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Coming dissertations at MedFak

  • Hip Revision Surgery : Identification of Genetic Markers and Evaluation of Novel Treatment Strategies Author: Anders Brüggemann Link: Publication date: 2020-02-07 09:34

    Total hip arthroplasty (THA) is, despite its overall good outcome, for some patients followed by hip revision surgery. This seems in parts to be because of genetic susceptibility to revision surgery. The most common reason for revision surgery is aseptic loosening followed by periprosthetic joint infection and dislocation. Cups made of porous tantalum (TM cups) were thought to be favorable in revision surgery to address aseptic loosening, but they seem to confer an increased risk of dislocation. The effectiveness and biocompatibility in vivo of TM cups have not been researched. Dual mobility cups (DMCs) with two articulating surfaces are proposed to prevent dislocation to a higher degree than standard polyethylene liners.

    Our hypotheses were that TM cups are superior to their historical treatment alternative in terms of re-revision rates; that the combination of DMC cemented into TM cups would decrease the risk for dislocation after revision surgery; that tantalum ion liberation is marginal after the use of TM cups; and that certain risk genes are associated with an increased risk for revision surgery after total joint arthroplasty.

    Studies I&II were register-based cohort studies comparing the implant survival of TM cups and conventional acetabular reinforcement rings (study I), and the combination of TM cups/DMC with TM cups/standard polyethylene liners (study II). We found that TM cups perform equally well as reinforcement rings, but that the two implants differ in their failure mechanisms. Cementing a DMC into TM cups adequately addressed the issue of recurrent dislocation. In study III we investigated whether tantalum ion liberation does occur after implantation of a TM cups and how this affects patients’ immunological response by comparison of three groups: primary non-tantalum THA, primary tantalum THA and revision tantalum THA. We found the highest concentration of tantalum ions in the revision cases, yet tantalum ions were not associated with an immunological response, and we found no signs of alteration in the investigated lymphocyte subsets. Study IV aimed to identify possible risk genes for revision surgery after total hip or knee replacement by a genome wide association study. We found six significant risk genes for the endpoint revision surgery for any reason, and three for the endpoint revision due to aseptic loosening. We found a variety of suggestive risk genes within the region coding for the ABO-system.

    In conclusion, the novel treatment options TM cups and DMC show good results in hip revision surgery, but longer follow-up is warranted. The use of porous tantalum seems not to be associated with the immunological activation that can be observed in metallosis. The risk for revision surgery is associated with certain risk genes.

  • Induction of Mast Cell Apoptosis via Granule Permeabilization : A Novel Approach to Target Mast Cells Author: Aida Paivandy Link: Publication date: 2020-02-06 09:23

    Mast cells are densely granulated tissue-resident immune cells that play an important role in orchestrating inflammatory responses. Dysregulated increases in the numbers and activation status of mast cells can have deleterious consequences for the body in various inflammatory diseases. Mast cells are best-known for their detrimental roles in allergic diseases, e.g., asthma. Thus, strategies that target mast cells and their harmful activities in such pathological conditions are potentially attractive therapeutic options. An efficient strategy to accomplish a full blockade of the harmful events mediated by various mast cell mediators is to locally eliminate mast cell populations altogether by inducing their apoptosis.

    Using in vitro-cultured mast cells, we identified that mefloquine, an antimalarial drug with lysosomotropic activity, causes permeabilization of secretory granules, increased production of reactive oxygen species (ROS), release of granule-localized proteases into the cytosol and apoptotic cell death (Paper I). Moreover, intraperitoneal injections of mefloquine in mice resulted in a reduced peritoneal mast cell population in vivo.

    To evaluate the possibility of using lysosomotropic agents for selectively depleting human lung mast cells by induction of apoptosis, human lung specimens were used. Exposure of either intact human lung tissue, purified lung mast cells or mixed populations of lung cells to mefloquine revealed that human lung mast cells are highly susceptible to ROS-induced apoptosis in this setting. In contrast, other cell populations of the lung were largely refractory (Paper II).

    Lastly, in an attempt to gain a deeper insight into the mechanism underlying ROS production and the downstream events in response to lysosomotropic challenge, we identified that the mast cell secretory granules comprise major subcellular compartments for ROS production in response to mefloquine (Paper III). Lysosomal iron, granzyme B and the ERK1/2 MAP kinase signaling pathway were found to contribute to production of ROS in response to mefloquine. Furthermore, granule acidification was shown to be essential for mefloquine-mediated effects in mast cells, i.e., granule permeabilization, ROS production and cell death. Collectively, the present thesis introduces the possibility of inducing selective mast cell apoptosis via granule permeabilization as a novel strategy to target mast cells. Thus, this strategy has a potential to be used therapeutically to ameliorate mast cell-mediated detrimental effects in inflammatory diseases, such as asthma.

  • Characterizing the spectrum of somatic alterations in canine and human cancers Author: Sharadha Sakthikumar Link: Publication date: 2020-01-30 12:35

    Cancers arise as a result of deleterious somatic alterations accumulating in the genome during the process of cell division. These alterations arise either via exposure to mutagens or due to errors occurring during DNA replication. In this thesis, a systematic exploration, from discovery to analyses of somatic alterations in three diverse cancers that affect dogs and humans, was undertaken.

    In Studies I and II, whole-exome sequencing of dogs affected by the cancers of osteosarcoma and hemangiosarcoma were done to delineate coding mutations that can contribute to their carcinogenesis. Besides, as these cancers mirror the corresponding human disease in clinical manifestation and histological features, a secondary objective was to confirm the molecular drivers found in the canines were also influencing factors in the human cancer(s).

    In the osteosarcoma investigations with three breeds, we found that tumors show a high frequency of somatic copy-number alterations, affecting key cancer genes. TP53 was the most frequently altered gene, akin to human osteosarcoma. The second most mutated gene, histone methyltransferase SETD2, has known epigenetic roles in multiple cancers but not in osteosarcoma. Our study highlights the strong genetic similarities between human and dog osteosarcoma, suggesting that canine disease may serve as an excellent model for developing treatment strategies in both species.

    In the hemangiosarcoma study in golden retrievers, putative driver alterations were identified in the tumor suppressor TP53 and in genes involved in the cell cycle regulating PI3K pathway, including PIK3CA and PIK3R1. Furthermore, we find several somatic alterations between the dog hemangiosarcoma and human angiosarcoma overlap, indicating we can use the canine model to apprise the infrequently occurring human disease.

    In Study III, we implemented whole-genome sequencing methodologies to define both coding and non-coding alterations in the glioblastoma cancer genome. We find the coding somatic alterations recapitulate what has been previously seen for the cancer, including driver alterations in the genes of EGFR, PTEN, and TP53. Significantly though, using the concept of evolutionary constraint, we find an enrichment of non-coding mutations in regulatory regions, around GBM-implicated genes. The mutated regions include splice sites, promoters, and transcription factor binding sites, suggesting the importance of regulatory mutations for the pathogenesis of glioblastoma.

    Overall, the insights garnered from the above exome- and genome-wide surveys provide novel insights into unraveling some of the complexities associated with somatic genomic alterations in cancer genomes. It also convincingly underscores the benefits of using sequencing technologies to comprehend complex biological diseases.