LE VESCICOLE EXTRACELLULARI RILASCIATE DALLE CELLULE MESENCHIMALI STAMINALI MODULANO IL PROCESSO INFIAMMATORIO

Mesenchymal stem cells (MSCs) are multipotent adult stem cells that originate from the mesoderm. They were first identified from bone marrow mononuclear cells but recently alternative sources of MSCs have been identified, including adipose tissue, placenta, synovial membrane, peripheral blood and umbilical cord. Human MSC can grow in adhesion in tissue culture dishes, express specific surface antigens such as CD105, CD73 and CD90 while lack expression of hematopoietic antigens (CD45, CD34, CD14 or CD11b, CD79α or CD19, MHC II). Finally, human MSCs are capable to differentiate into osteoblasts, adipocytes and chondroblasts under standard in vitro differentiation conditions. In the past two decades the mechanisms of MSC function during rescue and repair of injured organs and tissues have been explored in order to understand potential biological and clinical applications of MSCs. Intercellular communication is essential to multicellular organisms and the secretion of extracellular vesicles (EVs) contribute to that information exchange. Depending on their origin and size, these vesicles are classified in exosomes, shedding vesicles and microvesicles. Exosomes are intraluminal vesicles, released by multivesicular bodies after fusion with the plasma membrane. The endosomal origin of exosomes is reflected in their molecular composition. Shedding vesicles are larger than exosomes and are produced directly through plasma membrane blebbing, from regions enriched in lipid rafts. Microvesicles are circular membrane fragments released from the cell surface in the extracellular environment, both in physiological and pathological cellular conditions. MSC-derived EVs contain nucleic acids, proteins involved in several signaling pathways and transcription factors, have a specific lipid composition and may engulf some cytoplasm or organelles. EVs have been characterized as novel mediators of intercellular communication both in physiological conditions and during inflammatory process. Inflammation is a protective strategy enacted by the immune system in response to damaging events, but chronic inflammation might have an opposite effect by contributing to tissue damage. MSC-derived EVs can display a key role in immunomodulation through several mechanisms, such as influence on secretion pathway of cytokines and transfer of proteins, signal molecules and nucleic acids. The focus of this work is describing how MSCs exert an anti-inflammatory effect mediated by EVs, which can act on signaling pathways and cells involved in the immune system. This mechanism is evaluated through a series of experiments. First, in vitro analysis of immunomodulatory abilities of EVs derived from inflammation-stimulated and naïve MSCs is performed in order to measure differences in cytokines production. Then, in vivo experiments with an animal model of inflammation-induced brain injury demonstrate that MSC-EVs treatments ameliorate neurogenesis and long-term microstructural white matter alterations. Finally, the coordinated function of MSCs and macrophages within the haematopoietic stem niche is analysed under intracellular oxidative stress conditions. The consequences of such oxidative stress (MSCs toxicity and inflammation) are prevented through mobilization of damaged mitochondria from MSCs to macrophages via microvesicles and subsequently induced tolerance of macrophages against EVs.