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The adenomatous polyposis coli gene (APC) was initially identified through its link to colon cancer. It is associated with the regulation of cell cycle progression, survival, and differentiation of normal tissues. Recent studies have demonstrated that APC is also expressed in the adult brain at high levels. However, its role in glial cells under pathological progression remains unclear. In this study, we evaluated the expression of APC and its association with beta-catenin signaling pathway, following the induction of an excitotoxic lesion by kainic acid (KA) injection, which cause pyramidal cell degeneration. APC was predominantly present in oligodendrocytes in the normal brain, but was specifically associated with activated astrocytes in the KA-treated brain. Our quantitative analysis revealed that APC significantly increased from 1 day post lesion (PI), reached peak values at 3 days PI, and decreased thereafter. The phospho-GSK3beta levels also showed similar spatiotemporal patterns while beta-catenin expression was reduced at 1 and then increasingly returned to normal levels at 3, 7 days PI. For the first time, our data demonstrate the injury-induced astrocytic changes in the levels of APC, GSK3beta, and beta-catenin in vivo, which may actively be participate in cell adhesion and in the signaling pathway regulating cell survivals during brain insults.

The nonessential amino acid L-serine functions as a glia-derived trophic factor and strongly promotes the survival and differentiation of cultured neurons. The L-serine biosynthetic enzyme 3-phosphoglycerate dehydrogenase (Phgdh) and the small neutral amino acid transporter ASCT1 are preferentially expressed in specific glial cells in the brain. However, their roles in pathological progression remain unclear. We examined the expression of Phgdh and ASCT1 in kainic acid (KA)-induced neurodegeneration of the mouse hippocampus using immunohistochemistry and Western blots. Our quantitative analysis revealed that Phgdh and ASCT1 were constitutively expressed in the normal brain and transiently upregulated by KA-treatment. At the cellular level, Phgdh was expressed in astrocytes in control and in KA-treated mice while ASCT1 that was expressed primarily in the neurons of the normal brain appeared also in activated astrocytes in KA treated mouse brain. The preferential glial expression of ASCT1 was consistent with that of Phgdh. These results demonstrate injury-induced changes in Phgdh and ASCT1 expression. It is hypothesized that the secretion of L-serine is regulated by astrocytes in response to toxic molecules such as glutamate and free radicals that promote neurodegeneration, and may correspond to the level of L-serine needed for neuronal survival and glial activation during brain insults.

Interleukin (IL)-18, a member of the IL-1 cytokine family, is an important mediator of peripheral inflammation and host defence responses. However, although IL-1 is a key proinflammatory cytokine in the brain, little is known about IL-18 changes in glial cells under excitotoxic neurodegeneration. In this study, we characterized the expressions of IL-18 and IL-18 receptor (IL-18R) in kainic acid (KA)-induced excitotoxicity in mouse hippocampus by immunohistochemistry and Western blotting. IL-18 immunoreactivity was found in microglia whereas IL-18R immunoreactivity was observed in astrocytes. Levels of IL-18 and IL-18R in hippocampus homogenates increased progressively from day 1 post-KA and peaked at 3 days. This study demonstrates the cellular sources of IL-18 and IL-18R, and their temporal correlations after KA-insult, and suggests roles for IL-18 and IL-18R in glial cells in response to excitotoxic damage in the hippocampus.

In the present study, we examined patterns of A-myb expression in the kainic acid (KA)-treated mouse hippocampus. Western blot analysis revealed that A-myb expression was dramatically increased in brain 3 days after KA treatment, and was sustained for more than 7 days. A-myb immunoreactivity was restricted to hippocampal neurons in control mice. Three days after KA treatment, strong A-myb immunoreactivity was observed in reactive astrocytes throughout the CA3 region. Thereafter, A-myb immunoreactive astrocytes gradually concentrated around the CA3 region in parallel with selective neuronal loss, and only a few A-myb immunoreactive astrocytes persisted in the CA3 region 14 days after KA treatment. These findings suggest that the A-myb plays a role in the reactive gliosis signaling pathway in KA-induced excitotoxic lesions.

Heat shock proteins (HSPs) are immediately expressed in neuronal and glial cells under various stressful conditions and play a protective role through molecular chaperones. Although several studies have been focused on the expression of HSPs, little is known about HSP90s expression in glial cells under neuropathological conditions. In this study, we evaluated the expression pattern of the glial cell-related HSP90 and GRP94 proteins, following the induction of an excitotoxic lesion in the mouse brain. Adult mice received an intracerebroventricular injection of kainic acid; the brain tissue was then analyzed immunohistochemically for HSPs and double labeling using glial markers. HSPs expression was quantified by Western blot analysis. Excitotoxic damage was found to cause pyramidal cell degeneration in the CA3 region of the hippocampus. In the injured hippocampus, reactive microglia/macrophages expressed HSP90 from 12 h until 7 days postlesion (PL), showing maximal levels at day 1. In parallel, hippocampal reactive astrocytes showed the expression of GRP94 from 12 h until 7 days PL. In general, HSPs expression was transient, peaked at 1-3 days PL and reached basal levels by day 7. For the first time, our data demonstrate the injury-induced expression of HSP90 and GRP94 in glial cells, which may contribute to the mechanism of glial cell protection and adaptation in response to damage, thereby playing an important role in the evolution of the glial response and the excitotoxic lesion outcome. HSP90 may provide antioxidant protective mechanisms against microglia/macrophages, whereas GRP94 may stabilize the astroglial cytoskeleton and participate in astroglial antioxidant mechanisms., ((c) 2004 Wiley-Liss, Inc.)

The transcription factor c-myb is known to play an important role in the regulation of cellular proliferation and differentiation. Recently, the constitutive and aberrant expression of c-myb in the normal and Cu/Zn SOD mutant mouse brain was reported. However, the expression of c-myb in the process of reactive gliosis is not known yet. Here we report the delayed and protracted induction of c-myb in the brain of mice following kainic acid (KA) induced seizure. Our western blot analysis revealed that the amount of c-myb was dramatically increased in the brain 3 days after KA treatment. The induction of c-myb was sustained for more than 7 days after KA treatment. The c-myb immunoreactivity (IR) was restricted to neurons of the hippocampus in control mice. Three days after KA treatment, a strong c-myb IR was found in reactive astrocytes in the whole areas of the CA3 region. Thereafter, c-myb IR astrocytes were gradually concentrated around the CA3 region undergoing selective neuronal loss. A few c-myb IR astrocytes were continuously persisted in the CA3 region 14 days after KA treatment. These findings suggest a role of c-myb signal pathway in reactive gliosis in mice with KA induced seizure.

A phosphatase and tensin homolog (PTEN) has been known to play multiple biological roles. However, role of PTEN in astrocyte activation is not clear yet. In the present study, the expression pattern of PTEN in the process of reactive gliosis was immunohistochemically examined in intracerebroventricular (i.c.v.) injected kainic acid mouse hippocampus. Mice were grouped into three; 30 min, 1 day and 7 days after kainic acid i.c.v. injection. Thirty minutes after kainic acid i.c.v. injection, astrocytes were activated and PTEN was weakly expressed in immature astrocytes. Seven days after kainic acid i.c.v. injection, PTEN expression was decreased in highly activated astrocytes showing extensively spindled shape. Immunofluorescence double labeling experiment showed that PTEN was expressed in glial fibrillary acidic protein-positive astrocytes. These findings suggest that PTEN might have a role in early stage of reactive astrogliosis in vivo., (Copyright 2002 Elsevier Science Ireland Ltd.)

Although oxidative stress and excitotoxicity may be interdependent mechanisms that are involved in delayed neuronal death, the temporal participation of these events in the early stage after ischemia-reperfusion insult is unclear. Therefore, in the present study, using the gerbil global ischemic model we investigated whether oxidative stress could be correlated with the expression of the glutamate transporters in the hippocampus, and whether these events are related and cooperate in the events that link ischemia to neuronal death in vivo. Thirty minutes after ischemia, the intensities of glutamate transporter-1 (GLT-1), glutamate/aspar-tate transporter (GLAST), and 8-hydroxy2'-deoxy-guanosine (8-OHdG) immunoreactivities were markedly increased in the hippocampal CA1 area. In contrast, excitatory amino acid carrier-1 (EAAC-1) immunoreactivity was 30% lower in the CA1 area than in the sham level. At 3 h post-reperfusion, the EAAC-1 expression began to increase in the CA1 area. Twelve hours after reperfusion, the reduction of both GLT-1 and GLAST immunoreactivity was salient, while the EAAC-1 immunoreactivity level intensified significantly. The 8-OHdG immunoreactivity peaked at this time point. These findings suggest that oxidative stress and alterations in the glutamate transporter expression in the CA1 area may simultaneously trigger neuronal damages very early after ischemia.