Petra Goldin-Lang

Upregulation of tissue factor expression and thrombogenic activity in human aortic smooth muscle cells by irradiation, rapamycin and paclitaxel.

BACKGROUND Intracoronary brachytherapy as well as rapamycin or paclitaxel coated stents reduce restenosis rates after stenting, but are associated with an increased risk of late stent thrombosis. Tissue factor (TF) may contribute to late thrombosis. This study examined the impact of rapamycin and paclitaxel on TF expression and compares the TF activity induction of both drugs and irradiation in SMCs. METHODS SMCs were stimulated with rapamycin, paclitaxel or irradiation. Real-time PCR, a chromogenic TF activity assay and Western blotting were done. RESULTS Rapamycin or paclitaxel increased the TF mRNA expression 5-fold and the TF activity 4- to 6-fold with a maximum at 5 h. Irradiation induced TF activity 2- to 4-fold with a maximum at 7 days. CONCLUSION The fast increase of TF expression in SMCs post rapamycin and paclitaxel treatment may explain acute stent thrombosis when anti-thrombotic therapies are withdrawn, whereas the irradiation induced long term increase of cellular thrombogenicity may contribute to late thrombosis post intracoronary brachytherapy. Therapies counteracting these side effects may reduce the risk of thrombotic complications after the coronary application of anti-proliferative therapies.

The (pro)renin receptor ((P)RR) can act as a repressor of Wnt signalling

The (pro)renin receptor ((P)RR) and Wnt signalling are both involved in different diseases ranging from cardiac and renal end-organ damage to cancer. (P)RR function involves signalling via the transcription factor promyelocytic leukemia zinc finger protein (PLZF) as well as the furin-mediated generation of vacuolar proton-translocating ATPase (V-ATPase)-associated and soluble (P)RR isoforms. Recently, the (P)RR was described as adaptor protein of Wnt (co)receptors. The aim of this study was to analyse the contribution of these distinct (P)RR functions to Wnt signalling. Using Tcf/Lef reporter gene systems in HEK293T and HepG2 cells and quantification of endogenous axin2 mRNA and protein levels in HEK293T cells we were able to demonstrate that full-length (P)RR acts as a repressor of Wnt signalling in a system preactivated either by Wnt3a stimulation or by constitutively active β-catenin. These repressive effects are mediated by Dvl but are independent of the mutation status of β-catenin. Furthermore, the V-ATPase complex, but not PLZF translocation or renin enzymatic activity, is necessary for the induction of Tcf/Lef-responsive genes by Wnt3a. Our data indicate interference of (P)RR and Wnt cascades, a fact that has to be considered concerning pathophysiology of cardio-renal and oncological entities as well as in drug development programs targeting (P)RR or Wnt pathways.

The Promyelocytic Leukemia Zinc Finger (PLZF) Protein Exerts Neuroprotective Effects in Neuronal Cells and is Dysregulated in Experimental Stroke

Stroke is one of the major medical burdens in industrialized countries. Animal experiments indicate that blockade of the angiotensin AT1 receptor (AT1R) improves neurological outcome after cerebral ischemia. These protective effects are partially mediated by the angiotensin AT2 receptor (AT2R). The transcription factor promyelocytic leukemia zinc finger (PLZF) was identified as a direct adapter protein of the AT2R. Furthermore, our group was able to demonstrate that PLZF also directly binds and mediates the effects of the human (pro)renin receptor [(P)RR] which is involved in brain development. Therefore, we hypothesized that PLZF is involved in neuroprotection.

A Polymorphic Microsatellite Repeat within the ECE-1c Promoter Is Involved in Transcriptional Start Site Determination, Human Evolution, and Alzheimer's Disease

Genetic factors strongly contribute to the pathogenesis of sporadic Alzheimers disease (AD). Nevertheless, genome-wide association studies only yielded single nucleotide polymorphism loci of moderate importance. In contrast, microsatellite repeats are functionally less characterized structures within our genomes. Previous work has shown that endothelin-converting enzyme-1 (ECE-1) is able to reduce amyloid β content. Here we demonstrate that a CpG-CA repeat within the human ECE-1c promoter is highly polymorphic, harbors transcriptional start sites, is able to recruit the transcription factors poly(ADP-ribose) polymerase-1 and splicing factor proline and glutamine-rich, and is functional regarding haplotype-specific promoter activity. Furthermore, genotyping of 403 AD patients and 444 controls for CpG-CA repeat length indicated shifted allelic frequency distributions. Sequencing of 245 haplotype clones demonstrated that the overall CpG-CA repeat composition of AD patients and controls is distinct. Finally, we show that human and chimpanzee [CpG]m–[CA]n ECE-1c promoter repeats are genetically and functionally distinct. Our data indicate that a short genomic repeat structure constitutes a novel core promoter element, coincides with human evolution, and contributes to the pathogenesis of AD.

Prolonged clopidogrel application reduces tissue factor expression after percutaneous coronary intervention in the porcine model

BACKGROUND Late thrombotic events are important complications associated with intracoronary brachytherapy (ICBT) using ionizing radiation (IR) or with antiproliferative treatment modalities such as drug-eluting stents (DES). The mechanism mediating these thrombotic events is not well understood. This study assessed the effect of prolonged clopidogrel treatment on tissue factor (TF) expression in coronary arteries and on the circulating TF level after percutaneous transluminal coronary angioplasty /ICBT in a porcine coronary model. METHODS Pigs were treated with aspirin plus a 300 mg loading dose of clopidogrel one day before percutaneous coronary intervention (PCI), followed by a daily dose of clopidogrel and aspirin. During PCI one of the two balloon-injured arteries was treated by brachytherapy. Animals were sacrificed at different time points. The pigs, which were sacrificed 3 months post-PCI, were divided into two groups (Group I: clopidogrel for 3 months; Group II: clopidogrel for 1 month). Plasma TF was measured by enzyme-linked immunosorbent assay in blood samples taken from all pigs before and immediately after intervention and before sacrifice. Morphometric analysis was performed on digitalized images employing the software LUCIA G for TF staining. Vascular TF expression levels were assessed by quantitative real-time polymerase chain reaction. RESULTS Prolonged clopidogrel application significantly reduced coronary TF at the protein (Group I vs. II, 8.975 ± 3.947% vs. 26.44 ± 5.375%, P = .007) and mRNA level [Group I vs. II, (0.3501 ± 0.0519) × 10(-3) vs. (0.7073 ± 0.0436) × 10(-3), P<.0005]. Circulating TF protein tended to be lower after 3 months than after 1 month clopidogrel treatment post-PCI (Group I vs. Group II, 488.3 ± 35.37 pg/ml vs. 572.3 ± 39.9 pg/ml, P = .130). CONCLUSIONS Prolonged clopidogrel treatment reduced coronary TF expression and tended to reduce the blood TF level post-PCI, thus possibly modulating the risk of late thrombosis.

The (pro)renin receptor mediates constitutive PLZF-independent pro-proliferative effects which are inhibited by bafilomycin but not genistein

The (pro)renin receptor [(P)RR] is crucial for cardio-renal pathophysiology. The distinct molecular mechanisms of this receptor are still incompletely understood. The (P)RR is able to interact with different signalling proteins such as promyelocytic leukemia zinc finger protein (PLZF) and Wnt receptors. Moreover, domains of the (P)RR are essential for V-ATPase activity. V-ATPase- and Wnt-mediated effects imply constitutive, i.e., (pro)renin-independent functions of the (P)RR. Regarding ligand-dependent (P)RR signalling, the role of prorenin glycosylation is currently unknown. Therefore, the aim of this study was to analyse the contribution of constitutive (P)RR activity to its cellular effects and the relevance of prorenin glycosylation on its ligand activity. We were able to demonstrate that high glucose induces (P)RR signal transduction whereas deglycosylation of prorenin abolishes its intrinsic activity in neuronal and epithelial cells. By using siRNA against (P)RR or PLZF as well as the PLZF translocation blocker genistein and the specific V-ATPase inhibitor bafilomycin, we were able to dissect three distinct sub-pathways downstream of the (P)RR. The V-ATPase function is ligand-independently associated with strong pro-proliferative effects whereas prorenin causes moderate proliferation in vitro. In contrast, PLZF per se [i.e., in the absence of (pro)renin] does not interfere with cell number.

Distinct Signal Transduction Pathways Downstream of the (P)RR Revealed by Microarray and ChIP-chip Analyses

The (pro)renin receptor ((P)RR) signaling is involved in different pathophysiologies ranging from cardiorenal end-organ damage via diabetic retinopathy to tumorigenesis. We have previously shown that the transcription factor promyelocytic leukemia zinc finger (PLZF) is an adaptor protein of the (P)RR. Furthermore, recent publications suggest that major functions of the (P)RR are mediated ligand-independently by its transmembrane and intracellular part, which acts as an accessory protein of V-ATPases. The transcriptome and recruitmentome downstream of the V-ATPase function and PLZF in the context of the (P)RR are currently unknown. Therefore, we performed a set of microarray and chromatin-immunoprecipitation (ChIP)-chip experiments using siRNA against the (P)RR, stable overexpression of PLZF, the PLZF translocation inhibitor genistein and the specific V-ATPase inhibitor bafilomycin to dissect transcriptional pathways downstream of the (P)RR. We were able to identify distinct and overlapping genetic signatures as well as novel real-time PCR-validated target genes of the different molecular functions of the (P)RR. Moreover, bioinformatic analyses of our data confirm the role of (P)RŔs signal transduction pathways in cardiovascular disease and tumorigenesis.

Moderate Correlations of in vitro versus in vivo Pharmacokinetics Questioning the Need of Early Microsomal Stability Testing

Background/Aims: Putative in vitro-in vivo correlations of pharmacokinetic (PK) parameters are regarded as a prerequisite to filter hits derived from high-throughput screening (HTS) approaches for subsequent murine in vivo PK studies. Methods: In this study, we assessed stabilities in rat and human microsomes of 121 compounds from an early, academic drug discovery programme targeting the (pro)renin receptor and correlated the respective data with single-dose, in vivo PK parameters of 22 hits administered intravenously in rats. Results: After transformation of in vitro half-lives to predicted in vivo hepatic clearances, r2 regarding in vitro-in vivo clearance correlations were 0.31 and 0.27 for the rat and human species, respectively. Conclusions: Our data concerning structurally diverse real-world compounds indicate that microsomal stability testing is not a tool to triage early compounds for in vivo PK testing.