Background Histone lactylation has been recently described as a novel histone post-translational modification linking cellular metabolism to epigenetic regulation. Results Given the expected relevance of this modification and current limited knowledge of its function, we generate genome-wide datasets of H3K18la distribution in various in vitro and in vivo samples, including mouse embryonic stem cells, macrophages, adipocytes, and mouse and human skeletal muscle. We compare them to profiles of well-established histone modifications and gene expression patterns. Supervised and unsupervised bioinformatics analysis shows that global H3K18la distribution resembles H3K27ac, although we also find notable differences. H3K18la marks active CpG island-containing promoters of highly expressed genes across most tissues assessed, including many housekeeping genes, and positively correlates with H3K27ac and H3K4me3 as well as with gene expression. In addition, H3K18la is enriched at active enhancers that lie in proximity to genes that are functionally important for the respective tissue. Conclusions Overall, our data suggests that H3K18la is not only a marker for active promoters, but also a mark of tissue specific active enhancers.

The molecular mechanisms of angiogenesis have been intensely studied, but many genes that control endothelial behavior and fate still need to be described. Here, we characterize the role of Apold1 (Apolipoprotein L domain containing 1) in angiogenesis in vivo and in vitro. Single-cell analyses reveal that - across tissues - the expression of Apold1 is restricted to the vasculature and that Apold1 expression in endothelial cells (ECs) is highly sensitive to environmental factors. Using Apold1−/− mice, we find that Apold1 is dispensable for development and does not affect postnatal retinal angiogenesis nor alters the vascular network in adult brain and muscle. However, when exposed to ischemic conditions following photothrombotic stroke as well as femoral artery ligation, Apold1−/− mice display dramatic impairments in recovery and revascularization. We also find that human tumor endothelial cells express strikingly higher levels of Apold1 and that Apold1 deletion in mice stunts the growth of subcutaneous B16 melanoma tumors, which have smaller and poorly perfused vessels. Mechanistically, Apold1 is activated in ECs upon growth factor stimulation as well as in hypoxia, and Apold1 intrinsically controls EC proliferation but not migration. Our data demonstrate that Apold1 is a key regulator of angiogenesis in pathological settings, whereas it does not affect developmental angiogenesis, thus making it a promising candidate for clinical investigation.

The molecular mechanisms of angiogenesis have been intensely studied, but many genes that control endothelial behavior and fate still need to be described. Here, we characterize the role of Apold1 (Apolipoprotein L domain containing 1) in angiogenesis in vivo and in vitro. Single-cell analyses reveal that - across tissues - the expression of Apold1 is restricted to the vasculature, and that Apold1 expression in endothelial cells (ECs) is highly sensitive to environmental factors. Using Apold1-/- mice, we find that Apold1 is dispensable for development and does not affect postnatal retinal angiogenesis nor alters the vascular network in adult brain and muscle. However, when exposed to ischemic conditions following photothrombotic stroke as well as femoral artery ligation, Apold1-/- mice display dramatic impairments in recovery and revascularization. We also find that human tumor endothelial cells express strikingly higher levels of Apold1, and that Apold1 deletion in mice stunts the growth of subcutaneous B16 melanoma tumors, which have smaller and poorly perfused vessels. Mechanistically, Apold1 is activated in ECs upon growth factor stimulation as well as in hypoxia, and Apold1 intrinsically controls EC proliferation but not migration. Our data demonstrate that Apold1 is a key regulator of angiogenesis in pathological settings, whereas it does not affect developmental angiogenesis, thus making it a promising candidate for clinical investigation.

The molecular mechanisms of angiogenesis have been intensely studied, but many genes that control endothelial behavior and fate still need to be described. Here, we characterize the role of Apold1 (Apolipoprotein L domain containing 1) in angiogenesis in vivo and in vitro. Single-cell analyses reveal that - across tissues - the expression of Apold1 is restricted to the vasculature, and that Apold1 expression in endothelial cells (ECs) is highly sensitive to environmental factors. Using Apold1-/- mice, we find that Apold1 is dispensable for development and does not affect postnatal retinal angiogenesis nor alters the vascular network in adult brain and muscle. However, when exposed to ischemic conditions following photothrombotic stroke as well as femoral artery ligation, Apold1-/- mice display dramatic impairments in recovery and revascularization. We also find that human tumor endothelial cells express strikingly higher levels of Apold1, and that Apold1 deletion in mice stunts the growth of subcutaneous B16 melanoma tumors, which have smaller and poorly perfused vessels. Mechanistically, Apold1 is activated in ECs upon growth factor stimulation as well as in hypoxia, and Apold1 intrinsically controls EC proliferation but not migration. Our data demonstrate that Apold1 is a key regulator of angiogenesis in pathological settings, whereas it does not affect developmental angiogenesis, thus making it a promising candidate for clinical investigation.

BackgroundPeripheral artery disease (PAD) is caused by atherosclerosis and chronic narrowing of lower limb arteries leading to decreased muscle perfusion and oxygenation. Current guidelines for treating PAD include endovascular strategies or bypass surgery but long-term outcomes have been suboptimal. This is likely due to our limited understanding of the contribution of the microvasculature as well as other cell types, in particular macrophages, to PAD skeletal muscle pathophysiology. We used single cell sequencing to investigate cellular and transcriptional heterogeneity of the skeletal muscle microenvironment in PAD.MethodsSamples from the medial head of thegastrocnemiusmuscle of individuals undergoing either lower limb aneurysm surgery (controls) or PAD bypass surgery (PAD) were collected. Samples were either frozen for histological evaluation (control: n=4; PAD: n=6) or were immediately processed for single cell RNA sequencing of mononuclear cells (control: n=4; PAD: n= 4). Bioinformatic tools were used to annotate cell types and their subpopulations, to study transcriptional changes and to analyze cellular interactions.ResultsWe generated a dataset comprised of 106,566 high-quality, deep-sequenced cells that compose the muscle microenvironment. Focusing on endothelial cells (ECs) and macrophages, we confirmed the presence of ATF3/4+ECs with angiogenic and immune regulatory capacities in human muscle and found that their transcriptional profile profoundly alters during PAD. Also, capillary ECs display features of endothelial to mesenchymal transition. Furthermore, we identifiedLYVE1hiMHCIIlowresident macrophages as the dominant macrophage population in human muscle, even under a chronic inflammatory condition such as PAD. During PAD,LYVE1hiMHCIIlowmacrophages get activated and acquire a more pro-inflammatory profile. Finally, we map strong intercellular communication in the muscle microenvironment, which is significantly altered in PAD.ConclusionsThe dataset we present here provides a highly valuable resource for gaining deeper insights into the critical roles that cells in the muscle microenvironment may play in PAD skeletal muscle pathology. We propose that targeting the crosstalk between ECs and macrophages could provide novel insights for developing effective treatments against this disease.