Biomedical subjects

Thomas Langenickel

Publications and source records attributed to Thomas Langenickel.

6 recordsLinked to original sources

PubMed2006

The arginine methyltransferase PRMT2 binds RB and regulates E2F function.

The retinoblastoma gene product (RB) is an important regulator of E2F activity. RB recruits a number of proteins, including HDACs, SWI/SNF complex, lysine methyl transferase (SUV39H1) and DNA methyltransferase (DNMT1), all of which negatively regulate E2F activity with RB. Here, we show that RB interacts with PRMT2, a member of the protein arginine methyltransferase family, to regulate E2F activity. PRMT2 directly bound and interacted with RB through its AdoMet binding domain, in contrast to other PRMT proteins, including PRMT1, PRMT3 and PRMT4. In reporter assays, PRMT2 repressed E2F1 transcriptional activity in an RB-dependent manner. PRMT2 formed a ternary complex with E2F1 in the presence of RB. To further explore the role of endogenous PRMT2 in the regulation of E2F activity, the PRMT2 gene was ablated in mice by gene targeting. Compared with PRMT2(+/+) mouse embryonic fibroblasts (MEFs), PRMT2(-/-) MEFs demonstrated increased E2F activity and early S phase entry following release of serum starvation. Vascular injury to PRMT2(-/-) arteries results in a hyperplastic response, consistent with increased G1-S phase progression. Taken together, these findings demonstrate a novel mechanism for the regulation of E2F activity by a member of the protein arginine methyltransferase family.

Animals↗

PubMed2004

Regulation of caspase 3 and Fas in pressure overload-induced left ventricular dysfunction.

BACKGROUND: The presence of apoptotic cell death in cardiac myocytes is now well established and the contribution of apoptosis for the development of heart failure has been suggested. However, the mechanism responsible for the induction of apoptosis remains unclear. The present study was designed to investigate the involvement of Fas and caspase 3 in the transition from pressure overload-induced left ventricular hypertrophy (LVH) to left ventricular dysfunction (LVD). METHODS: Pressure overload induced LVH (10 days) and LVD (30 days) were induced by thoracic aortic banding. Changes in apoptosis-related genes were studied in rats with thoracic aortic banding. After 10 and 30 days, cardiac Fas mRNA expression was measured by RT-PCR. The mRNA expression of caspase 3 was detected by RNase protection assay. The activity of caspase 3 was measured by fluorometric assay. Protein levels of caspase 3 were measured by Western blot. RESULTS: Rats with aortic banding had increased heart/body weight ratios after 10 and 30 days, compared to controls. Central venous pressure and lung weights were increased, left ventricular contractility was significantly impaired only in rats after 30 days of aortic banding, indicating LVD. Caspase 3 mRNA expression (7.1+/-0.1 vs. 2.8+/-0.4, P<0.05), caspase 3 activity (1418+/-181 vs. 849+/-154 AU, P<0.05) as well as caspase 3 protein levels were increased in rats with LVD but not with LVH. Similarly, Fas mRNA was increased in rats with LVD. CONCLUSIONS: The activation of Fas and caspase 3 only after 30 days of aortic banding suggests that induction of these pathways may be involved in pressure overload-induced LVD.

Animals↗

PubMed2003

Forced homodimerization by site-directed mutagenesis alters guanylyl cyclase activity of natriuretic peptide receptor B.

Natriuretic peptides mediate their physiologic effects through activation of membrane-bound, guanylyl cyclase-coupled receptors (NPRs). Receptor dimerization is an important feature of signal transduction. This study was aimed at characterizing structurally important residues of the extracellular ligand-binding domain of NPR-B for receptor dimerization and cGMP generation. Deletion mutagenesis was used to replace cysteine residues at positions 53 (C53S), 417 (C417S), and 426 (C426S) by serine. Receptor expression, dimerization, whole-cell cGMP response, and guanylyl cyclase activity of membrane fractions were determined in stably transfected COS-7 cells. C53S, C417S, and C426S mutants were expressed and found to form disulfide-bridged covalent dimers. In contrast to NPR-B and C53S, C417S and C426S mutants displayed constitutive activity in whole cells (C417S, 146+/-12%, P<0.01; C426S, 153+/-7% of ligand-independent NPR-B cGMP generation, P<0.01). The cGMP response of C417S and C426S mutants in whole cells was dose dependent and approximately 4 times lower than that in NPR-B, whereas it was blunted in C53S-transfected cells (1 micromol/L CNP, NPR-B 2868+/-436%; C53S, 206+/-16% of control, P<0.001 vs NPR-B, C417S, and C426S). Guanylyl cyclase assay in transfected cells confirmed the constitutive activity of C417S and C426S mutants. These data suggest that receptor dimerization by covalent disulfide bridges alters ligand-independent as well as ligand-dependent receptor activity. Localization of the crosslink in relation to the cell membrane is important for configuration of the extracellular domain and the consecutive signal transduction.

Animals↗

PubMed2002

Increased expression of renal neutral endopeptidase in severe heart failure.

The enzyme neutral endopeptidase (NEP; EC 3.4.24.11) cleaves several vasoactive peptides such as the atrial natriuretic peptide (ANP). ANP is a hormone of cardiac origin with diuretic and natriuretic actions. Despite elevated circulating levels of ANP, congestive heart failure (CHF) is characterized by progressive sodium and water retention. In order to elucidate the loss of natriuretic and diuretic properties of ANP in CHF we analyzed activity, protein concentrations, mRNA and immunostaining of NEP in kidneys of different models of severe CHF in the rat.CHF was induced by either aortocaval shunt, aortic banding or myocardial infarction in the rat. All models were defined by increased left ventricular end-diastolic pressure and decreased contractility. The diminished effectiveness of ANP was reflected by reduced cGMP/ANP ratio in animals with shunt or infarction. Renal NEP activity was increased in rats with aortocaval shunt (203 +/- 7%, p < 0.001), aortic banding (184 +/- 11%, p < 0.001) and infarction (149 +/- 10%, p < 0.005). Western blot analysis revealed a significant increase in renal NEP protein content in two models of CHF (shunt: 214 +/- 57%, p < 0.05; infarction: 310 +/- 53 %, p < 0.01). The elevated protein expression was paralleled by a threefold increase in renal NEP-mRNA level in the infarction model. The increased renal NEP protein expression and activity may lead to enhanced degradation of ANP and may contribute to the decreased renal response to ANP in heart failure. Thus, the capacity to counteract sodium and water retention, would be diminished. The increased renal NEP activity may therefore be a hitherto unknown factor in the progression of CHF.

Animals↗

PubMed2002

Treatment with darusentan over 21 days improved cGMP generation in patients with chronic heart failure.

In heart failure, the cGMP to natriuretic peptide ratio is decreased and infusion of atrial natriuretic peptide (ANP) induces less cGMP generation. The ratio of the second messenger cGMP to plasma concentrations of ANP or brain natriuretic peptide (BNP) correlates with the effectiveness of natriuretic peptides. It was investigated whether blockade of the ET(A) receptor might improve the cGMP:NP ratio in heart failure. Patients with chronic heart failure (n=142; mean age=57 years) received oral treatment with the ET(A) antagonist darusentan (either 30, 100, 300 mg/day or placebo) on top of standard therapy over a period of 21 days in a randomized, double-blind, placebo-controlled, multicentre study. Plasma concentrations of ANP, BNP and cGMP were determined before randomization and after 21 days of treatment. In parallel with decreased pulmonary and systemic vascular resistance, 3 weeks of oral treatment with the ET(A) receptor antagonist darusentan reduced BNP plasma levels and increased the cGMP:BNP ratio significantly. The improved cGMP:BNP ratio might reflect the ability of chronic ET(A) receptor blockade to facilitate the generation of the second messenger cGMP, which points towards a favourable modulation of the natriuretic peptide effector system, in addition to haemodynamic improvement in heart failure patients.

Atrial Natriuretic Factor↗

PubMed2002

Cardiac and renal effects of growth hormone in volume overload-induced heart failure: role of NO.

Growth hormone (GH) application is a new strategy in the treatment of heart failure. However, clinical and experimental investigations have shown contradictory effects of GH on cardiac performance. We tested the hypothesis that GH could improve cardiac and renal function in volume overload-induced heart failure. The effect of 4 weeks of GH treatment (2 mg/kg daily) was investigated in Wistar rats with aortocaval shunt. GH application did not influence left ventricular contractility and end-diastolic pressure in rats with aortocaval shunt. In contrast, GH treatment normalized impaired diuresis (vehicle 10.8+/-0.6 mL/d, GH 15.8+/-0.7 mL/d; P<0.05) and sodium excretion (vehicle 1.5+/-0.1 mmol/d, GH 2.2+/-0.1 mmol/d; P<0.001) in shunt-operated rats, with a similar increase of fractional sodium excretion. The urinary excretion of cGMP, the second messenger of atrial natriuretic peptide and NO, was higher in animals with shunts than in sham-operated animals and was further increased by GH (vehicle 293+/-38 nmol/d, GH 463+/-57 nmol/d; P<0.01). Although the atrial natriuretic peptide plasma levels were unchanged after GH, the excretion of NO metabolites (nitrate/nitrite) was elevated (vehicle 2020+/-264 nmol/d, GH 2993+/-375 nmol/d; P<0.05) in parallel with increased renal mRNA levels of inducible NO synthase 2. The changes of renal function after GH and the increased excretion of NO metabolites and cGMP were abolished by simultaneous treatment with the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester. GH treatment did not influence cardiac function in rats with aortocaval shunts. However, GH improved renal function by increasing diuresis and sodium excretion. The responsible mechanism might be the enhanced activity of the renal NO system.

Angiotensin II↗