Autophagy is increased following either pharmacological or genetic silencing of mGluR5 signaling in Alzheimer's disease mouse models

Targeting autophagy in Alzheimer's disease: Animal models and mechanisms

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disorder that leads to cognitive impairment and memory loss. Emerging evidence suggests that autophagy plays an important role in the pathogenesis of AD through the regulation of amyloid-beta (Aβ) and tau metabolism, and that autophagy dysfunction exacerbates amyloidosis and tau pathology. Therefore, targeting autophagy may be an effective approach for the treatment of AD. Animal models are considered useful tools for investigating the pathogenic mechanisms and therapeutic strategies of diseases. This review aims to summarize the pathological alterations in autophagy in representative AD animal models and to present recent studies on newly discovered autophagy-stimulating interventions in animal AD models. Finally, the opportunities, difficulties, and future directions of autophagy targeting in AD therapy are discussed.

Co-Expression Network Analysis Identifies Molecular Determinants of Loneliness Associated with Neuropsychiatric and Neurodegenerative Diseases

Loneliness and social isolation are detrimental to mental health and may lead to cognitive impairment and neurodegeneration. Although several molecular signatures of loneliness have been identified, the molecular mechanisms by which loneliness impacts the brain remain elusive. Here, we performed a bioinformatics approach to untangle the molecular underpinnings associated with loneliness. Co-expression network analysis identified molecular 'switches' responsible for dramatic transcriptional changes in the nucleus accumbens of individuals with known loneliness. Loneliness-related switch genes were enriched in cell cycle, cancer, TGF-β, FOXO, and PI3K-AKT signaling pathways. Analysis stratified by sex identified switch genes in males with chronic loneliness. Male-specific switch genes were enriched in infection, innate immunity, and cancer-related pathways. Correlation analysis revealed that loneliness-related switch genes significantly overlapped with 82% and 68% of human studies on Alzheimer's (AD) and Parkinson's diseases (PD), respectively, in gene expression databases. Loneliness-related switch genes, BCAM, NECTIN2, NPAS3, RBM38, PELI1, DPP10, and ASGR2, have been identified as genetic risk factors for AD. Likewise, switch genes HLA-DRB5, ALDOA, and GPNMB are known genetic loci in PD. Similarly, loneliness-related switch genes overlapped in 70% and 64% of human studies on major depressive disorder and schizophrenia, respectively. Nine switch genes, HLA-DRB5, ARHGAP15, COL4A1, RBM38, DMD, LGALS3BP, WSCD2, CYTH4, and CNTRL, overlapped with known genetic variants in depression. Seven switch genes, NPAS3, ARHGAP15, LGALS3BP, DPP10, SMYD3, CPXCR1, and HLA-DRB5 were associated with known risk factors for schizophrenia. Collectively, we identified molecular determinants of loneliness and dysregulated pathways in the brain of non-demented adults. The association of switch genes with known risk factors for neuropsychiatric and neurodegenerative diseases provides a molecular explanation for the observed prevalence of these diseases among lonely individuals.

Lithium engages autophagy for neuroprotection and neuroplasticity: translational evidence for therapy

Here an overview is provided on therapeutic/neuroprotective effects of Lithium (Li⁺) in neurodegenerative and psychiatric disorders focusing on the conspicuous action of Li⁺ through autophagy. The effects on the autophagy machinery remain the key molecular mechanisms to explain the protective effects of Li⁺ for neurodegenerative diseases, offering potential therapeutic strategies for the treatment of neuropsychiatric disorders and emphasizes a crossroad linking autophagy, neurodegenerative disorders, and mood stabilization. Sensitization by psychostimulants points to several mechanisms involved in psychopathology, most also crucial in neurodegenerative disorders. Evidence shows the involvement of autophagy and metabotropic Glutamate receptors-5 (mGluR5) in neurodegeneration due to methamphetamine neurotoxicity as well as in neuroprotection, both in vitro and in vivo models. More recently, Li⁺ was shown to modulate autophagy through its action on mGluR5, thus pointing to an additional way of autophagy engagement by Li⁺ and to a substantial role of mGluR5 in neuroprotection related to neural e neuropsychiatry diseases. We propose Li⁺ engagement of autophagy through the canonical mechanisms of autophagy machinery and through the intermediary of mGluR5.

Inhibition of mGluR5/PI3K-AKT Pathway Alleviates Alzheimer's Disease-Like Pathology Through the Activation of Autophagy in 5XFAD Mice

BACKGROUND

The metabotropic glutamate receptor 5 (mGluR5) is widely expressed in postsynaptic neurons and plays a vital role in the synaptic plasticity of the central nervous system. mGluR5 is a coreceptor for amyloid-β (Aβ) oligomer, and downregulation or pharmacological blockade of mGluR5 presents the therapeutic potential of Alzheimer's disease (AD). However, the abnormality of mGluR5 in the pathogenesis of AD and its mechanism of pathology is not clear.

OBJECTIVE

In this study, we would like to investigate the expression of mGluR5 in the process of AD and explore the effects and the underlying mechanisms of antagonizing mGluR5 on cognitive function, synaptic structure, and inflammation in 5xFAD mice.

METHODS

mGluR5 expression and interactions with PrPc in 5XFAD mice were detected using western blot and co-immunoprecipitation. The selective mGluR5 antagonist MPEP was infused into 4-month-old 5XFAD mice for 60 consecutive days. Then, cognitive function, AD-like pathology and synaptic structure were measured. Further observations were made in mGluR5 knockdown 5XFAD mice.

RESULTS

mGluR5 expression was increased with Aβ levels at 6 months in 5XFAD mice. mGluR5 antagonist rescued cognitive disorders, promoted synaptic recovery, and alleviated both the Aβ plaque load and abnormal hyperphosphorylation in 6-month-old 5XFAD mice. Meanwhile, the results were validated in mGluR5 knockdown mice. Blockade of mGluR5 efficiently alleviates AD-like pathologies by inhibiting the PI3K/AKT/mTOR pathway and activates autophagy in 5XFAD mice. Furthermore, antagonism of mGluR5 attenuated neuroinflammation by inactivating the IKK/NF-κB pathway.

CONCLUSION

These findings suggest that mGluR5 may be an effective drug target for AD treatment, and inhibition of the mGluR5/PI3K-AKT pathway alleviates AD-like pathology by activating autophagy and anti-neuroinflammation in 5XFAD mice.

Noradrenaline and Seizures: A Perspective on the Role of Adrenergic Receptors in Limbic Seizures

BACKGROUND

Noradrenergic fibers originating from the locus coeruleus densely innervate limbic structures, including the piriform cortex, which is the limbic structure with the lowest seizure threshold. Noradrenaline (NA) modulates limbic seizures while stimulating autophagy through β2- adrenergic receptors (AR). Since autophagy is related to seizure threshold, this perspective questions whether modulating β2-AR focally within the anterior piriform cortex affects limbic seizures.

OBJECTIVE

In this perspective, we analyzed a potential role for β2-AR as an anticonvulsant target within the anterior piriform cortex, area tempestas (AT).

METHODS

We developed this perspective based on current literature on the role of NA in limbic seizures and autophagy. The perspective is also grounded on preliminary data obtained by microinfusing within AT either a β2-AR agonist (salbutamol) or a β2-AR antagonist (butoxamine) 5 minutes before bicuculline.

RESULTS

β2-AR stimulation fully prevents limbic seizures induced by bicuculline micro-infusion in AT. Conversely, antagonism at β2-AR worsens bicuculline-induced seizure severity and prolongs seizure duration, leading to self-sustaining status epilepticus. These data indicate a specific role for β2-AR as an anticonvulsant in AT.

CONCLUSION

NA counteracts limbic seizures. This relies on various receptors in different brain areas. The anterior piriform cortex plays a key role in patients affected by limbic epilepsy. The anticonvulsant effects of NA through β2-AR may be related to the stimulation of the autophagy pathway. Recent literature and present data draw a perspective where β2-AR stimulation while stimulating autophagy mitigates limbic seizures, focally within AT. The mechanism linking β2-AR to autophagy and seizure modulation should be extensively investigated.

The MK2 cascade mediates transient alteration in mGluR-LTD and spatial learning in a murine model of Alzheimer's disease

A key aim of Alzheimer disease research is to develop efficient therapies to prevent and/or delay the irreversible progression of cognitive impairments. Early deficits in long-term potentiation (LTP) are associated with the accumulation of amyloid beta in rodent models of the disease; however, less is known about how mGluR-mediated long-term depression (mGluR-LTD) is affected. In this study, we have found that mGluR-LTD is enhanced in the APP_swe /PS1dE9 mouse at 7 but returns to wild-type levels at 13 months of age. This transient over-activation of mGluR signalling is coupled with impaired LTP and shifts the dynamic range of synapses towards depression. These alterations in synaptic plasticity are associated with an inability to utilize cues in a spatial learning task. The transient dysregulation of plasticity can be prevented by genetic deletion of the MAP kinase-activated protein kinase 2 (MK2), a substrate of p38 MAPK, demonstrating that manipulating the mGluR-p38 MAPK-MK2 cascade at 7 months can prevent the shift in synapse dynamic range. Our work reveals the MK2 cascade as a potential pharmacological target to correct the over-activation of mGluR signalling.

Blocked metabotropic glutamate receptor 5 enhances chemosensitivity in hepatocellular carcinoma and attenuates chemotoxicity in the normal liver by regulating DNA damage

DNA damaging agents are used as chemotherapeutics in many cancers, including hepatocellular carcinoma (HCC). However, they are associated with problems such as low sensitivity to chemotherapy and the induction of liver injury, underscoring the need to identify new therapies. Here, we investigated the differential regulatory effect of metabotropic glutamate receptor 5 (mGlu5) on chemosensitivity in HCC and chemotoxicity to the normal liver. The expression of mGlu5 was higher in HCC than in the normal liver, and correlated with poor prognosis according to The Cancer Genome Atlas database and Integrative Molecular Database of Hepatocellular Carcinoma. Cisplatin, oxaliplatin or methyl methanesulfonate (MMS) caused cell death by decreasing mGlu5 expression in HCC cells and increased mGlu5 expression in hepatic cells. In HCC cells, inhibition of mGlu5 aggravated MMS-induced DNA damage by increasing intracellular Ca2+ overload and mitogen-activated protein kinase (MAPK) activation, thereby promoting cell death, and activation of mGlu5 rescued the effect of MMS. However, in hepatic cells, mGlu5 inhibition alleviated MMS-induced DNA damage by downregulating Ca2+-derived MAPK pathways to advance hepatic cell survival. The opposite effects of mGlu5 overexpression or knockdown on MMS-induced DNA damage supported that cell death is a result of the differential regulation of mGlu5 expression. Inhibition of mGlu5 increased chemosensitivity and decreased chemotoxicity in a rat tumor model. This study suggests that mGlu5 inhibition could act synergistically with HCC chemotherapeutics with minimal side effects, which may improve the treatment of patients with HCC in the future.

Therapeutic Aspects and Molecular Targets of Autophagy to Control Pancreatic Cancer Management

Pancreatic cancer (PC) begins within the organ of the pancreas, which produces digestive enzymes, and is one of the formidable cancers for which appropriate treatment strategies are urgently needed. Autophagy occurs in the many chambers of PC tissue, including cancer cells, cancer-related fibroblasts, and immune cells, and can be fine-tuned by various promotive and suppressive signals. Consequently, the impacts of autophagy on pancreatic carcinogenesis and progression depend greatly on its stage and conditions. Autophagy inhibits the progress of preneoplastic damage during the initial phase. However, autophagy encourages tumor formation during the development phase. Several studies have reported that both a tumor-promoting and a tumor-suppressing function of autophagy in cancer that is likely cell-type dependent. However, autophagy is dispensable for pancreatic ductal adenocarcinoma (PDAC) growth, and clinical trials with autophagy inhibitors, either alone or in combination with other therapies, have had limited success. Autophagy’s dual mode of action makes it therapeutically challenging despite autophagy inhibitors providing increased longevity in medical studies, highlighting the need for a more rigorous review of current findings and more precise targeting strategies. Indeed, the role of autophagy in PC is complicated, and numerous factors must be considered when transitioning from bench to bedside. In this review, we summarize the evidence for the tumorigenic and protective role of autophagy in PC tumorigenesis and describe recent advances in the understanding of how autophagy may be regulated and controlled in PDAC.

Targeting the Type 5 Metabotropic Glutamate Receptor: A Potential Therapeutic Strategy for Neurodegenerative Diseases?

The type 5 metabotropic glutamate receptor, mGlu₅, has been proposed as a potential therapeutic target for the treatment of several neurodegenerative diseases. In preclinical neurodegenerative disease models, novel allosteric modulators have been shown to improve cognitive performance and reduce disease-related pathology. A common pathological hallmark of neurodegenerative diseases is a chronic neuroinflammatory response, involving glial cells such as astrocytes and microglia. Since mGlu₅ is expressed in astrocytes, targeting this receptor could provide a potential mechanism by which neuroinflammatory processes in neurodegenerative disease may be modulated. This review will discuss current evidence that highlights the potential of mGlu₅ allosteric modulators to treat neurodegenerative diseases, including Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. Furthermore, this review will explore the role of mGlu₅ in neuroinflammatory responses, and the potential for this G protein-coupled receptor to modulate neuroinflammation.

VGLUT3 Ablation Differentially Modulates Glutamate Receptor Densities in Mouse Brain

Type 3 vesicular glutamate transporter (VGLUT3) represents a unique modulator of glutamate release from both nonglutamatergic and glutamatergic varicosities within the brain. Despite its limited abundance, VGLUT3 is vital for the regulation of glutamate signaling and, therefore, modulates the activity of various brain microcircuits. However, little is known about how glutamate receptors are regulated by VGLUT3 across different brain regions. Here, we used VGLUT3 constitutive knock-out (VGLUT3^-/-) mice and explored how VGLUT3 deletion influences total and cell surface expression of different ionotropic and metabotropic glutamate receptors. VGLUT3 deletion upregulated the overall expression of metabotropic glutamate receptors mGluR5 and mGluR2/3 in the cerebral cortex. In contrast, no change in the total expression of ionotropic NMDAR glutamate receptors were observed in the cerebral cortex of VGLUT3^-/- mice. We noted significant reduction in cell surface levels of mGluR5, NMDAR2A, NMDAR2B, as well as reductions in dopaminergic D₁ receptors and muscarinic M1 acetylcholine receptors in the hippocampus of VGLUT3^-/- mice. Furthermore, mGluR2/3 total expression and mGluR5 cell surface levels were elevated in the striatum of VGLUT3^-/- mice. Last, AMPAR subunit GluA1 was significantly upregulated throughout cortical, hippocampal, and striatal brain regions of VGLUT3^-/- mice. Together, these findings complement and further support the evidence that VGLUT3 dynamically regulates glutamate receptor densities in several brain regions. These results suggest that VGLUT3 may play an intricate role in shaping glutamatergic signaling and plasticity in several brain areas.

Metabotropic Glutamate Receptor 5 Antagonism Reduces Pathology and Differentially Improves Symptoms in Male and Female Heterozygous zQ175 Huntington’s Mice

Huntington’s disease (HD) is an inherited autosomal dominant neurodegenerative disorder that leads to progressive motor and cognitive impairment. There are currently no available disease modifying treatments for HD patients. We have previously shown that pharmacological blockade of metabotropic glutamate receptor 5 (mGluR5) signaling rescues motor deficits, improves cognitive impairments and mitigates HD neuropathology in male zQ175 HD mice. Mounting evidence indicates that sex may influence HD progression and we have recently reported a sex-specific pathological mGluR5 signaling in Alzheimer’s disease (AD) mice. Here, we compared the outcomes of treatment with the mGluR5 negative allosteric modulator CTEP (2-chloro-4-[2-[2,5-dimethyl-1-[4-(trifluoromethoxy)phenyl]imidazol-4-yl]ethynyl]pyridine) in both male and female symptomatic zQ175 mice. We found that female zQ175 mice required a longer treatment duration with CTEP than male mice to show improvement in their rotarod performance. Unlike males, chronic CTEP treatment did not improve the grip strength nor reverse the cognitive decline of female zQ175 mice. However, CTEP reduced the number of huntingtin aggregates, improved neuronal survival and decreased microglia activation in the striatum of both male and female zQ175 mice. Together, our results indicate that mGluR5 antagonism can reduce HD neuropathology in both male and female zQ175 HD mice, but sex has a clear impact on the efficacy of the treatment and must be taken into consideration for future HD drug development.

Brain-derived neurotrophic factor in Alzheimer's disease and its pharmaceutical potential

Synaptic abnormalities are a cardinal feature of Alzheimer's disease (AD) that are known to arise as the disease progresses. A growing body of evidence suggests that pathological alterations to neuronal circuits and synapses may provide a mechanistic link between amyloid β (Aβ) and tau pathology and thus may serve as an obligatory relay of the cognitive impairment in AD. Brain-derived neurotrophic factors (BDNFs) play an important role in maintaining synaptic plasticity in learning and memory. Considering AD as a synaptic disorder, BDNF has attracted increasing attention as a potential diagnostic biomarker and a therapeutical molecule for AD. Although depletion of BDNF has been linked with Aβ accumulation, tau phosphorylation, neuroinflammation and neuronal apoptosis, the exact mechanisms underlying the effect of impaired BDNF signaling on AD are still unknown. Here, we present an overview of how BDNF genomic structure is connected to factors that regulate BDNF signaling. We then discuss the role of BDNF in AD and the potential of BDNF-targeting therapeutics for AD.

Multi-omics integration and interactomics reveals molecular networks and regulators of the beneficial effect of yoga and exercise

Background

Yoga is a multifaceted spiritual tool that helps in maintaining health, peace of mind, and positive thoughts. In the context of asana, yoga is similar to physical exercise. This study aims to construct a molecular network to find hub genes that play important roles in physical exercise and yoga.

Methodology

We combined differentially expressed genes (DEGs) in yoga and exercise using computational bioinformatics from publicly available gene expression omnibus (GEO) datasets and identified the codifferentially expressed mRNAs with GEO2R. The co-DEGs were divided into four different groups and each group was subjected to protein-protein interaction (PPI) network, pathways analysis, and gene ontology.

Results

Our study identified immunological modulation as a dominant target of differential expression in yoga and exercise. Yoga predominantly modulated genes affecting the Th1 and NK cells, whereas Cytokines, Macrophage activation, and oxidative stress were affected by exercise. We also observed that while yoga regulated genes for two main physiological functions of the body, namely Circadian Rhythm (BHLHE40) and immunity (LBP, T-box transcription factor 21, CEACAM1), exercise-regulated genes involved in apoptosis (BAG3, protein kinase C alpha), angiogenesis, and cellular adhesion (EPH receptor A1).

Conclusion

The dissimilarity in the genetic expression patterns in Yoga and exercise highlights the discrete effect of each in biological systems. The integration and convergences of multi-omics signals can provide deeper and comprehensive insights into the various biological mechanisms through which yoga and exercise exert their beneficial effects and opens up potential newer research areas.

A M1 muscarinic acetylcholine receptor positive allosteric modulator improves pathology and cognitive deficits in female APPswe/PSEN1ΔE9 mice

BACKGROUND AND PURPOSE

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive cognitive decline and women account for 60% of diagnosed cases. Beta-amyloid (Aβ) oligomers is considered the principal neurotoxic species in AD brains. The M1 muscarinic acetylcholine receptor (M1 mAChR) plays a key role in memory and learning. M1 mAChR agonists show pro-cognitive activity but cause many adverse off-target effects. A new orally bioavailable M1 mAChR positive allosteric modulator (PAM), VU0486846, is devoid of direct agonist activity or adverse effects but was not tested for disease-modifying efficacy in female AD mice.

EXPERIMENTAL APPROACH

Nine-month-old female APPswe/PSEN1ΔE9 (APPswe) and wildtype mice were treated with VU0486846 in drinking water (10mg/kg/day) for 4 or 8 weeks. Cognitive function of mice was assessed after treatment and brains were harvested for biochemical and immunohistochemical assessment.

KEY RESULTS

VU0486846 improved cognitive function of APPswe mice when tested in novel object recognition and Morris water maze. This was paralleled by a significant reduction in Aβ oligomers and plaques and neuronal loss in hippocampus. VU0486846 reduced Aβ oligomer production in APPswe mice by increasing M1 mAChR expression and shifting the processing of amyloid precursor protein from amyloidogenic cleavage to non-amyloidogenic cleavage. Specifically, VU0486846 reduced the expression of β-secretase 1 (BACE1), whereas it enhanced the expression of the α-secretase ADAM10 in APPswe hippocampus.

CONCLUSION AND IMPLICATIONS

Using M1 mAChR PAMs can be a viable disease-modifying approach that should be exploited clinically to slow AD in women.

Noncanonical Metabotropic Glutamate Receptor 5 Signaling in Alzheimer's Disease

Metabotropic glutamate receptor 5 (mGluR5) is ubiquitously expressed in brain regions responsible for memory and learning. It plays a key role in modulating rapid changes in synaptic transmission and plasticity. mGluR5 supports long-term changes in synaptic strength by regulating the transcription and translation of essential synaptic proteins. β-Amyloid 42 (Aβ42) oligomers interact with a mGluR5/cellular prion protein (PrP^C) complex to disrupt physiological mGluR5 signal transduction. Aberrant mGluR5 signaling and associated synaptic failure are considered an emerging pathophysiological mechanism of Alzheimer's disease (AD). Therefore, mGluR5 represents an attractive therapeutic target for AD, and recent studies continue to validate the efficacy of various mGluR5 allosteric modulators in improving memory deficits and mitigating disease pathology. However, sex-specific differences in the pharmacology of mGluR5 and activation of noncanonical signaling downstream of the receptor suggest that its utility as a therapeutic target in female AD patients needs to be reconsidered. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Blocking glutamate mGlu5 receptors with the negative allosteric modulator CTEP improves disease course in SOD1G93A mouse model of amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE

The pathogenesis of amyotrophic lateral sclerosis (ALS) is not fully clarified, although excessive glutamate (Glu) transmission and the downstream cytotoxic cascades are major mechanisms for motor neuron death. Two metabotropic glutamate receptors (mGlu₁ and mGlu₅ ) are overexpressed in ALS and regulate cellular disease processes. Expression and function of mGlu₅ receptors are altered at early symptomatic stages in the SOD1^G93A mouse model of ALS and knockdown of mGlu5 receptors in SOD1^G93A mice improved disease progression.

EXPERIMENTAL APPROACH

We treated male and female SOD1^G93A mice with 2-chloro-4-((2,5-dimethyl-1-(4-(trifluoromethoxy)phenyl)-1H-imidazol-4-yl)ethynyl)pyridine (CTEP), an orally available mGlu₅ receptor negative allosteric modulator (NAM), using doses of 2 mg·kg^-1 per 48 h or 4 mg·kg^-1 per 24 h from Day 90, an early symptomatic disease stage. Disease progression was studied by behavioural and histological approaches.

KEY RESULTS

CTEP dose-dependently ameliorated clinical features in SOD1^G93A mice. The lower dose increased survival and improved motor skills in female mice, with barely positive effects in male mice. Higher doses significantly ameliorated disease symptoms and survival in both males and females, females being more responsive. CTEP also reduced motor neuron death, astrocyte and microglia activation, and abnormal glutamate release in the spinal cord, with equal effects in male and female mice. No differences were also observed in CTEP access to the brain.

CONCLUSION AND IMPLICATIONS

Our results suggest that mGlu₅ receptors are promising targets for the treatment of ALS and highlight mGlu5 receptor NAMs as effective pharmacological tools with translational potential.

Targeting Common Signaling Pathways for the Treatment of Stroke and Alzheimer's: a Comprehensive Review

Neurodegenerative diseases such as stroke and Alzheimer's disease (AD) are two inter-related disorders that affect the neurons in the brain and central nervous system. Alzheimer's is a disease by undefined origin and causes. Stroke and its most common type, ischemic stroke (IS), occurs due to the blockade of cerebral blood vessels. As an important feature, both of disorders are associated with irreversible damages to the brain and nervous system. In this regard, finding common signaling pathways and the same molecular origin between these two diseases may be a promising way for their solution. On the basis of literature appraisal, the most common signaling cascades implicated in the pathogenesis of AD and stroke including notch, autophagy, inflammatory, and insulin signaling pathways were reviewed. Furthermore, current therapeutic strategies including natural and synthetic pharmaceuticals aiming modulation of respective signaling factors were scrutinized to ameliorate neural deficits in AD and stroke. Taken together, digging deeper in the common connections and signal targeting can be greatly helpful in understanding and unified treating of these disorders.

Machine learning identifies candidates for drug repurposing in Alzheimer's disease

Clinical trials of novel therapeutics for Alzheimer's Disease (AD) have consumed a large amount of time and resources with largely negative results. Repurposing drugs already approved by the Food and Drug Administration (FDA) for another indication is a more rapid and less expensive option. We present DRIAD (Drug Repurposing In AD), a machine learning framework that quantifies potential associations between the pathology of AD severity (the Braak stage) and molecular mechanisms as encoded in lists of gene names. DRIAD is applied to lists of genes arising from perturbations in differentiated human neural cell cultures by 80 FDA-approved and clinically tested drugs, producing a ranked list of possible repurposing candidates. Top-scoring drugs are inspected for common trends among their targets. We propose that the DRIAD method can be used to nominate drugs that, after additional validation and identification of relevant pharmacodynamic biomarker(s), could be readily evaluated in a clinical trial.

A Destiny for Degradation: Interplay between Cullin-RING E3 Ligases and Autophagy

Autophagy and the ubiquitin-proteasome system (UPS) are two major pathways for protein degradation. The cullin-RING E3 ligases (CRLs) are the largest E3 ligase family and have key biological functions in maintaining protein homeostasis. We provide an updated review of the interactions between CRLs and autophagy, focusing on the regulatory effects of CRLs on the core autophagy machinery that consists of several autophagy-related protein (ATG) complexes and their key upstream signaling pathways. The involvement of such functional interactions in health and disease is also discussed. Understanding the role of CRLs in autophagy is helpful for the development of therapeutic strategies for diseases in which CRLs and autophagy are dysregulated, such as cancer and neurodegenerative conditions.

Optineurin deletion disrupts metabotropic glutamate receptor 5-mediated regulation of ERK1/2, GSK3β/ZBTB16, mTOR/ULK1 signaling in autophagy

Optineurin (OPTN) is a multifunctional protein that mediates a network of cellular processes regulating membrane trafficking, inflammatory responses and autophagy. The OPTN-rich interactome includes Group I metabotropic glutamate receptors (mGluR1 and 5), members of the Gα_q/11 protein receptor family. Recent evidence has shown that mGluR5, in addition to its canonical Gα_q/11 protein-coupled signaling, regulates autophagic machinery via mTOR/ULK1 and GSK3β/ZBTB16 pathways in both Alzheimer's and Huntington's disease mouse models. Despite its potential involvement, the role of OPTN in mediating mGluR5 downstream signaling cascades remains largely unknown. Here, we employed a CRISPR/Cas9 OPTN-deficient STHdh^Q7/Q7 striatal cell line and global OPTN knockout mice to investigate whether Optn gene deletion alters both mGluR5 canonical and noncanonical signaling. We find that OPTN is required for mGluR5-activated Ca²⁺ flux and ERK1/2 signaling following receptor activation in STHdh^Q7/Q7 cells and acute hippocampal slices. Deletion of OPTN impairs both GSK3β/ZBTB16 and mTOR/ULK1 autophagic signaling in STHdh^Q7/Q7 cells. Furthermore, mGluR5-dependent regulation of GSK3β/ZBTB16 and mTOR/ULK1 autophagic signaling is impaired in hippocampal slices of OPTN knockout mice. Overall, we show that the crosstalk between OPTN and mGluR5 can have major implication on receptor signaling and therefore potentially contribute to the pathophysiology of neurodegenerative diseases.

Downregulation of metabotropic glutamate receptor 5 alleviates central sensitization by activating autophagy via inhibiting mTOR pathway in a rat model of chronic migraine

Central sensitization is one of the important pathological mechanisms of chronic migraine (CM). Metabolic glutamate receptor 5 (mGluR5) mediates pain by activating various intracellular pathways. However, whether mGluR5 contributes to central sensitization in CM and the exact mechanism remains unclear. Male rats were used to establish a CM model by repeated infusions of inflammatory soup (IS) for 7 days to stimulate the activation of the dural nociceptor. The mechanical and thermal thresholds were used to evaluate allodynia, and central sensitization was assessed by measuring calcitonin gene-related peptide (CGRP) and substance P (SP). Microtubule associated protein 1 light chain 3 (LC3) and p62/SQSTM1 were used to assess autophagy. We found that the expression of mGluR5 in the trigeminal nucleus caudalis (TNC) of CM rats was significantly increased. In addition, the downregulation of mGluR5 activated autophagy by inhibiting the mTOR pathway. Moreover, the activation of autophagy alleviated allodynia and central sensitization in CM rats. This study identified a novel strategy for the treatment of CM; the downregulation of mGluR5 in a rat model of CM decreased the expression of the inflammatory factor interleukin-1 beta (IL-1β) and the central sensitization-associated proteins CGRP and SP by activating autophagy via inhibiting the mTOR pathway.

Aβ oligomers induce pathophysiological mGluR5 signaling in Alzheimer's disease model mice in a sex-selective manner

The prevalence, presentation, and progression of Alzheimer's disease (AD) differ between men and women, although β-amyloid (Aβ) deposition is a pathological hallmark of AD in both sexes. Aβ-induced activation of the neuronal glutamate receptor mGluR5 is linked to AD progression. However, we found that mGluR5 exhibits distinct sex-dependent profiles. Specifically, mGluR5 isolated from male mouse cortical and hippocampal tissues bound with high affinity to Aβ oligomers, whereas mGluR5 from female mice exhibited no such affinity. This sex-selective Aβ-mGluR5 interaction did not appear to depend on estrogen, but rather Aβ interaction with cellular prion protein (PrP^C), which was detected only in male mouse brain homogenates. The ternary complex between mGluR5, Aβ oligomers, and PrP^C was essential to elicit mGluR5-dependent pathological suppression of autophagy in primary neuronal cultures. Pharmacological inhibition of mGluR5 reactivated autophagy, mitigated Aβ pathology, and reversed cognitive decline in male APPswe/PS1ΔE9 mice, but not in their female counterparts. Aβ oligomers also bound with high affinity to human mGluR5 isolated from postmortem donor male cortical brain tissue, but not that from female samples, suggesting that this mechanism may be relevant to patients. Our findings indicate that mGluR5 does not contribute to Aβ pathology in females, highlighting the complexity of mGluR5 pharmacology and Aβ signaling that supports the need for sex-specific stratification in clinical trials assessing AD therapeutics.

The Dual Role of Glutamatergic Neurotransmission in Alzheimer's Disease: From Pathophysiology to Pharmacotherapy

Alzheimer's disease (AD) is an age-related dementia and neurodegenerative disorder, characterized by Aβ and tau protein deposition impairing learning, memory and suppressing synaptic plasticity of neurons. Increasing evidence suggests that there is a link between the glucose and glutamate alterations with age that down-regulates glucose utilization reducing glutamate levels in AD patients. Deviations in brain energy metabolism reinforce the development of AD by hampering glutamate levels in the brain. Glutamate is a nonessential amino acid and the major excitatory neurotransmitter synthesized from glucose. Alterations in cerebral glucose and glutamate levels precede the deposition of Aβ plaques. In the brain, over 40% of neuronal synapses are glutamatergic and disturbances in glutamatergic function have been implicated in pathophysiology of AD. Nevertheless, targeting the glutamatergic system seems to be a promising strategy to develop novel, improved therapeutics for AD. Here, we review data supporting the involvement of the glutamatergic system in AD pathophysiology as well as the efficacy of glutamatergic agents in this neurodegenerative disorder. We also discuss exciting new prospects for the development of improved therapeutics for this devastating disorder.

mGluR5 regulates REST/NRSF signaling through N-cadherin/β-catenin complex in Huntington's disease

Repressor element 1-silencing transcription factor/neuron-restrictive silencer factor (REST/NRSF) is a transcription repressor and its expression is regulated by the Wnt pathway through β-catenin. Metabotropic glutamate receptor 5 (mGluR5) signaling plays a key role in controlling neuronal gene expression. Interestingly, REST/NRSF nuclear translocation and signaling, as well as mGluR5 signaling are altered in the presence of mutant huntingtin. It remains unclear whether mGluR5 can modulate Wnt and REST/NRSF signaling under physiological conditions and whether this modulation is altered in Huntington's disease (HD). Using primary corticostriatal neurons derived from wild type mouse embryos, we find that targeting mGluR5 using the agonist, DHPG, or the negative allosteric modulator, CTEP, modulates REST/NRSF expression by regulating the assembly of N-cadherin/ β-catenin complex in a Src kinase-dependent manner. We have validated our in vitro findings in vivo using two HD mouse models. Specifically, we show that pharmacological inhibition of mGluR5 in zQ175 mice and genetic ablation of mGluR5 in BACHD mice corrected the pathological activation of Src and rescued REST/NRSF-dependent signaling. Together, our data provide evidence that mGluR5 regulates REST/NRSF expression via the Wnt pathway and highlight the contribution of impaired REST/ NRSF signaling to HD pathology.

mGluR5 Contribution to Neuropathology in Alzheimer Mice Is Disease Stage-Dependent

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease and is characterized by a progressive cognitive decline in affected individuals. Current therapeutic strategies are limited in their efficacy and some have proven to be even less effective at later disease stages or after extended use. We previously demonstrated that chronic inhibition of mGluR5 signaling using the selective negative allosteric modulator (NAM) CTEP in APPswe/PS1ΔE9 mice can rescue cognitive function, activating the ZBTB16-mediated autophagy pathway to reduce Aβ, the principal neurotoxic species in AD brains. Here, we evaluated the efficacy of long-term treatment with CTEP in 6 month old APPswe/PS1ΔE9 mice for either 24 or 36 weeks. CTEP maintained its efficacy in reversing working and spatial memory deficits and mitigating neurogliosis in APPswe/PS1ΔE9 mice when administered for 24 weeks. This was paralleled by a significant reduction in Aβ oligomer and plaque load as a result of autophagy activation via ZBTB16 and mTOR-dependent pathways. However, further extension of CTEP treatment for 36 weeks was found ineffective in reversing memory deficit, neurogliosis, or Aβ-related pathology. We found that this loss in CTEP efficacy in 15 month old APPswe/PS1ΔE9 mice was due to the abolished contribution of ZBTB16 and mTOR-mediated signaling to AD neuropathology at this advanced disease stage. Our findings indicate that the contribution of pathological mGluR5-signaling to AD may shift as the disease progresses. Thus, we provide the first evidence that the underlying pathophysiological mechanism(s) of AD may unfold along the course of the disease and treatment strategies should be modified accordingly to ensure maximal therapeutic outcomes.

Diet Associated with Inflammation and Alzheimer's Disease

Neurocognitive disorders, such as Alzheimer's disease (AD), affect millions of people worldwide and are characterized by cognitive decline. Human and animal studies have shown that chronic immune response and inflammation are important factors in the pathogenesis of AD. Chronic inflammation can accelerate the aggregation of amyloid-β peptides and later hyperphosphorylation of tau proteins. The exact etiology of AD is not clear, but genetics and environmental factors, such as age, family history, and lifestyle are linked to neurodegenerative diseases. Lifestyle habits, such as poor diet, are associated with inflammation and could accelerate or slow down the progression of neurodegenerative diseases. Here we provide a review of the potential conditions and factors that stimulate the inflammatory processes in AD. An understanding of inflammatory mechanisms influencing the development of AD may help to protect against dementia and AD.

Aβ oligomers induce sex-selective differences in mGluR5 pharmacology and pathophysiological signaling in Alzheimer mice.. [DOI: 10.1101/803262]

Sex is a key modifier of the prevalence and progression of Alzheimer’s disease (AD). β- Amyloid (Aβ) deposition is a pathological hallmark of AD and aberrant activation of metabotropic glutamate receptor 5 (mGluR5) by Aβ has been linked to AD progression. We find that mGluR5 exhibits distinct sex-dependent pharmacological profiles. Specifically, endogenous mGluR5 from male mouse cortex and hippocampus binds with high-affinity to Aβ oligomers whereas, female mGluR5 exhibits no affinity to Aβ oligomers. The binding affinity of mGluR5 to Aβ oligomer is dependent on its interaction with cellular prion protein (PrPC) as mGluR5 co-immunoprecipitates with PrPCfrom male, but not female, mouse brain. Aβ oligomers also bind with high-affinity to human mGluR5 in male, but not female, cortex. The mGluR5/Aβ oligomer/PrPCternary complex is essential to elicit mGluR5-dependent pathological signaling and as a consequence mGluR5-regulated GSK3β/ZBTB16 autophagic signaling is dysregulated in male, but not female, primary neuronal cultures. These sex-specific differences in mGluR5 signaling translate into in vivo differences in mGluR5-dependent pathological signaling between male and female AD mice. We show that the chronic inhibition of mGluR5 using a mGluR5-selective negative allosteric modulator reactivates GSK3β/ZBTB16-regulated autophagy, mitigates Aβ pathology and reverses cognitive decline in male, but not female, APPswe/PS1ΔE9 mice. Thus, it is evident that, unlike male brain, mGluR5 does not contribute to Aβ pathology in female AD mice. This study highlights the complexity of mGluR5 pharmacology and Aβ oligomer-activated pathological signaling and emphasizes the need for clinical trials redesign and analysis of sex-tailored treatment for AD.

A positive allosteric modulator of mGluR5 promotes neuroprotective effects in mouse models of Alzheimer's disease

Alzheimer's Disease (AD) is the most prevalent neurodegenerative disorder. Despite advances in the understanding of its pathophysiology, none of the available therapies prevents disease progression. Excess glutamate plays an important role in excitotoxicity by activating ionotropic receptors. However, the mechanisms modulating neuronal cell survival/death via metabotropic glutamate receptors (mGluRs) are not completely understood. Recent data indicates that CDPPB, a positive allosteric modulator of mGluR5, has neuroprotective effects. Thus, this work aimed to investigate CDPPB treatment effects on amyloid-β (Aβ) induced pathological alterations in vitro and in vivo and in a transgenic mouse model of AD (T41 mice). Aβ induced cell death in primary cultures of hippocampal neurons, which was prevented by CDPPB. Male C57BL/6 mice underwent stereotaxic surgery for unilateral intra-hippocampal Aβ injection, which induced memory deficits, neurodegeneration, neuronal viability reduction and decrease of doublecortin-positive cells, a marker of immature neurons and neuronal proliferation. Treatment with CDPPB for 8 days reversed neurodegeneration and doublecortin-positive cells loss and recovered memory function. Fourteen months old T41 mice presented cognitive deficits, neuronal viability reduction, gliosis and Aβ accumulation. Treatment with CDPPB for 28 days increased neuronal viability (32.2% increase in NeuN⁺ cells) and reduced gliosis in CA1 region (Iba-1⁺ area by 31.3% and GFAP⁺ area by 37.5%) in transgenic animals, without inducing hepatotoxicity. However, it did not reverse cognitive deficit. Despite a four-week treatment did not prevent memory loss in aged transgenic mice, CDPPB is protective against Aβ stimulus. Therefore, this drug represents a potential candidate for further investigations as AD treatment.

Enhanced Function and Overexpression of Metabotropic Glutamate Receptors 1 and 5 in the Spinal Cord of the SOD1G93A Mouse Model of Amyotrophic Lateral Sclerosis during Disease Progression

Glutamate (Glu)-mediated excitotoxicity is a major cause of amyotrophic lateral sclerosis (ALS) and our previous work highlighted that abnormal Glu release may represent a leading mechanism for excessive synaptic Glu. We demonstrated that group I metabotropic Glu receptors (mGluR1, mGluR5) produced abnormal Glu release in SOD1^G93A mouse spinal cord at a late disease stage (120 days). Here, we studied this phenomenon in pre-symptomatic (30 and 60 days) and early-symptomatic (90 days) SOD1^G93A mice. The mGluR1/5 agonist (S)-3,5-Dihydroxyphenylglycine (3,5-DHPG) concentration dependently stimulated the release of [³H]d-Aspartate ([³H]d-Asp), which was comparable in 30- and 60-day-old wild type mice and SOD1^G93A mice. At variance, [³H]d-Asp release was significantly augmented in 90-day-old SOD1^G93A mice and both mGluR1 and mGluR5 were involved. The 3,5-DHPG-induced [³H]d-Asp release was exocytotic, being of vesicular origin and mediated by intra-terminal Ca²⁺ release. mGluR1 and mGluR5 expression was increased in Glu spinal cord axon terminals of 90-day-old SOD1^G93A mice, but not in the whole axon terminal population. Interestingly, mGluR1 and mGluR5 were significantly augmented in total spinal cord tissue already at 60 days. Thus, function and expression of group I mGluRs are enhanced in the early-symptomatic SOD1^G93A mouse spinal cord, possibly participating in excessive Glu transmission and supporting their implication in ALS. Please define all abbreviations the first time they appear in the abstract, the main text, and the first figure or table caption.

Modulation of mTOR and CREB pathways following mGluR5 blockade contribute to improved Huntington's pathology in zQ175 mice

Huntington’s disease (HD) is a neurodegenerative disorder caused by a genetic abnormality in the huntingtin gene that leads to a polyglutamine repeat expansion of the huntingtin protein. The cleaved polyglutamine expansion of mutant huntingtin (mHTT) protein can form aggregates strongly correlated with HD progression. We have previously shown that the inhibition of mGluR5 using CTEP, a selective negative allosteric mGluR5 modulator, can delay disease progression and reduce in mHTT aggregates in the zQ175 mouse model of HD. This was paralleled by enhanced catalytic activity of Unc-51-like kinase 1 (ULK1), a kinase modulated by mammalian target of rapamycin (mTOR) and key regulator of autophagy initiation. In the present study, we show that CTEP can correct aberrant phosphoinositide 3-kinase (PI3K)/Akt/mTOR signaling detected in zQ175 mice that may underlie the enhanced ULK1 activity and activation of autophagy. We also show that CTEP can facilitate cAMP response element-binding protein (CREB)-mediated expression of brain-derived neurotrophic factor (BDNF) to foster neuronal survival and reduce apoptosis. Taken together, our findings provide the molecular evidence for how targeting mGluR5 using a well-tolerated selective NAM can mitigate two critical mechanisms of neurodegeneration, autophagy and apoptosis.

The beneficial roles of exercise training via autophagy in neurological diseases and possible mechanisms

Autophagy is a conservative catabolism process, participating in delivering the cytosol and cytosolic components to the lysosome. Abnormal autophagy is related to human pathologies, for instance diabetes, neurodegeneration, cardiovascular, macular degeneration, pulmonary, and cancer. Enormous evidences indicate that autophagy may mediate the cellular pathological condition in the process of neurological diseases. Exercise as a form of physiological stress may cause an adaptation, and autophagy is a necessary process for adaptational response to exercise. Autophagy during exercise may improve neurological function, control tissue maintain tissue integrity, and activate different signals pathway for adaptation. In this review, we summarize the possible mechanisms of exercise training via autophagy in neurological diseases.

Association between miRNAs expression and cognitive performances of Pediatric Multiple Sclerosis patients: A pilot study

INTRODUCTION

The Pediatric onset of Multiple Sclerosis (PedMS) occurs in up to 10% of all cases. Cognitive impairment is one of the frequent symptoms, exerting severe impact in patients' quality of life and school performances. The underlying pathogenic mechanisms are not fully understood, and molecular markers predictive of cognitive dysfunctions need to be identified. On these grounds, we searched for molecular signature/s (i.e., miRNAs and target genes) associated with cognitive impairment in a selected population of PedMS patients. Additionally, changes of their regional brain volumes associated with the miRNAs of interest were investigated.

METHODS

Nineteen PedMS subjects received a full cognitive evaluation; total RNA from peripheral blood samples was processed by next-generation sequencing followed by a bioinformatics/biostatistics analysis.

RESULTS

The expression of 11 miRNAs significantly correlated with the scores obtained at different cognitive tests; among the others, eight miRNAs correlated with the Trail Making Tests. The computational target prediction identified 337 genes targeted by the miRNAs of interest; a tangled network of molecular connections was hypothesized, where genes like BST1, NTNG2, SPTB, and STAB1, already associated with cognitive dysfunctions, were nodes of the net. Furthermore, the expression of some miRNAs significantly correlated with cerebral volumes, for example, four miRNAs with the cerebellum cortex.

CONCLUSIONS

As far as we know, this is the first evaluation exploring miRNAs in the cognitive performances of PedMS. Although none of these results survived the multiple tests' corrections, we believe that they may represent a step forward the identification of biomarkers useful for monitoring and targeting the onset/progression of cognitive impairments in MS.