Synaptic loss reflected by secretoneurin-like immunoreactivity in the human hippocampus in Alzheimer's disease

Damaged mitochondria coincide with presynaptic vesicle loss and abnormalities in alzheimer's disease brain

Loss of synapses is the most robust pathological correlate of Alzheimer's disease (AD)-associated cognitive deficits, although the underlying mechanism remains incompletely understood. Synaptic terminals have abundant mitochondria which play an indispensable role in synaptic function through ATP provision and calcium buffering. Mitochondrial dysfunction is an early and prominent feature in AD which could contribute to synaptic deficits. Here, using electron microscopy, we examined synapses with a focus on mitochondrial deficits in presynaptic axonal terminals and dendritic spines in cortical biopsy samples from clinically diagnosed AD and age-matched non-AD control patients. Synaptic vesicle density within the presynaptic axon terminals was significantly decreased in AD cases which appeared largely due to significantly decreased reserve pool, but there were significantly more presynaptic axons containing enlarged synaptic vesicles or dense core vesicles in AD. Importantly, there was reduced number of mitochondria along with significantly increased damaged mitochondria in the presynapse of AD which correlated with changes in SV density. Mitochondria in the post-synaptic dendritic spines were also enlarged and damaged in the AD biopsy samples. This study provided evidence of presynaptic vesicle loss as synaptic deficits in AD and suggested that mitochondrial dysfunction in both pre- and post-synaptic compartments contribute to synaptic deficits in AD.

Dense core vesicle markers in CSF and cortical tissues of patients with Alzheimer's disease

Background

New fluid biomarkers for Alzheimer's disease (AD) that reveal synaptic and neural network dysfunctions are needed for clinical practice and therapeutic trial design. Dense core vesicle (DCV) cargos are promising cerebrospinal fluid (CSF) indicators of synaptic failure in AD patients. However, their value as biomarkers has not yet been determined.

Methods

Immunoassays were performed to analyze the secretory proteins prohormone convertases PC1/3 and PC2, carboxypeptidase E (CPE), secretogranins SgIII and SgII, and Cystatin C in the cerebral cortex (n = 45, provided by Bellvitge University Hospital) and CSF samples (n = 66, provided by The Sant Pau Initiative on Neurodegeneration cohort) from AD patients (n = 56) and age-matched controls (n = 55).

Results

In AD tissues, most DCV proteins were aberrantly accumulated in dystrophic neurites and activated astrocytes, whereas PC1/3, PC2 and CPE were also specifically accumulated in hippocampal granulovacuolar degeneration bodies. AD individuals displayed an overall decline of secretory proteins in the CSF. Interestingly, in AD patients, the CSF levels of prohormone convertases strongly correlated inversely with those of neurodegeneration markers and directly with cognitive impairment status.

Conclusions

These results demonstrate marked alterations of neuronal-specific prohormone convertases in CSF and cortical tissues of AD patients. The neuronal DCV cargos are biomarker candidates for synaptic dysfunction and neurodegeneration in AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-021-00263-0.

A comprehensive systematic review of CSF proteins and peptides that define Alzheimer's disease

BACKGROUND

During the last two decades, over 100 proteomics studies have identified a variety of potential biomarkers in CSF of Alzheimer's (AD) patients. Although several reviews have proposed specific biomarkers, to date, the statistical relevance of these proteins has not been investigated and no peptidomic analyses have been generated on the basis of specific up- or down- regulation. Herein, we perform an analysis of all unbiased explorative proteomics studies of CSF biomarkers in AD to critically evaluate whether proteins and peptides identified in each study are consistent in distribution; direction change; and significance, which would strengthen their potential use in studies of AD pathology and progression.

METHODS

We generated a database containing all CSF proteins whose levels are known to be significantly altered in human AD from 47 independent, validated, proteomics studies. Using this database, which contains 2022 AD and 2562 control human samples, we examined whether each protein is consistently present on the basis of reliable statistical studies; and if so, whether it is over- or under-represented in AD. Additionally, we performed a direct analysis of available mass spectrometric data of these proteins to generate an AD CSF peptide database with 3221 peptides for further analysis.

RESULTS

Of the 162 proteins that were identified in 2 or more studies, we investigated their enrichment or depletion in AD CSF. This allowed us to identify 23 proteins which were increased and 50 proteins which were decreased in AD, some of which have never been revealed as consistent AD biomarkers (i.e. SPRC or MUC18). Regarding the analysis of the tryptic peptide database, we identified 87 peptides corresponding to 13 proteins as the most highly consistently altered peptides in AD. Analysis of tryptic peptide fingerprinting revealed specific peptides encoded by CH3L1, VGF, SCG2, PCSK1N, FBLN3 and APOC2 with the highest probability of detection in AD.

CONCLUSIONS

Our study reveals a panel of 27 proteins and 21 peptides highly altered in AD with consistent statistical significance; this panel constitutes a potent tool for the classification and diagnosis of AD.

Mossy cell synaptic dysfunction causes memory imprecision via miR-128 inhibition of STIM2 in Alzheimer's disease mouse model

Recently, we have reported that dentate mossy cells (MCs) control memory precision via directly and functionally innervating local somatostatin (SST) inhibitory interneurons. Here, we report a discovery that dysfunction of synaptic transmission between MCs and SST cells causes memory imprecision in a mouse model of early Alzheimer's disease (AD). Single-cell RNA sequencing reveals that miR-128 that binds to a 3'UTR of STIM2 and inhibits STIM2 translation is increasingly expressed in MCs from AD mice. Silencing miR-128 or disrupting miR-128 binding to STIM2 evokes STIM2 expression, restores synaptic function, and rescues memory imprecision in AD mice. Comparable findings are achieved by directly engineering MCs with the expression of STIM2. This study unveils a key synaptic and molecular mechanism that dictates how memory maintains or losses its details and warrants a promising target for therapeutic intervention of memory decays in the early stage of AD.

Proteome dynamics during homeostatic scaling in cultured neurons

Protein turnover, the net result of protein synthesis and degradation, enables cells to remodel their proteomes in response to internal and external cues. Previously, we analyzed protein turnover rates in cultured brain cells under basal neuronal activity and found that protein turnover is influenced by subcellular localization, protein function, complex association, cell type of origin, and by the cellular environment (Dörrbaum et al., 2018). Here, we advanced our experimental approach to quantify changes in protein synthesis and degradation, as well as the resulting changes in protein turnover or abundance in rat primary hippocampal cultures during homeostatic scaling. Our data demonstrate that a large fraction of the neuronal proteome shows changes in protein synthesis and/or degradation during homeostatic up- and down-scaling. More than half of the quantified synaptic proteins were regulated, including pre- as well as postsynaptic proteins with diverse molecular functions.

Secretoneurin A Directly Regulates the Proteome of Goldfish Radial Glial Cells In Vitro

Radial glial cells (RGCs) are the main macroglia in the teleost brain and have established roles in neurogenesis and neurosteroidogenesis. They are the only brain cell type expressing aromatase B (cyp19a1b), the enzyme that synthesizes estrogens from androgen precursors. There are few studies on the regulation of RGC functions, but our previous investigations demonstrated that dopamine stimulates cyp19a1b expression in goldfish RGCs, while secretoneurin A (SNa) inhibits the expression of this enzyme. Here, we determine the range of proteins and cellular processes responsive to SNa treatments in these steroidogenic cells. The focus here is on SNa, because this peptide is derived from selective processing of secretogranin II in magnocellular cells embedded within the RGC-rich preoptic nucleus. Primary cultures of RGCs were treated (24 h) with 10, 100, or 1,000 nM SNa. By using isobaric tagging for relative and absolute quantitation and a Hybrid Quadrupole Obritrap Mass Spectrometry system, a total of 1,363 unique proteins were identified in RGCs, and 609 proteins were significantly regulated by SNa at one or more concentrations. Proteins that showed differential expression with all three concentrations of SNa included H1 histone, glutamyl-prolyl-tRNA synthetase, Rho GDP dissociation inhibitor γ, vimentin A2, and small nuclear ribonucleoprotein-associated protein. At 10, 100, and 1,000 nM SNa, there were 5, 195, and 489 proteins that were downregulated, respectively, whereas the number of upregulated proteins were 72, 44, and 51, respectively. Subnetwork enrichment analysis of differentially regulated proteins revealed that processes such as actin organization, cytoskeleton organization and biogenesis, apoptosis, mRNA processing, RNA splicing, translation, cell growth, and proliferation are regulated by SNa based on the proteomic response. Moreover, we observed that, at the low concentration of SNa, there was an increase in the abundance of proteins involved in cell growth, proliferation, and migration, whereas higher concentration of SNa appeared to downregulate proteins involved in these processes, indicating a dose-dependent proteome response. At the highest concentration of SNa, proteins linked to the etiology of diseases of the central nervous system (brain injuries, Alzheimer disease, Parkinson's disease, cerebral infraction, brain ischemia) were also differentially regulated. These data implicate SNa in the control of cell proliferation and neurogenesis.

Secretoneurin A regulates neurogenic and inflammatory transcriptional networks in goldfish (Carassius auratus) radial glia

Radial glial cells (RGCs) are the most abundant macroglia in the teleost brain and have established roles in neurogenesis and neurosteroidogenesis; however, their transcriptome remains uncharacterized, which limits functional understanding of this important cell type. Using cultured goldfish RGCs, RNA sequencing and de novo transcriptome assembly were performed, generating the first reference transcriptome for fish RGCs with 17,620 unique genes identified. These data revealed that RGCs express a diverse repertoire of receptors and signaling molecules, suggesting that RGCs may respond to and synthesize an array of hormones, peptides, cytokines, and growth factors. Building upon neuroanatomical data and studies investigating direct neuronal regulation of RGC physiology, differential gene expression analysis was conducted to identify transcriptional networks that are responsive to the conserved secretogranin II-derived neuropeptide secretoneurin A (SNa). Pathway analysis of the transcriptome indicated that cellular processes related to the central nervous system (e.g., neurogenesis, synaptic plasticity, glial cell development) and immune functions (e.g., immune system activation, leukocyte function, macrophage response) were preferentially modulated by SNa. These data reveal an array of new functions that are proposed to be critical to neuronal-glial interactions through the mediator SNa.

Granin-derived peptides

The granin family comprises altogether 7 different proteins originating from the diffuse neuroendocrine system and elements of the central and peripheral nervous systems. The family is dominated by three uniquely acidic members, namely chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). Since the late 1980s it has become evident that these proteins are proteolytically processed, intragranularly and/or extracellularly into a range of biologically active peptides; a number of them with regulatory properties of physiological and/or pathophysiological significance. The aim of this comprehensive overview is to provide an up-to-date insight into the distribution and properties of the well established granin-derived peptides and their putative roles in homeostatic regulations. Hence, focus is directed to peptides derived from the three main granins, e.g. to the chromogranin A derived vasostatins, betagranins, pancreastatin and catestatins, the chromogranin B-derived secretolytin and the secretogranin II-derived secretoneurin (SN). In addition, the distribution and properties of the chromogranin A-derived peptides prochromacin, chromofungin, WE14, parastatin, GE-25 and serpinins, the CgB-peptide PE-11 and the SgII-peptides EM66 and manserin will also be commented on. Finally, the opposing effects of the CgA-derived vasostatin-I and catestatin and the SgII-derived peptide SN on the integrity of the vasculature, myocardial contractility, angiogenesis in wound healing, inflammatory conditions and tumors will be discussed.

Altered Machinery of Protein Synthesis in Alzheimer's: From the Nucleolus to the Ribosome

Ribosomes and protein synthesis have been reported to be altered in the cerebral cortex at advanced stages of Alzheimer's disease (AD). Modifications in the hippocampus with disease progression have not been assessed. Sixty-seven cases including middle-aged (MA) and AD stages I-VI were analyzed. Nucleolar chaperones nucleolin, nucleophosmin and nucleoplasmin 3, and upstream binding transcription factor RNA polymerase I gene (UBTF) mRNAs are abnormally regulated and their protein levels reduced in AD. Histone modifications dimethylated histone H3K9 (H3K9me2) and acetylated histone H3K12 (H3K12ac) are decreased in CA1. Nuclear tau declines in CA1 and dentate gyrus (DG), and practically disappears in neurons with neurofibrillary tangles. Subunit 28 ribosomal RNA (28S rRNA) expression is altered in CA1 and DG in AD. Several genes encoding ribosomal proteins are abnormally regulated and protein levels of translation initiation factors eIF2α, eIF3η and eIF5, and elongation factor eEF2, are altered in the CA1 region in AD. These findings show alterations in the protein synthesis machinery in AD involving the nucleolus, nucleus and ribosomes in the hippocampus in AD some of them starting at first stages (I-II) preceding neuron loss. These changes may lie behind reduced numbers of dendritic branches and reduced synapses of CA1 and DG neurons which cause hippocampal atrophy.

Systemic proteasome inhibition triggers neurodegeneration in a transgenic mouse model expressing human α-synuclein under oligodendrocyte promoter: implications for multiple system atrophy

Multiple system atrophy (MSA) is a progressive late onset neurodegenerative α-synucleinopathy with unclear pathogenesis. Recent genetic and pathological studies support a central role of α-synuclein (αSYN) in MSA pathogenesis. Oligodendroglial cytoplasmic inclusions of fibrillar αSYN and dysfunction of the ubiquitin–proteasome system are suggestive of proteolytic stress in this disorder. To address the possible pathogenic role of oligodendroglial αSYN accumulation and proteolytic failure in MSA we applied systemic proteasome inhibition (PSI) in transgenic mice with oligodendroglial human αSYN expression and determined the presence of MSA-like neurodegeneration in this model as compared to wild-type mice. PSI induced open field motor disability in transgenic αSYN mice but not in wild-type mice. The motor phenotype corresponded to progressive and selective neuronal loss in the striatonigral and olivopontocerebellar systems of PSI-treated transgenic αSYN mice. In contrast no neurodegeneration was detected in PSI-treated wild-type controls. PSI treatment of transgenic αSYN mice was associated with significant ultrastructural alterations including accumulation of fibrillar human αSYN in the cytoplasm of oligodendroglia, which resulted in myelin disruption and demyelination characterized by increased g-ratio. The oligodendroglial and myelin pathology was accompanied by axonal degeneration evidenced by signs of mitochondrial stress and dysfunctional axonal transport in the affected neurites. In summary, we provide new evidence supporting a primary role of proteolytic failure and suggesting a neurodegenerative pathomechanism related to disturbed oligodendroglial/myelin trophic support in the pathogenesis of MSA.

The visinin-like proteins VILIP-1 and VILIP-3 in Alzheimer's disease-old wine in new bottles

The neuronal Ca²⁺-sensor (NCS) proteins VILIP-1 and VILIP-3 have been implicated in the etiology of Alzheimer's disease (AD). Genome-wide association studies (GWAS) show association of genetic variants of VILIP-1 (VSNL1) and VILIP-3 (HPCAL1) with AD+P (+psychosis) and late onset AD (LOAD), respectively. In AD brains the expression of VILIP-1 and VILIP-3 protein and mRNA is down-regulated in cortical and limbic areas. In the hippocampus, for instance, reduced VILIP-1 mRNA levels correlate with the content of neurofibrillary tangles (NFT) and amyloid plaques, the pathological characteristics of AD, and with the mini mental state exam (MMSE), a test for cognitive impairment. More recently, VILIP-1 was evaluated as a cerebrospinal fluid (CSF) biomarker and a prognostic marker for cognitive decline in AD. In CSF increased VILIP-1 levels correlate with levels of Aβ, tau, ApoE4, and reduced MMSE scores. These findings tie in with previous results showing that VILIP-1 is involved in pathological mechanisms of altered Ca²⁺-homeostasis leading to neuronal loss. In PC12 cells, depending on co-expression with the neuroprotective Ca²⁺-buffer calbindin D28K, VILIP-1 enhanced tau phosphorylation and cell death. On the other hand, VILIP-1 affects processes, such as cyclic nucleotide signaling and dendritic growth, as well as nicotinergic modulation of neuronal network activity, both of which regulate synaptic plasticity and cognition. Similar to VILIP-1, its interaction partner α4β2 nicotinic acetylcholine receptor (nAChR) is severely reduced in AD, causing severe cognitive deficits. Comparatively little is known about VILIP-3, but its interaction with cytochrome b5, which is part of an antioxidative system impaired in AD, hint toward a role in neuroprotection. A current hypothesis is that the reduced expression of visinin-like protein (VSNLs) in AD is caused by selective vulnerability of subpopulations of neurons, leading to the death of these VILIP-1-expressing neurons, explaining its increased CSF levels. While the Ca²⁺-sensor appears to be a good biomarker for the detrimental effects of Aβ in AD, its early, possibly Aβ-induced, down-regulation of expression may additionally attenuate neuronal signal pathways regulating the functions of dendrites and neuroplasticity, and as a consequence, this may contribute to cognitive decline in early AD.

Chromogranin peptides in brain diseases

Synaptic disturbances may play a key role in the pathophysiology of neuropsychiatric diseases. In this article, we review immunohistological findings of chromogranin peptides in neurodegenerative and neurodevelopmental disorders, with particular emphasis on Alzheimer's disease, the disorder chromogranins have been studied most extensively. Data was collected from existing and new experimental data and medline research. This review focuses on synaptic changes elicited by chromogranin peptides immunoreactivity in Alzheimer's disease, as well in schizophrenia and amyotrophic lateral sclerosis (ALS). An imbalanced availability of chromogranin peptides may be responsible for impaired neurotransmission and a reduced functioning of dense core vesicles. Since chromogranin A was postulated as a potent proinflammatory agent, we focused on chromogranin A in neuroinflammation in Alzheimer's disease and ALS. Further understanding of role and function of chromogranin peptides in neuropathological conditions is still required.

Identification and validation of novel cerebrospinal fluid biomarkers for staging early Alzheimer's disease

BACKGROUND

Ideally, disease modifying therapies for Alzheimer disease (AD) will be applied during the 'preclinical' stage (pathology present with cognition intact) before severe neuronal damage occurs, or upon recognizing very mild cognitive impairment. Developing and judiciously administering such therapies will require biomarker panels to identify early AD pathology, classify disease stage, monitor pathological progression, and predict cognitive decline. To discover such biomarkers, we measured AD-associated changes in the cerebrospinal fluid (CSF) proteome.

METHODS AND FINDINGS

CSF samples from individuals with mild AD (Clinical Dementia Rating [CDR] 1) (n = 24) and cognitively normal controls (CDR 0) (n = 24) were subjected to two-dimensional difference-in-gel electrophoresis. Within 119 differentially-abundant gel features, mass spectrometry (LC-MS/MS) identified 47 proteins. For validation, eleven proteins were re-evaluated by enzyme-linked immunosorbent assays (ELISA). Six of these assays (NrCAM, YKL-40, chromogranin A, carnosinase I, transthyretin, cystatin C) distinguished CDR 1 and CDR 0 groups and were subsequently applied (with tau, p-tau181 and Aβ42 ELISAs) to a larger independent cohort (n = 292) that included individuals with very mild dementia (CDR 0.5). Receiver-operating characteristic curve analyses using stepwise logistic regression yielded optimal biomarker combinations to distinguish CDR 0 from CDR>0 (tau, YKL-40, NrCAM) and CDR 1 from CDR<1 (tau, chromogranin A, carnosinase I) with areas under the curve of 0.90 (0.85-0.94 95% confidence interval [CI]) and 0.88 (0.81-0.94 CI), respectively.

CONCLUSIONS

Four novel CSF biomarkers for AD (NrCAM, YKL-40, chromogranin A, carnosinase I) can improve the diagnostic accuracy of Aβ42 and tau. Together, these six markers describe six clinicopathological stages from cognitive normalcy to mild dementia, including stages defined by increased risk of cognitive decline. Such a panel might improve clinical trial efficiency by guiding subject enrollment and monitoring disease progression. Further studies will be required to validate this panel and evaluate its potential for distinguishing AD from other dementing conditions.

Hippocampal interneuron loss in an APP/PS1 double mutant mouse and in Alzheimer's disease

Hippocampal atrophy and neuron loss are commonly found in Alzheimer's disease (AD). However, the underlying molecular mechanisms and the fate in the AD hippocampus of subpopulations of interneurons that express the calcium-binding proteins parvalbumin (PV) and calretinin (CR) has not yet been properly assessed. Using quantitative stereologic methods, we analyzed the regional pattern of age-related loss of PV- and CR-immunoreactive (ir) neurons in the hippocampus of mice that carry M233T/L235P knocked-in mutations in presenilin-1 (PS1) and overexpress a mutated human beta-amyloid precursor protein (APP), namely, the APP(SL)/PS1 KI mice, as well as in APP(SL) mice and PS1 KI mice. We found a loss of PV-ir neurons (40-50%) in the CA1-2, and a loss of CR-ir neurons (37-52%) in the dentate gyrus and hilus of APP(SL)/PS1 KI mice. Interestingly, comparable PV- and CR-ir neuron losses were observed in the dentate gyrus of postmortem brain specimens obtained from patients with AD. The loss of these interneurons in AD may have substantial functional repercussions on local inhibitory processes in the hippocampus.

Synaptic degeneration in Alzheimer's disease

Synaptic loss is the major neurobiological substrate of cognitive dysfunction in Alzheimer's disease (AD). Synaptic failure is an early event in the pathogenesis that is clearly detectable already in patients with mild cognitive impairment (MCI), a prodromal state of AD. It progresses during the course of AD and in most early stages involves mechanisms of compensation before reaching a stage of decompensated function. This dynamic process from an initially reversible functionally responsive stage of down-regulation of synaptic function to stages irreversibly associated with degeneration might be related to a disturbance of structural brain self-organization and involves morpho-regulatory molecules such as the amyloid precursor protein. Further, recent evidence suggests a role for diffusible oligomers of amyloid beta in synaptic dysfunction. To form synaptic connections and to continuously re-shape them in a process of ongoing structural adaptation, neurons must permanently withdraw from the cell cycle. Previously, we formulated the hypothesis that differentiated neurons after having withdrawn from the cell cycle are able to use molecular mechanisms primarily developed to control proliferation alternatively to control synaptic plasticity. The existence of these alternative effector pathways within neurons might put them at risk of erroneously converting signals derived from plastic synaptic changes into the program of cell cycle activation, which subsequently leads to cell death. The molecular mechanisms involved in cell cycle activation might, thus, link aberrant synaptic changes to cell death.

Subfield and layer-specific depletion in calbindin-D28K, calretinin and parvalbumin immunoreactivity in the dentate gyrus of amyloid precursor protein/presenilin 1 transgenic mice

The depletion of neuronal calcium binding proteins deprives neurons of the capacity to buffer high levels of intracellular Ca(2+) and this leaves them vulnerable to pathological processes, such as those present in Alzheimer's disease (AD). The aim of the present study was to investigate the expression of the calcium binding proteins, calbindin-D28K, calretinin and parvalbumin in the dentate gyrus (DG) of amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic (Tg) mice and their non-Tg littermates, as well as the relation with the deposition of human amyloid beta (Abeta). We measured the expression of these three proteins at seven different rostro-caudal levels, and in the molecular, granular and polymorphic layers of the DG. We found that, except in the most caudal part of the DG, there is a substantial loss of calbindin-D28K immunoreactivity in all three layers of the DG in APP/PS1 mice compared with the non-Tg mice. Significant loss of calretinin immunoreactivity is present in most of the polymorphic layer of the DG of APP/PS1 mice compared with the non-Tg mice, as well as in the rostral and intermediate part of the inner molecular layer. Compared with the non-Tg mice parvalbumin immunoreactivity is significantly reduced throughout the whole polymorphic layer as well as in the rostral and intermediate part of the granular layer of DG in APP/PS1 mice. The relatively preservation of calbindin immunoreactivity in the caudal part of molecular and granular layers as well as calretinin immunoreactivity in the caudal part of polymorphic layer of the DG is likely related to the lower Abeta expression in those parts of DG. The present data suggest an involvement of calcium-dependent pathways in the pathogenesis of AD and indicate that there exists a subfield and layer-specific decrease in immunoreactivity which is related to the type of calcium-binding protein in APP/PS1 mice. Moreover, it seems that APP expression affects more the calbindin expression then parvalbumin and calretinin expression in the DG of APP/PS1 Tg mice.

Secretoneurin promotes neuroprotection and neuronal plasticity via the Jak2/Stat3 pathway in murine models of stroke

Secretoneurin (SN), a neuropeptide derived from secretogranin II, promotes neurite outgrowth of immature cerebellar granule cells. SN also aids in the growth and repair of neuronal tissue, although the precise mechanisms underlying the promotion of brain tissue neuroprotection and plasticity by SN are not understood. Here, in a rat model of stroke and in ischemic human brain tissue, SN was markedly upregulated in both neurons and endothelial cells. SN-mediated neuroprotection rescued primary cortical cell cultures from oxygen/glucose deprivation. SN also induced expression of the antiapoptotic proteins Bcl-2 and Bcl-xL through the Jak2/Stat3 pathway and inhibited apoptosis by blocking caspase-3 activation. In addition, rats with occluded right middle cerebral arteries showed less cerebral infarction, improved motor performance, and increased brain metabolic activity following i.v. administration of SN. Furthermore, SN injection enhanced stem cell targeting to the injured brain in mice and promoted the formation of new blood vessels to increase local cortical blood flow in the ischemic hemisphere. Both in vitro and in vivo, SN not only promoted neuroprotection, but also enhanced neurogenesis and angiogenesis. Our results demonstrate that SN acts directly on neurons after hypoxia and ischemic insult to further their survival by activating the Jak2/Stat3 pathway.

The dentate gyrus in Alzheimer's disease

As part of the hippocampus, the dentate gyrus is considered to play a crucial role in associative memory. The reviewed data suggest that the dentate gyrus withstands the formation of plaques, tangles and neuronal death until late stages of Alzheimer's disease (AD). However, changes related to a disconnecting process, and more subtle intrinsic alterations, may contribute to disturbances in memory and learning observed in early stages of AD.

Cell line dependent RNA expression profiles of prion-infected mouse neuronal cells

The overall impact of prion disease on gene expression is not well characterized. We have carried out a large-scale expression analysis of specific cell types commonly employed in studies of prion disease. Neuroblastoma cells (N2a) and hypothalamic neuronal cells (GT1) can be persistently infected with mouse-adapted scrapie prions, the latter demonstrating cytopathologic effects associated with prion neuropathology. Exploiting a mouse DNA microarray containing approximately 21,000 spotted cDNAs, we have identified several hundred differentially expressed sequences in the two cell lines when infected with prion strain RML. ScN2a and ScGT1 cells demonstrate unique changes in RNA profiles and both differ from the reported changes in human microglia and prion-infected brain studies albeit with some overlap. In addition, several of the identified changes are shared in common with other neurodegenerative diseases such as Alzheimer's disease. The results illustrate that prion infection differs in effect depending on cell type, which could be exploited for diagnostic or therapeutic intervention.

Gene expression profiling in fetal, aged, and Alzheimer hippocampus: a continuum of stress-related signaling

While specific components of normal brain aging and Alzheimer's disease (AD) appear to be genetically determined, it is not well understood whether AD is due to accelerated aging or if AD represents an independent disease entity superimposed upon senescence. Using gene expression profiling, significant alterations in brain-specific transcription patterns have been observed between AD and age-matched controls. In AD, although a general depression in brain genetic output has been reported, there are robust increases in the expression of potentially neuropathological genes. The data in this study show increases in the RNA abundance patterns for a stress-response, proinflammatory, apoptotic, and angiogenic gene family that occur during the transition from fetal to aged, and again during the transformation from aged to AD brain. Significantly up-regulated RNAs include those encoding stress-induced factors (HSP70), transcriptional repressors (DAXX), pentraxins (SAP), proapoptosis factors (FAS and DAXX), and several inflammatory markers (betaAPP, CEX1, NF-IL6, NF-kappaBp100, cyclooxygenase-2, IL-1alpha and IL-1beta precursors and cPLA2). These findings support the hypothesis that there is a continuum of stress-related gene expression as the brain ages and an advancement of inflammatory, apoptotic, and angiogenic gene signaling that correlates with the transition to AD.

Chromogranin peptides in Alzheimer's disease

Synaptic disturbances may play a key role in the pathophysiology of Alzheimer's disease. To characterize differential synaptic alterations in the brains of Alzheimer patients, chromogranin A, chromogranin B and secretoneurin were applied as soluble constituents for large dense core vesicles, synaptophysin as a vesicle membrane marker and calbindin as a cytosolic protein. In controls, chromogranin B and secretogranin are largely co-contained in interneurons, whereas chromogranin A is mostly found in pyramidal neurons. In Alzheimer's disease, about 30% of beta-amyloid plaques co-labelled with chromogranin A, 20% with secretoneurin and 15% with chromogranin B. Less than 5% of beta-amyloid plaques contained synaptophysin or calbindin, respectively. Semiquantitative immunohistochemistry revealed a significant loss for chromogranin B- and secretoneurin-like immunoreactivity in the dorsolateral, the entorhinal, and orbitofrontal cortex. Chromogranin A displayed more complex changes. It was the only chromogranin peptide to be expressed in glial fibrillary acidic protein containing cells. About 40% of chromogranin A immunopositive plaques and extracellular deposits were surrounded and pervaded by activated microglia. The present study demonstrates a loss of presynaptic proteins involved in distinct steps of exocytosis. An imbalanced availability of chromogranins may be responsible for impaired neurotransmission and a reduced functioning of dense core vesicles. Chromogranin A is likely to be a mediator between neuronal, glial and inflammatory mechanisms found in Alzheimer disease.

Alzheimer's disease proteins in cerebellar and hippocampal synapses during postnatal development and aging of the rat

Alzheimer's dementia may be considered a synaptic disease of central neurons: the loss of synapses, reflected by early cognitive impairments, precedes the appearance of extra cellular focal deposits of beta-amyloid peptide in the brain of patients. Distinct immunocytochemical patterns of amyloid precursor proteins (APPs) have previously been demonstrated in the synapses by ultrastructural analysis in the cerebellum and hippocampus of adult rats and mice. Now we show that during postnatal development and during aging in these structures, the immunocytochemical expression of APPs increases in the synapses in parallel with the known up-regulation of total APPs brain levels. Interestingly, as shown previously in the adult rodents, the presenilins (PSs) 1 and 2, which intervene in APPs metabolism, exhibit a synaptic distribution pattern similar to that of APPs with parallel quantitative changes throughout life. In the brain tissue, single and double immunocytochemistry at the ultrastructural level shows co-localisation of APPs and PSs in axonal and dendritic synaptic compartments during postnatal synaptogenesis, adulthood and aging. In addition, double-labelling immunocytofluorescence detects these proteins close to synaptophysin at the growth cones of developing cultured neurons. Thusly, the brain expression of APPs and PSs appears to be regulated synchronously during lifespan in the synaptic compartments where the proteins are colocated. This suggests that PS-dependent processing of important synaptic proteins such as APPs could intervene in age-induced adjustments of synaptic relationships between specific types of neurons.

Gene expression profiling of 12633 genes in Alzheimer hippocampal CA1: transcription and neurotrophic factor down-regulation and up-regulation of apoptotic and pro-inflammatory signaling

Alterations in transcription, RNA editing, translation, protein processing, and clearance are a consistent feature of Alzheimer's disease (AD) brain. To extend our initial study (Alzheimer Reports [2000] 3:161-167), RNA samples isolated from control and AD hippocampal cornu ammonis 1 (CA1) were analyzed for 12633 gene and expressed sequence tag (EST) expression levels using DNA microarrays (HG-U95Av2 Genechips; Affymetrix, Santa Clara, CA). Hippocampal CA1 tissues were carefully selected from several hundred potential specimens obtained from domestic and international brain banks. To minimize the effects of individual differences in gene expression, RNA of high spectral quality (A(260/280) > or= 1.9) was pooled from CA1 of six control or six AD subjects. Results were compared as a group; individual gene expression patterns for the most-changed RNA message levels were also profiled. There were no significant differences in age, postmortem interval (mean < or = 2.1 hr) nor tissue pH (range 6.6-6.9) between the two brain groups. AD tissues were derived from subjects clinically classified as CDR 2-3 (CERAD/NIA). Expression data were analyzed using GeneSpring (Silicon Genetics, Redwood City, CA) and Microarray Data Mining Tool (Affymetrix) software. Compared to controls and 354 background/alignment markers, AD brain showed a generalized depression in brain gene transcription, including decreases in RNA encoding transcription factors (TFs), neurotrophic factors, signaling elements involved in synaptic plasticity such as synaptophysin, metallothionein III, and metal regulatory factor-1. Three- or morefold increases in RNAs encoding DAXX, cPLA(2), CDP5, NF-kappaBp52/p100, FAS, betaAPP, DPP1, NFIL6, IL precursor, B94, HB15, COX-2, and CEX-1 signals were strikingly apparent. These data support the hypothesis of widespread transcriptional alterations, misregulation of RNAs involved in metal ion homeostasis, TF signaling deficits, decreases in neurotrophic support and activated apoptotic and neuroinflammatory signaling in moderately affected AD hippocampal CA1.

Hypoxia signaling to genes: significance in Alzheimer's disease

Aberrations in neural signaling, converging to and diverging from oxidative metabolism and blood supply, contribute to the initiation and maintenance of inflammatory responses, neuronal degeneration, and age-related cognitive decline in Alzheimer's disease (AD). Hypoxia/ischemia triggers phospholipase A2, leading to the accumulation of free arachidonic and docosahexaenoic acids (AA, DHA), as well as that of lysophospholipids. Some of these bioactive lipid messengers in turn give rise to several downstream lipid messengers, such as platelet-activating factor (PAF) and ecosanoids (prostaglandins and leukotrienes). Eicosanoid synthesis is highly regulated in hypoxia and in reperfusion subsequent to ischemia. As one of the consequences, mitochondrial function is disrupted and reactive oxygen species (ROS) both contribute to the expansion of cellular inflammatory responses and reduce the expression of genes required to maintain synaptic structure and function. On the other hand, pro-inflammatory genes are up-regulated. One of these, the inducible cyclooxygenase-2 (COX-2), along with oxygen-starved mitochondria, comprise the major sources of ROS in the brain during hypoxia, ischemia, and reperfusion. One outcome is a sustained metabolic stress that drives progressive dysfunction, apoptosis and/or necrosis, and brain cell death. How hypoxia modulates oxygen-sensitive gene expression is not well understood. Pro-inflammatory gene families that contribute to neurodegeneration are transiently activated in part by the heterodimeric oxygen-sensitive DNA-binding proteins nuclear factor for kappa B (NF-kappaB) and hypoxia-inducible factor-alpha (HIF-1alpha). Here the authors summarize current studies supporting the hypothesis that synaptically-derived lipid messengers play significant roles in ischemic stroke and that hypoxia is an important contributor to the onset and progression of AD neurodegeneration.

Synaptic proteins in Alzheimer's disease

Chromogranin A, chromogranin B, and secretogranin II are acidic proteins which are stored in large dense core vesicles of neurons. An antiserum, raised against a synthetic peptide (PE-11), present in the chromogranin B molecule, and an antiserum raised against secretoneurin contained in the secretogranin II sequence, was used to localize these peptides together with chromogranin A in the human hippocampal formation. The distribution of these peptides was investigated in Alzheimer's disease and compared to control subjects. Chromogranin A, chromogranin B, and secretogranin II are distinctly distributed with an overlap in their distribution patterns. They were only detected in neuronal structures. The highest density of immunoreactivity was found for chromogranin B. A layer specific distribution was especially obvious in the inner molecular layer of the dentate gyrus as secretoneurin-like immunoreactivity was restricted to its innermost part whereas that of chromogranin B was highly concentrated throughout the inner molecular layer. In Alzheimer's disease, about 10 to 20% of the amyloid-immunoreactive plaques contained either chromogranin A, chromogranin B or secretoneurin. The density of secretoneurin-and chromogranin B-like immunoreactivity was significantly reduced in the inner molecular layer of the dentate gyyrs, the CA1 area, the subiculum and in layers I, III and V of the entorhinal cortex. The present study demonstrates that chromogranin peptides are markers for human hippocampal pathways. Thee are particularly suitable to study nerve fibers, terminating at the inner molecular layer of the dentate gyrus. Chromogranin peptides have a potential as neuronal markers for synaptic degeneration in Alzheimer's disease.

Alzheimer's disease as a disorder of mechanisms underlying structural brain self-organization

Mental function has as its cerebral basis a specific dynamic structure. In particular, cortical and limbic areas involved in "higher brain functions" such as learning, memory, perception, self-awareness and consciousness continuously need to be self-adjusted even after development is completed. By this lifelong self-optimization process, the cognitive, behavioural and emotional reactivity of an individual is stepwise remodelled to meet the environmental demands. While the presence of rigid synaptic connections ensures the stability of the principal characteristics of function, the variable configuration of the flexible synaptic connections determines the unique, non-repeatable character of an experienced mental act. With the increasing need during evolution to organize brain structures of increasing complexity, this process of selective dynamic stabilization and destabilization of synaptic connections becomes more and more important. These mechanisms of structural stabilization and labilization underlying a lifelong synaptic remodelling according to experience, are accompanied, however, by increasing inherent possibilities of failure and may, thus, not only allow for the evolutionary acquisition of "higher brain function" but at the same time provide the basis for a variety of neuropsychiatric disorders. It is the objective of the present paper to outline the hypothesis that it might be the disturbance of structural brain self-organization which, based on both genetic and epigenetic information, constantly "creates" and "re-creates" the brain throughout life, that is the defect that underlies Alzheimer's disease (AD). This hypothesis is, in particular, based on the following lines of evidence. (1) AD is a synaptic disorder. (2) AD is associated with aberrant sprouting at both the presynaptic (axonal) and postsynaptic (dendritic) site. (3) The spatial and temporal distribution of AD pathology follows the pattern of structural neuroplasticity in adulthood, which is a developmental pattern. (4) AD pathology preferentially involves molecules critical for the regulation of modifications of synaptic connections, i.e. "morphoregulatory" molecules that are developmentally controlled, such as growth-inducing and growth-associated molecules, synaptic molecules, adhesion molecules, molecules involved in membrane turnover, cytoskeletal proteins, etc. (5) Life events that place an additional burden on the plastic capacity of the brain or that require a particularly high plastic capacity of the brain might trigger the onset of the disease or might stimulate a more rapid progression of the disease. In other words, they might increase the risk for AD in the sense that they determine when, not whether, one gets AD. (6) AD is associated with a reactivation of developmental programmes that are incompatible with a differentiated cellular background and, therefore, lead to neuronal death. From this hypothesis, it can be predicted that a therapeutic intervention into these pathogenetic mechanisms is a particular challenge as it potentially interferes with those mechanisms that at the same time provide the basis for "higher brain function".

Chromogranins in temporal lobe epilepsy

PURPOSE

Chromogranins are neuropeptide precursors stored in large dense core vesicles. Because physiological functions have been postulated for peptides originating from chromogranins, we investigated the distribution of chromogranins A and B and secretoneurin (a peptide derived from secretogranin II) in the control and epileptic hippocampus of humans and rats.

METHODS

Chromogranin immunoreactivity (IR) was investigated in paraformaldehyde-fixed hippocampal specimens from 24 temporal lobe epilepsy patients with intractable seizures, postmortem from 15 patients deceased from nonneurological disorders, in rats 30 days after kainate-induced limbic seizures, and in control rats.

RESULTS

In control rats and in humans, chromogranin A and B IR and secretoneurin IR were present in mossy fibers. In addition, chromogranin B IR was found in granule cells, and chromogranin A IR was found in granule and CA2 pyramidal cells in the human hippocampus. In both species, chromogranin B and secretoneurin were unevenly distributed in the molecular layer of the dentate gyrus. The most intriguing change seen in human temporal lobe epilepsy specimens and in the kainic acid model of the rat was the prominent staining of the inner molecular layer, indicating storage of chromogranins A and B and secretoneurin in terminals of reorganized mossy fibers, from which they may be released upon nerve stimulation.

CONCLUSION

Chromogranins A and B and secretoneurin are valid markers for hippocampal neurons and delineate epilepsy-induced reorganization of mossy fibers.

Respiration and parturition affected by conditional overexpression of the Ca2+-activated K+ channel subunit, SK3

In excitable cells, small-conductance Ca2+-activated potassium channels (SK channels) are responsible for the slow after-hyperpolarization that often follows an action potential. Three SK channel subunits have been molecularly characterized. The SK3 gene was targeted by homologous recombination for the insertion of a gene switch that permitted experimental regulation of SK3 expression while retaining normal SK3 promoter function. An absence of SK3 did not present overt phenotypic consequences. However, SK3 overexpression induced abnormal respiratory responses to hypoxia and compromised parturition. Both conditions were corrected by silencing the gene. The results implicate SK3 channels as potential therapeutic targets for disorders such as sleep apnea or sudden infant death syndrome and for regulating uterine contractions during labor.

Secretoneurin: a functional neuropeptide in health and disease

Chromogranins belong to an evolutionarily conserved family of proteins that serve as neuropeptide pro-proteins, besides having other functions. The secretogranin-II-derived peptide secretoneurin is a 33-amino-acid polypeptide generated by proteolytic cleavage at paired dibasic sequences that exerts its effect by binding to specific receptors. Secretoneurin receptors have been kinetically and functionally characterized indicating that they are G-protein linked. Localization of secretoneurin and functional studies have helped to elucidate roles for secretoneurin, ranging from effects in the central nervous system to the modulation of the inflammatory response in the periphery. It has been shown that secretoneurin possesses biologic activities such as stimulation of dopamine release from striatal neurons and activation of monocyte migration, suggesting that the peptide may modulate both neurotransmission and inflammatory response. With an array of actions as diverse as that seen with other sensory neuropeptides, there is scope for numerous studies and therapeutic possibilities.

Co-distribution patterns of chromogranin B-like immunoreactivity with chromogranin A and secretoneurin within the human brainstem

As members of the chromogranin family, chromogranin A, chromogranin B, and secretogranin II are acidic proteins found in large, dense core vesicles. They are endoproteolytically processed to smaller peptides and released after neuronal stimulation. Using immunocytochemistry, this study closely examines chromogranin B-like immunoreactivity within the human brainstem and then takes a comparative view of co-distribution patterns by chromogranin B, chromogranin A, and secretogranin II. We used an antiserum raised against a synthetic peptide (PE-11) present in the chromogranin B molecule. Secretogranin II was localized with an antiserum against secretoneurin, a 33 amino acid peptide, found within the secretogranin II precursor. Like chromogranin A and secretoneurin, chromogranin B is expressed through all levels of the human brainstem. Chromogranin B was exclusively detected in neuronal structures. The medial part of the substantia nigra pars reticulata, the nucleus interpeduncularis, the area of the central gray, and the raphe complex displayed a high density of PE-11-like immunoreactivity. Furthermore, a prominent staining was found in the medial, dorsal and gelatinous subnuclei of the solitary tract and the dorsal motor nucleus of vagus. The substantia gelatinosa of the caudal trigeminal nucleus and spinal cord were also very strongly PE-11-immunopositive. In conclusion, chromogranin B and secretogranin II showed similar distributions while neuronal localization typically differed from chromogranin A aside from a few exceptions. These findings may provide a framework for future research in revealing a functional role of chromogranin peptides in the human brainstem.

Use of Pichia pastoris for the expression, purification, and characterization of rat calretinin "EF-hand" domains

Calretinin (CR) is a calcium-binding, neuronal protein of undefined function. Related proteins either buffer intracellular calcium concentrations or are involved in calcium-signaling pathways. We transformed three CR gene fragment sequences, corresponding to its three complementary domains (I-II, III-IV, and V-VI), into Pichia pastoris. High yields of extracellular expression, of more than 200 mg/liter, were achieved. Simple purification protocols provide high yields of homogenous proteins: dialysis and DEAE-cellulose chromatography for domains I-II and III-IV or ammonium sulfate precipitation and octyl-Sepharose chromatography for domain V-VI. To our knowledge, this is the first report of the expression of an EF-hand protein using P. pastoris. Direct comparison of the purified yields of domain I-II indicates a approximately 20-fold improvement over Escherichia coli. N-terminal amino acid sequencing confirmed our gene products and two anti-calretinin antibodies recognized the appropriate domains. All three CR domains bind (45)Ca and the domain containing EF-hands V and VI seems to have a lower calcium capacity than the other domains. Circular dichroism indicates a high helix content for each of the domains. Calcium-induced structural changes in the first two domains, followed by tryptophan fluorescence, correspond with previous studies, while tyrosine emission fluorescence indicates calcium-induced structural changes also occur in domain V-VI. The methods and expression levels achieved are suitable for future NMR labeling of the proteins, with (15)N and (13)C, and structure-function studies that will help to further understand CR function.

PE-11, a peptide derived from chromogranin B, in the human brain

This study was performed to investigate the distribution of chromogranin B in the human central nervous system. We used an antiserum raised against a synthetic peptide (PE-11) present in the chromogranin B molecule. PE-11-like immunoreactivity was characterized by molecular size exclusion and reversed-phase high-performance liquid chromatography. Its localization was studied using immunocytochemistry. Only the free peptide and an N-terminally elongated peptide were detected by molecular size exclusion high-performance liquid chromatography, indicating that proteolytic processing of chromogranin B is quite extensive. PE-11-like immunoreactivity was present in differently shaped fibers, varicosities and neurons, but not in glial cells. Its density varied throughout the brain. An especially high density was observed in the bed nucleus of the stria terminalis, the central and cortical nuclei of the amygdala, the hypothalamus, the hippocampus, the raphe complex, the nucleus interpeduncularis, the nucleus of the solitary tract, and laminae I and II of the spinal cord. This study demonstrates a significant processing of chromogranin B and indicates that chromogranin B constitutes a precursor for smaller peptides which are derived by endoproteolytic processing. It provides the neuroanatomical basis to investigate the chromogranin B molecule as a widespread component of large dense-core vesicles in the human central nervous system.