Microvesicle signaling in cardiovascular biology under normal and pathobiological conditions

Sammanfattning: Cardiovascular disease (CVD) is one of the leading causes of death worldwide. Atherosclerosis, a chronic pathology directly related to the circulatory system, develops due to an interplay between several molecular events. Atherosclerotic plaque build-up can lead to a reduction in arterial blood flow and finally, myocardial infarction (MI). To prevent or slow down of the CVD progression, it is important to primarily address modifiable risk factors connected with lifestyle and nutrition. Microvesicles (MVs) belong to a larger group, called extracellular vesicles that also includes exosomes and apoptotic bodies. These small (<1 μm) vesicles are released from the cell by blebbing of plasma membrane, a complex process involving numerous signaling pathways. Circulating MVs originate mainly from blood cells, as well as vascular endothelial cells. The release is activated by pro-inflammatory and pro-coagulant conditions. MVs transport bioactive molecules both on their surface and inside the lumen that makes them an interesting target for biomarker discovery and potential diagnostic application. The overall aim of this thesis was to explore the role of MVs in cardiovascular-related pathologies. To analyse plasma MVs, we optimized an acoustic trapping machine based method, employing ultrasonic standing wave, that isolates vesicles in a non-contact manner. We demonstrated that the new method is comparable to standard protocols of MV enrichment and could potentially be used for vesicle-based diagnostics . Furthermore, the results of a clinical study revealed that exercise has a protective effect on the vasculature through decreasing a release of MVs from activated endothelium. The proteomic data showed that exercise changes the pattern of the vesicular cargo. Bilberries (Vaccinium myrtillus) are considered to be a beneficial dietary component for patients with CVD and in the BEARSMART randomized clinical study we explored if there was an effect of bilberry powder supplementation on circulating MVs in MI patients. After eight weeks of dietary intervention, there was a significant reduction in platelet and endothelial MV concentration. Moreover, the in vitro part of the study demonstrated that bilberry extract decreased endothelial vesiculation, which was related to the P2X7 purinergic receptor pathway. The results of this project showed for the first time that nutrional changes can directly affect MV release and underlined the protective influence of berries on vascular health. In the PROFLOW clinical study, we observed a negative relationship between coronary flow reserve (CFR), a parameter depicting blood flow in the heart, and levels of endothelial and platet MVs, circulating in patients with CVD. Proteomic profiling demonstrated similar connection for CFR and several vesicular biomarkers. The outcome of this clinical study pointed at a potential application of MVs for diagnosis of vascular dysfunction. Lastly, we showed that atherosclerotic plaque released MVs, following balloon angioplasty. The results revealed that the vesicles originated from several types of cells and exhibited a pro-atherogenic ‘pattern’ of proteins that represented the pathological processes within the cardiovascular system that can lead to the atheroma formation. We also demonstrated an advantage of analysing isolated EVs, compared to crude plasma samples. The outcome of the studies included in this thesis points at the important role of MVs in the cardiovascular system. Study I and II underlined the importance of exercise and nutrition for prevention of CVD through decrease in MVs, whereas the Western world is still characterized with physical inactivity and imbalanced diet. Study III and IV focused on potential application of MVs as biomarkers or targets of therapeutics, however it needs further, thorough research and possibly, personalized approach.