Expression of sphingosine kinase 1 in amoeboid microglial cells in the corpus callosum of postnatal rats

Haiyan Lin,Jiajun Xu,Eng-Ang Ling,Jia Lu,Chuansen Zhang,Nimmi Baby,S Thameem Dheen,Charanjit Kaur

doi:10.1186/1742-2094-8-13

Abstract

Sphingosine kinase 1 (SphK1), a key enzyme responsible for phosphorylating sphingosine into sphingosine-1-phosphate (S1P) has been shown to be expressed in monocytes and monocyte-derived peripheral macrophages. This study demonstrates SphK1 immunoexpression in amoeboid microglial cells (AMC), a nascent monocyte-derived brain macrophage in the corpus callosum of developing rat brain. SphK1 immunofluorescence expression, which appeared to be weak in AMC in normal brain, was markedly induced by lipopolysaccharide (LPS) or hypoxia treatment. Western blot analysis also showed increased expression level of SphK1 in the corpus callosum rich in AMC after LPS treatment. Detection of SphK1 mRNA and its upregulation after LPS treatment was confirmed in primary culture AMC by RT-PCR. Administration of N, N-dimethylsphingosine (DMS), a specific inhibitor of SphK1, effectively reduced upregulated SphK1 immunoexpression in AMC both in vivo and in vitro. This was corroborated by western blot which showed a decrease in SphK1 protein level of callosal tissue with DMS pretreatment. Remarkably, LPS-induced upregulation of the transcription factor NFκB was suppressed by DMS. We conclude that SphK1 expression in AMC may be linked to regulation of proinflammatory cytokines via an NFκB signaling pathway.

Highlights

Sphingosine kinase (SphK) is an enzyme that phosphorylates sphingosine to sphingosine-1-phosphate (S1P)
The intensity of Sphingosine kinase 1 (SphK1) expression in amoeboid microglial cells (AMC) was most intense in corpus callosum of 1- to 5-day-old rats compared to that of those aged 7 d (Figure 1Da-c, Figure 2C)
SphK1 is a key enzyme in the sphingolipid metabolic pathway, phosphorylating sphingosine into S1P and regulating intracellular levels of S1P

Summary

Introduction

Sphingosine kinase (SphK) is an enzyme that phosphorylates sphingosine to sphingosine-1-phosphate (S1P). SphK has two isoforms, SphK1 and SphK2, that have different properties and subcellular localizations [1,2]. While much has been reported on the expression and roles of SphK1 in different cells and its participation in distinct biological functions [1], the biological functions of SphK2 are not yet clearly defined. This study focused on SphK1 in view of its potential role in the central nervous system (CNS) [1]. SphK1 is mainly and abundantly expressed in cytosol of hippocampal neurons, endothelial cells, cerebellar granule cells and astrocytes of rat brain; and in cultured oligodendrocytes and murine BV2 cells [3,4,5,6,7].

Methods

Results

Conclusion