c-Jun N-Terminal Kinase Activation Responses Induced by Hippocampal Kindling Are Mediated by Reactive Astrocytes

Abstract

Hippocampal kindling, a model of mesial temporal lobe epilepsy, is developed through repetitive stimulation of the hippocampus and leads to increased after-discharges as measured by EEG and an enduring seizure-prone state. Synthesis of new proteins is thought to form the basis for sustained seizure-induced physiological and/or pathological changes in synaptic reorganization and apoptotic/necrotic neuronal death. Here we examined the effect of kindling on stimulus-induced c-Jun N-terminal kinase (JNK) and p38 phosphorylation, events postulated to lie upstream of seizure-induced changes in gene transcription. We found that stimulus-induced phosphorylation of JNK, but not of p38, is significantly enhanced in kindled animals compared with their naive counterparts in the CA1 subregion of the hippocampus. Immunofluorescent staining confirmed this region-specific pattern of JNK activation and revealed that reactive astrocytes mediate this effect. Astrocyte proliferation and hypertrophy, as well as upregulation of vimentin protein levels, common markers of astrogliosis, were present after 4 d of kindling. Moreover, this reactive astrogliosis was associated with neuronal death as visualized with Fluoro-jade B and anti-active caspase-3 staining. Stimulus-induced phosphorylation of the JNK substrate paxillin was enhanced in kindled animals, but not that of c-Jun. Moreover, a pan-antibody against MAPK/CDK (mitogen-activated protein kinases/cyclindependent kinase) substrates indicated the presence of phosphorylated proteins in cytosolic, membrane, and nuclear fractions. The consequence of these phosphorylation events is not completely understood, but these findings suggest a selective astrocytic signaling response to aberrant synaptic activity, signaling that may modulate kindling progression and/or neuronal death.

Endothelin-1 Regulates Astrocyte Proliferation and Reactive Gliosis via a JNK/c-Jun Signaling Pathway

“…A recent study demonstrated a functional link between JNK activation and GFAP accumulation in astrocytes (Tang et al, 2006). Furthermore, c-Jun activation and JNK phosphorylation have been demonstrated in reactive astrocytes in different animal models of pathology (Lee et al, 2004;Nakagawa and Schwartz, 2004;Hashimoto et al, 2005;Cole-Edwards et al, 2006). However, the extracellular signals that induce c-Jun expression in reactive astrocytes have not been identified, and a direct causal relationship between c-Jun activation and reactive gliosis has not been established.…”

“…Western blot analysis of GFAP protein expression in the lesion confirmed the immunocytochemical results. A peak of GFAP expression could be detected at 5 dpl, whereas no significant GFAP upregulation was observed at 2 dpl ( It has been demonstrated that JNK activation causes GFAP accumulation in astrocytes (Tang et al, 2006) and that JNK phosphorylation is induced in reactive astrocytes after partial sciatic nerve ligation or after kindling (Ma and Quirion, 2002;Cole-Edwards et al, 2006). Therefore, we examined whether increased JNK phosphorylation was detectable in reactive astrocytes in demyelinated lesions.…”

“…Proliferation of GFAP ϩ astrocytes after demyelination was assayed by anti-Ki-67 immunostaining, as previously described (Aguirre and Gallo, 2004;Aguirre et al, 2007). Anti-phosphorylated JNK staining was performed as described by Cole-Edwards et al (2006).…”

Stem Cell Marker Nestin and c-Jun NH2-Terminal Kinases in Tumor and Peritumor Areas of Glioblastoma Multiforme: Possible Prognostic Implications

“…Activated JNK has been found in rat glial cells after traumatic injuries (23) and in reactive astrocytes in a model of temporal lobe epilepsy (24). A possible JNK meaning has been suggested in the acquisition of the transformed phenotype.…”

Vitamin C Transporter (SVCT2) Distribution in Developing and Adult Brains

“…Moreover, our group has recently defined that SVCT2 protein is induced in reactive astrocytes in various in vivo pathological models that generate severe reactive astrogliosis. Specifically, such events involve neuroinflammation generated by intracerebroventricular injection of adenovirus-GFP or the bacterial enzyme, neuraminidase, mechanical damage of the brain cortex evaluated at 5 and 10 days post-injury, and astrogliosis observed in the brain cortex and hippocampus from "Kindled" rats, a widely used model of epilepsy at the mesial temporal lobe [16,17]. In vitro studies support these findings by showing that SVCT2 is induced in astrocytes that have been cultured for long periods and express markers of astrocytic activation [3].…”