Glutamine fuels proliferation but not migration of endothelial cells

Abstract

Endothelial metabolism is a key regulator of angiogenesis. Glutamine metabolism in endothelial cells (ECs) has been poorly studied. We used genetic modifications and C tracing approaches to define glutamine metabolism in these cells. Glutamine supplies the majority of carbons in the tricyclic acid (TCA) cycle of ECs and contributes to lipid biosynthesis via reductive carboxylation. EC-specific deletion in mice of glutaminase, the initial enzyme in glutamine catabolism, markedly blunts angiogenesis. In cell culture, glutamine deprivation or inhibition of glutaminase prevents EC proliferation, but does not prevent cell migration, which relies instead on aerobic glycolysis. Without glutamine catabolism, there is near complete loss of TCA intermediates, with no compensation from glucose-derived anaplerosis. Mechanistically, addition of exogenous alpha-ketoglutarate replenishes TCA intermediates and rescues cellular growth, but simultaneously unveils a requirement for Rac1-dependent macropinocytosis to provide non-essential amino acids, including asparagine. Together, these data outline the dependence of ECs on glutamine for cataplerotic processes; the need for glutamine as a nitrogen source for generation of biomass; and the distinct roles of glucose and glutamine in EC biology.

Role of glutamine and interlinked asparagine metabolism in vessel formation

“…Glutamine metabolism is crucial for ECs, since glutamine deprivation severely impaired EC proliferation and vessel sprouting. Of note, during final revision of our manuscript we became aware of another study under consideration at this same journal reporting complementary findings on the role of glutamine metabolism in ECs during angiogenesis (Kim et al , ). This adds further value to our findings on the crucial role for glutamine metabolism in vessel sprouting.…”

New Q(ues) to keep blood vessels growing

“…Notably, although both studies used the same conditional knockout allele, they also reported differences in some parameters. While Huang et al () observed that GLS1‐deficient ECs are less migratory and have fewer filopodia, Kim et al () did not find evidence for such changes. These disparities may be an indication that glutamine catabolism is not directly involved in the regulation of cellular rearrangements and migration during sprouting.…”

“…Surprisingly, Huang et al () reported that glutamine metabolism is dispensable for ATP production, perhaps because ECs use aerobic glycolysis for this purpose. In contrast, Kim et al () found that glutamine deprivation or knock‐down of glutaminase 1 (GLS1), the enzyme that catalyses the conversion of glutamine to glutamate, reduces the energy charge of ECs by half. Whether glutamine is used for endothelial ATP production might thus depend on environmental context and merits further investigation.…”

“…Sprouting ECs need to increase their biosynthetic activity to produce sufficient energy (ATP) and biomass (nucleotides, protein and lipids) required for vascular expansion. (B) Huang et al () and Kim et al () show that ECs consume large amounts of glutamine to produce nucleotides, amino acids and lipids required for cell growth and duplication. Endothelial GLS1 activity was found to be essential to replenish the TCA cycle, to produce biomass and to maintain redox balance.…”

“…They also indicate that ECs possess different nutrient acquisition strategies allowing them to sprout in metabolically challenging environments. However, the in vivo relevance of these findings is still elusive, and future (2017) and Kim et al (2017) show that ECs consume large amounts of glutamine to produce nucleotides, amino acids and lipids required for cell growth and duplication. Endothelial GLS1 activity was found to be essential to replenish the TCA cycle, to produce biomass and to maintain redox balance.…”