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Published on: September 4, 2013
Functional Expression of Choline Transporters in Microglia and Their Regulation of Microglial M1/M2 Polarization
Toshio Okada1, Eisuke Muto1, Tsuyoshi Yamanaka2
1Department of Anesthesiology, Tokyo Medical University, 6-7-1 Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan.
Background:
Microglia are key cells of the immune system in the central nervous system and are suggested to be deeply involved in the development of neurodegenerative diseases. It is well known that microglia have functional plasticity, with an inflammatory M1 phenotype and an anti-inflammatory M2 phenotype. Inhibition of choline transport in macrophages has been reported to suppress the secretion of inflammatory cytokines. However, the role of the choline transport system in regulating microglial M1/M2 polarization has not been fully elucidated to date. In this study, we investigated the mechanism of choline uptake in microglia, and its association with microglial M1/M2 polarization.
Methods:
The immortalized mouse microglial cell line SIM-A9 was used for [3H]choline uptake and expression analysis of choline transporters. The association between the choline uptake system and the M1/M2 polarization of microglia was also analyzed.
Results:
Choline transporter-like protein (CTL) 1 and CTL2 were highly expressed in SIM-A9 cells, and CTL1 and CTL2 were localized in the plasma membrane and mitochondria, respectively. Functional analysis of choline uptake demonstrated the existence of Na+-independent, pH-dependent, and intermediate-affinity choline transport systems. Choline uptake was concentration-dependently inhibited by hemicholinium-3 (HC-3), an inhibitor of choline uptake, and increased by lipopolysaccharide (LPS) and interleukin-4 (IL-4). Expression of the mRNA of M1 microglia markers IL-1β and IL-6 was increased by LPS, and their effects were suppressed by choline deprivation and HC-3. In contrast, mRNA expression of the M2 microglial marker arginase-1 (Arg-1) was increased by IL-4, and the effect was enhanced by choline deprivation and HC-3.
Conclusions:
Our results suggest that inhibition of CTL1-mediated choline uptake in microglia preferentially induces M2 microglia polarization, which is a potential therapeutic approach for inflammatory brain diseases.
Insights
Inhibition of choline transport in microglia promotes anti-inflammatory M2 polarization. This suggests targeting choline uptake could be a therapeutic strategy for brain inflammation.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia are central nervous system immune cells implicated in neurodegenerative diseases.
- Microglia exhibit functional plasticity, polarizing into M1 (inflammatory) and M2 (anti-inflammatory) phenotypes.
- Choline transport inhibition in macrophages reduces inflammatory cytokine secretion, but its role in microglial polarization is unclear.
Purpose of the Study:
- To investigate choline uptake mechanisms in microglia.
- To determine the association between choline transport and microglial M1/M2 polarization.
Main Methods:
- Utilized the SIM-A9 mouse microglial cell line for [3H]choline uptake assays.
- Analyzed choline transporter expression (CTL1, CTL2).
- Assessed M1/M2 polarization markers (IL-1β, IL-6, Arg-1) under varying choline conditions and with specific stimuli (LPS, IL-4) and inhibitors (HC-3).
Main Results:
- CTL1 and CTL2 were expressed in SIM-A9 cells, localized to plasma membrane and mitochondria, respectively.
- Microglia possess Na+-independent, pH-dependent choline transport systems, inhibited by HC-3.
- LPS-induced M1 markers (IL-1β, IL-6) were suppressed by choline deprivation and HC-3.
- IL-4-induced M2 marker (Arg-1) was enhanced by choline deprivation and HC-3.
Conclusions:
- Choline transporter-like protein 1 (CTL1)-mediated choline uptake inhibition favors M2 microglial polarization.
- Targeting CTL1-mediated choline uptake presents a potential therapeutic avenue for inflammatory brain diseases.
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