APP binds DR6 to trigger axon pruning and neuron death via distinct caspases

Visible-Light Optical Coherence Tomography Fibergraphy for Quantitative Imaging of Retinal Ganglion Cell Axon Bundles

Purpose

To develop a practical technique for visualizing and quantifying retinal ganglion cell (RGC) axon bundles in vivo.

Methods

We applied visible-light optical coherence tomography (vis-OCT) to image the RGC axon bundles, referred to as vis-OCT fibergraphy, of healthy wild-type C57BL/6 mice. After vis-OCT imaging, retinas were flat-mounted, immunostained with anti-beta-III tubulin (Tuj1) antibody for RGC axons, and imaged with confocal microscopy. We quantitatively compared the RGC axon bundle networks imaged by in vivo vis-OCT and ex vivo confocal microscopy using semi-log Sholl analysis.

Results

Side-by-side comparison of ex vivo confocal microscopy and in vivo vis-OCT confirmed that vis-OCT fibergraphy captures true RGC axon bundle networks. The semi-log Sholl regression coefficients extracted from vis-OCT fibergrams (3.7 ± 0.8 mm^–1) and confocal microscopy (3.6 ± 0.3 mm^–1) images also showed good agreement with each other (n = 6).

Conclusions

We demonstrated the feasibility of using vis-OCT fibergraphy to visualize RGC axon bundles. Further applying Sholl analysis has the potential to identify biomarkers for non-invasively assessing RGC health.

Translational Relevance

Our novel technique for visualizing and quantifying RGC axon bundles in vivo provides a potential measurement tool for diagnosing and tracking the progression of optic neuropathies.

Downregulation of synapse-associated protein expression and loss of homeostatic microglial control in cerebrospinal fluid of infectious patients with delirium and patients with Alzheimer's disease

Delirium is a complex and multifactorial condition associated with long-term cognitive decline. Due to the strong links between systemic inflammation, delirium and dementia we hypothesized that responses within the brain in patients who develop delirium could show biochemical overlap with patients with Alzheimer's disease (AD). In this observational study we analyzed protein expression signatures in cerebrospinal fluid (CSF) from 15 patients with infectious delirium and compared these to 29 patients with AD, 30 infectious patients without delirium and 15 non-infectious controls free of neurological disease. A proximity extension assay was performed measuring a total of 184 inflammatory and neurology-related proteins. Eight inflammatory proteins (4%), including the key neuron-microglia communication marker CX3CL1 (fractalkine), were significantly upregulated in both delirium and AD, compared to infectious patients without delirium. Likewise, 23 proteins (13%) showed downregulation in both delirium and AD, relative to infectious patients without delirium, which interestingly included CD200R1, another neuron-microglia communication marker, as well as a cluster of proteins related to synapse formation and function. Synaptopathy is an early event in AD and correlates strongly with cognitive dysfunction. These results were partially mediated by aging, which is an important predisposing risk factor among many others for both conditions. Within this study we report the first in vivo human evidence suggesting that synapse pathology and loss of homeostatic microglial control is involved in the pathophysiology of both infectious delirium and AD and thus may provide a link for the association between infections, delirium and long-term cognitive decline.

Modeling Mixed Vascular and Alzheimer's Dementia Using Focal Subcortical Ischemic Stroke in Human ApoE4-TR:5XFAD Transgenic Mice

Subcortical white matter ischemic lesions are increasingly recognized to have pathologic overlap in individuals with Alzheimer's disease (AD). The interaction of white matter ischemic lesions with amyloid pathology seen in AD is poorly characterized. We designed a novel mouse model of subcortical white matter ischemic stroke and AD that can inform our understanding of the cellular and molecular mechanisms of mixed vascular and AD dementia. Subcortical white matter ischemic stroke underlying forelimb motor cortex was induced by local stereotactic injection of an irreversible eNOS inhibitor. Subcortical white matter ischemic stroke or sham procedures were performed on human ApoE4-targeted-replacement (TR):5XFAD mice at 8 weeks of age. Behavioral tests were done at 7, 10, 15, and 20 weeks. A subset of animals underwent 18FDG-PET/CT. At 20 weeks of age, brain tissue was examined for amyloid plaque accumulation and cellular changes. Compared with sham E4-TR:5XFAD mice, those with an early subcortical ischemic stroke showed a significant reduction in amyloid plaque burden in the region of cortex overlying the subcortical stroke. Cognitive performance was improved in E4-TR:5XFAD mice with stroke compared with sham E4-TR:5XFAD animals. Iba-1+ microglial cells in the region of cortex overlying the subcortical stroke were increased in number and morphologic complexity compared with sham E4-TR:5XFAD mice, suggesting that amyloid clearance may be promoted by an interaction between activated microglia and cortical neurons in response to subcortical stroke. This novel approach to modeling mixed vascular and AD dementia provides a valuable tool for dissecting the molecular interactions between these two common pathologies.

Dysfunctional proteins in neuropsychiatric disorders: From neurodegeneration to autism spectrum disorders

Despite fundamental differences in disease course and outcomes, neurodevelopmental (autism spectrum disorders - ASD) and neurodegenerative disorders (Alzheimer's disease - AD and Parkinson's disease - PD) present surprising, common traits in their molecular pathomechanisms. Uncontrolled oligomerization and aggregation of amyloid β (Aβ), microtubule-associated protein (MAP) tau, or α-synuclein (α-syn) contribute to synaptic impairment and the ensuing neuronal death in both AD and PD. Likewise, the pathogenesis of ASD may be attributed, at least in part, to synaptic dysfunction; attention has also been recently paid to irregularities in the metabolism and function of the Aβ precursor protein (APP), tau, or α-syn. Commonly affected elements include signaling pathways that regulate cellular metabolism and survival such as insulin/insulin-like growth factor (IGF) - PI3 kinase - Akt - mammalian target of rapamycin (mTOR), and a number of key synaptic proteins critically involved in neuronal communication. Understanding how these shared pathomechanism elements operate in different conditions may help identify common targets and therapeutic approaches.

Stem cell therapy for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by memory loss and cognitive impairment. It is caused by synaptic failure and excessive accumulation of misfolded proteins. To date, almost all advanced clinical trials on specific AD-related pathways have failed mostly due to a large number of neurons lost in the brain of patients with AD. Also, currently available drug candidates intervene too late. Stem cells have improved characteristics of self-renewal, proliferation, differentiation, and recombination with the advent of stem cell technology and the transformation of these cells into different types of central nervous system neurons and glial cells. Stem cell treatment has been successful in AD animal models. Recent preclinical studies on stem cell therapy for AD have proved to be promising. Cell replacement therapies, such as human embryonic stem cells or induced pluripotent stem cell-derived neural cells, have the potential to treat patients with AD, and human clinical trials are ongoing in this regard. However, many steps still need to be taken before stem cell therapy becomes a clinically feasible treatment for human AD and related diseases. This paper reviews the pathophysiology of AD and the application prospects of related stem cells based on cell type.

The Ups and Downs of BACE1: Walking a Fine Line between Neurocognitive and Other Psychiatric Symptoms of Alzheimer's Disease

Although neurocognitive deficit is the best-recognized indicator of Alzheimer's disease (AD), psychotic and other noncognitive symptoms are the prime cause of institutionalization. BACE1 is the rate-limiting enzyme in the production of Aβ of AD, and one of the promising therapeutic targets in countering cognitive decline and amyloid pathology. Changes in BACE1 activity have also emerged to cause significant noncognitive neuropsychiatric symptoms and impairments of circadian rhythms, as evident from clinical trials and reports in transgenic models. In this study, we consider key characteristics of BACE1 with its contribution to neurocognitive deficit and other psychiatric symptoms of AD. We argue that a growing list of noncognitive mental impairments related to pharmacological modulation of BACE1 might present a major obstacle in clinical translation of emerging therapeutic leads targeting this protease. The adverse effects of BACE1 inhibition on mental health call for a revision of treatment strategies that assume indiscriminate inhibition of this key protease, and stress the need for further mechanistic and translational studies.

Cell death in animal development

Cell death is an important facet of animal development. In some developing tissues, death is the ultimate fate of over 80% of generated cells. Although recent studies have delineated a bewildering number of cell death mechanisms, most have only been observed in pathological contexts, and only a small number drive normal development. This Primer outlines the important roles, different types and molecular players regulating developmental cell death, and discusses recent findings with which the field currently grapples. We also clarify terminology, to distinguish between developmental cell death mechanisms, for which there is evidence for evolutionary selection, and cell death that follows genetic, chemical or physical injury. Finally, we suggest how advances in understanding developmental cell death may provide insights into the molecular basis of developmental abnormalities and pathological cell death in disease.

A broad perspective on the molecular regulation of retinal ganglion cell degeneration in glaucoma

Glaucoma is a complex neurodegenerative disease involving RGC axons, somas, and synapses at dendrites and axon terminals. Recent research advancements in the field have revealed a bigger picture of glaucomatous neurodegeneration that encompasses multiple stressors, multiple injury sites, multiple cell types, and multiple signaling pathways for asynchronous degeneration of RGCs during a chronic disease period. Optic nerve head is commonly viewed as the critical site of injury in glaucoma, where early injurious insults initiate distal and proximal signaling for axonal and somatic degeneration. Despite compartmentalized processes for degeneration of RGC axons and somas, there are intricate interactions between the two compartments and mechanistic overlaps between the molecular pathways that mediate degeneration in axonal and somatic compartments. This review summarizes the recent progress in the molecular understanding of RGC degeneration in glaucoma and highlights various etiological paths with biomechanical, metabolic, oxidative, and inflammatory components. Through this growing body of knowledge, the glaucoma community moves closer toward causative treatment of this blinding disease.

Molecular and cellular mechanisms underlying the pathogenesis of Alzheimer's disease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder seen in age-dependent dementia. There is currently no effective treatment for AD, which may be attributed in part to lack of a clear underlying mechanism. Studies within the last few decades provide growing evidence for a central role of amyloid β (Aβ) and tau, as well as glial contributions to various molecular and cellular pathways in AD pathogenesis. Herein, we review recent progress with respect to Aβ- and tau-associated mechanisms, and discuss glial dysfunction in AD with emphasis on neuronal and glial receptors that mediate Aβ-induced toxicity. We also discuss other critical factors that may affect AD pathogenesis, including genetics, aging, variables related to environment, lifestyle habits, and describe the potential role of apolipoprotein E (APOE), viral and bacterial infection, sleep, and microbiota. Although we have gained much towards understanding various aspects underlying this devastating neurodegenerative disorder, greater commitment towards research in molecular mechanism, diagnostics and treatment will be needed in future AD research.

Pharmacological BACE Inhibition Improves Axonal Regeneration in Nerve Injury and Disease Models

While the peripheral nervous system is able to repair itself following injury and disease, recovery is often slow and incomplete, with no available treatments to enhance the effectiveness of regeneration. Using knock-out and transgenic overexpressor mice, we previously reported that BACE1, an aspartyl protease, as reported by Hemming et al. (PLoS One 4:12, 2009), negatively regulates peripheral nerve regeneration. Here, we investigated whether pharmacological inhibition of BACE may enhance peripheral nerve repair following traumatic nerve injury or neurodegenerative disease. BACE inhibitor-treated mice had increased numbers of regenerating axons and enhanced functional recovery after a sciatic nerve crush while inhibition increased axonal sprouting following a partial nerve injury. In the SOD1G93A ALS mouse model, BACE inhibition increased axonal regeneration with improved muscle re-innervation. CHL1, a BACE1 substrate, was elevated in treated mice and may mediate enhanced regeneration. Our data demonstrates that pharmacological BACE inhibition accelerates peripheral axon regeneration after varied nerve injuries and could be used as a potential therapy.

The role of CREB and BDNF in neurobiology and treatment of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia worldwide. β-amyloid peptide (Aβ) is currently assumed to be the main cause of synaptic dysfunction and cognitive impairments in AD, but the molecular signaling pathways underlying its neurotoxic consequences have not yet been completely explored. Additional investigations regarding these pathways will contribute to development of new therapeutic targets. In context, developing evidence suggest that Aβ decreases brain-derived neurotrophic factor (BDNF) mostly by lowering phosphorylated cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) protein. In fact, it has been observed that brain or serum levels of BDNF appear to be beneficial markers for cognitive condition. In addition, the participation of transcription mediated by CREB has been widely analyzed in the memory process and AD development. Designing pharmacologic or genetic therapeutic approaches based on the targeting of CREB-BDNF signaling could be a promising treatment potential for AD. In this review, we summarize data demonstrating the role of CREB-BDNF signaling pathway in cognitive status and mediation of Aβ toxicity in AD. Finally, we also focus on the developing intervention methods for improvement of cognitive decline in AD based on targeting of CREB-BDNF pathway.

Matriptase processing of APLP1 ectodomain alters its homodimerization

The amyloid beta peptide (Aβ) is derived from the amyloid precursor protein (APP) by secretase processing. APP is also cleaved by numerous other proteases, such as the type II transmembrane serine protease matriptase, with consequences on the production of Aβ. Because the APP homolog protein amyloid-like protein 1 (APLP1) shares similarities with APP, we sought to determine if matriptase also plays a role in its processing. Here, we demonstrate that matriptase directly interacts with APLP1 and that APLP1 is cleaved in cellulo by matriptase in its E1 ectodomains at arginine 124. Replacing Arg124 with Ala abolished APLP1 processing by matriptase. Using a bioluminescence resonance energy transfer (BRET) assay we found that matriptase reduces APLP1 homodimeric interactions. This study identifies matriptase as the first protease cleaving APLP1 in its dimerization domain, potentially altering the multiple functions associated with dimer formation.

Assessing Axonal Degeneration in Embryonic Dorsal Root Ganglion Neurons In Vitro

The molecular players regulating the axon degeneration pathway have been identified using in vitro experimental models. Here, we describe an in vitro assay to assess the axonal fragmentation induced by mechanical injury to axons in cultured mouse embryonic dorsal root ganglion (DRG) neurons. DRG neurons are pseudounipolar and therefore suitable for an assay of axonal degeneration after injury. In addition, the time course of the axonal fragmentation is stereotyped, enabling the identification of reagents that either expedite or impede the degeneration process. With an image-based quantification method, the in vitro degeneration assay can be utilized as a platform supporting high-throughput screens for pharmacological or genetic reagents delaying axon degeneration.

The Role of Caspase-2 in Regulating Cell Fate

Caspase-2 is the most evolutionarily conserved member of the mammalian caspase family and has been implicated in both apoptotic and non-apoptotic signaling pathways, including tumor suppression, cell cycle regulation, and DNA repair. A myriad of signaling molecules is associated with the tight regulation of caspase-2 to mediate multiple cellular processes far beyond apoptotic cell death. This review provides a comprehensive overview of the literature pertaining to possible sophisticated molecular mechanisms underlying the multifaceted process of caspase-2 activation and to highlight its interplay between factors that promote or suppress apoptosis in a complicated regulatory network that determines the fate of a cell from its birth and throughout its life.

NrCAM is a marker for substrate-selective activation of ADAM10 in Alzheimer's disease

The metalloprotease ADAM10 is a drug target in Alzheimer's disease, where it cleaves the amyloid precursor protein (APP) and lowers amyloid‐beta. Yet, ADAM10 has additional substrates, which may cause mechanism‐based side effects upon therapeutic ADAM10 activation. However, they may also serve—in addition to APP—as biomarkers to monitor ADAM10 activity in patients and to develop APP‐selective ADAM10 activators. Our study demonstrates that one such substrate is the neuronal cell adhesion protein NrCAM. ADAM10 controlled NrCAM surface levels and regulated neurite outgrowth in vitro in an NrCAM‐dependent manner. However, ADAM10 cleavage of NrCAM, in contrast to APP, was not stimulated by the ADAM10 activator acitretin, suggesting that substrate‐selective ADAM10 activation may be feasible. Indeed, a whole proteome analysis of human CSF from a phase II clinical trial showed that acitretin, which enhanced APP cleavage by ADAM10, spared most other ADAM10 substrates in brain, including NrCAM. Taken together, this study demonstrates an NrCAM‐dependent function for ADAM10 in neurite outgrowth and reveals that a substrate‐selective, therapeutic ADAM10 activation is possible and may be monitored with NrCAM.

eIF3b regulates the cell proliferation and apoptosis processes in chronic myelogenous leukemia cell lines via regulating the expression of C3G

OBJECTIVE

To investigate the functions of eIF3b in chronic myelogenous leukemia (CML).

METHODS

The expression of eIF3b was inhibited by transfecting aspecifically designed shRNA into the CML cell lines of TK-6 and K562. The CCK8 assay was conducted to determine cell viability, and flow cytometry was used to examine the change in the cell cycle and cell apoptosis. RNAsequencing was applied to screen the candidate targets of eIF3b to identify the underlying mechanisms of eIF3b.An in vivo tumour xenograft mouse model was established by injecting shRNA transfected cells into the NCG mice. The tumour size and body weight of mice were monitored every other day. The mice were sacrificed 2 weeks after the tumour cell injection. The expression of eIF3b and target genes in the tumour tissues were determined by immunohistochemical staining and Western blotting.

RESULTS

The group with inhibited expression of eIF3b led to about 50% lower cell viability compared with that of the control group (P < 0.05). Flow cytometry suggested that the percentage of increase in apoptotic cells was eight times higher than those in control group for TK-6 and K562 cells (P < 0.05). However, the difference between the cell amounts in the S phase for the experiment and control groups was not significant. After RNAsequencing and further validation via qPCR, C3G was screened as the potential target of eIF3b involved in the cell proliferation and apoptosis of CML cell lines. Subsequent in vivo analysis proved that the inhibition of eIF3b suppressed tumour formation and decreased C3G expression, thereby indicating that C3G was the potential target of eIF3b.

CONCLUSION

eIF3b is correlated with the cell proliferation and cell apoptosis of CML. Moreover, eIF3b regulation most probably occurs via regulating the expression of C3G.

Polyornithine-based polyplexes to boost effective gene silencing in CNS disorders

Gene silencing therapies have successfully suppressed the translation of target proteins, a strategy that holds great promise for the treatment of central nervous system (CNS) disorders. Advances in the current knowledge on multimolecular delivery vehicles are concentrated on overcoming the difficulties in delivery of small interfering (si)RNA to target tissues, which include anatomical accessibility, slow diffusion, safety concerns, and the requirement for specific cell uptake within the unique environment of the CNS. The present work addressed these challenges through the implementation of polyornithine derivatives in the construction of polyplexes used as non-viral siRNA delivery vectors. Physicochemical and biological characterization revealed biodegradability and biocompatibility of our polyornithine-based system and the ability to silence gene expression in primary oligodendrocyte progenitor cells (OPCs) effectively. In summary, the well-defined properties and neurological compatibility of this polypeptide-based platform highlight its potential utility in the treatment of CNS disorders.

Molecular dissection of TNFR-TNFα bidirectional signaling reveals both cooperative and antagonistic interactions with p75 neurotrophic factor receptor in axon patterning

During neural development, complex organisms rely on progressive and regressive events whereby axons, synapses, and neurons are overproduced followed by selective elimination of a portion of these components. Tumor necrosis factor α (TNFα) together with its cognate receptor (Tumor necrosis factor receptor 1; TNFR1) have been shown to play both regressive (i.e. forward signaling from the receptor) and progressive (i.e. reverse signaling from the ligand) roles in sympathetic neuron development. In contrast, a paralog of TNFR1, p75 neurotrophic factor receptor (p75NTR) promotes mainly regressive developmental events in sympathetic neurons. Here we examine the interplay between these paralogous receptors in the regulation of axon branch elimination and arborization. We confirm previous reports that these TNFR1 family members are individually capable of promoting ligand-dependent suppression of axon growth and branching. Remarkably, p75NTR and TNFR1 physically interact and p75NTR requires TNFR1 for ligand-dependent axon suppression of axon branching but not vice versa. We also find that p75NTR forward signaling and TNFα reverse signaling are functionally antagonistic. Finally, we find that TNFα reverse signaling is necessary for nerve growth factor (NGF) dependent axon growth. Taken together these findings demonstrate several levels of synergistic and antagonistic interactions using very few signaling pathways and that the balance of these synergizing and opposing signals act to ensure proper axon growth and patterning.

Proteomics Analysis for Identification of Potential Cell Signaling Pathways and Protein Targets of Actions of Atractylodin and β-Eudesmol Against Cholangiocarcinoma

OBJECTIVE

The study aimed to identify potential cell signaling pathways and protein targets of actions of atractylodin and β-eudesmol in cholangiocarcinoma, the two active compounds isolated from Atracylodes lancea using proteomics approach.

METHOD

The cholangiocarcinoma cell line, CL-6, was treated with each compound for 3 and 6 hours, and the proteins from both intra- and extracellular components were extracted. LC-MS/MS was applied following the separation of the extract proteins by SDS-PAGE and digestion with trypsin. Signaling pathways and protein expression were analyzed by MASCOT and STITCH software.

RESULTS

A total of 4,323 and 4,318 proteins were identified from intra- and extracellular components, respectively. Six and 4 intracellular proteins were linked with the signaling pathways (apoptosis, cell cycle control, and PI3K-AKT) of atractylodin and β-eudesmol, respectively. Four and 3 extracellular proteins were linked with the signaling pathways (NF-κB and PI3K-AKT) of atractylodin and β-eudesmol, respectively.

CONCLUSION

In conclusion, a total of 17 proteins associated with four cell signaling pathways that could be potential molecular targets of anticholangiocarcinoma action of atractylodin and β-eudesmol were identified through the application of proteomics approach.

Caspase-6 Knockout in the 5xFAD Model of Alzheimer's Disease Reveals Favorable Outcome on Memory and Neurological Hallmarks

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and is the most common form of dementia in the elderly. Caspases, a family of cysteine proteases, are major mediators of apoptosis and inflammation. Caspase-6 is considered to be an up-stream modulator of AD pathogenesis as active caspase-6 is abundant in neuropil threads, neuritic plaques, and neurofibrillary tangles of AD brains. In order to further elucidate the role of caspase-6 activity in the pathogenesis of AD, we produced a double transgenic mouse model, combining the 5xFAD mouse model of AD with caspase-6 knock out (C6-KO) mice. Behavioral examinations of 5xFAD/C6-KO double transgenic mice showed improved performance in spatial learning, memory, and anxiety/risk assessment behavior, as compared to 5xFAD mice. Hippocampal mRNA expression analyses showed significantly reduced levels of inflammatory mediator TNF-α, while the anti-inflammatory cytokine IL-10 was increased in 5xFAD/C6-KO mice. A significant reduction in amyloid-β plaques could be observed and immunohistochemistry analyses showed reduced levels of activated microglia and astrocytes in 5xFAD/C6-KO, compared to 5xFAD mice. Together, these results indicate a substantial role for caspase-6 in the pathology of the 5xFAD model of AD and suggest further validation of caspase-6 as a potential therapeutic target for AD.

Opposite changes in APP processing and human Aβ levels in rats carrying either a protective or a pathogenic APP mutation

Cleavage of APP by BACE1/β-secretase initiates the amyloidogenic cascade leading to Amyloid-β (Aβ) production. α-Secretase initiates the non-amyloidogenic pathway preventing Aβ production. Several APP mutations cause familial Alzheimer's disease (AD), while the Icelandic APP mutation near the BACE1-cleavage site protects from sporadic dementia, emphasizing APP's role in dementia pathogenesis. To study APP protective/pathogenic mechanisms, we generated knock-in rats carrying either the protective (App^p) or the pathogenic Swedish mutation (App^s), also located near the BACE1-cleavage site. α-Cleavage is favored over β-processing in App^p rats. Consequently, non-amyloidogenic and amyloidogenic APP metabolites are increased and decreased, respectively. The reverse APP processing shift occurs in App^s rats. These opposite effects on APP β/α-processing suggest that protection from and pathogenesis of dementia depend upon combinatorial and opposite alterations in APP metabolism rather than simply on Aβ levels. The Icelandic mutation also protects from aging-dependent cognitive decline, suggesting that similar mechanisms underlie physiological cognitive aging.

Nongenetic engineering strategies for regulating receptor oligomerization in living cells

Nongenetic strategies for regulating receptor oligomerization in living cells based on DNA, protein, small molecules and physical stimuli.

Mechanisms of action of amyloid-beta and its precursor protein in neuronal cell death

Extracellular senile plaques and intracellular neurofibrillary tangles are the neuropathological findings of the Alzheimer's disease (AD). Based on the amyloid cascade hypothesis, the main component of senile plaques, the amyloid-beta (Aβ) peptide, and its derivative called amyloid precursor protein (APP) both have been found to place their central roles in AD development for years. However, the recent therapeutics have yet to reverse or halt this disease. Previous evidence demonstrates that the accumulation of Aβ peptides and APP can exert neurotoxicity and ultimately neuronal cell death. Hence, we discuss the mechanisms of excessive production of Aβ peptides and APP serving as pathophysiologic stimuli for the initiation of various cell signalling pathways including apoptosis, necrosis, necroptosis and autophagy which lead to neuronal cell death. Conversely, the activation of such pathways could also result in the abnormal generation of APP and Aβ peptides. An elucidation of actions of APP and its metabolite, Aβ, could be vital in suggesting novel therapeutic opportunities.

Oxidative stress, dysfunctional glucose metabolism and Alzheimer disease

Alzheimer disease (AD) is a major cause of age-related dementia. We do not fully understand AD aetiology and pathogenesis, but oxidative damage is a key component. The brain mostly uses glucose for energy, but in AD and amnestic mild cognitive impairment glucose metabolism is dramatically decreased, probably owing, at least in part, to oxidative damage to enzymes involved in glycolysis, the tricarboxylic acid cycle and ATP biosynthesis. Consequently, ATP-requiring processes for cognitive function are impaired, and synaptic dysfunction and neuronal death result, with ensuing thinning of key brain areas. We summarize current research on the interplay and sequence of these processes and suggest potential pharmacological interventions to retard AD progression.

Methylene blue inhibits Caspase-6 activity, and reverses Caspase-6-induced cognitive impairment and neuroinflammation in aged mice

Activated Caspase-6 (Casp6) is associated with age-dependent cognitive impairment and Alzheimer disease (AD). Mice expressing human Caspase-6 in hippocampal CA1 neurons develop age-dependent cognitive deficits, neurodegeneration and neuroinflammation. This study assessed if methylene blue (MB), a phenothiazine that inhibits caspases, alters Caspase-6-induced neurodegeneration and cognitive impairment in mice. Aged cognitively impaired Casp6-overexpressing mice were treated with methylene blue in drinking water for 1 month. Methylene blue treatment did not alter Caspase-6 levels, assessed by RT-PCR, western blot and immunohistochemistry, but inhibited fluorescently-labelled Caspase-6 activity in acute brain slice intact neurons. Methylene blue treatment rescued Caspase-6-induced episodic and spatial memory deficits measured by novel object recognition and Barnes maze, respectively. Methylene blue improved synaptic function of hippocampal CA1 neurons since theta-burst long-term potentiation (LTP), measured by field excitatory postsynaptic potentials (fEPSPs) in acute brain slices, was successfully induced in the Schaffer collateral-CA1 pathway in methylene blue-treated, but not in vehicle-treated, Caspase-6 mice. Increased neuroinflammation, measured by ionized calcium binding adaptor molecule 1 (Iba1)-positive microglia numbers and subtypes, and glial fibrillary acidic protein (GFAP)-positive astrocytes, were decreased by methylene blue treatment. Therefore, methylene blue reverses Caspase-6-induced cognitive deficits by inhibiting Caspase-6, and Caspase-6-mediated neurodegeneration and neuroinflammation. Our results indicate that Caspase-6-mediated damage is reversible months after the onset of cognitive deficits and suggest that methylene blue could benefit Alzheimer disease patients by reversing Caspase-6-mediated cognitive decline.

miR-195-Sirt3 Axis Regulates Angiotensin II-Induced Hippocampal Apoptosis and Learning Impairment in Mice

Objective

Apoptosis plays an essential role in cell development and aging, which is associated with a series of diseases, such as neurodegeneration. MircoRNAs exert important roles in the regulation of gene expression. As a stress-responsive deacetylase in mitochondria, sirtuin-3 (sirt3) is a key regulator for mitochondrial function and apoptosis. Also, miR-195 has been demonstrated to be involved in cell cycle and apoptosis. Therefore, this study aimed to investigate the effects of miR-195-sirt3 axis on angiotensin II (ANG II)-induced hippocampal apoptosis and behavioral influence.

Materials and methods

ANG II infusion was used to establish the hypertensive model in HT22 cells and 129S6/SvEvTac mice, respectively. TUNEL assay was used to evaluate the apoptosis level. Mitochondrial membrane potential (MMP) was measured to evaluate the mitochondrial property. Immunohistochemistry, RT-PCR, Western blotting, and luciferase reporter assay were conducted to determine the underlying molecular mechanism.

Results

The results revealed that ANG II treatment promoted apoptosis in the hippocampal cells and tissues, along with increased sirt3 and decreased miR-195 expression. Silencing sirt3 by genetic engineering or siRNA reversed ANG II-induced hippocampal apoptosis. Sirt3 was identified as a direct target gene of miR-195. Forced expression of miR-195 could play counteractive roles in hippocampal apoptosis induced by ANG II. Furthermore, the behavioral assay demonstrated that ANG II-induced hippocampal apoptosis impaired the performance in the spatial navigation task, but not in the spatial memory task.

Conclusion

The results suggested that miR-195-sirt3 axis plays an important role in the ANG II-induced hippocampal apoptosis via altering mitochondria-apoptosis proteins and mitochondria permeability and that hippocampal apoptosis is associated with impaired learning capability in hypertensive mice. This study provides insights into the molecular architecture of apoptosis-related neurodegenerative diseases.

High fat diet induces microbiota-dependent silencing of enteroendocrine cells

Enteroendocrine cells (EECs) are specialized sensory cells in the intestinal epithelium that sense and transduce nutrient information. Consumption of dietary fat contributes to metabolic disorders, but EEC adaptations to high fat feeding were unknown. Here, we established a new experimental system to directly investigate EEC activity in vivo using a zebrafish reporter of EEC calcium signaling. Our results reveal that high fat feeding alters EEC morphology and converts them into a nutrient insensitive state that is coupled to endoplasmic reticulum (ER) stress. We called this novel adaptation 'EEC silencing'. Gnotobiotic studies revealed that germ-free zebrafish are resistant to high fat diet induced EEC silencing. High fat feeding altered gut microbiota composition including enrichment of Acinetobacter bacteria, and we identified an Acinetobacter strain sufficient to induce EEC silencing. These results establish a new mechanism by which dietary fat and gut microbiota modulate EEC nutrient sensing and signaling.

p75NTR and DR6 Regulate Distinct Phases of Axon Degeneration Demarcated by Spheroid Rupture

The regressive events associated with trophic deprivation are critical for sculpting a functional nervous system. After nerve growth factor withdrawal, sympathetic axons derived from male and female neonatal mice maintain their structural integrity for ∼18 h (latent phase) followed by a rapid and near unison disassembly of axons over the next 3 h (catastrophic phase). Here we examine the molecular basis by which axons transition from latent to catastrophic phases of degeneration following trophic withdrawal. Before catastrophic degeneration, we observed an increase in intra-axonal calcium. This calcium flux is accompanied by p75 neurotrophic factor receptor-Rho-actin-dependent expansion of calcium-rich axonal spheroids that eventually rupture, releasing their contents to the extracellular space. Conditioned media derived from degenerating axons are capable of hastening transition into the catastrophic phase of degeneration. We also found that death receptor 6, but not p75 neurotrophic factor receptor, is required for transition into the catastrophic phase in response to conditioned media but not for the intra-axonal calcium flux, spheroid formation, or rupture that occur toward the end of latency. Our results support the existence of an interaxonal degenerative signal that promotes catastrophic degeneration among trophically deprived axons.SIGNIFICANCE STATEMENT Developmental pruning shares several morphological similarities to both disease- and injury-induced degeneration, including spheroid formation. The function and underlying mechanisms governing axonal spheroid formation, however, remain unclear. In this study, we report that axons coordinate each other's degeneration during development via axonal spheroid rupture. Before irreversible breakdown of the axon in response to trophic withdrawal, p75 neurotrophic factor receptor-RhoA signaling governs the formation and growth of spheroids. These spheroids then rupture, allowing exchange of contents ≤10 kDa between the intracellular and extracellular space to drive death receptor 6 and calpain-dependent catastrophic degeneration. This finding informs not only our understanding of regressive events during development but may also provide a rationale for designing new treatments toward myriad neurodegenerative disorders.

Modification of the gut microbiome to combat neurodegeneration

The gut microbiome was extensively researched for its biological variety and its potential role in propagating diseases outside of the gastrointestinal (GI) tract. Recently, a lot of effort was focused on comprehending the gut-brain axis and the bizarre communication between the GI system and the nervous system. Ample amount of studies being carried out also revealed the involvement of the gut microbiome in enhancing the degree of many neurological disorders, including neurodegenerative diseases. It was widely observed that there were distinct microbiome profiles and dysbiosis within patients suffering from Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, and multiple sclerosis. Various approaches to re-establish the balance of the gut microbiome, from antibiotic therapy, fecal microbiota transplant, or ingestion of psychobiotics, are discussed within this review within the specific context of combating neurodegenerative diseases. Present studies and clinical trials indicate that although there is an immense potential of gut microbiome modification to be preventive or therapeutic, there are still many intercalated components of the gut-brain axis at play and thus, more research needs to be carried out to delineate microbiome factors that may potentially alleviate symptoms of neurodegeneration.

The puzzle of preserved cognition in the oldest old

Although epidemiological studies predict an exponential increase in the prevalence of dementia with age, recent studies have demonstrated that the oldest old are actually less frequently affected by dementia than the younger elderly. To explain this, I suggest a parallel between brain ageing and Alzheimer's disease (AD) and assume that theories concerning the brain's vulnerability to AD and its individual variability may also explain why some of the oldest old remain cognitively efficient. Some theories argue that AD is due to the continuing presence of the immature neurones vulnerable to amyloid beta protein (Aß) that are normally involved in brain development and then removed as a result of cell selection by the proteins associated with both brain development and AD. If a dysfunction in cell selection allows these immature neurones to survive, they degenerate early as a result of the neurotoxic action of Aß accumulation, which their mature counterparts can withstand. Consequently, age at the time of onset of AD and its clinical presentations depend on the number and location of such immature cells. I speculate that the same mechanism is responsible for the variability of normal brain ageing: the oldest old with well-preserved cognitive function are people genetically programmed for extreme ageing who have benefited from better cell selection during prenatal and neonatal life and therefore have fewer surviving neurones vulnerable to amyloid-promoted degeneration, whereas the process of early life cell selection was less successful in the oldest old who develop dementia.

Lipid-Binding Proteins in Brain Health and Disease

A proper lipid management is paramount for a healthy brain. Lipid homeostasis alterations are known to be causative or risk factors for many neurodegenerative diseases, or key elements in the recovery from nervous system injuries of different etiology. In addition to lipid biogenesis and catabolism, non-enzymatic lipid-binding proteins play an important role in brain function and maintenance through aging. Among these types of lipoproteins, apolipoprotein E has received much attention due to the relationship of particular alleles of its gene with the risk and progression of Alzheimer's disease. However, other lipid-binding proteins whose role in lipid homeostasis and control are less known need to be brought to the attention of both researchers and clinicians. The aim of this review is to cover the knowledge of lipid-managing proteins in the brain, with particular attention to new candidates to be relevant for brain function and health.

Non-specific Detection of a Major Western Blotting Band in Human Brain Homogenates by a Multitude of Amyloid Precursor Protein Antibodies

The use of human post-mortem brain material is of great value when investigating which pathological mechanisms occur in human brain, and to avoid translational problems which have for example been evident when translating animal research into Alzheimer disease (AD) clinical trials. The amyloid β (Aβ)-peptide, its amyloid precursor protein (APP) and the intermediate APP-c-terminal fragments (APP-CTFs) are all important players in AD pathogenesis. In order to elucidate which APP CTF that are the most common in brain tissue of different species and developmental stages, and whether there are any differences in these fragments between AD and control brain, we investigated the occurrence of these fragments using different APP c-terminal antibodies. We noticed that whereas the conventional APP-CTFα and CTFβ fragments were most prominent in rat and mouse brain tissue, the major western blotting band detected in human, macaque and guinea pig was of approximately 20 kDa in size, possibly corresponding to the newly discovered APP-CTFη. However, this band was also intensely stained with a total protein stain, as well as by several other antibodies. The staining intensity of the 20 kDa band by the APP antibodies varied considerably between samples and correlated with the staining intensity of this band by the total protein stain. This could potentially be due to non-specific binding of the antibodies to another protein of this size. In-gel digestion and mass spectrometry confirmed that small amounts of APP were present in this band, but many other proteins were identified as well. The major hit of the mass spectrometry analysis was myelin basic protein (MBP) and a myelin removal protocol removed proportionally more of the 20 kDa APP band than the full-length APP and APP-CTFα/β bands. However, the signal could not be immunodepleted with an MBP antibody. In summary, we report on a potentially non-specific western blotting band of approximately 20 kDa and call for precaution when analyzing proteins of this size in human brain tissue.

Elucidating Critical Proteinopathic Mechanisms and Potential Drug Targets in Neurodegeneration

Neurodegeneration entails progressive loss of neuronal structure as well as function leading to cognitive failure, apathy, anxiety, irregular body movements, mood swing and ageing. Proteomic dysregulation is considered the key factor for neurodegeneration. Mechanisms involving deregulated processing of proteins such as amyloid beta (Aβ) oligomerization; tau hyperphosphorylation, prion misfolding; α-synuclein accumulation/lewy body formation, chaperone deregulation, acetylcholine depletion, adenosine 2A (A2A) receptor hyperactivation, secretase deregulation, leucine-rich repeat kinase 2 (LRRK2) mutation and mitochondrial proteinopathies have deeper implications in neurodegenerative disorders. Better understanding of such pathological mechanisms is pivotal for exploring crucial drug targets. Herein, we provide a comprehensive outlook about the diverse proteomic irregularities in Alzheimer's, Parkinson's and Creutzfeldt Jakob disease (CJD). We explicate the role of key neuroproteomic drug targets notably Aβ, tau, alpha synuclein, prions, secretases, acetylcholinesterase (AchE), LRRK2, molecular chaperones, A2A receptors, muscarinic acetylcholine receptors (mAchR), N-methyl-D-aspartate receptor (NMDAR), glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs) and mitochondrial/oxidative stress-related proteins for combating neurodegeneration and associated cognitive and motor impairment. Cross talk between amyloidopathy, synucleinopathy, tauopathy and several other proteinopathies pinpoints the need to develop safe therapeutics with ability to strike multiple targets in the aetiology of the neurodegenerative disorders. Therapeutics like microtubule stabilisers, chaperones, kinase inhibitors, anti-aggregation agents and antibodies could serve promising regimens for treating neurodegeneration. However, drugs should be target specific, safe and able to penetrate blood-brain barrier.

p110δ PI3-Kinase Inhibition Perturbs APP and TNFα Trafficking, Reduces Plaque Burden, Dampens Neuroinflammation, and Prevents Cognitive Decline in an Alzheimer's Disease Mouse Model

Alzheimer's disease (AD) is associated with the cleavage of the amyloid precursor protein (APP) to produce the toxic amyloid-β (Aβ) peptide. Accumulation of Aβ, together with the concomitant inflammatory response, ultimately leads to neuronal death and cognitive decline. Despite AD progression being underpinned by both neuronal and immunological components, therapeutic strategies based on dual targeting of these systems remains unexplored. Here, we report that inactivation of the p110δ isoform of phosphoinositide 3-kinase (PI3K) reduces anterograde axonal trafficking of APP in hippocampal neurons and dampens secretion of the inflammatory cytokine tumor necrosis factor-alpha by microglial cells in the familial AD APPswe/PS1ΔE9 (APP/PS1) mouse model. Moreover, APP/PS1 mice with kinase-inactive PI3Kδ (δD910A) had reduced Aβ peptides levels and plaques in the brain and an abrogated inflammatory response compared with APP/PS1 littermates. Mechanistic investigations reveal that PI3Kδ inhibition decreases the axonal transport of APP by eliciting the formation of highly elongated tubular-shaped APP-containing carriers, reducing the levels of secreted Aβ peptide. Importantly, APP/PS1/δD910A mice exhibited no spatial learning or memory deficits. Our data highlight inhibition of PI3Kδ as a new approach to protect against AD pathology due to its dual action of dampening microglial-dependent neuroinflammation and reducing plaque burden by inhibition of neuronal APP trafficking and processing.SIGNIFICANCE STATEMENT During Alzheimer's disease (AD), the accumulation of the toxic amyloid-β (Aβ) peptide in plaques is associated with a chronic excessive inflammatory response. Uncovering new drug targets that simultaneously reduce both Aβ plaque load and neuroinflammation holds therapeutic promise. Using a combination of genetic and pharmacological approaches, we found that the p110δ isoform of phosphoinositide 3-kinase (PI3K) is involved in anterograde trafficking of the amyloid precursor protein in neurons and in the secretion of tumor necrosis factor-alpha from microglial cells. Genetic inactivation of PI3Kδ reduces Aβ plaque deposition and abrogates the inflammatory response, resulting in a complete rescue of the life span and spatial memory performance. We conclude that inhibiting PI3Kδ represents a novel therapeutic approach to ameliorate AD pathology by dampening plaque accumulation and microglial-dependent neuroinflammation.

Eukaryotic translation initiation factor 3B downregulation inhibits cell proliferation and promotes cell apoptosis through negatively regulating tumor necrosis factor receptor superfamily member 21 in gastric cancer

BACKGROUND

This study aimed to detect eukaryotic translation initiation factor 3B (EIF3B) expression in gastric cancer (GC) cell lines, and further explore the effect of EIF3B downregulation on GC cell proliferation and apoptosis.

METHODS

EIF3B mRNA expression and protein expression in human GC cell lines (NCI-N87, AGS, HGC-27, BGC-823 and MGC80-3) and human gastric mucosal epithelial cell line (GES-1) were detected. Control siRNA (Si-NC group) and EIF3B siRNA (Si-EIF3B group) were transfected into NCI-N87 cells. Rescue experiment was performed by transfection of EIF3B siRNA (Si-EIF3B group) and EIF3B siRNA plus tumor necrosis factor receptor superfamily member 21 (TNFRSF21) siRNA (Si-EIF3B & Si-TNFRSF21 group) into NCI-N87 cells. Besides, cell proliferation, apoptosis, TNFRSF21 expression and TRAF1 expression were assessed.

RESULTS

EIF3B mRNA expression and protein expression were elevated in NCI-N87, AGS, HGC-27 and BGC-823 cell lines compared to GES-1 cell line. In NCI-N87 cells, proliferation was reduced in Si-EIF3B group compared to Si-NC group. For cell apoptosis, its rate and apoptotic marker C-Caspase 3 expression were increased but anti-apoptosis marker Bcl-2 expression was reduced in Si-EIF3B group compared to Si-NC group. Moreover, mRNA expression and protein expression of TNFRSF21 were increased in Si-EIF3B group compared to Si-NC group, while mRNA expression and protein expression of TRAF1 were reduced in Si-EIF3B group compared to Si-NC group. In rescue experiment, cell proliferation was increased but apoptosis was decreased in Si-EIF3B & Si-TNFRSF21 group compared to Si-EIF3B group.

CONCLUSIONS

EIF3B is overexpressed in GC cell lines, and its downregulation inhibits cell proliferation while promotes apoptosis through negatively regulating TNFRSF21 in GC.

Current and emerging avenues for Alzheimer's disease drug targets

Alzheimer's disease (AD), the most frequent cause of dementia, is escalating as a global epidemic, and so far, there is neither cure nor treatment to alter its progression. The most important feature of the disease is neuronal death and loss of cognitive functions, caused probably from several pathological processes in the brain. The main neuropathological features of AD are widely described as amyloid beta (Aβ) plaques and neurofibrillary tangles of the aggregated protein tau, which contribute to the disease. Nevertheless, AD brains suffer from a variety of alterations in function, such as energy metabolism, inflammation and synaptic activity. The latest decades have seen an explosion of genes and molecules that can be employed as targets aiming to improve brain physiology, which can result in preventive strategies for AD. Moreover, therapeutics using these targets can help AD brains to sustain function during the development of AD pathology. Here, we review broadly recent information for potential targets that can modify AD through diverse pharmacological and nonpharmacological approaches including gene therapy. We propose that AD could be tackled not only using combination therapies including Aβ and tau, but also considering insulin and cholesterol metabolism, vascular function, synaptic plasticity, epigenetics, neurovascular junction and blood-brain barrier targets that have been studied recently. We also make a case for the role of gut microbiota in AD. Our hope is to promote the continuing research of diverse targets affecting AD and promote diverse targeting as a near-future strategy.

Emerging Alternative Proteinases in APP Metabolism and Alzheimer's Disease Pathogenesis: A Focus on MT1-MMP and MT5-MMP

Processing of amyloid beta precursor protein (APP) into amyloid-beta peptide (Aβ) by β-secretase and γ-secretase complex is at the heart of the pathogenesis of Alzheimer’s disease (AD). Targeting this proteolytic pathway effectively reduces/prevents pathology and cognitive decline in preclinical experimental models of the disease, but therapeutic strategies based on secretase activity modifying drugs have so far failed in clinical trials. Although this may raise some doubts on the relevance of β- and γ-secretases as targets, new APP-cleaving enzymes, including meprin-β, legumain (δ-secretase), rhomboid-like protein-4 (RHBDL4), caspases and membrane-type matrix metalloproteinases (MT-MMPs/η-secretases) have confirmed that APP processing remains a solid mechanism in AD pathophysiology. This review will discuss recent findings on the roles of all these proteinases in the nervous system, and in particular on the roles of MT-MMPs, which are at the crossroads of pathological events involving not only amyloidogenesis, but also inflammation and synaptic dysfunctions. Assessing the potential of these emerging proteinases in the Alzheimer’s field opens up new research prospects to improve our knowledge of fundamental mechanisms of the disease and help us establish new therapeutic strategies.

Interferon beta ameliorates cognitive dysfunction in a rat model of Alzheimer's disease: Modulation of hippocampal neurogenesis and apoptosis as underlying mechanism

Neuronal apoptosis and impaired hippocampal neurogenesis are major players in cognitive/memory dysfunctions including Alzheimer's disease (AD). Interferon beta (IFNβ) is a cytokine with anti-apoptotic and neuroprotective properties on the central nervous system (CNS) cells which specifically affects neural progenitor cells (NPCs) even in the adult brain. In this study, we examined the effect of IFNβ on memory impairment as well as hippocampal neurogenesis and apoptosis in a rat model of AD. AD model was induced by lentiviral-mediated overexpression of mutant APP in the hippocampus of adult rats. Intranasal (IN) administration of IFNβ (0.5 μg/kg and 1 μg/kg doses) was started from day 23 after virus injection and continued every other day to the final day of experiments. The expression levels of APP, neurogenesis (Nestin, Ki67, DCX, and Reelin) and apoptosis (Bax/Bcl-2 ratio, cleaved-caspase-3 and seladin-1) markers were evaluated by immunohistochemistry, real-time PCR, immunofluorescence and western blotting. Moreover, thioflavin T and Nissl stainings were used to assess Aβ plaque levels and neuronal degeneration in the hippocampus, respectively. Our results showed that IFNβ treatment reduced APP expression and Aβ plaque formation, and concomitantly ameliorated spatial learning and memory deficits examined in Y-maze and Morris water maze tests. Moreover, in parallel with reducing apoptosis and neural loss in the hippocampal subfields, IFNβ decreased ectopic neurogenesis in the CA1 and CA3 regions of the AD rat hippocampus. However, IFNβ increased neurogenesis in the dentate gyrus neurogenic niche. Our findings suggest that IFNβ exerts neuroprotective effects at least partly by inhibition of apoptosis and modulation of neurogenesis. Taken together, IFNβ can be a promising therapeutic approach to improve cognitive performance in AD-like neurodegenerative context.

CSF sAPPα and sAPPβ levels in Alzheimer's Disease and Multiple Other Neurodegenerative Diseases: A Network Meta-Analysis

The soluble amyloid protein procurer α (sAPPα) and β (sAPPβ) have been postulated as promising new cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease (AD) and multiple other neurodegenerative diseases, but have failed to meet expectations with their often discordant and even contradictory findings to date. The aim of the study was to systematically explore this issue. Cochrane Library, PubMed, and CNKI were systematically searched without language or date restrictions. This network meta-analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and also adhered to the Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines. Twenty studies, comprising ten groups, were eligible and included. Overall, 19 eligible studies with 1634 patients contributed to the analysis of CSF sAPPα levels and 16 eligible studies with 1684 patients contributed to the analysis of CSF sAPPβ levels. CSF sAPPβ levels are significantly higher in AD than in corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP); higher in Control than in Depression, CBS and PSP; higher in Parkinson's disease dementia (PDD) than in CBS and PSP; higher in mild cognitive impairment progressed to AD dementia during the follow-up period (pMCI) than in Depression and PSP; higher in stable mild cognitive impairment (sMCI) than in Depression. With regard to CSF sAPPα levels, there were no significant difference among groups. However, surprisingly, the resultant rankings graphically showed that pMCI populations have the highest levels of CSF sAPPα and sAPPβ. Furthermore, it seemed there was a positive correlation between CSF sAPPα and sAPPβ levels. The measurement of CSF sAPPα and sAPPβ levels may provide an alternative method for the diagnosis of early-stage AD, pMCI, which is conducive to preventive therapy.

Matrix Metalloproteases as Influencers of the Cells' Social Media

Matrix metalloproteinases (MMPs) have been studied in the context of cancer due to their ability to increase cell invasion, and were initially thought to facilitate metastasis solely through the degradation of the extracellular matrix (ECM). MMPs have also been investigated in the context of their ECM remodeling activity in several acute and chronic inflammatory diseases. However, after several MMP inhibitors failed in phase III clinical trials, a global reassessment of their biological functions was undertaken, which has revealed multiple unanticipated functions including the processing of chemokines, cytokines, and cell surface receptors. Despite what their name suggests, the matrix aspect of MMPs could contribute to a lesser part of their physiological functions in inflammatory diseases, as originally anticipated. Here, we present examples of MMP substrates implicated in cell signaling, independent of their ECM functions, and discuss the impact for the use of MMP inhibitors.

Regulation of the alternative β-secretase meprin β by ADAM-mediated shedding

Alzheimer's Disease (AD) is the sixth-leading cause of death in industrialized countries. Neurotoxic amyloid-β (Aβ) plaques are one of the pathological hallmarks in AD patient brains. Aβ accumulates in the brain upon sequential, proteolytic processing of the amyloid precursor protein (APP) by β- and γ-secretases. However, so far disease-modifying drugs targeting β- and γ-secretase pathways seeking a decrease in the production of toxic Aβ peptides have failed in clinics. It has been demonstrated that the metalloproteinase meprin β acts as an alternative β-secretase, capable of generating truncated Aβ2-x peptides that have been described to be increased in AD patients. This indicates an important β-site cleaving enzyme 1 (BACE-1)-independent contribution of the metalloprotease meprin β within the amyloidogenic pathway and may lead to novel drug targeting avenues. However, meprin β itself is embedded in a complex regulatory network. Remarkably, the anti-amyloidogenic α-secretase a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) is a direct competitor for APP at the cell surface, but also a sheddase of inactive pro-meprin β. Overall, we highlight the current cellular, molecular and structural understanding of meprin β as alternative β-secretase within the complex protease web, regulating APP processing in health and disease.

Defining the binding interface of Amyloid Precursor Protein (APP) and Contactin3 (CNTN3) by site-directed mutagenesis

The Amyloid Precursor Protein (APP) and Contactin (CNTN) families of cell-surface proteins have been intensively studied in the context of neural development and neuropsychiatric diseases. Earlier studies demonstrated both genetic and biochemical interactions between the extracellular domains of APP and CNTN3, but their precise binding interfaces were not defined. In the present study, we have used binding assays between APP-alkaline phosphatase (AP) fusion proteins and CNTN-Fc fusion proteins, together with alanine substitution mutagenesis, to show that: (i) the second Fibronectin domain (Fn(2)) in CNTN3 mediates APP binding; (ii) the copper binding domain (CuBD) in APP mediates CNTN3 binding; and (iii) the most important amino acids for APP-CNTN3 binding reside on one face of CNTN3-Fn(2) and on one face of APP-CuBD. These experiments define the regions of direct contact that mediate the binding interaction between APP and CNTN3.

Cellular demolition: Proteins as molecular players of programmed cell death

Apoptosis, a well-characterized and regulated cell death programme in eukaryotes plays a fundamental role in developing or later-life periods to dispose of unwanted cells to maintain typical tissue architecture, homeostasis in a spatiotemporal manner. This silent cellular death occurs without affecting any neighboring cells/tissue and avoids triggering of immunological response. Furthermore, diminished forms of apoptosis result in cancer and autoimmune diseases, whereas unregulated apoptosis may also lead to the development of a myriad of neurodegenerative diseases. Unraveling the mechanistic events in depth will provide new insights into understanding physiological control of apoptosis, pathological consequences of abnormal apoptosis and development of novel therapeutics for diseases. Here we provide a brief overview of molecular players of programmed cell death with discussion on the role of caspases, modifications, ubiquitylation in apoptosis, removal of the apoptotic body and its relevance to diseases.

A Role for Drosophila Amyloid Precursor Protein in Retrograde Trafficking of L1-Type Cell Adhesion Molecule Neuroglian

The role of the Amyloid Precursor Protein (APP) in the pathology of Alzheimer's disease (AD) has been well studied. However, the normal function of APP in the nervous system is poorly understood. Here, we characterized the role of the Drosophila homolog (APPL) in the adult giant fiber (GF) neurons. We find that endogenous APPL is transported from the synapse to the soma in the adult. Live-imaging revealed that retrograde moving APPL vesicles co-traffic with L1-type cell adhesion molecule Neuroglian (Nrg). In APPL null mutants, stationary Nrg vesicles were increased along the axon, and the number of Nrg vesicles moving in retrograde but not anterograde direction was reduced. In contrast, trafficking of endo-lysosomal vesicles, which did not co-localize with APPL in GF axons, was not affected. This suggests that APPL loss of function does not generally disrupt axonal transport but that APPL has a selective role in the effectiveness of retrograde transport of proteins it co-traffics with. While the GF terminals of APPL loss of function animals exhibited pruning defects, APPL gain of function had no disruptive effect on GF morphology and function, or on retrograde axonal transport of Nrg. However, cell-autonomous developmental expression of a secretion-deficient form of APPL (APPL-SD), lacking the α-, β-, and, γ-secretase cleavage sites, resulted in progressive retraction of the GF terminals. Conditional expression of APPL-SD in mature GFs caused accumulation of Nrg in normal sized synaptic terminals, which was associated with severely reduced retrograde flux of Nrg labeled vesicles in the axons. Albeit β-secretase null mutants developed GF terminals they also exhibited Nrg accumulations. This suggests that cleavage defective APPL has a toxic effect on retrograde trafficking and that β-secretase cleavage has a function in Nrg sorting in endosomal compartments at the synapse. In summary, our results suggest a role for APPL and its proteolytic cleavage sites in retrograde trafficking, thus our findings are of relevance to the understanding of the endogenous role of APP as well as to the development of therapeutic treatments of Alzheimer's disease.

Axon injury signaling and compartmentalized injury response in glaucoma

Axonal degeneration is an active, highly controlled process that contributes to beneficial processes, such as developmental pruning, but also to neurodegeneration. In glaucoma, ocular hypertension leads to vision loss by killing the output neurons of the retina, the retinal ganglion cells (RGCs). Multiple processes have been proposed to contribute to and/or mediate axonal injury in glaucoma, including: neuroinflammation, loss of neurotrophic factors, dysregulation of the neurovascular unit, and disruption of the axonal cytoskeleton. While the inciting injury to RGCs in glaucoma is complex and potentially heterogeneous, axonal injury is ultimately thought to be the key insult that drives glaucomatous neurodegeneration. Glaucomatous neurodegeneration is a complex process, with multiple molecular signals contributing to RGC somal loss and axonal degeneration. Furthermore, the propagation of the axonal injury signal is complex, with injury triggering programs of degeneration in both the somal and axonal compartment. Further complicating this process is the involvement of multiple cell types that are known to participate in the process of axonal and neuronal degeneration after glaucomatous injury. Here, we review the axonal signaling that occurs after injury and the molecular signaling programs currently known to be important for somal and axonal degeneration after glaucoma-relevant axonal injuries.

Nitrite Protects Neurons Against Hypoxic Damage Through S-nitrosylation of Caspase-6

Aims: The coordination of neurons to execute brain functions requires plenty of oxygen. Thus, it is not surprising that the chronic hypoxia resulting from chronic obstructive pulmonary diseases (COPD) can cause neuronal damage. Injury in the cortex can give rise to anxiety and cognitive dysfunction. This study investigated what causes hypoxia-induced neuronal injury and what strategies might be used to protect neurons against such damage. Results: This study found that hypoxia in primary cortical neurons caused neurite retraction, a caspase-6-dependent process. The hypoxic stress activated caspase-6 within the neurite, leading to microtubule disassembly and neurite retraction. The effect of hypoxia on caspase-6 activation, microtubule disassembly, and neurite retraction was alleviated by nitrite treatment. The protective role of nitrite was further supported by the observation that the active-site Cys146 of caspase-6 was S-nitrosylated in hypoxic neuro-2a cells treated with nitrite. We further validated the beneficial effect of nitrite on neuronal function against hypoxic stress in vivo. Using the wild-type or Apo E^-/- mice exposed to chronic hypoxia as a model, we demonstrated that supplementing drinking water with nitrite suppressed active caspase-6 in the cortex of the brain, concomitant with the prevention of hypoxia-induced anxiety in the animals. Innovation: These results are the first evidence of a new pathway for the activation of caspase-6 and the first to indicate that nitrite can protect neurons against chronic hypoxic insult. Conclusion: Our findings suggest that nitrite holds great potential for the treatment of diseases such as COPD associated with hypoxia-induced neuronal injury.

Protein misfolding and aggregation in neurodegenerative diseases: a review of pathogeneses, novel detection strategies, and potential therapeutics

Protein folding is a complex, multisystem process characterized by heavy molecular and cellular footprints. Chaperone machinery enables proper protein folding and stable conformation. Other pathways concomitant with the protein folding process include transcription, translation, post-translational modifications, degradation through the ubiquitin-proteasome system, and autophagy. As such, the folding process can go awry in several different ways. The pathogenic basis behind most neurodegenerative diseases is that the disruption of protein homeostasis (i.e. proteostasis) at any level will eventually lead to protein misfolding. Misfolded proteins often aggregate and accumulate to trigger neurotoxicity through cellular stress pathways and consequently cause neurodegenerative diseases. The manifestation of a disease is usually dependent on the specific brain region that the neurotoxicity affects. Neurodegenerative diseases are age-associated, and their incidence is expected to rise as humans continue to live longer and pursue a greater life expectancy. We presently review the sequelae of protein misfolding and aggregation, as well as the role of these phenomena in several neurodegenerative diseases including Alzheimer's disease, Huntington's disease, amyotrophic lateral sclerosis, Parkinson's disease, transmissible spongiform encephalopathies, and spinocerebellar ataxia. Strategies for treatment and therapy are also conferred with respect to impairing, inhibiting, or reversing protein misfolding.