Developmental nonylphenol exposure triggers GPER‑dependent microglial activation and subsequent neuronal injury

Nonylphenol (NP), a significant environmental estrogen and pollutant, has attracted considerable attention for its neurotoxicity. Microglial activation may be a major contributor to NP-induced neuronal injury, but the mechanisms underlying this activation remain unknown. We hypothesized that GPER, a novel G protein-coupled estrogen receptor that is sensitive to NP, and its downstream signaling mediate NP-induced microglial activation and subsequent neuronal injury. To test this hypothesis, we established a rat model developmentally exposed to NP across a range of environmentally relevant concentrations. In addition, we developed a co-culture system comprising NP-exposed HMC3 microglia and differentiated SH-SY5Y neurons. Developmental NP exposure caused learning and memory deficits and hippocampal neuronal damage in rats, along with microglial activation featuring M1 polarization and a pro-inflammatory cytokine shift. Omics analyses indicated that GPER is a potential target of NP, which was further supported by the observed activation of GPER and downstream EGFR-STAT3 signaling in the hippocampus. These alterations, reflecting activation of microglia and GPER-EGFR-STAT3 signaling, were confirmed in NP-exposed HMC3 microglia in vitro. In co-culture, conditioned medium from NP-exposed microglia severely damaged SH-SY5Y neurons. GPER-KD alleviated NP-induced microglial activation, M1 polarization, and the pro-inflammatory cytokine shift, thereby reducing neuronal damage. Specific activation of microglial STAT3 counteracted these protective effects of GPER-KD. In summary, we demonstrate that NP exposure causes neuronal damage through microglia-centered inflammatory responses, with microglial GPER and downstream EGFR-STAT3 signaling acting as key drivers.