Prelimbic Cortical Stimulation with L-methionine Enhances Cognition through Hippocampal DNA Methylation and Neuroplasticity Mechanisms

: Declining global DNA methylation and cognitive impairment are reported to occur in the normal aging process. It is not known if DNA methylation plays a role in the efficacy of memory-enhancing therapies. In this study, aged animals were administered prelimbic cortical deep brain stimulation (PrL DBS) and/or L-methionine (MET) treatment. We found that PrL DBS and MET (MET-PrL DBS) co-administration resulted in hippocampal-dependent spatial memory enhancements in aged animals. Molecular data suggested MET-PrL DBS induced DNA methyltransferase DNMT3a-dependent methylation, robust synergistic upregulation of neuroplasticity-related genes, and simultaneous inhibition of the memory-suppressing gene calcineurin in the hippocampus. We further found that MET-PrL DBS also activated the PKA-CaMKIIα-BDNF pathway, increased hippocampal neurogenesis, and enhanced dopaminergic and serotonergic neurotransmission. We next inhibited the activity of DNA methyltransferase (DNMT) by RG108 infusion in the hippocampus of young animals to establish a causal relationship between DNMT activity and the effects of PrL DBS. Hippocampal DNMT inhibition in young animals was sufficient to recapitulate the behavioral deficits observed in aged animals and abolished the memory-enhancing and molecular effects of PrL DBS. Our findings implicate hippocampal DNMT as a therapeutic target for PrL DBS and pave way for the potential use of non-invasive neuromodulation modalities against dementia. Such a cellular response enhanced the capacity of de novo DNA methylation, which was further expanded by the MET treatment. The increased DNA methylation in turn altered the transcription of memory-related genes ( CaN and Bdnf exon IV) and subsequent protein cascades (PKA, CREB, and CaMKIIα phosphorylation). Dual treatment of MET and PrL DBS exerted a stronger inhibitory effect on CaN expression, which possibly induced more robust activation of PKA and CaMKIIα (A) . Meanwhile, inhibition of DNMT activity by RG108 resulted in global DNA hypomethylation and reduced Bdnf exon IV transcription. PrL DBS partially restored the DNA methylation level and rescued Bdnf exon IV transcription. RG108 also resulted in increased CaN transcript and protein levels, which may contribute to behavioral deficits and astrogliosis (B) . This proposed model was created in BioRender.