Studies on the Damage Associated Molecular Patterns (DAMPs)-induced Inflammatory Events in the Brain Immune Cells

Abstract

Innate immunity is vital for host defense against invasive pathogens. Innate immune system is programmed to recognize series of molecular patterns, pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). PAMPs are presented by microorganisms, whereas DAMPs include endogenous intracellular molecules released by activated or necrotic cells and extracellular matrix (ECM) molecules that are upregulated upon injury or degraded following tissue damage. Recently, the list of DAMPs candidate molecules is getting longer and DAMPs has been proposed to have multifaceted functions in sterile inflammatory diseases. Brain inflammation is a process of host defense against infection or injury. Microglial cells and astrocytes, major immune effector cells, have a pivotal role in the brain inflammation. Thus, to understanding how microglia and astrocytes are regulated by DAMPs is provide to clue for therapy of endogenous stimulator-induced inflammatory diseases including multiple sclerosis and cancer. The first part of this thesis, I showed that sulfatide, a major lipid component of myelin sheath, participates in diverse cellular events of the CNS. Sulfatide changed the morphology of primary microglia to their activated form, and it significantly induced the production of various inflammatory mediators in primary microglia and astrocytes. Moreover, sulfatide rapidly triggered the phosphorylation of p38, ERK, and JNK within 30 min. However, nonsulfated galactocerebroside, another major lipid component of myelin, had no effect on activation of glia. I further reveal that CD1d did not contribute to sulfatide-stimulated activation of MAPKs, although its expression was enhanced by sulfatide and sulfatide-treated microglial cells actually stimulated type II NKT cells. These results show that abnormally released sulfatide at demyelinated regions may act as an endogenous stimulator in the brain immune system. The second part, I showed that galectin-3 exerts cytokine-like regulatory actions in rat and mouse brain-resident immune cells. Expression and secretion of galectin-3 were significantly enhanced in glia under IFN--stimulated, inflamed conditions. After exposure to galectin-3, glial cells produced high levels of pro-inflammatory mediators and exhibited activated properties. Notably, within minutes after exposure to galectin-3, JAK2 and STAT1, STAT3, and STAT5 showed considerable enhancement of tyrosine phosphorylation; thereafter, downstream events of STAT signaling were also significantly enhanced. Using IFN- receptor 1-deficient mice, I further found that IFN-R1 might be required for galectin-3-dependent activation of the JAK-STAT cascade. These results indicate that galectin-3 acts as an endogenous danger signaling molecule under pathological conditions in the brain. The third part, I provide that galectin-1 could act as a regulatory molecule in pathological conditions such as tumor. I showed that expression level of galectin-1 was significantly higher in B35 brain tumor cell injected brain region than normal brain region. B35 brain tumor cells were more secreted galectin-1 compare to normal astrocytes. In treated with endogenous stimuli such as IFN-γ, microglial cells were markedly induced galectin-1 expression. Treatment of exogenous galectin-1 changed morphology of microglia, and induced expression of ICAM-1, adhesion molecule. In the contrast galectin-3, galectin-1 triggers production of not only pro-inflammatory mediators but also anti-inflammatory mediators. These findings indicate that galectin-1 in distinct from galectin3 can regulate activation and resolution state of microglial cells. Collectively, I suggest that endogenous stimulators, sulfatide, galectin-3, and galectin-1, are released at the pathological conditions, and activate brain resident glial cells thus, can regulate the CNS disease including multiple sclerosis and cancer.