Abstract
Microglia, the main resident immune cells in the CNS, are thought to participate in the pathogenesis of various neurological disorders. LPS and LPS + IFNγ are stimuli that are widely used to activate microglia. However, the transcriptomic profiles of microglia treated with LPS and LPS + IFNγ have not been properly compared. Here, we treated murine primary microglial cultures with LPS or LPS + IFNγ for 6 hours and then performed RNA-Sequencing. Gene expression patterns induced by the treatments were obtained by WGCNA and 11 different expression profiles were found, showing differential responses to LPS and LPS + IFNγ in many genes. Interestingly, a subset of genes involved in Parkinson’s, Alzheimer’s and Huntington’s disease were downregulated by both treatments. By DESeq analysis we found differentially upregulated and downregulated genes that confirmed LPS and LPS + IFNγ as inducers of microglial pro-inflammatory responses, but also highlighted their involvement in specific cell functions. In response to LPS, microglia tended to be more proliferative, pro-inflammatory and phagocytic; whereas LPS + IFNγ inhibited genes were involved in pain, cell division and, unexpectedly, production of some inflammatory mediators. In summary, this study provides a detailed description of the transcriptome of LPS- and LPS + IFNγ treated primary microglial cultures. It may be useful to determine whether these in vitro phenotypes resemble microglia in in vivo pathological conditions.
Highlights
Microglia are the main cells of myeloid origin in the central nervous system (CNS)
In order to analyse the expression pattern of genes affected by these stimuli, we performed RNA-Sequencing analysis (RNA-Seq) on primary microglial cells stimulated with LPS or LPS + IFNγ
Normalized data represented on a heatmap for the abovementioned genes show the same expression pattern as that observed in quantitative real-time PCR (qRT-PCR) experiments (Fig. 1B)
Summary
Microglia are the main cells of myeloid origin in the central nervous system (CNS). They are considered tissue-resident macrophages that constantly patrol the cerebral microenvironment and respond to pathogens and cell damage[1]. Injection of LPS into the substantia nigra results in the progressive and irreversible loss of dopaminergic neurons In both cases, LPS triggers rapid activation of microglia, which precedes neuronal death. Whereas in some cases IFNγ potentiates the effect of LPS, e.g., NO production; in others, IFNγ counteracts it, e.g., Ptges and Csf[3] expression[11] These results indicate that two stimuli are capable of activating different pathways and they are not redundant. In order to analyse the expression pattern of genes affected by these stimuli, we performed RNA-Sequencing analysis (RNA-Seq) on primary microglial cells stimulated with LPS or LPS + IFNγ. Our results confirm that the two stimuli generate distinct gene expression patterns and can constitute useful tools to induce different profiles of inflammation in microglia
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