Lactate modulates gene expression through histone lactylation in the retina

Abstract

Purpose : The retina is a high-energy-consuming and metabolically active tissue. Under normal physiological conditions, retinal photoreceptor cells critically rely on glycolysis for energy production even in the presence of oxygen, producing large amounts of lactate. Here we explored a new aspect of lactate's role as a substrate for histone lactylation (Kla), an epigenetic modification at lysine residues. This lactylation is proposed to play a direct role in stimulating gene transcription.

Methods : Histone proteins from the whole retina of adult C57BL/6J (n=3) mice were subjected to label-free chemical derivatization and high-resolution mass spectrometry for the identification of lactylation marks. Immunoblots were used to quantify the enrichment level of histone Kla in the retina. Seahorse glycolysis assays were performed on retinal punches (n=10) to assess the real-time changes in glycolytic activity by measuring the extracellular acidification rate at different developmental ages (P2, P4, P6, P10, P28). To understand if extracellular lactate can regulate histone Kla we exposed retinal explants to various concentrations of glucose (5mM and 25mM), a major source of lactate. Further, to explore the chromatin function of histone lactylation we performed CUT&RUN using H3K18la antibody in combination with RNA sequencing analyses.

Results : We identified 16 lysine lactylation sites on different histone proteins. As the status of histone Kla depends on the conversion of glucose to lactate, we demonstrated that changes in glycolytic activity led to a change in the level of lactylation of histone proteins in the retina. Western blotting revealed an increase in histone Kla (H3K18la) at later stages of retinal development. Retinal explants showed both increased lactate production as well as histone Kla levels when induced by glucose. Genomic profiling using CUT&RUN demonstrated that H3K18la is mainly located in active promoter regions resembling H3K27Ac marks (H3 acetylated at K27) with notable differences. Histone Kla acts as an epigenetic hallmark of highly expressed genes and regulates genes participating in biological processes such as DNA repair, transcription regulation and metabolism.

Conclusions : We have shown here for the first time the mechanisms by which changes in lactate states influence the establishment of histone lactylation, potentially playing diverse functional roles in the retina through chromatin state regulation.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.