Well-regulated microglial activation is important for the protection of the central nervous system against various threats. Poorly regulated and excessive microglial activation leads to an exaggerated inflammatory response, which damages the neurons and causes neurodegeneration, which in turn, leads to the development of life-threatening medical conditions, such as Parkinson's disease. Previous research has shown that activated microglia releases in addition to inflammatory factors and cytokines also cysteine cathepsins, including cathepsin X. The latter has already been designated as an important regulator of neurodegeneration, caused by an inflammatory process mediated by microglial cells. In the scope of the Master's thesis, the effect of the microglial activation through simultaneous activation of Toll-like receptors (TLR), TLR3 and TLR4 on the resulting inflammatory response was studied in detail as well as we defined the role of cathepsin X in this process. We performed the experiments on a cellular model of activated microglia using BV2 cells, that were stimulated with TLR3 and TLR4 agonists, respectively with poly(I:C) and LPS. With the help of spectrophotometry and flow cytometry, we examined the effect of microglial activation, in the presence or absence of cathepsin X inhibitor, AMS36 on cell survival and the level of inflammatory response. We also spectrophotometrically determined the activities of caspase-3 and cathepsin X, while the analysis of the cathepsin X expression was performed with the use of enzyme-linked immunosorbent assay (ELISA) and its intracellular localization with the use of immunofluorescent confocal microscopy. To determine the expression of inducible NO synthase (iNOS) we used western blot. Concurrent activation of TLR3 and TLR4 with poly (I:C) and LPS agonists exhibited a stronger, synergistic effect on the activation of microglial BV2 cells, compared to one-sided stimulation with a single agonist, which we determined by measuring the concentrations of released inflammatory factors, namely nitric oxide (NO), interleukin-6 (IL-6) and tumor necrosis factor ? (TNF-?). Measurements of the expression and activity of cathepsin X in cell lysates and supernatants of stimulated BV2 cells showed that co-activation of TLR3 and TLR4, with poly(I:C) and LPS, significantly increased the level as well as the activity of cathepsin X in BV2 cell supernatants, in approximately the same extent as one-sided stimulation with LPS, while the intracellular protein's activity was significantly decreased. Moreover, the intracellular localization analysis of cathepsin X showed that localization of cathepsin X is significantly increased at the plasma membrane after co-activation of microglial cells by LPS and poly(I:C), while the cathepsin X localization within the lysosomal vesicles is decreased, which further indicates the subcellular translocation of cathepsin X in activated microglia cells. Additionally, we confirmed the role of cathepsin X as a mediator of microglial activation by the use of the specific, irreversible inhibitor of cathepsin X AMS36. The presence of the AMS36 significantly reduced concentrations of released inflammatory factors, including NO, IL-6 and TNF-? from activated microglia, while at the same time AMS36 also influenced and reduced the expression of iNOS in microglial cells after co-stimulation with LPS and poly(I:C). Inhibition of cathepsin X also decreased cell death and apoptosis of activated microglia cells mediated by simultaneous stimulation with LPS and poly(I:C), and AMS36 also visibly affected the increased activity of caspase-3 in activated microglia. Last but not least we also demonstrated the protective action of cathepsin X inhibitor on neuronal cells, with the use of a co-culture model using microglial BV2 cells and neuronal SH-SY5Y cells. Indeed, the addition of AMS36 to microglial cells, simultaneously stimulated with LPS and poly(I:C), significantly reduced degeneration of neuronal cells, exposed to supernatants of co-activated microglia. Results, obtained in the scope of research for the Master's thesis, therefore indicate that cathepsin X plays an important role in the co-activation of microglia and regulation of resulting inflammatory response, which defines cathepsin X as an important target in the development of strategies for the treatment of neurodegenerative diseases caused by inflammation, such as Parkinson's disease.
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