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The role of the gluconeogenic enzyme PCK2 in endothelial cells

Boek - Dissertatie

Blood vessels supply tissues with vital nutrients and oxygen and they take part in controling systemic pH and temperature homeostasis. As such they are crucial for maintaining tissue homeostasis and normal health. Endothelial cells (ECs) form the inner lining of blood vessels, however, they are more than inert lining material of the vasculature. Instead, they are active players in the formation of new blood vessels from pre-existing ones (a process called vessel sprouting or angiogenesis) both in health and (life-threatening) diseases. Remarkably, aberrant EC behavior, either by dysfunctionality or by excessive vessel sprouting, contributes to the etiology of more diseases than any other tissue in the body.ECs display a remarkable behavioral plasticity; while quiescent for years, ECs can switch almost instantaneously to an activated, highly proliferative, and migratory state during vessel sprouting in response to growth factor stimuli, primarily through vascular endothelial growth factor (VEGF) signaling. Emerging evidence, mainly from the host lab, reveals that EC metabolism drives vessel sprouting (angiogenesis) in parallel to well-established growth factor-based signaling. Moreover, proof-of-principle studies have shown that targeting EC metabolism can inhibit pathological angiogenesis and can be exploited as an alternative for growth factor-based therapies, with a potentially advantageous reduction in resistance and escape mechanisms (as they occur for example in tumor vasculature upon anti-VEGF treatment). This highlights the therapeutic potential of targeting EC metabolism.Angiogenesis is an energy- and biomass-demanding process. It has been reported by the host lab that ECs are highly glycolytic and metabolize glucose for the synthesis of glycolytic intermediates, precursors of energy and biomass production and redox homeostasis. In mature vessels, quiescent ECs are exposed to ample glucose in the plasma (5.5 mM). However, angiogenic ECs constantly face a fluctuating nutrient supply and sprout into avascular areas, such as in tumor tissue in which glucose concentrations can be as low as 0.12 mM. Whether and how ECs synthesize glycolytic intermediates in such glucose-starved conditions, remains a fundamental question in vascular biology.For this doctoral research thesis, I explored whether ECs in glucose-deprived conditions switch to de novo synthesis of glycolytic intermediates, required for normal EC function, via gluconeogenesis (GNG). The gluconeogenic pathway has been considered to be for the most part the reversal of the glycolytic pathway. Here, I report that glucose-deprived ECs upregulate the expression of the key gluconeogenic enzyme PCK2 and rely on a PCK2-dependent abbreviated GNG pathway, whereby lactate and glutamine are used for the synthesis of lower glycolytic intermediates that enter the serine and glycerophospholipid biosynthesis pathways for respectively redox homeostasis and phospholipid synthesis. I show that endothelial PCK2 is essential for vessel sprouting and barrier integrity; and that increased oxidative stress and impaired glycerol-phospholipid synthesis in glucose-deprived PCK2KD ECs may be the underlying cause for their impaired angiogenic behavior and vascular barrier integrity. Unexpectedly, however, PCK2KD impaired the angiogenic behavior of ECs even in normal glucose conditions. Mechanistically, irrespective of extracellular glucose concentrations, PCK2KD ECs have an impaired unfolded protein response, leading to accumulation of misfolded proteins, which due to defective proteasomes and impaired autophagy, results in the accumulation of toxic protein aggregates in lysosomes and cellular demise.Overall, these results provide novel insights regarding the metabolic profile of ECs, as they show that glucose-deprived ECs have an active yet abbreviated GNG pathway under the control of PCK2 and that endothelial PCK2 is essential for vessel sprouting. Moreover, this study identifies an additional and previously unrecognized role of PCK2 in cellular proteostasis, beyond its traditional metabolic role in GNG.
Jaar van publicatie:2020
Toegankelijkheid:Closed