Exploration of potential shared gene signatures between periodontitis and multiple sclerosis

BACKGROUND

Although periodontitis has previously been reported to be linked with multiple sclerosis (MS), but the molecular mechanisms and pathological interactions between the two remain unclear. This study aims to explore potential crosstalk genes and pathways between periodontitis and MS.

METHODS

Periodontitis and MS data were obtained from the Gene Expression Omnibus (GEO) database. Shared genes were identified by differential expression analysis and weighted gene co-expression network analysis (WGCNA). Then, enrichment analysis for the shared genes was carried out by multiple methods. The least absolute shrinkage and selection operator (LASSO) regression was used to obtain potential shared diagnostic genes. Furthermore, the expression profile of 28 immune cells in periodontitis and MS was examined using single-sample GSEA (ssGSEA). Finally, real-time quantitative fluorescent PCR (qRT-PCR) and immune histochemical staining were employed to validate Hub gene expressions in periodontitis and MS samples.

RESULTS

FAM46C, SLC7A7, LY96, CFI, DDIT4L, CD14, C5AR1, and IGJ genes were the shared genes between periodontitis, and MS. GO analysis revealed that the shared genes exhibited the greatest enrichment in response to molecules of bacterial origin. LASSO analysis indicated that CFI, DDIT4L, and FAM46C were the most effective shared diagnostic biomarkers for periodontitis and MS, which were further validated by qPCR and immunohistochemical staining. ssGSEA analysis revealed that T and B cells significantly influence the development of MS and periodontitis.

CONCLUSIONS

FAM46C, SLC7A7, LY96, CFI, DDIT4L, CD14, C5AR1, and IGJ were the most important crosstalk genes between periodontitis, and MS. Further studies found that CFI, DDIT4L, and FAM46C were potential biomarkers in periodontitis and MS.

Delayed skeletal development and IGF-1 deficiency in a mouse model of lysinuric protein intolerance

SLC7A7 deficiency, or lysinuric protein intolerance (LPI), causes loss of function of the y+LAT1 transporter critical for efflux of arginine, lysine and ornithine in certain cells. LPI is characterized by urea cycle dysfunction, renal disease, immune dysregulation, growth failure, delayed bone age and osteoporosis. We previously reported that Slc7a7 knockout mice (C57BL/6×129/SvEv F2) recapitulate LPI phenotypes, including growth failure. Our main objective in this study was to characterize the skeletal phenotype in these mice. Compared to wild-type littermates, juvenile Slc7a7 knockout mice demonstrated 70% lower body weights, 87% lower plasma IGF-1 concentrations and delayed skeletal development. Because poor survival prevents evaluation of mature knockout mice, we generated a conditional Slc7a7 deletion in mature osteoblasts or mesenchymal cells of the osteo-chondroprogenitor lineage, but no differences in bone architecture were observed. Overall, global Slc7a7 deficiency caused growth failure with low plasma IGF-1 concentrations and delayed skeletal development, but Slc7a7 deficiency in the osteoblastic lineage was not a major contributor to these phenotypes. Future studies utilizing additional tissue-specific Slc7a7 knockout models may help dissect cell-autonomous and non-cell-autonomous mechanisms underlying phenotypes in LPI.

Perspectives of Rare Disease Experts on Newborn Genome Sequencing

Importance

Newborn genome sequencing (NBSeq) can detect infants at risk for treatable disorders currently undetected by conventional newborn screening. Despite broad stakeholder support for NBSeq, the perspectives of rare disease experts regarding which diseases should be screened have not been ascertained.

Objective

To query rare disease experts about their perspectives on NBSeq and which gene-disease pairs they consider appropriate to evaluate in apparently healthy newborns.

Design, Setting, and Participants

This survey study, designed between November 2, 2021, and February 11, 2022, assessed experts' perspectives on 6 statements related to NBSeq. Experts were also asked to indicate whether they would recommend including each of 649 gene-disease pairs associated with potentially treatable conditions in NBSeq. The survey was administered between February 11 and September 23, 2022, to 386 experts, including all 144 directors of accredited medical and laboratory genetics training programs in the US.

Exposures

Expert perspectives on newborn screening using genome sequencing.

Main Outcomes and Measures

The proportion of experts indicating agreement or disagreement with each survey statement and those who selected inclusion of each gene-disease pair were tabulated. Exploratory analyses of responses by gender and age were conducted using t and χ2 tests.

Results

Of 386 experts invited, 238 (61.7%) responded (mean [SD] age, 52.6 [12.8] years [range 27-93 years]; 126 [52.9%] women and 112 [47.1%] men). Among the experts who responded, 161 (87.9%) agreed that NBSeq for monogenic treatable disorders should be made available to all newborns; 107 (58.5%) agreed that NBSeq should include genes associated with treatable disorders, even if those conditions were low penetrance; 68 (37.2%) agreed that actionable adult-onset conditions should be sequenced in newborns to facilitate cascade testing in parents, and 51 (27.9%) agreed that NBSeq should include screening for conditions with no established therapies or management guidelines. The following 25 genes were recommended by 85% or more of the experts: OTC, G6PC, SLC37A4, CYP11B1, ARSB, F8, F9, SLC2A1, CYP17A1, RB1, IDS, GUSB, DMD, GLUD1, CYP11A1, GALNS, CPS1, PLPBP, ALDH7A1, SLC26A3, SLC25A15, SMPD1, GATM, SLC7A7, and NAGS. Including these, 42 gene-disease pairs were endorsed by at least 80% of experts, and 432 genes were endorsed by at least 50% of experts.

Conclusions and Relevance

In this survey study, rare disease experts broadly supported NBSeq for treatable conditions and demonstrated substantial concordance regarding the inclusion of a specific subset of genes in NBSeq.

Screening of Specific and Common Pathways in Breast Cancer Cell Lines MCF-7 and MDA-MB-231 Treated with Chlorophyllides Composites

Our previous findings have shown that the chlorophyllides composites have anticancer activities to breast cancer cell lines (MCF-7 and MDA-MB-231). In the present study, microarray gene expression profiling was utilized to investigate the chlorophyllides anticancer mechanism on the breast cancer cells lines. Results showed that chlorophyllides composites induced upregulation of 43 and 56 differentially expressed genes (DEG) in MCF-7 and MDA-MB-231 cells, respectively. In both cell lines, chlorophyllides composites modulated the expression of annexin A4 (ANXA4), chemokine C-C motif receptor 1 (CCR1), stromal interaction molecule 2 (STIM2), ethanolamine kinase 1 (ETNK1) and member of RAS oncogene family (RAP2B). Further, the KEGG annotation revealed that chlorophyllides composites modulated DEGs that are associated with the endocrine system in MCF-7 cells and with the nervous system in MDA-MB-231 cells, respectively. The expression levels of 9 genes were validated by quantitative reverse transcription PCR (RT-qPCR). The expression of CCR1, STIM2, ETNK1, MAGl1 and TOP2A were upregulated in both chlorophyllides composites treated-MCF-7 and MDA-MB-231 cells. The different expression of NLRC5, SLC7A7 and PKN1 provided valuable information for future investigation and development of novel cancer therapy.

[Clinical features of children with lysinuric protein intolerance and SLC7A7 gene mutation: an analysis of 3 cases]

Lysinuric protein intolerance (LPI) is an autosomal recessive disorder caused by SLC7A7 gene mutation and often involves severe lesions in multiple systems. Lung involvement is frequently seen in children with LPI and such children tend to have a poor prognosis. This article summarizes the clinical manifestations and gene mutation characteristics of three children diagnosed with LPI by SLC7A7 gene analysis. All three children had the manifestations of aversion to protein-rich food after weaning, delayed development, anemia, hepatosplenomegaly, and osteoporosis, as well as an increase in orotic acid in urine. In addition, interstitial pneumonia and diffuse pulmonary interstitial lesions were observed in two children. SLC7A7 gene detection showed three pathogenic mutations in these children, namely c.1387delG(p.V463CfsX56), c.1215G>A(p.W405X) and homozygous c.625+1G>A. After a definite diagnosis was made, all three children were given a low-protein diet and oral administration of citrulline [100 mg/(kg.d)], iron protein succinylate [4 mg/(kg.d)], calcium and zinc gluconates oral solution (10 mL/day) and vitamin D (400 IU/day). In addition, patient 3 was given prednisone acetate (5 mg/day). The children had varying degrees of improvement in symptoms and signs. It is hard to distinguish LPI from urea cycle disorder due to the features of amino acid and organic acid metabolism in LPI, and SLC7A7 gene analysis is the basis for a definite diagnosis of LPI.

Arginase 1 deletion in myeloid cells affects the inflammatory response in allergic asthma, but not lung mechanics, in female mice

BACKGROUND

(Over-)expression of arginase may limit local availability of arginine for nitric oxide synthesis. We investigated the significance of arginase1 (ARG1) for the development of airway hyperresponsiveness (AHR) and lung inflammation in female mice with ovalbumin (OVA)-induced allergic asthma.

METHODS

Arg1 was ablated in the lung by crossing Arg1 fl/fl and Tie2Cre tg/- mice. OVA sensitization and challenge were conducted, and AHR to methacholine was determined using the Flexivent system. Changes in gene expression, chemokine and cytokine secretion, plasma IgE, and lung histology were quantified using RT-qPCR, ELISA, and immunohistochemistry, respectively.

RESULTS

Arg1 ablation had no influence on the development of OVA-induced AHR, but attenuated OVA-induced increases in expression of Arg2 and Nos2, Slc7a1, Slc7a2, and Slc7a7 (arginine transporters), Il4, Il5 and Il13 (TH2-type cytokines), Ccl2 and Ccl11 (chemokines), Ifng (TH1-type cytokine), Clca3 and Muc5ac (goblet cell markers), and OVA-specific IgE. Pulmonary IL-10 protein content increased, but IL-4, IL-5, IL-13, TNFα and IFNγ content, and lung histopathology, were not affected. Arg1 elimination also decreased number and tightness of correlations between adaptive changes in lung function and inflammatory parameters in OVA/OVA-treated female mice. OVA/OVA-treated female mice mounted a higher OVA-IgE response than males, but the correlation between lung function and inflammation was lower. Arg1-deficient OVA/OVA-treated females differed from males in a more pronounced decline of arginine-metabolizing and -transporting genes, higher plasma arginine levels, a smaller OVA-specific IgE response, and no improvement of peripheral lung function.

CONCLUSION

Complete ablation of Arg1 in the lung affects mRNA abundance of arginine-transporting and -metabolizing genes, and pro-inflammatory genes, but not methacholine responsiveness or accumulation of inflammatory cells.

Biochemical and molecular characteristics of Malaysian patients with lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is an inborn error of dibasic amino acid transport due to a defect in the dibasic amino acid transporter in the renal and intestine and has a heterogenous presentation. Three Malaysian patients with LPI were studied and their biochemical and molecular findings compared. There were differences and similarities in the biochemical and molecular findings. Molecular analysis of SLC7A7 gene revealed a novel mutation c.235G>A; p.(Gly79Arg) in exon three in Patient 1 and a mutation c.1417C>T; p.(Arg473*) in exon 10 in patient 2 and 3. The degree of concentration of dibasic amino acids may determine the type of disease of the cell membrane transport, however, a positive molecular confirmation will secure the diagnosis.

CD69 controls the uptake of L-tryptophan through LAT1-CD98 and AhR-dependent secretion of IL-22 in psoriasis

The activation marker CD69 is expressed by skin γδ T cells. Here we found that CD69 controlled the aryl hydrocarbon receptor (AhR)-dependent secretion of interleukin 22 (IL-22) by γδ T cells, which contributed to the development of psoriasis induced by IL-23. CD69 associated with the aromatic-amino-acid-transporter complex LAT1-CD98 and regulated its surface expression and uptake of L-tryptophan (L-Trp) and the intracellular quantity of L-Trp-derived activators of AhR. In vivo administration of L-Trp, an inhibitor of AhR or IL-22 abrogated the differences between CD69-deficient mice and wild-type mice in skin inflammation. We also observed LAT1-mediated regulation of AhR activation and IL-22 secretion in circulating Vγ9(+) γδ T cells of psoriatic patients. Thus, CD69 serves as a key mediator of the pathogenesis of psoriasis by controlling LAT1-CD98-mediated metabolic cues.

1471 delTTCT a Common Mutation of Tunisian Patients with Lysinuric Protein Intolerance

BACKGROUND

Lysinuric protein intolerance is an inherited aminoaciduria caused by defective cationic amino acid transport. It is an autosomal recessive disease caused by mutations in the SLC7A 7 gene. The objective of this study was to identify the mutations of Tunisians patients in order to offer the genetic counseling and the prenatal diagnosis to families.

METHODS

Five affected Tunisian children (4 girls and 1 boy) belonging to four consanguineous families were considered. The diagnosis was made based on the plasma for amino acids quantification by Ion Exchange chromatography, the DNA for mutational analysis by DHPLC and sequencing, and the amniotic fluid for prenatal diagnosis.

RESULTS

For the 5 patients, clinical features were dominated by failure to thrive, bone marrow abnormalities, hepatosplenomegaly, and mental retardation. The diagnosis for all patients was confirmed by biochemical analysis with hyperammonemia, hyperexcretion of urinary dibasic amino acids, and a high amount of orotic acid in the urine. The 1471 delTTCT mutation was identified in exon 9 in the homozygous state for all Tunisian patients. Genetic counseling was performed for three out of four families, four heterozygous and two homozygous healthy siblings were identified. The result of prenatal diagnosis showed the presence of the 1471 de1TTCT mutation in the homozygous state for the third pregnancy and heterozygous state for the fourth.

CONCLUSIONS

The 1471 deITTCT mutation seems to be a common mutation of Tunisian population. The identification of this specific mutation provides a tool for confirmatory diagnosis, genetic counseling, and prenatal diagnosis.

Lung involvement in children with lysinuric protein intolerance

BACKGROUND AND OBJECTIVES

Lysinuric protein intolerance (LPI) is a rare multisystemic metabolic disease. The objective of the study was to describe presentation and course of lung involvement in a cohort of ten children.

PATIENTS AND METHODS

Retrospective review of patients followed at Necker-Enfants Malades University Hospital between 1980 and 2012 for a LPI. In patients with lung involvement, clinical data, chest radiographs, pulmonary function tests, bronchoalveolar lavages, and lung biopsies were analyzed. The first and last high-resolution computed tomography (HRCT) were also reviewed.

RESULTS

Lung involvement was observed in ten of 14 patients (71 %). Five patients had an acute onset of respiratory symptoms, three had a progressive onset and two were free of symptoms. During the period studied, six patients (60 %) died, all in a context of respiratory failure. Clinical presentation and course were highly variable, even in the same family. HRCT were performed in seven cases, showing in all cases an interstitial pattern and fibrosis in four. All ten patients had pulmonary alveolar proteinosis (PAP) confirmed by histopathological analysis. Five patients had pulmonary fibrosis (at biopsy and/or HRCT scan). Two patients underwent whole lung lavages, without efficiency.

CONCLUSION

PAP is a constant feature in children with LPI and lung involvement. Pulmonary fibrosis is frequent and these two pathologies may develop independently. This study shows the heterogeneity of presentation and outcome. Lung injury could be secondary to impaired phagocytic function and abnormal inflammatory and immune responses intrinsic to the SLC7A7 mutant phenotype. HRCT is recommended to detect lung involvement.

Maternal transfer of the cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) via milk to suckling offspring

The cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) has been implicated in the etiology of neurodegenerative disease and proposed to be biomagnified in terrestrial and aquatic food chains. We have previously shown that the neonatal period in rats, which in humans corresponds to the last trimester of pregnancy and the first few years of age, is a particularly sensitive period for exposure to BMAA. The present study aimed to examine the secretion of ¹⁴C-labeled L- and D-BMAA into milk in lactating mice and the subsequent transfer of BMAA into the developing brain. The results suggest that secretion into milk is an important elimination pathway of BMAA in lactating mothers and an efficient exposure route predominantly for L-BMAA but also for D-BMAA in suckling mice. Following secretion of [¹⁴C]L-BMAA into milk, the levels of [¹⁴C]L-BMAA in the brains of the suckling neonatal mice significantly exceeded the levels in the maternal brains. In vitro studies using the mouse mammary epithelial HC11 cell line confirmed a more efficient influx and efflux of L-BMAA than of D-BMAA in cells, suggesting enantiomer-selective transport. Competition experiments with other amino acids and a low sodium dependency of the influx suggests that the amino acid transporters LAT1 and LAT2 are involved in the transport of L-BMAA into milk. Given the persistent neurodevelopmental toxicity following injection of L-BMAA to neonatal rodent pups, the current results highlight the need to determine whether BMAA is enriched mother's and cow's milk.

Hyperexcretion of homocitrulline in a Malaysian patient with lysinuric protein intolerance

Lysinuric protein intolerance (LPI; MIM 222700) is an inherited aminoaciduria with an autosomal recessive mode of inheritance. Biochemically, affected patients present with increased excretion of the cationic amino acids: lysine, arginine, and ornithine. We report the first case of LPI diagnosed in Malaysia presented with excessive excretion of homocitrulline. The patient was a 4-year-old male who presented with delayed milestones, recurrent diarrhea, and severe failure to thrive. He developed hyperammonemic coma following a forced protein-rich diet. Plasma amino acid analysis showed increased glutamine, alanine, and citrulline but decreased lysine, arginine and ornithine. Urine amino acids showed a marked excretion of lysine and ornithine together with a large peak of unknown metabolite which was subsequently identified as homocitrulline by tandem mass spectrometry. Molecular analysis confirmed a previously unreported homozygous mutation at exon 1 (235 G > A, p.Gly79Arg) in the SLC7A7 gene. This report demonstrates a novel mutation in the SLC7A7 gene in this rare inborn error of diamino acid metabolism. It also highlights the importance of early and efficient treatment of infections and dehydration in these patients.

CONCLUSION

The diagnosis of LPI is usually not suspected by clinical findings alone, and specific laboratory investigations and molecular analysis are important to get a definitive diagnosis.

Changes in thyroid status during perinatal development of MCT8-deficient male mice

Patients with the monocarboxylate transporter 8 (MCT8) deficiency syndrome present with a severe psychomotor retardation and abnormal serum thyroid hormone (TH) levels, consisting of high T(3) and low T(4) and rT(3). Mice deficient in Mct8 replicate the thyroid phenotype of patients with the MCT8 gene mutations. We analyzed the serum TH levels and action in the cerebral cortex and in the liver during the perinatal period of mice deficient in Mct8 to assess how the thyroid abnormalities of Mct8 deficiency develop and to study the thyroidal status of specific tissues. During perinatal life, the thyroid phenotype of Mct8-deficient mice is different from that of adult mice. They manifest hyperthyroxinemia at embryonic day 18 and postnatal day 0. This perinatal hyperthyroxinemia is accompanied by manifestations of TH excess as evidenced by a relative increase in the expression of genes positively regulated by T3 in both the cerebral cortex and liver. An increased tissue accumulation of T(4) and T(3) and the expression of TH alternative transporters, including Lat1, Lat2, Oatp1c1, and Oatp3a1 in the cortex and Lat2 and Oatp1b2 in the liver, suggested that Mct8 deficiency either directly interferes with tissue efflux of TH or indirectly activates other transporters to increase TH uptake. This report is the first to identify that the ontogenesis of TH abnormalities in Mct8-deficient mice manifests with TH excess in the perinatal period.

The role of amino acid transporters in nutrition

PURPOSE OF REVIEW

We consider recent advances in epithelial amino acid transport physiology and our understanding of the functioning of amino acid transporters as sensors, as well as carriers, of tissue nutrient supplies.

RECENT FINDINGS

Gut hormones (e.g. leptin) may regulate intestinal amino acid transporter activity by a variety of mechanisms, although the overall functional significance of such regulation is not yet fully understood. Important functional interactions between amino acid transporters and nutrient-signalling pathways which regulate metabolism [e.g. the mammalian target of rapamycin (mTOR)C1 pathway which promotes cell growth] have been revealed in recent studies. Amino acid transporters on endosomal (e.g. lysosomal) membranes may be of unexpected significance as intracellular nutrient sensors. It is also now evident that certain amino acid transporters may have dual receptor-transporter functions and act as 'transceptors' to sense amino acid availability upstream of signal pathways.

SUMMARY

Increased knowledge on the timescale of the amino acid sensor-signal-effector process(es) should help in the optimization of protein-feeding regimes to gain maximum anabolic effect. New opportunities for nutritional therapy include targeting of amino acid transceptors to promote protein-anabolic signals and mechanisms up-regulating amino acid transporter expression to improve absorptive capacity for nutrients.

The first Korean case of lysinuric protein intolerance: presented with short stature and increased somnolence

Lysinuric protein intolerance (LPI) is a rare inherited metabolic disease, caused by defective transport of dibasic amino acids. Failure to thrive, hepatosplenomegaly, hematological abnormalities, and hyperammonemic crisis are major clinical features. However, there has been no reported Korean patient with LPI as of yet. We recently encountered a 3.7-yr-old Korean girl with LPI and the diagnosis was confirmed by amino acid analyses and the SLC7A7 gene analysis. Her initial chief complaint was short stature below the 3rd percentile and increased somnolence for several months. Hepatosplenomegaly was noted, as were anemia, leukopenia, elevated levels of ferritin and lactate dehydrogenase, and hyperammonemia. Lysine, arginine, and ornithine levels were low in plasma and high in urine. The patient was a homozygote with a splicing site mutation of IVS4+1G > A in the SLC7A7. With the implementation of a low protein diet, sodium benzoate, citrulline and L-carnitine supplementation, anemia, hyperferritinemia, and hyperammonemia were improved, and normal growth velocity was observed.

Impaired phagocytosis in macrophages from patients affected by lysinuric protein intolerance

Lysinuric Protein Intolerance (LPI, MIM 222700) is a recessive aminoaciduria caused by defective cationic amino acid transport in epithelial cells of intestine and kidney. SLC7A7, the gene mutated in LPI, codifies for the y+LAT1 subunit of system y(+)L amino acid transporter. LPI patients frequently display severe complications, such as pulmonary disease, haematological abnormalities and disorders of the immune response. The transport defect may explain only a part of the clinical aspects of the disease, while the mechanisms linking the genetic defect to the clinical features of the patients remain thus far obscure. The aim of the study is to investigate the consequences of SLC7A7 mutations on specific macrophage functions, so as to evaluate if a macrophage dysfunction may have a role in the development of pulmonary and immunological complications of LPI. The results presented 1) confirm previous data obtained in one LPI patient, demonstrating that arginine influx through system y(+)L is markedly compromised in LPI macrophages; 2) demonstrate that also system y(+)L-mediated arginine efflux is significantly lower in LPI macrophages than in normal cells and 3) demonstrate that the phagocytic activity of LPI macrophages is severely impaired. In conclusion, SLC7A7/y+LAT1 mutations lead to a defective phenotype of macrophages, supporting the pathogenetic role of these cells in the development of LPI-associated complications.

Exploring the transcriptomic variation caused by the Finnish founder mutation of lysinuric protein intolerance (LPI)

Lysinuric protein intolerance (LPI) is an autosomal recessive disorder caused by mutations in cationic amino acid transporter gene SLC7A7. Although all Finnish patients share the same homozygous mutation, their clinical manifestations vary greatly. The symptoms range from failure to thrive, protein aversion, anemia and hyperammonaemia, to immunological abnormalities, nephropathy and pulmonary alveolar proteinosis. To unravel the molecular mechanisms behind those symptoms not explained directly by the primary mutation, gene expression profiles of LPI patients were studied using genome-wide microarray technology. As a result, we discovered 926 differentially-expressed genes, including cationic and neutral amino acid transporters. The functional annotation analysis revealed a significant accumulation of such biological processes as inflammatory response, immune system processes and apoptosis. We conclude that changes in the expression of genes other than SLC7A7 may be linked to the various symptoms of LPI, indicating a complex interplay between amino acid transporters and various cellular processes.

The monocarboxylate transporter 8 and L-type amino acid transporters 1 and 2 are expressed in mouse skeletons and in osteoblastic MC3T3-E1 cells

BACKGROUND

Several plasma membrane transporters have been shown to mediate the cellular influx and/or efflux of iodothyronines, including the sodium-independent organic anion co-transporting polypeptide 1 (OATP1), the sodium taurocholate co-transporting polypeptide (NTCP), the L-type amino acid transporter 1 (LAT1) and 2 (LAT2), and the monocarboxylate transporter 8 (MCT8). The aim of this study was to investigate if the mRNAs of these transporters were expressed and regulated by thyroid hormone (TH) in mouse calvaria-derived osteoblastic MC3T3-E1 cells and in the fetal and postnatal bones of mice.

METHODS

The mRNA expression of the iodothyronine transporters was investigated with real-time polymerase chain reaction analysis in euthyroid and hypothyroid fetuses and litters of mice and in MC3T3-E1 cells treated with increasing doses of triiodothyronine (T(3); 10(-10) to 10(-6) M) or with 10(-8) M T(3) for 1-9 days.

RESULTS

MCT8, LAT1, and LAT2 mRNAs were detected in fetal and postnatal femurs and in MC3T3-E1 cells, while OATP1 and NTCP mRNAs were not. LAT1 and LAT2 mRNAs were not affected by TH status in vivo or in vitro or by the stage of bone development or osteoblast maturation (analyzed by the expression of osteocalcin and alkaline phosphatase, which are key markers of osteoblastic differentiation). In contrast, the femoral mRNA expression of MCT8 decreased significantly during post-natal development, whereas MCT8 mRNA expression increased as MC3T3-E1 cells differentiated. We also showed that MCT8 mRNA was up-regulated in the femur of hypothyroid animals, and that it was down-regulated by treatment with T(3) in MC3T3-E1 cells.

CONCLUSIONS

This is the first study to demonstrate the mRNA expression of LAT1, LAT2, and MCT8 in the bone tissue of mice and in osteoblast-like cells. In addition, the pattern of MCT8 expression observed in vivo and in vitro suggests that MCT8 may be important to modulate TH effects on osteoblast differentiation and on bone development and metabolism.

First reported case of lysinuric protein intolerance (LPI) in Lithuania, confirmed biochemically and by DNA analysis

We report on an 18-year-old Lithuanian girl with hepatosplenomegaly noticed at birth, which progressed thereafter. The patient had to wait about 17 years for an accurate diagnosis and appropriate therapy. Lactase deficiency, congenital cataract of the right eye, and osteoporosis were observed. Episodes of drowsiness were caused by intake of high-protein food. Laboratory findings included slight hyperammonaemia, high plasma Citr, Ala, Gly, Glu, Ser levels, as well as citrullinuria, lysinuria, glutaminuria, alaninuria, argininuria, prolinuria, hydroxyprolinuria, ornithinuria, and orotic aciduria. Aversion to high-protein diet strongly suggested a disorder resulting in hyperammonaemia. Citrullinaemia was suspected. Subsequently the diagnosis of LPI was made on the basis of biochemical and clinical features. Molecular genetic testing revealed a mutation in the SLC7A7 gene, confirming the diagnosis.

Slc7a7 disruption causes fetal growth retardation by downregulating Igf1 in the mouse model of lysinuric protein intolerance

The solute carrier family 7A member 7 gene ( SLC7A7) encodes the light chain of the heterodimeric carrier responsible for cationic amino acid (CAA) transport across the basolateral membranes of epithelial cells in intestine and kidney. Mutations affecting SLC7A7 cause lysinuric protein intolerance (LPI), a multiorgan disorder with clinical symptoms that include visceromegaly, growth retardation, osteoporosis, hyperammonemia, and hyperdibasicaminoaciduria. Here, we describe the consequences of inactivating Slc7a7 in a mouse model of LPI. The Slc7a7 mutation was generated by high-throughput retroviral gene-trapping in embryonic stem cells. The Slc7a7−/− mouse displayed intrauterine growth restriction (IUGR), commonly leading to neonatal lethality. After heavy protein ingestion, the surviving adult animals presented metabolic derangement consistent with that observed in human LPI. IUGR was investigated by examining the expression of main factors controlling fetal growth. Insulin-like growth factor 1, the dominant fetal growth regulator in late gestation, was markedly downregulated as demonstrated by quantitative real-time RT-PCR, immunostaining and Western blot analysis in fetal liver. To further explore the pathophysiology of LPI, gene expression profiling analyses were carried out by DNA microarray technology in intestine and liver of adult Slc7a7−/− mice. Significant upregulation or downregulation (twofold or greater) was observed for 488 transcripts in intestine, and for 521 transcripts in the liver. The largest category of differentially expressed genes corresponds to those involved in transport according to Gene Ontology classification. This mouse model offers new insights into the pathophysiology of LPI and into mechanisms linking CAA metabolic pathways and growth control.

Lysinuric protein intolerance: update and extended mutation analysis of theSLC7A7 gene

Lysinuric protein intolerance (LPI) is an inherited aminoaciduria caused by defective cationic amino acid (CAA) transport at the basolateral membrane of epithelial cells in the intestine and kidney. LPI is caused by mutations in the SLC7A7 gene, which encodes the y(+)LAT-1 protein, the catalytic light chain subunit of a complex belonging to the heterodimeric amino acid transporter family. Coexpression of 4F2hc (the heavy chain subunit) and y(+)LAT-1 induces y(+)L activity (CAA transport). So far a total of 43 different mutations of the SLC7A7 gene, nine of which newly reported here, have been identified in a group of 130 patients belonging to at least 98 independent families. The mutations are distributed along the entire gene and include all different types of mutations. Five polymorphisms within the SLC7A7 coding region and two variants found in the 5'UTR have been identified. A genuine founder effect mutation has been demonstrated only in Finland, where LPI patients share the same homozygous mutation, c.895-2A>T. LPI patients show extreme variability in clinical presentation, and no genotype-phenotype correlations have been defined. This phenotypic variability and the lack of a specific clinical presentation have caused various misdiagnoses. At the biochemical level, the elucidation of SLC7A7 function will be necessary to understand precise disease mechanisms and develop more specific and effective therapies. In this review, we summarize the current knowledge of SLC7A7 mutations and their role in LPI pathogenesis.

Regulation of renal amino acid transporters during metabolic acidosis

The kidney plays a major role in acid-base homeostasis by adapting the excretion of acid equivalents to dietary intake and metabolism. Urinary acid excretion is mediated by the secretion of protons and titratable acids, particularly ammonia. NH(3) is synthesized in proximal tubule cells from glutamine taken up via specific amino acid transporters. We tested whether kidney amino acid transporters are regulated in mice in which metabolic acidosis was induced with NH(4)Cl. Blood gas and urine analysis confirmed metabolic acidosis. Real-time RT-PCR was performed to quantify the mRNAs of 16 amino acid transporters. The mRNA of phosphoenolpyruvate carboxykinase (PEPCK) was quantified as positive control for the regulation and that of GAPDH, as internal standard. In acidosis, the mRNA of kidney system N amino acid transporter SNAT3 (SLC38A3/SN1) showed a strong induction similar to that of PEPCK, whereas all other tested mRNAs encoding glutamine or glutamate transporters were unchanged or reduced in abundance. At the protein level, Western blotting and immunohistochemistry demonstrated an increased abundance of SNAT3 and reduced expression of the basolateral cationic amino acid/neutral amino acid exchanger subunit y(+)-LAT1 (SLC7A7). SNAT3 was localized to the basolateral membrane of the late proximal tubule S3 segment in control animals, whereas its expression was extended to the earlier S2 segment of the proximal tubule during acidosis. Our results suggest that the selective regulation of SNAT3 and y(+)LAT1 expression may serve a major role in the renal adaptation to acid secretion and thus for systemic acid-base balance.

Lysinuric protein intolerance: identification and functional analysis of mutations of the SLC7A7 gene

Lysinuric protein intolerance (LPI) is an inherited hyperdibasic aminoaciduria caused by defective cationic amino acid (CAA) transport at the basolateral membrane of epithelial cells in the intestine and kidney. LPI is relatively common in Finland and a few clusters of patients are known in Italy and Japan. The SLC7A7 gene, mutated in LPI patients, encodes the y+LAT-1 protein which is the light subunit of a heterodimeric CAA transporter. We performed the mutation analysis in seven probands from five unrelated LPI families and identified five novel SLC7A7 mutations (p.M50K, p.T188I, p.R333M, p.Y457X, and c.499+?_629-?). By expression studies in X. laevis oocytes or patient's renal tubular cells, the functional analysis of altogether eight SLC7A7 mutations is here reported. Noteworthy, the p.R333M mutation, caused by a G to T transversion of the last nucleotide at 3' end of exon 7, disrupts a functional splicing motif generating misspliced transcripts. Three of the novel mutations were found in patients originating from Greece and Pakistan thus increasing the list of ethnic backgrounds where LPI mutant alleles are present. This reinforces the view that the rarity of LPI outside Finland might be ascribed to misdiagnosis of this disease.

Identification of Two Molecular Groups of Seminomas by Using Expression and Tissue Microarrays

Highly effective tailored clinical management of testicular germ cell tumors is based on the identification of two major histologic subtypes: seminomatous and nonseminomatous germ cell tumors. Expression array analysis of these two histologic subtypes using hierarchical clustering reveals two tumor groups, one composed solely of seminomas and the other containing embryonal carcinomas and seminomas. Supervised analysis between these groups identified 55 significantly dysregulated genes (false discovery rate = 2.3). The genes with the highest overexpression in the first group compared with the second included SLC43A1 (POV1), NET-7, IGF2, and JUP; down-regulated genes included GRB7, PFKP, and CDC6. In situ hybridization of SLC43A1 mRNA showed significantly increased signal intensity in the seminomas. At the protein level, expression of the immunohistochemical markers cytokeratins (pan-cytokeratin staining), placental-like alkaline phosphatase, anti-cytokeratin clone 5.2, CD30, anion exchanger 1/3, junction plakoglobulin (JUP), and POU domain, class 5, transcription factor 1 (octomer-binding transcription factor 3/4) was significantly different between seminomas and embryonal tumors. Hierarchical clustering based on a refined protein expression profile identified two groups, the first consisting solely of seminomas the other of seminomas and embryonal carcinomas. No histomorphologic differences were observed between the two seminoma groups such as the presence or absence of lymphocytes or extent of stromal elements. In summary, using independent methodologies and samples, we have identified two groups of seminomas. One group of seminomas has a molecular profile similar to embryonal carcinoma. The findings in the current study may help explain aberrant immunoprofiles seen with some seminomas.

A y+LAT-1 mutant protein interferes with y+LAT-2 activity: implications for the molecular pathogenesis of lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is an inherited aminoaciduria caused by defective cationic amino acid (CAA) transport at the basolateral membrane of epithelial cells in the intestine and kidney. The SLC7A7 gene, mutated in LPI, encodes the y(+)LAT-1 protein, which is the light subunit of the heterodimeric CAA transporter in which 4F2hc is the heavy chain subunit. Co-expression of 4F2hc and y(+)LAT-1 induces the y(+)L activity. This activity is also exerted by another complex composed of 4F2hc and y(+)LAT-2, the latter encoded by the SLC7A6 gene and more ubiquitously expressed than SLC7A7. On the basis of both the pattern of expression and the transport activity, y(+)LAT-2 might compensate for CAA transport when y(+)LAT-1 is defective. By expression in Xenopus laevis oocytes and mammalian cells, we functionally analysed two SLC7A7 mutants, E36del and F152L, respectively, the former displaying a partial dominant-negative effect. The results of the present study provide further insight into the molecular pathogenesis of LPI: a putative multiheteromeric structure of both [4F2hc/y(+)LAT-1] and [4F2hc/y(+)LAT-2], and the interference between y(+)LAT-1 and y(+)LAT-2 proteins. This interference can explain why the compensatory mechanism, that is, an increased expression of SLC7A6 as seen in lymphoblasts from LPI patients, may not be sufficient to restore the y(+)L system activity.

Increased NO production in lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is a disorder of dibasic amino acid transport secondary to mutation of the SLC7A7 gene characterized by renal failure, pulmonary alveolar proteinosis, lupus-like autoimmune symptoms and usually increased plasma citrulline. In order to better understand the underlying mechanism, we studied the plasma and urinary nitrite/nitrate (NO2-/NO3-) concentrations in three LPI patients and the in vitro NO2- production in cultured fibroblasts. Our data show that NO3- levels are increased in the plasma of patients with LPI. Similarly, NO2- release in the medium of cultured fibroblasts was increased. On this basis, we hypothesize that some of the poorly understood clinical signs of LPI could be related to the activation of the NO-citrulline pathway.

INFgamma stimulates arginine transport through system y+L in human monocytes

Freshly isolated human monocytes transport L-arginine mostly through a sodium independent, NEM insensitive pathway inhibited by L-leucine in the presence, but not in the absence of sodium. Interferon-gamma (IFNgamma) stimulates this pathway, identifiable with system y+L, and markedly enhances the expression of SLC7A7, the gene that encodes for system y+L subunit y+LAT1, but not of SLC7A6, that codes for the alternative subunit y+LAT2. System y+ plays a minor role in arginine uptake by monocytes and the expression of system y+-related genes, SLC7A1 and SLC7A2, is not changed by IFNgamma. These results demonstrate that system y+L is sensitive to IFNgamma.

Lysinuric protein intolerance: mechanisms of pathophysiology

Heteromeric amino acid transporters (HATs) are composed of two subunits, a polytopic membrane protein (the light subunit) and a disulfide-linked type II membrane glycoprotein (the heavy subunit). HATs represent several of the classic mammalian amino acid transport systems (e.g., L isoforms, y(+)L isoforms, asc, xc-, and b(0,+)). The light subunits confer the amino acid transport specificity to the HAT. Two transporters of this family are relevant for inherited aminoacidurias. Mutations in any of the two genes coding for the subunits of system b(0,+) (rBAT and b(0,+)AT) lead to cystinuria (MIM 220100). Transport defects in a system y(+)L isoform, composed of 4F2hc and y(+)LAT-1, result in lysinuric protein intolerance (LPI) (MIM 222700). In this case, only mutations in the light subunit y(+)LAT-1, but not in the heavy chain 4F2hc, cause the disease. LPI, in addition to affecting intestinal and renal reabsorption of amino acids, is a multisystemic disease affecting the urea cycle and presents also with symptoms related to the immune system. The pathogenesis of these alterations is less well, or not understood at all.

Evaluation of a mass screening program for lysinuric protein intolerance in the northern part of Japan

Lysinuric protein intolerance (LPI:MIM 222700) is an autosomal recessive disease characterized by defective transport of the dibasic amino acids. We recently reported a local cluster of LPI in the northern part of Japan (Koizumi et al., 2000). Mutational analysis of the LPI patients in this local cluster revealed they were exclusively homozygous for the R410X mutation. The effectiveness of early intervention with citrulline therapy (200 mg/kg per day) and protein restriction (1.5 g/kg per day) was confirmed in these patients. Mass screening was conducted in 4,568 newborn babies between 1999 and 2002, which was estimated to cover 100% of almost all newborns delivered in the screened area. Forty heterozygous newborns were found (0.88%), leading to an estimated incidence of LPI of 1:51,984. The number of people that required screening to detect one case was 51,984, and the cost for mass screening was 30 cents/person (a total of dollars 15,600). This is comparable to, or even less than, the cost of currently screened diseases in Japan. Therefore, we conclude that a mass screening program for LPI can be introduced effectively and economically into an area where an LPI cluster is located as the result of a founder mutation.

Basolateral LAT-2 has a major role in the transepithelial flux of L-cystine in the renal proximal tubule cell line OK

During renal reabsorption, the amino acid transporters b(o,+) and y(+)L have a major role in the apical uptake of cystine and dibasic amino acids and in the basolateral efflux of dibasic amino acids, respectively. In contrast, the transporters responsible for the basolateral efflux of the apically transported cystine are unknown. This study shows the expression of system L and y(+)L transport activities in the basolateral domain of the proximal tubule-derived cell line OK and the cloning of the corresponding LAT-2 and y(+)LAT-1 cDNAs. Stable transfection with a LAT-2 antisense sequence demonstrated the specific role of LAT-2 in the basolateral system L amino acid exchange activity in OK cells. This partial reduction of LAT-2 expression decreased apical-to-basolateral trans-epithelial flux of cystine and resulted in a twofold to threefold increase in the intracellular content of cysteine. In contrast, the content of serine, threonine, and alanine showed a tendency to decrease, whereas other LAT-2 substrates were not affected. This demonstrates that LAT-2 plays a major specific role in the net basolateral efflux of cysteine and points to LAT-2 as a candidate gene to modulate cystine reabsorption.

Promoter analysis of the human SLC7A7 gene encoding y+L amino acid transporter-1 (y+LAT-1)

The human SLC7A7 gene on chromosome 14q11.2 encodes the y+L amino acid transporter-1 (y+LAT-1) protein that transports, together with the 4F2hc cell surface antigen, cationic amino acids through the basolateral membrane of epithelial cells in the small intestine and kidney. The SLC7A7 gene comprises 11 exons, but the first two are not translated. Mutations in the coding region of the SLC7A7 gene cause a rare autosomal disorder, lysinuric protein intolerance (LPI). We have now investigated the expression levels and putative 5' promoter elements of the SLC7A7. The 5' region of the first untranslated exon contains no TATA-box, Inr elements nor other classical promoter elements, but has instead other putative transcription factor binding sequences. The E-box and AP-2 elements were able to bind proteins in HEK293 cells and adult kidney tissue extracts, but not in fibroblasts. Using transient transfection and luciferase reporter gene studies, we showed that the first two introns located in the untranslated region contained transcriptional enhancer elements. Northern blot analysis showed low and equal SLC7A7 mRNA levels in the control and LPI patient fibroblastoid and lymphoblast cells.

Expression of normal and mutant GFP-tagged y(+)L amino acid transporter-1 in mammalian cells

Lysinuric protein intolerance (LPI; MIM 222700) is an autosomal recessive disorder characterized by defective transport of cationic amino acids lysine, arginine and ornithine. The defect is localized in the basolateral membrane of polar epithelial cells of the renal tubules and intestine. The SLC7A7 (solute carrier family 7, member 7) gene that encodes y(+)LAT-1 (y(+)L amino acid transporter-1) is mutated in LPI, and leads to the malfunction of the heterodimer composed of y(+)LAT-1 and 4F2hc (4F2 heavy chain) responsible for the system y(+)L amino acid transport activity at the membrane. In this study, the intracellular trafficking and membrane expression of wild type and four mutant y(+)LAT-1 proteins (LPI(Fin), G54V, 1548delC, W242X) was studied in two human cell lines by expressing green fluorescent protein (GFP) tagged proteins. Different SLC7A7 mutations influenced the trafficking of y(+)LAT-1 in the cells differently, as the wild type and missense mutant fusion proteins localized to the plasma membrane, while the frameshift and nonsense mutants sequestered to the cytoplasmic membranes, never reaching the target areas of the cell.

Two-way arginine transport in human endothelial cells: TNF-alpha stimulation is restricted to system y(+)

Human umbilical vein endothelial cells transport arginine through two Na(+)-independent systems. System y(+)L is insensitive to N-ethylmaleimide (NEM), inhibited by L-leucine in the presence of Na(+), and referable to the expression of SLC7A6/y(+)LAT2, SLC7A7/y(+)LAT1, and SLC3A2/4F2hc. System y(+) is referable to the expression of SLC7A1/CAT1 and SLC7A2/CAT2B. Tumor necrosis factor-alpha (TNF-alpha) and bacterial lipopolysaccharide induce a transient stimulation of arginine influx and efflux through system y(+). Increased expression of SLC7A2/CAT2B is detectable from 3 h of treatment, while SLC7A1 expression is inhibited at later times of incubation. System y(+)L activity and expression remain unaltered. Nitric oxide synthase type 2 mRNA is not detected in the absence or presence of TNF-alpha, while the latter condition lowers nitric oxide synthase type 3 expression at the mRNA and the protein level. Nitrite accumulation is comparable in cytokine-treated and control cells up to 48 h of treatment. It is concluded that modulation of endothelial arginine transport by TNF-alpha or lipopolysaccharide occurs exclusively through changes in CAT2B and CAT1 expression and is dissociated from stimulation of nitric oxide production.

EEG1, a putative transporter expressed during epithelial organogenesis: comparison with embryonic transporter expression during nephrogenesis

A screen for genes differentially regulated in a model of kidney development identified the novel gene embryonic epithelia gene 1 (EEG1). EEG1 exists as two transcripts of 2.4 and 3.5 kb that are most highly expressed at embryonic day 7 and later in the fetal liver, lung, placenta, and kidney. The EEG1 gene is composed of 14 exons spanning a 20-kb region at human chromosome 11p12 and the syntenic region of mouse chromosome 2. Six EEG1 exons have previously been assigned to a longer isoform of eosinophil major basic protein termed proteoglycan 2. Another gene distantly related to EEG1, POV1/PB39, is located 88 kb upstream from the EEG1 gene on chromosome 11. Temporal expression of 65 members of the solute carrier (SLC)-class of transport proteins was followed during kidney development using DNA arrays. POV-1 and EEG1, like glucose transporters, displayed very early maximal gene expression. In contrast, other SLC genes, such as organic anion and cation transporters, amino acid permeases, and nucleoside transporters, had maximal expression later in development. Thus, although the bulk of transporters are expressed late in kidney development, a fraction are expressed near the onset of nephrogenesis. The data raise the possibility that EEG1 and POV1 may define a new family of transport proteins involved in the transport of nutrients or metabolites in rapidly growing and/or developing tissues.

Layered expression scanning: rapid molecular profiling of tumor samples

Layered expression scanning is a new approach to comprehensive molecular analysis of tumor samples that uses a layered array of capture membranes coupled to antibodies or DNA sequences to perform multiplex protein or mRNA analysis. Cell or tissue samples are transferred through a series of individual capture layers, each linked to a separate antibody or DNA sequence. As the biomolecules traverse the membrane set, each targeted protein or mRNA is specifically captured by the layer containing its antibody or cDNA sequence. The two-dimensional relationship of the cell populations is maintained during the transfer process, thereby producing a molecular profile of each cell type present. Reduction-to-practice of the technique is demonstrated by analysis of prostate-specific antigen (PSA) protein, gelatinase A protein, and POV1 (PB39) cDNA. As layered expression scanning technology progresses, we envision a laboratory method that will have multiple applications for high-throughput molecular profiling of normal and tumor samples.

cDNA sequencing and analysis of POV1 (PB39): a novel gene up-regulated in prostate cancer

We recently identified a novel gene (PB39) (HGMW-approved symbol POV1) whose expression is up-regulated in human prostate cancer using tissue microdissection-based differential display analysis. In the present study we report the full-length sequencing of PB39 cDNA, genomic localization of the PB39 gene, and genomic sequence of the mouse homologue. The full-length human cDNA is 2317 nucleotides in length and contains an open reading frame of 559 amino acids which does not show homology with any reported human genes. The N-terminus contains charged amino acids and a helical loop pattern suggestive of an srp leader sequence for a secreted protein. Fluorescence in situ hybridization using PB39 cDNA as probe mapped the gene to chromosome 11p11.1-p11.2. Comparison of PB39 cDNA sequence with murine sequence available in the public database identified a region of previously sequenced mouse genomic DNA showing 67% amino acid sequence homology with human PB39. Based on alignment and comparison to the human cDNA the mouse genomic sequence suggests there are at least 14 exons in the mouse gene spread over approximately 100 kb of genomic sequence. Further analysis of PB39 expression in human tissues shows the presence of a unique splice variant mRNA that appears to be primarily associated with fetal tissues and tumors. Interestingly, the unique splice variant appears in prostatic intraepithelial neoplasia, a microscopic precursor lesion of prostate cancer. The current data support the hypothesis that PB39 plays a role in the development of human prostate cancer and will be useful in the analysis of the gene product in further human and murine studies.