Lipopolysaccharide increases microglial GLT‐1 expression and glutamate uptake capacity in vitro by a mechanism dependent on TNF‐α

Abstract

This study investigates the effect of microglial activation on microglial glutamate transporters in vitro. Stimuli known to activate microglia and/or to be associated with pathological conditions with an impaired astroglial glutamate uptake were compared. Morphological changes and marked increases in ED1 antigen expression were found after 8-h incubation of rat microglia in 56 mM KCl, 1 ng/ml lipopolysaccharide (LPS), and 100 microM glutamate, as well as in acidic and basic conditions, showing that the cells were activated. Of the stimuli used, only LPS induced a significant release of the proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), and was the only stimulus that increased microglial GLT-1 expression and glutamate uptake capacity after 12-h incubation. This effect was probably mediated by TNF-alpha, since this cytokine mimicked the effect of LPS. Furthermore, the effect of LPS was blocked by thalidomide, an inhibitor of TNF-alpha synthesis. Additionally, neutralizing antibodies against TNF-alpha also blocked the increase, indicating TNF-alpha as an inducer of GLT-1 expression in microglia. It was also found that preincubation with glutamate dose-dependently inhibited the microglial glutamate uptake. This could suggest different physiological functions for microglial and astroglial glutamate uptake and might indicate a reciprocal control of GLT-1 expression between microglia and astrocytes.

Inflammation, Glutamate, and Glia: A Trio of Trouble in Mood Disorders

“…Immune mediators (such as TNF) regulate membrane trafficking and recycling of EAATs either alone or in association with several neurohumoral influences, including growth factors and neuropeptides (Gras et al, 2012;Takahashi et al, 2015). As mentioned previously, EAATs are expressed on astrocytes and oligodendrocyte cells both in resting and during activation states, whereas microglia express these transporters only when activated by immune factors such as LPS (Persson et al, 2005). Inflammatory molecules such as IL-1β and TNF released during immune activation suppress astrocytic expression of GLT-1 and GLAST glutamate transporters (similar to EAAT2 and EAAT1 in humans) in cell culture experiments (Korn et al, 2005;Szymocha et al, 2000;Wang et al, 2013a;Ye and Sontheimer, 1996), and EAAT2 expression is diminished in inflammatory CNS lesions of both laboratory animals and humans (Ohgoh et al, 2002;Vercellino et al, 2007).…”

Naloxone and Ouabain in Ultralow Concentrations Restore Na+/K+-ATPase and Cytoskeleton in Lipopolysaccharide-treated Astrocytes

“…The procedure was done according to Persson et al (37). Separate aliquots were taken for protein concentration determination.…”

The effect of electromagnetic radiation on the rat brain: an experimental study

“…Inflammatory cytokines, including TNF-α, IL-1β, and IL-6, are released by microglial cells during neuropathological states and in response to various neuropathological stimuli (21,25). IL-1β is a pro-inflammatory cytokine and an important upstream regulator of the inflammatory response that occurs following trauma (27).…”