Selective activation of the G protein‐coupled estrogen receptor has been proposed to avoid some of the side effects elicited by the activation of classical estrogen receptors α and β. Although its contribution to neuroprotection triggered by estradiol in brain disorders has been explored, the results regarding ischemic stroke are contradictory, and currently, there is no consensus on the role that this receptor may play. The present study aimed to investigate the role of GPER in the ischemic insult. For that, primary cortical cultures exposed to oxygen and glucose deprivation (OGD) were used as a model. Our results demonstrate that neuronal survival was strongly affected by the ischemic insult and concurrent GPER activation with G1 had no further impact. In contrast, OGD had a smaller impact on astrocytes survival but G1, alone or combined with OGD, promoted their apoptosis. This effect was prevented by the GPER antagonist G15. The results also show that ischemia did not change the expression levels of GPER in neurons and astrocytes. In this study, we also demonstrate that selective activation of GPER induced astrocyte apoptosis via the phospholipase C pathway and subsequent intracellular calcium rise, whereas in neurons, this effect was not observed. Taken together, this evidence supports a direct impact of GPER activity on the viability of astrocytes, which seems to be associated with the regulation of different signaling pathways in astrocytes and neurons.

Parkinson's disease (PD) is characterized by a selective degeneration of nigrostriatal dopaminergic pathway. Epidemiological studies revealed a male predominance of the disease that has been attributed to the female steroid hormones, mainly the estrogen. Estrogen neuroprotective effects have been shown in several studies, however the mechanisms responsible by these effects are still unclear. Previous data from our group revealed that glial cell line-derived neurotrophic factor (GDNF) is crucial to the dopaminergic protection provided by 17β-estradiol, and also suggest that the intracellular estrogen receptors (ERs) are not required for that neuroprotective effects. The present study aimed to investigate the contribution of the G protein-coupled ER (GPER) activation in estrogen-mediated dopaminergic neuroprotection against an insult induced by 1-methyl-4-phenylpyridinium (MPP(+)), and whether GPER neuroprotective effects involve the regulation of GDNF expression. Using primary mesencephalic cultures, we found that GPER activation protects dopaminergic neurons from MPP(+) toxicity in an extent similar to the promoted by a 17β-estradiol. Moreover, GPER activation promotes an increase in GDNF levels. Both, GDNF antibody neutralization or RNA interference-mediated GDNF knockdown prevented the GPER-mediated dopaminergic protection verified in mesencephalic cultures challenged with MPP(+). Overall, these results revealed that G1, a selective agonist of GPER, is able to protect dopaminergic neurons and that GDNF overexpression is a key feature to GPER induced the neuroprotective effects.

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Due to its ability to improve the most frequent clinical sequelae left by ischemia, repetitive transcranial magnetic stimulation has been considered a promising therapeutic strategy for stroke. Those improvements are associated with changes in neurons and their synaptic liaisons. However, the hypothesis that this technique modulates astrocytes, potentiating their neuroprotective capabilities, was also raised. This study aims to identify the effects triggered by high‐frequency repetitive magnetic stimulation (HF‐rMS) on astrocytes that contribute to its neuroprotective effects. Neuron–glia and astrocyte cortical cultures subject to oxygen and glucose deprivation were used as an in vitro model of ischemia. Neuroprotection promoted by HF‐rMS was evaluated by analysis of markers of neuronal activity and morphometric analysis of neurons. Glial reactivity was determined by immunocytochemistry. The levels of growth factors in the astrocyte‐conditioned medium (CM) were assessed through a Growth Factor Array and glial‐derived neurotrophic factor (GDNF) expression was analyzed by RT‐PCR and Western blot. Our results show that neurons injured by ischemia can be rescued through the modulation of astrocytes by HF‐rMS. This modulation helps to maintain the number and length of neurites and increases the number of neurons expressing ERK1/2 and c‐Fos. Analysis of the astrocyte‐CM showed that HF‐rMS stimulated the release of several trophic factors by astrocytes. Moreover, GDNF was one of the released factors that contributed to the recovery mechanisms triggered by HF‐rMS. Our results show that modulation of astrocytes by HF‐rMS effectively rescues neurons injured by ischemia and suggest that by targeting astrocytes this approach can also be used to promote neuroprotection in other brain lesions.