Immunohistochemical localization of 14.3.3 zeta protein in amyloid plaques in human spongiform encephalopathies

Fibril treatment changes protein interactions of tau and α-synuclein in human neurons

In several neurodegenerative disorders, the neuronal proteins tau and α-synuclein adopt aggregation-prone conformations capable of replicating within and between cells. To better understand how these conformational changes drive neuropathology, we compared the interactomes of tau and α-synuclein in the presence or the absence of recombinant fibril seeds. Human embryonic stem cells with an inducible neurogenin-2 transgene were differentiated into glutamatergic neurons expressing (1) WT 0N4R tau, (2) mutant (P301L) 0N4R tau, (3) WT α-synuclein, or (4) mutant (A53T) α-synuclein, each genetically fused to a promiscuous biotin ligase (BioID2). Neurons expressing unfused BioID2 served as controls. After treatment with fibrils or PBS, interacting proteins were labeled with biotin in situ and quantified using mass spectrometry via tandem mass tag labeling. By comparing interactions in mutant versus WT neurons and in fibril- versus PBS-treated neurons, we observed changes in protein interactions that are likely relevant to disease progression. We identified 45 shared interactors, suggesting that tau and α-synuclein function within some of the same pathways. Potential loci of shared interactions include microtubules, Wnt signaling complexes, and RNA granules. Following fibril treatment, physiological interactions decreased, whereas other interactions, including those between tau and 14-3-3 η, increased. We confirmed that 14-3-3 proteins, which are known to colocalize with protein aggregates during neurodegeneration, can promote or inhibit tau aggregation in vitro depending on the specific combination of 14-3-3 isoform and tau sequence.

Prion protein oligomers cause neuronal cytoskeletal damage in rapidly progressive Alzheimer's disease

Background

High-density oligomers of the prion protein (HDPs) have previously been identified in brain tissues of patients with rapidly progressive Alzheimer’s disease (rpAD). The current investigation aims at identifying interacting partners of HDPs in the rpAD brains to unravel the pathological involvement of HDPs in the rapid progression.

Methods

HDPs from the frontal cortex tissues of rpAD brains were isolated using sucrose density gradient centrifugation. Proteins interacting with HDPs were identified by co-immunoprecipitation coupled with mass spectrometry. Further verifications were carried out using proteomic tools, immunoblotting, and confocal laser scanning microscopy.

Results

We identified rpAD-specific HDP-interactors, including the growth arrest specific 2-like 2 protein (G2L2). Intriguingly, rpAD-specific disturbances were found in the localization of G2L2 and its associated proteins i.e., the end binding protein 1, α-tubulin, and β-actin.

Discussion

The results show the involvement of HDPs in the destabilization of the neuronal actin/tubulin infrastructure. We consider this disturbance to be a contributing factor for the rapid progression in rpAD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-021-00422-x.

Cellular Prion Protein (PrPc): Putative Interacting Partners and Consequences of the Interaction

Cellular prion protein (PrPc) is a small glycosylphosphatidylinositol (GPI) anchored protein most abundantly found in the outer leaflet of the plasma membrane (PM) in the central nervous system (CNS). PrPc misfolding causes neurodegenerative prion diseases in the CNS. PrPc interacts with a wide range of protein partners because of the intrinsically disordered nature of the protein’s N-terminus. Numerous studies have attempted to decipher the physiological role of the prion protein by searching for proteins which interact with PrPc. Biochemical characteristics and biological functions both appear to be affected by interacting protein partners. The key challenge in identifying a potential interacting partner is to demonstrate that binding to a specific ligand is necessary for cellular physiological function or malfunction. In this review, we have summarized the intracellular and extracellular interacting partners of PrPc and potential consequences of their binding. We also briefly describe prion disease-related mutations at the end of this review.

14-3-3ζ loss leads to neonatal lethality by microRNA-126 downregulation-mediated developmental defects in lung vasculature

Background

The 14-3-3 family of proteins have been reported to play an important role in development in various mouse models, but the context specific developmental functions of 14-3-3ζ remain to be determined. In this study, we identified a context specific developmental function of 14-3-3ζ.

Results

Targeted deletion of 14-3-3ζ in the C57Bl/6J murine genetic background led to neonatal lethality due to respiratory distress and could be rescued by out-breeding to the CD-1 or backcrossing to the FVB/NJ congenic background. Histological analysis of lung sections from 18.5 days post coitum embryos (dpc) showed that 14-3-3ζ−/− lung development is arrested at the pseudoglandular stage and exhibits vascular defects. The expression of miR-126, an endothelial-specific miRNA known to regulate lung vascular integrity was down-regulated in the lungs of the 14-3-3ζ−/− embryos in the C57Bl/6J background as compared to their wild-type counterparts. Loss of 14-3-3ζ in endothelial cells inhibited the angiogenic capability of the endothelial cells as determined by both trans-well migration assays and tube formation assays and these defects could be rescued by re-expressing miR-126. Mechanistically, loss of 14-3-3ζ led to reduced Erk1/2 phosphorylation resulting in attenuated binding of the transcription factor Ets2 on the miR-126 promoter which ultimately reduced expression of miR-126.

Conclusion

Our data demonstrates that miR-126 is an important angiogenesis regulator that functions downstream of 14-3-3ζ and downregulation of miR-126 plays a critical role in 14-3-3ζ-loss induced defects in lung vasculature in the C57Bl/6J genetic background.

Electronic supplementary material

The online version of this article (10.1186/s13578-017-0186-y) contains supplementary material, which is available to authorized users.

14-3-3 Isoforms Differentially Regulate NFκB Signaling in the Brain After Ischemia-Reperfusion

Mammalian 14-3-3 isoforms exist predominantly in the brain and are heavily involved in neurological diseases. However, the isoform-specific role of 14-3-3 proteins in the brain remains largely unclear. Here, we investigated the role of 14-3-3 isoforms in rat brains after transient middle cerebral artery occlusion and reperfusion. 14-3-3β, η, γ and ζ but not ε or τ were selectively upregulated in cerebral cortical neurons after ischemia-reperfusion (I/R). Selectively, 14-3-3β, γ and ζ were translocated from cytoplasm into the nuclei of neurons after I/R. 14-3-3 bound to p65 and suppressed p65 expression in N2a cells. In the brain, 14-3-3 could either colocalize with p65 in the nuclei of neurons or segregate from p65 expression in cortical neurons after I/R. All evidence together suggests that 14-3-3 isoforms are differentially induced to enter into the nuclei of neurons after I/R, which might regulate NFκB signaling directly or indirectly. Since 14-3-3 proteins are essential for cell survival and NFκB is a key transcriptional factor, our data suggest that the 14-3-3/p65 signaling pathway might be a potential therapeutic target for stroke.

Subtype and regional regulation of prion biomarkers in sporadic Creutzfeldt-Jakob disease

AIMS

Creutzfeldt-Jakob disease (CJD) is a rapid progressive neurological disease leading to dementia and death. Prion biomarkers are altered in the cerebrospinal fluid (CSF) of CJD patients, but the pathogenic mechanisms underlying these alterations are still unknown. The present study examined prion biomarker levels in the brain and CSF of sporadic CJD (sCJD) cases and their correlation with neuropathological lesion profiles.

METHODS

The expression levels of 14-3-3, Tau, phospho-Tau and α-synuclein were measured in the CSF and brain of sCJD cases in a subtype- and region-specific manner. In addition, the activity of prion biomarker kinases, the expression levels of CJD hallmarks and the most frequent neuropathological sCJD findings were analysed.

RESULTS

Prion biomarkers levels were increased in the CSF of sCJD patients; however, correlations between mRNA, total protein and their phosphorylated forms in brain were different. The observed downregulation of the main Tau kinase, GSK3, in sCJD brain samples may help to explain the differential phospho-Tau/Tau ratios between sCJD and other dementias in the CSF. Importantly, CSF biomarkers levels do not necessarily correlate with sCJD neuropathological findings.

INTERPRETATION

Present findings indicate that prion biomarkers levels in sCJD tissues and their release into the CSF are differentially regulated following specific modulated responses, and suggest a functional role for these proteins in sCJD pathogenesis.

Neuroprotective function of 14-3-3 proteins in neurodegeneration

14-3-3 proteins are abundantly expressed adaptor proteins that interact with a vast number of binding partners to regulate their cellular localization and function. They regulate substrate function in a number of ways including protection from dephosphorylation, regulation of enzyme activity, formation of ternary complexes and sequestration. The diversity of 14-3-3 interacting partners thus enables 14-3-3 proteins to impact a wide variety of cellular and physiological processes. 14-3-3 proteins are broadly expressed in the brain, and clinical and experimental studies have implicated 14-3-3 proteins in neurodegenerative disease. A recurring theme is that 14-3-3 proteins play important roles in pathogenesis through regulating the subcellular localization of target proteins. Here, we review the evidence that 14-3-3 proteins regulate aspects of neurodegenerative disease with a focus on their protective roles against neurodegeneration.

14-3-3 protein targets misfolded chaperone-associated proteins to aggresomes

The aggresome is a key cytoplasmic organelle for sequestration and clearance of toxic protein aggregates. Although loading misfolded proteins cargos to dynein motors has been recognized as an important step in the aggresome formation process, the molecular machinery that mediates the association of cargos with the dynein motor is poorly understood. Here, we report a new aggresome-targeting pathway that involves isoforms of 14-3-3, a family of conserved regulatory proteins. 14-3-3 interacts with both the dynein-intermediate chain (DIC) and an Hsp70 co-chaperone Bcl-2-associated athanogene 3 (BAG3), thereby recruiting chaperone-associated protein cargos to dynein motors for their transport to aggresomes. This molecular cascade entails functional dimerization of 14-3-3, which we show to be crucial for the formation of aggresomes in both yeast and mammalian cells. These results suggest that 14-3-3 functions as a molecular adaptor to promote aggresomal targeting of misfolded protein aggregates and may link such complexes to inclusion bodies observed in various neurodegenerative diseases.

Longitudinal characterization of the brain proteomes for the tg2576 amyloid mouse model using shotgun based mass spectrometry

Neurodegenerative disorders are often defined pathologically by the presence of protein aggregates, such as amyloid plaques composed of β-amyloid (Aβ) peptide in Alzheimer's disease. Such aggregates are the result of abnormal protein accumulation and may lead to neuronal dysfunction and cell death. In this study, APPSWE transgenic mice (Tg2576), which overexpress the Swedish mutated form of human amyloid precursor protein (APP), were used to study the brain proteome associated with amyloid plaque deposition. The major aim of the study was to map and compare the Tg2576 model brain proteome profiles during pathology progression using a shotgun approach based on label free quantification with mass spectrometry. Overall, 1085 proteins were identified and longitudinally quantified. Principal component analysis (PCA) showed the appearance of the pathology onset between twelve and fifteen months, correlating with sharp amyloid plaque accumulation within the same ages. Cluster analysis followed by protein-protein interaction analysis revealed an age-dependent decrease in mitochondrial protein expression. We identified 57 significantly affected mitochondrial proteins, several of which have been reported to alter expression in neurological diseases. We also found ten proteins that are upregulated early in the amyloid driven pathology progression with high confidence, some of which are directly involved in the onset of mitochondrial apoptosis and may represent potential markers for use in human neurological diseases prognosis. Our results further contribute to identifying common pathological pathways involved in both aging and progressive neurodegenerative disorders enhancing the understanding of disease pathogenesis.

Structure-oriented review of 14-3-3 protein isoforms in geriatric neuroscience

This review focuses on the possible relevance of 14-3-3 proteins in geriatric neuroscience. 14-3-3 proteins are mainly localized in the synapses and neuronal cytoplasm. These proteins regulate intracellular signal cascades for differentiation, development, growth, apoptosis and survival. Seven isoforms have so far been identified in mammals. The binding motifs and potential functions of 14-3-3 proteins are now recognized to have a wide range of functional relevance. First, we provide a brief summary of the molecular structure and multiple functions of 14-3-3 proteins. Second, we review the involvement of 14-3-3 proteins in common diseases of geriatric neurology, such as Alzheimer's disease and tauopathies, Parkinson's disease and α-synucleinopathies, Huntington's disease and polyglutamine diseases, Creutzfeldt-Jakob disease and prion diseases, cerebral infarction, and atherosclerosis. Finally, we discuss the immunohistochemical localization of 14-3-3 proteins and its isoforms during the postnatal development of rat brains as a basis for understanding adult neurogenesis. The elucidation of the isoform-dependent functions of 14-3-3 proteins with regard to brain development might be promising for the future development of novel therapeutic interventions for common diseases of geriatric neurology.

Proteomic characterization of an isolated fraction of synthetic proteasome inhibitor (PSI)-induced inclusions in PC12 cells might offer clues to aggresomes as a cellular defensive response against proteasome inhibition by PSI

BACKGROUND

Cooperation of constituents of the ubiquitin proteasome system (UPS) with chaperone proteins in degrading proteins mediate a wide range of cellular processes, such as synaptic function and neurotransmission, gene transcription, protein trafficking, mitochondrial function and metabolism, antioxidant defence mechanisms, and apoptotic signal transduction. It is supposed that constituents of the UPS and chaperone proteins are recruited into aggresomes where aberrant and potentially cytotoxic proteins may be sequestered in an inactive form.

RESULTS

To determinate the proteomic pattern of synthetic proteasome inhibitor (PSI)-induced inclusions in PC12 cells after proteasome inhibition by PSI, we analyzed a fraction of PSI-induced inclusions. A proteomic feature of the isolated fraction was characterized by identification of fifty six proteins including twenty previously reported protein components of Lewy bodies, twenty eight newly identified proteins and eight unknown proteins. These proteins, most of which were recognized as a profile of proteins within cellular processes mediated by the UPS, a profile of constituents of the UPS and a profile of chaperone proteins, are classed into at least nine accepted categories. In addition, prolyl-4-hydroxylase beta polypeptide, an endoplasmic reticulum member of the protein disulfide isomerase family, was validated in the developmental process of PSI-induced inclusions in the cells.

CONCLUSIONS

It is speculated that proteomic characterization of an isolated fraction of PSI-induced inclusions in PC12 cells might offer clues to appearance of aggresomes serving as a cellular defensive response against proteasome inhibition.

Cerebrospinal fluid biomarkers in human prion diseases

Cerebrospinal fluid (CSF) is the main component of the brain extracellular space and participates in the exchange of many biochemical products in the CNS. Consequently, CSF contains a dynamic and complex mixture of proteins that reflect the physiological or pathological state of the CNS. Changes in the CSF proteome have been described in various neurodegenerative disorders. These alterations are also thought to reflect pathological changes in the brain, and thus understanding them will contribute to a better awareness of the pathophysiology that underlies these disorders. Proteomics offers a new methodology for the analysis of pathological changes and mechanisms occurring in neurodegenerative processes and provides the possibility of novel biomarker discovery in order to supplement faster, earlier and more precise diagnosis. In general, the following criteria have to be applied in order to qualify a protein or a gene as a potential biomarker: the selected parameters have to be sensitive (able to detect the abnormalities at early stage of disease), specific (to allow differential diagnosis), reproducible with a high positive predictive value, and should allow for disease monitoring as well as a potential therapeutic response. In Creutzfeldt–Jakob disease, two major approaches have been followed that aim to detect the pathological form of the prion protein (PrPSc) in various peripheral tissues, while other approaches look for surrogate parameters that are a consequence of the neurodegenerative process. While the amount of abnormal disease-related PrPSc in CSF and blood in human transmissible spongiform encephalopathies appears to be extremely low, the development of a PrPSc-based biomarker was hampered by technical problems and detection limits. However, a variety of other proteins have been investigated in the CSF, and recently a variety of potential biomarkers have been reported that contribute to clinical diagnosis. Already established markers are 14-3-3, β-amyloid, tau-protein and phosphorylated isoforms, S100b, as well as neuron-specific enolase. Since some of these markers display certain limitations, the search continues. This review summarizes current knowledge of biomarker development in prion diseases and discusses perspectives for new approaches.

Interactions of prion protein with intracellular proteins: so many partners and no consequences?

Prion protein (PrP) plays a key role in the pathogenesis of transmissible spongiform encephalopathies (TSEs)--fatal diseases of the central nervous system. Its physiological function as well as exact role in neurodegeneration remain unclear, hence screens for proteins interacting with PrP seem to be the most promising approach to elucidating these issues. PrP is mostly a plasma membrane-anchored extracellular glycoprotein and only a small fraction resides inside the cell, yet the number of identified intracellular partners of PrP is comparable to that of its membranal or extracellular interactors. Since some TSEs are accompanied by significantly increased levels of cytoplasmic PrP and this fraction of the protein has been found to be neurotoxic, it is of particular interest to characterize the intracellular interactome of PrP. It seems reasonable that at elevated cytoplasmic levels, PrP may exert cytotoxic effect by affecting the physiological functions of its intracellular interactors. This review is focused on the cytoplasmic partners of PrP along with possible consequences of their binding.

Synaptic proteins linked to HIV-1 infection and immunoproteasome induction: proteomic analysis of human synaptosomes

Infection of the central nervous system with human immunodeficiency virus type 1 (HIV-1) can produce morphological changes in the neocortical synaptodendritic arbor that are correlated with neurocognitive impairment. To determine whether HIV-1 infection influences the protein composition of human synapses, a proteomic study of isolated nerve endings was undertaken. Synaptosomes from frontal neocortex were isolated using isopyknic centrifugation from 19 human brain specimens. Purity and enrichment were assessed by measuring pre- and postsynaptic protein markers. Two-dimensional polyacrylamide gel electrophoresis and matrix-assisted laser desorption ionization time-of-flight mass spectrometry was used to screen for proteins differentially expressed in HIV/AIDS. The concentrations of 31 candidate protein spots were potentially abnormal in HIV-infected decedents with HIV encephalitis and/or increased expression of immunoproteasome subunits. Immunoblots showed that the concentration of some of them was related to HIV-1 infection of the brain and immunoproteasome (IPS) induction. Synapsin 1b and stathmin were inversely related to brain HIV-1 load; 14-3-3zeta and 14-4-4epsilon proteins were higher in subjects with HIV-1 loads. Perturbed synaptosome proteins were linked with IPS subunit composition, and 14-3-3zeta was histologically colocalized with IPS subunits in stained neocortical neurons. Proteomics illustrates that certain human proteins within the synaptic compartment are involved with changes in the synaptodendritic arbor and neurocognitive impairment in HIV-1-infected people.

Copy number gain and oncogenic activity of YWHAZ/14-3-3zeta in head and neck squamous cell carcinoma

Gene amplification, a common mechanism for oncogene activation in cancers, has been used in the discovery of novel oncogenes. Low-level copy number gains are frequently observed in head and neck squamous cell carcinomas (HNSCCs) where numerous amplification events and potential oncogenes have already been reported. Recently, we applied restriction landmark genome scanning to study gene amplifications in HNSCC and located novel and uncharacterized regions in primary tumor samples. Gain on chromosome 8q22.3, the location of YWHAZ (14-3-3zeta), is found in 30-40% HNSCC cases. Data obtained from fluorescence in situ hybridization and immunohistochemistry on HNSCC tissue microarrays confirmed frequent low-level YWHAZ copy number gain and protein overexpression. YWHAZ mRNA was frequently upregulated in patients' tumor tissues. Furthermore, YWHAZ RNAi significantly suppressed the growth rate of HNSCC cell lines, and overexpression of YWHAZ in HaCaT immortalized human skin keratinocytes promotes overgrowth, as well as morphological changes. Reduced YWHAZ levels increased the G1/G0-phase proportion, decreased the S-phase proportion and the rate of DNA synthesis. Based on this evidence, we suggest that YWHAZ is a candidate proto-oncogene and deserves further investigation into its role in HNSCC carcinogenesis.

Chaperone proteins identified from synthetic proteasome inhibitor-induced inclusions in PC12 cells by proteomic analysis

Chaperone proteins are significant in Lewy bodies, but the profile of chaperone proteins is incompletely unraveled. Proteomic analysis is used to determine protein candidates for further study. Here, to identify potential chaperone proteins from agent-induced inclusions, we carried out proteomic analysis of artificially synthetic proteasome inhibitor (PSI)-induced inclusions formed in PC12 cells exposed to 10 microM PSI for 48 h. Using biochemical fractionation, 2-D electrophoresis, and identification through peptide mass fingerprints searched against multiple protein databases, we repeatedly identified eight reproducible chaperone proteins from the PSI-induced inclusions. Of these, 58 kDa glucose regulated protein, 75 kDa glucose regulated protein, and calcium-binding protein 1 were newly identified. The other five had been reported to be consistent components of Lewy bodies. These findings suggested that the three potential chaperone proteins might be recruited to PSI-induced inclusions in PC12 cells under proteasome inhibition.

Identification of Bombyx mori 14-3-3 orthologs and the interactor Hsp60

The 14-3-3 protein family consists of evolutionarily conserved, acidic 30 kDa proteins composed of seven isoforms named beta, gamma, epsilon, zeta, eta, theta, and sigma in mammalian cells. The dimeric complex of 14-3-3 isoforms, acting as a molecular adaptor, plays a central role in regulation of neuronal function. Since aberrant expression of 14-3-3 is identified in the brains of Alzheimer disease and Parkinson disease, a convenient insect model, if it is available, is highly valuable for studying a pathological role of 14-3-3 in neurodegeneration. Here, we identified the silkworm Bombyx mori 14-3-3 orthologs, zeta and epsilon isoforms highly homologous in amino acid sequences to the human 14-3-3zeta and 14-3-3epsilon. By Western blot, the expression of zeta and epsilon isoforms was identified at substantial levels in the first instar larva, markedly upregulated in the second instar larva, and the highest levels were maintained in the late stage of larva, the pupa, and the adult. Furthermore, by protein overlay and immunoprecipitation, we identified Hsp60 as a 14-3-3-binding partner. The 14-3-3 proteins interacted with the N-terminal fragment of Hsp60. The 14-3-3zeta and epsilon isoforms, along with Hsp60, were expressed widely with overlapping distribution in larval and adult tissues, including brain, fat body, silk gland, Malpighian tube, midgut, ovary, testis, antenna, and pheromone gland. These observations suggest that a molecular adaptor 14-3-3 and a molecular chaperone Hsp60 cooperate to achieve a wide range of cellular functions in B. mori.

14-3-3zeta is indispensable for aggregate formation of polyglutamine-expanded huntingtin protein

Huntington's disease (HD) is an autosomal dominant progressive neurodegenerative disorder caused by polyglutamine (polyQ) expansions in the huntingtin (Htt) protein. A hallmark of HD is the presence of aggregates-predominantly composed of NH(2)-terminal fragments of polyQ-expanded Htt-in the nucleus and cytoplasm of affected neurons. We previously proposed that 14-3-3zeta might act as a sweeper of misfolded proteins by facilitating the formation of aggregates possibly for neuroprotection; these aggregates are referred to as inclusion bodies. However, evidence available in this regard is indirect and circumstantial. In this study, analysis of the aggregation-prone protein Htt encoded by HD gene exon 1 containing polyglutamine expansions (Htt86Q) revealed that 17 residues in the NH(2)-terminal of this protein are indispensable for its aggregate formation. Immunoprecipitation assays revealed that 14-3-3beta, gamma, eta, and zeta interact with Htt86Q transfected in N2a cells. Interestingly, the small interfering ribonucleic acid (siRNA) suppression of 14-3-3zeta exclusively abolished Htt86Q aggregate formation, whereas 14-3-3beta or eta siRNA suppression did not. This indicates that 14-3-3zeta participates in aggregate formation under nonnative conditions. Our data support a novel role for 14-3-3zeta in the aggregate formation of nonnative, aggregation-prone proteins.

Catecholaminergic neuronal loss in locus coeruleus of aged female dtg APP/PS1 mice

Alzheimer's disease (AD) is the most common type of dementia afflicting the elderly. In addition to the presence of cortical senile plaques and neurofibrillary tangles, AD is characterized at autopsy by extensive degeneration of brainstem locus coeruleus (LC) neurons that provide noradrenergic innervation to cortical neuropil, together with relative stability of dopaminergic neuron number in substantia nigra (SN) and ventral tegmental area (VTA). The present study used design-based stereological methods to assess catecholaminergic neuronal loss in brains of double transgenic female mice that co-express two human mutations associated with familial AD, amyloid precursor protein (APP(swe)) and presenilin-1 (PS1(DeltaE9)). Mice were analyzed at two age groups, 3-6 months and 16-23 months, when deposition of AD-type beta-amyloid (Abeta) plaques occurs in cortical brain regions. Blocks of brain tissue containing the noradrenergic LC nucleus and two nuclei of dopaminergic neurons, the SN and VTA, were sectioned and sampled in a systematic-random manner and immunostained for tyrosine hydroxylase (TH), a specific marker for catecholaminergic neurons. Using the optical fractionator method we found a 24% reduction in the total number of TH-positive neurons in LC with no changes in SN-VTA of aged dtg APP/PS1 mice compared with non-transgenic controls. No significant differences were observed in numbers of TH-positive neurons in LC or SN-VTA in brains of young female dtg APP/PS1 mice compared to their age-matched controls. The findings of selective neurodegeneration of LC neurons in the brains of aged female dtg APP/PS1 mice mimic the neuropathology in the brains of AD patients at autopsy. These findings support the use of murine models of Abeta deposition to develop novel strategies for the therapeutic management of patients afflicted with AD.

The ε Isoform of 14-3-3 Protein Is a Component of the Prion Protein Amyloid Deposits of Gerstmann-Sträussler-Scheinker Disease

The 14-3-3 proteins are highly conserved, ubiquitous molecules involved in a variety of biologic events, such as transduction pathway modulation, cell cycle control, and apoptosis. Seven isoforms have been identified that are abundant in the brain, preferentially localized in neurons. Remarkable increases in 14-3-3 are seen in the cerebrospinal fluid of patients with Creutzfeldt-Jakob disease (CJD), and it has been found in pathologic inclusions of several neurodegenerative diseases. Moreover, the zeta isoform has been detected in prion protein (PrP) amyloid deposits of CJD patients. To further investigate the cerebral distribution of 14-3-3 in prion-related encephalopathies, we carried out an immunohistochemical and biochemical analysis of brain tissue from patients with Gerstmann-Sträussler-Scheinker disease (GSS) and sporadic, familial and acquired forms of CJD, using specific antibodies against the seven 14-3-3 isoforms. The study showed a strong immunoreactivity of PrP amyloid plaques of GSS patients for the 14-3-3 epsilon isoform, but not for the other isoforms. The epsilon isoform of 14-3-3 was not found in PrP deposits of CJD. These results indicate that the epsilon isoform of 14-3-3 is a component of PrP amyloid deposits of GSS and suggest that this is the sole 14-3-3 isoform specifically involved in the neuropathologic changes associated with this disorder.

alpha-Synuclein is colocalized with 14-3-3 and synphilin-1 in A53T transgenic mice

alpha-Synuclein is a major constituent of Lewy bodies, the neuropathological hallmark of Parkinson's disease (PD). Three types of alpha-synuclein mutations, A53T, A30P, and E46K, have been reported in familial PD. Wild-type alpha-synuclein accumulates at high concentrations in Lewy bodies, and this process is accelerated with mutated A53T alpha-synuclein. The accumulation of alpha-synuclein is thought to be toxic, and causes neuronal death when alpha-synuclein aggregates into protofibrils and fibrils. Lewy bodies contain not only alpha-synuclein, but also other proteins including 14-3-3 proteins and synphilin-1. 14-3-3 Proteins exist mainly as dimers and are related to intracellular signal transduction pathways. Synphilin-1 is known to interact with alpha-synuclein, promoting the formation of cytoplasmic inclusions like Lewy bodies in vitro. To investigate the colocalization of alpha-synuclein, synphilin-1, and 14-3-3 proteins, we performed immunohistochemical studies on alpha-synuclein, 14-3-3 proteins, and synphilin-1 in the brain and spinal cord of A53T transgenic mice. In homozygous mouse brains, alpha-synuclein immunoreactivity was observed in the neuronal somata and processes in the medial part of the brainstem, deep cerebellar nuclei, and spinal cord. The distribution of 14-3-3 proteins and synphilin-1 immunoreactivity was similar to that of alpha-synuclein in the homozygous mice. Double immunofluorescent staining showed that alpha-synuclein and synphilin-1 or 14-3-3 proteins were colocalized in the pons and spinal cord. These results indicate that the accumulation of mutant alpha-synuclein occurs in association with 14-3-3 proteins and synphilin-1, and may cause the sequestration of important proteins including 14-3-3 proteins and synphilin-1. The sequestration and subsequent decrease in 14-3-3 proteins and synphilin-1 levels may account for neuronal cell death.

The alternative role of 14-3-3 zeta as a sweeper of misfolded proteins in disease conditions

Here, we propose a novel hypothesis that 14-3-3 zeta might act as a sweeper of misfolded proteins by facilitating the formation of aggregates, which are referred to as inclusion bodies. Studies on the localization of the 14-3-3 proteins in different types of inclusion bodies in the brain including neurofibrillary tangle in Alzheimer's disease, pick bodies in Pick's disease, Lewy body-like hyaline inclusions in sporadic amyotrophic lateral sclerosis, prion/florid plaques in sporadic/variant Creutzfeldt-Jakob disease, nuclear inclusions in spinocerebellar ataxia-1, and possibly Lewy bodies in Parkinson's disease suggest a close association of these diseases with 14-3-3 zeta. The highly conserved hydrophobic surface of the amphipathic groove in 14-3-3 zeta represents a general mechanism with diverse cellular proteins, and it may also allow for the molecular recognition of misfolded proteins by hydrophobic interaction in disease conditions. When the abnormal processing of misfolded proteins overwhelms the quality control systems of the cell, it is likely that 14-3-3 zeta is recruited to form deposits of protein aggregates with nonnative, misfolded proteins in order to protect the cell against toxicity. Hence, 14-3-3 zeta may be considered as an auxiliary therapeutic tool in the protein aggregation disorders.

The 14-3-3 Protein Forms a Molecular Complex with Heat Shock Protein Hsp60 and Cellular Prion Protein

The 14-3-3 protein family consists of acidic 30-kDa proteins composed of 7 isoforms expressed abundantly in neurons and glial cells of the central nervous system (CNS). The 14-3-3 protein identified in the cerebrospinal fluid provides a surrogate marker for premortem diagnosis of Creutzfeldt-Jakob disease, although an active involvement of 14-3-3 in the pathogenesis of prion diseases remains unknown. By protein overlay and mass spectrometric analysis of protein extract of NTera2-derived differentiated neurons, we identified heat shock protein Hsp60 as a 14-3-3-interacting protein. The 14-3-3zeta and gamma isoforms interacted with Hsp60, suggesting that the interaction is not isoform-specific. Furthermore, the interaction was identified in SK-N-SH neuroblastoma, U-373MG astrocytoma, and HeLa cervical carcinoma cells. The cellular prion protein (PrPC) along with Hsp60 was coimmunoprecipitated with 14-3-3 in the human brain protein extract. By protein overlay, 14-3-3 interacted with both recombinant human Hsp60 and PrPC produced by Escherichia coli, indicating that the molecular interaction is phosphorylation-independent. The 14-3-3-binding domain was located in the N-terminal half (NTF) of Hsp60 spanning amino acid residues 27-287 and the NTF of PrPC spanning amino acid residues 23-137. By immunostaining, the 14-3-3 protein Hsp60 and PrPC were colocalized chiefly in the mitochondria of human neuronal progenitor cells in culture, and were coexpressed most prominently in neurons and reactive astrocytes in the human brain. These observations indicate that the 14-3-3 protein forms a molecular complex with Hsp60 and PrPC in the human CNS under physiological conditions and suggest that this complex might become disintegrated in the pathologic process of prion diseases.

Unchanged survival rates of 14-3-3gamma knockout mice after inoculation with pathological prion protein

The diagnosis of sporadic Creutzfeldt-Jakob disease (CJD) is based on typical clinical findings and is supported by a positive 14-3-3 Western blot of cerebrospinal fluid. However, it is not clear whether 14-3-3 indicates general neuronal damage or is of pathophysiological relevance in CJD. The fact that the 14-3-3 isoform spectrum in cerebrospinal fluid does not correspond to that found in the brain points to a regulated process. To investigate a possible role of 14-3-3 proteins in transmissible spongiform diseases, we generated a 14-3-3gamma-deficient mutant mouse line by using a classical knockout strategy. The anatomy and cage behavior of the mutant mice were normal. Western blot analyses of brain homogenates revealed no changes in the protein expression of other 14-3-3 isoforms (epsilon, beta, zeta, and eta). Proteomic analyses of mouse brains by two-dimensional differential gel electrophoresis showed that several proteins, including growth hormone, 1-Cys peroxiredoxin, CCT-zeta, glucose-6-phosphate isomerase, GRP170 precursor, and alpha-SNAP, were differentially expressed. Mutant and wild-type mice were inoculated either intracerebrally or intraperitoneally with the Rocky Mountain Laboratory strain of scrapie, but no differences were detected in the postinoculation survival rates. These results indicate that 14-3-3gamma is unlikely to play a causal role in CJD and related diseases.

14-3-3 proteins and zeta isoform containing neurofibrillary tangles in patients with Alzheimer's disease

Immunolocalization of 14-3-3 proteins in Alzheimer's disease (AD) brains was investigated using isoform-specific antibodies. Weak granular immunoreactivity of 14-3-3 proteins was found in neuronal cytoplasm in control subjects and AD brains. Both intracellular and extracellular neurofibrillary tangles (NFTs), as well as neuropil thread-like structures, were immunopositive for 14-3-3 proteins. This was corroborated by triple-fluorolabeling method visualizing paired helical filament (PHF) tau and 14-3-3 epitopes in relation to fibrillary state detected by thiazin red. Pretangle neurons (positive for PHF-tau without fibrillary structure detected by thiazin red) only contained fine granular immunoreactivity (IR) of 14-3-3, which was similarly found in unaffected neurons. Granular cytoplasmic IR of 14-3-3 proteins in pretangle neurons was not colocalized to granular tau-like IR, which suggests that participation of 14-3-3 proteins in NFT formation was restricted to its later stages. Its zeta isoform was most prominent in these NFTs, suggesting that this isoform is a major component involved in the formation of NFTs. In contrast, IR of epsilon isoform was found in the neuropil of the hippocampus and that of sigma isoform was localized to granule cells of the dentate gyrus in AD brains, as seen in the age-matched controls. Expression of 14-3-3 proteins were found to be highly variable and dependent on their isoforms, regions and cell types. Molecular, as well as topographical, dissection of 14-3-3 proteins will provide us with an improved understanding of this molecule in normal and pathological conditions.

Enhanced expression of 14-3-3 proteins in reactive astrocytes in Creutzfeldt-Jakob disease brains

14-3-3 proteins have been reported to be detected specifically in the cerebrospinal fluid (CSF) from patients with Creutzfeldt-Jakob disease (CJD). To elucidate the role of 14-3-3 proteins in patients with CJD, we performed immunohistochemical studies on 14-3-3 proteins in autopsied brains from five patients with sporadic CJD (sCJD), three patients with Alzheimer's disease (AD), and seven normal control subjects. Formalin-fixed, paraffin-embedded sections from all cases were immunostained with several types of specific anti-14-3-3 antibodies. In the normal control brains, 14-3-3 immunoreactivity was localized mainly in the neuronal somata and processes; in contrast, glial cells showed no or faint immunoreactivity. In the brains from the patients with AD, 14-3-3 immunoreactivity was observed in the surviving neurons as well as some neurofibrillary tangles. In the brains from the patients with sCJD, 14-3-3 immunoreactivity was well preserved in the remaining neurons. Furthermore, the glial cells, especially the reactive astrocytes, were intensely immunostained in the brains affected by sCJD. Our findings suggest that 14-3-3 proteins may be up-regulated in the glial cells, particularly in reactive astrocytes, and that the enhanced expression of 14-3-3 proteins in these glial elements may be associated with the pathogenesis of sCJD.

The 14-3-3 protein epsilon isoform expressed in reactive astrocytes in demyelinating lesions of multiple sclerosis binds to vimentin and glial fibrillary acidic protein in cultured human astrocytes

The 14-3-3 protein family consists of acidic 30-kd proteins expressed at high levels in neurons of the central nervous system. Seven isoforms form a dimeric complex that acts as a molecular chaperone that interacts with key signaling components. Recent studies indicated that the 14-3-3 protein identified in the cerebrospinal fluid of various neurological diseases including multiple sclerosis (MS) is a marker for extensive brain destruction. However, it remains unknown whether the 14-3-3 protein plays an active role in the pathological process of MS. To investigate the differential expression of seven 14-3-3 isoforms in MS lesions, brain tissues of four progressive cases were immunolabeled with a panel of isoform-specific antibodies. Reactive astrocytes in chronic demyelinating lesions intensely expressed beta, epsilon, zeta, eta, and sigma isoforms, among which the epsilon isoform is a highly specific marker for reactive astrocytes. Furthermore, protein overlay, mass spectrometry, immunoprecipitation, and double-immunolabeling analysis showed that the 14-3-3 protein interacts with both vimentin and glial fibrillary acidic protein in cultured human astrocytes. These results suggest that the 14-3-3 protein plays an organizing role in the intermediate filament network in reactive astrocytes at the site of demyelinating lesions in MS.