Distribution of glutamine synthetase and carbamoyl-phosphate synthetase I in vertebrate liver.

Smith, Darwin; Campbell, James W.

doi:10.1073/pnas.85.1.160

Cited by 74 publications

(38 citation statements)

References 25 publications

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“…Another important site of GS expression is the liver, where it is expressed in pericentral hepatocytes (14,19,53,61). Immunohistochemical examination of livers from control and PT-GS-KO mice (Fig.…”

Section: Gs Expression In Pt-gs-ko Micementioning

confidence: 99%

Proximal tubule-specific glutamine synthetase deletion alters basal and acidosis-stimulated ammonia metabolism

Lee

Osis

Handlogten

et al. 2016

American Journal of Physiology-Renal Physiology

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Lee H, Osis G, Handlogten ME, Lamers WH, Chaudhry FA, Verlander JW, Weiner ID. Proximal tubule-specific glutamine synthetase deletion alters basal and acidosis-stimulated ammonia metabolism. Am J Physiol Renal Physiol 310: F1229 -F1242, 2016. First published March 23, 2016 doi:10.1152/ajprenal.00547.2015.-Glutamine synthetase (GS) catalyzes the recycling of NH 4 ϩ with glutamate to form glutamine. GS is highly expressed in the renal proximal tubule (PT), suggesting ammonia recycling via GS could decrease net ammoniagenesis and thereby limit ammonia available for net acid excretion. The purpose of the present study was to determine the role of PT GS in ammonia metabolism under basal conditions and during metabolic acidosis. We generated mice with PT-specific GS deletion (PT-GS-KO) using Cre-loxP techniques. Under basal conditions, PT-GS-KO increased urinary ammonia excretion significantly. Increased ammonia excretion occurred despite decreased expression of key proteins involved in renal ammonia generation. After the induction of metabolic acidosis, the ability to increase ammonia excretion was impaired significantly by PT-GS-KO. The blunted increase in ammonia excretion occurred despite greater expression of multiple components of ammonia generation, including SN1 (Slc38a3), phosphate-dependent glutaminase, phosphoenolpyruvate carboxykinase, and Na ϩ -coupled electrogenic bicarbonate cotransporter. We conclude that 1) GS-mediated ammonia recycling in the PT contributes to both basal and acidosis-stimulated ammonia metabolism and 2) adaptive changes in other proteins involved in ammonia metabolism occur in response to PT-GS-KO and cause an underestimation of the role of PT GS expression.acid-base; ammonia; glutamine synthetase; proximal tubule A MAJOR FUNCTION of the kidney is to maintain acid-base homeostasis under basal conditions and in response to a variety of physiologic disturbances (29). In the kidney, ammonia 1 metabolism is a central component of basal net acid excretion, and changes in ammonia metabolism and urinary excretion are the primary components of the renal response to metabolic acidosis (62,64,66). Accordingly, understanding the molecular mechanisms of renal ammonia metabolism is central to understanding mammalian physiology and pathophysiology.Renal ammonia metabolism involves integrated functions of intrarenal ammoniagenesis and epithelial cell-specific NH 3 and NH 4 ϩ transport. Ammoniagenesis involves cellular glutamine uptake and metabolism through an enzymatic process involving phosphate-dependent glutaminase (PDG), glutamate dehydrogenase, and phosphoenolpyruvate carboxykinase (PEPCK) (7,59,60,63,65,66). Ammonia produced in the kidney undergoes regulated transport of both NH 3 and NH 4ϩ by a variety of specific proteins, including Naϩ -ATPase, and Rh glycoproteins B and C (Rhbg and Rhcg, respectively) (10,25,28,63,66,67). This integrated interaction of intrarenal ammonia production and transport facilitates highly regulated renal ammonia metabolism and excretion.However, not all ammonia...

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Section: Gs Expression In Pt-gs-ko Micementioning

confidence: 99%

Proximal tubule-specific glutamine synthetase deletion alters basal and acidosis-stimulated ammonia metabolism

Lee

Osis

Handlogten

et al. 2016

American Journal of Physiology-Renal Physiology

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“…Four-m sections were rehydrated and stained with hematoxylin and eosin and with a polyclonal rabbit antibody to rat FAH (graciously provided by Robert Tanguay, University of Laval, Laval, Quebec) or glutamine synthetase. 34 The antibody was diluted in PBS, pH 7.4, and applied at concentrations of 1:300,000 at 37°C for 30 minutes. The glutamine synthetase antibody was used at a dilution of 1:10,000.…”

Section: Histology and Immune Histologymentioning

confidence: 99%

Kinetics of Liver Repopulation after Bone Marrow Transplantation

Wang

Montini

Al‐Dhalimy

et al. 2002

The American Journal of Pathology

225

197

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Recent work has convincingly demonstrated that adult bone marrow contains cells capable of differentiating into liver epithelial cells in vivo. However, the frequency and time course with which fully functional hepatocytes emerge after bone marrow transplantation remained controversial. Here, we used the fumarylacetoacetate hydrolase knockout mouse to determine the kinetics of hepatocyte replacement after complete hematopoietic reconstitution. Single donorderived hepatocytes were first detected 7 weeks after lethal irradiation and bone marrow transplantation. Liver disease was not required for this transdifferentiation. In the presence of selective pressure the single cells evolved into hepatocyte nodules by 11 weeks after transplantation and resulted in >30% overall liver repopulation by 22 weeks. The frequency with which hepatocytes were produced was between 10 ؊4 and 10 ؊6 , resulting in only 50 to 500 repopulation events per liver. Hepatic engraftment was not observed without previous hematopoietic reconstitution even in the presence of liver injury. In addition, significant liver repopulation was completely dependent on hepatocyte growth selection. We conclude that hepatocyte replacement by bone marrow cells is a slow and rare event. Significant improvements in the efficiency of this process will be needed before clinical success can be expected.

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“…However, the subcellular localization of GS in liver cells is dependent on the ammonia detoxification system used. In higher vertebrates, such as mammals, which utilize the ureotelic system of ammoniadetoxification, GS is cytoplasmic in cells of both liver and neural tissue (Smith and Campbell, 1988;Wu, 1963). By contrast, in the marine elasmobranchs, such as dogfish shark, which utilize the ureosmotic system of ammonia detoxification, GS is cytoplasmic in neural tissue but mitochondrial in liver cells .…”

Section: Introductionmentioning

confidence: 99%

Weak mitochondrial targeting sequence determines tissue-specific subcellular localization of glutamine synthetase in liver and brain cells

Matthews

Gur

Koopman

et al. 2010

Journal of Cell Science

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SummaryEvolution of the uricotelic system for ammonia detoxification required a mechanism for tissue-specific subcellular localization of glutamine synthetase (GS). In uricotelic vertebrates, GS is mitochondrial in liver cells and cytoplasmic in brain. Because these species contain a single copy of the GS gene, it is not clear how tissue-specific subcellular localization is achieved. Here we show that in chicken, which utilizes the uricotelic system, the GS transcripts of liver and brain cells are identical and, consistently, there is no difference in the amino acid sequence of the protein. The N-terminus of GS, which constitutes a 'weak' mitochondrial targeting signal (MTS), is sufficient to direct a chimeric protein to the mitochondria in hepatocytes and to the cytoplasm in astrocytes. Considering that a weak MTS is dependent on a highly negative mitochondrial membrane potential () for import, we examined the magnitude of  in hepatocytes and astrocytes. Our results unexpectedly revealed that  in hepatocytes is considerably more negative than that of astrocytes and that converting the targeting signal into 'strong' MTS abolished the capability to confer tissue-specific subcellular localization. We suggest that evolutional selection of weak MTS provided a tool for differential targeting of an identical protein by taking advantage of tissue-specific differences in .

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Distribution of glutamine synthetase and carbamoyl-phosphate synthetase I in vertebrate liver.

Cited by 74 publications

References 25 publications

Proximal tubule-specific glutamine synthetase deletion alters basal and acidosis-stimulated ammonia metabolism

Proximal tubule-specific glutamine synthetase deletion alters basal and acidosis-stimulated ammonia metabolism

Kinetics of Liver Repopulation after Bone Marrow Transplantation

Weak mitochondrial targeting sequence determines tissue-specific subcellular localization of glutamine synthetase in liver and brain cells

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