Nesprin-1 and -2 are involved in the pathogenesis of Emery Dreifuss muscular dystrophy and are critical for nuclear envelope integrity

The MFN2 Q367H variant reveals a novel pathomechanism connected to mtDNA-mediated inflammation

Pathogenic variants in the mitochondrial protein MFN2 are typically associated with a peripheral neuropathy phenotype, but can also cause a variety of additional pathologies including myopathy. Here, we identified an uncharacterized MFN2 variant, Q367H, in a patient diagnosed with late-onset distal myopathy, but without peripheral neuropathy. Supporting the hypothesis that this variant contributes to the patient's pathology, patient fibroblasts and transdifferentiated myoblasts showed changes consistent with impairment of several MFN2 functions. We also observed mtDNA outside of the mitochondrial network that colocalized with early endosomes, and measured activation of both TLR9 and cGAS-STING inflammation pathways that sense mtDNA. Re-expressing the Q367H variant in MFN2 KO cells also induced mtDNA release, demonstrating this phenotype is a direct result of the variant. As elevated inflammation can cause myopathy, our findings linking the Q367H MFN2 variant with elevated TLR9 and cGAS-STING signalling can explain the patient's myopathy. Thus, we characterize a novel MFN2 variant in a patient with an atypical presentation that separates peripheral neuropathy and myopathy phenotypes, and establish a potential pathomechanism connecting MFN2 dysfunction to mtDNA-mediated inflammation.

Utilizing multi-omics analysis, a new signature has been identified and validated for predicting prognosis and response to immunotherapy in lung squamous cell carcinoma, which is based on tumor mutation burden

Immunotherapy is used extensively in treating non-small cell lung cancer (NSCLC) patients. Nevertheless, in contrast to lung adenocarcinoma (LUAD), the endeavors to develop effective targeted treatments for lung squamous cell carcinoma (LUSC) have not yielded positive outcomes. Hence, it is crucial to discover biomarkers for immunotherapy and investigate more potent treatments, which is an immediate requirement for individuals with LUSC. The LUSC somatic mutation data were obtained from The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) databases. Multivariate analysis was performed to create a signature related to tumor mutation burden (TMB). Next, we utilized the CIBERSORT algorithm to assess the correlation between TMB and immune infiltrates. Additionally, we identified prognostic immune cells of LUSC through Kaplan-Meier analysis. The TCGA and ICGC cohorts covered a combined total of 11 genes that were frequently mutated. SYNE1 and TTN mutation correlated with an increased TMB and suggested a positive clinical outlook. A TMB-related signature (SYNE1 and TTN) was constructed based on this. The outlook for the high-risk group in LUSC was considerably poorer than the low-risk group (p = 0.004). In LUSC, there was a correlation between the TMB-related signature and immune infiltrates, and a positive response to anti-PD-L1 therapy was observed in individuals with low-risk scores. Furthermore, based on Kaplan-Meier analysis, plasma cells were identified as predictive immune cells in LUSC samples. In conclusion, the GSEA examination demonstrated that the TMB-associated signature stimulated immune system-related signaling pathways. To sum up, the TMB-associated signature could be marker to anticipate the immune reaction in individuals with LUSC.

Downregulation of Nesprin1 by Runx2 deficiency is critical for the development of skeletal laminopathy-like pathology

Runx2 is a master regulator of bone formation, and its dysfunction causes cleidocranial dysplasia (CCD) in humans. When iPS cells were generated from patients with CCD and Runx2-deficient iPS cells were generated using gene-editing techniques, abnormal laminopathy-like nuclei were observed. Runx2-deficient cells showed reduced Lamin A/C expression, but not protein levels. However, in Runx2-deficient cells, both the gene expression and protein levels of Nesprin1 were reduced, perinuclear actin fibers were sparser, and nuclear stiffness was reduced. Forced expression of Lamin A/C increased nuclear stiffness but did not improve nuclear morphology. In contrast, the induction of Nesprin1 expression alone normalized nuclear stiffness and restored nuclear morphology and perinuclear actin distribution. In Runx2-null cells, mechanical stress-induced phosphorylation of emerin was not observed. In contrast, forced expression of Nesprin1 in Runx2-null cells resulted in phosphorylation of emerin, indicating the restoration of intracellular tension. These observations were confirmed by atomic force microscopy. Therefore, the intracellular tension was inferred to pull the nuclear membrane into its normal shape. CUT&RUN assay and single RNA-seq analysis showed that an aberrant nuclear membrane caused loss of nuclear lamina gene regulation machinery, making the progression of normal osteogenic differentiation impossible; however, supplementation with Nesprin1 restored gene regulation mechanisms and promoted preosteoblast formation with normal nuclear morphology. Nesprin1 expression induced by Runx2 is essential for epigenetic regulation of the nuclear lamina. We propose CCD as a type of laminopathy involving defective expression of Nesprin1 regulated by Runx2.

The role of inner nuclear membrane protein emerin in myogenesis

Emerin, a ubiquitously expressed inner nuclear membrane protein, plays a central role in maintaining nuclear structure and genomic organization, and in regulating gene expression and cellular signaling pathways. These functions are critical for proper myogenic differentiation and are closely linked to the pathology of Emery-Dreifuss muscular dystrophy 1 (EDMD1), a laminopathy caused by mutations in the EMD gene. Emerin, along with other nuclear lamina proteins, modulates chromatin organization, cell signaling, gene expression, and cellular mechanotransduction, processes essential for muscle development and homeostasis. Loss of emerin function disrupts chromatin localization, causes dysregulated gene expression, and alters nucleoskeletal organization, resulting in impaired myogenic differentiation. Recent findings suggest that emerin tethers repressive chromatin at the nuclear envelope, a process essential for robust myogenesis. This review provides an in-depth discussion of emerin's multifaceted roles in nuclear organization, gene regulation, and cellular signaling, highlighting its importance in myogenic differentiation and disease progression.

Comparative Analysis of Splicing Alterations in Three Muscular Dystrophies

Background/Objectives: Missplicing caused by toxic DMPK-mRNA is described as a hallmark of myotonic dystrophy type 1 (DM1). Yet, there is an expressional misregulation of additional splicing factors described in DM1, and missplicing has been observed in other myopathies. Here, we compare the expressional misregulation of splicing factors and the resulting splicing profiles between three different hereditary myopathies. Methods: We used publicly available RNA-sequencing datasets for the three muscular dystrophies-DM1, facioscapulohumeral muscular dystrophy (FSHD) and Emery-Dreifuss muscular dystrophy (EDMD)-to compare the splicing factor expression and missplicing genome-wide using DESeq2 and MAJIQ. Results: Upregulation of alternative splicing factors and downregulation of constitutive splicing factors were detected for all three myopathies, but to different degrees. Correspondingly, the missplicing events were mostly alternative exon usage and skipping events. In DM1, most events were alternative exon usage and intron retention, while exon skipping was prevalent in FSHD, with EDMD being in between the two other myopathies in terms of splice factor regulation as well as missplicing. Accordingly, the missplicing events were only partially shared between these three myopathies, sometimes with the same locus being spliced differently. Conclusions: This indicates a combination of primary (toxic RNA) and more downstream effects (splicing factor expression) resulting in the DM1 missplicing phenotype. Furthermore, this analysis allows the distinction between disease-specific missplicing and general myopathic splicing alteration to be used as biomarkers.

LMNA-related cardiomyopathy: From molecular pathology to cardiac gene therapy

BACKGROUND

The genetic variants of LMNA cause an array of diseases that often affect the heart. LMNA-related cardiomyopathy exhibits high-penetrance and early-onset phenotypes that lead to late-stage heart failure or lethal arrhythmia. As a subtype of dilated cardiomyopathy and arrhythmogenic cardiomyopathy, LMNA-related cardiac dysfunction is resistant to existing cardiac therapeutic strategies, leaving a major unmet clinical need in cardiomyopathy management.

AIM OF REVIEW

Here we comprehensively summarize current knowledge about the genetic basis, disease models and pathological mechanisms of LMNA-related cardiomyopathy. Recent translational studies were highlighted to indicate new therapeutic modalities such as gene supplementation, gene silencing and genome editing therapy, which offer potential opportunities to overcome the difficulties in the development of specific drugs for this disease.

KEY SCIENTIFIC CONCEPTS OF REVIEW

LMNA-related cardiomyopathy involves many diverse disease mechanisms that preclude small-molecule drugs that target only a small fraction of the mechanisms. Agreeing to this notion, the first-in-human clinical trial for this disease recently reported futility. By contrast, gene therapy offers the new hope to directly intervene LMNA variants and demonstrates a tremendous potential for breakthrough therapy for this disease. Concepts in this review are also applicable to studies of other genetic diseases that lack effective therapeutics.

A distinct isoform of Msp300 (nesprin) organizes the perinuclear microtubule organizing center in adipocytes

In many cell types, disparate non-centrosomal microtubule-organizing centers (ncMTOCs) replace functional centrosomes and serve the unique needs of the cell types in which they are formed. In Drosophila fat body cells (adipocytes), an ncMTOC is organized on the nuclear surface. This perinuclear ncMTOC is anchored by Msp300, encoded by one of two nesprin-encoding genes in Drosophila. Msp300 and the spectraplakin short stop (shot) are co-dependent for localization to the nuclear envelope to generate the ncMTOC where they recruit the microtubule minus-end stabilizer Patronin (CAMSAP). The Msp300 gene is complex, encoding at least eleven isoforms. Here we show that two Msp300 isoforms, Msp300-PE and - PG, are required and only one, Msp300-PE, appears sufficient for generation of the ncMTOC. Loss of Msp300-PE and -PG results in severe loss of localization of shot and Patronin, disruption of the MT array, nuclear mispositioning and loss of endosomal trafficking. Furthermore, upon loss of Msp300-PE and -PG, other isoforms are retained at the nuclear surface despite the loss of nuclear positioning and MT organization, indicating that they are not sufficient to generate the ncMTOC. Msp300-PE has an unusual domain structure including a lack of a KASH domain and very few spectrin repeats and appears therefore to have a highly derived function to generate an ncMTOC on the nuclear surface.

Nuclei as mechanical bumpers during epithelial remodeling

The morphogenesis of developing tissues relies on extensive cellular rearrangements in shape, position, and identity. A key process in reshaping tissues is cell intercalation-driven elongation, where epithelial cells align and intercalate along a common axis. Typically, analyses focus on how peripheral cortical forces influence cell shape changes. Less attention is given to how inhomogeneities in internal structures, particularly the nucleus, impact cell shaping. Here, we examine how pulsed contractile and extension dynamics interact with the nucleus in elongating Drosophila embryos. Our data show that tightly packed nuclei in apical layers hinder tissue remodeling/oscillatory behaviors. We identify two mechanisms for resolving internuclear tensions: nuclear deformation and dispersion. Embryos with non-deformable nuclei use nuclear dispersion to maintain near-normal extensile rates, while those with non-dispersible nuclei due to microtubule inhibition exhibit disruptions in contractile behaviors. Disrupting both mechanisms leads to severe tissue extension defects and cell extrusion. These findings highlight the critical role of nuclear shape and positioning in topological remodeling of epithelia.

Unraveling the nexus of nesprin in dilated cardiomyopathy: From molecular insights to therapeutic prospects

Dilated cardiomyopathy is a complex and debilitating heart disorder characterized by the enlargement and weakening of the cardiac chambers, leading to impaired contractility and heart failure. Nesprins, a family of nuclear envelope spectrin repeat proteins that include isoforms Nesprin-1/-2, are integral components of the LInker of Nucleoskeleton and Cytoskeleton complex. They facilitate the connection between the nuclear envelope and the cytoskeleton, crucial for maintaining nuclear architecture, migration and positioning, and mechanical transduction and signaling. Nesprin-1/-2 are abundantly expressed in cardiac and skeletal muscles.They have emerged as key players in the pathogenesis of dilated cardiomyopathy. Mutations in synaptic nuclear envelope-1/-2 genes encoding Nesprin-1/-2 are associated with dilated cardiomyopathy, underscoring their significance in cardiac health. This review highlights the all known cases of Nesprin-1/-2 related dilated cardiomyopathy, focusing on their interactions with the nuclear envelope, their role in mechanical transduction, and their influence on gene expression. Moreover, it delves into the underlying mechanisms through which Nesprin dysfunction disrupts nuclear-cytoskeletal coupling, leading to abnormal nuclear morphology, impaired mechanotransduction, and altered gene regulation. The exploration of Nesprin's impact on dilated cardiomyopathy offers a promising avenue for therapeutic interventions aimed at ameliorating the disease. This review provides a comprehensive overview of recent advancements in understanding the pivotal role of Nesprins in dilated cardiomyopathy research.

Challenging Diagnosis of a Patient with Two Novel Variants in the SYNE1 Gene

We report a case of SYNE1-associated autosomal recessive spinocerebellar ataxia (SCAR8) presenting with a complex multisystemic phenotype, including highly elevated creatine kinase levels and lower-leg muscle atrophy. In addition to identifying two novel pathogenic variants in the SYNE1 gene, whole-exome sequencing revealed three variants of uncertain significance in the DYSF gene. Electromyography and muscle magnetic resonance imaging indicated a neurogenic pattern of muscle involvement. These findings, along with the segregation analysis of the variants, allowed us to exclude DYSF-associated muscular dystrophy; however, we cannot entirely rule out the possibility that the DYSF gene variants may act as modifiers of the patient's phenotype.

Dominantly inherited muscle disorders: understanding their complexity and exploring therapeutic approaches

Treatments for disabling and life-threatening hereditary muscle disorders are finally close to becoming a reality. Research has thus far focused primarily on recessive forms of muscle disease. The gene replacement strategies that are commonly employed for recessive, loss-of-function disorders are not readily translatable to most dominant myopathies owing to the presence of a normal chromosome in each nucleus, hindering the development of novel treatments for these dominant disorders. This is largely due to their complex, heterogeneous disease mechanisms that require unique therapeutic approaches. However, as viral and RNA interference-based therapies enter clinical use, key tools are now in place to develop treatments for dominantly inherited disorders of muscle. This article will review what is known about dominantly inherited disorders of muscle, specifically their genetic basis, how mutations lead to disease, and the pathomechanistic implications for therapeutic approaches.

Common SYNE2 Genetic Variant Associated With Atrial Fibrillation Lowers Expression of Nesprin-2α1 With Downstream Effects on Nuclear and Electrophysiological Traits

BACKGROUND

Atrial fibrillation GWAS (genome-wide association studies) identified significant associations for rs1152591 and linked variants in the SYNE2 gene encoding Nesprin-2, which connects the nuclear membrane with the cytoskeleton.

METHODS

Reporter gene vector transfection and CRISPR-Cas9 editing were used to identify the causal variant regulating the expression of SYNE2α1. After SYNE2 knockdown or SYNE2α1 overexpression in human stem cell-derived cardiomyocytes, nuclear phenotypes were assessed by imaging and atomic force microscopy. Gene expression was assessed by RNAseq and gene set enrichment analysis. Fura-2 AM staining assessed calcium transients. Optical mapping assessed action potential duration and conduction velocity.

RESULTS

The risk allele of rs1152591 had lower promoter and enhancer activity and was significantly associated with lower expression of the short SYNE2α1 isoform in human stem cell-derived cardiomyocytes, without an effect on the expression of the full-length SYNE2 mRNA. SYNE2α1 overexpression had dominant negative effects on the nucleus with its overexpression or SYNE2 knockdown leading to increased nuclear area and decreased nuclear stiffness. Gene expression results from SYNE2α1 overexpression demonstrated both concordant and nonconcordant effects with SYNE2 knockdown. SYNE2α1 overexpression had a gain of function on electrophysiology, leading to significantly faster calcium reuptake and decreased assessed action potential duration, while SYNE2 knockdown showed both shortened assessed action potential duration and decreased conduction velocity.

CONCLUSIONS

rs1152591 was identified as a causal atrial fibrillation variant, with the risk allele decreasing SYNE2α1 expression. Downstream effects of SYNE2α1 overexpression include changes in nuclear stiffness and electrophysiology, which may contribute to the mechanism for the risk allele's association with AF.

Calpain-1 weakens the nuclear envelope and promotes the release of neutrophil extracellular traps

The inducers of neutrophil extracellular trap (NET) formation are heterogeneous and consequently, there is no specific pathway or signature molecule indispensable for NET formation. But certain events such as histone modification, chromatin decondensation, nuclear envelope breakdown, and NET release are ubiquitous. During NET formation, neutrophils drastically rearrange their cytoplasmic, granular and nuclear content. Yet, the exact mechanism for decoding each step during NET formation still remains elusive. Here, we investigated the mechanism of nuclear envelope breakdown during NET formation. Immunofluorescence microscopic evaluation revealed a gradual disintegration of outer nuclear membrane protein nesprin-1 and alterations in nuclear morphology during NET formation. MALDI-TOF analysis of NETs that had been generated by various inducers detected the accumulation of nesprin-1 fragments. This suggests that nesprin-1 degradation occurs before NET release. In the presence of a calpain-1, inhibitor nesprin-1 degradation was decreased in calcium driven NET formation. Microscopic evaluation confirmed that the disintegration of the lamin B receptor (LBR) and the collapse of the actin cytoskeleton occurs in early and later phases of NET release, respectively. We conclude that the calpain-1 degrades nesprin-1, orchestrates the weakening of the nuclear membrane, contributes to LBR disintegration, and promoting DNA release and finally, NETs formation.

YEATS domain-containing protein GAS41 regulates nuclear shape by working in concert with BRD2 and the mediator complex in colorectal cancer

The maintenance of nuclear shape is essential for cellular homeostasis and disruptions in this process have been linked to various pathological conditions, including cancer, laminopathies, and aging. Despite the significance of nuclear shape, the precise molecular mechanisms controlling it are not fully understood. In this study, we have identified the YEATS domain-containing protein 4 (GAS41) as a previously unidentified factor involved in regulating nuclear morphology. Genetic ablation of GAS41 in colorectal cancer cells resulted in significant abnormalities in nuclear shape and inhibited cancer cell proliferation both in vitro and in vivo. Restoration experiments revealed that wild-type GAS41, but not a YEATS domain mutant devoid of histone H3 lysine 27 acetylation or crotonylation (H3K27ac/cr) binding, rescued the aberrant nuclear phenotypes in GAS41-deficient cells, highlighting the importance of GAS41's binding to H3K27ac/cr in nuclear shape regulation. Further experiments showed that GAS41 interacts with H3K27ac/cr to regulate the expression of key nuclear shape regulators, including LMNB1, LMNB2, SYNE4, and LEMD2. Mechanistically, GAS41 recruited BRD2 and the Mediator complex to gene loci of these regulators, promoting their transcriptional activation. Disruption of GAS41-H3K27ac/cr binding caused BRD2, MED14 and MED23 to dissociate from gene loci, leading to nuclear shape abnormalities. Overall, our findings demonstrate that GAS41 collaborates with BRD2 and the Mediator complex to control the expression of crucial nuclear shape regulators.

The Drosophila Nesprin-1 homolog MSP300 is required for muscle autophagy and proteostasis

Nesprin proteins, which are components of the linker of nucleoskeleton and cytoskeleton (LINC) complex, are located within the nuclear envelope and play prominent roles in nuclear architecture. For example, LINC complex proteins interact with both chromatin and the cytoskeleton. Here, we report that the Drosophila Nesprin MSP300 has an additional function in autophagy within larval body wall muscles. RNAi-mediated MSP300 knockdown in larval body wall muscles resulted in defects in the contractile apparatus, muscle degeneration and defective autophagy. In particular, MSP300 knockdown caused accumulation of cytoplasmic aggregates that contained poly-ubiquitylated cargo, as well as the autophagy receptor ref(2)P (the fly homolog of p62 or SQSTM) and Atg8a. Furthermore, MSP300 knockdown larvae expressing an mCherry-GFP-tagged Atg8a transgene exhibited aberrant persistence of the GFP signal within these aggregates, indicating failure of autophagosome maturation. These autophagy deficits were similar to those exhibited by loss of the endoplasmic reticulum (ER) fusion protein Atlastin (Atl), raising the possibility that Atl and MSP300 might function in the same pathway. In support of this possibility, we found that a GFP-tagged MSP300 protein trap exhibited extensive localization to the ER. Alteration of ER-directed MSP300 might abrogate important cytoskeletal contacts necessary for autophagosome completion.

Life at the crossroads: the nuclear LINC complex and vascular mechanotransduction

Vascular endothelial cells line the inner surface of all blood vessels, where they are exposed to polarized mechanical forces throughout their lifespan. Both basal substrate interactions and apical blood flow-induced shear stress regulate blood vessel development, remodeling, and maintenance of vascular homeostasis. Disruption of these interactions leads to dysfunction and vascular pathologies, although how forces are sensed and integrated to affect endothelial cell behaviors is incompletely understood. Recently the endothelial cell nucleus has emerged as a prominent force-transducing organelle that participates in vascular mechanotransduction, via communication to and from cell-cell and cell-matrix junctions. The LINC complex, composed of SUN and nesprin proteins, spans the nuclear membranes and connects the nuclear lamina, the nuclear envelope, and the cytoskeleton. Here we review LINC complex involvement in endothelial cell mechanotransduction, describe unique and overlapping functions of each LINC complex component, and consider emerging evidence that two major SUN proteins, SUN1 and SUN2, orchestrate a complex interplay that extends outward to cell-cell and cell-matrix junctions and inward to interactions within the nucleus and chromatin. We discuss these findings in relation to vascular pathologies such as Hutchinson-Gilford progeria syndrome, a premature aging disorder with cardiovascular impairment. More knowledge of LINC complex regulation and function will help to understand how the nucleus participates in endothelial cell force sensing and how dysfunction leads to cardiovascular disease.

Nesprin-2 is a novel scaffold protein for telethonin and FHL-2 in the cardiomyocyte sarcomere

Nesprins comprise a family of multi-isomeric scaffolding proteins, forming the linker of nucleoskeleton-and-cytoskeleton complex with lamin A/C, emerin and SUN1/2 at the nuclear envelope. Mutations in nesprin-1/-2 are associated with Emery-Dreifuss muscular dystrophy (EDMD) with conduction defects and dilated cardiomyopathy (DCM). We have previously observed sarcomeric staining of nesprin-1/-2 in cardiac and skeletal muscle, but nesprin function in this compartment remains unknown. In this study, we show that specific nesprin-2 isoforms are highly expressed in cardiac muscle and localize to the Z-disc and I band of the sarcomere. Expression of GFP-tagged nesprin-2 giant spectrin repeats 52 to 53, localized to the sarcomere of neonatal rat cardiomyocytes. Yeast two-hybrid screening of a cardiac muscle cDNA library identified telethonin and four-and-half LIM domain (FHL)-2 as potential nesprin-2 binding partners. GST pull-down and immunoprecipitation confirmed the individual interactions between nesprin-2/telethonin and nesprin-2/FHL-2, and showed that nesprin-2 and telethonin binding was dependent on telethonin phosphorylation status. Importantly, the interactions between these binding partners were impaired by mutations in nesprin-2, telethonin, and FHL-2 identified in EDMD with DCM and hypertrophic cardiomyopathy patients. These data suggest that nesprin-2 is a novel sarcomeric scaffold protein that may potentially participate in the maintenance and/or regulation of sarcomeric organization and function.

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.

Long non-coding RNA-NONMMMUT004552.2 regulates the unloading-induced bone loss through the miRNA-15b-5p/Syne1 in mice

Exercise-induced mechanical loading can increase bone strength whilst mechanical unloading enhances bone-loss. Here, we investigated the role of lncRNA NONMMUT004552.2 in unloading-induced bone-loss. Knockout of lncRNA NONMMUT004552.2 in hindlimb-unloaded mice caused an increase in the bone formation and osteoblast activity. The silencing of lncRNA NONMMUT004552.2 also decreased the osteoblast apoptosis and expression of Bax and cleaved caspase-3, increased Bcl-2 protein expression in MC3T3-E1 cells. Mechanistic investigations demonstrated that NONMMUT004552.2 functions as a competing endogenous RNA (ceRNA) to facilitate the protein expression of spectrin repeat containing, nuclear envelope 1 (Syne1) by competitively binding miR-15b-5p and subsequently inhibits the osteoblast differentiation and bone formation in the microgravity unloading environment. These data highlight the importance of the lncRNA NONMMUT004552.2/miR-15b-5p/Syne1 axis for the treatment of osteoporosis.

Nesprin1 Deficiency Is Associated with Poor Prognosis of Renal Cell Carcinoma and Resistance to Sunitinib Treatment

INTRODUCTION

Nuclear envelope spectrin repeat protein (Nesprin) 1 encoded by SYNE1, crucially regulates the morphology and functions of the cell. Mutations in the SYNE1 gene are associated with various diseases; however, their significance in renal cell carcinoma (RCC) remains unknown. In this study, we have investigated the association of SYNE1/Nesprin1 with the progression and prognosis of clear cell RCC (ccRCC).

METHODS

In silico analyses of publicly available datasets of patients with RCC were performed. Based on the cohort data, Nesprin1 expression in nephrectomized tissue samples acquired from patients with ccRCC was analyzed using immunohistochemical staining. The invasion, migration, and proliferation of the SYNE1-knockdown human RCC cell lines were analyzed in vitro; moreover, RNA sequencing and gene set enrichment analysis were conducted to study the molecular mechanism underlying the association of SYNE1/Nesprin1 with prognosis of RCC.

RESULTS

Patients with RCC-associated SYNE1 gene mutations exhibited significantly worse overall and progression-free survivals. Patients with Nesprin1-negative ccRCC tumors exhibit significantly poorer overall, cancer-specific, and recurrence-free survival rates than those recorded in the Nesprin1-positive group. SYNE1 knockdown enhanced the invasion and migration of RCC cells; however, it did not influence the proliferation of cells. RNA sequencing and gene set enrichment analysis revealed that SYNE1 knockdown significantly altered the expression of genes associated with oxidative phosphorylation. Consistently, patients with RCC exhibiting low SYNE1 expression, who were treated with the vascular endothelial growth factor receptor inhibitor sunitinib, had worse progression-free survival.

CONCLUSIONS

The results indicate that the expression of SYNE1/Nesprin1 and SYNE1 mutations in patients with RCC are closely linked to their prognosis and responsiveness to sunitinib treatment.

Identification of Candidate Male-Reproduction-Related Genes from the Testis and Androgenic Gland of Macrobrachium nipponense, Regulated by PDHE1, through Transcriptome Profiling Analysis

The previous publication identified that pyruvate dehydrogenase E1 (PDHE1) positively regulated the process of male reproduction in M. nipponense through affecting the expressions of insulin-like androgenic gland hormone. The present study aimed to identify the potential male-reproduction-related genes that were regulated by PDHE1 through performing the transcriptome profiling analysis in the testis and androgenic gland after the knockdown of the expressions of PDHE1 by the injection of dsPDHE1. Both RNA-Seq and qPCR analysis identified the significant decreases in PDHE1 expressions in the testis and androgenic gland in dsPDHE1-injected prawns compared to those in dsGFP-injected prawns, indicating the efficiency of dsPDHE1 in the present study. Transcriptome profiling analysis identified 56 and 127 differentially expressed genes (DEGs) in the testis and androgenic gland, respectively. KEGG analysis revealed that the energy-metabolism-related pathways represented the main enriched metabolic pathways of DEGs in both the testis and androgenic gland, including pyruvate metabolism, the Citrate cycle (TCA cycle), Glycolysis/Gluconeogenesis, and the Glucagon signaling pathway. Thus, it is predicted that these metabolic pathways and the DEGs from these metabolic pathways regulated by PDHE1 may be involved in the regulation of male reproduction in M. nipponense. Furthermore, four genes were found to be differentially expressed in both the testis and androgenic gland, of which ribosomal protein S3 was down-regulated and uncharacterized protein LOC113829596 was up-regulated in both the testis and androgenic gland in dsPDHE1-injected prawns. The present study provided valuable evidence for the establishment of an artificial technique to regulate the process of male reproduction in M. nipponense.

LINC complex protein nesprin-2 has pro-apoptotic activity via Bcl-2 family proteins

The apoptotic intrinsic pathway is initiated by perforation of the mitochondrial outer membrane by the effector pro-apoptotic proteins of the Bcl-2 family, Bax and Bak. Bax and Bak need to be activated, a process facilitated by the action of BH3-only pro-apoptotic members of the Bcl-2 family. The latter either directly activates the effector proteins or antagonizes the action of pro-survival Bcl-2 family members such as Bcl-xL. The nuclear envelope is a known target of the apoptotic machinery; however, it may also act as mediator of apoptosis. We showed previously that the nuclear envelope protein nesprin-2, a component of the linker of nucleoskeleton and cytoskeleton (LINC) complex, can bind to Bax in close proximity to the mitochondria and that the binding increases in apoptotic cells. We now show that depleting nesprin-2 inhibits the apoptotic mitochondrial pathway as measured by Bax and Bak activation and cytochrome c release. This survival effect was Bcl-xL-dependent. Nesprin-2 depletion also inhibited spontaneous exposure of the N-terminus of Bak in cells lacking Bcl-xL and increased the presence of Bcl-xL and Bax in the mitochondria. These results indicate that nesprin-2 promotes Bak activation and regulates mitochondrial translocation/retrotranslocation of Bcl-2 family proteins. Our findings demonstrate a new apoptotic pathway whereby the nuclear envelope, via nesprin-2, regulates apoptosis.

Clinical and Genetic Heterogeneity of Nuclear Envelopathy Related Muscular Dystrophies in an Indian Cohort

Introduction

Nuclear envelopathies occur due to structural and/or functional defects in various nuclear envelope proteins such as lamin A/C and lamin related proteins. This study is the first report on the phenotype-genotype patterns of nuclear envelopathy-related muscular dystrophies from India.

Methods

In this retrospective study, we have described patients with genetically confirmed muscular dystrophy associated with nuclear envelopathy. Data on clinical, laboratory findings and muscle MRI were collected.

Results

Sixteen patients were included with median age at onset of 3 years (range: 1 month - 17 years). Three genes were involved: LMNA (11, 68.75%), EMD (4, 25%) and SYNE1 (1, 6.25%). The 11 patients with LMNA variants were Congenital muscular dystrophy (MDCL)=4, Limb Girdle Muscular Dystrophy (LGMD1B)=4 and Emery-Dreifuss Muscular Dystrophy (EDMD2)=3. On muscle biopsy, one patient from each laminopathy phenotype (n = 3) revealed focal perivascular inflammatory infiltrate. Other notable features were ophthalmoparesis in one and facial weakness in one. None had cardiac involvement. Patients with EDMD1 had both upper (UL) and lower limb (LL) proximo-distal weakness. Cardiac rhythm disturbances such as sick sinus syndrome and atrial arrhythmias were noted in two patients with EDMD1. Only one patient with variant c.654_658dup (EMD) lost ambulation in the 3rd decade, 18 years after disease onset. Two had finger contractures with EMD and SYNE1 variants respectively. All patients with LMNA and SYNE1 variants were ambulant at the time of evaluation. Mean duration of illness (years) was 11.6±13 (MDCL), 3.2±1.0 (EDMD2), 10.4±12.8 (LGMD1B), 11.8±8.4 (EDMD1) and 3 (EDMD4). One patient had a novel SYNE1 mutation (c.22472dupA, exon 123) and presented with UL phenotype and prominent finger and wrist contractures.

Conclusion

The salient features included ophthalmoparesis and facial weakness in LMNA, prominent finger contractures in EMD and SYNE1 and upper limb phenotype with the novel pathogenic variant in SYNE1.

In Vivo Monitoring of Nucleophagy in Caenorhabditis elegans

The autophagy-lysosomal pathway enables the controlled degradation of cellular contents. Nucleophagy is the selective autophagic recycling of nuclear components upon delivery to the lysosome. Although methods to monitor and quantify autophagy as well as selective types of autophagy have been developed and implemented in cells and in vivo, methods monitoring nucleophagy remain scarce. Here, we describe a procedure to monitor the autophagic engagement of an endogenous nuclear envelope component, i.e., ANC-1, the nematode homologue of the mammalian Nesprins in vivo, utilizing super-resolution microscopy.

Force transmission and SUN-KASH higher-order assembly in the LINC complex models

The linkers of the nucleoskeleton and cytoskeleton (LINC) complex comprises Sad-1 and UNC-84 (SUN) and Klarsicht, ANC-1, SYNE homology (KASH) domain proteins, whose conserved interactions provide a physical coupling between the cytoskeleton and the nucleoskeleton, thereby mediating the transfer of physical forces across the nuclear envelope. The LINC complex can perform distinct cellular functions by pairing various KASH domain proteins with the same SUN domain protein. Recent studies have suggested a higher-order assembly of SUN and KASH instead of a more widely accepted linear trimer model for the LINC complex. In the present study, we use molecular dynamics simulations to investigate the mechanism of force transfer across the two proposed models of LINC complex assembly, namely the 3:3 linear trimer model and the 6:6 higher-order model. Employing steered molecular dynamics simulations with various structures using forces at different rates and directions, we examine the structural stability of the two models under various biologically relevant conditions. Our results suggest that both models can withstand and transfer significant levels of force while retaining their structural integrity. However, the force response of various SUN/KASH assemblies depend on the force direction and pulling rates. Slower pulling rates result in higher mean square fluctuations of the 3:3 assembly compared to the fast pulling. Interestingly, the 6:6 assembly tends to provide an additional range of motion flexibility and might be more advantageous to the structural rigidity and pliability of the nuclear envelope. These findings offer insights into how the SUN and KASH proteins maintain the structural integrity of the nuclear membrane.

A Case Report of SYNE1 Deficiency-Mimicking Mitochondrial Disease and the Value of Pangenomic Investigations

Mitochondrial disorders are characterized by a huge clinical, biochemical, and genetic heterogeneity, which poses significant diagnostic challenges. Several studies report that more than 50% of patients with suspected mitochondrial disease could have a non-mitochondrial disorder. Thus, only the identification of the causative pathogenic variant can confirm the diagnosis. Herein, we describe the diagnostic journey of a family suspected of having a mitochondrial disorder who were referred to our Genetics Department. The proband presented with the association of cerebellar ataxia, COX-negative fibers on muscle histology, and mtDNA deletions. Whole exome sequencing (WES), supplemented by a high-resolution array, comparative genomic hybridization (array-CGH), allowed us to identify two pathogenic variants in the non-mitochondrial SYNE1 gene. The proband and her affected sister were found to be compound heterozygous for a known nonsense variant (c.13258C>T, p.(Arg4420Ter)), and a large intragenic deletion that was predicted to result in a loss of function. To our knowledge, this is the first report of a large intragenic deletion of SYNE1 in patients with cerebellar ataxia (ARCA1). This report highlights the interest in a pangenomic approach to identify the genetic basis in heterogeneous neuromuscular patients with the possible cause of mitochondrial disease. Moreover, even rare copy number variations should be considered in patients with a phenotype suggestive of SYNE1 deficiency.

Molecular Mechanisms for the Regulation of Nuclear Membrane Integrity

The nuclear membrane serves a critical role in protecting the contents of the nucleus and facilitating material and signal exchange between the nucleus and cytoplasm. While extensive research has been dedicated to topics such as nuclear membrane assembly and disassembly during cell division, as well as interactions between nuclear transmembrane proteins and both nucleoskeletal and cytoskeletal components, there has been comparatively less emphasis on exploring the regulation of nuclear morphology through nuclear membrane integrity. In particular, the role of type II integral proteins, which also function as transcription factors, within the nuclear membrane remains an area of research that is yet to be fully explored. The integrity of the nuclear membrane is pivotal not only during cell division but also in the regulation of gene expression and the communication between the nucleus and cytoplasm. Importantly, it plays a significant role in the development of various diseases. This review paper seeks to illuminate the biomolecules responsible for maintaining the integrity of the nuclear membrane. It will delve into the mechanisms that influence nuclear membrane integrity and provide insights into the role of type II membrane protein transcription factors in this context. Understanding these aspects is of utmost importance, as it can offer valuable insights into the intricate processes governing nuclear membrane integrity. Such insights have broad-reaching implications for cellular function and our understanding of disease pathogenesis.

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.

Exome Sequencing and Optical Genome Mapping in Molecularly Unsolved Cases of Duchenne Muscular Dystrophy: Identification of a Causative X-Chromosomal Inversion Disrupting the DMD Gene

Duchenne muscular dystrophy (DMD) is a severe progressive muscle disease that mainly affects boys due to X-linked recessive inheritance. In most affected individuals, MLPA or sequencing-based techniques detect deletions, duplications, or point mutations in the dystrophin-encoding DMD gene. However, in a small subset of patients clinically diagnosed with DMD, the molecular cause is not identified with these routine methods. Evaluation of the 60 DMD patients in our center revealed three cases without a known genetic cause. DNA samples of these patients were analyzed using whole-exome sequencing (WES) and, if unconclusive, optical genome mapping (OGM). WES led to a diagnosis in two cases: one patient was found to carry a splice mutation in the DMD gene that had not been identified during previous Sanger sequencing. In the second patient, we detected two variants in the fukutin gene (FKTN) that were presumed to be disease-causing. In the third patient, WES was unremarkable, but OGM identified an inversion disrupting the DMD gene (~1.28 Mb) that was subsequently confirmed with long-read sequencing. These results highlight the importance of reanalyzing unsolved cases using WES and demonstrate that OGM is a useful method for identifying large structural variants in cases with unremarkable exome sequencing.

Case report: Exome sequencing revealed disease-causing variants in a patient with spondylospinal thoracic dysostosis

Background

Spondylocostal dysostosis is a rare genetic disorder caused by mutations in DLL3, MESP2, LFNG, HES7, TBX6, and RIPPLY2. A particular form of this disorder characterized by the association of spondylocostal dysostosis with multiple pterygia has been reported and called spondylospinal thoracic dysostosis. Both disorders affect the spine and ribs, leading to abnormal development of the spine. Spondylospinal thoracic dysostosis is a rare syndrome characterized by the association of multiple vertebral segmentation defects, thoracic cage deformity, and multiple pterygia. This syndrome can be considered a different form of the described spondylocostal dysostosis. However, no genetic testing has been conducted for this rare disorder so far.

Methods

We report here the case of an 18-month-old female patient presenting the clinical and radiological features of spondylospinal thoracic dysostosis. To determine the underlying genetic etiology, whole exome sequencing (WES) and Sanger sequencing were performed.

Results

Using WES, we identified a variant in the TPM2 gene c. 628C>T, already reported in the non-lethal form of multiple pterygium syndrome. In addition, following the analysis of WES data, using bioinformatic tools, for oligogenic diseases, we identified candidate modifier genes, CAP2 and ADCY6, that could impact the clinical manifestations.

Conclusion

We showed a potential association between TPM2 and the uncommon spondylocostal dysostosis phenotype that would require further validation on larger cohort.

Nucleus Mechanosensing in Cardiomyocytes

Cardiac muscle contraction is distinct from the contraction of other muscle types. The heart continuously undergoes contraction-relaxation cycles throughout an animal's lifespan. It must respond to constantly varying physical and energetic burdens over the short term on a beat-to-beat basis and relies on different mechanisms over the long term. Muscle contractility is based on actin and myosin interactions that are regulated by cytoplasmic calcium ions. Genetic variants of sarcomeric proteins can lead to the pathophysiological development of cardiac dysfunction. The sarcomere is physically connected to other cytoskeletal components. Actin filaments, microtubules and desmin proteins are responsible for these interactions. Therefore, mechanical as well as biochemical signals from sarcomeric contractions are transmitted to and sensed by other parts of the cardiomyocyte, particularly the nucleus which can respond to these stimuli. Proteins anchored to the nuclear envelope display a broad response which remodels the structure of the nucleus. In this review, we examine the central aspects of mechanotransduction in the cardiomyocyte where the transmission of mechanical signals to the nucleus can result in changes in gene expression and nucleus morphology. The correlation of nucleus sensing and dysfunction of sarcomeric proteins may assist the understanding of a wide range of functional responses in the progress of cardiomyopathic diseases.

Nesprin-1: novel regulator of striated muscle nuclear positioning and mechanotransduction

Nesprins (nuclear envelope spectrin repeat proteins) are multi-isomeric scaffolding proteins. Giant nesprin-1 and -2 localise to the outer nuclear membrane, interact with SUN (Sad1p/UNC-84) domain-containing proteins at the inner nuclear membrane to form the LInker of Nucleoskeleton and Cytoskeleton (LINC) complex, which, in association with lamin A/C and emerin, mechanically couples the nucleus to the cytoskeleton. Despite ubiquitous expression of nesprin giant isoforms, pathogenic mutations in nesprin-1 and -2 are associated with tissue-specific disorders, particularly related to striated muscle such as dilated cardiomyopathy and Emery-Dreifuss muscular dystrophy. Recent evidence suggests this muscle-specificity might be attributable in part, to the small muscle specific isoform, nesprin-1α2, which has a novel role in striated muscle function. Our current understanding of muscle-specific functions of nesprin-1 and its isoforms will be summarised in this review to provide insight into potential pathological mechanisms of nesprin-related muscle disease and may inform potential targets of therapeutic modulation.

Identification of epigenetic modulators as determinants of nuclear size and shape

The shape and size of the human cell nucleus is highly variable among cell types and tissues. Changes in nuclear morphology are associated with disease, including cancer, as well as with premature and normal aging. Despite the very fundamental nature of nuclear morphology, the cellular factors that determine nuclear shape and size are not well understood. To identify regulators of nuclear architecture in a systematic and unbiased fashion, we performed a high-throughput imaging-based siRNA screen targeting 867 nuclear proteins including chromatin-associated proteins, epigenetic regulators, and nuclear envelope components. Using multiple morphometric parameters, and eliminating cell cycle effectors, we identified a set of novel determinants of nuclear size and shape. Interestingly, most identified factors altered nuclear morphology without affecting the levels of lamin proteins, which are known prominent regulators of nuclear shape. In contrast, a major group of nuclear shape regulators were modifiers of repressive heterochromatin. Biochemical and molecular analysis uncovered a direct physical interaction of histone H3 with lamin A mediated via combinatorial histone modifications. Furthermore, disease-causing lamin A mutations that result in disruption of nuclear shape inhibited lamin A-histone H3 interactions. Oncogenic histone H3.3 mutants defective for H3K27 methylation resulted in nuclear morphology abnormalities. Altogether, our results represent a systematic exploration of cellular factors involved in determining nuclear morphology and they identify the interaction of lamin A with histone H3 as an important contributor to nuclear morphology in human cells.

A genetic and developmental biological approach for a family with complex congenital heart diseases-evidence of digenic inheritance

Objective

Congenital heart disease (CHD) is caused by cardiovascular developmental defects and has a global prevalence of ∼1%. The etiology of CHD is multifactorial and remains generally unknown, despite advances in analytical techniques based on next-generation sequencing (NGS). The aim of our study was to elucidate the multi-genetic origin and pathogenesis of an intriguing familial case with complex CHD.

Methods

We performed an original trio-based gene panel analysis using NGS of the family, including two siblings with CHD of single ventricular phenotype, and their unaffected parents. The pathogenicity of the detected rare variants was investigated in silico, and the functional effects of the variants were confirmed in vitro using luciferase assays. The combinatorial effect of gene alterations of the putative responsible genes was tested in vivo using genetically engineered mutant mice.

Results

NGS-based gene panel analyses revealed two heterozygous rare variants in NODAL and in TBX20 common to the siblings and to just one of parents. Both variants were suspected pathogenic in silico, and decreased transcriptional activities of downstream signaling pathways were observed in vitro. The analyses of Nodal and Tbx20 double mutant mice demonstrated that Nodal+/-Tbx20-/- embryos showed more severe defects than Nodal+/+Tbx20-/- embryos during early heart development. The expression of Pitx2, a known downstream target of Nodal, was downregulated in Tbx20-/- mutants.

Conclusions

Two rare variants on NODAL and TBX20 genes detected in this family were considered to be loss-of-function mutations. Our results suggest that NODAL and TBX20 may be complementary for the cardiac development, and a combinatorial loss-of-function of NODAL and TBX20 could be implicated in digenic inherence as the etiology of complex CHD associated with single ventricle defects in this family.

Nuclear mechanosignaling in striated muscle diseases

Mechanosignaling describes processes by which biomechanical stimuli are transduced into cellular responses. External biophysical forces can be transmitted via structural protein networks that span from the cellular membrane to the cytoskeleton and the nucleus, where they can regulate gene expression through a series of biomechanical and/or biochemical mechanosensitive mechanisms, including chromatin remodeling, translocation of transcriptional regulators, and epigenetic factors. Striated muscle cells, including cardiac and skeletal muscle myocytes, utilize these nuclear mechanosignaling mechanisms to respond to changes in their intracellular and extracellular mechanical environment and mediate gene expression and cell remodeling. In this brief review, we highlight and discuss recent experimental work focused on the pathway of biomechanical stimulus propagation at the nucleus-cytoskeleton interface of striated muscles, and the mechanisms by which these pathways regulate gene regulation, muscle structure, and function. Furthermore, we discuss nuclear protein mutations that affect mechanosignaling function in human and animal models of cardiomyopathy. Furthermore, current open questions and future challenges in investigating striated muscle nuclear mechanosignaling are further discussed.

Nuclear envelope transmembrane proteins involved in genome organization are misregulated in myotonic dystrophy type 1 muscle

Myotonic dystrophy type 1 is a multisystemic disorder with predominant muscle and neurological involvement. Despite a well described pathomechanism, which is primarily a global missplicing due to sequestration of RNA-binding proteins, there are still many unsolved questions. One such question is the disease etiology in the different affected tissues. We observed alterations at the nuclear envelope in primary muscle cell cultures before. This led us to reanalyze a published RNA-sequencing dataset of DM1 and control muscle biopsies regarding the misregulation of NE proteins. We could identify several muscle NE protein encoding genes to be misregulated depending on the severity of the muscle phenotype. Among these misregulated genes were NE transmembrane proteins (NETs) involved in nuclear-cytoskeletal coupling as well as genome organization. For selected genes, we could confirm that observed gene-misregulation led to protein expression changes. Furthermore, we investigated if genes known to be under expression-regulation by genome organization NETs were also misregulated in DM1 biopsies, which revealed that misregulation of two NETs alone is likely responsible for differential expression of about 10% of all genes being differentially expressed in DM1. Notably, the majority of NETs identified here to be misregulated in DM1 muscle are mutated in Emery-Dreifuss muscular dystrophy or clinical similar muscular dystrophies, suggesting a broader similarity on the molecular level for muscular dystrophies than anticipated. This shows not only the importance of muscle NETs in muscle health and disease, but also highlights the importance of the NE in DM1 disease progression.

Childhood muscular dystrophies

Infancy- and childhood-onset muscular dystrophies are associated with a characteristic distribution and progression of motor dysfunction. The underlying causes of progressive childhood muscular dystrophies are heterogeneous involving diverse genetic pathways and genes that encode proteins of the plasma membrane, extracellular matrix, sarcomere, and nuclear membrane components. The prototypical clinicopathological features in an affected child may be adequate to fully distinguish it from other likely diagnoses based on four common features: (1) weakness and wasting of pelvic-femoral and scapular muscles with involvement of heart muscle; (2) elevation of serum muscle enzymes in particular serum creatine kinase; (3) necrosis and regeneration of myofibers; and (4) molecular neurogenetic assessment particularly utilizing next-generation sequencing of the genome of the likeliest candidates genes in an index case or family proband. A number of different animal models of therapeutic strategies have been developed for gene transfer therapy, but so far these techniques have not yet entered clinical practice. Treatment remains for the most part symptomatic with the goal of ameliorating locomotor and cardiorespiratory manifestations of the disease.

Nucleophagy delays aging and preserves germline immortality

Marked alterations in nuclear ultrastructure are a universal hallmark of aging, progeroid syndromes and other age-related pathologies. Here we show that autophagy of nuclear proteins is an important determinant of fertility and aging. Impairment of nucleophagy diminishes stress resistance, germline immortality and longevity. We found that the nematode Caenorhabditis elegans nuclear envelope anchor protein, nuclear anchorage protein 1 (ANC-1) and its mammalian ortholog nesprin-2 are cleared out by autophagy and restrict nucleolar size, a biomarker of aging. We further uncovered a germline immortality assurance mechanism, which involves nucleolar degradation at the most proximal oocyte by ANC-1 and key autophagic components. Perturbation of this clearance pathway causes tumor-like structures in C. elegans, and genetic ablation of nesprin-2 causes ovarian carcinomas in mice. Thus, autophagic recycling of nuclear components is a conserved soma longevity and germline immortality mechanism that promotes youthfulness and delays aging under conditions of stress.

Genotype-Phenotype Correlations in Human Diseases Caused by Mutations of LINC Complex-Associated Genes: A Systematic Review and Meta-Summary

Mutations in genes encoding proteins associated with the linker of nucleoskeleton and cytoskeleton (LINC) complex within the nuclear envelope cause different diseases with varying phenotypes including skeletal muscle, cardiac, metabolic, or nervous system pathologies. There is some understanding of the structure of LINC complex-associated proteins and how they interact, but it is unclear how mutations in genes encoding them can cause the same disease, and different diseases with different phenotypes. Here, published mutations in LINC complex-associated proteins were systematically reviewed and analyzed to ascertain whether patterns exist between the genetic sequence variants and clinical phenotypes. This revealed LMNA is the only LINC complex-associated gene in which mutations commonly cause distinct conditions, and there are no clear genotype-phenotype correlations. Clusters of LMNA variants causing striated muscle disease are located in exons 1 and 6, and metabolic disease-associated LMNA variants are frequently found in the tail of lamin A/C. Additionally, exon 6 of the emerin gene, EMD, may be a mutation "hot-spot", and diseases related to SYNE1, encoding nesprin-1, are most often caused by nonsense type mutations. These results provide insight into the diverse roles of LINC-complex proteins in human disease and provide direction for future gene-targeted therapy development.

Nuclear movement in multinucleated cells

Nuclear movement is crucial for the development of many cell types and organisms. Nuclear movement is highly conserved, indicating its necessity for cellular function and development. In addition to mononucleated cells, there are several examples of cells in which multiple nuclei exist within a shared cytoplasm. These multinucleated cells and syncytia have important functions for development and homeostasis. Here, we review a subset of the developmental contexts in which the regulation of the movement and positioning of multiple nuclei are well understood, including pronuclear migration, the Drosophila syncytial blastoderm, the Caenorhabditis elegans hypodermis, skeletal muscle and filamentous fungi. We apply the principles learned from these models to other systems.

The ANC-1 (Nesprin-1/2) organelle-anchoring protein functions through mitochondria to polarize axon growth in response to SLT-1

A family of giant KASH proteins, including C. elegans ANC-1 and mammalian Nesprin-1 and -2, are involved in organelle anchoring and are associated with multiple neurodevelopmental disorders including autism, bipolar disorder, and schizophrenia. However, little is known about how these proteins function in neurons. Moreover, the role of organelle anchoring in axon development is poorly understood. Here, we report that ANC-1 functions with the SLT-1 extracellular guidance cue to polarize ALM axon growth. This role for ANC-1 is specific to its longer ANC-1A and ANC-1C isoforms, suggesting that it is mechanistically distinct from previously described roles for ANC-1. We find that ANC-1 is required for the localization of a cluster of mitochondria to the base of the proximal axon. Furthermore, genetic and pharmacological studies indicate that ANC-1 functions with mitochondria to promote polarization of ALM axon growth. These observations reveal a mechanism whereby ANC-1 functions through mitochondria to polarize axon growth in response to SLT-1.

Determining the Likelihood of Disease Pathogenicity Among Incidentally Identified Genetic Variants in Rare Dilated Cardiomyopathy-Associated Genes

Background As utilization of clinical exome sequencing (ES) has expanded, criteria for evaluating the diagnostic weight of incidentally identified variants are critical to guide clinicians and researchers. This is particularly important in genes associated with dilated cardiomyopathy (DCM), which can cause heart failure and sudden death. We sought to compare the frequency and distribution of incidentally identified variants in DCM-associated genes between a clinical referral cohort with those in control and known case cohorts to determine the likelihood of pathogenicity among those undergoing genetic testing for non-DCM indications. Methods and Results A total of 39 rare, non-TTN DCM-associated genes were identified and evaluated from a clinical ES testing referral cohort (n=14 005, Baylor Genetic Laboratories) and compared with a DCM case cohort (n=9442) as well as a control cohort of population variants (n=141 456) derived from the gnomAD database. Variant frequencies in each cohort were compared. Signal-to-noise ratios were calculated comparing the DCM and ES cohort with the gnomAD cohort. The likely pathogenic/pathogenic variant yield in the DCM cohort (8.2%) was significantly higher than in the ES cohort (1.9%). Based on signal-to-noise and correlation analysis, incidental variants found in FLNC, RBM20, MYH6, DSP, ABCC9, JPH2, and NEXN had the greatest chance of being DCM-associated. Conclusions The distribution of pathogenic variants between the ES cohort and the DCM case cohort was gene specific, and variants found in the ES cohort were similar to variants found in the control cohort. Incidentally identified variants in specific genes are more associated with DCM than others.

The LEM-ESCRT toolkit: Repair and maintenance of the nucleus

The eukaryotic genome is enclosed in a nuclear envelope that protects it from potentially damaging cellular activities and physically segregates transcription and translation.Transport across the NE is highly regulated and occurs primarily via the macromolecular nuclear pore complexes.Loss of nuclear compartmentalization due to defects in NPC function and NE integrity are tied to neurological and ageing disorders like Alzheimer’s, viral pathogenesis, immune disorders, and cancer progression.Recent work implicates inner-nuclear membrane proteins of the conserved LEM domain family and the ESCRT machinery in NE reformation during cell division and NE repair upon rupture in migrating cancer cells, and generating seals over defective NPCs. In this review, we discuss the recent in-roads made into defining the molecular mechanisms and biochemical networks engaged by LEM and many other integral inner nuclear membrane proteins to preserve the nuclear barrier.

Effects of mutant lamins on nucleo-cytoskeletal coupling in Drosophila models of LMNA muscular dystrophy

The nuclei of multinucleated skeletal muscles experience substantial external force during development and muscle contraction. Protection from such forces is partly provided by lamins, intermediate filaments that form a scaffold lining the inner nuclear membrane. Lamins play a myriad of roles, including maintenance of nuclear shape and stability, mediation of nuclear mechanoresponses, and nucleo-cytoskeletal coupling. Herein, we investigate how disease-causing mutant lamins alter myonuclear properties in response to mechanical force. This was accomplished via a novel application of a micropipette harpooning assay applied to larval body wall muscles of Drosophila models of lamin-associated muscular dystrophy. The assay enables the measurement of both nuclear deformability and intracellular force transmission between the cytoskeleton and nuclear interior in intact muscle fibers. Our studies revealed that specific mutant lamins increase nuclear deformability while other mutant lamins cause nucleo-cytoskeletal coupling defects, which were associated with loss of microtubular nuclear caging. We found that microtubule caging of the nucleus depended on Msp300, a KASH domain protein that is a component of the linker of nucleoskeleton and cytoskeleton (LINC) complex. Taken together, these findings identified residues in lamins required for connecting the nucleus to the cytoskeleton and suggest that not all muscle disease-causing mutant lamins produce similar defects in subcellular mechanics.

Nesprin-1 LINC complexes recruit microtubule cytoskeleton proteins and drive pathology in Lmna-mutant striated muscle

Mutations in LMNA, the gene encoding A-type lamins, cause laminopathies-diseases of striated muscle and other tissues. The aetiology of laminopathies has been attributed to perturbation of chromatin organization or structural weakening of the nuclear envelope (NE) such that the nucleus becomes more prone to mechanical damage. The latter model requires a conduit for force transmission to the nucleus. NE-associated Linker of Nucleoskeleton and Cytoskeleton (LINC) complexes are one such pathway. Using clustered regularly interspaced short palindromic repeats to disrupt the Nesprin-1 KASH (Klarsicht, ANC-1, Syne Homology) domain, we identified this LINC complex protein as the predominant NE anchor for microtubule cytoskeleton components, including nucleation activities and motor complexes, in mouse cardiomyocytes. Loss of Nesprin-1 LINC complexes resulted in loss of microtubule cytoskeleton proteins at the nucleus and changes in nuclear morphology and positioning in striated muscle cells, but with no overt physiological defects. Disrupting the KASH domain of Nesprin-1 suppresses Lmna-linked cardiac pathology, likely by reducing microtubule cytoskeleton activities at the nucleus. Nesprin-1 LINC complexes thus represent a potential therapeutic target for striated muscle laminopathies.