Role Of Lamin Research Articles

Lamin A/C modulates spatial organization and function of the Hsp70 gene locus via nuclear myosin I.

The structure-function relationship of the nucleus is tightly regulated, especially during heat shock. Typically, heat shock activates molecular chaperones that prevent protein misfolding and preserve genome integrity. However, the molecular mechanisms that regulate nuclear structure-function relationships during heat shock remain unclear. Here, we show that lamin A and C (hereafter lamin A/C; both lamin A and C are encoded by LMNA) are required for heat-shock-mediated transcriptional induction of the Hsp70 gene locus (HSPA genes). Interestingly, lamin A/C regulates redistribution of nuclear myosin I (NM1) into the nucleus upon heat shock, and depletion of either lamin A/C or NM1 abrogates heat-shock-induced repositioning of Hsp70 gene locus away from the nuclear envelope. Lamins and NM1 also regulate spatial positioning of the SC35 (also known as SRSF2) speckles - important nuclear landmarks that modulates Hsp70 gene locus expression upon heat shock. This suggests an intricate crosstalk between nuclear lamins, NM1 and SC35 organization in modulating transcriptional responses of the Hsp70 gene locus during heat shock. Taken together, this study unravels a novel role for lamin A/C in the regulation of the spatial dynamics and function of the Hsp70 gene locus upon heat shock, via the nuclear motor protein NM1.This article has an associated First Person interview with the first author of the paper.

Lamin A/C negatively regulated by miR-124-3p modulates apoptosis of vascular smooth muscle cells during cyclic stretch application in rats.

Apoptosis of vascular smooth muscle cells (VSMCs) influenced by abnormal cyclic stretch is crucial for vascular remodelling during hypertension. Lamin A/C, a nuclear envelope protein, is mechano-responsive, but the role of lamin A/C in VSMC apoptosis is still unclear. FX-5000T Strain Unit provided cyclic stretch (CS) in vitro. AnnexinV/PI and cleaved Caspase 3 ELISA detected apoptosis. qPCR was used to investigate the expression of miR-124-3p and a luciferase reporter assay was used to evaluate the ability of miR-124-3p binding to the Lmna 3'UTR. Protein changes of lamin A/C and relevant molecules were detected using western blot. Ingenuity Pathway Analysis and Protein/DNA array detected the potential transcription factors. Renal hypertensive rats verified these changes. High cyclic stretch (15%-CS) induced VSMC apoptosis and repressed lamin A/C expressions compared with normal (5%-CS) control. Downregulation of lamin A/C enhanced VSMC apoptosis. In addition, 15%-CS had no significant effect on mRNA expression of Lmna, and lamin A/C degradation was not induced by autophagy. 15%-CS elevated miR-124-3p bound to the 3'UTR of Lmna and negatively regulated protein expression of lamin A/C. Similar changes occurred in renal hypertensive rats compared with sham controls. Lamin A/C repression affected activity of TP53, CREB1, MYC, STAT1/5/6 and JUN, which may in turn affect apoptosis. Our data suggested that the decreased expression of lamin A/C upon abnormal cyclic stretch and hypertension may induce VSMC apoptosis. These mechano-responsive factors play important roles in VSMC apoptosis and might be novel therapeutic targets for vascular remodelling in hypertension.

Genomic instability and innate immune responses to self-DNA in progeria.

In the last decade, we have seen increasing evidence of the importance of structural nuclear proteins such as lamins in nuclear architecture and compartmentalization of genome function and in the maintenance of mechanical stability and genome integrity. With over 400 mutations identified in the LMNA gene (encoding for A-type lamins) associated with more than ten distinct degenerative disorders, the role of lamins as genome caretakers and the contribution of lamins dysfunction to disease are unarguable. However, the molecular mechanisms whereby lamins mutations cause pathologies remain less understood. Here, we review pathways and mechanisms recently identified as playing a role in the pathophysiology of laminopathies, with special emphasis in Hutchinson Gilford Progeria Syndrome (HGPS). This devastating incurable accelerated aging disease is caused by a silent mutation in the LMNA gene that generates a truncated lamin A protein "progerin" that exerts profound cellular toxicity and organismal decline. Patients usually die in their teens due to cardiovascular complications such as myocardial infarction or stroke. To date, there are no efficient therapies that ameliorate disease progression, stressing the need to understand molecularly disease mechanisms that can be targeted therapeutically. We will summarize data supporting that replication stress is a major cause of genomic instability in laminopathies, which contributes to the activation of innate immune responses to self-DNA that in turn accelerate the aging process.

The role of lamin A/C in mesenchymal stem cell differentiation

Lamin A/C is the major architectural protein of cell nucleus in charge of the nuclear mechanosensing. By integrating extracellular mechanical and biochemical signals, lamin A/C regulates multiple intracellular events including mesenchymal stem cell (MSC) fate determination. Herein, we review the recent findings about the effects and mechanisms of lamin A/C in governing MSC lineage commitment, with a special focus on osteogenesis and adipogenesis. Better understanding of MSC differentiation regulated by lamin A/C could provide insights into pathogenesis of age-related osteoporosis.

Role of Lamin A/C Gene Mutations in the Signaling Defects Leading to Cardiomyopathies.

Nuclear lamin A/C are crucial components of the intricate protein mesh that underlies the inner nuclear membrane and confers mainly nuclear and cytosolic rigidity. However, throughout the years a number of other key physiological processes have been associated with lamins such as modulation of both genes expression and the activity of signaling mediators. To further solidify its importance in cell physiology, mutations in the lamin A/C gene (LMNA) have been associated to diverse pathological phenotypes with skeletal muscles and the heart being the most affected systems. When affected, the heart develops a wide array of phenotypes spanning from dilated cardiomyopathy with conduction defects to arrhythmogenic right ventricular cardiomyopathy. The surprising large number of cardiac phenotypes reflects the equally large number of specific mutations identified in the LMNA gene. In this review, we underlie how mutations in LMNA can impact the activity and the spatial/temporal organization of signaling mediators and transcription factors. We analyzed the ever-increasing amount of findings collected in LmnaH222P/H222P mice whose cardiomyopathy resemble the most important features of the disease in humans and a number of key evidences from other experimental models. With this mini review, we attempt to combine the newest insights regarding both the pathogenic effects of LMNA mutations in terms of signaling abnormalities and cardiac laminopathies.

Lamin A/C might be involved in the EMT signalling pathway

We have previously reported a heterogeneous expression pattern of the nuclear membrane protein lamin A/C in low- and high-Gleason score (GS) prostate cancer (PC) tissues, and we have now found that this change is not associated with LMNA mutations. This expression pattern appears to be similar to the process of epithelial to mesenchymal transition (EMT) or to that of mesenchymal to epithelial transition (MET). The role of lamin A/C in EMT or MET in PC remains unclear. Therefore, we first investigated the expression levels of and the associations between lamin A/C and several common EMT markers, such as E-cadherin, N-cadherin, β-catenin, snail, slug and vimentin in PC tissues with different GS values and in different cell lines with varying invasion abilities. Our results suggest that lamin A/C might constitute a type of epithelial marker that better signifies EMT and MET in PC tissue, since a decrease in lamin A/C expression in GS 4 + 5 cases is likely associated with the EMT process, while the re-expression of lamin A/C in GS 5 + 4 cases is likely linked with MET. The detailed GS better exhibited the changes in lamin A/C and the EMT markers examined. Lamin A/C overexpression or knockdown had an impact on EMT biomarkers in a cell model by direct regulation of β-catenin. Hence, we suggest that lamin A/C might serve as a reliable epithelial biomarker for the distinction of PC cell differentiation and might also be a fundamental factor in the occurrence of EMT or MET in PC.

Lamin A/C augments Th1 differentiation and response against vaccinia virus and Leishmania major

Differentiation of naive CD4+ T-cells into functionally distinct T helper (Th) subsets is critical to immunity against pathogen infection. Little is known about the role of signals emanating from the nuclear envelope for T-cell differentiation. The nuclear envelope protein lamin A/C is induced in naive CD4+ T-cells upon antigen recognition and acts as a link between the nucleus and the plasma membrane during T-cell activation. Here we demonstrate that the absence of lamin A/C in naive T-cell reduces Th1 differentiation without affecting Th2 differentiation in vitro and in vivo. Moreover, Rag1−/− mice reconstituted with Lmna−/−CD4+CD25− T-cells and infected with vaccinia virus show weaker Th1 responses and viral removal than mice reconstituted with wild-type T-cells. Th1 responses and pathogen clearance upon Leishmania major infection were similarly diminished in mice lacking lamin A/C in the complete immune system or selectively in T-cells. Lamin A/C mediates Th1 polarization by a mechanism involving T-bet and IFNγ production. Our results reveal a novel role for lamin A/C as key regulator of Th1 differentiation in response to viral and intracellular parasite infections.

Endothelial Nuclear Lamina in Mechanotransduction Under Shear Stress.

Endothelial cells that line the lumen of blood vessels are at the interface between hemodynamic forces and vascular wall biology. Endothelial cells transduce mechanical and biological signals from blood flow into intracellular signaling cascades through a process called mechanotransduction. Mechanotransduction is an important part of normal cell functions, as well as endothelial dysfunction which leads to inflammation and pathological conditions. For example, atherosclerosis preferentially develops in regions of disturbed fluid flow and low shear stress. The nuclear lamina, which sits underneath the nuclear envelope, serves to maintain the nuclear structure while acting as a scaffold for heterochromatin and many transcriptional proteins. Defects in lamina and its associated proteins cause a variety of human diseases including accelerated aging diseases such as Hutchinson-Gilford Progeria syndrome. The role of nuclear lamina in endothelial mechanotransduction, specifically how nuclear mechanics impact gene regulation under shear stress, is not fully understood. In one study, lamin A/C was silenced in bovine aortic endothelial cells to determine its role in both glucocorticoid receptor (GR) nuclear translocation and glucocorticoid response element (GRE) transcriptional activation in response to its natural ligand dexamethasone as well as fluid shear stress. Results suggest that absence of lamin A/C does not hinder passage of GR into the nucleus but nuclear lamina is important to properly regulate GRE transcription. Ongoing research continues to investigate how nuclear lamins contribute to endothelial mechanotransduction and to better understand the role of Lamin A in vascular aging and in the progression of cardiovascular diseases.

Overexpression of lamin B1 induces mitotic catastrophe in colon cancer LoVo cells and is associated with worse clinical outcomes.

Lamins are the major components of the nuclear lamina and play important roles in many cellular processes. The role of lamins in cancer development and progression is still unclear but it is known that reduced expression of lamin B1 has been observed in colon cancer. Thus, the aim of the present study was to elucidate the influence of LMNB1 upregulation on colon cancer cell line after treatment with 5-FU. The results indicate, that overexpression of LMNB1 induced dose-dependent cell death mainly by mitotic catastrophe pathway. Furthermore, after upregulation of this intermediate protein, lower expression of lamin A/C was observed. Moreover, we observed an increase in fluorescence intensity of nuclear β-catenin and decrease in cell-cell interaction area, that was connected with inhibition of colon cancer cells migration. We present the reorganization of actin filament and β-tubulin, because these cytoskeletal proteins are directly or indirectly linked with lamins, and analyzing publicly available mRNA data we show that patients with overexpression of LMNB1 are characterized by lower survival rates within the first 30 months from diagnosis. Summarizing our results, upregulation of LMNB1 induce mitotic catastrophe and only small percentage of apoptosis. Moreover, we showed inhibition of cell migration and promotion of cell-cell contact as a results of direct and indirect regulation of β-catenin, lamin A/C, actin and tubulin. However, it is possible that mitotic catastrophe cells in patients with colorectal cancer may be a reservoir of the cells responsible for faster disease progression, and further investigations are necessary to confirm this hypothesis.

A Perspective on the Experimental Techniques for Studying Lamins

Lamins are type V intermediate filaments that collectively form a meshwork underneath the inner nuclear membrane, called nuclear lamina. Furthermore, they are also present in the nucleoplasm. Lamins are experiencing a growing interest, since a wide range of diseases are induced by mutations in the gene coding for A-type lamins, globally known as laminopathies. Moreover, it has been demonstrated that lamins are involved in other pathological conditions, like cancer. The role of lamins has been studied from several perspectives, exploiting different techniques and procedures. This multidisciplinary approach has contributed to resolving the unique features of lamins and has provided a thorough insight in their role in living organisms. Yet, there are still many unanswered questions, which constantly generate research in the field. The present work is aimed to review some interesting experimental techniques performed so far to study lamins. Scientists can take advantage of this collection for their novel investigations, being aware of the already pursued and consolidated methodologies. Hopefully, advances in these research directions will provide insights to achieve better diagnostic procedures and effective therapeutic options.

Hepatocyte-Specific Deletion of Mouse Lamin A/C Leads to Male-Selective Steatohepatitis.

Background & AimsLamins are nuclear intermediate filament proteins that comprise the major components of the nuclear lamina. Mutations in LMNA, which encodes lamins A/C, cause laminopathies, including lipodystrophy, cardiomyopathy, and premature aging syndromes. However, the role of lamins in the liver is unknown, and it is unclear whether laminopathy-associated liver disease is caused by primary hepatocyte defects or systemic alterations.MethodsTo address these questions, we generated mice carrying a hepatocyte-specific deletion of Lmna (knockout [KO] mice) and characterized the KO liver and primary hepatocyte phenotypes by immunoblotting, immunohistochemistry, microarray analysis, quantitative real-time polymerase chain reaction, and Oil Red O and Picrosirius red staining.ResultsKO hepatocytes manifested abnormal nuclear morphology, and KO mice showed reduced body mass. KO mice developed spontaneous male-selective hepatosteatosis with increased susceptibility to high-fat diet–induced steatohepatitis and fibrosis. The hepatosteatosis was associated with up-regulated transcription of genes encoding lipid transporters, lipid biosynthetic enzymes, lipid droplet-associated proteins, and interferon-regulated genes. Hepatic Lmna deficiency led to enhanced signal transducer and activator of transcription 1 (Stat1) expression and blocked growth hormone–mediated Janus kinase 2 (Jak2), signal transducer and activator of transcription 5 (Stat5), and extracellular signal–regulated kinase (Erk) signaling.ConclusionsLamin A/C acts cell-autonomously to maintain hepatocyte homeostasis and nuclear shape and buffers against male-selective steatohepatitis by positively regulating growth hormone signaling and negatively regulating Stat1 expression. Lamins are potential genetic modifiers for predisposition to steatohepatitis and liver fibrosis. The microarray data can be found in the Gene Expression Omnibus repository (accession number: GSE93643).

Optomechanical measurement of the role of lamins in whole cell deformability.

There is mounting evidence that the nuclear envelope, and particularly the lamina, plays a critical role in the mechanical and regulation properties of the cell and changes to the lamina can have implications for the physical properties of the whole cell. In this study we demonstrate that the optical stretcher can measure changes in the time-dependent mechanical properties of living cells with different levels of A-type lamin expression. Results from the optical stretcher shows a decrease in the deformability of cells as the levels of lamin A increases, for cells which grow both adherently and in suspension. Further detail can be probed by combining the optical stretcher with fluorescence microscopy to investigate the nuclear mechanical properties which show a larger decrease in deformability than for the whole cell.

Lamin A and lamin-associated polypeptide 2 (LAP-2) in human skin fibroblasts in the process of aging

Mutations of lamin genes lead to diseases, one of which is progeria. This disease is caused by violation of splicing of lamin A gene and accumulation of farnesylated prelamin A (progerin) in the nucleus. LAP-2 is an important factor that regulates and stabilizes the nucleoplasmic pool of lamin A. However, roles of lamin A and LAP-2 in renewal regulation of the population of fibroblasts in the human dermis in different age periods still have not been investigated. The purpose of this investigation was to define expression of lamin A and LAP-2 in human dermal fibroblasts at different ages. Lamin A and LAP-2 were detected in skin sections by indirect immunohistochemistry. It was found that the number of fibroblasts containing lamin A gradually decreased from 90.4 to 76.9% from 20 weeks of pregnancy to 85 years. It was revealed that 32% of dermal fibroblasts were positively stained for LAP-2 in the period from 20 weeks of pregnancy to 20 years, 37.8% in the period of 21–40 years, and 49–51% in the period of 41–85 years. Lamin A expression levels in fibroblast nuclei were essentially constant from 20 weeks of pregnancy to 85 years, while LAP-2 content in fibroblast nuclei was reducing from 0 to 20 years as compared with the embryonic period and was gradually increasing after 21 year. The total number of fibroblasts and PCNA-positive fibroblasts in the dermis decreased with age. The most significant decrease in the number of fibroblasts was observed from 20 weeks of pregnancy to 20 years. The results suggest involvement of lamin A and LAP-2 in the age-related decrease in the number of fibroblasts in the human dermis.

Emerging perspectives on laminopathies

Laminopathies are a group of inherited disorders caused by mutations in the lamin A/C gene, and can affect diverse organs or tissues, or can be systemic, causing premature aging. In the present review, we report on the composition and structure of the nuclear lamina and the role of lamins in nuclear mechanics and their involvement in human diseases, and provide some examples of laminopathies and current therapeutic approaches.

Investigation in the Role of Lamin A (LMNA) Deficiency in Heart Block and Dilated Cardiomyopathy (DCM) Using Human Induced Pluripotent Stem Cell Derived Cardiomyocytes

Investigation in the Role of Lamin A (LMNA) Deficiency in Heart Block and Dilated Cardiomyopathy (DCM) Using Human Induced Pluripotent Stem Cell Derived Cardiomyocytes

Identification of lamin B-regulated chromatin regions based on chromatin landscapes.

Lamins, the major structural components of the nuclear lamina (NL) found beneath the nuclear envelope, are known to interact with most of the nuclear peripheral chromatin in metazoan cells. Although NL-chromatin associations correlate with a repressive chromatin state, the role of lamins in tethering chromatin to NL and how such tether influences gene expression have remained challenging to decipher. Studies suggest that NL proteins regulate chromatin in a context-dependent manner. Therefore understanding the context of chromatin states based on genomic features, including chromatin-NL interactions, is important to the study of lamins and other NL proteins. By modeling genome organization based on combinatorial patterns of chromatin association with lamin B1, core histone modification, and core and linker histone occupancy, we report six distinct large chromatin landscapes, referred to as histone lamin landscapes (HiLands)-red (R), -orange (O), -yellow (Y), -green (G), -blue (B), and -purple (P), in mouse embryonic stem cells (mESCs). This HiLands model demarcates the previously mapped lamin-associated chromatin domains (LADs) into two HiLands, HiLands-B and HiLands-P, which are similar to facultative and constitutive heterochromatins, respectively. Deletion of B-type lamins in mESCs caused a reduced interaction between regions of HiLands-B and NL as measured by emerin-chromatin interaction. Our findings reveal the importance of analyzing specific chromatin types when studying the function of NL proteins in chromatin tether and regulation.

Loss of lamin A but not lamin C expression in epithelial ovarian cancer cells is associated with metastasis and poor prognosis

ObjectiveTo elucidate the different roles of lamin A and lamin C in the metastasis of epithelial ovarian cancer (EOC) by examining their expression in EOC tissues and cell lines and their correlations with clinicopathological features. MethodsThe expression of lamin A and lamin C was assessed in ovarian tissues from 61 EOC patients and 13 normal, 14 benign controls, respectively, using immunohistochemistry. Two pairs of EOC cell lines: HO-8910, HO-8910PM, SKOV-3 and SKOV-3ip were also examined to see the differential expression patterns of lamin A and lamin C. ResultsLamin A expression was significantly lower in EOC tissues than that in normal and benign ovarian tissues (p<0.05), while lamin C expression was not. Lamin A expression level was closely associated with pathological grades, clinical stages, peritoneal metastasis and lymph node metastasis (all p<0.05). The progression-free survival rate of the EOC patients with low lamin A expression level was remarkably lower than that of the EOC patients with high expression level (p<0.05). Lamin A detected by PCR, Western Blot and immunocytochemistry also showed a significantly lower expression level in HO-8910PM than that in HO-8910 (p<0.05), but not for lamin C. There was no difference between SKOV-3 and SKOV-3ip cells. ConclusionsThe results suggested that loss of lamin A but not lamin C expression in EOC was related to metastasis and poor prognosis. Lamin A may play a critical role in the metastasis of EOC.

The Fate of Hematopoietic Nuclei: Major Roles for Lamins Before and After Marrow Release

The Fate of Hematopoietic Nuclei: Major Roles for Lamins Before and After Marrow Release

Broken nuclei – lamins, nuclear mechanics, and disease

Mutations in lamins, which are ubiquitous nuclear intermediate filaments, lead to a variety of disorders including muscular dystrophy and dilated cardiomyopathy. Lamins provide nuclear stability, help connect the nucleus to the cytoskeleton, and can modulate chromatin organization and gene expression. Nonetheless, the diverse functions of lamins remain incompletely understood. We focus here on the role of lamins on nuclear mechanics and their involvement in human diseases. Recent findings suggest that lamin mutations can decrease nuclear stability, increase nuclear fragility, and disturb mechanotransduction signaling, possibly explaining the muscle-specific defects in many laminopathies. At the same time, altered lamin expression has been reported in many cancers, where the resulting increased nuclear deformability could enhance the ability of cells to transit tight interstitial spaces, thereby promoting metastasis.

Hierarchical Determination of Nuclear Deformability by Lamin Isoforms During Adult Hematopoiesis: Implications in Blood Cell Trafficking

Abstract 1200Over the last few decades, it has become clear that different blood lineages have distinct deformability, and that some blood cell types become softer in maturation perhaps to facilitate trafficking from marrow through the endothelial barrier and into the circulation (Lichtman, NEJM, 1970; 283:943–8). However, any common molecular basis of this phenomenon remains unclear. Cellular deformability is determined by elasticity of the cortex and the nucleus, and the latter is dynamically regulated by changes in expression and organization of the lamins (Pajerowski… Discher, PNAS, 2007; 104:15619–24). While gene regulation of hematopoiesis has been extensively studied, roles of lamins in blood lineages are less well understood. To address this, we developed a novel protein isoform expression analysis algorithm, “mass spectrometry calibrated intracellular flow cytometry”, to quantify lamin stoichiometries in human hematopoietic stem cells and progenitors through different mature blood lineages. This approach reveals the hematopoietic lineage map of lamins, showing that lamin A varies by 4-fold, while the normally ‘constitutive' lamin B varies by 30-fold. During differentiation, lymphoid and myeloid lineages show decreased total lamin intensity and pliable nuclei as measured by micropipette aspiration, consistent with their ability to transmigrate into circulation. In contrast, megakaryocytes (MKs) remain in marrow because their polyploid nuclei are too large and rigid, as indicated by high lamin levels; this nuclear anchorage allows MKs to extend membrane projections into blood, where shear generates circulating platelets. Maturation of MKs is further regulated by serine phosphorylation of lamin A, since overexpression of a phospho-inactive mutant leads to increased polyploidization. Erythroid lineages share the same progenitor with MKs and migrate into blood as enucleated RBCs, because of high lamin A intensity relative to B in the progenitors and stiff chromatin. Consistent with this observation, microarray analysis of primary CD34+-derived cells indicates that some key erythroid genes are strongly correlated with lamin isoforms. Functional studies indicate that lamin A overexpression increases MK and erythroid differentiation by 2-fold, while the knockdown increases migration through pores by 2-fold. Surprisingly, increasing the lamin A to B ratio by lamin B1 knockdown decreases nuclear deformability by up to 50%, highlighting the importance of lamin isoform ratios, rather than absolute expression levels, in specifying nuclear rheology and hence traffickability of blood lineages. Finally, lamin A can be transcriptionally downregulated by retinoic acid by 2-fold, consistent with its well-established role in driving myeloid differentiation from progenitors. Together, the study suggests that nuclear deformability is hierarchically programmed by differential expression of the nucleoskeletal lamin A and B isoforms during hematopoietic differentiation, which in turn influence the ability of blood cells to migrate through marrow. Disclosures:No relevant conflicts of interest to declare.