Glutamine synthetase in human carotid plaque macrophages associates with features of plaque vulnerability: An immunohistological study.

BACKGROUND AND AIMS: Glutamine synthetase (GLUL), the sole generator of glutamine, is a metabolic nexus molecule also involved in atherosclerosis. We recently demonstrated a 2.2-fold upregulation of GLUL mRNA in stroke-causing carotid plaques when compared with plaques from asymptomatic patients. Here we compared in the same cohort GLUL mRNA expression with plaque gross morphology, and the colocalization of immunodetectable GLUL protein with histopathological changes and molecular and mechanical mediators linked to plaque development. METHODS: Endarterectomy specimens from 19 asymptomatic and 24 stroke patients were sectioned longitudinally and immunostained for GLUL, CD68, α-smooth muscle actin, iron, heme oxygenase-1 and CD163, and graded semiquantitatively in every 1 mm2. The amounts of cholesterol clefts and erythrocytes were graded. The fibrous cap thickness within each 1 mm2 area was measured. The association between the local pathological findings was analyzed by a hierarchical mixed modelling approach. RESULTS: The previously found correlation between GLUL mRNA and clinical symptomatology was supported by the increased GLUL mRNA in diseased tissue and increased local GLUL immunoreactivity in areas with multiple different atherosclerotic changes. A longer symptom-to-operation time correlated with lower GLUL mRNA (Rs = -0.423, p=0.050) but few outliers had a significantly higher GLUL mRNA levels, which persisted throughout the post-symptomatic period. Plaque ulceration associated with 1.8-fold higher GLUL mRNA (p=0.006). Macrophages were the main GLUL immunoreactive cells. GLUL immunostaining colocalized with erythrocytes, iron, CD163, and heme oxygenase-1. The correlations between local variables were consistent in both asymptomatic and stroke-causing plaques. An inverse correlation was found between the fibrous cap thickness and local GLUL immunoreactivity (p=0.012). Considerable variability in interplaque expression pattern of GLUL was present. CONCLUSIONS: Our results link connect macrophage GLUL expression with carotid plaque features characterizing plaque vulnerability.

Underlying mechanisms of phosphodiesterase 10A and glutamate-ammonia ligase genes that regulate inosine monophosphate deposition and thereby affect muscle tenderness in Jingyuan chickens.

OBJECTIVE: Inosine monophosphate (IMP) is a key factor that imparts of meat flavor. Differences in the IMP content in the muscles were evaluated to improve chicken meat quality. METHODS: For this study, the IMP content was detected by high performance liquid chromatography. The gene expression profiles of Jingyuan chickens with different feeding patterns and different sexes were analyzed by RNA-sequencing (RNA-seq). RESULTS: Breast muscle IMP content in free-range chickens was extremely significantly higher than that of caged chickens (p<0.01). Breast muscle IMP content in hens was also higher than that of cocks, but the difference was not significant. Correlation analysis showed that the breast muscle IMP content in caged hens and cocks was negatively correlated with the shear force, and the breast muscle IMP content in free-range hens was significantly negatively correlated with the shear force (p<0.05). The two key genes associated with IMP synthesis in chickens with different feeding patterns were glutamate-ammonia ligase (GLUL) and phosphodiesterase 10A (PDE10A). Bioinformatics analysis revealed that the GLUL and PDE10A genes are involved in glutamine biosynthesis and purine salvage pathways respectively. In addition, GLUL expression was positively correlated with the IMP content in caged and free-range chickens, and PDE10A expression was significantly positively correlated with the IMP content in caged and free-range chickens (p<0.05). CONCLUSION: These findings will facilitate the comprehension of the deposition of IMP in the muscles and thereby aid the process of selection and breeding of good quality local chickens.

Glutamine Anabolism Plays a Critical Role in Pancreatic Cancer by Coupling Carbon and Nitrogen Metabolism.

Glutamine is thought to play an important role in cancer cells by being deaminated via glutaminolysis to α-ketoglutarate (aKG) to fuel the tricarboxylic acid (TCA) cycle. Supporting this notion, aKG supplementation can restore growth/survival of glutamine-deprived cells. However, pancreatic cancers are often poorly vascularized and limited in glutamine supply, in alignment with recent concerns on the significance of glutaminolysis in pancreatic cancer. Here, we show that aKG-mediated rescue of glutamine-deprived pancreatic ductal carcinoma (PDAC) cells requires glutamate ammonia ligase (GLUL), the enzyme responsible for de novo glutamine synthesis. GLUL-deficient PDAC cells are capable of the TCA cycle but defective in aKG-coupled glutamine biosynthesis and subsequent nitrogen anabolic processes. Importantly, GLUL expression is elevated in pancreatic cancer patient samples and in mouse PDAC models. GLUL ablation suppresses the development of KrasG12D-driven murine PDAC. Therefore, GLUL-mediated glutamine biosynthesis couples the TCA cycle with nitrogen anabolism and plays a critical role in PDAC.

The Pleiotropic Effects of Glutamine Metabolism in Cancer.

Metabolic programs are known to be altered in cancers arising from various tissues. Malignant transformation can alter signaling pathways related to metabolism and increase the demand for both energy and biomass for the proliferating cancerous cells. This scenario is further complexed by the crosstalk between transformed cells and the microenvironment. One of the most common metabolic alterations, which occurs in many tissues and in the context of multiple oncogenic drivers, is the increased demand for the amino acid glutamine. Many studies have attributed this increased demand for glutamine to the carbon backbone and its role in the tricarboxylic acid (TCA) cycle anaplerosis. However, an increasing number of studies are now emphasizing the importance of glutamine functioning as a proteogenic building block, a nitrogen donor and carrier, an exchanger for import of other amino acids, and a signaling molecule. Herein, we highlight the recent literature on glutamine's versatile role in cancer, with a focus on nitrogen metabolism, and therapeutic implications of glutamine metabolism in cancer.

Changes in free amino acid concentrations and associated gene expression profiles in the abdominal muscle of kuruma shrimp (Marsupenaeus japonicus) acclimated at different salinities.

Shrimps inhabiting coastal waters can survive in a wide range of salinity. However, the molecular mechanisms involved in their acclimation to different environmental salinities have remained largely unknown. In the present study, we acclimated kuruma shrimp (Marsupenaeus japonicus) at 1.7%, 3.4% and 4.0% salinities. After acclimating for 6, 12, 24 and 72 h, we determined free amino acid concentrations in their abdominal muscle, and performed RNA sequencing analysis on this muscle. The concentrations of free amino acids were clearly altered depending on salinity after 24 h of acclimation. Glutamine and alanine concentrations were markedly increased following the increase of salinity. In association with such changes, many genes related to amino acid metabolism changed their expression levels. In particular, the increase of the expression level of the gene encoding glutamate-ammonia ligase, which functions in glutamine metabolism, appeared to be associated with the increased glutamine concentration at high salinity. Furthermore, the increased alanine concentration at high salinity was likely associated with the decrease in the expression levels of the the gene encoding alanine-glyoxylate transaminase. Thus, there is a possibility that changes in the concentration of free amino acids for osmoregulation in kuruma shrimp are regulated by changes in the expression levels of genes related to amino acid metabolism.

High expression of glutamate-ammonia ligase is associated with unfavorable prognosis in patients with ovarian cancer.

Glutamate-ammonia ligase (GLUL), which is also called GS (glutamine synthetase), is the enzyme that catalyzes the synthesis of glutamine from glutamate and ammonia in an ATP-dependent reaction. Here, we found higher expression of GLUL in the ovarian cancer patients was associated with worse disease-free survival (DFS) and overall survival (OS). In addition, GLUL was heterogeneously expressed in various ovarian cancer cells. The mRNA and protein expression levels of GLUL in NIH:OVCAR-3 and ES-2 cells were obviously higher than that in the other types of ovarian cancer cells. Knockdown of GLUL in NIH:OVCAR-3 or ES-2 cells could significantly decrease the proliferation ability. Furthermore, GLUL knockdown markedly inhibited the p38 MAPK signaling pathway in NIH:OVCAR-3 or ES-2 cells. Our findings suggest that decreasing expression of GLUL may be a new approach that can be used for ovarian cancer treatment.

Relationship between remifentanil-induced hyperalgesia and function of nitrated glutamate transpor-tor-1 and glutamine synthetase in spinal cord of rats with incisional pain / 中华麻醉学杂志

Objective To investigate the relationship remifentanil-induced hyperalgesia and func-tion of nitrated glutamate transportor-1 ( GLT-1) and glutamine synthetase ( GS) in the spinal cord of rats with incisional pain. Methods Thirty-two male Sprague-Dawley rats, weighing 260-280 g, aged 2-3 months, in which caudal catheters were successfully implanted, were divided into 4 groups (n=8 each) u-sing a random number table method: control group ( group C) , incisional pain group ( group I) , remifen-tanil group ( group R) and remifentanil plus incisional pain group ( group RI) . Normal saline was intrave-nously infused for 60 min at 0. 1 ml · kg-1 · min-1 in group C. The model of incisional pain was estab-lished, and normal saline was simultaneously infused for 60 min via the tail vein at 0. 1 ml·kg-1 ·min-1 in group I. Remifentanil was infused for 60 min via the tail vein at 1. 0 μg· kg-1 ·min-1 in group R. The model of incisional pain was established, and remifentanil was infused for 60 min via the tail vein at 1. 0μg· kg-1 ·min-1 in group RI. The mechanical paw withdrawal threshold ( MWT) and thermal paw with-drawal latency ( TWL) were measured at 24 h before infusion of remifentanil or normal saline ( T0 ) and at 2, 6, 24 and 48 h after infusion ( T1-4 ) . The rats were sacrificed after the last measuremnet of pain thresh-old, and the L4-6 segment of the spinal cord was removed for determination of the expression of GLT-1 and GS (by Western blot) and expression of nitrated GLT-1 (nGLT-1) and nitrated GS (nGS) (by Western blot) . Ratios of nGLT-1∕GLT-1 and nGS∕GS were calculated. Results Compared with group C, the MWT was significantly decreased and TWL was shortened at T1-4 , the expression of GLT-1 and GS was down-regu-lated, the expression of nGLT-1 and nGS was up-regulated, and ratios of nGLT-1∕GLT-1 and nGS∕GS were increased in I, R and RI groups ( P<0. 05) . Compared with group I and group R, the MWT was signifi-cantly decreased and TWL was shortened at T1-4 , the expression of GLT-1 and GS was down-regulated, the expression of nGLT-1 and nGS was up-regulated, and ratios of nGLT-1∕GLT-1 and nGS∕GS were increased in group RI ( P<0. 05) . Conclusion The mechanism of remifentanil-induced hyperalgesia may be related to impaired function of GLT-1 and GS in the spinal cord of rats with incisional pain.

SIRT5 regulation of ammonia-induced autophagy and mitophagy.

In liver the mitochondrial sirtuin, SIRT5, controls ammonia detoxification by regulating CPS1, the first enzyme of the urea cycle. However, while SIRT5 is ubiquitously expressed, urea cycle and CPS1 are only present in the liver and, to a minor extent, in the kidney. To address the possibility that SIRT5 is involved in ammonia production also in nonliver cells, clones of human breast cancer cell lines MDA-MB-231 and mouse myoblast C2C12, overexpressing or silenced for SIRT5 were produced. Our results show that ammonia production increased in SIRT5-silenced and decreased in SIRT5-overexpressing cells. We also obtained the same ammonia increase when using a new specific inhibitor of SIRT5 called MC3482. SIRT5 regulates ammonia production by controlling glutamine metabolism. In fact, in the mitochondria, glutamine is transformed in glutamate by the enzyme glutaminase, a reaction producing ammonia. We found that SIRT5 and glutaminase coimmunoprecipitated and that SIRT5 inhibition resulted in an increased succinylation of glutaminase. We next determined that autophagy and mitophagy were increased by ammonia by measuring autophagic proteolysis of long-lived proteins, increase of autophagy markers MAP1LC3B, GABARAP, and GABARAPL2, mitophagy markers BNIP3 and the PINK1-PARK2 system as well as mitochondrial morphology and dynamics. We observed that autophagy and mitophagy increased in SIRT5-silenced cells and in WT cells treated with MC3482 and decreased in SIRT5-overexpressing cells. Moreover, glutaminase inhibition or glutamine withdrawal completely prevented autophagy. In conclusion we propose that the role of SIRT5 in nonliver cells is to regulate ammonia production and ammonia-induced autophagy by regulating glutamine metabolism.

Glutamate, GABA, and glutamine are synchronously upregulated in the mouse lateral septum during the postpartum period.

Dramatic structural and functional remodeling occurs in the postpartum brain for the establishment of maternal care, which is essential for the growth and development of young offspring. Glutamate and GABA signaling are critically important in modulating multiple behavioral performances. Large scale signaling changes occur in the postpartum brain, but it is still not clear to what extent the neurotransmitters glutamate and GABA change and whether the ratio of glutamate/GABA remains balanced. In this study, we examined the glutamate/GABA-glutamine cycle in the lateral septum (LS) of postpartum female mice. In postpartum females (relative to virgins), tissue levels of glutamate and GABA were elevated in LS and increased mRNA was found for the respective enzymes producing glutamate and GABA, glutaminase (Gls) and glutamate decarboxylase 1 and 2 (Gad1 and Gad2). The common precursor, glutamine, was elevated as was the enzyme that produces it, glutamate-ammonia ligase (Glul). Additionally, glutamate, GABA, and glutamine were positively correlated and the glutamate/GABA ratio was almost identical in the postpartum and virgin females. Collectively, these findings indicate that glutamate and GABA signaling are increased and that the ratio of glutamate/GABA is well balanced in the maternal LS. The postpartum brain may provide a useful model system for understanding how glutamate and GABA are linked despite large signaling changes. Given that some mental health disorders, including depression and schizophrenia display dysregulated glutamate/GABA ratio, and there is increased vulnerability to mental disorders in mothers, it is possible that these postpartum disorders emerge when glutamate and GABA changes are not properly coordinated.

The structures of cytosolic and plastid-located glutamine synthetases from Medicago truncatula reveal a common and dynamic architecture.

The first step of nitrogen assimilation in higher plants, the energy-driven incorporation of ammonia into glutamate, is catalyzed by glutamine synthetase. This central process yields the readily metabolizable glutamine, which in turn is at the basis of all subsequent biosynthesis of nitrogenous compounds. The essential role performed by glutamine synthetase makes it a prime target for herbicidal compounds, but also a suitable intervention point for the improvement of crop yields. Although the majority of crop plants are dicotyledonous, little is known about the structural organization of glutamine synthetase in these organisms and about the functional differences between the different isoforms. Here, the structural characterization of two glutamine synthetase isoforms from the model legume Medicago truncatula is reported: the crystallographic structure of cytoplasmic GSII-1a and an electron cryomicroscopy reconstruction of plastid-located GSII-2a. Together, these structural models unveil a decameric organization of dicotyledonous glutamine synthetase, with two pentameric rings weakly connected by inter-ring loops. Moreover, rearrangement of these dynamic loops changes the relative orientation of the rings, suggesting a zipper-like mechanism for their assembly into a decameric enzyme. Finally, the atomic structure of M. truncatula GSII-1a provides important insights into the structural determinants of herbicide resistance in this family of enzymes, opening new avenues for the development of herbicide-resistant plants.

Effects of recombinant human erythropoietin on the expression of glutamine synthetase of cultured retinal Müller cells under high glucose condition / 中华眼底病杂志

Objective To investigate the effect of recombinant human erythropoietin (rhEPO) on the expression of glutamine synthetase (GS) of cultured rat retinal Müller cells in high glucose environment in vitro.Methods Mtüller cells were isolated from retinas of 10 Sprague-Dawley rats at postnatal day three to five by trypsin digestion,and were randomly divided into six groups,including normal control group,high glucose group,high glucose +5 U/ml rhEPO group,high glucose+ 10 U/ml rhEPO group,high glucose+ 20 U/ml rhEPO group,high glucose+40 U/ml rhEPO groups.After 48 hours,the apoptosis of retinal Müller cells were assayed by terminal transferase-mediated DNA end labelling assay,and the expression levels of GS protein were detected with semi-quantitative immunocytochemistry.Results Compared with the normal control group,the cell viability and GS protein were reduced while the cell death increased in Müller cells cultured in high glucose,the difference was statistically significant (t =27.4,P ＜ 0.01).Compared with the high glucose group,rhEPO treatment reduced the apoptotic Müller cells (t=857.2,2 374.6,2 473.2,2 537.7; P＜0.01),induced the expression of GS proteins (t=3.2,18.0,22.5,26.4; P＜0.05).Conclusions rhEPO can protect Müller cells from apoptosis under high glucose condition.The mechanism may be related to its function to up-regulate the GS protein expression,promote glutamic acid cycle,and reduce the excitotoxicity effects of high concentration of glutamate.

Verification of interaction between glutamate-ammonia ligase and nuclear localization signal-retinoic acid receptor α protein inside and outside cells / 第二军医大学学报

Objective: To verify the interaction between glutamate-ammonia ligase (GLUL) and nuclear localization signal-retinoic acid receptor α (NLS-RARα) protein by yeast two-hybrid and co-immunoprecipitation method. Methods: The two plasmids expressing NLS-RARα bait-protein and GLUL protein were co-transformed into yeast AH109 to investigate the interaction in vivo. Tagged fusion protein eukaryotic expression vectors were constructed and co-transfected into HEK 293 cells. Co-immunoprecipitation was used to investigate the interaction between NLS-RARα and GLUL in vitro. Results: Positive blue clones were found in the QDO/X-α-gal plate. Eukaryotic expression vectors were co-transfected into HEK 293 cells, then HA-NLS-RARα protein was immunoprecipitated by anti-HA polyclonal antibody, and GLUL-cMyc protein expression was confirmed by Western blotting analysis using anti c-Myc monoclonal antibody. Conclusion: The interaction between NLS-RARα and GLUL has been verified by both yeast two-hybrid and co-immunoprecipitation.