[Long-term weight reduction. Current therapy approaches in obesity]

A large percentage of obese patients can lose weight with a combination of various dietary measures. The following possibilities are available: 1. The fat-reduced, carbohydrate-enhanced diet. 2. Formula diets, which are applied when a mixed diet has failed, or, alternatively, as an "introduction" to a weight-reducing program. In addition, suitable exercise programs and behavior-modifying measures aimed at stabilizing weight losses over the long-term, are also recommended. If this basic program fails, adjunctive drug treatment is indicated. Surgical treatment may be considered when various conservative forms of treatment have proved unsuccessful over a period of years.

[Molecular principles of obesity]

BACKGROUND

The deposition of excess amounts of energy in adipose tissue is enhanced by high-fat diets and lack of physical activity. Furthermore, the existence of a specific genetic predisposition towards the development of obesity becomes evident by marked interindividual differences in the response to caloric oversupply.

GENETIC DEFECTS AND HORMONES

In recent years, numerous genes and genetic defects with importance for human obesity were identified, especially through studies in animal models. The adipocyte-derived hormone leptin and its hypothalamic receptor play a premier role, as they interact with a network of proteins and neuropeptides within the regulation of food intake and energy expenditure.

CONCLUSION

The search for the key molecular mechanisms in the pathogenesis of obesity will not only improve our understanding of energy metabolism, but may ultimately also lead to the development of new treatment strategies for obese patients.

Identification of a deletion variant in the gene encoding the human alpha(2A)-adrenergic receptor

OBJECTIVE

The alpha(2)-adrenergic receptors are involved in the effects of catecholamines on energy metabolism. Of three known subtypes with differential expression, alpha(2A)-adrenergic receptors are also localized in adipose tissue where they counteract the lipolytic activity of beta-adrenergic receptors. This study was undertaken to assess whether variants in the alpha(2A)-adrenergic receptor gene are associated with body weight.

DESIGN AND METHODS

Single strand conformation polymorphism (SSCP) screening and subsequent sequencing were applied to determine genetic variants in DNA samples from individuals with obesity, those of normal weight and those underweight.

RESULTS

Analysis of the coding region resulted in the identification of an 18 bp deletion, with no other mutation found. Of 429 genotyped subjects, 7 carried the deletion, with no significant differences between lean and obese subjects. A previously identified polymorphism in the promoter of the alpha(2A)-adrenergic receptor gene also did not show an association with any of the tested body weight categories.

CONCLUSION

Our data suggest that variants in the alpha(2A)-adrenergic receptor gene are unlikely to contribute to the predisposition for the lean or obese state.

Activation induces rapid and profound alterations in the trafficking of T cells

Activation and differentiation of lymphocytes have profound effects on their trafficking. Whereas naive T cells recirculate through lymphoid organs, activated cells localize predominantly in other compartments. Here, we report that changes in migratory properties of T cells occur immediately upon activation via the TCR. One hour stimulation is enough to target T cells into lung and liver following i.v. injection. The high localization within lung and liver and the lack of recirculation through lymphoid tissues are key features of activated lymphocytes. the source, in vitro as well as in vivo activated lymphocytes show this behavior, which is not caused by increased cell size. Accumulation in the lung requires protein synthesis and is partly mediated by LFA-1, in contrast to the acquisition of liver "homing" properties. Intravital microscopy reveals firm adhesion of activated cells within periportal sinusoids of the liver. Selective homing to other organs, such as skin or mucosa, was not observed, regardless of the cell's origin. These data indicate that activation quickly switches the trafficking program of lymphocytes from recirculation to sequestration; it is tempting to speculate that especially the induced trapping in the liver has a distinct role in limiting systemic T cell responses.

Molecular control of copper homeostasis in filamentous fungi: increased expression of a metallothionein gene during aging of Podospora anserina

The lifespan of the ascomycete Podospora anserina was previously demonstrated to be significantly increased in a copper-uptake mutant, suggesting that copper is a potential stressor involved in degenerative processes. In order to determine whether changes in copper stress occur in the cells during normal aging of cultures, we cloned and characterized a gene coding for a component of the molecular machinery involved in the control of copper homeostasis. This gene, PaMt1, is a single-copy gene that encodes a metallothionein of 26 amino acids. The coding sequence of PaMt1 is interrupted by a single intron. The deduced amino acid sequence shows a high degree of sequence identity to metallothioneins of the filamentous ascomycete Neurospora crassa and the basidiomycete Agaricus bisporus, and to the N-terminal portion of mammalian metallothioneins. Levels of PaMt1 transcript increase in response to elevated amounts of copper in the growth medium and during aging of wild-type cultures. In contrast, in the long-lived mutant grisea, transcript levels first increase but then decrease again. The ability of wild-type cultures to respond to exogenous copper stress via the induction of PaMt1 transcription is not affected as they grow older.

Activation induces rapid and profound alterations in the trafficking of T cells

Activation and differentiation of lymphocytes have profound effects on their trafficking. Whereas naive T cells recirculate through lymphoid organs, activated cells localize predominantly in other compartments. Here, we report that changes in migratory properties of T cells occur immediately upon activation via the TCR. One hour stimulation is enough to target T cells into lung and liver following i.v. injection. The high localization within lung and liver and the lack of recirculation through lymphoid tissues are key features of activated lymphocytes. the source, in vitro as well as in vivo activated lymphocytes show this behavior, which is not caused by increased cell size. Accumulation in the lung requires protein synthesis and is partly mediated by LFA-1, in contrast to the acquisition of liver "homing" properties. Intravital microscopy reveals firm adhesion of activated cells within periportal sinusoids of the liver. Selective homing to other organs, such as skin or mucosa, was not observed, regardless of the cell's origin. These data indicate that activation quickly switches the trafficking program of lymphocytes from recirculation to sequestration; it is tempting to speculate that especially the induced trapping in the liver has a distinct role in limiting systemic T cell responses.

Yeti--a degenerate gypsy-like LTR retrotransposon in the filamentous ascomycete Podospora anserina

In the filamentous ascomycete Podospora anserina a 6,935-bp retrotransposon, Yeti, has been identified and characterized. It is flanked by a 5-bp target site duplication and contains long terminal repeats (LTRs) 354 bp in length. The LTRs show a high degree of identity to the previously reported repetitive element repa, a sequence suggested to represent a solo-LTR element of an unknown transposon. In the investigated Podospora strains, the number of complete Yeti copies is significantly lower than the number of repa elements, with up to 25 copies. Yeti appears to be inactive: it is highly degenerate and no transcripts of the element have been detected even in Podospora cultures grown under elevated stress conditions. The amino acid sequences deduced from Yeti display significant homology, particularly in the reverse transcriptase region, to those of other fungal retrotransposons, indicating that it is a member of the gypsy family. As suggested by the unusual dinucleotide content, degeneration of Yeti appears to be the result of a molecular mechanism resembling repeat-induced point mutation in Neurospora crassa.

Transfer of IFNgamma-depleted CD4(+) T cells together with CD8(+) T cells leads to rejection of murine kidney sarcoma in mice

In the murine kidney sarcoma, vaccination with the tumor-specific large T antigen induces protective immunity against the tumor. Immunity is dependent both on CD8(+) cytotoxic T cells and on CD4(+) T-helper cells. We analyzed whether the cytokine phenotype of induced CD4(+) T-effector cells might determine whether or not the tumor is successfully rejected. By intracytoplasmic staining of CD4(+) cells, IFNgamma-producing (Th1), IL-4-producing (Th2), and IL-10-expressing cells could be identified in vaccinated and non-vaccinated animals responding to tumor growth. Vaccinated mice rejecting the tumor showed an increase in the percentage of IL-4-producing (Th2) cells. In contrast, in non-vaccinated mice succumbing to the tumor, the immunosuppressive IL-10-producing cells became more abundant and the frequency of IFNgamma-expressing cells dropped at later time points. Yet, dominance by either a Th1 or a Th2 response could not be observed. To further clarify the relevance of these subsets, Th1 cells were enriched by cell sorting according to IFNgamma surface expression. Enriched Th1 and depleted cells, mainly consisting of the Th2 phenotype, were transferred together with CD8(+) T cells. Surprisingly, immunity could be transferred either with Th1 or Th2 cells, but Th2 cells were slightly more efficient. This suggests that, at least in the effector phase, a Th1 phenotype is not crucial for the rejection. Our findings support the view that the Th1/Th2 dichotomy is not central in T-cell-mediated tumor rejection.

[Etiology of overweight and obesity]

Obesity results from a predominance of caloric intake over energy expenditure. Twin, adoption and family studies have demonstrated that, together with environmental conditions, various genetic factors play an important role in the pathogenesis of obesity. In recent years, it was possible to identify several defects in single genes responsible for obesity in rodents, some of which may also be involved in human obesity. Besides leptin as the most notable example, numerous other proteins and neuropeptides have been identified in recent years that participate in a complex network to regulate food intake and energy expenditure. The ongoing search for the important obesity genes should not only result in a better understanding of energy metabolism, but may also help in the development of new strategies for the treatment of obese patients.

The degenerate DNA transposon Pat and repeat-induced point mutation (RIP) in Podospora anserina

A degenerate DNA transposon, Pat, was identified in the genomes of various wild-type strains of the filamentous fungus Podospora anserina. In these strains, the number (approximately 20-25 copies per genome) and location of Pat sequences appear to be conserved. Two copies of Pat, one complete and one partial, were cloned and characterized. The sequence of the complete element is 1856 bp long and contains imperfect inverted terminal repeats (ITRs) of 53 bp. The target site duplication comprises the sequence TA. The amino acid sequence derived from one reading frame of Pat shows significant homology to members of the Fot1 family of transposons. However, this reading frame is interrupted by numerous stop codons. Since no transcripts of Pat were identified in different P. anserina strains grown under standard conditions and under increased stress, we conclude that none of the copies of Pat is active in the strains analyzed, under the environmental conditions investigated. Comparison of the sequences of the two cloned Pat sequences revealed 89% (589/747 nucleotides) identity. Most of the differences (82%, 129/158) can be attributed to transitions preferentially at CpA:TpG and CpT:ApG dinucleotides. The dinucleotide ratios in Pat are similar to those in a Neurospora crassa transposon which was subject to repeat-induced mutation (RIP), but differ significantly from those found in single-copy genes of P. anserina and in fungal DNA transposons not modified by this mechanism. Molecular analysis of the progeny of a cross between the wild-type strain and a transgenic strain in which a nuclear gene was duplicated by transformation yielded the first clear evidence that a RIP-like process is active in P. anserina.

Th1/Th2 subsets: distinct differences in homing and chemokine receptor expression?

The functional specialization of T effector cells according to cytokine secretion patterns has been recognized as an important parameter shaping local immune responses. Here we discuss evidence that T cell subsets might also develop distinctive properties related to homing and trafficking into inflamed sites. First, ligands for the inflammation-induced endothelial selectins were found to be induced by IL-12, and hence selectively expressed on Th1 cells generated in vitro. However, their expression on effector cells occurring in vivo is less well correlated with the Th subset. Second, a variety of receptors for and responses towards chemokines have been found to be differentially associated with Th subsets. Notably CCR5 and, to a lesser degree CXCR3 were preferentially found on Th1 cells, CCR4, CCR8 and, more controversial, CCR3 and CXCR4 on Th2 cells. Although many points, such as stability of the phenotype versus dependency on inducing cytokines and activation stages remain to be clarified, it appears that this field provides new insights into the regulation of locally balanced activities of Th subsets and might constitute a promising field for the development of new immunosuppressive drugs.

Association of impaired phosphatidylinositol 3-kinase activity in GLUT1-containing vesicles with malinsertion of glucose transporters into the plasma membrane of fibroblasts from a patient with severe insulin resistance and clinical features of Werner syndrome

The purpose of this study was to examine the molecular mechanism responsible for the defective insulin-stimulated glucose transport in cultured fibroblasts from a patient (VH) with clinical features of Werner syndrome and severe insulin resistance. Thus, in cells derived from VH, the subcellular distribution, structure, functional activity, as well as plasma membrane insertion of GLUT1 glucose transporters were analyzed. Furthermore, the insulin signal transduction pathway leading to activation of phosphatidylinositol (PI) 3-kinase as well as components of GLUT1-containing membrane vesicles were characterized. In fibroblasts derived from VH, GLUT1 glucose transporters were overexpressed by 8-fold in plasma membranes (PM) and by 5-fold in high density microsomes, respectively. Exofacial photolabeling revealed that only 14% of the overexpressed PM-GLUT1 transporters were properly inserted into the plasma membrane. The complementary DNA structure of the patient's insulin receptor and the GLUT1 glucose transporter, the intrinsic activity of plasma membrane glucose transporters, the tyrosine phosphorylation, as well as the protein expression of insulin receptor substrate-1/2 and p85 alpha/beta- and p110 alpha/beta-subunits of PI 3-kinase were normal. However, insulin-stimulated association of the p85 subunit of PI 3-kinase was defective in fibroblasts derived from VH compared to those from controls, and this defect was associated with a reduced IRS-1-dependent activation of PI 3-kinase by 50.2% and 63.6% after incubation for 5 and 10 min with 100 nmol/L insulin, respectively. Furthermore, immunodetection of small GTP-binding Rab proteins in subcellular membrane fractions indicated a decreased expression of Rab4 in total cellular homogenates as well as in high density microsomes by 70% and 58%, respectively. After preparation of GLUT1-containing vesicles, Rab4 was not detected to be a component of these vesicles. Analysis of the PI 3-kinase in GLUT1-containing membrane vesicles revealed insulin-dependent targeting of the p85 subunit to the vesicles immunoadsorbed from VH and control fibroblasts. Importantly, the association of the p85 subunit as well as the p85-immunoprecipitable PI 3-kinase activity were markedly reduced in GLUT1-vesicles derived from the patient. In conclusion, impaired PI 3-kinase activity in GLUT1-containing membrane vesicles derived from fibroblasts of VH is associated with a defective docking and/or fusion process of glucose transporters with the plasma membrane and thus might contribute to the molecular defect causing insulin resistance in this patient.

Leptin stimulates proliferation and TGF-beta expression in renal glomerular endothelial cells: potential role in glomerulosclerosis [seecomments]

BACKGROUND

Leptin inhibits food intake and increases energy expenditure. Although the kidney expresses abundant transcripts of the short form of the leptin receptor (Ob-Ra), a role for this hormone in renal function remains unclear. Because individuals with massive obesity who may exhibit increased leptin serum concentrations develop renal glomerulosclerosis, we studied whether leptin can influence renal growth and profibrogenic processes.

METHODS

The effects of recombinant leptin on proliferation and synthesis of transforming growth factor-beta1 (TGF-beta1) was investigated in cultured glomerular endothelial cells of the rat (GERs) and syngeneic mesangial cells. Furthermore, leptin receptor expression and potential signal transduction pathways were evaluated in GERs. In addition, leptin was also infused for different time periods (72 hr and 3 weeks) into naive rats.

RESULTS

Recombinant mouse leptin induced proliferation of GERs, but not of syngeneic mesangial cells. Coincubation with angiotensin II and leptin exerts additive proliferative effects in GERs. An antileptin-receptor antibody totally abolished this proliferation but did not influence serum-induced proliferation. GER expressed high affinity receptors of the Ob-Ra type (Kd, 4 nM; Bmax, 9700 receptors/cell). Leptin also stimulated phosphorylation of STAT1alpha, and kinase inhibitors attenuated proliferation, suggesting a pivotal role of phosphorylation in this process. Incubation of GERs with leptin also induced mRNA expression of TGF-beta1 and enhanced secretion of this profibrogenic cytokine. Short-term leptin infusion (72 hr) into naive rats induced a significant proliferation, mainly restricted to glomerular endothelial cells, and enhanced glomerular TGF-beta1 mRNA levels. In rats continuously infused for three weeks with leptin, glomerular TGF-beta1 expression was still enhanced, and an additional increase in glomerular collagen type IV mRNA and protein expression was detected. These animals revealed an increase in proteinuria compared with control-infused rats.

CONCLUSION

Our findings are the first in vitro and in vivo demonstration that leptin is a renal growth and profibrogenic factor. These results may be an important contribution to our understanding of how leptin can contribute to renal damage, characterized by endocapillary proliferation and subsequent development of glomerulosclerosis, in pathophysiological situations with high circulating levels such as in diabetics or obese individuals. Although the effects of leptin itself are moderate, growth-promoting and profibrogenic effects may be enhanced in concert with other factors such as angiotensin II.

Modulation of gene expression by (CA)n microsatellites in the filamentous ascomycete Podospora anserina

A microsatellite consisting of the alternating pyrimidine-purine sequence (CA)n. (TG)n is found to occur in very conserved form in the genome of various races of the filamentous ascomycete Podospora anserina. Screening of a cDNA library revealed that this sequence is frequently transcribed. In this study, we focused our attention on a short (CA)5 microsatellite located in the 5' untranslated sequence of the glyceraldehyde-3-phosphate dehydrogenase (gpd) gene of P. anserina. Specifically, we investigated whether or not the number of repeat units present in the microsatellite affects the expression of the beta-D-glucuronidase (gusA) reporter gene introduced on an autonomously replicating plasmid into fungal protoplasts. The results show that an increase in the number of microsatellite repeat units positively affects reporter gene expression.

Missense variants in the human peroxisome proliferator-activated receptor-gamma2 gene in lean and obese subjects

The peroxisome proliferator-activated receptor-gamma2 (PPARgamma2) is almost uniquely expressed in adipose tissue and is of major importance for fat cell differentiation and lipid metabolism. This study was undertaken to assess whether two missense variants in the PPARgamma2 gene are associated with early-onset obesity. A previously described polymorphism encoding for an amino acid exchange in codon 12 (Pro12Ala) was detected with allele frequencies of 0.13 in 296 markedly obese children and adolescents and 0.14 in 130 lean individuals. A Pro115Gln variant, which had been linked to obesity in Germans in a previous association study, was not detected in any of our obese or lean subjects, who are also of German origin. We conclude from our data that these two variants in the PPARgamma2 gene are unlikely to contribute to the high prevalence of early-onset obesity.

Insulin-mediated pseudoacromegaly in a patient with severe insulin resistance: association of defective insulin-stimulated glucose transport with impaired phosphatidylinositol 3-kinase activity in fibroblasts

The purpose of this study was to clinically and biochemically describe an insulin resistant patient with insulin-mediated pseudoacromegaly and in addition, to examine the molecular cause responsible for the defective insulin-stimulated glucose transport in cultured fibroblasts derived from the patient. The patient was a 64 year old female with severe insulin resistant diabetes mellitus, requiring up to 200 U insulin per day, associated with typical acromegaloid characteristics including increased hand and foot size, macroglossia and development of coarse facial features. Pituitary magnetic resonance imaging as well as multiple GH and IGF-1 measurements were normal. In cultured fibroblasts derived from the patient, (i) insulin-stimulated glucose transport, (ii) the subcellular distribution of GLUT1 glucose transporters, (iii) insulin-stimulated IRS-1-immunoprecipitable phosphatidylinositol (PI) 3-kinase activity, as well as (iv) protein expression of the small GTP-binding protein Rab4 was determined. The results indicate, that insulin's ability to stimulate glucose transport is defective in the patients fibroblasts although the GLUT1 content in the plasma membrane was increased by 34% when compared to control cells. Furthermore, the IRS-1 dependent activation of PI 3-kinase was reduced by 39.6% after incubation with 10 nM insulin for 5 min. Interestingly, immunodetection of the small GTP-binding protein Rab4, which is believed to be involved in the regulation of glucose transporter vesicle targeting to the plasma membrane, revealed a marked reduction of the expression of Rab4 protein in a total membrane fraction by 57.4%. In conclusion, in fibroblasts of a patient with clinical and biochemical evidence of pseudoacromegaly, the defective insulin-stimulated glucose transport was associated with impaired insulin-stimulated PI 3-kinase activity, which may contribute to the severe insulin resistant state of this patient.

Lymphocyte migration in lymphocyte function-associated antigen (LFA)-1-deficient mice

Using lymphocyte function-associated antigen (LFA)-1(-/-) mice, we have examined the role of LFA-1 and other integrins in the recirculation of lymphocytes. LFA-1 has a key role in migration to peripheral lymph nodes (pLNs), and influences migration into other LNs. Second, the alpha4 integrins, alpha4beta7 and alpha4beta1, have a hitherto unrecognized ability to compensate for the lack of LFA-1 in migration to pLNs. These findings are confirmed using normal mice and blocking LFA-1 and alpha4 monoclonal antibodies. Unexpectedly, vascular cell adhesion molecule (VCAM)-1, which is essential in inflammatory responses, serves as the ligand for the alpha4 integrins on pLN high endothelial venules. VCAM-1 also participates in trafficking into mesenteric LNs and Peyer's patch nodes where mucosal addressin cell adhesion molecule 1 (MAdCAM-1), the alpha4beta7-specific ligand, dominates. Both alpha4beta1, interacting with ligand VCAM-1, and also LFA-1 participate in substantial lymphocyte recirculation through bone marrow. These observations suggest that organ-specific adhesion receptor usage in mature lymphocyte recirculation is not as rigidly adhered to as previously considered, and that the same basic sets of adhesion receptors are used in both lymphocyte homing and inflammatory responses.

No evidence for involvement of the leptin gene in anorexia nervosa, bulimia nervosa, underweight or early onset extreme obesity: identification of two novel mutations in the coding sequence and a novel polymorphism in the leptin gene linked upstream region

Mutations in the leptin gene can result in profound obesity in both rodents and humans. In humans, serum leptin levels correlate with body mass index (BMI: kg m(-2)). However, in patients with anorexia nervosa (AN) leptin levels are lower than in BMI-matched healthy controls. We had previously argued that genes involved in weight regulation should be considered as candidate genes for AN. To investigate this hypothesis we screened the coding region of the leptin gene and part of the leptin gene linked upstream region (LEGLUR) in 49 patients with AN and 315 children and adolescents with extreme obesity. Two novel mutations in the coding region (Ser-91-Ser; Glu-126-Gln), each found in a single proband, and a novel polymorphism in the LEGLUR (position -1387 G/A; frequency of both alleles approximately 0.50) were identified. Tests for association of LEGLUR polymorphism alleles were negative by comparing allele frequencies between 115 AN patients, 71 bulimia nervosa patients, 315 extremely obese children and adolescents, 141 healthy underweights and 50 controls that were not selected for body weight. Tests for transmission disequilibrium were also negative. Hence, an influence of variations in the leptin gene on eating disorders or extreme early onset obesity could not be detected.

Analysis and sorting of T cells according to cytokine expression

Functional distinct populations of T helper cells can be defined according to the expression of cytokines. A remarkable diversity of cytokine expression has been demonstrated in single T cells even from clonal populations and up to now no stable surface markers have been described which on the single-cell level directly correlate with the secretion of a certain cytokine. Since cytokines are the major parameters of T cell effector function we have developed strategies which now allow to separate cells according to the specific cytokines they secrete. The "affinity matrix technology"--secreted molecules are relocated to the cell surface by an artificially created antibody matrix--allows to isolate cells according to a distinct secreted product. In addition to this universal, but laborious technology, we could demonstrate by high-sensitivity immunofluorescence that IFN-gamma and IL-10 but not IL-2 and IL-4 are specifically expressed in low copy number on the surface of cells secreting these cytokines. Surface IFN-gamma and IL-10 are the first unambiguous surface markers for pro-inflammatory IFN-gamma-secreting Th 0/1 cells and IL-10-producing anti-inflammatory Th2/3 cells. We have used purified cytokine-secreting T cells to study in individual T cells the sequential production of IL-2, IFN-gamma, and IL-10, the stability of IFN-gamma expression and the selective homing of IFN-gamma-producing cells into inflamed tissues.

Analysis of the uncoupling protein-1 (UCP1) gene in obese and lean subjects: identification of four amino acid variants

Uncoupling protein-1 (UCP1) is uniquely expressed in brown adipose tissue (BAT) and of major importance for the tissues thermogenic capacity. This study was undertaken to detect variants in the UCP1 gene by single strand conformational polymorphism (SSCP) analysis and subsequent sequencing, and determine their potential association with obesity. Four variants predicting for amino acid substitutions were detected, of which Arg40Trp (exon 1) and Lys257Arg (exon 5) were rare mutations. In contrast, the allele frequency of a polymorphism in exon 2 predicting for an Ala64Thr substitution was 8.2% in a cohort of 293 obese children and adolescents compared to 4.1% in 134 lean individuals, while the allele frequency of a Met229Leu variant (exon 5) was not markedly different between the obese (10.4%) and lean (12.0%) study groups. Although one of the identified polymorphisms tends to have a higher frequency in obese than in lean subjects, variants of the UCP1 gene do not seem to contribute significantly to the development of early-onset obesity in the German population.