Intestinal carbamoyl phosphate synthase I in human and rat. Expression during development shows species differences and mosaic expression in duodenum of both species

Aestivation induces widespread transcriptional changes in the African lungfish

Aestivation is a special ability possessed by some animals to cope with hot and dry environments utilizing dormancy. At a macroscopic level, dormant animals stop moving and eating. At the microscopic level, the expression of a large number of genes in these animals is strictly controlled. However, little is known about what changes occur during aestivation, especially in fish. In this study, we used transcriptome analysis to examine what changes occur in the gills and lungs of the African lungfish (Protopterus annectens) during the maintenance phase of aestivation and speculated on their causes. We found that aestivating transcriptomes were highly similar between gills and lungs. We also found that some genes showed differential expression or alternative splicing, which may be associated with different organs. In addition, differential expression analysis revealed that the lungs maintained significantly higher bioactivity during aestivation, which suggests that the main respiratory organ in aestivating lungfish can transform. Our study provides a reference point for studying the relationship between aestivation and hibernation and further increases understanding of aestivation.

CPS1: Looking at an ancient enzyme in a modern light

The mammalian urea cycle (UC) is responsible for siphoning catabolic waste nitrogen into urea for excretion. Disruptions of the functions of any of the enzymes or transporters lead to elevated ammonia and neurological injury. Carbamoyl phosphate synthetase 1 (CPS1) is the first and rate-limiting UC enzyme responsible for the direct incorporation of ammonia into UC intermediates. Symptoms in CPS1 deficiency are typically the most severe of all UC disorders, and current clinical management is insufficient to prevent the associated morbidities and high mortality. With recent advances in basic and translational studies of CPS1, appreciation for this enzyme's essential role in the UC has been broadened to include systemic metabolic regulation during homeostasis and disease. Here, we review recent advances in CPS1 biology and contextualize them around the role of CPS1 in health and disease.

Simultaneous tracing of carbon and nitrogen isotopes in human cells

Stable isotope tracing is a powerful method for interrogating metabolic enzyme activities across the metabolic network of living cells. However, most studies of mammalian cells have used (13)C-labeled tracers only and focused on reactions in central carbon metabolism. Cellular metabolism, however, involves other biologically important elements, including nitrogen, hydrogen, oxygen, phosphate and sulfur. Tracing stable isotopes of such elements may help shed light on poorly understood metabolic pathways. Here, we demonstrate the use of high-resolution mass spectrometry to simultaneously trace carbon and nitrogen metabolism in human cells cultured with (13)C- and (15)N-labeled glucose and glutamine. To facilitate interpretation of the complex isotopomer data generated, we extend current methods for metabolic flux analysis to handle multivariate mass isotopomer distributions (MMIDs). We find that observed MMIDs are broadly consistent with known biochemical pathways. Whereas measured (13)C MIDs were informative for central carbon metabolism, (15)N isotopes provided evidence for nitrogen-carrying reactions in amino acid and nucleotide metabolism. This computational and experimental methodology expands the scope of metabolic flux analysis beyond carbon metabolism, and may prove important to understanding metabolic phenotypes in health and disease.

Carbamoylphosphate synthetase 1 (CPS1) deficiency: clinical, biochemical, and molecular characterization in Malaysian patients

Carbamoyl phosphate synthetase 1 (CPS1) deficiency is a rare autosomal recessive disorder of ureagenesis presenting as life-threatening hyperammonemia. In this study, we present the main clinical features and biochemical and molecular data of six Malaysian patients with CPS1 deficiency. All the patients have neonatal-onset symptoms, initially diagnosed as infections before hyperammonemia was recognized. They have typical biochemical findings of hyperglutaminemia, hypocitrullinemia, and low to normal urinary excretion of orotate. One neonate succumbed to the first hyperammonemic decompensation. Five neonatal survivors received long-term treatment consisting of dietary protein restriction and ammonia-scavenging drugs. They have delayed neurocognitive development of varying severity. Genetic analysis revealed eight mutations in CPS1 gene, five of which were not previously reported. Five mutations were missense changes while another three were predicted to create premature stop codons. In silico analyses showed that these new mutations affected different CPS1 enzyme domains and were predicted to interrupt interactions at enzyme active sites, disturb local enzyme conformation, and destabilize assembly of intact enzyme complex.

CONCLUSION

All mutations are private except one mutation; p.Ile1254Phe was found in three unrelated families. Identification of a recurrent p.Ile1254Phe mutation suggests the presence of a common and unique mutation in our population. Our study also expands the mutational spectrum of the CPS1 gene.

HepPar-1 and Arginase-1 Immunohistochemistry in Adenocarcinoma of the Small Intestine and Ampullary Region

CONTEXT :HepPar-1 and Arginase-1 are urea cycle enzymes used to distinguish hepatocellular carcinoma from other carcinomas. HepPar-1, but not Arginase-1, is known to be immunoreactive with normal human small intestine.

OBJECTIVES

To better define and compare the immunohistochemical staining patterns of HepPar-1 and Arginase-1 in adenocarcinomas arising in the small intestine, including the ampullary region.

DESIGN

Staining for HepPar-1 and Arginase-1 was performed on 20 nonampullary small intestinal adenocarcinomas and 32 adenocarcinomas from the ampullary region. Ampullary adenocarcinomas were divided into intestinal morphology (15), pancreatobiliary morphology (14), and unclassifiable (3). Nonneoplastic small intestinal mucosa and colorectal adenocarcinomas were used as control groups.

RESULTS

HepPar-1 stained 12 of 20 nonampullary small intestinal adenocarcinomas, with a median of 63% of cells staining in positive cases. It also stained 11 of 15 ampullary carcinomas with intestinal morphology, with a median of 75% of cells staining in positive cases. Two of 14 ampullary carcinomas with pancreatobiliary morphology were positive for HepPar-1. Arginase-1 showed positivity in 2 ampullary region carcinomas and diffuse positivity in 1 duodenal adenocarcinoma. Two of 22 colorectal carcinomas stained for HepPar-1 with none positive for Arginase-1.

CONCLUSIONS

HepPar-1, but not Arginase-1, usually shows positivity in small intestinal adenocarcinomas and ampullary adenocarcinomas with intestinal morphology, but only rarely shows positivity in ampullary adenocarcinomas with pancreatobiliary morphology. HepPar-1 positivity in metastatic adenocarcinoma with intestinal morphology is suggestive of an upper gastrointestinal primary site.

Understanding carbamoyl phosphate synthetase (CPS1) deficiency by using the recombinantly purified human enzyme: effects of CPS1 mutations that concentrate in a central domain of unknown function

Carbamoyl phosphate synthetase 1 deficiency (CPS1D) is an inborn error of the urea cycle that is due to mutations in the CPS1 gene. In the first large repertory of mutations found in CPS1D, a small CPS1 domain of unknown function (called the UFSD) was found to host missense changes with high frequency, despite the fact that this domain does not host substrate-binding or catalytic machinery. We investigate here by in vitro expression studies using baculovirus/insect cells the reasons for the prominence of the UFSD in CPS1D, as well as the disease-causing roles and pathogenic mechanisms of the mutations affecting this domain. All but three of the 18 missense changes found thus far mapping in this domain in CPS1D patients drastically decreased the yield of pure CPS1, mainly because of decreased enzyme solubility, strongly suggesting misfolding as a major determinant of the mutations negative effects. In addition, the majority of the mutations also decreased from modestly to very drastically the specific activity of the fraction of the enzyme that remained soluble and that could be purified, apparently because they decreased V(max). Substantial although not dramatic increases in K(m) values for the substrates or for N-acetyl-L-glutamate were observed for only five mutations. Similarly, important thermal stability decreases were observed for three mutations. The results indicate a disease-causing role for all the mutations, due in most cases to the combined effects of the low enzyme level and the decreased activity. Our data strongly support the value of the present expression system for ascertaining the disease-causing potential of CPS1 mutations, provided that the CPS1 yield is monitored. The observed effects of the mutations have been rationalized on the basis of an existing structural model of CPS1. This model shows that the UFSD, which is in the middle of the 1462-residue multidomain CPS1 protein, plays a key integrating role for creating the CPS1 multidomain architecture leading us to propose here a denomination of "Integrating Domain" for this CPS1 region. The majority of these 18 mutations distort the interaction of this domain with other CPS1 domains, in many cases by causing improper folding of structural elements of the Integrating Domain that play key roles in these interactions.

Carbamoyl phosphate synthetase 1 deficiency in Italy: clinical and genetic findings in a heterogeneous cohort

Carbamoyl Phosphate Synthetase 1 deficiency (CPS1D) is a rare autosomal recessive urea cycle disorder, potentially leading to lethal hyperammonemia. Based on the age of onset, there are two distinct phenotypes: neonatal and late form. The CPS1 enzyme, located in the mitochondrial matrix of hepatocytes and epithelial cells of intestinal mucosa, is encoded by the CPS1 gene. At present more than 220 clear-cut genetic lesions leading to CPS1D have been reported. As most of them are private mutations diagnosis is complicated. Here we report an overview of the main clinical findings and biochemical and molecular data of 13 CPS1D Italian patients. In two of them, one with the neonatal form and one with the late form, cadaveric auxiliary liver transplant was performed. Mutation analysis in these patients identified 17 genetic lesions, 9 of which were new confirming their "private" nature. Seven of the newly identified mutations were missense/nonsense changes. In order to study their protein level effects, we performed an in silico analysis whose results indicate that the amino acid substitutions occur at evolutionary conserved positions and affect residues necessary for enzyme stability or function.

Loss of carbamoyl phosphate synthetase I in small-intestinal adenocarcinoma

Carbamoyl phosphate synthetase I (CPS1), normally found in hepatocytes and small-intestine (SI) enterocytes, is the antigen of Hep Par 1 antibody. Expression of CPS1 in invasive SI adenocarcinoma seems to be lost. We retrospectively collected 36 total specimens, which included 31 SI adenomas and 21 adenocarcinomas. We used 34 cases of duodenitis as a control group. Immunohistochemical and Western blot analyses were performed to determine CPS1 expression. The normal SI mucosa, all 34 cases of duodenitis, and all 29 adenomas with low-grade dysplasia demonstrated diffuse Hep Par 1 expression. Of the 21 invasive adenocarcinomas, 15 lost antigen expression (71%). These data are statistically significant (P < .05). Western blot analysis confirmed the immunohistochemical findings, with strong CPS1 expression within the normal mucosa and adenoma and complete loss in the invasive tumor. The differential expression of Hep Par 1 in dysplastic vs malignant tumors of the SI may be diagnostically useful in difficult cases.

The human neonatal small intestine has the potential for arginine synthesis; developmental changes in the expression of arginine-synthesizing and -catabolizing enzymes

Background

Milk contains too little arginine for normal growth, but its precursors proline and glutamine are abundant; the small intestine of rodents and piglets produces arginine from proline during the suckling period; and parenterally fed premature human neonates frequently suffer from hypoargininemia. These findings raise the question whether the neonatal human small intestine also expresses the enzymes that enable the synthesis of arginine from proline and/or glutamine. Carbamoylphosphate synthetase (CPS), ornithine aminotransferase (OAT), argininosuccinate synthetase (ASS), arginase-1 (ARG1), arginase-2 (ARG2), and nitric-oxide synthase (NOS) were visualized by semiquantitative immunohistochemistry in 89 small-intestinal specimens.

Results

Between 23 weeks of gestation and 3 years after birth, CPS- and ASS-protein content in enterocytes was high and then declined to reach adult levels at 5 years. OAT levels declined more gradually, whereas ARG-1 was not expressed. ARG-2 expression increased neonatally to adult levels. Neurons in the enteric plexus strongly expressed ASS, OAT, NOS1 and ARG2, while varicose nerve fibers in the circular layer of the muscularis propria stained for ASS and NOS1 only. The endothelium of small arterioles expressed ASS and NOS3, while their smooth-muscle layer expressed OAT and ARG2.

Conclusion

The human small intestine acquires the potential to produce arginine well before fetuses become viable outside the uterus. The perinatal human intestine therefore resembles that of rodents and pigs. Enteral ASS behaves as a typical suckling enzyme because its expression all but disappears in the putative weaning period of human infants.

Therapeutic use of citrulline in cardiovascular disease

L-citrulline is the natural precursor of L-arginine, substrate for nitric oxide synthase (NOS) in the production of NO. Supplemental administration L-arginine has been shown to be effective in improving NO production and cardiovascular function in cardiovascular diseases associated with endothelial dysfunction, such as hypertension, heart failure, atherosclerosis, diabetic vascular disease and ischemia-reperfusion injury, but the beneficial actions do not endure with chronic therapy. Substantial intestinal and hepatic metabolism of L-arginine to ornithine and urea by arginase makes oral delivery very ineffective. Additionally, all of these disease states as well as supplemental L-arginine enhance arginase expression and activity, thus reducing the effectiveness of L-arginine therapy. In contrast, L-citrulline is not metabolized in the intestine or liver and does not induce tissue arginase, but rather inhibits its activity. L-citrulline entering the kidney, vascular endothelium and other tissues can be readily converted to L-arginine, thus raising plasma and tissue levels of L-arginine and enhancing NO production. Supplemental L-citrulline has promise as a therapeutic adjunct in disease states associated with L-arginine deficiencies.

Citrobacter rodentium infection causes both mitochondrial dysfunction and intestinal epithelial barrier disruption in vivo: role of mitochondrial associated protein (Map)

Enteropathogenic Escherichia coli (EPEC) and enterohaemorrhagic E. coli are non-invasive attaching/effacing (A/E) bacterial pathogens that infect their host's intestinal epithelium, causing severe diarrhoeal disease. These bacteria utilize a type III secretion apparatus to deliver effector molecules into host cells, subverting cellular function. Mitochondrial associated protein (Map) is a multifunctional effector protein that targets host cell mitochondria and contributes to infection-induced epithelial barrier dysfunction in vitro. Unfortunately, the relevance of these actions to the pathogenesis of EPEC-induced disease is uncertain. Using Citrobacter rodentium, a mouse-adapted A/E bacterium, we found that Map colocalized with host cell mitochondria, and that in vivo infection led to a disruption of mitochondrial morphology in infected colonocytes as assessed by electron microscopy. Histochemical staining for the mitochondrial enzyme succinate dehydrogenase also revealed a significant loss of mitochondrial respiratory function in the infected intestinal epithelium; however, both pathologies were attenuated in mice infected with a Deltamap strain. C. rodentium Map was also implicated in the disruption of epithelial barrier function both in vitro and in vivo. These studies thus advance our understanding of how A/E pathogens subvert host cell functions and cause disease, demonstrating that Map contributes to the functional disruption of the intestinal epithelium during enteric infection by C. rodentium.

Modulated expression of a nuclear-associated glycoprotein during normal rat liver development and in various hepatoma cells

Liver plays a major role in systemic detoxification and drug metabolism. NF-164, a protein of 164 kDa predominantly localized in hepatocyte nuclei, was found to be present in increasing amounts during liver maturation. In addition, fetal rat hepatocytes had ten times, and neonatal five times less of this protein than adult hepatocytes. It was also detected in an albumin producing hepatoma cell line, but not in three other lines that have lost several differentiated functions. These data suggest that NF-164 expression is development-dependent and that it may be a marker for both normal and malignant hepatocyte differentiation. NF-164 seems to be liver-specific, since it was not detected in rat brain, spleen, kidney, lung and bovine thymus. It was purified from adult rat hepatocyte nuclei. Its estimated pI is 6.8. Its total amino acid composition and partial amino acid sequence is also being reported. Despite major differences between their respective contents in amino acids, partial sequences showed homologies with carbamyl phosphate synthetase I (CPSI). These observations may suggest that NF-164 also shares some functional features with this enzyme.

Specific responses in rat small intestinal epithelial mRNA expression and protein levels during chemotherapeutic damage and regeneration

The rapidly dividing small intestinal epithelium is very sensitive to the cytostatic drug methotrexate. We investigated the regulation of epithelial gene expression in rat jejunum during methotrexate-induced damage and regeneration. Ten differentiation markers were localized on tissue sections and quantified at mRNA and protein levels relative to control levels. We analyzed correlations in temporal expression patterns between markers. mRNA expression of enterocyte and goblet cell markers decreased significantly during damage for a specific period. Of these, sucrase-isomaltase (-62%) and CPS (-82%) were correlated. Correlations were also found between lactase (-76%) and SGLT1 (-77%) and between I-FABP (-52%) and L-FABP (-45%). Decreases in GLUT5 (-53%), MUC2 (-43%), and TFF3 (-54%) mRNAs occurred independently of any of the other markers. In contrast, lysozyme mRNA present in Paneth cells increased (+76%). At the protein level, qualitative and quantitative changes were in agreement with mRNA expression, except for Muc2 (+115%) and TFF3 (+81%), which increased significantly during damage, following independent patterns. During regeneration, expression of each marker returned to control levels. The enhanced expression of cytoprotective molecules (Muc2, TFF3, lysozyme) during damage represents maintenance of goblet cell and Paneth cell functions, most likely to protect the epithelium. Decreased expression of enterocyte-specific markers represents decreased enterocyte function, of which fatty acid transporters were least affected.

Cell-specific expression of mitochondrial carbonic anhydrase in the human and rat gastrointestinal tract

Mitochondrial carbonic anhydrase V (CA V) in liver provides HCO3- to pyruvate carboxylase for the first step in gluconeogenesis and HCO3- to carbamyl phosphate synthetase I for the first step in ureagenesis. Because carbamyl phosphate synthetase I and ornithine transcarbamylase are also expressed in enterocytes, we tested the hypothesis that CA V is expressed in the gastrointestinal tract in addition to liver. Polyclonal rabbit antisera were raised against a polypeptide of 17 C-terminal amino acids of human CA V and against purified recombinant mouse isozyme and were used in Western blotting and immunoperoxidase staining of human and rat tissues. Immunohistochemistry showed that CA V is expressed cell-specifically in the alimentary canal mucosa from stomach to rectum. Immunoreactions for CA V were detected in the parietal cells and gastrin-producing G-cells of the stomach and in intestinal enterocytes. Western blotting of human and rat gastrointestinal tissues with isozyme-specific antibodies showed positive signals for CA V with the expected molecular mass. The findings in human tissues paralleled those in rat. The cell-specific pattern of CA V expression suggests a role for CA V in alimentary canal physiology. We propose that mitochondrial CA V participates in the detoxification of ammonia produced in the gastrointestinal tract by providing bicarbonate to carbamyl phosphate synthetase I. (J Histochem Cytochem 47:517-524, 1999)

Tissue-selective expression of enzymes of arginine synthesis

Arginine is a non-essential amino acid in mammals as judged from nitrogen balance study. Citrulline is synthesized from glutamate in the small intestine, whilst kidneys and some other tissues convert citrulline to arginine. Ornithine transcarbamylase and carbamylphosphate synthetase are expressed in liver and small intestine. Tissue-selective expression depends on the regulatory elements in the promoter, or far 5', region of these genes to which tissue-selective transcription factors bind and activate transcription. Argininosuccinate synthetase and argininosuccinate lyase do not appear to have such elements, therefore their expression is more or less ubiquitous. The selective expression of pyrroline-5-carboxylate synthase activity in the intestine remains to be clarified.