Macrophage histone lactylation during ischemia induced-muscle regeneration [CUT&Tag]
After injury, muscles require fully functional macrophages to recover completely. During muscle regeneration, macrophages transition from a pro-inflammatory to a pro-restorative phenotype ensures the proper regeneration. Lactate is a crucial molecule for muscle-residing macrophage polarisation. Histone lactylation, a direct derivative of lactate, has been implicated in macrophage polarisation in vitro .  In this work, we show for the first time that macrophages recruited to the muscle after ischemic injury modify their histone lactylome between 2 and 4 days post injury. Absolute histone lactylation levels increase significantly. Although subtly, also the genomic enrichment of H3K18la changes from 2 to 4 days post injury and this correlates with gene expression changes. Interestingly, we find that H3K18la genomic enrichment changes from day 2 to day 4 post injury are predictive for gene expression changes later in time, from day 4 to day 7, rather than being a reflection of past gene expression changes from day 1 to day 2. Our results suggest that histone lactylation dynamics are functionally important for the resolving action of macrophages during muscle regeneration. Overall design: C57BL6J wild type males (Charles River) from 8 to 12 weeks old were used in this study. Animals were housed in a normal light cycle with access to food and water ad libitum. Hind-limb ischemia experiments were performed as described in Zhang et al., 2020. Briefly, mice were anesthetized with isoflurane. The hind limb was shaved, and the skin was incised. The proximal end of the femoral artery and the distal portion of the saphenous artery were ligated. The artery and all side-branches were dissected to be freed and the femoral artery and attached side-branches were excised. Procedures were approved by the ethics committee (number ZH050-2021). To label circulating CD45+ cells, mice were anaesthetised with a combination of ketamine and xylazine and i.v. injected with 3 µg of PE anti-mouse CD45 antibody (Biolegend [30-F11], 103106). Five minutes later, mice were sacrificed and muscle was processed for isolating macrophages.