Autophagy Mediates Astrogenesis in Adult Hippocampal Neural Stem Cells

Impaired olfactory bulb neurogenesis mediated by Notch1 contributes to olfactory dysfunction in mice chronically exposed to methamphetamine

Methamphetamine (Meth) is a potent central nervous system stimulant with high addictive potential and neurotoxic effects. Chronic use results in significant damage in various brain functions, including cognition, memory, and sensory perception. Olfactory dysfunction is a notable yet often overlooked consequence of Meth abuse, and its underlying mechanisms are not fully understood. This study investigates the mechanisms of Meth-induced olfactory impairment through a thorough examination of olfactory bulb (OB) neurogenesis. We found that chronic Meth abuse impaired olfactory function in mice by not only reducing the self-renewal of subventricular zone (SVZ) neural stem cells (NSCs) but also altering their differentiation potential, leading their differentiation into astrocytes at the expense of neurons. Mechanistically, Meth inhibits autophagosome-lysosome fusion by downregulating Syntaxin 17 (Stx17), which reduces autophagic flux. In NSCs, autophagy tightly regulates Notch1 levels, and impaired autophagic degradation of Notch1 leads to its abnormal activation. This alters NSCs fate determination, ultimately affecting OB neurogenesis. Our study reveals that Meth impairs olfactory function through autophagic dysfunction and aberrant Notch1 signaling. Understanding these mechanisms not only provides new insights into Meth-induced olfactory dysfunction but also offers potential targets for developing therapies to alleviate Meth-induced neurotoxicity and sensory damage in the future.

Autophagy in neural stem cells and glia for brain health and diseases

Autophagy is a multifaceted cellular process that not only maintains the homeostatic and adaptive responses of the brain but is also dynamically involved in the regulation of neural cell generation, maturation, and survival. Autophagy facilities the utilization of energy and the microenvironment for developing neural stem cells. Autophagy arbitrates structural and functional remodeling during the cell differentiation process. Autophagy also plays an indispensable role in the maintenance of stemness and homeostasis in neural stem cells during essential brain physiology and also in the instigation and progression of diseases. Only recently, studies have begun to shed light on autophagy regulation in glia (microglia, astrocyte, and oligodendrocyte) in the brain. Glial cells have attained relatively less consideration despite their unquestioned influence on various aspects of neural development, synaptic function, brain metabolism, cellular debris clearing, and restoration of damaged or injured tissues. Thus, this review composes pertinent information regarding the involvement of autophagy in neural stem cells and glial regulation and the role of this connexion in normal brain functions, neurodevelopmental disorders, and neurodegenerative diseases. This review will provide insight into establishing a concrete strategic approach for investigating pathological mechanisms and developing therapies for brain diseases.

The role of glial autophagy in Alzheimer's disease

Although Alzheimer's disease is the most pervasive neurodegenerative disorder, the mechanism underlying its development is still not precisely understood. Available data indicate that pathophysiology of this disease may involve impaired autophagy in glial cells. The dysfunction is manifested as reduced ability of astrocytes and microglia to clear abnormal protein aggregates. Consequently, excessive accumulation of amyloid beta plaques and neurofibrillary tangles activates microglia and astrocytes leading to decreased number of mature myelinated oligodendrocytes and death of neurons. These pathologic effects of autophagy dysfunction can be rescued by pharmacological activation of autophagy. Therefore, a deeper understanding of the molecular mechanisms involved in autophagy dysfunction in glial cells in Alzheimer's disease may lead to the development of new therapeutic strategies. However, such strategies need to take into consideration differences in regulation of autophagy in different types of neuroglia.

Neuronal acid-sensing ion channel 1a regulates neuron-to-glioma synapses

Neuronal activity promotes high-grade glioma progression via secreted proteins and neuron-to-glioma synapses, and glioma cells boost neuronal activity to further reinforce the malignant cycle. Whereas strong evidence supports that the activity of neuron-to-glioma synapses accelerates tumor progression, the molecular mechanisms that modulate the formation and function of neuron-to-glioma synapses remain largely unknown. Our recent findings suggest that a proton (H + ) signaling pathway actively mediates neuron-to-glioma synaptic communications by activating neuronal acid-sensing ion channel 1a (Asic1a), a predominant H + receptor in the central nervous system (CNS). Supporting this idea, our preliminary data revealed that local acid puff on neurons in high-grade glioma-bearing brain slices induces postsynaptic currents of glioma cells. Stimulating Asic1a knockout (Asic1a -/- ) neurons results in lower AMPA receptor-dependent excitatory postsynaptic currents (EPSCs) in glioma cells than stimulating wild-type (WT) neurons. Moreover, glioma-bearing Asic1a -/- mice exhibited reduced tumor size and survived longer than the glioma-bearing WT mice. Finally, pharmacologically targeting brain Asic1a inhibited high-grade glioma progression. In conclusion, our findings suggest that the neuronal H + -Asic1a axis plays a key role in regulating the neuron-glioma synapse. The outcomes of this study will greatly expand our understanding of how this deadly tumor integrates into the neuronal microenvironment.

CircHULC accelerates the growth of human liver cancer stem cells by enhancing chromatin reprogramming and chromosomal instability via autophagy

BACKGROUND

Although CircHULC was overexpressed in several cancers, the role of CircHULC in malignancies has yet to be elucidated.

METHODS

Gene infection, tumorigenesis test in vitro and in vivo and the signaling pathway analysis were performed.

RESULTS

our results indicate that CircHULC promotes growth of human liver cancer stem cells and the malignant differentiation of hepatocyte-like cells. Mechanistically, CircHULC enhances the methylation modification of PKM2 via CARM1 and the deacetylase Sirt1. Moreover, CircHULC enhances the binding ability of TP53INP2/DOR with LC3 and LC3 with ATG4, ATG3, ATG5, ATG12. Therefore, CircHULC promotes the formation of autophagosomes. In particular, the binding ability of phosphorylated Beclin1 (Ser14) to Vps15, Vps34, ATG14L were significantly increased after CircHULC was overexpressed. Strikingly, CircHULC affects the expression of chromatin reprogramming factors and oncogenes through autophagy. Thereafter, Oct4, Sox2, KLF4, Nanog, and GADD45 were significantly decreased and C-myc was increased after CircHULC was overexpressed. Thus, CircHULC promotes the expression of H-Ras, SGK, P70S6K, 4E-BP1, Jun, and AKT. Interestingly, both CARM1 and Sirt1 determine the cancerous function of CircHULC dependent on autophagy.

CONCLUSIONS

we shed light on the fact that the targeted attenuation of deregulated functioning of CircHULC could be a viable approach for cancer treatment, and CircHULC may acts as the potential biomarker and therapeutic target for liver cancer.

Aβ-induced mitochondrial dysfunction in neural progenitors controls KDM5A to influence neuronal differentiation

Mitochondria in neural progenitors play a crucial role in adult hippocampal neurogenesis by being involved in fate decisions for differentiation. However, the molecular mechanisms by which mitochondria are related to the genetic regulation of neuronal differentiation in neural progenitors are poorly understood. Here, we show that mitochondrial dysfunction induced by amyloid-beta (Aβ) in neural progenitors inhibits neuronal differentiation but has no effect on the neural progenitor stage. In line with the phenotypes shown in Alzheimer's disease (AD) model mice, Aβ-induced mitochondrial damage in neural progenitors results in deficits in adult hippocampal neurogenesis and cognitive function. Based on hippocampal proteome changes after mitochondrial damage in neural progenitors identified through proteomic analysis, we found that lysine demethylase 5A (KDM5A) in neural progenitors epigenetically suppresses differentiation in response to mitochondrial damage. Mitochondrial damage characteristically causes KDM5A degradation in neural progenitors. Since KDM5A also binds to and activates neuronal genes involved in the early stage of differentiation, functional inhibition of KDM5A consequently inhibits adult hippocampal neurogenesis. We suggest that mitochondria in neural progenitors serve as the checkpoint for neuronal differentiation via KDM5A. Our findings not only reveal a cell-type-specific role of mitochondria but also suggest a new role of KDM5A in neural progenitors as a mediator of retrograde signaling from mitochondria to the nucleus, reflecting the mitochondrial status.

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.

Brain Extract of Subacute Traumatic Brain Injury Promotes the Neuronal Differentiation of Human Neural Stem Cells via Autophagy

Background: After a traumatic brain injury (TBI), the cell environment is dramatically changed, which has various influences on grafted neural stem cells (NSCs). At present, these influences on NSCs have not been fully elucidated, which hinders the finding of an optimal timepoint for NSC transplantation. Methods: Brain extracts of TBI mice were used in vitro to simulate the different phase TBI influences on the differentiation of human NSCs. Protein profiles of brain extracts were analyzed. Neuronal differentiation and the activation of autophagy and the WNT/CTNNB pathway were detected after brain extract treatment. Results: Under subacute TBI brain extract conditions, the neuronal differentiation of hNSCs was significantly higher than that under acute brain extract conditions. The autophagy flux and WNT/CTNNB pathway were activated more highly within the subacute brain extract than in the acute brain extract. Autophagy activation by rapamycin could rescue the neuronal differentiation of hNSCs within acute TBI brain extract. Conclusions: The subacute phase around 7 days after TBI in mice could be a candidate timepoint to encourage more neuronal differentiation after transplantation. The autophagy flux played a critical role in regulating neuronal differentiation of hNSCs and could serve as a potential target to improve the efficacy of transplantation in the early phase.

Monitoring Autophagy in Neural Stem and Progenitor Cells

Autophagy is a critical cellular program that is necessary for cellular survival and adaptation to nutrient and metabolic stress. In addition to homeostatic maintenance and adaptive response functions, autophagy also plays an active role during development and tissue regeneration. Within the neural system, autophagy is important for stem cell maintenance and the ability of neural stem cells to undergo self-renewal. Autophagy also contributes toward neurogenesis and provides neural progenitor cells with sufficient energy to mediate cytoskeleton remodeling during the differentiation process. In differentiated neural cells, autophagy maintains neuronal homeostasis and viability by preventing the accumulation of toxic and pathological intracellular aggregates. However, prolonged autophagy or dysregulated upregulation of autophagy can result in autophagic cell death. Moreover, mutations or defects in autophagy that result in neural stem cell instability and cell death underlie many neurodegenerative disorders, such as Parkinson's disease. Thus, autophagy plays a multi-faceted role during neurogenesis from the stem cell to the differentiated neural cell. In this chapter, we describe methods to monitor autophagy at the protein and transcript level to evaluate alterations within the autophagy program in neural stem and progenitor cells. We describe immunoblotting and immunocytochemistry approaches for evaluating autophagy-dependent protein modifications, as well as quantitative real-time PCR to assess transcript levels of autophagy genes. As autophagy is a dynamic process, we highlight the importance of using late-stage inhibitors to be able to assess autophagic flux and quantify the level of autophagy occurring within cells.

Autophagy Promoted Neural Differentiation of Human Placenta-derived Mesenchymal Stem Cells

BACKGROUND/AIM

Human placenta-derived mesenchymal stem cells (hPMSCs) are multipotent and possess neurogenicity. Numerous studies have shown that Notch inhibition and DNA demethylation promote neural differentiation. Here, we investigated the modulation of autophagy during neural differentiation of hPMSCs, induced by DAPT and 5-Azacytidine.

MATERIALS AND METHODS

hPMSCs were treated with DAPT to induce neural differentiation, and the autophagy regulating molecules were used to assess the impact of autophagy on neural differentiation.

RESULTS

The hPMSCs presented with typical mesenchymal stem cell phenotypes, in which the majority of cells expressed CD73, CD90 and CD105. hPMSCs were multipotent, capable of differentiating into mesodermal cells. After treatment with DAPT, hPMSCs upregulated the expression of neuronal genes including SOX2, Nestin, and βIII-tubulin, and the autophagy genes LC3I/II and Beclin. These genes were further increased when 5-Azacytidine was co-supplemented in the culture medium. The inhibition of autophagy by chloroquine impeded the neural differentiation of hPMSCs, marked by the downregulation of βIII-tubulin, while the activation of autophagy by valproic acid (VPA) instigated the emergence of βIII-tubulin-positive cells.

CONCLUSION

During the differentiation process, autophagy was modulated, implying that autophagy could play a significant role during the differentiation of these cells. The blockage and stimulation of autophagy could either hinder or induce the formation of neural-like cells, respectively. Therefore, the refinement of autophagic activity at an appropriate level might improve the efficiency of stem cell differentiation.

GSK3B induces autophagy by phosphorylating ULK1

Unc-51-like autophagy activating kinase 1 (ULK1), a mammalian homolog of the yeast kinase Atg1, has an essential role in autophagy induction. In nutrient and growth factor signaling, ULK1 activity is regulated by various posttranslational modifications, including phosphorylation, acetylation, and ubiquitination. We previously identified glycogen synthase kinase 3 beta (GSK3B) as an upstream regulator of insulin withdrawal-induced autophagy in adult hippocampal neural stem cells. Here, we report that following insulin withdrawal, GSK3B directly interacted with and activated ULK1 via phosphorylation of S405 and S415 within the GABARAP-interacting region. Phosphorylation of these residues facilitated the interaction of ULK1 with MAP1LC3B and GABARAPL1, while phosphorylation-defective mutants of ULK1 failed to do so and could not induce autophagy flux. Furthermore, high phosphorylation levels of ULK1 at S405 and S415 were observed in human pancreatic cancer cell lines, all of which are known to exhibit high levels of autophagy. Our results reveal the importance of GSK3B-mediated phosphorylation for ULK1 regulation and autophagy induction and potentially for tumorigenesis.

Similar to cellular starvation conditions, insulin withdrawal may trigger the modification of an enzyme involved in the induction of autophagy, a key cellular recycling process. The ULK1 enzyme has a critical role in autophagy induction. Seong-Woon Yu at the Daegu Gyeongbuk Institute of Science and Technology, South Korea, and co-workers investigated how ULK1 is activated under insulin withdrawal condition. They found that another enzyme called GSK3B modifies two specific ULK1 amino acids, activating ULK1 and triggering autophagy. Further, they found high levels of this type of ULK1 modification in human pancreatic cancer cell lines that exhibited increased autophagy, suggesting possible implications for the development of certain cancerous tumors.

Unexpected Role of Nonimmune Cells: Amateur Phagocytes

Effective and efficient efferocytosis of dead cells and associated cellular debris are critical to tissue homeostasis and healing of injured tissues. This important task was previously thought to be restricted to professional phagocytes (PPs). However, accumulating evidence has revealed another type of phagocyte, the amateur phagocyte (AP), which can also participate in efferocytosis. APs are non-myeloid progenitor/nonimmune cells that include differentiated cells (e.g., epithelial cells, fibroblasts, and endothelial cells [ECs]) and stem cells (e.g., neuronal progenitor cells and mesenchymal cells) and can be found throughout the human body. Studies have shown that APs have two prominent roles: identifying and removing dead cells presumably before PPs reach the site of injury and assisting PPs in the removal of cell corpses and the resolution of inflamed tissue. With respect to the engulfment and degradation of dead cells, APs are slower and less efficient than PPs. However, APs are fundamental to preventing the spread of inflammation over a large area. In this review, we present the diversity and characteristics of healthy and non-neoplastic APs in mammals. We also propose a hypothetical mechanism of the efferocytosis of immunoglobulin G (IgG)-opsonized myelin debris by ECs (APs). Furthermore, the ingestion and clearance of dead cells can induce proinflammatory or anti-inflammatory cytokine production, endothelial activation, and cellular fate transition, which contribute to the progression of disease. An understanding of the role of APs is necessary to develop effective intervention strategies, including potential molecular targets for clinical diagnosis and drug development, for inflammation-related diseases.

Autophagy in Neuronal Development and Plasticity

Autophagy is a highly conserved intracellular clearance pathway in which cytoplasmic contents are trafficked to the lysosome for degradation. Within neurons, it helps to remove damaged organelles and misfolded or aggregated proteins and has therefore been the subject of intense research in relation to neurodegenerative disease. However, far less is understood about the role of autophagy in other aspects of neuronal physiology. Here we review the literature on the role of autophagy in maintaining neuronal stem cells and in neuronal plasticity in adult life and we discuss how these contribute to structural and functional deficits observed in a range of human disorders.

Cx3cr1CreERT2-driven Atg7 deletion in adult mice induces intestinal adhesion

Microglia are macrophages resident in the central nervous system. C-X3-C motif chemokine receptor 1 (CX3CR1) is a G_αi-coupled seven-transmembrane protein exclusively expressed in the mononuclear phagocyte system including microglia, as well as intestinal and kidney macrophages. Cx3cr1^CreERT2 mice express Cre recombinase in a tamoxifen-inducible manner and have been widely used to delete target genes in microglia, since microglia are long-lived cells and outlive peripheral macrophages, which continuously turn over and lose their gene modification over time. ATG7 is an E1-like enzyme that plays an essential role in two ubiquitin-like reactions, ATG12-ATG5 conjugation and LC3-lipidation in autophagy. To study the role of ATG7 in adult microglia, we generated Cx3cr1^CreERT2:Atg7^fl/fl mice and deleted Atg7 at the age of 8 weeks, and found induction of intestinal adhesion. Since intestinal adhesion is caused by excessive inflammation, these results suggest that deletion of Atg7 in intestinal macrophages even for a short time results in inflammation that cannot be rescued by replenishment with wild-type intestinal macrophages. Our finding suggests that, depending on the roles of the gene, Cx3cr1-Cre-mediated gene deletion may yield unanticipated physiological outcomes outside the central nervous system, and careful necropsy is necessary to assure the microglia-specific roles of the target gene.

The Contribution of Astrocyte Autophagy to Systemic Metabolism

Autophagy is an essential mechanism to maintain cellular homeostasis. Besides its role in controlling the quality of cytoplasmic components, it participates in nutrient obtaining and lipid mobilization under stressful conditions. Furthermore, autophagy is involved in the regulation of systemic metabolism as its blockade in hypothalamic neurons can affect the central regulation of metabolism and impact body energy balance. Moreover, hypothalamic autophagy can be altered during obesity, one of the main alterations of metabolism nowadays. In this review, we focus on the role of astrocytes, essential cells for brain homeostasis, which represent key metabolic regulators. Astrocytes can sense metabolic signals in the hypothalamus and modulate systemic functions as glucose homeostasis and feeding response. Moreover, the response of astrocytes to obesity has been widely studied. Astrocytes are important mediators of brain inflammation and can be affected by increased levels of saturated fatty acids associated with obesity. Although autophagy plays important roles for astrocyte homeostasis and functioning, the contribution of astrocyte autophagy to systemic metabolism has not been analyzed yet. Furthermore, how obesity can impact astrocyte autophagy is poorly understood. More studies are needed in order to understand the contribution of astrocyte autophagy to metabolism.

Autophagy and Stem Cells: Self-Eating for Self-Renewal

Autophagy is a fundamental cell survival mechanism that allows cells to adapt to metabolic stress through the degradation and recycling of intracellular components to generate macromolecular precursors and produce energy. The autophagy pathway is critical for development, maintaining cellular and tissue homeostasis, as well as immunity and prevention of human disease. Defects in autophagy have been attributed to cancer, neurodegeneration, muscle and heart disease, infectious disease, as well as aging. While autophagy has classically been viewed as a passive quality control and general house-keeping mechanism, emerging evidence demonstrates that autophagy is an active process that regulates the metabolic status of the cell. Adult stem cells, which are long-lived cells that possess the unique ability to self-renew and differentiate into specialized cells throughout the body, have distinct metabolic requirements. Research in a variety of stem cell types have established that autophagy plays critical roles in stem cell quiescence, activation, differentiation, and self-renewal. Here, we will review the evidence demonstrating that autophagy is a key regulator of stem cell function and how defective stem cell autophagy contributes to degenerative disease, aging and the generation of cancer stem cells. Moreover, we will discuss the merits of targeting autophagy as a regenerative medicine strategy to promote stem cell function and improve stem cell-based therapies.

Glial Cell Line-derived Neurotrophic Factor-overexpressing Human Neural Stem/Progenitor Cells Enhance Therapeutic Efficiency in Rat with Traumatic Spinal Cord Injury

Spinal cord injury (SCI) causes axonal damage and demyelination, neural cell death, and comprehensive tissue loss, resulting in devastating neurological dysfunction. Neural stem/progenitor cell (NSPCs) transplantation provides therapeutic benefits for neural repair in SCI, and glial cell linederived neurotrophic factor (GDNF) has been uncovered to have capability of stimulating axonal regeneration and remyelination after SCI. In this study, to evaluate whether GDNF would augment therapeutic effects of NSPCs for SCI, GDNF-encoding or mock adenoviral vector-transduced human NSPCs (GDNF-or Mock-hNSPCs) were transplanted into the injured thoracic spinal cords of rats at 7 days after SCI. Grafted GDNFhNSPCs showed robust engraftment, long-term survival, an extensive distribution, and increased differentiation into neurons and oligodendroglial cells. Compared with Mock-hNSPC- and vehicle-injected groups, transplantation of GDNF-hNSPCs significantly reduced lesion volume and glial scar formation, promoted neurite outgrowth, axonal regeneration and myelination, increased Schwann cell migration that contributed to the myelin repair, and improved locomotor recovery. In addition, tract tracing demonstrated that transplantation of GDNF-hNSPCs reduced significantly axonal dieback of the dorsal corticospinal tract (dCST), and increased the levels of dCST collaterals, propriospinal neurons (PSNs), and contacts between dCST collaterals and PSNs in the cervical enlargement over that of the controls. Finally grafted GDNF-hNSPCs substantially reversed the increased expression of voltage-gated sodium channels and neuropeptide Y, and elevated expression of GABA in the injured spinal cord, which are involved in the attenuation of neuropathic pain after SCI. These findings suggest that implantation of GDNF-hNSPCs enhances therapeutic efficiency of hNSPCs-based cell therapy for SCI.