EFhd2 is a novel amyloid protein associated with pathological tau in Alzheimer's disease

EFhd2 co-aggregates with monomeric and filamentous tau in vitro

Tauopathies are characterized by the abnormal buildup of tau protein, with early oligomeric forms associated with neurodegeneration and the later neurofibrillary tangles possibly conferring neuroprotection. The molecular mechanisms governing the formation of these tau species are unclear. Lately, there has been an increased focus on examining the interactions between tau and other proteins, along with their influence on the aggregation of tau. Our previous work revealed EFhd2's association with pathological tau in animal models and tauopathy brains. Herein, we examined the impact of EFhd2 on monomeric and filamentous tau in vitro. The results demonstrated that EFhd2 incubation with monomeric full length human tau (hTau40) formed amorphous aggregates, where both EFhd2 and hTau40 colocalized. Moreover, EFhd2 is entangled with arachidonic acid (ARA)-induced filamentous hTau40. Furthermore, EFhd2-induced aggregation with monomeric and filamentous hTau40 is EFhd2 concentration dependent. Using sandwich ELISA assays, we assessed the reactivity of TOC1 and Alz50-two conformation-specific tau antibodies-to EFhd2-hTau40 aggregates (in absence and presence of ARA). No TOC1 signal was detected in EFhd2 aggregates with monomeric hTau40 whereas EFhd2 aggregates with hTau in the presence of ARA showed a higher signal compared to hTau40 filaments. In contrast, EFhd2 aggregates with both monomeric and filamentous hTau40 reduced Alz50 reactivity. Taken together, our results illustrate for the first time that EFhd2, a tau-associated protein, interacts with monomeric and filamentous hTau40 to form large aggregates that are starkly different from tau oligomers and filaments. Given these findings and previous research, we hypothesize that EFhd2 may play a role in the formation of tau aggregates. Nevertheless, further in vivo studies are imperative to test this hypothesis.

Transcriptomic analysis reveals sex-specific patterns in the hippocampus in Alzheimer's disease

Background

The hippocampus, vital for memory and learning, is among the first brain regions affected in Alzheimer's Disease (AD) and exhibits adult neurogenesis. Women face twice the risk of developing AD compare to men, making it crucial to understand sex differences in hippocampal function for comprehending AD susceptibility.

Methods

We conducted a comprehensive analysis of bulk mRNA postmortem samples from the whole hippocampus (GSE48350, GSE5281) and its CA1 and CA3 subfields (GSE29378). Our aim was to perform a comparative molecular signatures analysis, investigating sex-specific differences and similarities in the hippocampus and its subfields in AD. This involved comparing the gene expression profiles among: (a) male controls (M-controls) vs. female controls (F-controls), (b) females with AD (F-AD) vs. F-controls, (c) males with AD (M-AD) vs. M-controls, and (d) M-AD vs. F-AD. Furthermore, we identified AD susceptibility genes interacting with key targets of menopause hormone replacement drugs, specifically the ESR1 and ESR2 genes, along with GPER1.

Results

The hippocampal analysis revealed contrasting patterns between M-AD vs. M-controls and F-AD vs. F-controls, as well as M-controls vs. F-controls. Notably, BACE1, a key enzyme linked to amyloid-beta production in AD pathology, was found to be upregulated in M-controls compared to F-controls in both CA1 and CA3 hippocampal subfields. In M-AD vs. M-controls, the GABAergic synapse was downregulated, and the Estrogen signaling pathway was upregulated in both subfields, unlike in F-AD vs. F-controls. Analysis of the whole hippocampus also revealed upregulation of the GABAergic synapse in F-AD vs. F-controls. While direct comparison of M-AD vs. F-AD, revealed a small upregulation of the ESR1 gene in the CA1 subfield of males. Conversely, F-AD vs. F-controls exhibited downregulation of the Dopaminergic synapse in both subfields, while the Calcium signaling pathway showed mixed regulation, being upregulated in CA1 but downregulated in CA3, unlike in M-AD vs. M-controls. The upregulated Estrogen signaling pathway in M-AD, suggests a compensatory response to neurodegenerative specifically in males with AD. Our results also identified potential susceptibility genes interacting with ESR1 and ESR2, including MAPK1, IGF1, AKT1, TP53 and CD44.

Conclusion

These findings underscore the importance of sex-specific disease mechanisms in AD pathogenesis. Region-specific analysis offers a more detailed examination of localized changes in the hippocampus, enabling to capture sex-specific molecular patterns in AD susceptibility and progression.

Liquid-liquid phase separation in Alzheimer's disease

The pathological aggregation and misfolding of tau and amyloid-β play a key role in Alzheimer's disease (AD). However, the underlying pathological mechanisms remain unclear. Emerging evidences indicate that liquid-liquid phase separation (LLPS) has great impacts on regulating human health and diseases, especially neurodegenerative diseases. A series of studies have revealed the significance of LLPS in AD. In this review, we summarize the latest progress of LLPS in AD, focusing on the impact of metal ions, small-molecule inhibitors, and proteinaceous partners on tau LLPS and aggregation, as well as toxic oligomerization, the role of LLPS on amyloid-β (Aβ) aggregation, and the cross-interactions between amyloidogenic proteins in AD. Eventually, the fundamental methods and techniques used in LLPS study are introduced. We expect to present readers a deeper understanding of the relationship between LLPS and AD.

EFHD2 cooperates with E3 ubiquitin ligase Smurf1 to facilitate virus infection by promoting the degradation of TRAF6 in teleost fish

The ubiquitin-proteasome system is one of the most important protein stability regulation systems. It can precisely regulate host immune responses by targeting signaling proteins. TRAF6 is a crucial E3 ubiquitin ligase in host antiviral signaling pathway. Here, we discovered that EF-hand domain-containing protein D2 (EFHD2) collaborated with the E3 ubiquitin ligase Smurf1 to potentiate the degradation of TRAF6, hence facilitating RNA virus Siniperca chuatsi rhabdovirus infection. The mechanism analysis revealed that EFHD2 interacted with Smurf1 and enhanced its protein stability by impairing K48-linked polyubiquitination of Smurf1, thereby promoting Smurf1-catalyzed degradation of TRAF6. This study initially demonstrated a novel mechanism by which viruses utilize host EFHD2 to achieve immune escape and provided a new perspective on the exploration of mammalian innate immunity.IMPORTANCEViruses induce host cells to activate several antiviral signaling pathways. TNF receptor-associated factor 6 (TRAF6) plays an essential role in these pathways. Numerous studies have been done on the mechanisms of TRAF6-mediated resistance to viral invasion. However, little is known about the strategies that viruses employ to antagonize TRAF6-mediated antiviral signaling pathway. Here, we discovered that EFHD2 functions as a host factor to promote viral replication. Mechanistically, EFHD2 potentiates Smurf1 to catalyze the ubiquitin-proteasomal degradation of TRAF6 by promoting the deubiquitination and stability of Smurf1, which in turn inhibits the production of proinflammatory cytokines and interferons. Our study also provides a new perspective on mammalian resistance to viral invasion.

Unraveling the role of miRNAs in the diagnosis, progression, and therapeutic intervention of Alzheimer's disease

Alzheimer's disease (AD) is a multifaceted, advancing neurodegenerative illness that is responsible for most cases of neurological impairment and dementia in the aged population. As the disease progresses, affected individuals may experience cognitive decline, linguistic problems, affective instability, and behavioral changes. The intricate nature of AD reflects the altered molecular mechanisms participating in the affected human brain. MicroRNAs (miRNAs, miR) are essential for the intricate control of gene expression in neurobiology. miRNAs exert their influence by modulating the transcriptome of brain cells, which typically exhibit substantial genetic activity, encompassing gene transcription and mRNA production. Presently, comprehensive studies are being conducted on AD to identify miRNA-based signatures that are indicative of the disease pathophysiology. These findings can contribute to the advancement of our understanding of the mechanisms underlying this disorder and can inform the development of therapeutic interventions based on miRNA and related RNA molecules. Therefore, this comprehensive review provides a detailed holistic analysis of the latest advances discussing the emerging role of miRNAs in the progression of AD and their possible application as potential biomarkers and targets for therapeutic interventions in future studies.

Liquid-liquid phase separation of protein tau: An emerging process in Alzheimer's disease pathogenesis

Metabolic reactions within cells occur in various isolated compartments with or without borders, the latter being known as membrane-less organelles (MLOs). The MLOs show liquid-like properties and are formed by a process known as liquid-liquid phase separation (LLPS). MLOs contribute to different molecules interactions such as protein-protein, protein-RNA, and RNA-RNA driven by various factors, such as multivalency of intrinsic disorders. MLOs are involved in several cell signaling pathways such as transcription, immune response, and cellular organization. However, disruption of these processes has been found in different pathologies. Recently, it has been demonstrated that protein aggregates, a characteristic of some neurodegenerative diseases, undergo similar phase separation. Tau protein is known as a major neurofibrillary tangles component in Alzheimer's disease (AD). This protein can undergo phase separation to form a MLO known as tau droplet in vitro and in vivo, and this process can be facilitated by several factors, including crowding agents, RNA, and phosphorylation. Tau droplet has been shown to mature into insoluble aggregates suggesting that this process may precede and induce neurodegeneration in AD. Here we review major factors involved in liquid droplet formation within a cell. Additionally, we highlight recent findings concerning tau aggregation following phase separation in AD, along with the potential therapeutic strategies that could be explored in this process against the progression of this pathology.

Structural and biochemical insights into Zn2+-bound EF-hand proteins, EFhd1 and EFhd2

EF-hand proteins, which contain a Ca²⁺-binding EF-hand motif, are involved in regulating diverse cellular functions. Ca²⁺ binding induces conformational changes that modulate the activities of EF-hand proteins. Moreover, these proteins occasionally modify their activities by coordinating metals other than Ca²⁺, including Mg²⁺, Pb²⁺ and Zn²⁺, within their EF-hands. EFhd1 and EFhd2 are homologous EF-hand proteins with similar structures. Although separately localized within cells, both are actin-binding proteins that modulate F-actin rearrangement through Ca²⁺-independent actin-binding and Ca²⁺-dependent actin-bundling activity. Although Ca²⁺ is known to affect the activities of EFhd1 and EFhd2, it is not known whether their actin-related activities are affected by other metals. Here, the crystal structures of the EFhd1 and EFhd2 core domains coordinating Zn²⁺ ions within their EF-hands are reported. The presence of Zn²⁺ within EFhd1 and EFhd2 was confirmed by analyzing anomalous signals and the difference between anomalous signals using data collected at the peak positions as well as low-energy remote positions at the Zn K-edge. EFhd1 and EFhd2 were also found to exhibit Zn²⁺-independent actin-binding and Zn²⁺-dependent actin-bundling activity. This suggests the actin-related activities of EFhd1 and EFhd2 could be regulated by Zn²⁺ as well as Ca²⁺.

Liquid-Liquid Phase Separation to Study the Association of Proteins in Solution

Liquid-liquid phase separation (LLPS) is a reversible biological process that contributes to the formation of critical concentration of proteins, forming membraneless compartments that are physiologically and pathologically relevant. Several proteins have been shown to demix into liquid droplets under in vitro crowding conditions. These studies are mainly conducted in isolation using purified recombinant proteins. Recently, we used LLPS to study the association between two proteins that are co-aggregated in Alzheimer's disease brain, tau, and EFhd2. Here, we describe how we used LLPS to determine the molecular components that contribute to the transition of these two proteins from liquid droplets to solid-like structures.

The Role of Intrinsically Disordered Proteins in Liquid–Liquid Phase Separation during Calcium Carbonate Biomineralization

Some animal organs contain mineralized tissues. These so-called hard tissues are mostly deposits of calcium salts, usually in the form of calcium phosphate or calcium carbonate. Examples of this include fish otoliths and mammalian otoconia, which are found in the inner ear, and they are an essential part of the sensory system that maintains body balance. The composition of ear stones is quite well known, but the role of individual components in the nucleation and growth of these biominerals is enigmatic. It is sure that intrinsically disordered proteins (IDPs) play an important role in this aspect. They have an impact on the shape and size of otoliths. It seems probable that IDPs, with their inherent ability to phase separate, also play a role in nucleation processes. This review discusses the major theories on the mechanisms of biomineral nucleation with a focus on the importance of protein-driven liquid–liquid phase separation (LLPS). It also presents the current understanding of the role of IDPs in the formation of calcium carbonate biominerals and predicts their potential ability to drive LLPS.

Role of Swiprosin-1/EFHD2 as a biomarker in the development of chronic diseases

Swiprosin-1 or EFHD2, is a Ca²⁺ binding actin protein and its expression has been shown to be distinct in various cell types. The expression of swiprosin-1 is upregulated during the activation of immune cells, epithelial and endothelial cells. The expression of swiprosin-1 is regulated by diverse signaling pathways that are contingent upon the specific type of cells. The aim of this review is to summarize and provide an overview of the role of swiprosin-1 in pathophysiological conditions of cancers, cardiovascular diseases, diabetic nephropathy, neuropsychiatric diseases, and in the process of inflammation, immune response, and inflammatory diseases. Novel approaches for the targeting of swiprosin-1 as a biomarker in the early detection and prevention of various development of chronic diseases are also explored.

Swiprosin-1 deficiency in macrophages alleviated atherogenesis

Macrophages play a vital role in the development of atherosclerosis. Previously, we have found that swiprosin-1 was abundantly expressed in macrophages. Here, we investigated the role of swiprosin-1 expressed in macrophages in atherogenesis. Bone marrow transplantation was performed from swiprosin-1-knockout (Swp-/-) mice and age-matched ApoE-/- mice. Atherosclerotic lesion, serum lipid, and interleukin-β (IL-β) levels were detected. In vitro, the peritoneal macrophages isolated from Swp-/- and wild-type mice were stimulated with oxidized low-density lipoprotein (ox-LDL) and the macrophage of foam degree, cellular lipid content, apoptosis, inflammatory factor, migration, and autophagy were determined. Our results showed that swiprosin-1 was mainly expressed in macrophages of atherosclerotic plaques in aorta from ApoE-/- mice fed with high-cholesterol diet (HCD). The expression of swiprosin-1 in the foaming of RAW264.7 macrophages gradually increased with the increase of the concentration and time stimulated with ox-LDL. Atherosclerotic plaques, accumulation of macrophages, collagen content, serum total cholesterol, LDL, and IL-β levels were decreased in Swp-/- → ApoE-/- mice compared with Swp+/+ → ApoE-/- mice fed with HCD for 16 weeks. The macrophage foam cell formation and cellular cholesterol accumulation were reduced, while the lipid uptake and efflux increased in macrophages isolated from Swp-/- compared to wild-type mice treated with ox-LDL. Swiprosin-1 deficiency in macrophages could inhibit apoptosis, inflammation, migration, and promote autophagy. Taken together, our results demonstrated that swiprosin-1 deficiency in macrophages could alleviate the development and progression of AS. The role of swiprosin-1 may provide a promising new target for ameliorating AS.

EFhd2 brain interactome reveals its association with different cellular and molecular processes

EFhd2 is a conserved calcium-binding protein that is highly expressed in the central nervous system. We have shown that EFhd2 interacts with tau protein, a key pathological hallmark in Alzheimer's disease and related dementias. However, EFhd2's physiological and pathological functions in the brain are still poorly understood. To gain insights into its physiological function, we identified proteins that co-immunoprecipitated with EFhd2 from mouse forebrain and hindbrain, using tandem mass spectrometry (MS). In addition, quantitative mass spectrometry was used to detect protein abundance changes due to the deletion of the Efhd2 gene in mouse forebrain and hindbrain regions. Our data show that mouse EFhd2 is associated with cytoskeleton components, vesicle trafficking modulators, cellular stress response-regulating proteins, and metabolic proteins. Moreover, proteins associated with the cytoskeleton, vesicular transport, calcium signaling, stress response, and metabolic pathways showed differential abundance in Efhd2^(-/-) mice. This study presents, for the first time, an EFhd2 brain interactome that it is associated with different cellular and molecular processes. These findings will help prioritize further studies to investigate the mechanisms by which EFhd2 modulates these processes in physiological and pathological conditions of the nervous system.

Liquid-liquid phase separation of tau: From molecular biophysics to physiology and disease

Biomolecular condensation via liquid-liquid phase separation (LLPS) of intrinsically disordered proteins/regions (IDPs/IDRs), with and without nucleic acids, has drawn widespread interest due to the rapidly unfolding role of phase-separated condensates in a diverse range of cellular functions and human diseases. Biomolecular condensates form via transient and multivalent intermolecular forces that sequester proteins and nucleic acids into liquid-like membrane-less compartments. However, aberrant phase transitions into gel-like or solid-like aggregates might play an important role in neurodegenerative and other diseases. Tau, a microtubule-associated neuronal IDP, is involved in microtubule stabilization, regulates axonal outgrowth and transport in neurons. A growing body of evidence indicates that tau can accomplish some of its cellular activities via LLPS. However, liquid-to-solid transition resulting in the abnormal aggregation of tau is associated with neurodegenerative diseases. The physical chemistry of tau is crucial for governing its propensity for biomolecular condensation which is governed by various intermolecular and intramolecular interactions leading to simple one-component and complex multi-component condensates. In this review, we aim at capturing the current scientific state in unveiling the intriguing molecular mechanism of phase separation of tau. We particularly focus on the amalgamation of existing and emerging biophysical tools that offer unique spatiotemporal resolutions on a wide range of length- and time-scales. We also discuss the link between quantitative biophysical measurements and novel biological insights into biomolecular condensation of tau. We believe that this account will provide a broad and multidisciplinary view of phase separation of tau and its association with physiology and disease.

Association between EFHD2 gene polymorphisms and schizophrenia among the Han population in northern China

Objective

Schizophrenia is a severe neurodevelopmental disorder with a complex genetic and environmental etiology. The gene encoding EF-hand domain-containing protein D2 (EFHD2) may be a genetic risk locus for schizophrenia.

Methods

We genotyped four EFHD2 single-nucleotide polymorphisms (281 schizophrenia cases [SCZ], 321 controls) from northern Chinese Han individuals using Sanger sequencing and polymerase chain reaction-restriction fragment length polymorphism analysis. Differences existed in genotype, allele, and haplotype frequency distributions between SCZ and control groups.

Results

The rs2473357 genotype and allele frequency distributions differed between SCZ and controls; however, this difference disappeared after Bonferroni correction. Differences in rs2473357 genotype and allele frequency distributions between SCZ and controls were more pronounced in men than in women. The G allele increased schizophrenia risk (odds ratio = 1.807, 95% confidence interval = 1.164–2.803). Among six haplotypes (G–, A–, G-insC, A-C, G-C, and G-T), the G– haplotype frequency distribution differed between SCZ and controls in women; the A-C and G-C haplotype frequency distributions differed between SCZ and controls in men.

Conclusions

EFHD2 may be involved in schizophrenia. Sex differences in EFHD2 genotype and allele frequency distributions existed among schizophrenia patients. Further research is needed to determine the role of EFHD2 in schizophrenia.

EFhd2 Affects Tau Liquid-Liquid Phase Separation

The transition of tau proteins from its soluble physiological conformation to the pathological aggregate forms found in Alzheimer's disease and related dementias, is poorly understood. Therefore, understanding the process that modulates the formation of toxic tau oligomers and their conversion to putative neuroprotective neurofibrillary tangles will lead to better therapeutic strategies. We previously identified that EFhd2 is associated with aggregated tau species in AD brains and the coiled-coil domain in EFhd2 mediates the interaction with tau. To further characterize the association between EFhd2 and tau, we examined whether EFhd2 could affect the liquid-liquid phase separation properties of tau under molecular crowding conditions. We demonstrate that EFhd2 alters tau liquid phase behavior in a calcium and coiled-coil domain dependent manner. Co-incubation of EFhd2 and tau in the absence of calcium leads to the formation of solid-like structures containing both proteins, while in the presence of calcium these two proteins phase separate together into liquid droplets. EFhd2's coiled-coil domain is necessary to alter tau's liquid phase separation, indicating that protein-protein interaction is required. The results demonstrate that EFhd2 affects the liquid-liquid phase separation of tau proteins in vitro, suggesting that EFhd2 modulates the structural dynamics of tau proteins.

Methylene Blue Blocks and Reverses the Inhibitory Effect of Tau on PMCA Function

Methylene blue (MB) is a synthetic phenothiazine dye that, in the last years, has generated much debate about whether it could be a useful therapeutic drug for tau-related pathologies, such as Alzheimer’s disease (AD). However, the molecular mechanism of action is far from clear. Recently we reported that MB activates the plasma membrane Ca²⁺-ATPase (PMCA) in membranes from human and pig tissues and from cells cultures, and that it could protect against inactivation of PMCA by amyloid β-peptide (Aβ). The purpose of the present study is to further examine whether the MB could also modulate the inhibitory effect of tau, another key molecular marker of AD, on PMCA activity. By using kinetic assays in membranes from several tissues and cell cultures, we found that this phenothiazine was able to block and even to completely reverse the inhibitory effect of tau on PMCA. The results of this work point out that MB could mediate the toxic effect of tau related to the deregulation of calcium homeostasis by blocking the impairment of PMCA activity by tau. We then could conclude that MB could interfere with the toxic effects of tau by restoring the function of PMCA pump as a fine tuner of calcium homeostasis.

Tau's Three-Repeat Domain and EFhd2 Co-incubation Leads to Increased Thioflavin Signal

Aggregation of the protein tau is a pathological hallmark of Alzheimer’s disease (AD) and related disorders. However, the molecular mechanisms that lead to tau protein aggregation are still unclear. Previously, we showed that EFhd2 protein is associated with pathological aggregated forms of tau in AD brain. Further, immuno-gold analyses of purified tau aggregates showed that EFhd2 co-localized with filamentous tau structures. We demonstrated that EFhd2’s coiled-coil domain is required for its association with tau proteins. However, it is unknown the role that EFhd2 plays in tau aggregation. Here, we show that incubation of K19-tau with substoichiometric amount of EFhd2 promote the formation of amyloid structures in vitro. The result suggests that EFhd2 may play a role in the biogenesis of aggregated tau.

iTRAQ-based Proteomic Analysis of APPSw,Ind Mice Provides Insights into the Early Changes in Alzheimer's Disease

BACKGROUND

Several proteins have been identified as potential diagnostic biomarkers in imaging, genetic, or proteomic studies in Alzheimer disease (AD) patients and mouse models. However, biomarkers for presymptom diagnosis of AD are still under investigation, as are the presymptom molecular changes in AD pathogenesis.

OBJECTIVE

In this study, we aim to analyzed the early proteomic changes in APPSw,Ind mice and to conduct further functional studies on interesting proteins.

METHODS

We used the isobaric tags for relative and absolute quantitation (iTRAQ) approach combined with mass spectrometry to examine the early proteomic changes in hippocampi of APPSw,Ind mice. Quantitative reverse transcription polymerase chain reaction (RT-PCR) and immuno-blotting were performed for further validation. Finally, the functions of interesting proteins β-spectrin and Rab3a in APP trafficking and processing were tested by shRNA knockdown, in N2A cells stably expressing β-amyloid precursor protein (APP).

RESULTS

The iTRAQ and RT-PCR results revealed the detailed molecular changes in oxidative stress, myelination, astrocyte activation, mTOR signaling and Rab3-dependent APP trafficking in the early stage of AD progression. Knock down of β -spectrin and Rab3a finally led to increased APP fragment production, indicating key roles of β-spectrin and Rab3a in regulating APP processing.

CONCLUSION

Our study provides the first insights into the proteomic changes that occur in the hippocampus in the early stages of the AD mouse model. In addition to improving the understanding of molecular alterations and functional cascades involved in early AD pathogenesis, our findings raise the possibility of developing potential biomarkers and therapeutic targets for early AD.

EFhd2/Swiprosin-1 is a common genetic determinator for sensation-seeking/low anxiety and alcohol addiction

In many societies, the majority of adults regularly consume alcohol. However, only a small proportion develops alcohol addiction. Individuals at risk often show a high sensation-seeking/low-anxiety behavioural phenotype. Here we asked which role EF hand domain containing 2 (EFhd2; Swiprosin-1) plays in the control of alcohol addiction-associated behaviours. EFhd2 knockout (KO) mice drink more alcohol than controls and spontaneously escalate their consumption. This coincided with a sensation-seeking and low-anxiety phenotype. A reversal of the behavioural phenotype with β-carboline, an anxiogenic inverse benzodiazepine receptor agonist, normalized alcohol preference in EFhd2 KO mice, demonstrating an EFhd2-driven relationship between personality traits and alcohol preference. These findings were confirmed in a human sample where we observed a positive association of the EFhd2 single-nucleotide polymorphism rs112146896 with lifetime drinking and a negative association with anxiety in healthy adolescents. The lack of EFhd2 reduced extracellular dopamine levels in the brain, but enhanced responses to alcohol. In confirmation, gene expression analysis revealed reduced tyrosine hydroxylase expression and the regulation of genes involved in cortex development, Eomes and Pax6, in EFhd2 KO cortices. These findings were corroborated in Xenopus tadpoles by EFhd2 knockdown. Magnetic resonance imaging (MRI) in mice showed that a lack of EFhd2 reduces cortical volume in adults. Moreover, human MRI confirmed the negative association between lifetime alcohol drinking and superior frontal gyrus volume. We propose that EFhd2 is a conserved resilience factor against alcohol consumption and its escalation, working through Pax6/Eomes. Reduced EFhd2 function induces high-risk personality traits of sensation-seeking/low anxiety associated with enhanced alcohol consumption, which may be related to cortex function.

Swiprosin-1 deficiency impairs macrophage immune response of septic mice

Despite the fact that many therapeutic strategies have been adopted to delay the development of sepsis, sepsis remains one of the leading causes of death in noncoronary intensive care units. Recently, sepsis-3 was defined as life-threatening organ dysfunction due to a dysregulated host response to infection. Here, we report that swiprosin-1 (also known as EFhd2) plays an important role in the macrophage immune response to LPS-induced or cecal ligation and puncture-induced (CLP-induced) sepsis in mice. Swiprosin-1 depletion causes higher mortality, more severe organ dysfunction, restrained macrophage recruitment in the lung and kidney, and attenuated inflammatory cytokine production (including IL-1β, IL-6, TNF-α, IL-10, and IFN-γ). The immunosuppression caused by swiprosin-1 deficiency is manifested by impaired bactericidal capacity and decreased HLA-DR expression in macrophages. Swiprosin-1 affects the activation of the JAK2/STAT1/STAT3 pathway by regulating the expression of IFN-γ receptors in macrophages. Our findings provide a potential target for the regulation of the macrophage immune response in sepsis.

Impact of Swiprosin-1/Efhd2 on Adult Hippocampal Neurogenesis

Swiprosin-1/Efhd2 (Efhd2) is highly expressed in the CNS during development and in the adult. EFHD2 is regulated by Ca²⁺ binding, stabilizes F-actin, and promotes neurite extension. Previous studies indicated a dysregulation of EFHD2 in human Alzheimer's disease brains. We hypothesized a detrimental effect of genetic ablation of Efhd2 on hippocampal integrity and specifically investigated adult hippocampal neurogenesis. Efhd2 was expressed throughout adult neuronal development and in mature neurons. We observed a severe reduction of the survival of adult newborn neurons in Efhd2 knockouts, starting at the early neuroblast stage. Spine formation and dendrite growth of newborn neurons were compromised in full Efhd2 knockouts, but not upon cell-autonomous Efhd2 deletion. Together with our finding of severe hippocampal tauopathy in Efhd2 knockout mice, these data connect Efhd2 to impaired synaptic plasticity as present in Alzheimer's disease and identify a role of Efhd2 in neuronal survival and synaptic integration in the adult hippocampus.

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Efhd2 is expressed in the dentate gyrus and its loss reduces adult neurogenesis

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Reduced neurite complexity and spine density in new neurons of Efhd2 knockout mice

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Role of cell-extrinsic EFHD2 for dendrite morphology of adult newborn neurons

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Increased levels of pathological TAU in the hippocampus of Efhd2 knockout mice

Ezrin Expression is Increased During Disease Progression in a Tauopathy Mouse Model and Alzheimer's Disease

BACKGROUND

The lack of diagnostic tools and disease-modifying treatments against Alzheimer's disease (AD) and related disorders, collectively known as tauopathies, has led to a socioeconomic burden of epidemic proportion. Proteomics approaches can be used to identify novel proteome changes that could help us understand the pathogenesis of tau-related pathological hallmarks and/or cellular stress responses associated with tauopathy. These studies, however, need to be conducted taking into consideration brain region specificity and stage of neurodegeneration in order to provide insights about the pathological role of the identified proteins.

METHODS

We used a tauopathy mouse model (JNPL3) that expresses human tau bearing a P301L mutation and develops motor impairment, the severity of which correlates with the increased accumulation of pathological tau. Tissue was dissected from asymptomatic and severely motor impaired JNPL3 mice as well as non-transgenic littermate controls and subjected to two-dimensional gel electrophoresis. Differentially abundant protein spots were identified by tandem mass spectrometry. Postmortem mild cognitive impairment (MCI), AD and normal aging controls were used to validate the pathological significance of the identified protein.

RESULTS

Ezrin was identified as a protein that is upregulated in tau-mediated neurodegeneration. We demonstrate that Ezrin protein abundance increased in JNPL3 mice preceded motor impairment and was sustained in severely motor impaired mice. Ezrin expression was also increased in the temporal cortex of MCI and AD patients.

CONCLUSION

The results demonstrate that increased Ezrin protein abundance changes are associated with the early stages of neurodegeneration in tauopathy models and human disease. Understanding the role of Ezrin in tauopathies such as AD may provide new insights for targeting tau-mediated neurodegeneration.

Physiological and pathophysiological functions of Swiprosin-1/EFhd2 in the nervous system

Synaptic dysfunction and dysregulation of Ca(2+) are linked to neurodegenerative processes and behavioural disorders. Our understanding of the causes and factors involved in behavioural disorders and neurodegeneration, especially Alzheimer's disease (AD), a tau-related disease, is on the one hand limited and on the other hand controversial. Here, we review recent data about the links between the Ca(2+)-binding EF-hand-containing cytoskeletal protein Swiprosin-1/EFhd2 and neurodegeneration. Specifically, we summarize the functional biochemical data obtained in vitro with the use of recombinant EFhd2 protein, and integrated them with in vivo data in order to interpret the emerging role of EFhd2 in synaptic plasticity and in the pathophysiology of neurodegenerative disorders, particularly involving the tauopathies. We also discuss its functions in actin remodelling through cofilin and small GTPases, thereby linking EFhd2, synapses and the actin cytoskeleton. Expression data and functional experiments in mice and in humans have led to the hypothesis that down-regulation of EFhd2, especially in the cortex, is involved in dementia.

Low level of swiprosin-1/EFhd2 in vestibular nuclei of spontaneously hypersensitive motion sickness mice

Susceptibility to motion sickness (MS) varies considerably among humans. However, the cause of such variation is unclear. Here, we used a classical genetic approach to obtain mouse strains highly sensitive and resistant to MS (SMS and RMS). Proteomics analysis revealed substantially lower swiprosin-1 expression in SMS mouse brains. Inducing MS via rotary stimulation decreased swiprosin-1 in the mouse brains. Swiprosin-1 knockout mice were much more sensitive to motion disturbance. Immunohistochemistry revealed strong swiprosin-1 expression in the vestibular nuclei (VN). Over-expressing swiprosin-1 in the VN of SMS mice decreased MS susceptibility. Down-regulating swiprosin-1 in the VN of RMS mice by RNAi increased MS susceptibility. Additional in vivo experiments revealed decreased swiprosin-1 expression by glutamate via the NMDA receptor. Glutamate increased neuronal excitability in SMS or swiprosin-1 knockout mice more prominently than in RMS or wild-type mice. These results indicate that swiprosin-1 in the VN is a critical determinant of the susceptibility to MS.

Structural implications of Ca2+-dependent actin-bundling function of human EFhd2/Swiprosin-1

EFhd2/Swiprosin-1 is a cytoskeletal Ca²⁺-binding protein implicated in Ca²⁺-dependent cell spreading and migration in epithelial cells. EFhd2 domain architecture includes an N-terminal disordered region, a PxxP motif, two EF-hands, a ligand mimic helix and a C-terminal coiled-coil domain. We reported previously that EFhd2 displays F-actin bundling activity in the presence of Ca²⁺ and this activity depends on the coiled-coil domain and direct interaction of the EFhd2 core region. However, the molecular mechanism for the regulation of F-actin binding and bundling by EFhd2 is unknown. Here, the Ca²⁺-bound crystal structure of the EFhd2 core region is presented and structures of mutants defective for Ca²⁺-binding are also described. These structures and biochemical analyses reveal that the F-actin bundling activity of EFhd2 depends on the structural rigidity of F-actin binding sites conferred by binding of the EF-hands to Ca²⁺. In the absence of Ca²⁺, the EFhd2 core region exhibits local conformational flexibility around the EF-hand domain and C-terminal linker, which retains F-actin binding activity but loses the ability to bundle F-actin. In addition, we establish that dimerisation of EFhd2 via the C-terminal coiled-coil domain, which is necessary for F-actin bundling, occurs through the parallel coiled-coil interaction.

EFhd2, a Protein Linked to Alzheimer's Disease and Other Neurological Disorders

EFhd2 is a conserved calcium binding protein linked to different neurological disorders and types of cancer. Although, EFhd2 is more abundant in neurons, it is also found in other cell types. The physiological function of this novel protein is still unclear, but it has been shown in vitro to play a role in calcium signaling, apoptosis, actin cytoskeleton, and regulation of synapse formation. Recently, EFhd2 was shown to promote cell motility by modulating the activity of Rac1, Cdc42, and RhoA. Although, EFhd2's role in promoting cell invasion and metastasis is of great interest in cancer biology, this review focusses on the evidence that links EFhd2 to Alzheimer's disease (AD) and other neurological disorders. Altered expression of EFhd2 has been documented in AD, Parkinson's disease, Huntington's disease, Amyotrophic Lateral Sclerosis, and schizophrenia, indicating that Efhd2 gene expression is regulated in response to neuropathological processes. However, the specific role that EFhd2 plays in the pathophysiology of neurological disorders is still poorly understood. Recent studies demonstrated that EFhd2 has structural characteristics similar to amyloid proteins found in neurological disorders. Moreover, EFhd2 co-aggregates and interacts with known neuropathological proteins, such as tau, C9orf72, and Lrrk2. These results suggest that EFhd2 may play an important role in the pathophysiology of neurodegenerative diseases. Therefore, the understanding of EFhd2's role in health and disease could lead to decipher molecular mechanisms that become activated in response to neuronal stress and degeneration.

Phosphoproteomic screening identifies Rab GTPases as novel downstream targets of PINK1

Mutations in the PTEN‐induced kinase 1 (PINK1) are causative of autosomal recessive Parkinson's disease (PD). We have previously reported that PINK1 is activated by mitochondrial depolarisation and phosphorylates serine 65 (Ser⁶⁵) of the ubiquitin ligase Parkin and ubiquitin to stimulate Parkin E3 ligase activity. Here, we have employed quantitative phosphoproteomics to search for novel PINK1‐dependent phosphorylation targets in HEK (human embryonic kidney) 293 cells stimulated by mitochondrial depolarisation. This led to the identification of 14,213 phosphosites from 4,499 gene products. Whilst most phosphosites were unaffected, we strikingly observed three members of a sub‐family of Rab GTPases namely Rab8A, 8B and 13 that are all phosphorylated at the highly conserved residue of serine 111 (Ser¹¹¹) in response to PINK1 activation. Using phospho‐specific antibodies raised against Ser¹¹¹ of each of the Rabs, we demonstrate that Rab Ser¹¹¹ phosphorylation occurs specifically in response to PINK1 activation and is abolished in HeLa PINK1 knockout cells and mutant PINK1 PD patient‐derived fibroblasts stimulated by mitochondrial depolarisation. We provide evidence that Rab8A GTPase Ser¹¹¹ phosphorylation is not directly regulated by PINK1 in vitro and demonstrate in cells the time course of Ser¹¹¹ phosphorylation of Rab8A, 8B and 13 is markedly delayed compared to phosphorylation of Parkin at Ser⁶⁵. We further show mechanistically that phosphorylation at Ser¹¹¹ significantly impairs Rab8A activation by its cognate guanine nucleotide exchange factor (GEF), Rabin8 (by using the Ser111Glu phosphorylation mimic). These findings provide the first evidence that PINK1 is able to regulate the phosphorylation of Rab GTPases and indicate that monitoring phosphorylation of Rab8A/8B/13 at Ser¹¹¹ may represent novel biomarkers of PINK1 activity in vivo. Our findings also suggest that disruption of Rab GTPase‐mediated signalling may represent a major mechanism in the neurodegenerative cascade of Parkinson's disease.

Localization of Nitric Oxide Synthase-containing Neurons in the Bat Visual Cortex and Co-localization with Calcium-binding Proteins

Microchiroptera (microbats) is a suborder of bats thought to have degenerated vision. However, many recent studies have shown that they have visual ability. In this study, we labeled neuronal nitric oxide synthase (nNOS)-the synthesizing enzyme of the gaseous non-synaptic neurotransmitter nitric oxide-and co-localized it with calbindin D28K (CB), calretinin (CR), and parvalbumin (PV) in the visual cortex of the greater horseshoe bat (Rhinolophus ferrumequinum, a species of microbats). nNOS-immunoreactive (IR) neurons were found in all layers of the visual cortex. Intensely labeled neurons were most common in layer IV, and weakly labeled neurons were most common in layer VI. Majority of the nNOS-IR neurons were round- or oval-type neurons; no pyramidal-type neurons were found. None of these neurons co-localized with CB, CR, or PV. However, the synthesis of nitric oxide in the bat visual cortex by nNOS does not depend on CB, CR, or PV.

Improvement of spatial memory disorder and hippocampal damage by exposure to electromagnetic fields in an Alzheimer's disease rat model

Although some epidemiological investigations showed a potential association between long-term exposure of extremely low frequency electromagnetic fields (ELF-EMF) and Alzheimer’s disease (AD), no reasonable mechanism can explain this association, and the related animal experiments are rare. In this study, ELF-EMF exposure (50Hz 400µT 60d) combined with D-galactose intraperitoneal (50mg/kg, q.d., 42d) and Aβ_25–35 hippocampal (5μl/unilateral, bilateral, single-dose) injection was implemented to establish a complex rat model. Then the effects of ELF-EMF exposure on AD development was studied by using the Morris water maze, pathological analysis, and comparative proteomics. The results showed that ELF-EMF exposure delayed the weight gain of rats, and partially improved cognitive and clinicopathologic symptoms of AD rats. The differential proteomic analysis results suggest that synaptic transmission, oxidative stress, protein degradation, energy metabolism, Tau aggregation, and inflammation involved in the effects mentioned above. Therefore, our findings indicate that certain conditions of ELF-EMF exposure could delay the development of AD in rats.

The influence of chronic ibuprofen treatment on proteins expressed in the mouse hippocampus

Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID), treatment with which has been shown to delay the onset, slows the cognitive decline, and decreases the incidence of Alzheimer׳s disease (AD) in epidemiological and clinical studies. However, a comprehensive understanding of its mechanism of action remains unclear. To elucidate the prophylactic effect of ibuprofen on the onset of the learning and memory disturbances of AD, we performed proteomic analysis of the hippocampus of chronic ibuprofen-treated mice using two-dimensional gel electrophoresis (2-DE) followed by mass spectrometry. Twenty-eight proteins and seven phosphoproteins were identified to be significantly changed in the hippocampus of chronic ibuprofen-treated mice: translationally controlled tumor protein, thioredoxin-dependent peroxide reductase, and peroxiredoxin 6 were increased, and glial fibrillary acidic protein, dihydropyrimidinase-related protein 2, EF-hand domain-containing protein D2, and 14-3-3ζ were decreased. These identified proteins and phosphoproteins could be classified as cytoskeletal, neuronal development, chaperone, metabolic, apoptosis, neurotransmitter release, ATP synthase, deubiquitination, proteasome, NOS inhibitor, adapter, vesicle transport, signal transduction, antioxidant enzyme, proton transport, synaptogenesis, and serine/threonine phosphatase types. Western blot analysis showed the changes in dihydropyrimidinase-related protein 2, heat shock protein 8, ubiquitin carboxyl-terminal hydrolase PGP9.5, and γ-enolase levels in the hippocampus of chronic ibuprofen-treated mice. These findings showed that the chronic treatment with ibuprofen changed the levels of some proteins and phosphoproteins in the hippocampus. We propose that these identified proteins and phosphoproteins play an important role in decreasing the incidence of AD, especially impaired learning and memory functions.

The calcium-binding protein EFhd2 modulates synapse formation in vitro and is linked to human dementia

EFhd2 is a calcium-binding adaptor protein that has been found to be associated with pathologically aggregated tau in the brain in Alzheimer disease and in a mouse model of frontotemporal dementia. EFhd2 has cell type-specific functions, including the modulation of intracellular calcium responses, actin dynamics, and microtubule transport. Here we report that EFhd2 protein and mRNA levels are reduced in human frontal cortex tissue affected by different types of dementia with and without tau pathology. We show that EFhd2 is mainly a neuronal protein in the brain and is abundant in the forebrain. Using short hairpin RNA-mediated knockdown of EFhd2 expression in cultured cortical neurons, we demonstrate that loss of EFhd2 affects the number of synapses developed in vitro whereas it does not alter neurite outgrowth per se. Our data suggest that EFhd2 is involved in the control of synapse development and maintenance through means other than affecting neurite development. The changes in expression levels observed in human dementias might, therefore, play a significant role in disease onset and progression of dementia, which is characterized by the loss of synapses.

The Ca2+ sensor protein swiprosin-1/EFhd2 is present in neurites and involved in kinesin-mediated transport in neurons

Swiprosin-1/EFhd2 (EFhd2) is a cytoskeletal Ca²⁺ sensor protein strongly expressed in the brain. It has been shown to interact with mutant tau, which can promote neurodegeneration, but nothing is known about the physiological function of EFhd2 in the nervous system. To elucidate this question, we analyzed EFhd2^−/−/lacZ reporter mice and showed that lacZ was strongly expressed in the cortex, the dentate gyrus, the CA1 and CA2 regions of the hippocampus, the thalamus, and the olfactory bulb. Immunohistochemistry and western blotting confirmed this pattern and revealed expression of EFhd2 during neuronal maturation. In cortical neurons, EFhd2 was detected in neurites marked by MAP2 and co-localized with pre- and post-synaptic markers. Approximately one third of EFhd2 associated with a biochemically isolated synaptosome preparation. There, EFhd2 was mostly confined to the cytosolic and plasma membrane fractions. Both synaptic endocytosis and exocytosis in primary hippocampal EFhd2^−/− neurons were unaltered but transport of synaptophysin-GFP containing vesicles was enhanced in EFhd2^−/− primary hippocampal neurons, and notably, EFhd2 inhibited kinesin mediated microtubule gliding. Therefore, we found that EFhd2 is a neuronal protein that interferes with kinesin-mediated transport.

Immunocytochemical Localization of Calbindin D28K, Calretinin, and Parvalbumin in Bat Superior Colliculus

The purpose of this study was to investigate the localization of cells containing the calcium-binding proteins (CBPs) calbindin D28K (CB), calretinin (CR), and parvalbumin (PV) in the superior colliculus (SC) of the bat using immunocytochemistry. CB-immunoreactive (IR) cells formed a laminar tier within the upper superficial gray layer (SGL), while CR-IR cells were widely distributed within the optic layer (OL). Scattered CR-IR cells were also found within the intermediate gray, white, and deep gray layers. By contrast, PV-IR cells formed a laminar tier within the lower SGL and upper OL. Scattered PV-IR cells were also found throughout the intermediate layers, but without a specific laminar pattern. The CBP-IR cells varied in size and morphology: While most of the CB-IR cells in the superficial layers were small round or oval cells, most CR-IR cells in the intermediate and deep layers were large stellate cells. By contrast, PV-IR cells were small to large in size and included round or oval, stellate, vertical fusiform, and horizontal cells. The average diameters of the CB-, CR-, and PV-IR cells were 11.59, 17.17, and 12.60 μm, respectively. Double-immunofluorescence revealed that the percentage of co-localization with GABA-IR cells was 0.0, 0.0, and 10.27% of CB-, CR-, and PV-IR cells, respectively. These results indicate that CBP distribution patterns in the bat SC are unique compared with other mammalian SCs, which suggest functional diversity of these proteins in visually guided behaviors.

Cdk5 phosphorylation of EFhd2 at S74 affects its calcium binding activity

EFhd2 is a calcium binding protein, which is highly expressed in the central nervous system and associated with pathological forms of tau proteins in tauopathies. Previous phosphoproteomics studies and bioinformatics analysis suggest that EFhd2 may be phosphorylated. Here, we determine whether Cdk5, a hyperactivated kinase in tauopathies, phosphorylates EFhd2 and influence its known molecular activities. The results indicated that EFhd2 is phosphorylated by brain extract of the transgenic mouse CK-p25, which overexpresses the Cdk5 constitutive activator p25. Consistently, in vitro kinase assays demonstrated that Cdk5, but not GSK3β, directly phosphorylates EFhd2. Biomass, tandem mass spectrometry, and mutagenesis analyses indicated that Cdk5 monophosphorylates EFhd2 at S74, but not the adjacent S76. Furthermore, Cdk5-mediated phosphorylation of EFhd2 affected its calcium binding activity. Finally, a phospho-specific antibody was generated against EFhd2 phosphorylated at S74 and was used to detect this phosphorylation event in postmortem brain tissue from Alzheimer's disease and normal-aging control cases. Results demonstrated that EFhd2 is phosphorylated in vivo at S74. These results imply that EFhd2's physiological and/or pathological function could be regulated by its phosphorylation state.