Protein Phosphorylation Cascades Associated with Methamphetamine‐induced Glial Activation

Abstract

Reactive gliosis is the most prominent response to diverse forms of central nervous system (CNS) injury. The signaling events that mediate this characteristic response to neural injury are under intense investigation. Several studies have demonstrated the activation of phosphoproteins within the mitogen-activated protein kinase (MAPK) and Janus kinase (JAK) pathways following neural insult. These signaling pathways may be involved or responsible for the glial response following injury, by virtue of their ability to phosphorylate and dynamically regulate the activity of various transcription factors. This study sought to delineate, in vivo, the relative contribution of MAPK- and JAK-signaling components to reactive gliosis as measured by induction of glial-fibrillary acidic protein (GFAP), following chemical-induced neural damage. At time points (6, 24, and 48 h) following methamphetamine (METH, 10 mg/kg x 4, s.c.) administration, female C57BL/6J mice were sacrificed by focused microwave irradiation, a technique that preserves steady-state phosphorylation. Striatal (target) and nontarget (hippocampus) homogenates were assayed for METH-induced changes in markers of dopamine (DA) neuron integrity as well as differences in the levels of activated phosphoproteins. GFAP upregulation occurred as early as 6 h, reaching a threefold induction 48 h following METH exposure. Neurotoxicant-induced reductions in striatal levels of DA and tyrosine hydroxylase (TH) paralleled the temporal profile of GFAP induction. Blots of striatal homogenates, probed with phosphorylation-state specific antibodies, demonstrated significant changes in activated forms of extracellular-regulated kinase 1/2 (ERK 1/2), c-jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK), MAPK/ERK kinase (MEK1/2), 70-kDa ribosomal S6 kinase (p70 S6), cAMP responsive element binding protein (CREB), and signal transducer and activator of transcription 3 (STAT3). MAPK-related phosphoproteins exhibited an activation profile that peaked at 6 h, remained significantly increased at 24, and fell to baseline levels 48 h following neurotoxicant treatment. The ribosomal S6 kinase was enhanced over 60% for all time points examined. Immunoreactivity profiles for the transcription factors CREB and STAT3 indicated maximal increases in phosphorylation occurring at 24 h, and measuring greater than 2- or 17-fold, respectively. Specific signaling events were found to occur with a time course suggestive of their involvement in the gliotic response. The toxicant-induced activation of these growth-associated signaling cascades suggests that these pathways could be obligatory for the triggering and/or persistence of reactive gliosis and may therefore serve as potential targets for modulation of glial response to neural damage.

Additive Effects of HIV and Chronic Methamphetamine Use on Brain Metabolite Abnormalities

“…These findings suggest an inflammatory response, or glial activation, because these metabolites are found in much higher concentrations in glial cells than in neurons (35), and are consistent with findings of acute methamphetamine-induced glial activation in rodents (36) and monkeys (37), as well as findings of chronic effects in monkeys up to 1.5 years after methamphetamine exposure (37). Methamphetamine, like HIV, has been reported to stimulate the production of the inflammatory cytokine, tumor necrosis factor α (38), and to increase binding and activation of the redox-responsive transcription factors, AP-1 and NF-kappaB (39).…”

Induction of Activating Transcription Factors (ATFs) ATF2, ATF3, and ATF4 in the Nucleus Accumbens and Their Regulation of Emotional Behavior

“…This observation raises the possibility that stress induction of ATF3 may be mediated via activation of intracellular stress cascades as opposed to being mediated by increased dopaminergic transmission. Thus, although very high doses of methamphetamine can cause cell death via cellular stress pathways (Hebert and O'Callaghan, 2000;Jayanthi et al, 2004), there is no evidence that the amphetamine dose used in the present experiments activates cellular stress pathways. In contrast, ATF3 is known to be induced in non-nervous tissue by nonstress-related stimuli (Cho et al, 2001).…”

Direct Evidence of Astrocytic Modulation in the Development of Rewarding Effects Induced by Drugs of Abuse

“…It has been reported that treatment with METH at neurotoxic doses induces the robust phosphorylation of STAT3 in the mouse brain (Hebert and O'Callaghan, 2000). These findings raise the possibility that exposure to the drugs of abuse could produce the synaptic plasticity and/or neuronal toxicity via Jak/STAT pathway.…”