GPR30 Regulates Glutamate Transporter GLT-1 Expression in Rat Primary Astrocytes

Abstract

The G protein-coupled estrogen receptor GPR30 contributes to the neuroprotective effects of 17β-estradiol (E2); however, the mechanisms associated with this protection have yet to be elucidated. Given that E2 increases astrocytic expression of glutamate transporter-1 (GLT-1), which would prevent excitotoxic-induced neuronal death, we proposed that GPR30 mediates E2 action on GLT-1 expression. To investigate this hypothesis, we examined the effects of G1, a selective agonist of GPR30, and GPR30 siRNA on astrocytic GLT-1 expression, as well as glutamate uptake in rat primary astrocytes, and explored potential signaling pathways linking GPR30 to GLT-1. G1 increased GLT-1 protein and mRNA levels, subject to regulation by both MAPK and PI3K signaling. Inhibition of TGF-α receptor suppressed the G1-induced increase in GLT-1 expression. Silencing GPR30 reduced the expression of both GLT-1 and TGF-α and abrogated the G1-induced increase in GLT-1 expression. Moreover, the G1-induced increase in GLT-1 protein expression was abolished by a protein kinase A inhibitor and an NF-κB inhibitor. G1 also enhanced cAMP response element-binding protein (CREB), as well as both NF-κB p50 and NF-κB p65 binding to the GLT-1 promoter. Finally, to model dysfunction of glutamate transporters, manganese was used, and G1 was found to attenuate manganese-induced impairment in GLT-1 protein expression and glutamate uptake. Taken together, the present data demonstrate that activation of GPR30 increases GLT-1 expression via multiple pathways, suggesting that GPR30 is worthwhile as a potential target to be explored for developing therapeutics of excitotoxic neuronal injury.

Gliopreventive effects of guanosine against glucose deprivation in vitro

“…The present data show that the PI3K signaling pathway is involved in the guanosine modulation of the glutamate uptake, which agrees with other studies that demonstrate the ability of guanosine to promote neuroprotection by activation of this pathway [85,90,107]. The MAPK signaling pathway has also been described as a modulator of glutamate uptake [70,71], and guanosine also modulates this pathway [85]. Here, guanosine reversed the decrease in glutamate uptake caused by glucose deprivation; however, this effect was abolished by the p38 MAPK and ERK specific inhibitors.…”

“…3d) inhibitors lost the ability to prevent the decreased glutamate uptake activity caused by glucose deprivation. The MAPK signaling pathway has also been described as a modulator of glutamate uptake [70,71]. Because guanosine modulates this pathway [14], we investigated whether the protective effect of guanosine on glutamate uptake was also dependent of p38 MAPK and ERK.…”

Yin Yang 1 Is a Repressor of Glutamate Transporter EAAT2, and It Mediates Manganese-Induced Decrease of EAAT2 Expression in Astrocytes

“…1E), we next examined if Mn regulates YY1 gene expression. This was driven by earlier observations that TNF-␣ activated the YY1 pathway in myoblasts (18) and that TNF-␣, as well as Mn, repressed EAAT2 expression (25). YY1 protein was expressed ubiquitously in astrocytes ( Fig.…”

“…NF-B activation represents the main mechanism for the positive regulation of EAAT2 expression, but negative EAAT2 regulators, such as TNF-␣ and Mn, also activate NF-B (10,25). This contradictory molecular event requires further study to provide a better understanding of the mechanism for the seemingly opposite directions of EAAT2 regulation in response to NF-B activation (25).…”

cAMP Response Element-binding Protein (CREB) and Nuclear Factor κB Mediate the Tamoxifen-induced Up-regulation of Glutamate Transporter 1 (GLT-1) in Rat Astrocytes

“…Western Blot Analysis-Whole cell lysates for SDS-PAGE were prepared as described previously (28). Astrocytes were treated with the designated compounds for the indicated time periods, followed by two washes with cold Hanks' buffered salt solution.…”