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D Rosskopf

Publications and source records attributed to D Rosskopf.

At least 19 recordsLinked to original sources
PubMed2006

Cluster headache is associated with the G1246A polymorphism in the hypocretin receptor 2 gene.

The G1246A polymorphism in the gene of the hypocretin receptor 2 (HCRTR2) has been linked to the risk for cluster headache (CH). The authors examined this association in a large sample of 226 patients with CH and 266 controls from Germany. The genotype and allele distribution varied significantly between patients and controls. Homozygous carriers of the G-allele had a twofold increase in risk for CH (OR 1.97; 95% CI 1.32 to 2.92; p = 0.0007).

Adult↗
PubMed2003

Glucose and lipid metabolism in young lean normotensive males with the G protein beta3 825T-allele.

The 825T-allele of the C825T polymorphism in GNB3, the gene for the G protein beta3 subunit, has been reported to be associated with essential hypertension and obesity. Expression of Gbeta3s, the gene product of GNB3 associated with the GNB3 825T-allele, causes increased signal transduction which may contribute to pathogenetic mechanisms ultimately resulting in hypertension and obesity. Given the known involvement of heterotrimeric G proteins in insulin secretion and insulin action on the cellular level, we analysed insulin sensitivity in each 15 young lean normotensive males with TC- and CC-genotypes, respectively. Blood glucose and serum insulin samples were taken during a standard oral glucose tolerance test. Insulin-stimulated glucose disposal was analysed by euglycemic-hyperinsulinemic clamp. Both groups did not differ with regard to the time-courses for glucose or insulin concentrations in the oral glucose tolerance test. Furthermore, insulin-stimulated glucose disposal was virtually independent of genotype. The TC-genotype is not associated with a primary defect in insulin secretion or sensitivity suggesting that obesity and hypertension in carriers of 825T do not likely result from primary alterations in glucose and insulin homeostasis. However, GNB3 825T-associated obesity may predispose to insulin resistance, an issue which remains to be investigated. Furthermore, fasting cholesterol was significantly higher in TC compared to CC genotype (4.71 versus 3.96 mmol/l; p = 0.007) suggesting that enhanced G protein signalling might be associated with alterations of cholesterol metabolism.

Adult↗
PubMed2001

Human G protein beta3 subunit variant does not alter hypercarbic or hypoxic ventilatory response.

Hypercarbic respiratory drive is mainly determined by PCO(2) and pH with activity of the intracellular Na+/H+ exchanger (NHE) playing an important role in maintaining intracellular pH and respiratory drive. Because NHE activity varies with genetically different G-protein beta3 subunits (GNB3) (C/T polymorphism at nucleotide position 825) different genotypes might alter respiratory regulation. To test the hypothesis that short-term ventilatory responses vary with different GNB3 healthy volunteers with different genotypes (CC, TC, TT) were exposed to either hyperoxic hypercarbia (n=33) or to isocapnic hypoxia (n=31), respectively. There was no difference between CC, TC, and TT genotypes in hypercarbic and hypoxic respiratory drive when assessed as the ratio of minute ventilation over endexpiratory PCO(2) changes (DeltaV.E/DeltaPETCO(2)), maximal tolerable PETCO(2), and ratio of changes in ventilation over arterial haemoglobin desaturation (DeltaV.E/DeltaSO(2)), respectively. Thus, short-term hypercarbic and hypoxic ventilatory drive do not differ between individuals with genotypes encoding different GNB3. Whilst respiratory control may still be influenced by G-protein aberration, other mechanisms seem to have a more important role in controlling ventilation.

Genotype↗
PubMed2000

Interaction of the G protein beta 3 subunit T825 allele and the IRS-1 Arg972 variant in type 2 diabetes.

BACKGROUND: Type 2 diabetes mellitus is a common late-onset disease with a strong genetic component. It is characterized by insulin resistance which results from alterations in insulin signal transduction. The G protein beta 3 subunit 825T allele was recently found to be associated with hypertension and obesity which makes it a sensible candidate gene for type 2 diabetes. METHODS: In a case-control study on 320 male patients and 962 male healthy controls we investigated the association of two candidate genes with diabetes, i.e. (i) the GNB3 825T allele, associated with a G protein beta 3 subunit splice variant and enhanced intracellular signal transduction, and (ii) the insulin receptor substrate-1 (IRS-1) 972Arg variant, which encodes a protein variant associated with cellular insulin resistance. RESULTS: The GNB3 825T allele and the IRS-1 972Arg variant were significantly associated with diabetes (odds ratios for either variant 1.4 1.8). Odds ratios were 3 4 in males carrying both alleles. CONCLUSIONS: The results document an association of a hypertension susceptibility gene with type 2 diabetes which may partially explain the frequent coexistence of both disorders.

Adult↗
PubMed2000

Enhanced epinephrine-induced platelet aggregation in individuals carrying the G protein beta3 subunit 825T allele.

The 825T allele of a common C825T polymorphism in the gene encoding the beta3 subunit of heterotrimeric G proteins is associated with enhanced activation of pertussis toxin (PTX)-sensitive G proteins. We investigated responses of human platelets upon stimulation with epinephrine, which activates PTX-sensitive G proteins, and with agonists which activate additionally, or exclusively PTX-insensitive pathways. Slopes and maximum of the secondary aggregation were significantly enhanced in platelets from 825T allele carriers after epinephrine, and after combined epinephrine/ADP. This effect was more pronounced after inhibition of the cyclooxygenase-2 pathway by acetylsalicylic acid. This phenomenon appeared independent of platelet secretion, or inhibition of the adenylyl cyclase.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2000

[Genetic polymorphism of the G-protein beta3 subunit, obesity and essential hypertension].

Following a classical candidate gene approach we have detected a C825T polymorphism in the gene GNB3 which encodes the G beta 3 subunit of heterotrimeric G proteins. The 825T allele causes alternative splicing of the gene and the generation of a truncated but functionally active splice variant of G beta 3 which is referred to as G beta 3s. Thus, genotyping for the C825T polymorphism is predictive for the activation of certain G proteins in humans. The 825T allele is significantly associated with an increased risk for hypertension in Caucasians, most likely "low renin hypertension" and it accumulates significantly in individuals with a strong family history of hypertension. Highest frequencies of the 825T allele (up to 80%) are found in old ethnicities, e.g. black Africans, African Americans, bushmen, and Australian aborigines. This suggests that enhanced G protein activation represents a thrifty genotype which might have facilitated survival in our ancestors. Frequencies of the 825T allele are significant lower in Asians (approximately 40 to 50%) and Caucasians (30%). More recent studies show that young 825T allele carriers are predisposed for obesity and this association could be confirmed across different ethnicities including young Germans, as well as Chinese and black African individuals. Thus, genotyping at the GNB3 locus represents an ideal tool for preventive medicine in that individuals at risk for obesity and hypertension can be identified early and counteract their genetic predisposition through changes in lifestyle. In individuals with borderline hypertension genotyping can facilitate the decision for medical treatment as a positive test result confirms an inherited form of hypertension.

Alleles↗
PubMed2000

G protein beta 3 gene: structure, promoter, and additional polymorphisms.

Recent studies have shown that a polymorphism (C825T) in the gene encoding the G protein beta 3 subunit (GNB3) is associated with hypertension and obesity. We characterized the entire GNB3 gene, which spans 7.5 kb and is composed of 11 exons and 10 introns. Its promoter lacks a TATA box but harbors GC-rich regions. The functional activity of the GNB3 promoter was verified with reporter gene assays that also demonstrated its inducibility by phorbol esters. A novel polymorphism in the promoter region A(-350)G occurred with frequencies (G allele) of 76%, 97%, and 61% in Africans, Chinese, and Germans, respectively. Reporter gene constructs with either the A or the G allele did not differ with regard to inducement of the reporter protein. A silent nucleotide exchange in the coding region (A657T) occurred with T allele frequencies ranging from 0.5% to 2.4%. Another polymorphism (G814A) results in the replacement of glycine by serine at position 272. In Germans, the A allele occurred at a frequency of 10%. Finally, a C1429T polymorphism in the 3' untranslated region of GNB3 was identified that occurred at T allele frequencies of 38%, 17%, and 30% in Africans, Chinese, and Germans, respectively. Haplotype prediction indicated in Germans an almost complete association of GNB3 825T with 1429T, and vice versa. An analysis of these polymorphic loci in nonhuman primates revealed that the ancestral GNB3 gene harbored the (-350)G, 825C, and 1429C alleles. This is the first complete characterization of the human GNB3 gene and its promoter region, which will enable refined epidemiological and biochemical investigations of GNB3 in hypertension and obesity.

Adolescent↗
PubMed1999

The G protein beta3 subunit splice variant Gbeta3-s causes enhanced chemotaxis of human neutrophils in response to interleukin-8.

A C825T polymorphism was recently described in GNB3, the gene encoding the Gbeta3 subunit of heterotrimeric G proteins. The 825T allele is associated with the expression of a shorter splice variant (Gbeta3-s) and enhanced signal transduction via pertussis toxin (PTX)-sensitive G proteins. Given the pivotal role of G protein betagamma dimers in chemotaxis, we related the genotype at the GNB3 locus as a marker for Gbeta3-s expression to chemotaxis of human neutrophils in response to stimulation with interleukin-8 (IL-8). IL-8, which activates a CXC receptor coupled to PTX-sensitive G proteins, induced at 10 nM an enhanced maximum chemotaxis of neutrophils from individuals with TC/TT genotype compared to CC genotype. Furthermore, migration of neutrophils from 825T allele carriers was 2.5-fold higher at 0.1 nM and 1 nM IL-8. At these concentrations of IL-8, no significant chemotaxis was observed in neutrophils from homozygous C825 allele carriers, indicating a genotype-dependent, different potency of IL-8 to chemoattract neutrophils. In contrast, IL-8-induced Ca2+ signals and O2- generation were independent of genotype. The role of Gbeta3-s in enhanced chemotaxis could be confirmed by determination of chemotaxis of COS-7 cells following transfection with either Gbeta3-s or "wild-type" Gbeta3. Upon stimulation of the transfected cells with the chemoattractant lysophosphatidic acid (LPA), we observed an enhanced chemotactic response of Gbeta3-s-transfected compared to Gbeta3-transfected COS-7 cells, confirming that Gbeta3-s actually causes enhanced chemotaxis.

Alleles↗
PubMed1999

Sodium-hydrogen exchange and platelet function.

On stimulation of platelets with agonists, for example, thrombin, a rapid rise in intracellular pH is observed. This alkalinization is mediated by an increase in transport activity of the Na(+)/H(+) exchanger isoform NHE1. In addition to this Na(+)/H(+) exchange mechanism, platelets express bicarbonate/chloride exchangers, which also contribute to pH(i) homeostasis. The main functions of NHE1 in platelets include pH(i) control, volume regulation, and participation in cell signaling. The isoform NHE1 is highly sensitive toward inhibition by EIPA, Hoe694, and Hoe642. The regulation of NHE1 activity is complex and is not completely understood. It includes the MAP kinase cascade, the Ca/calmodulin system, several heterotrimeric G proteins (Galpha12, Galpha13, Galphaq, and Galphai), small G proteins (ras, cdc42, rhoA), and downstream kinases (e.g., p160ROCK). Volume challenges stimulate tyrosine phosphorylation of cytoplasmic proteins, which ultimately activate NHE1. Thrombin, thromboxane, platelet-activating factor, angiotensin II, endothelin, phorbol ester, and Ca(2+) ionophors stimulate NHE1 activity in platelets. Blockade of platelet NHE1 can inhibit platelet activation. With the development of highly specific NHE1 inhibitors, detailed investigation of the relationships between NHE1 activity and platelet activation now becomes feasible.

Animals↗
PubMed1999

Worldwide ethnic distribution of the G protein beta3 subunit 825T allele and its association with obesity in Caucasian, Chinese, and Black African individuals.

Recently, it was demonstrated that one allele (825T) of the gene encoding the G protein beta3 subunit (GNB3) is associated with hypertension in Germans. This study investigates a possible association with obesity in young male Germans, Chinese, and black South Africans with low, intermediate, and high 825T allele frequencies, respectively. In each of these three distinct cohorts, the 825T allele frequency was increased significantly in overweight (body mass index [BMI] > or =25 kg/m2) and obese individuals (BMI >27 kg/m2) compared to those with normal weight. The 825T allele frequencies in these three BMI groups were, respectively, 29.5, 39.3, and 47.7% in Germans, 46.8, 53.9, and 58.6% in Chinese, and 83.1, 87.7, and 90.9% in South Africans. In each of these three distinct groups, the 825T allele was significantly associated with obesity with odds ratios between 2 and 3. More urban than rural black Africans were overweight despite similar 825T allele frequencies in both populations, which underscores the role of both genetic and environmental factors. BP values in young male whites increased significantly with increasing BMI values but were independent of the C825T polymorphism, suggesting that hypertension associated with the 825T allele could be a consequence of obesity. Genotyping of 5254 individuals from 55 native population samples from Africa, the Americas, Europe, Asia, Australia, and New Guinea demonstrated highest 825T allele frequencies in black Africans (82%) and intermediate values in east Asians (47%). It is anticipated that high frequencies of the 825T allele in Africans and Asians may contribute to an obesity and hypertension epidemic if Westernization of lifestyles continues.

Adolescent↗
PubMed1998

Expression, functional characterization and tissue distribution of a Na+/H+ exchanger cloned from Xenopus laevis oocytes (XL-NHE).

We examined the functional properties of a Na+/H+ exchanger cloned from Xenopus laevis oocytes (XL-NHE) upon stable transfection into PS120 fibroblasts which lack endogenous Na+/H+ exchange. In contrast to untransfected cells, XL-NHE-transfected cells displayed Na+-dependent alkalinization upon acidification with nigericin. XL-NHE activity was inhibited by amiloride, ethylisopropylamiloride, HOE694 [(3-methylsulphonyl-4-piperidinobenzoyl)-guanidine methanesulphonate] and HOE642 [4-isopropyl-3-methylsulphonylbenzoyl)-guanidine methanesulphonate], Ki values being calculated at 5 micromol/l, 25 nmol/l, 300 nmol/l and 180 nmol/l, respectively. The Na+ dependence of pHi recovery was compatible with simple Michaelis-Menten kinetics, the Km for Na+ being 22.0+/-3.2 mmol/l and the Hill coefficient for Na+ being approximately 1. XL-NHE was activated by phorbol ester, whereas forskolin exerted no effect, suggesting the involvement of phospholipase C/protein kinase C signalling pathways rather than protein kinase A signalling pathways in XL-NHE stimulation. Using reverse transcription polymerase chain reaction, XL-NHE message could be detected in various Xenopus tissues including heart, brain, skeletal muscle, reticulocytes, A6-kidney cells and oocytes.

Amiloride↗
PubMed1998

Association of a human G-protein beta3 subunit variant with hypertension.

Hypertension is a common disorder of multifactorial origin that constitutes a major risk factor for cardiovascular events such as stroke and myocardial infarction. Previous studies demonstrated an enhanced signal transduction via pertussis toxin-sensitive G proteins in lymphoblasts and fibroblasts from selected patients with essential hypertension. We have detected a novel polymorphism (C825T) in exon 10 of the gene encoding the beta3 subunit of heterotrimeric G proteins (GNB3). The T allele is associated with the occurrence of a splice variant, GNB3-s (encoding G beta3-s), in which the nucleotides 498-620 of exon 9 are deleted. This in-frame deletion causes the loss of 41 amino acids and one WD repeat domain of the G beta subunit. By western-blot analysis, G beta3-s appears to be predominantly expressed in cells from individuals carrying the T allele. Significant enhancement of stimulated GTPgammaS binding to Sf9 insect cells expressing G beta3-s together with G alpha(i)2 and G gamma5 indicates that this splice variant is biologically active. Genotype analysis of 427 normotensive and 426 hypertensive subjects suggests a significant association of the T allele with essential hypertension.

Alleles↗
PubMed1998

Growth factor-like action of lysophosphatidic acid on human B lymphoblasts.

Proliferation and immunoglobulin secretion of B lymphocytes are regulated by specific antigens and numerous accessory immunomodulatory factors. Lysophosphatidic acid (LPA) is a glycerophospholipid mediator that is released from activated blood platelets, attains high levels in serum, and exerts potent stimulatory effects on, e.g., neutrophils, monocytes, and T lymphocytes. LPA is also generated by a secretory, cytokine-inducible phospholipase A2 present in high concentrations in inflammatory exudates and septic states. We investigated effects of LPA on human Epstein-Barr virus-immortalized B lymphoblasts, a model for immunoglobulin-secreting B cells. Intracellular Ca2+ was determined with fura 2 and the formation of inositol 1,4, 5-trisphosphate by anion-exchange chromatography. LPA stimulated an increase in inositol 1,4,5-trisphosphate levels and induced a transient rise in intracellular free Ca2+ concentration from 105 +/- 17 to 226 +/- 21 nM. This Ca2+ signal resulted from Ca2+ mobilization and Ca2+ influx and was subject to homologous desensitization. Pertussis toxin inhibited these responses by approximately 70%. Furthermore, LPA stimulated a 27.5% increase in guanosine 5'-O-(3-thiotriphosphate) binding to permeabilized B lymphoblasts, which suggests the direct activation of pertussis toxin-sensitive G proteins by LPA. LPA stimulated a strong increase in the specific phosphorylation of the mitogen-activated protein kinase (immunoblot analysis) that was prevented by the MEK inhibitor PD-98059. Finally, LPA triggered a 2-fold increase in DNA synthesis ([3H]thymidine incorporation) and a 2-fold increase in B lymphoblast number and evoked a 20- to 50-fold increase in immunoglobulin formation. By RT-PCR we detected specific mRNA transcripts for the recently cloned human LPA receptor. Thus our data suggest that LPA behaves as a B cell growth factor.

Antibody Formation↗
PubMed1996

Selectively enhanced cellular signaling by Gi proteins in essential hypertension. G alpha i2, G alpha i3, G beta 1, and G beta 2 are not mutated.

Recent studies have shown an enhanced signaling capacity of receptors coupled to pertussis toxin (PTX)-sensitive guanine nucleotide-binding proteins (G proteins) in immortalized B lymphoblasts from patients with essential hypertension. In the present study, we analyzed (1) whether such alterations would also be expressed in nontransformed cells of these individuals and (2) whether other G protein-mediated signaling pathways were also altered. Therefore, we established primary cultures of skin fibroblasts from previously characterized normotensive and hypertensive individuals (NT and HT cells, respectively). [Ca2+]i rises induced by lyso-phosphatidic acid (LPA), thrombin, and sphingosine-1-phosphate as well as the formation of inositol 1,4,5-trisphosphate and [3H]thymidine incorporation evoked by LPA were PTX sensitive and enhanced twofold in HT fibroblasts. In contrast, cellular responses induced by bradykinin, endothelin-1, and angiotensin II (all PTX insensitive) were similar in NT and HT cells. Formation of cAMP induced by stimulation of Gs with isoproterenol was identical in NT and HT cells. Western blot analysis yielded no evidence for an overexpression of G alpha i2, G alpha i3, G beta 2, and G beta 4. Furthermore, sequencing of cDNAs encoding for the ubiquitously expressed PTX-sensitive G protein subunits G alpha i2, G alpha i3, G beta 1, and G beta 2 from NT and HT cell lines yielded no evidence for mutations in these genes. Although the molecular mechanisms remain to be defined, these data support the concept of a selective enhancement of signal transduction via PTX-sensitive G proteins in essential hypertension.

Base Sequence↗
PubMed1995

Kinetics of Na+/H+ exchange in vascular smooth muscle cells from WKY and SHR: effects of phorbol ester.

The kinetic properties of Na+/H+ exchange were investigated in vascular smooth muscle cells (VSMC) in culture from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Antiport activity was measured in 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein-loaded cells after nigericin-induced cytosolic acidification. Studies were performed without (control) and with pretreatment of the cells with phorbol 12-myristate 13-acetate (PMA; 200 nM). Na+/H+ exchange markedly differed between the two strains with lower Hill coefficients [1.56 +/- 0.17 (SE) vs. 2.62 +/- 0.36] and higher maximal activity (Vmax) values (55.85 +/- 5.24 vs. 31.11 +/- 2.38 mmol H+.l-1.min-1) in SHR compared with WKY cell lines. PMA markedly altered the antiport kinetics in WKY VSMC with a decrease in the Hill coefficient (1.75 +/- 0.14) without affecting Vmax (31.88 +/- 1.55 mmol H+.l-1.min-1). In VSMC from SHR, PMA had no effect on the kinetic variables investigated. Thus two kinetic abnormalities are present with respect to Na+/H+ antiport activity in VSMC from SHR compared with WKY, i.e., increased Vmax and decreased Hill coefficient. The observation that PMA does not affect the kinetics of the Na+/H+ antiport in VSMC from SHR suggests a marked degree of antiporter prestimulation in this animal model of genetic hypertension.

Animals↗
PubMed1995

Enhanced immunoglobulin formation of immortalized B cells from hypertensive patients.

Increased immunoglobulin levels and leukocyte counts have frequently been reported in essential hypertension. The underlying mechanisms, however, have remained obscure. Enhanced Na(+)-H+ exchanger activity is another frequently observed abnormality in essential hypertension that persists in immortalized B lymphoblasts and coincides with enhanced proliferation. We investigated the capacity of B lymphoblasts from essential hypertensive patients to synthesize and secrete immunoglobulins. Six B cell lines from essential hypertensive patients with enhanced Na(+)-H+ exchanger phenotype and six cell lines from normotensive subjects were studied. Lymphocyte markers were visualized by immunostaining. Immunoglobulin secretion was analyzed by enzyme-linked immunosorbent assay. These cell lines did not differ with respect to B cell markers. In response to 100 nmol/L platelet-activating factor, cells from hypertensive patients proliferated distinctly more quickly and their cell number increased by 3.9 +/- 0.4-fold (mean +/- SD) within 4 days, whereas the number of cells from normotensive subjects increased by only 2.6 +/- 0.1-fold. Furthermore, platelet-activating factor induced average increases in IgM and IgG formation of 13.3- and 5.4-fold, respectively, in lymphoblasts from hypertensive patients, which was significantly higher than increases in cells from normotensive subjects (1.4- and 1.2-fold, respectively). Thus, lymphoblasts from hypertensive patients proliferate more quickly and secrete more immunoglobulins in response to a physiological stimulus in vitro. This may contribute to the raised immunoglobulin levels and leukocyte counts reported in vivo.

Adult↗
PubMed1995

Enhanced G protein activation in immortalized lymphoblasts from patients with essential hypertension.

Epstein-Barr virus-immortalized B lymphoblasts obtained from hypertensive patients with enhanced Na+/H+ exchanger activity (HT cells) proliferate distinctly faster upon serum stimulation than those from normotensive controls with low exchanger activity (NT cells) (Rosskopf, D., E. Frömter, and W. Siffert. 1993. J. Clin. Invest. 92:2553-2559). Stimulation with platelet-activating factor (PAF) as well caused an enhanced proliferation of HT cells. In analyzing possible differences in signal transduction between the immortalized NT and HT lymphoblasts, we observed that cell stimulation with PAF and somatostatin caused a twofold higher increase in [Ca2+]i in HT than in NT cell lines. This difference was completely abrogated by pertussis toxin (PTX) treatment. Furthermore, PAF-stimulated formation of inositol 1,4,5-trisphosphate (IP3) was twofold enhanced in HT cell lines. On the other hand, PAF receptor density and affinity, total cellular phospholipase C activity, expression of PTX-sensitive G proteins, and control binding of the stable GTP analogue, guanosine 5'-[gamma-thio]triphosphate (GTP gamma S), to membrane G proteins were not different in NT and HT cell lines. However, PAF- and mastoparan-stimulated binding of GTP gamma S to G proteins, which was fully PTX-sensitive, was 2.5-fold higher in HT than NT cell lines. These data suggest an enhanced receptor-mediated activation of PTX-sensitive G proteins despite unchanged receptor and G protein expression. Thus, this study not only suggests that enhanced signal transduction and cell proliferation are abnormalities in a certain group of patients with essential hypertension but also explains these findings as a result of an enhanced G protein activation in this common disorder.

Animals↗