically binding to DNA. In combination with reports of a neuroprotective role for vitamin D in hippocampal cell survival, these data suggest that the endogenous vitamin D receptor may mitigate processes related to cellular homeostasis, perhaps through a calcium buffering mechanism.

Transglutaminase-induced cross-linking of tau proteins in progressive supranuclear palsy

The mechanisms leading to the abnormal self-polymerization of tau into straight and paired helical filaments (PHFs) and neurofibrillary tangles (NFT) in Alzheimer disease (AD) and progressive supranuclear palsy (PSP) are not known. However, transglutaminase-induced cross-linking of PHF-tau was observed in AD and thus may also contribute to the formation of NFT in other neurodegenerative disorders including PSP. Tissue homogenates from PSP and normal age-matched controls were used to immunoaffinity-purify proteins containing transglutaminase-induced epsilon-(gamma-glutamyl) lysine cross-links. The immunoaffinity-purified proteins were then examined on immunoblots with a PHF-tau antibody, PHF-1. There were significantly higher levels of epsilon-(gamma-glutamyl) lysine cross-linking of PHF-tau in globus pallidus and pons regions of PSP cases compared to barely detectable cross-links in controls. The occipital cortex, an area spared from neurofibrillary pathology in PSP, showed no detectable cross-linking of PHF-tau protein in either PSP cases or control cases. Double-label immunofluorescence demonstrated the colocalization of the cross-link and PHF-tau in NFT in pons of PSP Previous studies and present data are consistent with the hypothesis that transglutaminase-induced cross-linking may be a factor contributing to the abnormal polymerization and stabilization of tau in straight and PHFs leading to neurofibrillary tangle formation in neurodegenerative diseases, including PSP and AD.

Tissue transglutaminase: a possible role in neurodegenerative diseases

Tissue transglutaminase is a multifunctional protein that is likely to play a role in numerous processes in the nervous system. Tissue transglutaminase posttranslationally modifies proteins by transamidation of specific polypeptide bound glutamines. This action results in the formation of protein crosslinks or the incorporation of polyamines into substrate proteins, modifications that likely have significant effects on neural function. Tissue transglutaminase is a unique member of the transglutaminase family as in addition to catalyzing the calcium-dependent transamidation reaction, it also binds and hydrolyzes ATP and Guanosine 5'-triphosphate and may play a role in signal transduction. Tissue transglutaminase is a highly regulated and inducible enzyme that is developmentally regulated in the nervous system. In vitro, numerous substrates of tissue transglutaminase have been identified, and several of these proteins have been shown to be in situ substrates as well. Several specific roles for tissue transglutaminase have been described and there is evidence that tissue transglutaminase may also play a role in apoptosis. Recent findings have provided evidence that dysregulation of tissue transglutaminase may contribute to the pathology of several neurodegenerative conditions including Alzheimer's disease and Huntington's disease. In both of these diseases tissue transglutaminase and transglutaminase activity are elevated compared to age-matched controls. Further, immunohistochemical studies have demonstrated that there is an increase in tissue transglutaminase reactivity in affected neurons in both Alzheimer's and Huntington's disease. Although intriguing, many issues remain to be addressed to definitively establish a role for tissue transglutaminase in these neurodegenerative diseases.

Protective effects of neurotrophin-4/5 and transforming growth factor-alpha on striatal neuronal phenotypic degeneration after excitotoxic lesioning with quinolinic acid

Lesioning of the mammalian striatum with the excitotoxin quinolinic acid results in a pattern of neuropathology that resembles that of post mortem Huntington's disease brain. Certain neurotrophic factors can rescue degenerating cells in a variety of lesion types, including those produced by neurotoxins. Several neurotrophic factors promote the survival of striatal neurons and/or are localized within the striatum. Of these factors, neurotrophin-4/5 and transforming growth factor-alpha were chosen for administration to rats lesioned with quinolinic acid. Adult rats received a single unilateral intrastriatal injection of quinolinic acid (120 nmol) and either trophic factors or the control protein cytochrome c for seven days thereafter. The pattern of phenotypic degeneration was assessed by immunocytochemical labeling of various striatal neuronal populations at five rostrocaudal levels. Quinolinic acid produced a preferential loss in the number of cells immunoreactive for glutamate decarboxylase, with a relative sparing of the number of choline acetyltransferase-immunoreactive cells and, to a lesser degree, calretinin-immunoreactive cells. None of these phenotypic populations was protected by either neurotrophin-4/5 or transforming growth factor-alpha. In contrast, when glutamate decarboxylase cells were alternatively identified by calbindin immunolabeling, both factors were found to have partially reversed the loss in the number of calbindin-positive cells induced by excitolesioning. In addition, the loss in the number of parvalbumin-immunopositive cells due to quinolinic acid was partially reversed by neurotrophin-4/5, while the loss in the number of NADPH-diaphorase-stained cells was partially reversed by transforming growth factor-alpha. These findings reveal a new population of striatal cells, calretinin neurons, that are relatively resistant to quinolinic acid toxicity and that neurotrophin-4/5 and transforming growth factor-alpha partially protect against the phenotypic degeneration of striatal cell populations in an in vivo animal model of Huntington's disease.

Progressive decline in avoidance learning paralleled by inflammatory neurodegeneration in transgenic mice expressing interleukin 6 in the brain

Inflammation with expression of interleukin 6 (IL-6) in the brain occurs in many neurodegenerative disorders. To better understand the role of IL-6 in such disorders, we examined performance in a learning task in conjunction with molecular and cellular neuropathology in transgenic mice that express IL-6 chronically from astrocytes in the brain. Transgenic mice exhibited dose- and age-related deficits in avoidance learning that closely corresponded with specific progressive neuropathological changes. These results establish a link between the central nervous system expression of IL-6, inflammatory neurodegeneration, and a learning impairment in transgenic mice. They suggest a critical role for a proinflammatory cytokine in the cognitive deficits and associated neuroinflammatory changes that have been documented in neurodegenerative diseases such as Alzheimer disease and AIDS.

Calcium-binding proteins in primate basal ganglia

This paper describes the distribution of the calcium-binding proteins calbindin-D28k. Parvalbumin and calretinin in primate basal ganglia. The data derive from immunocytochemical studies undertaken in squirrel monkeys (Saimiri sciureus) and in normal human individuals. In the striatum, calbindin labels medium-sized spiny projection neurons whereas parvalbumin and calretinin mark two separate classes of aspiny interneurons. The striatal matrix compartment is markedly enriched with calbindin while striatal patches (striosomes) display a calretinin-rich neuropil. In the pallidum, virtually all neurons contain parvalbumin but none express calbindin. Calretinin occurs only in a small subpopulation of both large and small pallidal neurons. In the subthalamic nucleus, there exists a multitude of parvalbumun-positive cells and fibers but the number of calretinin and calbindin-positive neuronal elements is small. In the substantia nigra/ventral tegmental area complex, calbindin and calretinin occur principally in dopaminergic neurons of the dorsal tier of the pars compacta and in those of the ventral tegmental area. Parvalbumin is strictly confined to the GABAergic neurons of the pars reticulata and lateralis. Calbindin-rich fibers abound in the pars reticulata and lateralis, while calretinin-positive axons are confined to the pars compacta. These results indicate that calbindin and parvalbumin are distributed according to a strikingly complementary pattern in primate basal ganglia. Calretinin is less ubiquitous but occurs in all basal ganglia components where it labels distinct subsets of neurons. Such highly specific patterns of distribution indicate that calbindin, parvalbumin and calretinin may work in synergy within primate basal ganglia.

Age-related loss of calcium binding proteins in rabbit hippocampus

Using immunocytochemistry hippocampal levels of the calcium binding proteins calbindin 28K (CB) and parvalbumin (PV) was studied in young (1 month) to very old (60 month) Albino rabbits. Young (3 month) and senescent (30 month) Wistar rats were also examined to compare the distribution and age dependency of PV and CB in both species. The distribution of PV-ir is similar in the rabbit and rat hippocampus. Aging in both species yielded a small loss of PV-ir in axon terminals. The presence of CB-ir interneurons throughout the hippocampus, and the heavy investment of the dentate gyrus (DG) granular cells with CB-ir was also similar in both species. In rabbits, the number of CB-ir interneurons in the CA1, as well as the density of CB-ir in the DG decreased in the first year of life, and did not change between 12-48 months of age. A secondary reduction in the density of CB-ir in the DG was observed at ages beyond 48 months. A similar loss of CB-ir in the DG occurred in the rat. In the CA1, however, the density of CB-ir was similar in young and aged rats. Another remarkable finding was the total absence of CB-ir in CA1 pyramidal neurons of rabbits at any age. Thus, the distribution and age dependency of PV-ir in the hippocampus is similar in both species. The decline of CB-ir in the DG with advancing age is very prominent and may be related to an altered calcium homeostasis in these cells. However, the absence of CB-ir in the CA1 of rabbits makes a causal role for CB in the functional decline of CA1 pyramidal cells during aging unlikely.

Preferential loss of preproenkephalin versus preprotachykinin neurons from the striatum of Huntington's disease patients

Preferential loss of basal ganglia neurons and terminals occurs in Huntington's disease (HD). Terminals of preproenkephalin medium-size spiny neurons are more vulnerable than terminals of preprotachykinin neurons, but the peptidergic neurons of origin have not yet been shown to die preferentially. We sought to determine, in the striatum, whether preproenkephalin neurons were lost to a greater extent than preprotachykinin neurons and to determine whether there were decreases in specific messenger RNA (mRNA) levels of preproenkephalin, preprotachykinin, and calbindin D28k. We found a grade-related decrease in the number of preprotachykinin- and calbindin D28k-labeled neurons per measuring field in the caudate nucleus of patients with HD. Three measures of the neuronal level of preprotachykinin mRNA were all significantly reduced (6-65% of control values) in HD caudate nucleus. No decline in calbindin D28k mRNA levels per neuron were found in HD striata compared to control striata. We found a greater loss of preproenkephalin neurons per field than preprotachyknin neurons per field in the caudate nucleus of HD brains compared to control brains. Preprotachykinin neurons are lost in HD in a grade-related manner and surviving preprotachykinin neurons are impaired in function. However, preproenkephalin neurons are lost to a greater extent than preprotachykinin neurons, which may explain preferential changes found in projection regions of the striatum. Declines in neuropeptide mRNA may be specific in HD, since calbindin D28k mRNA levels were unchanged. Alterations in the levels of expression of preproenkephalin and preprotachykinin mRNA may be direct or indirect effects of the HD mutation.

Calbindin28kDa and calbindin30kDa (calretinin) are substantially localised in the particulate fraction of rat brain

Calbindin28kDa is implicated in cytosolic calcium transport and calciprotection functions, principally as a mobile calcium buffer. Using immunoblotting, we have found that 36% of total calbindin28kDa is in the particulate fraction of rat brain. Particulate calbindin28kDa was located both within and outside organelles and required detergent for solubilisation. Equivalent observations were made for calbindin30kDa, 27% of which was insoluble. These findings indicate that a substantial proportion of calbindin does not function as a mobile calcium buffer, and perhaps instead has a calcium signalling role through target ligands in the insoluble cellular fraction.

Calbindin D28k mRNA in hippocampus, superior temporal gyrus and cerebellum: comparison between control and Alzheimer disease subjects

To further investigate the role of calbindin D28k in Alzheimer's disease (AD); hippocampus, superior temporal gyrus and cerebellum from control and AD cases were examined by quantitative in situ hybridization. We report here a decrease in CaBD28k mRNA in the CA2 region of AD hippocampus compared to control subjects. There were no significant differences between AD and control subjects in the other regions studied.

Calbindin-D 28k immunoreactivity in the cerebellum of spinocerebellar degeneration

We studied immunoreactivity for calbindin-D 28k (CaBP), an intracellular calcium-binding protein, in the cerebellum of control subjects and of patients with spinocerebellar degeneration (SCD) including sporadic olivopontocerebellar atrophy and familial cortical cerebellar atrophy. In the cerebellum, CaBP immunoreactivity was seen exclusively in the Purkinje cell in both SCD and control groups. However, the number of CaBP-immunoreactive Purkinje cells was significantly reduced in SCD. CaBP immunohistochemistry also disclosed abnormal morphological changes of Purkinje cells, which was not visualized on conventional strains or not clearly demonstrated on immunohistochemistry for neurofilaments. Moreover, reduced CaBP immunoreactivity was observed even in some remaining Purkinje cells of SCD suggesting that loss of CaBP precedes neuronal loss of Purkinje cell. We conclude that CaBP is a useful marker for Purkinje cell degeneration, and that reduced CaBP expression might have some association with the mechanism of the Purkinje cell degeneration in SCD.

Differential electrophoretic behavior in aqueous polymer solutions of red blood cells from Alzheimer patients and from normal individuals

The recently reported phenomenon that red blood cells (RBC) from Alzheimer disease (AD) patients and normal individuals, which have identical electrophoretic mobilities (EPM) in phosphate-buffered saline (PBS), have different EPM in appropriately selected polymer solutions, has been further explored. Of a number of in vitro treatments to which AD and normal RBC were subjected prior to EPM measurements in bottom phase (from a dextran-poly(ethylene glycol) (PEG) aqueous phase system) only trypsin eliminated the difference. Thus, the differential polymer interaction between AD and normal RBC, thought to be the basis for their dissimilar EPM, can be abolished by appropriate proteolytic modification of the cell surfaces and suggests protein as a source of difference. Because young and old RBC from normal individuals, which have the same EPM in PBS, have different EPM in certain polymer solutions, and the RBC from AD patients have been reported to age abnormally, we also compared the young and old RBC subpopulations from these two sources. By the criterion of cell electrophoresis in polymer solutions the differences between AD and normal RBC and between young and old RBC are distinct. The EPM of AD and normal RBC differ in bottom phase or PEG but not in dextran solution; while the EPM of young and old RBC differ predominantly in dextran. We speculate that since the observed difference in EPM of RBC from AD patients and normals depends on protein(s) yet is anticoagulant-related (being obtained only when blood is collected in citrate or oxalate) it might be the result of an interaction (Ca(2+)-mediated?) between the surfaces of these cells and protein component(s) of their respective, compositionally differing sera.

Effect of treatment with the dihydropyridine-type calcium antagonist darodipine (PY 108-068) on the expression of calbindin D-28K immunoreactivity in the cerebellar cortex of aged rats

The influence of long term treatment with the dihydropyridine-type Ca2+ antagonist darodipine (PY 108-068) on age-dependent changes in calbindin D-28K immunoreactivity in the cerebellar cortex of male Wistar rats was assessed. In 12-month-old rats used as an adult reference group, specific calbindin D-28K immunoreactivity was found within the cytoplasm of Purkinje neurons and their dendritic processes. The number of Purkinje neurons displaying calbindin D-28K immunoreactivity was decreased in the cerebellar cortex of aged in comparison with adult rats. The pattern of calbindin D-28K immunoreactivity was similar in the cerebellar cortex of 24-month-old rats (aged), although a significant decrease in the intensity of immunoreactivity was noticeable. Treatment of aged rats with darodipine for 6 months increased the percentage of immunoreactive Purkinje neurons and the intensity of calbindin D-28K immunoreactivity in the cytoplasm of Purkinje neurons. Calbindin D-28K is a Ca2+ binding protein probably involved in the modulation of Ca2+ homeostasis. The observation of a positive effect of darodipine treatment on calbindin D-28K immunoreactivity in the cerebellar cortex suggests that manipulation of dihydropyridine-type Ca2+ channels may contribute to counter age-dependent changes of Ca2+ homeostasis.

Expression of intracellular calcium-binding proteins in cultured skin fibroblasts from Alzheimer and normal aged donors

Disturbed calcium homeostasis may play a role in the etiology in Alzheimer's and other neurodegenerative diseases. A protective role against cellular degeneration has been postulated for Ca(2+)-binding proteins in certain neuron populations. Recent data suggest that intracellular free calcium regulation is also altered in several non-neuronal cells, including skin fibroblasts, from patients with Alzheimer's disease. In this study we analyzed the expression of several EF-hand Ca(2+)-binding proteins in cultured skin fibroblasts from Alzheimer patients and age-matched normal donors. We detected a strong expression of some members of the S100 Ca(2+)-binding protein family and of calcineurin A. However, no significant differences were found between both types of donors by Northern blot and Western blot analysis. In addition, similar signals were detected on 45Ca(2+)-blots of fibroblasts extracts of Alzheimer patients and control donors. The present findings indicate that the altered level of some intracellular calcium-binding proteins in certain brain areas of Alzheimer patients is not found in skin fibroblasts of these patients.

Calbindin D-28k immunoreactivity in the rat cerebellar cortex: age-related changes

The present study was designed to analyze age-dependent changes in the expression of calbindin D-28k immunoreactivity in the cerebellar cortex of male Wistar rats aged 3 months (young), 12 months (adult) and 24 months (old). Calbindin D-28k immunoreactivity was localized primarily in the cytoplasm of Purkinje neurons and in the basal portion of their dendritic processes entering in the molecular layer. The expression of calbindin D-28k immunoreactivity was highest in Purkinje neurons of adult rats and lowest in Purkinje neurons of old rats. Moreover, the number of Purkinje neurons displaying calbindin D-28k immunoreactivity was decreased in aged rats. These results demonstrate the occurrence of age-related-changes in the expression of immunoreactivity of the Ca2+ binding protein calbindin D-28k in the rat cerebellar cortex. The possibility that impairment in the expression of Ca2+ binding proteins may be involved in changes of intracellular Ca2+ homeostasis reported in aging and in some neuro-degenerative disorders is discussed.

Cortical neurons containing calretinin are selectively resistant to calcium overload and excitotoxicity in vitro

Calbindin and the more recently identified protein calretinin are structurally related calcium-binding proteins having a broad distribution in the brain. Recent evidence supports a neuroprotective role for calbindin in regulating calcium homeostasis during periods of heightened Ca2+ influx. It is not known if calretinin might have a similar function. We investigated if calretinin-containing neurons have a survival advantage in rat neocortical cultures treated with a calcium ionophore or excitatory amino acids. Neuronal cultures were challenged with the calcium ionophore A23187 at different concentrations to produce a broad range of cell death. Cell loss was quantified for both the calretinin immunopositive and the calretinin immunonegative populations of neurons. We found that 3 h after exposure to 2 microM A23187 there was a 48% loss of the calretinin immunonegative population of neurons whereas the calretinin immunopositive set of neurons was reduced by only 18%. Calretinin positive neurons were still relatively spared after treatment with 3 microM A23187. The ionophore had no cytotoxic effect when calcium ions were removed from the extracellular medium. We also studied glutamate excitotoxicity by treating the neuronal cultures with the excitatory amino acids glutamate, N-methyl-D-aspartate or kainate for 5 min and examining survival three hours later. We found again that calretinin-containing neurons were relatively spared after exposure to the excitatory amino acids; at doses of N-methyl-D-aspartate and kainate that produced a 32-40% loss of calretinin immunonegative neurons, only 2-10% of calretinin immunopositive neurons died. Similar results were obtained for glutamate. These results demonstrate that neurons containing calretinin are better able to survive disturbances in calcium homeostasis than cells not containing this calcium-binding protein. The fact that this effect was observed with ionophore treatment, as well as excitatory amino acids, suggests that neither the density nor distribution of glutamate receptors on the different cell types was a factor in determining selective vulnerability. We hypothesize that the neuroprotective effect of calretinin is due to the buffering capacities of the protein in a manner analogous to that suggested for calbindin.