Autophagy in Neurons

Uncovering the Impact of Aggrephagy in the Development of Alzheimer's Disease: Insights Into Diagnostic and Therapeutic Approaches from Machine Learning Analysis

BACKGROUND

Alzheimer's disease (AD) stands as a widespread neurodegenerative disorder marked by the gradual onset of memory impairment, predominantly impacting the elderly. With projections indicating a substantial surge in AD diagnoses, exceeding 13.8 million individuals by 2050, there arises an urgent imperative to discern novel biomarkers for AD.

METHODS

To accomplish these objectives, we explored immune cell infiltration and the expression patterns of immune cells and immune function-related genes of AD patients. Furthermore, we utilized the consensus clustering method combined with aggrephagy-related genes (ARGs) for typing AD patients and categorized AD specimens into distinct clusters (C1, C2). A total of 272 candidate genes were meticulously identified through a combination of differential analysis and Weighted Gene Co-Expression Network Analysis (WGCNA). Subsequently, we applied three machine learning algorithms-namely random forest (RF), support vector machine (SVM), and generalized linear model (GLM)-to pinpoint a pathogenic signature comprising five genes associated with AD. To validate the predictive accuracy of these identified genes in discerning AD progression, we constructed nomograms.

RESULTS

Our analyses uncovered that cluster C2 exhibits a higher immune expression than C1. Based on the ROC(0.956). We identified five characteristic genes (PFKFB4, PDK3, KIAA0319L, CEBPD, and PHC2T) associated with AD immune cells and function. The nomograms constructed on the basis of these five diagnostic genes demonstrated effectiveness. In the validation group, the ROC values were found to be 0.760 and 0.838, respectively. These results validate the robustness and reliability of the diagnostic model, affirming its potential for accurate identification of AD.

CONCLUSION

Our findings not only contribute to a deeper understanding of the molecular mechanisms underlying AD but also offer valuable insights for drug development and clinical analysis. The limitation of our study is the limited sample size, and although AD-related genes were identified and some of the mechanisms elucidated, further experiments are needed to elucidate the more in-depth mechanisms of these characterized genes in the disease.

S1PR2 Regulates Autophagy Through the AKT/mTOR Pathway to Promote Pathological Damage in Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a fatal and debilitating neurodegenerative disease. Sphingosine-1-phosphate receptor 2 (S1PR2), one of the receptors of S1P, is a key regulatory factor for various diseases.

OBJECTIVE

This study aimed to explore the role and possible mechanism of S1PR2 in AD.

METHODS

S1PR2 expression in the AD mice was detected, and after intervening S1PR2 expression with sh-S1PR2 in AD mice, the behavioral changes, pathological lesions of the hippocampus, autophagy level, and AKT/mTOR pathway activation were analyzed. Furthermore, SH-SY5Y cells were induced by Aβ25-35 to construct an AD cell model, and the effects of sh-S1PR2 on proliferation, apoptosis, autophagy, and AKT/mTOR pathway of AD cells were investigated. In addition, the effects of pathway inhibitor rapamycin on model cells were further analyzed.

RESULTS

The expression of S1PR2 was significantly increased in AD mice, the sh-S1PR2 significantly improved behavioral dysfunction, alleviated pathological injury of the hippocampus, increased the number of neurons, and inhibited Aβ production and p-tau expression, showing a positive effect on the AD pathology. In addition, silencing of S1PR2 expression significantly promoted the autophagy level and inhibited the activation of the AKT/mTOR pathway in AD model mice. In vitro experiments further confirmed that sh-S1PR2 promoted cell proliferation, inhibited apoptosis, relieved cytopathology, promoted autophagy, and inhibited the activation of the AKT/mTOR pathway in the cell model. The use of rapamycin further confirmed the role of AKT/mTOR pathway-mediated autophagy in the regulation of AD by S1PR2.

CONCLUSION

S1PR2 promoted AD pathogenesis by inhibiting autophagy through the activation of AKT/mTOR pathway.

The HERC proteins and the nervous system

The HERC protein family is one of three subfamilies of Homologous to E6AP C-terminus (HECT) E3 ubiquitin ligases. Six HERC genes have been described in humans, two of which encode Large HERC proteins -HERC1 and HERC2- with molecular weights above 520 kDa that are constitutively expressed in the brain. There is a large body of evidence that mutations in these Large HERC genes produce clinical syndromes in which key neurodevelopmental events are altered, resulting in intellectual disability and other neurological disorders like epileptic seizures, dementia and/or signs of autism. In line with these consequences in humans, two mice carrying mutations in the Large HERC genes have been studied quite intensely: the tambaleante mutant for Herc1 and the Herc2^+/530 mutant for Herc2. In both these mutant mice there are clear signs that autophagy is dysregulated, eliciting cerebellar Purkinje cell death and impairing motor control. The tambaleante mouse was the first of these mice to appear and is the best studied, in which the Herc1 mutation elicits: (i) delayed neural transmission in the peripheral nervous system; (ii) impaired learning, memory and motor control; and (iii) altered presynaptic membrane dynamics. In this review, we discuss the information currently available on HERC proteins in the nervous system and their biological activity, the dysregulation of which could explain certain neurodevelopmental syndromes and/or neurodegenerative diseases.

Logistics of neuronal protein turnover: Numbers and mechanisms

Research in the past twenty years or so has revealed that neurons synthesize and degrade proteins at their synapses to enable synaptic proteome remodelling on demand and in real-time. Here we provide a quantitative overview of the decentralized neuronal protein-turnover logistics. We first analyse the huge neuronal protein turnover demand that arises from subcellular compartments outside the cell body, followed by an overview of key quantities and modulation strategies in neuronal protein turnover logistics. In the end, we briefly review recent progress in neuronal local protein synthesis and summarize diverse protein-degradation mechanisms that are found near synapses.

Autophagy and Its Association with Genetic Mutations in Parkinson Disease

Parkinson disease is the second most common neurodegenerative disorder, affecting 0.1-0.2% of the general population. It is a progressive debilitating disorder caused by degeneration of dopaminergic neurons in the substantia nigra pars compacta. It is characterized by motor and non-motor symptoms. Parkinson disease can be caused by mutations in genes that encode proteins involved in the autophagic process, resulting in impaired autophagy. Indeed, autophagy has been implicated in the pathogenesis of Parkinson disease, particularly because its impairment causes the buildup of proteins. Thus, this review aims to provide an overview of Parkinson disease-related genetic mutations and their association with autophagy impairment in Parkinson disease, which can be helpful in improving the understanding of the pathogenesis of Parkinson disease, illustrating the potential therapeutic implications of agents that can enhance autophagy in Parkinson disease. Additionally, we will highlight the essential need for the development of highly sensitive and specific assays for gene-based diagnostic biomarkers. Finally, we will provide an overview on the potential gene-based therapeutic approaches for Parkinson disease, which have been most advanced and are associated with the most common targets being alpha-synuclein (SNCA), leucine-rich repeat kinase-2 (LRRK2), and glucocerebrosidase (GBA).

Spatiotemporal analysis of axonal autophagosome-lysosome dynamics reveals limited fusion events and slow maturation

Macroautophagy is a homeostatic process required to clear cellular waste. Neuronal autophagosomes form constitutively in the distal tip of the axon and are actively transported toward the soma, with cargo degradation initiated en route. Cargo turnover requires autophagosomes to fuse with lysosomes to acquire degradative enzymes; however, directly imaging these fusion events in the axon is impractical. Here we use a quantitative model, parameterized and validated using data from primary hippocampal neurons, to explore the autophagosome maturation process. We demonstrate that retrograde autophagosome motility is independent of fusion and that most autophagosomes fuse with only a few lysosomes during axonal transport. Our results indicate that breakdown of the inner autophagosomal membrane is much slower in neurons than in nonneuronal cell types, highlighting the importance of this late maturation step. Together, rigorous quantitative measurements and mathematical modeling elucidate the dynamics of autophagosome-lysosome interaction and autophagosomal maturation in the axon.

Parkinsonism in Genetic Neurodevelopmental Disorders: A Systematic Review

Background

With advances in clinical genetic testing, associations between genetic neurodevelopmental disorders and parkinsonism are increasingly recognized. In this review, we aimed to provide a comprehensive overview of reports on parkinsonism in genetic neurodevelopmental disorders and summarize findings related to genetic diagnosis, clinical features and proposed disease mechanisms.

Methods

A systematic literature review was conducted in PubMed and Embase on June 15, 2021. Search terms for parkinsonism and genetic neurodevelopmental disorders, using generic terms and the Human Phenotype Ontology, were combined. Study characteristics and descriptive data were extracted from the articles using a modified version of the Cochrane Consumers and Communication Review Group's data extraction template. The protocol was registered in PROSPERO (CRD42020191035).

Results

The literature search yielded 208 reports for data-extraction, describing 69 genetic disorders in 422 patients. The five most reported from most to least frequent were: 22q11.2 deletion syndrome, beta-propeller protein-associated neurodegeneration, Down syndrome, cerebrotendinous xanthomatosis, and Rett syndrome. Notable findings were an almost equal male to female ratio, an early median age of motor onset (26 years old) and rigidity being more common than rest tremor. Results of dopaminergic imaging and response to antiparkinsonian medication often supported the neurodegenerative nature of parkinsonism. Moreover, neuropathology results showed neuronal loss in the majority of cases. Proposed disease mechanisms included aberrant mitochondrial function and disruptions in neurotransmitter metabolism, endosomal trafficking, and the autophagic-lysosomal and ubiquitin-proteasome system.

Conclusion

Parkinsonism has been reported in many GNDs. Findings from this study may provide clues for further research and improve management of patients with GNDs and/or parkinsonism.

Regulation of α-synuclein homeostasis and inflammasome activation by microglial autophagy

Autophagy clears protein aggregates, damaged cellular organelles, and pathogens through the lysosome. Although autophagy is highly conserved across all cell types, its activity in each cell is specifically adapted to carry out distinct physiological functions. The role of autophagy in neurons has been well characterized; however, in glial cells, its function remains largely unknown. Microglia are brain-resident macrophages that survey the brain to remove injured neurons, excessive synapses, protein aggregates, and infectious agents. Current studies have demonstrated that dysfunctional microglia contribute to neurodegenerative diseases. In Alzheimer's disease animal models, microglia play a critical role in regulating amyloid plaque formation and neurotoxicity. However, how microglia are involved in Parkinson's disease (PD) remains poorly understood. Propagation of aggregated α-synuclein via cell-to-cell transmission and neuroinflammation have emerged as important mechanisms underlying neuropathologies in PD. Here, we review converging evidence that microglial autophagy maintains α-synuclein homeostasis, regulates neuroinflammation, and confers neuroprotection in PD experimental models.

The autophagy inducer SMER28 attenuates microtubule dynamics mediating neuroprotection

SMER28 originated from a screen for small molecules that act as modulators of autophagy. SMER28 enhanced the clearance of autophagic substrates such as mutant huntingtin, which was additive to rapamycin-induced autophagy. Thus, SMER28 was established as a positive regulator of autophagy acting independently of the mTOR pathway, increasing autophagosome biosynthesis and attenuating mutant huntingtin-fragment toxicity in cellular- and fruit fly disease models, suggesting therapeutic potential. Despite many previous studies, molecular mechanisms mediating SMER28 activities and its direct targets have remained elusive. Here we analyzed the effects of SMER28 on cells and found that aside from autophagy induction, it significantly stabilizes microtubules and decelerates microtubule dynamics. Moreover, we report that SMER28 displays neurotrophic and neuroprotective effects at the cellular level by inducing neurite outgrowth and protecting from excitotoxin-induced axon degeneration. Finally, we compare the effects of SMER28 with other autophagy-inducing or microtubule-stabilizing drugs: whereas SMER28 and rapamycin both induce autophagy, the latter does not stabilize microtubules, and whereas both SMER28 and epothilone B stabilize microtubules, epothilone B does not stimulate autophagy. Thus, the effect of SMER28 on cells in general and neurons in particular is based on its unique spectrum of bioactivities distinct from other known microtubule-stabilizing or autophagy-inducing drugs.

The emerging role of autophagy and mitophagy in tauopathies: From pathogenesis to translational implications in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease, affecting more than 55 million individuals worldwide in 2021. In addition to the "amyloid hypothesis," an increasing number of studies have demonstrated that phosphorylated tau plays an important role in AD pathogenesis. Both soluble tau oligomers and insoluble tau aggregates in the brain can induce structural and functional neuronal damage through multiple pathways, eventually leading to memory deficits and neurodegeneration. Autophagy is an important cellular response to various stress stimuli and can generally be categorized into non-selective and selective autophagy. Recent studies have indicated that both types of autophagy are involved in AD pathology. Among the several subtypes of selective autophagy, mitophagy, which mediates the selective removal of mitochondria, has attracted increasing attention because dysfunctional mitochondria have been suggested to contribute to tauopathies. In this review, we summarize the latest findings on the bidirectional association between abnormal tau proteins and defective autophagy, as well as mitophagy, which might constitute a vicious cycle in the induction of neurodegeneration. Neuroinflammation, another important feature in the pathogenesis and progression of AD, has been shown to crosstalk with autophagy and mitophagy. Additionally, we comprehensively discuss the relationship between neuroinflammation, autophagy, and mitophagy. By elucidating the underlying molecular mechanisms governing these pathologies, we highlight novel therapeutic strategies targeting autophagy, mitophagy and neuroinflammation, such as those using rapamycin, urolithin, spermidine, curcumin, nicotinamide, and actinonin, for the prevention and treatment of AD.

Prepubertal exposure to Pb alters autophagy in the brain of aging mice: A time-series based model

As a ubiquitous toxic heavy metal, lead (Pb) exposure is known to be implicated in the onset and development of neurodegenerative diseases which may cause more serious health hazards with age and the accumulation of Pb in the body. Autophagy is the main degradation route for abnormal aggregated proteins and damaged cell organelles. Here, we aimed to study the effects of adolescent Pb exposure on autophagy at different life nodes. In this study, we developed a time-series model of Pb exposure in mice and randomly divided 4-week-old male C57BL/6 mice into six groups (4 C, 13 C, 16 C, 4Pb, 13Pb and 16Pb). Mice in Pb groups was consumed deionized water containing 0.2 % Pb(Ac)2 for 3 months and then reared to anticipated life nodes, while the control group consumed deionized water. Western blot and Real-time qPCR were used to assess the effects of developmental Pb exposure on individual components of the autophagy machinery and modulation of microtubule-associated protein 1 light chain 3 (LC3) at each age stage. Our results showed that Pb exposure during adolescence reduced the p-mTOR/mTOR ratios with enhanced expression of Beclin-1, Atg12 and Atg7in both the hippocampus (HPC) and prefrontal cortex (PFC) of senescent mice while upregulation of LC3II/LC3I ratios and p62 suggested that autophagy mediates degradation was interrupted. Overall, we confirm that Pb exposure during adolescence promotes autophagic processes in the aged mice brain and that autophagic degradation is hindered, ultimately leading to a failure of autophagic degradation.

The Potential Role of Voltage-Dependent Anion Channel in the Treatment of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disease second only to Alzheimer’s disease in terms of prevalence. Previous studies have indicated that the occurrence and progression of PD are associated with mitochondrial dysfunction. Mitochondrial dysfunction is one of the most important causes for apoptosis of dopaminergic neurons. Therefore, maintaining the stability of mitochondrial functioning is a potential strategy in the treatment of PD. Voltage-dependent anion channel (VDAC) is the main component in the outer mitochondrial membrane, and it participates in a variety of biological processes. In this review, we focus on the potential roles of VDACs in the treatment of PD. We found that VDACs are involved in PD by regulating apoptosis, autophagy, and ferroptosis. VDAC1 oligomerization, VDACs ubiquitination, regulation of mitochondrial permeability transition pore (mPTP) by VDACs, and interaction between VDACs and α-synuclein (α-syn) are all promising methods for the treatment of PD. We proposed that inhibition of VDAC1 oligomerization and promotion of VDAC1 ubiquitination as an effective approach for the treatment of PD. Previous studies have proven that the expression of VDAC1 has a significant change in PD models. The expression levels of VDAC1 are decreased in the substantia nigra (SN) of patients suffering from PD compared with the control group consisting of normal individuals by using bioinformatics tools. VDAC2 is involved in PD mainly through the regulation of apoptosis. VDAC3 may have a similar function to VDAC1. It can be concluded that the functional roles of VDACs contribute to the therapeutic strategy of PD.

The brain-specific splice variant of the CDC42 GTPase works together with the kinase ACK to downregulate the EGF receptor in promoting neurogenesis

The small GTPase CDC42 plays essential roles in neurogenesis and brain development. Previously, we showed that a CDC42 splice variant that has a ubiquitous tissue distribution specifically stimulates the formation of neural progenitor cells, whereas a brain-specific CDC42 variant, CDC42b, is essential for promoting the transition of neural progenitor cells to neurons. These specific roles of CDC42 and CDC42b in neurogenesis are ascribed to their opposing effects on mTORC1 activity. Specifically, the ubiquitous form of CDC42 stimulates mTORC1 activity and thereby upregulates tissue-specific transcription factors that are essential for neuroprogenitor formation, whereas CDC42b works together with activated CDC42-associated kinase (ACK) to downregulate mTOR expression. Here, we demonstrate that the EGF receptor (EGFR) is an additional and important target of CDC42b and ACK, which is downregulated by their combined actions in promoting neurogenesis. The activation status of the EGFR determines the timing by which neural progenitor cells derived from P19 embryonal carcinoma terminally differentiate into neurons. By promoting EGFR degradation, we found that CDC42b and ACK stimulate autophagy, which protects emerging neurons from apoptosis and helps trigger neural progenitor cells to differentiate into neurons. Moreover, our results reveal that CDC42b is localized in phosphatidylinositol (3,4,5)-triphosphate-enriched microdomains on the plasma membrane, mediated through its polybasic sequence ¹⁸⁵KRK¹⁸⁷, which is essential for determining its distinct functions. Overall, these findings now highlight a molecular mechanism by which CDC42b and ACK regulate neuronal differentiation and provide new insights into the functional interplay between EGFR degradation and autophagy that occurs during embryonic neurogenesis.

Role of mitophagy in the neurodegenerative diseases and its pharmacological advances: A review

Neurodegenerative diseases are a class of incurable and debilitating diseases characterized by progressive degeneration and death of cells in the central nervous system. They have multiple underlying mechanisms; however, they all share common degenerative features, such as mitochondrial dysfunction. According to recent studies, neurodegenerative diseases are associated with the accumulation of dysfunctional mitochondria. Selective autophagy of mitochondria, called mitophagy, can specifically degrade excess or dysfunctional mitochondria within cells. In this review, we highlight recent findings on the role of mitophagy in neurodegenerative disorders. Multiple studies were collected, including those related to the importance of mitochondria, the mechanism of mitophagy in protecting mitochondrial health, and canonical and non-canonical pathways in mitophagy. This review elucidated the important function of mitophagy in neurodegenerative diseases, discussed the research progress of mitophagy in neurodegenerative diseases, and summarized the role of mitophagy-related proteins in neurological diseases. In addition, we also highlight pharmacological advances in neurodegeneration.

Interaction between autophagy and the NLRP3 inflammasome in Alzheimer’s and Parkinson’s disease

Autophagy degrades phagocytosed damaged organelles, misfolded proteins, and various pathogens through lysosomes as an essential way to maintain cellular homeostasis. Autophagy is a tightly regulated cellular self-degradation process that plays a crucial role in maintaining normal cellular function and homeostasis in the body. The NLRP3 inflammasome in neuroinflammation is a vital recognition receptor in innate cellular immunity, sensing external invading pathogens and endogenous stimuli and further triggering inflammatory responses. The NLRP3 inflammasome forms an inflammatory complex by recognizing DAMPS or PAMPS, and its activation triggers caspase-1-mediated cleavage of pro-IL-1β and pro-IL-18 to promote the inflammatory response. In recent years, it has been reported that there is a complex interaction between autophagy and neuroinflammation. Strengthening autophagy can regulate the expression of NLRP3 inflammasome to reduce neuroinflammation in neurodegenerative disease and protect neurons. However, the related mechanism is not entirely clear. The formation of protein aggregates is one of the standard features of Neurodegenerative diseases. A large number of toxic protein aggregates can induce inflammation. In theory, activation of the autophagy pathway can remove the potential toxicity of protein aggregates and delay the progression of the disease. This article aims to review recent research on the interaction of autophagy, NLRP3 inflammasome, and protein aggregates in Alzheimer’s disease (AD) and Parkinson’s disease (PD), analyze the mechanism and provide theoretical references for further research in the future.

The contribution of altered neuronal autophagy to neurodegeneration

Defects in cellular functions related to altered protein homeostasis and associated progressive accumulation of pathological intracellular material is a critical process involved in the pathogenesis of many neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Autophagy is an essential mechanism that ensures neuronal health by removing long-lived proteins or defective organelles and by doing so prevents cell toxicity and death within the central nervous system. Abundant evidence has shown that neuronal autophagy pathways are altered in Alzheimer's disease, Parkinson's disease and traumas of the central nervous system including Spinal Cord Injury and Traumatic Brain Injury. In this review, we aimed to summarize the latest studies on the role that altered neuronal autophagy plays in brain health and these pathological conditions, and how this knowledge can be leveraged for the development of novel therapeutics against them.

Deciphering the Heterogeneity of the Internal Environment of Hippocampal Neurons during Maturation by Raman Spectroscopy

Hippocampal neurons are sensitive to changes in the internal environment and play a significant role in controlling learning, memory, and emotions. A remarkable characteristic of the aging brain is its ability to shift from a state of normal inflammation to excessive inflammation. Various cognitive abilities of the elderly may suffer from serious harm due to the change in the neural environment. Hippocampal neurons may have various subsets involved in controlling their internal environment at different stages of development. Developmental differences may eventually result from complex changes in the dynamic neuronal system brought on by metabolic changes. In this study, we used an in vitro hippocampal neuron model cultured in C57BL/6J mice in conjugation with Raman spectroscopy to examine the relative alterations in potential biomarkers, such as levels of metabolites in the internal environment of hippocampal neurons at various developmental stages. The various differentially expressed genes (DEGs) of hippocampal neurons at various developmental stages were simultaneously screened using bioinformatics, and the biological functions as well as the various regulatory pathways of DEGs were preliminarily analyzed, providing an essential reference for investigating novel therapeutic approaches for diseases that cause cognitive impairment, such as Alzheimer's disease. A stable hippocampal neuron model was established using the GIBCO C57BL/6J hippocampal neuron cell line as a donor and in vitro hippocampal neuron culture technology. The Raman peak intensities of culture supernatants from the experimental groups incubated for 0, 7, and 14 days in vitro(DIV) were examined. The GEO database was used to screen for different DEGs associated with various developmental stages. The data was then analyzed using a statistical method called orthogonal partial least squares discriminant analysis (OPLS-DA). The levels of ketogenic and glycogenic amino acids (such as tryptophan, phenylalanine, and tyrosine), lipid intake rate, glucose utilization rate, and nucleic acid expression in the internal environment of hippocampal neurons were significantly different in the 14 DIV group compared to the 0 DIV and 7 DIV groups (P < 0.01). The top 10 DEGs with neuronal maturation were screened, and the results were compared to the OPLS-DA model's analysis of the differential peaks. It was found that different genes involved in maturation can directly relate to changes in the body's levels of ketogenic and glycogenic amino acids (P < 0.01). The altered expression of the maturation-related genes epidermal growth factor receptor, protein tyrosine kinase 2-beta, discs large MAGUK scaffold protein 2, and Ras protein-specific guanine nucleotide releasing factor 1 may be connected to the altered uptake of ketogenic and glycogenic amino acids and nucleic acids in the internal environment of neurons at different developmental stages. The levels of ketogenic, glycogenic amino acids, and lipid intake increased while glucose utilization decreased, which may be related to mature neurons' metabolism and energy use. The decline in nucleic acid consumption could be connected to synaptic failure. The Raman spectroscopy fingerprint results of relevant biomarkers in conjugation with multivariable analysis and biological action targets suggested by differential genes interpret the heterogeneity of the internal environment of mature hippocampal neurons in the process of maturation, open a new idea for exploring the dynamic mechanism of the exchange energy metabolism of information molecules in the internal environment of hippocampal neurons, and provide a new method for studying this process.

Drug repurposing in cancer neuroscience: From the viewpoint of the autophagy-mediated innervated niche

Based on the bidirectional interactions between neurology and cancer science, the burgeoning field “cancer neuroscience” has been proposed. An important node in the communications between nerves and cancer is the innervated niche, which has physical contact with the cancer parenchyma or nerve located in the proximity of the tumor. In the innervated niche, autophagy has recently been reported to be a double-edged sword that plays a significant role in maintaining homeostasis. Therefore, regulating the innervated niche by targeting the autophagy pathway may represent a novel therapeutic strategy for cancer treatment. Drug repurposing has received considerable attention for its advantages in cost-effectiveness and safety. The utilization of existing drugs that potentially regulate the innervated niche via the autophagy pathway is therefore a promising pharmacological approach for clinical practice and treatment selection in cancer neuroscience. Herein, we present the cancer neuroscience landscape with an emphasis on the crosstalk between the innervated niche and autophagy, while also summarizing the underlying mechanisms of candidate drugs in modulating the autophagy pathway. This review provides a strong rationale for drug repurposing in cancer treatment from the viewpoint of the autophagy-mediated innervated niche.

Molecular Mechanism and Regulation of Autophagy and Its Potential Role in Epilepsy

Autophagy is an evolutionally conserved degradation mechanism for maintaining cell homeostasis whereby cytoplasmic components are wrapped in autophagosomes and subsequently delivered to lysosomes for degradation. This process requires the concerted actions of multiple autophagy-related proteins and accessory regulators. In neurons, autophagy is dynamically regulated in different compartments including soma, axons, and dendrites. It determines the turnover of selected materials in a spatiotemporal control manner, which facilitates the formation of specialized neuronal functions. It is not surprising, therefore, that dysfunctional autophagy occurs in epilepsy, mainly caused by an imbalance between excitation and inhibition in the brain. In recent years, much attention has been focused on how autophagy may cause the development of epilepsy. In this article, we overview the historical landmarks and distinct types of autophagy, recent progress in the core machinery and regulation of autophagy, and biological roles of autophagy in homeostatic maintenance of neuronal structures and functions, with a particular focus on synaptic plasticity. We also discuss the relevance of autophagy mechanisms to the pathophysiology of epileptogenesis.

Total flavonoids of hawthorn leaves protect spinal motor neurons via promotion of autophagy after spinal cord injury

The death of spinal motor neurons (SMNs) after spinal cord injury (SCI) is a crucial cause, contributing to a permanent neurological deficit. Total flavonoids of hawthorn leaves (TFHL) have been confirmed to have potentially therapeutic for SCI. Nonetheless, the roles and mechanisms of TFHL in recovering neuromotor function and regenerating axons of SMNs have not been fully elucidated. In this study, TFHL was applied to treat rats with SCI and injured SMNs for 7 days. In vivo experiment, rats with SCI were evaluated by a BBB (Basso-Beattie-Bresnahan) score to assess their motor functional recovery. The morphology, microstructure, apoptosis, Nissl bodies, and autophagy of SMNs in spinal cord tissue were detected by Hematoxylin-eosin (HE) staining, transmission electron microscopy, TUNEL staining, Nissl staining, and immunohistochemistry respectively. In vitro experiment, the co-culture model of SMNs and astrocytes was constructed to simulate the internal environment around SMNs in the spinal cord tissue. The cell morphology, microstructure, axonal regeneration, and autophagy were observed via optical microscope, transmission electron microscopy, and immunofluorescence. The content of neurotrophic factors in the cell culture medium of the co-culture model was detected by ELISA. Moreover, the expression of axon-related and autophagy-related proteins in the spinal cord tissue and SMNs was measured by Western Blot. We demonstrated that TFHL improved the neuromotor function recovery in rats after SCI. We then found that TFHL significantly promoted injured spinal cord tissue repair, reduced apoptosis, and improved the functional status of neurons in spinal cord tissue in vivo. Meanwhile, the cell morphology, microstructure, and axonal regeneration of damaged SMNs also obviously were improved, and the secretion of neurotrophic factors was facilitated after treatment with TFHL in vitro. Further, we revealed that TFHL promoted autophagy and related protein expression in vivo and vitro. Taken together, our study suggested that TFHL might facilitate autophagy and have neuroprotective properties in SMNs to enhance the recovery of neuromotor function of rats with SCI.

Unraveling Pathophysiological Link Between Mitophagy Pathway and Vascular Dementia

Context: Vascular dementia (VaD) is the second most common type of dementia after Alzheimer’s disease worldwide. Vascular dementia is a neurodegenerative disorder characterized by gradual cognitive impairment. Ischemic and hemorrhagic strokes result in VaD, markedly distributing cerebral blood flow and decreasing patients’ cognitive and memory performance. Due to their high energy demands, neurons are more sensitive to cellular architecture changes and exposed to mitochondrial stress than other cell types. Mitochondrial dysfunction and selective autophagy of mitochondria, known as mitophagy, are associated with VaD. This review aims to elucidate the association between mitophagy and VaD. Evidence Acquisition: This review was conducted independently by at least two researchers dominant in various VaD studies. We searched databases including Elsevier, Google Scholar, and PubMed using the terms ‘vascular dementia’, ‘vascular cognitive impairment’, and ‘mitophagy’. We evaluated 70 articles on the relationship between VaD and mitophagy and interpreted the results. Adobe Photoshop 2022 was used for drawing figures by researchers. Results: The autophagy process plays a protective role in experimental VaD models via preserving vascular integrity and the structure of the blood-brain barrier, upregulating occludin and claudin protein expressions, reducing oxidative stress, and decreasing cognitive dysfunction. Some studies claim that autophagy could have adverse effects in a time-dependent manner against neuronal injury. Prolonged autophagy and overexpressed autophagic proteins induce ischemic injury and cause neuronal cells to undergo apoptotic cell death. Conclusions: Although there are limited studies on the activation of mitophagy-related pathways in VaD, and the definitive role of mitophagy in neuronal healing is unclear, further research is needed to elucidate mitophagy pathways in neurons.

The Emerging Role of Astrocytic Autophagy in Central Nervous System Disorders

Astrocytes act as "housekeeping cells" for maintaining cerebral homeostasis and play an important role in many disorders. Recent studies further highlight the contribution of autophagy to astrocytic functions, including astrogenesis, the astrocytic removal of neurotoxins or stressors, and astrocytic polarization. More importantly, genetic and pharmacological approaches have provided evidence that outlines the contributions of astrocytic autophagy to several brain disorders, including neurodegeneration, cerebral ischemia, and depression. In this study, we summarize the emerging role of autophagy in regulating astrocytic functions and discuss the contributions of astrocytic autophagy to different CNS disorders.

Lignin-carbohydrate complexes suppress SCA3 neurodegeneration via upregulating proteasomal activities

Lignin-carbohydrate complexes (LCCs) represent a group of macromolecules with diverse biological functions such as antioxidative properties. Polyglutamine (polyQ) diseases such as spinocerebellar ataxia type 3 (SCA3) comprise a set of neurodegenerative disorders characterized by the formation of polyQ protein aggregates in patient neurons. LCCs have been reported to prevent such protein aggregation. In this study, we identified a potential mechanism underlying the above anti-protein aggregation activity. We isolated and characterized multiple LCC fractions from bamboo and poplar and found that lignin-rich LCCs (BM-LCC-AcOH and PR-LCC-AcOH) effectively eliminated both monomeric and aggregated mutant ataxin-3 (ATXN3polyQ) proteins in neuronal cells and a Drosophila melanogaster SCA3 disease model. In addition, treatment with BM-LCC-AcOH or PR-LCC-AcOH rescued photoreceptor degeneration in vivo. At the mechanistic level, we demonstrated that BM-LCC-AcOH and PR-LCC-AcOH upregulated proteasomal activity. When proteasomal function was impaired, the ability of the LCCs to suppress ATXN3polyQ aggregation was abolished. Thus, we identified a previously undescribed proteasome-inducing function of LCCs and showed that such activity is indispensable for the beneficial effects of LCCs on SCA3 neurotoxicity.

Differences in the Autophagy Response to Hypoxia in the Hippocampus and Neocortex of Rats

Autophagy is a regulated mechanism of degradation of misfolded proteins and organelles in the cell. Neurons are highly differentiated cells with extended projections, and therefore, their functioning largely depends on the mechanisms of autophagy. For the first time in an animal model using immunohistochemistry, dot analysis, and qRT-PCR, the autophagy (macroautophagy) activity in neurons of two brain regions (hippocampus and neocortex) under normoxia and after exposure to hypoxia was studied. It was found that under normoxia, the autophagic activity was higher in the hippocampal neurons than in the neocortex of rats. In the hippocampus, the exposure of rats to hypoxia resulted in a decrease in the content of autophagy markers LC3 and p62, which was followed by activation of the autophagy-related gene expression. In the neocortex, no changes in these marker proteins were observed after the exposure to hypoxia. These data indicate that the neurons in the hippocampus and neocortex differ in the autophagy response to hypoxia, which may reflect the physiological and functional differences of the pyramidal cells of these brain regions and may to some extent account for the extreme vulnerability of the CA1 hippocampal neurons and relatively high resistance of the neocortical neurons to hypoxia.

Progranulin Preserves Autophagy Flux and Mitochondrial Function in Rat Cortical Neurons Under High Glucose Stress

Chronic hyperglycemia in type II diabetes results in impaired autophagy function, accumulation of protein aggregates, and neurodegeneration. However, little is known about how to preserve autophagy function under hyperglycemic conditions. In this study, we tested whether progranulin (PGRN), a neurotrophic factor required for proper lysosome function, can restore autophagy function in neurons under high-glucose stress. We cultured primary cortical neurons derived from E18 Sprague-Dawley rat pups to maturity at 10 days in vitro (DIV) before incubation in high glucose medium and PGRN for 24-72 h before testing for autophagy flux, protein turnover, and mitochondrial function. We found that although PGRN by itself did not upregulate autophagy, it attenuated impairments in autophagy seen under high-glucose conditions. Additionally, buildup of the autophagosome marker light chain 3B (LC3B) and lysosome marker lysosome-associated membrane protein 2A (LAMP2A) changed in both neurons and astrocytes, indicating a possible role for glia in autophagy flux. Protein turnover, assessed by remaining advanced glycation end-product levels after a 6-h incubation, was preserved with PGRN treatment. Mitochondrial activity differed by complex, although PGRN appeared to increase overall activity in high glucose. We also found that activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and glycogen synthase kinase 3β (GSK3β), kinases implicated in autophagy function, increased with PGRN treatment under stress. Together, our data suggest that PGRN prevents hyperglycemia-induced decreases in autophagy by increasing autophagy flux via increased ERK1/2 kinase activity in primary rat cortical neurons.

Upregulation of PGC-1α Attenuates Oxygen-Glucose Deprivation-Induced Hippocampal Neuronal Injury

Hippocampal neuronal damage likely underlies cognitive impairment in vascular dementia (VaD). PPARγ coactivator-1α (PGC-1α) is a master regulator of mitochondrial biogenesis. However, the role and the precise mechanism of how PGC-1α alleviates hippocampal neuronal injury remain unknown. To address this question, HT-22 cells, an immortalized hippocampal neuron cell line, with or without PGC-1α overexpression were subjected to oxygen-glucose deprivation (OGD), which mimics the circumstance of chronic cerebral hypoperfusion in VaD. After OGD, cell viability was assessed using the MTS assay. The mitochondrial function and reactive oxygen species (ROS) were both detected. ChIP-Seq analysis was employed to discover the underlying molecular mechanism of PGC-1α-mediated neuroprotective effects. Our results showed that mitochondrial membrane potentials were increased and ROS production was decreased in PGC-1α overexpressing cells, which increased cell viability. The further bioinformatics analysis from ChIP-Seq data indicated that PGC-1α may participate in the regulation of apoptosis, autophagy, and mitophagy pathways in HT-22 cells. We found that PGC-1α promoted the LC3-II formation and reduced the neuronal apoptosis determined by TUNEL staining. In addition, PGC-1α upregulated the expressions of mitochondrial antioxidants, including SOD2, Trx2, and Prx3. In summary, our findings indicate that PGC-1α may attenuate OGD-induced hippocampal neuronal damage by regulating multiple mechanisms, like autophagy and mitochondrial function. Thus, PGC-1α may be a potential therapeutic target for hippocampal damage associated with cognitive impairment.

Does propofol definitely improve postoperative cognitive dysfunction?-a review of propofol-related cognitive impairment

Postoperative cognitive dysfunction (POCD) is a common brain function-related complication after surgery. In addition to old age being an independent risk factor, anesthetics are also important predisposing factors. Among them, propofol is the most commonly used intravenous anesthetic in clinical practice. It has a rapid onset, short half-life, and high recovery quality. Many studies report that propofol can attenuate surgery-induced cognitive impairment, however, some other studies reveal that propofol also induces cognitive dysfunction. Therefore, this review summarizes the effects of propofol on the cognition, and discusses possible related mechanisms, which aims to provide some evidence for the follow-up studies.

Dynein Is Required for Rab7-Dependent Endosome Maturation, Retrograde Dendritic Transport, and Degradation

In all cell types, endocytosed cargo is transported along a set of endosomal compartments, which are linked maturationally from early endosomes (EEs) via late endosomes (LEs) to lysosomes. Lysosomes are critical for degradation of proteins that enter through endocytic as well as autophagic pathways. Rab7 is the master regulator of early-to-late endosome maturation, motility, and fusion with lysosomes. We previously showed that most degradative lysosomes are localized in the soma and in the first 25 µm of the dendrite and that bulk degradation of dendritic membrane proteins occurs in/near the soma. Dendritic late endosomes therefore move retrogradely in a Rab7-dependent manner for fusion with somatic lysosomes. We now used cultured E18 rat hippocampal neurons of both sexes to determine which microtubule motor is responsible for degradative flux of late endosomes. Based on multiple approaches (inhibiting dynein/dynactin itself or inhibiting dynein recruitment to endosomes by expressing the C-terminus of the Rab7 effector, RILP), we now demonstrate that net retrograde flux of late endosomes in dendrites is supported by dynein. Inhibition of dynein also delays maturation of somatic endosomes, as evidenced by excessive accumulation of Rab7. In addition, degradation of dendritic cargos is inhibited. Our results also suggest that GDP-GTP cycling of Rab7 appears necessary not only for endosomal maturation but also for fusion with lysosomes subsequent to arrival in the soma. In conclusion, Rab7-dependent dynein/dynactin recruitment to dendritic endosomes plays multifaceted roles in dendritic endosome maturation as well as retrograde transport of late endosomes to sustain normal degradative flux.SIGNIFICANCE STATEMENT Lysosomes are critical for degradation of membrane and extracellular proteins that enter through endocytosis. Lysosomes are also the endpoint of autophagy and thus responsible for protein and organelle homeostasis. Endosomal-lysosomal dysfunction is linked to neurodegeneration and aging. We identify roles in dendrites for two proteins with links to human diseases, Rab7 and dynein. Our previous work identified a process that requires directional retrograde transport in dendrites, namely, efficient degradation of short-lived membrane proteins. Based on multiple approaches, we demonstrate that Rab7-dependent recruitment of dynein motors supports net retrograde transport to lysosomes and is needed for endosome maturation. Our data also suggest that GDP-GTP cycling of Rab7 is required for fusion with lysosomes and degradation, subsequent to arrival in the soma.

The Interplay Between Autophagy and RNA Homeostasis: Implications for Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

Amyotrophic lateral sclerosis and frontotemporal dementia are neurodegenerative disorders that lie on a disease spectrum, sharing genetic causes and pathology, and both without effective therapeutics. Two pathways that have been shown to play major roles in disease pathogenesis are autophagy and RNA homeostasis. Intriguingly, there is an increasing body of evidence suggesting a critical interplay between these pathways. Autophagy is a multi-stage process for bulk and selective clearance of malfunctional cellular components, with many layers of regulation. Although the majority of autophagy research focuses on protein degradation, it can also mediate RNA catabolism. ALS/FTD-associated proteins are involved in many stages of autophagy and autophagy-mediated RNA degradation, particularly converging on the clearance of persistent pathological stress granules. In this review, we will summarise the progress in understanding the autophagy-RNA homeostasis interplay and how that knowledge contributes to our understanding of the pathobiology of ALS/FTD.

Inhibiting Microglia-Derived NLRP3 Alleviates Subependymal Edema and Cognitive Dysfunction in Posthemorrhagic Hydrocephalus after Intracerebral Hemorrhage via AMPK/Beclin-1 Pathway

For posthemorrhagic hydrocephalus (PHH) patients, whether occur subependymal edema indicates poor outcomes, partially manifested as cognitive impairment. In the brain, NLRP3 inflammasome mainly derived from microglia/macrophages is involved in proinflammatory and neurodeficits after hemorrhage, and autophagy is vital for neuronal homeostasis and functions. Accumulating evidence suggest that NLRP3 inflammasome and autophagy played an essential role after intracerebral hemorrhage (ICH). We aimed to dissect the mechanisms underlying subependymal edema formation and cognitive dysfunction. Here, based on the hydrocephalus secondary to ICH break into ventricular (ICH-IVH) in rats, this study investigated whether microglia/macrophage-derived NLRP3 induced subependymal edema formation and neuron apoptosis in subventricular zones (SVZ). In the acute phase of ICH-IVH, both the expression of NLRP3 inflammasome of microglia/macrophages and the autophagy of neurons were upregulated. The activated NLRP3 in microglia/macrophages promoted the release of IL-1beta to extracellular, which contributed to excessive autophagy, leading to neurons apoptosis both in vivo and in vitro through the AMPK/Beclin-1 pathway combined with transcriptomics. Administration of MCC950 (NLRP3 inflammasome specific inhibitor) after ICH-IVH significantly reduced edema formation and improved cognitive dysfunction. Thus, inhibiting NLRP3 activation in SVZ may be a promising therapeutic strategy for PHH patients that warrants further investigation.

Macroautophagy in CNS health and disease

Macroautophagy is an evolutionarily conserved process that delivers diverse cellular contents to lysosomes for degradation. As our understanding of this pathway grows, so does our appreciation for its importance in disorders of the CNS. Once implicated primarily in neurodegenerative events owing to acute injury and ageing, macroautophagy is now also linked to disorders of neurodevelopment, indicating that it is essential for both the formation and maintenance of a healthy CNS. In parallel to understanding the significance of macroautophagy across contexts, we have gained a greater mechanistic insight into its physiological regulation and the breadth of cargoes it can degrade. Macroautophagy is a broadly used homeostatic process, giving rise to questions surrounding how defects in this single pathway could cause diseases with distinct clinical and pathological signatures. To address this complexity, we herein review macroautophagy in the mammalian CNS by examining three key features of the process and its relationship to disease: how it functions at a basal level in the discrete cell types of the brain and spinal cord; which cargoes are being degraded in physiological and pathological settings; and how the different stages of the macroautophagy pathway intersect with diseases of neurodevelopment and adult-onset neurodegeneration.

Targeting brain Renin-Angiotensin System for the prevention and treatment of Alzheimer's disease: Past, present and future

Alzheimer's disease (AD) is a well-known neurodegenerative disease characterized by the presence of two main hallmarks - Tau hyperphosphorylation and Aβ deposits. Notwithstanding, in the last few years the scientific evidence about the drivers of AD have been changing and nowadays age-related vascular alterations and several cardiovascular risk factors have been shown to trigger the development of AD. In this context, drugs targeting the Renin Angiotensin System (RAS), commonly used for the treatment of hypertension, are evidencing a high potential to delay AD development due to their action on brain RAS. Indeed, the ACE 1/Ang II/AT1R axis is believed to be upregulated in AD and to be responsible for deleterious effects such as increased oxidative stress, neuroinflammation, blood-brain barrier (BBB) hyperpermeability, astrocytes dysfunction and a decrease in cerebral blood flow. In contrast, the alternative axis - ACE 1/Ang II/AT2R; ACE 2/Ang (1-7)/MasR; Ang IV/ AT4R(IRAP) - seems to counterbalance the deleterious effects of the principal axis and to exert beneficial effects on memory and cognition. Accordingly, retrospective studies demonstrate a reduced risk of developing AD among people taking RAS medication as well as several in vitro and in vivo pre-clinical studies as it is herein critically reviewed. In this review, we first revise, at a glance, the pathophysiology of AD focused on its classic hallmarks. Secondly, an overview about the impact of the RAS on the pathophysiology of AD is also provided, focused on their four essential axes ACE 1/Ang II/AT2R; ACE 2/Ang (1-7)/MasR; Ang IV/ AT4R(IRAP) and ACE 1/Ang II/AT1R. Finally, the therapeutic potential of available drugs targeting RAS on AD, namely angiotensin II receptor blockers (ARBs) and angiotensin converting enzyme inhibitors (ACEIs), is highlighted and data supporting this hope will be presented, from in vitro and in vivo pre-clinical to clinical studies.

Cylindromatosis drives synapse pruning and weakening by promoting macroautophagy through Akt-mTOR signaling

The lysine-63 deubiquitinase cylindromatosis (CYLD) is long recognized as a tumor suppressor in immunity and inflammation, and its loss-of-function mutations lead to familial cylindromatosis. However, recent studies reveal that CYLD is enriched in mammalian brain postsynaptic densities, and a gain-of-function mutation causes frontotemporal dementia (FTD), suggesting critical roles at excitatory synapses. Here we report that CYLD drives synapse elimination and weakening by acting on the Akt-mTOR-autophagy axis. Mice lacking CYLD display abnormal sociability, anxiety- and depression-like behaviors, and cognitive inflexibility. These behavioral impairments are accompanied by excessive synapse numbers, increased postsynaptic efficacy, augmented synaptic summation, and impaired NMDA receptor-dependent hippocampal long-term depression (LTD). Exogenous expression of CYLD results in removal of established dendritic spines from mature neurons in a deubiquitinase activity-dependent manner. In search of underlying molecular mechanisms, we find that CYLD knockout mice display marked overactivation of Akt and mTOR and reduced autophagic flux, and conversely, CYLD overexpression potently suppresses Akt and mTOR activity and promotes autophagy. Consequently, abrogating the Akt-mTOR-autophagy signaling pathway abolishes CYLD-induced spine loss, whereas enhancing autophagy in vivo by the mTOR inhibitor rapamycin rescues the synaptic pruning and LTD deficits in mutant mice. Our findings establish CYLD, via Akt-mTOR signaling, as a synaptic autophagy activator that exerts critical modulations on synapse maintenance, function, and plasticity.

Toxic Effects of Glyphosate on the Nervous System: A Systematic Review

Glyphosate, a non-selective systemic biocide with broad-spectrum activity, is the most widely used herbicide in the world. It can persist in the environment for days or months, and its intensive and large-scale use can constitute a major environmental and health problem. In this systematic review, we investigate the current state of our knowledge related to the effects of this pesticide on the nervous system of various animal species and humans. The information provided indicates that exposure to glyphosate or its commercial formulations induces several neurotoxic effects. It has been shown that exposure to this pesticide during the early stages of life can seriously affect normal cell development by deregulating some of the signaling pathways involved in this process, leading to alterations in differentiation, neuronal growth, and myelination. Glyphosate also seems to exert a significant toxic effect on neurotransmission and to induce oxidative stress, neuroinflammation and mitochondrial dysfunction, processes that lead to neuronal death due to autophagy, necrosis, or apoptosis, as well as the appearance of behavioral and motor disorders. The doses of glyphosate that produce these neurotoxic effects vary widely but are lower than the limits set by regulatory agencies. Although there are important discrepancies between the analyzed findings, it is unequivocal that exposure to glyphosate produces important alterations in the structure and function of the nervous system of humans, rodents, fish, and invertebrates.

Role of the endoplasmic reticulum in synaptic transmission

Neurons possess a complex morphology spanning long distances and a large number of subcellular specializations such as presynaptic terminals and dendritic spines. This structural complexity is essential for maintenance of synaptic junctions and associated electrical as well as biochemical signaling events. Given the structural and functional complexity of neurons, neuronal endoplasmic reticulum is emerging as a key regulator of neuronal function, in particular synaptic signaling. Neuronal endoplasmic reticulum mediates calcium signaling, calcium and lipid homeostasis, vesicular trafficking, and proteostasis events that underlie autonomous functions of numerous subcellular compartments. However, based on its geometric complexity spanning the whole neuron, endoplasmic reticulum also integrates the activity of these autonomous compartments across the neuron and coordinates their interactions with the soma. In this article, we review recent work regarding neuronal endoplasmic reticulum function and its relationship to neurotransmission and plasticity.

Organization of Presynaptic Autophagy-Related Processes

Brain synapses pose special challenges on the quality control of their protein machineries as they are far away from the neuronal soma, display a high potential for plastic adaptation and have a high energy demand to fulfill their physiological tasks. This applies in particular to the presynaptic part where neurotransmitter is released from synaptic vesicles, which in turn have to be recycled and refilled in a complex membrane trafficking cycle. Pathways to remove outdated and damaged proteins include the ubiquitin-proteasome system acting in the cytoplasm as well as membrane-associated endolysosomal and the autophagy systems. Here we focus on the latter systems and review what is known about the spatial organization of autophagy and endolysomal processes within the presynapse. We provide an inventory of which components of these degradative systems were found to be present in presynaptic boutons and where they might be anchored to the presynaptic apparatus. We identify three presynaptic structures reported to interact with known constituents of membrane-based protein-degradation pathways and therefore may serve as docking stations. These are (i) scaffolding proteins of the cytomatrix at the active zone, such as Bassoon or Clarinet, (ii) the endocytic machinery localized mainly at the peri-active zone, and (iii) synaptic vesicles. Finally, we sketch scenarios, how presynaptic autophagic cargos are tagged and recruited and which cellular mechanisms may govern membrane-associated protein turnover in the presynapse.

Enhancing autophagy in Alzheimer's disease through drug repositioning

Alzheimer's disease (AD) is one of the biggest human health threats due to increases in aging of the global population. Unfortunately, drugs for treating AD have been largely ineffective. Interestingly, downregulation of macroautophagy (autophagy) plays an essential role in AD pathogenesis. Therefore, targeting autophagy has drawn considerable attention as a therapeutic approach for the treatment of AD. However, developing new therapeutics is time-consuming and requires huge investments. One of the strategies currently under consideration for many diseases is "drug repositioning" or "drug repurposing". In this comprehensive review, we have provided an overview of the impact of autophagy on AD pathophysiology, reviewed the therapeutics that upregulate autophagy and are currently used in the treatment of other diseases, including cancers, and evaluated their repurposing as a possible treatment option for AD. In addition, we discussed the potential of applying nano-drug delivery to neurodegenerative diseases, such as AD, to overcome the challenge of crossing the blood brain barrier and specifically target molecules/pathways of interest with minimal side effects.

The different autophagy degradation pathways and neurodegeneration

The term autophagy encompasses different pathways that route cytoplasmic material to lysosomes for degradation and includes macroautophagy, chaperone-mediated autophagy, and microautophagy. Since these pathways are crucial for degradation of aggregate-prone proteins and dysfunctional organelles such as mitochondria, they help to maintain cellular homeostasis. As post-mitotic neurons cannot dilute unwanted protein and organelle accumulation by cell division, the nervous system is particularly dependent on autophagic pathways. This dependence may be a vulnerability as people age and these processes become less effective in the brain. Here, we will review how the different autophagic pathways may protect against neurodegeneration, giving examples of both polygenic and monogenic diseases. We have considered how autophagy may have roles in normal CNS functions and the relationships between these degradative pathways and different types of programmed cell death. Finally, we will provide an overview of recently described strategies for upregulating autophagic pathways for therapeutic purposes.

The needs of a synapse—How local organelles serve synaptic proteostasis

Synaptic function crucially relies on the constant supply and removal of neuronal membranes. The morphological complexity of neurons poses a significant challenge for neuronal protein transport since the machineries for protein synthesis and degradation are mainly localized in the cell soma. In response to this unique challenge, local micro‐secretory systems have evolved that are adapted to the requirements of neuronal membrane protein proteostasis. However, our knowledge of how neuronal proteins are synthesized, trafficked to membranes, and eventually replaced and degraded remains scarce. Here, we review recent insights into membrane trafficking at synaptic sites and into the contribution of local organelles and micro‐secretory pathways to synaptic function. We describe the role of endoplasmic reticulum specializations in neurons, Golgi‐related organelles, and protein complexes like retromer in the synthesis and trafficking of synaptic transmembrane proteins. We discuss the contribution of autophagy and of proteasome‐mediated and endo‐lysosomal degradation to presynaptic proteostasis and synaptic function, as well as nondegradative roles of autophagosomes and lysosomes in signaling and synapse remodeling. We conclude that the complexity of neuronal cyto‐architecture necessitates long‐distance protein transport that combines degradation with signaling functions.

Bradykinin postconditioning protects rat hippocampal neurons after restoration of spontaneous circulation following cardiac arrest via activation of the AMPK/mTOR signaling pathway

Bradykinin (BK) is an active component of the kallikrein-kinin system that has been shown to have cardioprotective and neuroprotective effects. We previously showed that BK postconditioning strongly protects rat hippocampal neurons upon restoration of spontaneous circulation (ROSC) after cardiac arrest. However, the precise mechanism underlying this process remains poorly understood. In this study, we treated a rat model of ROSC after cardiac arrest (induced by asphyxiation) with 150 μg/kg BK via intraperitoneal injection 48 hours after ROSC following cardiac arrest. We found that BK postconditioning effectively promoted the recovery of rat neurological function after ROSC following cardiac arrest, increased the amount of autophagosomes in the hippocampal tissue, inhibited neuronal cell apoptosis, up-regulated the expression of autophagy-related proteins LC3 and NBR1 and down-regulated p62, inhibited the expression of the brain injury marker S100β and apoptosis-related protein caspase-3, and affected the expression of adenosine monophosphate-activated protein kinase/mechanistic target of rapamycin pathway-related proteins. Adenosine monophosphate-activated protein kinase inhibitor compound C clearly inhibited BK-mediated activation of autophagy in rats after ROSC following cardiac arrest, which aggravated the injury caused by ROSC. The mechanistic target of rapamycin inhibitor rapamycin enhanced the protective effects of BK by stimulating autophagy. Our findings suggest that BK postconditioning protects against injury caused by ROSC through activating the adenosine monophosphate-activated protein kinase/mechanistic target of the rapamycin pathway.

AAV9-coGLB1 Improves Lysosomal Storage and Rescues Central Nervous System Inflammation in a Mutant Mouse Model of GM1 Gangliosidosis

BACKGROUND

GM1 gangliosidosis (GM1) is an autosomal recessive disorder characterized by deficiency of beta-galactosidase (β-gal), a ubiquitous lysosomal enzyme that catalyzes the hydrolysis of GM1 ganglioside.

OBJECTIVE

To explore the application of the AAV9-coGLB1 for effective treatment in a GM1 gangliosidosis mutant mouse model.

METHODS

We designed a novel adeno-associated virus 9 (AAV9) vector expressing β-gal (AAV9-coGLB1) to treat GM1 gangliosidosis. The vector, injected via the caudal vein at 4 weeks of age, drove the widespread and sustained expression of β-gal for up to 32 weeks in the Glb1G455R/G455R mutant mice (GM1 mice).

RESULTS

The increased levels of β-gal reduced the pathological damage occurring in GM1 mice. Histological analyses showed that myelin deficits and neuron-specific pathology were reduced in cerebral cortex region of AAV9-coGLB1-treated mice. Immunohistochemical staining showed that the accumulation of GM1 ganglioside was also reduced after gene therapy. The reduction of the storage in these regions was accompanied by a decrease in activated microglia. In addition, AAV9 treatment reversed the blockade of autophagic flux in GM1 mice.

CONCLUSION

These results show that AAV9-coGLB1 reduces the pathological signs of GM1 gangliosidosis in a mouse model.

Presynaptic autophagy is coupled to the synaptic vesicle cycle via ATG-9

Autophagy is a cellular degradation pathway essential for neuronal health and function. Autophagosome biogenesis occurs at synapses, is locally regulated, and increases in response to neuronal activity. The mechanisms that couple autophagosome biogenesis to synaptic activity remain unknown. In this study, we determine that trafficking of ATG-9, the only transmembrane protein in the core autophagy pathway, links the synaptic vesicle cycle with autophagy. ATG-9-positive vesicles in C. elegans are generated from the trans-Golgi network via AP-3-dependent budding and delivered to presynaptic sites. At presynaptic sites, ATG-9 undergoes exo-endocytosis in an activity-dependent manner. Mutations that disrupt endocytosis, including a lesion in synaptojanin 1 associated with Parkinson's disease, result in abnormal ATG-9 accumulation at clathrin-rich synaptic foci and defects in activity-induced presynaptic autophagy. Our findings uncover regulated key steps of ATG-9 trafficking at presynaptic sites and provide evidence that ATG-9 exo-endocytosis couples autophagosome biogenesis at presynaptic sites with the activity-dependent synaptic vesicle cycle.

Ouabain-Na+/K+-ATPase Signaling Regulates Retinal Neuroinflammation and ROS Production Preventing Neuronal Death by an Autophagy-Dependent Mechanism Following Optic Nerve Axotomy In Vitro

Ouabain is a classic Na+K+ATPase ligand and it has been described to have neuroprotective effects on neurons and glial cells at nanomolar concentrations. In the present work, the neuroprotective and immunomodulatory potential of ouabain was evaluated in neonatal rat retinal cells using an optic nerve axotomy model in vitro. After axotomy, cultured retinal cells were treated with ouabain (3 nM) at different periods. The levels of important inflammatory receptors in the retina such as TNFR1/2, TLR4, and CD14 were analyzed. We observed that TNFR1, TLR4, and CD14 were decreased in all tested periods (15 min, 45 min, 24 h, and 48 h). On the other hand, TNFR2 was increased after 24 h, suggesting an anti-inflammatory potential for ouabain. Moreover, we showed that ouabain also decreased Iba-1 (microglial marker) density. Subsequently, analyses of retrograde labeling of retinal ganglion cells (RGC) were performed after 48 h and showed that ouabain-induced RGC survival depends on autophagy. Using an autophagy inhibitor (3-methyladenine), we observed a complete blockage of the ouabain effect. Western blot analyses showed that ouabain increases the levels of autophagy proteins (LC3 and Beclin-1) coupled to p-CREB transcription factor and leads to autophagosome formation. Additionally, we found that the ratio of cleaved/pro-caspase-3 did not change after ouabain treatment; however, p-JNK density was enhanced. Also, ouabain decreased reactive oxygen species production immediately after axotomy. Taken together, our results suggest that ouabain controls neuroinflammation in the retina following optic nerve axotomy and promotes RGC neuroprotection through activation of the autophagy pathway.

The Complex Mechanisms by Which Neurons Die Following DNA Damage in Neurodegenerative Diseases

Human cells are exposed to numerous exogenous and endogenous insults every day. Unlike other molecules, DNA cannot be replaced by resynthesis, hence damage to DNA can have major consequences for the cell. The DNA damage response contains overlapping signalling networks that repair DNA and hence maintain genomic integrity, and aberrant DNA damage responses are increasingly described in neurodegenerative diseases. Furthermore, DNA repair declines during aging, which is the biggest risk factor for these conditions. If unrepaired, the accumulation of DNA damage results in death to eliminate cells with defective genomes. This is particularly important for postmitotic neurons because they have a limited capacity to proliferate, thus they must be maintained for life. Neuronal death is thus an important process in neurodegenerative disorders. In addition, the inability of neurons to divide renders them susceptible to senescence or re-entry to the cell cycle. The field of cell death has expanded significantly in recent years, and many new mechanisms have been described in various cell types, including neurons. Several of these mechanisms are linked to DNA damage. In this review, we provide an overview of the cell death pathways induced by DNA damage that are relevant to neurons and discuss the possible involvement of these mechanisms in neurodegenerative conditions.

Acetyl CoA synthase 2 potentiates ATG5-induced autophagy against neuronal apoptosis after subarachnoid hemorrhage

ATG5-induced autophagy is triggered in the early stages after SAH, which plays a vital role in subarachnoid hemorrhage (SAH). Acyl-CoA synthetase short-chain family 2 (ACSS2) is not just involved in energy metabolism but also binds to TEFB to form a complex translocated to related autophagy genes to regulate the expression of autophagy-related genes. However, the contribution of ACSS2 to the activation of autophagy in early brain injury (EBI) after SAH has barely been discussed. The purpose of this study was to investigate the alterations of ACSS2 and its neuroprotective effects following SAH. We first evaluated the expression of ACSS2 at different time points (6, 12, 24, and 72 h after SAH) in vivo and primary cortical neurons stimulated by oxyhemoglobin (OxyHb). Subsequently, adeno-associated virus and lentivirus were used to regulate ACSS2 expression to investigate the effect of ACSS2 after SAH. The results showed that the ACSS2 level decreased significantly in the early stages of SAH and was minimized at 24 h post-SAH. After artificial intervention to overexpress ACSS2, ATG5-induced autophagy was further enhanced in EBI after SAH, and neuronal apoptosis was alleviated to protect brain injury. In addition, brain edema and neurological function scores were improved. These results suggest that ACSS2 plays an important role in the neuroprotection against EBI after SAH by increasing ATG5-induce autophagy and inhibiting apoptosis.

Endoplasmic Reticulum Stress in Chemotherapy-Induced Peripheral Neuropathy: Emerging Role of Phytochemicals

Chemotherapy-induced peripheral neuropathy (CIPN) is a significant dose-limiting long-term sequela in cancer patients undergoing treatment, often leading to discontinuation of treatment. No established therapy exists to prevent and/or ameliorate CIPN. Reactive oxygen species (ROS) and mitochondrial dysregulation have been proposed to underlie the pathobiology of CIPN. However, interventions to prevent and treat CIPN are largely ineffective. Additional factors and mechanism-based targets need to be identified to develop novel strategies to target CIPN. The role of oxidative stress appears to be central, but the contribution of endoplasmic reticulum (ER) stress remains under-examined in the pathobiology of CIPN. This review describes the significance of ER stress and its contribution to CIPN, the protective role of herbal agents in countering ER stress in nervous system-associated disorders, and their possible repurposing for preventing CIPN.

Melatonin Attenuates Ropivacaine-Induced Apoptosis by Inhibiting Excessive Mitophagy Through the Parkin/PINK1 Pathway in PC12 and HT22 Cells

Melatonin, as an endogenous circadian indoleamine secreted by the pineal gland, executes extensive biological functions, including antioxidant, anti-inflammatory, anti-tumor, and neuroprotective effects. Although melatonin has been reported to serve as a potential therapeutic against many nerve injury diseases, its effect on ropivacaine-induced neurotoxicity remains obscure. Our research aimed to explore the impact and mechanism of melatonin on ropivacaine-induced neurotoxicity. Our results showed that melatonin pretreatment protected the cell viability, morphology, and apoptosis of PC12 and HT22 cells, and it also improved ropivacaine-induced mitochondrial dysfunction and the activation of mitophagy. In addition, we found that autophagy activation with rapamycin significantly weakened the protective effect of melatonin against ropivacaine-induced apoptosis, whereas autophagy inhibition with 3-MA enhanced the effect of melatonin. We also detected the activation of Parkin and PINK1, a canonical mechanism for mitophagy regulation, and results shown that melatonin downregulated the expression of Parkin and PINK1, and upregulated Tomm20 and COXIV proteins, so that those results indicated that melatonin protected ropivacaine-induced apoptosis through suppressing excessive mitophagy by inhibiting the Parkin/PINK1 pathway. Melatonin may be a useful potential therapeutic agent against ropivacaine-induced neurotoxicity.

Autophagy Dysfunction as a Phenotypic Readout in hiPSC-Derived Neuronal Cell Models of Neurodegenerative Diseases

Autophagy is an evolutionarily conserved catabolic pathway for the degradation of cytoplasmic constituents in eukaryotic cells. It is the primary disposal route for selective removal of undesirable cellular materials like aggregation-prone proteins and damaged organelles for maintaining cellular homeostasis, and for bulk degradation of intracellular macromolecules and recycling the breakdown products for providing energy homeostasis during starvation. These functions of autophagy are attributed to cellular survival and thus pertinent for human health; however, malfunction of this process is detrimental to the cells, particularly for post-mitotic neurons. Thus, basal autophagy is vital for maintaining neuronal homeostasis, whereas autophagy dysfunction contributes to neurodegeneration. Defective autophagy has been demonstrated in several neurodegenerative diseases wherein pharmacological induction of autophagy is beneficial in many of these disease models. Elucidating the mechanisms underlying defective autophagy is imperative for the development of therapies targeting this process. Disease-affected human neuronal cells can be established from patient-derived human induced pluripotent stem cells (hiPSCs) that provide a clinically relevant platform for studying disease mechanisms and drug discovery. Thus, modeling autophagy dysfunction as a phenotypic readout in patient-derived neurons provides a more direct platform for investigating the mechanisms underlying defective autophagy and evaluating the therapeutic efficacy of autophagy inducers. Toward this, several hiPSC-derived neuronal cell models of neurodegenerative diseases have been employed. In this review, we highlight the key methodologies pertaining to hiPSC maintenance and neuronal differentiation, and studying autophagy at an endogenous level in hiPSC-derived neuronal cells.