Thematic review series: Adipocyte Biology. Lipodystrophies: windows on adipose biology and metabolism.
The lipodystrophies are characterized by loss of adipose tissue in some anatomical sites, frequently with fat accumulation in nonatrophic depots and ectopic sites such as liver and muscle. Molecularly characterized forms include Dunnigan-type familial partial lipodystrophy (FPLD), partial lipodystrophy with mandibuloacral dysplasia (MAD), Berardinelli-Seip congenital generalized lipodystrophy (CGL), and some cases with Barraquer-Simons acquired partial lipodystrophy (APL). The associated mutant gene products include 1) nuclear lamin A in FPLD type 2 and MAD type A; 2) nuclear lamin B2 in APL; 3) nuclear hormone receptor peroxisome proliferator-activated receptor gamma in FPLD type 3; 4) lipid biosynthetic enzyme 1-acylglycerol-3-phosphate O-acyltransferase 2 in CGL type 1; 5) integral endoplasmic reticulum membrane protein seipin in CGL type 2; and 6) metalloproteinase ZMPSTE24 in MAD type B. An unresolved question is whether metabolic disturbances are secondary to adipose repartitioning or result from a direct effect of the mutant gene product. Careful analysis of clinical, biochemical, and imaging phenotypes, using an approach called "phenomics," reveals differences between genetically stratified subtypes that can be used to guide basic experiments and to improve our understanding of common clinical entities, such as metabolic syndrome or the partial lipodystrophy syndrome associated with human immunodeficiency virus infection. (+info)
Long-term efficacy of leptin replacement in patients with Dunnigan-type familial partial lipodystrophy.
The Dunnigan-type familial partial lipodystrophy (FPLD) is characterized by a variable loss of fat from the extremities and trunk and excess subcutaneous fat in the chin and supraclavicular area. Associated metabolic abnormalities include hypoleptinemia, insulin resistance, and dyslipidemia. Our goal was to observe changes in metabolic parameters for patients with FPLD on long-term leptin replacement and to compare the metabolic characteristics seen in FPLD with those seen in generalized lipodystrophy (GL) from our previous studies. This was an open-label study of 6 patients with FPLD receiving maximal doses of oral antidiabetic and lipid-lowering medications at baseline. Recombinant leptin was given through twice-daily subcutaneous injections at a maximal dose of 0.08 mg/kg per day over 12 months to simulate normal to high normal physiologic levels. Triglycerides were reduced by 65% at 4 months (749+/-331 to 260+/-58 mg/dL) and significantly reduced at 12 months for 5 patients (433+/-125 to 247+/-69 mg/dL; P=.03). Total cholesterol also decreased (280+/-49 to 231+/-41 mg/dL; P=.01). Insulin sensitivity and fasting glucose levels (190+/-26 to 151+/-15 mg/dL; P<.01) improved. Glucose tolerance and glycosylated hemoglobin levels (8.4%+/-0.6% to 8.0%+/-0.4%; P=.07) did not change. As shown in patients with GL, patients with FPLD have improvement in triglycerides, fasting glucose, and insulin sensitivity with leptin replacement. In contrast to the patients with GL, the patients with FPLD are older, have higher leptin levels, and notably lower insulin secretion for a similar degree of hyperglycemia. Low-dose recombinant methionyl human leptin for patients with FPLD has an important role in improving triglycerides, beyond that of available lipid-lowering agents. In improving glycemic control, normalization of glucose tolerance in hypoinsulinemic patients with FPLD requires insulin and leptin therapy. This is the first study to examine the effects of long-term leptin replacement in patients with FPLD. (+info)
A pathogenic mechanism leading to partial lipodistrophy and prospects for pharmacological treatment of insulin resistance syndrome.
The understanding of a common complex phenotype such as insulin resistance can be favoured by evaluation of monogenic syndromes. Clinical definition, pathogenesis, and therapeutical strategies for the insulin resistance syndrome can thus be improved by the characterization at the molecular genetic level of monogenic forms of lipodystrophies. Here we report experimental evidence on the pathogenic mechanism underlying insulin resistance in a rare form of laminopathy, due to mutation of the LMNA gene coding for lamin A/C, the Dunnigan-type familial partial lipodystrophy (FPLD). The defect, consisting in the intranuclear accumulation of mutant unprocessed precursors of lamin A, reduces the amount of the DNA-bound adipocyte transcription factor sterol regulatory element binding protein 1 (SREBP1) and lowers the peroxisome proliferator-activated receptor (PPARgamma) expression, causing the impairment of pre-adipocyte differentiation. The treatment with the PPARgamma ligand troglitazone (TDZ) is able to rescue the adipogenic program. Since FPLD recapitulates the essential metabolic abnormalities of the common insulin resistance syndrome, the beneficial effects of TDZ on monogenic lipodystrophies might provide a clue as to the future treatment strategies also for the common syndrome of insulin resistance. (+info)
The retinol acid receptor B gene is hypermethylated in patients with familial partial lipodystrophy.
Mutations in the LMNA gene cause various phenotypes including partial lipodystrophy, muscular dystrophies, and progeroid syndromes. The specific mutation position within the LMNA sequence can partially predict the phenotype, but the underlying mechanisms for the development of these different phenotypes are still unclear. To investigate whether different DNA methylation patterns contribute to the development of different phenotypes caused by LMNA mutations, we analyzed a panel of ten candidate genes related to fat metabolism, aging, and a tendency to different methylation patterns: CSPG2, ESR1, IGF1R, IGFR2, LMNA, MLH1, RANBP1, RARB, ZMPSTE24, and TGFBR1. We studied two independent families each comprising three individuals affected by familial partial lipodistrophy type 2 (FPLD2). Affected members in each family carried two different mutations of the LMNA gene (R482L and R471G respectively). In addition, we analyzed four progeria patients (2xLMNA/C G608G, 1xLMNA/C S143F, and 1xZMPSTE24 IVS9-Ex10) and seven healthy adults. The gene encoding retinoic acid receptor B (RARB) showed a higher methylation in all six patients with FPLD2 when compared with the progeria patients with other LMNA mutations as well as the healthy controls (P<0.05). All other investigated genes showed no difference in the methylation patterns between the groups. A drug-induced inhibition of the retinol pathway is discussed as the key pathway for developing HAART-associated lipodystrophy and our data support a possible role of the retinol pathway in the development of lipodystrophy phenotypes. (+info)
Human lipodystrophies linked to mutations in A-type lamins and to HIV protease inhibitor therapy are both associated with prelamin A accumulation, oxidative stress and premature cellular senescence.
Lipodystrophic syndromes associated with mutations in LMNA, encoding A-type lamins, and with HIV antiretroviral treatments share several clinical characteristics. Nuclear alterations and prelamin A accumulation have been reported in fibroblasts from patients with LMNA mutations and adipocytes exposed to protease inhibitors (PI). As genetically altered lamin A maturation also results in premature ageing syndromes with lipodystrophy, we studied prelamin A expression and senescence markers in cultured human fibroblasts bearing six different LMNA mutations or treated with PIs. As compared to control cells, fibroblasts with LMNA mutations or treated with PIs had nuclear shape abnormalities and reduced proliferative activity that worsened with increasing cellular passages. They exhibited prelamin A accumulation, increased oxidative stress, decreased expression of mitochondrial respiratory chain proteins and premature cellular senescence. Inhibition of prelamin A farnesylation prevented cellular senescence and oxidative stress. Adipose tissue samples from patients with LMNA mutations or treated with PIs also showed retention of prelamin A, overexpression of the cell cycle checkpoint inhibitor p16 and altered mitochondrial markers. Thus, both LMNA mutations and PI treatment result in accumulation of farnesylated prelamin A and oxidative stress that trigger premature cellular senescence. These alterations could participate in the pathophysiology of lipodystrophic syndromes and lead to premature ageing complications. (+info)
New PPARG mutation leads to lipodystrophy and loss of protein function that is partially restored by a synthetic ligand.
PURPOSE: Familial partial lipodystrophy caused by mutations in the PPARG gene is characterised by altered distribution of subcutaneous fat, muscular hypertrophy and symptoms of metabolic syndrome. PPARG encodes peroxisome proliferator-activated receptor (PPAR)gamma, a nuclear hormone receptor playing a crucial role in lipid and glucose metabolism and in several other cellular regulatory processes. METHODS: PPARG was screened for mutations by direct sequencing in two patients with lipodystrophy, one unaffected family member and 124 controls. Body composition was examined in affected patients, and they were investigated for abnormalities in laboratory results. Functional analysis of the mutant protein was assessed by determining transcriptional activity and possible interference with the wild-type protein. RESULTS: In two patients with familial partial lipodystrophy, we identified a nucleotide substitution in the PPARG gene. This mutation results in the substitution of aspartate by asparagine at residue 424 (D424N) in the ligand-binding domain of PPARgamma. The unaffected family member and all 124 controls did not carry this mutation. D424N PPARgamma had a significantly lower ability than wild-type PPARgamma to activate a PPARgamma-stimulated reporter gene, but did not exert a negative effect on the wild-type protein. Partial activation of D424N PPARgamma was achieved in the presence of the agonist rosiglitazone. CONCLUSION: We report a new PPARG mutation, D424N, which is located in the ligand-binding domain of the protein and leads to familial partial lipodystrophy. D424N PPARgamma exhibited a loss of function, which was partially restored by adding the PPARgamma agonist rosiglitazone, suggesting possible treatment potential of this agent. (+info)
Efficacy of pioglitazone in familial partial lipodystrophy of the Dunnigan type: a case report.
A 25 year old woman consulted for a severe acanthosis nigricans and central distribution of fat. Her masculine type morphology was associated with muscular appearance of the limbs and excess fat deposits in the face and neck. Biological testing confirmed glucose intolerance associated with a severe insulin resistance, hypertriglyceridemia and polycystic ovary syndrome. The detection of a heterozygous missense mutation in LAMIN A/C gene at position 482 confirmed the diagnosis of Familial Partial Lipodystrophy (FPLD2). Due to a deterioration of clinical and metabolic status, 15 and then 30 mg per day of pioglitazone were added to her previous treatment with metformin, bezafibrate and omega-3 fatty acids. Metabolic status improved rapidly after 3 months and continued thereafter. Weight remained stable, body mass composition and waist circumference improved. After 18 months of treatment, glycaemia and triglycerides levels normalized, hepatic enzymes and liver echographic features improved. Insulin sensitivity improved dramatically with a HOMA % S value of 73% with metformin and of 98.2% when pioglitazone was added. Leptin levels increased from 6.6 to 10.2 microg/ml. We report a very rapid and good efficacy of pioglitazone added to metformin without side effects in FPLD2. If confirmed on more patients, early use of pioglitazone in association with metformin could be proposed in FPLD2. (+info)
Resistance to high-fat diet-induced obesity but exacerbated insulin resistance in mice overexpressing preadipocyte factor-1 (Pref-1): a new model of partial lipodystrophy.