Chronic dysregulated microglial activation may lead to persistent inflammation and progressive neurodegeneration. A previous study reported that ADX88178, a putative metabotropic glutamate receptor 4 (mGluR4) positive allosteric modulator (PAM), exerts anti-inflammatory effects in microglia by activating mGluR4. We employed in vitro models of immortalized microglia cell lines and primary microglia to elucidate the molecular mechanisms responsible for the regulation of inflammatory pathways by ADX88178 and other mGluR4 PAMs. ADX88178 downregulated lipopolysaccharide (LPS)-induced expression of pro-inflammatory mediators, including TNF-α, IL-1β, CCL-2, IL-6, NOS2, and miR-155, as well as NO levels, in BV2 cells and primary microglia. Other mGluR4 modulators had divergent activities; VU0361737 (PAM) showed anti-inflammatory effects, whereas the orthosteric group III agonist, L-AP4, and VU0155041 (PAM) displayed no anti-inflammatory actions. In contrast to the earlier report, ADX88178 anti-inflammatory effects appeared to be mGluR4-independent as mGluR4 expression in our in vitro models was very low and its actions were not altered by pharmacological or molecular inhibition of mGluR4. Moreover, we showed that ADX88178 activated G_i-independent, alternative signaling pathways as indicated by the absence of pertussis toxin-mediated inhibition and by increased phosphorylation of cAMP-response element binding protein (CREB), an inhibitor of the NFkB pro-inflammatory pathway. ADX88178 also attenuated NFkB activation by reducing the degradation of IkB and the associated translocation of NFkB-p65 to the nucleus. ADX88178 did not exert its anti-inflammatory effects through adenosine receptors, reported as mGluR4 heteromerization partners. Thus, our results indicate that in microglia, putative mGluR4 PAMs activate mGluR4/G_i-independent mechanisms to attenuate pro-inflammatory pathways.

慢性失调的小胶质细胞激活可能导致持续性炎症和进行性神经变性。之前的一项研究报告称，ADX88178 是一种推定的代谢型谷氨酸受体 4 (mGluR4) 正变构调节剂 (PAM)，通过激活 mGluR4 在小胶质细胞中发挥抗炎作用。我们在体外使用永生化小胶质细胞系和原代小胶质细胞的模型，以阐明负责 ADX88178 和其他 mGluR4 PAM 调节炎症通路的分子机制。ADX88178 下调脂多糖 (LPS) 诱导的促炎介质的表达，包括 TNF-α、IL-1β、CCL-2、IL-6、NOS2 和 miR-155，以及 BV2 细胞和原代细胞中的 NO 水平小胶质细胞。其他 mGluR4 调节剂具有不同的活性；VU0361737 (PAM) 显示出抗炎作用，而正构组 III 激动剂 L-AP4 和 VU0155041 (PAM) 没有显示出抗炎作用。与之前的报告相反，ADX88178 抗炎作用似乎不依赖于 mGluR4，因为在我们的体外mGluR4 表达模型非常低，并且其作用不会因 mGluR4 的药理学或分子抑制而改变。此外，我们发现 ADX88178 激活了 G _i独立的替代信号通路，如百日咳毒素介导的抑制作用的缺失和 cAMP 反应元件结合蛋白 (CREB) 的磷酸化增加所表明的，CREB ​​是 NF k B的抑制剂。炎症通路。ADX88178 还通过减少 I k B的降解和相关的 NF k易位来减弱 NF k B 激活B-p65 到细胞核。ADX88178 没有通过腺苷受体发挥其抗炎作用，报告为 mGluR4 异聚化伙伴。因此，我们的结果表明，在小胶质细胞中，假定的 mGluR4 PAM 会激活 mGluR4/G _i独立机制以减弱促炎途径。