Disruption of nuclear envelope integrity as a possible initiating event in tauopathies

Nuclear translocation of the LINE-1 encoded ORF1 protein alters nuclear envelope integrity in human neurons

LINE-1 retrotransposons are increasingly implicated in aging and neurodegenerative diseases, yet the precise pathogenic mechanisms remain elusive. While the endonuclease and reverse transcriptase activities of LINE-1-encoded ORF2p can induce DNA damage and inflammation, a role of LINE-1 ORF1p in cellular dysfunctions stays unassigned. Here we demonstrate, using a neuronal cellular model, that ORF1p translocates into the nucleus upon arsenite-induced stress, directly interacting with nuclear import (KPNB1), nuclear pore complex (NUP153), and nuclear lamina (Lamin B1) proteins. Nuclear translocation of ORF1p disrupts nuclear integrity, nucleocytoplasmic transport, and heterochromatin structure, features linked to neurodegeneration and aging. Elevated nuclear ORF1p levels induced either by arsenite-induced stress, ORF1p overexpression, or as observed in Parkinson's disease post-mortem brain tissues correlate with impaired nuclear envelope (NE) morphology. Stress-induced nuclear alterations are mitigated by blocking ORF1p nuclear import or with the anti-aging drug remodelin. This study thus reveals a pathogenic action of nuclear ORF1p in human neurons driving NE alterations and thereby contributing to LINE-1-mediated cell toxicity.

Diverse influences on tau aggregation and implications for disease progression

Tau is an intrinsically disordered protein that accumulates in fibrillar aggregates in neurodegenerative diseases. The misfolding of tau can be understood as an equilibrium between different states and their propensity to form higher-order fibers, which is affected by several factors. First, modulation of the biochemical state of tau due to ionic conditions, post-translational modifications, cofactors, and interacting molecules or assemblies can affect the formation and structure of tau fibrils. Second, cellular processes impact tau aggregation through modulating stability, clearance, disaggregation, and transport. Third, through interactions with glial cells, the neuronal microenvironment can affect intraneuronal conditions with impacts on tau fibrilization and toxicity. Importantly, tau fibrils propagate through the brain via a "prion-like" manner, contributing to disease progression. This review highlights the biochemical and cellular pathways that modulate tau aggregation and discusses implications for pathobiology and tau-directed therapeutic approaches.

Centrosomes and cilia in neurodegeneration: main actors or mere spectators?

Centrosomes are intracellular organelles traditionally recognized as the primary microtubule (MT) organizing centres (MTOCs) in the cell, playing a crucial role in organizing the cytoskeleton and forming the MT-based spindle during cell division. However, it is now well established that centrosomes also function as central hubs for a wide range of signalling pathways. In non-dividing cells, they give rise to the primary cilium, a surface antenna that serves as a key structure for signalling. Neurons are highly specialized cells with a distinctive morphology, and most neurons have cilia. During brain development, cilia regulate the self-renewal of neural progenitors, as well as the differentiation, migration and synapse formation of newly generated neurons. As a consequence, defects in cilia result in various neurodevelopmental disorders. The role of centrosomes and cilia in neurodegeneration, or the progressive loss of neurons, is less understood. Centrosomes take part in several cellular processes that are often disrupted in neurodegenerative diseases (NDDs), and many proteins associated with these conditions have been found at centrosomes or cilia suggesting a link between these organelles and the underlying mechanisms that contribute to neuronal decline. Unravelling if and how centrosome dysfunction contributes to neurodegeneration could significantly deepen our understanding of the underlying biology of these disorders. Such insights may pave the way for new therapeutic approaches to address these debilitating conditions.

Piezo1, F-Actin Remodeling, and Podocyte Survival and Regeneration

Key Points

Background

Podocytes and podocyte progenitors are interdependent components of the kidney's glomerular structure, with podocytes forming the glomerular filtration barrier and progenitors being key players in podocyte regeneration during pathophysiologic processes. Both cell types are subjected to constant mechanical forces, whose alterations can initiate podocytopathy and worsen glomerular injury. Despite this, the specific mechanosensors and mechanotransduction pathways involved in their response to mechanical cues remain only partially explored.

Methods

We used transcriptomics, immunofluorescence, and silencing experiments on human primary podocyte progenitor cell cultures to demonstrate the expression and function of Piezo1 channels. We generated inducible podocyte-specific and podocyte progenitor–specific Piezo1 knockout (KO) mice to evaluate the effects of Piezo1 loss in the context of adriamycin nephropathy and over 10 months of aging.

Results

Silencing of Piezo1 in progenitors triggered F-actin remodeling, which induced cell shape modification and nuclear envelope defects with accumulation of DNA damage that led to mitotic catastrophe in differentiated podocytes. Podocyte-specific KO of Piezo1 induced higher susceptibility to podocyte injury in adriamycin nephropathy and led to accumulation of DNA damage and mild albuminuria starting from adult age. Podocyte progenitor–specific KO of Piezo1 in mouse resulted in severe albuminuria during adriamycin nephropathy, leading to the generation of defective podocytes.

Conclusions

These results demonstrated that Piezo1, thanks to its role in F-actin cytoskeleton maintenance, is essential for the survival of podocytes exposed to mechanical stress conditions and for their correct regeneration.

Cell redistribution of G quadruplex-structured DNA is associated with morphological changes of nuclei and nucleoli in neurons during tau pathology progression

While the double helical structure has long been its iconic representation, DNA is structurally dynamic and can adopt alternative secondary configurations. Specifically, guanine-rich DNA sequences can fold in guanine quadruplexes (G4) structures. These G4 play pivotal roles as regulators of gene expression and genomic stability, and influence protein homeostasis. Despite their significance, the association of G4 with neurodegenerative diseases such as Alzheimer's disease (AD) has been underappreciated. Recent findings have identified DNA sequences predicted to form G4 in sarkosyl-insoluble aggregates from AD brains, questioning the involvement of G4-structured DNA (G4 DNA) in the pathology. Using immunofluorescence coupled to confocal microscopy analysis we investigated the impact of tau pathology, a hallmark of tauopathies including AD, on the distribution of G4 DNA in murine neurons and its relevance to AD brains. In healthy neurons, G4 DNA is detected in nuclei with a notable presence in nucleoli. However, in a transgenic mouse model of tau pathology (THY-Tau22), early stages of the disease exhibit an impairment in the nuclear distribution of G4 DNA. In addition, G4 DNA accumulates in the cytoplasm of neurons exhibiting oligomerized tau and oxidative DNA damage. This altered distribution persists in the later stage of the pathology when larger tau aggregates are present. Still cytoplasmic deposition of G4 DNA does not appear to be a critical factor in the tau aggregation process. Similar patterns are observed in neurons from the AD cortex. Furthermore, the disturbance in G4 DNA distribution is associated with various changes in the size of neuronal nuclei and nucleoli, indicative of responses to stress and the activation of pro-survival mechanisms. Our results shed light on a significant impact of tau pathology on the dynamics of G4 DNA and on nuclear and nucleolar mechanobiology in neurons. These findings reveal new dimensions in the etiopathogenesis of tauopathies.

Nuclear and degradative functions of the ESCRT-III pathway: implications for neurodegenerative disease

The ESCRT machinery plays a pivotal role in membrane-remodeling events across multiple cellular processes including nuclear envelope repair and reformation, nuclear pore complex surveillance, endolysosomal trafficking, and neuronal pruning. Alterations in ESCRT-III functionality have been associated with neurodegenerative diseases including Frontotemporal Dementia (FTD), Amyotrophic Lateral Sclerosis (ALS), and Alzheimer's Disease (AD). In addition, mutations in specific ESCRT-III proteins have been identified in FTD/ALS. Thus, understanding how disruptions in the fundamental functions of this pathway and its individual protein components in the human central nervous system (CNS) may offer valuable insights into mechanisms underlying neurodegenerative disease pathogenesis and identification of potential therapeutic targets. In this review, we discuss ESCRT components, dynamics, and functions, with a focus on the ESCRT-III pathway. In addition, we explore the implications of altered ESCRT-III function for neurodegeneration with a primary emphasis on nuclear surveillance and endolysosomal trafficking within the CNS.

Regulation of TAR DNA binding protein 43 (TDP-43) homeostasis by cytosolic DNA accumulation

TAR DNA-binding protein 43 (TDP-43) is a DNA/RNA binding protein predominantly localized in the nucleus under physiological conditions. TDP-43 proteinopathy, characterized by cytoplasmic aggregation and nuclear loss, is associated with many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Thus it is crucial to understand the molecular mechanism regulating TDP-43 homeostasis. Here, we show that the uptake of oligodeoxynucleotides (ODNs) from the extracellular space induces reversible TDP-43 cytoplasmic puncta formation in both neurons and glia. ODNs facilitate the liquid-liquid phase separation of TDP-43 in vitro. Importantly, persistent accumulation of DNA in the cytoplasm leads to nuclear depletion of TDP-43 and enhanced production of a short isoform of TDP-43 (sTDP-43). In addition, in response to ODN uptake, the nuclear import receptor karyopherin subunit β1 (KPNB1) is sequestered in the cytosolic TDP-43 puncta. ALS-linked Q331K mutation decreases the dynamics of cytoplasmic TDP-43 puncta and increases the levels of sTDP-43. Moreover, the TDP-43 cytoplasmic puncta are induced by DNA damage and by impaired nuclear envelope integrity due to Lamin A/C deficiency. In summary, our data support that abnormal DNA accumulation in the cytoplasm may be one of the key mechanisms leading to TDP-43 proteinopathy and provides novel insights into molecular mechanisms of ALS caused by TDP-43 mutations.

Nuclear pore dysfunction and disease: a complex opportunity

The separation of genetic material from bulk cytoplasm has enabled the evolution of increasingly complex organisms, allowing for the development of sophisticated forms of life. However, this complexity has created new categories of dysfunction, including those related to the movement of material between cellular compartments. In eukaryotic cells, nucleocytoplasmic trafficking is a fundamental biological process, and cumulative disruptions to nuclear integrity and nucleocytoplasmic transport are detrimental to cell survival. This is particularly true in post-mitotic neurons, where nuclear pore injury and errors to nucleocytoplasmic trafficking are strongly associated with neurodegenerative disease. In this review, we summarize the current understanding of nuclear pore biology in physiological and pathological contexts and discuss potential therapeutic approaches for addressing nuclear pore injury and dysfunctional nucleocytoplasmic transport.

Nuclear functions regulated by the VRK1 kinase

In the nucleus, the VRK1 Ser-Thr kinase is distributed in nucleoplasm and chromatin, where it has different roles. VRK1 expression increases in response to mitogenic signals. VRK1 regulates cyclin D1 expression at G0 exit and facilitates chromosome condensation at the end of G2 and G2/M progression to mitosis. These effects are mediated by the phosphorylation of histone H3 at Thr3 by VRK1, and later in mitosis by haspin. VRK1 regulates the apigenetic patterns of histones in processes requiring chromating remodeling, such as transcription, replication and DNA repair. VRK1 is overexpressed in tumors, facilitating tumor progression and resistance to genotoxic treatments. VRK1 also regulates the organization of Cajal bodies assembled on coilin, which are necessary for the assembly of different types of RNP complexes. VRK1 pathogenic variants cuase defects in Cajal bodies, functionally altering neurons with long axons and leading to neurological diseases, such as amyotrophic laterla sclerosis, spinal muscular atrophy, distal hereditay motor neuropathies and Charcot-Marie-Tooth.

A novel role for CSA in the regulation of nuclear envelope integrity: uncovering a non-canonical function

Cockayne syndrome (CS) is a premature ageing condition characterized by microcephaly, growth failure, and neurodegeneration. It is caused by mutations in ERCC6 or ERCC8 encoding for Cockayne syndrome B (CSB) and A (CSA) proteins, respectively. CSA and CSB have well-characterized roles in transcription-coupled nucleotide excision repair, responsible for removing bulky DNA lesions, including those caused by UV irradiation. Here, we report that CSA dysfunction causes defects in the nuclear envelope (NE) integrity. NE dysfunction is characteristic of progeroid disorders caused by a mutation in NE proteins, such as Hutchinson-Gilford progeria syndrome. However, it has never been reported in Cockayne syndrome. We observed CSA dysfunction affected LEMD2 incorporation at the NE and increased actin stress fibers that contributed to enhanced mechanical stress to the NE. Altogether, these led to NE abnormalities associated with the activation of the cGAS/STING pathway. Targeting the linker of the nucleoskeleton and cytoskeleton complex was sufficient to rescue these phenotypes. This work reveals NE dysfunction in a progeroid syndrome caused by mutations in a DNA damage repair protein, reinforcing the connection between NE deregulation and ageing.

Disruption of nuclear speckle integrity dysregulates RNA splicing in C9ORF72-FTD/ALS

Expansion of an intronic (GGGGCC)n repeat within the C9ORF72 gene is the most common genetic cause of both frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) (C9-FTD/ALS), characterized with aberrant repeat RNA foci and noncanonical translation-produced dipeptide repeat (DPR) protein inclusions. Here, we elucidate that the (GGGGCC)n repeat RNA co-localizes with nuclear speckles and alters their phase separation properties and granule dynamics. Moreover, the essential nuclear speckle scaffold protein SRRM2 is sequestered into the poly-GR cytoplasmic inclusions in the C9-FTD/ALS mouse model and patient postmortem tissues, exacerbating the nuclear speckle dysfunction. Impaired nuclear speckle integrity induces global exon skipping and intron retention in human iPSC-derived neurons and causes neuronal toxicity. Similar alternative splicing changes can be found in C9-FTD/ALS patient postmortem tissues. This work identified novel molecular mechanisms of global RNA splicing defects caused by impaired nuclear speckle function in C9-FTD/ALS and revealed novel potential biomarkers or therapeutic targets.

Microglial-derived C1q integrates into neuronal ribonucleoprotein complexes and impacts protein homeostasis in the aging brain

Neuroimmune interactions mediate intercellular communication and underlie critical brain functions. Microglia, CNS-resident macrophages, modulate the brain through direct physical interactions and the secretion of molecules. One such secreted factor, the complement protein C1q, contributes to complement-mediated synapse elimination in both developmental and disease models, yet brain C1q protein levels increase significantly throughout aging. Here, we report that C1q interacts with neuronal ribonucleoprotein (RNP) complexes in an age-dependent manner. Purified C1q protein undergoes RNA-dependent liquid-liquid phase separation (LLPS) in vitro, and the interaction of C1q with neuronal RNP complexes in vivo is dependent on RNA and endocytosis. Mice lacking C1q have age-specific alterations in neuronal protein synthesis in vivo and impaired fear memory extinction. Together, our findings reveal a biophysical property of C1q that underlies RNA- and age-dependent neuronal interactions and demonstrate a role of C1q in critical intracellular neuronal processes.

Tau, RNA, and RNA-Binding Proteins: Complex Interactions in Health and Neurodegenerative Diseases

The tau protein is a key contributor to multiple neurodegenerative diseases. The pathology of tau is thought to be related to tau's propensity to form self-templating fibrillar structures that allow tau fibers to propagate in the brain by prion-like mechanisms. Unresolved issues with respect to tau pathology are how the normal function of tau and its misregulation contribute to disease, how cofactors and cellular organelles influence the initiation and propagation of tau fibers, and determining the mechanism of tau toxicity. Herein, we review the connection between tau and degenerative diseases, the basis for tau fibrilization, and how that process interacts with cellular molecules and organelles. One emerging theme is that tau interacts with RNA and RNA-binding proteins, normally and in pathologic aggregates, which may provide insight into alterations in RNA regulation observed in disease.

Effects of heterologous human tau protein expression in yeast models of proteotoxic stress response

BACKGROUND

The primary histological characteristic of Alzheimer's disease is the presence of neurofibrillary tangles, which are large aggregates of tau protein. Aging is the primary risk factor for the development of Alzheimer's disease, however, the underlying causes of tau protein aggregation and toxicity are unclear.

AIMS

Here we investigated tau aggregation and toxicity under the conditions of compromised protein homeostasis.

METHODS

We used heterologous expression of human tau protein in the unicellular eukaryote yeast Saccharomyces cerevisiae with evolutionarily conserved protein quality control pathways and examined tau-dependent toxicity and aggregation using growth assays, fluorescence microscopy, and a split luciferase-based reporter NanoBiT.

RESULTS

Tau protein expressed in yeast under mild proteotoxic stress, or in mutants with impaired pathways for proteotoxic stress response, did not lead to synthetic toxicity or the formation of obvious aggregates. Chronologically old cells also did not develop observable tau aggregates. Our examination of tau oligomerization in living cells using NanoBiT reporter suggests that tau does not form significant levels of oligomers under basal conditions or under mild proteotoxic stress.

CONCLUSION

Together our data suggest that human tau protein does not represent a major burden to the protein quality control system in yeast cells.

DLK-MAPK Signaling Coupled with DNA Damage Promotes Intrinsic Neurotoxicity Associated with Non-Mutated Tau

Alzheimer's disease (AD) is the most prevalent form of neurodegeneration. Despite the well-established link between tau aggregation and clinical progression, the major pathways driven by this protein to intrinsically damage neurons are incompletely understood. To model AD-relevant neurodegeneration driven by tau, we overexpressed non-mutated human tau in primary mouse neurons and observed substantial axonal degeneration and cell death, a process accompanied by activated caspase 3. Mechanistically, we detected deformation of the nuclear envelope and increased DNA damage response in tau-expressing neurons. Gene profiling analysis further revealed significant alterations in the mitogen-activated protein kinase (MAPK) pathway; moreover, inhibitors of dual leucine zipper kinase (DLK) and c-Jun N-terminal kinase (JNK) were effective in alleviating wild-type human tau-induced neurodegeneration. In contrast, mutant P301L human tau was less toxic to neurons, despite causing comparable DNA damage. Axonal DLK activation induced by wild-type tau potentiated the impact of DNA damage response, resulting in overt neurotoxicity. In summary, we have established a cellular tauopathy model highly relevant to AD and identified a functional synergy between the DLK-MAPK axis and DNA damage response in the neuronal degenerative process.

Molecular functions of ANKLE2 and its implications in human disease

Ankyrin repeat and LEM domain-containing 2 (ANKLE2) is a scaffolding protein with established roles in cell division and development, the dysfunction of which is increasingly implicated in human disease. ANKLE2 regulates nuclear envelope disassembly at the onset of mitosis and its reassembly after chromosome segregation. ANKLE2 dysfunction is associated with abnormal nuclear morphology and cell division. It regulates the nuclear envelope by mediating protein-protein interactions with barrier to autointegration factor (BANF1; also known as BAF) and with the kinase and phosphatase that modulate the phosphorylation state of BAF. In brain development, ANKLE2 is crucial for proper asymmetric division of neural progenitor cells. In humans, pathogenic loss-of-function mutations in ANKLE2 are associated with primary congenital microcephaly, a condition in which the brain is not properly developed at birth. ANKLE2 is also linked to other disease pathologies, including congenital Zika syndrome, cancer and tauopathy. Here, we review the molecular roles of ANKLE2 and the recent literature on human diseases caused by its dysfunction.

Novel avenues of tau research

INTRODUCTION

The pace of innovation has accelerated in virtually every area of tau research in just the past few years.

METHODS

In February 2022, leading international tau experts convened to share selected highlights of this work during Tau 2022, the second international tau conference co-organized and co-sponsored by the Alzheimer's Association, CurePSP, and the Rainwater Charitable Foundation.

RESULTS

Representing academia, industry, and the philanthropic sector, presenters joined more than 1700 registered attendees from 59 countries, spanning six continents, to share recent advances and exciting new directions in tau research.

DISCUSSION

The virtual meeting provided an opportunity to foster cross-sector collaboration and partnerships as well as a forum for updating colleagues on research-advancing tools and programs that are steadily moving the field forward.

Altered nuclear envelope homeostasis is a key pathogenic event in C9ORF72-linked ALS/FTD

ALS and FTD are complex neurodegenerative disorders that primarily affects motor neurons in the brain and spinal cord, and cortical neurons in the frontal lobe. Although the pathogenesis of ALS/FTD is unclear, recent research spotlights nucleocytoplasmic transport impairment, DNA damage, and nuclear abnormalities as drivers of neuronal death. In this study, we show that loss of nuclear envelope (NE) integrity is a key pathology associated with nuclear pore complex (NPC) injury in C9ORF72 mutant neurons. Importantly, we show that mechanical stresses generated by cytoskeletal forces on the NE can lead to NPC injury, loss of nuclear integrity, and accumulation of DNA damage. Importantly, we demonstrate that restoring NE tensional homeostasis, by disconnecting the nucleus from the cytoskeleton, can rescue NPC injury and reduce DNA damage in C9ORF72 mutant cells. Together, our data suggest that modulation of NE homeostasis and repair may represent a novel and promising therapeutic target for ALS/FTD.

How nuclear envelope dynamics can direct laminopathy phenotypes

The nuclear envelope separates the genome from the cytoplasmic environment. However, the nuclear envelope is also physically associated with the genome and exerts influence on gene expression and genome modification. The nucleus is dynamic, changing shape and responding to cell movement, disassembling and assembling during cell division, and undergoing rupture and repair. These dynamics can be impacted by genetic disease, leading to a family of diseases called laminopathies. Their disparate phenotypes suggest that multiple processes are affected. We highlight three such processes here, which we believe can be used to classify most of the laminopathies. While much still needs to be learned, some commonalities between these processes, such as proteins involved in nuclear envelope formation and rupture repair, may drive a variety of laminopathies. Here we review the latest information regarding nuclear dynamics and its role in laminopathies related to mutations in the nuclear lamina and linker of nucleoskeleton and cytoskeleton complex (LINC) proteins.

Nuclear face of Tau: an inside player in neurodegeneration

Tau (Tubulin associated unit) protein is a major hallmark of Alzheimer's disease (AD) and tauopathies. Tau is predominantly an axonal protein with a crucial role in the stabilization and dynamics of the microtubules. Since the discovery of Tau protein in 1975, research efforts were concentrated on the pathophysiological role of Tau protein in the context of the microtubules. Although, for more than three decades, different localizations of Tau protein have been discovered e.g., in the nuclear compartments. Discovery of the role of Tau protein in various cellular compartments especially in the nucleus opens up a new fold of complexity in tauopathies. Data from cellular models, animal models, and the human brain indicate that nuclear Tau is crucial for genome stability and to cope with cellular distress. Moreover, it's nature of nuclear translocation, its interactions with the nuclear DNA/RNA and proteins suggest it could play multiple roles in the nucleus. To comprehend Tau pathophysiology and efficient Tau-based therapies, there is an urgent need to understand whole repertoire of Tau species (nuclear and cytoplasmic) and their functional relevance. To complete the map of Tau repertoire, understanding of various species of Tau in the nucleus and cytoplasm, identification if specific transcripts of Tau, isoforms and post-translational modifications could foretell Tau's localizations and functions, and how they are modified in neurodegenerative diseases like AD, is urgently required. In this review, we explore the nuclear face of Tau protein, its nuclear localizations and functions and its linkage with Alzheimer's disease.

The dynamic nuclear envelope: resilience in health and dysfunction in disease

The canonical appearance of the nucleus depends on constant adaptation and remodeling of the nuclear envelope in response to changing biomechanical forces and metabolic demands. Dynamic events at the nuclear envelope play a vital role in supporting key nuclear functions as well as conferring plasticity to this organelle. Moreover, imbalance of these dynamic processes is emerging as a central feature of disease etiology. This review focuses on recent advances that shed light on the myriad events at the nuclear envelope that contribute to resilience and flexibility in nuclear architecture.

Patent Highlights April-May 2023

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

Cx43 can form functional channels at the nuclear envelope and modulate gene expression in cardiac cells

Classically associated with gap junction-mediated intercellular communication, connexin43 (Cx43) is increasingly recognized to possess non-canonical biological functions, including gene expression regulation. However, the mechanisms governing the localization and role played by Cx43 in the nucleus, namely in transcription modulation, remain unknown. Using comprehensive and complementary approaches encompassing biochemical assays, super-resolution and immunogold transmission electron microscopy, we demonstrate that Cx43 localizes to the nuclear envelope of different cell types and in cardiac tissue. We show that translocation of Cx43 to the nucleus relies on Importin-β, and that Cx43 significantly impacts the cellular transcriptome, likely by interacting with transcriptional regulators. In vitro patch-clamp recordings from HEK293 and adult primary cardiomyocytes demonstrate that Cx43 forms active channels at the nuclear envelope, providing evidence that Cx43 can participate in nucleocytoplasmic shuttling of small molecules. The accumulation of nuclear Cx43 during myogenic differentiation of cardiomyoblasts is suggested to modulate expression of genes implicated in this process. Altogether, our study provides new evidence for further defining the biological roles of nuclear Cx43, namely in cardiac pathophysiology.

Mechanisms controlling the mechanical properties of the nuclei

The mechanical properties of the nucleus influence different cellular and nuclear functions and have relevant implications for several human diseases. The nucleus protects genetic information while acting as a mechano-sensory hub in response to internal and external forces. Cells have evolved mechano-transduction signaling to respond to physical cellular and nuclear perturbations and adopted a multitude of molecular pathways to maintain nuclear shape stability and prevent morphological abnormalities of the nucleus. Here we describe those key biological processes that control nuclear mechanics and discuss emerging perspectives on the mechanobiology of the nucleus as a diagnostic tool and clinical target.

Nuclear pore complex and nucleocytoplasmic transport disruption in neurodegeneration

Nuclear pore complexes (NPCs) play a critical role in maintaining the equilibrium between the nucleus and cytoplasm, enabling bidirectional transport across the nuclear envelope, and are essential for proper nuclear organization and gene regulation. Perturbations in the regulatory mechanisms governing NPCs and nuclear envelope homeostasis have been implicated in the pathogenesis of several neurodegenerative diseases. The ESCRT-III pathway emerges as a critical player in the surveillance and preservation of well-assembled, functional NPCs, as well as nuclear envelope sealing. Recent studies have provided insights into the involvement of nuclear ESCRT-III in the selective reduction of specific nucleoporins associated with neurodegenerative pathologies. Thus, maintaining quality control of the nuclear envelope and NPCs represents a pivotal element in the pathological cascade leading to neurodegenerative diseases. This review describes the constituents of the nuclear-cytoplasmic transport machinery, encompassing the nuclear envelope, NPC, and ESCRT proteins, and how their structural and functional alterations contribute to the development of neurodegenerative diseases.

Can accelerated ageing models inform us on age-related tauopathies?

Ageing is the greatest risk factor of late-onset neurodegenerative diseases. In the realm of sporadic tauopathies, modelling the process of biological ageing in experimental animals forms the foundation of searching for the molecular origin of pathogenic tau and developing potential therapeutic interventions. Although prior research into transgenic tau models offers valuable lessons for studying how tau mutations and overexpression can drive tau pathologies, the underlying mechanisms by which ageing leads to abnormal tau accumulation remains poorly understood. Mutations associated with human progeroid syndromes have been proposed to be able to mimic an aged environment in animal models. Here, we summarise recent attempts in modelling ageing in relation to tauopathies using animal models that carry mutations associated with human progeroid syndromes, or genetic elements unrelated to human progeroid syndromes, or have exceptional natural lifespans, or a remarkable resistance to ageing-related disorders.

Modeling Alzheimer's disease in primary neurons reveals DNA damage response coupled with MAPK-DLK signaling in wild-type tau-induced neurodegeneration

Background

Alzheimer's disease (AD) is the most prevalent form of neurodegeneration. Despite the well-established link between tau aggregation and clinical progression, the major pathways driven by this protein to intrinsically damage neurons are incompletely understood.

Methods

To model AD-relevant neurodegeneration driven by tau, we overexpressed wild-type human tau in primary mouse neurons and characterized the subsequent cellular and molecular changes. RNAseq profiling and functional investigation were performed as well. A direct comparison with a mutant human tau was conducted in detail.

Results

We observed substantial axonal degeneration and cell death associated with wild-type tau, a process accompanied by activated caspase 3. Mechanistically, we detected deformation of the nuclear envelope and increased DNA damage response in tau-expressing neurons. Gene profiling analysis further revealed significant alterations in the mitogen-activated protein kinase (MAPK) pathway; moreover, inhibitors of dual leucine zipper kinase (DLK) and c-Jun N-terminal kinase (JNK) were effective in alleviating wild-type human tau-induced neurodegeneration. In contrast, mutant P301L human tau was less toxic to neurons, despite causing comparable DNA damage. Axonal DLK activation induced by wild-type tau potentiated the impact of DNA damage response, resulting in overt neurotoxicity.

Conclusions

We have established a cellular tauopathy model highly relevant to AD and identified a functional synergy between DNA damage response and the MAPK-DLK axis in the neuronal degenerative process.

Pathogenic tau decreases nuclear tension in cultured neurons

Neurodegenerative tauopathies, including Alzheimer's disease, are pathologically defined by the presence of aggregated forms of tau protein in brains of affected individuals. Previous studies report that the negative effects of pathogenic tau on the actin cytoskeleton and microtubules cause a toxic destabilization of the lamin nucleoskeleton and formation of nuclear invaginations and blebs. Based on the known function of the nucleus as a mechanosensor, as well as the high incidence of nuclear pleomorphism in human Alzheimer's disease and related tauopathies, we investigated the effects of pathogenic tau on nuclear tension. We first find that tau-dependent nuclear envelope invagination and relocalization of LInker of Nucleoskeleton and Cytoskeleton (LINC) complex components are conserved in a newly-developed neuroblastoma cell line that features doxycycline-inducible expression of a tau mutant associated with autosomal dominant frontotemporal dementia. We next determine that a Förster resonance energy transfer (FRET)-based sensor of nuclear tension responds to cytoskeletal stabilization and destabilization when expressed in neuroblastoma cells. Using this nuclear tension sensor, we find that induced expression of pathogenic tau is sufficient to decrease nuclear tension. This work provides the initial proof-of-concept evidence that pathogenic forms of tau alter nuclear tension, paving the way for the future study of altered nuclear mechanosensing in the context of tau-mediated neurodegenerative disorders.

CRISPRi screening reveals regulators of tau pathology shared between exosomal and vesicle-free tau

The aggregation of the microtubule-associated protein tau is a defining feature of Alzheimer's disease and other tauopathies. Tau pathology is believed to be driven by free tau aggregates and tau carried within exosome-like extracellular vesicles, both of which propagate trans-synaptically and induce tau pathology in recipient neurons by a corrupting process of seeding. Here, we performed a genome-wide CRISPRi screen in tau biosensor cells and identified cellular regulators shared by both mechanisms of tau seeding. We identified ANKLE2, BANF1, NUSAP1, EIF1AD, and VPS18 as the top validated regulators that restrict tau aggregation initiated by both exosomal and vesicle-free tau seeds. None of our validated hits affected the uptake of either form of tau seeds, supporting the notion that they operate through a cell-autonomous mechanism downstream of the seed uptake. Lastly, validation studies with human brain tissue also revealed that several of the identified protein hits are down-regulated in the brains of Alzheimer's patients, suggesting that their decreased activity may be required for the emergence or progression of tau pathology in the human brain.