Neuropathy-causing mutations in HSPB1 impair autophagy by disturbing the formation of SQSTM1/p62 bodies

Autophagy induction by piplartine ameliorates axonal degeneration caused by mutant HSPB1 and HSPB8 in Charcot-Marie-Tooth type 2 neuropathies

HSPB1 [heat shock protein family B (small) member 1] and HSPB8 are essential molecular chaperones for neuronal proteostasis, as they prevent protein aggregation. Mutant HSPB1 and HSPB8 primarily harm peripheral neurons, resulting in axonal Charcot-Marie-Tooth neuropathies (CMT2). Macroautophagy/autophagy is a shared mechanism by which HSPB1 and HSPB8 mutations cause neuronal dysfunction. Autophagosome formation is reduced in mutant HSPB1-induced pluripotent stem-cell-derived motor neurons from CMT type 2F patients. Likewise, the HSPB8K141N knockin mouse model, mimicking CMT type 2 L, exhibits axonal degeneration and muscle atrophy, with SQSTM1/p62-positive deposits. We show here that mouse embryonic fibroblasts isolated from a HSPB8K141N/green fluorescent protein (GFP)-LC3 model have diminished autophagosome production under conditions of MTOR inhibition. To correct the autophagic deficits in the HSPB1 and HSPB8 models, we screened by high-throughput autophagosome quantification the repurposing Spectrum Collection library for molecules that could boost the autophagic activity above the canonical MTOR inhibition. Hit compounds were validated on motor neurons obtained by differentiation of HSPB1P182L and HSPB8K141N patient-derived induced pluripotent stem cells, focusing on autophagy induction as well as neurite network density, axonal degeneration, and mitochondrial morphology. We identified molecules that specifically stimulate autophagosome formation in the HSPB8K141N cells, without affecting autophagy flux. Two top lead compounds induced autophagy and reduced axonal degeneration, thus promoting neuronal network maturation in the CMT2 patient-derived motor neurons. Based on these findings, the phenotypical screen revealed that piplartine rescued autophagy deficiencies in both the HSPB1 and HSPB8 models, demonstrating autophagy induction as an effective therapeutic strategy for CMT neuropathies and other chaperonopathies.

Heat-shock chaperone HSPB1 mitigates poly-glycine-induced neurodegeneration via restoration of autophagic flux

The CGG repeat expansions in the 5'-UTR regions of certain genes have been implicated in various neurodegenerative and muscular disorders. However, the underlying pathogenic mechanisms are not well understood. In this study, we explore the role of the small molecular chaperone HSPB1 in counteracting neurodegeneration induced by poly-glycine (poly-G) aggregates. Employing a reporter system, we demonstrate that CGG repeat expansions within the 5'-UTR of the GIPC1 gene produce poly-G proteins, by repeat-associated non-AUG (RAN) translation. Through proximity labeling and subsequent mass spectrometry analysis, we characterize the composition of poly-G insoluble aggregates and reveal that these aggregates sequester key macroautophagy/autophagy receptors, SQSTM1/p62 and TOLLIP. This sequestration disrupts MAP1LC3/LC3 recruitment and impairs autophagosome formation, thereby compromising the autophagic pathway. Importantly, we show that HSPB1 facilitates the dissociation of these receptors from poly-G aggregates and consequently restores autophagic function. Overexpressing HSPB1 alleviates poly-G-induced neurodegeneration in mouse models. Taken together, these findings highlight a mechanistic basis for the neuroprotective effects of HSPB1 and suggest its potential as a therapeutic target in treating poly-G-associated neurodegenerative diseases.Abbreviations: AD: Alzheimer disease; AIF1/Iba1: allograft inflammatory factor 1; Baf A1: bafilomycin A1; BFP: blue fluorescent protein; CQ: chloroquine; EIF2A/eIF-2α: eukaryotic translation initiation factor 2A; FRAP: fluorescence recovery after photobleaching; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFAP: glial fibrillary acidic protein; GFP: green fluorescent protein; HSPB1: heat shock protein family B (small) member 1; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; NOTCH2NLC: notch 2 N-terminal like C; PD: Parkinson disease; PFA: paraformaldehyde; poly-A: poly-alanine; poly-G: poly-glycine; poly-R: poly-arginine; RAN translation: repeat-associated non-AUG translation; RBFOX3/NeuN: RNA binding fox-1 homolog 3; STED: stimulated emission depletion; TARDBP/TDP-43: TAR DNA binding protein; TG: thapsigargin; TOLLIP: toll interacting protein.

From in vivo models to in vitro bioengineered neuromuscular junctions for the study of Charcot-Marie-Tooth disease

Peripheral neuropathies are disorders affecting the peripheral nervous system. Among them, Charcot-Marie-Tooth disease is an inherited sensorimotor neuropathy for which no effective treatment exists yet. Research on Charcot-Marie-Tooth disease has been hampered by difficulties in accessing relevant cells, such as sensory and motor neurons, Schwann cells, and myocytes, which interact at the neuromuscular junction, the specialized synapses formed between nerves and skeletal muscles. This review first outlines the various in vivo models and methods used to study neuromuscular junction deficiencies in Charcot-Marie-Tooth disease. We then explore novel in vitro techniques and models, including complex hiPSC-derived cultures, which offer promising isogenic and reproducible neuromuscular junction models. The adaptability of in vitro culture methods, including cell origin, cell-type combinations, and choice of culture format, adds complexity and excitement to this rapidly evolving field. This review aims to recapitulate available tools for studying Charcot-Marie-Tooth disease to understand its pathophysiological mechanisms and test potential therapies.

Lysosomal damage triggers a p38 MAPK-dependent phosphorylation cascade to promote lysophagy via the small heat shock protein HSP27

Maintenance of lysosomal integrity is essential for cell viability. Upon injury, lysosomes may be targeted for degradation via a selective form of autophagy known as lysophagy. The engulfment of a damaged lysosome by an autophagosome is mediated by the recruitment of adaptor proteins, including SQSTM1/p62. p62 promotes lysophagy via the formation of phase-separated condensates in a mechanism that is regulated by the heat shock protein HSP27. Here, we demonstrate a direct interaction between HSP27 and p62. We used structural modeling to predict the binding interface between HSP27 and p62 and identify several disease-associated mutations that map to this interface. We used proteomics to identify post-translational modifications of HSP27 that regulate HSP27 recruitment to stressed lysosomes, finding robust phosphorylation at several serine residues. Next, we characterized the upstream signaling mechanism leading to HSP27 phosphorylation and found that p38 mitogen-activated protein kinase (MAPK) and its effector kinase MAP kinase-activated protein kinase 2 (MK2) are activated upon lysosomal damage by the kinase mTOR and the production of intracellular reactive oxygen species (ROS). Increased ROS activates p38 MAPK, which in turn allows MK2-dependent phosphorylation of HSP27. Depletion of HSP27 or the inhibition of HSP27 phosphorylation alters the dynamics of p62 condensates on stressed lysosomes, significantly inhibiting p62-dependent lysophagy. Thus, we define a novel lysosomal quality control mechanism in which lysosomal injury triggers a p38 MAPK/MK2 signaling cascade promoting p62-dependent lysophagy. Further, this signaling cascade is activated by many cellular stressors, including oxidative and heat stress, suggesting that other forms of selective autophagy may be regulated by p38 MAPK/MK2/HSP27.

Force-induced dephosphorylation activates the cochaperone BAG3 to coordinate protein homeostasis and membrane traffic

Proteome maintenance in contracting skeletal and cardiac muscles depends on the chaperone-regulating protein BAG3. Reduced BAG3 activity leads to muscle weakness and heart failure in animal models and patients. BAG3 and its chaperone partners recognize mechanically damaged muscle proteins and initiate their disposal through chaperone-assisted selective autophagy (CASA). However, molecular details of the force-dependent regulation of BAG3 have remained elusive so far. Here, we demonstrate that mechanical stress triggers the dephosphorylation of BAG3 in human muscle and in isolated cells. We identify force-regulated phospho-switches in BAG3 that control CASA complex assembly and CASA activity. Differential proteomics reveal RAB GTPases, which organize membrane traffic and fusion, as dephosphorylation-dependent interactors of BAG3. In fact, RAB7A and RAB11B are shown here to be essential for CASA in skeletal muscle cells. Moreover, BAG3 dephosphorylation is also observed upon induction of mitophagy, suggesting an involvement of the cochaperone in the RAB7A-dependent autophagic engulfment of damaged mitochondria in exercised muscle. Cooperation of BAG3 with RAB7A relies on a direct interaction of both proteins, which is regulated by the nucleotide state of the GTPase and by association with the autophagosome membrane protein LC3B. Finally, we provide evidence that BAG3 and RAB7A also cooperate in non-muscle cells and propose that overactivation of CASA in RAB7A-L129F patients contributes to the loss of peripheral neurons in Charcot-Marie-Tooth neuropathy.

The biphasic role of Hspb1 on ferroptotic cell death in Parkinson's disease

Rationale: Ferroptosis-driven loss of dopaminergic neurons plays a pivotal role in the pathogenesis of Parkinson's disease (PD). In PD patients, Hspb1 is commonly observed at abnormally high levels in the substantia nigra. The precise consequences of Hspb1 overexpression in PD, however, have yet to be fully elucidated. Methods: We used human iPSC-derived dopaminergic neurons and Coniferaldehyde (CFA)-an Nrf2 agonist known for its ability to cross the blood-brain barrier-to investigate the role of Hspb1 in PD. We examined the correlation between Hspb1 overexpression and Nrf2 activation and explored the transcriptional regulation of Hspb1 by Nrf2. Gene deletion techniques were employed to determine the necessity of Nrf2 and Hspb1 for CFA's neuroprotective effects. Results: Our research demonstrated that Nrf2 can upregulate the transcription of Hspb1 by directly binding to its promoter. Deletion of either Nrf2 or Hspb1 gene abolished the neuroprotective effects of CFA. The Nrf2-Hspb1 pathway, newly identified as a defense mechanism against ferroptosis, was shown to be essential for preventing neurodegeneration progression. Additionally, we discovered that prolonged overexpression of Hspb1 leads to neuronal death and that Hspb1 released from ruptured cells can trigger secondary cell death in neighboring cells, exacerbating neuroinflammatory responses. Conclusions: These findings highlight a biphasic role of Hspb1 in PD, where it initially provides neuroprotection through the Nrf2-Hspb1 pathway but ultimately contributes to neurodegeneration and inflammation when overexpressed. Understanding this dual role is crucial for developing therapeutic strategies targeting Hspb1 and Nrf2 in PD.

Neurotropic virus infection and neurodegenerative diseases: Potential roles of autophagy pathway

Neurodegenerative diseases (NDs) constitute a group of disorders characterized by the progressive deterioration of nervous system functionality. Currently, the precise etiological factors responsible for NDs remain incompletely elucidated, although it is probable that a combination of aging, genetic predisposition, and environmental stressors participate in this process. Accumulating evidence indicates that viral infections, especially neurotropic viruses, can contribute to the onset and progression of NDs. In this review, emerging evidence supporting the association between viral infection and NDs is summarized, and how the autophagy pathway mediated by viral infection can cause pathological aggregation of cellular proteins associated with various NDs is discussed. Furthermore, autophagy-related genes (ARGs) involved in Herpes simplex virus (HSV-1) infection and NDs are analyzed, and whether these genes could link HSV-1 infection to NDs is discussed. Elucidating the mechanisms underlying NDs is critical for developing targeted therapeutic approaches that prevent the onset and slow the progression of NDs.

Advances and challenges in modeling inherited peripheral neuropathies using iPSCs

Inherited peripheral neuropathies (IPNs) are a group of diseases associated with mutations in various genes with fundamental roles in the development and function of peripheral nerves. Over the past 10 years, significant advances in identifying molecular disease mechanisms underlying axonal and myelin degeneration, acquired from cellular biology studies and transgenic fly and rodent models, have facilitated the development of promising treatment strategies. However, no clinical treatment has emerged to date. This lack of treatment highlights the urgent need for more biologically and clinically relevant models recapitulating IPNs. For both neurodevelopmental and neurodegenerative diseases, patient-specific induced pluripotent stem cells (iPSCs) are a particularly powerful platform for disease modeling and preclinical studies. In this review, we provide an update on different in vitro human cellular IPN models, including traditional two-dimensional monoculture iPSC derivatives, and recent advances in more complex human iPSC-based systems using microfluidic chips, organoids, and assembloids.

Hspb1 and Lgals3 in spinal neurons are closely associated with autophagy following excitotoxicity based on machine learning algorithms

Excitotoxicity represents the primary cause of neuronal death following spinal cord injury (SCI). While autophagy plays a critical and intricate role in SCI, the specific mechanism underlying the relationship between excitotoxicity and autophagy in SCI has been largely overlooked. In this study, we isolated primary spinal cord neurons from neonatal rats and induced excitotoxic neuronal injury by high concentrations of glutamic acid, mimicking an excitotoxic injury model. Subsequently, we performed transcriptome sequencing. Leveraging machine learning algorithms, including weighted correlation network analysis (WGCNA), random forest analysis (RF), and least absolute shrinkage and selection operator analysis (LASSO), we conducted a comprehensive investigation into key genes associated with spinal cord neuron injury. We also utilized protein-protein interaction network (PPI) analysis to identify pivotal proteins regulating key gene expression and analyzed key genes from public datasets (GSE2599, GSE20907, GSE45006, and GSE174549). Our findings revealed that six genes-Anxa2, S100a10, Ccng1, Timp1, Hspb1, and Lgals3-were significantly upregulated not only in vitro in neurons subjected to excitotoxic injury but also in rats with subacute SCI. Furthermore, Hspb1 and Lgals3 were closely linked to neuronal autophagy induced by excitotoxicity. Our findings contribute to a better understanding of excitotoxicity and autophagy, offering potential targets and a theoretical foundation for SCI diagnosis and treatment.

Neurofilaments: Novel findings and future challenges

Neurofilaments (NFs) are abundant cytoskeletal proteins that emerge as a critical hub for cell signalling within neurons. As we start to uncover essential roles of NFs in regulating microtubule and organelle dynamics, nerve conduction and neurotransmission, novel discoveries are expected to arise in genetics, with NFs identified as causal genes for various neurodegenerative diseases. This review will discuss how the latest advances in fundamental and translational research illuminate our understanding of NF biology, particularly their assembly, organisation, transport and degradation. We will emphasise the notion that filaments are not one entity and that future challenges will be to apprehend their diverse composition and structural heterogeneity and to scrutinize how this regulates signalling, sustains neuronal physiology and drives pathophysiology in disease.

Ascorbic acid mitigates the impact of oxidative stress in a human model of febrile seizure and mesial temporal lobe epilepsy

Prolonged febrile seizures (FS) in children are linked to the development of temporal lobe epilepsy (MTLE). The association between these two pathologies may be ascribed to the long-term effects that FS exert on neural stem cells, negatively affecting the generation of new neurons. Among the insults associated with FS, oxidative stress is noteworthy. Here, we investigated the consequences of exposure to hydrogen peroxide (H2O2) in an induced pluripotent stem cell-derived neural stem cells (iNSCs) model of a patient affected by FS and MTLE. In our study, we compare the findings from the MTLE patient with those derived from iNSCs of a sibling exhibiting a milder phenotype defined only by FS, as well as a healthy individual. In response to H2O2 treatment, iNSCs derived from MTLE patients demonstrated an elevated production of reactive oxygen species and increased apoptosis, despite the higher expression levels of antioxidant genes and proteins compared to other cell lines analysed. Among the potential causative mechanisms of enhanced vulnerability of MTLE patient iNSCs to oxidative stress, we found that these cells express low levels of the heat shock protein HSPB1 and of the autophagy adaptor SQSTM1/p62. Pre-treatment of diseased iNSCs with the antioxidant molecule ascorbic acid restored HSBP1 and p62 expression and simultaneously reduced the levels of ROS and apoptosis. Our findings suggest the potential for rescuing the impaired oxidative stress response in diseased iNSCs through antioxidant treatment, offering a promising mechanism to prevent FS degeneration in MTLE.

TSP-1 increases autophagy level in cartilage by upregulating HSP27 which delays progression of osteoarthritis

This study aimed to determine whether Thrombospondin-1 (TSP-1) can be used as a biomarker to diagnose early osteoarthritis (OA) and whether it has a chondroprotective effect against OA. We examined TSP-1 expression in cartilage, synovial fluid, and serum at different time points after anterior cruciate ligament transection (ACLT) surgery in rats. Subsequently, TSP-1 was overexpressed or silenced to detect its effects on extracellular matrix (ECM) homeostasis, autophagy level, proliferation and apoptosis in chondrocytes. Adenovirus encoding TSP-1 was injected into the knee joints of ACLT rats to test its effect against OA. Combined with proteomic analysis, the molecular mechanism of TSP-1 in cartilage degeneration was explored. Intra-articular injection of an adenovirus carrying the TSP-1 sequence showed chondroprotective effects against OA. Moreover, TSP-1 expression decreases with OA progression and can effectively promote cartilage proliferation, inhibit apoptosis, and helps to sustain the balance between ECM anabolism and catabolism. Overexpression of TSP-1 also can increase autophagy by upregulating Heat Shock Protein 27 (HSP27, hspb1), thereby enhancing its effect as a stimulator of autophagy. TSP-1 is a hopeful strategy for OA treatment.

Shared Proteins and Pathways of Cardiovascular and Cognitive Diseases: Relation to Vascular Cognitive Impairment

One of the primary goals of systems medicine is the detection of putative proteins and pathways involved in disease progression and pathological phenotypes. Vascular cognitive impairment (VCI) is a heterogeneous condition manifesting as cognitive impairment resulting from vascular factors. The precise mechanisms underlying this relationship remain unclear, which poses challenges for experimental research. Here, we applied computational approaches like systems biology to unveil and select relevant proteins and pathways related to VCI by studying the crosstalk between cardiovascular and cognitive diseases. In addition, we specifically included signals related to oxidative stress, a common etiologic factor tightly linked to aging, a major determinant of VCI. Our results show that pathways associated with oxidative stress are quite relevant, as most of the prioritized vascular cognitive genes and proteins were enriched in these pathways. Our analysis provided a short list of proteins that could be contributing to VCI: DOLK, TSC1, ATP1A1, MAPK14, YWHAZ, CREB3, HSPB1, PRDX6, and LMNA. Moreover, our experimental results suggest a high implication of glycative stress, generating oxidative processes and post-translational protein modifications through advanced glycation end-products (AGEs). We propose that these products interact with their specific receptors (RAGE) and Notch signaling to contribute to the etiology of VCI.

Exosomal miR-4645-5p from hypoxic bone marrow mesenchymal stem cells facilitates diabetic wound healing by restoring keratinocyte autophagy

BACKGROUND

Refractory diabetic wounds are a common occurrence in patients with diabetes and epidermis-specific macroautophagy/autophagy impairment has been implicated in their pathogenesis. Therefore, identifying and developing treatment strategies capable of normalizing epidermis-specific macroautophagy/autophagy could facilitate diabetic wound healing. The study aims to investigate the potential of bone marrow mesenchymal stem cell-derived exosomes (BMSC-exos) from hypoxic conditions as a treatment to normalize epidermis-specific autophagy for diabetic wound healing.

METHODS

We compared the effects of bone marrow mesenchymal stem cell (BMSC)-sourced exosomes (BMSC-Exos) from hypoxic conditions to those of BMSC in normoxic conditions (noBMSC-Exos). Our studies involved morphometric assessment of the exosomes, identification of the microRNA (miRNA) responsible for the effects, evaluation of keratinocyte functions and examination of effects of the exosomes on several molecules involved in the autophagy pathway such as microtubule-associated protein 1 light chain 3 beta, beclin 1, sequestosome 1, autophagy-related 5 and autophagy-related 5. The experiments used human BMSCs from the American Type Culture Collection, an in vivo mouse model of diabetes (db/db) to assess wound healing, as well as the human keratinocyte HaCaT cell line. In the methodology, the authors utilized an array of approaches that included electron microscopy, small interfering RNA (siRNA) studies, RNA in situ hybridization, quantitative real-time reverse transcription PCR (qRT-PCR), the isolation, sequencing and differential expression of miRNAs, as well as the use of miR-4645-5p-specific knockdown with an inhibitor.

RESULTS

Hypoxia affected the release of exosomes from hypoxic BMSCs (hy-BMSCs) and influenced the size and morphology of the exosomes. Moreover, hyBMSC-Exo treatment markedly improved keratinocyte function, including keratinocyte autophagy, proliferation and migration. miRNA microarray and bioinformatics analysis showed that the target genes of the differentially expressed miRNAs were mainly enriched in 'autophagy' and 'process utilizing autophagic mechanism' in the 'biological process' category and miR-4645-5p as a major contributor to the pro-autophagy effect of hyBMSC-Exos. Moreover, mitogen-activated protein kinase-activated protein kinase 2 (MAPKAPK2) was identified as a potential target of exosomal miR-4645-5p; this was confirmed using a dual luciferase assay. Exosomal miR-4645-5p mediates the inactivation of the MAPKAPK2-induced AKT kinase group (comprising AKT1, AKT2, and AKT3), which in turn suppresses AKT-mTORC1 signaling, thereby facilitating miR-4645-5p-mediated autophagy.

CONCLUSIONS

Overall, the results of this study showed that hyBMSC-Exo-mediated transfer of miR-4645-5p inactivated MAPKAPK2-induced AKT-mTORC1 signaling in keratinocytes, which activated keratinocyte autophagy, proliferation and migration, resulting in diabetic wound healing in mice. Collectively, the findings could aid in the development of a novel therapeutic strategy for diabetic wounds.

Neuronal Autophagy: Regulations and Implications in Health and Disease

Autophagy is a major degradative pathway that plays a key role in sustaining cell homeostasis, integrity, and physiological functions. Macroautophagy, which ensures the clearance of cytoplasmic components engulfed in a double-membrane autophagosome that fuses with lysosomes, is orchestrated by a complex cascade of events. Autophagy has a particularly strong impact on the nervous system, and mutations in core components cause numerous neurological diseases. We first review the regulation of autophagy, from autophagosome biogenesis to lysosomal degradation and associated neurodevelopmental/neurodegenerative disorders. We then describe how this process is specifically regulated in the axon and in the somatodendritic compartment and how it is altered in diseases. In particular, we present the neuronal specificities of autophagy, with the spatial control of autophagosome biogenesis, the close relationship of maturation with axonal transport, and the regulation by synaptic activity. Finally, we discuss the physiological functions of autophagy in the nervous system, during development and in adulthood.

Neurofilaments in health and Charcot-Marie-Tooth disease

Neurofilaments (NFs) are the most abundant component of mature neurons, that interconnect with actin and microtubules to form the cytoskeleton. Specifically expressed in the nervous system, NFs present the particularity within the Intermediate Filament family of being formed by four subunits, the neurofilament light (NF-L), medium (NF-M), heavy (NF-H) proteins and α-internexin or peripherin. Here, we review the current knowledge on NF proteins and neurofilaments, from their domain structures and their model of assembly to the dynamics of their transport and degradation along the axon. The formation of the filament and its behaviour are regulated by various determinants, including post-transcriptional (miRNA and RBP proteins) and post-translational (phosphorylation and ubiquitination) modifiers. Altogether, the complex set of modifications enable the neuron to establish a stable but elastic NF array constituting the structural scaffold of the axon, while permitting the local expression of NF proteins and providing the dynamics necessary to fulfil local demands and respond to stimuli and injury. Thus, in addition to their roles in mechano-resistance, radial axonal outgrowth and nerve conduction, NFs control microtubule dynamics, organelle distribution and neurotransmission at the synapse. We discuss how the studies of neurodegenerative diseases with NF aggregation shed light on the biology of NFs. In particular, the NEFL and NEFH genes are mutated in Charcot-Marie-Tooth (CMT) disease, the most common inherited neurological disorder of the peripheral nervous system. The clinical features of the CMT forms (axonal CMT2E, CMT2CC; demyelinating CMT1F; intermediate I-CMT) with symptoms affecting the central nervous system (CNS) will allow us to further investigate the physiological roles of NFs in the brain. Thus, NF-CMT mouse models exhibit various degrees of sensory-motor deficits associated with CNS symptoms. Cellular systems brought findings regarding the dominant effect of NF-L mutants on NF aggregation and transport, although these have been recently challenged. Neurofilament detection without NF-L in recessive CMT is puzzling, calling for a re-examination of the current model in which NF-L is indispensable for NF assembly. Overall, we discuss how the fundamental and translational fields are feeding each-other to increase but also challenge our knowledge of NF biology, and to develop therapeutic avenues for CMT and neurodegenerative diseases with NF aggregation.

The beauty and complexity of the small heat shock proteins: a report on the proceedings of the fourth workshop on small heat shock proteins

The Fourth Cell Stress Society International workshop on small heat shock proteins (sHSPs), a follow-up to successful workshops held in 2014, 2016 and 2018, took place as a virtual meeting on the 17-18 November 2022. The meeting was designed to provide an opportunity for those working on sHSPs to reconnect and discuss their latest work. The diversity of research in the sHSP field is reflected in the breadth of topics covered in the talks presented at this meeting. Here we summarise the presentations at this meeting and provide some perspectives on exciting future topics to be addressed in the field.

Studies of Genetic and Proteomic Risk Factors of Amyotrophic Lateral Sclerosis Inspire Biomarker Development and Gene Therapy

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease affecting the upper and lower motor neurons, leading to muscle weakness, motor impairments, disabilities and death. Approximately 5-10% of ALS cases are associated with positive family history (familial ALS or fALS), whilst the remainder are sporadic (sporadic ALS, sALS). At least 50 genes have been identified as causative or risk factors for ALS. Established pathogenic variants include superoxide dismutase type 1 (SOD1), chromosome 9 open reading frame 72 (c9orf72), TAR DNA Binding Protein (TARDBP), and Fused In Sarcoma (FUS); additional ALS-related genes including Charged Multivesicular Body Protein 2B (CHMP2B), Senataxin (SETX), Sequestosome 1 (SQSTM1), TANK Binding Kinase 1 (TBK1) and NIMA Related Kinase 1 (NEK1), have been identified. Mutations in these genes could impair different mechanisms, including vesicle transport, autophagy, and cytoskeletal or mitochondrial functions. So far, there is no effective therapy against ALS. Thus, early diagnosis and disease risk predictions remain one of the best options against ALS symptomologies. Proteomic biomarkers, microRNAs, and extracellular vehicles (EVs) serve as promising tools for disease diagnosis or progression assessment. These markers are relatively easy to obtain from blood or cerebrospinal fluids and can be used to identify potential genetic causative and risk factors even in the preclinical stage before symptoms appear. In addition, antisense oligonucleotides and RNA gene therapies have successfully been employed against other diseases, such as childhood-onset spinal muscular atrophy (SMA), which could also give hope to ALS patients. Therefore, an effective gene and biomarker panel should be generated for potentially "at risk" individuals to provide timely interventions and better treatment outcomes for ALS patients as soon as possible.

Functional Diversity of Mammalian Small Heat Shock Proteins: A Review

The small heat shock proteins (sHSPs), whose molecular weight ranges from 12∼43 kDa, are members of the heat shock protein (HSP) family that are widely found in all organisms. As intracellular stress resistance molecules, sHSPs play an important role in maintaining the homeostasis of the intracellular environment under various stressful conditions. A total of 10 sHSPs have been identified in mammals, sharing conserved α-crystal domains combined with variable N-terminal and C-terminal regions. Unlike large-molecular-weight HSP, sHSPs prevent substrate protein aggregation through an ATP-independent mechanism. In addition to chaperone activity, sHSPs were also shown to suppress apoptosis, ferroptosis, and senescence, promote autophagy, regulate cytoskeletal dynamics, maintain membrane stability, control the direction of cellular differentiation, modulate angiogenesis, and spermatogenesis, as well as attenuate the inflammatory response and reduce oxidative damage. Phosphorylation is the most significant post-translational modification of sHSPs and is usually an indicator of their activation. Furthermore, abnormalities in sHSPs often lead to aggregation of substrate proteins and dysfunction of client proteins, resulting in disease. This paper reviews the various biological functions of sHSPs in mammals, emphasizing the roles of different sHSPs in specific cellular activities. In addition, we discuss the effect of phosphorylation on the function of sHSPs and the association between sHSPs and disease.

The HSPB1-p62/SQSTM1 functional complex regulates the unconventional secretion and transcellular spreading of the HD-associated mutant huntingtin protein

Conformational diseases, such as Alzheimer, Parkinson and Huntington diseases, are part of a common class of neurological disorders characterized by the aggregation and progressive accumulation of proteins bearing aberrant conformations. Huntington disease (HD) has autosomal dominant inheritance and is caused by mutations leading to an abnormal expansion in the polyglutamine (polyQ) tract of the huntingtin (HTT) protein, leading to the formation of HTT inclusion bodies in neurons of affected patients. Interestingly, recent experimental evidence is challenging the conventional view by which the disease pathogenesis is solely a consequence of the intracellular accumulation of mutant protein aggregates. These studies reveal that transcellular transfer of mutated huntingtin protein is able to seed oligomers involving even the wild-type (WT) forms of the protein. To date, there is still no successful strategy to treat HD. Here, we describe a novel functional role for the HSPB1-p62/SQSTM1 complex, which acts as a cargo loading platform, allowing the unconventional secretion of mutant HTT by extracellular vesicles. HSPB1 interacts preferentially with polyQ-expanded HTT compared with the WT protein and affects its aggregation. Furthermore, HSPB1 levels correlate with the rate of mutant HTT secretion, which is controlled by the activity of the PI3K/AKT/mTOR signalling pathway. Finally, we show that these HTT-containing vesicular structures are biologically active and able to be internalized by recipient cells, therefore providing an additional mechanism to explain the prion-like spreading properties of mutant HTT. These findings might also have implications for the turn-over of other disease-associated, aggregation-prone proteins.

Proximity Proteomics and Biochemical Analysis Reveal a Noncanonical Function for UFM1-Specific Protease 1 in the p62 Body Formation

Protein aggregates play crucial roles in the development of neurodegenerative diseases and p62 is one of the key proteins regulating the formation of protein aggregates. Recently, it has been discovered that depletion of several key enzymes including UFM1-activating enzyme UBA5, UFM1-conjugating enzyme UFC1, UFM1-protein ligase UFL1, and UFM1-specific protease UfSP2 in the UFM1-conjugation system induces p62 accumulation to form p62 bodies in the cytosol. However, it is unknown whether UfSP1 participates in the formation of p62 bodies and whether its enzymatic activity is required for this process. Here, the proximity labeling technique and quantitative proteomics identify SQSTM1/p62 as a UfSP1-interacting protein. Coimmunoprecipitation reveals that p62 indeed interacts with UfSP1 and the immunofluorescence experiment discloses that UfSP1 colocalizes with p62 and promotes the formation of p62-mediated protein aggregates. Mechanistic studies unveil that UfSP1 binds to the ubiquitin-associated domain of p62 and promotes the interaction between p62 and ubiquitinated proteins, thereby increasing the formation of p62 bodies. Interestingly, we further demonstrate that both the catalytic active and inactive UfSP1 promote the formation of p62 bodies through the same mechanism. Taken together, this work discovers that UfSP1 exhibits a noncanonical function independent of its protease activity in the p62 body formation.

The selective autophagy adaptor p62/SQSTM1 forms phase condensates regulated by HSP27 that facilitate the clearance of damaged lysosomes via lysophagy

In response to lysosomal damage, cells engage several quality-control mechanisms, including the selective isolation and degradation of damaged lysosomes by lysophagy. Here, we report that the selective autophagy adaptor SQSTM1/p62 is recruited to damaged lysosomes in both HeLa cells and neurons and is required for lysophagic flux. The Phox and Bem1p (PB1) domain of p62 mediates oligomerization and is specifically required for lysophagy. Consistent with this observation, we find that p62 forms condensates on damaged lysosomes. These condensates are precisely tuned by the small heat shock protein HSP27, which is phosphorylated in response to lysosomal injury and maintains the liquidity of p62 condensates, facilitating autophagosome formation. Mutations in p62 have been identified in patients with amyotrophic lateral sclerosis (ALS); ALS-associated mutations in p62 impair lysophagy, suggesting that deficits in this pathway may contribute to neurodegeneration. Thus, p62 condensates regulated by HSP27 promote lysophagy by forming platforms for autophagosome biogenesis at damaged lysosomes.

Re-Analysis of Single-Nucleus Transcriptomics Reveals Diverse Dorsal Root Ganglia Macrophage Responses Following Peripheral Nerve Injury

An increasing amount of evidence points to an important role of macrophages in peripheral nerve injury (PNI) and associated pain. Peripheral nerve macrophages facilitate the regeneration, while dorsal root ganglia (DRG) macrophages might propagate the injury after a PNI. These differences might be explained by various in vivo models of PNIs or non-uniform methodologies to phenotype the macrophages. Unbiased methods to phenotype macrophages using single whole cell or nucleus transcriptomics have been rarely applied on PNIs outside the nerves themselves. Here, we compare the effects of the transection or crush of the sciatic nerve and spinal nerve transection on the DRG macrophage phenotypes utilizing a publicly available single-nucleus transcriptomic DRG dataset. Our results demonstrate that unique and time-dependent DRG macrophage gene expression profiles were produced by the three PNI models with particular macrophage clusters being enriched that were dependent on the severity of the neuronal injury score. PNI associated DRG macrophages were not purely anti- or pro-inflammatory. These results suggest that various functions of DRG macrophage subtypes are carefully orchestrated upon a PNI. These findings open a new avenue for studying the DRG macrophage subtypes in PNIs and encourage further unbiased phenotyping efforts to better understand their relevance in neuropathic pain.

Targeting small heat shock proteins to degrade aggregates as a potential strategy in neurodegenerative diseases

Neurodegenerative diseases (NDs) are aging-related diseases that involve the death of neurons in the brain. Dysregulation of protein homeostasis leads to the production of toxic proteins or the formation of aggregates, which is the pathological basis of NDs. Small heat shock proteins (HSPB) is involved in the establishment of a protein quality control (PQC) system to maintain cellular homeostasis. HSPB can be secreted into the extracellular space and delivered by various routes, especially extracellular vehicles (EVs). HSPB plays an important role in influencing the aggregation phase of toxic proteins involved in heat shock transcription factor (HSF) regulation, oxidative stress, autophagy and apoptosis pathways. HSPB conferred neuroprotective effects by resisting toxic protein aggregation, reducing autophagy and reducing neuronal apoptosis. The HSPB treatment strategies, including targeted PQC system therapy and delivery of EVs-HSPB, can improve disease manifestations for NDs. This review aims to provide a comprehensive insight into the impact of HSPB in NDs and the feasibility of new technology to enhance HSPB expression and EVs-HSPB delivery for neurodegenerative disease.

HSPB1 Regulates Autophagy and Apoptosis in Vascular Smooth Muscle Cells in Arteriosclerosis Obliterans

Objective

Small heat shock protein-1 (HSPB1) is a small heat shock protein that participates in many cellular processes and alleviates stress-induced cell injury. Autophagy protects cells from many types of stress and plays a key role in preventing stress in arteriosclerosis obliterans (ASO). However, the roles of HSPB1 in autophagy and apoptosis in the context of ASO pathogenesis remain unclear.

Methods

In vivo and in vitro studies were used to determine whether HSPB1 is associated with ASO progression. The expression of HSPB1 was measured in normal and sclerotic blood vessels. The role of HSPB1 and its potential downstream signaling pathway were determined in VSMCs by overexpressing and silencing HSPB1.

Results

A total of 91 ASO patients admitted to and treated at our hospital from Sep. 2020 to Sep. 2021 were selected, and plasma HSPB1 expression was assessed. We divided the patients with ASO into the grade I (n = 39), II (n = 29), III (n = 10), and IV (n = 13) groups according to Fontaine's classification. Plasma HSPB1 levels were markedly decreased in patients with grade III (n = 10) and IV (n = 13) ASO compared with patients with grade I ASO. Furthermore, HSPB1 expression was significantly decreased, and p62 and cleaved caspase-3 were increased in the sclerotic vasculature compared to the normal vasculature (p < 0.05). Overexpression of HSPB1 promoted apoptosis of VSMCs following ox-LDL treatment. Knockdown of HSPB1 led to a marked increase in the expression of LC3II and Beclin-1 in ox-LDL-stimulated VSMCs, whereas knockdown of HSPB1 attenuated these changes (p < 0.05). Importantly, overexpression of HSPB1 promoted the dephosphorylation of JNK in ox-LDL-stimulated VSMCs. Conversely, downregulation of HSPB1 induced the opposite change.

Conclusion

Loss of HSPB1 promotes VSMC autophagy and inhibits VSMC apoptosis, which are associated with ASO. HSPB1 and its downstream signaling pathways could be potential therapeutic targets for ASO treatment.

The Role of Small Heat Shock Proteins in Protein Misfolding Associated Motoneuron Diseases

Motoneuron diseases (MNDs) are neurodegenerative conditions associated with death of upper and/or lower motoneurons (MNs). Proteostasis alteration is a pathogenic mechanism involved in many MNDs and is due to the excessive presence of misfolded and aggregated proteins. Protein misfolding may be the product of gene mutations, or due to defects in the translation process, or to stress agents; all these conditions may alter the native conformation of proteins making them prone to aggregate. Alternatively, mutations in members of the protein quality control (PQC) system may determine a loss of function of the proteostasis network. This causes an impairment in the capability to handle and remove aberrant or damaged proteins. The PQC system consists of the degradative pathways, which are the autophagy and the proteasome, and a network of chaperones and co-chaperones. Among these components, Heat Shock Protein 70 represents the main factor in substrate triage to folding, refolding, or degradation, and it is assisted in this task by a subclass of the chaperone network, the small heat shock protein (sHSPs/HSPBs) family. HSPBs take part in proteostasis by bridging misfolded and aggregated proteins to the HSP70 machinery and to the degradative pathways, facilitating refolding or clearance of the potentially toxic proteins. Because of its activity against proteostasis alteration, the chaperone system plays a relevant role in the protection against proteotoxicity in MNDs. Here, we discuss the role of HSPBs in MNDs and which HSPBs may represent a valid target for therapeutic purposes.

Heterogeneous Clinical Phenotypes of dHMN Caused by Mutation in HSPB1 Gene: A Case Series

Mutations in HSPB1 are known to cause Charcot-Marie-Tooth disease type 2F (CMT2F) and distal hereditary motor neuropathy (dHMN). In this study, we presented three patients with mutation in HSPB1 who were diagnosed with dHMN. Proband 1 was a 14-year-old male with progressive bilateral lower limb weakness and walking difficulty for four years. Proband 2 was a 65-year-old male with chronic lower limb weakness and restless legs syndrome from the age of 51. Proband 3 was a 50-year-old female with progressive weakness, lower limbs atrophy from the age of 44. The nerve conduction studies (NCS) suggested axonal degeneration of the peripheral motor nerves and needle electromyography (EMG) revealed chronic neurogenic changes in probands. Open sural nerve biopsy for proband 2 and the mother of proband 1 showed mild to moderate loss of myelinated nerve fibers with some nerve fiber regeneration. A novel p.V97L in HSPB1 was identified in proband 3, the other two variants (p.P182A and p.R127W) in HSPB1 have been reported previously. The functional studies showed that expressing mutant p.V97L HSPB1 in SH-SY5Y cells displayed a decreased cell activity and increased apoptosis under stress condition. Our study expands the clinical phenotypic spectrum and etiological spectrum of HSPB1 mutation.

A Charcot-Marie-Tooth-Causing Mutation in HSPB1 Decreases Cell Adaptation to Repeated Stress by Disrupting Autophagic Clearance of Misfolded Proteins

Charcot-Marie-Tooth (CMT) disease is the most common inherited neurodegenerative disorder with selective degeneration of peripheral nerves. Despite advances in identifying CMT-causing genes, the underlying molecular mechanism, particularly of selective degeneration of peripheral neurons remains to be elucidated. Since peripheral neurons are sensitive to multiple stresses, we hypothesized that daily repeated stress might be an essential contributor to the selective degeneration of peripheral neurons induced by CMT-causing mutations. Here, we mainly focused on the biological effects of the dominant missense mutation (S135F) in the 27-kDa small heat-shock protein HSPB1 under repeated heat shock. HSPB1S135F presented hyperactive binding to both α-tubulin and acetylated α-tubulin during repeated heat shock when compared with the wild type. The aberrant interactions with tubulin prevented microtubule-based transport of heat shock-induced misfolded proteins for the formation of perinuclear aggresomes. Furthermore, the transport of autophagosomes along microtubules was also blocked. These results indicate that the autophagy pathway was disrupted, leading to an accumulation of ubiquitinated protein aggregates and a significant decrease in cell adaptation to repeated stress. Our findings provide novel insights into the molecular mechanisms of HSPB1S135F-induced selective degeneration of peripheral neurons and perspectives for targeting autophagy as a promising therapeutic strategy for CMT neuropathy.

Stress Granule Homeostasis, Aberrant Phase Transition, and Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease. In recent years, a large number of ALS-related mutations have been discovered to have a strong link to stress granules (SGs). SGs are cytoplasmic ribonucleoprotein condensates mediated by liquid-liquid phase separation (LLPS) of biomacromolecules. They help cells cope with stress. The normal physiological functions of SGs are dependent on three key aspects of SG "homeostasis": SG assembly, disassembly, and SG components. Any of these three aspects can be disrupted, resulting in abnormalities in the cellular stress response and leading to cytotoxicity. Several ALS-related pathogenic mutants have abnormal LLPS abilities that disrupt SG homeostasis, and some of them can even cause aberrant phase transitions. As a result, ALS-related mutants may disrupt various aspects of SG homeostasis by directly disturbing the intermolecular interactions or affecting core SG components, thus disrupting the phase equilibrium of the cytoplasm during stress. Considering that the importance of the "global view" of SG homeostasis in ALS pathogenesis has not received enough attention, we first systematically summarize the physiological regulatory mechanism of SG homeostasis based on LLPS and then examine ALS pathogenesis from the perspective of disrupted SG homeostasis and aberrant phase transition of biomacromolecules.

Ubiquitin profiling of lysophagy identifies actin stabilizer CNN2 as a target of VCP/p97 and uncovers a link to HSPB1

Lysosomal membrane permeabilization (LMP) is an underlying feature of diverse conditions including neurodegeneration. Cells respond by extensive ubiquitylation of membrane-associated proteins for clearance of the organelle through lysophagy that is facilitated by the ubiquitin-directed AAA-ATPase VCP/p97. Here, we assessed the ubiquitylated proteome upon acute LMP and uncovered a large diversity of targets and lysophagy regulators. They include calponin-2 (CNN2) that, along with the Arp2/3 complex, translocates to damaged lysosomes and regulates actin filaments to drive phagophore formation. Importantly, CNN2 needs to be ubiquitylated during the process and removed by VCP/p97 for efficient lysophagy. Moreover, we identified the small heat shock protein HSPB1 that assists VCP/p97 in the extraction of CNN2 and show that other membrane regulators including SNAREs, PICALM, AGFG1, and ARL8B are ubiquitylated during lysophagy. Our data reveal a framework of how ubiquitylation and two effectors, VCP/p97 and HSPB1, cooperate to protect cells from the deleterious effects of LMP.

Human HspB1, HspB3, HspB5 and HspB8: Shaping these disease factors during vertebrate evolution

Small heat shock proteins (sHSPs) emerged early in evolution and occur in all domains of life and nearly in all species, including humans. Mutations in four sHSPs (HspB1, HspB3, HspB5, HspB8) are associated with neuromuscular disorders. The aim of this study is to investigate the evolutionary forces shaping these sHSPs during vertebrate evolution. We performed comparative evolutionary analyses on a set of orthologous sHSP sequences, based on the ratio of non-synonymous: synonymous substitution rates for each codon. We found that these sHSPs had been historically exposed to different degrees of purifying selection, decreasing in this order: HspB8 > HspB1, HspB5 > HspB3. Within each sHSP, regions with different degrees of purifying selection can be discerned, resulting in characteristic selective pressure profiles. The conserved α-crystallin domains were exposed to the most stringent purifying selection compared to the flanking regions, supporting a 'dimorphic pattern' of evolution. Thus, during vertebrate evolution the different sequence partitions were exposed to different and measurable degrees of selective pressures. Among the disease-associated mutations, most are missense mutations primarily in HspB1 and to a lesser extent in the other sHSPs. Our data provide an explanation for this disparate incidence. Contrary to the expectation, most missense mutations cause dominant disease phenotypes. Theoretical considerations support a connection between the historic exposure of these sHSP genes to a high degree of purifying selection and the unusual prevalence of genetic dominance of the associated disease phenotypes. Our study puts the genetics of inheritable sHSP-borne diseases into the context of vertebrate evolution.

Insights on Human Small Heat Shock Proteins and Their Alterations in Diseases

The family of the human small Heat Shock Proteins (HSPBs) consists of ten members of chaperones (HSPB1-HSPB10), characterized by a low molecular weight and capable of dimerization and oligomerization forming large homo- or hetero-complexes. All HSPBs possess a highly conserved centrally located α-crystallin domain and poorly conserved N- and C-terminal domains. The main feature of HSPBs is to exert cytoprotective functions by preserving proteostasis, assuring the structural maintenance of the cytoskeleton and acting in response to cellular stresses and apoptosis. HSPBs take part in cell homeostasis by acting as holdases, which is the ability to interact with a substrate preventing its aggregation. In addition, HSPBs cooperate in substrates refolding driven by other chaperones or, alternatively, promote substrate routing to degradation. Notably, while some HSPBs are ubiquitously expressed, others show peculiar tissue-specific expression. Cardiac muscle, skeletal muscle and neurons show high expression levels for a wide variety of HSPBs. Indeed, most of the mutations identified in HSPBs are associated to cardiomyopathies, myopathies, and motor neuropathies. Instead, mutations in HSPB4 and HSPB5, which are also expressed in lens, have been associated with cataract. Mutations of HSPBs family members encompass base substitutions, insertions, and deletions, resulting in single amino acid substitutions or in the generation of truncated or elongated proteins. This review will provide an updated overview of disease-related mutations in HSPBs focusing on the structural and biochemical effects of mutations and their functional consequences.

Comparative proteomic profiling reveals a pathogenic role for the O-GlcNAcylated AIMP2-PARP1 complex in aging-related hepatic steatosis in mice

The prevalence of non-alcoholic fatty liver disease (NAFLD) increases with aging. However, the mechanism of aging-related NAFLD remains unclear. Herein, we constructed an aging-related hepatic steatosis model and analyzed the differentially expressed proteins (DEPs) in livers from young and old mice using liquid chromatography-mass spectrometry. Five hundred and eighty-eight aging-related DEPs and novel pathways were identified. Aminoacyl tRNA synthetase complex-interacting multifunctional protein 2 (AIMP2), the most significantly upregulated protein, promoted poly(ADP-ribose) polymerase 1 (PARP1) activation in aging-related hepatic steatosis. Additionally, mice liver-specific O-GlcNAcase knockout promoted AIMP2 and PARP1 expression. O-GlcNAc transferase (OGT) overexpression and O-GlcNAcase inhibition by genetic or pharmaceutical manipulations increased AIMP2 and PARP1 levels in vitro. Mechanistically, O-GlcNAcylation increased AIMP2 protein stability, leading to its aggregation. Our study reveals O-GlcNAcylated AIMP2 as a novel pathogenic regulator of aging-related hepatic steatosis.

Extracellular vesicle-associated small heat shock proteins as therapeutic agents in neurodegenerative diseases and beyond

Increasing evidence points towards using extracellular vesicles (EVs) as a therapeutic strategy in neurodegenerative diseases such as multiple sclerosis, Parkinson's, and Alzheimer's disease. EVs are nanosized carriers that play an essential role in intercellular communication and cellular homeostasis by transporting an active molecular cargo, including a large variety of proteins. Recent publications demonstrate that small heat shock proteins (HSPBs) exhibit a beneficial role in neurodegenerative diseases. Moreover, it is defined that HSPBs target the autophagy and the apoptosis pathway, playing a prominent role in chaperone activity and cell survival. This review elaborates on the therapeutic potential of EVs and HSPBs, in particular HSPB1 and HSPB8, in neurodegenerative diseases. We conclude that EVs and HSPBs positively influence neuroinflammation, central nervous system (CNS) repair, and protein aggregation in CNS disorders. Moreover, we propose the use of HSPB-loaded EVs as advanced nanocarriers for the future development of neurodegenerative disease therapies.

m6A reader YTHDC1 modulates autophagy by targeting SQSTM1 in diabetic skin

Dysregulation of macroautophagy/autophagy contributes to the delay of wound healing in diabetic skin. N⁶-methyladenosine (m⁶A) RNA modification is known to play a critical role in regulating autophagy. In this study, it was found that SQSTM1/p62 (sequestosome 1), an autophagy receptor, was significantly downregulated in two human keratinocyte cells lines with short-term high-glucose treatment, as well as in the epidermis of diabetic patients and a db/db mouse model with long-term hyperglycemia. Knockdown of SQSTM1 led to the impairment of autophagic flux, which was consistent with the results of high-glucose treatment in keratinocytes. Moreover, the m⁶A reader protein YTHDC1 (YTH domain containing 1), which interacted with SQSTM1 mRNA, was downregulated in keratinocytes under both the acute and chronic effects of hyperglycemia. Knockdown of YTHDC1 affected biological functions of keratinocytes, which included increased apoptosis rates and impaired wound-healing capacity. In addition, knockdown of endogenous YTHDC1 resulted in a blockade of autophagic flux in keratinocytes, while overexpression of YTHDC1 rescued the blockade of autophagic flux induced by high glucose. In vivo, knockdown of endogenous Ythdc1 or Sqstm1 inhibited autophagy in the epidermis and delayed wound healing. Interestingly, we found that a decrease of YTHDC1 drove SQSTM1 mRNA degradation in the nucleus. Furthermore, the results revealed that YTHDC1 interacted and cooperated with ELAVL1/HuR (ELAV like RNA binding protein 1) in modulating the expression of SQSTM1. Collectively, this study uncovered a previously unrecognized function for YTHDC1 in modulating autophagy via regulating the stability of SQSTM1 nuclear mRNA in diabetic keratinocytes.

Abbreviations: ACTB: actin beta; AGEs: glycation end products; AL: autolysosome; AP: autophagosome; ATG: autophagy related; AKT: AKT serine/threonine kinase; ANOVA: analysis of variance; BECN1: beclin 1; Co-IP: co-immunoprecipitation; DEGs: differentially expressed genes; DM: diabetes mellitus; ELAVL1: ELAV like RNA binding protein 1; FTO: FTO alpha-ketoglutarate dependent dioxygenase; G: glucose; HaCaT: human keratinocyte; GO: Gene Ontology; GSEA: Gene Set Enrichment Analysis; HE: hematoxylin-eosin; IHC: immunohistochemical; IRS: immunoreactive score; KEAP1: kelch like ECH associated protein 1; KEGG: Kyoto Encyclopedia of Genes and Genomes; m⁶A: N⁶-methyladenosine; M: mannitol; MANOVA: multivariate analysis of variance; MAP1LC3: microtubule associated protein 1 light chain 3; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MeRIP: methylated RNA immunoprecipitation; METTL3: methyltransferase 3, N6-adenosine-methytransferase complex catalytic subunit; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin complex 1; NBR1: NBR1 autophagy cargo receptor; NFE2L2: nuclear factor, erythroid 2 like 2; NG: normal glucose; NHEK: normal human epithelial keratinocyte; OE: overexpressing; p-: phospho-; PI: propidium iodide; PPIN: Protein-Protein Interaction Network; RBPs: RNA binding proteins; RIP: RNA immunoprecipitation; RNA-seq: RNA-sequence; RNU6–1: RNA, U6 small nuclear 1; ROS: reactive oxygen species; siRNAs: small interfering RNAs; SQSTM1: sequestosome 1; SRSF: serine and arginine rich splicing factor; T2DM: type 2 diabetes mellitus; TEM: transmission electron microscopy; TUBB: tubulin beta class I; WT: wild-type; YTHDC1: YTH domain containing 1.

Held Up in Traffic-Defects in the Trafficking Machinery in Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth disease (CMT), also known as motor and sensory neuropathy, describes a clinically and genetically heterogenous group of disorders affecting the peripheral nervous system. CMT typically arises in early adulthood and is manifested by progressive loss of motor and sensory functions; however, the mechanisms leading to the pathogenesis are not fully understood. In this review, we discuss disrupted intracellular transport as a common denominator in the pathogenesis of different CMT subtypes. Intracellular transport via the endosomal system is essential for the delivery of lipids, proteins, and organelles bidirectionally to synapses and the soma. As neurons of the peripheral nervous system are amongst the longest neurons in the human body, they are particularly susceptible to damage of the intracellular transport system, leading to a loss in axonal integrity and neuronal death. Interestingly, defects in intracellular transport, both in neurons and Schwann cells, have been found to provoke disease. This review explains the mechanisms of trafficking and subsequently summarizes and discusses the latest findings on how defects in trafficking lead to CMT. A deeper understanding of intracellular trafficking defects in CMT will expand our understanding of CMT pathogenesis and will provide novel approaches for therapeutic treatments.

Maintaining proteostasis under mechanical stress

Cell survival, tissue integrity and organismal health depend on the ability to maintain functional protein networks even under conditions that threaten protein integrity. Protection against such stress conditions involves the adaptation of folding and degradation machineries, which help to preserve the protein network by facilitating the refolding or disposal of damaged proteins. In multicellular organisms, cells are permanently exposed to stress resulting from mechanical forces. Yet, for long time mechanical stress was not recognized as a primary stressor that perturbs protein structure and threatens proteome integrity. The identification and characterization of protein folding and degradation systems, which handle force-unfolded proteins, marks a turning point in this regard. It has become apparent that mechanical stress protection operates during cell differentiation, adhesion and migration and is essential for maintaining tissues such as skeletal muscle, heart and kidney as well as the immune system. Here, we provide an overview of recent advances in our understanding of mechanical stress protection.

Hereditary motor neuropathies

PURPOSE OF REVIEW

Hereditary motor neuropathies (HMN) comprise a broad genotypic and phenotypic spectrum of rare, progressively disabling diseases manifesting with length-dependent muscle weakness and atrophy. To date, more than half of the cases cannot be genetically explained. To provide symptomatic and disease-modifying treatments in the future, a better understanding of disease mechanisms is required.

RECENT FINDINGS

By whole exome and genome sequencing, the discovery of several novel genes (SCO2, TDRKH, SPTAN1, CADM3, and SORD) involved in the pathogenesis of HMN has now relevantly changed the pathophysiological knowledge. This recent success in causative understanding has mainly been driven by the development of functional models including cell culture, animal, and patient-derived induced pluripotent stem cell platforms. These models have an important impact on therapeutic advances including broader approaches to prevent or reverse axonal degeneration and individualized gene silencing attempts using sequence-specific RNA degradation mechanisms.

SUMMARY

In rare diseases such as HMN, the recent development of genetic sequencing and data interpretation methods has enabled a broader diagnostic approach, whereas treatment strategies are becoming more individualized. Significant milestones have been reached in the discovery of new genes, the establishment of functional disease models, and the preclinical development of mechanistic-based therapies.

A weakened interface in the P182L variant of HSP27 associated with severe Charcot-Marie-Tooth neuropathy causes aberrant binding to interacting proteins

HSP27 is a human molecular chaperone that forms large, dynamic oligomers and functions in many aspects of cellular homeostasis. Mutations in HSP27 cause Charcot-Marie-Tooth (CMT) disease, the most common inherited disorder of the peripheral nervous system. A particularly severe form of CMT disease is triggered by the P182L mutation in the highly conserved IxI/V motif of the disordered C-terminal region, which interacts weakly with the structured core domain of HSP27. Here, we observed that the P182L mutation disrupts the chaperone activity and significantly increases the size of HSP27 oligomers formed in vivo, including in motor neurons differentiated from CMT patient-derived stem cells. Using NMR spectroscopy, we determined that the P182L mutation decreases the affinity of the HSP27 IxI/V motif for its own core domain, leaving this binding site more accessible for other IxI/V-containing proteins. We identified multiple IxI/V-bearing proteins that bind with higher affinity to the P182L variant due to the increased availability of the IxI/V-binding site. Our results provide a mechanistic basis for the impact of the P182L mutation on HSP27 and suggest that the IxI/V motif plays an important, regulatory role in modulating protein-protein interactions.

The expanding genetic landscape of hereditary motor neuropathies

Hereditary motor neuropathies are clinically and genetically diverse disorders characterized by length-dependent axonal degeneration of lower motor neurons. Although currently as many as 26 causal genes are known, there is considerable missing heritability compared to other inherited neuropathies such as Charcot-Marie-Tooth disease. Intriguingly, this genetic landscape spans a discrete number of key biological processes within the peripheral nerve. Also, in terms of underlying pathophysiology, hereditary motor neuropathies show striking overlap with several other neuromuscular and neurological disorders. In this review, we provide a current overview of the genetic spectrum of hereditary motor neuropathies highlighting recent reports of novel genes and mutations or recent discoveries in the underlying disease mechanisms. In addition, we link hereditary motor neuropathies with various related disorders by addressing the main affected pathways of disease divided into five major processes: axonal transport, tRNA aminoacylation, RNA metabolism and DNA integrity, ion channels and transporters and endoplasmic reticulum.

Virus-Host Interactions in Foot-and-Mouth Disease Virus Infection

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals, which has been regarded as a persistent challenge for the livestock industry in many countries. Foot-and-mouth disease virus (FMDV) is the etiological agent of FMD that can spread rapidly by direct and indirect transmission. FMDV is internalized into host cell by the interaction between FMDV capsid proteins and cellular receptors. When the virus invades into the cells, the host antiviral system is quickly activated to suppress the replication of the virus and remove the virus. To retain fitness and host adaptation, various viruses have evolved multiple elegant strategies to manipulate host machine and circumvent the host antiviral responses. Therefore, identification of virus-host interactions is critical for understanding the host defense against virus infections and the pathogenesis of the viral infectious diseases. This review elaborates on the virus-host interactions during FMDV infection to summarize the pathogenic mechanisms of FMD, and we hope it can provide insights for designing effective vaccines or drugs to prevent and control the spread of FMD and other diseases caused by picornaviruses.

[Rare variants of HSPB1 are probably associated with amyotrophic lateral sclerosis]

OBJECTIVE

To explore the association between rare HSPB1 variants and amyotrophic lateral sclerosis (ALS).

METHODS

We performed next-generation sequencing for 166 Chinese ALS patients to screen for possible pathogenic rare variants of HSPB1. The control individuals were obtained from 1000 Genome Project and an in-house whole-exome sequencing database. The Sequence Kernel Association Test (SKAT) and the SKAT-optimal test (SKAT-O) were used to identify the association between rare HSPB1 variants and ALS.

RESULTS

We identified 3 possible pathogenic rare variants of HSPB1 (all were missenses), including c.379C>T (p.R127W), c.446A>C (p.D149A) and c.451A>C (p.T151P). Compared with 1000 Genome Project, SKAT p=3.61×10^-7 and SKAT-O p=1.62×10^-6; while compared with the in-house database, SKAT p=9.99×10^-4, SKAT-O p= 1.80×10^-3. We analyzed the phenotypes of rare HSPB1 variant carriers and found no specific clinical characteristics associated with these variants.

CONCLUSIONS

Rare variants of HSPB1 are probably associated with the pathogenesis of ALS.

The dazzling rise of neurofilaments: Physiological functions and roles as biomarkers

In the last two years, neurofilaments (NFs) have become one of the most blazing topics in clinical neuroscience. NFs are major cytoskeletal constituents of neurons, can be detected in body fluids, and have recently emerged as universal biomarkers of neuronal injury and neurological diseases. This review will examine the evolving landscape of NFs, from their specific cellular functions within neurons to their broad clinical value as biomarkers. Particular attention will be given to the dynamic nature of the NF network and its novel roles in microtubule regulation, neurotransmission, and nanomedicine. Building from the initial evidence of causative mutations in NF genes in Charcot-Marie-Tooth diseases, the latest advances at the frontiers of basic and clinical sciences have expanded the scope and relevance of NFs for human health remarkably and have poised to fuel innovation in cell biology and neuroscience.

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

Identification of contributing genes of Huntington's disease by machine learning

Background

Huntington’s disease (HD) is an inherited disorder caused by the polyglutamine (poly-Q) mutations of the HTT gene results in neurodegeneration characterized by chorea, loss of coordination, cognitive decline. However, HD pathogenesis is still elusive. Despite the availability of a wide range of biological data, a comprehensive understanding of HD’s mechanism from machine learning is so far unrealized, majorly due to the lack of needed data density.

Methods

To harness the knowledge of the HD pathogenesis from the expression profiles of postmortem prefrontal cortex samples of 157 HD and 157 controls, we used gene profiling ranking as the criteria to reduce the dimension to the order of magnitude of the sample size, followed by machine learning using the decision tree, rule induction, random forest, and generalized linear model.

Results

These four Machine learning models identified 66 potential HD-contributing genes, with the cross-validated accuracy of 90.79 ± 4.57%, 89.49 ± 5.20%, 90.45 ± 4.24%, and 97.46 ± 3.26%, respectively. The identified genes enriched the gene ontology of transcriptional regulation, inflammatory response, neuron projection, and the cytoskeleton. Moreover, three genes in the cognitive, sensory, and perceptual systems were also identified.

Conclusions

The mutant HTT may interfere with both the expression and transport of these identified genes to promote the HD pathogenesis.

Apoptosis, autophagy and atherosclerosis: Relationships and the role of Hsp27

Atherosclerosis is a multifactorial chronic inflammatory disease of the arterial wall, and an important pathological basis of coronary heart disease. Endothelial cells, vascular smooth muscle cells, and macrophages play important roles in the development of atherosclerosis. Of note, apoptosis and autophagy, two types of programmed cell death, influence the development and progression of atherosclerosis via the modulation of such cells. The small heat shock protein Hsp27 is a multifunctional protein induced by various stress factors and has a protective effect on cells. A large number of studies have demonstrated that Hsp27 plays an important role in regulating apoptosis. Recently, some studies have suggested that Hsp27 also participates in the autophagic process. Moreover, Hsp27 is closely related to the occurrence and development of atherosclerosis. Here, we summarize the molecular mechanisms of apoptosis and autophagy and discuss their effects on endothelial cells, vascular smooth muscle cells, and macrophages in the context of atherosclerotic procession. We further explore the involvement of Hsp27 in apoptosis, autophagy, and atherosclerosis. We speculate that Hsp27 may exert its anti-atherosclerotic role via the regulation of apoptosis and autophagy; this may provide the basis for the development of new approaches for the prevention and treatment of atherosclerosis.

Tissue Clearing and Expansion Methods for Imaging Brain Pathology in Neurodegeneration: From Circuits to Synapses and Beyond

Studying the structural alterations occurring during diseases of the nervous system requires imaging heterogeneous cell populations at the circuit, cellular and subcellular levels. Recent advancements in brain tissue clearing and expansion methods allow unprecedented detailed imaging of the nervous system through its entire scale, from circuits to synapses, including neurovascular and brain lymphatics elements. Here, we review the state-of-the-art of brain tissue clearing and expansion methods, mentioning their main advantages and limitations, and suggest their parallel implementation for circuits-to-synapses brain imaging using conventional (diffraction-limited) light microscopy -such as confocal, two-photon and light-sheet microscopy- to interrogate the cellular and molecular basis of neurodegenerative diseases. We discuss recent studies in which clearing and expansion methods have been successfully applied to study neuropathological processes in mouse models and postmortem human brain tissue. Volumetric imaging of cleared intact mouse brains and large human brain samples has allowed unbiased assessment of neuropathological hallmarks. In contrast, nanoscale imaging of expanded cells and brain tissue has been used to study the effect of protein aggregates on specific subcellular structures. Therefore, these approaches can be readily applied to study a wide range of brain processes and pathological mechanisms with cellular and subcellular resolution in a time- and cost-efficient manner. We consider that a broader implementation of these technologies is necessary to reveal the full landscape of cellular and molecular mechanisms underlying neurodegenerative diseases.

Lidocaine promotes autophagy of SH-SY5Y cells through inhibiting PI3K/AKT/mTOR pathway by upregulating miR-145

Lidocaine is one of the most common local anesthetics (LA) used in clinical practice and it is neurotoxic. Recent studies suggested that LA, including lidocaine, could exert protective effect over neurotoxicity by promoting autophagy. However, the underlying mechanism was not sufficiently elucidated. This study aimed to explore the mechanism behind. Human neuroblastoma cell line SH-SY5Y was used throughout the whole study. The effect of lidocaine on viability, toxicity of SH-SY5Y cells were analyzed by MTT and lactate dehydrogenase (LDH) assays, respectively. The relative expression of miR-145 was assessed by quantitative reverse transcription-polymerase chain reaction. The impact which lidocaine brought on PI3K/AKT/mTOR pathway and autophagy-related proteins were examined by the western blot assay. LC3B was assessed by immunofluorescence staining. The interaction between miR-145 and AKT3 was conducted by the dual-luciferase reporting assay. Lidocaine inhibited viability of SH-SY5Y cells in a time and dose dependent manner and enhanced the release of LDH in SH-SY5Y cells. Furthermore, the expression of miR-145 and autophagy were enhanced by lidocaine. Transfection with miR-145 inhibitor inhibited the release of LDH and autophagy. miR-145 targeted AKT3 to inhibit PI3K/AKT/mTOR pathway. Finally, lidocaine inactivated PI3K/AKT/mTOR pathways via upregulation of miR-145, and it subsequently promoted autophagy of SH-SY5Y cells. However, silence of miR-145 could reverse the promotion of the autophagy of SH-SY5Y cells. Our results showed that lidocaine promoted autophagy of nerve cells via regulating miR-145 expression and further inactivation of PI3K/AKT/mTOR signaling pathway.