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Coming dissertations at MedFak

  • Zebrafish models for large-scale genetic screens in dyslipidemia and atherosclerosis : Validation and application Author: Manoj Kumar Bandaru Link: Publication date: 2019-12-20 09:02

    Hundreds of loci have been robustly associated with circulating lipids, atherosclerosis and coronary artery disease; but for most loci the causal genes and mechanisms remain uncharacterized. The overall aim of my thesis is to develop and validate novel in vivo model systems that are suitable for high-throughput, image-based genetic screens in coronary artery disease and related traits, and use these model systems to systematically characterize positional candidate genes.

    In Study I, I developed an experimental pipeline to validate the suitability of zebrafish larvae as a model system for systematic, large-scale characterization of drugs and genes associated with dyslipidemia and atherosclerosis. Using this pipeline, I showed that five days of overfeeding and cholesterol supplementation have independent pro-atherogenic effects in zebrafish larvae, which could be diminished by concomitant treatment with atorvastatin and ezetimibe. CRISPR-Cas9-induced mutations in orthologues of proof-of-concept genes resulted in higher LDL cholesterol levels (apoea), and more early stage atherosclerosis (apobb.1). Finally, the pipeline helped me to identify putative causal genes for circulating lipids and early-stage atherosclerosis (LPAR2 and GATAD2A).

    In Study II, I characterized cardiometabolic traits in apoc2 mutant zebrafish larvae and found that, similar to humans, larvae with two non-functional apoc2 alleles have higher whole-body levels of triglycerides and total cholesterol, and more vascular lipid deposition than larvae without mutations in apoc2. Interestingly, apoc2 mutant larvae also had lower glucose levels after adjusting for triglyceride levels, suggesting that therapeutic stimulation of apoc2 to prevent hypertriglyceridemia may result in hyperglycemia. Still, zebrafish larvae with mutations in apoc2 can be a useful model to identify and characterize additional causal genes for triglyceride metabolism.

    In Study III, I examined the effects of mutations in pcsk9 on atherosclerosis and diabetes-related traits in nearly 5,000 zebrafish larvae. Similar to the loss-of-function mutations in PCSK9 in humans, larvae with mutations in pcsk9 had lower LDLc levels and were protected from early-stage atherosclerosis. Interestingly, mutations in pcsk9 also resulted in fewer pancreatic β-cells in 10 days old larvae, which suggests the higher risk of diabetes in humans with mutations in PCSK9 may result from a direct effect on the beta cell.

    Based on these large-scale proof-of-concept studies, my thesis confirms that zebrafish larvae can be used for large-scale, systematic genetic screens in dyslipidemia and early-stage atherosclerosis.

  • Melatonin in the gastrointestinal tract Author: Fanny Söderquist Link: Publication date: 2019-12-18 13:38

    Melatonin is recognised as the pineal hormone regulating sleep and circadian rhythm. It has also been identified in peripheral tissues (mainly in animals) and thought to display a variety of actions, including anti-inflammatory properties, regulation of gastrointestinal (GI) functions, glucose homeostasis and beneficial effects in different tumour types. Patients with irritable bowel disorder commonly exhibit psychiatric co-morbidity and disturbances of the gut-brain axis have been proposed to play a role in these disorders. The focus of this thesis was to study melatonin and melatonin receptors in the normal human GI tract, the pancreas and small intestinal neuroendocrine tumours. The thesis also explores the complex relationship between GI symptoms and underlying psychiatric traits in the context of elevated levels of peripheral melatonin during waking hours.

    In paper I-II, tissue samples from the normal human GI tract and pancreas and tumour tissue from small intestinal neuroendocrine tumours were analysed for expression of melatonin and melatonin receptors using immunohistochemistry. For tumour patients, melatonin was also analysed in plasma and set in relation to symptoms and outcome. In paper III-IV, a cohort of young adults (18-25 years) seeking psychiatric care was examined for GI symptoms, melatonin levels in saliva, depressive symptoms and anxiety traits. Psychiatric assessments were performed using structured or semi structured interviews. Depressive symptoms were measured using the self-rating version of the Montgomery-Åsberg Depression Rating Scale; GI symptoms were measured using the Gastrointestinal Symptoms Rating Scale for Irritable Bowel Syndrome; and personality traits were evaluated using the Swedish Universities Scales of Personality.

    Melatonin and melatonin receptors were widely expressed in the normal human gut and pancreas (paper I) but even in small intestinal neuroendocrine tumours known to produce serotonin (paper II). The intensity of the melatonin immunoreactivity in tumour tissue was found to correlate with lower proliferation index. After treatment, plasma levels of melatonin were reduced in tumour patients. Young adult patients seeking psychiatric care reported more GI symptoms than healthy controls, regardless of the currently active psychotropic medication. The level of GI symptoms was associated with severity of depressive symptoms and trait anxiety (paper III). Higher postprandial levels of melatonin were associated with the GI symptoms of bloating and pain (paper IV).

    In summary, these findings demonstrate the widespread presence of melatonin in the human gut and confirm a link between melatonin, psychiatric health and GI symptoms.

  • Antibiotic resistance gone wild : A One Health perspective on carriage, selection and transmission of Extended-Spectrum Cephalosporinase- and Carbapenemase-producing Enterobacteriaceae Author: Clara Atterby Link: Publication date: 2019-12-18 13:34

    Antibiotics have saved millions of lives since they came into clinical use during the Second World War in the 1940s. Today, our effective use of antibiotics is under great threat due to emerging antibiotic resistance in bacteria. This thesis addresses the problems of antibiotic resistance from a ”One Health” perspective. The focus is on antibiotic resistant Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) in the environment and wildlife, and also considering the situation in healthy humans and livestock. 

    In Paper I-III, high occurrence of Extended-Spectrum Beta-Lactamase (ESBL) -producing E. coli and/or K. pneumoniae was detected in fecal samples from wild birds, and the bacteria had genetic similarities to bacteria that cause disease in humans. Proximity to humans was associated with higher occurrence of cephalosporinase (ESBL and pAmpC)-producing E. coli in wild gulls. In Paper IV, ciprofloxacin resistant E. coli was enriched in the gut of mallards exposed to low concentrations of ciprofloxacin, and plasmid conjugation between E. coli bacteria readily took place. In Paper V, carbapenem resistant and blaOXA-48 harbouring- E. coli/K. pneumoniae was rare, but present in healthy humans in rural Cambodia, while cephalosporinase-producing E. coli/K. pneumoniae was common in both humans and livestock. The same ESBL/pAmpC genes were detected in humans and livestock, and exposure to animal manure and slaughter products were risk factors for fecal carriage in humans.

    In conclusion, wild birds can function as potential resistance reservoirs and sentinels for antibiotic resistant E. coli. Environmental pollution from humans is the primary source for antibiotic resistant Enterobacteriaceae found in wildlife, but selection for antibiotic resistant bacteria may also occur in wild birds. The results indicate that transmission of cephalosporinase-producing E. coli/K. pneumoniae occur between wildlife, humans and livestock, but more in-depth molecular work is needed to determine the mechanisms of dissemination. The high community carriage of multidrug-resistant bacteria in rural Cambodia is worrying and highlights Southeast Asia as a hotspot for antibiotic resistance. Antibiotic resistance surveillance is biased towards high-income countries and research should be focused more on low- and middle-income countries, and also include the important “One Health” perspective.