Two-dimensional gel analysis of secreted proteins induced by interleukin-1 beta in rat astrocytes

Interleukin-1 beta (IL-1 beta) is a pro-inflammatory cytokine produced in the brain by endogenous microglial cells responding to injury. Levels of IL-1 beta are elevated in several neurodegenerative disorders, including Alzheimer's disease. IL-1 beta, which can act as a mitogen for astrocytes, also elicits the expression and secretion of multiple factors and paracrine 'second messengers' such as other cytokines, nerve growth factor, prostaglandins and nitric oxide that may in turn modulate neuronal and glial responses to injury. Utilizing giant, high-resolution two-dimensional gel electrophoresis, we have sought to more fully define the potential range of protein mediators that are secreted by astrocytes treated with IL-1 beta. In cultured rat astrocytes, we observe dramatic increases in the secretion of eight different protein species after 24 h of treatment with human recombinant IL-1 beta (1 U/ml). Seven of the proteins are also induced by tumor necrosis factor-alpha or basic fibroblast growth factor. Based on immunoprecipitation with specific antisera, we have identified three of these proteins as plasminogen activator inhibitor type-1, ceruloplasmin, and complement component C3. The identities of the other proteins, including the IL-1 beta-specific induction, are currently unknown. Characterization of these downstream modulators of IL-1 beta action complements gene-based approaches and will provide a better understanding of astrocyte responses to injury as well as markers for astrocyte activation in neurodegenerative diseases.

Clathrin assembly protein AP-2 is detected in both neurons and glia, and its reduction is prominent in layer II of frontal cortex in Alzheimer's disease

There are several adaptor proteins associated with clathrin coated vesicles. Among them are AP180 and AP-2. We and others have previously described synaptic localization of AP180. AP180 immunoreactivity is altered in both the superior frontal gyrus and hippocampus in Alzheimer's disease (AD). We here investigate the location and alteration of another adaptor protein, AP-2. In contrast to AP180, we have found that AP-2 is expressed by both neurons and glia. Furthermore, the only noticeable change of AP-2 in AD is a loss of its immunoreactivity in layer II of the superior frontal gyrus.

Changes in synaptic expression of clathrin assembly protein AP180 in Alzheimer's disease analysed by immunohistochemistry

Clathrin assembly protein AP180 plays a regulatory role in clathrin-mediated synaptic vesicle recycling in synapses. Previously, using immunoblot analysis, we observed a significant reduction of AP180 protein in Alzheimer's disease neocortex. In this study, we examined immunohistochemically the expression of AP180 in post mortem brains with Alzheimer's disease (n = 5) in comparison with neurologically normal controls (n = 5). Overall, AP180 was revealed as immunoreactive punctate granules located in the neuropil, and around neuronal cell bodies and their processes, consistent with the typical expression of synaptic proteins. Reduced density of AP180 immunoreactive puncta was seen throughout all layers of the superior frontal gyrus in Alzheimer's disease, but the loss of AP180 immunoreactivity was not as prominent in the cerebellum. This regional difference is in agreement with our previous results from immunoblot analyses. In the hippocampus, cell body AP180 immunoreactivity normally seen in the hilus and the CA3 regions of control brains was completely lost in Alzheimer's disease. In addition, AP180 immunoreactivity in the molecular layer of the dentate gyrus showed several changes in Alzheimer's disease. These appeared to be expansion of the inner molecular layer and relative changes in immunoreactivity that resulted in clearer delineation of the inner and outer molecular layers. These results provide anatomical and spatial information on AP180 expression in Alzheimer's disease brains. The variations in altered AP180 immunoreactivity in different brain regions of Alzheimer's disease may underlie the dysfunction of the corresponding synapses.

Non-HPLC separation of water-soluble choline metabolites by two-dimensional high voltage electrophoresis and thin layer chromatography

In cholinergic neurons choline is directed to three main pathways; (1) conversion to phosphorylcholine (PCh) and cytidine diphosphate choline (CDP-choline) for the synthesis of phosphatidylcholine, (2) acylation to the neurotransmitter acetylcholine and (3) oxidation to betaine for the formation of methionine. Thus, the distribution of choline among the different metabolites is important for a better understanding of the regulation of these pathways in neurons. A non-HPLC method for the simultaneous separation of five choline metabolites found in neurons is described. High voltage electrophoresis (HVE) was combined with thin layer chromatography (TLC) to separate choline, PCh, CDP-choline, acetylcholine and betaine. This method is useful in studying the distribution of choline among its different metabolites in radiotracer experiments. Aqueous metabolites from leukemia inhibitory factor treated LA-N-2 cells labeled with [methyl-3H]choline were separated by HVE followed by TLC in the same dimension. Although the separation appeared to be complete, some 'tailing' by PCh significantly elevated the radioactivity measured in CDP-choline. This tailing of PCh was confirmed by subjecting radiolabeled PCh alone to this multiple separation method. Contamination of CDP-choline by PCh was eliminated by subjecting the samples to HVE followed by TLC in the second dimension. This two-dimensional approach was consistently reproducible and achieved excellent resolution of all five metabolites. In addition, this technique also resolved a sixth choline-containing metabolite, glycerophosphorylcholine (GPC), a breakdown product of phosphatidylcholine.

Quantitative decrease in synaptophysin message expression and increase in cathepsin D message expression in Alzheimer disease neurons containing neurofibrillary tangles

Combining immunocytochemistry with in situ hybridization of Alzheimer disease (AD) hippocampus demonstrated a 50% reduction in grain density for synaptophysin message over CA1 pyramidal neurons containing neurofibrillary tangles (NFT) relative to near neighbor NFT-free neurons. This decrease was not global, but was selective since message grain density for the lysosomal protein, cathepsin D, increased 33% in these neurons (relative to NFT-free neurons). Poly A+ message grain density decreased by 25% in NFT neurons. Percent of the cell body containing NFT correlated -0.35 (p < 0.0001) with grain density for synaptophysin message. These data verify the concept of altered profiles of gene expression as a function of disease state within single cells and suggest that events associated with NFT formation may lead to altered expression of synaptic messages.

Neurons may live for decades with neurofibrillary tangles

Neurons containing neurofibrillary tangles (NFT) are one of the pathological hallmarks of Alzheimer disease (AD). It is known that this population of neurons express gene products and thus function to some degree, but it is unknown how long these neurons may survive with NFT. It is also thought that the formation of NFT results in the death of neurons. Using quantitative data on neuron loss and NFT formation as a function of disease duration, we have generated a computer program that models both the degeneration of CA1 hippocampal neurons and the formation of NFT in these neurons in AD. Modeling various neuron survival times with NFT and altering selected assumptions upon which the models are based, we arrive at the conclusions that 1) CA1 hippocampal neurons survive with NFT for about 20 years, and 2) NFT may not be obligatory for death of CA1 hippocampal neurons in AD.

Identification of a neuronal calmodulin-binding peptide, CAP-19, containing an IQ motif

Neurons produce polypeptides which can bind the calcium-poor or pre-activated form of calmodulin. It is expected that this class of peptide will serve an important role in maintaining cellular homeostasis since it would modulate calcium-dependent target regulation and redirect intracellular signaling. The lack of conserved sequence has made the identification of these peptides difficult, consequently leading us to exploit their property of binding calcium-poor calmodulin as a means of finding new species. A new peptide termed Calmodulin-Associated Peptide-19 (CAP-19) was purified and characterized. The protein-sequence information was employed in order to recover a cDNA clone from rat which included the entire reading frame for the peptide. Like its counterparts, neuromodulin (GAP-43), neurogranin (RC3) and PEP-19, it contains an IQ motif although the remainder of the peptide is quite different. Northern blot analysis of ribonucleic acid (RNA) from animals of differing ages indicated that the message appears at birth and then persists into adulthood. Antibodies to synthetic peptide were employed for localizing CAP-19. The results indicated that the peptide was localized to neurons in several brain regions. CAP-19 is similar to other calmodulin-binding proteins in that the domain spanning the IQ motif was demonstrated to participate in binding to calmodulin. Database searching showed CAP-19 to be homologous to the silkworm protein, multiprotein bridging factor 1 (MBF1). This homology suggests a potential new role for calmodulin-associated proteins in cellular homeostasis.

PEP-19 immunohistochemistry defines the basal ganglia and associated structures in the adult human brain, and is dramatically reduced in Huntington's disease

We have investigated the distribution of PEP-19, a neuron-specific protein, in the adult human brain. Immunohistochemistry for PEP-19 appears to define the basal ganglia and related structures. The strongest immunoreactivity is seen in the caudate nucleus and putamen, each of which showed both cell body and neuropil PEP-19 immunoreactivity. The substantia nigra and both segments of the globus pallidus showed PEP-19 immunoreactivity only in the neuropil. Cell bodies and dendrites of the thalamic nuclei ventralis lateralis and ventralis anterioralis were less strongly immunoreactive. Cerebellar Purkinje cells and their dendrites were immunoreactive, as were the presubiculum/subiculum regions and dentate gyrus granule cells of the hippocampus. The CA zones of the hippocampus were not immunoreactive. Preliminary data from immunoblotting experiments indicate that PEP-19 immunoreactivity is significantly reduced in cerebellum in Alzheimer's disease. While there were no apparent alterations of immunoreactivity in Down's syndrome or in Parkinson's disease, immunohistochemical analysis showed a massive loss of PEP-19 immunoreactivity in the caudate nucleus, putamen, globus pallidus and substantia nigra in Huntington's disease. These results show that PEP-19, a neuron-specific, calmodulin-binding protein, is distributed in specific areas of the adult human brain. The reduction in PEP-19 immunoreactivity in Alzheimer's disease and Huntington's disease suggests that PEP-19 may play a role in the pathophysiology of these diseases through a mechanism of calcium/calmodulin disregulation. This may be especially apparent in Huntington's disease where the distribution of the product of the abnormal gene, huntingtin, alone is not sufficient to explain the pattern of pathology. Abnormal huntingtin associates more strongly with calmodulin than does normal huntingtin [Bao et al. (1996) Proc. natn. Acad. Sci. U.S.A., 93, 5037-5042] suggesting a disruption of calmodulin-mediated intracellular mechanism(s), very likely involving PEP-19.

Reduced O-glycosylated clathrin assembly protein AP180: implication for synaptic vesicle recycling dysfunction in Alzheimer's disease

Synapse loss is one of the neuropathologies in Alzheimer's disease (AD) that may play a crucial role in the mechanism of its distinct cognitive impairment and dementia. In a previous study [18], a significant reduction of O-glycosylated clathrin assembly protein AP180 was observed in neocortex of AD. The reduction correlated with the density of neurofibrillary tangles. In this study we further determine that the O-GlcNAc/AP180 ratio is not changed, but the level of AP180 protein decreases in AD. Furthermore, whereas the level of neurofilament (NF-M) remains relatively unchanged, another clathrin assembly protein, AP-2, is also reduced in AD along with a small loss of synaptophysin. Our findings suggest that synaptic vesicle recycling dysfunction may be involved in the pathology of synapse loss in AD.

Expression profiles of multiple genes in single neurons of Alzheimer's disease

Many changes have been described in the brains of Alzheimer's disease (AD) patients, including loss of neurons and formation of senile plaques and neurofibrillary tangles. The molecular mechanisms underlying these pathologies are unclear. Northern blot, dot-blot, and reverse transcription-coupled PCR analyses have demonstrated altered expression levels of multiple messages in AD brain. Because not all cells are equally affected by the disease, these methods obviously cannot study the changes in relation to disease states of individual cells. We address this problem by using antisense RNA profiling of single cells. We present expression profiles of single neurons at early and late stages of AD and describe statistical tools for data analysis. With multivariate canonical analysis, we were able to distinguish the disease state on the basis of altered expression of multiple messages. To validate this approach, we compared results obtained by this approach with results obtained by in situ hybridization analysis. When the neurofilament medium subunit was used as a marker, our results from an antisense RNA profiling revealed no change in neurofilament medium subunit expression between early- and late-stage AD, consistent with findings obtained with in situ hybridization. However, our results obtained by either analysis at the single-cell level differed from the reported decrease in AD neocortex obtained by Northern blot analysis [Kittur, S., Hoh, J., Endo, H., Tourtellotte, W., Weeks, B. S., Markesbery, W. & Adler, W. (1994) J. Geriatr. Psychiatry Neurol. 7, 153-158]. Thus, the strategy of using the single-cell antisense RNA approach to identify altered gene expression in postmortem AD brain, followed by detailed in situ hybridization studies for genes of interest, is valuable in the study of the molecular mechanisms underlying AD neuropathology.

Developmental regulation and PKC dependence of Alzheimer's-type tau phosphorylations in cultured fetal rat hippocampal neurons

Attempts to describe a mechanism of neurofibrillary tangle formation often focus on site specific phosphorylations of tau protein. These have typically been described in both Alzheimer's disease and developing brains. Therefore, study of the developmental regulation of Alzheimer epitope tau phosphorylations may help explain their persistence or recurrence during Alzheimer's disease. Using fetal rat hippocampal cultures, we report a spatial and temporal expression of tau phosphorylation during neuronal differentiation. We have examined phosphorylation at the epitopes recognized by monoclonal antibodies, PHF-1 and Tau 1. Tau was highly phosphorylated at the PHF-1 epitope at all culture ages examined using both immunohistochemical staining and Western blots. Tau was heavily phosphorylated at the Tau 1 epitope only in older cultures. The populations of tau recognized by the two antibodies also exhibited different solubilities, suggesting different microtubule binding behaviors: tau phosphorylated at PHF-1 was retained in axons following solubilization whereas Tau 1 immunoreactive tau was not retained in any cell compartment. Finally, in this culture system, maintenance of phosphorylation at the PHF-1 epitope, but not the Tau 1 epitope, required protein kinase C activity. These results indicate unique regulatory mechanisms and roles for each of these phosphorylated tau epitopes.

Reduction of O-linked N-acetylglucosamine-modified assembly protein-3 in Alzheimer's disease

Abnormal protein processing and modification is associated with Alzheimer's disease (AD) pathology. The role of phosphorylation in AD has been studied extensively because the presumed abnormal phosphorylation of tau protein is believed to play a role in the formation of paired helical filaments. Glycosylation with O-linked N-acetylglucosamine (O-GlcNAc) to serine and threonine residues is a dynamic protein modification of intracellular proteins, and it shares similar features with protein phosphorylation. In this study, O-GlcNAc glycosylation of proteins from autopsied human brains with confirmed AD and non-AD age-matched controls was examined. O-GlcNAcylation was demonstrated by labeling protein extracts with [3H]galactose in the presence of galactosyltransferase and subsequent analyses of saccharide-protein linkage and saccharide structure. The number of O-GlcNAc-containing proteins and the overall O-GlcNAc level do not appear to be different between AD and control brain tissues. The only significant change observed is a marked reduction of O-GlcNAcylated clathrin assembly protein-3 (AP-3) in AD. The reduction is more evident in brain neocortical regions, and there appears to be a negative correlation between O-glycosylated AP-3 and the density of neurofibrillary tangles. These data suggest a possible association between the O-glycosylated AP-3 and AD pathology.

Interleukin-1 beta stimulates mitogen-activated protein kinase in U373 astrocytoma cells without the production of lipid second messengers

IL-1 beta is one of the cytokines known to affect astroglial cells in normal brain development, brain injury and neurodegenerative diseases. IL-1 beta causes astrocytes to become more reactive, alter the expression and release of molecules and in some cases to proliferate. We have investigated the mitogenic effect and signal transduction pathway induced by IL-1 beta in U373 cells, a human astrocytoma cell-line. Recombinant human IL-1 beta induced mitogenesis of U373 cells in a dose-dependent fashion as assessed by tritiated thymidine incorporation. The following signal transduction mechanisms, reported to be induced in other systems by IL-1 beta, were investigated in U373 cells: (1) activation of phosphatidylcholine-specific phospholipase C as assayed by incorporation of tritiated choline into cellular phospholipids, (2) production of diacylglycerol, a lipid second messenger, (3) activation of sphingomyelinase, and (4) activation of mitogen-activated protein kinase (MAPK). Of these, IL-1 beta activated only MAPK. In cultured rat astrocytes, IL-1 beta caused activation of MAPK without inducing proliferation.

Analysis of message expression in single neurons of Alzheimer's disease brain

Because many cell types and disease states exist in the sample of cells in even a very small region of Alzheimer's disease (AD) brain tissue, optimal understanding of disease mechanisms requires study at the level of the single cell. Our Golgi studies of single neurons in the AD brain have revealed reduced dendritic extent in many, but not all, brain regions. This reduced dendritic extent is interpreted as reduced capacity of neurons in AD to proliferate new dendritic material. Studies of message expression in single neurons reveal that neurons containing neurofibrillary tangles (NFTs) show reduced expression of messages for proteins related to growth of neuronal processes and to synapses. Neighboring neurons free of NFTs express these messages at levels approximating the levels expressed by single neurons from control brain. This reduction of expression of messages related to growth of neuronal processes and to synapses is selective, because expression of message for the lysosomal enzyme, cathepsin D, is increased in neurons containing NFTs. Simultaneous analysis of the expression of multiple genes by single neurons using an aRNA technique offers powerful capacity to profile message expression as a function of disease state of single cells.

Isolation of single immunohistochemically identified whole neuronal cell bodies from post-mortem human brain for simultaneous analysis of multiple gene expression

In Alzheimer's disease (AD), one cell in the brain may clearly be affected, while an adjacent cell appears healthy or unaffected. Previous technology has allowed us to examine one message at a time, at the level of a single cell (in situ hybridization, ISH), or multiple messages in a heterogeneous population of cells (Northern analysis). We have developed a methodology to build up a profile of multiple mRNA expression in single, whole, post-mortem cells that have been immunohistochemically (IHC) characterized. Fresh post-mortem tissue is spread into a layer one cell thick and fixed. Neurons are identified using an antibody to neurofilament and isolated using a micropipette. The mRNA is reverse transcribed and PCR carried out to confirm that material is present. A radioactively labeled antisense aRNA probe, which is representative of the messages contained in the cell is then amplified. This aRNA is used as a probe for a reverse Northern blot, allowing us to profile many genes from one cell at the same time. This technology has the potential to be applied to a wide variety of diseases encompassing many different cell types.

Low initial tau phosphorylation in human brain biopsy samples

A rapid reversible tau phosphorylation at Ser 396/404 was observed in adult human cortical biopsy tissue and rat primary cortical cell cultures. Tau phosphorylation increased usually during the first 20-30 min in phosphate-buffered saline, followed by a decrease. The time course of tau phosphorylation and dephosphorylation in biopsy tissue could be lengthened by culturing in defined, oxygenated medium, instead of in phosphate-buffered saline. Phosphorylation of total protein in biopsy tissue occurred in two phases, with peaks at 30 and 90 min. The first peak of total protein phosphorylation coincided with the peak of tau phosphorylation, although both the first and second peaks of total protein phosphorylation coincided with the first and second peaks of neurofilament-H phosphorylation.

Research uses of neuropathological data

The study of relationships between neuropathological characteristics and behavioral, structural, chemical, and molecular variables offers immense promise for understanding the basic pathophysiology of Alzheimer's disease. This position paper examines the need for standardized procedures and quantitation if neuropathological data are to be optimally useful among laboratories investigating the biology of Alzheimer's disease. These requirements include standardized fixation, embedding, sectioning, staining, brain regions and sampling methods. In addition, the definition of the structures to be quantified, such as plaque type(s), needs to be rigorously specified. Unbiased stereological methods for quantification should be used. These needs for optimal research utility exceed the needs and practicality for diagnostic purposes, suggesting a two-tiered approach to the neuropathology of Alzheimer's disease: diagnostic and research.

Prostaglandin G/H synthase-2 (cyclooxygenase-2) mRNA expression is decreased in Alzheimer's disease

Recent evidence suggests that the use of nonsteroidal anti-inflammatory drugs (NSAIDS) is beneficial for therapy or prevention of Alzheimer's disease (AD). The major anti-inflammatory action of NSAIDS is to inhibit prostaglandin G/H synthase-2 (PGHS-2), the first committed enzymatic step for prostaglandin biosynthesis. We have previously shown that PGHS-2 message is induced by Interleukin-1 beta and other inflammatory mediators in primary cultures of rodent astrocytes. To determine whether similar elevations of PGHS-2 occur as part of the gliosis in AD, we quantified PGHS-2 mRNA levels in control and AD brain by Northern hybridization analysis. To our surprise we found that PGHS-2 mRNA levels were reduced threefold in AD neocortex relative to control brain tissue. In contrast, levels were not reduced in putamen, an area that is relatively spared in AD. To localize PGHS-2 mRNA production in control and AD brain, sections of neocortex and hippocampus were hybridized with a 35S-labeled riboprobe for human PGHS-2 followed by immunocytochemistry with antibodies against neuron specific enolase (NSE) or glial fibrillary acidic protein (GFAP). Our findings indicate that PGHS-2 message is primarily localized to cells that stain for NSE rather than GFAP. Furthermore, in the three cases we examined, PGHS-2 hybridization per neuron appeared to be reduced in AD. Thus, the decrease we observe in overall PGSH-2 mRNA levels is likely to reflect both the known decline in numbers of neurons in AD as well as a lowered capacity for neuronal synthesis of PGHS-2, perhaps due to dysfunction or a loss of synaptic input.

Interleukin-1 beta induces prostaglandin G/H synthase-2 (cyclooxygenase-2) in primary murine astrocyte cultures

Activation of glial cells and the consequent release of cytokines, proteins, and other intercellular signaling molecules is a well-recognized phenomenon in brain injury and neurodegenerative disease. We and others have previously described an inducible prostaglandin G/H synthase, known as PGHS-2 or cyclooxygenase-2, that is up-regulated in many cell systems by cytokines and growth factors and down-regulated by glucocorticoid hormones. In cultured mouse astrocytes we observed increased production of prostaglandin E2 (PGE2) after stimulation with either interleukin-1 beta (IL-1 beta) or the protein kinase C activator phorbol 12-myristate 13-acetate (TPA). This increase in PGE2 content was blocked by pretreatment with dexamethasone and correlated with increases in cyclooxygenase activity measured at 4 h. Northern blots revealed concomitant increases in PGHS-2 mRNA levels that peaked at 2 h and were dependent on the dosage of IL-1 beta. Dexamethasone inhibited this induction of PGHS-2 mRNA by IL-1 beta. TPA, basic fibroblast growth factor, and the proinflammatory factors tumor necrosis factor alpha and lipopolysaccharide, but not interleukin-6, also stimulated PGHS-2 mRNA expression. Relative to IL-1 beta, the greater increases in PGE2 production and cyclooxygenase activity caused by TPA correlated with a greater induction of PGHS-2 mRNA. Furthermore NS-398, a specific inhibitor of cyclooxygenase-2, blocked > 80% of the cyclooxygenase activity in TPA-treated astrocytes. These findings indicate that increased expression of PGHS-2 contributes to prostaglandin production in cultured astrocytes exposed to cytokines and other factors.

Gap-43 message levels in anterior cerebellum in Alzheimer's disease

We have previously reported that decreased growth-associated protein (GAP-43) message in frontal association cortex (area 9) of Alzheimer's disease (AD) patients is associated with increased density of neurons containing neurofibrillary tangles (NFTs) [9]. This finding leads to the hypothesis that decreased GAP-43 message in AD may be related to NFTs, rather than to some other aspect of AD pathology. Therefore, we predicted that in areas of brain unaffected by NFTs in AD the GAP-43 message levels should be similar to those of controls. The cerebellum is known to have a number of pathologies of AD, including diffuse plaques (DPs), microglial activation and reactive astrocytes. NFTs, however, are not typically found in the cerebellum. mRNA was extracted from anterior cerebellum of AD and control cases, Northern- and slot-blotted and hybridized against a GAP-43 probe. Poly(dT) and glucose-3-phosphate dehydrogenase probes were used for normalization. The average relative GAP-43 message level was 0.582 in the AD cases and 0.448 in control cases. This 23% difference failed to reach statistical significance. Regression analysis within the AD group demonstrated that GAP-43 message level in cerebellar cortex was not significantly correlated with diffuse plaque density in cerebellar cortex. GAP-43 message levels in cerebellar cortex were also not correlated with summed density of neuritic plaques or summed density of NFTs in cortical regions-here used as an index of severity of disease. The data reported here also emphasize that the (NFT-dependent) reduction in GAP-43 mRNA levels previously reported in frontal association cortex in Alzheimer's disease [9] appears to be region specific and not a general brain phenomenon. The preservation of normal GAP-43 message levels in the cerebellum in AD is consistent with the hypothesis that events related to NFT formation have a major impact on the expression of GAP-43 in Alzheimer's disease.

Müller cell changes precede photoreceptor cell degeneration in the age-related retinal degeneration of the Fischer 344 rat

Previously, we have used descriptive pathology and histomorphometry, as well as functional testing to characterize the age-related retinal degeneration in the Fischer 344 rat. These studies suggested an association between Müller cells and photoreceptor cells in this process. The purpose of the present study was to further investigate the respective roles of these cell types in the development and progression of the retinal degeneration. Retinas from male Fischer 344 rats aged 3-24 months were first studied by light and electron microscopy. Since Müller cells abundantly express GFAP during pathological states, GFAP content was studied by immunocytochemistry and by immunoblotting following one- and two-dimensional gel electrophoresis. Microscopically, at 12 months, Müller cells showed a gradient of immunoreactivity for GFAP that was minimal in the central retina, positive for their radial processes in the equator, and abundantly expressed in the periphery. At this age, the photoreceptor cells were just beginning to degenerate in the far periphery, while they appeared healthy in the equatorial and central regions. By 24 months, Müller cell hypertrophy was seen in the peripheral regions where photoreceptor cell degeneration was most severe, while the immunoreactivity of the Müller cell processes spread further toward the central regions, ahead of the degeneration of the photoreceptor cells. Thus, Müller cell changes actually preceded photoreceptor degeneration in time and location. This phenomenon was confirmed by measurement of GFAP after one- and two-dimensional PAGE. These findings show that Müller cell changes precede chronic photoreceptor cell degeneration in the aging Fischer 344 rat and are consistent with the hypothesis that Müller cell alteration may be the primary mechanism of this age-related retinal degeneration.

[Differential neuronal loss in the hippocampus in normal aging and in patients with Alzheimer disease]

The causal relationship between the neurodegenerative changes that accompany normal ageing and those that characterize Alzheimer's disease is unclear. The high incidence of Alzheimer's disease associated with old age and the presence of its neuropathological signs in non-demented older individuals suggest that these two phenomena involve the same neurodegenerative processes and mechanisms and that Alzheimer's disease is an extension of normal ageing. On the other hand, the identification of environmental and genetic risk factors associated with Alzheimer's disease suggests the involvement of a specific disease process that is not related to normal ageing. The resolution of this fundamental issue is of importance in the design of investigative and therapeutic strategies. In this report, we describe differences in the regional patterns of neuronal loss, in the hippocampal region of the brains of Alzheimer's patients and normal ageing subjects, that indicate that Alzheimer's disease is not the manifestation of accelerated ageing, but the expression of a distinct pathological process.

Neurons bearing neurofibrillary tangles are responsible for selected synaptic deficits in Alzheimer's disease

The observation that neurons containing neurofibrillary tangles are usually adjacent to neurons free of any morphological indication of disease, suggests the hypothesis that it is NFT-bearing neurons that are primarily responsible for the loss of function in AD. Quantitative Golgi postmortem studies from our laboratories have indicated that there is in many regions of the brains of nondemented humans an age-related increase in dendritic extent of single neurons. In Alzheimer's disease, this normal, age-related increase in dendritic extent was not found, leading to the hypothesis that one of the neurobiological defects in AD is a failure of neuronal plasticity. Message levels of the growth-associated protein, GAP-43, in frontal association cortex (area 9/46) indicated that AD brains with the highest density of neurofibrillary tangle-bearing neurons, showed GAP-43 message levels decreased of the order of 6-fold relative to AD brains with the lowest density of NFT. Combined immunocytochemistry to differentiate tangle-bearing from tangle-free neurons with in situ hybridization to define relative GAP-43 message levels in single neurons revealed that grain density over tangle-bearing neurons containing nuclei was reduced 3-fold compared to that over adjacent tangle-free neurons. This reduction in expression of GAP-43 message in tangle-bearing neurons was selective, because using probes for other messages showed that grain density over tangle-bearing neurons was, on average, increased or similar to that over adjacent non-tangle-bearing neurons. Message levels for the synaptic vesicle-associated protein, synaptophysin, have also been found to be reduced in tangle-bearing neurons relative to adjacent tangle-free neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in the pattern of hippocampal neuronal loss in normal ageing and Alzheimer's disease

The distinction between the neurodegenerative changes that accompany normal ageing and those that characterise Alzheimer's disease is not clear. The resolution of this issue has important implications for the design of therapeutic and investigative strategies. To this end we have used modern stereological techniques to compare the regional pattern of neuronal cell loss in the hippocampus related to normal ageing to that associated with Alzheimer's disease. The loss related to normal ageing was evaluated from estimates of the total number of neurons in each of the major hippocampal subdivisions of 45 normal ageing subjects who ranged in age from 13 to 101 years. The Alzheimer's disease related losses were evaluated from similar data obtained from 7 cases of Alzheimer's disease and 14 age matched controls. Qualitative differences were observed in the regional patterns of neuronal loss related to normal ageing and Alzheimer's disease. The most distinctive Alzheimer's disease related neuron loss was seen in the CA1 region of the hippocampus. In the normal ageing group there was almost no neuron loss in this region (final neuron count in the CA1 region: 4.40 x 10(6) neurons for the Alzheimer's disease group vs 14.08 x 10(6) neurons in the normal ageing group). It is concluded that the neurodegenerative processes associated with normal ageing and with Alzheimer's disease are qualitatively different and that Alzheimer's disease is not accelerated by ageing but is a distinct pathological process.

Preliminary evidence: decreased GAP-43 message in tangle-bearing neurons relative to adjacent tangle-free neurons in Alzheimer's disease parahippocampal gyrus

Loss of synapses has been shown to correlate with the severity of dementia in Alzheimer's disease (AD). Intracellular neurofibrillary tangles (NFTs) have also been shown to correlate to the severity of AD dementia. We have been investigating the influence of NFTs on mRNAs related to neuronal plasticity and synaptic function. We recently reported a decrease in message for the plasticity marker, GAP-43, in AD cases with high tangle densities. The study did not permit us to determine if: a) the decrease in GAP-43 message was specific to the NFT-bearing neurons, b) a general decrease in GAP-43 message was occurring in all surviving neurons, or c) the decrease in GAP-43 message was due to a loss of neurons. It is unlikely a loss of neurons could explain the sixfold GAP-43 message loss we reported, because only a 19% excess decrease in density of hippocampal neurons occurs in AD cases with high tangle densities. Consequently, the study reported here was undertaken to determine if a general decrease in GAP-43 message was occurring in all surviving AD neurons or if the decrease in GAP-43 message was specific to NFT-bearing neurons. We combined immunocytochemistry for neurofibrillary tangles with in situ hybridization for GAP-43 message. We report here preliminary evidence indicating a decrease in GAP-43 message in NFT-bearing neurons compared to adjacent nontangle bearing neurons in parahippocampal cortex of AD patients.

Altered phosphorylation of growth-associated protein B50/GAP-43 in Alzheimer disease with high neurofibrillary tangle density

The growth-associated phosphoprotein B50/GAP-43, associated with axonal proliferation and regeneration, was isolated from superior temporal gyrus (area 22) of seven control and eight Alzheimer disease (AD) postmortem human brains. Membrane and cytoplasmic proteins were fractionated and B50/GAP-43 was isolated by reverse-phase HPLC and gel electrophoresis. B50/GAP-43 was identified with rabbit polyclonal antibodies 4P3 (generated against the calmodulin binding domain of B50/GAP-43) and 1B5 (generated against whole bovine B50/GAP-43). B50/GAP-43 protein was further separated into phosphorylated and dephosphorylated species by calmodulin-Sepharose chromatography. The amounts of phosphorylated and dephosphorylated B50/GAP-43 forms were determined by electrophoresis, protein staining, and densitometry. Data on the relative phosphorylation of B50/GAP-43 protein in membrane and cytoplasmic fractions show a 10-fold difference in the ratio of cytoplasmic/membrane phosphorylation of B50/GAP-43 in AD brains with high neurofibrillary tangle (NFT) density compared to AD brains with low NFT density. This difference is due to a decreased percentage of phosphorylated B50/GAP-43 in the membrane fraction relative to that in the cytosolic fraction from high NFT density. No analogous relationship was found between the phosphorylation of B50/GAP-43 and the density of neuritic plaques in the brains examined. These data indicate differential distribution of phosphorylated and dephosphorylated B50/GAP-43 in normal and AD brains is related to NFT density but not to neuritic plaque density.

Characterization of brain samples in studies of aging, Alzheimer's, and other neurodegenerative diseases

We review current understanding of the clinical and pathologic information needed for the determination of optimal brain tissue samples for the conduct of studies of Alzheimer's disease (AD). Characteristics that may distinguish AD from other dementing disorders are discussed. Selected considerations in the conduct of basic neurobiological studies are also outlined. Although the 28 NIA-funded Alzheimer's Centers can provide excellent clinical and neuropathological data, studies conducted outside these centers should also strive to gather the information suggested here. Clinical and neuropathological data should be used not only to classify subjects as control or AD, but also as variables that may significantly contribute to the analysis of neurobiological data obtained in the laboratory.

Dendritic regression dissociated from neuronal death but associated with partial deafferentation in aging rat supraoptic nucleus

As neurons are lost in normal aging, the dendrites of surviving neighbor neurons may proliferate, regress, or remain unchanged. In the case of age-related dendritic regression, it has been difficult to distinguish whether the regression precedes neuronal death or whether it is a consequence of loss of afferent supply. The rat supraoptic nucleus (SON) represents a model system in which there is no age-related loss of neurons, but in which there is an age-related loss of afferents. The magnocellular neurosecretory neurons of the SON, that produce vasopressin and oxytocin for release in the posterior pituitary, were studied in male Fischer 344 rats at 3, 12, 20, 27, 30, and 32 months of age. Counts in Nissl-stained sections showed no neuronal loss with age, and confirmed similar findings in other strains of rat and in mouse and human. Nucleolar size increased between 3 and 12 months of age, due, in part, to nucleolar fusion, and was unchanged between 12 and 32 months of age, indicating maintenance of general cellular function in old age. Dendritic extent quantified in Golgi-stained tissue increased between 3 and 12 months of age, was stable between 12 and 20 months, and decreased between 20 and 27 months. We interpret the increase between 3 and 12 months as a late maturational change. Dendritic regression between 20 and 27 months was probably the result of deafferentation due to the preceding age-related loss of the noradrenergic input to the SON from the ventral medulla.

The human brain homeogene, DLX-2: cDNA sequence and alignment with the murine homologue

A novel homeobox-containing cDNA from the developing human brain has been cloned and sequenced. The transcript is most closely related to the Distal-less (Dll) homeogene of Drosophila melanogaster and to the Dlx genes in the mouse, specifically to Dlx-2. As such, it is the first report of a human Dll-like gene.

Selective vulnerability and early progression of hippocampal CA1 pyramidal cell degeneration and GFAP-positive astrocyte reactivity in the rat four-vessel occlusion model of transient global ischemia

Selective, delayed-onset vulnerability of hippocampal CA1 pyramidal cells has been reported as a unique phenomenon in man and the rat four-vessel occlusion (4-VO) model of global ischemia. This has become of great interest for clarification of CA1 pathophysiology and pharmacological intervention after global ischemia. Studies of pathophysiology and pharmacotherapy appear to be impeded by variability in specific criteria and duration of 4-VO ischemia for producing selective CA1 and differential CA1-CA3 damage. The goals of this study were to: (1) develop specific criteria for 4-VO ischemia to ensure selective, bilaterally symmetrical CA1 pyramidal cell damage, (2) examine the effects of 15 min of ischemia on concomitant CA1 cell necrosis and presence of remaining and/or "viable" neurons postischemia, (3) compare 15 and 30 min of ischemia on differential vulnerability of CA1-CA3 subfields, and (4) evaluate the effects of 15 min of ischemia on CA1 pyramidal cell necrosis and glial fibrillary acidic protein (GFAP)-positive astrocyte reactivity in CA1. After 15 min of ischemia, hippocampal pyramidal cell damage was well delineated, with CA1 severely damaged, but leaving CA3 virtually intact. In contrast, 30 min of ischemia produced severe CA1 and less severe CA3 necrosis. Histological evaluations across Days 1, 3, 6, and 14 indicated a significant delayed onset of CA1-CA3 cell necrosis by Day 3. Counting of remaining cells indicated a detectable loss of some large pyramidal neurons even 1 day after ischemia. Compared to controls, there was a differential increase in GFAP-positive astrocytes in CA1-CA3 after ischemia. The results provided quantitative data on the effects of specific 4-VO criteria and durations on: (1) selective CA1 cell necrosis, (2) differential CA1-CA3 cell vulnerability, (3) presence of postischemic remaining and/or viable neurons, and (4) prospect of a "therapeutic window" for pharmacological treatment of CA1 neuronal injury.

Reduced GAP-43 message levels are associated with increased neurofibrillary tangle density in the frontal association cortex (area 9) in Alzheimer's disease

We previously suggested the hypothesis that defective neuronal plasticity is a major neurobiological deficit causing the dementia of Alzheimer's disease (AD). We used message levels of the growth-associated protein, GAP-43, as a marker of axonal plasticity to examine the hypothesis of defective neuronal plasticity in AD. When all AD cases are combined, the average level of GAP-43 message in area 9 of the AD frontal association cortex was not significantly different from the level in the comparably aged control cortex. Differentiation of AD cases on the basis of neurofibrillary tangle (NFT) density revealed that in AD cases with high tangle density average GAP-43 message level was reduced fivefold relative to levels in AD cases with low NFT density. AD cases with low neurofibrillary tangle density had levels of GAP-43 message that were not significantly different from the levels of normal controls. Differentiation of AD cases on the basis of neuritic plaque density did not indicate as strong a relationship to GAP-43 message level. The association between neurofibrillary tangle density and GAP-43 message level suggests the hypothesis that neurofibrillary tangles may reduce GAP-43 expression. Data of others show a relationship between high NFT density and reduced levels of synaptophysin-like immunoreactivity and reduced cerebral glucose metabolism. These data combine to suggest a set of AD cases with high NFT density, reduced axonal plasticity, reduced synaptic density, and reduced cerebral glucose metabolism--all variables that may be directly related to the functioning of the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Divergence of biological and chronological aging: evidence from rodent studies

Literature on aging populations of rodents supports the intuitive view that significant functional variation exists among like-aged, elderly individuals: chronological age as a solitary measure is a poor indicator of biological age. In this report, we review a variety of studies which classify aged rodents based on genetic and/or behavioral similarities, in addition to chronological age, and have provided valuable neurobiological and physiological information on age-related changes which accompany functional impairments, or the lack of them. Beyond their descriptive value for gerontological research, these findings suggest ways in which biological aging can be manipulated to promote good function in aged individuals.

Net dendritic stability of layer II pyramidal neurons in F344 rat entorhinal cortex from 12 to 37 months

Dendritic extent of Golgi-Cox stained layer II entorhinal cortex pyramidal neurons was quantified in five groups of male F344 rats aged 12, 20, 27, 30 and 37 months. Over the age range studied, neither the apical nor the basal dendritic trees showed any statistically significant change in total dendritic length, numbers of segments or average segment length. This finding of average stability of the dendritic tree does not imply absence of remodelling of connections, but does require that if remodeling does occur, retraction and proliferation of dendrites must, on average, be equal. We hypothesized that in groups of animals with similar genetic and environmental histories neighbor neuron death provides the major stimulus for dendritic proliferation. Since we found dendritic stability in the cells reported here, we would predict that there should be no age-related loss of layer II pyramidal neurons in the entorhinal cortex of the normally aging F344 male rat between 12 and 37 months. This hypothesis may be tested by counting neurons within this region.

Hippocampal plasticity in normal aging and decreased plasticity in Alzheimer's disease

Different patterns of age-related dendritic change have been reported in different zones of the human hippocampal region in the normal and Alzheimer's disease (AD) brain. In normal aging there is an increase in average (net) dendritic extent (which we interpret as plasticity) in the parahippocampal gyrus and dentate gyrus. There is net stability of dendritic extent in CA2-3, CA1, and subiculum. In regions that show plasticity in normal aging, dendrites in AD show reduced or aberrant plasticity. In regions that show stability in normal aging, dendrites either are stable or regress in AD, depending upon how severely involved the region is with the pathology of AD.

Neuron numbers and sizes in aging brain: comparisons of human, monkey, and rodent data

One of the several sources of interest in aging animal brains is their potential as models of the aging human brain. In this review we examine whether neuron numbers and sizes change similarly in aging human, monkey and rodent brain regions which data are available from more than one species. The number of brain regions studied in more than one species is surprisingly limited. Some regions show correspondence in age-related changes between humans and selected animal models (primary visual cortex, CA1 of hippocampus). For the majority of regions the data are conflicting, even within one species (e.g., somatosensory cortex, frontal cortex, cerebellum, cholinergic forebrain areas, locus coeruleus). Although some of the conflicting data may be attributed to procedural differences, particularly when data are expressed as density changes, much must be attributed to real species and/or strain differences in rodents. We conclude that neuron numbers and sizes may show similar age-related changes in human and animal brains only for sharply defined brain regions, animal species and/or strains, and age ranges.

Estimating the number of granule cells in the dentate gyrus with the disector

A practical example is given of how a newly developed stereological estimator of particle number, the disector, can be used to make estimates of neuron number in the dentate gyrus of rats. The estimates are free of biases related to lost caps, overprojection and assumptions about size, shape and orientation of the objects that are counted. The disector principle and the practical considerations relating to histological preparations and sampling are presented.

Volumes of the components of the hippocampus in the aging F344 rat

Much of the recent data on cells, synapses, and other structures in the dentate gyrus and hippocampus as a function of age are packing density or volume fraction data. In order to estimate total numbers, volumes, or surface areas of cells, synapses, vessels, etc., as a function of age, the total volumes of the subregions of the dentate gyrus and hippocampus must be known. The volumes of these subregions, visualized with the Timm stain, have been determined in 24 F344 rats from 4 to 37 months of age. Volumes of the various structures showed age-related increases which were statistically significant for the perforant path zone of the dentate gyrus molecular layer, as well as the total molecular layer, the hilus, and regio inferior and total mossy fiber systems. If the 4-month age group is eliminated from consideration, only the ratio of the volume of the mossy fiber zones to the volume of the perforant path zones of the dentate molecular layer increases significantly with age. Our general finding of lack of volumetric reorganization of the subdivisions of the hippocampal region between 12 and 37 months suggests that studies of the packing densities of structures in most of these zones may be considered comparable across ages, assuming comparability of sampling regions.

Neuron numbers and dendritic extent in normal aging and Alzheimer's disease

Factors which limit the interpretation of studies of aging brain include: secular trends, species and strain differences, effects of tissue processing, and bias which may be introduced at many levels of an experimental design. With these limitations considered, evidence is reviewed regarding neuron numbers and dendritic extent in normally aging rodent, monkey and human brain and in Alzheimer's disease. It is concluded that neuron loss and change in dendritic extent in normal aging are regionally specific, and that corresponding brain regions do not always change in similar ways in rodents and primates. It is suggested that such differences may, in part, be due to inconsistent definitions of 'aged' among species. In Alzheimer's disease there is excess neuron loss and dendritic regression in some, but not all, brain regions. Measures of the morphological substrates of brain function show appreciable overlap between AD and control groups. It is hypothesized that the static, post-mortem status of brain morphology may not adequately reflect the functional capabilities of the dynamic morphology of the living brain.

Dendritic extent in human CA2-3 hippocampal pyramidal neurons in normal aging and senile dementia

The extent of dendritic trees of pyramidal neurons of the CA2-3 field of the hippocampus of 20 human brains obtained at autopsy was quantified in Golgi Cox-stained tissue. Fifteen cases were neurologically and psychiatrically normal and ranged in age from 43 to 95 years. Five cases had a progressive, dementing disease consistent with the diagnosis of senile dementia (SD) of the Alzheimer's type. Dendritic extent of both the apical and basal trees of CA2-3 pyramidal neurons was found to be unchanged from middle age to very old age. This finding of net stability of dendritic extent is in contrast to previous quantitative reports of either continued dendritic growth in human parahippocampal gyrus or of dendritic growth followed by regression in human dentate gyrus. This finding is consistent with the suggestion that changes in dendritic extent in normal aging are a function of the balance between regressive and proliferative influences and are region specific. In cases with SD, dendritic extent of both the apical and basal trees was found to be similar to that of the normal age-matched cases. These data are consistent with those of others suggesting relative sparing of the CA2-3 field from the degenerative changes in senile dementia.