Abstract
BackgroundActivation of glial cells, including astrocytes and microglia, has been implicated in the inflammatory responses underlying brain injury and neurodegenerative diseases including Alzheimer's and Parkinson's diseases. Although cultured astrocytes and microglia are capable of responding to pro-inflammatory cytokines and lipopolysaccharide (LPS) in the induction and release of inflammatory factors, no detailed analysis has been carried out to compare the induction of iNOS and sPLA2-IIA. In this study, we investigated the effects of cytokines (TNF-alpha, IL-1beta, and IFN-gamma) and LPS + IFN-gamma to induce temporal changes in cell morphology and induction of p-ERK1/2, iNOS and sPLA2-IIA expression in immortalized rat (HAPI) and mouse (BV-2) microglial cells, immortalized rat astrocytes (DITNC), and primary microglia and astrocytes.Methods/ResultsCytokines (TNF-alpha, IL-1beta, and IFN-gamma) and LPS + IFN-gamma induced a time-dependent increase in fine processes (filopodia) in microglial cells but not in astrocytes. Filopodia production was attributed to IFN-gamma and was dependent on ERK1/2 activation. Cytokines induced an early (15 min) and a delayed phase (1 ~ 4 h) increase in p-ERK1/2 expression in microglial cells, and the delayed phase increase corresponded to the increase in filopodia production. In general, microglial cells are more active in responding to cytokines and LPS than astrocytes in the induction of NO. Although IFN-gamma and LPS could individually induce NO, additive production was observed when IFN-gamma was added together with LPS. On the other hand, while TNF-alpha, IL-1beta, and LPS could individually induce sPLA2-IIA mRNA and protein expression, this induction process does not require IFN-gamma. Interestingly, neither rat immortalized nor primary microglial cells were capable of responding to cytokines and LPS in the induction of sPLA2-IIA expression.ConclusionThese results demonstrated the utility of BV-2 and HAPI cells as models for investigation on cytokine and LPS induction of iNOS, and DITNC astrocytes for induction of sPLA2-IIA. In addition, results further demonstrated that cytokine-induced sPLA2-IIA is attributed mainly to astrocytes and not microglial cells.
Highlights
Activation of glial cells, including astrocytes and microglia, has been implicated in the inflammatory responses underlying brain injury and neurodegenerative diseases including Alzheimer’s and Parkinson’s diseases
These results demonstrated the utility of BV-2 and Highly Aggressive Proliferating Immortalized microglial cells (HAPI) cells as models for investigation on cytokine and LPS induction of iNOS, and DITNC astrocytes for induction of secretory phospholipase A2 (sPLA2)-IIA
We further examined the ability for BV-2 and HAPI cells, as well as primary rat microglial cells, to respond to cytokines and LPS in the induction of sPLA2-IIA mRNA and protein expression
Summary
Activation of glial cells, including astrocytes and microglia, has been implicated in the inflammatory responses underlying brain injury and neurodegenerative diseases including Alzheimer’s and Parkinson’s diseases. Despite obvious differences in morphology and functional properties, they are regarded as immune active cells and in some instances, they share common innate immune responses. Both astrocytes and microglial cells have been shown to respond to pro-inflammatory cytokines and lipopolysaccharide (LPS) in the induction of iNOS as well as other inflammatory factors [6,7,8,9,10,11]. In recent years, immortalized microglial cells, such as the murine derived BV-2 cells, have been extensively used as cell models to elucidate signaling pathways and responses to pro-inflammatory cytokines and LPS [9,12]
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