[SREBP-1 and fatty liver. Clinical relevance for diabetes, obesity, dyslipidemia and atherosclerosis]. / SREBP-1 und Fettleber. Klinische Bedeutung für Diabetes, Adipositas, Dyslipidämie und Atherosklerose.

Insulin resistance and visceral fat distribution usually play a major role in the development of clinical aspects of the metabolic syndrome, such as dyslipidemia, diabetes and atherosclerosis. In this review, the focus will be on some novel relationships with a fatty liver, for which susceptibility appears to be mediated by the activity of transcription factors, such as sterol regulatory element-binding protein 1 (SREBP-1). In addition to this molecular aspect therapeutic life-style modifications, such as weight reduction which are associated with increased insulin sensitivity and a decrease of fat in the liver will be discussed.

The natural history of classic galactosemia: lessons from the GalNet registry.

BACKGROUND: Classic galactosemia is a rare inborn error of carbohydrate metabolism, caused by a severe deficiency of the enzyme galactose-1-phosphate uridylyltransferase (GALT). A galactose-restricted diet has proven to be very effective to treat the neonatal life-threatening manifestations and has been the cornerstone of treatment for this severe disease. However, burdensome complications occur despite a lifelong diet. For rare diseases, a patient disease specific registry is fundamental to monitor the lifespan pathology and to evaluate the safety and efficacy of potential therapies. In 2014, the international Galactosemias Network (GalNet) developed a web-based patient registry for this disease, the GalNet Registry. The aim was to delineate the natural history of classic galactosemia based on a large dataset of patients. METHODS: Observational data derived from 15 countries and 32 centers including 509 patients were acquired between December 2014 and July 2018. RESULTS: Most affected patients experienced neonatal manifestations (79.8%) and despite following a diet developed brain impairments (85.0%), primary ovarian insufficiency (79.7%) and a diminished bone mineral density (26.5%). Newborn screening, age at onset of dietary treatment, strictness of the galactose-restricted diet, p.Gln188Arg mutation and GALT enzyme activity influenced the clinical picture. Detection by newborn screening and commencement of diet in the first week of life were associated with a more favorable outcome. A homozygous p.Gln188Arg mutation, GALT enzyme activity of ≤ 1% and strict galactose restriction were associated with a less favorable outcome. CONCLUSION: This study describes the natural history of classic galactosemia based on the hitherto largest data set.

Increased low grade inflammatory serum markers in patients with Polycystic ovary syndrome (PCOS) and their relationship to PPARgamma gene variants.

The Polycystic ovary syndrome (PCOS) is the most frequent endocrine disorder in premenopausal women and is associated with features of the insulin resistance syndrome, altered glucose homeostasis, and central obesity. Inflammation appears to be a link between obesity and insulin resistance, because adipose tissue is one major source of proinflammatory cytokines. Since peroxisome proliferator-activated receptor (PPAR)gamma affects adipocyte differentiation as well as insulin sensitivity, we investigated whether the levels of proinflammatory factors in PCOS patients are related to sequence variations of the PPAR gamma gene. Proinflammatory cytokine levels, i.e. IL-1 beta, IL-6, IL-7, IL-8, IL-17 and TNFalpha, were evaluated in PCOS patients (n=21) in comparison to obese controls (n=120). Next to this the complete coding sequence of the PPAR gamma gene was investigated by resequencing all probands. We show that the levels of IL-8 and IL-17 were unchanged, IL-1 beta, IL-6 and TNFalpha were elevated and the level of IL-7 was decreased in PCOS patients compared to obese controls. Sequence analyses of the PPAR gamma gene indicated that neither the common polymorphisms P12A or H478 H, nor novel polymorphisms (E79Q, V32G, -39 T>C, c.480 +33 t > g,) or unique sequence variations (S22S, A23A, T41A, S226C, K272 T, I484I, c.819 +24 a>c) detected in this investigation revealed evidence for a direct association of PPAR gamma with altered IL-7, IL-1beta, IL-6 and TNFalpha levels in PCOS patients. So, alterations in inflammatory serum markers appear to be a feature of PCOS per se, and are independent of PPAR gamma variants.

[LDL cholesterol--why lower and lower?]. / Wie weit sollen wir die Cholesterinwerte noch senken? Für Hochrisikopatienten kann das LDL nicht niedrig genug sein.

Large interventional studies with statins have confirmed that drug-lowering of LDL cholesterol by at least 25-30% is associated with a significant reduction in the cardiovascular risk. In high-risk patients, the plasma LDL cholesterol level should be < 100 mg/dl. If the levels are initially low, the aim is to achieve a reduction of at least 30-40%. More recent studies have shown that reducing the LDL cholesterol to < 70 mg/dl can stop the further growth of plaques, and can possibly even bring about their regression.

An association between NIDDM and a GAA trinucleotide repeat polymorphism in the X25/frataxin (Friedreich's ataxia) gene.

Friedreich's ataxia is the most common hereditary ataxia and is frequently associated with disturbances of glucose metabolism. This autosomal recessive disease is caused by the decreased expression of a mitochondrial protein, frataxin, encoded by the X25 gene. Homozygous expansion of a GAA repeat in the first intron of X25 inhibits frataxin expression and is associated with clinical disease. We evaluated whether heterozygous expansions of the triplet repeat in the frataxin gene X25 may be associated with NIDDM in two genetically distinct populations--one in Germany (n = 358) and the other in the U.S. (n = 292)--using a polymerase chain reaction-based assay. Intermediate expansions (10-36 repeats), which are longer than normal but not sufficient for the appearance of the ataxia phenotype, were found in 24.7 and 27.3% of these two NIDDM cohorts compared with 7.6 and 6.3% of the matched control subjects (both P < 0.001). The odds ratios were 3.36 (95% CI 1.72-6.55) for the German group and 4.01 (2.08-7.74) for the U.S. group. Therefore, we conclude that the X25/frataxin GAA repeat polymorphism is associated with NIDDM in a frequency higher than any other mutation heretofore described. Further studies are needed to elucidate the possible role of frataxin in the pathogenesis of NIDDM.

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

The effect of insulin and growth factor mediated signaling to gene regulation was investigated in cultured fibroblasts of a patient with a premature aging syndrome (metageria) and severe insulin resistance. Insulin receptor structure and function as well as major pathways activated by insulin, i.e. phosphatidyl inositol-3 kinase (PI-3 K) cascade or mitogen-activated protein kinase (MAPK) cascades, were functional. Inducibility of the proto-oncogene cfos, a representative endpoint of signaling pathways related to gene expression, by growth factors or insulin was reduced in patient cells. This reduced induction persisted in cfos promoter reporter gene studies indicating that the post receptor defect is localized proximal to the cfos promoter itself. Abundances of the transcription factors Elk-1 and SRF being major players in coupling of MAPKs to cfos promoter activation were not altered. However, basal and inducible phosphorylation of Elk-1 was impaired. In addition, basal and stimulated transcriptional activity mediated by Elk-1 was almost abolished in patient cells. Therefore these results identify a post receptor defect in cFos induction, which appears to be related to a functional alteration of Elk-1. A possible relation of this signal transduction defect to the specific premature aging syndrome remains to be elucidated.

Correction of insulin resistance and the metabolic syndrome.

Insulin resistance is a common phenomenon of the metabolic syndrome, which is clinically characterized by a clustering of various cardiovascular risk factors in a single individual and a higher prevalence of respective complications, such as coronary heart disease and stroke. At the cellular level, insulin resistance is defined as a reduced insulin action, which can affect not only glucose uptake, but also gene regulation. Elucidation of novel signaling networks within the cell which are mediating and affecting insulin action will reveal many new genes and drug targets that are potentially of clinical relevance in the future. In this chapter, we propose that the metabolic syndrome might be a clinical consequence of altered gene regulation. This is illuminated in the context of transcription factors, e.g., sterol regulatory element binding proteins (SREBPs), coupling signals from nutrients, metabolites, and hormones at the gene regulatory level with pathobiochemical features of increased lipid accumulation in lean nonadipose tissues. The phenomenon of ectopic lipid accumulation (lipotoxicity) appears to be a novel link between insulin resistance, obesity, and possibly other features of the metabolic syndrome. Therefore, the investigation of specific gene regulatory networks and their alterations might be a clue to understanding the development and clustering of different cardiovascular risk factors in different individuals. As cellular sensors transcription factors--as common denominators of gene regulatory networks--might thereby also determine the susceptibility of individuals to cardiovascular risk factors and their complications.

Identification of mutations of the arginine vasopressin-neurophysin II gene in two kindreds with familial central diabetes insipidus.

Familial central diabetes insipidus is transmitted as an autosomal dominant trait with almost complete penetrance. Twenty-three different mutations of the arginine vasopressin-neurophysin II gene have been reported to date, located within the signal peptide-, the arginine vasopressin-, or the neurophysin II-coding region. In the present study two kindreds with familial central diabetes insipidus were examined. The entire coding region of the arginine vasopressin-neurophysin II gene of one affected subject of each family was amplified by PCR and subcloned into a pUC 18 plasmid, and six positive clones were sequenced. After identification of the mutation, direct sequencing was performed on the respective sequence of family members and 28 healthy control subjects. In family A, a missense mutation (C-->T) at nucleotide position 280 was detected, predicting the substitution of alanine by valine at position -1 of the signal peptide. All affected subjects were heterozygote for the mutation, whereas none of the unaffected family members or control subjects displayed the mutant sequence. In family B, a missense mutation within the neurophysin II-coding sequence was identified (nucleotide 1757, G-->C), predicting the substitution of glycine by arginine at position 23. Again, affected family members were found to be heterozygote for the mutation, which was not observed in unaffected family members or in control subjects. Although the mutation of family A was recently described in 3 other kindreds as well, the mutation within the neurophysin II-coding region represents a novel mutation of the AVP-NP II gene.

Identification of a novel mutation in the arginine vasopressin-neurophysin II gene in familial central diabetes insipidus.

Familial central diabetes insipidus is an inherited disease of predominant autosomal dominant trait characterized by a deficiency of arginine vasopressin. The arginine vasopressin-neurophysin II ( AVP-NPII) gene consists of three exons and is located on chromosome 20p13 encoding for the precursor protein of AVP. We investigated two Caucasian families with a typical autosomal dominant trait of familial central diabetes insipidus, defined by deficiency of arginine vasopressin. After PCR amplification of exon 1 and exon 2/3, fragments were pooled and purified. Nucleotide sequencing was performed with the Taq DyeDeoxy-terminator cycle sequencing method using nested primers. Two mutations in the coding region of NPII were identified. In family C we found a heterozygous G ==> C missense mutation (AA61) in exon 2 leading to the substitution of cystein with serine. In family D a novel heterozygous nonsense mutation in exon 3 (AA 83, GAG ==> TAG) was indentified, leading to a stop codon instead of glutamine. Both mutations were confirmed by restriction analysis and were found in all affected but not in healthy family members or control subjects. We therefore have identified a missense mutation of the AVP-NPII gene and a novel mutation predicting a truncated protein.

A novel nonsense mutation in GCK exon 9 co-segregates with diabetes phenotype.

Maturity-onset diabetes of the young is an autosomal dominant form of non-insulin dependent diabetes mellitus and is caused by mutations in at least six different genes. In the most common forms, i.e. MODY2 and MODY3, the glucokinase (GCK) and the hepatocyte nuclear factor (HNF)-1alpha gene is affected, respectively. We have screened the GCK gene and HNF-1alpha gene by direct sequencing in three German families with early onset type-2-diabetes, possibly MODY. Next to known polymorphisms we have identified two novel intronic insertions in GCK and a novel non-sense mutation in exon 9 (C364 X). The latter mutation has an autosomal dominant inheritance pattern. Accordingly, this novel mutation segregates with diabetes phenotype in this family.

[Combined analyses of paraoxonase-1 and IGF-2 polymorphism in polycystic ovary syndrome]. / Kombinierte Analyse von Paraoxonase-1- und IGF-2-Polymorphismen bei polyzystischem Ovarsyndrom.

BACKGROUND: Apart from impaired reproductive function patients with polycystic ovary syndrome (PCOS) also have signs and symptoms belonging to the metabolic syndrome. A genetic basis for PCOS is likely as the syndrome clusters in families. Putative candidate genes are paraoxonase (PON)-1 gene and the IGF-2 INS1/VTR IGF cluster, which have been shown to be genetically linked to lipid metabolism o insulin sensitivity, two major aspects of the PCOS phenotype. PATIENTS AND METHODS: The ApaI polymorphism (rs:680) in the IGF-2 cluster and the -108 polymorphism (rs:705 379) in PON-1 were evaluated in a collective of 153 PCOS patients and 178 age and BMI matched controls for an association to PCOS. RESULTS: The polymorphism in the IGF-2 cluster was identified in both groups in comparable frequencies (PCOS/control: A: 0.351/0.325; G: 0.648/0.674; OR: 0.8886, 95 %CI 0,648-1.2236) and equal genotype distribution (PCOS/control: GG: 0.399/0.461; AG: 0.4962/0.4277; AA: 0.1042/0.111). Frequencies of the PON-1 polymorphism were also comparable (PCOS/control: T: 0.493/0.483; C: 0.5633/0.5168; OR: 0.9569 95 % CI: 0.707-1.43024), but the distribution (PCOS/control: CC: 0.2679/0.2032; CT: 0.4768/0.628; TT: 0.258/0.169) was significantly different. The combined analyses of both polymorphism revealed that the genotypes IGF-2 (GG)/ PON-1 (TT) with OR 1.64741 (95 % CI 0.7388 - 3.6735) and IGF-2 (AA)/ PON-1 (TT) with OR 2.6733 (95 % CI 0.7579 - 9.4291) were more frequent in the PCOS group, whereas the genotype IGF-2 (AA)/ PON-1 (CC) did not occur in the PCOS group at all. According to the molecular analyses significant differences in serum parameters were identified. CONCLUSION: This investigation indicates, that only the combined analyses of putative candidate genes allowed a genotype-phenotype correlation in PCOS.

The Pro387Leu variant of protein tyrosine phosphatase-1B is not associated with diabetes mellitus type 2 in a German population.

OBJECTIVES: Diabetes mellitus type 2 (DM-2) is a complex disorder with a strong genetic background. Protein tyrosine phosphatase-1B (PTP-1B) dephosphorylates various receptor protein kinases in vitro, including the beta subunit of the insulin receptor, therefore representing a potential candidate to be involved in the polygenic pathogenesis of DM-2. Recently a Pro387Leu variant of the PTP-1B gene has been associated with an increased risk of DM-2 in a Danish population. Reports from China and Finland failed to confirm this association. DESIGN, SETTING AND SUBJECTS: The purpose of the present study was to examine the possible association between the presence of DM-2 and the Pro387Leu polymorphism in a German Caucasian population. A total of 836 subjects (age 20-92 years) participated in the study. The presence of the Pro387Leu variant of the PTP-1B gene was investigated using polymerase chain reaction (PCR) restriction fragment-length polymorphism in 402 subjects with DM-2 (231 men, 171 women, age 63.1 +/- 10.8 years, BMI 28.7 +/- 5.1 kg m(-2)) and in 434 normoglycemic age- and sex-matched control subjects (248 men, 186 women, age 64.4 +/- 6.5 years, BMI 26.5 +/- 3.7 kg m(-2)). RESULTS: Nine subjects in the control group and nine in the diabetic group (allelic frequency 0.99% in both groups) carried the Pro387Leu polymorphism. A meta-analysis on published data of >3000 subjects including our own data did not find an association between the polymorphism and DM-2. In addition, the polymorphism had no significant influence on the presence of atherosclerotic disease, whilst the influence of other known cardiovascular risk factors was confirmed. Furthermore, the impact of the mutation on metabolic and anthropometric parameters in both groups was examined. Amongst the controls there were no significant differences in BMI, HDL and LDL cholesterol or blood pressure between the two groups with or without the Pro387Leu polymorphism. The same was true for the diabetic group. Interestingly, in both diabetics and controls, Pro387Leu carriers had significantly higher triglycerides. In a logistic regression model only BMI and family history but not polymorphism were predictors of DM-2. CONCLUSIONS: In conclusion, the present data suggest that in a German Caucasian population the Pro387Leu polymorphism of the PTP-1B gene is not associated with DM-2 but may play a role in other metabolic phenotypes.

Reduction of postchallenge hyperglycaemia prevents acute endothelial dysfunction in subjects with impaired glucose tolerance.

OBJECTIVES: To investigate whether selective reduction of postchallenge hyperglycaemia influences acute endothelial dysfunction, a very early manifestation of vascular disease, in patients with impaired glucose tolerance. METHODS: In a randomized, double-blind, placebo-controlled, cross-over study the acute effect of 200-mg acarbose was investigated in 28 subjects with diagnosed impaired glucose tolerance. Flow-mediated dilation (FMD) of the brachial artery was determined as a measure of endothelial function before and 2 and 3 h after ingestion of 100-g saccharose. Asymmetrical dimethylarginine (ADMA) was measured by high-performance liquid chromatography. RESULTS: A negative correlation was observed between the changes of glucose and FMD (r = 0.416, P = 0.0018) 2 h after ingestion of saccharose. At 3 h, neither blood glucose nor FMD were different from baseline. Changes of both blood glucose (P = 0.0007) and FMD (P = 0.046) were significantly lower after administration of acarbose. Subgroup analysis revealed that the effect of acarbose was restricted to those subjects with an increase of blood glucose above the median increase of glycaemia. No changes of plasma ADMA were observed. CONCLUSIONS: Our data clearly demonstrate that the postchallenge alteration of vascular function in patients with impaired glucose tolerance is caused by the acute elevation of glycaemia but not mediated by ADMA.

Metabolic syndrome and hypertension: pathophysiology and molecular basis of insulin resistance.

Several recent studies indicate that type 2 diabetes, arterial hypertension, lipid disorders as well as visceral obesity are coronary risk factors which might belong to a syndrome which is caused by decreased insulin sensitivity with compensatory hyperinsulinaemia. More than 50% of patients with essential hypertension have some degree of insulin resistance, but in contrast to dyslipoproteinaemia and glucose intolerance the causal relation between insulin resistance and elevated arterial blood pressure appears not to be as evident. One explanation is that the link between blood pressure and insulin sensitivity might be mainly related to concomitant obesity. Accordingly, obesity can be associated with an increased activity of the sympathetic nervous system, elevated plasma levels of the vasoconstrictor endothelin-1, and decreased insulin-induced endothelium-dependent vasodilation. Furthermore, adipocytes can secrete vasogenic peptides, such as angiotensinogen. Since insulin resistance is a polygenic disorder, the two basic genetic approaches we follow is to identify genetic defects of insulin action in cells of patients with inherited syndromes of insulin resistance and to characterize molecular mechanisms of insulin regulated gene expression. The results show that insulin can affect the expression rate of various genes, e.g. involved in cholesterol and fatty acid metabolism, by modulating the activity of transcription factors coupled to the MAP kinase cascade and that a genetic postreceptor defect in these intracellular signaling pathways might have a pleiotropic effect on cell metabolism and clinical phenotype.

[Mechanisms of plaque stabilization]. / Mechanismen der Plaquestabilisierung.

Numerous angiographic control regression studies have demonstrated that aggressive reduction of plasma cholesterol significantly reduces the incidence of clinical overt cardiovascular complications, but has almost no effect on the angiographically determined luminal diameter of the coronary arteries. These, as well as other morphological and molecular studies have led to a new paradigm of coronary heart disease, i.e. clinical prognosis is not mainly determined by the extent of a single stenosis but by the number and biological nature of atherosclerotic plaque. Accordingly, stable plaques can be differentiated from instable or vulnerable plaques. The vulnerable or instable plaque is characterized by a large lipid-rich core with surrounding inflammation and a thin friable overlying fibrous cap susceptible to rupture or fissuring and thereby a high risk of thrombus formation. Rupture and thrombus formation can cause an acute coronary syndrome, such as unstable angina or myocardial infarction. There is increasing clinical and experimental evidence that statins do not only lower plasma cholesterol, but might also have direct effects on the vessel wall, possibly explaining early benefits in cardiovascular complications. Reduction of plasma cholesterol by lipid lowering therapy has been shown to significantly improve paradoxic vasoconstriction of cardiac vessels, a phenomenon indicating endothelial dysfunction. In addition, lipid lowering therapy can result in a diminution of the lipid-rich core, a reduction of inflammatory cells within the plaques, decreased macrophage activation as well as foam cell formation and events related to thickening of the fibrous cap. A clinical prospective should be to better clinically morphologically characterize the vulnerability of plaques in order to therapeutically and preventively reduced specific events leading to acute coronary syndromes, such as unstable angina or myocardial infarction.

Regulation of the LDL receptor gene expression by hormones.

Promoter activity of the LDL receptor gene is stimulated by insulin and estradiol and mediated by SRE-1, which acts as a hormone sensitive cis-elemente. Using the antisense technique we reveal that SREBP-1 is selectively involved in the signal transduction pathway of insulin and IGF-I.

Stabilization of atherosclerotic plaque during lipid lowering.

Lipid lowering therapy leads to a great reduction of cardiovascular complications, but has almost no effect on the degree of stenosis of coronary arteries. These findings have lead to a new paradigm of coronary artery disease, i.e. clinical prognosis is not only determined by the extent of a single stenosis, but mainly by the number and structure of atherosclerotic plaque. Rupture of an instable or vulnerable plaque, characterized by a large lipid-rich central core, inflammatory cells, and a thin fibrous cap, causes sudden thrombus formation and thereby acute coronary syndromes. There is accumulating evidence that cholesterol lowering can result in plaque stabilization and improvement of endothelial dysfunction, reviewed recently in this journal. Accordingly, this review focuses on new molecular mechanisms which provide evidence that reduction of cellular cholesterol activates novel transcription factors, called sterol regulatory element binding proteins, which can regulate not only the LDL receptor, thereby reducing plasma cholesterol levels, but also a diverse number of other genes. These gene regulatory events might link cholesterol lowering not only to cellular cholesterol metabolism, but also to triglyceride metabolism, cell differentiation and other events potentially stabilizing vulnerable plaque.

MAP kinases Erk1/2 phosphorylate sterol regulatory element-binding protein (SREBP)-1a at serine 117 in vitro.

Sterol regulatory element-binding protein (SREBP)-1a is a transcription factor sensing cellular cholesterol levels and integrating gene regulatory signals mediated by MAP kinase cascades. Here we report the identification of serine 117 in SREBP-1a as the major phosphorylation site of the MAP kinases Erk1/2. This site was identified by nanoelectrospray mass spectrometry and peptide sequencing of recombinant fusion proteins phosphorylated by Erk1/2 in vitro. Serine 117 was verified as the major phosphorylation site by in vitro mutagenesis. Mutation of serine 117 to alanine abolished Erk2-mediated phosphorylation in vitro and the MAP kinase-related transcriptional activation of SREBP-1a by insulin and platelet-derived growth factor in vivo. Our data indicate that the MAP kinase-mediated effects on SREBP-1a-regulated target genes are linked to this phosphorylation site.

SREBP-1 mediates activation of the low density lipoprotein receptor promoter by insulin and insulin-like growth factor-I.

Transcription of the low density lipoprotein (LDL) receptor gene is regulated by intracellular cholesterol concentration, hormones, and growth factors. We studied the mechanisms by which insulin and estradiol stimulate promoter activity of the LDL receptor gene. Hormonal effects were analyzed in HepG2 cells after transient transfection with promotor reporter gene constructs. Successive 5' deletions of the LDL receptor promoter fragment from -537 to +88 revealed the sterol regulatory element 1 (SRE-1) between -65 and -56 as an insulin- and estradiol-sensitive cis-element. If the SRE-1 is point mutated at position -59 (C to G), which abolishes the binding of the SRE binding proteins (SREBP-1 and SREBP-2), no insulin or estradiol stimulatory effect on reporter gene expression was observed, indicating a role of SRE binding proteins in this regulatory mechanism. The concentration of the 125-kDa membrane-integrated SREBP-1 precursor protein in LDL repressed HepG2 cells is not altered by hormone treatment. Concentrations of SREBP-1 mRNA and precursor protein are reduced significantly by high and stable expression of an SREBP-1 antisense cDNA fragment in HepG2 cells (SREBP1(-) cells). Transfection of SREBP1(-) cells with promoter construct phLDL4 (-105 to +88) reduces induction of reporter gene activity by insulin and insulin-like growth factor-I to 35 and 17%, respectively, compared with HepG2 cells. The stimulatory effect of estradiol remains unchanged, and the inductions by pravastatin are enlarged. We conclude that different regulatory effects converge at SRE-1, but that SREBP-1 is selectively involved in the signal transduction pathway of insulin and insulin-like growth factor-I leading to LDL receptor gene activation.