Reduced phosphorylation of transcription factor Elk-1 in cultured fibroblasts of a patient with premature aging syndrome and insulin resistance

A mutation in the c-fos gene associated with congenital generalized lipodystrophy

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.

Revealing system-level correlations between aging and calorie restriction using a mouse transcriptome

Although systems biology is a perfect framework for investigating system-level declines during aging, only a few reports have focused on a comprehensive understanding of system-level changes in the context of aging systems. The present study aimed to understand the most sensitive biological systems affected during aging and to reveal the systems underlying the crosstalk between aging and the ability of calorie restriction (CR) to effectively slow-down aging. We collected and analyzed 478 aging- and 586 CR-related mouse genes. For the given genes, the biological systems that are significantly related to aging and CR were examined according to three aspects. First, a global characterization by Gene Ontology (GO) was performed, where we found that the transcriptome (a set of genes) for both aging and CR were strongly related in the immune response, lipid metabolism, and cell adhesion functions. Second, the transcriptional modularity found in aging and CR was evaluated by identifying possible functional modules, sets of genes that show consistent expression patterns. Our analyses using the given functional modules, revealed systemic interactions among various biological processes, as exemplified by the negative relation shown between lipid metabolism and the immune response at the system level. Third, transcriptional regulatory systems were predicted for both the aging and CR transcriptomes. Here, we suggest a systems biology framework to further understand the most important systems as they age.

Plasma FGF-21 levels in type 2 diabetic patients with ketosis

FGF-21 has been recently characterized as a potent metabolic regulator, but its pathophysiologic role in human remains unknown. In this study we investigate whether plasma FGF-21 level is different in patients with new-onset type 2 diabetes mellitus (T2DM) and diabetic ketosis (T2DK). Sixty-eight patients with T2DM, 41 subjects with T2DK, and 52 sex- and age-matched normal controls participated in the study. Plasma FGF-21 levels were measured with a radioimmunoassay. The relationship between plasma FGF-21 levels and anthropometric and metabolic parameters was also analyzed. Plasma FGF-21 levels were higher in patients with T2DK and T2DM than in controls (4.05+/-0.18microg/L and 2.82+/-0.14microg/L vs. 2.28+/-0.16microg/L, P<0.01 and P<0.05, respectively). Fasting plasma FGF-21 was found to correlate positively and significantly with SBP, DBP, FBG, 2hPBG, HbA(1)c, HDL-C and FFA, but negatively with fasting plasma insulin, 2hIns and HOMA(IS). Multiple regression analysis showed that DBP, WHR, 2hIns, 2hPBG and FFA were independent to the factors influencing plasma FGF-21 levels. Increasing concentrations of FGF-21 were independently and significantly associated with T2DM and T2DK. The present work suggests that FGF-21 may play a role in the pathogenesis of T2DM and T2DK.

Two novel mutations in the insulin binding subunit of the insulin receptor gene without insulin binding impairment in a patient with Rabson-Mendenhall syndrome

Homozygous or compound heterozygous mutations within the insulin binding domain of the human insulin receptor (INSR) are usually associated with severe impairment of insulin binding leading to Donohue syndrome ("Leprechaunism"), which is characterized by excessive hyperglycemia with hyperinsulinism, pre- and postnatal growth retardation, distinct dysmorphism and early death. Missense mutations in the beta subunits are commonly associated with a milder impairment of insulin binding and milder phenotype with prolonged survival and less dysmorphism, the so called Rabson-Mendenhall syndrome. We report on a 13-year-old girl with Donohue syndrome like dysmorphism, hyperinsulinism and prolonged survival due to two novel INSR missense mutations within the insulin binding domain. Unexpectedly, insulin binding assays and investigations of activation of central insulin signaling pathways in fibroblasts revealed no significant alterations. Instead, immunofluorescence studies showed abnormal perinuclear distribution of the INSR alpha and beta subunits. Our data indicate that the quality of insulin binding activity is correlated with survival, not with the dysmorphic phenotype, and it is not always a valid parameter for predicting INSR mutations as proposed.

Alleles in the HtrA serine peptidase 1 gene alter the risk of neovascular age-related macular degeneration

OBJECTIVE

To examine if the genes encoding the pleckstrin homology domain-containing protein gene (PLEKHA1), hypothetical LOC387715/ARMS2 gene, and HtrA serine peptidase 1 gene (HTRA1) located on the long arm of chromosome 10 (10q26 region) confer risk for neovascular age-related macular degeneration (AMD) in an independent or interactive manner when controlling for complement factor H gene (CFH) genotype and smoking exposure.

DESIGN

Retrospective matched-pair case-control study.

PARTICIPANTS

Hospital clinic-based sample of 134 unrelated patients with neovascular AMD who have a sibling with normal maculae (268 subjects).

METHODS

Disease status was ascertained by at least 2 investigators by review of fundus photographs and/or fluorescein angiography according to the Age-Related Eye Disease Study grading scale. If necessary, a home retinal examination was performed (n = 6). A combination of direct sequencing and analysis of 8 highly polymorphic microsatellite markers was used to genotype 33 megabases of the 10q26 region on leukocyte DNA. Smoking history was obtained via a standardized questionnaire and measured in pack-years. The family-based association test, haplotype analysis, multiple conditional logistic regression, and linkage analysis were used to determine significant associations.

MAIN OUTCOME MEASURE

Neovascular AMD status.

RESULTS

Of the 23 variants we identified in the 10q26 region, 6 were significant. Four of the 6 were novel and included 2 genotypes that reduced risk of AMD. Many single-nucleotide polymorphisms (SNPs), including the previously reported variants rs10490924 (hypothetical LOC387715/ARMS2) and rs11200638 (HTRA1), defined 2 significant haplotypes associated with increased risk of neovascular AMD. The coding HTRA1 SNP rs2293870, not part of the significant haplotypes containing rs10490924 and rs11200638, showed as strong an association with increased susceptibility to neovascular AMD. Linkage analysis supported our findings of SNP association (P<10(-15)). No significant interactions were found between any of the SNPs in the 10q26 and smoking or between these SNPs and CFH genotype.

CONCLUSIONS

Independent of CFH genotype or smoking history, an individual's risk of AMD could be increased or decreased, depending on their genotype or haplotype in the 10q26 region.