@phdthesis{Fusi2023,
  author    = {Fusi, Lorenza},
  title     = {Crosstalk between the MEK5/ERK5 and PKB/FoxO pathways: underlying mechanism and its relevance for vasoprotection and tumorigenesis},
  doi       = {10.25972/OPUS-29676},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-296769},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {Forkhead box O transcription factors are a family of proteins involved in cellular processes downstream of the Insulin-PI3K-PKB pathway. In response to extra- or intracellular stresses, for example starvation or oxidative stress, FoxOs are required to direct cell cycle progression and apoptosis. In endothelial cells, they induce apoptosis, and their deregulation is linked to diseases involving the insulin pathway, such as diabetes. FoxOs also exhibit a complex role in tumour transformation: here their main function is to suppress tumorigenesis. In both physiological and cancer contexts, FoxO activation leads to the transcription of some general targets, such as p27kip1 or IGFBP1. The FoxOs can also induce tissue-specific genes, as ANGPT2 and BIM in the endothelium. In endothelial cells, another pathway with a pivotal function is the MEK5/ERK5 MAPK signalling way. Its activation promotes cell survival and proliferation in stressful conditions, e.g., when blood vessels are exposed to the shear forces exerted by the blood stream. Furthermore, recent data described ERK5 as a kinase directing tumour resistance upon therapy-induced stress. Comparing their reported roles in various tumours and in the endothelium, FoxO proteins and the MEK5/ERK5 MAPK cascade appear to exert opposite functions. First non-published data confirmed the hypothesis that FoxO factors are subject to a negative modulation by the MEK5/ERK5 pathway. Hence, one goal of this PhD project was to further characterise this crosstalk at molecular level. The major mechanism of FoxO regulation is the balance among several post translational modifications, such as phosphorylation, acetylation, and ubiquitination. Most importantly, the PKB dependent phosphorylation of FoxOs negatively controls their activity, and it is critical for their subcellular localization. Therefore, the regulation of FoxO localization as mechanism of ERK5 dependent suppression was studied, but the results presented in this thesis argue against this hypothesis. However, additional experiments are required to explore the impact of ERK5 activity on FoxO post-translational modifications. FoxO activity can also be modulated by the interaction with other proteins, which in turn could explain general- and tissue-specific gene expression. Thus, another objective of this work was to investigate FoxO3-interactome in endothelial cells and the impact of MEK5/ERK5 activation on it. As published in (Fusi et al. 2022) and presented here, this analysis unveiled TRRAP as new FoxO bound protein in several cell types. Moreover, the interaction did not rely on the capacity of the FoxOs to bind their consensus DNA sequences at the promoter of target genes. Functional data demonstrated that TRRAP is required for FoxO-dependent gene transcription in endothelial and osteosarcoma cells. In addition, TRRAP expression in the endothelium is important for FoxO induced apoptosis. In summary, the interaction between FoxO factors and TRRAP revealed a new regulatory mechanism of FoxO-dependent gene transcription. It remains to be analysed whether the MEK5/ERK5 cascade may exert its suppressive effect on FoxO activity by interfering with their binding to TRRAP and whether such a mechanism may be relevant for tumorigenesis.},
  subject      = {Endothel},
  language  = {en}
}
@phdthesis{Dirimanov2019,
  author    = {Dirimanov, Stoyan Dinkov},
  title     = {Molecular Effects of Polyphenols in Experimental Type 2 Diabetes Mellitus and Metabolic Syndrome},
  doi       = {10.25972/OPUS-18570},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-185701},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2019},
  abstract  = {The growing prevalence of type 2 diabetes mellitus (T2DM) demands novel therapeutic and adjuvant strategies. Polyphenols (PPs) are plant secondary metabolites. Epidemiological studies demonstrate an inverse relationship between their increased intake and the risk of development of T2DM and cardiovascular complications. However, the PPs' mechanism of action remains largely unknown. The present work aimed to expand knowledge regarding the effects of PPs on diabetes relevant molecular targets. Pycnogenol® (PYC) is a standardized pine bark extract which consists of oligomeric and monomeric PPs. Its anti-diabetic effects have been demonstrated in clinical trials. As a part of a human study involving 20 healthy volunteers, the extract's effects on dipeptidyl peptidase IV (DPP IV) were investigated. This protease terminates the insulin secretagogue action of incretins. Its inhibition is a promising strategy in T2DM treatment. This study uncovered that PYC-intake of 100 mg daily over 14 days statistically significantly reduced DPP IV serum concentrations by 8.2 \% (n= 38, p= 0.032). Contrary to expectations, this decrease was not paralleled by a reduction in the serum DPP IV enzymatic activity. To the best of our knowledge, the present study was the first investigating the effects of PPs on DPP IV serum concentrations and activities in humans. The finding that PYC is capable of reducing DPP IV serum concentrations might be important with regard to diabetes, where DPP IV levels are increased. Screenings for PPs' in vitro effects on DPP IV activity were performed employing a purified enzyme. The effects of tested PPs (among which PYC ingredients) at a physiologically relevant concentration of 5 µM were weak (< 10 \%) and too small compared to the reference compound sitagliptin, and thus not likely to be clinically relevant. This result is in discordance with some published data, but consistent with the outcome from the present human study. In addition, fluorescence interactions with the experimental setup were registered: under certain conditions urolithin B exhibited an autofluorescence which might mask eventual inhibitory activity. Quercetin quenched the fluorescence slightly which might contribute to false positive results. No statistically significant effects of selected constituents and metabolites of PYC on the total DPP IV protein expression were observed in 3T3-L1 adipocytes. Thus, the lower DPP IV in vivo concentrations after intake of PYC cannot be explained with down-regulation of the DPP IV expression in adipocytes. Akt kinase is responsible for the transmission of insulin signals and its dysregulation is related to insulin resistance and plays an important role in development of cardiovascular complications in T2DM. Thus, the modulation of the phosphorylation status of endothelial Akt-kinase, respectively its activity, might be a promising strategy in the management of these pathologies. This work aimed to uncover the effects of PPs from different structural subclasses on Akt-phosphorylation (pAkt) in endothelial cells (Ea.hy926). Short-term effects (5 - 30 min) were investigated at a concentration of 10 µM. In a pilot study two model PPs induced a moderate, but reproducible inhibition of pAkt Ser473 of 52.37 ± 21.01 \% (quercetin; p= 0.006, n= 3) and 37.79 ± 7.14 \% (resveratrol; p= 0.021, n= 4) compared to the negative control. A primary screening with Western blot analysis investigated the effects of eight compounds from different subclasses on pAkt Ser473 and Thr308 to reveal whether the observed inhibition PPs a group effect or specific to certain compounds. In addition to resveratrol and quercetin, statistically significant inhibitions of pAkt Ser473 were induced by luteolin (29.96 ± 11.06 \%, p< 0.01, n= 6) and apigenin (22.57 ± 10.30 \%, p< 0.01, n= 6). In contrast, genistein, 3,4,5-trimethoxystilbene, taxifolin and (+)-catechin caused no inhibition. A strong positive and statistically significant correlation between the mean inhibitory effects of the tested PPs on both Akt-residues Ser473 and Thr308 (r= 0.9478, p= 0.0003) was determined. A comprehensive secondary screening via ELISA involving 44 compounds from nine structural groups quantified the effects of PPs on pAkt Ser473 to uncover potential structure-activity features. The most potent inhibitors were luteolin (44.31 ± 17.95 \%), quercetin (35.71 ± 8.33 \%), urolithin A (35.28 ± 11.80 \%), apigenin (31.79 ± 6.16 \%), fisetin (28.09 ± 9.09 \%), and resveratrol (26.04 ± 5.58 \%). These effects were statistically significant (p< 0.01, n= 3 to 6). Further lead structure optimization might be based on the fact that the effects of luteolin and resveratrol also differed statistically significantly from each other (p= 0.008). To the best of our knowledge, the present study is the first to compare quantitatively the short term effects of PPs from different subclasses on pAkt in endothelial cells. Basic structure-activity relationships revealed that for flavones and flavonols the presence of a C2=C3 double bond (ring C) was essential for inhibitory activity and hydroxylation on the m- and p- positions in the ring B contributed to it. For stilbenoids, three free OH-groups appeared to be optimal. The comparison of the inhibitory potentials of ellagic acid and its microbial metabolites showed that urolithin A was statistically significantly more effective than its progenitor compound. Despite their structural similarities, the only active compound among all urolithins tested was urolithin A, hydroxylated at the C3 and C8 positions. This suggested a specific effect for urolithin A. Based on the common structural determinants and molecular geometry of the most active PPs a pharmacophore model regarding Akt-inhibition was proposed. In summary, the effects of a wide variety of PPs from diverse structural subclasses on the in vitro phosphorylation of endothelial Akt were quantitatively analyzed for the first time, the effects of previously undescribed compounds were determined and structure activity relationships were elucidated. The inhibitory potential of individual PPs might be beneficial in cases of sustained over-activation of Akt-kinase and its substrates such as S6 kinase as reported for certain T2DM-related pathological states, such as insulin resistance, endothelial dysfunction, excessive angiogenesis, vascular calcification, and insulin triggered DNA-damage. The results of the present work suggest potential molecular mechanisms of action of PP involving Akt-inhibition and DPP IV-down-regulation and thus contribute to the understanding of anti-diabetic effects of these compounds on the molecular level.},
  subject      = {Polyphenole},
  language  = {en}
}
@phdthesis{Hafen2015,
  author    = {Hafen, Bettina},
  title     = {Physical contact between mesenchymal stem cells and endothelial precursors induces distinct signatures with relevance to tissue regeneration and engineering},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-119417},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2015},
  abstract  = {The goal of the project VascuBone is to develop a tool box for bone regeneration, which on one hand fulfills basic requirements (e.g. biocompatibility, properties of the surface, strength of the biomaterials) and on the other hand is freely combinable with what is needed in the respective patient's situation. The tool box will include a variation of biocompatible biomaterials and cell types, FDA-approved growth factors, material modification technologies, simulation and analytical tools like molecular imaging-based in vivo diagnostics, which can be combined for the specific medical need. This tool box will be used to develop translational approaches for regenerative therapies of different types of bone defects. This project receives funding from the European Union's Seventh Framework Program (VascuBone 2010). The present study is embedded into this EU project. The intention of this study is to assess the changes of the global gene expression patterns of endothelial progenitor cells (EPCs) and mesenchymal stem cells (MSCs) after direct cell-cell contact as well as the influence of conditioned medium gained from MSCs on EPCs and vice versa. EPCs play an important role in postnatal vasculogenesis. An intact blood vessel system is crucial for all tissues, including bone. Latest findings in the field of bone fracture healing and repair by the use of tissue engineering constructs seeded with MSCs raised the idea of combining MSCs and EPCs to enhance vascularization and therefore support survival of the newly built bone tissue. RNA samples from both experimental set ups were hybridized on Affymetrix GeneChips® HG-U133 Plus 2.0 and analyzed by microarray technology. Bioinformatic analysis was applied to the microarray data and verified by RT-PCR. This study gives detailed information on how EPCs and MSCs communicate with each other and therefore gives insights into the signaling pathways of the musculoskeletal system. These insights will be the base for further functional studies on protein level for the purpose of tissue regeneration. A better understanding of the cell communication of MSCs and EPCs and subsequently the targeting of relevant factors opens a variety of new opportunities, especially in the field of tissue engineering. The second part of the present work was to develop an ELISA (enzyme-linked immunosorbent assay) for a target protein from the lists of differentially expressed genes revealed by the microarray analysis. This project was in cooperation with Immundiagnostik AG, Bensheim, Germany. The development of the ELISA aimed to have an in vitro diagnostic tool to monitor e.g. the quality of cell seeded tissue engineering constructs. The target protein chosen from the lists was klotho. Klotho seemed to be a very promising candidate since it is described in the literature as anti-aging protein. Furthermore, studies with klotho knock-out mice showed that these animals suffered from several age-related diseases e.g. osteoporosis and atherosclerosis. As a co-receptor for FGF23, klotho plays an important role in bone metabolism. The present study will be the first one to show that klotho is up-regulated in EPCs after direct cell-cell contact with MSCs. The development of an assay with a high sensitivity on one hand and the capacity to differentiate between secreted and shedded klotho on the other hand will allow further functional studies of this protein and offers a new opportunity in medical diagnostics especially in the field of metabolic bone disease.},
  subject      = {Vorl{\"a}uferzelle},
  language  = {en}
}
@phdthesis{Heupel2010,
  author    = {Heupel, Wolfgang-Moritz Felix},
  title     = {Role and modulation of cadherins in pathologic processes},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-52716},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {Ca2+ dependent cell adhesion molecules (cadherins) are central for a variety of cell and tissue functions such as morphogenesis, epithelial and endothelial barrier formation, synaptic function and cellular signaling. Of paramount importance for cadherin function is their specific extracellular adhesive trans-interaction. Cadherins are embedded in a cellular environment of intracellular and extracellular regulators that modify cadherin binding in response to various physiological and pathological stimuli. Most experimental approaches used for studying cadherin interaction however lack a physiological proof of principle mostly by not investigating cadherins in their physiological environment. In the present cumulative dissertation, experimental approaches were applied to characterize and modulate vascular endothelial (VE)-cadherin and desmocadherin functions in the (patho-)physiological contexts of endothelial permeability regulation and disturbance of epidermal barrier function, which is typical to the blistering skin disease pemphigus, respectively. Whereas VE-cadherin is a key regulator of the endothelial barrier that separates the blood compartment from the interstitial space of tissues, desmosomal cadherins are crucial for maintenance of epidermal integrity and separation of the external environment from the body's internal milieu. Cadherin functions were both investigated in cell-free and cell-based conditions: by using biophysical single molecule techniques like atomic force microscopy (AFM), cadherin function could be investigated in conditions, where contributions of intracellular signaling were excluded. These experiments were, however, compared and combined with cell-based experiments in which cadherins of epidermal or endothelial cell cultures were probed by laser force microscopy (laser tweezers), fluorescence recovery after photobleaching (FRAP) and other techniques. The autoimmune blistering skin diseases pemphigus foliaceus (PF) and pemphigus vulgaris (PV) are caused by autoantibodies directed against the extracellular domains of the desmosomal cadherins desmoglein (Dsg) 1 and 3, which are important for epidermal adhesion. The mechanism of autoantibody-induced cell dissociation (acantholysis) in pemphigus, however, is still not fully understood. For the first time, it is shown by AFM force spectroscopy that pemphigus autoantibodies directly inhibit Dsg3 adhesion by steric hindrance but do not inhibit adhesion of Dsg1. However, the full pathogenicity of the autoantibodies depended on cellular signaling processes, since autoantibodies targeting Dsg1 also resulted in loss of cadherin-mediated adhesion in cell-based experiments. However, two other signaling pathways that have been reported to be involved in pemphigus pathogenesis, i.e. epidermal growth factor receptor (EGFR) and c-Src activation, were not found to be important in this context. Furthermore, peptide-based modulators of cadherin functions were generated for Dsg1/3 and VE-cadherin. By comparing Dsg1, Dsg3 and VE-cadherin sequences to published X-ray structures of cadherin trans-interactions, specific amino acid sequences of the binding pockets of these cadherins were identified. Peptide versions of these motifs were synthesized and the antagonistic functions of these "single peptides" were validated by AFM force spectroscopy as well as by cell-based assays. By linking two single peptides in tandem, stabilization of cadherin bonds because of by cross-bridge formation between trans-interacting cadherins was demonstrated. Protective effects of tandem peptides were shown by partly preventing pemphigus autoantibody-induced acantholysis, or in the case of VE-cadherin, by stabilizing endothelial barrier properties against barrier disrupting agents like the Ca2+ ionophore A23187 and an inhibitory VE-cadherin antibody. Most importantly, VE-cadherin tandem peptides abolished microvascular hyperpermeability induced by the physiologic inflammatory agent tumor necrosis factor-α in the rat mesentery in vivo. Both classes of tandem peptides therefore can be considered as a starting point for the generation of potential therapeutic agents that might prevent cell dissociation in pemphigus and breakdown of the endothelial barrier under inflammatory conditions.},
  subject      = {Cadherine},
  language  = {en}
}
@phdthesis{Schenk2007,
  author    = {Schenk, Rita},
  title     = {Impact of the CCN-proteins CYR61/CCN1 and WISP3/CCN6 on mesenchymal stem cells and endothelial progenitor cells},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-27766},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2007},
  abstract  = {CYR61 and WISP3 belong to the family of CCN-proteins. These proteins are characterised by 10\% cysteine residues whose positions are strictly conserved. The proteins are extracellular signalling molecules that can be associated with the extracellular matrix. CCN-proteins function in a cell- and tissue specific overlapping yet distinct manner. CCN-proteins are expressed and function in several cells and tissues of the musculoskeletal system. In this study the impact of the angiogenic inducer cysteine-rich protein 61 (CYR61/CCN1) on endothelial progenitor cells (EPCs) and mesenchymal stem cells (MSCs) as well as the wnt1 inducible signalling pathway protein 3 (WISP3/CCN6) on MSCs were elucidated. EPCs are promising cells to induce neovascularisation in ischemic regions as tissue engineered constructs. A major drawback is the small amount of cells that can be obtained from patients; therefore a stimulating factor to induce in vitro propagation of EPCs is urgently needed. In this study, mononuclear cells obtained from peripheral blood were treated with 0.5 µg/ml CYR61, resulting in an up to 7-fold increased cell number within one week compared to untreated control cells. To characterise if EPCs treated with CYR61 display altered or maintained EPC phenotype, the expression of the established markers CD34, CD133 and KDR as well as the uptake of acLDL and concurrent staining for ulex lectin was analysed. Both CYR61 treated and untreated control cells displayed EPCs characteristics, indicating that CYR61 treatment induces EPC number without altering their phenotype. Further studies revealed that the stimulating effect of CYR61 on EPCs is due to enhanced adhesion, rather than improved proliferation. Usage of mutated CYR61-proteins showed that the adhesive effect is mediated, at least partly, by the integrin \&\#945;6\&\#946;1, while the integrin \&\#945;\&\#965;\&\#946;3 has no influence. Endogenous expression of CYR61 was not detectable in EPCs, which indicated that control cells are not influenced by endogenous secretion of CYR61 and also could explain the dose-dependent effect of CYR61 that is measured at a low concentration of 0.05 µg/ml. MSCs were treated with 0.5 µg/ml CYR61, a combination of growth factors including VEGF, both together and compared to untreated control cells. Matrigel angiogenesis assay revealed an induction of angiogenesis, detected by induced sprouting of the cells, after CYR61 treatment of the MSC. Induced sprouting and vessel like structure formation after CYR61 treatment was similar to the results obtained after treatment with growth factors including the established angiogenesis inducer VEGF. This result clearly demonstrates the angiogenic potential of CYR61 on MSCs. Further studies revealed a migrative and proliferative effect of CYR61 on MSCs. Both properties are crucial for the induction of angiogenesis thus further strengthening the view of CYR61 as an angiogenic inducer. MSCs and EPCs are promising cells for tissue engineering applications in bone remodelling and reconstruction. MSCs due to their potential to differentiate into other lineages; EPCs induce neovascularisation within the construct. Both cell types respond to CYR61 treatment. Furthermore EPCs home to sides were CYR61 expression is detectable and both are induced by similar stimulators. Therefore CYR61 is a promising factor for tissue engineered bone reconstruction applications. WISP3 is expressed in cartilage in vivo and in chondrocytes in vitro. Loss of function mutations in the WISP3 gene are associated to the inherited human disease progressive pseudorheumatoid dysplasia (PPD), that is characterised by cartilage loss and bone and joint destruction. Since MSCs also express the protein, the aim of this study was to elucidate if recombinant protein targets MSCs. A migratory effect of WISP3 treatment on MSCs and osteogenic differentiated MSCs has been proven in this study. To elucidate if global gene expression patterns are influenced by WISP3, cells were treated with 0.5 µg/ml WISP3 and compared to untreated control MSCs. Gene expression study by using affymetrix technology revealed an induction of interferon inducible genes including CXCL chemokines and members of the TNFSF family. Reevaluation by RT-PCR on identical RNA and an additional time series confirmed the results. Although no established cartilage associated genes were detected as regulated genes within this 24h treatment, anti-angiogenic and immunosuppressive genes indicate a protective role of WISP3 for the cartilage, which is sensitive to inflammatory processes. Both CCN-proteins CYR61 and WISP3 are valuable for the musculoskeletal system. This and previous studies revealed the role of CYR61 for osteogenesis and angiogenesis of tissue engineered applications. WISP3 is responsible for development, protection and maintenance of cartilage. Therefore further studies with the proteins in the musculoskeletal system are of high relevance.},
  subject      = {Endothel},
  language  = {en}
}