M-CSF increases proliferation and phagocytosis while modulating receptor and transcription factor expression in adult human microglia

Abstract

BackgroundMicroglia are the primary immune cells of the brain whose phenotype largely depends on their surrounding micro-environment. Microglia respond to a multitude of soluble molecules produced by a variety of brain cells. Macrophage colony-stimulating factor (M-CSF) is a cytokine found in the brain whose receptor is expressed by microglia. Previous studies suggest a critical role for M-CSF in brain development and normal functioning as well as in several disease processes involving neuroinflammation.MethodsUsing biopsy tissue from patients with intractable temporal epilepsy and autopsy tissue, we cultured primary adult human microglia to investigate their response to M-CSF. Mixed glial cultures were treated with 25 ng/ml M-CSF for 96 hours. Proliferation and phagocytosis assays, and high through-put immunocytochemistry, microscopy and image analysis were performed to investigate microglial phenotype and function.ResultsWe found that the phenotype of primary adult human microglia was markedly changed following exposure to M-CSF. A greater number of microglia were present in the M-CSF- treated cultures as the percentage of proliferating (BrdU and Ki67-positive) microglia was greatly increased. A number of changes in protein expression occurred following M-CSF treatment, including increased transcription factors PU.1 and C/EBPβ, increased DAP12 adaptor protein, increased M-CSF receptor (CSF-1R) and IGF-1 receptor, and reduced HLA-DP, DQ, DR antigen presentation protein. Furthermore, a distinct morphological change was observed with elongation of microglial processes. These changes in phenotype were accompanied by a functional increase in phagocytosis of Aβ1-42 peptide.ConclusionsWe show here that the cytokine M-CSF dramatically influences the phenotype of adult human microglia. These results pave the way for future investigation of M-CSF-related targets for human therapeutic benefit.

Microglial proliferation in the brain of chronic alcoholics with hepatic encephalopathy

“…Plasma levels of IL-6 are known to be elevated in HE patients (Shawcross et al 2007), however it is unclear whether circulating IL-6 can enter the brain in HE as the BBB remains largely intact (Rangroo Thrane et al 2012). Microglial proliferation can be stimulated in vitro by a number of cytokines such as M-CSF (Smith et al 2013), MCP-1 (Hinojosa et al 2011), GM-CSF and IL-3, however the addition of IL-6 to microglial cultures did not stimulate proliferation (Kloss et al 1997). It seems more likely therefore that IL-6 up-regulation in pHEs is a by-product of microglial activation rather than stimulating proliferation.…”

“…It seems more likely therefore that IL-6 up-regulation in pHEs is a by-product of microglial activation rather than stimulating proliferation. An important caveat here is that our exploration of proinflammatory cytokines was limited, excluding for example macrophage colony-stimulating factor (M-CSF) that was recently shown to stimulate proliferation in ex vivo human microglial cultures (Smith et al 2013). …”

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

“…C/EBPβ microglial expression is also upregulated by excitotoxic neuronal death in rat neuronalmicroglial co-cultures(Perez-Capote et al 2006). Recent studies in adult human microglial cultures have shown that C/EBPβ expression is upregulated by macrophage colony-stimulating factor, a microglial mitogen,(Smith et al 2013) and by the proinflammatory cytokines IL-1β, IL6 or TNFα(Strohmeyer et al 2014). The upregulation of microglial C/EBPβ and C/EBPδ upon pro-inflammatory stimulation has also been observed in experiments with the microglial cell lines BV2Ejarque-Ortiz et al 2010;Ejarque-Ortiz et al 2007a;Gresa-Arribas et al 2010;Jana et al 2003) and N9.…”

MCSF orchestrates branching morphogenesis in developing submandibular gland tissue

“…MCSF has potent neuroprotective effects following auditory injury and in neuroinflammation (Smith et al, 2013;Yagihashi et al, 2005). We found that MCSF induces the expression of NRTN, which can explain at least in part the MCSF-induced formation of a neuronal network surrounding SMG tissue.…”