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Coming dissertations at MedFak

  • Avian Influenza Virus : Deciphering receptor interactions and their role in interspecies transmission Author: Per Eriksson Link: Publication date: 2019-11-21 14:17

    Influenza A virus (IAV) annually infects approximately 5–15 % of the human population, causing ~500,000 deaths globally. Novel IAVs have emerged and spread pandemically in the human population, but have over time established endemic circulation with reduced pathogenicity causing seasonal influenza. The natural reservoir of IAVs is wild waterfowl. The past pandemics have been associated with host switch and have partly or entirely originated from birds, or adapted via passage through pigs (postulated IAV mixing vessel). Understanding IAV interspecies transmission mechanisms is essential for pandemic preparedness. Enzootic circulation of avian IAV (AIV) is concentrated to a few waterfowl species, while other bird species seldom are infected. A species barrier preventing IAV interspecies transmission has been suggested. To investigate IAV host range and mixing vessels, histochemistry studies were conducted with tissues from avian species, pigs, and humans. Virus adaptation to new hosts was studied by challenging tufted ducks and chickens with mallard-derived AIVs, together with AIV receptor tropism and glycoproteomic analysis of receptor distribution. Finally, receptor and tissue tropism in ducks was studied systematically for AIV (H1–16). More abundant AIV attachment to human than pig tissues was observed, questioning the pig mixing vessel theory. Attachment patterns of AIVs to bird tissues was generally broad with abundant attachment to trachea. However, among ducks, pronounced attachment was observed to colon of Anas spp., suggesting that intestinal infection might be restricted to Anas spp., whereas other species may be susceptible to respiratory infection. Tufted ducks and chickens could not be infected by intraesophageal inoculation further supporting this hypothesis. Glycan array analysis revealed 3’SLN, 3’STF, and their fucosylated and sulfated analogues as main AIV receptors. Moreover, AIV Neu5Acα2,6 recognition was widespread. Avian respiratory and intestinal tracts glycoproteomic analysis revealed that avian and mammalian receptor structures are much more similar than earlier thought. Furthermore, observed AIV subtype titer variation in challenged tufted ducks and chickens did not correlate with virus receptor tropism. In summary, this thesis suggests that IAV receptor recognition, in particular α2,3 vs. α2,6 sialylated receptor structures, is less important for the IAV interspecies barrier than previously thought.

  • Importance of peripheral arterial disease as a risk marker in patients with myocardial infarction Author: Birgitta Jönelid Link: Publication date: 2019-11-20 13:10

    The purpose of this thesis was to describe the true prevalence of widespread arterial disease in a cohort with patients with a recent myocardial infarction (MI) to find valuable clinical methods to detect these patients. Our aim was also to investigate biomarker relationships with peripheral artery disease (PAD) and the importance of PAD in patients’ long-term outcomes.

    We studied patients with a recent MI in a prospective observational study, the REBUS ((Relevance of Biomarkers for Future Risk of Thromboembolic Events in Unselected Post-myocardial Infarction Patients) trial. A total of 421 patients were included in the study, 390 of whom had their ankle-brachial index (ABI) measured and a mean-time follow up of 5.5 years. Atherosclerotic changes were assessed in three arterial beds by coronary angiography, measuring the ABI and carotid ultrasound. Ninety-two biochemical biomarkers were assessed at baseline by a proximity extension assay (PEA) chip. 263 out of 421 filled in a self-administered Walking Impairment Questionnaire (WIQ). Polyvascular (PvD) disease was defined as pathological findings in all three arterial beds.

    We found that PAD and PvD are underdiagnosed in patients who suffered a recent MI. We also found the ABI to be a strong and useful method to identify patients with PAD as well as patients with more widespread arterial disease, such as PvD (paper I).

    The results of the scoring system, the WIQ, showed it is useful for finding patients with PAD and PvD, even when completed soon after an acute MI event (paper II).

    We also found that biochemical biomarkers associated with the inflammatory pathway – tumour necrosis factor receptor 1 (TNFR-1), tumor necrosis factor receptor 2 (TNFR-2) and growth differentiation factor 15 (GDF-15) – were able to predict pathological ABI, i.e. PAD, in these MI patients. These results could also be validated in another observational study and cohort of MI patients, the VaMIS cohort (paper III). Pathological ABI was also found to be a strong predictor for cardiovascular events of all-cause mortality, new ACS, and a composite endpoint of all-cause mortality, new ACS, new stroke/TIA or new PAD event. When evaluating the three inflammatory biomarkers as a surrogate marker for ABI, they showed a similar association with all-cause death and the composite endpoint (paper IV).

  • Towards Better Understanding of Etiological Mechanisms at the Neuromuscular Junction Author: Evgenii Bogatikov Link: Publication date: 2019-11-20 12:05

    The neuromuscular junction (NMJ) serves as a model for understanding the mechanisms that determine communication between neurons and their target cells. Disorders of the NMJ can be either autoimmune or genetic (hereditary). The autoimmune disorder myasthenia gravis (MG) is caused by antibodies against the presynaptic nerve terminal or the postsynaptic muscle membrane, which make up the NMJ. The most common antibodies are directed against the acetylcholine receptor (AChR) or muscle specific tyrosine kinase (MuSK). An alternative to expand on preclinical in-vivo methods for studying mechanisms underlying diseases of neuromuscular transmission is to apply physiologic in-vitro models that would allow tissue-tissue as well as cell-cell interactions. A system that would allow cell-cell interactions in a biological fashion is the micro-electrode array (MEA) chip that allows co-culturing of motor neurons and muscle cells.

    The primary hypothesis is that the suggested MEA can be used in creating a reliable model for healthy and diseased NMJ, allowing for manipulations and treatment assays. The secondary hypothesis is that small non-coding RNA, so called microRNAs (miRNA) have a specific role in neuromuscular transmission and in MG.

    Study I demonstrated a method of long-term muscle cell culture on the MEA chips, which allows us to trace the development of muscle cells through the observation of their electrical activity at subcellular resolution. The maturation of skeletal muscle tissue was accompanied by a gradual increase in the amplitude and frequency of extracellular individual electrical spikes. The mature muscle tissue demonstrated the steady electrical activity with synchronized spike propagation in different directions across the chip.

    Study II showed a specific upregulated profile of miRNAs in the muscles of MuSK antibody seropositive MG mice. Transfection of these miRNAs, miR-1933 and miR-1930, promoted downregulation of several proteins and further confirmation with qPCR revealed a specific blocking of IMPA1 and MRPL27, which are involved in intracellular signal transduction and mitochondrial biogenesis in skeletal muscles.

    Study III revealed no correlation between the morphology of skeletal muscle cells and their electrical activity at an early developmental stage. However, the application of recombinant rat agrin increased the number of AChRs clusters in the culture of skeletal muscle and promoted a higher degree of spontaneous activity.