Eco-friendly poly(butylene adipate-co-terephthalate) (PBAT) is widely marketed as biodegradable, yet the neurotoxicity of derived PBAT microplastics (PBAT-MPs) and their underlying mechanisms remain poorly characterized. Here we identify a previously unrecognized "gut microbiota-butyrate-neuro-lipid" axis linking intestinal PBAT-MPs exposure to hippocampal microglial lipotoxicity and cognitive impairment. By integrating fecal microbiota transplantation (FMT) with multi-omics analyses, we demonstrate that orally administered PBAT-MPs preferentially accumulate in the colon, impair epithelial barrier integrity, deplete butyrate-associated taxa, including Muribaculaceae and Alloprevotella, and enrich Escherichia-Shigella. Butyrate depletion elevates systemic lipopolysaccharide (LPS) levels and, via the gut-brain inflammatory route, activates mTORC1-integrated stress response (ISR) signaling in microglia. Consequently, microglia acquire a lipotoxic phenotype characterized by transcriptional up-regulation of DGAT- and ACSL-dependent lipid droplet (LD) biogenesis genes, accumulation of toxic lipids and inflammatory mediators, synaptic stripping, and memory loss. In vivo butyrate supplementation in PBAT-MP-exposed mice alleviates hippocampal pathology, normalizes microglial lipid accumulation, suppresses neuroinflammation, reduces ceramide levels, and improves cognitive performance. Mechanistically, butyrate inhibits mTORC1, attenuates eIF2α-ATF4-dependent ISR signaling, and represses DGAT/ACSL-dependent LD biogenesis, whereas microglial Rptor overexpression abolishes these protective effects, identifying mTORC1 as an upstream metabolic checkpoint. Collectively, our findings establish the microbiota-butyrate-mTORC1-ISR relay as a core driver of PBAT-MPs-induced neurotoxicity and highlight restoration of butyrate signaling as a promising microbiota-based strategy for preventing microplastic-induced brain lipotoxic injury.
