Homozygous missense mutation in the lamin A/C gene causes autosomal recessive Hutchinson-Gilford progeria syndrome

The structure and function of lamin A/C: Special focus on cardiomyopathy and therapeutic interventions

Lamins are inner nuclear membrane proteins that belong to the intermediate filament family. Lamin A/C lie adjacent to the heterochromatin structure in polymer form, providing skeletal to the nucleus. Based on the localization, lamin A/C provides nuclear stability and cytoskeleton to the nucleus and modulates chromatin organization and gene expression. Besides being the structural protein making the inner nuclear membrane in polymer form, lamin A/C functions as a signalling molecule involved in gene expression as an enhancer inside the nucleus. Lamin A/C regulates various cellular pathways like autophagy and energy balance in the cytoplasm. Its expression is highly variable in differentiated tissues, higher in hard tissues like bone and muscle cells, and lower in soft tissues like the liver and brain. In muscle cells, including the heart, lamin A/C must be expressed in a balanced state. Lamin A/C mutation is linked with various diseases, such as muscular dystrophy, lipodystrophy, and cardiomyopathies. It has been observed that a good number of mutations in the LMNA gene impact cardiac activity and its function. Although several works have been published, there are still several unexplored areas left regarding the lamin A/C function and structure in the cardiovascular system and its pathological state. In this review, we focus on the structural organization, expression pattern, and function of lamin A/C, its interacting partners, and the pathophysiology associated with mutations in the lamin A/C gene, with special emphasis on cardiovascular diseases. With the recent finding on lamin A/C, we have summarized the possible therapeutic interventions to treat cardiovascular symptoms and reverse the molecular changes.

Structurally-informed human interactome reveals proteome-wide perturbations by disease mutations

Human genome sequencing studies have identified numerous loci associated with complex diseases. However, translating human genetic and genomic findings to disease pathobiology and therapeutic discovery remains a major challenge at multiscale interactome network levels. Here, we present a deep-learning-based ensemble framework, termed PIONEER (Protein-protein InteractiOn iNtErfacE pRediction), that accurately predicts protein binding partner-specific interfaces for all known protein interactions in humans and seven other common model organisms, generating comprehensive structurally-informed protein interactomes. We demonstrate that PIONEER outperforms existing state-of-the-art methods. We further systematically validated PIONEER predictions experimentally through generating 2,395 mutations and testing their impact on 6,754 mutation-interaction pairs, confirming the high quality and validity of PIONEER predictions. We show that disease-associated mutations are enriched in PIONEER-predicted protein-protein interfaces after mapping mutations from ~60,000 germline exomes and ~36,000 somatic genomes. We identify 586 significant protein-protein interactions (PPIs) enriched with PIONEER-predicted interface somatic mutations (termed oncoPPIs) from pan-cancer analysis of ~11,000 tumor whole-exomes across 33 cancer types. We show that PIONEER-predicted oncoPPIs are significantly associated with patient survival and drug responses from both cancer cell lines and patient-derived xenograft mouse models. We identify a landscape of PPI-perturbing tumor alleles upon ubiquitination by E3 ligases, and we experimentally validate the tumorigenic KEAP1-NRF2 interface mutation p.Thr80Lys in non-small cell lung cancer. We show that PIONEER-predicted PPI-perturbing alleles alter protein abundance and correlates with drug responses and patient survival in colon and uterine cancers as demonstrated by proteogenomic data from the National Cancer Institute's Clinical Proteomic Tumor Analysis Consortium. PIONEER, implemented as both a web server platform and a software package, identifies functional consequences of disease-associated alleles and offers a deep learning tool for precision medicine at multiscale interactome network levels.

Nucleoplasmic lamin C rapidly accumulates at sites of nuclear envelope rupture with BAF and cGAS

In mammalian cell nuclei, the nuclear lamina (NL) underlies the nuclear envelope (NE) to maintain nuclear structure. The nuclear lamins, the major structural components of the NL, are involved in the protection against NE rupture induced by mechanical stress. However, the specific role of the lamins in repair of NE ruptures has not been fully determined. Our analyses using immunofluorescence and live-cell imaging revealed that the nucleoplasmic pool of lamin C rapidly accumulated at sites of NE rupture induced by laser microirradiation in mouse embryonic fibroblasts. The accumulation of lamin C at the rupture sites required both the immunoglobulin-like fold domain that binds to barrier-to-autointegration factor (BAF) and a nuclear localization signal. The accumulation of nuclear BAF and cytoplasmic cyclic GMP-AMP synthase (cGAS) at the rupture sites was in part dependent on lamin A/C. These results suggest that nucleoplasmic lamin C, BAF, and cGAS concertedly accumulate at sites of NE rupture for rapid repair.

The LMNA p.R541C mutation causes dilated cardiomyopathy in human and mice

Dilated cardiomyopathy (DCM) is a major cause of heart failure. LMNA variants contribute to 6-10% DCM cases, but the underlying mechanisms remain incompletely understood. Here, we reported two patients carrying the LMNA c.1621C > T/ p.R541C variant and generated a knock-in mouse model (Lmna^RC) to study the role of this variant in DCM pathogenesis. We found Lmna^RC/RC mice exhibited ventricular dilation and reduced systolic functions at 6 months after birth. The Lmna^RC/RC cardiomyocytes increased in size but no nuclear morphology defects were detected. Transcriptomic and microscopic analyses revealed suppressed gene expression and perturbed ultrastructure in Lmna^RC/RC mitochondria. These defects were associated with increased heterochromatin structures and epigenetic markers including H3K9me2/3. Together, these data implied that the LMNA c.1621C > T/ p.R541C variant enhanced heterochromatic gene suppression and disrupted mitochondria functions as a cause of DCM.

Transient expression of an adenine base editor corrects the Hutchinson-Gilford progeria syndrome mutation and improves the skin phenotype in mice

Hutchinson-Gilford progeria syndrome (HGPS) is a rare premature ageing disorder caused by a point mutation in the LMNA gene (LMNA c.1824 C > T), resulting in the production of a detrimental protein called progerin. Adenine base editors recently emerged with a promising potential for HGPS gene therapy. However adeno-associated viral vector systems currently used in gene editing raise concerns, and the long-term effects of heterogeneous mutation correction in highly proliferative tissues like the skin are unknown. Here we use a non-integrative transient lentiviral vector system, expressing an adenine base editor to correct the HGPS mutation in the skin of HGPS mice. Transient adenine base editor expression corrected the mutation in 20.8-24.1% of the skin cells. Four weeks post delivery, the HGPS skin phenotype was improved and clusters of progerin-negative keratinocytes were detected, indicating that the mutation was corrected in both progenitor and differentiated skin cells. These results demonstrate that transient non-integrative viral vector mediated adenine base editor expression is a plausible approach for future gene-editing therapies.

Mechanisms of A-Type Lamin Targeting to Nuclear Ruptures Are Disrupted in LMNA- and BANF1-Associated Progerias

Mutations in the genes LMNA and BANF1 can lead to accelerated aging syndromes called progeria. The protein products of these genes, A-type lamins and BAF, respectively, are nuclear envelope (NE) proteins that interact and participate in various cellular processes, including nuclear envelope rupture and repair. BAF localizes to sites of nuclear rupture and recruits NE-repair machinery, including the LEM-domain proteins, ESCRT-III complex, A-type lamins, and membranes. Here, we show that it is a mobile, nucleoplasmic population of A-type lamins that is rapidly recruited to ruptures in a BAF-dependent manner via BAF’s association with the Ig-like β fold domain of A-type lamins. These initially mobile lamins become progressively stabilized at the site of rupture. Farnesylated prelamin A and lamin B1 fail to localize to nuclear ruptures, unless that farnesylation is inhibited. Progeria-associated LMNA mutations inhibit the recruitment affected A-type lamin to nuclear ruptures, due to either permanent farnesylation or inhibition of BAF binding. A progeria-associated BAF mutant targets to nuclear ruptures but is unable to recruit A-type lamins. Together, these data reveal the mechanisms that determine how lamins respond to nuclear ruptures and how progeric mutations of LMNA and BANF1 impair recruitment of A-type lamins to nuclear ruptures.

Hutchinson-Gilford Progeria Syndrome (Hgps) And Application Of Gene Therapy Based Crispr/Cas Technology As A Promising Innovative Treatment Approach

BACKGROUND

Hutchinson-Gilford progeria syndrome (HGPS) also known as progeria of childhood or progeria is a rare, rapid, autosomal dominant genetic disorder characterized by premature aging which occurs shortly after birth. HGPS occurs as a result of de novo point mutation in the gene recognized as LMNA gene that encodes two proteins Lamin A protein and Lamin C protein which are the structural components of the nuclear envelope. Mutations in the gene trigger abnormal splicing and induce internal deletion of 50 amino acids leading to the development of a truncated form of Lamin A protein known as Progerin. Progerin generation can be considered as the crucial step in HGPS since the protein is highly toxic to human cells, permanently farnesylated, and exhibits variation in several biochemical and structural properties within the individual. HGPS also produces complications such as skin alterations, growth failure, atherosclerosis, hair and fat loss, and bone and joint diseases. We have also revised all relevant patents relating to Hutchinson-gilford progeria syndrome and its therapy in the current article.

METHOD

The goal of the present review article is to provide information about Hutchinson-Gilford progeria syndrome (HGPS) and the use of CRISPR/Cas technology as a promising treatment approach in the treatment of the disease. The review also discusses about different pharmacological and non-pharmacological methods of treatment currently used for HGPS.

RESULTS

The main limitation associated with progeria is the lack of a definitive cure. The existing treatment modality provides only symptomatic relief. Therefore, it is high time to develop a therapeutic method that hastens premature aging in such patients.

CONCLUSION

CRISPR/Cas technology is a novel gene-editing tool that allows genome editing at specific loci, and is found to be a promising therapeutic approach for the treatment of genetic disorders such as HGPS where dominant-negative mutations take place.

Two Decades after Mandibuloacral Dysplasia Discovery: Additional Cases and Comprehensive View of Disease Characteristics

Pathogenic variants in the LMNA gene cause a group of heterogeneous genetic disorders, called laminopathies. In particular, homozygous or compound heterozygous variants in LMNA have been associated with “mandibuloacral dysplasia type A” (MADA), an autosomal recessive disorder, characterized by mandibular hypoplasia, growth retardation mainly postnatal, pigmentary skin changes, progressive osteolysis of the distal phalanges and/or clavicles, and partial lipodystrophy. The detailed characteristics of this multisystemic disease have yet to be specified due to its rarity and the limited number of cases described. Here, we report three unrelated Egyptian patients with variable severity of MAD features. Next-generation sequencing using a gene panel revealed a homozygous c.1580G>A-p.Arg527His missense variant in LMNA exon 9 in an affected individual with a typical MADA phenotype. Another homozygous c.1580G>T-p.Arg527Leu variant affecting the same amino acid was identified in two additional patients, who both presented with severe manifestations very early in life. We combined our observations together with data from all MADA cases reported in the literature to get a clearer picture of the phenotypic variability in this disease. This work raises the number of reported MADA families, argues for the presence of the founder effect in Egypt, and strengthens genotype–phenotype correlations.

A 13-Year-Old Boy from Thailand with Hutchinson-Gilford Progeria Syndrome with Coronary Artery and Aortic Calcification and Non-ST-Segment Elevation Myocardial Infarction (NSTEMI)

Patient: Male, 13-year-old

Final Diagnosis: Hutchinson-Gilford progeria syndrome with coronary artery and aortic calcification and non-ST-segment elevation myocardial infarction

Symptoms: Chest discomfort

Medication: —

Clinical Procedure: —

Specialty: Cardiology

Mandibuloacral dysplasia type A in five tunisian patients

Mandibuloacral dysplasia with type A lipodystrophy is a rare autosomal recessive disorder characterized by craniofacial dysmorphism, type A lipodystrophy, clavicular dysplasia, and acroostelolysis. It is caused by homozygous or compound heterozygous missense mutations in LMNA gene. We report five Tunisian patients harboring the same homozygous c.1580G > A; p. (Arg527His) mutation in LMNA gene. The patients presented with typical features of mandibuloacral dysplasia including, prominent eyes, thin or beaked nose, dental overcrowding, mandibular hypoplasia, short and broad finger's distal phalanges with round tips and lipodystrophy type A. Newly recognized signs are growth hormone deficiency and dilated cardiomyopathy. Genotype-phenotype correlation found that at least one of the disease's LMNA mutant alleles involve one of the highly conserved aminoacids, residing in a key site domain for protein function within the C-terminal globular domain of A-type lamins. Also, the severity of the disease depends on the position in the protein's domain and on the type of substitution of the concerned aminoacid.

Structural analysis of the ternary complex between lamin A/C, BAF and emerin identifies an interface disrupted in autosomal recessive progeroid diseases

Lamins are the main components of the nucleoskeleton. Whereas their 3D organization was recently described using cryoelectron tomography, no structural data highlights how they interact with their partners at the interface between the inner nuclear envelope and chromatin. A large number of mutations causing rare genetic disorders called laminopathies were identified in the C-terminal globular Igfold domain of lamins A and C. We here present a first structural description of the interaction between the lamin A/C immunoglobulin-like domain and emerin, a nuclear envelope protein. We reveal that this lamin A/C domain both directly binds self-assembled emerin and interacts with monomeric emerin LEM domain through the dimeric chromatin-associated Barrier-to-Autointegration Factor (BAF) protein. Mutations causing autosomal recessive progeroid syndromes specifically impair proper binding of lamin A/C domain to BAF, thus destabilizing the link between lamin A/C and BAF in cells. Recent data revealed that, during nuclear assembly, BAF’s ability to bridge distant DNA sites is essential for guiding membranes to form a single nucleus around the mitotic chromosome ensemble. Our results suggest that BAF interaction with lamin A/C also plays an essential role, and that mutations associated with progeroid syndromes leads to a dysregulation of BAF-mediated chromatin organization and gene expression.

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.

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.

Hutchinson-Gilford Progeria Syndrome: A Premature Aging Disease

Progeria is sporadic, very rare, autosomal dominant, deadly childhood disorder. It is one of the progeroid syndromes also known as Hutchinson-Gilford progeria syndrome (HGPS). Aging is a developmental process that begins with fertilization and ends up with death involving a lot of environmental and genetic factors. The disease firstly involves premature aging and then death from complications of atherosclerosis such as myocardial infarction, stroke, atherosclerosis, or heart failure. The lifespan of the patient is normally up to teen age or early twenties. It is usually not inherited because a patient normally dies before the age of reproduction. The most important genetic linkage between progeria and aging is shortening of telomere ends with each replication cycle. The patients are normally observed to have extremely short telomeres. Currently, 90% of the patients are said to have de novo point mutations in the LMNA gene that substitute cytosine with thymine and have been found in individuals with HGPS. Lmna encodes lamins A and C, and the A-type lamins have important structural function in the nuclear envelope. The most common type of HGPS mutation is located at codon 608 (G608G). It could not be diagnosed at birth, but after the age of 2 years, visible, prominent symptoms can be observed. Still, lot of research is needed to solve this mystery; hopefully, future research on HGPS would provide important clues for progeria and other fatal age-related disorders.

LMNA Sequences of 60,706 Unrelated Individuals Reveal 132 Novel Missense Variants in A-Type Lamins and Suggest a Link between Variant p.G602S and Type 2 Diabetes

Mutations in LMNA, encoding nuclear intermediate filament proteins lamins A and C, cause multiple diseases ('laminopathies') including muscular dystrophy, dilated cardiomyopathy, familial partial lipodystrophy (FPLD2), insulin resistance syndrome and progeria. To assess the prevalence of LMNA missense mutations ('variants') in a broad, ethnically diverse population, we compared missense alleles found among 60,706 unrelated individuals in the ExAC cohort to those identified in 1,404 individuals in the laminopathy database (UMD-LMNA). We identified 169 variants in the ExAC cohort, of which 37 (∼22%) are disease-associated including p.I299V (allele frequency 0.0402%), p.G602S (allele frequency 0.0262%) and p.R644C (allele frequency 0.124%), suggesting certain LMNA mutations are more common than previously recognized. Independent analysis of LMNA variants via the type 2 diabetes (T2D) Knowledge Portal showed that variant p.G602S associated significantly with type 2 diabetes (p = 0.02; odds ratio = 4.58), and was more frequent in African Americans (allele frequency 0.297%). The FPLD2-associated variant I299V was most prevalent in Latinos (allele frequency 0.347%). The ExAC cohort also revealed 132 novel LMNA missense variants including p.K108E (limited to individuals with psychiatric disease; predicted to perturb coil-1B), p.R397C and p.R427C (predicted to perturb filament biogenesis), p.G638R and p.N660D (predicted to perturb prelamin A processing), and numerous Ig-fold variants predicted to perturb phenotypically characteristic protein-protein interactions. Overall, this two-pronged strategy- mining a large database for missense variants in a single gene (LMNA), coupled to knowledge about the structure, biogenesis and functions of A-type lamins- revealed an unexpected number of LMNA variants, including novel variants predicted to perturb lamin assembly or function. Interestingly, this study also correlated novel variant p.K108E with psychiatric disease, identified known variant p.I299V as a potential risk factor for metabolic disease in Latinos, linked variant p.G602 with type 2 diabetes, and identified p.G602S as a predictor of diabetes risk in African Americans.

Mandibuloacral dysplasia and LMNA A529V mutation in Turkish patients with severe skeletal changes and absent breast development

Mandibuloacral dysplasia (MAD) is an autosomal recessive disorder characterized by acroosteolysis (resorption of terminal phalanges), skin changes (hyperpigmentation), clavicular hypoplasia, craniofascial anomalies, a hook nose and prominent eyes, delayed closures of the cranial sutures, lipodystrophy, alopecia, and skeletal anomalies. MAD patients are classified according to lipodystrophy patterns: type A and type B. The vast majority of MAD cases are caused by LMNA gene mutations. MAD patients with type A lipodystrophy (MADA) have been reported to have LMNA R527H, A529V, or A529T mutations. In this report, we describe two MADA patients with progressive skeletal changes, absent breast development, and cataract in addition to the classical MAD phenotype. Both patients were found to be homozygous for the Ala529Val mutation of the LMNA gene. Our female patient is the oldest MADA patient (59 years old) who has ever been reported with the LMNA mutation and also the LMNA Ala529Val mutation. This study is the second report on MADA patients with a homozygous Ala529Val mutation.

Cardiac arrhythmia and late-onset muscle weakness caused by a myofibrillar myopathy with unusual histopathological features due to a novel missense mutation in FLNC

Myofibrillar myopathies (MFM) are mostly adult-onset diseases characterized by progressive morphological alterations of the muscle fibers beginning in the Z-disk and the presence of protein aggregates in the sarcoplasm. They are mostly caused by mutations in different genes that encode Z-disk proteins, including DES, CRYAB, LDB3, MYOT, FLNC and BAG3. A large family of French origin, presenting an autosomal dominant pattern, characterized by cardiac arrhythmia associated to late-onset muscle weakness, was evaluated to clarify clinical, morphological and genetic diagnosis. Muscle weakness began during adult life (over 30 years of age), and had a proximal distribution. Histology showed clear signs of a myofibrillar myopathy, but with unusual, large inclusions. Subsequently, genetic testing was performed in MFM genes available for screening at the time of clinical/histological diagnosis, and desmin (DES), αB-crystallin (CRYAB), myotilin (MYOT) and ZASP (LDB3), were excluded. LMNA gene screening found the p.R296C variant which did not co-segregate with the disease. Genome wide scan revealed linkage to 7q.32, containing the FLNC gene. FLNC direct sequencing revealed a heterozygous c.3646T>A p.Tyr1216Asn change, co-segregating with the disease, in a highly conserved amino acid of the protein. Normal filamin C levels were detected by Western-blot analysis in patient muscle biopsies and expression of the mutant protein in NIH3T3 showed filamin C aggregates. This is an original FLNC mutation in a MFM family with an atypical clinical and histopathological presentation, given the presence of significantly focal lesions and prominent sarcoplasmic masses in muscle biopsies and the constant heart involvement preceding significantly the onset of the myopathy. Though a rare etiology, FLNC gene should not be excluded in early-onset arrhythmia, even in the absence of myopathy, which occurs later in the disease course.

Red meat and colorectal cancer: Nrf2-dependent antioxidant response contributes to the resistance of preneoplastic colon cells to fecal water of hemoglobin- and beef-fed rats

Epidemiological studies have associated red meat intake with risk of colorectal cancer. Experimental studies explain this positive association by the oxidative properties of heme iron released in the colon. This latter is a potent catalyst for lipid peroxidation, resulting in the neoformation of deleterious aldehydes in the fecal water of heme-fed rats. The toxicity of fecal water of heme-fed rats was associated to such lipid peroxidation. This study demonstrated that fecal water of hemoglobin- and beef-fed rats preferentially induced apoptosis in mouse normal colon epithelial cells than in those carrying mutation on Apc (Adenomatous polyposis coli) gene, considered as preneoplastic. Highlighting the importance of lipid peroxidation and neoformation of secondary aldehydes like 4-hydroxy-2-nonenal (HNE), we optimized the depletion of carbonyl compounds in the fecal water which turned out to abolish the differential apoptosis in both cell lines. To explain the resistance of preneoplastic cells towards fecal water toxicity, we focused on Nrf2, known to be activated by aldehydes, including HNE. Fecal water activated Nrf2 in both cell lines, associated with the induction of Nrf2-target genes related to aldehydes detoxification. However, the antioxidant defense appeared to be higher in preneoplastic cells, favoring their survival, as evidenced by Nrf2 inactivation. Taken together, our results suggest that Nrf2-dependent antioxidant response was involved in the resistance of preneoplastic cells upon exposure to fecal water of hemoglobin- and beef-fed rats. This difference could explain the promoting effect of red meat and heme-enriched diet on colorectal cancer, by initiating positive selection of preneoplastic cells.

Mandibular hypoplasia, deafness, progeroid features and lipodystrophy (MDPL) syndrome in the context of inherited lipodystrophies

BACKGROUND

Lipodystrophies are a large heterogeneous group of genetic or acquired disorders characterized by generalized or partial fat loss, usually associated with metabolic complications such as diabetes mellitus, hypertriglyceridemia and hepatic steatosis. Many efforts have been made in the last years in identifying the genetic etiologies of several lipodystrophy forms, although some remain to be elucidated.

METHODS

We report here the clinical description of a woman with a rare severe lipodystrophic and progeroid syndrome associated with hypertriglyceridemia and diabetes whose genetic bases have been clarified through whole-exome sequencing (WES) analysis.

RESULTS

This article reports the 5th MDPL (Mandibular hypoplasia, deafness, progeroid features, and lipodystrophy syndrome) patient with the same de novo p.S605del mutation in POLD1. We provided further genetic evidence that this is a disease-causing mutation along with a plausible molecular mechanism responsible for this recurring event. Moreover we overviewed the current classification of the inherited forms of lipodystrophy, along with their underlying molecular basis.

CONCLUSIONS

Progress in the identification of lipodystrophy genes will help in better understanding the role of the pathways involved in the complex physiology of fat. This will lead to new targets towards develop innovative therapeutic strategies for treating the disorder and its metabolic complications, as well as more common forms of adipose tissue redistribution as observed in the metabolic syndrome and type 2 diabetes.

Functional architecture of the cell's nucleus in development, aging, and disease

In eukaryotes, the function of the cell's nucleus has primarily been considered to be the repository for the organism's genome. However, this rather simplistic view is undergoing a major shift, as it is increasingly apparent that the nucleus has functions extending beyond being a mere genome container. Recent findings have revealed that the structural composition of the nucleus changes during development and that many of these components exhibit cell- and tissue-specific differences. Increasing evidence is pointing to the nucleus being integral to the function of the interphase cytoskeleton, with changes to nuclear structural proteins having ramifications affecting cytoskeletal organization and the cell's interactions with the extracellular environment. Many of these functions originate at the nuclear periphery, comprising the nuclear envelope (NE) and underlying lamina. Together, they may act as a "hub" in integrating cellular functions including chromatin organization, transcriptional regulation, mechanosignaling, cytoskeletal organization, and signaling pathways. Interest in such an integral role has been largely stimulated by the discovery that many diseases and anomalies are caused by defects in proteins of the NE/lamina, the nuclear envelopathies, many of which, though rare, are providing insights into their more common variants that are some of the major issues of the twenty-first century public health. Here, we review the contributions that mouse mutants have made to our current understanding of the NE/lamina, their respective roles in disease and the use of mice in developing potential therapies for treating the diseases.

LMNA-associated cardiocutaneous progeria: an inherited autosomal dominant premature aging syndrome with late onset

Hutchinson-Gilford Progeria Syndrome (HGPS) is a premature aging disorder caused by mutations in LMNA, which encodes the nuclear scaffold proteins lamin A and C. In HGPS and related progerias, processing of prelamin A is blocked at a critical step mediated by the zinc metalloprotease ZMPSTE24. LMNA-linked progerias can be grouped into two classes: (1) the processing-deficient, early onset "typical" progerias (e.g., HGPS), and (2) the processing-proficient "atypical" progeria syndromes (APS) that are later in onset. Here we describe a previously unrecognized progeria syndrome with prominent cutaneous and cardiovascular manifestations belonging to the second class. We suggest the name LMNA-associated cardiocutaneous progeria syndrome (LCPS) for this disorder. Affected patients are normal at birth but undergo progressive cutaneous changes in childhood and die in middle age of cardiovascular complications, including accelerated atherosclerosis, calcific valve disease, and cardiomyopathy. In addition, the proband demonstrated cancer susceptibility, a phenotype rarely described for LMNA-based progeria disorders. The LMNA mutation that caused LCPS in this family is a heterozygous c.899A>G (p.D300G) mutation predicted to alter the coiled-coil domain of lamin A/C. In skin fibroblasts isolated from the proband, the processing and levels of lamin A and C are normal. However, nuclear morphology is aberrant and rescued by treatment with farnesyltransferase inhibitors, as is also the case for HGPS and other laminopathies. Our findings advance knowledge of human LMNA progeria syndromes, and raise the possibility that typical and atypical progerias may converge upon a common mechanism to cause premature aging disease.

Accumulation of the inner nuclear envelope protein Sun1 is pathogenic in progeric and dystrophic laminopathies

Human LMNA gene mutations result in laminopathies that include Emery-Dreifuss muscular dystrophy (AD-EDMD) and Hutchinson-Gilford progeria, the premature aging syndrome (HGPS). The Lmna null (Lmna(-/-)) and progeroid LmnaΔ9 mutant mice are models for AD-EDMD and HGPS, respectively. Both animals develop severe tissue pathologies with abbreviated life spans. Like HGPS cells, Lmna(-/-) and LmnaΔ9 fibroblasts have typically misshapen nuclei. Unexpectedly, Lmna(-/-) or LmnaΔ9 mice that are also deficient for the inner nuclear membrane protein Sun1 show markedly reduced tissue pathologies and enhanced longevity. Concordantly, reduction of SUN1 overaccumulation in LMNA mutant fibroblasts and in cells derived from HGPS patients corrected nuclear defects and cellular senescence. Collectively, these findings implicate Sun1 protein accumulation as a common pathogenic event in Lmna(-/-), LmnaΔ9, and HGPS disorders.

A novel homozygous p.Arg527Leu LMNA mutation in two unrelated Egyptian families causes overlapping mandibuloacral dysplasia and progeria syndrome

Mandibuloacral dysplasia (MAD) is a rare disease resulting from a mutation of LMNA gene encoding lamins A and C. The most common mutation associated with this disease is a homozygous arginine 527 replacement by histidine. Three female patients originating from two unrelated families from Northeast Egypt were examined. Their growth was retarded; they had microcephaly, widened cranial sutures, prominent eyes and cheeks, micrognathia, dental crowding, hypoplastic mandible, acro-osteolysis of distal phalanges, and joint contractures. In addition, they presented some progeroid features, such as pinched nose, premature loss of teeth, loss of hair, scleroderma-like skin atrophy, spine rigidity, and waddling gait. The clinical presentation of the disease varied between the patient originating from Family 1 and patients from Family 2, suggesting that unknown, possibly epigenetic factors, modify the course of the disease. The first symptoms of the disease appeared at the age of 2.5 (a girl from Family 1), 5, and 3 years (girls from Family 2). All patients had the same, novel homozygous c.1580G>T LMNA mutation, resulting in the replacement of arginine 527 by leucine. Computational predictions of such substitution effects suggested that it might alter protein stability and increase the tendency for protein aggregation, and as a result, might influence its interaction with other proteins. In addition, restriction fragment-length polymorphism analysis performed in 178 unrelated individuals showed that up to 1.12% of inhabitants of Northeast Egypt might be heterozygous carriers of this mutation, suggesting the presence of a founder effect in this area.

Nuclear mechanics in disease

Over the past two decades, the biomechanical properties of cells have emerged as key players in a broad range of cellular functions, including migration, proliferation, and differentiation. Although much of the attention has focused on the cytoskeletal networks and the cell's microenvironment, relatively little is known about the contribution of the cell nucleus. Here, we present an overview of the structural elements that determine the physical properties of the nucleus and discuss how changes in the expression of nuclear components or mutations in nuclear proteins can not only affect nuclear mechanics but also modulate cytoskeletal organization and diverse cellular functions. These findings illustrate that the nucleus is tightly integrated into the surrounding cellular structure. Consequently, changes in nuclear structure and composition are highly relevant to normal development and physiology and can contribute to many human diseases, such as muscular dystrophy, dilated cardiomyopathy, (premature) aging, and cancer.

Hypoparathyroidism in an Egyptian child with Hutchinson-Gilford progeria syndrome: a case report

INTRODUCTION

Hutchinson-Gilford progeria syndrome is a rare genetic disorder. It is reported to be present in one in eight million and is characterized by severe growth failure, early loss of hair, lipodystrophy, scleroderma, decreased joint mobility, osteolysis, early atherosclerosis and facial features that resemble those of an aged person. Apart from diabetes mellitus, there are no reported abnormalities of thyroid, parathyroid, pituitary or adrenal function. Here, we report the case of a 10-year-old Egyptian child with Hutchinson-Gilford progeria syndrome and hypoparathyroidism.

CASE PRESENTATION

A 10-year-old Egyptian boy was referred to our institution for an evaluation of recurrent attacks of muscle cramps, paresthesia of his fingertips and perioral numbness of two months duration. On examination, we found dilated veins present over his scalp with alopecia and frontal bossing, a beaked nose, thin lips, protruding ears, a high pitched voice with sparse hair over his eyebrows and eyelashes and micrognathia but normal dentition. His eyes appeared prominent and our patient appeared to have poor sexual development. A provisional diagnosis of progeria was made, which was confirmed by molecular genetics study. Chvostek's and Trousseau's signs were positive. He had low total calcium (5.4 mg/dL), low ionized calcium (2.3 mg/dL), raised serum phosphate (7.2 mg/dL), raised alkaline phosphatase (118 U/L) and low intact parathyroid hormone (1.2 pg/mL) levels. He was started on oral calcium salt and vitamin D; his symptoms improved with the treatment and his serum calcium, urinary calcium and alkaline phosphates level were monitored every three months to ensure adequacy of therapy and to avoid hypercalcemia.

CONCLUSION

Routine checking of serum calcium, phosphorus and parathyroid hormone will help in the early detection of hypoparathyrodism among children with progeria.

Premature aging syndrome

Hutchinson-Gilford progeria syndrome and Werner syndrome are two of the best characterized human progeroid diseases with clinical features mimicking physiological aging at an early age. Both disorders have been the focus of intense research in recent years since they might provide insights into the pathology of normal human aging. The chapter contains a detailed description of the clinical features of both disorders and then it focuses on the genetics, the resulting biochemical alterations at the protein level and the most recent findings and hypotheses concerning the molecular basis of the premature aging phenotypes. A description of available diagnostic and therapeutic approaches is included.

[Laminopathies: one gene, several diseases]

Lamins A and C, encoded by the LMNA gene, are nuclear proteins expressed in all post-mitotic cells. Together with B-type lamins, they form a meshwork of proteins beneath the inner nuclear membrane, the lamina, in connection with the cytoskeleton. Lamins A/C also interact with chromatin and numerous proteins, including transcription factors. Mutations in LMNA are responsible for more than ten different disorders, commonly called "laminopathies". These diseases affect tissues in a specific (striated muscle, adipose tissue, peripheral nerve) or in a systemic manner (premature ageing syndromes). This wide spectrum of phenotypes is associated to a wide variety of mutations. This large clinical and genetic heterogeneity, unique to the LMNA gene, makes genotype-phenotype relations particularly difficult to establish. However, correlations have been obtained in several cases. Hence, LMNA mutations identified in premature ageing syndromes lead to the accumulation of immature proteins with a toxic effect for cells. Mutations in laminopathies of the adipose tissue mainly localize in the Ig-like domain of the proteins, potentially affecting the interaction with the SREBP-1 transcription factor. In laminopathies of the striated muscles, the mutations are spread throughout the gene. These mutations are thought to induce structural modifications of the proteins, thereby affecting their polymerization into nuclear lamina. Such defect would lead to a mechanical weakness of the nuclear lamina and of the cells, particularly in striated muscles continuously stretching. The exploration of pathophysiological mechanisms of LMNA mutations largely benefits from the numerous mouse models created, which have been widely used to analyze affected molecular pathways and to test putative therapeutic treatments.

Discordant gene expression signatures and related phenotypic differences in lamin A- and A/C-related Hutchinson-Gilford progeria syndrome (HGPS)

Hutchinson-Gilford progeria syndrome (HGPS) is a genetic disorder displaying features reminiscent of premature senescence caused by germline mutations in the LMNA gene encoding lamin A and C, essential components of the nuclear lamina. By studying a family with homozygous LMNA mutation (K542N), we showed that HGPS can also be caused by mutations affecting both isoforms, lamin A and C. Here, we aimed to elucidate the molecular mechanisms underlying the pathogenesis in both, lamin A- (sporadic) and lamin A and C-related (hereditary) HGPS. For this, we performed detailed molecular studies on primary fibroblasts of hetero- and homozygous LMNA K542N mutation carriers, accompanied with clinical examinations related to the molecular findings. By assessing global gene expression we found substantial overlap in altered transcription profiles (13.7%; 90/657) in sporadic and hereditary HGPS, with 83.3% (75/90) concordant and 16.7% (15/90) discordant transcriptional changes. Among the concordant ones we observed down-regulation of TWIST2, whose inactivation in mice and humans leads to loss of subcutaneous fat and dermal appendages, and loss of expression in dermal fibroblasts and periadnexial cells from a LMNA^K542N/K542N patient further confirming its pivotal role in skin development. Among the discordant transcriptional profiles we identified two key mediators of vascular calcification and bone metabolism, ENPP1 and OPG, which offer a molecular explanation for the major phenotypic differences in vascular and bone disease in sporadic and hereditary HGPS. Finally, this study correlates reduced TWIST2 and OPG expression with increased osteocalcin levels, thereby linking altered bone remodeling to energy homeostasis in hereditary HGPS.

Beyond membrane channelopathies: alternative mechanisms underlying complex human disease

Over the past fifteen years, our understanding of the molecular mechanisms underlying human disease has flourished in large part due to the discovery of gene mutations linked with membrane ion channels and transporters. In fact, ion channel defects ("channelopathies" - the focus of this review series) have been associated with a spectrum of serious human disease phenotypes including cystic fibrosis, cardiac arrhythmia, diabetes, skeletal muscle defects, and neurological disorders. However, we now know that human disease, particularly excitable cell disease, may be caused by defects in non-ion channel polypeptides including in cellular components residing well beneath the plasma membrane. For example, over the past few years, a new class of potentially fatal cardiac arrhythmias has been linked with cytoplasmic proteins that include sub-membrane adapters such as ankyrin-B (ANK2), ankyrin-G (ANK3), and alpha-1 syntrophin, membrane coat proteins including caveolin-3 (CAV3), signaling platforms including yotiao (AKAP9), and cardiac enzymes (GPD1L). The focus of this review is to detail the exciting role of lamins, yet another class of gene products that have provided elegant new insight into human disease.

Early onset mandibuloacral dysplasia due to compound heterozygous mutations in ZMPSTE24

Mandibuloacral dysplasia (MAD) is an autosomal recessive disorder characterized by hypoplasia of the mandible and clavicles, acro-osteolysis, and lipodystrophy due to mutations in LMNA or ZMPSTE24. Only six MAD patients are reported so far with ZMPSTE24 mutations and limited phenotypic data are available for them. Here, we report on two brothers (4 years and 9-month old) with early onset MAD due to ZMPSTE24 mutations in whom thin skin was noted as early as 5 months of age. Both had micrognathia, mottled hyperpigmentation, and enlarged fontanelles but little evidence of lipodystrophy. There was no delay of mental development. The older brother had small pinched nose, short clavicles, acro-osteolysis, stunted growth, joint stiffness, and repeated fractures. There was no evidence of renal disease. Both patients were compound heterozygotes harboring a previously reported missense ZMPSTE24 mutation, p.Pro248Leu, and a novel null mutation, p.Trp450stop. These patients and the review of literature reveal that compared to MAD patients with LMNA mutations, those with ZMPSTE24 mutations develop manifestations earlier in life. Other distinguishing features in MAD due to ZMPSTE24 mutations may include premature birth, renal disease, calcified skin nodules, and lack of acanthosis nigricans. We conclude that in patients with MAD due to ZMPSTE24 mutations, the onset of disease manifestations such as thin skin and micrognathia occurs as early as 5 months of age. In these patients, skeletal phenotype presents earlier whereas lipodystrophy and renal disease may occur later in life.

[Three cases of Hutchinson-Gilford progeria syndrome]

Progeria, or Hutchinson-Gilford syndrome, is a rare genetic disease, characterized by several clinical features that develop in childhood, in particular, an accelerated aging aspect. Its incidence is 1-4 per 8 million newborns. Children with progeria syndrome usually appear normal at birth and in early infancy. Profound failure to thrive occurs during the 1st year. Characteristic facies, partial alopecia progressing to total alopecia, loss of subcutaneous fat, stiffness of joints, bone changes, and abnormal tightness of the skin over the abdomen and upper thighs usually become apparent during the 2nd to 3rd years. Motor and mental development is normal. Patients develop severe atherosclerosis. Death occurs as a result of complications of cardiac or cerebrovascular disease (heart attack or stroke) generally between ages 6 and 20 years. The diagnosis of Hutchinson-Gilford progeria syndrome (HGPS) is based on recognition of common clinical features and the detection of the recurrent p.Gly608Gly mutation in exon 11 of the LMNA gene, which is present in almost all individuals with HGPS. We present here 3 patients aged 5, 11, and 12 years referred to genetic consultation for dysmorphic facies and failure to thrive. After careful clinical examination and paraclinical assessment, the diagnosis of progeria syndrome was raised. We performed molecular analysis for the 3 patients by searching for the recurrent mutation c.1824C>T (p.Gly608Gly) of the LMNA gene, which was found only in 1 patient. We discuss the geneticist's role in the diagnosis of rare dysmorphic syndromes and their genetic counseling. We also analyze the clinical spectrum of HGPS by comparing the 3 patients.

Skeletal phenotype of mandibuloacral dysplasia associated with mutations in ZMPSTE24

Mandibuloacral dysplasia (MAD) is a rare recessively inherited premature aging disease characterized by skeletal and metabolic anomalies. It is part of the spectrum of diseases called laminopathies and results from mutations in genes regulating the synthesis of the nuclear laminar protein, lamin A. Homozygous or compound heterozygous mutations in the LMNA gene, which encodes both the precursor protein prelamin A and lamin C, are the commonest cause of MAD type A. In a few cases of MAD type B, mutations have been identified in the ZMPSTE24 gene encoding a zinc metalloproteinase important in the post-translational modification of lamin A. Here we describe a new case of MAD resulting from compound heterozygote mutations in ZMPSTE24 (p.N256S/p.Y70fs). The patient had typical skeletal changes of MAD, but in addition a number of unusual skeletal features including neonatal tooth eruption, amorphous calcific deposits, submetaphyseal erosions, vertebral beaking, severe cortical osteoporosis and delayed fracture healing. Treatment with conventional doses of pamidronate improved estimated volumetric bone density in the spine but did not arrest cortical bone loss. We reviewed the literature on cases of MAD associated with proven LMNA and ZMPSTE24 mutations and found that the unusual features described above were all substantially more prevalent in patients with mutations in ZMPSTE24 than in those with LMNA mutations. We conclude that MAD associated with ZMPSTE24 mutations has a more severe phenotype than that associated with LMNA mutations--probably reflecting the greater retention of unprocessed farnesylated prelamin A in the nucleus, which is toxic to cells.

Lamin A-linked progerias: is farnesylation the be all and end all?

HGPS (Hutchinson–Gilford progeria syndrome) is a severe childhood disorder that appears to mimic an accelerated aging process. The disease is most commonly caused by gene mutations that disrupt the normal post-translational processing of lamin A, a structural component of the nuclear envelope. Impaired processing results in aberrant retention of a farnesyl group at the C-terminus of lamin A, leading to altered membrane dynamics. It has been widely proposed that persistence of the farnesyl moiety is the major factor responsible for the disease, prompting clinical trials of farnesyltransferase inhibitors to prevent lamin A farnesylation in children afflicted with HGPS. Although there is evidence implicating farnesylation in causing some of the cellular defects of HGPS, results of several recent studies suggest that aberrant lamin A farnesylation is not the only determinant of the disease. These findings have important implications for the design of treatments for this devastating disease.

Mandibuloacral dysplasia type A in childhood

Mandibuloacral dysplasia type A (MADA) is characterized by growth retardation, postnatal onset of craniofacial anomalies with mandibular hypoplasia, progressive acral osteolysis, and skin changes including mottled pigmentation, skin atrophy, and lipodystrophy. Owing to its slowly progressive course, the syndrome has been recognized in adults, and pediatric case reports are scarce. We present the clinical case of two children in whom the diagnosis of MADA was made at an unusually early age. A 5-year-old boy presented with ocular proptosis, thin nose, and short and bulbous distal phalanges of fingers. A 4-year-old girl presented with round face and chubby cheeks, thin nose, bulbous fingertips, and type A lipodystrophy. In both, a skeletal survey showed wormian bones, thin clavicles, short distal phalanges of fingers and toes with acro-osteolysis. Both children were found to be homozygous for the recurrent missense mutation, c.1580G>A, (p.R527H) in exon 9 of the LMNA gene. Thus, the phenotype of MADA can be manifest in preschool age; diagnosis may be suggested by short and bulbous fingertips, facial features, and lipodystrophy, supported by the finding of acral osteolysis, and confirmed by mutation analysis.

Atypical progeroid syndrome due to heterozygous missense LMNA mutations

CONTEXT

Hutchinson-Gilford progeria syndrome (HGPS) and mandibuloacral dysplasia are well-recognized allelic autosomal dominant and recessive progeroid disorders, respectively, due to mutations in lamin A/C (LMNA) gene. Heterozygous LMNA mutations have also been reported in a small number of patients with a less well-characterized atypical progeroid syndrome (APS).

OBJECTIVE

The objective of the study was to investigate the underlying genetic and molecular basis of the phenotype of patients presenting with APS.

RESULTS

We report 11 patients with APS from nine families, many with novel heterozygous missense LMNA mutations, such as, P4R, E111K, D136H, E159K, and C588R. These and previously reported patients now reveal a spectrum of clinical features including progeroid manifestations such as short stature, beaked nose, premature graying, partial alopecia, high-pitched voice, skin atrophy over the hands and feet, partial and generalized lipodystrophy with metabolic complications, and skeletal anomalies such as mandibular hypoplasia and mild acroosteolysis. Skin fibroblasts from these patients when assessed for lamin A/C expression using epifluorescence microscopy revealed variable nuclear morphological abnormalities similar to those observed in patients with HGPS. However, these nuclear abnormalities in APS patients could not be rescued with 48 h treatment with farnesyl transferase inhibitors, geranylgeranyl transferase inhibitors or trichostatin-A, a histone deacetylase inhibitor. Immunoblots of cell lysates from fibroblasts did not reveal prelamin A accumulation in any of these patients.

CONCLUSIONS

APS patients have a few overlapping but some distinct clinical features as compared with HGPS and mandibuloacral dysplasia. The pathogenesis of clinical manifestations in APS patients seems not to be related to accumulation of mutant farnesylated prelamin A.

Homozygous LMNA mutation R527C in atypical Hutchinson-Gilford progeria syndrome: evidence for autosomal recessive inheritance

AIM

To describe two Chinese siblings of atypical Hutchinson-Gilford progeria syndrome (HGPS), with genetic diagnosis and special clinical manifestation.

METHODS

We screened the LMNA gene in four members of a consanguineous family, in which two children were suffering from atypical HGPS. Besides general HGPS features, such as growth retardation and characteristic appearance, special clinical phenotypes including disorders of digestive system and severe skeletal damages were observed.

RESULTS

Homozygous mutation 1579C>T, which predicts R527C, was identified in the exon 9 of LMNA among the affected siblings. Heterozygous carrier status 1579C>T was detected in both of the asymptomatic parents.

CONCLUSION

Homozygous mutation R527C in LMNA yields atypical HGPS, and it suggests an autosomal recessive inheritance in this family.

Recent insights into the molecular mechanisms involved in aging and the malignant transformation of adult stem/progenitor cells and their therapeutic implications

Recent advancements in tissue-resident adult stem/progenitor cell research have revealed that enhanced telomere attrition, oxidative stress, ultraviolet radiation exposure and oncogenic events leading to severe DNA damages and genomic instability may occur in these immature and regenerative cells during chronological aging. Particularly, the alterations in key signaling components controlling their self-renewal capacity and an up-regulation of tumor suppressor gene products such as p16(INK4A), p19(ARF), ataxia-telangiectasia mutated (ATM) kinase, p53 and/or the forkhead box O (FOXOs) family of transcription factors may result in their dysfunctions, growth arrest and senescence or apoptotic death during the aging process. These molecular events may culminate in a progressive decline in the regenerative functions and the number of tissue-resident adult stem/progenitor cells, and age-related disease development. Conversely, the telomerase re-activation and accumulation of numerous genetic and/or epigenetic alterations in adult stem/progenitor cells with advancing age may result in their immortalization and malignant transformation into highly leukemic or tumorigenic cancer-initiating cells and cancer initiation. Therefore, the cell-replacement and gene therapies and molecular targeting of aged and dysfunctional adult stem/progenitor cells including their malignant counterpart, cancer-initiating cells, hold great promise for treating and even curing diverse devastating human diseases. These diseases include premature aging diseases, hematopoietic, cardiovascular, musculoskeletal, pulmonary, ocular, urogenital, neurodegenerative and skin disorders and aggressive and recurrent cancers.

Microcephalia with mandibular and dental dysplasia in adult Zmpste24-deficient mice

ZMPSTE24 (also called FACE-1) is a zinc-metalloprotease involved in the post-translational processing of prelamin A to mature lamin A, a major component of the nuclear envelope. Mutations in the ZMPSTE24 gene or in that encoding its substrate prelamin A (LMNA) result in a series of human inherited diseases known collectively as laminopathies and showing regional or systemic manifestations (i.e. the Hutchinson-Gilford progeria syndrome). Typically, patients suffering some laminopathies show craniofacial or mandible anomalies, aberrant dentition or facial features characteristic of aged persons. To analyse whether Zmpste24(-/-) mice reproduce the cranial phenotype observed in humans due to mutations in ZMPSTE24 or LMNA, we conducted a craniometric study based on micro-computer tomography (microCT) images. Furthermore, using simple radiology, microCT, microCT-densitometry and scanning electron microscopy, we analysed the mandible and the teeth from Zmpste24(-/-) mice. Finally, the structure of the lower incisor was investigated using an H&E technique. The results demonstrate that Zmpste24(-/-) mice are microcephalic and show mandibular and dental dysplasia affecting only the mandible teeth. In all cases, the lower incisor of mice lacking Zmpste24 was smaller than in control animals, showed cylindrical morphology and a transverse fissure at the incisal edge, and the pulpal cavity was severely reduced. Structurally, the dental layers were normally arranged but cellular layers were disorganized. The inferior molars showed a reduced cusp size. Taken together, these data strongly suggest that Zmpste24(-/-) mice represent a good model to analyse the craniofacial and teeth malformations characteristic of lamin-related pathologies, and might contribute to a better understanding of the molecular events underlying these diseases.

Severe mandibuloacral dysplasia-associated lipodystrophy and progeria in a young girl with a novel homozygous Arg527Cys LMNA mutation

CONTEXT

Mandibuloacral dysplasia (MAD) is a rare autosomal recessive progeroid syndrome due to mutations in genes encoding nuclear lamina proteins, lamins A/C (LMNA) or prelamin A processing enzyme, and zinc metalloproteinase (ZMPSTE24).

OBJECTIVE

The aim of the study was to investigate the underlying genetic and molecular basis of the phenotype of a 7-yr-old girl with MAD belonging to a consanguineous pedigree and with severe progeroid features and lipodystrophy.

DESIGN AND PATIENT

The patient developed mandibular hypoplasia during infancy and joint stiffness, skin thinning, and mottled hyperpigmentation at 15 months. Progressive clavicular hypoplasia, acroosteolysis, and severe loss of hair from the temporal and occipital areas were noticed at 3 yr. At 5 yr, cranial sutures were still open and lipodystrophy of the limbs was prominent. GH therapy from the ages of 3-7 yr did not improve the short stature. Severe joint contractures resulted in abnormal posture and decreased mobility. We studied her skin fibroblasts for nuclear morphology and immunoblotting and determined the in vitro effects of various pharmacological interventions on fibroblasts.

RESULTS

LMNA gene sequencing revealed a homozygous missense mutation, c.1579C>T, p.Arg527Cys. Immunoblotting of skin fibroblast lysate with lamin A/C antibody revealed no prelamin A accumulation. Immunofluorescence staining of the nuclei for lamin A/C in fibroblasts revealed marked nuclear morphological abnormalities. This abnormal phenotype could not be rescued with inhibitors of farnesyl transferase, geranylgeranyl transferase, or histone deacetylase.

CONCLUSION

Severe progeroid features in MAD could result from LMNA mutation, which does not lead to accumulation of prenylated lamin A or prelamin A.

Is schizophrenia a syndrome of accelerated aging?

Schizophrenia is associated with a number of anatomical and physiological abnormalities outside of the brain, as well as with a decrease in average life span estimated at 20% in the United States. Some studies suggest that this increased mortality is not entirely due to associated causes such as suicide and the use of psychotropic medications. In this article, in order to focus greater attention on the increased mortality associated with schizophrenia, we present a special case of the hypothesis that physiological abnormalities associated with schizophrenia make a contribution to the increased mortality of schizophrenia: specifically, the hypothesis that schizophrenia is a syndrome of accelerated aging. Evidence consistent with this hypothesis comes from several areas. The biological plausibility of the hypothesis is supported by the existence of established syndromes of accelerated aging and by the sharing of risk factors between schizophrenia and other age-related conditions. We propose methods for testing the hypothesis.

Progeria caused by a rare LMNA mutation p.S143F associated with mild myopathy and atrial fibrillation

We present a 6-year-old girl with premature aging associated with mild myopathy, displaying muscle weakness, joint contractures and hyporeflexia. Genetic analysis revealed rare heterozygous point mutation in lamin A/C gene, g.428C>T. Cardiological evaluation showed atrial fibrillation, but we did not find signs of coronary heart disease, which is life-threatening cardiovascular complication in progeria. Electron microscopy of the muscle revealed abnormalities in nuclear architecture, i.e. blebbing, thick lamina and peripheral distribution of heterochromatin. As some diagnostic criteria characteristic for classic progeria are not fulfilled, this case could be regarded as atypical progeria associated with myopathy and atrial fibrillation. To our knowledge, this is the second case of such association described in the literature.

Severe mandibuloacral dysplasia caused by novel compound heterozygous ZMPSTE24 mutations in two Japanese siblings

Mandibuloacral dysplasia (MAD) is a rare autosomal recessive progeroid syndrome, characterized by mandibular hypoplasia, acroosteolysis affecting distal phalanges and clavicles, delayed closure of the cranial sutures, atrophic skin, and lipodystrophy. Recently, mutations in lamin A/C (LMNA) and zinc metalloprotease (ZMPSTE24), involved in post-translational processing of prelamin A to mature lamin A, have been identified in MAD kindreds. We now report novel compound heterozygous mutations in exon 1 (c.121C>T; p.Q41X) and exon 6 (c.743C>T; p.P248L) in ZMPSTE24 in two Japanese sisters, 7- and 3-year old, with severe MAD and characteristic facies and atrophic skin. The older sister had lipodystrophy affecting the chest and thighs but sparing abdomen. Their parents and a brother, who were healthy, had heterozygous mutations. The missense mutation, P248L, was not found in 100 normal subjects of Japanese origin. The mutant Q41X was inactive in a yeast halo assay; however, the mutant P248L retained near normal ZMPSTE24 activity. Immunoblots demonstrated accumulation of prelamin A in the patients' cell lysates from lymphoblasts. The lymphoblasts from the patients also revealed less intense staining for lamin A/C on immunofluorescence. We conclude that ZMPSTE24 deficiency results in accumulation of farnesylated prelamin A, which may be responsible for cellular toxicity and the MAD phenotype.

The laminopathies: the functional architecture of the nucleus and its contribution to disease

Most inherited diseases are associated with mutations in a specific gene. Often, mutations in two or more different genes result in diseases with a similar phenotype. Rarely do different mutations in the same gene result in a multitude of seemingly different and unrelated diseases. Mutations in the Lamin A gene (LMNA), which encodes largely ubiquitously expressed nuclear proteins (A-type lamins), are associated with at least eight different diseases, collectively called the laminopathies. Studies examining how different tissue-specific diseases arise from unique LMNA mutations are providing unanticipated insights into the structural organization of the nucleus, and how disruption of this organization relates to novel mechanisms of disease.

Genetic disorders of adipose tissue development, differentiation, and death

Lack of adipose tissue, either complete or partial, is the hallmark of disorders known as lipodystrophies. Patients with lipodystrophies suffer from metabolic complications similar to those associated with obesity, including insulin resistance, type 2 diabetes, hypertriglyceridemia, and hepatic steatosis. The loss of body fat in inherited lipodystrophies can be caused by defects in the development and/or differentiation of adipose tissue as a consequence of mutations in a number of genes, including PPARG (encoding a nuclear hormone receptor), AGPAT2 (encoding an enzyme involved in the biosynthesis of triglyceride and phospholipids), AKT2 (encoding a protein involved in insulin signal transduction), and BSCL2 (encoding seipin, whose role in the adipocyte biology remains unclear). The loss of body fat can also be caused by the premature death of adipocytes due to mutations in lamin A/C, nuclear lamina proteins, and ZMPSTE24, which modifies the prelamin A post-translationally. In this review, we focus on the molecular basis of inherited lipodystrophies as they relate to adipocyte biology and their associated phenotypic manifestations.