Polyglutamine-expanded androgen receptor interferes with TFEB to elicit autophagy defects in SBMA

Design and validation of a reporter mouse to study the dynamic regulation of TFEB and TFE3 activity through in vivo imaging techniques

TFEB and TFE3 belong to the MiT/TFE family of transcription factors that bind identical DNA responsive elements in the regulatory regions of target genes. They are involved in regulating lysosomal biogenesis, function, exocytosis, autophagy, and lipid catabolism. Precise control of TFEB and TFE3 activity is crucial for processes such as senescence, stress response, energy metabolism, and cellular catabolism. Dysregulation of these factors is implicated in various diseases, thus researchers have explored pharmacological approaches to modulate MiT/TFE activity, considering these transcription factors as potential therapeutic targets. However, the physiological complexity of their functions and the lack of suitable in vivo tools have limited the development of selective MiT/TFE modulating agents. Here, we have created a reporter-based biosensor, named CLEARoptimized, facilitating the pharmacological profiling of TFEB- and TFE3-mediated transcription. This innovative tool enables the measurement of TFEB and TFE3 activity in living cells and mice through imaging and biochemical techniques. CLEARoptimized consists of a promoter with six coordinated lysosomal expression and regulation motifs identified through an in-depth bioinformatic analysis of the promoters of 128 TFEB-target genes. The biosensor drives the expression of luciferase and tdTomato reporter genes, allowing the quantification of TFEB and TFE3 activity in cells and in animals through optical imaging and biochemical assays. The biosensor's validity was confirmed by modulating MiT/TFE activity in both cell culture and reporter mice using physiological and pharmacological stimuli. Overall, this study introduces an innovative tool for studying autophagy and lysosomal pathway modulation at various biological levels, from individual cells to the entire organism.Abbreviations: CLEAR: coordinated lysosomal expression and regulation; MAR: matrix attachment regions; MiT: microphthalmia-associated transcription factor; ROI: region of interest; TBS: tris-buffered saline; TF: transcription factor; TFE3: transcription factor binding to IGHM enhancer 3; TFEB: transcription factor EB; TH: tyrosine hydroxylase; TK: thymidine kinase; TSS: transcription start site.

Reviewing the Structure-Function Paradigm in Polyglutamine Disorders: A Synergistic Perspective on Theoretical and Experimental Approaches

Polyglutamine (polyQ) disorders are a group of neurodegenerative diseases characterized by the excessive expansion of CAG (cytosine, adenine, guanine) repeats within host proteins. The quest to unravel the complex diseases mechanism has led researchers to adopt both theoretical and experimental methods, each offering unique insights into the underlying pathogenesis. This review emphasizes the significance of combining multiple approaches in the study of polyQ disorders, focusing on the structure-function correlations and the relevance of polyQ-related protein dynamics in neurodegeneration. By integrating computational/theoretical predictions with experimental observations, one can establish robust structure-function correlations, aiding in the identification of key molecular targets for therapeutic interventions. PolyQ proteins' dynamics, influenced by their length and interactions with other molecular partners, play a pivotal role in the polyQ-related pathogenic cascade. Moreover, conformational dynamics of polyQ proteins can trigger aggregation, leading to toxic assembles that hinder proper cellular homeostasis. Understanding these intricacies offers new avenues for therapeutic strategies by fine-tuning polyQ kinetics, in order to prevent and control disease progression. Last but not least, this review highlights the importance of integrating multidisciplinary efforts to advancing research in this field, bringing us closer to the ultimate goal of finding effective treatments against polyQ disorders.

A Proteomic Approach Identified TFEB as a Key Player in the Protective Action of Novel CB2R Bitopic Ligand FD22a against the Deleterious Effects Induced by β-Amyloid in Glial Cells

Neurodegenerative diseases (NDDs) are progressive multifactorial disorders of the nervous system sharing common pathogenic features, including intracellular misfolded protein aggregation, mitochondrial deficit, and inflammation. Taking into consideration the multifaceted nature of NDDs, development of multitarget-directed ligands (MTDLs) has evolved as an attractive therapeutic strategy. Compounds that target the cannabinoid receptor type II (CB2R) are rapidly emerging as novel effective MTDLs against common NDDs, such as Alzheimer's disease (AD). We recently developed the first CB2R bitopic/dualsteric ligand, namely FD22a, which revealed the ability to induce neuroprotection with fewer side effects. To explore the potential of FD22a as a multitarget drug for the treatment of NDDs, we investigated here its ability to prevent the toxic effect of β-amyloid (Aβ25-35 peptide) on human cellular models of neurodegeneration, such as microglia (HMC3) and glioblastoma (U87-MG) cell lines. Our results displayed that FD22a efficiently prevented Aβ25-35 cytotoxic and proinflammatory effects in both cell lines and counteracted β-amyloid-induced depression of autophagy in U87-MG cells. Notably, a quantitative proteomic analysis of U87-MG cells revealed that FD22a was able to potently stimulate the autophagy-lysosomal pathway (ALP) by activating its master transcriptional regulator TFEB, ultimately increasing the potential of this novel CB2R bitopic/dualsteric ligand as a multitarget drug for the treatment of NDDs.

Unveiling the interplay of AMPK/SIRT1/PGC-1α axis in brain health: Promising targets against aging and NDDs

The escalating prevalence of neurodegenerative diseases (NDDs) within an aging global population presents a pressing challenge. The multifaceted pathophysiological mechanisms underlying these disorders, including oxidative stress, mitochondrial dysfunction, and neuroinflammation, remain complex and elusive. Among these, the AMPK/SIRT1/PGC-1α pathway emerges as a pivotal network implicated in neuroprotection against these destructive processes. This review sheds light on the potential therapeutic implications of targeting this axis, specifically emphasizing the promising role of flavonoids in mitigating NDD-related complications. Expanding beyond conventional pharmacological approaches, the exploration of non-pharmacological interventions such as exercise and calorie restriction (CR), coupled with the investigation of natural compounds, offers a beacon of hope. By strategically elucidating the intricate connections within these pathways, this review aims to pave the ways for novel multi-target agents and interventions, fostering a renewed optimism in the quest to combat and manage the debilitating impacts of NDDs on global health and well-being.

Scalable, optically-responsive human neuromuscular junction model reveals convergent mechanisms of synaptic dysfunction in familial ALS

Neuromuscular junctions (NMJs) are specialized synapses that mediate communication between motor neurons and skeletal muscles and are essential for movement. The degeneration of this system can lead to symptoms observed in neuromuscular and motor neuron diseases. Studying these synapses and their degeneration has proven challenging. Prior NMJ studies heavily relied upon the use of mouse, chick, or isolated primary human cells, which have demonstrated limited fidelity for disease modeling. To enable the study of NMJ dysfunction and model genetic diseases, we, and others, have developed methods to generate human NMJs from pluripotent stem cells (PSCs), embryonic stem cells, and induced pluripotent stem cells. However, published studies have highlighted technical limitations associated with these complex in vitro NMJ models. In this study, we developed a robust PSC-derived motor neuron and skeletal muscle co-culture method, and demonstrated its sensitivity in modeling motor neuron disease. Our method spontaneously and reproducibly forms human NMJs. We developed multiwell-multielectrode array (MEA) parameters to quantify the activity of PSC-derived skeletal muscles, as well as measured the electrophysiological activity of functional human PSC-derived NMJs. We further leveraged our method to morphologically and functionally assess NMJs from the familial amyotrophic lateral sclerosis (fALS) PSCs, C9orf72 hexanucleotide (G4C2)n repeat expansion (HRE), SOD1 A5V , and TDP43 G298S to define the reproducibility and sensitivity of our system. We observed a significant decrease in the numbers and activity of PSC-derived NMJs developed from the different ALS lines compared to their respective controls. Furthermore, we evaluated a therapeutic candidate undergoing clinical trials and observed a variant-dependent rescue of functionality of NMJs. Our newly developed method provides a platform for the systematic investigation of genetic causes of NMJ neurodegeneration and highlights the need for therapeutic avenues to consider patient genotype.

Skeletal muscle TFEB signaling promotes central nervous system function and reduces neuroinflammation during aging and neurodegenerative disease

Skeletal muscle has recently arisen as a regulator of central nervous system (CNS) function and aging, secreting bioactive molecules known as myokines with metabolism-modifying functions in targeted tissues, including the CNS. Here, we report the generation of a transgenic mouse with enhanced skeletal muscle lysosomal and mitochondrial function via targeted overexpression of transcription factor E-B (TFEB). We discovered that the resulting geroprotective effects in skeletal muscle reduce neuroinflammation and the accumulation of tau-associated pathological hallmarks in a mouse model of tauopathy. Muscle-specific TFEB overexpression significantly ameliorates proteotoxicity, reduces neuroinflammation, and promotes transcriptional remodeling of the aged CNS, preserving cognition and memory in aged mice. Our results implicate the maintenance of skeletal muscle function throughout aging in direct regulation of CNS health and disease and suggest that skeletal muscle originating factors may act as therapeutic targets against age-associated neurodegenerative disorders.

The post-translational regulation of transcription factor EB (TFEB) in health and disease

Transcription factor EB (TFEB) is a basic helix-loop-helix leucine zipper transcription factor that acts as a master regulator of lysosomal biogenesis, lysosomal exocytosis, and macro-autophagy. TFEB contributes to a wide range of physiological functions, including mitochondrial biogenesis and innate and adaptive immunity. As such, TFEB is an essential component of cellular adaptation to stressors, ranging from nutrient deprivation to pathogenic invasion. The activity of TFEB depends on its subcellular localisation, turnover, and DNA-binding capacity, all of which are regulated at the post-translational level. Pathological states are characterised by a specific set of stressors, which elicit post-translational modifications that promote gain or loss of TFEB function in the affected tissue. In turn, the resulting increase or decrease in survival of the tissue in which TFEB is more or less active, respectively, may either benefit or harm the organism as a whole. In this way, the post-translational modifications of TFEB account for its otherwise paradoxical protective and deleterious effects on organismal fitness in diseases ranging from neurodegeneration to cancer. In this review, we describe how the intracellular environment characteristic of different diseases alters the post-translational modification profile of TFEB, enabling cellular adaptation to a particular pathological state.

Reduction of nemo-like kinase increases lysosome biogenesis and ameliorates TDP-43-related neurodegeneration

Protein aggregation is a hallmark of many neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). Although mutations in TARDBP, encoding transactive response DNA-binding protein 43 kDa (TDP-43), account for less than 1% of all ALS cases, TDP-43-positive aggregates are present in nearly all ALS patients, including patients with sporadic ALS (sALS) or carrying other familial ALS-causing (fALS-causing) mutations. Interestingly, TDP-43 inclusions are also present in subsets of patients with frontotemporal dementia, Alzheimer's disease, and Parkinson's disease; therefore, methods of activating intracellular protein quality control machinery capable of clearing toxic cytoplasmic TDP-43 species may alleviate disease-related phenotypes. Here, we identify a function of nemo-like kinase (Nlk) as a negative regulator of lysosome biogenesis. Genetic or pharmacological reduction of Nlk increased lysosome formation and improved clearance of aggregated TDP-43. Furthermore, Nlk reduction ameliorated pathological, behavioral, and life span deficits in 2 distinct mouse models of TDP-43 proteinopathy. Because many toxic proteins can be cleared through the autophagy/lysosome pathway, targeted reduction of Nlk represents a potential approach to therapy development for multiple neurodegenerative disorders.

Treponema pallidum promoted microglia apoptosis and prevented itself from clearing by human microglia via blocking autophagic flux

Treponema pallidum (Tp) has a well-known ability to evade the immune system and can cause neurosyphilis by invading the central nervous system (CNS). Microglia are resident macrophages of the CNS that are essential for host defense against pathogens, this study aims to investigate the interaction between Tp and microglia and the potential mechanism. Here, we found that Tp can exert significant toxic effects on microglia in vivo in Tg (mpeg1: EGFP) transgenic zebrafish embryos. Single-cell RNA sequencing results showed that Tp downregulated autophagy-related genes in human HMC3 microglial cells, which is negatively associated with apoptotic gene expression. Biochemical and cell biology assays further established that Tp inhibits microglial autophagy by interfering with the autophagosome-lysosome fusion process. Transcription factor EB (TFEB) is a master regulator of lysosome biogenesis, Tp activates the mechanistic target of rapamycin complex 1 (mTORC1) signaling to inhibit the nuclear translocation of TFEB, leading to decreased lysosomal biogenesis and accumulated autophagosome. Importantly, the inhibition of autophagosome formation reversed Tp-induced apoptosis and promoted microglial clearance of Tp. Taken together, these findings show that Tp blocks autophagic flux by inhibiting TFEB-mediated lysosomal biosynthesis in human microglia. Autophagosome accumulation was demonstrated to be a key mechanism underlying the effects of Tp in promoting apoptosis and preventing itself from clearing by human microglia. This study offers novel perspectives on the potential mechanism of immune evasion employed by Tp within CNS. The results not only establish the pivotal role of autophagy dysregulation in the detrimental effects of Tp on microglial cells but also bear considerable implications for the development of therapeutic strategies against Tp, specifically involving mTORC1 inhibitors and autophagosome formation inhibitors, in the context of neurosyphilis patients.

Transcriptional regulation of autophagy and its implications in human disease

Macroautophagy/autophagy is a conserved catabolic pathway that is vital for maintaining cell homeostasis and promoting cell survival under stressful conditions. Dysregulation of autophagy is associated with a variety of human diseases, such as cancer, neurodegenerative diseases, and metabolic disorders. Therefore, this pathway must be precisely regulated at multiple levels, involving epigenetic, transcriptional, post-transcriptional, translational, and post-translational mechanisms, to prevent inappropriate autophagy activity. In this review, we focus on autophagy regulation at the transcriptional level, summarizing the transcription factors that control autophagy gene expression in both yeast and mammalian cells. Because the expression and/or subcellular localization of some autophagy transcription factors are altered in certain diseases, we also discuss how changes in transcriptional regulation of autophagy are associated with human pathophysiologies.

Bicalutamide and Trehalose Ameliorate Spinal and Bulbar Muscular Atrophy Pathology in Mice

Spinal and bulbar muscular atrophy (SBMA) is characterized by motor neuron (MN) degeneration that leads to slowly progressive muscle weakness. It is considered a neuromuscular disease since muscle has a primary role in disease onset and progression. SBMA is caused by a CAG triplet repeat expansion in the androgen receptor (AR) gene. The translated poly-glutamine (polyQ) tract confers a toxic gain of function to the mutant AR altering its folding, causing its aggregation into intracellular inclusions, and impairing the autophagic flux. In an in vitro SBMA neuronal model, we previously showed that the antiandrogen bicalutamide and trehalose, a natural disaccharide stimulating autophagy, block ARpolyQ activation, reduce its nuclear translocation and toxicity and facilitate the autophagic degradation of cytoplasmic AR aggregates. Here, in a knock-in SBMA mouse model (KI AR113Q), we show that bicalutamide and trehalose ameliorated SBMA pathology. Bicalutamide reversed the formation of the AR insoluble forms in KI AR113Q muscle, preventing autophagic flux blockage. We demonstrated that apoptosis is activated in KI AR113Q muscle, and that both compounds prevented its activation. We detected a decrease of mtDNA and an increase of OXPHOS enzymes, already at early symptomatic stages; these alterations were reverted by trehalose. Overall, bicalutamide and/or trehalose led to a partial recovery of muscle morphology and function, and improved SBMA mouse motor behavior, inducing an extension of their survival. Thus, bicalutamide and trehalose, by counteracting ARpolyQ toxicity in skeletal muscle, are valuable candidates for future clinical trials in SBMA patients.

Helicobacter pylori-positive chronic atrophic gastritis and cellular senescence

BACKGROUND

Chronic atrophic gastritis (CAG) is a pathological stage in the Correa's cascade, whereby Helicobacter pylori (H. pylori) infection is the primary cause. Cellular senescence is an inducing factor for cancer occurrence and cellular senescence is an obvious phenomenon in gastric mucosal tissues of H. pylori-positive CAG patients.

METHODS

In this review, we collated the information on cellular senescence and H. pylori-positive CAG.

RESULTS

At present, only a few studies have observed the effect of cellular senescence on precancerous lesions. In combination with the latest research, this review has collated the information on cellular senescence and H. pylori-positive CAG from four aspects- telomere shortening, DNA methylation, increased reacive oxygen species (ROS) production, and failure of autophagy.

CONCLUSION

This is expected to be helpful for exploring the relevant mechanisms underlying inflammatory cancerous transformation and formulating appropriate treatment strategies.

Transcription factor EB as a key molecular factor in human health and its implication in diseases

Transcription factor EB, as a component of the microphthalmia family of transcription factors, has been demonstrated to be a key controller of autophagy-lysosomal biogenesis. Transcription factor EB is activated by stressors such as nutrition and deprivation of growth factors, hypoxia, lysosomal stress, and mitochondrial injury. To achieve the ultimate functional state, it is controlled in a variety of modes, such as in its rate of transcription, post-transcriptional control, and post-translational alterations. Due to its versatile role in numerous signaling pathways, including the Wnt, calcium, AKT, and mammalian target of rapamycin complex 1 signaling pathways, transcription factor EB-originally identified to be an oncogene-is now well acknowledged as a regulator of a wide range of physiological systems, including autophagy-lysosomal biogenesis, response to stress, metabolism, and energy homeostasis. The well-known and recently identified roles of transcription factor EB suggest that this protein might play a central role in signaling networks in a number of non-communicable illnesses, such as cancer, cardiovascular disorders, drug resistance mechanisms, immunological disease, and tissue growth. The important developments in transcription factor EB research since its first description are described in this review. This review helps to advance transcription factor EB from fundamental research into therapeutic and regenerative applications by shedding light on how important a role it plays in human health and disease at the molecular level.

An mTORC1-mediated negative feedback loop constrains amino acid-induced FLCN-Rag activation in renal cells with TSC2 loss

The mechanistic target of rapamycin complex 1 (mTORC1) integrates inputs from growth factors and nutrients, but how mTORC1 autoregulates its activity remains unclear. The MiT/TFE transcription factors are phosphorylated and inactivated by mTORC1 following lysosomal recruitment by RagC/D GTPases in response to amino acid stimulation. We find that starvation-induced lysosomal localization of the RagC/D GAP complex, FLCN:FNIP2, is markedly impaired in a mTORC1-sensitive manner in renal cells with TSC2 loss, resulting in unexpected TFEB hypophosphorylation and activation upon feeding. TFEB phosphorylation in TSC2-null renal cells is partially restored by destabilization of the lysosomal folliculin complex (LFC) induced by FLCN mutants and is fully rescued by forced lysosomal localization of the FLCN:FNIP2 dimer. Our data indicate that a negative feedback loop constrains amino acid-induced, FLCN:FNIP2-mediated RagC activity in renal cells with constitutive mTORC1 signaling, and the resulting MiT/TFE hyperactivation may drive oncogenesis with loss of the TSC2 tumor suppressor.

The role of autophagy-lysosomal pathway in motor neuron diseases

Motor neuron diseases (MNDs) include a broad group of diseases in which neurodegeneration mainly affects upper and/or lower motor neurons (MNs). Although the involvement of specific MNs, symptoms, age of onset, and progression differ in MNDs, the main pathogenic mechanism common to most MNDs is represented by proteostasis alteration and proteotoxicity. This pathomechanism may be directly related to mutations in genes encoding proteins involved in the protein quality control system, particularly the autophagy-lysosomal pathway (ALP). Alternatively, proteostasis alteration can be caused by aberrant proteins that tend to misfold and to aggregate, two related processes that, over time, cannot be properly handled by the ALP. Here, we summarize the main ALP features, focusing on different routes utilized to deliver substrates to the lysosome and how the various ALP pathways intersect with the intracellular trafficking of membranes and vesicles. Next, we provide an overview of the mutated genes that have been found associated with MNDs, how these gene products are involved in different steps of ALP and related processes. Finally, we discuss how autophagy can be considered a valid therapeutic target for MNDs treatment focusing on traditional autophagy modulators and on emerging approaches to overcome their limitations.

The evolution and polymorphism of mono-amino acid repeats in androgen receptor and their regulatory role in health and disease

Androgen receptor (AR) is a key member of nuclear hormone receptors with the longest intrinsically disordered N-terminal domain (NTD) in its protein family. There are four mono-amino acid repeats (polyQ1, polyQ2, polyG, and polyP) located within its NTD, of which two are polymorphic (polyQ1 and polyG). The length of both polymorphic repeats shows clinically important correlations with disease, especially with cancer and neurodegenerative diseases, as shorter and longer alleles exhibit significant differences in expression, activity and solubility. Importantly, AR has also been shown to undergo condensation in the nucleus by liquid-liquid phase separation, a process highly sensitive to protein solubility and concentration. Nonetheless, in prostate cancer cells, AR variants also partition into transcriptional condensates, which have been shown to alter the expression of target gene products. In this review, we summarize current knowledge on the link between AR repeat polymorphisms and cancer types, including mechanistic explanations and models comprising the relationship between condensate formation, polyQ1 length and transcriptional activity. Moreover, we outline the evolutionary paths of these recently evolved amino acid repeats across mammalian species, and discuss new research directions with potential breakthroughs and controversies in the literature.

The regulatory mechanism and therapeutic potential of transcription factor EB in neurodegenerative diseases

The autophagy-lysosomal pathway (ALP) is involved in the degradation of protein aggregates and damaged organelles. Transcription factor EB (TFEB), a major regulator of ALP, has emerged as a leading factor in addressing neurodegenerative disease pathology, including Alzheimer's disease (AD), Parkinson's disease (PD), PolyQ diseases, and Amyotrophic lateral sclerosis (ALS). In this review, we delineate the regulation of TFEB expression and its functions in ALP. Dysfunctions of TFEB and its role in the pathogenesis of several neurodegenerative diseases are reviewed. We summarize the protective effects and molecular mechanisms of some TFEB-targeted agonists in neurodegenerative diseases. We also offer our perspective on analyzing the pros and cons of these agonists in the treatment of neurodegenerative diseases from the perspective of drug development. More studies on the regulatory mechanisms of TFEB in other biological processes will aid our understanding of the application of TFEB-targeted therapy in neurodegeneration.

A survey of protein interactions and posttranslational modifications that influence the polyglutamine diseases

The presence and aggregation of misfolded proteins has deleterious effects in the nervous system. Among the various diseases caused by misfolded proteins is the family of the polyglutamine (polyQ) disorders. This family comprises nine members, all stemming from the same mutation—the abnormal elongation of a polyQ repeat in nine different proteins—which causes protein misfolding and aggregation, cellular dysfunction and disease. While it is the same type of mutation that causes them, each disease is distinct: it is influenced by regions and domains that surround the polyQ repeat; by proteins with which they interact; and by posttranslational modifications they receive. Here, we overview the role of non-polyQ regions that control the pathogenicity of the expanded polyQ repeat. We begin by introducing each polyQ disease, the genes affected, and the symptoms experienced by patients. Subsequently, we provide a survey of protein-protein interactions and posttranslational modifications that regulate polyQ toxicity. We conclude by discussing shared processes and pathways that bring some of the polyQ diseases together and may serve as common therapeutic entry points for this family of incurable disorders.

A lysosomal regulatory circuit essential for the development and function of microglia

As the primary phagocytic cells of the central nervous system, microglia exquisitely regulate their lysosomal activity to facilitate brain development and homeostasis. However, mechanisms that coordinate lysosomal activity with microglia development, chemotaxis, and function remain unclear. Here, we show that embryonic macrophages require the lysosomal guanosine triphosphatase (GTPase) RagA and the GTPase-activating protein Folliculin to colonize the brain in zebrafish. We demonstrate that embryonic macrophages in rraga mutants show increased expression of lysosomal genes but display significant down-regulation of immune- and chemotaxis-related genes. Furthermore, we find that RagA and Folliculin repress the key lysosomal transcription factor Tfeb and its homologs Tfe3a and Tfe3b in the macrophage lineage. Using RNA sequencing, we establish that Tfeb and Tfe3 are required for activation of lysosomal target genes under conditions of stress but not for basal expression of lysosomal pathways. Collectively, our data define a lysosomal regulatory circuit essential for macrophage development and function in vivo.

Skeletal Muscle Pathogenesis in Polyglutamine Diseases

Polyglutamine diseases are characterized by selective dysfunction and degeneration of specific types of neurons in the central nervous system. In addition, nonneuronal cells can also be affected as a consequence of primary degeneration or due to neuronal dysfunction. Skeletal muscle is a primary site of toxicity of polyglutamine-expanded androgen receptor, but it is also affected in other polyglutamine diseases, more likely due to neuronal dysfunction and death. Nonetheless, pathological processes occurring in skeletal muscle atrophy impact the entire body metabolism, thus actively contributing to the inexorable progression towards the late and final stages of disease. Skeletal muscle atrophy is well recapitulated in animal models of polyglutamine disease. In this review, we discuss the impact and relevance of skeletal muscle in patients affected by polyglutamine diseases and we review evidence obtained in animal models and patient-derived cells modeling skeletal muscle.

Exploring the Role of Posttranslational Modifications in Spinal and Bulbar Muscular Atrophy

Spinal and Bulbar Muscular Atrophy (SBMA) is an X-linked adult-onset progressive neuromuscular disease that affects the spinal and bulbar motor neurons and skeletal muscles. SBMA is caused by expansion of polymorphic CAG trinucleotide repeats in the Androgen Receptor (AR) gene, resulting in expanded glutamine tract in the AR protein. Polyglutamine (polyQ) expansion renders the mutant AR protein toxic, resulting in the formation of mutant protein aggregates and cell death. This classifies SBMA as one of the nine known polyQ diseases. Like other polyQ disorders, the expansion of the polyQ tract in the AR protein is the main genetic cause of the disease; however, multiple other mechanisms besides the polyQ tract expansion also contribute to the SBMA disease pathophysiology. Posttranslational modifications (PTMs), including phosphorylation, acetylation, methylation, ubiquitination, and SUMOylation are a category of mechanisms by which the functionality of AR has been found to be significantly modulated and can alter the neurotoxicity of SBMA. This review summarizes the different PTMs and their effects in regulating the AR function and discusses their pathogenic or protective roles in context of SBMA. This review also includes the therapeutic approaches that target the PTMs of AR in an effort to reduce the mutant AR-mediated toxicity in SBMA.

AR cooperates with SMAD4 to maintain skeletal muscle homeostasis

Androgens and androgen-related molecules exert a plethora of functions across different tissues, mainly through binding to the transcription factor androgen receptor (AR). Despite widespread therapeutic use and misuse of androgens as potent anabolic agents, the molecular mechanisms of this effect on skeletal muscle are currently unknown. Muscle mass in adulthood is mainly regulated by the bone morphogenetic protein (BMP) axis of the transforming growth factor (TGF)-β pathway via recruitment of mothers against decapentaplegic homolog 4 (SMAD4) protein. Here we show that, upon activation, AR forms a transcriptional complex with SMAD4 to orchestrate a muscle hypertrophy programme by modulating SMAD4 chromatin binding dynamics and enhancing its transactivation activity. We challenged this mechanism of action using spinal and bulbar muscular atrophy (SBMA) as a model of study. This adult-onset neuromuscular disease is caused by a polyglutamine expansion (polyQ) in AR and is characterized by progressive muscle weakness and atrophy secondary to a combination of lower motor neuron degeneration and primary muscle atrophy. Here we found that the presence of an elongated polyQ tract impairs AR cooperativity with SMAD4, leading to an inability to mount an effective anti-atrophy gene expression programme in skeletal muscle in response to denervation. Furthermore, adeno-associated virus, serotype 9 (AAV9)-mediated muscle-restricted delivery of BMP7 is able to rescue the muscle atrophy in SBMA mice, supporting the development of treatments able to fine-tune AR-SMAD4 transcriptional cooperativity as a promising target for SBMA and other conditions associated with muscle loss.

Material properties of phase-separated TFEB condensates regulate the autophagy-lysosome pathway

Very little is known about how the material properties of protein condensates assembled via liquid–liquid phase separation (LLPS) are maintained and affect physiological functions. Here we show that liquid-like condensates of the transcription factor TFEB exhibit low fusion propensity in vitro and in living cells. We directly measured the attraction force between droplets, and we characterized the interfacial tension, viscosity, and elasticity of TFEB condensates. TFEB condensates contain rigid interfacial boundaries that govern their interaction behaviors. Several small molecules, including Ro-3306, modify the material properties of TFEB condensates, increasing their size and fusion propensity. These compounds promote lysosomal biogenesis and function in a TFEB-dependent manner without changing its cytoplasmic-nuclear translocation. Ro-3306 promotes autophagy activity, facilitating degradation of toxic protein aggregates. Our study helps explain how protein condensates are maintained as physically separate entities and reveals that the material properties of TFEB condensates can be harnessed to modulate TFEB activity.

Elabela ameliorates doxorubicin-induced cardiotoxicity by promoting autophagic flux through TFEB pathway

Doxorubicin (DOX) is a widely used and effective antineoplastic drug; however, its clinical application is limited by cardiotoxicity. A safe and effective strategy to prevent from doxorubicin-induced cardiotoxicity (DIC) is still beyond reach. Elabela (ELA), a new APJ ligand, has exerted cardioprotective effect against multiple cardiovascular diseases. Here, we asked whether ELA alleviates DIC. Mice were injected with DOX to established acute DIC. In vivo studies were assessed with echocardiography, serum cTnT and CK-MB, HW/BW ratio and WGA staining. Cell death and atrophy were measured by AM/PI staining and phalloidin staining respectively in vitro. Autophagic flux was monitored with Transmission electron microscopy in vivo, as well as LysoSensor and mRFP-GFP-LC3 puncta in vitro. Our results showed that ELA improved cardiac dysfunction in DIC mice. ELA administration also attenuated cell death and atrophy in DOX-challenged neonatal rat cardiomyocytes (NRCs). Additionally, we found that ELA restored DOX-induced autophagic flux blockage, which was evidenced by the reverse of p62 and LC3II, improvement of lysosome function and accelerated degradation of accumulated autolysosomes. Chloroquine, a classical autophagic flux inhibitor, blunted the improvement of ELA on cardiac dysfunction. At last, we revealed that ELA reversed DOX-induced downregulation of transcription factor EB (TFEB), and silencing TFEB by siRNA abrogated the effects of ELA on autophagic flux as well as cell death and atrophy in NRCs. In conclusion, this study indicated that ELA ameliorated DIC through enhancing autophagic flux via activating TFEB. ELA may become a potential target against DIC.

Ion channels and neuronal excitability in polyglutamine neurodegenerative diseases

Polyglutamine (polyQ) diseases are a family composed of nine neurodegenerative inherited disorders (NDDs) caused by pathological expansions of cytosine-adenine-guanine (CAG) trinucleotide repeats which encode a polyQ tract in the corresponding proteins. CAG polyQ repeat expansions produce neurodegeneration via multiple downstream mechanisms; among those the neuronal activity underlying the ion channels is affected directly by specific channelopathies or indirectly by secondary dysregulation. In both cases, the altered excitability underlies to gain- or loss-of-function pathological effects. Here we summarize the repertoire of ion channels in polyQ NDDs emphasizing the biophysical features of neuronal excitability and their pathogenic role. The aim of this review is to point out the value of a deeper understanding of those functional mechanisms and processes as crucial elements for the designing and targeting of novel therapeutic avenues.

The nerve-tumour regulatory axis GDNF-GFRA1 promotes tumour dormancy, imatinib resistance and local recurrence of gastrointestinal stromal tumours by achieving autophagic flux

Complete surgical resection, accessible therapeutic targets and effective tyrosine kinase inhibitors (TKIs) have not completely cured gastrointestinal stromal tumours (GISTs), with most patients suffering from residual tumours and recurrence. The existence of nerve infiltration in GIST provides a way for tumour cells to escape local resection and systemic targeted therapy, which may challenge the previous understanding of its behaviour patterns and inspire the development of more radical excision and more precise targeted therapy. Moreover, tumour dormancy has emerged as a major cause of drug resistance and tumour relapse. Among these pathways, the nerve-tumour regulatory axis GDNF-GFRA1 is activated in GISTs, assists tumour cells in achieving dormancy and protects them from apoptosis under environmental stress by enhancing autophagic flux. The concrete mechanism is that the GDNF-regulating interaction between GFRA1 and the lysosomal calcium channel MCOLN1 activates Ca²⁺-dependent TFEB signalling. Activated TFEB transcriptionally regulates intracellular lysosome levels, which could achieve feedback upregulation of cellular autophagy flux during TKI treatment. This dormancy-transition axis fills parts of the mechanistic vacancy before the onset of secondary mutations, and strategies for TKIs combined with targeting GFRA1-dependent autophagy have distinct promise as prospective clinical therapies.

Exploring Motor Neuron Diseases Using iPSC Platforms

The degeneration of motor neurons is a pathological hallmark of motor neuron diseases (MNDs), but emerging evidence suggests that neuronal vulnerability extends well beyond this cell subtype. The ability to assess motor function in the clinic is limited to physical examination, electrophysiological measures, and tissue-based or neuroimaging techniques which lack the resolution to accurately assess neuronal dysfunction as the disease progresses. Spinal muscular atrophy (SMA), spinal and bulbar muscular atrophy (SBMA), hereditary spastic paraplegia (HSP), and amyotrophic lateral sclerosis (ALS) are all MNDs with devastating clinical outcomes that contribute significantly to disease burden as patients are no longer able to carry out normal activities of daily living. The critical need to accurately assess the cause and progression of motor neuron dysfunction, especially in the early stages of those diseases, has motivated the use of human iPSC-derived motor neurons (hiPSC-MN) to study the neurobiological mechanisms underlying disease pathogenesis and to generate platforms for therapeutic discovery and testing. As our understanding of MNDs has grown, so too has our need to develop more complex in vitro models which include hiPSC-MN co-cultured with relevant non-neuronal cells in 2D as well as in 3D organoid and spheroid systems. These more complex hiPSC-derived culture systems have led to the implementation of new technologies, including microfluidics, multielectrode array, and machine learning which offer novel insights into the functional correlates of these emerging model systems.

Amyloid-like aggregating proteins cause lysosomal defects in neurons via gain-of-function toxicity

Using cryo-ET, cell biology, and proteomics, this study shows that aggregating proteins impair the autophagy-lysosomal pathway in neurons by sequestering a subunit of the AP-3 adaptor complex.

The autophagy-lysosomal pathway is impaired in many neurodegenerative diseases characterized by protein aggregation, but the link between aggregation and lysosomal dysfunction remains poorly understood. Here, we combine cryo-electron tomography, proteomics, and cell biology studies to investigate the effects of protein aggregates in primary neurons. We use artificial amyloid-like β-sheet proteins (β proteins) to focus on the gain-of-function aspect of aggregation. These proteins form fibrillar aggregates and cause neurotoxicity. We show that late stages of autophagy are impaired by the aggregates, resulting in lysosomal alterations reminiscent of lysosomal storage disorders. Mechanistically, β proteins interact with and sequester AP-3 μ1, a subunit of the AP-3 adaptor complex involved in protein trafficking to lysosomal organelles. This leads to destabilization of the AP-3 complex, missorting of AP-3 cargo, and lysosomal defects. Restoring AP-3μ1 expression ameliorates neurotoxicity caused by β proteins. Altogether, our results highlight the link between protein aggregation, lysosomal impairments, and neurotoxicity.

The Role and Regulatory Mechanism of Transcription Factor EB in Health and Diseases

Transcription factor EB (TFEB) is a member of the microphthalmia-associated transcription factor/transcription factor E (MiTF/TFE) family and critically involved in the maintenance of structural integrity and functional balance of multiple cells. In this review, we described the effects of post-transcriptional modifications, including phosphorylation, acetylation, SUMOylation, and ubiquitination, on the subcellular localization and activation of TFEB. The activated TFEB enters into the nucleus and induces the expressions of targeted genes. We then presented the role of TFEB in the biosynthesis of multiple organelles, completion of lysosome-autophagy pathway, metabolism regulation, immune, and inflammatory responses. This review compiles existing knowledge in the understanding of TFEB regulation and function, covering its essential role in response to cellular stress. We further elaborated the involvement of TFEB dysregulation in the pathophysiological process of various diseases, such as the catabolic hyperactivity in tumors, the accumulation of abnormal aggregates in neurodegenerative diseases, and the aberrant host responses in inflammatory diseases. In this review, multiple drugs have also been introduced, which enable regulating the translocation and activation of TFEB, showing beneficial effects in mitigating various disease models. Therefore, TFEB might serve as a potential therapeutic target for human diseases. The limitation of this review is that the mechanism of TFEB-related human diseases mainly focuses on its association with lysosome and autophagy, which needs deep description of other mechanism in diseases progression after getting more advanced information.

Molecular targets and approaches to restore autophagy and lysosomal capacity in neurodegenerative disorders

Autophagy is a catabolic process that promotes cellular fitness by clearing aggregated protein species, pathogens and damaged organelles through lysosomal degradation. The autophagic process is particularly important in the nervous system where post-mitotic neurons rely heavily on protein and organelle quality control in order to maintain cellular health throughout the lifetime of the organism. Alterations of autophagy and lysosomal function are hallmarks of various neurodegenerative disorders. In this review, we conceptualize some of the mechanistic and genetic evidence pointing towards autophagy and lysosomal dysfunction as a causal driver of neurodegeneration. Furthermore, we discuss rate-limiting pathway nodes and potential approaches to restore pathway activity, from autophagy initiation, cargo sequestration to lysosomal capacity.

The unfolded protein response regulates hepatic autophagy by sXBP1-mediated activation of TFEB

Defective macroautophagy/autophagy and a failure to initiate the adaptive unfolded protein response (UPR) in response to the endoplasmic reticulum (ER) stress contributes to obesity-associated metabolic dysfunction. However, whether and how unresolved ER stress leads to defects in the autophagy pathway and to the progression of obesity-associated hepatic pathologies remains unclear. Obesity suppresses the expression of hepatic spliced XBP1 (X-box binding protein 1; sXBP1), the key transcription factor that promotes the adaptive UPR. Our RNA-seq analysis revealed that sXBP1 regulates genes involved in lysosomal function in the liver under fasting conditions. Chromatin immunoprecipitation (ChIP) analyzes of both primary hepatocytes and whole livers further showed that sXBP1 occupies the -743 to -523 site of the promoter of Tfeb (transcription factor EB), a master regulator of autophagy and lysosome biogenesis. Notably, this occupancy was significantly reduced in livers from patients with steatosis. In mice, hepatic deletion of Xbp1 (xbp1 LKO) suppressed the transcription of Tfeb as well as autophagy, whereas hepatic overexpression of sXbp1 enhanced Tfeb transcription and autophagy. Moreover, overexpression of Tfeb in the xbp1 LKO mouse liver ameliorated glucose intolerance and steatosis in mice with diet-induced obesity (DIO). Conversely, loss of TFEB function impaired the protective role of sXBP1 in hepatic steatosis in mice with DIO. These data indicate that sXBP1-Tfeb signaling has direct functional consequences in the context of obesity. Collectively, our data provide novel insight into how two organelle stress responses are integrated to protect against obesity-associated metabolic dysfunction.Abbreviations: AAV8: adeno-associated virus serotype 8; ACTB: actin, beta; ANOVA: analysis of variance; ATF6: activating transcription factor-6; ATG: autophagy related; BECN1: beclin 1; BMI: body mass index; ChIP: chromatin immunoprecipitation; CLEAR: coordinated lysosomal expression and regulation; Cre: cre recombinase; DIO: diet-induced obesity; EBSS: Earle's balanced salt solution; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; ERN1/IRE1: endoplasmic reticulum (ER) to nucleus signaling 1; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; HFD: high-fat diet; h: hours; HSCs: hepatic stellate cells; INS: insulin; L/A: ammonium chloride and leupeptin; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; mRNA: messenger RNA; NAFLD: nonalcoholic fatty liver disease; NASH: nonalcoholic steatohepatitis; RD: regular diet; RFP: red fluorescent protein; SERPINA7/TBG: serpin family A member 7; SQSTM1/p62: sequestome 1; sXbp1 LOE: liver-specific overexpression of spliced Xbp1; TFEB: transcription factor EB; TG: thapsigargin; TN: tunicamycin; UPR: unfolded protein response; wks: weeks; WT: wild type; XBP1: X-box binding protein 1; xbp1 LKO: liver-specific Xbp1 knockout.

TFEB protein expression is reduced in aged brains and its overexpression mitigates senescence-associated biomarkers and memory deficits in mice

Identification of molecules and molecular pathways that can ameliorate aging-associated decline in cognitive function is crucial. Here we report that the protein levels of transcription factor EB (TFEB) were markedly reduced in both the cytosolic and nuclear fractions of the frontal cortex and hippocampus at 18-months of age relative to 6 months in the normal male wild-type mice. In the transgenic mice with ectopic expression of flag-TFEB in neurons, we observed that the levels of actin-normalized PGC1α and mtTFA were significantly increased in both the cortex and the hippocampus. Additionally, we confirmed increased mitochondria numbers in the flag-TFEB mice by transmission electron microscopy. Most importantly, TFEB expression in the 18-month-old transgenic mice mitigated markers of senescence including P16INK4a, γ-H2AX, and lamin B1, and improved memory skills implying that TFEB may exert an anti-aging effect by modulating neuronal senescence. Taken together these data strongly support that TFEB can be a useful therapeutic target for brain senescent cells to help overcome the age-related issues in cognition and possibly, achieve healthy aging.

Role of Polyphenols on Gut Microbiota and the Ubiquitin-Proteasome System in Neurodegenerative Diseases

Today, neurodegenerative diseases have become a remarkable public health challenge due to their direct relation with aging. Accordingly, understanding the molecular and cellular mechanisms occurring in the pathogenesis of them is essential. Both protein aggregations as a result of the ubiquitin-proteasome system (UPS) inefficiency and gut microbiota alternation are the main pathogenic hallmarks. Polyphenols upregulating this system may decrease the developing rate of neurodegenerative diseases. Most of the dietary intake of polyphenols is converted into other microbial metabolites, which have completely different biological properties from the original polyphenols and should be thoroughly investigated. Herein, several prevalent neurodegenerative diseases are pinpointed to explain the role of gut microbiota alternations and the role of molecular changes, especially UPS down-regulation in their pathogenesis. Some of the most important polyphenols found in our diet are explained along with their microbial metabolites in the body.

Molecular pathogenesis of spinal bulbar muscular atrophy (Kennedy's disease) and avenues for treatment

PURPOSE OF REVIEW

The aim of this study was to illustrate the current understanding and avenues for developing treatment in spinal and bulbar muscular atrophy (SBMA), an inherited neuromuscular disorder caused by a CAG trinucleotide repeat expansion in the androgen receptor (AR) gene.

RECENT FINDINGS

Important advances have been made in characterizing the molecular mechanism of the disease, including the disruption of protein homeostasis, intracellular trafficking and signalling pathways. Biomarkers such as MRI quantification of muscle volume and fat fraction have been used to track disease progression, and will be useful in future clinical studies. Therapies tested and under development have been based on diverse strategies, including targeting mutant AR gene expression, stability and activity, and pathways that mitigate disease toxicity.

SUMMARY

We provide an overview of the recent advances in understanding the SBMA disease mechanism and highlight efforts to translate these insights into well tolerated and effective therapy.

Coxsackievirus B3 targets TFEB to disrupt lysosomal function

Coxsackievirus B3 (CVB3) is a prevalent etiological agent for viral myocarditis and neurological disorders, particularly in infants and young children. Virus-encoded proteinases have emerged as cytopathic factors that contribute to disease pathogenesis in part through targeting the cellular recycling machinery of autophagy. Although it is appreciated that CVB3 can usurp cellular macroautophagy/autophagy for pro-viral functions, the precise mechanisms by which viral proteinases disrupt autophagy remain incompletely understood. Here we identified TFEB (transcription factor EB), a master regulator of autophagy and lysosome biogenesis, as a novel target of CVB3 proteinase 3 C. Time-course infections uncovered a significant loss of full-length TFEB and the emergence of a lower-molecular mass (~63 kDa) fragment. Cellular and in vitro cleavage assays revealed the involvement of viral proteinase 3 C in the proteolytic processing of TFEB, while site-directed mutagenesis identified the site of cleavage after glutamine 60. Assessment of TFEB transcriptional activity using a reporter construct discovered a loss of function of the cleavage fragment despite nuclear localization and retaining of the ability of DNA and protein binding. Furthermore, we showed that CVB3 infection was also able to trigger cleavage-independent nuclear translocation of TFEB that relied on the serine-threonine phosphatase PPP3/calcineurin. Finally, we demonstrated that both TFEB and TFEB [Δ60] serve roles in viral egress albeit through differing mechanisms. Collectively, this study reveals that CVB3 targets TFEB for proteolytic processing to disrupt host lysosomal function and enhance viral infection.

Abbreviations:ACTB: actin beta; CLEAR: coordinated lysosomal enhancement and regulation; CVB3: coxsackievirus B3; DAPI: 4′,6-diamidino-2-phenylindole; GFP: green fluorescent protein; LAMP1: lysosomal associated membrane protein 1; LTR: LysoTracker Red; PPP3/calcineurin: protein phosphatase 3; PPP3CA: protein phosphatase 3 catalytic subunit A; p-TFEB: phospho-Ser211 TFEB; si-CON: scramble control siRNA; TFEB: transcription factor EB; TFEB [Δ60]: TFEB cleavage fragment that lacks the first 60 amino acids; VP1: viral capsid protein 1

Systemic Administration of Fibroblast Growth Factor 21 Improves the Recovery of Spinal Cord Injury (SCI) in Rats and Attenuates SCI-Induced Autophagy

Protecting the death of nerve cells is an essential tactic for spinal cord injury (SCI) repair. Recent studies show that nerve growth factors can reduce the death of nerve cells and promote the healing of nerve injury. To investigate the conducive effect of fibroblast growth factor 21 (FGF21) on SCI repair. FGF21 proteins were systemically delivered into rat model of SCI via tail vein injection. We found that administration of FGF21 significantly promoted the functional recovery of SCI as assessed by BBB scale and inclined plane test, and attenuated cell death in the injured area by histopathological examination with Nissl staining. This was accompanied with increased expression of NeuN, GAP43 and NF200, and deceased expression of GFAP. Interestingly, FGF21 was found to attenuate the elevated expression level of the autophagy marker LC3-II (microtubules associated protein 1 light chain 3-II) induced by SCI in a dose-dependent manner. These data show that FGF21 promotes the functional recovery of SCI via restraining injury-induced cell autophagy, suggesting that systemic administration of FGF21 could have a therapeutic potential for SCI repair.

20-Deoxyingenol alleviates osteoarthritis by activating TFEB in chondrocytes

Osteoarthritis (OA) is an age-related degenerative disease and currently cannot be cured. Transcription factor EB (TFEB) is one of the major transcriptional factors that regulates autophagy and lysosomal biogenesis. TFEB has been shown to be an effective therapeutic target for many diseases including OA. The current study explores the therapeutic effects of 20-Deoxyingenol (20-DOI) on OA as well as its working mechanism on TFEB regulation. The in vitro study showed that 20-DOI may suppress apoptosis and senescence induced by oxidative stress in chondrocytes; it may also promote the nuclear localization of TFEB in chondrocytes. Knock-down of TFEB compromised the effects of 20-DOI on apoptosis and senescence. The in vivo study demonstrated that 20-DOI may postpone the progression of OA in mouse destabilization of the medial meniscus (DMM) model; it may also suppress apoptosis and senescence and promote the nuclear localization of TFEB in chondrocytes in vivo. This work suggests that 20-Deoxyingenol may alleviate osteoarthritis by activating TFEB in chondrocytes, while 20-DOI may become a potential drug for OA therapy.

Autophagy-Dependent Increased ADAM10 Mature Protein Induced by TFEB Overexpression Is Mediated Through PPARα

Nonamyloidogenic processing of amyloid precursor protein (APP) by augmenting ADAM10 is a promising therapeutic strategy for Alzheimer's disease (AD). Therefore identification of molecular pathways that regulate ADAM10 expression is crucial. Autophagy is strongly dysregulated in AD, and TFEB was recently shown to be a master regulator of autophagy-lysosome pathway (ALP). Here, we report that TFEB expression in HeLa cells increased ADAM10 mature form by 72% (p < 0.01, n = 4), while TFEB knockdown by CRISPR strategy reduced ADAM10 mature form by 36% (p < 0.05, n = 4). Autophagy inhibition by 3-methyladenine (3-MA), but not bafilomycin A1 (BAF1), reduced ADAM10 mature form by 49% (p < 0.05, n = 4) in the TFEB expressing HeLa cells. Autophagy activation by 3 h of starvation increased ADAM10 to 91% (p < 0.001, n = 6) relative to 51% (p < 0.01, n = 6) in the nutrient-fed cells. Further, siRNAs targeted against PPARα in HeLa cells decreased ADAM10 levels by 28% (p < 0.05, n = 6) relative to the cells treated with scrambled siRNAs. Further, incubation of EGFP-TFEB expressing HeLa cells with PPARα antagonist, but not PPARβ or PPARγ antagonists, prevented TFEB-induced increase in ADAM10 levels. Importantly, flag-TFEB expression in the brain also increased ADAM10 by 60% (p < 0.05, n = 3) in the cortical and 34% (p < 0.001, n = 3) in the hippocampal homogenates. ADAM10 activity also increased by 57% (p < 0.01, n = 3) in the HeLa cells. Finally, TFEB-induced ADAM10 potentiation led to increased secretion of sAPPα by 154% (p < 0.001, n = 3) in the cortex and 62% (p < 0.001, n = 3) in the hippocampus. Thus, TFEB expression enhances nonamyloidogenic processing of APP. In conclusion, TFEB expression induces ADAM10 in an autophagy-dependent manner through PPARα.

Machinery, regulation and pathophysiological implications of autophagosome maturation

Autophagy is a versatile degradation system for maintaining cellular homeostasis whereby cytosolic materials are sequestered in a double-membrane autophagosome and subsequently delivered to lysosomes, where they are broken down. In multicellular organisms, newly formed autophagosomes undergo a process called 'maturation', in which they fuse with vesicles originating from endolysosomal compartments, including early/late endosomes and lysosomes, to form amphisomes, which eventually become degradative autolysosomes. This fusion process requires the concerted actions of multiple regulators of membrane dynamics, including SNAREs, tethering proteins and RAB GTPases, and also transport of autophagosomes and late endosomes/lysosomes towards each other. Multiple mechanisms modulate autophagosome maturation, including post-translational modification of key components, spatial distribution of phosphoinositide lipid species on membranes, RAB protein dynamics, and biogenesis and function of lysosomes. Nutrient status and various stresses integrate into the autophagosome maturation machinery to coordinate the progression of autophagic flux. Impaired autophagosome maturation is linked to the pathogenesis of various human diseases, including neurodegenerative disorders, cancer and myopathies. Furthermore, invading pathogens exploit various strategies to block autophagosome maturation, thus evading destruction and even subverting autophagic vacuoles (autophagosomes, amphisomes and autolysosomes) for survival, growth and/or release. Here, we discuss the recent progress in our understanding of the machinery and regulation of autophagosome maturation, the relevance of these mechanisms to human pathophysiology and how they are harnessed by pathogens for their benefit. We also provide perspectives on targeting autophagosome maturation therapeutically.

Therapeutic Targeting of Histone Deacetylation to Prevent Alzheimer's Disease

Efforts to find disease-modifying treatments for Alzheimer's disease (AD) have been largely unsuccessful. The relative lack of progress and the age-related incidence of AD suggest that modulation of aging per se may be a useful alternative treatment approach. Therapeutics aimed at preventing or reversing aging should be effective in preventing or reversing dementia and the pathology associated with progressive AD. Epigenetic dysregulation of neuronal gene expression occurs with age, propagating deficits in cellular homeostasis. Regulators of epigenetic processes, such as histone deacetylases (HDACs), are well documented and may represent promising therapeutic targets. HDAC activity becomes dysregulated with age and in AD. An intriguing concept is that HDAC inhibition effectively forestalls AD pathology measured more broadly, addressing the notion that rectifying homeostatic gene expression may be the critical step in ameliorating AD pathogenesis at the earliest stage of disease initiation. HDAC inhibitors target several pathways associated with aging and AD neuropathology including loss of synaptic function, mitochondrial dysfunction, increased oxidative stress, and decreased autophagy activity. Since transcriptional levels of numerous genes are shown to decrease with increasing age, a recovery of their transcriptional activity through HDAC inhibition could prevent or delay age-associated declines in neurological function and provide pathways for treating AD.

Human stem cell models of polyglutamine diseases: Sources for disease models and cell therapy

Polyglutamine (polyQ) diseases are a group of neurodegenerative disorders involving expanded CAG repeats in pathogenic genes that are translated into extended polyQ tracts and lead to progressive neuronal degeneration in the affected brain. To date, there is no effective therapy for these diseases. Due to the complex pathologic mechanisms of these diseases, intensive research on the pathogenesis of their progression and potential treatment strategies is being conducted. However, animal models cannot recapitulate all aspects of neuronal degeneration. Pluripotent stem cells (PSCs), such as induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs), can be used to study the pathological mechanisms of polyQ diseases, and the ability of autologous stem cell transplantation to treat these diseases. Differentiated PSCs, neuronal precursor cells/neural progenitor cells (NPCs) and mesenchymal stem cells (MSCs) are valuable resources for preclinical and clinical cell transplantation therapies. Here, we discuss diverse stem cell models and their ability to generate neurons involved in polyQ diseases, such as medium spiny neurons (MSNs), cortical neurons, cerebellar Purkinje cells (PCs) and motor neurons. In addition, we discuss potential therapeutic approaches, including stem cell replacement therapy and gene therapy.

Morphological damage in Sertoli, myoid and interstitial cells in a mouse model of mucopolysaccharidosis type I (MPS I)

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disease caused by a mutation in the IDUA gene, which codes α-L-iduronidase (IDUA), a lysosomal hydrolase that degrades two glycosaminoglycans (GAGs): heparan sulfate (HS) and dermatan sulfate (DS). GAGs are macromolecules found mainly in the extracellular matrix and have important signaling and structural roles which are essential to the maintenance of cell and tissue physiology. Nondegraded GAGs accumulate in various cell types, which characterizes MPS I as a multisystemic progressive disease. Many tissues and vital organs have been described in MPS I models, but there is a lack of studies focused on their effects on the reproductive tract. Our previous studies indicated lower sperm production and morphological damage in the epididymis and accessory glands in male MPS I mice, despite their ability to copulate and to impregnate females. Our aim was to improve the testicular characterization of the MPS I model, with a specific focus on ultrastructural observation of the different cell types that compose the seminiferous tubules and interstitium. We investigated the testicular morphology of 6-month-old male C57BL/6 wild-type (Idua+/+) and MPS I (Idua-/-) mice. We found vacuolated cells widely present in the interstitium and important signs of damage in myoid, Sertoli and Leydig cells. In the cytoplasmic region of Sertoli cells, we found an increased number of vesicles with substrates under digestion and a decreased number of electron-dense vesicles similar to lysosomes, suggesting an impaired flux of substrate degradation. Conclusions: Idua exerts an important role in the morphological maintenance of the seminiferous tubules and the testicular interstitium, which may influence the quality of spermatogenesis, having a greater effect with the progression of the disease.

Evaluating and modulating TFEB in the control of autophagy: toward new treatments in CNS disorders

TFEB is a mammalian transcription factor that binds directly to the CLEAR consensus sequence (5'-GTCACGTGAC-3') present in the regulatory regions of genes inducing autophagosome formation, autophagosome-lysosome fusion, hydrolase enzyme expression, and lysosomal exocytosis. By modulating these activities, TFEB coordinates on-demand control over each cell's degradation pathway. Thus, a nuclear signaling pathway regulates cellular energy metabolism through TFEB. Our growing understanding of the role of TFEB and CLEAR in the promotion of healthy clearance together with in vitro and in vivo preclinical findings in various animal models of disease supports the conclusion that the pharmacological activation of TFEB could clear toxic proteins to treat both rare and common forms of neurodegenerative disease.

The Role of iPSC Modeling Toward Projection of Autophagy Pathway in Disease Pathogenesis: Leader or Follower

Autophagy is responsible for degradation of non-essential or damaged cellular constituents and damaged organelles. The autophagy pathway maintains efficient cellular metabolism and reduces cellular stress by removing additional and pathogenic components. Dysfunctional autophagy underlies several diseases. Thus, several research groups have worked toward elucidating key steps in this pathway. Autophagy can be studied by animal modeling, chemical modulators, and in vitro disease modeling with induced pluripotent stem cells (iPSC) as a loss-of-function platform. The introduction of iPSC technology, which has the capability to maintain the genetic background, has facilitated in vitro modeling of some diseases. Furthermore, iPSC technology can be used as a platform to study defective cellular and molecular pathways during development and unravel novel steps in signaling pathways of health and disease. Different studies have used iPSC technology to explore the role of autophagy in disease pathogenesis which could not have been addressed by animal modeling or chemical inducers/inhibitors. In this review, we discuss iPSC models of autophagy-associated disorders where the disease is caused due to mutations in autophagy-related genes. We classified this group as "primary autophagy induced defects (PAID)". There are iPSC models of diseases in which the primary cause is not dysfunctional autophagy, but autophagy is impaired secondary to disease phenotypes. We call this group "secondary autophagy induced defects (SAID)" and discuss them. Graphical abstract.

Ubiquitin signaling in neurodegenerative diseases: an autophagy and proteasome perspective

Ubiquitin signaling is a sequence of events driving the fate of a protein based on the type of ubiquitin modifications attached. In the case of neurodegenerative diseases, ubiquitin signaling is mainly associated with degradation signals to process aberrant proteins, which form aggregates often fatal for the brain cells. This signaling is often perturbed by the aggregates themselves and leads to the accumulation of toxic aggregates and inclusion bodies that are deleterious due to a toxic gain of function. Decrease in quality control pathways is often seen with age and is a critical onset for the development of neurodegeneration. Many aggregates are now thought to propagate in a prion-like manner, where mutated proteins acting like seeds are transitioning from cell to cell, converting normal proteins to toxic aggregates. Modulation of ubiquitin signaling, by stimulating ubiquitin ligase activation, is a potential therapeutic strategy to treat patients with neurodegeneration diseases.

Transcription factor EB: an emerging drug target for neurodegenerative disorders

The discovery of transcription factor EB (TFEB) as a master regulator of the autophagy-lysosomal pathway (ALP) has triggered increasing numbers of studies that aim to explore the therapeutic potential of targeting TFEB to treat neurodegenerative disorders (NDs) such as Alzheimer's disease and Parkinson's disease. So far, the findings are exciting and promising. Here, we delineate the dysfunction of the TFEB-mediated ALP in NDs, and we summarize small molecules that have been identified as TFEB activators, along with their protective effects in NDs. We discuss the molecular mechanisms and targets, and the pros and cons of these TFEB activators from the perspective of drug development. Specific and potent small-molecule TFEB activators with ideal brain bioavailability could provide a method for treating NDs.

Merging the Multi-Target Effects of Phytochemicals in Neurodegeneration: From Oxidative Stress to Protein Aggregation and Inflammation

Wide experimental evidence has been provided in the last decade concerning the neuroprotective effects of phytochemicals in a variety of neurodegenerative disorders. Generally, the neuroprotective effects of bioactive compounds belonging to different phytochemical classes are attributed to antioxidant, anti-aggregation, and anti-inflammatory activity along with the restoration of mitochondrial homeostasis and targeting alterations of cell-clearing systems. Far from being independent, these multi-target effects represent interconnected events that are commonly implicated in the pathogenesis of most neurodegenerative diseases, independently of etiology, nosography, and the specific misfolded proteins being involved. Nonetheless, the increasing amount of data applying to a variety of neurodegenerative disorders joined with the multiple effects exerted by the wide variety of plant-derived neuroprotective agents may rather confound the reader. The present review is an attempt to provide a general guideline about the most relevant mechanisms through which naturally occurring agents may counteract neurodegeneration. With such an aim, we focus on some popular phytochemical classes and bioactive compounds as representative examples to design a sort of main highway aimed at deciphering the most relevant protective mechanisms which make phytochemicals potentially useful in counteracting neurodegeneration. In this frame, we emphasize the potential role of the cell-clearing machinery as a kernel in the antioxidant, anti-aggregation, anti-inflammatory, and mitochondrial protecting effects of phytochemicals.

A Crucial Role for the Protein Quality Control System in Motor Neuron Diseases

Motor neuron diseases (MNDs) are fatal diseases characterized by loss of motor neurons in the brain cortex, in the bulbar region, and/or in the anterior horns of the spinal cord. While generally sporadic, inherited forms linked to mutant genes encoding altered RNA/protein products have also been described. Several different mechanisms have been found altered or dysfunctional in MNDs, like the protein quality control (PQC) system. In this review, we will discuss how the PQC system is affected in two MNDs—spinal and bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis (ALS)—and how this affects the clearance of aberrantly folded proteins, which accumulate in motor neurons, inducing dysfunctions and their death. In addition, we will discuss how the PQC system can be targeted to restore proper cell function, enhancing the survival of affected cells in MNDs.

mTORC1 feedback to AKT modulates lysosomal biogenesis through MiT/TFE regulation

The microphthalmia family of transcription factors (MiT/TFEs) controls lysosomal biogenesis and is negatively regulated by the nutrient sensor mTORC1. However, the mechanisms by which cells with constitutive mTORC1 signaling maintain lysosomal catabolism remain to be elucidated. Using the murine epidermis as a model system, we found that epidermal Tsc1 deletion resulted in a phenotype characterized by wavy hair and curly whiskers, and was associated with increased EGFR and HER2 degradation. Unexpectedly, constitutive mTORC1 activation with Tsc1 loss increased lysosomal content via upregulated expression and activity of MiT/TFEs, whereas genetic deletion of Rheb or Rptor or prolonged pharmacologic mTORC1 inactivation had the reverse effect. This paradoxical increase in lysosomal biogenesis by mTORC1 was mediated by feedback inhibition of AKT, and a resulting suppression of AKT-induced MiT/TFE downregulation. Thus, inhibiting hyperactive AKT signaling in the context of mTORC1 loss-of-function fully restored MiT/TFE expression and activity. These data suggest that signaling feedback loops work to restrain or maintain cellular lysosomal content during chronically inhibited or constitutively active mTORC1 signaling, respectively, and reveal a mechanism by which mTORC1 regulates upstream receptor tyrosine kinase signaling.

Cell-Clearing Systems Bridging Repeat Expansion Proteotoxicity and Neuromuscular Junction Alterations in ALS and SBMA

The coordinated activities of autophagy and the ubiquitin proteasome system (UPS) are key to preventing the aggregation and toxicity of misfold-prone proteins which manifest in a number of neurodegenerative disorders. These include proteins which are encoded by genes containing nucleotide repeat expansions. In the present review we focus on the overlapping role of autophagy and the UPS in repeat expansion proteotoxicity associated with chromosome 9 open reading frame 72 (C9ORF72) and androgen receptor (AR) genes, which are implicated in two motor neuron disorders, amyotrophic lateral sclerosis (ALS) and spinal-bulbar muscular atrophy (SBMA), respectively. At baseline, both C9ORF72 and AR regulate autophagy, while their aberrantly-expanded isoforms may lead to a failure in both autophagy and the UPS, further promoting protein aggregation and toxicity within motor neurons and skeletal muscles. Besides proteotoxicity, autophagy and UPS alterations are also implicated in neuromuscular junction (NMJ) alterations, which occur early in both ALS and SBMA. In fact, autophagy and the UPS intermingle with endocytic/secretory pathways to regulate axonal homeostasis and neurotransmission by interacting with key proteins which operate at the NMJ, such as agrin, acetylcholine receptors (AChRs), and adrenergic beta2 receptors (B2-ARs). Thus, alterations of autophagy and the UPS configure as a common hallmark in both ALS and SBMA disease progression. The findings here discussed may contribute to disclosing overlapping molecular mechanisms which are associated with a failure in cell-clearing systems in ALS and SBMA.