Anti-inflammatory effect of IGF-1 is mediated by IGF-1R cross talk with GPER in MPTP/MPP+-induced astrocyte activation

Insulin-like growth factor-1 (IGF-1) is a potent neuroprotective polypeptide that exerts neuroprotective effects via the IGF-1 receptor (IGF-1R). Our previous study reported that G protein-coupled estrogen receptor (GPER) was involved in the anti-apoptotic effect of IGF-1. The present study was designed to investigate the anti-inflammatory effect of IGF-1 in association with astrocyte activation and the molecular details of the interaction between IGF-1R and GPER. We showed that IGF-1 could improve 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced motor deficits and attenuate the upregulation of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) both in vivo and in vitro. The IGF-1R antagonist JB-1 and the GPER antagonist G15 could antagonize the anti-inflammatory effect of IGF-1. Silencing GPER abrogated the inhibitory effect of IGF-1 on 1-methyl-4-phenylpyridinium (MPP+)-induced upregulation of COX-2 and iNOS in primary astrocytes. Moreover, the MPP+-induced inflammatory response was related to the activation of mitogen-activated protein kinases (MAPKs) and NF-kappa B signaling pathways. The inhibitory effects of IGF-1 on the phosphorylation of p38, JNK and I kappa B could be blocked by JB-1. G15 antagonized the inhibitory effects of IGF-1 on p-JNK and p-I kappa B, but not p-p38. Furthermore, IGF-1 treatment alone increased the expression of GPER, which was blocked by JB-1, the phosphatidylinositol 3-kinase (PI3-K) antagonist LY294002 and the MEK antagonist PD98059 in primary astrocytes. Overall, we show for the first time that GPER may contribute to the anti-inflammatory effect of IGF-1 against MPTP/MPP+-induced astrocyte activation. IGF-1 could regulate the expression of GPER via the IGF-1R/PI3-K/MAPK signaling pathway in primary astrocytes.