The nuclear lamins: flexibility in function

Molecular plasticity of herpesvirus nuclear egress analysed in situ

The viral nuclear egress complex (NEC) allows herpesvirus capsids to escape from the nucleus without compromising the nuclear envelope integrity. The NEC lattice assembles on the inner nuclear membrane and mediates the budding of nascent nucleocapsids into the perinuclear space and their subsequent release into the cytosol. Its essential role makes it a potent antiviral target, necessitating structural information in the context of a cellular infection. Here we determined structures of NEC-capsid interfaces in situ using electron cryo-tomography, showing a substantial structural heterogeneity. In addition, while the capsid is associated with budding initiation, it is not required for curvature formation. By determining the NEC structure in several conformations, we show that curvature arises from an asymmetric assembly of disordered and hexagonally ordered lattice domains independent of pUL25 or other viral capsid vertex components. Our results advance our understanding of the mechanism of nuclear egress in the context of a living cell.

Mechanobiology of Adipocytes

The growing obesity epidemic necessitates increased research on adipocyte and adipose tissue function and disease mechanisms that progress obesity. Historically, adipocytes were viewed simply as storage for excess energy. However, recent studies have demonstrated that adipocytes play a critical role in whole-body homeostasis, are involved in cell communication, experience forces in vivo, and respond to mechanical stimuli. Changes to the adipocyte mechanical microenvironment can affect function and, in some cases, contribute to disease. The aim of this review is to summarize the current literature on the mechanobiology of adipocytes. We reviewed over 100 papers on how mechanical stress is sensed by the adipocyte, the effects on cell behavior, and the use of cell culture scaffolds, particularly those with tunable stiffness, to study adipocyte behavior, adipose cell and tissue mechanical properties, and computational models. From our review, we conclude that adipocytes are responsive to mechanical stimuli, cell function and adipogenesis can be dictated by the mechanical environment, the measurement of mechanical properties is highly dependent on testing methods, and current modeling practices use many different approaches to recapitulate the complex behavior of adipocytes and adipose tissue. This review is intended to aid future studies by summarizing the current literature on adipocyte mechanobiology.

Nuclear actin structure regulates chromatin accessibility

Polymerized β-actin may provide a structural basis for chromatin accessibility and actin transport into the nucleus can guide mesenchymal stem cell (MSC) differentiation. Using MSC, we show that using CK666 to inhibit Arp2/3 directed secondary actin branching results in decreased nuclear actin structure, and significantly alters chromatin access measured with ATACseq at 24 h. The ATAC-seq results due to CK666 are distinct from those caused by cytochalasin D (CytoD), which enhances nuclear actin structure. In addition, nuclear visualization shows Arp2/3 inhibition decreases pericentric H3K9me3 marks. CytoD, alternatively, induces redistribution of H3K27me3 marks centrally. Such alterations in chromatin landscape are consistent with differential gene expression associated with distinctive differentiation patterns. Further, knockdown of the non-enzymatic monomeric actin binding protein, Arp4, leads to extensive chromatin unpacking, but only a modest increase in transcription, indicating an active role for actin-Arp4 in transcription. These data indicate that dynamic actin remodeling can regulate chromatin interactions.

Genetic and pharmacological modulation of lamin A farnesylation determines its function and turnover

Hutchinson-Gilford Progeria syndrome (HGPS) is a severe premature ageing disorder caused by a 50 amino acid truncated (Δ50AA) and permanently farnesylated lamin A (LA) mutant called progerin. On a cellular level, progerin expression leads to heterochromatin loss, impaired nucleocytoplasmic transport, telomeric DNA damage and a permanent growth arrest called cellular senescence. Although the genetic basis for HGPS has been elucidated 20 years ago, the question whether the Δ50AA or the permanent farnesylation causes cellular defects has not been addressed. Moreover, we currently lack mechanistic insight into how the only FDA-approved progeria drug Lonafarnib, a farnesyltransferase inhibitor (FTI), ameliorates HGPS phenotypes. By expressing a variety of LA mutants using a doxycycline-inducible system, and in conjunction with FTI, we demonstrate that the permanent farnesylation, and not the Δ50AA, is solely responsible for progerin-induced cellular defects, as well as its rapid accumulation and slow clearance. Importantly, FTI does not affect clearance of progerin post-farnesylation and we demonstrate that early, but not late FTI treatment prevents HGPS phenotypes. Collectively, our study unravels the precise contributions of progerin's permanent farnesylation to its turnover and HGPS cellular phenotypes, and how FTI treatment ameliorates these. These findings are applicable to other diseases associated with permanently farnesylated proteins, such as adult-onset autosomal dominant leukodystrophy.

Nesprin proteins: bridging nuclear envelope dynamics to muscular dysfunction

This review presents a comprehensive exploration of the pivotal role played by the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, with a particular focus on Nesprin proteins, in cellular mechanics and the pathogenesis of muscular diseases. Distinguishing itself from prior works, the analysis delves deeply into the intricate interplay of the LINC complex, emphasizing its indispensable contribution to maintaining cellular structural integrity, especially in mechanically sensitive tissues such as cardiac and striated muscles. Additionally, the significant association between mutations in Nesprin proteins and the onset of Dilated Cardiomyopathy (DCM) and Emery-Dreifuss Muscular Dystrophy (EDMD) is highlighted, underscoring their pivotal role in disease pathogenesis. Through a comprehensive examination of DCM and EDMD cases, the review elucidates the disruptions in the LINC complex, nuclear morphology alterations, and muscular developmental disorders, thus emphasizing the essential function of an intact LINC complex in preserving muscle physiological functions. Moreover, the review provides novel insights into the implications of Nesprin mutations for cellular dynamics in the pathogenesis of muscular diseases, particularly in maintaining cardiac structural and functional integrity. Furthermore, advanced therapeutic strategies, including rectifying Nesprin gene mutations, controlling Nesprin protein expression, enhancing LINC complex functionality, and augmenting cardiac muscle cell function are proposed. By shedding light on the intricate molecular mechanisms underlying nuclear-cytoskeletal interactions, the review lays the groundwork for future research and therapeutic interventions aimed at addressing genetic muscle disorders.

Nuclear blebs are associated with destabilized chromatin packing domains

Disrupted nuclear shape is associated with multiple pathological processes including premature aging disorders, cancer-relevant chromosomal rearrangements, and DNA damage. Nuclear blebs (i.e., herniations of the nuclear envelope) have been induced by (1) nuclear compression, (2) nuclear migration (e.g., cancer metastasis), (3) actin contraction, (4) lamin mutation or depletion, and (5) heterochromatin enzyme inhibition. Recent work has shown that chromatin transformation is a hallmark of bleb formation, but the transformation of higher-order structures in blebs is not well understood. As higher-order chromatin has been shown to assemble into nanoscopic packing domains, we investigated if (1) packing domain organization is altered within nuclear blebs and (2) if alteration in packing domain structure contributed to bleb formation. Using Dual-Partial Wave Spectroscopic microscopy, we show that chromatin packing domains within blebs are transformed both by B-type lamin depletion and the inhibition of heterochromatin enzymes compared to the nuclear body. Pairing these results with single-molecule localization microscopy of constitutive heterochromatin, we show fragmentation of nanoscopic heterochromatin domains within bleb domains. Overall, these findings indicate that translocation into blebs results in a fragmented higher-order chromatin structure.

SUMMARY STATEMENT

Nuclear blebs are linked to various pathologies, including cancer and premature aging disorders. We investigate alterations in higher-order chromatin structure within blebs, revealing fragmentation of nanoscopic heterochromatin domains.

Changes Induced by P2X7 Receptor Stimulation of Human Glioblastoma Stem Cells in the Proteome of Extracellular Vesicles Isolated from Their Secretome

Extracellular vesicles (EVs) are secreted from many tumors, including glioblastoma multiforme (GBM), the most common and lethal brain tumor in adults, which shows high resistance to current therapies and poor patient prognosis. Given the high relevance of the information provided by cancer cell secretome, we performed a proteomic analysis of microvesicles (MVs) and exosomes (EXOs) released from GBM-derived stem cells (GSCs). The latter, obtained from the brain of GBM patients, expressed P2X7 receptors (P2X7Rs), which positively correlate with GBM growth and invasiveness. P2X7R stimulation of GSCs caused significant changes in the EV content, mostly ex novo inducing or upregulating the expression of proteins related to cytoskeleton reorganization, cell motility/spreading, energy supply, protection against oxidative stress, chromatin remodeling, and transcriptional regulation. Most of the induced/upregulated proteins have already been identified as GBM diagnostic/prognostic factors, while others have only been reported in peripheral tumors. Our findings indicate that P2X7R stimulation enhances the transport and, therefore, possible intercellular exchange of GBM aggressiveness-increasing proteins by GSC-derived EVs. Thus, P2X7Rs could be considered a new druggable target of human GBM, although these data need to be confirmed in larger experimental sets.

ABHD7-mediated depalmitoylation of lamin A promotes myoblast differentiation

LMNA gene mutation can cause muscular dystrophy, and post-translational modification plays a critical role in regulating its function. Here, we identify that lamin A is palmitoylated at cysteine 522, 588, and 591 residues, which are reversely catalyzed by palmitoyltransferase zinc finger DHHC-type palmitoyltransferase 5 (ZDHHC5) and depalmitoylase α/β hydrolase domain 7 (ABHD7). Furthermore, the metabolite lactate promotes palmitoylation of lamin A by inhibiting the interaction between it and ABHD7. Interestingly, low-level palmitoylation of lamin A promotes, whereas high-level palmitoylation of lamin A inhibits, murine myoblast differentiation. Together, these observations suggest that ABHD7-mediated depalmitoylation of lamin A controls myoblast differentiation.

Deciphering the Clinical Presentations in LMNA-related Lipodystrophy: Report of 115 Cases and a Systematic Review

CONTEXT

Lipodystrophy syndromes are a heterogeneous group of rare genetic or acquired disorders characterized by generalized or partial loss of adipose tissue. LMNA-related lipodystrophy syndromes are classified based on the severity and distribution of adipose tissue loss.

OBJECTIVE

We aimed to annotate all clinical and metabolic features of patients with lipodystrophy syndromes carrying pathogenic LMNA variants and assess potential genotype-phenotype relationships.

METHODS

We retrospectively reviewed and analyzed all our cases (n = 115) and all published cases (n = 379) curated from 94 studies in the literature.

RESULTS

The study included 494 patients. The most common variants in our study, R482Q and R482W, were associated with similar metabolic characteristics and complications though those with the R482W variant were younger (aged 33 [24] years vs 44 [25] years; P < .001), had an earlier diabetes diagnosis (aged 27 [18] vs 40 [17] years; P < .001) and had lower body mass index levels (24 [5] vs 25 [4]; P = .037). Dyslipidemia was the earliest biochemical evidence described in 83% of all patients at a median age of 26 (10) years, while diabetes was reported in 61% of cases. Among 39 patients with an episode of acute pancreatitis, the median age at acute pancreatitis diagnosis was 20 (17) years. Patients who were reported to have diabetes had 3.2 times, while those with hypertriglyceridemia had 12.0 times, the odds of having pancreatitis compared to those who did not.

CONCLUSION

This study reports the largest number of patients with LMNA-related lipodystrophy syndromes to date. Our report helps to quantify the prevalence of the known and rare complications associated with different phenotypes and serves as a comprehensive catalog of all known cases.

PIGB maintains nuclear lamina organization in skeletal muscle of Drosophila

The nuclear lamina (NL) plays various roles and participates in nuclear integrity, chromatin organization, and transcriptional regulation. Lamin proteins, the main components of the NL, form a homogeneous meshwork structure under the nuclear envelope. Lamins are essential, but it is unknown whether their homogeneous distribution is important for nuclear function. Here, we found that PIGB, an enzyme involved in glycosylphosphatidylinositol (GPI) synthesis, is responsible for the homogeneous lamin meshwork in Drosophila. Loss of PIGB resulted in heterogeneous distributions of B-type lamin and lamin-binding proteins in larval muscles. These phenotypes were rescued by expression of PIGB lacking GPI synthesis activity. The PIGB mutant exhibited changes in lamina-associated domains that are large heterochromatic genomic regions in the NL, reduction of nuclear stiffness, and deformation of muscle fibers. These results suggest that PIGB maintains the homogeneous meshwork of the NL, which may be essential for chromatin distribution and nuclear mechanical properties.

Long lifetime and tissue-specific accumulation of lamin A/C in Hutchinson-Gilford progeria syndrome

LMNA mutations cause laminopathies that afflict the cardiovascular system and include Hutchinson-Gilford progeria syndrome. The origins of tissue specificity in these diseases are unclear as the lamin A/C proteins are broadly expressed. We show that LMNA transcript levels are not predictive of lamin A/C protein levels across tissues and use quantitative proteomics to discover that tissue context and disease mutation each influence lamin A/C protein's lifetime. Lamin A/C's lifetime is an order of magnitude longer in the aorta, heart, and fat, where laminopathy pathology is apparent, than in the liver and intestine, which are spared from the disease. Lamin A/C is especially insoluble in cardiovascular tissues, which may limit degradation and promote protein stability. Progerin is even more long lived than lamin A/C in the cardiovascular system and accumulates there over time. Progerin accumulation is associated with impaired turnover of hundreds of abundant proteins in progeroid tissues. These findings identify impaired lamin A/C protein turnover as a novel feature of laminopathy syndromes.

Mechanisms by which barrier-to-autointegration factor regulates dynamics of nucleocytoplasmic leakage and membrane repair following nuclear envelope rupture

The nuclear envelope (NE) creates a barrier between the cytosol and nucleus during interphase that is key for cellular compartmentalization and protecting genomic DNA. NE rupture can expose genomic DNA to the cytosol and allow admixture of the nuclear and cytosolic constituents, a proposed mechanism of cancer and NE-associated diseases. Barrier-to-autointegration factor (BAF) is a DNA-binding protein that localizes to NE ruptures where it recruits LEM-domain proteins, A-type lamins, and participates in rupture repair. To further reveal the mechanisms by which BAF responds to and aids in repairing NE ruptures, we investigated known properties of BAF including LEM domain binding, lamin binding, compartmentalization, phosphoregulation of DNA binding, and BAF dimerization. We demonstrate that it is the cytosolic population of BAF that functionally repairs NE ruptures, and phosphoregulation of BAF's DNA-binding that enables its ability to facilitate that repair. Interestingly, BAF's LEM or lamin binding activity appears dispensable for its role in functional repair. Furthermore, we demonstrate that BAF functions to reduce the extent of leakage though NE ruptures, suggesting that BAF effectively forms a diffusion barrier prior to NE repair. Collectively, these results enhances our knowledge of the mechanisms by which BAF responds to NE ruptures and facilitates their repair.

The Functions of Pt-DIC and Pt-Lamin B in Spermatogenesis of Portunus trituberculatus

Cytoplasmic Dynein is a multiple-subunit macromolecular motor protein involved in the transport process of cells. The Dynein intermediate chain (DIC) is one of the subunits of Dynein-1. In our previous studies, we showed that Pt-DIC may play an important role in the nuclear deformation of spermiogenesis in Portunus trituberculatus. Lamin B is essential for maintaining nuclear structure and functions. Surprisingly, Pt-Lamin B was expressed not only in the perinucleus but also in the pro-acrosome during spermiogenesis in P. trituberculatus. Studies have also shown that Dynein-1 can mediate the transport of Lamin B in mammals. Thus, to study the relationship of Pt-DIC and Pt-Lamin B in the spermatogenesis of P. trituberculatus, we knocked down the Pt-DIC gene in P. trituberculatus by RNAi. The results showed that the distribution of Pt-DIC and Pt-Lamin B in spermiogenesis was abnormal, and the colocalization was weakened. Moreover, we verified the interaction of Pt-DIC and Pt-Lamin B via coimmunoprecipitation. Therefore, our results suggested that both Pt-DIC and Pt-Lamin B were involved in the spermatogenesis of P. trituberculatus, and one of the functions of Dynein-1 is to mediate the transport of Lamin B in the spermiogenesis of P. trituberculatus.

Biomarkers in Cancer Detection, Diagnosis, and Prognosis

Biomarkers are vital in healthcare as they provide valuable insights into disease diagnosis, prognosis, treatment response, and personalized medicine. They serve as objective indicators, enabling early detection and intervention, leading to improved patient outcomes and reduced costs. Biomarkers also guide treatment decisions by predicting disease outcomes and facilitating individualized treatment plans. They play a role in monitoring disease progression, adjusting treatments, and detecting early signs of recurrence. Furthermore, biomarkers enhance drug development and clinical trials by identifying suitable patients and accelerating the approval process. In this review paper, we described a variety of biomarkers applicable for cancer detection and diagnosis, such as imaging-based diagnosis (CT, SPECT, MRI, and PET), blood-based biomarkers (proteins, genes, mRNA, and peptides), cell imaging-based diagnosis (needle biopsy and CTC), tissue imaging-based diagnosis (IHC), and genetic-based biomarkers (RNAseq, scRNAseq, and spatial transcriptomics).

Interdependent changes of nuclear lamins, nuclear pore complexes, and ploidy regulate cellular regeneration and stress response in the heart

In adult mammals, many heart muscle cells (cardiomyocytes) are polyploid, do not proliferate (post-mitotic), and, consequently, cannot contribute to heart regeneration. In contrast, fetal and neonatal heart muscle cells are diploid, proliferate, and contribute to heart regeneration. We have identified interdependent changes of the nuclear lamina, nuclear pore complexes, and DNA-content (ploidy) in heart muscle cell maturation. These results offer new perspectives on how cells alter their nuclear transport and, with that, their gene regulation in response to extracellular signals. We present how changes of the nuclear lamina alter nuclear pore complexes in heart muscle cells. The consequences of these changes for cellular regeneration and stress response in the heart are discussed.

Discriminating Between Apoptosis, Necrosis, Necroptosis, and Ferroptosis by Microscopy and Flow Cytometry

Apoptosis is a mode of programmed cell death that plays important roles in tissue sculpting during development, in the maintenance of tissue homeostasis in the adult, and in the eradication of injured or infected cells during pathological processes. Numerous physiological as well as pathological stimuli trigger apoptosis, such as engagement of plasma-membrane-associated Fas, TRAIL, or TNF receptors, growth factor deprivation, hypoxia, radiation, and exposure to diverse cytotoxic drugs. Apoptosis is coordinated by members of the caspase family of cysteine proteases, which, upon activation, trigger a series of dramatic morphological and biochemical changes including retraction from the substratum, cell shrinkage, extensive and protracted plasma membrane blebbing, chromatin condensation, DNA hydrolysis, nuclear fragmentation, and proteolytic cleavage of numerous caspase substrates. These dramatic structural and biochemical alterations result not only in the controlled dismantling of the cell, but also in the rapid recognition and removal of apoptotic cells by phagocytes through the cell surface display of phagocytotic triggers such as phosphatidylserine. Necrosis, which is typically nonprogrammed or imposed upon the cell by overwhelming membrane or organelle damage, is characterized by high-amplitude cell swelling, followed by rapid plasma membrane rupture and release of cellular contents into the extracellular space. Necrosis is often provoked by infectious agents or severe departure from physiological conditions due to toxins, temperature extremes, or physical injury. However, forms of programmed necrosis (necroptosis, pyroptosis, ferroptosis) can also occur in specific circumstances. Nonprogrammed and programmed necrosis can be distinguished from apoptosis by morphological features, based on the rapid uptake of vital dyes, and through the application of specific inhibitors of key molecules associated with the latter modes of cell death. This unit describes protocols for the measurement of apoptosis and necrosis and for distinguishing apoptosis from programmed as well as conventional necrosis. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Analysis of cell morphology by phase-contrast microscopy Alternative Protocol 1: Assessment of morphological changes using eosin-methylene blue staining Alternative Protocol 2: Analysis of nuclear morphology by fluorescence microscopy Support Protocol: Preparation of cytospins Basic Protocol 2: Measurement of plasma membrane composition with annexin V and propidium iodide Basic Protocol 3: Measurement of DNA fragmentation by flow cytometry Alternative Protocol 3: Analysis of DNA fragmentation by the TUNEL assay Basic Protocol 4: Measurement of caspase activation by flow cytometry Basic Protocol 5: Discriminating between apoptosis, necrosis, necroptosis, and ferroptosis.

Understanding the Ultra-Rare Disease Autosomal Dominant Leukodystrophy: an Updated Review on Morpho-Functional Alterations Found in Experimental Models

Autosomal dominant leukodystrophy (ADLD) is an ultra-rare, slowly progressive, and fatal neurodegenerative disorder associated with the loss of white matter in the central nervous system (CNS). Several years after its first clinical description, ADLD was found to be caused by coding and non-coding variants in the LMNB1 gene that cause its overexpression in at least the brain of patients. LMNB1 encodes for Lamin B1, a protein of the nuclear lamina. Lamin B1 regulates many cellular processes such as DNA replication, chromatin organization, and senescence. However, its functions have not been fully characterized yet. Nevertheless, Lamin B1 together with the other lamins that constitute the nuclear lamina has firstly the key role of maintaining the nuclear structure. Being the nucleus a dynamic system subject to both biochemical and mechanical regulation, it is conceivable that changes to its structural homeostasis might translate into functional alterations. Under this light, this review aims at describing the pieces of evidence that to date have been obtained regarding the effects of LMNB1 overexpression on cellular morphology and functionality. Moreover, we suggest that further investigation on ADLD morpho-functional consequences is essential to better understand this complex disease and, possibly, other neurological disorders affecting CNS myelination.

Autophagy as a caretaker of nuclear integrity

Due to their essential functions, dysregulation of nuclear pore complexes (NPCs) is strongly associated with numerous human diseases, including neurodegeneration and cancer. On a cellular level, longevity of scaffold nucleoporins in postmitotic cells of both C. elegans and mammals renders them vulnerable to age-related damage, which is associated with an increase in pore leakiness and accumulation of intranuclear aggregates in rat brain cells. Thus, understanding the mechanisms which underpin the homeostasis of this complex, as well as other nuclear proteins, is essential. In this review, autophagy-mediated degradation pathways governing nuclear components in yeast will be discussed, with a particular focus on NPCs. Furthermore, the various nuclear degradation mechanisms identified thus far in diverse eukaryotes will also be highlighted.

Scaffold, mechanics and functions of nuclear lamins

Nuclear lamins are type-V intermediate filaments that are involved in many nuclear processes. In mammals, A- and B-type lamins assemble into separate physical meshwork underneath the inner nuclear membrane, the nuclear lamina, with some residual fraction localized within the nucleoplasm. Lamins are the major part of the nucleoskeleton, providing mechanical strength and flexibility to protect the genome and allow nuclear deformability, while also contributing to gene regulation via interactions with chromatin. While lamins are the evolutionary ancestors of all intermediate filament family proteins, their ultimate filamentous assembly is markedly different from their cytoplasmic counterparts. Interestingly, hundreds of genetic mutations in the lamina proteins have been causally linked with a broad range of human pathologies, termed laminopathies. These include muscular, neurological and metabolic disorders, as well as premature aging diseases. Recent technological advances have contributed to resolving the filamentous structure of lamins and the corresponding lamina organization. In this review, we revisit the multiscale lamin organization and discuss its implications on nuclear mechanics and chromatin organization within lamina-associated domains.

Use of Farnesyl Transferase Inhibitors in an Ageing Model in Drosophila

The presence of farnesylated proteins at the inner nuclear membrane (INM), such as the Lamins or Kugelkern in Drosophila, leads to specific changes in the nuclear morphology and accelerated ageing on the organismal level reminiscent of the Hutchinson-Gilford progeria syndrome (HGPS). Farnesyl transferase inhibitors (FTIs) can suppress the phenotypes of the nuclear morphology in cultured fibroblasts from HGPS patients and cultured cells overexpressing farnesylated INM proteins. Similarly, FTIs have been reported to suppress the shortened lifespan in model organisms. Here, we report an experimental system combining cell culture and Drosophila flies for testing the activity of substances on the HGPS-like nuclear morphology and lifespan, with FTIs as an experimental example. Consistent with previous reports, we show that FTIs were able to ameliorate the nuclear phenotypes induced by the farnesylated nuclear proteins Progerin, Kugelkern, or truncated Lamin B in cultured cells. The subsequent validation in Drosophila lifespan assays demonstrated the applicability of the experimental system: treating adult Drosophila with the FTI ABT-100 reversed the nuclear phenotypes and extended the lifespan of experimentally induced short-lived flies. Since kugelkern-expressing flies have a significantly shorter average lifespan, half the time is needed for testing substances in the lifespan assay.

Physical model of the nuclear membrane permeability mechanism

Nuclear cytoplasmic transport is mediated by many receptors that recognize specific nuclear localization signals on proteins and RNA and transport these substrates through nuclear pore complexes. Facilitated diffusion through nuclear pore complexes requires the attachment of transport receptors. Despite the relatively large tunnel diameter, some even small proteins (less than 20-30 kDa), such as histones, pass through the nuclear pore complex only with transport receptors. Over several decades, considerable material has been accumulated on the structure, architecture, and amino acid composition of the proteins included in this complex and the sequence of many receptors. We consider the data available in the literature on the structure of the nuclear pore complex and possible mechanisms of nuclear-cytoplasmic transport, applying the theory of electrostatic interactions in the context of our data on changes in the electrokinetic potential of nuclei and our previously proposed physical model of the mechanism of facilitated diffusion through the nuclear pore complex (NPC). According to our data, the main contribution to the charge of the nuclear membrane is made by anionic phospholipids, which are part of both the nuclear membrane and the nuclear matrix, which creates a potential difference between them. The nuclear membrane is a four-layer phospholipid dielectric, so the potential vector can only pass through the NPC, creating an electrostatic funnel that "pulls in" the positively charged load-NLS-NTR trigger complexes. Considering the newly obtained data, an improved model of the previously proposed physical model of the mechanism of nuclear-cytoplasmic transport is proposed. This model considers the contribution of electrostatic fields to the transportation speed when changing the membrane's thickness in the NPC basket at a higher load.

Intermediate, but not average: The unusual lives of the nuclear lamin proteins

The nuclear lamins are polymeric intermediate filament proteins that scaffold the nucleus and organize the genome in nearly all eukaryotic cells. This review focuses on the dynamic regulation of lamin filaments through their biogenesis, assembly, disassembly, and degradation. The lamins are unusually long-lived proteins under homeostatic conditions, but their turnover can be induced in select contexts that are highlighted in this review. Finally, we discuss recent investigations into the influence of laminopathy-linked mutations on the assembly, folding, and stability of the nuclear lamins.

Multi-omic analysis of mandibuloacral dysplasia type A patient iPSC-derived MSC senescence reveals miR-311 as a novel biomarker for MSC senescence

Mandibuloacral dysplasia type A (MADA) is a rare genetic progeroid syndrome associated with lamin A/C (LMNA) mutations. Pathogenic mutations of LMNA result in nuclear structural abnormalities, mesenchymal tissue damage and progeria phenotypes. However, it remains elusive how LMNA mutations cause mesenchymal-derived cell senescence and disease development. Here, we established an in vitro senescence model using induced pluripotent stem cell-derived mesenchymal stem cells (iMSCs) from MADA patients with homozygous LMNA p.R527C mutation. When expanded to passage 13 in vitro, R527C iMSCs exhibited marked senescence and attenuation of stemness potential, accompanied by immunophenotypic changes. Transcriptome and proteome analysis revealed that cell cycle, DNA replication, cell adhesion and inflammation might play important roles in senescence. In-depth evaluation of changes in extracellular vesicle (EV) derived iMSCs during senescence revealed that R527C iMSC-EVs could promote surrounding cell senescence by carrying pro-senescence microRNAs (miRNAs), including a novel miRNA called miR-311, which can serve as a new indicator for detecting chronic and acute mesenchymal stem cell (MSC) senescence and play a role in promoting senescence. Overall, this study advanced our understanding of the impact of LMNA mutations on MSC senescence and provided novel insights into MADA therapy as well as the link between chronic inflammation and aging development.

Intermediate filament proteins are reliable immunohistological biomarkers to help diagnose multiple tissue-specific diseases

Cytoskeletal networks are proteins that effectively maintain cell integrity and provide mechanical support to cells by actively transmitting mechanical signals. Intermediate filaments, which are from the cytoskeleton family and are 10 nanometres in diameter, are unlike actin and microtubules, which are highly dynamic cytoskeletal elements. Intermediate filaments are flexible at low strain, harden at high strain and resist breaking. For this reason, these filaments fulfil structural functions by providing mechanical support to the cells through their different strain-hardening properties. Intermediate filaments are suitable in that cells both cope with mechanical forces and modulate signal transmission. These filaments are composed of fibrous proteins that exhibit a central α-helical rod domain with a conserved substructure. Intermediate filament proteins are divided into six groups. Type I and type II include acidic and basic keratins, type III, vimentin, desmin, peripheralin and glial fibrillary acidic protein (GFAP), respectively. Type IV intermediate filament group includes neurofilament proteins and a fourth neurofilament subunit, α-internexin proteins. Type V consists of lamins located in the nucleus, and the type VI group consists of lens-specific intermediate filaments, CP49/phakinin and filen. Intermediate filament proteins show specific immunoreactivity in differentiating cells and mature cells of various types. Various carcinomas such as colorectal, urothelial and ovarian, diseases such as chronic pancreatitis, cirrhosis, hepatitis and cataract have been associated with intermediate filaments. Accordingly, this section reviews available immunohistochemical antibodies to intermediate filament proteins. Identification of intermediate filament proteins by methodological methods may contribute to the understanding of complex diseases.

Comparative membrane proteomics reveals diverse cell regulators concentrated at the nuclear envelope

The nuclear envelope (NE) is a subdomain of the ER with prominent roles in nuclear organization, which are largely mediated by its distinctive protein composition. We developed methods to reveal low-abundance transmembrane (TM) proteins concentrated at the NE relative to the peripheral ER. Using label-free proteomics that compared isolated NEs with cytoplasmic membranes, we first identified proteins with apparent NE enrichment. In subsequent authentication, ectopically expressed candidates were analyzed by immunofluorescence microscopy to quantify their targeting to the NE in cultured cells. Ten proteins from a validation set were found to associate preferentially with the NE, including oxidoreductases, enzymes for lipid biosynthesis, and regulators of cell growth and survival. We determined that one of the validated candidates, the palmitoyltransferase Zdhhc6, modifies the NE oxidoreductase Tmx4 and thereby modulates its NE levels. This provides a functional rationale for the NE concentration of Zdhhc6. Overall, our methodology has revealed a group of previously unrecognized proteins concentrated at the NE and additional candidates. Future analysis of these can potentially unveil new mechanistic pathways associated with the NE.

Lamin B1 as a key modulator of the developing and aging brain

Lamin B1 is an essential protein of the nuclear lamina that plays a crucial role in nuclear function and organization. It has been demonstrated that lamin B1 is essential for organogenesis and particularly brain development. The important role of lamin B1 in physiological brain development and aging has only recently been at the epicenter of attention and is yet to be fully elucidated. Regarding the development of brain, glial cells that have long been considered as supporting cells to neurons have overturned this representation and current findings have displayed their active roles in neurogenesis and cerebral development. Although lamin B1 has increased levels during the differentiation of the brain cells, during aging these levels drop leading to senescent phenotypes and inciting neurodegenerative disorders such as Alzheimer's and Parkinson's disease. On the other hand, overexpression of lamin B1 leads to the adult-onset neurodegenerative disease known as Autosomal Dominant Leukodystrophy. This review aims at highlighting the importance of balancing lamin B1 levels in glial cells and neurons from brain development to aging.

DYT-TOR1A dystonia: an update on pathogenesis and treatment

DYT-TOR1A dystonia is a neurological disorder characterized by involuntary muscle contractions and abnormal movements. It is a severe genetic form of dystonia caused by mutations in the TOR1A gene. TorsinA is a member of the AAA + family of adenosine triphosphatases (ATPases) involved in a variety of cellular functions, including protein folding, lipid metabolism, cytoskeletal organization, and nucleocytoskeletal coupling. Almost all patients with TOR1A-related dystonia harbor the same mutation, an in-frame GAG deletion (ΔGAG) in the last of its 5 exons. This recurrent variant results in the deletion of one of two tandem glutamic acid residues (i.e., E302/303) in a protein named torsinA [torsinA(△E)]. Although the mutation is hereditary, not all carriers will develop DYT-TOR1A dystonia, indicating the involvement of other factors in the disease process. The current understanding of the pathophysiology of DYT-TOR1A dystonia involves multiple factors, including abnormal protein folding, signaling between neurons and glial cells, and dysfunction of the protein quality control system. As there are currently no curative treatments for DYT-TOR1A dystonia, progress in research provides insight into its pathogenesis, leading to potential therapeutic and preventative strategies. This review summarizes the latest research advances in the pathogenesis, diagnosis, and treatment of DYT-TOR1A dystonia.

Cellular and Genomic Features of Muscle Differentiation from Isogenic Fibroblasts and Myoblasts

The ability to recapitulate muscle differentiation in vitro enables the exploration of mechanisms underlying myogenesis and muscle diseases. However, obtaining myoblasts from patients with neuromuscular diseases or from healthy subjects poses ethical and procedural challenges that limit such investigations. An alternative consists in converting skin fibroblasts into myogenic cells by forcing the expression of the myogenic regulator MYOD. Here, we directly compared cellular phenotype, transcriptome, and nuclear lamina-associated domains (LADs) in myo-converted human fibroblasts and myotubes differentiated from myoblasts. We used isogenic cells from a 16-year-old donor, ruling out, for the first time to our knowledge, genetic factors as a source of variations between the two myogenic models. We show that myo-conversion of fibroblasts upregulates genes controlling myogenic pathways leading to multinucleated cells expressing muscle cell markers. However, myotubes are more advanced in myogenesis than myo-converted fibroblasts at the phenotypic and transcriptomic levels. While most LADs are shared between the two cell types, each also displays unique domains of lamin A/C interactions. Furthermore, myotube-specific LADs are more gene-rich and less heterochromatic than shared LADs or LADs unique to myo-converted fibroblasts, and they uniquely sequester developmental genes. Thus, myo-converted fibroblasts and myotubes retain cell type-specific features of radial and functional genome organization. Our results favor a view of myo-converted fibroblasts as a practical model to investigate the phenotypic and genomic properties of muscle cell differentiation in normal and pathological contexts, but also highlight current limitations in using fibroblasts as a source of myogenic cells.

Decreased lamin A and B1 expression results in nuclear enlargement in serous ovarian carcinoma, whereas lamin A-expressing tumor cells metastasize to lymph nodes

BACKGROUND

Lamins, located beneath the nuclear membrane, are involved in maintaining nuclear stiffness and morphology. The nuclei of tumor cells are enlarged in serous carcinoma, a histologic subtype of ovarian cancer that is notable for its poor prognosis. The present study investigated the association of lamin A, B1, and B2 expression with nuclear morphology and metastatic route in serous ovarian carcinoma.

METHODS

We performed immunohistochemistry for lamins A, B1, and B2 using specimens of patients who underwent surgery for serous ovarian carcinoma in Gunma University Hospital between 2009 and 2020. Following staining, the specimens were scanned using a whole-slide scanner and processed using computer-assisted image analysis.

RESULTS

The positivity rates for lamins A and B1 as well as the rank sum of the positivity rates for lamins A, B1, and B2 were negatively correlated with the mean and standard deviation of the nuclear area. Interestingly, the positivity rate for lamin A was significantly higher in metastatic lesions than in primary tumors in cases with lymph node metastasis.

DISCUSSION

Previous studies indicated that decreased lamin A led to nuclear enlargement and deformation and that lamin B1 was required to maintain the meshworks of lamins A and B2 to maintain nuclear morphology. The present study findings suggest that decreased lamin A and B1 expression might lead to nuclear enlargement and deformation and raise the possibility that tumor cells maintaining or not losing lamin A expression might metastasize to lymph nodes.

CaaX-less lamins: Lophotrochozoa provide a glance at the playground of evolution

Nuclear lamins are the main components of the nuclear lamina in many eukaryotes. They are members of the intermediate filament (IF) protein family. Lamins differ from cytoplasmic IF proteins by the presence of a nuclear localisation sequence (NLS) and a C-terminal tetrapeptide, the CaaX motif. The CaaX motif is target of post-translational modifications including isoprenylation, proteolytic processing, and carboxyl-methylation. These modifications, in conjunction with the NLS, direct lamins to the inner nuclear membrane where they assemble into filaments. Lamins lacking a CaaX motif are unable to associate independently with nuclear membranes and remain in the nucleoplasm. So far, three species have been reported to exclusively express CaaX-less lamins. All three belong to the lophotrochozoan lineage. To find out whether they represent rare exceptions, we analysed lamins of representatives of 17 lophotrochozoan phyla. Here we report that all four clades of Rotifera as well as individual taxa of Mollusca and Annelida lack CaaX-lamins, but express lamins with alternative C-termini. Of note, the respective mollusc and annelid groups occupy very different phylogenetic ranks. Most of these alternative C-termini are rich in aromatic residues. A possible function of these residues in membrane association is discussed. Alternative splicing of terebellid lamin transcripts gives rise to two lamin variants, one with a CaaX motif and one with an alternative C-terminus. A similar situation is found in Arenicolidae, Opheliidae, Capitellidae, and Echiura. This points a way, how the switch from lamins carrying a CaaX motif to lamins with alternative C-termini may have occurred.

InterLINCing Chromatin Organization and Mechanobiology in Laminopathies

PURPOSE OF REVIEW

In this review, we explore the chromatin-related consequences of laminopathy-linked mutations through the lens of mechanotransduction.

RECENT FINDINGS

Multiple studies have highlighted the role of the nuclear lamina in maintaining the integrity of the nucleus. The lamina also has a critical role in 3D genome organization. Mutations in lamina proteins associated with various laminopathies result in the loss of organization of DNA at the nuclear periphery. However, it remains unclear if or how these two aspects of lamin function are connected. Recent data suggests that unlinking the cytoskeleton from the nuclear lamina may be beneficial to slow progress of deleterious phenotypes observed in laminopathies. In this review, we highlight emerging data that suggest interlinked chromatin- and mechanical biology-related pathways are interconnected in the pathogenesis of laminopathies.

The role of Lamin B2 in human diseases

Lamin B2 (LMNB2), on the inner side of the nuclear envelope, constitutes the nuclear skeleton by connecting with other nuclear proteins. LMNB2 is involved in a wide range of nuclear functions, including DNA replication and stability, regulation of chromatin, and nuclear stiffness. Moreover, LMNB2 regulates several cellular processes, such as tissue development, cell cycle, cellular proliferation and apoptosis, chromatin localization and stability, and DNA methylation. Besides, the influence of abnormal expression and mutations of LMNB2 has been gradually discovered in cancers and laminopathies. Therefore, this review summarizes the recent advances of LMNB2-associated biological roles in physiological or pathological conditions, with a particular emphasis on cancers and laminopathies, as well as the potential mechanism of LMNB2 in related cancers.

TOR1AIP1-Associated Nuclear Envelopathies

Human TOR1AIP1 encodes LAP1, a nuclear envelope protein expressed in most human tissues, which has been linked to various biological processes and human diseases. The clinical spectrum of diseases related to mutations in TOR1AIP1 is broad, including muscular dystrophy, congenital myasthenic syndrome, cardiomyopathy, and multisystemic disease with or without progeroid features. Although rare, these recessively inherited disorders often lead to early death or considerable functional impairment. Developing a better understanding of the roles of LAP1 and mutant TOR1AIP1-associated phenotypes is paramount to allow therapeutic development. To facilitate further studies, this review provides an overview of the known interactions of LAP1 and summarizes the evidence for the function of this protein in human health. We then review the mutations in the TOR1AIP1 gene and the clinical and pathological characteristics of subjects with these mutations. Lastly, we discuss challenges to be addressed in the future.

Myocardial Inflammation as a Manifestation of Genetic Cardiomyopathies: From Bedside to the Bench

Over recent years, preclinical and clinical evidence has implicated myocardial inflammation (M-Infl) in the pathophysiology and phenotypes of traditionally genetic cardiomyopathies. M-Infl resembling myocarditis on imaging and histology occurs frequently as a clinical manifestation of classically genetic cardiac diseases, including dilated and arrhythmogenic cardiomyopathy. The emerging role of M-Infl in disease pathophysiology is leading to the identification of druggable targets for molecular treatment of the inflammatory process and a new paradigm in the field of cardiomyopathies. Cardiomyopathies constitute a leading cause of heart failure and arrhythmic sudden death in the young population. The aim of this review is to present, from bedside to bench, the current state of the art about the genetic basis of M-Infl in nonischemic cardiomyopathies of the dilated and arrhythmogenic spectrum in order to prompt future research towards the identification of novel mechanisms and treatment targets, with the ultimate goal of lowering disease morbidity and mortality.

Characterization of cardiac involvement in children with LMNA-related muscular dystrophy

Introduction: LMNA-related muscular dystrophy is a rare entity that produce "laminopathies" such as Emery-Dreifuss muscular dystrophy (EDMD), limb-girdle muscular dystrophy type 1B (LGMD1B), and LMNA-related congenital muscular dystrophy (L-CMD). Heart failure, malignant arrhythmias, and sudden death may occur. No consensus exists on cardiovascular management in pediatric laminopathies. The aim was to perform an exhaustive cardiologic follow-up in pediatric patients diagnosed with LMNA-related muscular dystrophy. Methods: Baseline cardiac work-up consisted of clinical assessment, transthoracic Doppler echocardiography, 12-lead electrocardiogram, electrophysiological study, and implantation of a long-term implantable cardiac loop recorder (ILR). Results: We enrolled twenty-eight pediatric patients diagnosed with EDMD (13 patients), L-CMD (11 patients), LGMD1B (2 patients), and LMNA-related mild weakness (2 patients). Follow-up showed dilated cardiomyopathy (DCM) in six patients and malignant arrhythmias in five (four concomitant with DCM) detected by the ILR that required implantable cardioverter defibrillator (ICD) implantation. Malignant arrhythmias were detected in 20% of our cohort and early-onset EDMD showed worse cardiac prognosis. Discussion: Patients diagnosed with early-onset EDMD are at higher risk of DCM, while potentially life-threatening arrhythmias without DCM appear earlier in L-CMD patients. Early onset neurologic symptoms could be related with worse cardiac prognosis. Specific clinical guidelines for children are needed to prevent sudden death.

Epigenetics in LMNA-Related Cardiomyopathy

Mutations in the gene for lamin A/C (LMNA) cause a diverse range of diseases known as laminopathies. LMNA-related cardiomyopathy is a common inherited heart disease and is highly penetrant with a poor prognosis. In the past years, numerous investigations using mouse models, stem cell technologies, and patient samples have characterized the phenotypic diversity caused by specific LMNA variants and contributed to understanding the molecular mechanisms underlying the pathogenesis of heart disease. As a component of the nuclear envelope, LMNA regulates nuclear mechanostability and function, chromatin organization, and gene transcription. This review will focus on the different cardiomyopathies caused by LMNA mutations, address the role of LMNA in chromatin organization and gene regulation, and discuss how these processes go awry in heart disease.

Comparative membrane proteomics reveals diverse cell regulators concentrated at the nuclear envelope

The nuclear envelope (NE) is a subdomain of the ER with prominent roles in nuclear organization, largely mediated by its distinctive protein composition. We developed methods to reveal novel, low abundance transmembrane (TM) proteins concentrated at the NE relative to the peripheral ER. Using label-free proteomics that compared isolated NEs to cytoplasmic membranes, we first identified proteins with apparent NE enrichment. In subsequent authentication, ectopically expressed candidates were analyzed by immunofluorescence microscopy to quantify their targeting to the NE in cultured cells. Ten proteins from a validation set were found to associate preferentially with the NE, including oxidoreductases, enzymes for lipid biosynthesis and regulators of cell growth and survival. We determined that one of the validated candidates, the palmitoyltransferase Zdhhc6, modifies the NE oxidoreductase Tmx4 and thereby modulates its NE levels. This provides a functional rationale for the NE concentration of Zdhhc6. Overall, our methodology has revealed a group of previously unrecognized proteins concentrated at the NE and additional candidates. Future analysis of these can potentially unveil new mechanistic pathways associated with the NE.

The Vast Utility of Drosophila Oogenesis

In this chapter, we highlight examples of the diverse array of developmental, cellular, and biochemical insights that can be gained by using Drosophila melanogaster oogenesis as a model tissue. We begin with an overview of ovary development and adult oogenesis. Then we summarize how the adult Drosophila ovary continues to advance our understanding of stem cells, cell cycle, cell migration, cytoplasmic streaming, nurse cell dumping, and cell death. We also review emerging areas of study, including the roles of lipid droplets, ribosomes, and nuclear actin in egg development. Finally, we conclude by discussing the growing conservation of processes and signaling pathways that regulate oogenesis and female reproduction from flies to humans.

4-Methylumbelliferone Targets Revealed by Public Data Analysis and Liver Transcriptome Sequencing

4-methylumbelliferone (4MU) is a well-known hyaluronic acid synthesis inhibitor and an approved drug for the treatment of cholestasis. In animal models, 4MU decreases inflammation, reduces fibrosis, and lowers body weight, serum cholesterol, and insulin resistance. It also inhibits tumor progression and metastasis. The broad spectrum of effects suggests multiple and yet unknown targets of 4MU. Aiming at 4MU target deconvolution, we have analyzed publicly available data bases, including: 1. Small molecule library Bio Assay screening (PubChemBioAssay); 2. GO pathway databases screening; 3. Protein Atlas Database. We also performed comparative liver transcriptome analysis of mice on normal diet and mice fed with 4MU for two weeks. Potential targets of 4MU public data base analysis fall into two big groups, enzymes and transcription factors (TFs), including 13 members of the nuclear receptor superfamily regulating lipid and carbohydrate metabolism. Transcriptome analysis revealed changes in the expression of genes involved in bile acid metabolism, gluconeogenesis, and immune response. It was found that 4MU feeding decreased the accumulation of the glycogen granules in the liver. Thus, 4MU has multiple targets and can regulate cell metabolism by modulating signaling via nuclear receptors.

Effect of the Rho-Kinase/ROCK Signaling Pathway on Cytoskeleton Components

The mechanical properties of cells are important in tissue homeostasis and enable cell growth, division, migration and the epithelial-mesenchymal transition. Mechanical properties are determined to a large extent by the cytoskeleton. The cytoskeleton is a complex and dynamic network composed of microfilaments, intermediate filaments and microtubules. These cellular structures confer both cell shape and mechanical properties. The architecture of the networks formed by the cytoskeleton is regulated by several pathways, a key one being the Rho-kinase/ROCK signaling pathway. This review describes the role of ROCK (Rho-associated coiled-coil forming kinase) and how it mediates effects on the key components of the cytoskeleton that are critical for cell behaviour.

A-type lamins involvement in transport and implications in cancer?

Nuclear lamins and transport are intrinsically linked, but their relationship is yet to be fully unraveled. A multitude of complex, coupled interactions between lamins and nucleoporins (Nups), which mediate active transport into and out of the nucleus, combined with well documented dysregulation of lamins in many cancers, suggests that lamins and nuclear transport may play a pivotal role in carcinogenesis and the preservation of cancer. Changes of function related to lamin/Nup activity can principally lead to DNA damage, further increasing the genetic diversity within a tumor, which could lead to the reduction the effectiveness of antineoplastic treatments. This review discusses and synthesizes different connections of lamins to nuclear transport and offers a number of outlook questions, the answers to which could reveal a new perspective on the connection of lamins to molecular transport of cancer therapeutics, in addition to their established role in nuclear mechanics.

Redundant and Specific Roles of A-Type Lamins and Lamin B Receptor in Herpes Simplex Virus 1 Infection

We investigated whether A-type lamins (lamin A/C) and lamin B receptor (LBR) are redundant during herpes simplex virus 1 (HSV-1) infection in HeLa cells expressing lamin A/C and LBR. Lamin A/C and LBR double knockout (KO) in HSV-1-infected HeLa cells significantly impaired expressions of HSV-1 early and late genes, maturation of replication compartments, marginalization of host chromatin to the nuclear periphery, enlargement of host cell nuclei, and viral DNA replication. Phenotypes of HSV-1-infected HeLa cells were restored by the ectopic expression of lamin A/C or LBR in lamin A/C and LBR double KO cells. Of note, lamin A/C single KO, but not LBR single KO, promoted the aberrant accumulation of virus particles outside the inner nuclear membrane (INM) and viral replication, as well as decreasing the frequency of virus particles inside the INM without affecting viral gene expression and DNA replication, time-spatial organization of replication compartments and host chromatin, and nuclear enlargement. These results indicated that lamin A/C and LBR had redundant and specific roles during HSV-1 infection. Thus, lamin A/C and LBR redundantly regulated the dynamics of the nuclear architecture, including the time-spatial organization of replication compartments and host chromatin, as well as promoting nuclear enlargement for efficient HSV-1 gene expression and DNA replication. In contrast, lamin A/C inhibited HSV-1 nuclear export through the INM during viral nuclear egress, which is a unique property of lamin A/C. IMPORTANCE This study demonstrated that lamin A/C and LBR had redundant functions associated with HSV-1 gene expression and DNA replication by regulating the dynamics of the nuclear architecture during HSV-1 infection. This is the first report to demonstrate the redundant roles of lamin A/C and LBR as well as the involvement of LBR in the regulation of these viral and cellular features in HSV-1-infected cells. These findings provide evidence for the specific property of lamin A/C to inhibit HSV-1 nuclear egress, which has long been considered but without direct proof.

Nuclear Shape-Shifters: Lipid and Protein Dynamics at the Nuclear Envelope

The nuclear envelope constitutes a selective barrier that segregates chromatin into the nucleus of eukaryotic cells [...].

Transcriptome Analysis Reveals Vimentin-Induced Disruption of Cell-Cell Associations Augments Breast Cancer Cell Migration

In advanced metastatic cancers with reduced patient survival and poor prognosis, expression of vimentin, a type III intermediate filament protein is frequently observed. Vimentin appears to suppress epithelial characteristics and augments cell migration but the molecular basis for these changes is not well understood. Here, we have ectopically expressed vimentin in MCF-7 and investigated its genomic and functional implications. Vimentin changed the cell shape by decreasing major axis, major axis angle and increased cell migration, without affecting proliferation. Vimentin downregulated major keratin genes KRT8, KRT18 and KRT19. Transcriptome-coupled GO and KEGG analyses revealed that vimentin-affected genes were linked to either cell-cell/cell-ECM or cell cycle/proliferation specific pathways. Using shRNA mediated knockdown of vimentin in two cell types; MCF-7FV (ectopically expressing) and MDA-MB-231 (endogenously expressing), we identified a vimentin-specific signature consisting of 13 protein encoding genes (CDH5, AXL, PTPRM, TGFBI, CDH10, NES, E2F1, FOXM1, CDC45, FSD1, BCL2, KIF26A and WISP2) and two long non-coding RNAs, LINC00052 and C15ORF9-AS1. CDH5, an endothelial cadherin, which mediates cell-cell junctions, was the most downregulated protein encoding gene. Interestingly, downregulation of CDH5 by shRNA significantly increased cell migration confirming our RNA-Seq data. Furthermore, presence of vimentin altered the lamin expression in MCF-7. Collectively, we demonstrate, for the first time, that vimentin in breast cancer cells could change nuclear architecture by affecting lamin expression, which downregulates genes maintaining cell-cell junctions resulting in increased cell migration.

Chondrocyte De-Differentiation: Biophysical Cues to Nuclear Alterations

Autologous chondrocyte implantation (ACI) is a cell therapy to repair cartilage defects. In ACI a biopsy is taken from a non-load bearing area of the knee and expanded in-vitro. The expansion process provides the benefit of generating a large number of cells required for implantation; however, during the expansion these cells de-differentiate and lose their chondrocyte phenotype. In this review we focus on examining the de-differentiation phenotype from a mechanobiology and biophysical perspective, highlighting some of the nuclear mechanics and chromatin changes in chondrocytes seen during the expansion process and how this relates to the gene expression profile. We propose that manipulating chondrocyte nuclear architecture and chromatin organization will highlight mechanisms that will help to preserve the chondrocyte phenotype.

p53 regulates expression of nuclear envelope components in cancer cells

Nuclear organisation and architecture are essential for the maintenance of genomic integrity as well as for the epigenetic regulations and gene expression. Disruption of lamin B1, major structural and functional member of the nuclear lamina, is observed in human laminopathies and in sporadic cancers, and leads to chromosomal rearrangements and alterations of gene expression. The tumour suppressor p53 has been shown to direct specific transcriptional programmes by regulating lamin A/C, however its relationship with lamin B1 has remained elusive. Here, we show that loss of p53 correlates with increased expression of members belonging to the nuclear pore complex and nuclear lamina and directly regulates transcription of lamin B1. We show that the genomic loci of a fraction of p53-dependent genes physically interact with lamin B1 and Nup210. This observation provides a possible mechanistic explanation for the p53-depedent changes of chromatin accessibility, with the consequent influence of expression and rearrangement of these genomic sites in pancreatic cancer. Overall, these data suggest a potential functional and biochemical regulatory network connecting p53 and nuclear architecture.

Mechanical characterization of isolated mitochondria under conditions of oxidative stress

Mechanical properties have been proven to be a pivotal parameter to enhance our understanding of living systems. While research during the last decades focused on cells and tissues, little is known about the role of organelle mechanics in cell function. Here, mitochondria are of specific interest due to their involvement in numerous physiological and pathological processes, e.g., in the production and homeostasis of reactive oxygen species (ROS). Using real-time fluorescence and deformability cytometry, we present a microfluidic technology that is capable to determine the mechanical properties of individual mitochondria at a throughput exceeding 100 organelles per second. Our data on several thousands of viable mitochondria isolated from rat C6 glial cells yield a homogenous population with a median deformation that scales with the applied hydrodynamic stress. In two proof-of-principle studies, we investigated the impact of exogenously and endogenously produced ROS on mitochondria mechanics. Exposing C6 cells to hydrogen peroxide (H₂O₂) triggers superoxide production and leads to a reduction in mitochondria size while deformation is increased. In a second study, we focused on the knockout of tafazzin, which has been associated with impaired remodeling of the mitochondrial membrane and elevated levels of ROS. Interestingly, our results reveal the same mechanical alterations as observed after the exposure to H₂O₂, which points to a unified biophysical mechanism of how mitochondria respond to the presence of oxidative stress. In summary, we introduce high-throughput mechanical phenotyping into the field of organelle biology with potential applications for understanding sub-cellular dynamics that have not been accessible before.

Regulation of fenestra formation via actin-dynamin2 interaction in rat pituitary endothelial cells

Endothelial fenestrae are transcellular pores divided by a diaphragm consisting of plasmalemma vesicle-associated protein (PLVAP). They function as a channel for peptide hormones and other substances. Invagination of the plasma membrane is necessary for the fenestra formation. The actin cytoskeleton is essential for scission of endocytic vesicles from the invaginated plasma membrane. Therefore, we examined the involvement of the actin cytoskeleton in fenestra formation in cultured endothelial cells isolated from the anterior lobe (AL) of the rat pituitary, using immunofluorescence and scanning electron microscopy. Inhibition of polymerization and depolymerization of the actin cytoskeleton by latrunculin A and jasplakinolide, respectively, remarkably increased the PLVAP-positive sieve plate area and number of fenestrae. Jasplakinolide significantly affected the arrangement of the fenestra on the cell surface, resulting in parallel serpentine furrows of the fenestra. These results suggest that the actin cytoskeleton not only induces fenestra formation but also regulates cell arrangement. Dynamin is a scission protein of the invaginated plasma membrane and interacts with the actin cytoskeleton. We found that dynamin2 is mainly expressed in the endothelial cells of the rat AL. We then investigated the function of dynamin2 by the treatment with dyngo-4a, a potent inhibitor of dynamin1 and dynamin2, on the fenestra formation. As a result, the PLVAP-positive area is significantly increased by the treatment. These results show that the actin-dynamin2 interaction is essential for the control of the fenestra formation in endothelial cells of rat AL. In conclusion, the actin cytoskeleton and dynamin2 function as regulators of endothelial fenestra formation.