Brain endothelial cells metabolize glutamate via glutamate dehydrogenase to replenish TCA‐intermediates and produce ATP under hypoglycemic conditions

Abstract

The endothelial cells of the blood–brain barrier participate in the regulation of glutamate concentrations in the brain interstitial fluid by taking up brain glutamate. However, endothelial glutamate metabolism has not been characterized, nor is its role in brain glutamate homeostasis and endothelial energy production known. The aim of this study was to investigate endothelial glutamate dehydrogenase (GDH) expression and glutamate metabolism and probe its functional significance. The primary brain endothelial cells were isolated from bovine and mouse brains, and human brain endothelial cells were derived from induced pluripotent stem cells. GDH expression on the protein level and GDH function were investigated in the model systems using western blotting, confocal microscopy, 13C‐glutamate metabolism, and Seahorse assay. In this study, it was shown that GDH was expressed in murine and bovine brain capillaries and in cultured primary mouse and bovine brain endothelial cells as well as in human‐induced pluripotent stem cell‐derived endothelial cells. The endothelial GDH expression was confirmed in brain capillaries from mice carrying a central nervous system‐specific GDH knockout. Endothelial cells from all tested species metabolized 13C‐glutamate to α‐ketoglutarate, which subsequently entered the tricarboxylic acid (TCA)‐cycle. Brain endothelial cells maintained mitochondrial oxygen consumption rates, when supplied with glutamate alone, whereas glutamate supplied in addition to glucose did not lead to additional oxygen consumption. In conclusion, brain endothelial cells directly take up and metabolize glutamate and utilize the resulting α‐ketoglutarate in the tricarboxylic acid cycle to ultimately yield ATP if glucose is unavailable.

Uncovering the Gene Regulatory Network of Endothelial Cells in Mouse Duchenne Muscular Dystrophy: Insights from Single-Nuclei RNA Sequencing Analysis

“…Glutathione (GSH), superoxide dismutase (SOD), and glutathione peroxidase (GPX) are major antioxidant molecules in ECs [ 28 ]. A recent report showed that brain ECs directly absorb and metabolize glutamate and utilize the resulting α-ketoglutarate in the tricarboxylic acid cycle, ultimately producing ATP in the absence of glucose [ 29 ]. Our “scMetabolism” analysis shows that ECs from DMD mut showed high activities of glycine, serine, and threonine metabolism, glutathione metabolism, and alanine, aspartate, and glutamate metabolism, but low activity of cysteine and methionine metabolism compared to ECs from control muscle ( Figure 4 ).…”

Aging related impairment of brain microvascular bioenergetics involves oxidative phosphorylation and glycolytic pathways

“…Recent studies have reported GDH activity in the cerebral capillaries and endothelial cells. 57 Interestingly, metabolism of glutamate through OXPHOS was found to be increased in the absence of glucose in the brain endothelial cells. 57 In mammalian cells with impaired mitochondrial respiration resulting from mitochondrial DNA mutations, elevated glutamine metabolism was found to be critical for energy production and for anaplerosis.…”

“…57 Interestingly, metabolism of glutamate through OXPHOS was found to be increased in the absence of glucose in the brain endothelial cells. 57 In mammalian cells with impaired mitochondrial respiration resulting from mitochondrial DNA mutations, elevated glutamine metabolism was found to be critical for energy production and for anaplerosis. 58 Supporting our respiration measurements, we found that the activity of GDH was increased in aged BMVs.…”

Biomarkers and the outcomes of ischemic stroke

“…Besides astrocytes and neurons, EAATs have been identified in the endothelial cells of brain vasculature ( Hawkins et al, 2006 ; Hawkins, 2009 ), indicating a potential important role of vascular endothelial cells in the regulation of glutamate dynamics. In fact, it has been described that glutamate carriers are present in the luminal membrane of endothelial cells and EAATs in the abluminal membrane ( Cohen-Kashi-Malina et al, 2012 ; Hinca et al, 2021 ). The distributions of glutamate carriers and EAATs in endothelial cells could allow glutamate diffusion from brain tissue to blood following its concentration gradient.…”