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Characterization of a caveolin-1 mutation associated with both pulmonary arterial hypertension and congenital generalized lipodystrophy.

ABSTRACT: Congenital generalized lipodystrophy (CGL) and pulmonary arterial hypertension (PAH) have recently been associated with mutations in the caveolin-1 ( CAV1 ) gene, which encodes the primary structural protein of caveolae. However, little is currently known about how these CAV1 mutations impact caveolae formation or contribute to the development of disease. Here, we identify a heterozygous F160X CAV1 mutation predicted to generate a C-terminally truncated mutant protein in a patient with both PAH and CGL using whole exome sequencing, and characterize the properties of CAV1 , caveolae-associated proteins and caveolae in skin fibroblasts isolated from the patient. We show that morphologically defined caveolae are present in patient fibroblasts and that they function in mechanoprotection. However, they exhibited several notable defects, including enhanced accessibility of the C-terminus of wild-type CAV1 in caveolae, reduced colocalization of cavin-1 with CAV1 and decreased stability of both 8S and 70S oligomeric CAV1 complexes that are necessary for caveolae formation. These results were verified independently in reconstituted CAV1 -/- mouse embryonic fibroblasts. These findings identify defects in caveolae that may serve as contributing factors to the development of PAH and CGL and broaden our knowledge of CAV1 mutations associated with human disease.

SUBMITTER: Han B

PROVIDER: S-EPMC5197452 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature

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Characterization of a caveolin-1 mutation associated with both pulmonary arterial hypertension and congenital generalized lipodystrophy.

Han Bing B Copeland Courtney A CA Kawano Yumeko Y Rosenzweig Erika Berman EB Austin Eric D ED Shahmirzadi Layla L Tang Sha S Raghunathan Krishnan K Chung Wendy K WK Kenworthy Anne K AK

Traffic (Copenhagen, Denmark) 20161102 12

Congenital generalized lipodystrophy (CGL) and pulmonary arterial hypertension (PAH) have recently been associated with mutations in the caveolin-1 ( CAV1 ) gene, which encodes the primary structural protein of caveolae. However, little is currently known about how these CAV1 mutations impact caveolae formation or contribute to the development of disease. Here, we identify a heterozygous F160X CAV1 mutation predicted to generate a C-terminally truncated mutant protein in a patient with both PAH ...[more]

PMID: 27717241

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Project description:BACKGROUND: Congenital generalized lipodystrophy (CGL) or Berardinelli-Seip congenital lipodystrophy (BSCL) is a rare genetic syndrome characterized by the absence of adipose tissue. As CGL is thought to be related to malfunctions in adipocyte development, genes involved in the mechanisms of adipocyte biology and maintenance or differentiation of adipocytes, especially transcription factors are candidates. Several genes (BSCL1-4) were found to be associated to the syndrome but not all CGL patients carry mutations in these genes. METHODS AND RESULTS: In a patient with CGL and insulin resistance we investigated the known candidate genes but the patient did not carry a relevant mutation. Analyses of the insulin activated signal transduction pathways in isolated fibroblasts of the patient revealed a postreceptor defect altering expression of the immediate early gene c-fos. Sequence analyses revealed a novel homozygous point mutation (c.-439, T?A) in the patients' c-fos promoter. The point mutation was located upstream of the well characterized promoter elements in a region with no homology to any known cis-elements. The identified mutation was not detected in a total of n=319 non lipodystrophic probands. In vitro analyses revealed that the mutation facilitates the formation of a novel and specific protein/DNA complex. Using mass spectrometry we identified the proteins of this novel complex. Cellular investigations demonstrate that the wild type c-fos promoter can reconstitute the signaling defect in the patient, excluding further upstream signaling alterations, and vice versa the investigations with the c-fos promoter containing the identified mutation generally reduce basal and inducible c-fos transcription activity. As a consequence of the identified point mutation gene expression including c-Fos targeted genes is significantly altered, shown exemplified in cells of the patient. CONCLUSION: The immediate-early gene c-fos is one essential transcription factor to initiate adipocyte differentiation. According to the role of c-fos in adipocyte differentiation our findings of a mutation that initiates a repression mechanism at c-fos promoter features the hypothesis that diminished c-fos expression might play a role in CGL by interfering with adipocyte development.

Project description:Background: In 2012, mutations in Cav1 were found to be the driving mutation in several cases of heritable pulmonary arterial hypertension (PAH). These mutations replaced the last 21 amino acids of Cav1 with a novel 22-amino-acid sequence. Because previously only Cav1 knockouts had been studied in the context of PAH, examining the in vivo effects of this novel mutation holds promise for new understanding of the role of Cav1 in disease etiology. Methods: The new 22 amino acids created by the human mutation were knocked into the native mouse Cav1 locus. The mice underwent hemodynamic, energy balance, and inflammatory measurements, both at baseline and after being stressed with either a metabolic or an inflammatory challenge [low-dose lipopolysaccharide (LPS)]. To metabolically challenge the mice, they were injected with streptozotocin (STZ) and fed a high-fat diet for 12 weeks. Results: Very little mutant protein was found in vivo (roughly 2% of wild-type by mass spectrometry), probably because of degradation after failure to traffic from the endoplasmic reticulum. The homozygous mutants developed a mild, low-penetrance PAH similar to that described previously in knockouts, and neither baseline nor metabolic nor inflammatory stress resulted in pressures above normal in heterozygous animals. The homozygous mutants had increased lean mass and worsened oral glucose tolerance, as previously described in knockouts. Novel findings include the preservation of Cav2 and accessory proteins in the liver and the kidney, while they are lost with homozygous Cav1 mutation in the lungs. We also found that the homozygous mutants had a significantly lower tolerance to voluntary spontaneous exercise than the wild-type mice, with the heterozygous mice at an intermediate level. The mutants also had higher circulating monocytes, with both heterozygous and homozygous animals having higher pulmonary MCP1 and MCP5 proteins. The heterozygous animals also lost weight at an LPS challenge level at which the wild-type mice continued to gain weight. Conclusions: The Cav1 mutation identified in human patients in 2012 is molecularly similar to a knockout of Cav1. It results in not only metabolic deficiencies and mild pulmonary hypertension, as expected, but also an inflammatory phenotype and reduced spontaneous exercise.

Project description:Abstract Background: Congenital generalized lipodystrophy (CGL) is a rare inherited disease characterized by widespread loss of subcutaneous fat and severe metabolic abnormalities. Metreleptin, a synthetic analog of leptin, is a treatment modality that has been shown to decrease fasting triglycerides, fasting glucose, and HbA1c. Metformin use in infants has only been described in a few case reports of CGL and Donohue syndrome (insulin receptor mutation), and there is no established dosing for this age group. We report metreleptin, insulin, and metformin use in an infant with type 1 CGL who presented with marked hypertriglyceridemia, hypoleptinemia, hyperglycemia, and transaminitis. Clinical Case: A 2-month-old African American female born SGA at term presented to her primary care physician for a well child check where she was noted to have poor weight gain, hyperphagia, and abdominal distension. She was subsequently admitted for failure to thrive with weight z-score of -2.17 and length z-score of -0.15. Initial labs were notable for triglycerides of 5,167 mg/dL, HDL 10 mg/dL, blood glucose 324 mg/dL, ALT 212 units/L, AST 215 units/L, and bicarbonate of 17 mmol/L. A random insulin level was elevated at 257 mcIU/mL. Adiponectin was undetectable and leptin was low at 0.3 ng/mL. Hemoglobin A1c was in diabetes mellitus range at 8.9%. She was started on detemir 1.0 units/kg/day on day 1 (titrated to a maximum dose of 4.4 units/kg/day) and metformin 50 mg/kg/day on day 3 of hospitalization. By day 4, triglycerides decreased to 758 mg/dL, AST to 119 units/L and ALT to 124 units/L. Pre-prandial glucoses improved ranging from 113 to 138 mg/dL. As her insurance denied coverage for detemir, she was discharged home on glargine 0.7 units/kg/day and metformin suspension. One month later, she was started on subcutaneous metreleptin, and glargine was discontinued. At 5 months of age, she had triglycerides 229 mg/dl, normal liver enzymes, and normal blood glucoses while on 0.056 mg/kg/day of subcutaneous metreleptin and metformin. Medications were well tolerated without side effects. She had improved growth and met all developmental milestones. Genetic evaluation revealed that she was homozygous for a pathogenic variant, c.589-2A>G; p.Gln196fs*228 (rs116807569), in the AGPAT2 gene. Conclusion: Leptin is important in regulation of lipid and glucose metabolism, and patients with CGL are deficient due to lack of adipose tissue. Metabolic abnormalities, including stabilization of glucoses and improved hypertriglyceridemia, in our patient markedly improved with initiation of metreleptin, metformin, and insulin. We present successful dosing of these treatment modalities without adverse reactions in an infant with CGL.

Dataset Information

Characterization of a caveolin-1 mutation associated with both pulmonary arterial hypertension and congenital generalized lipodystrophy.

Publications

Characterization of a caveolin-1 mutation associated with both pulmonary arterial hypertension and congenital generalized lipodystrophy.

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