Blood-brain barrier (BBB) is a structure that maintains central nervous system (CNS) homeostasis by isolating it from the normal blood flow. In physiological conditions BBB prevents CNS penetration by blood-derived molecules and is a barrier for the immune system. BBB is built by tight junctions between endothelial cells of microvessels, pericytes, and astroglial end-feets. Pericytes are very important part of BBB showing a great impact on properties of endothelial cells and BBB tightness. In pathological conditions (i.e. inflammation) the structure of BBB is loosened and cells of the immune system have a free access to the brain and the spinal cord. That is the main mechanism of pathogenesis in both multiple sclerosis (MS) and the rodent model of the disease – experimental autoimmune encephalomyelitis (EAE). Overactivation of purinergic receptor P2X7, is a possible mechanism leading to neurodegeneration observed during the course of MS/EAE. This receptor has two distinct functions: it participates in maturation and release of proinflammatory cytokines or can polymerase to create transmembrane pores which can drive cell to death by apoptosis or necrosis. Thus, we hypothesized that overactivation of this receptor on pericytes may lead to cell damage and/or loss of the protective function towards BBB. In this study we first analyzed status of BBB which was determined by expression of claudin 5 – a marker of BBB tightness – in correlation with the expression of P2X7R in microvessels’ fractions and brain sections of rats subjected to EAE. Using immunoblots and confocal microscopic method we found negative correlation between P2X7R and claudin 5 expression which decreased significantly in all examined time points of the disease, reaching the minimum level (45% and 70% of control) at days 2 p.i. and 4 p.i., respectively. Additionally, we present the results of pericytes features and P2X7R expression in microvessels in early time after EAE induction. Condition of pericytes was visualized by immunofluorescent staining against PDGFRβ (a marker protein). Semiquantitative level of this protein was measured using Western blot analysis of brain homogenates and isolated microvessels fraction. The pattern of observed changes suggests contribution of pericyte-located P2X7R on BBB state and the involvement of this receptor into pathological mechanisms connected with development of EAE.
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