Coming dissertations at MedFak
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Exploring Vascular Specialization at the Organotypic and Cellular Levels
Link: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-543745
The lymphatic system is a unidirectional network that drains fluid and macromolecules, consisting of functionally specialized lymphatic capillaries and collecting vessels. Similarly, the blood vascular system is composed of the functionally arteries, capillaries, and veins, which together enable the distribution of oxygen and nutrients. Certain tissues exhibit organ-specific vascular adaptations, including hybrid vascular identities that combine features of different vessel types. In Paper I, I identified the penile cavernous sinusoids (pc-Ss) as a novel hybrid vascular bed that maintains both blood and lymphatic vessel-specific characteristics in both mice and humans. Notably, this highly specialized PROX1-positive vascular bed developed independently of the key lymphangiogenic growth factor VEGF-C, distinguishing it from other lymphatic and hybrid vessels analyzed so far.
The vascular system is continuously subjected to mechanical forces generated by fluid flow, including laminar and turbulent flows in different vessel segments. Unique to the lymphatic system, the oak leaf-shaped lymphatic endothelial cells (LECs) that line the capillaries and facilitate the uptake of interstitial fluid are primarily subjected to transmural flow and isotropic stretch, caused by fluid uptake-induced changes in vessel caliber. To investigate how capillary LECs adapt to these mechanical stressors at the cellular level, I established in Paper II in vitro models that mimic transmural flow and isotropic stretch. Using these models, in Paper III, I identified cyclic isotropic stretch as a driver of key features associated with capillary LECs in vivo, including prominent cellular overlaps and curvature of cell-cell contacts. We also found that dynamic remodeling of capillary LEC overlaps and the cytoskeleton is essential to maintaining monolayer integrity during isotropic stretch in vitro and in homeostasis in vivo. This process is mediated through a CDC42-dependent mechanism independent of integrin ß1.
In summary, this thesis provides new molecular and functional insights into organ-specific vascular heterogeneity, which may ultimately help identify targets for the development of improved therapies for conditions such as dysregulated penile vasculature or lymphedema. Furthermore, by applying new tools to study different mechanical forces in vitro, this thesis uncovers how publisherpus contribute to the functional specialization of LECs and regulate the homeostatic maintenance of lymphatic vessels - insights that may be applicable to other vascular beds.
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Reliability and prognostic value of systolic left ventricular function assessments by echocardiography following Acute Coronary Syndrome
Link: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-542295
This thesis investigates the accuracy and prognostic utility of left ventricular ejection fraction (LVEF) and global longitudinal strain (GLS) in acute coronary syndrome (ACS), analyzing data from Swedish myocardial infarction patients across four studies. The first paper evaluated the accuracy and reliability of LVEF recorded in the SWEDEHEART registry. Although good agreement was observed using Gwet’s weighted coefficient, unweighted metrics showed moderate consistency particularly for subnormal LVEF (<50%) with SWEDEHEART values tending to underestimate LVEF compared to the reference method. This highlights the need for caution when interpreting LVEF data from the years of inclusion (2008-2014).
In the second study, GLS was examined as a potential metric to improve risk prediction in ACS beyond LVEF. Although GLS was independently predictive of adverse outcomes, its additional prognostic value over LVEF for differentiating patients at risk was limited, particularly when systolic function was normal or mildly reduced. The third study reassessed LVEF and GLS one year post-myocardial infarction, finding that changes in GLS may offer improved prognostic insights in selected patients beyond initial LVEF and GLS values. Patients with improved systolic function showed comparable outcomes to those with stable normal function, while a small subset with deteriorating GLS faced elevated risk of heart failure (HF) hospitalization.
The final study explored the impact of adding LVEF and GLS to the GRACE 2.0 score for mortality risk stratification. Neither LVEF nor GLS significantly enhanced risk discrimination whereas the biomarker GDF-15 did improve predictive accuracy when combined with GRACE 2.0, suggesting that in ACS populations with predominantly normal ejection fraction, comorbidities and age, rather than myocardial dysfunction, influence mortality risk.
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The islet hormone exocytosis machinery in type-2 diabetes
Link: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-543091
Type-2 diabetes (T2D) is characterized by progressive β-cell dysfunction and impaired insulin secretion, yet the molecular mechanisms remain incompletely understood. In pancreatic β-cells, insulin secretion occurs through exocytosis, a process whereby insulin-containing secretory granules dock at the plasma membrane, recruit proteins that make up the SNARE-dependent exocytosis machinery (priming), and ultimately fuse with the membrane to release their content to the extracellular space. This thesis investigates the molecular machinery governing insulin granule dynamics and exocytosis in both healthy and diabetic conditions. Through analysis of secretory machinery components, we demonstrate distinct roles for SNARE binding protein Munc18 isoforms. Both Munc18 isoforms support granule docking, but Munc18-1 is strikingly required for exocytosis. On a molecular level, both isoforms bind to syntaxin, but are not recruited to the granule release site to the same extent. Our investigation of the v-SNARE protein VAMP8 reveals its predominant localization to endosomal compartments rather than insulin granules. Furthermore, we identify VAMP8 as a negative regulator of insulin secretion, likely by competing with VAMP2 at the release site, suggesting a new regulatory mechanism in β-cell function. We further examine phosphatidylinositol transfer protein alpha (PITPNA) as a critical regulator of insulin granule maturation. Modulation of PITPNA levels in human islets directly impacts insulin granule exocytosis, its silencing impairs secretion while overexpression enhances it. Importantly, restoring PITPNA expression in T2D islets reverses diabetes-related secretory defects, suggesting its loss may contribute to β-cell failure. Finally, using a novel ATP biosensor, we demonstrate that insulin granules can undergo either complete fusion, releasing both peptides and small molecules, or partial fusion that selectively releases only small transmitter molecules. This differential cargo release is regulated through cellular polarity and becomes dysregulated in T2D. Collectively, these findings provide insight into the molecular mechanisms controlling insulin granule trafficking and release, revealing multiple points of dysregulation in T2D.