Abstract
Cadmium (Cd) is an emerging environmental risk factor for cognitive decline and Alzheimer's disease, and few interventions limit its effects on the brain. Akkermansia muciniphila, a human gut commensal, is neuroprotective through mechanisms that remain unclear. Building on our finding that A. muciniphila prevented Cd-induced memory deficits without reducing brain Cd burden (Wang et al., 2026a), we tested whether it reprograms Cd-disrupted hippocampal RNA regulation. Male C57BL/6J mice received A. muciniphila (1x10^9 CFU, oral gavage, 5 days/week) before and throughout 9 weeks of 3 mg/L CdCl2 exposure; hippocampi were analyzed by RNA-seq, m6A epitranscriptomic profiling, and rMATS-based alternative-splicing analysis. Cd disrupted hippocampal neuropeptide signaling, neuronal excitability, and synaptic plasticity. Co-exposure with A. muciniphila reversed signatures enriched for Nrf2-centered cytoprotective signaling and opposed m6A and splicing changes across more than a thousand genes, largely without changes in total mRNA abundance. Restored events converged on machinery governing local translation, calcium-dependent plasticity, and synaptic transmission. Projected onto predicted protein structures, most introduced a premature termination codon predicted to trigger nonsense-mediated decay or edited short loop and linker segments rather than rebuilding folded domains, regulation largely invisible to gene-level expression analysis. Among these, paired events amplifying semaphorin-plexin signaling, an axis linked to oligodendrocyte injury and memory consolidation, were reversed. These findings identify restoration of hippocampal transcript fate and splice-isoform selection as a mechanism potentially underlying A. muciniphila-mediated protection against Cd neurotoxicity, and establish post-transcriptional RNA regulation as a gut-brain target for mitigating environmentally driven neurotoxicity.