# H3K18 lactylation potentiates microglial polarization via the TLR4 pathway in diabetes-induced cognitive impairment

## TL;DR

This study shows how a specific histone modification, H3K18 lactylation, promotes brain inflammation in diabetes-related cognitive decline.

## Contribution

The study identifies a novel mechanism involving H3K18 lactylation and TLR4 signaling in microglial polarization linked to diabetes-induced cognitive impairment.

## Key findings

- Lactic acid levels and histone lactylation are elevated in T2DM mouse brains and high glucose-treated microglia.
- H3K18 lactylation activates TLR4 signaling, promoting M1 microglial polarization and cognitive decline.
- Targeting the H3K18la/TLR4 axis may offer a therapeutic strategy for diabetes-associated cognitive impairment.

## Abstract

The present study aimed to explore the role and possible underlying mechanisms of histone lactylation (Kla) modifications in diabetes-associated cognitive impairment (DACD). In this study, behavioral tests, H&E staining, and immunohistochemistry were used to evaluate cognitive function and the extent of cerebral tissue injury. We quantified the levels of lactic acid and pan-lysine Kla (Pan-Kla) in the brains of type 2 diabetes mellitus (T2DM) mice and in high glucose–treated microglia. We also identified all Kla sites in isolated microglia. Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were subsequently conducted to identify the functions and pathways that were enriched at the differentially expressed modification sites. Cleavage under targets and tagmentation (CUT&Tag) technology was used to identify candidate genes that are regulated by histone H3 lactylated at Lys-18 (H3K18la). siRNA and H3K18R mutant sequences were used to knock down crucial components in key signaling pathways to assess the effects of histone Kla on microglial polarization. We found that lactic acid levels were significantly greater in the brains of T2DM mice and high glucose–treated microglia than in those of their corresponding controls, which increased the level of Pan-Kla. We discovered that lactate can directly stimulate an increase in H3K18la. The global landscape of the lactylome reveals information about modification sites, indicating a correlation between the upregulation of H3K18la and protein Kla and Toll-like receptor (TLR) signaling. CUT&Tag demonstrated that enhanced H3K18la directly stimulates the NF-κB signaling pathway by increasing binding to the promoter of TLR4, thereby promoting M1 microglial polarization. The present study demonstrated that enhanced H3K18la directly stimulates TLR4 signaling to promote M1 microglial polarization, thereby facilitating DACD phenotypes. Targeting such loop may be a potential therapeutic approach for the treatment of DACD.

H3K18la/TLR4 axis orchestrates neuroinflammation by regulating microglial polarization, thereby fostering the emergence of diabetes-associated cognitive decline phenotypes.