Thomas Knorpp

Gender-Specific Interplay of Signaling through β-Catenin and CAR in the Regulation of Xenobiotic-Induced Hepatocyte Proliferation

Aberrant signaling through the Wnt/β-catenin pathway is a critical determinant in human and rodent liver carcinogenesis and generally accepted to be a potent driver of proliferation. Xenobiotic agonists of the constitutive androstane receptor (CAR) induce massive acute hyperplasia of mouse liver and facilitate the outgrowth of hepatocellular carcinomas with activated β-catenin. In the present study, the interplay of β-catenin-dependent and CAR-dependent signaling in the liver and its effect on hepatocyte proliferation were analyzed in transgenic mice with hepatocyte-specific knockout of Ctnnb1 (encoding β-catenin) following treatment with two CAR agonists, 1,4-bis[2-(3,5-dichloropyridyloxy)]-benzene (TCPOBOP) and phenobarbital. Hepatocyte-specific knockout of β-catenin inhibited CAR agonists-induced hepatocyte proliferation in male mice. By contrast, the proliferative effect of CAR agonists was strongly augmented in female β-catenin knockout animals. This was due to prolonged proliferation of the knockout hepatocytes. CAR-mediated hepatocyte proliferation was, at least in part, dependent on estrogen signaling and was associated with enhanced expression of FoxM1 and elevated activity of the PDK1/p90RSK pathway. In conclusion, our study shows that gender-specific factors determine whether β-catenin signaling plays a pro- or an antiproliferative role in the regulation of mouse hepatocyte proliferation induced by CAR agonists.

Hepatocarcinogenesis in mice with a conditional knockout of the hepatocyte growth factor receptor c-Met

The receptor for the hepatocyte growth factor/scatter factor (HGF/SF), c‐Met, plays a role in tumour promotion, progression and metastasis. In this study, we analysed chemically induced hepatocarcinogenesis in mice lacking a functional HGF receptor in their liver. Control and c‐Met deficient mice were injected with a single dose of N‐nitrosodiethylamine (DEN, 90 μg/g b.wt.) at 6 weeks of age and mice were subsequently kept on a phenobarbital (PB) containing diet (0.05%) for 35 weeks or on control diet. At the end of the experiment, the carcinogenic response in liver of the animals was monitored. Conditional c‐met knockout (KO) mice showed a higher prevalence of macroscopically visible liver tumours and of glutamine synthetase positive and glucose‐6‐phosphatase deficient lesions in liver. Tumour promotion by PB led to significant increases in the number of preneoplastic and neoplastic lesions in liver of both wild‐type and c‐met knockout mice, with only minor differences in response. Our results indicate that a defect in c‐Met‐mediated signaling increases chemically induced tumour initiation in liver but does not significantly affect PB‐mediated tumour promotion.

Ha‐ras and β‐catenin oncoproteins orchestrate metabolic programs in mouse liver tumors

The process of hepatocarcinogenesis in the diethylnitrosamine (DEN) initiation/phenobarbital (PB) promotion mouse model involves the selective clonal outgrowth of cells harboring oncogene mutations in Ctnnb1, while spontaneous or DEN‐only‐induced tumors are often Ha‐ras‐ or B‐raf‐mutated. The molecular mechanisms and pathways underlying these different tumor sub‐types are not well characterized. Their identification may help identify markers for xenobiotic promoted versus spontaneously occurring liver tumors. Here, we have characterized mouse liver tumors harboring either Ctnnb1 or Ha‐ras mutations via integrated molecular profiling at the transcriptional, translational and post‐translational levels. In addition, metabolites of the intermediary metabolism were quantified by high resolution 1H magic angle nuclear magnetic resonance. We have identified tumor genotype‐specific differences in mRNA and miRNA expression, protein levels, post‐translational modifications, and metabolite levels that facilitate the molecular and biochemical stratification of tumor phenotypes. Bioinformatic integration of these data at the pathway level led to novel insights into tumor genotype‐specific aberrant cell signaling and in particular to a better understanding of alterations in pathways of the cell intermediary metabolism, which are driven by the constitutive activation of the β‐Catenin and Ha‐ras oncoproteins in tumors of the two genotypes.

Tumor promotion in liver of mice with a conditional Cx26 knockout.

Connexin (Cx) 26 and 32 are the major gap junction proteins in liver. We recently demonstrated that Cx32 is essential for phenobarbital (PB)-mediated tumor promotion in mouse liver. To investigate whether Cx26 plays a similar role, an initiation-promotion experiment was conducted using mice with a liver-specific knockout of Cx26. Control and Cx26-deficient mice were injected a single dose of N-nitrosodiethylamine (DEN, 90 microg/g b.wt.) at 6 weeks of age and groups of mice were subsequently kept on a PB (0.05%) containing or control diet for 35 weeks. At the end of the experiment, the carcinogenic response in the liver was monitored. Mice from PB treatment groups showed strongly increased liver weights compared with mice treated with DEN alone, which was mostly due to a much higher tumor burden. The tumor response in PB-treated mice of both strains was quite similar, but the number of smaller tumors and of enzyme-altered neoplastic lesions was somewhat larger in PB-treated Cx26 knockout (Cx26 KO) compared with wild-type mice, whereas the volume fraction of enzyme-altered lesions was slightly reduced in PB-treated Cx26-deficient mice. There was no significant difference in tumor prevalence between Cx26 KO and wild-type mice. Altogether our present data show that elimination of Cx26 has only minor effects on chemically induced mouse hepatocarcinogenesis, in striking contrast to the effects seen in Cx32 KO mice.

Inflammatory profile in LRRK2-associated prodromal and clinical PD

BackgroundThere is evidence for a relevant role of inflammation in the pathogenesis of Parkinson’s disease (PD). Mutations in the LRRK2 gene represent the most frequent genetic cause for autosomal dominant PD. LRRK2 is highly expressed in macrophages and microglia suggesting an involvement in inflammatory pathways. The objectives are to test (1) whether idiopathic PD and LRRK2-associated PD share common inflammatory pathways or present distinct profiles and (2) whether non-manifesting LRRK2 mutation carriers present with similar aspects of inflammatory profiles as seen in PD-affected patients.MethodsWe assessed serum profiles of 23 immune-associated markers and the brain-derived neurotrophic factor in 534 individuals from the MJFF LRRK2 consortium.ResultsA large proportion of inflammatory markers were gender-dependent. Both PD-affected cohorts showed increased levels of the pro-inflammatory marker fatty-acid-binding protein. Additionally, idiopathic PD but not LRRK2-associated PD patients showed increased levels of the pro-inflammatory marker interleukin-12-p40 as well as the anti-inflammatory species interleukin-10, brain-derived neurotrophic factor, and stem cell factor. Non-manifesting LRRK2 mutation carriers including those with prodromal characteristics of PD presented with control-like inflammatory profiles.ConclusionsConcomitant inflammation seems to be associated with idiopathic and LRRK2-associated PD. Identifying PD patients in whom inflammatory processes play a major role in their pathophysiology might offer a new therapeutic window at least for a subgroup of patients. Since non-manifesting LRRK2 mutation carriers with symptoms of the prodromal phase of PD did not show inflammatory profiles, activation of the immune system seems not an early event in the disease cascade.

Inflammatory profile discriminates clinical subtypes in LRRK2‐associated Parkinson's disease

The presentation of Parkinsons disease patients with mutations in the LRRK2 gene (PDLRRK2) is highly variable, suggesting a strong influence of modifying factors. In this context, inflammation is a potential candidate inducing clinical subtypes.

On display on a bug: a systematic approach to characterize antibodies

Efficient methods to characterize the binding properties of affinity reagents are required. A combination of bacterial surface display, flow cytometry and pyrosequencing is now used for high-speed mapping of the epitopes recognized by antibodies.

Kinase analysis in alcoholic hepatitis identifies p90RSK as a potential mediator of liver fibrogenesis

Objective Alcoholic hepatitis (AH) is often associated with advanced fibrosis, which negatively impacts survival. We aimed at identifying kinases deregulated in livers from patients with AH and advanced fibrosis in order to discover novel molecular targets. Design Extensive phosphoprotein analysis by reverse phase protein microarrays was performed in AH (n=12) and normal human livers (n=7). Ribosomal S6 kinase (p90RSK) hepatic expression was assessed by qPCR, Western blot and immunohistochemistry. Kaempferol was used as a selective pharmacological inhibitor of the p90RSK pathway to assess the regulation of experimentally-induced liver fibrosis and injury, using in vivo and in vitro approaches. Results Proteomic analysis identified p90RSK as one of the most deregulated kinases in AH. Hepatic p90RSK gene and protein expression was also upregulated in livers with chronic liver disease. Immunohistochemistry studies showed increased p90RSK staining in areas of active fibrogenesis in cirrhotic livers. Therapeutic administration of kaempferol to carbon tetrachloride-treated mice resulted in decreased hepatic collagen deposition, and expression of profibrogenic and proinflammatory genes, compared to vehicle administration. In addition, kaempferol reduced the extent of hepatocellular injury and degree of apoptosis. In primary hepatic stellate cells, kaempferol and small interfering RNA decreased activation of p90RSK, which in turn regulated key profibrogenic actions. In primary hepatocytes, kaempferol attenuated proapoptotic signalling. Conclusions p90RSK is upregulated in patients with chronic liver disease and mediates liver fibrogenesis in vivo and in vitro. These results suggest that the p90RSK pathway could be a new therapeutic approach for liver diseases characterised by advanced fibrosis.

Selective p38α MAP kinase/MAPK14 inhibition in enzymatically modified LDL-stimulated human monocytes: implications for atherosclerosis.

The first ATP‐competitive p38a MAPK/MAPK14 inhibitor with excellent in vivo efficacy and selectivity, skepinone‐L, is now available. We investigated the impact of selective p38a MAPK/MAPK14 inhibition on enzymatically modified LDL (eLDL) stimulated human monocytes with its implications for atherosclerosis. Among the different p38 MAPK isoforms, p38a/MAPK14 was the predominantly expressed and activated isoform in isolated human peripheral blood monocytes. Moreover, eLDL colocalized with macrophages positive for p38a MAPK/ MAPK14 in human carotid endarterectomy specimens. Using the human leukemia cell line THP‐1 and/or primary monocyte‐derived macrophages, skepinone‐L inhibited eLDL‐induced activation of the p38 MAPK pathway, inhibited eLDL induced expression of both cluster of differentiation 36 (CD36) and ATP‐binding cassette, subfamily A, member 1 (ABCA1), without a net effect on foam cell formation, had a cell‐and time‐dependent effect on eLDLtriggered apoptosis, and inhibited eLDL‐stimulated secretion of IL‐8 and MIP‐1b/CCL4 (macrophage inflammatory protein‐1b/chemokine, CC motif, ligand 4). Inhibition of a key signaling molecule of the p38 MAPK pathway, p38a MAPK/MAPK14, by selective inhibitors like skepinone‐L, conclusively facilitates elucidation of the impact of the complex network of p38 MAPK signaling on atherogenesis and might provide a promising therapeutic tool to prevent inflammatory cascades in atherosclerosis.—Cheng, F., Twardowski, L., Fehr, S., Aner, C., Schaeffeler, E., Joos, T., Knorpp, T., Dorweiler, B., Laufer, S., Schwab, M., Torzewski, M. Selective p38a MAP kinase/MAPK14 inhibition in enzymatically modified LDL‐stimulated human monocytes: implications for atherosclerosis. FASEB J. 31, 674–686 (2017). www.fasebj.org

Development of a novel assay for proprotein converting enzyme activity on a multiplex bead-based array system

We describe the development of a novel, robust assay system for determining the changes in activity of proprotein converting enzymes. An assay for prolyl oligopeptidase (POP) activity was constructed using a peptide‐streptavidin substrate coupled to magnetic microspheres and cleavage was detected by loss of streptavidin on the MAGPIX reader. Test analysis of postmortem pituitary extracts from schizophrenia patients showed an increase in POP activity compared to controls. The results were validated using both fluorometric and Western blot analyses for POP activity and immunoreactivity, respectively. The assays can be multiplexed for measuring the activity of multiple proprotein cleaving enzymes simultaneously in laboratory and clinical settings and should add valuable new information for conditions such as neuropsychiatric diseases, diabetes, endocrine dysfunction, and cancer, where effects on proteolysis of biologically active peptides play a key role.