Highlights d Endothelial loss of pfkfb3 impairs ischemic muscle revascularization and regeneration d EC-derived lactate instructs MCT1-dependent macrophage functional polarization d Lactate-polarized macrophages promote muscle revascularization and regeneration d Restoring lactate levels improves macrophage polarization and recovery from ischemia

Graphical Abstract Highlights d HIF1a reduces intracellular aspartate levels d HIF1a impairs oxidative and reductive aspartate biosynthesis d The aspartate-generating GOT1 and GOT2 enzymes are repressed by HIF1a d Aspartate supplementation counteracts the antiproliferative influence of HIF1a In Brief Melé ndez-Rodríguez et al. show that HIF1a impairs oxidative and reductive aspartate biogenesis, which consequently drives HIF1a-dependent suppression of tumor cell proliferation. Mechanistically, HIF1a represses the aspartate-producing enzymes GOT1 and GOT2 in several biological settings, including human VHL-deficient renal cell carcinoma, in which HIF1a can act as a tumor suppressor.

Summary Exercise is a powerful driver of physiological angiogenesis during adulthood, but the mechanisms of exercise-induced vascular expansion are poorly understood. We explored endothelial heterogeneity in skeletal muscle and identified two capillary muscle endothelial cell (mEC) populations that are characterized by differential expression of ATF3/4. Spatial mapping showed that ATF3/4 + mECs are enriched in red oxidative muscle areas while ATF3/4 low ECs lie adjacent to white glycolytic fibers. In vitro and in vivo experiments revealed that red ATF3/4 + mECs are more angiogenic when compared with white ATF3/4 low mECs. Mechanistically, ATF3/4 in mECs control genes involved in amino acid uptake and metabolism and metabolically prime red (ATF3/4 + ) mECs for angiogenesis. As a consequence, supplementation of non-essential amino acids and overexpression of ATF4 increased proliferation of white mECs. Finally, deleting Atf4 in ECs impaired exercise-induced angiogenesis. Our findings illustrate that spatial metabolic angiodiversity determines the angiogenic potential of muscle ECs.

Fatty infiltration, the ectopic deposition of adipose tissue within skeletal muscle, is mediated via the adipogenic differentiation of fibro-adipogenic progenitors (FAPs). We used single-nuclei and single-cell RNA sequencing to characterize FAP heterogeneity in patients with fatty infiltration. We identified an MME+ FAP subpopulation which, based on ex vivo characterization as well as transplantation experiments, exhibits high adipogenic potential. MME+ FAPs are characterized by low activity of WNT, known to control adipogenic commitment, and are refractory to the inhibitory role of WNT activators. Using preclinical models for muscle damage versus fatty infiltration, we show that many MME+ FAPs undergo apoptosis during muscle regeneration and differentiate into adipocytes under pathological conditions, leading to a reduction in their abundance. Finally, we utilized the varying fat infiltration levels in human hip muscles and found less MME+ FAPs in fatty infiltrated human muscle. Altogether, we have identified the dominant adipogenic FAP subpopulation in skeletal muscle.