Coordinate developmental regulation of purine catabolic enzyme expression in gastrointestinal and postimplantation reproductive tracts

Metabolomics in endometriosis: challenges and perspectives for future studies

Endometriosis is a complex disease characterized by inflammation and the growth of endometrial- like glands and stroma outside the uterine cavity. The pathophysiology of endometriosis is not entirely understood, however, with a prevalence of ~10% of women in their reproductive years, the disease symptoms significantly affect the quality of life of millions of women globally. Metabolomic studies have previously identified specific metabolites that could be a signature of endometriosis. This approach could potentially be used as a non-invasive tool for early diagnosis and provide a better understanding of endometriosis pathophysiology. This review aims to provide insight as to how endometriosis affects the metabolome by reviewing different studies that have used this approach to design follow-up studies. The search query included the term 'endometriosis' in combination with 'metabolomics', 'lipidomics', or 'sphingolipidomics' published between 2012 and 2020. We included studies in humans and animal models. Most studies reported differences in the metabolome of subjects with endometriosis in comparison to healthy controls and used samples taken from serum, endometrial tissue, follicular fluid, urine, peritoneal fluid, or endometrial fluid. Statistically significant metabolites contributed to group separation between patients and healthy controls. Reported metabolites included amino acids, lipids, organic acids, and other organic compounds. Differences in methods, analytical techniques, and the presence of confounding factors can interfere with results and interpretation of data. Metabolomics seems to be a promising tool for identifying significant metabolites in patients with endometriosis. Nonetheless, more investigation is needed in order to understand the significance of the study results.

Lay summary

Endometriosis is a chronic disease affecting the quality of life in one out of every ten women during their reproductive years, causing pain and infertility. It is characterized by inflammation and growth of tissue like the endometrium (uterus lining) outside the uterine cavity. Studies have searched for a predictor of endometriosis-associated changes by observing small molecules necessary for metabolism on a large scale (metabolomics). Metabolomics could serve to resolve one of the biggest challenges that patients with endometriosis face: a delay in diagnosis. In this review, the authors summarize identified potential biomarkers from various bodily fluids and tissues that are characteristic of metabolic processes observed in endometriosis. Biomarkers include cell growth, cell survival, high energy demand, oxidative stress, and fatty acid levels. A metabolomics approach offers promise as a non-invasive tool to identify significant metabolite changes in patients with endometriosis, potentially leading to earlier diagnoses and new opportunities for back-translational strategies.

Combination of urine and faeces metabolomics to reveal the intervention mechanism of Polygala tenuifolia compatibility with Magnolia officinalis on gastrointestinal motility disorders

OBJECTIVES

To explore the intervention mechanism of combining Polygala tenuifolia (PT) with Magnolia officinalis (MO) on gastrointestinal motility disorders caused by PT.

METHODS

Urine and faeces of rats were collected; the effects of PT and MO on the gastric emptying and small intestine advancing rates in mice were analysed via ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) to determine the potential metabolites. Changes in the metabolic profiles of the urine and faeces were revealed by untargeted metabolomics, followed by multivariate statistical analysis. The integration of urine and faeces was applied to reveal the intervention mechanism of PT-MO on PT-induced disorders.

KEY FINDINGS

PT + MO (1:2) improved the gastrointestinal function in mice suffering from PT-induced gastrointestinal motility disorder. Metabolomics indicated that the PT-MO mechanism was mainly associated with the regulations of 17 and 12 metabolites and 11 and 10 pathways in urine and faeces, respectively. The common metabolic pathways were those of tyrosine, purine, tricarboxylic acid cycle, pyruvate and gluconeogenesis, which were responsible for the PT-MO intervention mechanism.

CONCLUSIONS

The PT-MO (1:2) couple mechanism mitigated the PT-induced disorders, which were related to the energy, amino acid and fatty metabolisms.

Zonation of Ribosomal DNA Transcription Defines a Stem Cell Hierarchy in Colorectal Cancer

Colorectal cancers (CRCs) are composed of an amalgam of cells with distinct genotypes and phenotypes. Here, we reveal a previously unappreciated heterogeneity in the biosynthetic capacities of CRC cells. We discover that the majority of ribosomal DNA transcription and protein synthesis in CRCs occurs in a limited subset of tumor cells that localize in defined niches. The rest of the tumor cells undergo an irreversible loss of their biosynthetic capacities as a consequence of differentiation. Cancer cells within the biosynthetic domains are characterized by elevated levels of the RNA polymerase I subunit A (POLR1A). Genetic ablation of POLR1A-high cell population imposes an irreversible growth arrest on CRCs. We show that elevated biosynthesis defines stemness in both LGR5⁺ and LGR5^- tumor cells. Therefore, a common architecture in CRCs is a simple cell hierarchy based on the differential capacity to transcribe ribosomal DNA and synthesize proteins.

Endometrium metabolomic profiling reveals potential biomarkers for diagnosis of endometriosis at minimal-mild stages

BACKGROUND

The sensitivity and specificity of non-invasive diagnostic methods for endometriosis, especially at early stages, are not optimal. The clinical diagnostic indicator cancer antigen 125 (CA125) performs poorly in the diagnosis of minimal endometriosis, with a sensitivity of 24%. Therefore, it is urgent to explore novel diagnostic biomarkers. We evaluated the metabolomic profile variation of the eutopic endometrium between minimal-mild endometriosis patients and healthy women by ultra-high-performance liquid chromatography coupled with electrospray ionization high-resolution mass spectrometry (UHPLC-ESI-HRMS).

METHODS

Our study comprised 29 patients with laparoscopically confirmed endometriosis at stages I-II and 37 infertile women who underwent diagnostic laparoscopy combined with hysteroscopy from January 2014 to January 2015. Eutopic endometrium samples were collected by pipelle endometrial biopsy. The metabolites were quantified by UHPLC-ESI-HRMS. The best combination of biomarkers was then selected by performing step-wise logistic regression analysis with backward elimination.

RESULTS

Twelve metabolites were identified as endometriosis-associated biomarkers. The eutopic endometrium metabolomic profile of the endometriosis patients was characterized by a significant increase in the concentration of hypoxanthine, L-arginine, L-tyrosine, leucine, lysine, inosine, omega-3 arachidonic acid, guanosine, xanthosine, lysophosphatidylethanolamine and asparagine. In contrast, the concentration of uric acid was decreased. Metabolites were filtered by step-wise logistic regression with backward elimination, and a model containing uric acid, hypoxanthine, and lysophosphatidylethanolamine was constructed. Receiver-operating characteristic (ROC) analysis confirmed the prognostic value of these parameters for the diagnosis of minimal/mild endometriosis with a sensitivity of 66.7% and a specificity of 90.0%.

CONCLUSIONS

Metabolomics analysis of the eutopic endometrium in endometriosis was effectively characterized by UHPLC-ESI-HRMS-based metabolomics. Our study supports the importance of purine and amino acid metabolites in the pathophysiology of endometriosis and provides potential biomarkers for semi-invasive diagnosis of early-stage endometriosis.

Alterations in the brain adenosine metabolism cause behavioral and neurological impairment in ADA-deficient mice and patients

Adenosine Deaminase (ADA) deficiency is an autosomal recessive variant of severe combined immunodeficiency (SCID) caused by systemic accumulation of ADA substrates. Neurological and behavioral abnormalities observed in ADA-SCID patients surviving after stem cell transplantation or gene therapy represent an unresolved enigma in the field. We found significant neurological and cognitive alterations in untreated ADA-SCID patients as well as in two groups of patients after short- and long-term enzyme replacement therapy with PEG-ADA. These included motor dysfunction, EEG alterations, sensorineural hypoacusia, white matter and ventricular alterations in MRI as well as a low mental development index or IQ. Ada-deficient mice were significantly less active and showed anxiety-like behavior. Molecular and metabolic analyses showed that this phenotype coincides with metabolic alterations and aberrant adenosine receptor signaling. PEG-ADA treatment corrected metabolic adenosine-based alterations, but not cellular and signaling defects, indicating an intrinsic nature of the neurological and behavioral phenotype in ADA deficiency.

Functional analysis of purine nucleoside phosphorylase as a key enzyme in ribavirin metabolism

Ribavirin is a purine nucleoside analogue that possesses potent anti-hepatitis C virus activity, and it has long been considered likely that ribavirin undergoes a first-pass metabolism at the small intestine. Although purine nucleoside phosphorylase (PNP) is assumed to be involved in this metabolism, this has not been conclusively demonstrated. Furthermore, no pharmacogenomic studies related to PNP-mediated ribavirin phosphorolysis have previously been conducted. In this study, we sought to identify the role of PNP in ribavirin phosphorolysis in the human small intestine, and to clarify the effect of the single nucleotide polymorphism (rs1049564) on PNP's ribavirin phosphorolysis activity. The results of our investigations show that PNP is abundantly expressed in the human small intestine, and that intestinal ribavirin phosphorolysis is severely inhibited by ganciclovir, a PNP-inhibitor. Therefore, PNP is likely to play a primary role in the ribavirin phosphorolysis in the human small intestine. On the other hand, the results of our attempt to clarify the function of rs1049564 show that it does not affect PNP's ribavirin phosphorolysis activity. We believe that the present study will facilitate further pharmacogenomic and biochemical characterization of PNP as a key metabolic enzyme of ribavirin.

Effect of asynchronous transfer on bovine embryonic development and relationship with early cycle uterine proteome profiles

The uterus provides the nurturing environment that supports the growth of the early preimplantation bovine conceptus. To determine critical time points of uterine influence, in vitro-produced Day 7 blastocysts were transferred into synchronous (Day 7) uteri and asynchronous uteri (Days 5 or 9). Embryo growth was evaluated 7 and 15 days after transfer and compared with that of embryos generated by AI. Conceptuses recovered from asynchronous Day 9 transfers were fourfold larger than synchronous transfer or gestational Day 14 AI conceptuses; by 15 days after transfer, differences were less marked. Two-dimensional gel electrophoresis was used to compare the histotroph protein composition of uterine luminal flushings (ULF) on Days 5 and 9 after oestrous to determine any protein differences that would promote embryo growth. The ULF were collected by serially flushing the uteri of the same heifers and mature cows at different times of the cycle. Ten proteins that differed in abundance between Day 5 and 9 were identified by mass spectrometry. Three, namely phosphoserine aminotransferase 1, purine nucleoside phosphorylase and aldose reductase, were verified by western blot analysis as more abundant on Day 9 (P < 0.002). Myostatin was present in only in Day 9 ULF, whereas tissue inhibitor of matrix metalloproteinase 2 (TIMP2) and legumain were only detected in Day 14 ULF. Although mature cows had lower progesterone concentrations on Days 5 and 14 (P < 0.05) and tended to have less TIMP2 than heifer groups, no other protein differences were detected. Thus, the embryo growth-enhancing environment on Day 9 was associated with temporal changes in the expression of several proteins of the histotroph.

Endogenous luminal surface adenosine signaling regulates duodenal bicarbonate secretion in rats

Luminal ATP increases duodenal bicarbonate secretion (DBS) via brush border P2Y receptors. Because ATP is sequentially dephosphorylated to adenosine (ADO) and the brush border highly expresses adenosine deaminase (ADA), we hypothesized that luminal [ADO] regulators and sensors, including P1 receptors, ADA, and nucleoside transporters (NTs) regulate DBS. We measured DBS with pH and CO(2) electrodes, perfusing ADO ± adenosine receptor agonists or antagonists or the cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTR(inh)-172 on DBS. Furthermore, we examined the effect of inhibitors of ADA or NT on DBS. Perfusion of AMP or ADO (0.1 mM) uniformly increased DBS, whereas inosine had no effect. The A(1/2) receptor agonist 5'-(N-ethylcarboxamido)-adenosine (0.1 mM) increased DBS, whereas ADO-augmented DBS was inhibited by the potent A(2B) receptor antagonist N-(4-cyanophenyl)-2-[4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)phenoxy]-acetamide (MRS1754) (10 μM). Other selective adenosine receptor agonists or antagonists had no effect. The A(2B) receptor was immunolocalized to the brush border membrane of duodenal villi, whereas the A(2A) receptor was immunolocalized primarily to the vascular endothelium. Furthermore, ADO-induced DBS was enhanced by 2'-deoxycoformycin (1 μM) and formycin B (0.1 mM), but not by S-(4-nitrobenzyl)-6-thioinosine (0.1 mM), and it was abolished by CFTR(inh)-172 pretreatment (1 mg/kg i.p). Moreover, ATP (0.1 mM)-induced DBS was partially reduced by (1R,2S,4S,5S)-4-2-iodo-6-(methylamino)-9H-purin-9-yl]-2-(phosphonooxy)bicyclo[3.1.0]hexane-1-methanol dihydrogen phosphate ester tetraammonium salt (MRS2500) or 8-[4-[4-(4-chlorophenzyl)piperazide-1-sulfonyl)phenyl]]-1-propylxanthine (PSB603) and abolished by both, suggesting that ATP is sequentially degraded to ADO. Luminal ADO stimulates DBS via A(2B) receptors and CFTR. ATP release, ecto-phosphohydrolases, ADA, and concentrative NT may coordinately regulate luminal surface ADO concentration to modulate ADO-P1 receptor signaling in rat duodenum.

Identification and functional characterization of the first nucleobase transporter in mammals: implication in the species difference in the intestinal absorption mechanism of nucleobases and their analogs between higher primates and other mammals

Nucleobases are important compounds that constitute nucleosides and nucleic acids. Although it has long been suggested that specific transporters are involved in their intestinal absorption and uptake in other tissues, none of their molecular entities have been identified in mammals to date. Here we describe identification of rat Slc23a4 as the first sodium-dependent nucleobase transporter (rSNBT1). The mRNA of rSNBT1 was expressed highly and only in the small intestine. When transiently expressed in HEK293 cells, rSNBT1 could transport uracil most efficiently. The transport of uracil mediated by rSNBT1 was sodium-dependent and saturable with a Michaelis constant of 21.2 microM. Thymine, guanine, hypoxanthine, and xanthine were also transported, but adenine was not. It was also suggested by studies of the inhibitory effect on rSNBT1-mediated uracil transport that several nucleobase analogs such as 5-fluorouracil are recognized by rSNBT1, but cytosine and nucleosides are not or only poorly recognized. Furthermore, rSNBT1 fused with green fluorescent protein was mainly localized at the apical membrane, when stably expressed in polarized Madin-Darby canine kidney II cells. These characteristics of rSNBT1 were almost fully in agreement with those of the carrier-mediated transport system involved in intestinal uracil uptake. Therefore, it is likely that rSNBT1 is its molecular entity or at least in part responsible for that. It was also found that the gene orthologous to the rSNBT1 gene is genetically defective in humans. This may have a biological and evolutional meaning in the transport and metabolism of nucleobases. The present study provides novel insights into the specific transport and metabolism of nucleobases and their analogs for therapeutic use.

Effect of a Soy Protein-Based Diet on Ribonucleic Acid Metabolism in the Small Intestinal Mucosa of Goat Kids

This study was designed to investigate the effect of soy protein inclusion in milk replacer diets for goat kids on protein, RNA, and DNA contents in small intestinal mucosa, on the importance of RNA biosynthesis from dietary RNA precursors for mucosal RNA synthesis, and on the activities of enzymes involved in nucleotide degradation in small intestinal mucosa. Diets were based on cow's milk. In the control group, 35% of the milk protein was replaced by casein (CN) protein, and in the soy group (SPAA), the same amount of milk protein was replaced by soy protein supplemented with essential AA known to be at lower concentrations in soy than in CN (Thr, Val, Ile, Leu, His, Lys, Met). Diets were isonitrogenous and isoenergetic. At 47 d of age, goats were harvested and samples of proximal, middle, and distal jejunal mucosa were collected 5 h after feeding 15N-labeled RNA from yeast (13 mg/kg of body weight). Growth and feed conversion did not differ between the control and SPAA kids. Mucosal protein concentrations were lower in the SPAA than the control kids. Concentrations of RNA and DNA did not differ between feeding groups, but in all kids mucosal RNA concentrations were higher in proximal than in middle and distal jejunum. Protein:RNA ratios were higher in the control than the SPAA kids and were lowest in proximal jejunum. Activities of alkaline phosphatase in enterocytes were higher in proximal than in middle and distal jejunum. Activities of mucosal xanthine oxidase were highest in distal jejunum and were higher in the SPAA than the control kids, especially in the middle and distal sites. The 15N-enrichment of mucosal RNA was higher in the control than the SPAA kids, especially in distal jejunum, and was lowest in distal jejunum. In contrast, 15N-enrichment of urea in plasma tended to be higher and Gly concentration in plasma was lower in the SPAA than the control kids. Data indicate that protein content and the protein:RNA ratio were lower in jejunal mucosa of goat kids fed milk replacer with partial replacement of CN protein by soy protein. These findings were accompanied by a lower level of reutilization of preformed dietary RNA precursors for RNA biosynthesis in jejunal mucosa and a higher activity of xanthine oxidase. Thus, feeding soy protein instead of CN protein reduced the incorporation of preformed dietary RNA precursors for RNA biosynthesis in the mucosa and activated key enzymes involved in nucleic acid breakdown.

Exogenous nucleic acids and nucleotides are efficiently hydrolysed and taken up as nucleosides by intestinal explants from suckling piglets

Human milk is a rich source of RNA, free nucleotides (NT) and nucleosides (NS). To determine the uptake of different NS sources by the intestinal epithelium, jejunal explants from suckling piglets were cultured in a medium supplemented with a mixture of NS (adenosine, cytidine, guanosine, inosine, uridine; 10 mg/l each), a mixture of five NT (AMP, CMP, GMP, IMP, UMP; 7 mg/l each) or RNA (60 mg/l), respectively. Aliquots from the media were taken at different times (0.5, 2, 5, 15, 30, 60, 180 min). NS and NT concentrations were analysed in the different supernatants at those periods using solid-phase extraction followed by HPLC. When explants were cultured in the presence of NS the concentration of these compounds, excepting cytidine, rapidly decreased, suggesting that they are efficiently taken up. When explants were incubated in the presence of NT, the total concentration of these compounds decreased while the total concentration of NS increased, suggesting that enterocytes efficiently hydrolyse NT into NS. Likewise, when explants were incubated in the presence of RNA, the total concentration of both NT and NS increased, indicating that intestinal explants are able to hydrolyse RNA to NT and then to NS in the absence of luminal enzymes. In conclusion, the jejunum of piglets at weaning is able to hydrolyse RNA and free NT to NS, and NS, excepting cytidine, are efficiently taken up by the small intestine. These results suggest that the current concentration of NT used to supplement infant formulas should be reconsidered.

Temporal regulation of enhancer function in intestinal epithelium: a role for Onecut factors

An intestine-specific gene regulatory region was previously identified near the second exon of the human adenosine deaminase (ADA) gene. In mammalian intestine, ADA is expressed at high levels only along the villi of the duodenal epithelium, principally if not exclusively in enterocytes. Within the ADA intestinal regulatory region, a potent duodenum-specific enhancer was identified that controls this pattern of expression. This enhancer has been shown to rely on PDX-1, GATA factors, and Cdx factors for its function. Upstream of the enhancer, a separate temporal regulatory region was identified that has no independent enhancer capability but controls the timing of enhancer activation. DNase I footprinting and electrophoretic mobility shift assays were used to begin to characterize temporal region function at the molecular level. In this manner, binding sites for the Onecut (OC) family of factors, YY1, and NFI family members were identified. Identification of the OC site was especially interesting, because almost nothing is known about the function of OC factors in intestine. In transgenic mice, mutation of the OC site to ablate binding resulted in a delay of 2-3 weeks in enhancer activation in the developing postnatal intestine, a result very similar to that observed previously when the entire temporal region was deleted. In mammals, the OC family is comprised of OC-1/HNF-6, OC-2, and OC-3. An examination of intestinal expression patterns showed that all three OC factors are expressed at detectable levels in adult mouse duodenum, with OC-2 predominant. In postnatal day 2 mice only OC-2 and OC-3 were detected in intestine, with OC-2 again predominant.

Pentose phosphates in nucleoside interconversion and catabolism

Ribose phosphates are either synthesized through the oxidative branch of the pentose phosphate pathway, or are supplied by nucleoside phosphorylases. The two main pentose phosphates, ribose-5-phosphate and ribose-1-phosphate, are readily interconverted by the action of phosphopentomutase. Ribose-5-phosphate is the direct precursor of 5-phosphoribosyl-1-pyrophosphate, for both de novo and 'salvage' synthesis of nucleotides. Phosphorolysis of deoxyribonucleosides is the main source of deoxyribose phosphates, which are interconvertible, through the action of phosphopentomutase. The pentose moiety of all nucleosides can serve as a carbon and energy source. During the past decade, extensive advances have been made in elucidating the pathways by which the pentose phosphates, arising from nucleoside phosphorolysis, are either recycled, without opening of their furanosidic ring, or catabolized as a carbon and energy source. We review herein the experimental knowledge on the molecular mechanisms by which (a) ribose-1-phosphate, produced by purine nucleoside phosphorylase acting catabolically, is either anabolized for pyrimidine salvage and 5-fluorouracil activation, with uridine phosphorylase acting anabolically, or recycled for nucleoside and base interconversion; (b) the nucleosides can be regarded, both in bacteria and in eukaryotic cells, as carriers of sugars, that are made available though the action of nucleoside phosphorylases. In bacteria, catabolism of nucleosides, when suitable carbon and energy sources are not available, is accomplished by a battery of nucleoside transporters and of inducible catabolic enzymes for purine and pyrimidine nucleosides and for pentose phosphates. In eukaryotic cells, the modulation of pentose phosphate production by nucleoside catabolism seems to be affected by developmental and physiological factors on enzyme levels.

The emerging role of adenosine deaminases in insects

Adenosine deaminases catalyze the deamination of adenosine and deoxyadenosine into their respective inosine nucleosides. Recent sequencing of the genomes of several model organisms and human reveal that Metazoa usually have more than one adenosine deaminase gene. A deficiency in the gene encoding the major enzyme is lethal in mouse and Drosophila and leads to severe combined deficiency (SCID) in human. In these organisms, enzyme deficiency causes increased adenosine/deoxyadenosine concentration in body fluids and some organs. Elevated levels of adenosine and deoxyadenosine are toxic to certain mammalian and insect cells, and it was shown for human and mouse that it is a primary cause of pathophysiological effects. Data suggest that the major role of adenosine deaminases in various taxa is the protection of tissues against increased levels of adenosine and deoxyadenosine. This review also discusses potential roles of adenosine deaminases in Drosophila metamorphosis and the employment of a Drosophila model to study the cell-specific toxicity of elevated nucleoside levels.

Cdx binding determines the timing of enhancer activation in postnatal duodenum

In mammalian intestine, adenosine deaminase (ADA) is expressed at high levels only along the villi of the duodenal epithelium. A duodenum-specific enhancer identified in the second intron of the human ADA gene controls this pattern of expression. This enhancer faithfully recapitulates this expression pattern in transgenic mice, when included in CAT reporter gene constructions. Multiple binding sites for PDX-1 and GATA factors were previously identified within the approximately 300-bp region that encompasses the enhancer. Mutation analyses demonstrated that binding of PDX-1 and of GATA-4 was absolutely essential for enhancer function. In the present study, we have identified additional enhancer binding sites for Cdx factors, for YY1, and for NFI family members. Detailed EMSA studies were used to confirm binding at these sites. This brings the number of confirmed binding sites within the enhancer to thirteen, with five different factors or family of factors contributing to the putative enhanceosome complex. Mutation analysis was utilized to examine the specific roles of the newly identified sites. Two sites were identified that bound both Cdx1 and Cdx2. Mutations were identified in these two sites that completely and specifically eliminated Cdx binding. In transgenic mice, these enhancer mutations dramatically changed the developmental timing of enhancer activation (delaying it by 2-3 weeks) without affecting other aspects of enhancer function. In the chromatin context of certain transgenic insertion sites, mutation of the two YY1 sites to specifically ablate binding caused a delay in enhancer activation similar to that observed with the Cdx mutations. No overt changes were observed from mutation of the NFI site.

Adenosine Deaminase Deficiency: Metabolic Basis of Immune Deficiency and Pulmonary Inflammation

Genetic deficiencies in the purine catabolic enzyme adenosine deaminase (ADA) in humans results primarily in a severe lymphopenia and immunodeficiency that can lead to the death of affected individuals early in life. The metabolic basis of the immunodeficiency is likely related to the sensitivity of lymphocytes to the accumulation of the ADA substrates adenosine and 2'-deoxyadenosine. Investigations using ADA-deficient mice have provided compelling evidence to support the hypothesis that T and B cells are sensitive to increased concentrations of 2'-deoxyadenosine that kill cells through mechanisms that involve the accumulation of dATP and the induction of apoptosis. In addition to effects on the developing immune system, ADA-deficient humans exhibit phenotypes in other physiological systems including the renal, neural, skeletal, and pulmonary systems. ADA-deficient mice develop similar abnormalities that are dependent on the accumulation of adenosine and 2'-deoxyadenosine. Detailed analysis of the pulmonary insufficiency seen in ADA-deficient mice suggests that the accumulation of adenosine in the lung can directly access cellular signaling pathways that lead to the development and exacerbation of chronic lung disease. The ability of adenosine to regulate aspects of chronic lung disease is likely mediated by specific interactions with adenosine receptor subtypes on key regulatory cells. Thus, the examination of ADA deficiency has identified the importance of purinergic signaling during lymphoid development and in the regulation of aspects of chronic lung disease.

Iron supplementation during infancy—effects on expression of iron transporters, iron absorption, and iron utilization in rat pups

BACKGROUND

Studies conducted in human infants suggest developmental changes in the regulation of iron absorption; however, little is known about the molecular mechanisms regulating iron absorption during infancy. Two intestinal iron transporters, divalent metal transporter 1 (DMT1) and ferroportin 1 (FPN1), were recently identified.

OBJECTIVE

The objective was to investigate at a molecular level the regulation of iron absorption during infancy in a rat pup model. We examined the developmental expression of DMT1 and FPN1 and the effects of iron supplementation on their expression and on iron absorption and utilization during infancy.

DESIGN

Rat pups were given daily oral doses of 0, 30, or 150 microg Fe from day 2 to day 20 after birth. On days 10 and 20 after birth, (59)Fe absorption, tissue minerals, and intestinal DMT1, FPN1, and ferritin expression were examined. To assess developmental expression, DMT1 and FPN1 were examined in control rats from days 1 to 50 after birth.

RESULTS

Intestinal DMT1 and FPN1 were significantly affected by age; expression increased dramatically by day 40. On day 10, no significant effect of iron supplementation on DMT1 and FPN1 gene expression or on iron absorption was observed. By day 20, DMT1 and FPN1 expression and iron absorption had decreased significantly with iron supplementation.

CONCLUSIONS

During early infancy, rat pups are unable to down-regulate intestinal iron transporters or iron absorption in response to iron supplementation, whereas down-regulation occurs during late infancy. The current findings provide evidence of the developmental regulation of iron absorption, which emphasizes the need for caution when giving iron supplements to infants at an early age.

Expression profiling of endometrium from women with endometriosis reveals candidate genes for disease-based implantation failure and infertility

Endometriosis is clinically associated with pelvic pain and infertility, with implantation failure strongly suggested as an underlying cause for the observed infertility. Eutopic endometrium of women with endometriosis provides a unique experimental paradigm for investigation into molecular mechanisms of reproductive dysfunction and an opportunity to identify specific markers for this disease. We applied paralleled gene expression profiling using high-density oligonucleotide microarrays to investigate differentially regulated genes in endometrium from women with vs. without endometriosis. Fifteen endometrial biopsy samples (obtained during the window of implantation from eight subjects with and seven subjects without endometriosis) were processed for expression profiling on Affymetrix Hu95A microarrays. Data analysis was conducted with GeneChip Analysis Suite, version 4.01, and GeneSpring version 4.0.4. Nonparametric testing was applied, using a P value of 0.05, to assess statistical significance. Of the 12,686 genes analyzed, 91 genes were significantly increased more than 2-fold in their expression, and 115 genes were decreased more than 2-fold. Unsupervised clustering demonstrated down-regulation of several known cell adhesion molecules, endometrial epithelial secreted proteins, and proteins not previously known to be involved in the pathogenesis of endometriosis, as well as up-regulated genes. Selected dysregulated genes were randomly chosen and validated with RT-PCR and/or Northern/dot-blot analyses, and confirmed up-regulation of collagen alpha2 type I, 2.6-fold; bile salt export pump, 2.0-fold; and down-regulation of N-acetylglucosamine-6-O-sulfotransferase (important in synthesis of L-selectin ligands), 1.7-fold; glycodelin, 51.5-fold; integrin alpha2, 1.8-fold; and B61 (Ephrin A1), 4.5-fold. Two-way overlapping layer analysis used to compare endometrial genes in the window of implantation from women with and without endometriosis further identified three unique groups of target genes, which differ with respect to the implantation window and the presence of disease. Group 1 target genes are up-regulated during the normal window of implantation but significantly decreased in women with endometriosis: IL-15, proline-rich protein, B61, Dickkopf-1, glycodelin, N-acetylglucosamine-6-O-sulfotransferase, G0S2 protein, and purine nucleoside phosphorylase. Group 2 genes are normally down-regulated during the window of implantation but are significantly increased with endometriosis: semaphorin E, neuronal olfactomedin-related endoplasmic reticulum localized protein mRNA and Sam68-like phosphotyrosine protein alpha. Group 3 consists of a single gene, neuronal pentraxin II, normally down-regulated during the window of implantation and further decreased in endometrium from women with endometriosis. The data support dysregulation of select genes leading to an inhospitable environment for implantation, including genes involved in embryonic attachment, embryo toxicity, immune dysfunction, and apoptotic responses, as well as genes likely contributing to the pathogenesis of endometriosis, including aromatase, progesterone receptor, angiogenic factors, and others. Identification and validation of selected genes and their functions will contribute to uncovering previously unknown mechanism(s) underlying implantation failure in women with endometriosis and infertility, mechanisms underlying the pathogenesis of endometriosis and providing potential new targets for diagnostic screening and intervention.

High-level activation by a duodenum-specific enhancer requires functional GATA binding sites

The purine metabolic gene adenosine deaminase (ADA) is expressed at high levels in a well-defined spatiotemporal pattern in the villous epithelium of proximal small intestine. A duodenum-specific enhancer module responsible for this expression pattern has been identified in the second intron of the human ADA gene. It has previously been shown that binding of the factor PDX-1 is essential for function of this enhancer. The studies presented here examine the proposed roles of GATA factors in the enhancer. Site-directed mutagenesis of the enhancer's GATA binding sites crippled enhancer function in 10 lines of transgenic mice, with 9 of the lines demonstrating <1% of normal activity. Detailed studies along the longitudinal axis of mouse small intestine indicate that GATA-4 and GATA-5 mRNA levels display a reciprocal pattern, with low levels of GATA-6 throughout. Interestingly, gel shift studies with duodenal nuclear extracts showed binding only by GATA-4.

Ribonucleic acid hydrolysis by intestinal explants of neonatal piglets

BACKGROUND

Healthy human adults are able to hydrolyze dietary nucleic acids and nucleotides in the gastrointestinal tract, thus facilitating absorption of the resulting nucleosides. However, little is directly known of the ability of infants to hydrolyze nucleic acids early in life.

METHODS

Purified RNA (50, 100, 250, and 500 mg/L) in a suitable medium was exposed to jejunal explants of weaning piglets to determine if enzymes expressed by the explants were sufficient to hydrolyze the nucleic acid. Aliquots from the media were taken at time intervals, from 0 to 6 hours, and assayed for ribonucleoside content by high-performance liquid chromatography.

RESULTS

The investigators found a significant increase of free ribonucleosides during the study period and for all RNA concentrations tested, thus suggesting that intestinal explants are able to hydrolyze RNA. The kinetics of nucleoside concentrations varied for each nucleoside. For example, inosine increased over the entire 6-hour period and adenosine increased for the first 2 hours, decreasing afterward.

CONCLUSIONS

It is concluded that cells from the intestinal epithelium are capable of hydrolyzing RNA. These results suggest that RNA present in human milk is hydrolyzed in the intestinal tract of the breast-fed infant, thus providing an additional source of nucleosides. The results indicate that current supplementation of infant formulas with nucleotides should be reconsidered to take into account the contribution of RNA present in human milk to the pool of bioavailable nucleotides.

Pdx-1 is required for activation in vivo from a duodenum-specific enhancer

The purine metabolic gene adenosine deaminase (ADA) is expressed along a defined spatiotemporal pattern in the developing mammalian small intestine, where high-level expression is limited to the villous epithelium of the duodenum. This activation is observed in rodents as the intestine completes the final maturation resulting in adult crypt-villus structures at 2-3 weeks postpartum. A regulatory module responsible for this pattern of expression has been identified in the second intron of the human ADA gene. Of the multiple duodenal proteins that can interact with this small duodenal enhancer region, the studies contained in this work describe the identification of five of these proteins as the dispersed homeobox protein PDX-1. This transcription factor exhibits a profile of expression in the small intestine similar to that observed for ADA, making it an ideal candidate factor for the duodenum-specific ADA enhancer. Loss of PDX-1 binding, via a PDX-1 mutated enhancer transgenic construction, resulted in complete loss of high-level activation in the duodenum, demonstrating the absolute requirement for this factor in vivo. However, co-transfection experiments suggest that other proteins that bind the enhancer are also required for enhancer function because PDX-1 alone was incapable of significant transactivation.

Adenosine deaminase: functional implications and different classes of inhibitors

Adenosine deaminase (ADA) is an enzyme of the purine metabolism which catalyzes the irreversible deamination of adenosine and deoxyadenosine to inosine and deoxyinosine, respectively. This ubiquitous enzyme has been found in a wide variety of microorganisms, plants, and invertebrates. In addition, it is present in all mammalian cells that play a central role in the differentiation and maturation of the lymphoid system. However, despite a number of studies performed to date, the physiological role played by ADA in the different tissues is not clear. Inherited ADA deficiency causes severe combined immunodeficiency disease (ADA-SCID), in which both B-cell and T-cell development is impaired. ADA-SCID has been the first disorder to be treated by gene therapy, using polyethylene glycol-modified bovine ADA (PEG-ADA). Conversely, there are several diseases in which the level of ADA is above normal. A number of ADA inhibitors have been designed and synthesized, classified as ground-state and transition-state inhibitors. They may be used to mimic the genetic deficiency of the enzyme, in lymphoproliferative disorders or immunosuppressive therapy (i.e., in graft rejection), to potentiate the effect of antileukemic or antiviral nucleosides, and, together with adenosine kinase, to reduce breakdown of adenosine in inflammation, hypertension, and ischemic injury.

Nutritional regulation of nucleoside transporter expression in rat small intestine

BACKGROUND & AIMS

Concentrative nucleoside transporters CNT1 (pyrimidine preferring) and CNT2 (purine preferring) may be involved in the uptake of nucleoside-derived drugs used in antiviral and chemical therapies. The possibility that nucleoside carrier isoform expression is modulated by nutrient availability has been studied.

METHODS

CNT1 and CNT2 tissue distribution was determined by Western blot analysis. The effect of 48-hour starvation on CNT expression was then studied. Nucleoside transporter expression and uptake activity were measured in jejunal brush border plasma membrane vesicles from fed and starved rats. The expression of nucleoside transporters was later determined in a second model of nutrient deficiency: rats fed a purified diet with or without nucleotides for 10 days.

RESULTS

CNT1 and CNT2 nucleoside transporters were expressed in a wider variety of tissues than expected from messenger RNA distribution analysis. CNT1 was sensitive to nutrient availability in small intestine and, accordingly, jejunal brush border membrane vesicles from 48-hour-fasted rats showed increased expression of CNT1 and enhanced Na(+)-dependent thymidine and gemcitabine uptake. This effect was mimicked by feeding semipurified diets lacking nucleotides.

CONCLUSIONS

Substrate availability modulates nucleoside transporter expression (CNT1) in rat jejunum in vivo.

A duodenum-specific enhancer regulates expression along three axes in the small intestine

Adenosine deaminase (ADA) is expressed at high levels in the epithelium of proximal small intestine. Transgenic mice were used to characterize the regulatory region governing this activation. A duodenum-specific enhancer is located in intron 2 of the human ADA gene at the central site among a cluster of seven DNase I-hypersensitive sites present in duodenal DNA. Flanking DNA, including the remaining hypersensitive sites, is required for consistent high-level enhancer function. The enhancer activates expression in a pattern identical to endogenous ADA along both the anterior-posterior axis of the small intestine and the crypt-villus differentiation axis of the intestinal epithelium. Timing of activation by the central enhancer mimics endogenous mouse ADA activation, occurring at 2-3 wk of age. However, two upstream DNA segments, one proximal and one distal, collaborate to change enhancer activation to a perinatal time point. Studies with duodenal nuclear extracts identified five distinct DNase I footprints within the enhancer. Protected regions encompass six putative binding sites for the transcription factor PDX-1, as well as proposed CDX, hepatocyte nuclear factor-4, and GATA-type sites.

Expression of guanylin is downregulated in mouse and human intestinal adenomas

Guanylin is a pro-secretory hormone that is expressed in intestinal epithelia. Previously, we mapped the guanylin gene to mouse and human chromosomal regions containing multiple intestinal tumor-modifying loci. Here, we investigate whether guanylin expression is downregulated in precancerous human and mouse intestinal adenomas and whether diminished guanylin expression increases adenoma susceptibility in an animal model of intestinal cancer, the multiple intestinal neoplasia (Min) mouse. In situ hybridization analysis indicated diminished guanylin expression in both mouse and human adenomas. Northern analysis of mouse intestinal tissues showed strain-specific levels of guanylin expression but no correlation with the resistance or susceptibility of each strain to adenoma formation. Similarly, cDNA sequence analysis indicated no inactivating mutations or polymorphisms common to either the high or low adenoma-risk groups. Nonetheless, we have shown that significant loss of guanylin RNA in adenomas of mouse and human is a marker of intestinal epithelial cell transformation.

Ontogeny of adenosine deaminase in developing trophoblast and decidual cells of rat and hamster

The enzyme adenosine deaminase (ADA) is expressed at high level in the tissue of foeto-maternal interface during early pregnancy. As the main constituents of this interface are trophoblast (TR) and decidual cells (DC), the enzyme was estimated in isolated TR and DC to determine the extent of contribution by the respective cells. The enzyme level was estimated in cytosolic fraction, cell lysate and in conditioned media of these cells in rat and hamster. In both species the concentration of ADA was found to be markedly high in cytosolic fraction over to the cell lysate and the conditioned media in both TR and DC. Species-wise, it was higher in hamster. Cell-wise, the enzyme activity was significantly higher in TR than DC in rat but equal in hamster. In the conditioned medium, also, the enzyme activity was higher in TR in both species. The inference drawn from the results are: 1) the maximum enzyme activity in cytosolic fraction of TR and DC of both species clearly indicates equal involvement of the cells that constitute foeto-maternal unit, 2) the enhanced level of enzyme in TR and DC of hamster over to those of rat is possibly due to the higher proliferative activity in the cells of this species because of shorter gestation (16-17 days in hamster and 22-23 days in rats).

Function of murine adenosine deaminase in the gastrointestinal tract

Adenosine deaminase (ADA) deficiency in humans leads to a combined immunodeficiency characterized by severe T and B cell lymphopenia. ADA-deficient humans also display defective development of gut-associated lymphoid tissues (GALT). They lack lymphoid cells, and the Peyer's patches are without germinal centers. In mice, ADA-deficient fetuses die perinatally due to liver damage, but they also exhibit pathology in the thymus, spleen, and the small intestine. The GI phenotype associated with ADA-deficient humans prompted us to examine the effect of ADA-deficiency on mouse small intestine tissue. The work presented here focuses on understanding the physiological role of ADA in the GI tract, using ADA-deficient mice rescued from perinatal lethality by restoring Ada expression to trophoblast cells. Histologically and immunologically, the GALT was compromised at all sites in ADA-/- mice, with the most dramatic changes seen in the Peyer's patches. Profound disturbances in purine metabolism were detected in all the gastrointestinal tissues. In particular, adenosine and deoxyadenosine, the ADA substrates, increased markedly while the product inosine decreased. The activity of S-adenosylhomocysteine hydrolase decreased throughout the GI tract, indicating a possible disruption of cellular transmethylation and activation of apoptotic pathways. There were also disturbances in the purine metabolic pathway with a decrease in the production of downstream nucleosides hypoxanthine and xanthine.

Dietary nucleotides: effects on the immune and gastrointestinal systems

Nucleotides (NT) and their related metabolic products play key roles in many biological processes. NT can be synthesized endogenously and thus are not considered essential nutrients. Studies have demonstrated, however, that dietary NT can have beneficial effects; the term "conditionally essential" has been used to describe their role in human nutrition. These nutrients may become essential when the endogenous supply is insufficient for normal function, even though their absence from the diet does not lead to a classic clinical deficiency syndrome. Most dietary NT are rapidly metabolized and excreted. However, some are incorporated into tissues, particularly at younger ages and with fasting. Under conditions of limited NT intake, rapid growth or certain disease states, dietary NT may spare the cost of de novo NT synthesis and optimize the function of rapidly dividing tissues such as those of the gastrointestinal and immune systems. Animals fed NT-supplemented versus non-NT supplemented diets have enhanced gastrointestinal growth and maturation, and improved recovery following small and large bowel injury. Indices of humoral and cellular immunity are enhanced, and survival rates are higher following infection with pathogens. Infants receive NT in human milk, where they are present as nucleic acids, nucleosides, nucleotides and related metabolic products. The NT content of human milk is significantly higher than most cow's milk-based infant formulae. Dietary NT are reported to enhance the gastrointestinal and immune systems of formula-fed infants. Infants fed NT-supplemented versus non-supplemented formula have a lower incidence of diarrhea, higher antibody titers following Haemophilus influenzae type b vaccination and higher natural killer cell activity. These data suggest that human milk NT may contribute to the superior clinical performance of the breastfed infant.

Diverse developing mouse lineages exhibit high-level c-Myb expression in immature cells and loss of expression upon differentiation

The c-myb gene encodes a sequence specific transactivator that is required for fetal hematopoiesis, but its potential role in other tissues is less clear because of the early fetal demise of mice with targeted deletions of the c-myb gene and incomplete of knowledge about c-myb's expression pattern. In the hematopoietic system, c-Myb protein acts on target genes whose expression is restricted to individual lineages, despite Myb's presence and role in multiple immature lineages. This suggests that c-Myb actions within different cell type-specific contexts are strongly affected by combinatorial interactions. To consider the possibility of similar c-Myb actions could extend into non-hematopoietic systems in other cell and tissue compartments, we characterized c-myb expression in developing and adult mice using in situ hybridization and correlated this with stage-specific differentiation and mitotic activity. Diverse tissues exhibited strong c-myb expression during development, notably tooth buds, the thyroid primordium, developing trachea and proximal branching airway epithelium, hair follicles, hematopoietic cells, and gastrointestinal crypt epithelial cells. The latter three of these all maintained high expression into adulthood, but with characteristic restriction to immature cell lineages prior to their terminal differentiation. In all sites, during fetal and adult stages, loss of c-Myb expression correlated strikingly with the initiation of terminal differentiation, but not the loss of mitotic activity. Based on these data, we hypothesize that c-Myb's function during cellular differentiation is both an activator of immature gene expression and a suppressor of terminal differentiation in diverse lineages.

Estrogen induces adenosine deaminase gene expression in MCF-7 human breast cancer cells: role of estrogen receptor-Sp1 interactions

Adenosine deaminase (ADA) gene expression is induced by 17beta-estradiol (E2) in MCF-7 human breast cancer cells, whereas the antiestrogens 4'-hydroxytamoxifen and ICI 182,780 exhibit partial estrogen receptor (ER) agonist/antagonist and antagonist activities, respectively. Previous studies have shown that the -211 to +11 region of the ADA gene promoter contains six GC-rich sites (I-VI) that bind Sp1 protein, and these elements are required for high basal expression. In transient transfection studies with pADA211, which contains the -211 to +11 ADA gene promoter linked to a bacterial chloramphenicol acetyl transferase (CAT) reporter gene, E2 and tamoxifen (but not ICI 182,780) induced CAT activity. Ligand-induced transactivation was observed only in cells cotransfected with expression plasmids for wild-type ER or HE11, which does not contain the DNA-binding domain of the ER. Cotransfection with HE15 and HE19, which contain the DNA-binding domain and activation function-1 (AF-1) and AF-2 of the ER, respectively, did not result in E2-induced activity. Subsequent deletion analysis of the ADA gene promoter showed that Sp1 binding site IV (-79 to -73) was primarily responsible for hormone responsiveness. ER activation of ADA gene expression is another example of an E2-induced gene that is dependent on ER/Sp1 interactions with a site-specific GC-rich motif.

Transcription factor AP-2gamma regulates murine adenosine deaminase gene expression during placental development

Trophoblast cells are specialized extra-embryonic cells present only in eutherian mammals. They play a major role in the implantation and placentation processes. To understand better the molecular mechanisms that control the development and function of trophoblast cells, we sought to identify the transcription factors that regulate murine adenosine deaminase (ADA) gene expression in the placenta. Here we report a detailed characterization of a placenta-specific footprinting region (FP1) in the Ada placental regulatory element. The sequence of FP1 was mapped by DNase I footprinting and was found to match a consensus AP-2 transcription factor-binding site. Electrophoretic mobility shift assays demonstrated that FP1 interacted with AP-2-like proteins. Further analysis using AP-2 antibody confirmed that AP-2 protein was indeed present in the placenta and bound to FP1. Mutation at the AP-2 site in FP1 abolished the ability of the Ada placental regulatory element to bind AP-2 proteins and failed to target chloramphenicol acetyltransferase reporter gene expression to placentas in transgenic mice, indicating that AP-2 is required for Ada expression in the placenta. In addition, RNase protection assays demonstrated that AP-2gamma was the predominant AP-2 family member expressed in the placenta. In situ hybridization analysis revealed that AP-2gamma expression was enriched in the trophoblast lineage throughout development, suggesting that AP-2gamma may be critical for trophoblast development and differentiation.

Dietary nucleotides correct plasma and liver microsomal fatty acid alterations in rats with liver cirrhosis induced by oral intake of thioacetamide

BACKGROUND/AIMS

Dietary nucleotides modulate a number of metabolic processes, including long-chain polyunsaturated fatty acid metabolism. In this study, we evaluated the effect of dietary nucleotides on plasma and liver microsomal fatty acid profiles in a rat model of liver cirrhosis induced by oral intake of thioacetamide.

METHODS

Fifty-four female Wistar rats were assigned to one of the following groups: rats in the thioacetamide group (n=45) were given 300 mg thioacetamide/l in their drinking water for 4 months, and rats in the control group (n=9) received water during the same period. After 4 months of treatment, 9 rats in each group were killed. The remaining rats in the thioacetamide group were divided into two new groups, and the animals in each were allowed to recover for 1 or 2 weeks on either a nucleotide-free diet or the same diet supplemented with 50 mg of each of the following: AMP, GMP, CMP, IMP and UMP per 100 g diet.

RESULTS

Saturated (mainly stearic acid), monounsaturated, and n-6 long-chain polyunsaturated fatty acids (mainly arachidonic acid), and also the unsaturation index decreased in plasma of rats with experimental cirrhosis. Administration of the diet supplemented with nucleotides to thioacetamide-treated rats corrected plasma levels of saturated, n-6 long-chain polyunsaturated fatty acids and the unsaturation index. In liver microsomes, the cirrhotic rats showed lower levels of protein and higher levels of palmitic, oleic, linoleic and arachidonic acids. Protein concentrations and levels of all the above-mentioned fatty acids were corrected with the nucleotide-enriched diet.

CONCLUSIONS

Dietary nucleotides contribute to correcting plasma and liver microsomal fatty acid alterations in rats with liver cirrhosis induced by chronic oral administration of thioacetamide.

Regulation of duodenal specific expression of the human adenosine deaminase gene

Formation of the mammalian gastrointestinal tract is an ordered process of development and differentiation. Yet, the adult small intestine also retains the plasticity to respond to cues both internal and environmental to modulate intestinal function. The components that regulate this development, differentiation, and modulation at the molecular level are only now being elucidated. We have used the human adenosine deaminase (ADA) gene as a model to identify potential cis-regulatory components involved in these processes within the small intestine. In mammals, high levels of ADA in the small intestine are limited specifically to the differentiated enterocytes within the duodenal region. These studies describe the identification of a region of the human ADA gene, completely distinct from the previously identified T-cell enhancer, which is capable of directing the human intestinal expression pattern in the intestine of transgenic mice. The reporter gene expression pattern observed in these transgenic mice is identical to the endogenous gene along both the cephalocaudal and crypt/villus axis of development. Timing of this transgene activation, however, varies from that of the endogenous mouse gene in that the transgene is activated approximately 2 weeks earlier in development. Even so, this precocious activation is also limited to the epithelium of the developing villi strictly within the duodenal region of the small intestine.

Genetically engineered mice demonstrate that adenosine deaminase is essential for early postimplantation development

Adenosine deaminase (ADA) is an essential enzyme of purine metabolism that is enriched at the maternal-fetal interface of mice throughout postimplantation development. During early postimplantation stages Ada is highly expressed in both maternally derived decidual cells and zygotically derived trophoblast cells. For the current study we utilized genetically modified mice to delineate the relative contribution and importance of decidual and trophoblast ADA at the maternal-fetal interface. In females genetically engineered to lack decidual ADA a striking pattern of expression was revealed in giant trophoblast cells that surround the early postimplantation embryo. Embryos within gestation sites lacking both decidual and trophoblast ADA died during the early postimplantation period, whereas expression in trophoblast cells alone was sufficient for survival through this period. Severe disturbances in purine metabolism were observed in gestation sites lacking decidual ADA, including the accumulation of the potentially toxic ADA substrates adenosine and 2′-deoxyadenosine. These experiments provide genetic evidence that Ada expression at the maternal-fetal interface is essential for early postimplantation development in mice.

Channelling of deoxyribose moiety of exogenous DNA into carbohydrate metabolism: role of deoxyriboaldolase

In bacteria, the addition of (deoxy)nucleosides or (deoxy)ribose to the growth medium causes induction of enzymes involved in their catabolism, leading to the utilisation of the pentose moiety as carbon and energy source. In this respect, deoxyriboaldolase appears the key enzyme, allowing the utilisation of deoxyribose 5-P through glycolysis. We observed that not only deoxynucleosides, but also DNA added to the growth medium of Bacillus cereus induced deoxyriboaldolase; furthermore, the switch of the culture from aerobic to anaerobic conditions caused a further increase in enzyme activity, leading to a more efficient channelling of deoxyribose 5-P into glycolysis, probably as a response to the low energy yield of the sugar fermentation. In eukaryotes, the catabolism of (deoxy)nucleosides is well known. However, the research in this field has been mainly devoted to the salvage of the bases formed by the action of nucleoside phosphorylases, whereas the metabolic fate of the sugar moiety has been largely neglected. Our results indicate that the deoxyriboaldolase activity is present in the liver of several vertebrates and in a number of cell lines. We discuss our observations looking at the nucleic acids not only as informational molecules, but also as a not negligible source of readily usable phosphorylated sugar.

Nucleotides in human milk: sources and metabolism by the newborn infant

Ribonucleotides in human milk have been claimed to have several effects in recipient infants. It is, however, not known whether the nucleotides found in human milk result from degradation of nucleic acids or are actively secreted as a response to a nutritional demand of the infant. Furthermore, little is known of the newborn infant's endogenous capacity to digest nucleic acids to absorbable products. We therefore analyzed human milk, during established lactation, with respect to the concentration of nucleic acid and ribonucleotide metabolites. Expressed as nucleotide equivalents, 68 +/- 55 mumol/L were present as nucleic acid, 84 +/- 25 mumol/L as nucleotides, and 10 +/- 2 mumol/L as nucleosides. The nucleotide/nucleoside profile showed a substantial predominance for pyrimidines and uric acid. This specific profile could, at least to some extent, result from limited catalysis during storage of the milk in the breast, because enzymes capable of degrading nucleotides were found in the milk. To evaluate the endogenous capability of newborn infants to metabolize RNA and nucleotides, fetal small intestine was analyzed for relevant digestive enzymes. Such intestine, from a fetus of 22-wk gestation, digested RNA to cytidine, uridine, and uric acid in vitro. Furthermore, a fetal small intestinal homogenate generated a net increase in pyrimidines and purines when incubated with human milk, whereas when incubated with infant formula, devoid of nucleic acids, it did not.

Metabolic and immunologic consequences of limited adenosine deaminase expression in mice

Adenosine deaminase (ADA; EC 3.5.4.4) deficiency in humans is an autosomal recessive genetic disorder that results in severe combined immunodeficiency disease. ADA-deficient mice generated by targeted gene disruption die perinatally, preventing postnatal analysis of ADA deficiency. We have recently rescued ADA-deficient fetuses from perinatal lethality by expression of an ADA minigene in the placentas of ADA-deficient fetuses, thus generating postnatal mice admissible to analysis of ADA deficiency. The minigene used also directed ADA expression to the forestomach postnatally, producing adult animals that lacked ADA enzymatic activity in all tissues outside the gastrointestinal tract. Mice with limited ADA expression exhibited profound disturbances in purine metabolism, including thymus-specific accumulations of deoxyadenosine and dATP, and inhibition of S-adenosylhomocysteine hydrolase in the thymus, spleen, and, to a lesser extent, the liver. Lymphopenia and mild immunodeficiency were associated with these tissue-specific metabolic disturbances. These mice represent the first genetic animal model for ADA deficiency and provide insight into the tissue-specific requirements of ADA.

Apolipoprotein J/clusterin induction in myocarditis: A localized response gene to myocardial injury

The function of apolipoprotein J (apoJ) is unknown, but it has been hypothesized to be cytoprotective. In the normal heart, abundant apoJ mRNA and protein are expressed in atrial myocytes; no expression is detected in ventricular myocytes. To provide clues about the role of apoJ in the heart, the response of apoJ to heart disease, including three models of myocarditis and two models of in vivo pressure overload hypertrophy, were examined. In the disease model studied extensively, myosin-induced myocarditis, in situ hybridization detected induction of apoJ mRNA in ventricular myocytes immediately before histological evidence of injury. ApoJ message in ventricular myocytes reached high levels as myocarditis became more severe. Evidence of early apoJ induction, before inflammation and injury, also occurred in viral myocarditis. ApoJ mRNA was not present in the inflammatory or interstitial cells during myocarditis. In areas of severe inflammation and myocardial fiber degeneration, apoJ showed a gradient of expression, with highest levels in myocytes immediately surrounding the lesion and diminishing with increasing distance. ApoJ protein also accumulated in myocytes at the interface between degenerated myocardial tissue and the surrounding cardiac tissue. During cardiac hypertrophy that occurred without associated inflammation or cell damage, ventricular apoJ mRNA was not detected. When ischemic damage accompanied hypertrophy, apoJ was induced in the ventricular myocytes near the lesion borders. The correlation of apoJ induction with ventricular tissue damage, but not hypertrophy, suggests that apoJ is a repair response protein. We propose that apoJ functions to limit tissue injury and/or promote tissue remodeling.

Modelling of purine nucleoside metabolism during mouse embryonic development: relative routes of adenosine, deoxyadenosine, and deoxyguanosine metabolism

The individual activities for adenosine kinase, deoxyadenosine kinase, adenosine deaminase, deoxyguanosine kinase, and purine nucleoside phosphorylase were determined during days 7 to 13 of mouse embryonic development. Adenosine deaminase increased 74-fold between days 7 and 9; deoxyadenosine kinase increased 5.4-fold during the same interval. Adenosine kinase, deoxyguanosine kinase, and purine nucleoside phosphorylase exhibited less than 2-fold changes in activity between days 7 and 13. Using Michaelis constants for each enzyme and the maximal velocities determined from enzyme assay, the relative routes of adenosine and deoxyadenosine metabolism via phosphorylation or deamination were modeled as a function of nucleoside concentration for days 7 through 13. For days 7 and 8, phosphorylation of adenosine is the principle route of metabolism at physiological concentrations. A switch occurred at day 9 and following where deamination is at least 5-fold greater than phosphorylation at all substrate concentrations. Deoxyadenosine phosphorylation was at most 10% of deamination at day 7 and then declined to less than 1% for days 9 to 13. Phosphorolysis was the principle route of deoxyguanosine metabolism through the 7 to 13 day period. Thus catabolism rather than phosphorylation was the principle pathway for purine deoxynucleoside metabolism during this period.

Patterns of gene expression along the crypt-villus axis in mouse jejunal epithelium

BACKGROUND

There is considerable interest in gene expression along the crypt-villus axis of the small intestinal epithelium, particularly in the identification of genes expressed in intestinal crypts.

METHODS

In an attempt to identify crypt-expressed genes, single-stranded cDNA made from normal mouse jejunal epithelium was used in subtractive hybridization against single-stranded cDNA from epithelium from which crypt cells were depleted by 2,000 rads of gamma irradiation. Partial DNA sequence and in situ hybridization of 72 resulting clones were determined.

RESULTS

The sequence of 45 clones matched previously published genes. Gene expression patterns fell into three categories: expression throughout the crypt-villus axis, expression restricted to the villus, and expression restricted to the crypt. Clones in the first two categories could be further divided into three subgroups: those with uniform expression, those with an increasing gradient of expression, and those with a decreasing gradient of expression along the crypt-villus axis. Twenty two clones showed a stronger expression in crypt and lower villus cells, four of these were differentially localized to the crypt. Two of the crypt localized clones were uniformly expressed throughout the crypt, expression of one was stronger in the lower crypt, and expression of the remaining clone was enhanced Paneth cells. We report the full-length cDNA sequence of the Paneth-cell-enhanced clone.

CONCLUSIONS

The screen isolated crypt-expressed genes that may prove useful tools in the study of crypt biology. In a companion report, we characterize one of the crypt clones.

Tissue-specific rescue suggests that placental adenosine deaminase is important for fetal development in mice

Adenosine deaminase (ADA, EC 3.5.4.4) is an essential enzyme of purine metabolism that is expressed at very high levels in the murine placenta where it accounts for over 95% of the ADA present at the fetal gestation site. We have recently shown that ADA-deficient fetuses, which also lack ADA in their adjoining placentas, die during late fetal development in association with profound purine metabolic disturbances and hepatocellular impairment. We have now investigated the potential importance of placental ADA by genetically restoring the enzyme to placentas of ADA-deficient fetuses. This genetic engineering strategy corrected most of the purine metabolic disturbances, prevented serious fetal liver damage, and rescued the fetuses from perinatal lethality. Our findings suggest that placental ADA is important for murine fetal development and illustrate a general strategy for the tissue specific correction of phenotypes associated with null mutations in mice.

Adenosine-deaminase-deficient mice die perinatally and exhibit liver-cell degeneration, atelectasis and small intestinal cell death

We report the generation and characterization of mice lacking adenosine deaminase (ADA). In humans, absence of ADA causes severe combined immunodeficiency. In contrast, ADA-deficient mice die perinatally with marked liver-cell degeneration, but lack abnormalities in the thymus. The ADA substrates, adenosine and deoxyadenosine, are increased in ADA-deficient mice. Adenine deoxyribonucleotides are only modestly elevated, whereas S-adenosylhomocysteine hydrolase activity is reduced more than 85%. Consequently, the ratio of S-adenosylhomocysteine (AdoMet) to S-adenosyl homocysteine (AdoHcy) is reduced threefold in liver. We conclude that ADA plays a more critical role in murine than human fetal development. The murine liver pathology may be due to AdoHcy-mediated inhibition of AdoMet-dependent transmethylation reactions.

Dissecting a locus control region: facilitation of enhancer function by extended enhancer-flanking sequences

Using transgenic mice, we have defined novel gene regulatory elements, termed "facilitators." These elements bilaterally flank, by up to 1 kb, a 200-bp T-cell-specific enhancer domain in the human adenosine deaminase (ADA) gene. Facilitators were essential for gene copy-proportional and integration site-independent reporter expression in transgenic thymocytes, but they had no effect on the enhancer in transfected T cells. Both segments were required. Individual segments had no activity. A lack of facilitator function caused positional susceptibility and prevented DNase I-hypersensitive site formation at the enhancer. The segments were required to be at opposed ends of the enhancer, and they could not be grouped together. Reversing the orientation of a facilitator segment caused a partial loss of function, suggesting involvement of a stereospecific chromatin structure. trans-acting factor access to enhancer elements was modeled by exposing nuclei to a restriction endonuclease. The enhancer domain was accessible to the 4-cutter DpnII in a tissue- and cell-type-specific fashion. However, unlike DNase I hypersensitivity and gene expression, accessibility to the endonuclease could occur without the facilitator segments, suggesting that an accessible chromatin domain is an intermediate state in the activational pathway. These results suggest that facilitators (i) are distinct from yet positionally constrained to the enhancer, (ii) participate in a chromatin structure transition that is necessary for the DNase I hypersensitivity and the transcriptional activating function of the enhancer, and (iii) act after cell-type-specific accessibility to the enhancer sequences is established by factors that do not require the facilitators to be present.

Comparative enzyme histochemistry of the early and term rat decidua with special attention to decidual regression

As the early rat decidua is believed to fulfil functions other than the late or basal decidua, the question as to whether this difference is reflected in decidual cell metabolism was investigated. Using cryosections of pregnant rat uteri of the 10th, 15th and 21st gestational day, activities of oxyradical-forming enzymes and hydrolases were analysed histochemically. The enzyme activities of decidual stromal cells and fibroblasts of the metrial gland exhibited three main fluctuations. One group of enzyme activities did not change during gestation, a second group decreased or disappeared, and a third group increased or was expressed in the late decidua only. Enzymes of the purine and polyamine pathway, including oxyradical-forming oxidases, were absent from early mesometrial decidual cells, but were highly active in the late regressing decidua and metrial gland. Some acid hydrolases and neutral proteases became active in the mature decidua. The possibility that purine-degrading and oxyradical-forming enzymes support decidual as well as metrial gland regression, and thus placental separation, by direct tissue damage and/or by indirect rupture of lysosomal membranes, inducing the release of acid hydrolases, is considered.

Sp1 is essential for both enhancer-mediated and basal activation of the TATA-less human adenosine deaminase promoter

Tissue-specific expression of the human adenosine deaminase (ADA) gene is mediated by transcriptional activation over a thousand-fold range. Cis-regulatory regions responsible for high and basal levels of activation include an enhancer and the proximal promoter region. While analyses of the T-cell specific enhancer have been carried out, detailed studies of the the promoter region or promoter-enhancer interactions have not. Examination of the promoter region by homology searches revealed six putative Sp1 binding sites. DNase I footprinting showed that Sp1 is able to bind these sites. Deletion analysis indicated that the proximal Sp1 site is required for activation of a reporter gene to detectable levels and that the more distal Sp1 sites further activate the level of expression. Inclusion of an ADA enhancer-containing fragment in these deletion constructions demonstrated that Sp1 sites are also essential for enhancer function. Apparently Sp1 controls not only low level expression but is also an integral part of the mechanism by which the enhancer achieves high level ADA expression. Mutagenesis of a potential TBP binding site at base pairs -21 to -26 decreased activity only two-fold indicating that it is not essential for transcriptional activation or enhancement.