The accumulation of un-repairable DNA damage in laminopathy progeria fibroblasts is caused by ROS generation and is prevented by treatment with N-acetyl cysteine

Pathological modelling of pigmentation disorders associated with Hutchinson-Gilford Progeria Syndrome (HGPS) revealed an impaired melanogenesis pathway in iPS-derived melanocytes

Hutchinson-Gilford Progeria Syndrome (HGPS) is a rare genetic disorder that leads to premature aging. In this study, we used induced pluripotent stem cells to investigate the hypopigmentation phenotypes observed in patients with progeria. Accordingly, two iPS cell lines were derived from cells from HGPS patients and differentiated into melanocytes. Measurements of melanin content revealed a lower synthesis of melanin in HGPS melanocytes as compared to non-pathologic cells. Analysis of the melanosome maturation process by electron microscopy revealed a lower percentage of mature, fully pigmented melanosomes. Finally, a functional rescue experiment revealed the direct role of progerin in the regulation of melanogenesis. Overall, these results report a new dysregulated pathway in HGPS and open up novel perspectives in the study of pigmentation phenotypes that are associated with normal and pathological aging.

Radiation-induced unrepairable DSBs: their role in the late effects of radiation and possible applications to biodosimetry

Although the vast majority of DNA damage induced by radiation exposure disappears rapidly, some lesions remain in the cell nucleus in very small quantities for days to months. These lesions may cause a considerable threat to an organism and include certain types of DNA double-strand breaks (DSBs) called 'unrepairable DSBs'. Unrepairable DSBs are thought to cause persistent malfunctioning of cells and tissues or cause late effects of radiation, especially the induction of delayed cell death, mutation, senescence, or carcinogenesis. Moreover, the measurement of unrepairable DSBs could potentially be used for retrospective biodosimetry or for identifying individuals at greater risk for developing the adverse effects associated with radiotherapy or chemotherapy. This review summarizes the concept of unrepairable DSBs in the context of persistent repair foci formed at DSBs.

Mandibuloacral dysplasia: A premature ageing disease with aspects of physiological ageing

Mandibuloacral dysplasia (MAD) is a rare genetic condition characterized by bone abnormalities including localized osteolysis and generalized osteoporosis, skin pigmentation, lipodystrophic signs and mildly accelerated ageing. The molecular defects associated with MAD are mutations in LMNA or ZMPSTE24 (FACE1) gene, causing type A or type B MAD, respectively. Downstream of LMNA or ZMPSTE24 mutations, the lamin A precursor, prelamin A, is accumulated in cells and affects chromatin dynamics and stress response. A new form of mandibuloacral dysplasia has been recently associated with mutations in POLD1 gene, encoding DNA polymerase delta, a major player in DNA replication. Of note, involvement of prelamin A in chromatin dynamics and recruitment of DNA repair factors has been also determined under physiological conditions, at the border between stress response and cellular senescence. Here, we review current knowledge on MAD clinical and pathogenetic aspects and highlight aspects typical of physiological ageing.

Emerging candidate treatment strategies for Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS, progeria) is an extremely rare premature aging disorder affecting children, with a disease incidence of ∼1 in 18 million individuals. HGPS is usually caused by a de novo point mutation in exon 11 of the LMNA gene (c.1824C>T, p.G608G), resulting in the increased usage of a cryptic splice site and production of a truncated unprocessed lamin A protein named progerin. Since the genetic cause for HGPS was published in 2003, numerous potential treatment options have rapidly emerged. Strategies to interfere with the post-translational processing of lamin A, to enhance progerin clearance, or directly target the HGPS mutation to reduce the progerin-producing alternative splicing of the LMNA gene have been developed. Here, we give an up-to-date resume of the contributions made by our and other research groups to the growing list of different candidate treatment strategies that have been tested, both in vitro, in vivo in mouse models for HGPS and in clinical trials in HGPS patients.

Protein sequestration at the nuclear periphery as a potential regulatory mechanism in premature aging

Serebryannyy and Misteli provide a perspective on how protein sequestration at the inner nuclear membrane and nuclear lamina might influence aging.

Despite the extensive description of numerous molecular changes associated with aging, insights into the driver mechanisms of this fundamental biological process are limited. Based on observations in the premature aging syndrome Hutchinson–Gilford progeria, we explore the possibility that protein regulation at the inner nuclear membrane and the nuclear lamina contributes to the aging process. In support, sequestration of nucleoplasmic proteins to the periphery impacts cell stemness, the response to cytotoxicity, proliferation, changes in chromatin state, and telomere stability. These observations point to the nuclear periphery as a central regulator of the aging phenotype.

Reprogramming progeria fibroblasts re-establishes a normal epigenetic landscape

Ideally, disease modeling using patient‐derived induced pluripotent stem cells (iPSCs) enables analysis of disease initiation and progression. This requires any pathological features of the patient cells used for reprogramming to be eliminated during iPSC generation. Hutchinson–Gilford progeria syndrome (HGPS) is a segmental premature aging disorder caused by the accumulation of the truncated form of Lamin A known as Progerin within the nuclear lamina. Cellular hallmarks of HGPS include nuclear blebbing, loss of peripheral heterochromatin, defective epigenetic inheritance, altered gene expression, and senescence. To model HGPS using iPSCs, detailed genome‐wide and structural analysis of the epigenetic landscape is required to assess the initiation and progression of the disease. We generated a library of iPSC lines from fibroblasts of patients with HGPS and controls, including one family trio. HGPS patient‐derived iPSCs are nearly indistinguishable from controls in terms of pluripotency, nuclear membrane integrity, as well as transcriptional and epigenetic profiles, and can differentiate into affected cell lineages recapitulating disease progression, despite the nuclear aberrations, altered gene expression, and epigenetic landscape inherent to the donor fibroblasts. These analyses demonstrate the power of iPSC reprogramming to reset the epigenetic landscape to a revitalized pluripotent state in the face of widespread epigenetic defects, validating their use to model the initiation and progression of disease in affected cell lineages.

Chemical screening identifies ROCK as a target for recovering mitochondrial function in Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) constitutes a genetic disease wherein an aging phenotype manifests in childhood. Recent studies indicate that reactive oxygen species (ROS) play important roles in HGPS phenotype progression. Thus, pharmacological reduction in ROS levels has been proposed as a potentially effective treatment for patient with this disorder. In this study, we performed high-throughput screening to find compounds that could reduce ROS levels in HGPS fibroblasts and identified rho-associated protein kinase (ROCK) inhibitor (Y-27632) as an effective agent. To elucidate the underlying mechanism of ROCK in regulating ROS levels, we performed a yeast two-hybrid screen and discovered that ROCK1 interacts with Rac1b. ROCK activation phosphorylated Rac1b at Ser71 and increased ROS levels by facilitating the interaction between Rac1b and cytochrome c. Conversely, ROCK inactivation with Y-27632 abolished their interaction, concomitant with ROS reduction. Additionally, ROCK activation resulted in mitochondrial dysfunction, whereas ROCK inactivation with Y-27632 induced the recovery of mitochondrial function. Furthermore, a reduction in the frequency of abnormal nuclear morphology and DNA double-strand breaks was observed along with decreased ROS levels. Thus, our study reveals a novel mechanism through which alleviation of the HGPS phenotype is mediated by the recovery of mitochondrial function upon ROCK inactivation.

Cigarette smoke extract induces EGFR-TKI resistance via promoting EGFR signaling pathway and ROS generation in NSCLC cell lines

OBJECTIVES

Epithelial growth factor receptor (EGFR) somatic-mutated non-small cell lung cancer (NSCLC) patients with smoking history always show a poor response to EGFR tyrosine kinase inhibitors (EGFR-TKIs). The aim of the study is to explore the molecular mechanism of EGFR-TKI resistance induced by cigarette smoke extract and investigate the novel anti-resistance strategies.

METHODS

The effect of cigarette smoke extract (CSE) on gefitinib sensitivity, EGFR signaling, apoptosis and reactive oxygen species (ROS) levels were detected in vitro by MTT assays, western blot, flow cytometry and laser scanning confocal microscope, respectively.

RESULTS

MTT assays presented that CSE claimed antagonistic effect on gefitinib sensitivity via the up-regulated half maximal inhibitory concentration (IC50) values, western blot showed that CSE instigated EGFR, AKT phosphorylation, while N-Acetyl-l-Cysteine (NAC) could alleviate gefitinib resistance and abort the aberrant phosphorylation in both PC-9 and A549 cells. Confocal microscope and flow cytometry displayed that ROS generation increased after CSE exposure in NSCLC cells and this change could be inhibited by NAC.

CONCLUSION

Cigarette smoke extract induces EGFR-TKI resistance via promoting EGFR signaling and ROS generation in NSCLC cell lines which could be suppressed by NAC. Alternatively, combined NAC with EGFR-TKIs to treat EGFR mutated NSCLC patients with smoking history may be a potential choice in clinical setting.

Expression of progerin does not result in an increased mutation rate

In the premature ageing disease Hutchinson-Gilford progeria syndrome (HGPS), the underlying genetic defect in the lamin A gene leads to accumulation at the nuclear lamina of progerin—a mutant form of lamin A that cannot be correctly processed. This has been reported to result in defects in the DNA damage response and in DNA repair, leading to the hypothesis that, as in normal ageing and in other progeroid syndromes caused by mutation of genes of the DNA repair and DNA damage response pathways, increased DNA damage may be responsible for the premature ageing phenotypes in HGPS patients. However, this hypothesis is based upon the study of markers of the DNA damage response, rather than measurement of DNA damage per se or the consequences of unrepaired DNA damage—mutation. Here, using a mutation reporter cell line, we directly compared the inherent and induced mutation rates in cells expressing wild-type lamin A or progerin. We find no evidence for an elevated mutation rate in progerin-expressing cells. We conclude that the cellular defect in HGPS cells does not lie in the repair of DNA damage per se.

Metformin alleviates ageing cellular phenotypes in Hutchinson-Gilford progeria syndrome dermal fibroblasts

Metformin is a popular antidiabetic biguanide, which has been considered as a candidate drug for cancer treatment and ageing prevention. Hutchinson-Gilford progeria syndrome (HGPS) is a devastating disease characterized by premature ageing and severe age-associated complications leading to death. The effects of metformin on HGPS dermal fibroblasts remain largely undefined. In this study, we investigated whether metformin could exert a beneficial effect on nuclear abnormalities and delay senescence in fibroblasts derived from HGPS patients. Metformin treatment partially restored normal nuclear phenotypes, delayed senescence, activated the phosphorylation of AMP-activated protein kinase and decreased reactive oxygen species formation in HGPS dermal fibroblasts. Interestingly, metformin reduced the number of phosphorylated histone variant H2AX-positive DNA damage foci and suppressed progerin protein expression, compared to the control. Furthermore, metformin-supplemented aged mice showed higher splenocyte proliferation and mRNA expression of the antioxidant enzyme, superoxide dismutase 2 than the control mice. Collectively, our results show that metformin treatment alleviates the nuclear defects and premature ageing phenotypes in HGPS fibroblasts. Thus, metformin can be considered a promising therapeutic approach for life extension in HGPS.

Basics of Radiation Biology When Treating Hyperproliferative Benign Diseases

For decades, low- and moderate-dose radiation therapy (RT) has been shown to exert a beneficial therapeutic effect in a multitude of non-malignant conditions including painful degenerative muscoloskeletal and hyperproliferative disorders. Dupuytren and Ledderhose diseases are benign fibroproliferative diseases of the hand/foot with fibrotic nodules and fascial cords, which determine debilitating contractures and deformities of fingers/toes, while keloids are exuberant scar formations following burn damage, surgery, and trauma. Although RT has become an established and effective option in the management of these diseases, experimental studies to illustrate cellular composites and factors involved remain to be elucidated. More recent findings, however, indicate the involvement of radiation-sensitive targets like mitotic fibroblasts/myofibroblasts as well as inflammatory cells. Radiation-related molecular mechanisms affecting these target cells include the production of free radicals to hamper proliferative activity and interference with growth factors and cytokines. Moreover, an impairment of activated immune cells involved in both myofibroblast proliferative and inflammatory processes may further contribute to the clinical effects. We here aim at briefly describing mechanisms contributing to a modulation of proliferative and inflammatory processes and to summarize current concepts of treating hyperproliferative diseases by low and moderate doses of ionizing radiation.

GNG11 (G-protein subunit γ 11) suppresses cell growth with induction of reactive oxygen species and abnormal nuclear morphology in human SUSM-1 cells

Enforced expression of GNG11, G-protein subunit γ 11, induces cellular senescence in normal human diploid fibroblasts. We here examined the effect of the expression of GNG11 on the growth of immortalized human cell lines, and found that it suppressed the growth of SUSM-1 cells, but not of HeLa cells. We then compared these two cell lines to understand the molecular basis for the action of GNG11. We found that expression of GNG11 induced the generation of reactive oxygen species (ROS) and abnormal nuclear morphology in SUSM-1 cells but not in HeLa cells. Increased ROS generation by GNG11 would likely be caused by the down-regulation of the antioxidant enzymes in SUSM-1 cells. We also found that SUSM-1 cells, even under normal culture conditions, showed higher levels of ROS and higher incidence of abnormal nuclear morphology than HeLa cells, and that abnormal nuclear morphology was relevant to the increased ROS generation in SUSM-1 cells. Thus, SUSM-1 and HeLa cells showed differences in the regulation of ROS and nuclear morphology, which might account for their different responses to the expression of GNG11. Thus, SUSM-1 cells may provide a unique system to study the regulatory relationship between ROS generation, nuclear morphology, and G-protein signaling.

Nuclear lamins and progerin are dispensable for antioxidant Nrf2 response to arsenic and cadmium

Lamins are important constituents of the nuclear inner membrane and provide a platform for transcription factors and chromatin. Progerin, a C-terminal truncated lamin A mutant, causes premature aging termed Hutchinson-Gilford Progeria Syndrome (HGPS). Oxidative stress appears to be involved in the pathogenesis of HGPS, although the mechanistic role of progerin remains elusive. Here we examined whether nuclear lamins are important for a cellular antioxidant mechanism, and whether progerin compromises it. We investigated the activation of nuclear factor-E2-related factor 2 (Nrf2) which regulates various antioxidant genes including heme oxygenase-1 (HMOX1), following exposure to sodium arsenite or cadmium chloride in lamin knockdown human cell lines and primary HGPS human fibroblasts. Knocking down lamin A/C, or B, or all nuclear lamins simultaneously in three human cell lines (HaCaT, SW480, and K562) did not impair arsenite- or cadmium-induced activation of Nrf2. Progerin-expressing human primary HGPS fibroblasts showed lower basal levels of HMOX1 and NQO1 expression; however, in response to arsenic stress both normal and HGPS primary fibroblasts showed Nrf2 nuclear accumulation along with upregulation and phosphorylation of p62/SQSTM1 at Ser351, downregulation of Keap1, and comparable expression of an array of downstream Nrf2-regulated antioxidant genes. We also observed new forms of cleaved lamin A, B1 and B2 induced by cadmium stress although their roles in the Nrf2 antioxidant system need further investigation. These results suggest that the nuclear lamins and progerin have marginal roles in the activation of the antioxidant Nrf2 response to arsenic and cadmium.

Hutchinson-Gilford Progeria Syndrome: A premature aging disease caused by LMNA gene mutations

Products of the LMNA gene, primarily lamin A and C, are key components of the nuclear lamina, a proteinaceous meshwork that underlies the inner nuclear membrane and is essential for proper nuclear architecture. Alterations in lamin A and C that disrupt the integrity of the nuclear lamina affect a whole repertoire of nuclear functions, causing cellular decline. In humans, hundreds of mutations in the LMNA gene have been identified and correlated with over a dozen degenerative disorders, referred to as laminopathies. These diseases include neuropathies, muscular dystrophies, lipodystrophies, and premature aging diseases. This review focuses on one of the most severe laminopathies, Hutchinson-Gilford Progeria Syndrome (HGPS), which is caused by aberrant splicing of the LMNA gene and expression of a mutant product called progerin. Here, we discuss current views about the molecular mechanisms that contribute to the pathophysiology of this devastating disease, as well as the strategies being tested in vitro and in vivo to counteract progerin toxicity. In particular, progerin accumulation elicits nuclear morphological abnormalities, misregulated gene expression, defects in DNA repair, telomere shortening, and genomic instability, all of which limit cellular proliferative capacity. In patients harboring this mutation, a severe premature aging disease develops during childhood. Interestingly, progerin is also produced in senescent cells and cells from old individuals, suggesting that progerin accumulation might be a factor in physiological aging. Deciphering the molecular mechanisms whereby progerin expression leads to HGPS is an emergent area of research, which could bring us closer to understanding the pathology of aging.

Temsirolimus Partially Rescues the Hutchinson-Gilford Progeria Cellular Phenotype

Hutchinson-Gilford syndrome (HGPS, OMIM 176670, a rare premature aging disorder that leads to death at an average age of 14.7 years due to myocardial infarction or stroke, is caused by mutations in the LMNA gene. Lamins help maintain the shape and stability of the nuclear envelope in addition to regulating DNA replication, DNA transcription, proliferation and differentiation. The LMNA mutation results in the deletion of 50 amino acids from the carboxy-terminal region of prelamin A, producing the truncated, farnesylated protein progerin. The accumulation of progerin in HGPS nuclei causes numerous morphological and functional changes that lead to premature cellular senescence. Attempts to reverse this HGPS phenotype have identified rapamycin, an inhibitor of mammalian target of rapamycin (mTOR), as a drug that is able to rescue the HGPS cellular phenotype by promoting autophagy and reducing progerin accumulation. Rapamycin is an obvious candidate for the treatment of HGPS disease but is difficult to utilize clinically. To further assess rapamycin's efficacy with regard to proteostasis, mitochondrial function and the degree of DNA damage, we tested temsirolimus, a rapamycin analog with a more favorable pharmacokinetic profile than rapamycin. We report that temsirolimus decreases progerin levels, increases proliferation, reduces misshapen nuclei, and partially ameliorates DNA damage, but does not improve proteasome activity or mitochondrial dysfunction. Our findings suggest that future therapeutic strategies should identify new drug combinations and treatment regimens that target all the dysfunctional hallmarks that characterize HGPS cells.

Repression of the Antioxidant NRF2 Pathway in Premature Aging

Hutchinson-Gilford progeria syndrome (HGPS) is a rare, invariably fatal premature aging disorder. The disease is caused by constitutive production of progerin, a mutant form of the nuclear architectural protein lamin A, leading, through unknown mechanisms, to diverse morphological, epigenetic, and genomic damage and to mesenchymal stem cell (MSC) attrition in vivo. Using a high-throughput siRNA screen, we identify the NRF2 antioxidant pathway as a driver mechanism in HGPS. Progerin sequesters NRF2 and thereby causes its subnuclear mislocalization, resulting in impaired NRF2 transcriptional activity and consequently increased chronic oxidative stress. Suppressed NRF2 activity or increased oxidative stress is sufficient to recapitulate HGPS aging defects, whereas reactivation of NRF2 activity in HGPS patient cells reverses progerin-associated nuclear aging defects and restores in vivo viability of MSCs in an animal model. These findings identify repression of the NRF2-mediated antioxidative response as a key contributor to the premature aging phenotype.

Progeroid syndrome patients with ZMPSTE24 deficiency could benefit when treated with rapamycin and dimethylsulfoxide

Patients with progeroid syndromes such as mandibuloacral dysplasia, type B (MADB) and restrictive dermopathy (RD) harbor mutations in zinc metalloproteinase (ZMPSTE24), an enzyme essential for posttranslational proteolysis of prelamin A to form mature lamin A. Dermal fibroblasts from these patients show increased nuclear dysmorphology and reduced proliferation; however, the efficacy of various pharmacological agents in reversing these cellular phenotypes remains unknown. In this study, fibroblasts from MADB patients exhibited marked nuclear abnormalities and reduced proliferation that improved upon treatment with rapamycin and dimethylsulfoxide but not with other agents, including farnesyl transferase inhibitors. Surprisingly, fibroblasts from an RD patient with a homozygous null mutation in ZMPSTE24, resulting in exclusive accumulation of prelamin A with no lamin A on immunoblotting of cellular lysate, exhibited few nuclear abnormalities and near-normal cellular proliferation. An unbiased proteomic analysis of the cellular lysate from RD fibroblasts revealed a lack of processing of vimentin, a cytoskeletal protein. Interestingly, the assembly of the vimentin microfibrils in MADB fibroblasts improved with rapamycin and dimethylsulfoxide. We conclude that rapamycin and dimethylsulfoxide are beneficial for improving nuclear morphology and cell proliferation of MADB fibroblasts. Data from a single RD patient's fibroblasts also suggest that prelamin A accumulation by itself might not be detrimental and requires additional alterations at the cellular level to manifest the phenotype.

Recent advances in understanding the role of lamins in health and disease

Lamins are major components of the nuclear lamina, a network of proteins that supports the nuclear envelope in metazoan cells. Over the past decade, biochemical studies have provided support for the view that lamins are not passive bystanders providing mechanical stability to the nucleus but play an active role in the organization of the genome and the function of fundamental nuclear processes. It has also become apparent that lamins are critical for human health, as a large number of mutations identified in the gene that encodes for A-type lamins are associated with tissue-specific and systemic genetic diseases, including the accelerated aging disorder known as Hutchinson-Gilford progeria syndrome. Recent years have witnessed great advances in our understanding of the role of lamins in the nucleus and the functional consequences of disease-associated A-type lamin mutations. Many of these findings have been presented in comprehensive reviews. In this mini-review, we discuss recent breakthroughs in the role of lamins in health and disease and what lies ahead in lamin research.

DNA damage-induced inflammation and nuclear architecture

Nuclear architecture and the chromatin state affect most-if not all- DNA-dependent transactions, including the ability of cells to sense DNA lesions and restore damaged DNA back to its native form. Recent evidence points to functional links between DNA damage sensors, DNA repair mechanisms and the innate immune responses. The latter raises the question of how such seemingly disparate processes operate within the intrinsically complex nuclear landscape and the chromatin environment. Here, we discuss how DNA damage-induced immune responses operate within chromatin and the distinct sub-nuclear compartments highlighting their relevance to chronic inflammation.

All-trans retinoic acid and rapamycin normalize Hutchinson Gilford progeria fibroblast phenotype

Hutchinson Gilford progeria syndrome is a fatal disorder characterized by accelerated aging, bone resorption and atherosclerosis, caused by a LMNA mutation which produces progerin, a mutant lamin A precursor. Progeria cells display progerin and prelamin A nuclear accumulation, altered histone methylation pattern, heterochromatin loss, increased DNA damage and cell cycle alterations. Since the LMNA promoter contains a retinoic acid responsive element, we investigated if all-trans retinoic acid administration could lower progerin levels in cultured fibroblasts. We also evaluated the effect of associating rapamycin, which induces autophagic degradation of progerin and prelamin A. We demonstrate that all-trans retinoic acid acts synergistically with low-dosage rapamycin reducing progerin and prelamin A, via transcriptional downregulation associated with protein degradation, and increasing the lamin A to progerin ratio. These effects rescue cell dynamics and cellular proliferation through recovery of DNA damage response factor PARP1 and chromatin-associated nuclear envelope proteins LAP2α and BAF. The combined all-trans retinoic acid-rapamycin treatment is dramatically efficient, highly reproducible, represents a promising new approach in Hutchinson-Gilford Progeria therapy and deserves investigation in ageing-associated disorders.

The nuclear lamina in health and disease

The nuclear lamina (NL) is a structural component of the nuclear envelope and makes extensive contacts with integral nuclear membrane proteins and chromatin. These interactions are critical for many cellular processes, such as nuclear positioning, perception of mechanical stimuli from the cell surface, nuclear stability, 3-dimensional organization of chromatin and regulation of chromatin-binding proteins, including transcription factors. The NL is present in all nucleated metazoan cells but its composition and interactome differ between tissues. Most likely, this contributes to the broad spectrum of disease manifestations in humans with mutations in NL-related genes, ranging from muscle dystrophies to neurological disorders, lipodystrophies and progeria syndromes. We review here exciting novel insight into NL function at the cellular level, in particular in chromatin organization and mechanosensation. We also present recent observations on the relation between the NL and metabolism and the special relevance of the NL in muscle tissues. Finally, we discuss new therapeutic approaches to treat NL-related diseases.

Molecular insights into the premature aging disease progeria

Hutchinson-Gilford progeria syndrome (HGPS) is an extremely rare premature aging disease presenting many features resembling the normal aging process. HGPS patients die before the age of 20 years due to cardiovascular problems and heart failure. HGPS is linked to mutations in the LMNA gene encoding the intermediate filament protein lamin A. Lamin A is a major component of the nuclear lamina, a scaffold structure at the nuclear envelope that defines mechanochemical properties of the nucleus and is involved in chromatin organization and epigenetic regulation. Lamin A is also present in the nuclear interior where it fulfills lamina-independent functions in cell signaling and gene regulation. The most common LMNA mutation linked to HGPS leads to mis-splicing of the LMNA mRNA and produces a mutant lamin A protein called progerin that tightly associates with the inner nuclear membrane and affects the dynamic properties of lamins. Progerin expression impairs many important cellular processes providing insight into potential disease mechanisms. These include changes in mechanosignaling, altered chromatin organization and impaired genome stability, and changes in signaling pathways, leading to impaired regulation of adult stem cells, defective extracellular matrix production and premature cell senescence. In this review, we discuss these pathways and their potential contribution to the disease pathologies as well as therapeutic approaches used in preclinical and clinical tests.

Closing a gap in the nuclear envelope

The nuclear envelope (NE) ensures nucleo-cytoplasmic compartmentalization, with trafficking of macromolecules across this double membrane controlled by embedded nuclear pore complexes (NPCs). The NE and associated proteins are dismantled during open mitosis and reestablishment of this barrier during mitotic exit requires dynamic remodeling of endoplasmic reticulum (ER) membranes and coordination with NPC reformation, with NPC deposition continuing during subsequent interphase. In this review, we discuss recent progress in our understanding of NE reformation and nuclear pore complex generation, with special focus on work implicating the endosomal sorting complex required for transport (ESCRT) membrane remodeling machinery in these events.

A high-content imaging-based screening pipeline for the systematic identification of anti-progeroid compounds

Hutchinson-Gilford Progeria Syndrome (HGPS) is an early onset lethal premature aging disorder caused by constitutive production of progerin, a mutant form of the nuclear architectural protein lamin A. The presence of progerin causes extensive morphological, epigenetic and DNA damage related nuclear defects that ultimately disrupt tissue and organismal functions. Hypothesis-driven approaches focused on HGPS affected pathways have been used in attempts to identify druggable targets with anti-progeroid effects. Here, we report an unbiased discovery approach to HGPS by implementation of a high-throughput, high-content imaging based screening method that enables systematic identification of small molecules that prevent the formation of multiple progerin-induced aging defects. Screening a library of 2816 FDA approved drugs, we identified retinoids as a novel class of compounds that reverses aging defects in HGPS patient skin fibroblasts. These findings establish a novel approach to anti-progeroid drug discovery.

Lamin A is involved in the development of vascular calcification induced by chronic kidney failure and phosphorus load

Vascular calcification remains one of the main factors associated to morbidity and mortality in both ageing and chronic kidney disease. Both hyperphosphataemia, a well-known promoter of vascular calcification, and abnormal processing defects of lamin A/C have been associated to ageing. The main aim of this study was to analyse the effect of phosphorus load in the differential expression pattern of genes and proteins, particularly of lamin A/C, which are involved in phenotypic change of the vascular smooth muscle cells to osteoblast-like cells. The in vivo study of the calcified abdominal aortas from nephrectomized rats receiving a high phosphorus diet showed among others, a repression of muscle related proteins and overexpression of lamin A/C. Similar results were observed in vitro, where primary vascular smooth muscle cells cultured in calcifying medium showed increased expression of prelamin A and lamin A and abnormalities in the nuclear morphology. Co-immunoprecipitation assays showed novel and important physical interactions between lamin A and RUNX2 during the process of calcification. In fact, the knockdown of prelamin A and lamin A inhibited the increase of Runx2, osteocalcin and osteopontin gene expression, calcium deposition, nuclear abnormalities and the RUNX2 protein translocation into the nucleus of the cell. These in vivo and in vitro results highlight the important role played by lamin A in the process of vascular calcification.

Genome Integrity in Aging: Human Syndromes, Mouse Models, and Therapeutic Options

Human syndromes and mouse mutants that exhibit accelerated but bona fide aging in multiple organs and tissues have been invaluable for the identification of nine denominators of aging: telomere attrition, genome instability, epigenetic alterations, mitochondrial dysfunction, deregulated nutrient sensing, altered intercellular communication, loss of proteostasis, cellular senescence and adult stem cell exhaustion. However, whether and how these instigators of aging interrelate or whether they have one root cause is currently largely unknown. Rare human progeroid syndromes and corresponding mouse mutants with resolved genetic defects highlight the dominant importance of genome maintenance for aging. A second class of aging-related disorders reveals a cross connection with metabolism. As genome maintenance and metabolism are closely interconnected, they may constitute the main underlying biology of aging. This review focuses on the role of genome stability in aging, its crosstalk with metabolism, and options for nutritional and/or pharmaceutical interventions that delay age-related pathology.

Progerin, the protein responsible for the Hutchinson-Gilford progeria syndrome, increases the unrepaired DNA damages following exposure to ionizing radiation

Introduction

Progerin, the protein responsible for the Hutchinson-Gilford Progeria Syndrome (HGPS), is a partially deleted form of nuclear lamin A, and its expression has been suggested as a cause for dysfunctional nuclear membrane and premature senescence. To examine the role of nuclear envelop architecture in regulating cellular aging and DNA repair, we used ionizing radiation to increase the number of DNA double strand breaks (DSBs) in normal and HGPS cells, and analyzed possible relationship between unrepaired DSBs and cellular aging.

Results

We found that HGPS cells are normal in repairing a major fraction of radiation-induced double strand breaks (M-DSBs)but abnormal to show increased amount of residual unrepaired DSBs (R-DSBs). Such unrepaired DSBs were 2.6 times (CI 95 %: 2.2–3.2) higher than that in normal cells one week after the irradiation, and 1.6 times (CI 95 %: 1.3–1.9) higher even one month after the irradiation. These damages tend to increase as the nuclear envelope become abnormal, a characteristic of both HGPS and normal human cells which undergo replicative senescence. The artificial, enforced over-expression of progerin further impaired the repair of M-DSBs, implying lamin A-associated nuclear membrane has an important role for DNA DSB repair. Introduction of telomerase gene function in HGPS cells reversed such aging phenotypes along with upregulation of lamin B1 and downregulation of progerin, which is a hallmark of young cells.

Conclusion

We suggest that lamin A- or progerin-associated nuclear envelope is involved in cellular aging associated with DNA damage repair.

Electronic supplementary material

The online version of this article (doi:10.1186/s41021-015-0018-4) contains supplementary material, which is available to authorized users.

Nuclear stiffening and chromatin softening with progerin expression leads to an attenuated nuclear response to force

Progerin is a mutant form of the nucleoskeletal protein lamin A, and its expression results in the rare premature aging disorder Hutchinson-Gilford progeria syndrome (HGPS). Patients with HGPS demonstrate several characteristic signs of aging including cardiovascular and skeletal dysfunction. Cells from HGPS patients show several nuclear abnormalities including aberrant morphology, nuclear stiffening and loss of epigenetic modifications including heterochromatin territories. However, it is unclear why these changes disproportionately impact mechanically-responsive tissues. Using micropipette aspiration, we show that nuclei in progerin-expressing cells are stiffer than control cells. Conversely, our particle tracking reveals the nuclear interior becomes more compliant in cells from HGPS patients or with progerin expression, as consistent with decreased chromatin condensation as shown previously. Additionally, we find the nuclear interior is less responsive to external mechanical force from shear or compression likely resulting from damped force propagation due to nucleoskeletal stiffening. Collectively our findings suggest that force is similarly transduced into the nuclear interior in normal cells. In HGPS cells a combination of a stiffened nucleoskeleton and softened nuclear interior leads to mechanical irregularities and dysfunction of mechanoresponsive tissues in HGPS patients.

Diverse lamin-dependent mechanisms interact to control chromatin dynamics. Focus on laminopathies

Interconnected functional strategies govern chromatin dynamics in eukaryotic cells. In this context, A and B type lamins, the nuclear intermediate filaments, act on diverse platforms involved in tissue homeostasis. On the nuclear side, lamins elicit large scale or fine chromatin conformational changes, affect DNA damage response factors and transcription factor shuttling. On the cytoplasmic side, bridging-molecules, the LINC complex, associate with lamins to coordinate chromatin dynamics with cytoskeleton and extra-cellular signals.

 

Consistent with such a fine tuning, lamin mutations and/or defects in their expression or post-translational processing, as well as mutations in lamin partner genes, cause a heterogeneous group of diseases known as laminopathies. They include muscular dystrophies, cardiomyopathy, lipodystrophies, neuropathies, and progeroid syndromes. The study of chromatin dynamics under pathological conditions, which is summarized in this review, is shedding light on the complex and fascinating role of the nuclear lamina in chromatin regulation.

Rapamycin treatment of Mandibuloacral dysplasia cells rescues localization of chromatin-associated proteins and cell cycle dynamics

Lamin A is a key component of the nuclear lamina produced through post-translational processing of its precursor known as prelamin A. LMNA mutations leading to farnesylated prelamin A accumulation are known to cause lipodystrophy, progeroid and developmental diseases, including Mandibuloacral dysplasia, a mild progeroid syndrome with partial lipodystrophy and altered bone turnover. Thus, degradation of prelamin A is expected to improve the disease phenotype. Here, we show different susceptibilities of prelamin A forms to proteolysis and further demonstrate that treatment with rapamycin efficiently and selectively triggers lysosomal degradation of farnesylated prelamin A, the most toxic processing intermediate. Importantly, rapamycin treatment of Mandibuloacral dysplasia cells, which feature very low levels of the NAD-dependent sirtuin SIRT-1 in the nuclear matrix, restores SIRT-1 localization and distribution of chromatin markers, elicits release of the transcription factor Oct-1 and determines shortening of the prolonged S-phase. These findings indicate the drug as a possible treatment for Mandibuloacral dysplasia.

DNA repair defects and genome instability in Hutchinson-Gilford Progeria Syndrome

The integrity of the nuclear lamina has emerged as an important factor in the maintenance of genome stability. In particular, mutations in the LMNA gene, encoding A-type lamins (lamin A/C), alter nuclear morphology and function, and cause genomic instability. LMNA gene mutations are associated with a variety of degenerative diseases and devastating premature aging syndromes such as Hutchinson-Gilford Progeria Syndrome (HGPS) and Restrictive Dermopathy (RD). HGPS is a severe laminopathy, with patients dying in their teens from myocardial infarction or stroke. HGPS patient-derived cells exhibit nuclear shape abnormalities, changes in epigenetic regulation and gene expression, telomere shortening, genome instability, and premature senescence. This review highlights recent advances in identifying molecular mechanisms that contribute to the pathophysiology of HGPS, with a special emphasis on DNA repair defects and genome instability.

Study of the anti-inflammatory effects of low-dose radiation: The contribution of biphasic regulation of the antioxidative system in endothelial cells

BACKGROUND

We examined (a) the expression of the antioxidative factor glutathione peroxidase (GPx) and the transcription factor nuclear factor E2-related factor 2 (Nrf2) following low-dose X-irradiation in endothelial cells (ECs) and (b) the impact of reactive oxygen species (ROS) and Nrf2 on functional properties of ECs to gain further knowledge about the anti-inflammatory mode of action of low doses of ionizing radiation.

MATERIAL AND METHODS

EA.hy926 ECs and primary human dermal microvascular ECs (HMVEC) were stimulated by tumor necrosis factor-α (TNF-α, 20 ng/ml) 4 h before irradiation with single doses ranging from 0.3 to 3 Gy. The expression and activity of GPx and Nrf2 were analyzed by flow cytometry, colorimetric assays, and real-time PCR. The impact of ROS and Nrf2 on peripheral blood mononuclear cell (PBMC) adhesion was assayed in the presence of the ROS scavenger N-acetyl-L-cysteine (NAC) and Nrf2 activator AI-1.

RESULTS

Following a low-dose exposure, we observed in EA.hy926 EC and HMVECs a discontinuous expression and enzymatic activity of GPx concomitant with a lowered expression and DNA binding activity of Nrf2 that was most pronounced at a dose of 0.5 Gy. Scavenging of ROS by NAC and activation of Nrf2 by AI-1 significantly diminished a lowered adhesion of PBMC to EC at a dose of 0.5 Gy.

CONCLUSION

Low-dose irradiation resulted in a nonlinear expression and activity of major compounds of the antioxidative system that might contribute to anti-inflammatory effects in stimulated ECs.

LMNA Mutation c.917T>G (p.L306R) Leads to Deleterious Hyper-Assembly of Lamin A/C and Associates with Severe Right Ventricular Cardiomyopathy and Premature Aging

Mutations in the LMNA gene coding for the nuclear lamina proteins lamin A and its smaller splice form lamin C associate with a heterogeneous group of diseases collectively called laminopathies. Here, we describe a 2-year-old patient with a previously undescribed phenotype including right ventricular cardiomyopathy, progeroid features, and premature death. Sequencing of LMNA revealed a novel heterozygous de novo mutation p.L306R located in the α-helical rod domain of A-type lamins. Fibroblasts from the patient showed reduced proliferation and early premature replicative senescence, as characterized by progressive hyperlobulation of the nuclei, abnormally clustered centromeres, loss of lamin B1, and reorganization of promyelocytic leukemia nuclear bodies. Furthermore, the patient cells were more sensitive to double-strand DNA breaks. Similar structural and phenotypic defects were observed in normal fibroblasts transfected with FLAG-tagged p.L306R lamin A. Correspondingly, in vitro assembly studies revealed that the p.L306R generates a "hyper-assembly" mutant of lamin A that forms extensive fiber arrays under physiological conditions where wild-type lamin A is still largely soluble. In summary, we report a novel LMNA p.L306R mutation that leads to previously undescribed hyper-assembly of lamin A, heavy distortion of nuclear shape and that manifests as right ventricular cardiomyopathy and premature aging.

Sustained accumulation of prelamin A and depletion of lamin A/C both cause oxidative stress and mitochondrial dysfunction but induce different cell fates

The cell nucleus is structurally and functionally organized by lamins, intermediate filament proteins that form the nuclear lamina. Point mutations in genes that encode a specific subset of lamins, the A-type lamins, cause a spectrum of diseases termed laminopathies. Recent evidence points to a role for A-type lamins in intracellular redox homeostasis. To determine whether lamin A/C depletion and prelamin A accumulation differentially induce oxidative stress, we have performed a quantitative microscopy-based analysis of reactive oxygen species (ROS) levels and mitochondrial membrane potential (Δψ_m) in human fibroblasts subjected to sustained siRNA-mediated knockdown of LMNA and ZMPSTE24, respectively. We measured a highly significant increase in basal ROS levels and an even more prominent rise of induced ROS levels in lamin A/C depleted cells, eventually resulting in Δψ_m hyperpolarization and apoptosis. Depletion of ZMPSTE24 on the other hand, triggered a senescence pathway that was associated with moderately increased ROS levels and a transient Δψ_m depolarization. Both knockdowns were accompanied by an upregulation of several ROS detoxifying enzymes. Taken together, our data suggest that both persistent prelamin A accumulation and lamin A/C depletion elevate ROS levels, but to a different extent and with different effects on cell fate. This may contribute to the variety of disease phenotypes witnessed in laminopathies.

Nuclear envelope and chromatin, lock and key of genome integrity

More than as an inert separation between the inside and outside of the nucleus, the nuclear envelope (NE) constitutes an active toll, which controls the import and export of molecules, and also a hub for a diversity of genomic processes, such as transcription, DNA repair, and chromatin dynamics. Proteins localized at the inner surface of the NE (such as lamins, nuclear pore proteins, lamin-associated proteins) interact with chromatin in a dynamic manner, contributing to the establishment of topological domains. In this review, we address the complex interplay between chromatin and NE. We discuss the divergence of this cross talk during evolution and comment both on the current established models and the most recent findings. In particular, we focus our attention on how the NE cooperates with chromatin in protecting the genome integrity.

Lamins: nuclear intermediate filament proteins with fundamental functions in nuclear mechanics and genome regulation

Lamins are intermediate filament proteins that form a scaffold, termed nuclear lamina, at the nuclear periphery. A small fraction of lamins also localize throughout the nucleoplasm. Lamins bind to a growing number of nuclear protein complexes and are implicated in both nuclear and cytoskeletal organization, mechanical stability, chromatin organization, gene regulation, genome stability, differentiation, and tissue-specific functions. The lamin-based complexes and their specific functions also provide insights into possible disease mechanisms for human laminopathies, ranging from muscular dystrophy to accelerated aging, as observed in Hutchinson-Gilford progeria and atypical Werner syndromes.

Sulforaphane enhances progerin clearance in Hutchinson-Gilford progeria fibroblasts

Hutchinson-Gilford progeria syndrome (HGPS, OMIM 176670) is a rare multisystem childhood premature aging disorder linked to mutations in the LMNA gene. The most common HGPS mutation is found at position G608G within exon 11 of the LMNA gene. This mutation results in the deletion of 50 amino acids at the carboxyl-terminal tail of prelamin A, and the truncated protein is called progerin. Progerin only undergoes a subset of the normal post-translational modifications and remains permanently farnesylated. Several attempts to rescue the normal cellular phenotype with farnesyltransferase inhibitors (FTIs) and other compounds have resulted in partial cellular recovery. Using proteomics, we report here that progerin induces changes in the composition of the HGPS nuclear proteome, including alterations to several components of the protein degradation pathways. Consequently, proteasome activity and autophagy are impaired in HGPS cells. To restore protein clearance in HGPS cells, we treated HGPS cultures with sulforaphane (SFN), an antioxidant derived from cruciferous vegetables. We determined that SFN stimulates proteasome activity and autophagy in normal and HGPS fibroblast cultures. Specifically, SFN enhances progerin clearance by autophagy and reverses the phenotypic changes that are the hallmarks of HGPS. Therefore, SFN is a promising therapeutic avenue for children with HGPS.

Opposite roles for p38MAPK-driven responses and reactive oxygen species in the persistence and resolution of radiation-induced genomic instability

We report the functional and temporal relationship between cellular phenotypes such as oxidative stress, p38MAPK-dependent responses and genomic instability persisting in the progeny of cells exposed to sparsely ionizing low-Linear Energy Transfer (LET) radiation such as X-rays or high-charge and high-energy (HZE) particle high-LET radiation such as ⁵⁶Fe ions. We found that exposure to low and high-LET radiation increased reactive oxygen species (ROS) levels as a threshold-like response induced independently of radiation quality and dose. This response was sustained for two weeks, which is the period of time when genomic instability is evidenced by increased micronucleus formation frequency and DNA damage associated foci. Indicators for another persisting response sharing phenotypes with stress-induced senescence, including beta galactosidase induction, increased nuclear size, p38MAPK activation and IL-8 production, were induced in the absence of cell proliferation arrest during the first, but not the second week following exposure to high-LET radiation. This response was driven by a p38MAPK-dependent mechanism and was affected by radiation quality and dose. This stress response and elevation of ROS affected genomic instability by distinct pathways. Through interference with p38MAPK activity, we show that radiation-induced stress phenotypes promote genomic instability. In contrast, exposure to physiologically relevant doses of hydrogen peroxide or increasing endogenous ROS levels with a catalase inhibitor reduced the level of genomic instability. Our results implicate persistently elevated ROS following exposure to radiation as a factor contributing to genome stabilization.

Mouse models of the fragile X premutation and fragile X-associated tremor/ataxia syndrome

Carriers of the fragile X premutation (FPM) have CGG trinucleotide repeat expansions of between 55 and 200 in the 5'-UTR of FMR1, compared to a CGG repeat length of between 5 and 54 for the general population. Carriers were once thought to be without symptoms, but it is now recognized that they can develop a variety of early neurological symptoms as well as being at risk for developing the late onset neurodegenerative disorder fragile X-associated tremor/ataxia syndrome (FXTAS). Several mouse models have contributed to our understanding of FPM and FXTAS, and findings from studies using these models are summarized here. This review also discusses how this information is improving our understanding of the molecular and cellular abnormalities that contribute to neurobehavioral features seen in some FPM carriers and in patients with FXTAS. Mouse models show much of the pathology seen in FPM carriers and in individuals with FXTAS, including the presence of elevated levels of Fmr1 mRNA, decreased levels of fragile X mental retardation protein, and ubiquitin-positive intranuclear inclusions. Abnormalities in dendritic spine morphology in several brain regions are associated with neurocognitive deficits in spatial and temporal memory processes, impaired motor performance, and altered anxiety. In vitro studies have identified altered dendritic and synaptic architecture associated with abnormal Ca(2+) dynamics and electrical network activity. FPM mice have been particularly useful in understanding the roles of Fmr1 mRNA, fragile X mental retardation protein, and translation of a potentially toxic polyglycine peptide in pathology. Finally, the potential for using these and emerging mouse models for preclinical development of therapies to improve neurological function in FXTAS is considered.

Redox regulation by Pitx2 and Pitx3 is critical for fetal myogenesis

During development, major metabolic changes occur as cells become more specialized within a lineage. In the case of skeletal muscle, differentiation is accompanied by a switch from a glycolytic proliferative progenitor state to an oxidative postmitotic differentiated state. Such changes require extensive mitochondrial biogenesis leading to increased reactive oxygen species (ROS) production that needs to be balanced by an antioxidant system. Our analysis of double conditional Pitx2/3 mouse mutants, both in vivo during fetal myogenesis and ex vivo in primary muscle cell cultures, reveals excessive upregulation of ROS levels leading to DNA damage and apoptosis of differentiating cells. This is a consequence of downregulation of Nrf1 and genes for antioxidant enzymes, direct targets of Pitx2/3, leading to decreased expression of antioxidant enzymes, as well as impairment of mitochondrial function. Our analysis identifies Pitx2 and Pitx3 as key regulators of the intracellular redox state preventing DNA damage as cells undergo differentiation.

Oxidative stress and mitochondrial dysfunction across broad-ranging pathologies: toward mitochondria-targeted clinical strategies

Beyond the disorders recognized as mitochondrial diseases, abnormalities in function and/or ultrastructure of mitochondria have been reported in several unrelated pathologies. These encompass ageing, malformations, and a number of genetic or acquired diseases, as diabetes and cardiologic, haematologic, organ-specific (e.g., eye or liver), neurologic and psychiatric, autoimmune, and dermatologic disorders. The mechanistic grounds for mitochondrial dysfunction (MDF) along with the occurrence of oxidative stress (OS) have been investigated within the pathogenesis of individual disorders or in groups of interrelated disorders. We attempt to review broad-ranging pathologies that involve mitochondrial-specific deficiencies or rely on cytosol-derived prooxidant states or on autoimmune-induced mitochondrial damage. The established knowledge in these subjects warrants studies aimed at elucidating several open questions that are highlighted in the present review. The relevance of OS and MDF in different pathologies may establish the grounds for chemoprevention trials aimed at compensating OS/MDF by means of antioxidants and mitochondrial nutrients.

The hallmarks of fibroblast ageing

Ageing is influenced by the intrinsic disposition delineating what is maximally possible and extrinsic factors determining how that frame is individually exploited. Intrinsic and extrinsic ageing processes act on the dermis, a post-mitotic skin compartment mainly consisting of extracellular matrix and fibroblasts. Dermal fibroblasts are long-lived cells constantly undergoing damage accumulation and (mal-)adaptation, thus constituting a powerful indicator system for human ageing. Here, we use the systematic of ubiquitous hallmarks of ageing (Lopez-Otin et al., 2013, Cell 153) to categorise the available knowledge regarding dermal fibroblast ageing. We discriminate processes inducible in culture from phenomena apparent in skin biopsies or primary cells from old donors, coming to the following conclusions: (i) Fibroblasts aged in culture exhibit most of the established, ubiquitous hallmarks of ageing. (ii) Not all of these hallmarks have been detected or investigated in fibroblasts aged in situ (in the skin). (iii) Dermal fibroblasts aged in vitro and in vivo exhibit additional features currently not considered ubiquitous hallmarks of ageing. (iv) The ageing process of dermal fibroblasts in their physiological tissue environment has only been partially elucidated, although these cells have been a preferred model of cell ageing in vitro for decades.

WITHDRAWN: Nuclear matrix, nuclear envelope and premature aging syndromes in a translational research perspective

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.semcdb.2014.03.022. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Nuclear matrix, nuclear envelope and premature aging syndromes in a translational research perspective

Lamin A-related progeroid syndromes are genetically determined, extremely rare and severe. In the past ten years, our knowledge and perspectives for these diseases has widely progressed, through the progressive dissection of their pathophysiological mechanisms leading to precocious and accelerated aging, from the genes mutations discovery until therapeutic trials in affected children. A-type lamins are major actors in several structural and functional activities at the nuclear periphery, as they are major components of the nuclear lamina. However, while this is usually poorly considered, they also play a key role within the rest of the nucleoplasm, whose defects are related to cell senescence. Although nuclear shape and nuclear envelope deformities are obvious and visible events, nuclear matrix disorganization and abnormal composition certainly represent the most important causes of cell defects with dramatic pathological consequences. Therefore, lamin-associated diseases should be better referred as laminopathies instead of envelopathies, this later being too restrictive, considering neither the key structural and functional roles of soluble lamins in the entire nucleoplasm, nor the nuclear matrix contribution to the pathophysiology of lamin-associated disorders and in particular in defective lamin A processing-associated aging diseases. Based on both our understanding of pathophysiological mechanisms and the biological and clinical consequences of progeria and related diseases, therapeutic trials have been conducted in patients and were terminated less than 10 years after the gene discovery, a quite fast issue for a genetic disease. Pharmacological drugs have been repurposed and used to decrease the toxicity of the accumulated, unprocessed and truncated prelaminA in progeria. To date, none of them may be considered as a cure for progeria and these clinical strategies were essentially designed toward reducing a subset of the most dramatic and morbid features associated to progeria. New therapeutic strategies under study, in particular targeting the protein expression pathway at the mRNA level, have shown a remarkable efficacy both in vitro in cells and in vivo in mice models. Strategies intending to clear the toxic accumulated proteins from the nucleus are also under evaluation. However, although exceedingly rare, improving our knowledge of genetic progeroid syndromes and searching for innovative and efficient therapies in these syndromes is of paramount importance as, even before they can be used to save lives, they may significantly (i) expand the affected childrens' lifespan and preserve their quality of life; (ii) improve our understanding of aging-related disorders and other more common diseases; and (iii) expand our fundamental knowledge of physiological aging and its links with major physiological processes such as those involved in oncogenesis.

A pathway linking oxidative stress and the Ran GTPase system in progeria

Maintaining the Ran GTPase at a proper concentration in the nucleus is important for nucleocytoplasmic transport. Previously we found that nuclear levels of Ran are reduced in cells from patients with Hutchinson-Gilford progeria syndrome (HGPS), a disease caused by constitutive attachment of a mutant form of lamin A (termed progerin) to the nuclear membrane. Here we explore the relationship between progerin, the Ran GTPase, and oxidative stress. Stable attachment of progerin to the nuclear membrane disrupts the Ran gradient and results in cytoplasmic localization of Ubc9, a Ran-dependent import cargo. Ran and Ubc9 disruption can be induced reversibly with H2O2. CHO cells preadapted to oxidative stress resist the effects of progerin on Ran and Ubc9. Given that HGPS-patient fibroblasts display elevated ROS, these data suggest that progerin inhibits nuclear transport via oxidative stress. A drug that inhibits pre-lamin A cleavage mimics the effects of progerin by disrupting the Ran gradient, but the effects on Ran are observed before a substantial ROS increase. Moreover, reducing the nuclear concentration of Ran is sufficient to induce ROS irrespective of progerin. We speculate that oxidative stress caused by progerin may occur upstream or downstream of Ran, depending on the cell type and physiological setting.

DNA damage and lamins

The spatial and temporal organization of the genome has emerged as an additional level of regulation of nuclear functions. Structural proteins associated with the nuclear envelope play important roles in the organization of the genome. The nuclear lamina, a polymeric meshwork formed by lamins (A- and B-type) and lamin-associated proteins, is viewed as a scaffold for tethering chromatin and protein complexes regulating a variety of nuclear functions. Alterations in lamins function impact DNA transactions such as transcription, replication, and repair, as well as epigenetic modifications that change chromatin structure. These data, and the association of defective lamins with a whole variety of degenerative disorders, premature aging syndromes, and cancer, provide evidence for these proteins operating as caretakers of the genome. In this chapter, we summarize current knowledge about the function of lamins in the maintenance of genome integrity, with special emphasis on the role of A-type lamins in the maintenance of telomere homeostasis and mechanisms of DNA damage repair. These findings have begun to shed some light onto molecular mechanisms by which alterations in A-type lamins induce genomic instability and contribute to the pathophysiology of aging and aging-related diseases, especially cancer.

The role of the nuclear lamina in cancer and apoptosis

Not long after the discovery of lamin proteins, it became clear that not all lamin subtypes are ubiquitously expressed in cells and tissues. Especially, A-type lamins showed an inverse correlation with proliferation and were thus initially called statins. Here we compare the findings of both A- and B-type lamin expression in various normal tissues and their neoplastic counterparts. Based on immunocytochemistry it becomes clear that lamin expression patterns are much more complicated than initially assumed: while normally proliferative cells are devoid of A-type lamin expression, many neoplastic tissues do show prominent A-type lamin expression. Conversely, cells that do not proliferate can be devoid of lamin expression. Yet, within the different types of tissues and tumors, lamins can be used to distinguish between tumor subtypes. The link between the appearance of A-type lamins in differentiation and the appearance of A-type lamins in a tumor likely relates the proliferative capacity of the tumor to its differentiation state.While lamins are targets for degradation in the apoptotic process, and accordingly are often used as markers for apoptosis, intriguing studies on an active role of lamins in the initiation or the prevention of apoptosis have been published recently and give rise to a renewed interest in the role of lamins in cancer.