The glutamate receptors are important to the glioma

The glutamate receptors are important to the glioma LIMKi 3 from escaping the excitotoxicity under physiological conditions. There are three subtypes of ionotropic glutamate receptors, including NMDA, kainate, and AMPA receptors, which are relating to diverse Ca2+ permeability. Glioma cells also express receptors for glutamate. Unlike granule cells, they express a subclass of Ca2+ permeable AMPA receptors instead of NMDA receptor (Lyons et al., 2007). Yoshioka (Yoshioka et al., 2000) has described that oligodendroglia are vulnerable to oxygen and glucose deprivation, which results in Ca2+-influx induced cell death via non-NMDAR channels. The Ca2+-permeable AMPAR and its association with increased [Ca2+]i and neuron death has also been shown (Beique and Huganir, 2009, Weiss and Sensi, 2000). So we detected the changes of glutamate AMPA receptors during PDT. The results showed C6 cells expressed GluR1 and few GluR2 proteins in physiological conditions. But when PDT was administered, expression of GluR1 and GluR2 proteins increased evidently. AMPA receptors are composed of subunits taken from a set of four proteins, GluR1 through GluR4. There are two editing variants in the GluR2 subunit, the edited and unedited form (GluR2Q). AMPA receptors are permeable to Ca2+ only when AMPA receptors are composed of the unedited GluR2Q. Our results showed the levels of [Ca2+]i increased evidently after PDT, which was partly blocked by CNQX. These indicated that the increased expression of GluR2 proteins were possible unedited form (GluR2Q), which was consistent with previous reports that GluR2 is expressed in the unedited form in glioma cells (Ishiuchi et al., 2002, Maas et al., 2001, Yoshida et al., 2006). We found that PDT decreased cell viability and increased apoptosis rate of C6 glioma cells in vitro. Though C6 glioma cells were killed by PDT in PDT treated groups in the end, AMPAR antagonist, CNQX, delayed this process significantly, which showed a protective effect on C6 glioma cells during PDT. Additionally, the levels of [Ca2+]i increased evidently after PDT, which was also partly blocked by CNQX. These results indicated that the increased [Ca2+]i was partly caused by Ca2+ influx through Ca2+-permeable AMPAR, which could lead to apoptosis when the [Ca2+]i exceeds certain level (Hong et al., 2009). Therefore, Ca2+ influx through Ca2+-permeable AMPAR played an important role during PDT. The increased [Ca2+]i may mainly come from two sources during PDT. One is released by mitochondria, endoplasmic reticulum (ER), Golgi apparatus, and nuclear calcium stores, the other is Ca2+ influx from the activation of plasma membrane-associated receptor. Our data showed CNQX partly decreased [Ca2+]i and cell apoptosis at 4h after PDT. Hence, the Ca2+ influx through the Ca2+-permeable AMPAR at membrane was one of mechanism of PDT. PDT has been regarded as an effective adjuvant therapy to surgical resection of glioma. Our study indicated that PDT could increase glutamate release and AMPAR expression, which induced Ca2+ influx and increased [Ca2+]i and then enhanced cells apoptosis during PDT. These results allow us to further understand the effects and molecular mechanism of PDT on glioma.
Experimental procedures
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Dendritic spines are small signaling compartments in neurons and house important signaling networks, receptors, and molecules associated with learning and memory. In particular, Ca/calmodulin-dependent protein kinase II (CaMKII), protein phosphatase 1 (PP1), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) have been identified as molecular markers of memory, suggesting that their spatio-temporal dynamics play an important role in structural plasticity. Furthermore, dendritic spines have characteristic shapes that have been linked to healthy state, disease, aging, and other factors; however, the exact relationship between shape and function remains unknown.