Differential Regulation of AMPA Receptor and GABA Receptor Trafficking by Tumor Necrosis Factor-α

“These new synaptic AMPARs are likely replaced over time by GluR2-containing receptors, because HPP-spermine had no effect on mEPSCs recorded from control neurons despite the finding that constitutive TNF release is necessary to maintain normal levels of surface AMPARs.”

“Trafficking of these receptors is thought to underlie, at least in part, both rapid forms of synaptic plasticity and slower homeostatic changes in transmission (Malinow and Malenka, 2002; Turrigiano and Nelson, 2004).”

“…circuit activity is pharmacologically reduced, excitatory synapses are strengthened and inhibitory synapses weakened (Turrigiano and Nelson, 2004), at least in part through changes in the synaptic surface expression of AMPARs and GABAA receptors (Kilman et al., 2002; Turrigiano and Nelson, 2004).”

“TNFR1 initiates signaling through an array of downstream pathways, most known for their roles in gene expression and apoptosis (Pan et al., 1997; Baud and Karin, 2001).”

“Recently, the proinflammatory cytokine tumor necrosis factor- (TNF ) was found to be a novel, gliareleased factor that increases the surface expression of AMPARs (Beattie et al., 2002).”

“In contrast, consistent with our previous results (Beattie et al., 2002), a recombinant soluble form of the TNF receptor TNFR1 (sTNFR), which binds endogenous TNF (Bezzi et al., 2001), decreased surface GluR1 staining (10 g/ ml; 72 5%; n 59) (Fig.”

“It is possible that the antibodies to GluR1 might somehow sterically inhibit antibody staining of surface GluR2, and, therefore, we used an alternative technique, biotinylation of surface AMPARs (Ehlers, 2000; Kim and von Zastrow, 2003), to reexamine whether GluR2 surface expression was increased by TNF .”

“Similarly, the effects of TNF could contribute to the modification of circuit behavior that underlies the hyperalgesia after peripheral nerve damage, a neuropathological state that involves glia-released cytokines, including TNF (Watkins et al., 2001; Milligan et al., 2003).”

“However, glycine treatment caused an increase in surface expression of both GluR1 and GluR2 (Lu et al., 2001; Man et al., 2003), although we observed a large increase in surface GluR1 with TNF but no significant change in surface GluR2.”

“…Nagatsu et al., 2000; Perry et al., 2001), and preventing its signaling in vivo can, for example, prevent or reduce neuron loss after cerebral ischemia (Dawson et al., 1996; Barone et al., 1997; Meistrell et al., 1997) and head injury (for review, see Barone et al., 1997; Shohami et al., 1999).”

“Specifically, secretion of the proinflammatory cytokine tumor necrosis factor-a from glial cells appears to be necessary for the increase in the level of synaptic AMPARs caused by extended periods of activity blockade (Beattie et al, 2002; Stellwagen et al, 2005; Stellwagen and Malenka, 2006).”

“The pro-inflammatory cytokine tumour necrosis factor-&alpha”

“AMPA receptors have abnormal stoichiometry, as they lack the GluR2 subunit; thus, they become Ca2+ permeable and may contribute to neurotoxicity (Stellwagen et al., 2005).”

“TNFα also enhanced AMPA-induced current in dorsal horn neurons, in agreement with a previous report from hippocampal neurons (Stellwagen et al., 2005).”

“…activity blockade, acute application of TNFa (or conditioned media from activity-blocked cultures) increases mEPSC amplitude, and scaling up in response to prolonged activity blockade is prevented by blocking TNFa signaling (Beattie et al. 2002; Stellwagen et al. 2005; Stellwagen and Malenka 2006).”

“Conversely, TNF-α causes endocytosis of GABAA receptors, thus resulting in decreased inhibitory strength (27,82).”

“, TNFα) modulate the expression of synaptic AMPA and GABA receptors rendering neurons more susceptible to excitotoxicity (13;160).”

“Interestingly, TNF-a has the opposite effect on GABAARs, causing a decrease in the surface levels of these inhibitory receptors (Stellwagen et al. 2005).”

“further exacerbate excitotoxicity during an ischemic insult [42].”

“Indeed, experimenters have now uncovered a rich variety of homeostatic synaptic mechanisms that operate on both excitatory and inhibitory synapses, which I describe below in turn.”

“However, in the striatum, TNF/ signaling that was upregulated by application of dopamine D2 receptor antagonists led to a reduction of calcium-permeable AMPA receptors [31,32].”

“TNF-α not only amplifies the number of glutamate receptors but also induces GABA receptor endocytosis, reducing the inhibitory drive and causing pertinent changes in excitability [26].”

“These effects are likely to be mediated by TNF-a ability to activate the recruitment of AMPA receptors lacking the GluR2 subunit at neuronal membranes, thus in a molecular conformation which favor Ca influx into neurons, and to induce endocytosis of GABAA receptors (Beattie et al., 2002; Stellwagen et al., 2005).”

“Previous work in hippocampal neurons had shown that TNFα promoted the delivery of GluA2-lacking AMPA receptors to the cell surface and the removal of GABAA receptors from the cell surface (Beattie et al., 2002; Stellwagen et al., 2005).”

“, 1992) and TNFa (Stellwagen et al., 2005), have been shown to regulate inhibitory synaptic transmission.”

“Similarly, short-term exposure of hippocampal neurons to TNF-a (15–30 min) has been found to induce endocytosis of GABA-A receptors and increase trafficking of excitatory AMPA receptors to the plasma membrane (Stellwagen et al, 2005).”

“For example, TNF-alpha can induce a dramatic increase in the surface expression of glutamate receptors in cultured hippocampal neurons, and glial-derived TNF-alpha is necessary for quantal scaling in vitro (Beattie et al. 2002, Stellwagen et al. 2005; Stellwagen & Malenka 2006).”

“Because another prototype inflammatory cytokine, TNF- , has also been shown to regulate neuronal activity by affecting AMPA receptor trafficking (Stellwagen et al., 2005), we tested the effect of TNF- .”

“…cytokines are demonstrated to support homeostatic neuroplasticity, these signaling pathways could be further augmented during inflammatory conditions and mediate neurotoxicity (Stellwagen et al., 2005; Parkhurst et al., 2013; Pribiag and Stellwagen, 2014; Stellwagen and Lewitus, 2014).”

“In addition to the actions of TNFα to cause increased surface expression of glutamate receptors, it also induces endocytosis of GABAA receptors and thus reduces inhibitory drive [149].”

“TNF can independently enhance excitatory synaptic strength by increasing membrane trafficking of AMPA receptors in cultured hippocampal pyramidal neurons (2) and reduce the overall inhibitory currents mediated through GABAA receptors in vitro (2, 5).”

“Interestingly, TNFα, present at the site of injury (Crespo et al., 2007), increases the synaptic levels of GluR2-lacking receptors and therefore exacerbates the excitotoxic damage (Stellwagen et al., 2005).”

“This predisposes the neuron to glutamate induced excitotoxicity.(60)”

“, 2005); up-regulation of cell surface expression of N-methyl-Daspartic acid (NMDA) receptors (Stellwagen et al., 2005); expression of phosphorylated NMDA receptors that exhibit increased calcium conductance (Viviani et al.”

“Combined with the aforementioned evidence from Stellwagen et al. (2005) that TNF-α causes increased expression of AMPA receptors which may be more calcium permeable, the intracellular calcium concentrations may become sufficiently elevated in the presence of TNF-α to contribute to the impairment of…”

“C1q has recently been shown to play a role in synapse elimination during development and in neurodegeneration (Stevens et al., 2007).”

“Among these factors, TNF has been shown recently to induce significant changes of glutamate transmission in the hippocampus, by altering the composition of glutamate AMPA receptor subunit (Stellwagen et al., 2005; Stellwagen and Malenka, 2006; Leonoudakis et al., 2008).”

“It could be, in contrast, post-synaptic, consistent with the reported capacity of TNFα to promote surface insertion of AMPAR subunits at dendritic spines via stimulation of neuronal TNFR1 (Stellwagen et al., 2005).”

“…to a lesser extent, IL-1, upregulate the neuronal cell surface expression of both AMPA and NMDA receptors while downregulating cell surface expression of receptors for the inhibitory neurotransmitter, GABA; hence, creating an overall increase in neuronal excitatory tone (Stellwagen et al., 2005).”

“Interestingly, in animal models of traumatic brain injury, microglia were found to express P2X4Rs and phosphorylated p38 [103, 104], which is known to be themain upstream signal for BDNF synthesis and release in microglia [67].”

“The application or release of ytokines also leads to enhanced glutamatergic transmision by increasing excitatory receptor activity (Beattie et l., 2002; Emch et al., 2001; Furukawa and Mattson, 1998; tellwagen et al., 2005; Viviani et al., 2003) and suppressing nhibitory tone through gamma-aminobutyric acid (GABA) Kaw…”

“…synaptic strength by increasing membrane insertion of AMPA receptors in cultured hippocampal pyramidal neurons (Beattie et al., 2002; Stellwagen et al., 2005), and reduce the overall inhibitory currents mediated through GABAA receptors in vitro (Wang et al., 2000; Stellwagen et al., 2005).”

“To assess synaptic activity, we measured spontaneous and miniature excitatory postsynaptic currents (s- and m-EPSCs) mediated by AMPA receptors (AMPAR) and found a striking increase in the frequency of AMPAR-mediated (Fig.”

“…by their neuroexcitatory effects (Watkins et al., 2009) of glutamate transporter downregulation (Wang et al., 2003), GABA receptor downregulation (Stellwagen et al., 2005), upregulation of AMPA/NMDA expression and function (De et al., 2003), and enhancement of neurotransmitter release (Youn et…”

“Experimental Procedures Dissociated Neuronal Cultures Dissociated neuronal cultures were prepared from newborn Sprague-Dawley pups as previously described with minor changes (Stellwagen et al., 2005).”

“TNF-α also can increase AMPA-receptor density at the neuronal membrane in a molecular conformation lacking the GLUR2 subunit, which results in enhanced calcium influx (23).”

“TNF-a regulates AMPA receptor-mediated currents and receptor trafficking (Lewitus et al., 2014; Stellwagen et al., 2005).”

“We did not intend to use high concentrations, in order to avoid possible neurotoxic effects of TNF-a at higher concentrations (>10 ng/mL) [3,60].”

“…that TNF- may also drive inflammatory pain via postsynaptic mechanisms, such as inducing trafficking and surface expression of AMPA receptors (Beattie et al., 2002; Stellwagen et al., 2005; Choi et al., 2010) and increasing NMDA-induced currents in spinal lamina II neurons (Kawasaki et al., 2008).”

“In addition, TNF-α via TNFR1 could increase the AMPARs (α-amino3-hydroxy-5-methyl-4-isoxazole propionic acid receptors) on the cell surface of neurons, which triggers excitotoxic neuronal damage and susceptibility to seizure and highlights the proconvulsive function of TNFR1 (84, 152).”

“These observations are compatible with previous findings showing that TNF- potentiates the glutamatergic synaptic strength by increasing the surface expression of AMPA receptors (Beattie et al., 2002; Stellwagen et al., 2005), because this effect may contribute to potentiate neurodegeneration caused by non-NMDA recept…”

“…cytokines (especially TNF ) and microglial activation; thus, the increased contribution of GluR2-lacking AMPA receptors is entirely consistent with reports of TNF action to insert GluR2-lacking AMPA receptors in the membrane (Stellwagen et al., 2005; for review, see Pribiag and Stellwagen, 2014).”

“Cytokines also promote changes in neuronal glutamate (N-methyl-D-aspartate [NMDA] and AMPA) and g-aminobutyric acid (GABA)A receptor expression, and alter their molecular subunit composition by activating protein kinases (Stellwagen et al. 2005; Balosso et al. 2009).”

“These effects are mediated by its ability to activate the recruitment of AMPA receptors lacking the GluR2 subunit at neuronal membranes (thus in a molecular conformation which favors Ca(21) influx into neurons) and to induce endocytosis of GABAA receptors (Beattie et al., 2002; Stellwagen et al., 2005).”

“…that constitutive TNFα is necessary for maintaining AMPAR at the synapse, and described how TNF-α also triggered GABAA receptors internalisation, highlighting the unique ability of this cytokine to modulate both excitatory and inhibitory plasticity (Stellwagen et al., 2005; Stück et al., 2012).”

“Proictogenic effects induced by brain inflammation have been reported also in rodents exposed to lipopolysaccaride (LPS), a bacterial toxin, (Sayyah et al., 2003) or to specific pathogens mimicking systemic infection (Yuhas et al., 1999; Stringer et al., 2003; Meli et al., 2004).”

“Additionally, application of TNFR1 antibody decreased GluR1 surface expression in hippocampal neurons [46], indicating the necessary and constitutive role of TNF in regulating AMPAR membrane insertion and in modifying synaptic strength.”

“The role of TNFα in LTP and LTD has been questioned, however, by recent results published by two groups showing no impairment in hippocampal and cortical LTP and LTD in TNFα- and TNFR-deficient mice (Stellwagen and Malenka, 2006; Kaneko et al., 2008).”

“For example, it has been shown that there is an enhancing destructive interaction between tumor necrosis factor receptor-1 (TNFR1) and AMPA receptors.[15,219] [Figure 4].”

“The release of TNFa also acts upon the AMPA receptors and reduces expression of GluR2, which worsens excitotoxicity (d) (Beattie et al., 2002; Stellwagen et al., 2005).”

“…surface in the hippocampus after status epilepticus (Naylor et al., 2005), in the amygdala during fear conditioning (Chhatwal et al., 2005), and by treatment with phorbol esters (Connolly et al., 1999), the GABAAR agonist muscimol (Barnes, 1996), or tumor necrosis factor (Stellwagen et al., 2005).”