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Triggering Receptor Expressed on Myeloid Cell-2 Protects PC12 Cells Injury by Inhibiting BV2 Microglial Activation
Jian-Wu Ni1, Cai-Xia Li2, Xiong-Wei Chen1
1Department of Anesthesiology, Wenzhou Hospital of Traditional Chinese Medicine, Wenzhou, P.R. China.
Abstract:
Microglia play a crucial role in the activation of immune defense mechanism as the resident macrophages in the central nervous system (CNS). Microglia can eliminate damaged neurons, plaques, and other infectious agents. Triggering receptor expressed on myeloid cell-2 (TREM-2) speculates to be beneficial in preventing inflammation-induced bystander damage of neurons. However, the precise molecular mechanisms underlying the regulation of TREM-2 on neurons are not clarified. We cultured PC12 cells with conditioned medium which was the supernatant of LPS-treated BV2 cells and six groups of PC12 cells (control group, LPS group, TREM-2 WT + LPS group, TREM-2 over-expression + LPS group, siRNA control + LPS group, and siRNA TREM-2 + LPS group) were investigated. The mRNA levels of inflammatory mediators: Nitric oxide synthase (iNOS) and Arginase-1(Arg-1) were quantified by using RT-PCR. Assessment of apoptosis in PC12 cells mediated by BV2 microglia was analyzed using TUNEL assays. The result showed that LPS stimulation significantly enhanced inducible iNOS (M1) production in BV2 cells (P < 0.01), and increased PC12 cells apoptosis (P < 0.01), while reduced the production of Arg-1 (M2) in BV2 cells (P < 0.01). These effects were attenuated by TREM-2 over-expression, but enhanced by TREM-2 silencing. It indicated that TREM-2 inhibited LPS-mediated neuronal apoptosis by down-regulating iNOS and up-regulating the expression of Arg-1 in BV2 microglia. Therefore, our findings may provide new insights in the regulation of TREM-2 on neuronal apoptosis via BV2 microglial M1/M2 modulation.
Insights
Triggering receptor expressed on myeloid cell-2 (TREM-2) protects neurons from inflammation. Overexpressing TREM-2 reduces neuronal apoptosis by modulating microglial responses, while silencing it exacerbates damage.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia are central nervous system immune cells crucial for defense.
- Triggering receptor expressed on myeloid cell-2 (TREM-2) may protect neurons from inflammatory damage.
- The exact molecular mechanisms of TREM-2's regulation of neurons remain unclear.
Purpose of the Study:
- To investigate the role of TREM-2 in regulating neuronal apoptosis induced by lipopolysaccharide (LPS)-activated microglia.
- To elucidate the molecular mechanisms by which TREM-2 influences microglial M1/M2 polarization and subsequent neuronal damage.
Main Methods:
- PC12 cells were treated with conditioned medium from LPS-stimulated BV2 microglia.
- Groups included control, LPS, TREM-2 wild-type + LPS, TREM-2 over-expression + LPS, siRNA control + LPS, and siRNA TREM-2 + LPS.
- Messenger RNA (mRNA) levels of inducible nitric oxide synthase (iNOS) and Arginase-1 (Arg-1) were quantified using RT-PCR.
- Neuronal apoptosis was assessed using TUNEL assays.
Main Results:
- LPS stimulation significantly increased iNOS (M1 marker) production and PC12 cell apoptosis while decreasing Arg-1 (M2 marker) in BV2 cells.
- TREM-2 over-expression attenuated LPS-induced neuronal apoptosis and modulated microglial polarization towards an M2 phenotype.
- TREM-2 silencing enhanced LPS-induced iNOS production and neuronal apoptosis, shifting microglia towards an M1 phenotype.
Conclusions:
- TREM-2 inhibits lipopolysaccharide-mediated neuronal apoptosis.
- TREM-2 exerts its neuroprotective effects by down-regulating iNOS and up-regulating Arg-1 expression in BV2 microglia.
- Modulating TREM-2 expression offers a potential therapeutic strategy for neuroinflammation-related neuronal damage.
