Changes in Human Endothelial Cell Energy Metabolic Capacities during in vitro Cultivation. The Role of “Aerobic Glycolysis” and Proliferation

Abstract

Background: In this study the influence of cultivation and proliferation on energy metabolic characteristics of human umbilical vein endothelial cells (HUVEC) has been examined. The energy metabolic capacities of human endothelial cells freshly isolated from the umbilical vein were compared with those after cultivation for three passages and as subconfluent and confluent cultures. Methods: Expression of cell type-specific differentiation markers and proliferative activity were studied in dependency on cultivation characteristics. Furthermore, the energy metabolic characteristics of HUVEC were analyzed by measurement of the maximum catalytic activities of marker enzymes of various metabolic pathways. Results: Examination of a typical marker of proliferation, Ki67, confirmed that HUVEC changed in culture from a non-proliferative to a proliferative state. Compared to other cell types, the enzyme pattern of HUVEC showed a high glycolytic and a high NADPH regenerating capacity. These capacities increased by cultivation nearly to the same degree as marker enzymes of other metabolic pathways (e.g. citric acid cycle). Conclusion: Our data support the theory that metabolism of EC is primarily by “aerobic glycolysis”, i.e. the conversion of glucose to lactate in the presence of oxygen. These characteristics were independent of whether the cells are freshly isolated/non-proliferating or cell culture-adapted/proliferating.

Angiogenesis revisited – role and therapeutic potential of targeting endothelial metabolism

“…Interestingly, endothelial cells under pathological conditions exhibit characteristics of the Warburg effect -which is commonly associated with hyperproliferative cells -whereby glycolysis increases and oxidative phosphorylation decreases (Delgado et al, 2010;Fijalkowska et al, 2010;Metallo and Vander Heiden, 2013;Mullen and DeBerardinis, 2012). Upon activation by factors such as VEGF, endothelial cells increase expression of GLUT-1 as well as that of glycolytic enzymes, such as lactate dehydrogenase-A (LDH-A) and 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3), among others (De Bock et al, 2013b;Parra-Bonilla et al, 2010;Peters et al, 2009;Yeh et al, 2008). By contrast, DLL4-Notch signaling, which suppresses VEGFR2 expression and vascular branching, also decreases glycolytic flux in endothelial cells in vitro by downregulating PFKFB3 (De Bock et al, 2013b) (Fig.…”

Transendothelial glucose transport is not restricted by extracellular hyperglycaemia

“…Endothelial cells in different vessels or organs are finely tuned to their specific functions [5][6][7]; for example, the permeability of the endothelial monolayer ranges from tightly controlled in blood brain barrier [8] to leaky in fenestrated endothelium of sinusoidal tissue in liver [9,10]. One of the characteristic features of endothelial cells is their reliance on glycolysis for energy production [11][12][13], with sustained glucose consumption being critical for endothelial cell viability especially during angiogenesis [14,15]. Thus glucose uptake and metabolism is critical for healthy endothelial physiology, and endothelial glucose transporters are especially important in the brain, where glucose can only cross the blood brain barrier via this mechanism [16].…”

Manipulating Angiogenesis by Targeting Endothelial Metabolism: Hitting the Engine Rather than the Drivers—A New Perspective?

“…Surprisingly, however, ECs do not rely on mitochondrial respiration, but rather on glycolysis (Murphy, 1960;Feiden et al, 2007;Koppenol et al, 2011;De Bock et al, 2013). Indeed, ECs from macro-and microvessels exhibit high glycolytic rates (Dobrina and Rossi, 1983;Krutzfeldt et al, 1990;Mertens et al, 1990;Culic et al, 1997) and generate 85% of their total ATP content via glycolysis, whereas mitochondrial respiration is low in ECs relative to other cell types (Peters et al, 2009;De Bock et al, 2013).…”

“…The ATP yield of glycolysis is much lower than that of mitochondrial respiration (2 versus 36 moles of ATP per mole of glucose, respectively). Nonetheless, ECs generate more than 85% of their cellular energy via glycolysis (Peters et al, 2009;De Bock et al, 2013), raising the question of why ECs rely so much on this pathway. We speculate that this reliance on glycolysis may be due to several reasons.…”

“…Second, because the primary function of blood vessels is to deliver oxygen, glycolysis helps to preserve oxygen for transfer to perivascular cells. Third, nonoxidative metabolism generates less reactive oxygen species (ROS) than oxidative metabolism, and the pentose phosphate pathway, or PPP, a glycolytic side pathway, synthesizes NADPH (nicotinamide adenine dinucleotide phosphate), used by glutathione reductase to convert oxidized glutathione to reduced glutathione (GSH), a major antioxidant (Dobrina and Rossi, 1983;Krutzfeldt et al, 1990;Peters et al, 2009).…”