title: The Toll-like receptor 4-activated neuroprotective microglia subpopulation survives via granulocyte macrophage colony-stimulating factor and JAK2/STAT5 signaling.
abstract: Toll-like receptor (TLR) 4 mediates inflammation and is also known to trigger apoptosis in microglia. Our time-lapse observations showed that lipopolysaccharide (LPS) stimulation induced rapid death in primary cultures of rat microglia, while a portion of the microglia escaped from death and survived for much longer than 2 days, in which time, all of the control cells had died. However, it remains unclear how the LPS-stimulated microglia subpopulation could continue to survive in the absence of any supplied growth factors. In the present study, to clarify the mechanism underlying the LPS-stimulated survival, we investigated whether microglia could produce their own survival factors in response to LPS, focusing on macrophage colony-stimulating factor (M-CSF), granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-34, which are mainly supplied by astrocytes or neurons. The LPS-stimulated microglia drastically induced the expression of the GM-CSF mRNA and protein, while M-CSF and IL-34 levels were unchanged. The surviving microglia also significantly upregulated the expression of GM-CSF receptor (GM-CSFR) mRNA without affecting M-CSFR. As for the GM-CSFR downstream signal, LPS resulted in the phosphorylation of STAT5 and its translocation to the nucleus in the surviving microglia. Moreover, a specific JAK2 inhibitor, NVP-BSK805, suppressed STAT5 phosphorylation and microglia survival in response to LPS, indicating a critical role of the JAK2/STAT5 pathway in this survival mechanism. Together, these results suggest that a subpopulation of TLR4-activated microglia may survive by producing GM-CSF and up-regulating GM-CSFR. This autocrine GM-CSF pathway may activate the JAK2/STAT5 signaling pathway, which controls the transcription of survival-related genes. Finally, these surviving microglia may have neuroprotective functions because the neurons remained viable in co-cultures with these microglia.
authors.affiliation: Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
authors.forename: Mayumi
authors.initials: M
authors.lastname: Kamigaki
authors.affiliation: Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan. Electronic address: ihide@hiroshima-u.ac.jp.
authors.forename: Izumi
authors.initials: I
authors.lastname: Hide
authors.affiliation: Department of Dermatology, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
authors.forename: Yuhki
authors.initials: Y
authors.lastname: Yanase
authors.affiliation: Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Shiraki
authors.affiliation: Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
authors.forename: Kana
authors.initials: K
authors.lastname: Harada
authors.affiliation: Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Tanaka
authors.affiliation: Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Seki
authors.affiliation: Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Shirafuji
authors.affiliation: Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Tanaka
authors.affiliation: Department of Dermatology, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
authors.forename: Michihiro
authors.initials: M
authors.lastname: Hide
authors.affiliation: Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
authors.forename: Norio
authors.initials: N
authors.lastname: Sakai
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism*; D053614:Janus Kinase 2 / Q000378:metabolism*; D017628:Microglia / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000502:physiology*
chemical_list: D050799:STAT5 Transcription Factor; C494094:Stat5a protein, rat; D051197:Toll-Like Receptor 4; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; C507927:Jak2 protein, rat; D053614:Janus Kinase 2
keywords: GM-CSF; LPS; Microglia; Neuroprotection; Survival; TLR4