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Coming dissertations at MedFak

  • Lupus Nephritis – Genetic Impact on Clinical Phenotypes, Disease Severity and Renal Outcome Author: Karin Bolin Link: Publication date: 2020-04-22 10:44

    Systemic lupus erythematosus (SLE) is an autoimmune inflammatory disease that can affect every organ system. Lupus nephritis (LN) is one of the more serious SLE manifestations. Whilst the genetic background of SLE has been thoroughly investigated, less is known about the background of LN. The aim of this thesis was to further elucidate the genetic background of LN, its subtypes and outcome.

    In paper I, we analysed genetic variations for association with LN, its severe form proliferative nephritis and renal outcome, in two SLE cohorts. Patients and controls were genotyped and association analyses were performed for patients versus controls and for patients with or without a specific clinical manifestation. In the case-control analysis of cohort I, four highly linked risk alleles in the STAT4 gene were associated with LN with genome-wide significance. In the case-only meta-analysis of the two cohorts, a STAT4 risk allele was associated with severe renal insufficiency. We conclude that genetic variations in STAT4 predispose to LN and a worse outcome with severe renal insufficiency.

    In paper II, we describe a case of severe SLE on the basis of C1q deficiency. By sequencing, a mutation in the C1qC gene leading to a premature stop codon was found. The patient was also found to carry risk alleles in several SLE-associated variants. Interferon alpha (IFN-α) levels were analysed over time in patient serum, and were found to correlate with disease activity. The patient’s serum had a strong interferogenic capacity when stimulating peripheral blood mononuclear cells from healthy individuals. With this study, we further emphasise the role of IFN-α in C1q deficiency and highlight the need to consider inherited impairments in the complement system in SLE with childhood onset.

    In paper III, we studied the impact of sex on disease manifestations in SLE. Female SLE patients more often presented with malar rash, photosensitivity, oral ulcers and arthritis, whilst the frequency of serositis, renal disorder and immunologic disorder were higher among male patients. Women were younger at LN onset, whereas men had a higher risk for progression into end-stage renal disease.

    In paper IV, we analysed genetic variations for association with LN and its subtypes in three SLE cohorts. Patients were genotyped and association analyses were performed for patients with versus without different phenotypes. We found genetic variations in the BANK1 gene to be associated with LN.

    In conclusion, this thesis provides further insight into the genetic background of renal manifestations in patients with SLE.

  • Membrane lipids and their transfer proteins in β-cells Author: Beichen Xie Link: Publication date: 2020-04-20 11:43

    Insulin secretion from β-cells is essential for glucose homeostasis and is often dysregulated in diabetes. Intracellular Ca2+ and membrane lipids cooperate to control insulin secretion with high spatial and temporal precision. Phosphoinositide lipids (PIs) and products from their hydrolysis regulate processes such as ion channel conductance and protein localization and activation, but the role of these lipids in insulin secretion from β-cells remains poorly understood. In the present study, live cell Ca2+ imaging combined with molecular tools for acute depletion or synthesis of the major PI in the plasma membrane (PM), PI(4,5)P2, revealed that this lipid positively regulates Ca2+ influx. As a consequence of reduced PI(4,5)P2 and impaired Ca2+ influx, β-cells failed to secrete appropriate amounts of insulin in response to glucose stimulation. In stimulated β-cells, ATP is co-released with insulin, which leads to autocrine purinergic receptor signaling with resulting phospholipase C activation, PI(4,5)P2 hydrolysis and local formation of diacylglycerol (DAG) in the PM. The ER-anchored protein extended synaptotagmin-1 (E-Syt1) binds to PI(4,5)P2 in the PM and transfers DAG from the site of production to the ER in a Ca2+-dependent manner. It was now found that DAG forms locally in microdomains around exocytotic sites and that E-Syt1 was selectively recruited to these sites, where it removed DAG by a mechanism that required an intact lipid transport domain. The DAG removal was part of a negative feedback mechanism, and loss of this feedback as a consequence of reduced E-Syt1 expression resulted in increased glucose-stimulated insulin secretion, likely via enhanced protein kinase C activity. TMEM24, an ER-anchored protein structurally similar to E-Syt1, dynamically localizes to ER-PM contact sites in a Ca2+-dependent manner, where it is responsible for transporting a PI(4,5)P2 precursor to the PM. TMEM24 was now shown to be spatially and temporally regulated by both Ca2+ and DAG. Ca2+ induced TMEM24 dissociation from the PM and this process was counteracted by E-Syt1-mediated DAG transport and subsequent suppression of PKC activity. Although TMEM24 was involved in maintaining the ER Ca2+ stores and in membrane reuptake following insulin granule exocytosis, the protein was dispensable for glucose-stimulated insulin secretion. Together, the work presented in this thesis defines new and important roles of PIs and lipid transfer proteins for normal β-cell function.

  • Remote Ischemic Preconditioning and its Effects on the Respiratory System Author: Astrid Bergmann Link: Publication date: 2020-04-20 11:20

    Mechanical ventilation in itself can lead to pulmonary damage, and one-lung ventilation (OLV), necessary for thoracic surgery, accentuates this injury. Remote ischemic preconditioning (RIP) is a potential tool to reduce lung injury after mechanical ventilation, including OLV.  However, current data on pulmonary RIP-effects are contradictory. Therefore, the overall purpose of this Ph.D. project was to assess the effects of RIP on the respiratory system. In Study I, in healthy spontaneously breathing volunteers, oxygenation was impaired early after RIP, which was possibly induced by transient ventilation-perfusion inequality. Studies II, III, and IV were performed in a porcine OLV model. In Study II, we found that RIP possibly enhances alveolar injury, but attenuates the immune response. In Study III, we confirmed that an immune response to RIP takes place, which shows a different time pattern in each cytokine, depending on the site of measurement as well. In Study IV, we studied the porcine model for eight hours and found that RIP improved oxygenation after two hours of OLV and impeded the decline of exhaled nitric oxide (NO) during and after OLV. These findings indicate that RIP mitigates hypoxic pulmonary vasoconstriction (HPV).

    In summary, RIP has a complex effect on the respiratory system, which partly explains the previous contradictory findings.