Abstract
Microglia are the primary immune cells of the central nervous system (CNS). Membrane bound sensors on their processes monitor the extracellular environment and respond to perturbations of the CNS such as injury or infection. Once activated, microglia play a crucial role in determining neuronal survival. Recent studies suggest that microglial functional response properties vary across different regions of the CNS. However, the activation profiles of microglia derived from the spinal cord have not been evaluated against brain microglia in vitro. Here, we studied the morphological properties and secretion of inflammatory and trophic effectors by microglia derived from the brain or spinal cord of neonatal rats under basal culture conditions and after activation with lipopolysaccharide (LPS). Our results demonstrate that spinal microglia assume a less inflammatory phenotype after LPS activation, with reduced release of the inflammatory effectors tumor necrosis factor alpha, interleukin-1 beta, and nitric oxide, a less amoeboid morphology, and reduced phagocytosis relative to brain-derived microglia. Phenotypic differences between brain and spinal microglia are an important consideration when evaluating anti-inflammatory or immunomodulatory therapies for brain versus spinal injury.
Highlights
Microglia are a unique population of cells in the central nervous system (CNS), constituting 5 to 15% of its total cell population, and were first identified by Rio-Hortega in 1932 [1,2,3]
DMEM/F12 with 10% Fetal Bovine Serum (FBS) was removed after 5 minutes and DMEM/F12 containing 2% P/S was added to the isolated brain microglia (BM) and spinal cord microglia (SCM)
For LPS activation, brain microglia cultures (BM) and SCM were treated with 1 mg/ml LPS for 24 hours. 24 hours after the LPS treatment the media from BM and SCM were assayed either for pro- and antiinflammatory effectors released in the media, phagocytic activity or fixed with 10% formalin for morphometric analysis
Summary
Microglia are a unique population of cells in the central nervous system (CNS), constituting 5 to 15% of its total cell population, and were first identified by Rio-Hortega in 1932 [1,2,3]. In basal physiological conditions (i.e. prior to injury or activation), microglia have ramified morphology with long processes that monitor the extracellular environment surrounding the cells of the CNS [4]. After brain trauma or infection, microglia become activated and withdraw their processes to assume amoeboid and spherical morphologies [5]. Amoeboid microglia are capable of secreting anti-inflammatory factors, pro-inflammatory factors, prostaglandins, cytokines and reactive oxygen species [5,6,7]. These microglial effectors interact with surrounding neurons and other glial cells and can initiate trophic as well as toxic signaling pathways [5,6,7]. Microglia assume a spherical morphology and become predominantly phagocytic, acting to clear the CNS of dying cells and other debris [5,6,7]
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