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Coming dissertations at MedFak

  • 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.

  • PET in Prostate Cancer – Detection, Tumour Biology and Prognosis Author: Naresh Kumar Regula Link: Publication date: 2020-04-16 14:18

    Prostate cancer (PCa) is the most common non-cutaneous malignancy in men and the leading cause of cancer-related deaths in Sweden. Despite the major advances, the current diagnostic modalities fall short of standards, specifically, precise localization required for effective management of the PCa. positron emission tomography (PET) combined with computed tomography (CT) has evolved as a promising diagnostic imaging technique for PCa. The progression of the PCa is often associated with metabolic alterations and overexpression of several proteins. Increased de novo fatty acid synthesis and prostate-specific membrane antigen (PSMA) overexpression are some of the distinctive features linked with PCa growth and the potential targets for the development of PET radiotracers.       

    This thesis is based on four original articles and focuses on the utilization of some of several different PET tracers available to visualize PCa spread. The work can be divided into two distinctive parts: (1) evaluate the prognostic value of 11C-acetate PET/CT towards survival in the setting of biochemical relapse after surgery, investigate tumour biology using single-tissue compartment model derived parametric images of 11C-acetate dynamic PET/CT both at patient and cell level and (2) the comparison of 68Ga-PSMA-11 PET/CT with 11C-acetate PET/CT and 18F-NaF PET/CT in patients with PCa relapse depicting different aspects of PCa biology.

    We demonstrated that quantification of 11C-acetate accumulation in PCa lesions was a strong predictor of survival in patients with biochemical relapse. Furthermore, parametric images of 11C-acetate dynamic PET/CT enabled visualization of tumour biology exhibiting elevated extraction of 11C-acetate associated with cancer aggressiveness also confirmed in in-vitro studies. 68Ga-PSMA-11 PET/CT located more widespread disease and performed significantly better in locating lymph node and bone metastases compared to 11C-acetate PET/CT. Similarly, 68Ga-PSMA-11 PET/CT was able to detect most of the bone lesions detected with 18F-NaF PET/CT along with additional soft tissue lesions.

    In conclusion, we showed the role of 11C-acetate PET/CT in PCa prognosis with additional understanding of tumour biology. Further, we successfully showed better performance of 68Ga-PSMA-11 PET/CT in locating PCa relapse and established it as a promising option for PCa re-staging.