Slingshot-Cofilin activation mediates mitochondrial and synaptic dysfunction via Aβ ligation to β1-integrin conformers

Rational Design of Dual-Functionalized Gd@C82 Nanoparticles to Relieve Neuronal Cytotoxicity in Alzheimer's Disease via Inhibition of Aβ Aggregation

The accumulation of amyloid-β (Aβ) peptides is a major hallmark of Alzheimer's disease (AD) and plays a crucial role in its pathogenesis. Particularly, the structured oligomeric species rich in β-sheet formations were implicated in neuronal organelle damage. Addressing this formidable challenge requires identifying candidates capable of inhibiting peptide aggregation or disaggregating preformed oligomers for effective antiaggregation-based AD therapy. Here, we present a dual-functional nanoinhibitor meticulously designed to target the aggregation driving force and amyloid fibril spatial structure. Leveraging the exceptional structural stability and facile tailoring capability of endohedral metallofullerene Gd@C82, we introduce desired hydrogen-binding sites and charged groups, which are abundant on its surface for specific designs. Impressively, these designs endow the resultant functionalized-Gd@C82 nanoparticles (f-Gd@C82 NPs) with high capability of redirecting peptide self-assembly toward disordered, off-pathway species, obstructing the early growth of protofibrils, and disaggregating the preformed well-ordered protofibrils or even mature Aβ fibrils. This results in considerable alleviation of Aβ peptide-induced neuronal cytotoxicity, rescuing neuronal death and synaptic loss in primary neuron models. Notably, these modifications significantly improved the dispersibility of f-Gd@C82 NPs, thus substantially enhancing its bioavailability. Moreover, f-Gd@C82 NPs demonstrate excellent cytocompatibility with various cell lines and possess the ability to penetrate the blood-brain barrier in mice. Large-scale molecular dynamics simulations illuminate the inhibition and disaggregation mechanisms. Our design successfully overcomes the limitations of other nanocandidates, which often overly rely on hydrophobic interactions or photothermal conversion properties, and offers a viable direction for developing anti-AD agents through the inhibition and even reversal of Aβ aggregation.

Cofilactin rod formation mediates inflammation-induced neurite degeneration

Stroke, trauma, and neurodegenerative disorders cause loss of neurites (axons and dendrites) in addition to neuronal death. Neurite loss may result directly from a primary insult, secondary to parental neuron death, or secondary to a post-injury inflammatory response. Here, we use lipopolysaccharide and the alarmin S100β to selectively evaluate neurite loss caused by the inflammatory response. Activation of microglia and infiltrating macrophages by these stimuli causes neurite loss that far exceeds neuronal death, both in vitro and in vivo. Neurite loss is accompanied by the formation of cofilactin rods and aggregates (CARs), which are polymers of cofilin-1 and actin induced by oxidative stress and other factors. Mice deficient in either cofilin-1 or the superoxide-generating enzyme NADPH oxidase-2 show reduced CAR formation, neurite loss, and motor impairment. The findings identify a mechanism by which inflammation leads to neurite loss via CAR formation and highlight the relevance of neurite loss to functional impairment.

Slingshot homolog-1-mediated Nrf2 sequestration tips the balance from neuroprotection to neurodegeneration in Alzheimer's disease

Oxidative damage in the brain is one of the earliest drivers of pathology in Alzheimer's disease (AD) and related dementias, both preceding and exacerbating clinical symptoms. In response to oxidative stress, nuclear factor erythroid 2-related factor 2 (Nrf2) is normally activated to protect the brain from oxidative damage. However, Nrf2-mediated defense against oxidative stress declines in AD, rendering the brain increasingly vulnerable to oxidative damage. Although this phenomenon has long been recognized, its mechanistic basis has been a mystery. Here, we demonstrate through in vitro and in vivo models, as well as human AD brain tissue, that Slingshot homolog-1 (SSH1) drives this effect by acting as a counterweight to neuroprotective Nrf2 in response to oxidative stress and disease. Specifically, oxidative stress-activated SSH1 suppresses nuclear Nrf2 signaling by sequestering Nrf2 complexes on actin filaments and augmenting Kelch-like ECH-associated protein 1 (Keap1)-Nrf2 interaction, independently of SSH1 phosphatase activity. We also show that Ssh1 elimination in AD models increases Nrf2 activation, which mitigates tau and amyloid-β accumulation and protects against oxidative injury, neuroinflammation, and neurodegeneration. Furthermore, loss of Ssh1 preserves normal synaptic function and transcriptomic patterns in tauP301S mice. Importantly, we also show that human AD brains exhibit highly elevated interactions of Nrf2 with both SSH1 and Keap1. Thus, we demonstrate here a unique mode of Nrf2 blockade that occurs through SSH1, which drives oxidative damage and ensuing pathogenesis in AD. Strategies to inhibit SSH1-mediated Nrf2 suppression while preserving normal SSH1 catalytic function may provide new neuroprotective therapies for AD and related dementias.

Resveratrol Preconditioning Protects Against Ischemia-Induced Synaptic Dysfunction and Cofilin Hyperactivation in the Mouse Hippocampal Slice

Perturbations in synaptic function are major determinants of several neurological diseases and have been associated with cognitive impairments after cerebral ischemia (CI). Although the mechanisms underlying CI-induced synaptic dysfunction have not been well defined, evidence suggests that early hyperactivation of the actin-binding protein, cofilin, plays a role. Given that synaptic impairments manifest shortly after CI, prophylactic strategies may offer a better approach to prevent/mitigate synaptic damage following an ischemic event. Our laboratory has previously demonstrated that resveratrol preconditioning (RPC) promotes cerebral ischemic tolerance, with many groups highlighting beneficial effects of resveratrol treatment on synaptic and cognitive function in other neurological conditions. Herein, we hypothesized that RPC would mitigate hippocampal synaptic dysfunction and pathological cofilin hyperactivation in an ex vivo model of ischemia. Various electrophysiological parameters and synaptic-related protein expression changes were measured under normal and ischemic conditions utilizing acute hippocampal slices derived from adult male mice treated with resveratrol (10 mg/kg) or vehicle 48 h prior. Remarkably, RPC significantly increased the latency to anoxic depolarization, decreased cytosolic calcium accumulation, prevented aberrant increases in synaptic transmission, and rescued deficits in long-term potentiation following ischemia. Additionally, RPC upregulated the expression of the activity-regulated cytoskeleton associated protein, Arc, which was partially required for RPC-mediated attenuation of cofilin hyperactivation. Taken together, these findings support a role for RPC in mitigating CI-induced excitotoxicity, synaptic dysfunction, and pathological over-activation of cofilin. Our study provides further insight into mechanisms underlying RPC-mediated neuroprotection against CI and implicates RPC as a promising strategy to preserve synaptic function after ischemia.

Impaired Insulin Signaling Alters Mediators of Hippocampal Synaptic Dynamics/Plasticity: A Possible Mechanism of Hyperglycemia-Induced Cognitive Impairment

Alzheimer's disease (AD) is a neurological condition that affects the elderly and is characterized by progressive and irreversible neurodegeneration in the cerebral cortex [...].

Slingshot homolog-1 amplifies mitochondrial abnormalities by distinctly impairing health and clearance of mitochondria

Accumulating toxic protein assemblies, including Aβ and tau, and dysfunctional mitochondria are associated with synaptic and neuronal loss in Alzheimer's disease (AD). Such accumulations are thought to be owing to clearance defects in the autophagy-lysosome pathway. Mitochondrial dysfunction is evident in AD brains and animal models at multiple levels, such as mitochondrial genomic mutations, disrupted bioenergetics, deregulated mitochondrial dynamics and impaired clearance of damaged mitochondria (mitophagy). Slingshot homolog-1 (SSH1) is a phosphatase activated by oxidative stress, high intracellular levels of Ca2+ and Aβ42 oligomers (Aβ42O), known for its function to dephosphorylate/activate cofilin through the N-terminal region. SSH1-mediated cofilin dephosphorylation results in Ab42O-induced severing of F-actin and translocation of cofilin to mitochondria, which promotes mitochondria-mediated apoptosis, synaptic loss and synaptic deficits. On the other hand, SSH1-mediated dephosphorylation/deactivation of the autophagy-cargo receptor p62 (SQSTM1), through its C-terminal region, inhibits p62 autophagy flux. However, the interplay between these two different activities of SSH1 in Aβ42O-induced mitochondrial toxicity remains unclear. In this study, we assessed the role of endogenous SSH1 and different regions of SSH1 in regulating mitochondrial health, mitochondrial respiration, clearance of damaged mitochondria and synaptic integrity in vitro and in vivo. Our results indicate that SSH1 suppresses mitochondrial health and respiration through the cofilin-binding N-terminal region, whereas SSH1 impairs mitophagy through a newly identified ~ 100 residue p62-binding domain in the C-terminal region. These results indicate that both N-terminal and C-terminal regions negatively impact mitochondria by distinct and independent modalities to amplify mitochondrial abnormalities, making SSH1 an excellent target to mitigate AD pathogenesis.

Cofilin Inhibitor Protects against Traumatic Brain Injury-Induced Oxidative Stress and Neuroinflammation

Microglial activation and failure of the antioxidant defense mechanisms are major hallmarks in different brain injuries, particularly traumatic brain injury (TBI). Cofilin is a cytoskeleton-associated protein involved in actin binding and severing. In our previous studies, we identified the putative role of cofilin in mediating microglial activation and apoptosis in ischemic and hemorrhagic conditions. Others have highlighted the involvement of cofilin in ROS production and the resultant neuronal death; however, more studies are needed to delineate the role of cofilin in oxidative stress conditions. The present study aims to investigate the cellular and molecular effects of cofilin in TBI using both in vitro and in vivo models as well as the first-in-class small-molecule cofilin inhibitor (CI). An in vitro H2O2-induced oxidative stress model was used in two different types of cells, human neuroblastoma (SH-SY5Y) and microglia (HMC3), along with an in vivo controlled cortical impact model of TBI. Our results show that treatment with H2O2 increases the expression of cofilin and slingshot-1 (SSH-1), an upstream regulator of cofilin, in microglial cells, which was significantly reduced in the CI-treated group. Cofilin inhibition significantly attenuated H2O2-induced microglial activation by reducing the release of proinflammatory mediators. Furthermore, we demonstrate that CI protects against H2O2-induced ROS accumulation and neuronal cytotoxicity, activates the AKT signaling pathway by increasing its phosphorylation, and modulates mitochondrial-related apoptogenic factors. The expression of NF-E2-related factor 2 (Nrf2) and its associated antioxidant enzymes were also increased in CI-treated SY-SY5Y. In the mice model of TBI, CI significantly activated the Nrf2 and reduced the expression of oxidative/nitrosative stress markers at the protein and gene levels. Together, our data suggest that cofilin inhibition provides a neuroprotective effect in in vitro and in vivo TBI mice models by inhibiting oxidative stress and inflammatory responses, the pivotal mechanisms involved in TBI-induced brain damage.

Gα13-Mediated Signaling Cascade Is Related to the Tau Pathology Caused by Anesthesia and Surgery in 5XFAD Transgenic Mice

BACKGROUND

Our previous studies indicated that anesthesia and surgery could aggravate cognitive impairment of 5XFAD transgenic (Tg) mice, and this aggravation was associated with tau hyperphosphorylation. We previously identified that GNA13 (the gene encoding Gα13) was a hub gene with tau hyperphosphorylation.

OBJECTIVE

This study aims to further investigate the mechanism that whether the Gα13-mediated signaling pathway acts as an instigator to regulate cofilin activation and autophagy impairment in this process.

METHODS

5XFAD Tg mice and their littermate (LM) mice were randomly allocated into four groups: LM Control group, LM Anesthesia/Surgery group, AD Control group, and AD Anesthesia/Surgery group. For mice in the Anesthesia/Surgery groups, abdominal surgery was performed under 1.4% isoflurane anesthesia followed by sustaining anesthetic inhalation for up to 2 h.

RESULTS

Compared with the AD Control group, protein levels of Gα13, ROCK2, LPAR5, and p-tau/tau46 ratio were increased, while p-cofilin/cofilin protein expression ratio was decreased in the AD Anesthesia/Surgery group. However, the differences in these protein levels were not significant among LM groups.

CONCLUSION

This study demonstrated that anesthesia and surgery might exacerbate p-tau accumulation in 5XFAD Tg mice but not in LM mice. And this might be closely related to cofilin activation via Gα13-mediated signaling cascade.

Immunotherapy with Cleavage-Specific 12A12mAb Reduces the Tau Cleavage in Visual Cortex and Improves Visuo-Spatial Recognition Memory in Tg2576 AD Mouse Model

Tau-targeted immunotherapy is a promising approach for treatment of Alzheimer's disease (AD). Beyond cognitive decline, AD features visual deficits consistent with the manifestation of Amyloid β-protein (Aβ) plaques and neurofibrillary tangles (NFT) in the eyes and higher visual centers, both in animal models and affected subjects. We reported that 12A12-a monoclonal cleavage-specific antibody (mAb) which in vivo neutralizes the neurotoxic, N-terminal 20-22 kDa tau fragment(s)-significantly reduces the retinal accumulation in Tg(HuAPP695Swe)2576 mice of both tau and APP/Aβ pathologies correlated with local inflammation and synaptic deterioration. Here, we report the occurrence of N-terminal tau cleavage in the primary visual cortex (V1 area) and the beneficial effect of 12A12mAb treatment on phenotype-associated visuo-spatial deficits in this AD animal model. We found out that non-invasive administration of 12 A12mAb markedly reduced the pathological accumulation of both truncated tau and Aβ in the V1 area, correlated to significant improvement in visual recognition memory performance along with local increase in two direct readouts of cortical synaptic plasticity, including the dendritic spine density and the expression level of activity-regulated cytoskeleton protein Arc/Arg3.1. Translation of these findings to clinical therapeutic interventions could offer an innovative tau-directed opportunity to delay or halt the visual impairments occurring during AD progression.

Prevention of microgliosis halts early memory loss in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline, the neuropathological formation of amyloid-beta (Aβ) plaques and neurofibrillary tangles. The best cellular correlates of the early cognitive deficits in AD patients are synapse loss and gliosis. In particular, it is unclear whether the activation of microglia (microgliosis) has a neuroprotective or pathological role early in AD. Here we report that microgliosis is an early mediator of synaptic dysfunction and cognitive impairment in APP/PS1 mice, a mouse model of increased amyloidosis. We found that the appearance of microgliosis, synaptic dysfunction and behavioral impairment coincided with increased soluble Aβ₄₂ levels, and occurred well before the presence of Aβ plaques. Inhibition of microglial activity by treatment with minocycline (MC) reduced gliosis, synaptic deficits and cognitive impairments at early pathological stages and was most effective when provided preventive, i.e., before the onset of microgliosis. Interestingly, soluble Aβ levels or Aβ plaques deposition were not affected by preventive MC treatment at an early pathological stage (4 months) whereas these were reduced upon treatment at a later stage (6 months). In conclusion, this study demonstrates the importance of early-stage prevention of microgliosis on the development of cognitive impairment in APP/PS1 mice, which might be clinically relevant in preventing memory loss and delaying AD pathogenesis.

Amyloid precursor protein (APP) and amyloid β (Aβ) interact with cell adhesion molecules: Implications in Alzheimer’s disease and normal physiology

Alzheimer’s disease (AD) is an incurable neurodegenerative disorder in which dysfunction and loss of synapses and neurons lead to cognitive impairment and death. Accumulation and aggregation of neurotoxic amyloid-β (Aβ) peptides generated via amyloidogenic processing of amyloid precursor protein (APP) is considered to play a central role in the disease etiology. APP interacts with cell adhesion molecules, which influence the normal physiological functions of APP, its amyloidogenic and non-amyloidogenic processing, and formation of Aβ aggregates. These cell surface glycoproteins also mediate attachment of Aβ to the neuronal cell surface and induce intracellular signaling contributing to Aβ toxicity. In this review, we discuss the current knowledge surrounding the interactions of cell adhesion molecules with APP and Aβ and analyze the evidence of the critical role these proteins play in regulating the processing and physiological function of APP as well as Aβ toxicity. This is a necessary piece of the complex AD puzzle, which we should understand in order to develop safe and effective therapeutic interventions for AD.

Pathological characterization of a novel mouse model expressing the PD-linked CHCHD2-T61I mutation

Coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) is a mitochondrial protein that plays important roles in cristae structure, oxidative phosphorylation and apoptosis. Multiple mutations in CHCHD2 have been associated with Lewy body disorders (LBDs), such as Parkinson's disease (PD) and dementia with Lewy bodies, with the CHCHD2-T61I mutation being the most widely studied. However, at present, only CHCHD2 knockout or CHCHD2/CHCHD10 double knockout mouse models have been investigated. They do not recapitulate the pathology seen in patients with CHCHD2 mutations. We generated the first transgenic mouse model expressing the human PD-linked CHCHD2-T61I mutation driven by the mPrP promoter. We show that CHCHD2-T61I Tg mice exhibit perinuclear mitochondrial aggregates, neuroinflammation, and have impaired long-term synaptic plasticity associated with synaptic dysfunction. Dopaminergic neurodegeneration, a hallmark of PD, is also observed along with α-synuclein pathology. Significant motor dysfunction is seen with no changes in learning and memory at 1 year of age. A minor proportion of the CHCHD2-T61I Tg mice (~10%) show a severe motor phenotype consistent with human Pisa Syndrome, an atypical PD phenotype. Unbiased proteomics analysis reveals surprising increases in many insoluble proteins predominantly originating from mitochondria and perturbing multiple canonical biological pathways as assessed by ingenuity pathway analysis, including neurodegenerative disease-associated proteins such as tau, cofilin, SOD1 and DJ-1. Overall, CHCHD2-T61I Tg mice exhibit pathological and motor changes associated with LBDs, indicating that this model successfully captures phenotypes seen in human LBD patients with CHCHD2 mutations and demonstrates changes in neurodegenerative disease-associated proteins, which delineates relevant pathological pathways for further investigation.

Modulation of synaptic plasticity, motor unit physiology, and TDP-43 pathology by CHCHD10

Mutations in CHCHD10, a gene coding for a mitochondrial intermembrane space protein, are associated with Frontotemporal dementia (FTD)-Amyotrophic lateral sclerosis (ALS) spectrum disorders, which are pathologically characterized by cytoplasmic inclusions containing TDP-43. FTD/ALS-linked CHCHD10 mutations and TDP-43 inclusions similarly induce mitochondrial defects in respiration, fusion/fission, mtDNA stability, and cristae structure, while sizeable amounts of cytoplasmic TDP-43 aggregates are found in mitochondria. However, the mechanistic link between CHCHD10 and TDP-43 pathogenesis remains unclear. In this study, we present immunohistochemical and biochemical evidence demonstrating that insoluble CHCHD10 aggregates accumulate and colocalize with phospho-TDP-43 inclusions in brains of FTLD-TDP and AD patients, and that insoluble CHCHD10 levels tightly correlate with insoluble TDP-43 levels in control and FTLD-TDP brains. In an experimental exploration of this pathological phenotype, transgenic mice neuronally expressing FTD/ALS-linked CHCHD10R15L or CHCHDS59L mutations but not CHCHD10WT transgenic mice exhibit significantly increased CHCHD10 aggregation and phospho-TDP-43 pathology, which often colocalize within the same inclusions. Such pathologies are reflected in poor functional outcomes in long-term synaptic plasticity, motor unit physiology, and behavior in CHCHD10R15L and CHCHDS59L transgenic mice. In contrast, expression of CHCHD10WT in hTDP-43 transgenic mice (TAR4;CHCHD10WT) significantly mitigates phospho-TDP-43 pathology and rescues TDP-43-induced impairments in synaptic integrity and long-term synaptic plasticity. In isolated mitochondria, the S59L mutation induces the aggregation of resident CHCHD10S59L protein as well as the aggregation and slower turnover of recombinant TDP-43 imported into mitochondria. Likewise, in an in vitro cell-free system, the S59L mutation induces the aggregation of CHCHD10S59L protein while simultaneously enhancing the aggregation of recombinant TDP-43, as evidenced by filter trap assays and atomic force microscopy. In contrast, recombinant CHCHD10WT inhibits the growth of TDP-43 aggregates. These results in human brains, transgenic mice, and in vitro systems substantiate the role of wild type and mutant CHCHD10 in modulating mitochondrial CHCHD10 and TDP-43 pathogenesis together with associated phenotypes in long-term synaptic plasticity and motor unit physiology in mice and humans.

Cepharanthine sensitizes human triple negative breast cancer cells to chemotherapeutic agent epirubicin via inducing cofilin oxidation-mediated mitochondrial fission and apoptosis

Inhibition of autophagy has been accepted as a promising therapeutic strategy in cancer, but its clinical application is hindered by lack of effective and specific autophagy inhibitors. We previously identified cepharanthine (CEP) as a novel autophagy inhibitor, which inhibited autophagy/mitophagy through blockage of autophagosome-lysosome fusion in human breast cancer cells. In this study we investigated whether and how inhibition of autophagy/mitophagy by cepharanthine affected the efficacy of chemotherapeutic agent epirubicin in triple negative breast cancer (TNBC) cells in vitro and in vivo. In human breast cancer MDA-MB-231 and BT549 cells, application of CEP (2 μM) greatly enhanced cepharanthine-induced inhibition on cell viability and colony formation. CEP interacted with epirubicin synergistically to induce apoptosis in TNBC cells via the mitochondrial pathway. We demonstrated that co-administration of CEP and epirubicin induced mitochondrial fission in MDA-MB-231 cells, and the production of mitochondrial superoxide was correlated with mitochondrial fission and apoptosis induced by the combination. Moreover, we revealed that co-administration of CEP and epirubicin markedly increased the generation of mitochondrial superoxide, resulting in oxidation of the actin-remodeling protein cofilin, which promoted formation of an intramolecular disulfide bridge between Cys39 and Cys80 as well as Ser3 dephosphorylation, leading to mitochondria translocation of cofilin, thus causing mitochondrial fission and apoptosis. Finally, in mice bearing MDA-MB-231 cell xenografts, co-administration of CEP (12 mg/kg, ip, once every other day for 36 days) greatly enhanced the therapeutic efficacy of epirubicin (2 mg/kg) as compared with administration of either drug alone. Taken together, our results implicate that a combination of cepharanthine with chemotherapeutic agents could represent a novel therapeutic strategy for the treatment of breast cancer.

A potential biomarker of preclinical Alzheimer's disease: The olfactory dysfunction and its pathogenesis-based neural circuitry impairments

The olfactory dysfunction can signal and act as a potential biomarker of preclinical AD. However, the precise regulatory mechanism of olfactory function on the neural pathogenesis of AD is still unclear. The impairment of neural networks in olfaction system has been shown to be tightly associated with AD. As key brain regions of the olfactory system, the olfactory bulb (OB) and the piriform cortex (PCx) have a profound influence on the olfactory function. Therefore, this review will explore the mechanism of olfactory dysfunction in preclinical AD in the perspective of abnormal neural networks in the OB and PCx and their associated brain regions, especially from two aspects of aberrant oscillations and synaptic plasticity damages, which help better understand the underlying mechanism of olfactory neural network damages related to AD.

Cofilin Signaling in the CNS Physiology and Neurodegeneration

All eukaryotic cells are composed of the cytoskeleton, which plays crucial roles in coordinating diverse cellular functions such as cell division, morphology, migration, macromolecular stabilization, and protein trafficking. The cytoskeleton consists of microtubules, intermediate filaments, and actin filaments. Cofilin, an actin-depolymerizing protein, is indispensable for regulating actin dynamics in the central nervous system (CNS) development and function. Cofilin activities are spatiotemporally orchestrated by numerous extra- and intra-cellular factors. Phosphorylation at Ser-3 by kinases attenuate cofilin’s actin-binding activity. In contrast, dephosphorylation at Ser-3 enhances cofilin-induced actin depolymerization. Cofilin functions are also modulated by various binding partners or reactive oxygen species. Although the mechanism of cofilin-mediated actin dynamics has been known for decades, recent research works are unveiling the profound impacts of cofilin dysregulation in neurodegenerative pathophysiology. For instance, oxidative stress-induced increase in cofilin dephosphorylation is linked to the accumulation of tau tangles and amyloid-beta plaques in Alzheimer’s disease. In Parkinson’s disease, cofilin activation by silencing its upstream kinases increases α-synuclein-fibril entry into the cell. This review describes the molecular mechanism of cofilin-mediated actin dynamics and provides an overview of cofilin’s importance in CNS physiology and pathophysiology.

Synaptic tau: A pathological or physiological phenomenon?

In this review, we discuss the synaptic aspects of Tau pathology occurring during Alzheimer's disease (AD) and how this may relate to memory impairment, a major hallmark of AD. Whilst the clinical diagnosis of AD patients is a loss of working memory and long-term declarative memory, the histological diagnosis is the presence of neurofibrillary tangles of hyperphosphorylated Tau and Amyloid-beta plaques. Tau pathology spreads through synaptically connected neurons to impair synaptic function preceding the formation of neurofibrillary tangles, synaptic loss, axonal retraction and cell death. Alongside synaptic pathology, recent data suggest that Tau has physiological roles in the pre- or post- synaptic compartments. Thus, we have seen a shift in the research focus from Tau as a microtubule-stabilising protein in axons, to Tau as a synaptic protein with roles in accelerating spine formation, dendritic elongation, and in synaptic plasticity coordinating memory pathways. We collate here the myriad of emerging interactions and physiological roles of synaptic Tau, and discuss the current evidence that synaptic Tau contributes to pathology in AD.

Reactive astrocytes as treatment targets in Alzheimer's disease-Systematic review of studies using the APPswePS1dE9 mouse model

Astrocytes regulate synaptic communication and are essential for proper brain functioning. In Alzheimer's disease (AD) astrocytes become reactive, which is characterized by an increased expression of intermediate filament proteins and cellular hypertrophy. Reactive astrocytes are found in close association with amyloid-beta (Aβ) deposits. Synaptic communication and neuronal network function could be directly modulated by reactive astrocytes, potentially contributing to cognitive decline in AD. In this review, we focus on reactive astrocytes as treatment targets in AD in the APPswePS1dE9 AD mouse model, a widely used model to study amyloidosis and gliosis. We first give an overview of the model; that is, how it was generated, which cells express the transgenes, and the effect of its genetic background on Aβ pathology. Subsequently, to determine whether modifying reactive astrocytes in AD could influence pathogenesis and cognition, we review studies using this mouse model in which interventions were directly targeted at reactive astrocytes or had an indirect effect on reactive astrocytes. Overall, studies specifically targeting astrocytes to reduce astrogliosis showed beneficial effects on cognition, which indicates that targeting astrocytes should be included in developing novel therapies for AD.

Cofilin and Neurodegeneration: New Functions for an Old but Gold Protein

Cofilin is an actin-binding protein that plays a major role in the regulation of actin dynamics, an essential cellular process. This protein has emerged as a crucial molecule for functions of the nervous system including motility and guidance of the neuronal growth cone, dendritic spine organization, axonal branching, and synaptic signalling. Recently, other important functions in cell biology such as apoptosis or the control of mitochondrial function have been attributed to cofilin. Moreover, novel mechanisms of cofilin function regulation have also been described. The activity of cofilin is controlled by complex regulatory mechanisms, with phosphorylation being the most important, since the addition of a phosphate group to cofilin renders it inactive. Due to its participation in a wide variety of key processes in the cell, cofilin has been related to a great variety of pathologies, among which neurodegenerative diseases have attracted great interest. In this review, we summarized the functions of cofilin and its regulation, emphasizing how defects in these processes have been related to different neurodegenerative diseases.

Subcommissural Organ-Spondin-Derived Peptide Restores Memory in a Mouse Model of Alzheimer's Disease

Alzheimer’s disease (AD) is a devastating neurodegenerative disease that affects millions of older people worldwide and is characterized by a progressive deterioration of cognitive functions, including learning and memory. There are currently very few approved treatments (i.e., acetylcholinesterase inhibitors such as donepezil), all of which are limited to the symptomatic control of AD and are associated with side effects that may result in discontinuation of treatment. Therefore, there is an urgent need to develop disease-modifying treatments to prevent AD-induced cognitive deficits. Subcommissural organ (SCO)-spondin is a brain-specific glycoprotein produced during embryogenesis and has a substantial impact on neuronal development. In the current study, we sought to evaluate the protective effects of the linear (NX210) and cyclized (NX210c) forms of a SCO-spondin-derived peptide on learning and memory in a mouse model of AD. Mice received an intracerebroventricular injection of Aβ_25–35 oligomers and were subsequently treated with intraperitoneal injections of vehicle, NX210 or NX210c of different doses (ranging from 0.1 to 30 mg/kg) and therapy paradigms (early or late stand-alone treatments, combination with donepezil or second-line treatment). Cognitive function was evaluated using Y-Maze, step-through latency passive avoidance (STPA) and Morris water maze (MWM) tests for up to 4 months. Early stage daily treatment with NX210 and NX210c decreased the levels of common pathological markers and features of AD, including Aβ_1–42, phosphorylated-tau, inflammation, astrogliosis and lipid peroxidation. Meanwhile, use of these drugs increased the levels of synaptophysin and postsynaptic density protein 95. Regardless of the experimental paradigm used, NX210 and NX210c prevented Aβ_25–35-induced decrease in spontaneous alternations (Y-Maze) and step-through latency into the dark compartment (STPA), and Aβ_25–35-induced increase in time needed to locate the immersed platform during the learning phase and decrease in time spent in the target quadrant during the retention phase (MWM). Interestingly, this study provides the novel evidence that the native and oxidized cyclic forms of the SCO-spondin-derived peptide reduce pathological factors associated with AD and restore learning and memory at both early and late disease stages. Overall, this study sheds light on the therapeutic potential of this innovative disease-modifying peptide to restore memory function in patients with AD.

Direct interaction of HIV gp120 with neuronal CXCR4 and CCR5 receptors induces cofilin-actin rod pathology via a cellular prion protein- and NOX-dependent mechanism

Nearly 50% of individuals with long-term HIV infection are affected by the onset of progressive HIV-associated neurocognitive disorders (HAND). HIV infiltrates the central nervous system (CNS) early during primary infection where it establishes persistent infection in microglia (resident macrophages) and astrocytes that in turn release inflammatory cytokines, small neurotoxic mediators, and viral proteins. While the molecular mechanisms underlying pathology in HAND remain poorly understood, synaptodendritic damage has emerged as a hallmark of HIV infection of the CNS. Here, we report that the HIV viral envelope glycoprotein gp120 induces the formation of aberrant, rod-shaped cofilin-actin inclusions (rods) in cultured mouse hippocampal neurons via a signaling pathway common to other neurodegenerative stimuli including oligomeric, soluble amyloid-β and proinflammatory cytokines. Previous studies showed that synaptic function is impaired preferentially in the distal proximity of rods within dendrites. Our studies demonstrate gp120 binding to either chemokine co-receptor CCR5 or CXCR4 is capable of inducing rod formation, and signaling through this pathway requires active NADPH oxidase presumably through the formation of superoxide (O2-) and the expression of cellular prion protein (PrPC). These findings link gp120-mediated oxidative stress to the generation of rods, which may underlie early synaptic dysfunction observed in HAND.

Role of Cofilin in Alzheimer's Disease

Alzheimer's disease (AD) is a degenerative neurological disease and has an inconspicuous onset and progressive development. Clinically, it is characterized by severe dementia manifestations, including memory impairment, aphasia, apraxia, loss of recognition, impairment of visual-spatial skills, executive dysfunction, and changes in personality and behavior. Its etiology is unknown to date. However, several cellular biological signatures of AD have been identified such as synaptic dysfunction, β-amyloid plaques, hyperphosphorylated tau, cofilin-actin rods, and Hirano bodies which are related to the actin cytoskeleton. Cofilin is one of the most affluent and common actin-binding proteins and plays a role in cell motility, migration, shape, and metabolism. They also play an important role in severing actin filament, nucleating, depolymerizing, and bundling activities. In this review, we summarize the structure of cofilins and their functional and regulating roles, focusing on the synaptic dysfunction, β-amyloid plaques, hyperphosphorylated tau, cofilin-actin rods, and Hirano bodies of AD.

SSH1 impedes SQSTM1/p62 flux and MAPT/Tau clearance independent of CFL (cofilin) activation

Accumulation of toxic protein assemblies and damaged mitochondria are key features of neurodegenerative diseases, which arise in large part from clearance defects in the Macroautophagy/autophagy-lysosome system. The autophagy cargo receptor SQSTM1/p62 plays a major role in the clearance of ubiquitinated cargo through Ser403 phosphorylation by multiple kinases. However, no phosphatase is known to physiologically dephosphorylate SQSTM1 on this activating residue. RNAi-mediated knockdown and overexpression experiments using genetically encoded fluorescent reporters and defined mutant constructs in cell lines, primary neurons, and brains show that SSH1, the canonical CFL (cofilin) phosphatase, mediates the dephosphorylation of phospho-Ser403-SQSTM1, thereby impairing SQSTM1 flux and phospho-MAPT/tau clearance. The inhibitory action of SSH1 on SQSTM1 is fully dependent on SQSTM1 Ser403 phosphorylation status and is separable from SSH1-mediated CFL activation. These findings reveal a unique action of SSH1 on SQSTM1 independent of CFL and implicate an inhibitory role of SSH1 in SQSTM1-mediated clearance of autophagic cargo, including phospho-MAPT/tau. Abbreviations: AAV: adeno-associated virus; Aβ42_O: amyloid β1-42 oligomers; AD: Alzheimer disease; CA3: cornu Ammonis 3; CSNK2/CK2: casein kinase 2; FCCP: 2-[2-[4-(trifluoromethoxy)phenyl]hydrazinylidene]-propanedinitrile; FTLD: frontotemporal lobar degeneration; GFP: green fluorescent protein; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; SQSTM1/p62: sequestosome-1; PLA: proximity ligation assay; RFP: red fluorescent protein; RIPA: radioimmunoprecipitation assay; shRNA: short hairpin RNA; siRNA: small interfering RNA; Ser403: Serine403; SSH1: slingshot protein phosphatase 1; TBK1: TANK-binding kinase 1; ULK: unc-51 like kinase 1.

Small-molecule modulation of the p75 neurotrophin receptor inhibits a wide range of tau molecular pathologies and their sequelae in P301S tauopathy mice

In tauopathies, phosphorylation, acetylation, cleavage and other modifications of tau drive intracellular generation of diverse forms of toxic tau aggregates and associated seeding activity, which have been implicated in subsequent synaptic failure and neurodegeneration. Suppression of this wide range of pathogenic species, seeding and toxicity mechanisms, while preserving the physiological roles of tau, presents a key therapeutic goal. Identification and targeting of signaling networks that influence a broad spectrum of tau pathogenic mechanisms might prevent or reverse synaptic degeneration and modify disease outcomes. The p75 neurotrophin receptor (p75NTR) modulates such networks, including activation of multiple tau kinases, calpain and rhoA-cofilin activity. The orally bioavailable small-molecule p75NTR modulator, LM11A-31, was administered to tauP301S mice for 3 months starting at 6 months of age, when tau pathology was well established. LM11A-31 was found to reduce: excess activation of hippocampal cdk5 and JNK kinases and calpain; excess cofilin phosphorylation, tau phosphorylation, acetylation and cleavage; accumulation of multiple forms of insoluble tau aggregates and filaments; and, microglial activation. Hippocampal extracts from treated mice had substantially reduced tau seeding activity. LM11A-31 treatment also led to a reversal of pyramidal neuron dendritic spine loss, decreased loss of dendritic complexity and improvement in performance of hippocampal behaviors. These studies identify a therapeutically tractable upstream signaling module regulating a wide spectrum of basic mechanisms underlying tauopathies.

Dysregulation of cofilin-1 activity-the missing link between herpes simplex virus type-1 infection and Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial disease triggered by environmental factors in combination with genetic predisposition. Infectious agents, in particular herpes simplex virus type 1 (HSV-1), are gradually being recognised as important factors affecting the development of AD. However, the mechanism linking HSV-1 and AD remains unknown. Of note, HSV-1 manipulates the activity of cofilin-1 to ensure their efficient infection in neuron cells. Cofilin-1, the main regulator of actin cytoskeleton reorganization, is implicating for the plastic of dendritic spines and axon regeneration of neuronal cells. Moreover, dysfunction of cofilin-1 is observed in most AD patients, as well as in mice with AD and ageing. Further, inhibition of cofilin-1 activity ameliorates the host cognitive impairment in an animal model of AD. Together, dysregulation of cofilin-1 led by HSV-1 infection is a potential link between HSV-1 and AD. Herein, we critically summarize the role of cofilin-1-mediated actin dynamics in both HSV-1 infection and AD, respectively. We also propose several hypotheses regarding the connecting roles of cofilin-1 dysregulation in HSV-1 infection and AD. Our review provides a foundation for future studies targeting individuals carrying HSV-1 in combination with cofilin-1 to promote a more individualised approach for treatment and prevention of AD.

Actin(g) on mitochondria - a role for cofilin1 in neuronal cell death pathways

Actin dynamics, the coordinated assembly and disassembly of actin filaments (F-actin), are essential for fundamental cellular processes, including cell shaping and motility, cell division or organelle transport. Recent studies highlighted a novel role for actin dynamics in the regulation of mitochondrial morphology and function, for example, through mitochondrial recruitment of dynamin-related protein 1 (Drp1), a key factor in the mitochondrial fission machinery. Mitochondria are dynamic organelles, and permanent fission and fusion is essential to maintain their function in energy metabolism, calcium homeostasis and regulation of reactive oxygen species (ROS). Here, we summarize recent insights into the emerging role of cofilin1, a key regulator of actin dynamics, for mitochondrial shape and function under physiological conditions and during cellular stress, respectively. This is of peculiar importance in neurons, which are particularly prone to changes in actin regulation and mitochondrial integrity and function. In neurons, cofilin1 may contribute to degenerative processes through formation of cofilin-actin rods, and through enhanced mitochondrial fission, mitochondrial membrane permeabilization, and the release of cytochrome c. Overall, mitochondrial impairment induced by dysfunction of actin-regulating proteins such as cofilin1 emerge as important mechanisms of neuronal death with relevance to acute brain injury and neurodegenerative diseases, such as Parkinson's or Alzheimer's disease.

Decreased circadian fluctuation in cognitive behaviors and synaptic plasticity in APP/PS1 transgenic mice

Cognitive decline, memory impairment and circadian rhythm disturbance are iconic manifestations of Alzheimer's disease (AD). APPswe/PS1dE9 (APP/PS1) mice, a model of AD, show deficits in multiple learning and memory abilities, synaptic plasticity, and behavioral circadian rhythm, but whether circadian differences in cognitive performance and synaptic plasticity could be affected in AD remain unclear. Here, the cognitive behaviors of 6-month-old APP/PS1 mice were assessed by multiple behavior tests in the rest phase (light period) or active phase (dark period) of the day. The possible electrophysiological mechanism was subsequently investigated by in vivo hippocampal long-term potentiation (LTP) recording, and the locomotor activity rhythm of the mice was detected using wheel-running activities. Compared to wild-type (WT) mice, APP/PS1 mice exhibited long-term spatial memory impairment and in vivo hippocampal LTP suppression. In addition, in APP/PS1 mice, circadian differences in new object recognition memory and LTP were lost, and the circadian difference in long-term spatial memory was decreased, accompanied by a less robust locomotor activity rhythm. These results indicate that the loss of circadian differences in new object recognition memory and the decrease in the circadian difference in long-term spatial memory in APP/PS1 mice, which are closely associated with the loss of the circadian difference in LTP and less robust locomotor activity, might occur early in the course of AD.

Biased TAS2R Bronchodilators Inhibit Airway Smooth Muscle Growth by Downregulating Phosphorylated Extracellular Signal-regulated Kinase 1/2

Bitter taste receptor (TAS2R) agonists dilate airways by receptor-dependent smooth muscle relaxation. Besides their coupling to relaxation, we have found that human airway smooth muscle (HASM) cell TAS2Rs activate (phosphorylate) extracellular signal-related kinase 1/2 (ERK1/2), but the cellular effects are not known. In the present study, we show in HASM cells that TAS2R agonists initially stimulate phosphorylated ERK1/2 (pERK1/2) but by 24 hours cause a marked (50-70%) downregulation of pERK1/2 without a change in total ERK1/2. It was hypothesized that TAS2R agonists suppress cell growth through this pERK1/2 downregulation. Agonist-dependent inhibition of cell proliferation was indeed found in HASM cells derived from normal and asthmatic human lungs, as well as in an immortalized HASM cell line. pERK1/2 downregulation was linked to downregulation of the upstream kinase MEK1/2 (mitogen-activated protein kinase/extracellular signal-regulated kinase). Various structurally diverse TAS2R agonists evoked a range of inhibition of HASM proliferation, the magnitude of which directly correlated with the downregulation of pERK1/2 (R² = 0.86). Some TAS2R agonists were as effective as pharmacological inhibitors of Raf1 and MEK1/2 in suppressing growth. siRNA silencing of TAS2Rs (subtypes 10, 14, and 31) ablated the pERK1/2 and growth-inhibitory effects of TAS2R agonists. These phenotypes were attenuated by inhibiting the TAS2R G protein G_αi and by knocking down β-arrestin 1/2, indicating a dual pathway, although there may be additional mechanisms involved in this HASM TAS2R multidimensional signaling. Thus, TAS2R agonist structure can be manipulated to maintain the relaxation response and can be biased toward suppression of HASM growth. The latter response is of potential therapeutic benefit in asthma, in which an increase in smooth muscle mass contributes to airway obstruction.

The new genetic landscape of Alzheimer's disease: from amyloid cascade to genetically driven synaptic failure hypothesis?

A strong genetic predisposition (60–80% of attributable risk) is present in Alzheimer’s disease (AD). In view of this major genetic component, identification of the genetic risk factors has been a major objective in the AD field with the ultimate aim to better understand the pathological processes. In this review, we present how the genetic risk factors are involved in APP metabolism, β-amyloid peptide production, degradation, aggregation and toxicity, innate immunity, and Tau toxicity. In addition, on the basis of the new genetic landscape, resulting from the recent high-throughput genomic approaches and emerging neurobiological information, we propose an over-arching model in which the focal adhesion pathway and the related cell signalling are key elements in AD pathogenesis. The core of the focal adhesion pathway links the physiological functions of amyloid precursor protein and Tau with the pathophysiological processes they are involved in. This model includes several entry points, fitting with the different origins for the disease, and supports the notion that dysregulation of synaptic plasticity is a central node in AD. Notably, our interpretation of the latest data from genome wide association studies complements other hypotheses already developed in the AD field, i.e., amyloid cascade, cellular phase or propagation hypotheses. Genetically driven synaptic failure hypothesis will need to be further tested experimentally within the general AD framework.

HIV Associated Neurodegenerative Disorders: A New Perspective on the Role of Lipid Rafts in Gp120-Mediated Neurotoxicity

The implementation of combination antiretroviral therapy (cART) as the primary means of treatment for HIV infection has achieved a dramatic decline in deaths attributed to AIDS and the reduced incidence of severe forms of HIV-associated neurocognitive disorders (HAND) in infected individuals. Despite these advances, milder forms of HAND persist and prevalence of these forms of neurocognitive impairment are rising with the aging population of HIV infected individuals. HIV enters the CNS early in the pathophysiology establishing persistent infection in resident macrophages and glial cells. These infected cells, in turn, secrete neurotoxic viral proteins, inflammatory cytokines, and small metabolites thought to contribute to neurodegenerative processes. The viral envelope protein gp120 has been identified as a potent neurotoxin affecting neurodegeneration via indirect and direct mechanisms involving interactions with chemokine co-receptors CCR5 and CXCR4. This short review focuses on gp120 neurotropism and associated mechanisms of neurotoxicity linked to chemokine receptors CCR5 and CXCR4 with a new perspective on plasma membrane lipid rafts as an active participant in gp120-mediated neurodegeneration underlying HIV induced CNS pathology.

Endothelin type B receptor promotes cofilin rod formation and dendritic loss in neurons by inducing oxidative stress and cofilin activation

Endothelin-1 (ET-1) is a neuroactive peptide produced by neurons, reactive astrocytes, and endothelial cells in the brain. Elevated levels of ET-1 have been detected in the post-mortem brains of individuals with Alzheimer's disease (AD). We have previously demonstrated that overexpression of astrocytic ET-1 exacerbates memory deficits in aged mice or in APP^K670/M671 mutant mice. However, the effects of ET-1 on neuronal dysfunction remain elusive. ET-1 has been reported to mediate superoxide formation in the vascular system via NADPH oxidase (NOX) and to regulate the actin cytoskeleton of cancer cell lines via the cofilin pathway. Interestingly, oxidative stress and cofilin activation were both reported to mediate one of the AD histopathologies, cofilin rod formation in neurons. This raises the possibility that ET-1 mediates neurodegeneration via oxidative stress- or cofilin activation-driven cofilin rod formation. Here, we demonstrate that exposure to 100 nm ET-1 or to a selective ET type B receptor (ET_B) agonist (IRL1620) induces cofilin rod formation in dendrites of primary hippocampal neurons, accompanied by a loss of distal dendrites and a reduction in dendritic length. The 100 nm IRL1620 exposure induced superoxide formation and cofilin activation, which were abolished by pretreatment with a NOX inhibitor (5 μm VAS2870). Moreover, IRL1620-induced cofilin rod formation was partially abolished by pretreatment with a calcineurin inhibitor (100 nm FK506), which suppressed cofilin activation. In conclusion, our findings suggest a role for ET_B in neurodegeneration by promoting cofilin rod formation and dendritic loss via NOX-driven superoxide formation and cofilin activation.

Early Synaptic Alterations and Selective Adhesion Signaling in Hippocampal Dendritic Zones Following Organophosphate Exposure

Organophosphates account for many of the world's deadliest poisons. They inhibit acetylcholinesterase causing cholinergic crises that lead to seizures and death, while survivors commonly experience long-term neurological problems. Here, we treated brain explants with the organophosphate compound paraoxon and uncovered a unique mechanism of neurotoxicity. Paraoxon-exposed hippocampal slice cultures exhibited progressive declines in synaptophysin, synapsin II, and PSD-95, whereas reduction in GluR1 was slower and NeuN and Nissl staining showed no indications of neuronal damage. The distinctive synaptotoxicity was observed in dendritic zones of CA1 and dentate gyrus. Interestingly, declines in synapsin II dendritic labeling correlated with increased staining for β1 integrin, a component of adhesion receptors that regulate synapse maintenance and plasticity. The paraoxon-induced β1 integrin response was targeted to synapses, and the two-fold increase in β1 integrin was selective as other synaptic adhesion molecules were unchanged. Additionally, β1 integrin-cofilin signaling was triggered by the exposure and correlations were found between the extent of synaptic decline and the level of β1 integrin responses. These findings identified organophosphate-mediated early and lasting synaptotoxicity which can explain delayed neurological dysfunction later in life. They also suggest that the interplay between synaptotoxic events and compensatory adhesion responses influences neuronal fate in exposed individuals.

Impaired osteoblastic behavior and function on saliva-contaminated titanium and its restoration by UV treatment

The objective of this study was to examine behavior and function of osteoblasts on saliva-contaminated titanium and its potential improvement after UV light treatment. Acid-etched titanium disks were contaminated with human saliva. Osteoblasts derived from rat femur were cultured on contaminated and clean titanium disks. Contaminated disks further treated with UV light were also tested. The number of attached cells, the degree of cell spreading, and the expression of adhesion protein were significantly decreased on saliva-contaminated surfaces compared with clean surfaces. The gene expression of osteocalcin was also downregulated on contaminated surfaces, whereas ALP activity and mineralization were not significantly influenced. The impaired functions on contaminated surfaces were significantly increased if the surfaces were further treated with UV and even outperformed the ones on clean titanium surfaces. XPS analysis revealed that the atomic percentage of carbon and nitrogen detected on contaminated surfaces were substantially decreased after UV treatment. These results suggest that osteoblastic behavior and function were compromised on titanium surfaces contaminated with saliva. The compromised functions no longer happened if the surfaces were further treated with UV light, providing the basis to understand the effect of biological contamination on osseointegration and to explore UV treatment as a decontaminating technology.

Modulating Conformation of Aβ-Peptide: An Effective Way to Prevent Protein-Misfolding Disease

Alzheimer's disease (AD) is a typical protein-misfolding disease. Aggregation of amyloid β-peptide (Aβ) plays a key role in the etiology of AD. The misfolding of Aβ results in the formation of β-sheet-rich aggregates and damages the function of neurons. A modified polyoxometalate (POM), [CoL(H₂O)]₂[CoL]₂[HAs^VMo^V₆Mo^VI₆O₄₀] [CAM, L = 2-(1 H-pyrazol-3-yl)pyridine], was designed to disaggregate the Aβ aggregates, where L acts as an Aβ-targeting group and POM as a conformational modulator. X-ray crystallography shows that CAM is composed of a ε-Keggin unit and four coordination units. CAM can disaggregate the β-sheet-rich fibrils and metal-induced or self-aggregated Aβ aggregates, and it further inhibits the production of ROS; as a result, it can protect the neurons from synaptic toxicity induced by Zn²⁺- or Cu²⁺-Aβ aggregates or Aβ self-aggregation. The mechanism of disaggregation involves a transformation of Aβ conformation from β-sheet to other conformers. The nature of the process is an interference of the β-sheet conformation by CAM via hydrogen bonding. CAM specifically interacts with Aβ aggregates but does not disturb the cerebral metal homeostasis and enzymatic systems. Molecular simulation suggests that the appropriate size of CAM and the cavity of β-sheets facilitate the interaction between CAM and Aβ aggregates; additionally, the H-bonding-favored amino acid residues in the cavity provide a precondition for the interaction. Moreover, CAM is lipophilic and capable of penetrating the blood-brain barrier, and it is metabolizable without causing an untoward effect to mice at high dosages. In view of the significant inhibitory effect on the Aβ aggregation and related neurotoxicity, CAM represents a new type of leading compounds with a distinctive mechanism of action for the treatment of Alzheimer' disease. The conception of this study may be applied to other protein-misfolding diseases caused by conformational changes.

Synaptotoxicity in Alzheimer's Disease Involved a Dysregulation of Actin Cytoskeleton Dynamics through Cofilin 1 Phosphorylation

Amyloid-β (Aβ) drives the synaptic impairment and dendritic spine loss characteristic of Alzheimer's disease (AD), but how Aβ affects the actin cytoskeleton remains unknown and contentious. The actin-binding protein, cofilin-1 (cof1), is a major regulator of actin dynamics in dendritic spines, and is subject to phospho-regulation by multiple pathways, including the Rho-associated protein kinase (ROCK) pathway. While cof1 is implicated as a driver of the synaptotoxicity characteristic of the early phases of AD pathophysiology, questions remain about the molecular mechanisms involved. Cofilin-actin rods are observed in neurons exposed to Aβ oligomers (Aβo) and in tissue from AD patients, and others have described an increased cofilin phosphorylation (p-cof1) in AD patients. Here, we report elevated p-cof1 of the postsynaptic enriched fraction of synaptosomes from cortical samples of male APP/PS1 mice and human AD cases of either sex. In primary cortical neurons, Aβo induced rapid actin stabilization and increased p-cof1 in the postsynaptic compartment of excitatory synapses within 30 min. Fluorescence recovery after photobleaching of actin-GFP and calcium imaging in live neurons expressing active or inactive cof1 mutants suggest that cof1 phosphorylation is necessary and sufficient for Aβo-induced synaptic impairment via actin stabilization before the reported formation of cofilin-actin rods. Moreover, the clinically available and well-tolerated ROCK inhibitor, fasudil, prevented Aβo-induced actin stabilization, synaptic impairment, and synaptic loss by blocking cofilin phosphorylation. Aβo also blocked the LTP-induced insertion of the AMPAR subunit, GluA1, at the postsynaptic density, in a fasudil-sensitive manner. These data support an important role for ROCKs and cofilin in mediating Aβ-induced synaptic impairment.SIGNIFICANCE STATEMENT We report that amyloid-β oligomers rapidly induce aberrant stabilization of F-actin within dendritic spines, which impairs synaptic strength and plasticity. Activation of the Rho-associated protein kinase (ROCK) pathway results in phosphorylation of cof1 and is sufficient to mediate Aβo-induced actin stabilization synaptic impairment and synaptic loss. Further, the ROCK inhibitor, fasudil, prevents cofilin phosphorylation, acute synaptic disruption, and synaptotoxicity in primary cortical neurons. Together, the herein presented data provide strong support for further study of the ROCK pathway as a therapeutic target for the cognitive decline and synaptotoxicity in Alzheimer's disease.

Colivelin Ameliorates Impairments in Cognitive Behaviors and Synaptic Plasticity in APP/PS1 Transgenic Mice

Alzheimer's disease (AD) is the most common cause of dementia, and effective therapeutics are lacking. Colivelin (CLN), a novel, strong humanin derivative, is effective in vitro in preventing cell death induced by AD-causative genes and amyloid-β protein (Aβ) even at a low concentration. We recently demonstrated that intrahippocampal injection of CLN prevents Aβ25-35-induced deficits in spatial memory and synaptic plasticity in normal rats. Here, we further observed the effects of chronically intranasally (i.n.) administered CLN on cognitive behaviors and pathological hallmarks in 9-month-old APPswe/PS1dE9 (APP/PS1) AD mice using multiple behavioral tests and immunochemistry. The electrophysiological mechanism of CLN neuroprotection was also investigated by recording in vivo hippocampal long-term potentiation (LTP). CLN pretreatment effectively prevented impairments in new object recognition, working memory, and long-term spatial memory and reversed the depression of in vivo hippocampal LTP in APP/PS1 mice. Additionally, chronic application of CLN obviously reduced Aβ deposition in the hippocampus in APP/PS1 mice. These results indicate that CLN has strong neuroprotective effects on learning and memory behaviors in APP/PS1 mice and that this behavioral improvement is closely associated with the reduction of Aβ deposition and alleviation of LTP suppression in the hippocampus, supporting the potential of CLN for the prevention and treatment of AD.

Isolation and Proteomic Analysis of Microvesicles and Exosomes from HT22 Cells and Primary Neurons

Exosomes and microvesicles are extracellular vesicles (EVs) released by most cell types. The role of EVs as a method of intercellular communication has led to these vesicles becoming a major area of interest in a variety of scientific fields including neuroscience. Emerging evidence is now demonstrating that the biomolecular composition of EVs, especially exosomes, can play a role in the progression of disease including various neurodegenerative diseases and cancer. In addition to the miRNA profiles of EVs, these vesicles also show interesting changes in protein expression profiles under different physiological and pathological conditions. Characterization of these profiles could prove valuable for both understanding disease pathogenesis and for the discovery of new biomarkers of disease. In this chapter, we describe a protocol for isolation of exosomes and microvesicles from immortalized HT22 cells and primary cortical neurons with sufficient yield and low serum contamination required for downstream analysis and label-free relative quantitation by mass spectrometry.

Integrin-β4 is a novel transcriptional target of TAp73

As a member of p53 family, p73 has attracted intense investigations due to its structural and functional similarities to p53. Among more than ten p73 variants, the transactivation (TA) domain-containing isoform TAp73 is the one that imitates the p53's behavior most. TAp73 induces apoptosis and cell cycle arrest, which endows it the capacity of tumour suppression. Also, it can exert diverse biological influences on cells through activating a complex and context dependent transcriptional programme. The transcriptional activities further broaden its roles in more intricate biological processes. In this article, we report that p73 is a positive regulator of a cell adhesion related gene named integrin β4 (ITGB4). This finding may have implications for the dissection of the biological mechanisms underlining p73 functions.

Aβ mediates F-actin disassembly in dendritic spines leading to cognitive deficits in Alzheimer's disease

Dendritic spine loss is recognized as an early feature of Alzheimer's disease (AD), but the underlying mechanisms are poorly understood. Dendritic spine structure is defined by filamentous actin (F-actin) and we observed depolymerization of synaptosomal F-actin accompanied by increased globular-actin (G-actin) at as early as 1 month of age in a mouse model of AD (APPswe/PS1ΔE9, male mice). This led to recall deficit after contextual fear conditioning (cFC) at 2 months of age in APPswe/PS1ΔE9 male mice, which could be reversed by the actin-polymerizing agent jasplakinolide. Further, the F-actin-depolymerizing agent latrunculin induced recall deficit after cFC in WT mice, indicating the importance of maintaining F-/G-actin equilibrium for optimal behavioral response. Using direct stochastic optical reconstruction microscopy (dSTORM), we show that F-actin depolymerization in spines leads to a breakdown of the nano-organization of outwardly radiating F-actin rods in cortical neurons from APPswe/PS1ΔE9 mice. Our results demonstrate that synaptic dysfunction seen as F-actin disassembly occurs very early, before onset of pathological hallmarks in AD mice, and contributes to behavioral dysfunction, indicating that depolymerization of F-actin is causal and not consequent to decreased spine density. Further, we observed decreased synaptosomal F-actin levels in postmortem brain from mild cognitive impairment and AD patients compared with subjects with normal cognition. F-actin decrease correlated inversely with increasing AD pathology (Braak score, Aβ load, and tangle density) and directly with performance in episodic and working memory tasks, suggesting its role in human disease pathogenesis and progression.SIGNIFICANCE STATEMENT Synaptic dysfunction underlies cognitive deficits in Alzheimer's disease (AD). The cytoskeletal protein actin plays a critical role in maintaining structure and function of synapses. Using cultured neurons and an AD mouse model, we show for the first time that filamentous actin (F-actin) is lost selectively from synapses early in the disease process, long before the onset of classical AD pathology. We also demonstrate that loss of synaptic F-actin contributes directly to memory deficits. Loss of synaptosomal F-actin in human postmortem tissue correlates directly with decreased performance in memory test and inversely with AD pathology. Our data highlight that synaptic cytoarchitectural changes occur early in AD and they may be targeted for the development of therapeutics.

Partial Amelioration of Synaptic and Cognitive Deficits by Inhibiting Cofilin Dephosphorylation in an Animal Model of Alzheimer's Disease

The loss of synaptic structure and function has been linked to the cognitive impairment of Alzheimer's disease (AD). Dysregulation of the actin cytoskeleton, which plays a key role in regulating the integrity of synapses and the transport of synaptic proteins, has been suggested to contribute to the pathology of AD. In this study, we found that glutamate receptor surface expression and synaptic function in frontal cortical neurons were significant diminished in a familial AD (FAD) model, which was correlated with the reduction of phosphorylated cofilin, a key protein regulating the dynamics of actin filaments. Injecting a cofilin dephosphorylation inhibitory peptide to FAD mice led to the partial rescue of the surface expression of AMPA and NMDA receptor subunits, as well as the partial restoration of AMPAR- and NMDAR-mediated synaptic currents. Moreover, the impaired working memory and novel object recognition memory in FAD mice were partially ameliorated by injections of the cofilin dephosphorylation inhibitory peptide. These results suggest that targeting the cofilin-actin signaling holds promise to mitigate the physiological and behavioral abnormality in AD.

Inhibitor of Endocannabinoid Deactivation Protects Against In Vitro and In Vivo Neurotoxic Effects of Paraoxon

The anticholinesterase paraoxon (Pxn) is related to military nerve agents that increase acetylcholine levels, trigger seizures, and cause excitotoxic damage in the brain. In rat hippocampal slice cultures, high-dose Pxn was applied resulting in a presynaptic vulnerability evidenced by a 64% reduction in synapsin IIb (syn IIb) levels, whereas the postsynaptic protein GluR1 was unchanged. Other signs of Pxn-induced cytotoxicity include the oxidative stress-related production of stable 4-hydroxynonenal (4-HNE)-protein adducts. Next, the Pxn toxicity was tested for protective effects by the fatty acid amide hydrolase (FAAH) inhibitor AM5206, a compound linked to enhanced repair signaling through the endocannabinoid pathway. The Pxn-mediated declines in syn IIb and synaptophysin were prevented by AM5206 in the slice cultures. To test if the protective results in the slice model translate to an in vivo model, AM5206 was injected i.p. into rats, followed immediately by subcutaneous Pxn administration. The toxin caused a pathogenic cascade initiated by seizure events, leading to presynaptic marker decline and oxidative changes in the hippocampus and frontal cortex. AM5206 exhibited protective effects including the reduction of seizure severity by 86%, and improving balance and coordination measured 24 h post-insult. As observed in hippocampal slices, the FAAH inhibitor also prevented the Pxn-induced loss of syn IIb in vivo. In addition, the AM5206 compound reduced the 4-HNE modifications of proteins and the β1 integrin activation events both in vitro and in vivo. These results indicate that Pxn exposure produces oxidative and synaptic toxicity that leads to the behavioral deficits manifested by the neurotoxin. In contrast, the presence of FAAH inhibitor AM5206 offsets the pathogenic cascade elicited by the Pxn anticholinesterase.

Peptide regulation of cofilin activity in the CNS: A novel therapeutic approach for treatment of multiple neurological disorders

Cofilin is a ubiquitous protein which cooperates with many other actin-binding proteins in regulating actin dynamics. Cofilin has essential functions in nervous system development including neuritogenesis, neurite elongation, growth cone pathfinding, dendritic spine formation, and the regulation of neurotransmission and spine function, components of synaptic plasticity essential for learning and memory. Cofilin's phosphoregulation is a downstream target of many transmembrane signaling processes, and its misregulation in neurons has been linked in rodent models to many different neurodegenerative and neurological disorders including Alzheimer disease (AD), aggression due to neonatal isolation, autism, manic/bipolar disorder, and sleep deprivation. Cognitive and behavioral deficits of these rodent models have been largely abrogated by modulation of cofilin activity using viral-mediated, genetic, and/or small molecule or peptide therapeutic approaches. Neuropathic pain in rats from sciatic nerve compression has also been reduced by modulating the cofilin pathway within neurons of the dorsal root ganglia. Neuroinflammation, which occurs following cerebral ischemia/reperfusion, but which also accompanies many other neurodegenerative syndromes, is markedly reduced by peptides targeting specific chemokine receptors, which also modulate cofilin activity. Thus, peptide therapeutics offer potential for cost-effective treatment of a wide variety of neurological disorders. Here we discuss some recent results from rodent models using therapeutic peptides with a surprising ability to cross the rodent blood brain barrier and alter cofilin activity in brain. We also offer suggestions as to how neuronal-specific cofilin regulation might be achieved.

Loss of function CHCHD10 mutations in cytoplasmic TDP-43 accumulation and synaptic integrity

Although multiple CHCHD10 mutations are associated with the spectrum of familial and sporadic frontotemporal dementia–amyotrophic lateral sclerosis (FTD–ALS) diseases, neither the normal function of endogenous CHCHD10 nor its role in the pathological milieu (that is, TDP-43 pathology) of FTD/ALS have been investigated. In this study, we made a series of observations utilizing Caenorhabditis elegans models, mammalian cell lines, primary neurons and mouse brains, demonstrating that CHCHD10 normally exerts a protective role in mitochondrial and synaptic integrity as well as in the retention of nuclear TDP-43, whereas FTD/ALS-associated mutations (R15L and S59L) exhibit loss of function phenotypes in C. elegans genetic complementation assays and dominant negative activities in mammalian systems, resulting in mitochondrial/synaptic damage and cytoplasmic TDP-43 accumulation. As such, our results provide a pathological link between CHCHD10-associated mitochondrial/synaptic dysfunction and cytoplasmic TDP-43 inclusions.

Mutations in CHCHD10 have been recently associated with frontotemporal dementia and amyotrophic lateral sclerosis. Here the authors study the functions of endogenous CHCHD10 in Caenorhabditis elegans, primary neurons, and mouse, and show that it normally protects mitochondria and synaptic integrity, and retains TDP-43 in the nucleus.

Cytoskeleton-Associated Risk Modifiers Involved in Early and Rapid Progression of Sporadic Creutzfeldt-Jakob Disease

A high priority in the prion field is to identify pre-symptomatic events and associated profile of molecular changes. In this study, we demonstrate the pre-symptomatic dysregulation of cytoskeleton assembly and its associated cofilin-1 pathway in strain and brain region-specific manners in MM1 and VV2 subtype-specific Creutzfeldt-Jakob disease at clinical and pre-clinical stage. At physiological level, PrP^C interaction with cofilin-1 and phosphorylated form of cofilin (p-cofilin(Ser3)) was investigated in primary cultures of mouse cortex neurons (PCNs) of PrP^C wild-type and knockout mice (PrP^-/-). Short-interfering RNA downregulation of active form of cofilin-1 resulted in the redistribution/downregulation of PrP^C, increase of activated form of microglia, accumulation of dense form of F-actin, and upregulation of p-cofilin(Ser3). This upregulated p-cofilin(Ser3) showed redistribution of expression predominantly in the activated form of microglia in PCNs. At pathological level, cofilin-1 expression was significantly altered in cortex and cerebellum in both humans and mice at pre-clinical stage and at early symptomatic clinical stage of the disease. Further, to better understand the possible mechanism of dysregulation of cofilin-1, we also demonstrated alterations in upstream regulators; LIM kinase isoform 1 (LIMK1), slingshot phosphatase isoform 1 (SSH1), RhoA-associated kinase (Rock2), and amyloid precursor protein (APP) in sporadic Creutzfeldt-Jakob disease MM1 mice and in human MM1 and VV2 frontal cortex and cerebellum samples. In conclusion, our findings demonstrated for the first time a key pre-clinical response of cofilin-1 and the associated pathway in prion disease.

Cellular levels of Grb2 and cytoskeleton stability are correlated in a neurodegenerative scenario

Alzheimer's disease (AD) manifests as neuronal loss. On the premise of Grb2 overexpression in AD mouse brain and brain tissues of AD patients, our study primarily focuses on the stability of cytoskeletal proteins in the context of degenerative AD-like conditions. Two predominant molecular features of AD, extracellular accumulation of β-amyloid oligomers and intracellular elevation of amyloid precursor protein intracellular domain levels, have been used to closely inspect the series of signalling events. In their presence, multiple signalling pathways involving ROCK and PAK1 proteins lead to disassembly of the cytoskeleton, and Grb2 partially counterbalances the cytoskeletal loss. Increased Grb2-NOX4 interactions play a preventive role against cytoskeletal disassembly, in turn blocking the activity of nitrogen oxides and decreasing the expression of slingshot homolog 1 (SSH-1) protein, a potent inducer of cytoskeleton disassembly. This study unravels a unique role of Grb2 in protecting the cytoskeletal architecture in AD-like conditions and presents a potential new strategy for controlling neurodegeneration.

Actin dynamics and cofilin-actin rods in alzheimer disease

Cytoskeletal abnormalities and synaptic loss, typical of both familial and sporadic Alzheimer disease (AD), are induced by diverse stresses such as neuroinflammation, oxidative stress, and energetic stress, each of which may be initiated or enhanced by proinflammatory cytokines or amyloid-β (Aβ) peptides. Extracellular Aβ-containing plaques and intracellular phospho-tau-containing neurofibrillary tangles are postmortem pathologies required to confirm AD and have been the focus of most studies. However, AD brain, but not normal brain, also have increased levels of cytoplasmic rod-shaped bundles of filaments composed of ADF/cofilin-actin in a 1:1 complex (rods). Cofilin, the major ADF/cofilin isoform in mammalian neurons, severs actin filaments at low cofilin/actin ratios and stabilizes filaments at high cofilin/actin ratios. It binds cooperatively to ADP-actin subunits in F-actin. Cofilin is activated by dephosphorylation and may be oxidized in stressed neurons to form disulfide-linked dimers, required for bundling cofilin-actin filaments into stable rods. Rods form within neurites causing synaptic dysfunction by sequestering cofilin, disrupting normal actin dynamics, blocking transport, and exacerbating mitochondrial membrane potential loss. Aβ and proinflammatory cytokines induce rods through a cellular prion protein-dependent activation of NADPH oxidase and production of reactive oxygen species. Here we review recent advances in our understanding of cofilin biochemistry, rod formation, and the development of cognitive deficits. We will then discuss rod formation as a molecular pathway for synapse loss that may be common between all three prominent current AD hypotheses, thus making rods an attractive therapeutic target. © 2016 Wiley Periodicals, Inc.

Epigenetic Treatment of Neurodegenerative Disorders: Alzheimer and Parkinson Diseases

Preclinical Research In this review, we discuss epigenetic-driven methods for treating neurodegenerative disorders associated with mitochondrial dysfunction, focusing on carnitinoid antioxidant-histone deacetylase inhibitors that show an ability to reinvigorate synaptic plasticity and protect against neuromotor decline in vivo. Aging remains a major risk factor in patients who progress to dementia, a clinical syndrome typified by decreased mental capacity, including impairments in memory, language skills, and executive function. Energy metabolism and mitochondrial dysfunction are viewed as determinants in the aging process that may afford therapeutic targets for a host of disease conditions, the brain being primary in such thinking. Mitochondrial dysfunction is a core feature in the pathophysiology of both Alzheimer and Parkinson diseases and rare mitochondrial diseases. The potential of new therapies in this area extends to glaucoma and other ophthalmic disorders, migraine, Creutzfeldt-Jakob disease, post-traumatic stress disorder, systemic exertion intolerance disease, and chemotherapy-induced cognitive impairment. An emerging and hopefully more promising approach to addressing these hard-to-treat diseases leverages their sensitivity to activation of master regulators of antioxidant and cytoprotective genes, antioxidant response elements, and mitophagy. Drug Dev Res 77 : 109-123, 2016. © 2016 Wiley Periodicals, Inc.