[Show abstract][Hide abstract] ABSTRACT: We previously showed that striated muscle-selective depletion of lamina-associated polypeptide 1 (LAP1), an integral inner nuclear membrane protein, leads to profound muscular dystrophy with premature death in mice. As LAP1 is also depleted in hearts of these mice, we examined their cardiac phenotype. Striated muscle-selective LAP1 knockout mice display ventricular systolic dysfunction with abnormal induction of genes encoding cardiomyopathy related proteins. To eliminate possible confounding effects due to skeletal muscle pathology, we generated a new mouse line in which LAP1 is deleted in a cardiomyocyte-selective manner. These mice had no skeletal muscle pathology and appeared overtly normal at 20 weeks of age. However, cardiac echocardiography revealed that they developed left ventricular systolic dysfunction and cardiac gene expression analysis revealed abnormal induction of cardiomyopathy-related genes. Our results demonstrate that LAP1 expression in cardiomyocytes is required for normal left ventricular function, consistent with a report of cardiomyopathy in a human subject with mutation in the gene encoding LAP1.
[Show abstract][Hide abstract] ABSTRACT: Some LMNA mutations responsible for insulin-resistant lipodystrophic syndromes are associated with peripheral subcutaneous lipoatrophy and faciocervical fat accumulation. Their pathophysiologic characteristics are unknown. We compared histologic, immunohistologic, ultrastructural, and protein expression features of enlarged cervical subcutaneous adipose tissue (scAT) obtained during plastic surgery from four patients with LMNA p.R482W, p.R439C, or p.H506D mutations versus cervical fat from eight control subjects, buffalo humps from five patients with HIV infection treated or not with protease inhibitors, and dorsocervical lipomas from two patients with mitochondrial DNA mutations. LMNA-mutated cervical scAT and HIV-related buffalo humps were dystrophic, with an increased percentage of small adipocytes, increased fibrosis without inflammatory features, and decreased number of blood vessels, as compared with control samples. Samples from patients with LMNA mutations or protease inhibitor-based therapy demonstrated accumulation of prelamin A, altered expression of adipogenic proteins and brown fat-like features, with an increased number of mitochondria and overexpression of uncoupling protein 1 (UCP1). These features were absent in samples from control subjects and from patients with HIV not treated with protease inhibitors. Mitochondrial DNA-mutated cervical lipomas demonstrated inflammatory fibrosis with distinct mitochondrial abnormalities but neither UCP1 expression nor prelamin A accumulation. In conclusion, Enlarged cervical scAT from patients with lipodystrophy demonstrated small adipocytes, fibrosis, and decreased vessel numbers. However, only cervical fat from patients with LMNA mutations or who had received protease inhibitor therapy accumulated prelamin A and exhibited similar remodeling toward a brown-like phenotype with UCP1 overexpression and mitochondrial alterations.
American Journal Of Pathology 09/2011; 179(5):2443-53. DOI:10.1016/j.ajpath.2011.07.049 · 4.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Introduction
Les syndromes lipodystrophiques associent une perte de tissu adipeux et des troubles métaboliques, en particulier une insulino-résistance et une hypertriglycéridémie. Ils sont d’origine génétique ou acquise, et de nombreux cas restent d’origine inconnue.
Nous avons utilisé une approche gène-candidat pour rechercher de nouvelles causes génétiques à ces syndromes.
Des études récentes suggérant que l’altération de certaines protéines de la gouttelette lipidique adipocytaire pourraient participer à la physiopathologie des lipodystrophies, nous avons étudié le gène de la périlipine.
Cette protéine adipocytaire, qui participe à la structure de la gouttelette, possède un double rôle régulateur: elle protège les triglycérides de la lipolyse à l’état basal, tandis qu’elle active leur hydrolyse sous l’effet des catécholamines.
Patients et méthodes
Nous avons séquencé les régions codantes du gène de la périlipine chez des patients atteints de syndromes lipodystrophiques de cause inconnue.
Deux mutations hétérozygotes différentes, entraînant la synthèse d’acides aminés aberrants dans la région C-terminale de la périlipine, ont été identifiées chez trois patientes non apparentées présentant une lipoatrophie partielle avec diabète insulino-résistant, hypertriglycéridémie et stéatose hépatique. Les mutations étaient absentes chez plus de 200 témoins. La maladie, de transmission autosomique dominante dans les familles, co-ségrégeait avec les mutations. L’analyse du tissu adipeux des patients a montré des adipocytes de taille diminuée et une fibrose intercellulaire avec infiltration macrophagique. L’expression des deux formes mutées de périlipine, comparées à la périlipine sauvage dans un modèle pré-adipocytaire, a révélé leur incapacité à former des gouttelettes de triglycérides et à inhiber la lipolyse basale. Les expériences de co-expression n’étaient pas en faveur d’un rôle dominant-négatif des mutations, mais plutôt d’un mécanisme d’haplo-insuffisance.
L’implication d’un défaut d’activité de la périlipine, protéine quasi-exclusivement adipocytaire, dans une nouvelle forme de syndrome lipodystrophique chez l’homme montre clairement les conséquences métaboliques sévères d’une dysfonction primitive du tissu adipeux.
[Show abstract][Hide abstract] ABSTRACT: Adipose tissue is now recognized for its major role in the control of energy metabolism and insulin sensitivity. We review here the human lipodystrophies, that are rare conditions in which total or partial fat loss is associated with severe lipid and glucose abnormalities leading to diabetes with early cardiovascular and hepatic complications. The genetic origin of a number of human lipodystrophies has been recently unraveled, emphasizing the importance of proteins of previously unknown or unexpected functions. Major adipose functions were also illuminated when studying acquired forms of lipodystrophies linked to human immunodeficiency virus-antiretrovirals. Overall, most of the proteins or functions affected by mutations or antiretrovirals result in altered adipogenesis and insulin sensitivity, triglyceride storage and formation of the unique adipocyte lipid droplet, oxidative stress and fat remodeling. Some mutations or antiretrovirals could affect directly (peroxisome proliferator-activated receptor-γ, Akt2) or indirectly (lamin A/C, human immunodeficiency virus-protease inhibitors) adipogenesis, through the transcription factors peroxisome proliferator-activated receptor gamma-γ or sterol regulatory element binding protein 1c, and insulin signaling through Akt2 that controls adipocyte lipolysis. A number of proteins mutated in genetic lipodystrophies are involved in the control of triglyceride synthesis towards the lipid droplet (1-acylglycerol-3-phosphate-O-acyltransferase 2), or its functions (seipin, cell death-inducing DFF45-like effector C, perilipin, caveolin-1, cavin-1). Decreased triglyceride storage leads to adipocyte lipotoxicity, mitochondrial dysfunction and increased oxidative stress, which could also be induced by some thymidine analogue antiretrovirals. This results in production of inflammatory mediators and deregulated release of free fatty acids. Thus, the impaired ability of adipose tissue to safely store triglycerides inside the lipid droplet results in impaired insulin sensitivity and adverted liver, muscles and heart functions leading to early complications.
The international journal of biochemistry & cell biology 03/2011; 43(6):862-76. DOI:10.1016/j.biocel.2011.03.002 · 4.05 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Perilipin is the most abundant adipocyte-specific protein that coats lipid droplets, and it is required for optimal lipid incorporation and release from the droplet. We identified two heterozygous frameshift mutations in the perilipin gene (PLIN1) in three families with partial lipodystrophy, severe dyslipidemia, and insulin-resistant diabetes. Subcutaneous fat from the patients was characterized by smaller-than-normal adipocytes, macrophage infiltration, and fibrosis. In contrast to wild-type perilipin, mutant forms of the protein failed to increase triglyceride accumulation when expressed heterologously in preadipocytes. These findings define a novel dominant form of inherited lipodystrophy and highlight the serious metabolic consequences of a primary defect in the formation of lipid droplets in adipose tissue.
New England Journal of Medicine 02/2011; 364(8):740-8. DOI:10.1056/NEJMoa1007487 · 55.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mutations in LMNA, encoding A-type lamins, lead to multiple laminopathies, including lipodystrophies, progeroid syndromes, and cardiomyopathies. Alterations in the prelamin-A posttranslational maturation, resulting in accumulation of farnesylated isoforms, cause human progeroid syndromes. Accumulation of mutant nonfarnesylated prelamin-A leads to cardiomyopathy or progeria in mice, but no data have been provided in humans. OBJECTIVE, DESIGN, SETTING, AND PATIENTS: We searched for LMNA mutations in seven women originating from Reunion Island who were referred for a severe lipodystrophic syndrome. Clinical, molecular, genealogical, and cellular studies were performed in probands and relatives.
The seven probands showed a severe partial lipodystrophic syndrome with diabetes and/or acanthosis nigricans, liver steatosis, hypertriglyceridemia, and low serum leptin and adiponectin levels. Three probands also had severe cardiac rhythm and conduction disturbances. We identified in all probands a homozygous LMNA p.T655fsX49 mutation leading to expression of a mutated prelamin-A with 48 aberrant C-terminal amino acids, preventing its physiological posttranslational farnesylation and maturation. Genealogical and haplotype analyses were consistent with a founder mutation transmitted from a common ancestor in the 17th century. In probands' cultured fibroblasts, mutated prelamin-A was associated with typical laminopathic nuclear dysmorphies, increased oxidative stress, and premature senescence. Heterozygous relatives were asymptomatic or partially affected, in favor of a codominant transmission of the disease with incomplete penetrance in heterozygotes.
We reveal that a homozygous mutation of prelamin-A preventing its farnesylation leads to a severe lipodystrophic laminopathy in humans, which can be associated with cardiac conduction disturbances, stressing the pathogenicity of nonfarnesylated prelamin-A in human laminopathies.
The Journal of Clinical Endocrinology and Metabolism 02/2011; 96(5):E856-62. DOI:10.1210/jc.2010-2234 · 6.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Lamin A is a component of the nuclear lamina mutated in a group of human inherited disorders known as laminopathies. Among laminopathies, progeroid syndromes and lipodystrophies feature accumulation of prelamin A, the precursor protein which, in normal cells, undergoes a multi-step processing to yield mature lamin A. It is of utmost importance to characterize the prelamin A form accumulated in each laminopathy, since existing evidence shows that drugs acting on protein processing can improve some pathological aspects.We report that two antibodies raised against differently modified prelamin A peptides show a clear specificity to full-length prelamin A or carboxymethylated farnesylated prelamin A, respectively. Using these antibodies, we demonstrated that inhibition of the prelamin A endoprotease ZMPSTE24 mostly elicits accumulation of full-length prelamin A in its farnesylated form, while loss of the prelamin A cleavage site causes accumulation of carboxymethylated prelamin A in progeria cells. These results suggest a major role of ZMPSTE24 in the first prelamin A cleavage step.
European journal of histochemistry: EJH 03/2009; 53(1):43-52. DOI:10.4081/ejh.2009.43 · 2.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dunnigan-type familial partial lipodystrophy (FPLD) is a laminopathy characterized by an aberrant fat distribution and a metabolic syndrome for which oxidative stress has recently been suggested as one of the disease-causing mechanisms. In a family affected with FPLD, we identified a heterozygous missense mutation c.1315C>T in the LMNA gene leading to the p.R439C substitution. Cultured patient fibroblasts do not show any prelamin A accumulation and reveal honeycomb-like lamin A/C formations in a significant percentage of nuclei. The mutation affects a region in the C-terminal globular domain of lamins A and C, different from the FPLD-related hot spot. Here, the introduction of an extra cysteine allows for the formation of disulphide-mediated lamin A/C oligomers. This oligomerization affects the interaction properties of the C-terminal domain with DNA as shown by gel retardation assays and causes a DNA-interaction pattern that is distinct from the classical R482W FPLD mutant. Particularly, whereas the R482W mutation decreases the binding efficiency of the C-terminal domain to DNA, the R439C mutation increases it. Electron spin resonance spectroscopy studies show significantly higher levels of reactive oxygen species (ROS) upon induction of oxidative stress in R439C patient fibroblasts compared to healthy controls. This increased sensitivity to oxidative stress seems independent of the oligomerization and enhanced DNA binding typical for R439C, as both the R439C and R482W mutants show a similar and significant increase in ROS upon induction of oxidative stress by H2O2.
Journal of Cellular and Molecular Medicine 02/2009; 13(5):959-71. DOI:10.1111/j.1582-4934.2009.00690.x · 4.01 Impact Factor