Cell-extrinsic defective lymphocyte development in Lmna(-/-) mice

Capn3b-deficient zebrafish model reveals a key role of autoimmune response in LGMDR1

Mutations in calcium-dependent papain-like protease CALPAIN3 (CAPN3) cause Limb-Girdle Muscular Dystrophy Recessive Type 1 (LGMDR1), the most common limb-girdle muscular dystrophy in humans. In addition to progressive muscle weakness, persistent inflammatory infiltration is also a feature of LGMDR1. Despite the underlying mechanism remaining poorly understood, we consider that it may relate to the newly defined role of CAPN3/Capn3b in the nucleolus. Here, we report that the loss-of-function of zebrafish capn3b, the counterpart of human CAPN3, induces autoimmune response akin to that in LGMDR1 patients. Mutant capn3b larvae are more susceptible to Listeria monocytogenes injection, characterized by recruiting more macrophages. Under germ-free conditions, transcriptome analysis of the capn3b mutant muscle reveals a significant upregulation of the chemokine-production-related genes. Coincidently, more neutrophils are recruited to the injury site imposed by either muscle stabbing or tail fin amputation. Nucleolar proteomic analysis and enzymatic assays reveal NKAP, an activating factor of the NF-κB pathway, to be a target of CAPN3. We conclude that the accumulation of Nkap and other factors in the capn3b mutant may be involved in the over-activation of innate immunity. Our studies indicate that the zebrafish capn3b mutant is a powerful model for studying the immunity-related progression of human LGMDR1.

Protean Regulation of Leukocyte Function by Nuclear Lamins

The leukocyte nucleus must be sufficiently elastic to squeeze through tissue barriers during migration, but not so collapsible as to risk damaging chromatin. The proper balance is struck in part by the composition of the nuclear lamina, a flexible meshwork composed mainly of intermediate filaments woven from type A and type B lamin proteins, that is located subjacent to the inner nuclear membrane. There is now increasing evidence that, in addition to influencing nuclear shape and stiffness and cell migration, lamins and lamin-interacting proteins may also interact functionally with chromatin to influence leukocyte gene expression, differentiation, and effector function, including T cell differentiation, B cell somatic hypermutation, and the formation of neutrophil extracellular traps (NETosis).

Lamin A/C and the Immune System: One Intermediate Filament, Many Faces

Nuclear envelope lamin A/C proteins are a major component of the mammalian nuclear lamina, a dense fibrous protein meshwork located in the nuclear interior. Lamin A/C proteins regulate nuclear mechanics and structure and control cellular signaling, gene transcription, epigenetic regulation, cell cycle progression, cell differentiation, and cell migration. The immune system is composed of the innate and adaptive branches. Innate immunity is mediated by myeloid cells such as neutrophils, macrophages, and dendritic cells. These cells produce a rapid and nonspecific response through phagocytosis, cytokine production, and complement activation, as well as activating adaptive immunity. Specific adaptive immunity is activated by antigen presentation by antigen presenting cells (APCs) and the cytokine microenvironment, and is mainly mediated by the cellular functions of T cells and the production of antibodies by B cells. Unlike most cell types, immune cells regulate their lamin A/C protein expression relatively rapidly to exert their functions, with expression increasing in macrophages, reducing in neutrophils, and increasing transiently in T cells. In this review, we discuss and summarize studies that have addressed the role played by lamin A/C in the functions of innate and adaptive immune cells in the context of human inflammatory and autoimmune diseases, pathogen infections, and cancer.

Phenotypic diversity and glucocorticoid sensitivity in patients with familial partial lipodystrophy type 2

Familial partial lipodystrophy type 2 (FPLD2) is characterized by insulin resistance, adipose atrophy of the extremities and central obesity. Due to the resemblance with Cushing's syndrome, we hypothesized a putative role of glucocorticoid in the pathogenesis of metabolic abnormalities in FPLD2.

OBJECTIVE

To evaluate the phenotypic heterogeneity and glucocorticoid sensitivity in FPLD2 patients exhibiting the p.R482W or p.R644C LMNA mutations.

DESIGN, PATIENTS AND MEASUREMENTS

Prospective study with FPLD2 patients (n = 24) and controls (n = 24), who underwent anthropometric, body composition, metabolic profile and adipokines/cytokine plasma measurements. Plasma and salivary cortisol were measured in basal conditions and after 0.25, 0.5 and 1.0 mg of dexamethasone (DEX) given at 23:00 hours. Glucocorticoid receptor (GR) and 11βHSD isoforms expression were assessed by qPCR.

RESULTS

Familial partial lipodystrophy type 2 individuals presented increased waist and neck circumferences, decreased hip circumference, peripheral skinfold thickness and fat mass. Patients presented increased HOMA-IR, triglycerides, TNF-α, IL-1β, IL-6 and IL-10, and decreased adiponectin and leptin plasma levels. FPLD2 patients showed decreased ability to suppress the HPA axis compared with controls after 0.5 mg DEX. The phenotype was more pronounced in patients harbouring the p.R482W LMNA mutation. GRβ overexpression in PBMC was observed in female patients compared with female controls.

CONCLUSIONS

Familial partial lipodystrophy type 2 patients exhibited anthropometric, clinical and biochemical phenotypic heterogeneity related to LMNA mutation sites and to gender. LMNA mutations affecting both lamin A and lamin C lead to more severe phenotype. FPLD2 patients also showed blunted HPA axis response to DEX, probably due to the association of increased levels of proinflammatory cytokines with GRβ overexpression leading to a more severe phenotype in female.

Epigenomic drivers of immune dysfunction in aging

Aging inevitably leads to reduced immune function, leaving the elderly more susceptible to infections, less able to respond to pathogen challenges, and less responsive to preventative vaccinations. No cell type is exempt from the ravages of age, and extensive studies have found age-related alterations in the frequencies and functions of both stem and progenitor cells, as well as effector cells of both the innate and adaptive immune systems. The intrinsic functional reduction in immune competence is also associated with low-grade chronic inflammation, termed "inflamm-aging," which further perpetuates immune dysfunction. While many of these age-related cellular changes are well characterized, understanding the molecular changes that underpin the functional decline has proven more difficult. Changes in chromatin are increasingly appreciated as a causative mechanism of cellular and organismal aging across species. These changes include increased genomic instability through loss of heterochromatin and increased DNA damage, telomere attrition, and epigenetic alterations. In this review, we discuss the connections between chromatin, immunocompetence, and the loss of function associated with mammalian immune aging. Through understanding the molecular events which underpin the phenotypic changes observed in the aged immune system, it is hoped that the aged immune system can be restored to provide youthful immunity once more.

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.

The emerging role of ECM crosslinking in T cell mobility as a hallmark of immunosenescence in humans

Immunosenescence is thought to result from cellular aging and to reflect exposure to environmental stressors and antigens, including cytomegalovirus (CMV). However, not all of the features of immunosenescence are consistent with this view, and this has led to the emergence of the sister theory of "inflammaging". The recently discovered diffuse tissue distribution of resident memory T cells (T_RM) which don't recirculate, calls these theories into question. These cells account for most T cells residing in barrier epithelia which sit in and travel through the extracellular matrix (ECM). With almost all studies to date carried out on peripheral blood, the age-related changes of the ECM and their consequences for T cell mobility, which is crucial for the function of these cells, have been largely ignored. We propose an update of the theoretical framework of immunosenescence, based on a novel hypothesis: the increasing stiffness and cross-linking of the senescent ECM lead to a progressive immunodeficiency due to an age-related decrease in T cell mobility and eventually the death of these cells. A key element of this mechanism is the mechanical stress to which the cell cytoplasm and nucleus are subjected during passage through the ECM. This hypothesis is based on an "evo-devo" perspective bringing together some major characteristics of aging, to create a single interpretive framework for immunosenescence.

Molecular impact of selective NFKB1 and NFKB2 signaling on DLBCL phenotype

Diffuse large B-cell lymphoma (DLBCL) has been categorized into two molecular subtypes that have prognostic significance, namely germinal center B-cell like (GCB) and activated B-cell like (ABC). Although ABC-DLBCL has been associated with NF-κB activation, the relationships between activation of specific NF-κB signals and DLBCL phenotype remain unclear. Application of novel gene expression classifiers identified two new DLBCL categories characterized by selective p100 (NF-κB2) and p105 (NF-κB1) signaling. Interestingly, our molecular studies showed that p105 signaling is predominantly associated with GCB subtype and histone mutations. Conversely, most tumors with p100 signaling displayed ABC phenotype and harbored ABC-associated mutations in genes such as MYD88 and PIM1. In vitro, MYD88 L265P mutation promoted p100 signaling through TAK1/IKKα and GSK3/Fbxw7a pathways, suggesting a novel role for this protein as an upstream regulator of p100. p100 signaling was engaged during activation of normal B cells, suggesting p100's role in ABC phenotype development. Additionally, silencing p100 in ABC-DLBCL cells resulted in a GCB-like phenotype, with suppression of Blimp, IRF4 and XBP1 and upregulation of BCL6, whereas introduction of p52 or p100 into GC cells resulted in differentiation toward an ABC-like phenotype. Together, these findings identify specific roles for p100 and p105 signaling in defining DLBCL molecular subtypes and posit MYD88/p100 signaling as a regulator for B-cell activation.

Infection susceptibility and immune senescence with advancing age replicated in accelerated aging Lmna(Dhe) mice

Aging confers increased susceptibility to common pathogens including influenza A virus. Despite shared vulnerability to infection with advancing age in humans and rodents, the relatively long time required for immune senescence to take hold practically restricts the use of naturally aged mice to investigate aging‐induced immunological shifts. Here, we show accelerated aging Lmna^Dhe mice with spontaneous mutation in the nuclear scaffolding protein, lamin A, replicate infection susceptibility, and substantial immune cell shifts that occur with advancing age. Naturally aged (≥20 month) and 2‐ to 3‐month‐old Lmna^Dhe mice share near identically increased influenza A susceptibility compared with age‐matched Lmna^WT control mice. Increased mortality and higher viral burden after influenza infection in Lmna^Dhe mice parallel reduced accumulation of lung alveolar macrophage cells, systemic expansion of immune suppressive Foxp3⁺ regulatory T cells, and skewed immune dominance among viral‐specific CD8⁺T cells similar to the immunological phenotype of naturally aged mice. Thus, aging‐induced infection susceptibility and immune senescence are replicated in accelerated aging Lmna^Dhe mice.

Lamin A Is an Endogenous SIRT6 Activator and Promotes SIRT6-Mediated DNA Repair

The nuclear lamins are essential for various molecular events in the nucleus, such as chromatin organization, DNA replication, and provision of mechanical support. A specific point mutation in the LMNA gene creates a truncated prelamin A termed progerin, causing Hutchinson-Gilford progeria syndrome (HGPS). SIRT6 deficiency leads to defective genomic maintenance and accelerated aging similar to HGPS, suggesting a potential link between lamin A and SIRT6. Here, we report that lamin A is an endogenous activator of SIRT6 and facilitates chromatin localization of SIRT6 upon DNA damage. Lamin A promotes SIRT6-dependent DNA-PKcs (DNA-PK catalytic subunit) recruitment to chromatin, CtIP deacetylation, and PARP1 mono-ADP ribosylation in response to DNA damage. The presence of progerin jeopardizes SIRT6 activation and compromises SIRT6-mediated molecular events in response to DNA damage. These data reveal a critical role for lamin A in regulating SIRT6 activities, suggesting that defects in SIRT6 functions contribute to impaired DNA repair and accelerated aging in HGPS.

Nuclear envelope lamin-A as a coordinator of T cell activation

Nuclear lamins A/C control several critical cellular functions, e.g., chromatin organization, gene transcription, DNA replication, DNA damage responses, cell cycle progression, cell differentiation, and cell polarization during migration. However, few studies have addressed the role of lamins A/C in the control of the functions of immune cells. Recently, we have demonstrated that lamins A/C are induced in T cells upon antigen recognition. Lamins A/C enhance T cell responses by coupling the plasma membrane to the nucleus via the linker of nucleoskeleton and cytoskeleton (LINC) complex and the actin cytoskeleton. Here, we discuss the possible physiological relevance and functional context of lamin A/C in T cell activation and propose a model in which lamins A/C are key modulators of immune cell functions.

Nuclear envelope lamin-A couples actin dynamics with immunological synapse architecture and T cell activation

In many cell types, nuclear A-type lamins regulate multiple cellular functions, including higher-order genome organization, DNA replication and repair, gene transcription, and signal transduction; however, their role in specialized immune cells remains largely unexplored. We showed that the abundance of A-type lamins was almost negligible in resting naïve T lymphocytes, but was increased upon activation of the T cell receptor (TCR). The increase in lamin-A was an early event that accelerated formation of the immunological synapse between T cells and antigen-presenting cells. Polymerization of F-actin in T cells is a critical step for immunological synapse formation, and lamin-A interacted with the linker of nucleoskeleton and cytoskeleton (LINC) complex to promote F-actin polymerization. We also showed that lamin-A expression accelerated TCR clustering and led to enhanced downstream signaling, including extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, as well as increased target gene expression. Pharmacological inhibition of the ERK pathway reduced lamin-A-dependent T cell activation. Moreover, mice lacking lamin-A in immune cells exhibited impaired T cell responses in vivo. These findings underscore the importance of A-type lamins for TCR activation and identify lamin-A as a previously unappreciated regulator of the immune response.

Lamins regulate cell trafficking and lineage maturation of adult human hematopoietic cells

Hematopoietic stem and progenitor cells, as well as nucleated erythroblasts and megakaryocytes, reside preferentially in adult marrow microenvironments whereas other blood cells readily cross the endothelial barrier into the circulation. Because the nucleus is the largest organelle in blood cells, we hypothesized that (i) cell sorting across microporous barriers is regulated by nuclear deformability as controlled by lamin-A and -B, and (ii) lamin levels directly modulate hematopoietic programs. Mass spectrometry-calibrated intracellular flow cytometry indeed reveals a lamin expression map that partitions human blood lineages between marrow and circulating compartments (P = 0.00006). B-type lamins are highly variable and predominate only in CD34(+) cells, but migration through micropores and nuclear flexibility in micropipette aspiration both appear limited by lamin-A:B stoichiometry across hematopoietic lineages. Differentiation is also modulated by overexpression or knockdown of lamins as well as retinoic acid addition, which regulates lamin-A transcription. In particular, erythroid differentiation is promoted by high lamin-A and low lamin-B1 expression whereas megakaryocytes of high ploidy are inhibited by lamin suppression. Lamins thus contribute to both trafficking and differentiation.

Accumulation of prelamin A compromises NF-κB-regulated B-lymphopoiesis in a progeria mouse model

BACKGROUND

Alteration in the immune system is one of the most profound aspects of aging. Progressive changes in the number of B lymphocyte progenitors during aging have been reported but the underlying mechanisms are still elusive. A heterozygous G608G mutation in the LMNA gene leads to a deletion of 50 amino acids in lamin A protein, termed progerin, and is the predominant cause of Hutchinson-Gilford progeria syndrome (HGPS). Lack of Zmpste24, a metalloproteinase responsible for prelamin A processing, leads to progeroid features resembling HGPS. Therefore Zmpste24-deficient mice provide an ideal mouse model to study the impact of lamin A and (premature) aging on the aging-related decline of B lymphopoiesis.

RESULTS

Analysis of bone marrow (BM) nucleated cells revealed a decline of early B cell progenitors in Zmpste24 (-/-) mice. BM transplantation in a congenic strain completely rescued the defects in B lymphopoiesis, indicating that the decline in B cell progenitors in Zmpste24 (-/-) mice is attributable to defective BM microenvironments rather than to cell-intrinsic defects. Further investigation revealed downregulation of a set of important early B lymphopoiesis factors in Zmpste24 (-/-) bone marrow stromal cells (BMSCs), such as Vcam-1, SDF-1α, Flt3L and TSLP, and most of them are under transcriptional control of NF-κB signaling. Though TNFα stimulates IκBα degradation and NF-κB nuclear translocation in Zmpste24 (-/-) BMSCs, NF-κB fails to stimulate IκBα re-expression, which mediates a negative feedback loop of NF-κB signaling in wild-type BMSCs.

CONCLUSIONS

Our data demonstrate a cell-extrinsic defect of B cell development in a progeroid mouse model and a critical role for lamin A in the regulation of NF-κB signaling and cytokines that are essential for lymphopoiesis.

Nuclear lamina defects cause ATM-dependent NF-κB activation and link accelerated aging to a systemic inflammatory response

Alterations in the architecture and dynamics of the nuclear lamina have a causal role in normal and accelerated aging through both cell-autonomous and systemic mechanisms. However, the precise nature of the molecular cues involved in this process remains incompletely defined. Here we report that the accumulation of prelamin A isoforms at the nuclear lamina triggers an ATM- and NEMO-dependent signaling pathway that leads to NF-κB activation and secretion of high levels of proinflammatory cytokines in two different mouse models of accelerated aging (Zmpste24(-/-) and Lmna(G609G/G609G) mice). Causal involvement of NF-κB in accelerated aging was demonstrated by the fact that both genetic and pharmacological inhibition of NF-κB signaling prevents age-associated features in these animal models, significantly extending their longevity. Our findings provide in vivo proof of principle for the feasibility of pharmacological modulation of the NF-κB pathway to slow down the progression of physiological and pathological aging.

Splicing-directed therapy in a new mouse model of human accelerated aging

Hutchinson-Gilford progeria syndrome (HGPS) is caused by a point mutation in the LMNA gene that activates a cryptic donor splice site and yields a truncated form of prelamin A called progerin. Small amounts of progerin are also produced during normal aging. Studies with mouse models of HGPS have allowed the recent development of the first therapeutic approaches for this disease. However, none of these earlier works have addressed the aberrant and pathogenic LMNA splicing observed in HGPS patients because of the lack of an appropriate mouse model. Here, we report a genetically modified mouse strain that carries the HGPS mutation. These mice accumulate progerin, present histological and transcriptional alterations characteristic of progeroid models, and phenocopy the main clinical manifestations of human HGPS, including shortened life span and bone and cardiovascular aberrations. Using this animal model, we have developed an antisense morpholino-based therapy that prevents the pathogenic Lmna splicing, markedly reducing the accumulation of progerin and its associated nuclear defects. Treatment of mutant mice with these morpholinos led to a marked amelioration of their progeroid phenotype and substantially extended their life span, supporting the effectiveness of antisense oligonucleotide-based therapies for treating human diseases of accelerated aging.

Identification of early gene expression changes during human Th17 cell differentiation

Th17 cells play an essential role in the pathogenesis of autoimmune and inflammatory diseases. Most of our current understanding on Th17 cell differentiation relies on studies carried out in mice, whereas the molecular mechanisms controlling human Th17 cell differentiation are less well defined. In this study, we identified gene expression changes characterizing early stages of human Th17 cell differentiation through genome-wide gene expression profiling. CD4(+) cells isolated from umbilical cord blood were used to determine detailed kinetics of gene expression after initiation of Th17 differentiation with IL1β, IL6, and TGFβ. The differential expression of selected candidate genes was further validated at protein level and analyzed for specificity in initiation of Th17 compared with initiation of other Th subsets, namely Th1, Th2, and iTreg. This first genome-wide profiling of transcriptomics during the induction of human Th17 differentiation provides a starting point for defining gene regulatory networks and identifying new candidates regulating Th17 differentiation in humans.

Laminopathies: the molecular background of the disease and the prospects for its treatment

Laminopathies are rare human degenerative disorders with a wide spectrum of clinical phenotypes, associated with defects in the main protein components of the nuclear envelope, mostly in the lamins. They include systemic disorders and tissue-restricted diseases. Scientists have been trying to explain the pathogenesis of laminopathies and find an efficient method for treatment for many years. In this review, we discuss the current state of knowledge about laminopathies, the molecular mechanisms behind the development of particular phenotypes, and the prospects for stem cell and/or gene therapy treatments.

Nuclear mechanics during cell migration

During cell migration, the movement of the nucleus must be coordinated with the cytoskeletal dynamics at the leading edge and trailing end, and, as a result, undergoes complex changes in position and shape, which in turn affects cell polarity, shape, and migration efficiency. We here describe the steps of nuclear positioning and deformation during cell polarization and migration, focusing on migration through three-dimensional matrices. We discuss molecular components that govern nuclear shape and stiffness, and review how nuclear dynamics are connected to and controlled by the actin, tubulin and intermediate cytoskeleton-based migration machinery and how this regulation is altered in pathological conditions. Understanding the regulation of nuclear biomechanics has important implications for cell migration during tissue regeneration, immune defence and cancer.