Role of glutamine synthetase in angiogenesis beyond glutamine synthesis

Abstract

Glutamine synthetase, encoded by the gene GLUL, is an enzyme that converts glutamate and ammonia to glutamine. It is expressed by endothelial cells, but surprisingly shows negligible glutamine-synthesizing activity in these cells at physiological glutamine levels. Here we show in mice that genetic deletion of Glul in endothelial cells impairs vessel sprouting during vascular development, whereas pharmacological blockade of glutamine synthetase suppresses angiogenesis in ocular and inflammatory skin disease while only minimally affecting healthy adult quiescent endothelial cells. This relies on the inhibition of endothelial cell migration but not proliferation. Mechanistically we show that in human umbilical vein endothelial cells GLUL knockdown reduces membrane localization and activation of the GTPase RHOJ while activating other Rho GTPases and Rho kinase, thereby inducing actin stress fibres and impeding endothelial cell motility. Inhibition of Rho kinase rescues the defect in endothelial cell migration that is induced by GLUL knockdown. Notably, glutamine synthetase palmitoylates itself and interacts with RHOJ to sustain RHOJ palmitoylation, membrane localization and activation. These findings reveal that, in addition to the known formation of glutamine, the enzyme glutamine synthetase shows unknown activity in endothelial cell migration during pathological angiogenesis through RHOJ palmitoylation.

Integrated Transcriptomic and Proteomic Analyses of the Interaction Between Chicken Synovial Fibroblasts and Mycoplasma synoviae

“…An investigation conducted by Kerr and Olson (1970) observed the formation of granulomatous pannus in the medullary spaces of chickens inoculated experimentally or contact-infected with MS. The present study demonstrated that several proangiogenic factors were upregulated, including ECM1 (Mongiat et al, 2003), IL-8 (Bodolay et al, 2002), TGF-β2 (Elshabrawy et al, 2015), SAA (Connolly et al, 2016), MMP-9 (Burrage et al, 2006), NRP1 (Kong et al, 2010), GLUL (Eelen et al, 2018), and THBS2 (Park et al, 2004), while antiangiogenic factors, including RGCC (An et al, 2009), as well as TIMP3 (Chen et al, 2014), were downregulated at both the mRNA and protein levels. These findings suggest that MS-infected CSF may contribute to blood vessel growth, which is necessary for sustaining pannus formation and the arthritis process.…”

Hyperoxia induces glutamine-fuelled anaplerosis in retinal Müller cells

“…GLS1 and GLS2 isoforms are differentially expressed in RECs; the latter is more concentrated in endothelial tip cells necessary to new blood vessel formation 7 . Glutamine synthetase (GS) ablation prevents normal development of retinal vasculature, further confirming the importance of glutamine to endothelial cell growth and development 8 . Previous studies have also reported that RECs express the glutamine transporter SLC1A5 9 .…”

ST6GAL1: A key player in cancer (Review)

“…For a cancer to sustain macroscopic tumour development and promote metastasis, the formation of neovasculature is necessary for the supply of nutrients and oxygen. This process, known as angiogenesis, is tightly regulated by opposing factors; stimulating and inhibiting the receptors displayed on the surface of vascular endothelial cells (4,5,60,61). Although key molecular regulators of angiogenesis have been identified, such as VEGF and TSP-1, it is now widely accepted that regulation of angiogenesis is a highly complex process, heavily influenced by the tumour microenvironment, gaining influence from things such as tumour metabolism, immune infiltrate and cancer-associated fibroblasts (CAFs) (62).…”