Lipopolisakkaritle Oluşturulan Nöroinflamasyon Modelinde Pro-İnflamatuar Sitokinlerin ve Yolaklarının Glia Limitans Üzerine Etkileri
Özet
The term Neuroinflammation (NI) that is unique for Central Nervous System (CNS), defines a process that includes complex cellular and intercellular relationships. The inflammatory responses of microglia and astrocytes formed after damage or intensive stimulus might fortify the effects of acute injury or contribute to activation of neurodegenerative mechanisms. Microglia and astrocytes activated by NI increase the expression of many potential neurotoxic chemo-attractant molecules and cytokines. Glia limitans (GL) is the outermost layer of cortex and is formed by astrocytic end feet and basal membrane surrounding vascular structures, thereby functioning like modified blood-brain barrier for the regulation of the movement of small molecules and cells to the brain parenchyma. Although the relationship between neural tissue and its adventia layer was investigated in other tissues, the similar interaction between the brain parenchyma and its adventia layer, which is composed of GL and meninges, is not studied. In this study, we investigated the expression of pro-inflammatory cytokines (Interleukin 1 beta - IL1β, Interleukin 6 - IL6, Tumor necrosis factor alfa - TNFα) and their receptors (tumor necrosis factor receptor 1, 2- TNFR1, TNFR2, interleukin1 receptor1- IL1R1) in both superficial and perivascular GL, in a mice model of neuroinflammation induced by bacterial lipopolysaccharide (LPS) in 2th and 4th hour. We used molecular (Western blotting) and imaging (immunohistochemistry, immuno-gold and transmission electron microscopy) techniques. Swelling on the astrocytic end feet as an indicator of NI and syncytial mitochondria supporting increased energy demand on the distal poles of these structures were seen with transmission electron microscopy (TEM) images in intracerebroventricular (ICV) LPS induced NI mice model. Vesicles filled with cytokines, which were ready to be secreted from activated astrocytes, were visualized by TEM and immune-gold TEM. IL1β were determined in GLs of surface associated astrocytes and descending parts, directed towards parenchyma, which mainly found in superficial cortical areas, fitting the astrocytic activity occurred at the same time period of immunocytochemistry findings. TNFα visualized as patchy, cytoplasmic and diffuse both in GLs and GLp. IL6, which has both inflammatory and neuroprotective features and maybe secreted later and less than other two cytokines, could not be visualized in a distinct pattern on GL. IL1R1 were detected in both GLs and GLp with the distribution resembling IL1β. Western blotting of GL of mice containing the superficial cortex showed a significant increase of IL6 and IL1β at the 4th hour of NI. These findings indicate that, inflammatory changes occur in astrocytes and GL at the hyper-acute period of ICV LPS induced NI and is thought that astrocytes are important for processes of neurodegenerative diseases.
