Acidifying Endolysosomes Prevented Low-Density Lipoprotein-Induced Amyloidogenesis

Cholesterol dyshomeostasis has been linked to the pathogenesis of sporadic Alzheimer's disease (AD). In furthering the understanding of mechanisms by which increased levels of circulating cholesterol augments the risk of developing sporadic AD, others and we have reported that low-density lipoprotein (LDL) enters brain parenchyma by disrupting the blood-brain barrier and that endolysosome de-acidification plays a role in LDL-induced amyloidogenesis in neurons. Here, we tested the hypothesis that endolysosome de-acidification was central to amyloid-β (Aβ) generation and that acidifying endolysosomes protects against LDL-induced increases in Aβ levels in neurons. We demonstrated that LDL, but not HDL, de-acidified endolysosomes and increased intraneuronal and secreted levels of Aβ. ML-SA1, an agonist of endolysosome-resident TRPML1 channels, acidified endolysosomes, and TRPML1 knockdown attenuated ML-SA1-induced endolysosome acidification. ML-SA1 blocked LDL-induced increases in intraneuronal and secreted levels of Aβ as well as Aβ accumulation in endolysosomes, prevented BACE1 accumulation in endolysosomes, and decreased BACE1 activity levels. LDL downregulated TRPML1 protein levels, and TRPML1 knockdown worsens LDL-induced increases in Aβ. Our findings suggest that endolysosome acidification by activating TRPML1 may represent a protective strategy against sporadic AD.

The Autophagy Lysosomal Pathway and Neurodegeneration

The autophagy lysosomal pathway (ALP) is a major mechanism for degrading intracellular macromolecules. The catabolic products can then be used by the cell for energy or as building blocks to make other macromolecules. Since its discovery, a variety of cellular pathways have emerged that target components with varying specificity for lysosomal degradation. Under some circumstances, lysosomes may release their contents into the extracellular space where they may serve signaling or pathogenic functions. The ALP is active in healthy cells, and the level of activity can be regulated by nutrient-sensing and metabolic signaling pathways. The ALP is the primary pathway by which lipids and damaged organelles are degraded and may be the only pathway capable of degrading aggregated proteins. As such, there has been intense interest in understanding the role of the ALP in the accumulation of aggregated misfolded proteins characteristic of many of the major adult-onset neurodegenerative diseases. This review focuses on recent advances in our understanding of the ALP and its potential relationship to the pathogenesis and treatment of neurodegenerative diseases.

PLA2G4A/cPLA2-mediated lysosomal membrane damage leads to inhibition of autophagy and neurodegeneration after brain trauma

Lysosomal membrane permeabilization (LMP) is observed under many pathological conditions, leading to cellular dysfunction and death. However, the mechanisms by which lysosomal membranes become leaky in vivo are not clear. Our data demonstrate that LMP occurs in neurons following controlled cortical impact induced (CCI) traumatic brain injury (TBI) in mice, leading to impaired macroautophagy (autophagy) and neuronal cell death. Comparison of LC-MS/MS lysosomal membrane lipid profiles from TBI and sham animals suggested a role for PLA2G4A/cPLA2 (phospholipase A2, group IVA [cytosolic, calcium-dependent]) in TBI-induced LMP. Activation of PLA2G4A caused LMP and inhibition of autophagy flux in cell lines and primary neurons. In vivo pharmacological inhibition of PLA2G4A attenuated TBI-induced LMP, as well as subsequent impairment of autophagy and neuronal loss, and was associated with improved neurological outcomes. Inhibition of PLA2G4A in vitro limited amyloid-β-induced LMP and inhibition of autophagy. Together, our data indicate that PLA2G4A -mediated lysosomal membrane damage is involved in neuronal cell death following CCI-induced TBI and potentially in other neurodegenerative disorders.Abbreviations: AACOCF3, arachidonyl trifluoromethyl ketone; ACTB/β-actin, actin, beta; AD, Alzheimer disease; ATG5, autophagy related 5; ATG7, autophagy related 7; ATG12, autophagy related 12; BECN1, beclin 1, autophagy related; C1P, ceramide-1-phosphate; CCI, controlled cortical impact; CTSD, cathepsin D; CTSL, cathepsin L; GFP, green fluorescent protein; IF, immunofluorescence; LAMP1, lysosomal-associated membrane protein 1; LAMP2, lysosomal-associated membrane protein 2; LC-MS/MS, liquid chromatography-tandem mass spectrometry; LMP, Lysosomal membrane permeabilization; LPC, lysophosphatidylcholine; LPE, lysophosphatidylethanolamine; MAP1LC3/LC3, microtuble-associated protein 1 light chain 3; NAGLU, alpha-N-acetylglucosaminidase (Sanfilippo disease IIIB); PC, diacyl glycerophosphatidylcholine; PE, diacyl glycerophosphatidylethanolamine; PE-O, plasmanyl glycerophosphatidylethanolamine; PE-P, plasmenyl glycerophosphatidylethanolamine; PLA2G4A/cPLA2, phospholipase A2, group IVA (cytosolic, calcium-dependent); RBFOX3, RNA binding protein, fox-1 homolog (C. elegans) 3; RFP, red fluorescent protein; ROS, reactive oxygen species; SQSTM1, sequestosome 1; TUBA1/α-tubulin, tubulin, alpha; TBI, traumatic brain injury; TFEB, transcription factor EB; ULK1, unc-51 like kinase 1.

Endosomal dysfunction impacts extracellular vesicle release: Central role in Aβ pathology

Alzheimer's Disease (AD) is characterized by progressive loss of cognitive abilities; senile plaques represent the major histopathological findings. Amyloid precursor protein (APP) processing machinery, and its product amyloid-beta (Aβ) peptide, have been found in extracellular vesicles (EVs), specifically exosomes, which allows for Aβ peptide aggregation and subsequent senile plaques deposition. We review the APP processing imbalance in EVs, autophagic and endosomal pathways in AD. Increased intraluminal vesicle (ILV) production and exosome release appear to counteract the endosomal dysfunction of APP processing; however, this process results in elevated amyloidogenic processing of APP and augmented senile plaque deposition. Several players related to APP processing and dysfunctional endosomal-lysosomal-exosomal (and other EVs) pathway are described, and the interconnected systems are discussed. The components Arc, p75, Rab11 and retromer complex emerge as candidates for key convergent mechanisms that lead to increased EVs loaded with APP machinery and Aβ levels, in atrophy and damage of basal forebrain cholinergic neurons in AD.

CHIP modulates APP-induced autophagy-dependent pathological symptoms in Drosophila

Dysregulation of autophagy is associated with the neurodegenerative processes in Alzheimer's disease (AD), yet it remains controversial whether autophagy is a cause or consequence of AD. We have previously expressed the full-length human APP in Drosophila and established a fly AD model that exhibits multiple AD-like symptoms. Here we report that depletion of CHIP effectively palliated APP-induced pathological symptoms, including morphological, behavioral, and cognitive defects. Mechanistically, CHIP is required for APP-induced autophagy dysfunction, which promotes Aβ production via increased expression of BACE and Psn. Our findings suggest that aberrant autophagy is not only a consequence of abnormal APP activity, but also contributes to dysregulated APP metabolism and subsequent AD pathogenesis.

A small molecule transcription factor EB activator ameliorates beta-amyloid precursor protein and Tau pathology in Alzheimer's disease models

Accumulating studies have suggested that targeting transcription factor EB (TFEB), an essential regulator of autophagy‐lysosomal pathway (ALP), is promising for the treatment of neurodegenerative disorders, including Alzheimer's disease (AD). However, potent and specific small molecule TFEB activators are not available at present. Previously, we identified a novel TFEB activator named curcumin analog C1 which directly binds to and activates TFEB. In this study, we systematically investigated the efficacy of curcumin analog C1 in three AD animal models that represent beta‐amyloid precursor protein (APP) pathology (5xFAD mice), tauopathy (P301S mice) and the APP/Tau combined pathology (3xTg‐AD mice). We found that C1 efficiently activated TFEB, enhanced autophagy and lysosomal activity, and reduced APP, APP C‐terminal fragments (CTF‐β/α), β‐amyloid peptides and Tau aggregates in these models accompanied by improved synaptic and cognitive function. Knockdown of TFEB and inhibition of lysosomal activity significantly inhibited the effects of C1 on APP and Tau degradation in vitro. In summary, curcumin analog C1 is a potent TFEB activator with promise for the prevention or treatment of AD.

Targeting Aggrephagy for the Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is one of the most common neurodegenerative diseases in older individuals with specific neuropsychiatric symptoms. It is a proteinopathy, pathologically characterized by the presence of misfolded protein (Aβ and Tau) aggregates in the brain, causing progressive dementia. Increasing studies have provided evidence that the defect in protein-degrading systems, especially the autophagy-lysosome pathway (ALP), plays an important role in the pathogenesis of AD. Recent studies have demonstrated that AD-associated protein aggregates can be selectively recognized by some receptors and then be degraded by ALP, a process termed aggrephagy. In this study, we reviewed the role of aggrephagy in AD development and discussed the strategy of promoting aggrephagy using small molecules for the treatment of AD.

Autophagy as a Cellular Stress Response Mechanism in the Nervous System

Cells of an organism face with various types of insults during their lifetime. Exposure to toxins, metabolic problems, ischaemia/reperfusion, physical trauma, genetic diseases, neurodegenerative diseases are among the conditions that trigger cellular stress responses. In this context, autophagy is one of the mechanisms that supports cell survival under stressful conditions. Autophagic vesicle engulfs the cargo and transports it to lysosome for degradation and turnover. As such, autophagy eliminates abnormal proteins, clears damaged organelles, limits oxidative stress and helps to improve metabolic balance. Nervous system cells and particularly postmitotic neurons are highly sensitive to a spectrum of insults, and autophagy emerges as one of the key stress response mechanism, ensuring health and survival of these vulnerable cell types. In this review, we will overview mechanisms through which cells cope with stress, and how these stress responses regulate autophagy, with a special focus on the nervous system.

β-Asarone Inhibits Amyloid-β by Promoting Autophagy in a Cell Model of Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common types of dementia that causes memory, thinking, and behavior problems. The most important feature of AD is the gradual irreversible loss of cognitive ability through the formation of amyloid β (Aβ) plaques and neurofibrillary tangles composed of tau protein. The metabolism of Aβ and tau proteins is closely related to and is affected by autophagy. Current research speculates that autophagy dysfunction leads to an increase in harmful proteins in AD. β-Asarone is the main constituent of Acorus tatarinowii Schott and has important effects on the central nervous system. In this paper, we primarily explored the effects of β-asarone on the clearance of noxious proteins and the associated potential mechanisms via autophagy in a PC12 cell AD model. A CCK-8 assay and LDH experiments were used to assess cell viability/toxicity, and SPiDER-βGal was used to detect cellular senescence. The important proteins associated with the pathogenesis of AD including APP, PS1, Aβ, BACE1, and SYN1 were analyzed by immunofluorescence (IF) and Western blot analysis. Antimycin A (A3) and cyclosporine A (CSA) were selected as the activators and inhibitors of autophagy, respectively. LC3, BECN, P62, PINK1, and Parkin protein expression were also examined by IF and Western blot analysis. The data showed that β-asarone administration significantly dose-dependently increased cell proliferation and decreased cytotoxicity; moreover, β-asarone inhibited SA-βGal and improved cell senescence. The results further showed that, compared to the model, APP, PS1, Aβ, BACE1, and p62 were reduced, while SYN1, BECN1, and LC3 were increased after treatment with β-asarone. The results of Canonical Correlation Analysis (CCA) showed a highly significant relationship between the pathological factors of AD and the protein expression of autophagy. In conclusion, our study demonstrated that β-asarone can inhibit Aβ, and this effect may occur by promoting autophagy in a cell model of AD.

The inducible amphisome isolates viral hemagglutinin and defends against influenza A virus infection

The emergence of drug-resistant influenza type A viruses (IAVs) necessitates the development of novel anti-IAV agents. Here, we target the IAV hemagglutinin (HA) protein using multivalent peptide library screens and identify PVF-tet, a peptide-based HA inhibitor. PVF-tet inhibits IAV cytopathicity and propagation in cells by binding to newly synthesized HA, rather than to the HA of the parental virus, thus inducing the accumulation of HA within a unique structure, the inducible amphisome, whose production from the autophagosome is accelerated by PVF-tet. The amphisome is also produced in response to IAV infection in the absence of PVF-tet by cells overexpressing ABC transporter subfamily A3, which plays an essential role in the maturation of multivesicular endosomes into the lamellar body, a lipid-sorting organelle. Our results show that the inducible amphisomes can function as a type of organelle-based anti-viral machinery by sequestering HA. PVF-tet efficiently rescues mice from the lethality of IAV infection.

Beclin 1 Complex and Neurodegenerative Disorders

Beclin1 is the mammalian orthologue of yeast Atg6/vacuolar protein sorting-30 (VPS30). Beclin1 interacts with various biological macromolecules like ATG14, BIF-1, NRBF2, RUBICON, UVRAG, AMBRA1, HMGB1, PINK1, and PARKIN. Such interactions promote Beclin1-PI3KC3 complex formation. Autophagy is blocked in apoptosis owing to the breakdown of Beclin1 by caspase whereas autophagy induction inhibits effector caspase degradation, therefore, blocks apoptosis. Thus, the Beclin1 is an essential biomolecular species for cross-regulation between autophagy and apoptosis. Various studies carried out in neurodegenerative animal models associated with aggregated proteins have confirmed that multifunctional Beclin1 protein is necessary for neuronal integrity. The role of Beclin1 protein has been investigated and was reported in various human neurodegeneration disorders. This chapter aims to provide an insight into the role of Beclin1 in the development of neurodegenerative disorders.

Activation of PPARA-mediated autophagy reduces Alzheimer disease-like pathology and cognitive decline in a murine model

Alzheimer disease (AD) is the most common neurodegenerative disease. An imbalance between the production and clearance of Aβ (amyloid beta) is considered to be actively involved in AD pathogenesis. Macroautophagy/autophagy is a major cellular pathway leading to the removal of aggregated proteins, and upregulation of autophagy represents a plausible therapeutic strategy to combat overproduction of neurotoxic Aβ. PPARA/PPARα (peroxisome proliferator activated receptor alpha) is a transcription factor that regulates genes involved in fatty acid metabolism and activates hepatic autophagy. We hypothesized that PPARA regulates autophagy in the nervous system and PPARA-mediated autophagy affects AD. We found that pharmacological activation of PPARA by the PPARA agonists gemfibrozil and Wy14643 induces autophagy in human microglia (HM) cells and U251 human glioma cells stably expressing the human APP (amyloid beta precursor protein) mutant (APP-p.M671L) and this effect is PPARA-dependent. Administration of PPARA agonists decreases amyloid pathology and reverses memory deficits and anxiety symptoms in APP-PSEN1ΔE9 mice. There is a reduced level of soluble Aβ and insoluble Aβ in hippocampus and cortex tissues from APP-PSEN1ΔE9 mice after treatment with either gemfibrozil or Wy14643, which promoted the recruitment of microglia and astrocytes to the vicinity of Aβ plaques and enhanced autophagosome biogenesis. These results indicated that PPARA is an important factor regulating autophagy in the clearance of Aβ and suggested gemfibrozil be assessed as a possible treatment for AD.Abbreviation: Aβ: amyloid beta; ACTB: actin beta; ADAM10: ADAM metallopeptidase domain 10; AD: Alzheimer disease; AIF1/IBA1: allograft inflammatory factor 1; ANOVA: analysis of variance; APOE: apolipoprotein E; APP: amyloid beta precursor protein; APP-PSEN1ΔE9: APPswe/PSEN1dE9; BAFA1: bafilomycin A1; BDNF: brain derived neurotrophic factor; BECN1: beclin 1; CD68: CD68 molecule; CREB1: cAMP responsive element binding protein 1; DAPI: 4',6-diamidino-2-phenylindole; DLG4/PSD-95: discs large MAGUK scaffold protein 4; DMSO: dimethyl sulfoxide; ELISA: enzyme linked immunosorbent assay; FDA: U.S. Food and Drug Administration; FKBP5: FK506 binding protein 5; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; gemfibrozil: 5-(2,5-dimethylphenoxy)-2,2-dimethylpentanoic acid; GFAP: glial fibrillary acidic protein; GLI2/THP1: GLI family zinc finger 2; HM: human microglia; IL6: interleukin 6; LAMP1: lysosomal associated membrane protein 1; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; NC: negative control; OQ: opposite quadrant; PPARA/PPARα, peroxisome proliferator activated receptor alpha; PSEN1/PS1: presenilin 1; SEM: standard error of the mean; SQSTM1: sequestosome 1; SYP: synaptophysin; TFEB: transcription factor EB; TNF/TNF-α: tumor necrosis factor; TQ: target quadrant; WT: wild type; Wy14643: 2-[4-chloro-6-(2,3-dimethylanilino)pyrimidin-2-yl]sulfanylacetic acid.

Autophagy, Cellular Aging and Age-related Human Diseases

Macroautophagy/autophagy is a conserved degradation system that engulfs intracytoplasmic contents, including aggregated proteins and organelles, which is crucial for cellular homeostasis. During aging, cellular factors suggested as the cause of aging have been reported to be associated with progressively compromised autophagy. Dysfunctional autophagy may contribute to age-related diseases, such as neurodegenerative disease, cancer, and metabolic syndrome, in the elderly. Therefore, restoration of impaired autophagy to normal may help to prevent age-related disease and extend lifespan and longevity. Therefore, this review aims to provide an overview of the mechanisms of autophagy underlying cellular aging and the consequent disease. Understanding the mechanisms of autophagy may provide potential information to aid therapeutic interventions in age-related diseases.

Cell-to-Cell Communication in Learning and Memory: From Neuro- and Glio-Transmission to Information Exchange Mediated by Extracellular Vesicles

Most aspects of nervous system development and function rely on the continuous crosstalk between neurons and the variegated universe of non-neuronal cells surrounding them. The most extraordinary property of this cellular community is its ability to undergo adaptive modifications in response to environmental cues originating from inside or outside the body. Such ability, known as neuronal plasticity, allows long-lasting modifications of the strength, composition and efficacy of the connections between neurons, which constitutes the biochemical base for learning and memory. Nerve cells communicate with each other through both wiring (synaptic) and volume transmission of signals. It is by now clear that glial cells, and in particular astrocytes, also play critical roles in both modes by releasing different kinds of molecules (e.g., D-serine secreted by astrocytes). On the other hand, neurons produce factors that can regulate the activity of glial cells, including their ability to release regulatory molecules. In the last fifteen years it has been demonstrated that both neurons and glial cells release extracellular vesicles (EVs) of different kinds, both in physiologic and pathological conditions. Here we discuss the possible involvement of EVs in the events underlying learning and memory, in both physiologic and pathological conditions.

Effect of atorvastatin on Aβ1-42 -induced alteration of SESN2, SIRT1, LC3II and TPP1 protein expressions in neuronal cell cultures

OBJECTIVES

Sestrins (SESNs) and sirtuins (SIRTs) are antioxidant and antiapoptotic genes and crucial mediators for lysosomal autophagy regulation that play a pivotal role in the Alzheimer's disease (AD). Recently, statins have been linked to the reduced prevalence of AD in statin-prescribed populations yet molecular basis for the neuroprotective action of statins is still under debate.

METHODS

This study was undertaken whether Aβ-induced changes of SESN2 and SIRT1 protein expression, autophagy marker LC3II and lysosomal enzyme TPP1 affected by atorvastatin (Western blot) and its possible role in Aβ neurotoxicity (ELISA).

KEY FINDINGS/RESULTS

We showed that SESN2 and LC3II expressions were elevated, whereas SIRT1 and TPP1 expressions were decreased in the Aβ_1-42 -exposed human neuroblastoma cells (SH-SY5Y). Co-administration of atorvastatin with Aβ_1-42 compensates SESN2 increase and recovers SIRT1 decline by reducing oxidative stress, decreasing SESN2 expression and increasing SIRT1 expression by its neuroprotective action. Atorvastatin induced LC3II but not TPP1 level in the Aβ_1-42 -exposed cells suggested that atorvastatin is effective in the formation of autophagosome but not on the expression of the specific lysosomal enzyme TPP1.

DISCUSSION AND CONCLUSION

Together, these results indicate that atorvastatin induced SESN2, SIRT1 and LC3II levels play a protective role against Aβ_1-42 neurotoxicity.

The role of isoaspartate in fibrillation and its prevention by Protein-L-isoaspartyl methyltransferase

BACKGROUND

Isomerization of aspartate to isoaspartate (isoAsp) on aging causes protein damage and malfunction. Protein-L-isoaspartyl methyltransferase (PIMT) performs a neuroprotective role by repairing such residues. A hexapeptide, Val-Tyr-Pro-(isoAsp)-His-Ala (VA6), a substrate of PIMT, is shown to form fibrils, while the normal Asp-containing peptide does not. Considering the role of PIMT against epileptic seizure, the combined effect of PIMT and two antiepileptic drugs (AEDs) (valproic acid and stiripentol) was investigated for anti-fibrillation activity.

METHODS

Structural/functional modulations due to the binding of AEDs to PIMT were investigated using biophysical techniques. Thioflavin T (ThT) fluorescence assay and microscopic methods were employed to study fibril formation by VA6. In vitro experiments with PC12 cells were carried out with PIMT/AEDs.

RESULTS

ThT assay indicated reduction of fibrillation of VA6 by PIMT. AEDs stabilize PIMT, bind close to the cofactor binding site, possibly exerting allosteric effect, increase the enzymatic activity, and anti-fibrillation efficacy. Furthermore, Aβ42, implicated in Alzheimer's disease, undergoes β-sheet to α-helix transition in presence of PIMT. Studies with PC12 derived neurons showed that PIMT and PIMT/AEDs exerted neuroprotective effect against anti-NGF induced neurotoxicity. This was further validated against neurotoxicity induced by Aβ42 in primary rat cortical neurons.

CONCLUSIONS

The study provides a new perspective to the role isoAsp in protein fibrillation, PIMT in its prevention and AEDs in enhancing the activity of the enzyme.

GENERAL SIGNIFICANCE

IsoAsp, with an additional C atom in the main-chain of polypeptide chain, may make it more susceptible to fibrillation. PIMT alone, or in association with AEDs prevents this.

Alzheimer's Disease Progression in the 5×FAD Mouse Captured with a Multiplex Gene Expression Array

BACKGROUND

Alzheimer's disease (AD) is an incurable complex neurodegenerative condition with no new therapies licensed in the past 20 years. AD progression is characterized by the up- and downregulation of distinct biological processes that can be followed through the expression level changes of associated genes and gene networks.

OBJECTIVE

Our study aims to establish a multiplex gene expression tracking platform to follow disease progression in an animal model facilitating the study of treatment paradigms.

METHODS

We have established a multiplex platform covering 47 key genes related to immunological, neuronal, mitochondrial, and autophagy cell types and processes that capture disease progression in the 5×FAD mouse model.

RESULTS

We show that the immunological response is the most pronounced change in aged 5×FAD mice (8 months and above), and in agreement with early stage human disease samples, observe an initial downregulation of microglial genes in one-month-old animals. The less dramatic downregulation of neuronal and mitochondrial gene sets is also reported.

CONCLUSION

This study provides the basis for a quantitative multi-dimensional platform to follow AD progression and monitor the efficacy of treatments in an animal model.

Ghrelin in Alzheimer's disease: Pathologic roles and therapeutic implications

Ghrelin, which has many important physiological roles, such as stimulating food intake, regulating energy homeostasis, and releasing insulin, has recently been studied for its roles in a diverse range of neurological disorders. Despite the several functions of ghrelin in the central nervous system, whether it works as a therapeutic agent for neurological dysfunction has been unclear. Altered levels and various roles of ghrelin have been reported in Alzheimer's disease (AD), which is characterized by the accumulation of misfolded proteins resulting in synaptic loss and cognitive decline. Interestingly, treatment with ghrelin or with the agonist of ghrelin receptor showed attenuation in several cases of AD-related pathology. These findings suggest the potential therapeutic implications of ghrelin in the pathogenesis of AD. In the present review, we summarized the roles of ghrelin in AD pathogenesis, amyloid beta (Aβ) homeostasis, tau hyperphosphorylation, neuroinflammation, mitochondrial deficit, synaptic dysfunction and cognitive impairment. The findings from this review suggest that ghrelin has a novel therapeutic potential for AD treatment. Thus, rigorously designed studies are needed to establish an effective AD-modifying strategy.

Targeting Mitochondria in Alzheimer Disease: Rationale and Perspectives

A decline in mitochondrial function plays a key role in the aging process and increases the incidence of age-related disorders, including Alzheimer disease (AD). Mitochondria-the power station of the organism-can affect several different cellular activities, including abnormal cellular energy generation, response to toxic insults, regulation of metabolism, and execution of cell death. In AD subjects, mitochondria are characterized by impaired function such as lowered oxidative phosphorylation, decreased adenosine triphosphate production, significant increased reactive oxygen species generation, and compromised antioxidant defense. The current review discusses the most relevant mitochondrial defects that are considered to play a significant role in AD and that may offer promising therapeutic targets for the treatment/prevention of AD. In addition, we discuss mechanisms of action and translational potential of some promising mitochondrial and bioenergetic therapeutics for AD including compounds able to potentiate energy production, antioxidants to scavenge reactive oxygen species and reduce oxidative damage, glucose metabolism, and candidates that target mitophagy. While mitochondrial therapeutic strategies have shown promise at the preclinical stage, there has been little progress in clinical trials. Thus, there is an urgent need to better understand the mechanisms regulating mitochondrial homeostasis in order to identify powerful drug candidates that target 'in and out' the mitochondria to preserve cognitive functions.

Chronic sleep fragmentation shares similar pathogenesis with neurodegenerative diseases: Endosome-autophagosome-lysosome pathway dysfunction and microglia-mediated neuroinflammation

Aims

Insufficient sleep has been found to result in varying degrees of cognitive impairment and emotional changes. Sleep was reported probably responsible for cleaning metabolic wastes in brain by increasing extracellular bulk flow. Herein, we propose that chronic sleep insufficiency in young adult wild‐type mice is also linked with dysfunction of intracellular protein degradation pathways and microglia‐mediated neuroinflammation, which are potentially important mechanisms in the initiation of neurodegeneration.

Methods

We applied the chronic sleep fragmentation (CSF) model to induce chronic sleep insufficiency in wild‐type mice. After 2 months of CSF, cognitive function, amyloid‐β accumulation, dysfunction of endosome‐autophagosome‐lysosome pathway, and microglia activation were evaluated.

Results

Following CSF, impairment of spatial learning and memory, and aggravated anxiety‐like behavior in mice were identified by behavioral experiments. Increased intracellular amyloid‐β accumulation was observed in cortex and hippocampus. Mechanistically, CSF could significantly enhance the expression of Rab5 (early endosome marker), Rab7 (late endosome marker), as well as LC3B (autophagosome marker), and autophagy‐positive regulatory factors in brain detected by immunofluorescent staining and Western blot. In addition, activation of microglia was evident by enhanced CD68, CD16/32, and CD206 levels after CSF treatment.

Conclusions

Chronic sleep fragmentation could initiate pathogenetic processes similar to the early stage of neurodegeneration, including dysfunction of endosome‐autophagosome‐lysosome pathway and microglia‐mediated neuroinflammation. Our findings further strengthen the link between chronic sleep insufficiency and the initiation of neurodegeneration even if lack of genetic predisposition.

Enhancing the retrograde axonal transport by curcumin promotes autophagic flux in N2a/APP695swe cells

The accumulation of autophagosomes and dysfunction at the axonal terminal of neurons play crucial roles in the genesis and development of Alzheimer’s disease (AD). Abnormalities in neuron axonal transport-related proteins prevent autophagosome maturation in AD. Curcumin, a polyphenol plant compound, has been shown to exert neuroprotective effects by increasing autophagy in AD, but the underlying mechanism of its effect on autophagy axon transport remains elusive. This study investigated the effects of curcumin on autophagosome formation and axonal transport in N2a/APP695swe cells (AD cell model) as well as the mechanism underlying those effects. Curcumin treatment significantly increased the expression of Beclin1, Atg5, and Atg16L1, induced the formation of autophagosomes, and promoted autophagosome–lysosome fusion in N2a/APP695swe cells. At the same time, curcumin promoted the expression of dynein, dynactin, and BICD2 as well as their binding to form the retrograde axonal transport molecular motor complex. Moreover, curcumin also increased the expression of the scaffolding proteins Rab7- interacting lysosomal protein (RILP) and huntingtin in N2a/APP695swe cells. Taken together, our findings indicate that curcumin increases autophagic flux by promoting interactions among autophagic axonal transport-related proteins and inducing lysosome–autophagosome fusion. This study provides evidence suggesting the potential use of curcumin as a novel treatment for AD.

Sequential formation of different layers of dystrophic neurites in Alzheimer's brains

Alzheimer's disease (AD) is characterized by the presence of neuritic plaques in which dystrophic neurites (DNs) are typical constituents. We recently showed that DNs labeled by antibodies to the tubular endoplasmic reticulum (ER) protein reticulon-3 (RTN3) are enriched with clustered tubular ER. However, multi-vesicle bodies are also found in DNs, suggesting that different populations of DNs exist in brains of AD patients. To understand how different DNs evolve to surround core amyloid plaques, we monitored the growth of DNs in AD mouse brains (5xFAD and APP/PS1ΔE9 mice) by multiple approaches, including two-dimensional and three-dimensional (3D) electron microscopy (EM). We discovered that a pre-autophagosome protein ATG9A was enriched in DNs when a plaque was just beginning to develop. ATG9A-positive DNs were often closer to the core amyloid plaque, whereas RTN3 immunoreactive DNs were mostly located in the outer layers of ATG9A-positive DNs. Proteins such as RAB7 and LC3 appeared in DNs at later stages during plaque growth, likely accumulated as a part of large autophagy vesicles, and were distributed relatively furthest from the core amyloid plaque. Reconstructing the 3D structure of different morphologies of DNs revealed that DNs in AD mouse brains were constituted in three layers that are distinct by enriching different types of vesicles, as validated by immune-EM methods. Collectively, our results provide the first evidence that DNs evolve from dysfunctions of pre-autophagosomes, tubular ER, mature autophagosomes, and the ubiquitin proteasome system during plaque growth.

Protective effect of potassium 2-(l-hydroxypentyl)-benzoate on hippocampal neurons, synapses and dystrophic axons in APP/PS1 mice

RATIONALE

As the hub of memory and space, hippocampus is very sensitive to a wide variety of injuries and is one of the earliest brain structures to develop neurodegenerative changes in AD. Previous research has showed a protective effect of potassium 2-(l-hydroxypentyl)-benzoate (PHPB) on cognitive deficits in animal models of AD. However, it is unclear whether this protective effect is associated with hippocampal alterations.

OBJECTIVES

The present study was conducted to evaluate the protective effect of PHPB on hippocampal neurodegenerative changes in middle-aged APP/PS1 mice.

METHODS

Ten-month-old male APP/PS1 transgenic mice and age-matched wild-type mice were randomly divided into three groups. PHPB-treated APP/PS1 group received 30 mg/kg PHPB by oral gavage once daily for 12 weeks. Wild-type group and APP/PS1 group received the same volume of water alone. Twelve weeks later, mice (13-month-old) were tested for in vivo 1H-MRS examination and then sacrificed for subsequent biochemical and pathological examinations using transmission electron microscopy, Golgi staining, immunohistochemistry, and western blotting.

RESULTS

We found that PHPB treatment significantly improved the micromorphology of hippocampal neurons and subcellular organelles, ameliorated synapse loss and presynaptic axonal dystrophy, increased hippocampal dendritic spine density and dendritic complexity, enhanced the expression of hippocampal synapse-associated proteins, and improved hippocampal metabolism in middle-aged APP/PS1 mice.

CONCLUSIONS

Our study showed for the first time the protective effect of PHPB on hippocampal neurons, synapses, and dystrophic axons in APP/PS1 mice, which to some extent revealed the possible mechanism for its ability to improve cognition in animal models of AD.

Herpes simplex virus type 1 and Alzheimer's disease: link and potential impact on treatment

Introduction: Alzheimer's disease (AD), the most common form of dementia worldwide, is a multifactorial disease with a still unknown etiology. Herpes simplex virus 1 (HSV-1) has long been suspected to be one of the factors involved in the pathogenesis of the disease. Areas covered: We review the literature focusing on viral characteristics of HSV-1, the mechanisms this virus uses to infect neural cells, its interaction with the host immune system and genetic background and summarizes results and research that support the hypothesis of an association between AD and HSV-1. The possible usefulness of virus-directed pharmaceutical approaches as potential treatments for AD will be discussed as well. Expert opinion: We highlight crucial aspects that must be addressed to clarify the possible role of HSV-1 in the pathogenesis of the disease, and to allow the design of new therapeutical approaches for AD.

Targeting Autophagy for the Treatment of Alzheimer's Disease: Challenges and Opportunities

Alzheimer's disease (AD) is the most common type of dementia which characterized by a progressive loss of memory and cognitive function due to degeneration of synapses and axons. Currently, there is no cure for AD. Deposition of extracellular amyloid-β (Aβ) plaques and intracellular tau neurofibrillary tangles (NFTs) are two hallmark pathologic changes in the brains of Alzheimer's patients. Autophagy is the major mechanism in cells responsible for removing protein aggregates. Accumulation of immature autophagic vacuoles (AVs) in dystrophic neurites of Alzheimer patients' brains suggests that autophagy process is disrupted. Till now, it is far from clear what role autophagy plays in AD, a causative role, a protective role, or just a consequence of the disease process itself. To design more effective therapeutic strategies towards this devastating disorder, it is essential to understand the exact role of autophagy played during different stages of AD.

Oleocanthal-Rich Extra-Virgin Olive Oil Restores the Blood-Brain Barrier Function through NLRP3 Inflammasome Inhibition Simultaneously with Autophagy Induction in TgSwDI Mice

Alzheimer's disease (AD) is a complex neurodegenerative disorder characterized by multiple hallmarks including extracellular amyloid (Aβ) plaques, neurofibrillary tangles, dysfunctional blood-brain barrier (BBB), neuroinflammation, and impaired autophagy. Thus, novel strategies that target multiple disease pathways would be essential to prevent, halt, or treat the disease. A growing body of evidence including our studies supports a protective effect of oleocanthal (OC) and extra-virgin olive oil (EVOO) at early AD stages before the onset of pathology. In addition, we reported previously that OC and EVOO exhibited such effect by restoring the BBB function; however, the mechanism(s) by which OC and EVOO exert such an effect and whether this effect extends to a later stage of AD remain unknown. In this work, we sought first to test the effect of OC-rich EVOO consumption at an advanced stage of the disease in TgSwDI mice, an AD mouse model, starting at the age of 6 months for 3 months treatment, and then to elucidate the mechanism(s) by which OC-rich EVOO exerts the observed beneficial effect. Overall findings demonstrated that OC-rich EVOO restored the BBB function and reduced AD-associated pathology by reducing neuroinflammation through inhibition of NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome and inducing autophagy through activation of AMP-activated protein kinase (AMPK)/Unc-51-like autophagy activating kinase 1 (ULK1) pathway. Thus, diet supplementation with OC-rich EVOO could provide beneficial effect to slow or halt the progression of AD.

α-Tocopherol Modulates Non-Amyloidogenic Pathway and Autophagy in an In Vitro Model of Alzheimer's Disease: A Transcriptional Study

Alzheimer's disease (AD) is the most common form of dementia worldwide. The hallmarks of AD are the extracellular amyloid plaques, which are formed by amyloid β (Aβ) aggregates derived from the processing of the amyloid precursor protein (APP), and the intraneuronal neurofibrillary tangles, which are formed by the hyperphosphorylated tau protein. The aim of this work was to study the effects of α-tocopherol in retinoic acid differentiated SH-SY5Y neuroblastoma cells exposed to Aβ1-42 evaluating the transcriptional profile by next-generation sequencing. We observed that α-tocopherol was able to reduce the cytotoxicity induced by Aβ treatment, as demonstrated by Thiazolyl Blue Tetrazolium Bromide (MTT) assay. Moreover, the transcriptomic analysis evidenced that α-tocopherol treatment upregulated genes involved in the non-amyloidogenic processing of APP, while it downregulated the amyloidogenic pathway. Moreover, α-tocopherol modulated the expression of the genes involved in autophagy and the cell cycle, which are both known to be altered in AD. The treatment with α-tocopherol was also able to reduce oxidative stress, restoring nuclear factor erythroid-derived 2-like 2 (Nrf2) and decreasing inducible nitric oxide synthase (iNOS) levels, as demonstrated by immunocytochemistry.

Reciprocal Predictive Relationships between Amyloid and Tau Biomarkers in Alzheimer's Disease Progression: An Empirical Model

There is an urgent need to understand the relationships between amyloid-β (Aβ) and tau in the progression of Alzheimer's disease to identify treatment targets. Here we examine reciprocal predictions of brain Aβ burden quantified by positron emission tomography and CSF concentrations of Aβ42 and phosphorylated tau (p-tau). Each biomarker was examined over 48 months in two separate cross-lagged models; one in asymptomatic healthy elderly people (men and women), and one in patients with Alzheimer's disease (AD) dementia or mild cognitive impairment (MCI). The models examine predictions of each biomarker on the progression of the others, considering each previous and concurrent measure. In healthy elderly, lower CSF Aβ42 predicted Aβ deposition and reciprocally, Aβ burden predicted a decrease in CSF Aβ42. Lower CSF Aβ42 predicted an increase in CSF p-tau, and CSF p-tau predicted Aβ deposition. In AD/MCI, lower CSF Aβ42 predicted Aβ deposition and Aβ burden reciprocally predicted CSF Aβ42 changes; however, in contrast to healthy elderly, CSF p-tau concentrations did not predict Aβ biomarkers, or vice versa. In post hoc models examining cognitive status, CSF Aβ42 predicted Mini Mental State Examination (MMSE) scores in healthy elderly, whereas Aβ burden and CSF p-tau predicted MMSE scores in AD/MCI. The findings describe reciprocal predictions between Aβ and tau biomarkers in healthy elderly and they implicate mechanisms underlying low CSF Aβ42 in Alzheimer's disease pathogenesis and progression. In symptomatic Alzheimer's disease, CSF Aβ42 and Aβ deposition predicted each other; however, Aβ and CSF p-tau progressed independently and they independently predicted cognitive decline.SIGNIFICANCE STATEMENT This study offers empirical evidence concerning the hypothesized "amyloid cascade", as it progressed over 4 years in healthy elderly people and in Alzheimer's disease patients. In healthy elderly, CSF amyloid changes predicted amyloid deposition, CSF phosphorylated tau concentrations, and a decline in cognitive status. Phosphorylated tau concentrations specifically predicted amyloid deposition. In Alzheimer's disease patients, although amyloid deposition and CSF amyloid changes continued to "cascade", there was no evidence to suggest that amyloid and tau biomarkers predicted each other, although both amyloid deposition and CSF tau progression predicted cognitive decline independently. Taking advantage of repeated amyloid PET and CSF measures, this dynamic view offers new insight into the progression of Alzheimer's disease biomarkers and their relationships with cognitive decline.

Restoring synaptic function through multimodal therapeutics

Alzheimer's disease (AD) is the major form of dementia and a growing epidemic for which no disease-modifying treatments exist. AD is characterized by the early loss of synapses in the brain and, at later stages, neuronal death accompanied with progressive loss of cognitive functions. Here we focus on the mechanisms involved in the maintenance of the synapse and how their perturbation leads to synaptic loss. We suggest treatment strategies that particularly target energy metabolism in terms of cholesterol and glucose biochemistry in neurons and astrocytes We also discuss the potential of restoring impaired protein homeostasis through autophagy. These pathways are analyzed from a basic science perspective and suggest new avenues for discovery. We also propose several targets for both basic and translational therapeutics in these pathways and provide perspective on future AD treatment.

Spleen tyrosine kinase (SYK) blocks autophagic Tau degradation in vitro and in vivo

Spleen tyrosine kinase (SYK) plays a major role in inflammation and in adaptive immune responses and could therefore contribute to the neuroinflammation observed in various neurodegenerative diseases. Indeed, previously we have reported that SYK also regulates β-amyloid (Aβ) production and hyperphosphorylation of Tau protein involved in these diseases. Moreover, SYK hyperactivation occurs in a subset of activated microglia, in dystrophic neurites surrounding Aβ deposits, and in neurons affected by Tau pathology both in individuals with Alzheimer's disease (AD) and in AD mouse models. SYK activation increases Tau phosphorylation and accumulation, suggesting that SYK could be an attractive target for treating AD. However, the mechanism by which SYK affects Tau pathology is not clear. In this study, using cell biology and biochemical approaches, along with immunoprecipitation and immunoblotting, quantitative RT-PCR, and ELISAs, we found that SYK inhibition increases autophagic Tau degradation without impacting Tau production. Using neuron-like SH-SY5Y cells, we demonstrate that SYK acts upstream of the mammalian target of rapamycin (mTOR) pathway and that pharmacological inhibition or knockdown of SYK decreases mTOR pathway activation and increases autophagic Tau degradation. Interestingly, chronic SYK inhibition in a tauopathy mouse model profoundly reduced Tau accumulation, neuroinflammation, neuronal and synaptic loss, and also reversed defective autophagy. Our results further suggest that the SYK up-regulation observed in the brains of individuals with AD contributes to defective autophagic clearance leading to the accumulation of pathogenic Tau species. These findings further highlight SYK as a therapeutic target for the treatment of tauopathies and other neurodegenerative proteinopathies associated with defective autophagic clearance.

Elevated TREM2 Gene Dosage Reprograms Microglia Responsivity and Ameliorates Pathological Phenotypes in Alzheimer's Disease Models

Variants of TREM2 are associated with Alzheimer's disease (AD). To study whether increasing TREM2 gene dosage could modify the disease pathogenesis, we developed BAC transgenic mice expressing human TREM2 (BAC-TREM2) in microglia. We found that elevated TREM2 expression reduced amyloid burden in the 5xFAD mouse model. Transcriptomic profiling demonstrated that increasing TREM2 levels conferred a rescuing effect, which includes dampening the expression of multiple disease-associated microglial genes and augmenting downregulated neuronal genes. Interestingly, 5xFAD/BAC-TREM2 mice showed further upregulation of several reactive microglial genes linked to phagocytosis and negative regulation of immune cell activation. Moreover, these mice showed enhanced process ramification and phagocytic marker expression in plaque-associated microglia and reduced neuritic dystrophy. Finally, elevated TREM2 gene dosage led to improved memory performance in AD models. In summary, our study shows that a genomic transgene-driven increase in TREM2 expression reprograms microglia responsivity and ameliorates neuropathological and behavioral deficits in AD mouse models.

Lewy pathology in Parkinson's disease consists of crowded organelles and lipid membranes

Parkinson's disease, the most common age-related movement disorder, is a progressive neurodegenerative disease with unclear etiology. Key neuropathological hallmarks are Lewy bodies and Lewy neurites: neuronal inclusions immunopositive for the protein α-synuclein. In-depth ultrastructural analysis of Lewy pathology is crucial to understanding pathogenesis of this disease. Using correlative light and electron microscopy and tomography on postmortem human brain tissue from Parkinson's disease brain donors, we identified α-synuclein immunopositive Lewy pathology and show a crowded environment of membranes therein, including vesicular structures and dysmorphic organelles. Filaments interspersed between the membranes and organelles were identifiable in many but not all α-synuclein inclusions. Crowding of organellar components was confirmed by stimulated emission depletion (STED)-based super-resolution microscopy, and high lipid content within α-synuclein immunopositive inclusions was corroborated by confocal imaging, Fourier-transform coherent anti-Stokes Raman scattering infrared imaging and lipidomics. Applying such correlative high-resolution imaging and biophysical approaches, we discovered an aggregated protein-lipid compartmentalization not previously described in the Parkinsons' disease brain.

Mitochondrial dynamics and transport in Alzheimer's disease

Mitochondrial dysfunction is now recognized as a contributing factor to the early pathology of multiple human conditions including neurodegenerative diseases. Mitochondria are signaling organelles with a multitude of functions ranging from energy production to a regulation of cellular metabolism, energy homeostasis, stress response, and cell fate. The success of these complex processes critically depends on the fidelity of mitochondrial dynamics that include the ability of mitochondria to change shape and location in the cell, which is essential for the maintenance of proper function and quality control, particularly in polarized cells such as neurons. This review highlights several aspects of alterations in mitochondrial dynamics in Alzheimer's disease, which may contribute to the etiology of this debilitating condition. We also discuss therapeutic strategies to improve mitochondrial dynamics and function that may provide an alternative approach to failed amyloid-directed interventions.

Endo-lysosomal pathway and ubiquitin-proteasome system dysfunction in Alzheimer's disease pathogenesis

Several lines of evidence have shown that defects in the endo-lysosomal autophagy degradation pathway and the ubiquitin-proteasome system play a role in Alzheimer's Disease (AD) pathogenesis and pathophysiology. Early pathological changes, such as marked enlargement of endosomal compartments, gradual accumulation of autophagic vacuoles (AVs) and lysosome dyshomeostasis, are well-recognized in AD. In addition to these pathological indicators, many genetic variants of key regulators in the endo-lysosomal autophagy networks and the ubiquitin-proteasome system have been found to be associated with AD. Furthermore, altered expression levels of key proteins in these pathways have been found in AD human brain tissues, primary cells and AD mouse models. In this review, we discuss potential disease mechanisms underlying the dysregulation of protein homeostasis governing systems. While the importance of two major protein degradation pathways in AD pathogenesis has been highlighted, targeted therapy at key components of these pathways has great potential in developing novel therapeutic interventions for AD. Future investigations are needed to define molecular mechanisms by which these complex regulatory systems become malfunctional at specific stages of AD development and progression, which will facilitate future development of novel therapeutic interventions. It is also critical to investigate all key components of the protein degradation pathways, both upstream and downstream, to improve our abilities to manipulate transport pathways with higher efficacy and less side effects.

Dual Role of Autophagy in Diseases of the Central Nervous System

Autophagy is a vital lysosomal degradation and recycling pathway in the eukaryotic cell, responsible for maintaining an intricate balance between cell survival and cell death, necessary for neuronal survival and function. This dual role played by autophagy raises the question whether this process is a protective or a destructive pathway, the contributor of neuronal cell death or a failed attempt to repair aberrant processes? Deregulated autophagy at different steps of the pathway, whether excessive or downregulated, has been proposed to be associated with neurodegenerative disorders such as Alzheimer's-, Huntington's-, and Parkinson's-disease, known for their intracellular accumulation of protein aggregates. Recent observations of impaired autophagy also appeared in psychiatric disorders such as schizophrenia and bipolar disorder suggesting an additional contribution to the pathophysiology of mental illness. Here we review the current understanding of autophagy's role in various neuropsychiatric disorders and, hitherto, the prevailing new potential autophagy-related therapeutic strategies for their treatment.

Gemfibrozil, a Lipid-Lowering Drug, Lowers Amyloid Plaque Pathology and Enhances Memory in a Mouse Model of Alzheimer's Disease via Peroxisome Proliferator-Activated Receptor α

Deposition of extracellular senile plaques containing amyloid-β is one of the major neuropathological characteristics of Alzheimer’s disease (AD). Therefore, targeting amyloid-β dyshomeostasis is an important therapeutic strategy for treatment of AD. In this study, we demonstrate that gemfibrozil, an FDA-approved drug for hyperlipidemia, can lower the amyloid plaque burden in the hippocampus and cortex of the 5XFAD model of AD. Additionally, gemfibrozil reduced microgliosis and astrogliosis associated with plaque in these mice. Administration of gemfibrozil also improved spatial learning and memory of the 5XFAD mice. Finally, we delineate that gemfibrozil requires the transcription factor peroxisome proliferator-activated receptor alpha (PPARα) to exhibit its amyloid lowering and memory enhancing effects in 5XFAD mice. These results highlight a new therapeutic property of gemfibrozil and suggest that this drug may be repurposed for treatment of AD.

Type II Diabetes Mellitus Accelerates Age-Dependent Aβ Pathology in Cynomolgus Monkey Brain

Accumulating evidence suggests that diabetes mellitus (DM) is one of the strongest risk factors for developing Alzheimer's disease (AD). However, it remains unclear how DM accelerates AD pathology in the brain. Cynomolgus monkey (Macaca fascicularis) is one of the nonhuman primates used for biomedical research, and we can observe spontaneous formation of AD pathology, such as senile plaques (SPs) and neurofibrillary tangles (NFTs), with the advance of aging. Furthermore, obesity is occasionally observed and frequently leads to development of type II DM (T2DM) in laboratory-housed cynomolgus monkeys. These findings suggest that cynomolgus monkey is a useful species to study the relationship between T2DM and AD pathology. In T2DM-affected monkey brains, SPs were observed in frontal and temporal lobe cortices almost 5 years earlier than healthy control monkeys. Moreover, age-related endocytic pathology, such as intraneuronal accumulation of enlarged endosomes, was exacerbated in T2DM-affected monkey brains. Since accumulating evidences suggest that endocytic dysfunction is involved in Aβ pathology, T2DM may aggravate age-related endocytic dysfunction, leading to the acceleration of Aβ pathology.

Ultrastructural evidence of microglial heterogeneity in Alzheimer's disease amyloid pathology

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disease, characterized by the deposition of extracellular fibrillar amyloid β (fΑβ) and the intracellular accumulation of neurofibrillary tangles. As AD progresses, Aβ drives a robust and prolonged inflammatory response via its recognition by microglia, the brain's immune cells. Microglial reactivity to fAβ plaques may impair their normal surveillance duties, facilitating synaptic loss and neuronal death, as well as cognitive decline in AD.

METHODS

In the current study, we performed correlative light, transmission, and scanning electron microscopy to provide insights into microglial structural and functional heterogeneity. We analyzed microglial cell bodies and processes in areas containing fAβ plaques and neuronal dystrophy, dystrophy only, or appearing healthy, among the hippocampus CA1 of 14-month-old APPSwe-PS1Δe9 mice versus wild-type littermates.

RESULTS

Our quantitative analysis revealed that microglial cell bodies in the AD model mice were larger and displayed ultrastructural signs of cellular stress, especially nearby plaques. Microglial cell bodies and processes were overall less phagocytic in AD model mice. However, they contained increased fibrillar materials and non-empty inclusions proximal to plaques. Microglial cell bodies and processes in AD model mice also displayed reduced association with extracellular space pockets that contained debris. In addition, microglial processes in healthy subregions of AD model mice encircled synaptic elements more often compared with plaque-associated processes. These observations in mice were qualitatively replicated in post-mortem hippocampal samples from two patients with AD (Braak stage 5).

CONCLUSION

Together, our findings identify at the ultrastructural level distinct microglial transformations common to mouse and human in association with amyloid pathology.

Autophagy-dependent secretion: mechanism, factors secreted, and disease implications

Although best understood as a degradative pathway, recent evidence demonstrates pronounced involvement of the macroautophagic/autophagic molecular machinery in cellular secretion. With either overexpression or inhibition of autophagy mediators, dramatic alterations in the cellular secretory profile occur. This affects secretion of a plethora of factors ranging from cytokines, to granule contents, and even viral particles. Encompassing a wide range of secreted factors, autophagy-dependent secretion is implicated in diseases ranging from cancer to neurodegeneration. With a growing body of evidence shedding light onto the molecular mediators, this review delineates the molecular machinery involved in selective targeting of the autophagosome for either degradation or secretion. In addition, we summarize the current understanding of factors and cargo secreted through this unconventional route, and describe the implications of this pathway in both health and disease. Abbreviations: BECN1, beclin 1; CAF, cancer associated fibroblast; CUPS, compartment for unconventional protein secretion; CXCL, C-X-C motif chemokine ligand; ER, endoplasmic reticulum; FGF2, fibroblast growth factor 2; HMGB1, high mobility group box 1; IDE, insulin degrading enzyme; IL, Interleukin; MAP1LC3/LC3, microtubule associated protein 1 light chain 3; MAPS, misfolding associated protein secretion; MEF, mouse embryonic fibroblast; MTORC1, MTOR complex I; PtdIns, phosphatidyl inositol; SEC22B, SEC22 homolog B, vesicle trafficking protein (gene/pseudogene); SFV, Semliki forest virus; SNCA, synuclein alpha; SQSTM1, sequestosome 1; STX, Syntaxin; TASCC, TOR-associated spatial coupling compartment; TGFB, transforming growth factor beta; TRIM16, tripartite motif containing 16; UPS, unconventional protein secretion; VWF, von Willebrand factor.

Extracellular Vesicle as a Source of Alzheimer's Biomarkers: Opportunities and Challenges

Alzheimer’s disease (AD) is a chronic progressive neurodegenerative disease characterized by memory decline and cognitive dysfunction. Although the primary causes of AD are not clear, it is widely accepted that the accumulation of amyloid beta (Aβ) and consecutive hyper-phosphorylation of tau, synaptic loss, oxidative stress and neuronal death might play a vital role in AD pathogenesis. Recently, it has been widely suggested that extracellular vesicles (EVs), which are released from virtually all cell types, are a mediator in regulating AD pathogenesis. Clinical evidence for the diagnostic performance of EV-associated biomarkers, particularly exosome biomarkers in the blood, is also emerging. In this review, we briefly introduce the biological function of EVs in the central nervous system and discuss the roles of EVs in AD pathogenesis. In particular, the roles of EVs associated with autophagy and lysosomal degradation systems in AD proteinopathy and in disease propagation are discussed. Next, we summarize candidates for biochemical AD biomarkers in EVs, including proteins and miRNAs. The accumulating data brings hope that the application of EVs will be helpful for early diagnostics and the identification of new therapeutic targets for AD. However, at the same time, there are several challenges in developing valid EV biomarkers. We highlight considerations for the development of AD biomarkers from circulating EVs, which includes the standardization of pre-analytical sources of variability, yield and purity of isolated EVs and quantification of EV biomarkers. The development of valid EV AD biomarkers may be facilitated by collaboration between investigators and the industry.

Alborixin clears amyloid-β by inducing autophagy through PTEN-mediated inhibition of the AKT pathway

Imbalance in production and clearance of amyloid beta (Aβ) is the primary reason for its deposition in Alzheimer disease. Macroautophagy/autophagy is one of the important mechanisms for clearance of both intracellular and extracellular Aβ. Here, through screening, we identified alborixin, an ionophore, as a potent inducer of autophagy. We found that autophagy induced by alborixin substantially cleared Aβ in microglia and primary neuronal cells. Induction of autophagy was accompanied by up regulation of autophagy proteins BECN1/Beclin 1, ATG5, ATG7 and increased lysosomal activities. Autophagy induced by alborixin was associated with inhibition of the phosphoinositide 3-kinase (PI3K)-AKT pathway. A knock down of PTEN and consistent, constitutive activation of AKT inhibited alborixin-induced autophagy and consequent clearance of Aβ. Furthermore, clearance of Aβ by alborixin led to significant reduction of Aβ-mediated cytotoxicity in primary neurons and differentiated N2a cells. Thus, our findings put forward alborixin as a potential anti-Alzheimer therapeutic lead. Abbreviations: Aβ: amyloid beta; ALB: alborixin; ATG: autophagy-related; BECN1: beclin 1; DAPI: 4, 6-diamidino-2-phenylindole; DCFH-DA: 2,7-dichlorodihydrofluorescein diacetate; fAβ: fibrillary form of amyloid beta; GFAP: glial fibrillary acidic protein; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MAP2: microtubule-associated protein 2; MTOR: mechanistic target of rapamycin kinase; PTEN: phosphatase and tensin homolog; ROS: reactive oxygen species; SQSTM1: sequestosome 1; TMRE: tetramethylrhodamine, ethyl ester.

Down-regulated TMED10 in Alzheimer disease induces autophagy via ATG4B activation

Several studies have shown that dysfunction of macroautophagy/autophagy is associated with many human diseases, including neurodegenerative disease and cancer. To explore the molecular mechanisms of autophagy, we performed a cell-based functional screening with SH-SY5Y cells stably expressing GFP-LC3, using an siRNA library and identified TMED10 (transmembrane p24 trafficking protein 10), previously known as the γ-secretase-modulating protein, as a novel regulator of autophagy. Further investigations revealed that depletion of TMED10 induced the activation of autophagy. Interestingly, protein-protein interaction assays showed that TMED10 directly binds to ATG4B (autophagy related gene 4B cysteine peptidase), and the interaction is diminished under autophagy activation conditions such as rapamycin treatment and serum deprivation. In addition, inhibition of TMED10 significantly enhanced the proteolytic activity of ATG4B for LC3 cleavage. Importantly, the expression of TMED10 in AD (Alzheimer disease) patients was considerably decreased, and downregulation of TMED10 increased amyloid-β (Aβ) production. Treatment with Aβ increased ATG4B proteolytic activity as well as dissociation of TMED10 and ATG4B. Taken together, our results suggest that the AD-associated protein TMED10 negatively regulates autophagy by inhibiting ATG4B activity.Abbreviations: Aβ: amyloid-β; AD: Alzheimer disease; ATG: autophagy related; BECN1: beclin 1; BiFC: bimolecular fluorescence complementation; CD: cytosolic domain; GFP: green fluorescent protein; GLUC: Gaussia luciferase; IP: immunoprecipitation; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; LD: luminal domain; PD: Parkinson disease; ROS: reactive oxygen species; siRNA: small interfering RNA; SNP: single-nucleotide polymorphisms; TD: transmembrane domain; TMED10: transmembrane p24 trafficking protein 10; VC: C terminus of Venus fluorescent protein; VN: N terminus of Venus fluorescent protein.

Restoration of aberrant mTOR signaling by intranasal rapamycin reduces oxidative damage: Focus on HNE-modified proteins in a mouse model of down syndrome

Increasing evidences support the notion that the impairment of intracellular degradative machinery is responsible for the accumulation of oxidized/misfolded proteins that ultimately results in the deposition of protein aggregates. These events are key pathological aspects of "protein misfolding diseases", including Alzheimer disease (AD). Interestingly, Down syndrome (DS) neuropathology shares many features with AD, such as the deposition of both amyloid plaques and neurofibrillary tangles. Studies from our group and others demonstrated, in DS brain, the dysfunction of both proteasome and autophagy degradative systems, coupled with increased oxidative damage. Further, we observed the aberrant increase of mTOR signaling and of its down-stream pathways in both DS brain and in Ts65Dn mice. Based on these findings, we support the ability of intranasal rapamycin treatment (InRapa) to restore mTOR pathway but also to restrain oxidative stress resulting in the decreased accumulation of lipoxidized proteins. By proteomics approach, we were able to identify specific proteins that showed decreased levels of HNE-modification after InRapa treatment compared with vehicle group. Among MS-identified proteins, we found that reduced oxidation of arginase-1 (ARG-1) and protein phosphatase 2A (PP2A) might play a key role in reducing brain damage associated with synaptic transmission failure and tau hyperphosphorylation. InRapa treatment, by reducing ARG-1 protein-bound HNE levels, rescues its enzyme activity and conceivably contribute to the recovery of arginase-regulated functions. Further, it was shown that PP2A inhibition induces tau hyperphosphorylation and spatial memory deficits. Our data suggest that InRapa was able to rescue PP2A activity as suggested by reduced p-tau levels. In summary, considering that mTOR pathway is a central hub of multiple intracellular signaling, we propose that InRapa treatment is able to lower the lipoxidation-mediated damage to proteins, thus representing a valuable therapeutic strategy to reduce the early development of AD pathology in DS population.

Protective role of Apelin-13 on amyloid β25-35-induced memory deficit; Involvement of autophagy and apoptosis process

Alzheimer's disease (AD) by progressive neurodegenerative pattern is associated with autophagy stress which is suggested as a potential cause of amyloid β (Aβ) aggregation and neural loss. Apelin-13, a neuropeptide with modulatory effect on autophagy, has been shown the beneficial effects on neural cell injuries. We investigated the effect of Apelin-13 on Aβ-induced memory deficit as well as autophagy and apoptosis processes. We performed bilateral intra-CA1 injection of Aβ25-35 alone or in combination with Apelin-13. Spatial reference and working memory was evaluated using the Morris water maze (MWM) and Y-maze tests. Hippocampus was harvested on 2, 5, 10 and 21 days after Aβ injection. The light chain 3 (LC3II/I) ratio, histone deacetylase 6 (HDAC6) level, Caspase-3 cleavage, and mTOR phosphorylation were assessed using western blot technique. Intra-CA1 injection of Aβ caused impairment of working and spatial memory. We observed higher LC3II/I ratio, cleaved caspase-3 and lower HDAC6, and p-mTOR/mTOR ratio in Aβ-treated animals. Apelin-13 provided significant protection against the destructive effects of Aβ on working and spatial memory. Apelin-13 prevented the increase of LC3II/I ratio and cleaved caspase-3 on days 10 and 21 after injection of Aβ. It also limited the Aβ-induced reduction in HDAC6 expression. This implies that Apelin-13 has suppressed both autophagy and apoptosis. Our findings suggested that the neuroprotection of Apelin-13 may be in part related to autophagy and apoptosis inhibition via the mTOR signaling pathway. Apelin-13 may be a promising approach to improve memory impairment and potentially pave the way for new therapeutic plans in AD.

Dysregulation of autophagy in the central nervous system of sheep naturally infected with classical scrapie

Autophagy is a dynamic cellular mechanism involved in protein and organelle turnover through lysosomal degradation. Autophagy regulation modulates the pathologies associated with many neurodegenerative diseases. Using sheep naturally infected with scrapie as a natural animal model of prion diseases, we investigated the regulation of autophagy in the central nervous system (CNS) during the clinical phase of the disease. We present a gene expression and protein distribution analysis of different autophagy-related markers and investigate their relationship with prion-associated lesions in several areas of the CNS. Gene expression of autophagy markers ATG5 and ATG9 was downregulated in some areas of scrapie brains. In contrast, ATG5 protein accumulates in medulla oblongata and positively correlates with prion deposition and scrapie-related lesions. The accumulation of this protein and p62, a marker of autophagy impairment, suggests that autophagy is decreased in the late phases of the disease. However, the increment of LC3 proteins and the mild expression of p62 in basal ganglia and cerebellum, primarily in Purkinje cells, suggests that autophagy machinery is still intact in less affected areas. We hypothesize that specific cell populations of the CNS may display neuroprotective mechanisms against prion-induced toxicity through the induction of PrP^Sc clearance by autophagy.