Autophagy core machinery: overcoming spatial barriers in neurons

Critical roles of lncRNA-mediated autophagy in urologic malignancies

Urologic oncology is a significant public health concern on a global scale. Recent research indicates that long chain non-coding RNAs (lncRNAs) and autophagy play crucial roles in various cancers, including urologic malignancies. This article provides a summary of the latest research findings, suggesting that lncRNA-mediated autophagy could either suppress or promote tumors in prostate, kidney, and bladder cancers. The intricate network involving different lncRNAs, target genes, and mediated signaling pathways plays a crucial role in urological malignancies by modulating the autophagic process. Dysregulated expression of lncRNAs can disrupt autophagy, leading to tumorigenesis, progression, and enhanced resistance to therapy. Consequently, targeting particular lncRNAs that control autophagy could serve as a dependable diagnostic tool and a promising prognostic biomarker in urologic oncology, while also holding potential as an effective therapeutic approach.

ATG9 resides on a unique population of small vesicles in presynaptic nerve terminals

In neurons, autophagosome biogenesis occurs mainly in distal axons, followed by maturation during retrograde transport. Autophagosomal growth depends on the supply of membrane lipids which requires small vesicles containing ATG9, a lipid scramblase essential for macroautophagy/autophagy. Here, we show that ATG9-containing vesicles are enriched in synapses and resemble synaptic vesicles in size and density. The proteome of ATG9-containing vesicles immuno-isolated from nerve terminals showed conspicuously low levels of trafficking proteins except of the AP2-complex and some enzymes involved in endosomal phosphatidylinositol metabolism. Super resolution microscopy of nerve terminals and isolated vesicles revealed that ATG9-containing vesicles represent a distinct vesicle population with limited overlap not only with synaptic vesicles but also other membranes of the secretory pathway, uncovering a surprising heterogeneity in their membrane composition. Our results are compatible with the view that ATG9-containing vesicles function as lipid shuttles that scavenge membrane lipids from various intracellular membranes to support autophagosome biogenesis.Abbreviations: AP: adaptor related protein complex: ATG2: autophagy related 2; ATG9: autophagy related 9; DNA PAINT: DNA-based point accumulation for imaging in nanoscale topography; DyMIN STED: dynamic minimum stimulated emission depletion; EL: endosome and lysosome; ER: endoplasmic reticulum; GA: Golgi apparatus; iBAQ: intensity based absolute quantification; LAMP: lysosomal-associated membrane protein; M6PR: mannose-6-phosphate receptor, cation dependent; Minflux: minimal photon fluxes; Mito: mitochondria; MS: mass spectrometry; PAS: phagophore assembly site; PM: plasma membrane; Px: peroxisome; RAB26: RAB26, member RAS oncogene family; RAB3A: RAB3A, member RAS oncogene family; RAB5A: RAB5A, member RAS oncogene family; SNARE: soluble N-ethylmaleimide-sensitive-factor attachment receptor; SVs: synaptic vesicles; SYP: synaptophysin; TGN: trans-Golgi network; TRAPP: transport protein particle; VTI1: vesicle transport through interaction with t-SNAREs.

Clearance of β-amyloid mediated by autophagy is enhanced by MTORC1 inhibition but not AMPK activation in APP/PSEN1 astrocytes

Proteostasis mechanisms mediated by macroautophagy/autophagy are altered in neurodegenerative diseases such as Alzheimer disease (AD) and their recovery/enhancement has been proposed as a therapeutic approach. From the two central nodes in the anabolism-catabolism balance, it is generally accepted that mechanistic target of rapamycin kinase complex 1 (MTORC1)_ activation leads to the inhibition of autophagy, whereas adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) has the opposite role. In AD, amyloid beta (Aβ) production disturbs the optimal neuronal/glial proteostasis. As astrocytes are essential for brain homeostasis, the purpose of this work was to analyze if the upregulation of autophagy in this cell type, either by MTORC1 inhibition or AMPK activation, could modulate the generation/degradation of β-amyloid. By using primary astrocytes from amyloid beta precursor protein (APP)/Presenilin 1 (PSEN1) mouse model of AD, we confirmed that MTORC1 inhibition reduced Aβ secretion through moderate autophagy induction. Surprisingly, pharmacologically increased activity of AMPK did not enhance autophagy but had different effects on Aβ secretion. Conversely, AMPK inhibition did not affect autophagy but reduced Aβ secretion. These puzzling data were confirmed through the overexpression of different mutant AMPK isoforms: while only the constitutively active AMPK increased autophagy, all versions augmented Aβ secretion. We conclude that AMPK has a significantly different role in primary astrocytes than in other reported cells, similar to our previous findings in neurons. Our data support that perhaps only a basal AMPK activity is needed to maintain autophagy whereas the increased activity, either physiologically or pharmacologically, has no direct effect on autophagy-dependent amyloidosis. These results shed light on the controversy about the therapeutic effect of AMPK activation on autophagy induction.

AutophagyNet: high-resolution data source for the analysis of autophagy and its regulation

Macroautophagy/autophagy is a highly-conserved catabolic procss eliminating dysfunctional cellular components and invading pathogens. Autophagy malfunction contributes to disorders such as cancer, neurodegenerative and inflammatory diseases. Understanding autophagy regulation in health and disease has been the focus of the last decades. We previously provided an integrated database for autophagy research, the Autophagy Regulatory Network (ARN). For the last eight years, this resource has been used by thousands of users. Here, we present a new and upgraded resource, AutophagyNet. It builds on the previous database but contains major improvements to address user feedback and novel needs due to the advancement in omics data availability. AutophagyNet contains updated interaction curation and integration of over 280,000 experimentally verified interactions between core autophagy proteins and their protein, transcriptional and post-transcriptional regulators as well as their potential upstream pathway connections. AutophagyNet provides annotations for each core protein about their role: 1) in different types of autophagy (mitophagy, xenophagy, etc.); 2) in distinct stages of autophagy (initiation, expansion, termination, etc.); 3) with subcellular and tissue-specific localization. These annotations can be used to filter the dataset, providing customizable download options tailored to the user's needs. The resource is available in various file formats (e.g. CSV, BioPAX and PSI-MI), and data can be analyzed and visualized directly in Cytoscape. The multi-layered regulation of autophagy can be analyzed by combining AutophagyNet with tissue- or cell type-specific (multi-)omics datasets (e.g. transcriptomic or proteomic data). The resource is publicly accessible at http://autophagynet.org.Abbreviations: ARN: Autophagy Regulatory Network; ATG: autophagy related; BCR: B cell receptor pathway; BECN1: beclin 1; GABARAP: GABA type A receptor-associated protein; IIP: innate immune pathway; LIR: LC3-interacting region; lncRNA: long non-coding RNA; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; miRNA: microRNA; NHR: nuclear hormone receptor; PTM: post-translational modification; RTK: receptor tyrosine kinase; TCR: T cell receptor; TLR: toll like receptor.

Role of autophagy in the pathogenesis and regulation of pain

Pain is a ubiquitous and highly concerned clinical symptom, usually caused by peripheral or central nervous injury, tissue damage, or other diseases. The long-term existence of pain can seriously affect daily physical function and quality of life and produce great torture on the physiological and psychological levels. However, the complex pathogenesis of pain involving molecular mechanisms and signaling pathways has not been fully elucidated, and managing pain remains highly challenging. As a result, finding new targets to pursue effective and long-term pain treatment strategies is required and urgent. Autophagy is an intracellular degradation and recycling process that maintains tissue homeostasis and energy supply, which can be cytoprotective and is vital in maintaining neural plasticity and proper nervous system function. Much evidence has shown that autophagy dysregulation is linked to the emergence of neuropathic pain, such as postherpetic neuralgia and cancer-related pain. Autophagy has also been connected to pain caused by osteoarthritis and lumbar disc degeneration. It is worth noting that in recent years, studies on traditional Chinese medicine have also proved that several traditional Chinese medicine monomers involve autophagy in the mechanism of pain relief. Therefore, autophagy can serve as a potential regulatory target to provide new ideas and inspiration for pain management.

Histone lysine demethylase 3B regulates autophagy via transcriptional regulation of GABARAPL1 in acute myeloid leukemia cells

Macroautophagy (hereafter referred to as autophagy) is a highly conserved self‑digestion process that is critical for maintaining homeostasis in response to various stresses. The autophagy‑related protein family, including the GABA type A receptor‑associated protein (GABARAP) and microtubule‑associated protein 1 light chain 3 subfamilies, is crucial for autophagosome biogenesis. Although the regulatory machinery of autophagy in the cytoplasm has been widely studied, its transcriptional and epigenetic regulatory mechanisms still require more targeted investigations. The present study identified histone lysine demethylase 3B (KDM3B) as a crucial component of autophagy on a panel of leukemia cell lines, including K562, THP1 and U937, resulting in transcriptional activation of the autophagy‑related gene GABA type A receptor‑associated protein like 1 (GABARAPL1). KDM3B expression promoted autophagosome formation and affected the autophagic flux in leukemia cells under the induction of external stimuli. Notably, RNA‑sequencing and reverse transcription‑quantitative PCR analysis showed that KDM3B knockout inhibited the expression of GABARAPL1. Chromatin immunoprecipitation‑quantitative PCR and luciferase assay showed that KDM3B was associated with the GABARAPL1 gene promoter under stimulation and enhanced its transcription. The present findings demonstrated that KDM3B was critical for regulating the GABARAPL1 gene and influencing the process of autophagy in leukemia cells. These results provide a new insight for exploring the association between autophagy and KDM3B epigenetic regulation in leukemia.

The AMPK-dependent inhibition of autophagy plays a crucial role in protecting photoreceptor from photooxidative injury

Excessive light exposure can potentially cause irreversible damage to the various photoreceptor cells, and this aspect has been considered as an important factor leading to the progression of the different retinal diseases. AMP-activated protein kinase (AMPK) and the mammalian target of rapamycin (mTOR) are crucial intracellular signaling hubs involved in the regulation of cellular metabolism, energy homeostasis, cellular growth and autophagy. A number of previous studies have indicated that either AMPK activation or mTOR inhibition can promote autophagy in most cases. In the current study, we have established an in vitro as well as in vivo photooxidation-damaged photoreceptor model and investigated the possible influence of visible light exposure in the AMPK/mTOR/autophagy signaling pathway. We have also explored the potential regulatory effects of AMPK/mTOR on light-induced autophagy and protection achieved by suppressing autophagy in photooxidation-damaged photoreceptors. We observed that light exposure led to a significant activation of mTOR and autophagy in the photoreceptor cells. However, intriguingly, AMPK activation or mTOR inhibition significantly inhibited rather than promoting autophagy, which was termed as AMPK-dependent inhibition of autophagy. In addition, either indirectly suppressing autophagy by AMPK activation/ mTOR inhibition or directly blocking autophagy with an inhibitor exerted a significant protective effect on the photoreceptor cells against the photooxidative damage. Neuroprotective effects caused by the AMPK-dependent inhibition of autophagy were also verified with a retinal light injured mouse model in vivo. Overall, our findings demonstrated that AMPK / mTOR pathway could inhibit autophagy through AMPK-dependent inhibition of autophagy to significantly protect the photoreceptors from photooxidative injury, which may aid to further develop novel targeted retinal neuroprotective drugs.

Current and potential roles of RNA modification-mediated autophagy dysregulation in cancer

Autophagy, a cellular lysosomal degradation and survival pathway, supports nutrient recycling and adaptation to metabolic stress and participates in various stages of tumor development, including tumorigenesis, metastasis, and malignant state maintenance. Among the various factors contributing to the dysregulation of autophagy in cancer, RNA modification can regulate autophagy by directly affecting the expression of core autophagy proteins. We propose that autophagy disorder mediated by RNA modification is an important mechanism for cancer development. Therefore, this review mainly discusses the role of RNA modification-mediated autophagy regulation in tumorigenesis. We summarize the molecular basis of autophagy and the core proteins and complexes at different stages of autophagy, especially those involved in cancer development. Moreover, we describe the crosstalk of RNA modification and autophagy and review the recent advances and potential role of the RNA modification/autophagy axis in the development of multiple cancers. Furthermore, the dual role of the RNA modification/autophagy axis in cancer drug resistance is discussed. A comprehensive understanding and extensive exploration of the molecular crosstalk of RNA modifications with autophagy will provide important insights into tumor pathophysiology and provide more options for cancer therapeutic strategies.

Autophagy and Apoptosis in Acute Brain Injuries: From Mechanism to Treatment

Significance: Autophagy and apoptosis are two important cellular mechanisms behind brain injuries, which are severe clinical situations with increasing incidences worldwide. To search for more and better treatments for brain injuries, it is essential to deepen the understanding of autophagy, apoptosis, and their interactions in brain injuries. This article first analyzes how autophagy and apoptosis participate in the pathogenetic processes of brain injuries respectively and mutually, then summarizes some promising treatments targeting autophagy and apoptosis to show the potential clinical applications in personalized medicine and precision medicine in the future. Recent Advances: Most current studies suggest that apoptosis is detrimental to brain recovery. Several studies indicate that autophagy can cause unnecessary death of neurons after brain injuries, while others show that autophagy is beneficial for acute brain injuries (ABIs) by facilitating the removal of damaged proteins and organelles. Whether autophagy is beneficial or detrimental in ABIs depends on many factors, and the results from different research groups are diverse or even controversial, making this topic more appealing to be explored further. Critical Issues: Neuronal autophagy and apoptosis are two primary pathological processes in ABIs. How they interact with each other and how their regulations affect the outcome and prognosis of brain injuries remain uncertain, making these answers more critical. Future Directions: Insights into the interplay between autophagy and apoptosis and the accurate regulations of their balance in ABIs may promote personalized and precise treatments in the field of brain injuries. Antioxid. Redox Signal. 38, 234-257.

Autophagic degradation of CNS myelin maintains axon integrity

(Macro)autophagy is a major lysosome-dependent degradation mechanism which engulfs, removes and recycles unwanted cytoplasmic material, including damaged organelles and toxic protein aggregates. Although a few studies implicate autophagy in CNS demyelinating pathologies, its role, particularly in mature oligodendrocytes and CNS myelin, remains poorly studied. Here, using both pharmacological and genetic inhibition of the autophagic machinery, we provide evidence that autophagy is an essential mechanism for oligodendrocyte maturation in vitro. Our study reveals that two core myelin proteins, namely proteolipid protein (PLP) and myelin basic protein (MBP) are incorporated into autophagosomes in oligodendrocytes, resulting in their degradation. Furthermore, we ablated atg5, a core gene of the autophagic machinery, specifically in myelinating glial cells in vivo by tamoxifen administration (plp-Cre ERT2 ; atg5 f/f ) and showed that myelin maintenance is perturbed, leading to PLP accumulation. Significant morphological defects in myelin membrane such as decompaction accompanied with increased axonal degeneration are observed. As a result, the mice exhibit behavioral deficits. In summary, our data highlight that the maintenance of adult myelin homeostasis in the CNS requires the involvement of a fully functional autophagic machinery.

Molecular mechanisms of programmed cell death in methamphetamine-induced neuronal damage

Methamphetamine, commonly referred to as METH, is a highly addictive psychostimulant and one of the most commonly misused drugs on the planet. Using METH continuously can increase your risk for drug addiction, along with other health complications like attention deficit disorder, memory loss, and cognitive decline. Neurotoxicity caused by METH is thought to play a significant role in the onset of these neurological complications. The molecular mechanisms responsible for METH-caused neuronal damage are discussed in this review. According to our analysis, METH is closely associated with programmed cell death (PCD) in the process that causes neuronal impairment, such as apoptosis, autophagy, necroptosis, pyroptosis, and ferroptosis. In reviewing this article, some insights are gained into how METH addiction is accompanied by cell death and may help to identify potential therapeutic targets for the neurological impairment caused by METH abuse.

PS-NPs Induced Neurotoxic Effects in SHSY-5Y Cells via Autophagy Activation and Mitochondrial Dysfunction

Polystyrene nanoparticles (PS-NPs) are organic pollutants that are widely detected in the environment and organisms, posing potential threats to both ecosystems and human health. PS-NPs have been proven to penetrate the blood–brain barrier and increase the incidence of neurodegenerative diseases. However, information relating to the pathogenic molecular mechanism is still unclear. This study investigated the neurotoxicity and regulatory mechanisms of PS-NPs in human neuroblastoma SHSY-5Y cells. The results show that PS-NPs caused obvious mitochondrial damages, as evidenced by inhibited cell proliferation, increased lactate dehydrogenase release, stimulated oxidative stress responses, elevated Ca2+ level and apoptosis, and reduced mitochondrial membrane potential and adenosine triphosphate levels. The increased release of cytochrome c and the overexpression of apoptosis-related proteins apoptotic protease activating factor-1 (Apaf-1), cysteinyl aspartate specific proteinase-3 (caspase-3), and caspase-9 indicate the activation of the mitochondrial apoptosis pathway. In addition, the upregulation of autophagy markers light chain 3-II (LC3-II), Beclin-1, and autophagy-related protein (Atg) 5/12/16L suggests that PS-NPs could promote autophagy in SHSY-5Y cells. The RNA interference of Beclin-1 confirms the regulatory role of autophagy in PS-NP-induced neurotoxicity. The administration of antioxidant N-acetylcysteine (NAC) significantly attenuated the cytotoxicity and autophagy activation induced by PS-NP exposure. Generally, PS-NPs could induce neurotoxicity in SHSY-5Y cells via autophagy activation and mitochondria dysfunction, which was modulated by mitochondrial oxidative stress. Mitochondrial damages caused by oxidative stress could potentially be involved in the pathological mechanisms for PS-NP-induced neurodegenerative diseases.

Activated Endolysosomal Cation Channel TRPML1 Facilitates Maturation of α-Synuclein-Containing Autophagosomes

Background: Protein aggregates are degraded via the autophagy-lysosome pathway and alterations in the lysosomal system leading to the accumulation of pathogenic proteins, including aggregates of α-synuclein in Parkinson’s disease (PD). The importance of the endolysosomal transient receptor potential cation channel, mucolipin subfamily 1 (TRPML1) for the lysosomal function is highlighted by the fact that TRPML1 mutations cause the lysosomal storage disease mucolipidosis type IV. In this study, we investigated the mechanism by which activation of TRPML1 affects the degradation of α-synuclein.

Methods: As a model of α-synuclein pathology, we expressed the pathogenic A53Tα-synuclein mutant in HEK293T cells. These cells were treated with the synthetic TRPML1 agonist ML-SA1. The amount of α-synuclein protein was determined by immunoblots. The abundance of aggregates and autolysosomal vesicles was determined by fluorescence microscopy and immunocytochemistry. Findings were confirmed by life-cell imaging and by application of ML-SA1 and the TRPML1 antagonist ML-SI3 to human dopaminergic neurons and human stem cell-derived neurons.

Results: ML-SA1 reduced the percentage of HEK293T cells with α-synuclein aggregates and the amount of α-synuclein protein. The effect of ML-SA1 was blocked by pharmacological and genetic inhibition of autophagy. Consistent with TRPML function, it required the membrane lipid PI(3,5)P_2, and cytosolic calcium. ML-SA1 shifted the composition of autophagosomes towards a higher fraction of mature autolysosomes, also in presence of α-synuclein. In neurons, inhibition of TRPML1 by its antagonist ML-SI3 blocked autophagosomal clearance, whereas the agonist ML-SA1 shifted the composition of a-synuclein particles towards a higher fraction of acidified particles. ML-SA1 was able to override the effect of Bafilomycin A1, which blocks the fusion of the autophagosome and lysosome and its acidification.

Conclusion: These findings suggest, that activating TRPML1 with ML-SA1 facilitates clearance of α-synuclein aggregates primarily by affecting the late steps of the autophagy, i.e., by promoting autophagosome maturation. In agreement with recent work by others, our findings indicate that TRPML1 might constitute a plausible therapeutic target for PD, that warrants further validation in rodent models of α-synuclein pathology.

Diclofenac: A Nonsteroidal Anti-Inflammatory Drug Inducing Cancer Cell Death by Inhibiting Microtubule Polymerization and Autophagy Flux

Diclofenac, a nonsteroidal anti-inflammatory drug (NSAID) used to treat inflammatory diseases induces cellular toxicity by increasing the production of reactive oxygen species (ROS) and impairing autophagic flux. In this study, we investigated whether diclofenac induces cancer cell death and the mechanism by which diclofenac causes cell death. We observed that diclofenac induces mitotic arrest with a half-maximal effective concentration of 170 μM and cell death with a half-maximal lethal dose of 200 µM during 18-h incubation in HeLa cells. Cellular microtubule imaging and in vitro tubulin polymerization assays demonstrated that treatment with diclofenac elicits microtubule destabilization. Autophagy relies on microtubule-mediated transport and the fusion of autophagic vesicles. We observed that diclofenac inhibits both phagophore movement, an early step of autophagy, and the fusion of autophagosomes and lysosomes, a late step of autophagy. Diclofenac also induces the fragmentation of mitochondria and the Golgi during cell death. We found that diclofenac induces cell death further in combination with 5-fuorouracil, a DNA replication inhibitor than in single treatment in cancer cells. Pancreatic cancer cells, which have high basal autophagy, are particularly sensitive to cell death by diclofenac. Our study suggests that microtubule destabilization by diclofenac induces cancer cell death via compromised spindle assembly checkpoints and increased ROS through impaired autophagy flux. Diclofenac may be a candidate therapeutic drug in certain type of cancers by inhibiting microtubule-mediated cellular events in combination with clinically utilized nucleoside metabolic inhibitors, including 5-fluorouracil, to block cancer cell proliferation.

In Vitro Study on the Biological Characteristics of Adipose-Derived Stem Cells from Liposuction Area in Patients with Progressive Hemifacial Atrophy

OBJECTIVE

In this study, we investigate the biological characteristics of ADSCs from the liposuction area in patients with hemifacial atrophy in vitro.

METHODS

ADSCs were respectively extracted from the donor site of patients with hemifacial atrophy and healthy ones. ADSCs of two groups were respectively tested for proliferation ability, phenotype, multipotency, migration ability, self-repair ability, apoptosis, and autophagy. Exosomes extracted from the supernatant of two groups were detected by NTA particle size, electron microscopy (TEM), and WB for CD63 and TSG10, respectively.

RESULTS

CCK-8 showed a statistically less increase in cell proliferation in PHA-ADSCs after the sixth day. ADSCs in both groups had typical phenotypes and multidirectional abilities. PHA-ADSCs exhibited weaker droplet formation. The cell migration ability in PHA-ADSCs was weaker tested by Transwell assay. The live/dead proportion calculated by ImageJ following calcein-AM/PI double staining revealed live cells in PHA-ADSCs was 46.11% compared with 54.21% in NORM-ADSCs after OGD treatment. A significant down-regulation of ATG7 and ATG12 and a higher percentage of apoptosis were found in PHA-ADSCs. A significant up-regulation of BAX occurred in PHA-ADSCs.ARPC5 expression in the PHA group was extremely distinct down-regulated.CDKN1A and CDKN2A expression in the PHA group was significantly up-regulated.WB analyses confirmed that both groups' ADSCs-Exosomes surface markers CD63 and TSG101 were positively expressed but varied significantly.

CONCLUSIONS

PHA-ADSCs exhibited a poorer proliferation ability, higher apoptosis percentage, weaker lipid droplets formation, weaker cell migration, poorer intolerance to OGD, aging earlier, and weaker self-renewal and repairability.PHA-ADSCs-Exosomes showed low expressions of CD63 and TSG101.This study provides strong evidence that the addition of exosomes with specific cytokines can improve the fat survival rate after fat filling in patients with hemifacial atrophy.

NO LEVEL ASSIGNED

This journal requires that authors 42 assign a level of evidence to each submission to which 43 Evidence-Based Medicine rankings are applicable. This 44 excludes Review Articles, Book Reviews, and manuscripts 45 that concern Basic Science, Animal Studies, Cadaver 46 Studies, and Experimental Studies. For a full description of 47 these Evidence-Based Medicine ratings, please refer to the 48 Table of Contents or the online Instructions to Authors 49 https://www.springer.com/00266 .

The spectrum of neurodevelopmental, neuromuscular and neurodegenerative disorders due to defective autophagy

Primary dysfunction of autophagy due to Mendelian defects affecting core components of the autophagy machinery or closely related proteins have recently emerged as an important cause of genetic disease. This novel group of human disorders may present throughout life and comprises severe early-onset neurodevelopmental and more common adult-onset neurodegenerative disorders. Early-onset (or congenital) disorders of autophagy often share a recognizable "clinical signature," including variable combinations of neurological, neuromuscular and multisystem manifestations. Structural CNS abnormalities, cerebellar involvement, spasticity and peripheral nerve pathology are prominent neurological features, indicating a specific vulnerability of certain neuronal populations to autophagic disturbance. A typically biphasic disease course of late-onset neurodegeneration occurring on the background of a neurodevelopmental disorder further supports a role of autophagy in both neuronal development and maintenance. Additionally, an associated myopathy has been characterized in several conditions. The differential diagnosis comprises a wide range of other multisystem disorders, including mitochondrial, glycogen and lysosomal storage disorders, as well as ciliopathies, glycosylation and vesicular trafficking defects. The clinical overlap between the congenital disorders of autophagy and these conditions reflects the multiple roles of the proteins and/or emerging molecular connections between the pathways implicated and suggests an exciting area for future research. Therapy development for congenital disorders of autophagy is still in its infancy but may result in the identification of molecules that target autophagy more specifically than currently available compounds. The close connection with adult-onset neurodegenerative disorders highlights the relevance of research into rare early-onset neurodevelopmental conditions for much more common, age-related human diseases.Abbreviations: AC: anterior commissure; AD: Alzheimer disease; ALR: autophagic lysosomal reformation; ALS: amyotrophic lateral sclerosis; AMBRA1: autophagy and beclin 1 regulator 1; AMPK: AMP-activated protein kinase; ASD: autism spectrum disorder; ATG: autophagy related; BIN1: bridging integrator 1; BPAN: beta-propeller protein associated neurodegeneration; CC: corpus callosum; CHMP2B: charged multivesicular body protein 2B; CHS: Chediak-Higashi syndrome; CMA: chaperone-mediated autophagy; CMT: Charcot-Marie-Tooth disease; CNM: centronuclear myopathy; CNS: central nervous system; DNM2: dynamin 2; DPR: dipeptide repeat protein; DVL3: disheveled segment polarity protein 3; EPG5: ectopic P-granules autophagy protein 5 homolog; ER: endoplasmic reticulum; ESCRT: homotypic fusion and protein sorting complex; FIG4: FIG4 phosphoinositide 5-phosphatase; FTD: frontotemporal dementia; GBA: glucocerebrosidase; GD: Gaucher disease; GRN: progranulin; GSD: glycogen storage disorder; HC: hippocampal commissure; HD: Huntington disease; HOPS: homotypic fusion and protein sorting complex; HSPP: hereditary spastic paraparesis; LAMP2A: lysosomal associated membrane protein 2A; MEAX: X-linked myopathy with excessive autophagy; mHTT: mutant huntingtin; MSS: Marinesco-Sjoegren syndrome; MTM1: myotubularin 1; MTOR: mechanistic target of rapamycin kinase; NBIA: neurodegeneration with brain iron accumulation; NCL: neuronal ceroid lipofuscinosis; NPC1: Niemann-Pick disease type 1; PD: Parkinson disease; PtdIns3P: phosphatidylinositol-3-phosphate; RAB3GAP1: RAB3 GTPase activating protein catalytic subunit 1; RAB3GAP2: RAB3 GTPase activating non-catalytic protein subunit 2; RB1: RB1-inducible coiled-coil protein 1; RHEB: ras homolog, mTORC1 binding; SCAR20: SNX14-related ataxia; SENDA: static encephalopathy of childhood with neurodegeneration in adulthood; SNX14: sorting nexin 14; SPG11: SPG11 vesicle trafficking associated, spatacsin; SQSTM1: sequestosome 1; TBC1D20: TBC1 domain family member 20; TECPR2: tectonin beta-propeller repeat containing 2; TSC1: TSC complex subunit 1; TSC2: TSC complex subunit 2; UBQLN2: ubiquilin 2; VCP: valosin-containing protein; VMA21: vacuolar ATPase assembly factor VMA21; WDFY3/ALFY: WD repeat and FYVE domain containing protein 3; WDR45: WD repeat domain 45; WDR47: WD repeat domain 47; WMS: Warburg Micro syndrome; XLMTM: X-linked myotubular myopathy; ZFYVE26: zinc finger FYVE-type containing 26.

Specific microRNAs for Modulation of Autophagy in Spinal Cord Injury

The treatment of spinal cord injury (SCI) is currently a major challenge, with a severe lack of effective therapies for yielding meaningful improvements in function. Therefore, there is a great opportunity for the development of novel treatment strategies for SCI. The modulation of autophagy, a process by which a cell degrades and recycles unnecessary or harmful components (protein aggregates, organelles, etc.) to maintain cellular homeostasis and respond to a changing microenvironment, is thought to have potential for treating many neurodegenerative conditions, including SCI. The discovery of microRNAs (miRNAs), which are short ribonucleotide transcripts for targeting of specific messenger RNAs (mRNAs) for silencing, shows prevention of the translation of mRNAs to the corresponding proteins affecting various cellular processes, including autophagy. The number of known miRNAs and their targets continues to grow rapidly. This review article aims to explore the relationship between autophagy and SCI, specifically with the intent of identifying specific miRNAs that can be useful to modulate autophagy for neuroprotection and the improvement of functional recovery in SCI.

Mechanistic Insight on Autophagy Modulated Molecular Pathways in Cerebral Ischemic Injury: From Preclinical to Clinical Perspective

Cerebral ischemia is one of the most devastating brain injuries and a primary cause of acquired and persistent disability worldwide. Despite ongoing therapeutic interventions at both the experimental and clinical levels, options for stroke-related brain injury are still limited. Several evidence suggests that autophagy is triggered in response to cerebral ischemia, therefore targeting autophagy-related signaling pathways can provide a new direction for the therapeutic implications in the ischemic injury. Autophagy is a highly conserved lysosomal-dependent pathway that degrades and recycles damaged or non-essential cellular components to maintain neuronal homeostasis. But, whether autophagy activation promotes cell survival against ischemic injury or, on the contrary, causes neuronal death is still under debate. We performed an extensive literature search from PubMed, Bentham and Elsevier for various aspects related to molecular mechanisms and pathobiology involved in autophagy and several pre-clinical studies justifiable further in the clinical trials. Autophagy modulates various downstream molecular cascades, i.e., mTOR, NF-κB, HIF-1, PPAR-γ, MAPK, UPR, and ROS pathways in cerebral ischemic injury. In this review, the various approaches and their implementation in the translational research in ischemic injury into practices has been covered. It will assist researchers in finding a way to cross the unbridgeable chasm between the pre-clinical and clinical studies.

Pharmacological modulation of autophagy for Alzheimer’s disease therapy: Opportunities and obstacles

Alzheimer's disease (AD) is a prevalent and deleterious neurodegenerative disorder characterized by an irreversible and progressive impairment of cognitive abilities as well as the formation of amyloid β (Aβ) plaques and neurofibrillary tangles (NFTs) in the brain. By far, the precise mechanisms of AD are not fully understood and no interventions are available to effectively slow down progression of the disease. Autophagy is a conserved degradation pathway that is crucial to maintain cellular homeostasis by targeting damaged organelles, pathogens, and disease-prone protein aggregates to lysosome for degradation. Emerging evidence suggests dysfunctional autophagy clearance pathway as a potential cellular mechanism underlying the pathogenesis of AD in affected neurons. Here we summarize the current evidence for autophagy dysfunction in the pathophysiology of AD and discuss the role of autophagy in the regulation of AD-related protein degradation and neuroinflammation in neurons and glial cells. Finally, we review the autophagy modulators reported in the treatment of AD models and discuss the obstacles and opportunities for potential clinical application of the novel autophagy activators for AD therapy.

A perspective on the role of autophagy in cancer

Autophagy refers to a ubiquitous set of catabolic pathways required to achieve proper cellular homeostasis. Aberrant autophagy has been implicated in a multitude of diseases including cancer. In this review, we highlight pioneering and groundbreaking research that centers on delineating the role of autophagy in cancer initiation, proliferation and metastasis. First, we discuss the autophagy-related (ATG) proteins and their respective roles in the de novo formation of autophagosomes and the subsequent delivery of cargo to the lysosome for recycling. Next, we touch upon the history of cancer research that centers upon ATG proteins and regulatory mechanisms that control an appropriate autophagic response and how these are altered in the diseased state. Then, we discuss the various discoveries that led to the idea of autophagy as a double-edged sword when it comes to cancer therapy. This review also briefly narrates how different types of autophagy-selective macroautophagy and chaperone-mediated autophagy, have been linked to different cancers. Overall, these studies build upon a steadfast trajectory that aims to solve the monumentally daunting challenge of finding a cure for many types of cancer by modulating autophagy either through inhibition or induction.

Lanthanum chloride induces autophagy in primary cultured rat cortical neurons through Akt/mTOR and AMPK/mTOR signaling pathways

Autophagy is a lysosome dependent degradation pathway occurring in eukaryotic cells. Autophagy ensures balance and survival mechanism of cells during harmful stress. Excessive or weak autophagy leads to abnormal function and death in some cases. Lanthanum (La), a rare earth element (REE), damages the central nervous system (CNS) and promotes learning and memory dysfunction. However, underlying mechanism has not been fully elucidated. La induces oxidative stress, inhibits Nrf2/ARE and Akt/mTOR signaling pathways, and activates JNK/c-Jun and JNK/Foxo signaling pathways, resulting in abnormal induction of autophagy in rat hippocampus. In addition, La activates PINK1- Parkin signaling pathway and induces mitochondrial autophagy. However, the relationship between La and autophagy in rat neurons at the cellular level has not been explored previously. The aim of this study was to explore adverse effects of La. Primary culture of rat neurons were exposed to 0 mmol/L, 0.025 mmol/L, 0.05 mmol/L and 0.1 mmol/L lanthanum chloride (LaCl₃). The results showed that La upregulates p-AMPK, inhibits levels of p-Akt and p-mTOR, increases levels of autophagy related proteins (Beclin1 and LC3B-II), and downregulates expression of p-Bcl-2 and p62. Upstream and downstream intervention agents of autophagy were used to detect autophagy flux to verify accuracy of our results. Electron microscopy results showed significant increase in the number of autophagosomes in LaCl₃ exposed groups. These findings imply that LaCl₃ inhibits Akt/mTOR signaling pathway and activates AMPK/mTOR signaling pathway, resulting in abnormal autophagy in primary cultured rat cortical neurons. In addition, LaCl₃ induces neuronal damage through excessive autophagy.

Neurotoxicity of methamphetamine: Main effects and mechanisms

Methamphetamine (METH) is an illicit psychostimulant that is abused throughout the world. METH addiction is also a major public health concern and the abuse of large doses of the drug is often associated with serious neuropsychiatric consequences that may include agitation, anxiety, hallucinations, paranoia, and psychosis. Some human methamphetamine users can also suffer from attention, memory, and executive deficits. METH-associated neurological and psychiatric complications might be related, in part, to METH-induced neurotoxic effects. Those include altered dopaminergic and serotonergic functions, neuronal apoptosis, astrocytosis, and microgliosis. Here we have endeavored to discuss some of the main effects of the drug and have presented the evidence supporting certain of the molecular and cellular bases of METH neurotoxicity. The accumulated evidence suggests the involvement of transcription factors, activation of dealth pathways that emanate from mitochondria and endoplasmic reticulum (ER), and a role for neuroinflammatory mechanisms. Understanding the molecular processes involved in METH induced neurotoxicity should help in developing better therapeutic approaches that might also serve to attenuate or block the biological consequences of use of large doses of the drug by some humans who meet criteria for METH use disorder.

Protocol to study starvation-induced autophagy in developing rat neurons

Autophagy is being involved in an increasing number of cellular pathways. It now appears that autophagy stimulation and inhibition have complex effects in neurons. Here, we present a simple yet powerful protocol to induce autophagy in primary neurons in culture by partial nutrient deprivation, in neurons with or without transfection of plasmids encoding the Longin domain of VAMP7 or a nanobody directed against VAMP7. Although limited to cells in culture, this protocol can facilitate the study of autophagy in neurons.

For complete details on the use and execution of this protocol, please refer to Wojnacki et al. (2020).

•

Primary neuron hippocampal culture for morphological analysis after starvation

•

In vitro neuronal starvation by culture media dilution

•

Fixation and immuno staining for morphological analysis

•

Image acquisition and determination of axonal length after 24 h starvation

Trehalose Reduces the Secreted Beta-Amyloid Levels in Primary Neurons Independently of Autophagy Induction

The disaccharide trehalose was described as possessing relevant neuroprotective properties as an mTORC1-independent inducer of autophagy, with the ability to protect cellular membranes and denaturation, resulting from desiccation, and preventing the cellular accumulation of protein aggregates. These properties make trehalose an interesting therapeutic candidate against proteinopathies such as Alzheimer’s disease (AD), which is characterized by deposits of aggregated amyloid-beta (Aβ) and hyperphosphorylated tau. In this study, we observed that trehalose was able to induce autophagy in neurons only in the short-term, whereas long-term treatment with trehalose provoked a relevant anti-amyloidogenic effect in neurons from an AD mouse model that was not mediated by autophagy. Trehalose treatment reduced secreted Aβ levels in a manner unrelated to its intracellular accumulation or its elimination through endocytosis or enzymatic degradation. Moreover, the levels of Aβ precursor protein (APP) and beta-secretase (BACE1) remained unaltered, as well as the proper acidic condition of the endo-lysosome system. Instead, our results support that the neuroprotective effect of trehalose was mediated by a reduced colocalization of APP and BACE1 in the cell, and, therefore, a lower amyloidogenic processing of APP. This observation illustrates that the determination of the mechanism, or mechanisms, that associate APP and BACE is a relevant therapeutic target to investigate.

Neuronal Autophagy: Characteristic Features and Roles in Neuronal Pathophysiology

Autophagy is an important degradative pathway that eliminates misfolded proteins and damaged organelles from cells. Autophagy is crucial for neuronal homeostasis and function. A lack of or deficiency in autophagy leads to the accumulation of protein aggregates, which are associated with several neurodegenerative diseases. Compared with non-neuronal cells, neurons exhibit rapid autophagic flux because damaged organelles or protein aggregates cannot be diluted in post-mitotic cells; because of this, these cells exhibit characteristic features of autophagy, such as compartment-specific autophagy, which depends on polarized structures and rapid autophagy flux. In addition, neurons exhibit compartment-specific autophagy, which depends on polarized structures. Neuronal autophagy may have additional physiological roles other than amino acid recycling. In this review, we focus on the characteristics and regulatory factors of neuronal autophagy. We also describe intracellular selective autophagy in neurons and its association with neurodegenerative diseases.

Characterization of the role of autophagy in retinal ganglion cell survival over time using a rat model of chronic ocular hypertension

Autophagy is an essential cellular process for the degradation and recycling of cellular components, and its dysregulation has been linked to neuronal cell death and neurodegeneration. In glaucoma, the role of autophagy in retinal ganglion cell (RGC) survival remains contradictory. Moreover, the effects of autophagy modulation at different time-points on RGC survival in a glaucoma model have not been investigated. In this study, we assessed the time-dependent role of autophagy in RGC survival in a circumlimbal suture-induced ocular hypertensive (OHT) rat model. Intraocular pressure (IOP) elevation led to a gradual autophagy induction, which reached a maximum between 1 and 4 weeks after OHT induction. On the other hand, early autophagy was impaired between 1 and 3 days after circumlimbal suturing, indicated by increased p62 levels due to reduced autophagosomal turnover. The intravitreal administration of rapamycin at different time-points after the application of the circumlimbal suture indicated that autophagy induction early during OHT development had potent survival-promoting effects in RGCs. In conclusion, our findings suggest that the role of autophagy in RGCs during OHT development might differ in a time-dependent manner. Modulating autophagy at the appropriate time might serve as a potential therapeutic approach to enhance RGC survival in OHT.

The interplay between lipid and Aβ amyloid homeostasis in Alzheimer's Disease: risk factors and therapeutic opportunities

Alzheimer's Diseases (AD) is characterized by the accumulation of amyloid deposits of Aβ peptide in the brain. Besides genetic background, the presence of other diseases and an unhealthy lifestyle are known risk factors for AD development. Albeit accumulating clinical evidence suggests that an impaired lipid metabolism is related to Aβ deposition, mechanistic insights on the link between amyloid fibril formation/clearance and aberrant lipid interactions are still unavailable. Recently, many studies have described the key role played by membrane bound Aβ assemblies in neurotoxicity. Moreover, it has been suggested that a derangement of the ubiquitin proteasome pathway and autophagy is significantly correlated with toxic Aβ aggregation and dysregulation of lipid levels. Thus, studies focusing on the role played by lipids in Aβ aggregation and proteostasis could represent a promising area of investigation for the design of valuable treatments. In this review we examine current knowledge concerning the effects of lipids in Aβ aggregation and degradation processes, focusing on the therapeutic opportunities that a comprehensive understanding of all biophysical, biochemical, and biological processes involved may disclose.

AMPK activation does not enhance autophagy in neurons in contrast to MTORC1 inhibition: different impact on β-amyloid clearance

The physiological AKT-MTORC1 and AMPK signaling pathways are considered key nodes in the regulation of anabolism-catabolism, and particularly of macroautophagy/autophagy. Indeed, it is reported that these are altered processes in neurodegenerative proteinopathies such as Alzheimer disease (AD), mainly characterized by deposits of β-amyloid (Aβ) and hyperphosphorylated MAPT. These accumulations disrupt the optimal neuronal proteostasis, and hence, the recovery/enhancement of autophagy has been proposed as a therapeutic approach against these proteinopathies. The purpose of the present study was to characterize the modulation of autophagy by MTORC1 and AMPK signaling pathways in the highly specialized neurons, as well as their repercussions on Aβ production. Using a double transgenic mice model of AD, we demonstrated that MTORC1 inhibition, either in vivo or ex vivo (primary neuronal cultures), was able to reduce amyloid secretion through moderate autophagy induction in neurons. The pharmacological prevention of autophagy in neurons augmented the Aβ secretion and reversed the effect of rapamycin, confirming the anti-amyloidogenic effects of autophagy in neurons. Inhibition of AMPK with compound C generated the expected decrease in autophagy induction, though surprisingly did not increase the Aβ secretion. In contrast, increased activity of AMPK with metformin, AICAR, 2DG, or by gene overexpression did not enhance autophagy but had different effects on Aβ secretion: whereas metformin and 2DG diminished the secreted Aβ levels, AICAR and PRKAA1/AMPK gene overexpression increased them. We conclude that AMPK has a significantly different role in primary neurons than in other reported cells, lacking a direct effect on autophagy-dependent amyloidosis.Abbreviations: 2DG: 2-deoxy-D-glucose; Aβ: β-amyloid; ACACA: acetyl-CoA carboxylase alpha; ACTB: actin beta; AD: Alzheimer disease; AICAR: 5-aminoimidazole-4-carboxamide-1-β-riboside; AKT: AKT kinases group (AKT1 [AKT serine/threonine kinase 1], AKT2 and AKT3); AMPK: adenosine 5'-monophosphate (AMP)-activated protein kinase; APP: amyloid beta precursor protein; APP/PSEN1: B6.Cg-Tg (APPSwe, PSEN1dE9) 85Dbo/J; ATG: autophagy related; ATP: adenosine triphosphate; BafA1: bafilomycin A1; CA: constitutively active; CGN: cerebellar granule neuron; CoC/compound C: dorsommorphin dihydrochloride; ELISA: enzyme-linked immunosorbent assay; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; Gmax: GlutaMAX™; IN1: PIK3C3/VPS34-IN1; KI: kinase-inactive; MAP1LC3B/LC3: microtubule associated protein 1 light chain 3; MAPT/TAU: microtubule associated protein tau; Metf: metformin; MRT: MRT68921; MTORC1: mechanistic target of rapamycin kinase complex 1; NBR1: NBR1 autophagy cargo receptor; PRKAA: 5'-AMP-activated protein kinase catalytic subunit alpha; PtdIns3K: phosphatidylinositol 3-kinase; Rapa: rapamycin; RPS6KB1/S6K: ribosomal protein S6 (RPS6) kinase polypeptide 1; SCR: scramble; SQSTM1/p62: sequestosome 1; ULK1/2: unc-51 like autophagy activating kinase 1/2; WT: wild type.

Stem cell-derived mitochondria transplantation: A promising therapy for mitochondrial encephalomyopathy

Mitochondrial encephalomyopathies are disorders caused by mitochondrial and nuclear DNA mutations which affect the nervous and muscular systems. Current therapies for mitochondrial encephalomyopathies are inadequate and mostly palliative. However, stem cell‐derived mitochondria transplantation has been demonstrated to play an key part in metabolic rescue, which offers great promise for mitochondrial encephalomyopathies. Here, we summarize the present status of stem cell therapy for mitochondrial encephalomyopathy and discuss mitochondrial transfer routes and the protection mechanisms of stem cells. We also identify and summarize future perspectives and challenges for the treatment of these intractable disorders based on the concept of mitochondrial transfer from stem cells.

Downregulation of autophagy by Met30-mediated Atg9 ubiquitination

Macroautophagy/autophagy is a highly conserved eukaryotic molecular process that facilitates the recycling of superfluous cytoplasmic materials, damaged organelles, and invading pathogens, resulting in proper cellular homeostasis and survival during stress conditions. Autophagy is stringently regulated at multiple stages, including control at transcriptional, translational, and posttranslational levels. In this work, we identified a mechanism by which regulation of autophagy is achieved through the posttranslational modification of Atg9. Here, we show that, in order to limit autophagy to a low, basal level during normal conditions, Atg9 is ubiquitinated and subsequently targeted for degradation in a proteasome-dependent manner through the action of the E3 ligase Met30. When cells require increased autophagy flux to respond to nutrient deprivation, the proteolysis of Atg9 is significantly reduced. Overall, this work reveals an additional layer of mechanistic regulation that allows cells to further maintain appropriate levels of autophagy and to rapidly induce this process in response to stress.

microRNA-146a-5p negatively modulates PM2.5 caused inflammation in THP-1 cells via autophagy process

Ambient fine particulate matter (PM_2.5) can change the expression profile of microRNAs (miRs), which may play important roles in mediating inflammatory responses. The present study attempts to investigate the roles of miR-146a-5p in regulating cytokine expression in a human monocytic leukemia cell line (THP-1). Four types of PM_2.5 extracts obtained from Beijing, China, were subjected to cytotoxic tests in THP-1 cells. These four PM_2.5 extracts included two water extracts collected from non-heating and heating season (WN and WH), and two organic extracts from non-heating and heating season (DN and DH). Firstly, the four PM_2.5 extracts caused cytotoxicity, oxidative stress responses, cytokine gene expressions and interleukin 8 (IL-8) release in THP-1 cells, with WH showing the highest cytotoxicity, WN showing the highest oxidative stress and inflammatory responses. Additionally, we observed expression of miR-146a-5p was significantly increased, with the maximal response of six folds in WN group. Cellular autophagy was initiated by PM_2.5 indicated by related protein and gene expressions. Both RNA interference and autophagy inhibitor were applied to interrupt autophagy process in THP-1 cells. Autophagy dysfunction could alleviate IL-8 expression, suggesting autophagy process regulated cytokine expression and inflammatory response caused by PM_2.5. A chemical inhibitor was applied to inhibit the function of miR-146a-5p, and then the expressions of IL-8 and autophagic genes were significantly aggravated. Meanwhile, two target genes of miR-146a-5p, interleukin-1 associated-kinase-1 (IRAK1) and tumor-necrosis factor receptor-associated factor-6 (TRAF6) were increased dramatically, which also played important roles in regulation of autophagy. These data suggested miR-146a-5p negatively modulated cytokine expression caused by PM_2.5 via autophagy process through the target genes of IRAK1 and TRAF6. Our findings raised the concerns of the changes of miR expression profile and following responses caused by PM_2.5.

Autophagy and the endolysosomal system in presynaptic function

The complex morphology of neurons, the specific requirements of synaptic neurotransmission and the accompanying metabolic demands create a unique challenge for proteostasis. The main machineries for neuronal protein synthesis and degradation are localized in the soma, while synaptic junctions are found at vast distances from the cell body. Sophisticated mechanisms must, therefore, ensure efficient delivery of newly synthesized proteins and removal of faulty proteins. These requirements are exacerbated at presynaptic sites, where the demands for protein turnover are especially high due to synaptic vesicle release and recycling that induces protein damage in an intricate molecular machinery, and where replacement of material is hampered by the extreme length of the axon. In this review, we will discuss the contribution of the two major pathways in place, autophagy and the endolysosomal system, to presynaptic protein turnover and presynaptic function. Although clearly different in their biogenesis, both pathways are characterized by cargo collection and transport into distinct membrane-bound organelles that eventually fuse with lysosomes for cargo degradation. We summarize the available evidence with regard to their degradative function, their regulation by presynaptic machinery and the cargo for each pathway. Finally, we will discuss the interplay of both pathways in neurons and very recent findings that suggest non-canonical functions of degradative organelles in synaptic signalling and plasticity.

Autophagy in the Regulation of Tissue Differentiation and Homeostasis

Autophagy is a constitutive pathway that allows the lysosomal degradation of damaged components. This conserved process is essential for metabolic plasticity and tissue homeostasis and is crucial for mammalian post-mitotic cells. Autophagy also controls stem cell fate and defective autophagy is involved in many pathophysiological processes. In this review, we focus on established and recent breakthroughs aimed at elucidating the impact of autophagy in differentiation and homeostasis maintenance of endothelium, muscle, immune system, and brain providing a suitable framework of the emerging results and highlighting the pivotal role of autophagic response in tissue functions, stem cell dynamics and differentiation rates.

Neuronal Autophagy Regulates Presynaptic Neurotransmission by Controlling the Axonal Endoplasmic Reticulum

Neurons are known to rely on autophagy for removal of defective proteins or organelles to maintain synaptic neurotransmission and counteract neurodegeneration. In spite of its importance for neuronal health, the physiological substrates of neuronal autophagy in the absence of proteotoxic challenge have remained largely elusive. We use knockout mice conditionally lacking the essential autophagy protein ATG5 and quantitative proteomics to demonstrate that loss of neuronal autophagy causes selective accumulation of tubular endoplasmic reticulum (ER) in axons, resulting in increased excitatory neurotransmission and compromised postnatal viability in vivo. The gain in excitatory neurotransmission is shown to be a consequence of elevated calcium release from ER stores via ryanodine receptors accumulated in axons and at presynaptic sites. We propose a model where neuronal autophagy controls axonal ER calcium stores to regulate neurotransmission in healthy neurons and in the brain.

•

Neuronal autophagy controls the endoplasmic reticulum (ER) in axons

•

Loss of neuronal autophagy leads to increased excitatory neurotransmission

•

Increased neurotransmission is due to elevated calcium release from ER stores

Pathogenic Single Nucleotide Polymorphisms on Autophagy-Related Genes

In recent years, the study of single nucleotide polymorphisms (SNPs) has gained increasing importance in biomedical research, as they can either be at the molecular origin of a determined disorder or directly affect the efficiency of a given treatment. In this regard, sequence variations in genes involved in pro-survival cellular pathways are commonly associated with pathologies, as the alteration of these routes compromises cellular homeostasis. This is the case of autophagy, an evolutionarily conserved pathway that counteracts extracellular and intracellular stressors by mediating the turnover of cytosolic components through lysosomal degradation. Accordingly, autophagy dysregulation has been extensively described in a wide range of human pathologies, including cancer, neurodegeneration, or inflammatory alterations. Thus, it is not surprising that pathogenic gene variants in genes encoding crucial effectors of the autophagosome/lysosome axis are increasingly being identified. In this review, we present a comprehensive list of clinically relevant SNPs in autophagy-related genes, highlighting the scope and relevance of autophagy alterations in human disease.

An Update on Autophagy in Prion Diseases

Autophagy is a dynamic intracellular mechanism involved in protein and organelle turnover through lysosomal degradation. When properly regulated, autophagy supports normal cellular and developmental processes, whereas defects in autophagic degradation have been associated with several pathologies, including prion diseases. Prion diseases, or transmissible spongiform encephalopathies (TSE), are a group of fatal neurodegenerative disorders characterized by the accumulation of the pathological misfolded isoform (PrP^Sc) of the physiological cellular prion protein (PrP^c) in the central nervous system. Autophagic vacuoles have been described in experimental models of TSE and in the natural disease in humans. The precise connection of this process with prion-related neuropathology, or even whether autophagy is completely beneficial or pathogenic during neurodegeneration, is poorly understood. Thus, the biological role of autophagy in these diseases is still open to debate. During the last years, researchers have used a wide range of morphological, genetic and biochemical methods to monitor and manipulate the autophagic pathway and thus determine the specific role of this process in TSE. It has been suggested that PrP^c could play a crucial role in modulating the autophagic pathway in neuronal cells, and the presence of abnormal autophagic activity has been frequently observed in several models of TSE both in vitro and in vivo, as well as in human prion diseases. Altogether, these findings suggest that autophagy is implicated in prion neuropathology and points to an impairment or failure of the process, potentially contributing to the pathogenesis of the disease. Additionally, autophagy is now emerging as a host defense response in controlling prion infection that plays a protective role by facilitating the clearance of aggregation-prone proteins accumulated within neurons. Since autophagy is one of the pathways of PrP^Sc degradation, and drug-induced stimulation of autophagic flux (the dynamic process of autophagic degradation activity) produces anti-prion effects, new treatments based on its activation have been tested to develop therapeutic strategies for prion diseases. In this review, we summarize previous and recent findings concerning the role of autophagy in TSE.

Enhanced autophagic retrograde axonal transport by dynein intermediate chain upregulation improves Aβ clearance and cognitive function in APP/PS1 double transgenic mice

Autophagosome accumulation is observed in the distal axons of Alzheimer disease (AD) patients and AD animal models, suggesting that deficient retrograde transport and impaired autophagic clearance of beta-amyloid (A β) contribute to AD pathogenesis. Expression of the retrograde axonal transport-related protein dynein intermediate chain (DIC) is also reduced in AD patients, but the contributions of DIC to AD pathology remain elusive. This study investigated the effects of DIC expression levels on cognitive function, autophagosome axonal transport, and A β clearance in the APP/PS1 double transgenic mouse model of AD. Autophagic activity was enhanced in the hippocampus of young (3-month-old) AD mice, as evidenced by greater expression of autophagosome markers, lysosome markers, axonal transport motors (including DIC), and dynein regulatory proteins. The expression levels of autophagosome markers remained elevated, whereas those of autophagic and axonal transport proteins decreased progressively with age, accompanied by spatial learning and memory deficits, axonal autophagosome accumulation, and A β deposition. Knockdown of DIC exacerbated while overexpression improved axonal transport, autophagosome maturation, Aβ clearance, and spatial learning and memory in aged AD mice. Our study provides evidence that age-dependent failure of axonal autophagic flux contributes to AD-associated neuropathology and cognitive deficits, suggesting DIC as a potential therapeutic target for AD.

Neuronal Autophagy in Synaptic Functions and Psychiatric Disorders

Homeostatic maintenance of physiological functions is fundamental to organismal well-being. Disruption or imbalance in homeostasis results in functional disturbances at molecular, cellular, and tissue levels, leading to manifestation as physical and mental illnesses. Homeostatic imbalance is caused by a range of pathophysiological mechanisms, including disrupted reduction-oxidation reactions, inflammatory responses, metabolic disturbances, or failure in quality control of cellular proteins and organelles. However, the roles for the protein/organelle quality control in the regulation of behaviors, in particular of cognitive processes, had not been well documented, until recent reports finally supported this concept. The frontline studies in neuroscience have revealed that synaptic components (e.g., synaptic proteins, organelles, neurotransmitters and their receptors) are selectively degraded by autophagy, a cellular recycling machinery implicated in surveillance and quality control of proteins and organelles responsible for the maintenance of cellular homeostasis. Apart from the canonical role of autophagy in supporting cell viability, synaptic autophagy appears to regulate synapse remodeling and plasticity. Consistently, emerging evidence suggests novel roles of autophagy in memory encoding, information processing, or cognitive functions. In this review, we overview recent progress in understanding the roles of neuronal autophagy in homeostatic maintenance of synaptic functions, with particular focus on how disruptions in these processes may contribute to the pathophysiology of psychiatric disorders.

Autophagy Modulators and Neuroinflammation

BACKGROUND

Neuroinflammation plays a critical role in the development and progression of various neurological disorders. Therefore, various studies have focused on the development of neuroinflammation inhibitors as potential therapeutic tools. Recently, the involvement of autophagy in the regulation of neuroinflammation has drawn substantial scientific interest, and a growing number of studies support the role of impaired autophagy in the pathogenesis of common neurodegenerative disorders.

OBJECTIVE

The purpose of this article is to review recent research on the role of autophagy in controlling neuroinflammation. We focus on studies employing both mammalian cells and animal models to evaluate the ability of different autophagic modulators to regulate neuroinflammation.

METHODS

We have mostly reviewed recent studies reporting anti-neuroinflammatory properties of autophagy. We also briefly discussed a few studies showing that autophagy modulators activate neuroinflammation in certain conditions.

RESULTS

Recent studies report neuroprotective as well as anti-neuroinflammatory effects of autophagic modulators. We discuss the possible underlying mechanisms of action of these drugs and their potential limitations as therapeutic agents against neurological disorders.

CONCLUSION

Autophagy activators are promising compounds for the treatment of neurological disorders involving neuroinflammation.

Battling Neurodegenerative Diseases with Adeno-Associated Virus-Based Approaches

Neurodegenerative diseases (NDDs) are most commonly found in adults and remain essentially incurable. Gene therapy using AAV vectors is a rapidly-growing field of experimental medicine that holds promise for the treatment of NDDs. To date, the delivery of a therapeutic gene into target cells via AAV represents a major obstacle in the field. Ideally, transgenes should be delivered into the target cells specifically and efficiently, while promiscuous or off-target gene delivery should be minimized to avoid toxicity. In the pursuit of an ideal vehicle for NDD gene therapy, a broad variety of vector systems have been explored. Here we specifically outline the advantages of adeno-associated virus (AAV)-based vector systems for NDD therapy application. In contrast to many reviews on NDDs that can be found in the literature, this review is rather focused on AAV vector selection and their preclinical testing in experimental and preclinical NDD models. Preclinical and in vitro data reveal the strong potential of AAV for NDD-related diagnostics and therapeutic strategies.

Autophagy and disease: unanswered questions

Autophagy is a process in which intracellular components and dysfunctional organelles are delivered to the lysosome for degradation and recycling. Autophagy has various connections to a large number of human diseases, as its functions are essential for cell survival, bioenergetic homeostasis, organism development, and cell death regulation. In the past two decades, substantial effort has been made to identify the roles of autophagy in tumor suppression and promotion, neurodegenerative disorders, and other pathophysiologies. This review summarizes the current advances and discusses the unanswered questions in understanding the involvement of autophagy in pathogenic mechanisms of disease, primarily focusing on cancer and neurodegenerative diseases.

Protein Quality Control in Neurodegeneration and Neuroprotection

Proteostasis is essential for regulating the integrity of the proteome. Disruption of proteostasis under some rigorous conditions leads to the aggregation and accumulation of misfolded toxic proteins, which plays a central role in the pathogenesis of protein conformational disorders. The protein quality control (PQC) system serves as a multi-level security system to shield cells from abnormal proteins. The intrinsic PQC systems maintaining proteostasis include the ubiquitin-proteasome system (UPS), chaperon-mediated autophagy (CMA), and autophagy-lysosome pathway (ALP) that serve to target misfolded proteins for unfolding, refolding, or degradation. Alterations of PQC systems in neurons have been implicated in the pathogenesis of various neurodegenerative disorders. This chapter provides an overview of PQC pathways to set a framework for discussion of the role of PQC in neurodegenerative disorders. Additionally, various pharmacological approaches targeting PQC are summarized.

Differential regulation of autophagy during metabolic stress in astrocytes and neurons

Macroautophagy/autophagy is a key homeostatic process that targets cytoplasmic components to the lysosome for breakdown and recycling. Autophagy plays critical roles in glia and neurons that affect development, functionality, and viability of the nervous system. The mechanisms that regulate autophagy in glia and neurons, however, are poorly understood. Here, we define the molecular underpinnings of autophagy in primary cortical astrocytes in response to metabolic stress, and perform a comparative study in primary hippocampal neurons. We find that inducing metabolic stress by nutrient deprivation or pharmacological inhibition of MTOR (mechanistic target of rapamycin kinase) robustly activates autophagy in astrocytes. While both paradigms of metabolic stress dampen MTOR signaling, they affect the autophagy pathway differently. Further, we find that starvation-induced autophagic flux is dependent on the buffering system of the starvation solution. Lastly, starvation conditions that strongly activate autophagy in astrocytes have less pronounced effects on autophagy in neurons. Combined, our study reveals the complexity of regulating autophagy in different paradigms of metabolic stress, as well as in different cell types of the brain. Our findings raise important implications for how neurons and glia may collaborate to maintain homeostasis in the brain.

ABBREVIATIONS

ACSF: artificial cerebrospinal fluid; baf A₁: bafilomycin A₁; EBSS: earle's balanced salt solution; GFAP: glial fibrillary acidic protein; Glc: glucose; GM: glial media; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; p-RPS6: phospho-RPS6; p-ULK1: phospho-ULK1; RPS6: ribosomal protein S6; SQSTM1/p62: sequestosome 1; ULK1: unc-51-like kinase 1.

The Endolysosomal System and Proteostasis: From Development to Degeneration

How do neurons adapt their endolysosomal system to address the particular challenge of membrane transport across their elaborate cellular landscape and to maintain proteostasis for the lifetime of the organism? Here we review recent findings that address this central question. We discuss the cellular and molecular mechanisms of endolysosomal trafficking and the autophagy pathway in neurons, as well as their role in neuronal development and degeneration. These studies highlight the importance of understanding the basic cell biology of endolysosomal trafficking and autophagy and their roles in the maintenance of proteostasis within the context of neurons, which will be critical for developing effective therapies for various neurodevelopmental and neurodegenerative disorders.

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

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

Autophagy dysfunction in neuropathic pain

Autophagy is a lysosomal degradation pathway that maintains tissue homeostasis by recycling damaged and aged cellular components, which plays important roles in development of the nervous system, as well as in neuronal function and survival. In addition, autophagy dysfunction underlies neuropathic pain. Thus, the modulation of autophagy can alleviate neuropathic pain. Here, we describe the definition, mechanisms of autophagy and neuropathic pain. On this basis, we further discuss the role of autophagy dysfunction in neuropathic pain. This review updates our knowledge on autophagy mechanisms which propose potential therapeutic targets for the treatment of neuropathic pain.

p62 aggregates mediated Caspase 8 activation is responsible for progression of ovarian cancer

Increasing evidence suggests that p62/SQSTM1 functions as a signalling centre in cancer. However, the role of p62 in tumour development depends on the interacting factors it recruits and its precise regulatory mechanism remains unclear. In this study, we investigated the pro‐death signalling recruitment of p62 with the goal of improving anti‐tumour drug effects in ovarian cancer treatment. We found that p62 with Caspase 8 high expression is correlated with longer survival time compared with cases of low Caspase 8 expression in ovarian cancer. In vivo experiments suggested that insoluble p62 and ubiquitinated protein accumulation induced by autophagy impairment promoted the activation of Caspase 8 and increased cell sensitivity to cisplatin. Furthermore, p62 functional domain UBA and LIR mutants regulated autophagic flux and attenuated Caspase 8 activation, which indicates that autophagic degradation is involved in p62‐mediated activation of Caspase 8 in ovarian cancer cells. Collectively, our study demonstrates that p62 promotes Caspase 8 activation through autophagy flux blockage with cisplatin treatment. We have provided evidence that autophagy induction followed by its blockade increases cell sensitivity to chemotherapy which is dependent on p62‐Caspase 8 mediated apoptosis signalling. p62 exhibits pro‐death functions through its interaction with Caspase 8. p62 and Caspase 8 may become novel prognostic biomarkers and oncotargets for ovarian cancer treatment.