Abolishing the prelamin A ZMPSTE24 cleavage site leads to progeroid phenotypes with near-normal longevity in mice.

Prelamin A is a farnesylated precursor of lamin A, a nuclear lamina protein. Accumulation of the farnesylated prelamin A variant progerin, with an internal deletion including its processing site, causes Hutchinson-Gilford progeria syndrome. Loss-of-function mutations in ZMPSTE24, which encodes the prelamin A processing enzyme, lead to accumulation of full-length farnesylated prelamin A and cause related progeroid disorders. Some data suggest that prelamin A also accumulates with physiological aging. Zmpste24-/- mice die young, at ∼20 wk. Because ZMPSTE24 has functions in addition to prelamin A processing, we generated a mouse model to examine effects solely due to the presence of permanently farnesylated prelamin A. These mice have an L648R amino acid substitution in prelamin A that blocks ZMPSTE24-catalyzed processing to lamin A. The LmnaL648R/L648R mice express only prelamin and no mature protein. Notably, nearly all survive to 65 to 70 wk, with ∼40% of male and 75% of female LmnaL648R/L648R mice having near-normal lifespans of 90 wk (almost 2 y). Starting at ∼10 wk of age, LmnaL648R/L648R mice of both sexes have lower body masses than controls. By ∼20 to 30 wk of age, they exhibit detectable cranial, mandibular, and dental defects similar to those observed in Zmpste24-/- mice and have decreased vertebral bone density compared to age- and sex-matched controls. Cultured embryonic fibroblasts from LmnaL648R/L648R mice have aberrant nuclear morphology that is reversible by treatment with a protein farnesyltransferase inhibitor. These novel mice provide a model to study the effects of farnesylated prelamin A during physiological aging.

A recurrent homozygous LMNA missense variant p.Thr528Met causes atypical progeroid syndrome characterized by mandibuloacral dysostosis, severe muscular dystrophy, and skeletal deformities.

Atypical progeroid syndromes (APS) are premature aging syndromes caused by pathogenic LMNA missense variants, associated with unaltered expression levels of lamins A and C, without accumulation of wild-type or deleted prelamin A isoforms, as observed in Hutchinson-Gilford progeria syndrome (HGPS) or HGPS-like syndromes. A specific LMNA missense variant, (p.Thr528Met), was previously identified in a compound heterozygous state in patients affected by APS and severe familial partial lipodystrophy, whereas heterozygosity was recently identified in patients affected by Type 2 familial partial lipodystrophy. Here, we report four unrelated boys harboring homozygosity for the p.Thr528Met, variant who presented with strikingly homogeneous APS clinical features, including osteolysis of mandibles, distal clavicles and phalanges, congenital muscular dystrophy with elevated creatine kinase levels, and major skeletal deformities. Immunofluorescence analyses of patient-derived primary fibroblasts showed a high percentage of dysmorphic nuclei with nuclear blebs and typical honeycomb patterns devoid of lamin B1. Interestingly, in some protrusions emerin or LAP2α formed aberrant aggregates, suggesting pathophysiology-associated clues. These four cases further confirm that a specific LMNA variant can lead to the development of strikingly homogeneous clinical phenotypes, in these particular cases a premature aging phenotype with major musculoskeletal involvement linked to the homozygous p.Thr528Met variant.

PRMT6/LMNA/CXCL12 signaling pathway regulated the osteo/odontogenic differentiation ability in dental stem cells isolated from apical papilla.

Tooth loss and maxillofacial bone defect are common diseases, which seriously affect people's health. Effective tooth and maxillofacial bone tissue regeneration is a key problem that need to be solved. In the present study, we investigate the role of PRMT6 in osteo/odontogenic differentiation and migration capacity by using SCAPs. Our results showed that knockdown of PRMT6 promoted the osteo/odontogenic differentiation compared with the control group, as detected by alkaline phosphatase activity, alizarin red staining, and the indicators of osteo/odontogenic differentiation measured by Western blot. In addition, overexpression of PRMT6 inhibited the osteo/odontogenic differentiation potentials of SCAPs. Then, knockdown of PRMT6 promoted the migration ability and overexpression of PRMT6 inhibited the migration ability in SCAPs. Mechanically, we discovered that the depletion of PRMT6 promoted the expression of CXCL12 by decreasing H3R2 methylation in the promoter region of CXCL12. In addition, PRMT6 formed a protein complex with LMNA, a nuclear structural protein. Depletion of LMNA inhibited the osteo/odontogenic differentiation and CXCL12 expression and increased the intranucleus PRMT6 in SCAPs. To sum up, PRMT6 might inhibit the osteo/odontogenic differentiation and migration ability of SCAPs via inhibiting CXCL12. And LMNA might be a negative regulator of PRMT6. It is suggested that PRMT6 may be a key target for SCAP-mediated bone and tooth tissue regeneration.

Diagnosis and genetic analysis of a case with mandibuloacral dysplasia type B due to compound heterozygous mutations of the ZMPSTE24 gene.

Mandibuloacral dysplasia (MAD) is a rare autosomal recessive disorder, mainly caused by pathogenic variants of the LMNA and ZMPSTE24 genes. In this study, we reported the first case of a patient with type B cranial and mandibular dysplasia in China. The patient presented with distinctive facial features, feeding difficulties, significant physical retardation, and overall developmental delay with abnormal tooth and bone development. Trio-whole exome sequencing analysis showed that the patient carried compound heterozygous mutations of c.743C>T (p.Pro248Leu) (dbSNP: rs121908095) and the loss of exons 1-10 of the ZMPSTE24 gene. Sanger sequencing and real-time quantitative PCR (RT-qPCR) showed that these two mutations were inherited from the patient's phenotypically normal mother and father, respectively. By summarizing and analyzing the characteristics of this case and the pedigree of the family, we suggested that trio-whole-exome sequencing could be performed to assist in the diagnosis of diseases that are difficult to be diagnosed definitively based on clinical phenotypes. The publication of this case has improved clinicians' understanding of MAD disease and provide new clinical information for the subsequent genetic study of this disease.

A novel autosomal recessive lipodystrophy syndrome due to homozygous LMNA variant.

BACKGROUND: Despite major advances in understanding the molecular basis of various genetic lipodystrophy syndromes, some rare patients still remain unexplained. CASES: We report a novel autosomal recessive lipodystrophy affecting two sisters aged 17 and 19 years and characterised by early onset intellectual disability, and subsequent development of near-generalised loss of subcutaneous fat with diabetes mellitus, extreme hypertriglyceridemia, hepatic steatosis, short stature, clinodactyly, joint contractures, leiomyoma of uterus and cataracts in childhood. The lipodystrophy was more pronounced in the upper and lower extremities, and there was no associated muscular hypertrophy. Using whole exome sequencing in this consanguineous Hispanic pedigree, we report disease-causing homozygous p.Arg545His LMNA variant in the affected subjects, and confirm the lack of pathogenic variants in other known lipodystrophy genes. The mother and a younger brother were both heterozygous for p.Arg545His LMNA variant and were overweight with acanthosis nigricans without any evidence of lipodystrophy. Our patients are distinct from previously reported autosomal recessive lipodystrophy syndromes and have no overlap with other autosomal recessive laminopathies, including mandibuloacral dysplasia, Emery-Dreifuss muscular dystrophy and Charcot-Marie-Tooth neuropathy. CONCLUSION: Our report of this unusual familial generalised lipodystrophy syndrome adds to the pleiotropy associated with biallelic autosomal recessive LMNA variants.

Hutchinson-Gilford Progeria syndrome: Report of the first Togolese case.

The aim of this article is to describe the first case of Hutchinson-Gilford Progeria Syndrome (HGPS) in Togo and review all Africans cases. Our patient was a 12.8-year-old Togolese boy followed in our unit till he was 15-year-old for HGPS. He was the only child of non-consanguineous parents. The phenotypic findings were craniofacial dysmorphy, dwarfism, lipodystrophy, diffusely scattered hyperpigmented foci, pyriform thorax, nail dystrophy, decreased joint mobility, and camptodactyly. He had characteristic facies with prominent forehead, prominent eyes, absent ear lobule, thin nasal skin, convex nasal profile, micrognathia, and crowded teeth. Radiologicals findings were bilateral coxa valga, pyriform thorax, and acro-osteolysis. We sequenced the entire coding region of LMNA gene, and mutation analysis revealed a heterozygous mutation c.1824C>T (p.Gly608Gly). Our patient is therefore the fifth African and the fourth with classical mutation, first of Western Africa, and second of (sub-Saharan) African black race. The recurrence of HGPS is low like the cause is neomutation or germinal mosaicism.

A case of generalized lipodystrophy-associated progeroid syndrome treated by leptin replacement with short and long-term monitoring of the metabolic and endocrine profiles.

We herein report a case of a 28-year-old man with generalized lipodystrophy-associated progeroid syndrome treated by leptin replacement. He showed symptoms of generalized lipodystrophy around onset of puberty. His body mass index was 11.9 kg/m2, and he had a short stature, birdlike facies, dental crowding due to micrognathia, partial graying and loss of hair, and a high-pitched voice, all of which are typical features of the progeroid syndrome. Laboratory examinations and abdominal ultrasonography revealed diabetes mellitus, insulin-resistance, dyslipidemia, decreased serum leptin levels (2.2 ng/mL), elevated serum hepatobiliary enzyme levels and fatty liver. Whole exome sequencing revealed de novo heterozygous LMNA p.T10I mutation, indicating generalized lipodystrophy-associated progeroid syndrome, which is a newly identified subtype of atypical progeroid syndrome characterized by severe metabolic abnormalities. Daily injection of metreleptin [1.2 mg (0.04 mg/kg)/day] was started. Metreleptin treatment significantly improved his diabetes from HbA1c 11.0% to 5.4% in six months. It also elevated serum testosterone levels. Elevated serum testosterone levels persisted even 1 year after the initiation of metreleptin treatment. To the best of our knowledge, this is the first Japanese case report of generalized lipodystrophy-associated progeroid syndrome. Furthermore, we evaluated short and long-term effectiveness of leptin replacement on generalized lipodystrophy by monitoring metabolic and endocrine profiles.

Forced expression of mouse progerin attenuates the osteoblast differentiation interrupting ß-catenin signal pathway in vitro.

Nuclear protein, lamin A, which is a component of inner membrane on nucleoplasm, plays a role in nuclear formation and cell differentiation. The expression of mutated lamin A, termed progerin, causes a rare genetic aging disorder, Hutchinson-Gilford progeria syndrome, which shows abnormal bone formation with the decrease in a number of osteoblasts and osteocytes. However, exact molecular mechanism how progerin exerts depressive effects on osteogenesis has not been fully understood. Here, we created mouse lamin A dC50 cDNA encoding progerin that lacks 50 amino acid residues at C-terminus, transfected it in mouse preosteoblast-like MC3T3-E1 cells, and examined the changes in osteoblast phenotype. When lamin A dC50-expressed cells were cultured with differentiation-inductive medium, alkaline phosphatase (ALP) activity and mRNA levels of major osteoblast markers, type I collagen (Col1), bone sialoprotein (BSP), dentine matrix protein 1 (DMP1), and Runx2 were significantly decreased, and no mineralized nodules were detected as seen in control cells expressing empty vector. In the culture with mineralization-inductive medium, mRNA levels of BSP, osteocalcin, DMP1, Runx2, and osterix were strongly decreased parallel with loss of mineralization in lamin A dC50-expressed cells, while mineralized nodules appear at 21 days in control cells. Furthermore, lamin A dC50 expression was depressed nuclear localization of ß-catenin with the decrease of GSK-3ß phosphorylation level. These results suggest that lamin A dC50 depresses osteoblast differentiation in both early and late stages, and it negatively regulates ß-catenin activity interacting with GSK-3ß in cytoplasm.

Differential basal-to-apical accessibility of lamin A/C epitopes in the nuclear lamina regulated by changes in cytoskeletal tension.

Nuclear lamins play central roles at the intersection between cytoplasmic signalling and nuclear events. Here, we show that at least two N- and C-terminal lamin epitopes are not accessible at the basal side of the nuclear envelope under environmental conditions known to upregulate cell contractility. The conformational epitope on the Ig-domain of A-type lamins is more buried in the basal than apical nuclear envelope of human mesenchymal stem cells undergoing osteogenesis (but not adipogenesis), and in fibroblasts adhering to rigid (but not soft) polyacrylamide hydrogels. This structural polarization of the lamina is promoted by compressive forces, emerges during cell spreading, and requires lamin A/C multimerization, intact nucleoskeleton-cytoskeleton linkages (LINC), and apical-actin stress-fibre assembly. Notably, the identified Ig-epitope overlaps with emerin, DNA and histone binding sites, and comprises various laminopathy mutation sites. Our findings should help decipher how the physical properties of cellular microenvironments regulate nuclear events.

LMNA-Mediated Arrhythmogenic Right Ventricular Cardiomyopathy and Charcot-Marie-Tooth Type 2B1: A Patient-Discovered Unifying Diagnosis.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an uncommon cardiomyopathy most classically associated with mutations in genes encoding desmosomal proteins. Recent literature has identified mutations in several non-desmosomal proteins including lamins that may result in the ARVC phenotype. We describe a patient who discovered her own pathogenic LMNA mutation that offered a unifying diagnosis explaining her ARVC and Charcot-Marie-Tooth phenotypes as well as musculoskeletal abnormalities. Suspicion for LMNA-mediated cardiomyopathy should arise in patients with extracardiac manifestations of laminopathies and testing for specific gene mutations may be helpful in establishing an unifying diagnosis.

Transgene silencing of the Hutchinson-Gilford progeria syndrome mutation results in a reversible bone phenotype, whereas resveratrol treatment does not show overall beneficial effects.

Hutchinson-Gilford progeria syndrome (HGPS) is a rare premature aging disorder that is most commonly caused by a de novo point mutation in exon 11 of the LMNA gene, c.1824C>T, which results in an increased production of a truncated form of lamin A known as progerin. In this study, we used a mouse model to study the possibility of recovering from HGPS bone disease upon silencing of the HGPS mutation, and the potential benefits from treatment with resveratrol. We show that complete silencing of the transgenic expression of progerin normalized bone morphology and mineralization already after 7 weeks. The improvements included lower frequencies of rib fractures and callus formation, an increased number of osteocytes in remodeled bone, and normalized dentinogenesis. The beneficial effects from resveratrol treatment were less significant and to a large extent similar to mice treated with sucrose alone. However, the reversal of the dental phenotype of overgrown and laterally displaced lower incisors in HGPS mice could be attributed to resveratrol. Our results indicate that the HGPS bone defects were reversible upon suppressed transgenic expression and suggest that treatments targeting aberrant progerin splicing give hope to patients who are affected by HGPS.

A novel lamin A/C gene mutation causing spinal muscular atrophy phenotype with cardiac involvement: report of one case.

BACKGROUND: Mutations of the lamin A/C gene have been associated with several diseases such as Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy and Charcot-Marie-Tooth disease, referred to as laminopathies. Only one report of spinal muscular atrophy and cardiomyopathy phenotype with lamin A/C gene mutations has been published. The concept that lamin A/C gene mutations cause spinal muscular atrophy has not been established. CASE PRESENTATION: We report a man aged 65 years who presented with amyotrophy of lower limbs, arrhythmia and cardiac hypofunction. He showed gait disturbance since childhood, and his family showed similar symptoms. Neurological and electrophysiological findings suggested spinal muscular atrophy type 3. Gene analysis of lamin A/C gene showed a novel nonsense mutation p.Q353X (c.1057C > T). Further investigations revealed that he and his family members had cardiac diseases including atrioventricular block. CONCLUSIONS: We report the first Japanese case of spinal muscular atrophy phenotype associated with lamin A/C mutation. When a patient presents a spinal muscular atrophy phenotype and unexplained cardiac disease, especially when the family history is positive, gene analysis of lamin A/C gene should be considered.

Mandibuloacral dysplasia type A-associated progeria caused by homozygous LMNA mutation in a family from Southern China.

BACKGROUND: Mandibuloacral dysplasia type A (MADA) is a rare autosomal recessive disorder, characterized by growth retardation, skeletal abnormality with progressive osteolysis of the distal phalanges and clavicles, craniofacial anomalies with mandibular hypoplasia, lipodystrophy and mottled cutaneous pigmentation. Some patients may show progeroid features. MADA with partial lipodystrophy, more marked acral, can be caused by homozygous or compound heterozygous mutation in the gene encoding lamin A and lamin C (LMNA). MADA and Hutchinson-Gilford progeria syndrome are caused by the same gene and may represent a single disorder with varying degrees of severity. MAD patients characterized by generalized lipodystrophy (type B) affecting the face as well as extremities and severe progressive glomerulopathy present heterozygous compound mutations in the ZMPSTE24 gene. CASES PRESENTATIONS: We described a rare pedigree from Southern China, among them all three children presented with phenotypes of MADA associated progeria. The two elder sisters had developed severe mandibular hypoplasia associated progeria since the age of 1 year. The eldest sister showed a progressive osteolysis. The youngest son of 10 months showed severer lesions than those of his sisters at the same age, and presented possible muscle damage, and his symptoms progressed gradually. Three genes mutations including LMNA, ZMPSTE24 and BANF1 were tested in the family. LMNA gene sequencing revealed a homozygous missense mutation, c.1579C > T, p.R527C for all three siblings, and heterozygous mutations for their parents, whereas no mutations of ZMPSTE24 and BANF1 genes was detected among them. CONCLUSIONS: The same homozygous mutation of c.1579C > T of LMNA gene led to MADA associated progeria for the present family. The course of osteolysis for MADA is progressive.

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.

A rare LMNA missense mutation causing a severe phenotype of mandibuloacral dysplasia type A: a case report.

OBJECTIVE: To report the case of a girl presenting a severe phenotype of mandibuloacral dysplasia type A (MADA) characterized by prominent osteolytic changes and ectodermal defects, associated with a rare homozygous LMNA missense mutation (c.1579C>T). CASE DESCRIPTION: A 6-year-old girl was evaluated during hospitalization exhibiting the following dysmorphic signs: subtotal alopecia, dysmorphic facies with prominent eyes, marked micrognathia and retrognathia, small beaked nose, teeth crowding and thin lips, generalized lipodystrophy, narrow and sloping shoulders, generalized joint stiffness and bone reabsorption in the terminal phalanges. In dermatological examination, atrophic skin, loss of cutaneous elasticity, hyperkeratosis, dermal calcinosis, and hyperpigmented and hypochromic patches were observed. Radiology exams performed showed bilateral absence of the mandibular condyles, clavicle resorption with local amorphous bone mass confluence with the scapulae, shoulder joints with subluxation and severe bone dysplasia, hip dysplasia, osteopenia and subcutaneous calcifications. COMMENTS: MADA is a rare autosomal recessive disease caused by mutations in LMNA gene. It is characterized by craniofacial deformities, skeletal anomalies, skin alterations, lipodystrophy in certain regions of the body and premature ageing. Typical MADA is caused by the p.R527H mutation in the LMNA gene. However, molecular analysis performed from oral epithelial cells obtained from the patient showed the rare mutation c.1579C>T, p. R527C in the exon 9 of LMNA. This is the sixth family identified with this mutation described in the literature.

Expression of the Hutchinson-Gilford progeria mutation during osteoblast development results in loss of osteocytes, irregular mineralization, and poor biomechanical properties.

Hutchinson-Gilford progeria syndrome (HGPS) is a very rare genetic disorder that is characterized by multiple features of premature aging and largely affects tissues of mesenchymal origin. In this study, we describe the development of a tissue-specific mouse model that overexpresses the most common HGPS mutation (LMNA, c.1824C>T, p.G608G) in osteoblasts. Already at the age of 5 weeks, HGPS mutant mice show growth retardation, imbalanced gait and spontaneous fractures. Histopathological examination revealed an irregular bone structure, characterized by widespread loss of osteocytes, defects in mineralization, and a hypocellular red bone marrow. Computerized tomography analysis demonstrated impaired skeletal geometry and altered bone structure. The skeletal defects, which resemble the clinical features reported for bone disease in HGPS patients, was associated with an abnormal osteoblast differentiation. The osteoblast-specific expression of the HGPS mutation increased DNA damage and affected Wnt signaling. In the teeth, irregular dentin formation, as was previously demonstrated in human progeria cases, caused severe dental abnormalities affecting the incisors. The observed phenotype also shows similarities to reported bone abnormalities in aging mice and may therefore help to uncover general principles of the aging process.

Acro-osteolysis, keloid like-lesions, distinctive facial features, and overgrowth: two newly recognized patients with premature aging syndrome, Penttinen type.

We report on two unrelated patients with a rare progeroid syndrome first described by Penttinen. Patients presented with prematurely aged appearance, delayed dental development, acro-osteolysis, diffuse keloid-like lesions, and ocular pterygia. Facial features are progressive but recognizable at birth. Premaxillary and maxillary retraction with pseudo-prognathism and palpebral malocclusion are characteristic. Thumbs and halluces are broad and spatulated. Linear growth is increased and intellectual functions are preserved. Skin retractions and joint contractures progressively developed during adolescence. Death occurred in the second decade in one of the patient due to restrictive respiratory insufficiency and cachexia. LMNA and ZMPSTE24 sequencing were normal. The molecular basis of the disorder remains unknown.

Bone dysplasia in Hutchinson-Gilford progeria syndrome is associated with dysregulated differentiation and function of bone cell populations.

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disorder affecting tissues of mesenchymal origin. Most individuals with HGPS harbor a de novo c.1824C > T (p.G608G) mutation in the gene encoding lamin A (LMNA), which activates a cryptic splice donor site resulting in production of the toxic "progerin" protein. Clinical manifestations include growth deficiency, lipodystrophy, sclerotic dermis, cardiovascular defects, and bone dysplasia. Here we utilized the LmnaG609G knock-in (KI) mouse model of HGPS to further define mechanisms of bone loss associated with normal and premature aging disorders. Newborn skeletal staining of KI mice revealed altered rib cage shape and spinal curvature, and delayed calvarial mineralization with increased craniofacial and mandibular cartilage content. MicroCT analysis and mechanical testing of adult femurs indicated increased fragility associated with reduced bone mass, recapitulating the progressive bone deterioration that occurs in HGPS patients. We investigated mechanisms of bone loss in KI mice at the cellular level in bone cell populations. Formation of wild-type and KI osteoclasts from marrow-derived precursors was inhibited by KI osteoblast-conditioned media in vitro, suggesting a secreted factor(s) responsible for decreased osteoclasts on KI trabecular surfaces in vivo. Cultured KI osteoblasts exhibited abnormal differentiation characterized by reduced deposition and mineralization of extracellular matrix with increased lipid accumulation compared to wild-type, providing a mechanism for altered bone formation. Furthermore, quantitative analyses of KI transcripts confirmed upregulation of adipogenic genes both in vitro and in vivo. Thus, osteoblast phenotypic plasticity, inflammation and altered cellular cross-talk contribute to abnormal bone formation in HGPS mice.

Altered chromatin organization and SUN2 localization in mandibuloacral dysplasia are rescued by drug treatment.

Mandibuloacral dysplasia type A (MADA) is a rare laminopathy characterized by growth retardation, craniofacial anomalies, bone resorption at specific sites including clavicles, phalanges and mandibula, mottled cutaneous pigmentation, skin rigidity, partial lipodystrophy, and insulin resistance. The disorder is caused by recessive mutations of the LMNA gene encoding for A-type lamins. The molecular feature of MADA consists in the accumulation of the unprocessed lamin A precursor, which is detected at the nuclear rim and in intranuclear aggregates. Here, we report the characterization of prelamin A post-translational modifications in MADA cells that induce alterations in the chromatin arrangement and dislocation of nuclear envelope-associated proteins involved in correct nucleo-cytoskeleton relationships. We show that protein post-translational modifications change depending on the passage number, suggesting the onset of a feedback mechanism. Moreover, we show that treatment of MADA cells with the farnesyltransferase inhibitors is effective in the recovery of the chromatin phenotype, altered in MADA, provided that the cells are at low passage number, while at high passage number, the treatment results ineffective. Moreover, the distribution of the lamin A interaction partner SUN2, a constituent of the nuclear envelope, is altered by MADA mutations, as argued by the formation of a highly disorganized lattice. Treatment with statins partially rescues proper SUN2 organization, indicating that its alteration is caused by farnesylated prelamin A accumulation. Given the major role of SUN1 and SUN2 in the nucleo-cytoskeleton interactions and in regulation of nuclear positioning in differentiating cells, we hypothesise that mechanisms regulating nuclear membrane-centrosome interplay and nuclear movement may be affected in MADA fibroblasts.

Homozygous null mutations in ZMPSTE24 in restrictive dermopathy: evidence of genetic heterogeneity.

Restrictive dermopathy (RD) results in stillbirth or early neonatal death. RD is characterized by prematurity, intrauterine growth retardation, fixed facial expression, micrognathia, mouth in the 'o' position, rigid and tense skin with erosions and denudations and multiple joint contractures. Nearly all 25 previously reported neonates with RD had homozygous or compound heterozygous null mutations in the ZMPSTE24 gene. Here, we report three new cases of RD; all died within 3 weeks of birth. One of them had a previously reported homozygous c.1085dupT (p.Leu362PhefsX19) mutation, the second case had a novel homozygous c.1020G>A (p.Trp340X) null mutation in ZMPSTE24, but the third case, a stillborn with features of RD except for the presence of tapering rather than rounded, bulbous digits, harbored no disease-causing mutations in LMNA or ZMPSTE24. In the newborn with a novel ZMPSTE24 mutation, unique features included butterfly-shaped thoracic 5 vertebra and the bulbous appearance of the distal clavicles. Skin biopsies from both the stillborn fetus and the newborn with c.1020G>A ZMPSTE24 mutation showed absence of elastic fibers throughout the dermis. This report provides evidence of genetic heterogeneity among RD and concludes that there may be an additional locus for RD which remains to be identified.