γ-Aminobutyric Acid Is Synthesized and Released by the Endothelium

Abstract

Rationale: Gamma aminobutyric acid (GABA), a neurotransmitter of the central nervous system, is found in the systemic circulation of humans at a concentration between 0.5 and 3 μmol/L. However, the potential source of circulating GABA and its significance on the vascular system remains unknown. We hypothesized that endothelial cells (ECs) may synthesize and release GABA to modulate some functions in the EC and after its release into the circulation.Objective: To assess whether GABA is synthesized and released by the EC and its potential functions. Methods and Results: Utilizing the human umbilical vein ECs and aortic ECs, we demonstrated for the first time that ECs synthesize and release GABA from [1-14 C]glutamate. Localization of GABA and the presence of the GABA-synthesizing enzyme, glutamic acid decarboxylase in EC were confirmed by immunostaining and immunoblot analysis, respectively. The presence of GABA was further confirmed by immunohistochemistry in the EC lining the human coronary vessel. EC-derived GABA regulated the key mechanisms of ATP synthesis, fatty acid, and pyruvate oxidation in EC. GABA protected EC by inhibiting the reactive oxygen species generation and prevented monocyte adhesion by attenuating vascular cell adhesion molecule -1 and monocyte chemoattractant protein-1 expressions. GABA had no relaxing effect on rat aortic rings. GABA exhibited a dose-dependent fall in blood pressure. However, the fall in BP was abolished after pretreatment with pentolinium. from Perkin Elmer, MA, catalog NEC290E050UC, NEC255050UC, and NEC559010UC. All other chemicals unless specified were obtained from Sigma. Conclusions: Cell CultureHuman umbilical vein endothelial cells (HUVECs) were freshly isolated from umbilical cords from different donors after normal delivery (with approval from the Institutional Review Board of University of California at Los Angeles, LA, CA). Primary cultures of HUVEC were prepared as described 14 and used at passages 1 or 2. Primary cultures of human aortic endothelial cells (HAEC) at passage 2 or 3 were a generous gift from Dr M. Navab in the Department of Medicine, University of California, Los Angeles, 90095-1732, USA. Both HAEC and HUVEC were cultured in endothelial cell basal medium-2 (Lonza), and the medium was supplemented with Endothelial Growth Medium-2 Bullet kit (CC3162; Lonza) as per the manufacturer's instructions as described previously. 15PC12 cells were a generous gift from Dr E. Schweitzer, Semel Institute of Neuroscience and Human Behavior, University of California, Los Angeles. PC12 cells were cultured in DMEM supplemented with 5% FCS and 5% Horse serum. Human skin fibroblast (HSF) cells were a gift from Dr H. Coller, Molecular Cell and Developmental Biology, University of California, Los Angeles. HSF and THP1 were cultured in DMEM supplemented with 10% FBS. All cells were cultured until 70% confluent before downstream manipulations. Cell culture treatments were done under sterile conditions, for 24 hours unless specified. Glutamic acid decarboxylase (GAD) doubl...

The circulating metabolome of human starvation

“…Of the 77 total metabolites, BAIBA was 1 of 3 that demonstrated an inverse correlation: BAIBA (R 2 = 0.46, P = 0.046), SM (22:0) (R 2 = 0.46, P = 0.044), and γ-aminobutyric acid (GABA) (R 2 = 0.58, P = 0.018). Two of these three metabolites (BAIBA and GABA) have been previously suggested to promote fatty acid oxidation in different contexts (20)(21)(22). Collectively, these data raise the possibility that cluster 1 marks an intermediate phase of starvation, bridging the early reliance on glucose metabolism and the subsequent shift to utilization of lipids for fuel.…”

A Buttery Taste to Vascular Biology

“…In conclusion, with the present work of Sen et al, 11 the research field on endothelial GABA metabolism has been pioneered. Additional work will have to demonstrate whether GABA level are subject to disease-related control, mediators of endothelial signaling, and how GABA acts mechanistically within endothelial cells.…”

“…11 Homogenates of human aortic endothelial cells and human umbilical vein endothelial cells converted radiolabeled [1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]glutamate into [1-14 C]GABA, and incubation of living human umbilical vein endothelial cells with [1-14 C]glutamate resulted in the release of [1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]GABA into the culture medium. Inhibition of GABA transaminase, which degrades GABA and, thus, limits the half-life of this amino acid, increased its release by ≈18%, whereas inhibition or siRNAmediated knockdown of GABA producing GADs decreased GABA release by ≈50%.…”

“…What is the mechanistic action of intracellular GABA? Although the study by Sen et al 11 identified several important intracellular downstream events, it remained fairly unclear how GABA elicits these effects. The authors only demonstrate that mitogen activated protein kinase activation is not altered, but important other pathways could have been studied.…”

Gamma-Aminobutyric Acid Signaling in Brown Adipose Tissue Promotes Systemic Metabolic Derangement in Obesity

“…also express leptin receptors, and suppression of this system leads to overeating and obesity (Xu et al, 2012). GABA is also detected in various peripheral organs, including the pancreas, endothelium, gastrointestinal tract, adrenal medulla, and placenta (Gladkevich et al, 2006;Sen et al, 2016). In patients with diabetes, GABA is reportedly decreased in the pancreas (Al-Salam et al, 2009).…”