Annalisa Zecchin

Fatty acid carbon is essential for dNTP synthesis in endothelial cells

The metabolism of endothelial cells during vessel sprouting remains poorly studied. Here we report that endothelial loss of CPT1A, a rate-limiting enzyme of fatty acid oxidation (FAO), causes vascular sprouting defects due to impaired proliferation, not migration, of human and murine endothelial cells. Reduction of FAO in endothelial cells did not cause energy depletion or disturb redox homeostasis, but impaired de novo nucleotide synthesis for DNA replication. Isotope labelling studies in control endothelial cells showed that fatty acid carbons substantially replenished the Krebs cycle, and were incorporated into aspartate (a nucleotide precursor), uridine monophosphate (a precursor of pyrimidine nucleoside triphosphates) and DNA. CPT1A silencing reduced these processes and depleted endothelial cell stores of aspartate and deoxyribonucleoside triphosphates. Acetate (metabolized to acetyl-CoA, thereby substituting for the depleted FAO-derived acetyl-CoA) or a nucleoside mix rescued the phenotype of CPT1A-silenced endothelial cells. Finally, CPT1 blockade inhibited pathological ocular angiogenesis in mice, suggesting a novel strategy for blocking angiogenesis.

The role of fatty acid β-oxidation in lymphangiogenesis

Lymphatic vessels are lined by lymphatic endothelial cells (LECs), and are critical for health. However, the role of metabolism in lymphatic development has not yet been elucidated. Here we report that in transgenic mouse models, LEC-specific loss of CPT1A, a rate-controlling enzyme in fatty acid β-oxidation, impairs lymphatic development. LECs use fatty acid β-oxidation to proliferate and for epigenetic regulation of lymphatic marker expression during LEC differentiation. Mechanistically, the transcription factor PROX1 upregulates CPT1A expression, which increases acetyl coenzyme A production dependent on fatty acid β-oxidation. Acetyl coenzyme A is used by the histone acetyltransferase p300 to acetylate histones at lymphangiogenic genes. PROX1–p300 interaction facilitates preferential histone acetylation at PROX1-target genes. Through this metabolism-dependent mechanism, PROX1 mediates epigenetic changes that promote lymphangiogenesis. Notably, blockade of CPT1 enzymes inhibits injury-induced lymphangiogenesis, and replenishing acetyl coenzyme A by supplementing acetate rescues this process in vivo.

Role of glutamine and interlinked asparagine metabolism in vessel formation

Endothelial cell (EC) metabolism is emerging as a regulator of angiogenesis, but the precise role of glutamine metabolism in ECs is unknown. Here, we show that depriving ECs of glutamine or inhibiting glutaminase 1 (GLS1) caused vessel sprouting defects due to impaired proliferation and migration, and reduced pathological ocular angiogenesis. Inhibition of glutamine metabolism in ECs did not cause energy distress, but impaired tricarboxylic acid (TCA) cycle anaplerosis, macromolecule production, and redox homeostasis. Only the combination of TCA cycle replenishment plus asparagine supplementation restored the metabolic aberrations and proliferation defect caused by glutamine deprivation. Mechanistically, glutamine provided nitrogen for asparagine synthesis to sustain cellular homeostasis. While ECs can take up asparagine, silencing asparagine synthetase (ASNS, which converts glutamine‐derived nitrogen and aspartate to asparagine) impaired EC sprouting even in the presence of glutamine and asparagine. Asparagine further proved crucial in glutamine‐deprived ECs to restore protein synthesis, suppress ER stress, and reactivate mTOR signaling. These findings reveal a novel link between endothelial glutamine and asparagine metabolism in vessel sprouting.

Metabolic pathway compartmentalization: an underappreciated opportunity?

For eukaryotic cells to function properly, they divide their intracellular space in subcellular compartments, each harboring specific metabolic activities. In recent years, it has become increasingly clear that compartmentalization of metabolic pathways is a prerequisite for certain cellular functions. This has for instance been documented for cellular migration, which relies on subcellular localization of glycolysis or mitochondrial respiration in a cell type-dependent manner. Although exciting, this field is still in its infancy, partly due to the limited availability of methods to study the directionality of metabolic pathways and to visualize metabolic processes in distinct cellular compartments. Nonetheless, advances in this field may offer opportunities for innovative strategies to target deregulated compartmentalized metabolism in disease.

Endothelial cells and cancer cells: metabolic partners in crime?

Purpose of reviewEndothelial cells line the blood vessel lumen and are critical for blood flow homeostasis. Excessive and deregulated vessel overgrowth is a hallmark of pathological (tumor) angiogenesis. The purpose of this review is to describe the metabolic features of endothelial cells, in comparison with those of the cancer cells, and to discuss novel antiangiogenesis approaches based on targeting endothelial cell metabolism. Recent findingsTo form new blood vessels, endothelial cells switch from quiescence to a highly active state, characterized by migration and proliferation of endothelial cells. To date, growth factors, cytokines, and other molecules have been demonstrated to regulate vessel sprouting. However, recent evidence indicates that endothelial cell metabolism also importantly regulates angiogenesis. Whereas cancer cell metabolism has been studied extensively, endothelial cell metabolism is still in its infancy. SummaryWe will discuss metabolic pathways that regulate vessel sprouting, and highlight the commonalities with cancer cells for as much as studied. We will also consider new opportunities for the development of alternative antiangiogenic therapies by targeting endothelial cell metabolism.

Corrigendum: Fatty acid carbon is essential for dNTP synthesis in endothelial cells.

This corrects the article DOI: 10.1038/nature14362

How Endothelial Cells Adapt Their Metabolism to Form Vessels in Tumors

Endothelial cells (ECs) line blood vessels, i.e., vital conduits for oxygen and nutrient delivery to distant tissues. While mostly present as quiescent “phalanx” cells throughout adult life, ECs can rapidly switch to a migratory “tip” cell and a proliferative “stalk” cell, and sprout into avascular tissue to form new blood vessels. The angiogenic switch has long been considered to be primarily orchestrated by the activity of angiogenic molecules. However, recent evidence illustrates an instrumental role of cellular metabolism in vessel sprouting, whereby ECs require specific metabolic adaptations to grow. Here, we overview the emerging picture that tip, stalk, and phalanx cells have distinct metabolic signatures and discuss how these signatures can become deregulated in pathological conditions, such as in cancer.

Endothelial Cell Differentiation by SOX17: Promoting the Tip Cell or Stalking Its Neighbor Instead?

Vessel sprouting relies on the differentiation of endothelial cells (ECs) into a migratory tip cell leading at the forefront, proliferating stalk cells elongating the vessel stalk, and quiescent phalanx cells lining the perfused vessel.1 The tip versus stalk cell balance is under the control of vascular endothelial growth factor (VEGF) and Notch signaling, respectively.1 During recent years, the transcription factor SRY-related HMG box 17 (SOX17) has emerged as a regulator of arterial (at the expense of venous) EC specification, but its role in inducing the tip versus stalk EC behavior remained incompletely defined. In this issue of Circulation Research , Lee et al2 identified SOX17 as an inducer of the tip cell phenotype and showed that Notch signaling suppresses SOX17 levels to promote a stalk cell phenotype (Figure). However, using similar genetic mouse models, another recent study reported noncongruent findings.3 Can we explain these divergent interpretations and what are the possible implications of these results? Figure. Scheme illustrating the proposed models of the mechanism of Sox17 in vessel sprouting according to Lee et al.2 Sox17 plays a central role in the induction of tip cell differentiation. Expression of Sox17 in tip cells induces tip cell behavior, whereas Notch signaling downregulates Sox17 in endothelial cells to induce stalk cell specification. These results contradict with previous observations from Corada et al3 (discussed in insets) who report that Sox17 is a tip cell suppressor, upstream, not downstream, of Notch signaling. Red arrows indicate novel regulatory pathways dissected by Lee et al.2 Ang2 indicates angiopoietin-2; Dll4, Delta-like 4; ESM1, endothelial cell-specific molecule 1; NICD, Notch intracellular domain; and VEGFR2, vascular endothelial growth factor receptor 2. Article, see p 215 Except for a brief period of embryonic vasculogenesis during which the primitive vascular plexus is established, tissues are vascularized …

Targeting endothelial cell metabolism: new therapeutic prospects?

Endothelial cells (ECs) line blood vessels and function as a vital conduit for oxygen and nutrients, but can also form vascular niches for various types of stem cells. While mostly quiescent throughout adult life, ECs can rapidly switch to a highly active state, and start to sprout in order to form new blood vessels. ECs can also become dysfunctional, as occurs in diabetes and atherosclerosis. Recent studies have demonstrated a key role for EC metabolism in the regulation of angiogenesis, and showed that EC metabolism is even capable of overriding genetic signals. In this review, we will review the basic principles of EC metabolism and focus on the metabolic alterations that accompany EC dysfunction in diabetes and vessel overgrowth in cancer. We will also highlight how EC metabolism influences EC behavior by modulating post-translational modification and epigenetic changes, and illustrate how dietary supplementation of metabolites can change EC responses. Finally, we will discuss the potential of targeting EC metabolism as a novel therapeutic strategy.

Emerging Concepts in Organ-Specific Lymphatic Vessels and Metabolic Regulation of Lymphatic Development

The lymphatic system has been less well characterized than the blood vascular system; however, work in recent years has uncovered novel regulators and non-venous lineages that contribute to lymphatic formation in various organs. Further, the identification of organ-specific lymphatic beds underscores their potential interaction with organ development and function, and highlights the possibility of targeting these organ-specific lymphatics beds in disease. This review focuses on newly described metabolic and epigenetic regulators of lymphangiogenesis and the interplay between lymphatic development and function in a number of major organ systems.