Virus-transformed Lymphoblasts Research Articles

Knockdown of the Shwachman-Diamond syndrome gene, SBDS, induces galectin-1 expression and impairs cell growth.

Shwachman-Diamond syndrome (SDS) is an autosomal recessive disorder characterized by exocrine pancreatic insufficiency and bone marrow failure. The depletion of SBDS protein by RNA interference has been shown to cause inhibition of cell proliferation in several cell lines. However, the precise mechanism by which the loss of SBDS leads to inhibition of cell growth remains unknown. To evaluate the impaired growth of SBDS-knockdown cells, we analyzed Epstein-Barr virus-transformed lymphoblast cells (LCLs) derived from two patients with SDS (c. 183_184TA > CT and c. 258 + 2T > C). After 3days of culture, the growth of LCL-SDS cell lines was considerably less than that of control donor cells. By annealing control primer-based GeneFishing PCR screening, we found that galectin-1 (Gal-1) mRNA expression was elevated in LCL-SDS cells. Western blot analysis showed that the level of Gal-1 protein expression was also increased in LCL-SDS cells as well as in SBDS-knockdown 32Dcl3 murine myeloid cells. We confirmed that recombinant Gal-1 inhibited the proliferation of both LCL-control and LCL-SDS cells and induced apoptosis (as determined by annexin V-positive staining). These results suggest that the overexpression of Gal-1 contributes to abnormal cell growth in SBDS-deficient cells.

Regulation of Folate-Mediated One-Carbon Metabolism by Glycine N-Methyltransferase (GNMT) and Methylenetetrahydrofolate Reductase (MTHFR).

Folate-mediated one-carbon metabolism is an important therapeutic target of human diseases. We extensively investigated how gene-nutrient interactions may modulate human cancer risk in 2 major folate metabolic genes, MTHFR and GNMT. The biochemical impacts of MTHFR and GNMT on methyl group supply, global DNA methylation, nucleotide biosynthesis, DNA damage, and partitioning of the folate dependent 1-carbon group were carefully studied. The distinct model systems used included: EB virus-transformed lymphoblasts expressing human MTHFR polymorphic genotypes; liver-derived GNMT-null cell-lines with and without GNMT overexpression; and HepG2 cells with stabilized inhibition of MTHFR using shRNA, GNMT wildtype, heterozygotous (GNMT(het)) and knockout (GNMT(nul)) mice. We discovered that the MTHFR TT genotype significantly reduces folate-dependent remethylation under folate restriction, but it assists purine synthesis when folate is adequate. The advantage of de novo purine synthesis found in the MTHFR TT genotype may account for the protective effect of MTHFR in human hematological malignancies. GNMT affects transmethylation kinetics and S-adenosylmethionine (adoMet) synthesis, and facilitates the conservation of methyl groups by limiting homocysteine remethylation fluxes. Restoring GNMT assists methylfolate-dependent reactions and ameliorates the consequences of folate depletion. GNMT expression in vivo improves folate retention and bioavailability in the liver. Loss of GNMT impairs nucleotide biosynthesis. Over-expression of GNMT enhances nucleotide biosynthesis and improves DNA integrity by reducing uracil misincorporation in DNA both in vitro and in vivo. The systematic series of studies gives new insights into the underlying mechanisms by which MTHFR and GNMT may participate in human tumor prevention.

Functional Variants of the <emph type="ital">HMGA1</emph> Gene and Type 2 Diabetes Mellitus

High-mobility group A1 (HMGA1) protein is a key regulator of insulin receptor (INSR) gene expression. We previously identified a functional HMGA1 gene variant in 2 insulin-resistant patients with decreased INSR expression and type 2 diabetes mellitus (DM). To examine the association of HMGA1 gene variants with type 2 DM. Case-control study that analyzed the HMGA1 gene in patients with type 2 DM and controls from 3 populations of white European ancestry. Italian patients with type 2 DM (n = 3278) and 2 groups of controls (n = 3328) were attending the University of Catanzaro outpatient clinics and other health care sites in Calabria, Italy, during 2003-2009; US patients with type 2 DM (n = 970) were recruited in Northern California clinics between 1994 and 2005 and controls (n = 958) were senior athletes without DM collected in 2004 and 2009; and French patients with type 2 DM (n = 354) and healthy controls (n = 50) were enrolled at the University of Reims in 1992. Genomic DNA was either directly sequenced or analyzed for specific HMGA1 mutations. Messenger RNA and protein expression for HMGA1 and INSR were measured in both peripheral lymphomonocytes and cultured Epstein-Barr virus-transformed lymphoblasts from patients with type 2 DM and controls. The frequency of HMGA1 gene variants among cases and controls. Odds ratios (ORs) for type 2 DM were estimated by logistic regression analysis. The most frequent functional HMGA1 variant, IVS5-13insC, was present in 7% to 8% of patients with type 2 DM in all 3 populations. The prevalence of IVS5-13insC variant was higher among patients with type 2 DM than among controls in the Italian population (7.23% vs 0.43% in one control group; OR, 15.77 [95% confidence interval {CI}, 8.57-29.03]; P < .001 and 7.23% vs 3.32% in the other control group; OR, 2.03 [95% CI, 1.51-3.43]; P < .001). In the US population, the prevalence of IVS5-13insC variant was 7.7% among patients with type 2 DM vs 4.7% among controls (OR, 1.64 [95% CI, 1.05-2.57]; P = .03). In the French population, the prevalence of IVS5-13insC variant was 7.6% among patients with type 2 DM and 0% among controls (P = .046). In the Italian population, 3 other functional variants were observed. When all 4 variants were analyzed, HMGA1 defects were present in 9.8% of Italian patients with type 2 DM and 0.6% of controls. In addition to the IVS5 C-insertion, the c.310G>T (p.E104X) variant was found in 14 patients and no controls (Bonferroni-adjusted P = .01); the c.*82G>A variant (rs2780219) was found in 46 patients and 5 controls (Bonferroni-adjusted P < .001); the c.*369del variant was found in 24 patients and no controls (Bonferroni-adjusted P < .001). In circulating monocytes and Epstein-Barr virus-transformed lymphoblasts from patients with type 2 DM and the IVS5-13insC variant, the messenger RNA levels and protein content of both HMGA1 and the INSR were decreased by 40% to 50%, and these defects were corrected by transfection with HMGA1 complementary DNA. Compared with healthy controls, the presence of functional HMGA1 gene variants in individuals of white European ancestry was associated with type 2 DM.

Folate restriction and methylenetetrahydrofolate reductase 677T polymorphism decreases adoMet synthesis via folate-dependent remethylation in human-transformed lymphoblasts

The homozygous mutation (677TT) in the methylenetetrahydrofolate reductase (MTHFR) gene reduces enzyme activity and alters cellular folate composition. Previous epidemiological studies reported a potential protective effect of MTHFR677C --> T against acute lymphocytic leukemia and malignant lymphoma, but the mechanism remains to be determined. We investigated the biochemical impacts of MTHFR677C --> T on cellular S-adenosyl methionine (adoMet) synthesis, global DNA methylation, and de novo purine synthesis, all of which are potential regulatory pathways involved in tumorigenesis. Metabolic fluxes of homocysteine remethylation and de novo purine synthesis were compared between Epstein-Barr virus-transformed lymphoblasts expressing MTHFR 677C and MTHFR 677T using stable isotopic tracers and GCMS. MTHFR TT genotype significantly reduced folate-dependent remethylation under folate restriction, reflecting limited methylated folates under folate restriction. Data also suggested increased formylated folate pool and increased purine synthesis when folate is adequate. The impacts of MTHFR 677T polymorphism appeared closely related to folate status, and such alterations may modulate metabolic pathways involved in cancer onset/progression. The advantage of de novo purine synthesis found in the MTHFR TT genotype may account for the protective effect of MTHFR in hematological malignancies. These transformed cells are potential models for studying the consequences of human genetic variation and cancer pathogenesis.

Strategies for the Characterization of Disorders in Cortisol Sensitivity

The clinical presentation of abnormalities in glucocorticoid (GC) sensitivity is diverse, and therefore it is difficult to diagnose this condition. The objective of the study was to develop strategies for the characterization of GC sensitivity disorders. The study was conducted in an outpatient clinic. Nine patients with GC sensitivity disorders participated. Sequence analysis of the GC receptor (GR), determination of GR number per cell, GR ligand-binding affinity, and GR splice regulation were performed in freshly prepared peripheral blood mononuclear lymphocytes and Epstein-Barr virus-transformed lymphoblasts. Cellular GC sensitivity was determined ex vivo by measuring the effect of dexamethasone on GC-induced leucine-zipper and IL-2 mRNA levels and on cell proliferation. Differences in GR number per cell, GR affinity, GR splice variants, and effects on transactivation or transrepression of GC-sensitive genes were observed between patients and controls. Epstein-Barr virus transformation of lymphoblasts had no influence on GR affinity but increased the GR number 5-fold in healthy controls. In patients diagnosed as cortisol resistant, however, GR number after transformation was increased significantly less than 5-fold, whereas a higher GR number was observed in a patient suspected of cortisol hypersensitivity. This study illustrates several strategies to define abnormalities in GC sensitivity by describing nine patients with affected GC sensitivity, all with a unique clinical course and background.

Telomere length and heredity: Indications of paternal inheritance

Cellular telomere length is linked to replicative life span. Telomere repeats are lost in peripheral blood cells in vivo by age, and women show less telomere attrition than men. Previous reports have indicated that telomere length and chromosome-specific telomere-length patterns partly are inherited. The mode of heredity has not been clarified, but a link to the X chromosome was recently suggested. We analyzed peripheral mononuclear cells from 49 unrelated families for telomere length using a real-time PCR method. Short-term cultured Epstein-Barr virus-transformed lymphoblasts from the same individuals (n = 130) were analyzed for ability to maintain telomere length and possible gender-linked inheritance. A statistically significant association between telomere lengths comparing father-son (P = 0.011, n = 20) and father-daughter (P = 0.005, n = 22) pairs was found. However, no correlation was observed between mother-daughter (P = 0.463, n = 23) or mother-son (P = 0.577, n = 18). The father-offspring correlation was highly significant (P < 0.0001), in contrast to mother-offspring (P = 0.361). Epstein-Barr virus cultures demonstrated in most cases telomere preservation inversely related to initial mononuclear cell telomere length with short telomeres displaying the most pronounced elongation. Telomere length is inherited, and evidence for a father-to-offspring heritage of this trait was obtained, whereas in vitro telomere length maintenance was found to be dependent on the initial telomere length.

Cellular insulin resistance in Epstein-Barr virus-transformed lymphoblasts from young insulin-resistant Japanese men

The metabolic syndrome is characterized by a blunted insulin-mediated glucose uptake in various cell types. We compared the glucose uptake characteristics of Epstein-Barr virus (EBV)–transformed lymphoblasts obtained from young men with vs without metabolic and cardiovascular evidence of metabolic syndrome. From a population of 218 men, 20- to 25-year-old, 10 men with a systolic blood pressure (BP) ≥130 mm Hg and family history of hypertension were assigned to a high BP (HBP) group, and 10 with a BP ≤110 mm Hg, and no family history of hypertension was assigned to a low BP (LBP) group. Multiple clinical and metabolic characteristics were examined in both groups and compared. Peripheral lymphocytes from HBP and LBP subjects were EBV-transformed, and the glucose transporter (Glut)–mediated glucose uptake from each group was compared in lymphoblasts. Body mass index, fasting glucose, immunoreactive insulin, insulin resistance index based on a homeostasis model assessment (HOMA-R), and total and low-density lipoprotein cholesterol were significantly higher in the HBP than the LBP subgroup (whole-body insulin resistance). Baseline Glut-mediated and Glut-mediated insulin-stimulated glucose uptake by lymphoblasts from the HBP group were significantly lower than by lymphoblasts from the LBP group (cellular insulin resistance). The net increment in Glut-mediated glucose uptake by insulin was inversely correlated with HOMA-R. In conclusion, cellular insulin resistance in EBV-transformed lymphoblasts is associated with young Japanese subjects with HBP. The net increment in Glut-mediated glucose uptake by insulin in lymphoblasts may be a useful intermediate phenotype to study genetic aspects of the metabolic syndrome.

Denaturing Gradient Gel Electrophoresis for the Molecular Characterization of Six Patients with Guanidinoacetate Methyltransferase Deficiency

Guanidinoacetate methyltransferase [(GAMT); EC 2.1.1.2] deficiency is the first recognized inborn error of creatine biosynthesis, manifesting in infancy with severe neurologic symptoms such as epilepsy, mental retardation, muscular hypotonia, and progressive extrapyramidal movement disorder (1). Patients with GAMT deficiency have shown favorable responses to oral supplementation of creatine-monohydrate, but complete reversal of symptoms has not been observed (2). Biochemical findings include high urinary excretion of guanidinoacetate (the immediate precursor of creatine and substrate of GAMT), low urinary excretion of creatinine [conversion product of intracellular creatine; see Ref. (3)], and depletion of creatine in brain and muscle (4). After assessing two index patients (5)(6), we aimed to establish methods for the noninvasive molecular diagnosis of GAMT deficiency. We recently developed a radiochemical method for the determination of GAMT activity in cultured skin fibroblasts and in virus-transformed lymphoblasts (7). Here we report a denaturing gradient gel electrophoresis (DGGE) technique for the screening of mutations in the GAMT gene in DNA extracted from dried-blood spot filter-paper samples and from fibroblasts and virus-transformed lymphoblasts. Three index patients with mutations confirmed by techniques other than DGGE [P1, P2, and P6; see Refs. (5), (8)] and three new patients (P3, P4, and P5) with undetectable GAMT activity but unknown GAMT deficiency mutations (9)(10) were investigated. Details of the patient studies are summarized in Table 1⇓ , and the locations and frequencies of the mutations identified in these patients are shown in Fig. 1⇓ . We extracted DNA from dried-blood spot, filter-paper samples and from fibroblasts and lymphoblasts using …

Arginine:Glycine Amidinotransferase Deficiency: The Third Inborn Error of Creatine Metabolism in Humans

Arginine:glycine amidinotransferase (AGAT) catalyzes the first step of creatine synthesis, resulting in the formation of guanidinoacetate, which is a substrate for creatine formation. In two female siblings with mental retardation who had brain creatine deficiency that was reversible by means of oral creatine supplementation and had low urinary guanidinoacetate concentrations, AGAT deficiency was identified as a new genetic defect in creatine metabolism. A homozygous G-A transition at nucleotide position 9297, converting a tryptophan codon (TGG) to a stop codon (TAG) at residue 149 (T149X), resulted in undetectable cDNA, as investigated by reverse-transcription PCR, as well as in undetectable AGAT activity, as investigated radiochemically in cultivated skin fibroblasts and in virus-transformed lymphoblasts of the patients. The parents were heterozygous for the mutant allele, with intermediate residual AGAT activities. Recognition and treatment with oral creatine supplements may prevent neurological sequelae in affected patients.

Oxidation of galactose by galactose-1-phosphate uridyltransferase-deficient lymphoblasts.

The ability of EB virus-transformed lymphoblasts with undetectable galactose-1-phosphate uridyltransferase (GALT) from 15 galactosaemic patients to oxidize [1-(14)C]galactose to 14CO2 was compared to that of cells from 7 normal subjects. The oxidation of galactose but not of glucose was markedly diminished by cells from Q188R homozygous galactosaemic patients but was not absent. After 2.5 h these cells liberated 14CO2 at nearly 3% and at 5 h up to 9% of normal. Cells from patients homozygous for the S135L mutation produced much larger amounts of 14CO2 (15-17% of normal) and were distinguishable from the Q188R homozygous cells. A cell line with a homozygous deletion of the GALT gene oxidized galactose at 7% of the normal rate, suggesting that pathways(s) other than GALT exist in these cells as well as Q188R homozygous cells for oxidation of galactose to CO2. Concentration dependence studies are consistent with the presence of a pathway that is unsaturable or has a very high Km The ability of 10(7) lymphoblasts with the S135L genotype to oxidize more than 7% of the sugar to 14CO2 in 5 h suggests the presence of residual GALT despite the inability to detect the activity by enzymatic analysis.

The Fanconi anemia group C gene product modulates apoptotic responses to tumor necrosis factor-α and Fas ligand but does not suppress expression of receptors of the tumor necrosis factor receptor superfamily

Exposure of hematopoietic progenitor cells (HPC) from mice and humans with Fanconi anemia group C (FAC) to interferon-γ (IFN- γ) or tumor necrosis factor- α (TNF- α) at doses too low to inhibit growth of normal HPC induces profound apoptotic responses. Because the IFN- γ hypersensitivity of cells lacking the FAC protein is mediated, in part, through priming of the Fas pathway, and because several other members of this family are capable of inducing apoptosis either alone or in concert with each other, we tested the hypothesis that IFN- γ induces increased expression of members of the TNF receptor (TNFR) superfamily in cells nullizygous for the FAC gene. Using isogenic human Epstein–Barr virus-transformed lymphoblast cell lines and c-kit + bone marrow cells from mice with inactivating mutations of the FAC locus, we quantified mRNA levels by reverse transcriptase polymerase chain reaction and surface expression of the gene products by flow cytometry of TNFR1, TNFR2, Fas, CD30, CD40, and nerve growth factor receptor. We found that neither constitutive nor IFN- γ–induced expression of these receptors was influenced by the absence of a functional FAC gene product, and expression of these receptors was not suppressed in nullizygous cells complemented with the normal FAC cDNA. We conclude that, although exaggerated apoptotic responses in FAC-deficient cells are at least partially mediated through activation of members of the TNFR superfamily, the normal FAC protein does not function as a direct suppressor of this family of molecules and inactivation of FAC does not augment expression of these proteins.

Masking and unmasking of the sialic acid-binding lectin activity of CD22 (Siglec-2) on B lymphocytes.

CD22 is a B cell-restricted glycoprotein involved in signal transduction and modulation of cellular activation. It is also an I-type lectin (now designated Siglec-2), whose extracellular domain can specifically recognize alpha2-6-linked sialic acid (Sia) residues. This activity is postulated to mediate intercellular adhesion and/or to act as a coreceptor in antigen-induced B cell activation. However, studies with recombinant CD22 indicate that the lectin function can be inactivated by expression of alpha2-6-linked Sia residues on the same cell surface. To explore whether this masking phenomenon affects native CD22 on B cells, we first developed a probe to detect the lectin activity of recombinant CD22 expressed on Chinese hamster ovary cells (which have no endogenous alpha2-6-linked Sia residues). This probe is inactive against CD22-positive B lymphoma cells and Epstein-Barr virus-transformed lymphoblasts which express high levels of alpha2-6-linked Sia residues. Enzymatic desialylation unmasks the CD22 lectin activity, indicating that endogenous Sia residues block the CD22 lectin-binding site. Truncation of the side chains of cell surface Sia residues by mild periodate oxidation (known to abrogate Sia recognition by CD22) also had this unmasking effect, indicating that the effects of desialylation are not due to a loss of negative charge. Normal resting B cells from human peripheral blood gave similar findings. However, the lectin is partially unmasked during in vitro activation of these cells. Thus, the lectin activity of CD22 is restricted by endogenous sialylation in resting B cells and may be transiently unmasked during in vivo activation, perhaps to modulate intercellular or intracellular interactions at this critical stage in the humoral response.

Structural and numerical chromosomal aberrations in a metabolically competent human lymphoblast cell line (MCL-5).

MCL-5 cells are Epstein Barr virus-transformed human lymphoblasts which have been genetically engineered for use in mutagenicity testing. We have examined the modal chromosome number, karyotype and spontaneous micronucleus (MN) and sister chromatid exchange (SCE) frequencies of the cell line. Replicate experiments were conducted on two different shipments purchased from Gentest Corp. Although the modal chromosome number was 48 (range 40-54, n = 400 metaphases) for both cell shipments, the second stock showed greater variation in chromosome number than the first. A total of 60 G-banded metaphase cells was analyzed and seven karyotypes were prepared. Consistent structural abnormalities (translocations, deletions and isochromosomes) were found involving the X chromosome and seven autosomes (1-3, 5, 6, 9 and 11). The karyotype typical of this cell line was: 48,der(X)t(X;?)(p22.3;?)Y,t(1;2)(q23;p23),del(3)(q12q21), + i(3q),t(5;6) (q31;p23),+i(9p),der(11)t(11;13)(q23;q12). The mean MN frequency was 41.8 MN/1000 binucleate cells (n = 5000). When compared with our historical controls for primary lymphocyte cultures this number (41.8) is significantly (8.4-fold) higher. The mean SCE frequency was 7.3 per metaphase (n = 100). We observed a hyperdiploid chromosome number of 48 in the majority of metaphase spreads, indicating a significant deviation from the normal diploid number characteristic of the parent cells (RPMI 1788) established in 1969. The variation in chromosome number distribution observed between shipments suggests the potential for further changes. The elevated MN frequency suggests that evaluating mutagenicity using this cytogenetic end-point may require excessive dosing to produce a significant response over background. We conclude that careful interpretation of cytogenetic end-points is necessary when using MCL-5 cells in the light of the possibility of clonal evolution presented here.

Linkage analysis using platelet-activating factor Ca2+ response in transformed lymphoblasts.

Epstein-Barr virus-transformed lymphoblasts from patients with essential hypertension demonstrate enhanced G protein-mediated cytosolic free calcium ([Ca2+]i) response to platelet-activating factor (PAF). To map genes responsible for variation in G protein-coupled signaling, we used this cellular phenotype for a linkage study of transformed cell lines from the Centre d'Etude du Polymorphisme Humain (CEPH) reference pedigrees. The PAF-evoked change in [Ca2+]i ranged from 20 to 392 mmol/L and was highly reproducible within each cell line. PAF-elicited [Ca2+]i responses were obtained in lymphoblastic cell lines from five densely mapped pedigrees of the CEPH collection. Using PAF-evoked [Ca2+]i responses as a quantitative trait, two-point sibpair linkage analyses were conducted using 5150 markers from the Collaborative Human Linkage Center (CHLC) database. Nine loci, located on chromosomes 1, 4, 10, 11, 13, 16, and 17, were suggestive of linkage, with values of P < 7.4 x 10(-4). Multipoint linkage analysis produced a significant linkage finding (P = 2.1 x 10(-5) in one family at D16S151, with suggestive linkage results for seven additional markers spanning a 40-cM interval of chromosome 16. Multipoint analysis produced suggestive findings of linkage to eight loci from two distinct regions of chromosome 11 in another family. These results indicate that loci involved in the control of G protein-mediated mechanisms, suggested to be involved in the pathophysiology of essential hypertension, can be identified using cell lines from general pedigrees selected without any knowledge of the blood pressure status of the donors. This strategy represents an approach to rapidly and inexpensively mapping loci related to common, complex disorders, using phenotypes that are stable in immortalized lymphoblasts together with existing reference pedigree cell lines and genotype databases.

Chimpanzee dendritic cells with potent immunostimulatory function can be propagated from peripheral blood

We have established dendritic cell (DC) cultures from chimpanzee peripheral blood mononuclear cells (PBMC) by using recombinant human (rh) granulocyte-macrophage colony-stimulating factor (GM-CSF) and rh interleukin-4 (IL-4) and demonstrate that these cells have all the characteristics of DC as described for other species. We consistently can obtain 1 x 10(7) DC per 100 ml of blood, a yield of 5% DC as compared to 0.1 to 0.5% DC reported in fresh human PBMC. The cultured DC have a varied morphology with typical cytoplasmic extensions. Phenotypically, the blood-derived DC lack expression of most lineage antigens, but express CD83, an antigen specifically expressed on human blood DC. Chimpanzee DC express very high levels of major histocompatability complex class II antigens, adhesion and costimulatory molecules. Consistent with this phenotype of a powerful antigen-presenting cell, chimpanzee DC generate allogeneic mixed leukocyte responses 15 to 20 times more potent than that elicited by macrophages, Epstein-Barr virus-transformed lymphoblasts and fresh PBMC. In addition, chimpanzee DC very efficiently present tetanus toxoid to PBMC-derived CD4+ T cells as compared to macrophages and PBMC. The DC generated by culturing chimpanzee PBMC with rhGM-CSF and rhIL-4 thus closely resemble human blood-derived DC propagated in the same manner. This technology provides a powerful animal model with which to apply DC to clinical studies with relevance to human disease. In particular, chimpanzee DC can be tested as immunotherapeutic agents for cancer, and be studied in relation to the pathogenesis of human immunodeficiency virus (HIV) infection.

Use of Transmitochondrial Cybrids To Assign a Complex I Defect to the Mitochondrial DNA-Encoded NADH Dehydrogenase Subunit 6 Gene Mutation at Nucleotide Pair 14459 That Causes Leber Hereditary Optic Neuropathy and Dystonia

A heteroplasmic G-to-A transition at nucleotide pair (np) 14459 within the mitochondrial DNA (mtDNA)-encoded NADH dehydrogenase subunit 6 (ND6) gene has been identified as the cause of Leber hereditary optic neuropathy (LHON) and/or pediatric-onset dystonia in three unrelated families. This ND6 np 14459 mutation changes a moderately conserved alanine to a valine at amino acid position 72 of the ND6 protein. Enzymologic analysis of mitochondrial NADH dehydrogenase (complex I) with submitochondrial particles isolated from Epstein-Barr virus-transformed lymphoblasts revealed a 60% reduction (P < 0.005) of complex I-specific activity in patient cell lines compared with controls, with no differences in enzymatic activity for complexes II plus III, III and IV. This biochemical defect was assigned to the ND6 np 14459 mutation by using transmitochondrial cybrids in which patient Epstein-Barr virus-transformed lymphoblast cell lines were enucleated and the cytoplasts were fused to a mtDNA-deficient (p 0) lymphoblastoid recipient cell line. Cybrids harboring the np 14459 mutation exhibited a 39% reduction (p < 0.02) in complex I-specific activity relative to wild-type cybrid lines but normal activity for the other complexes. Kinetic analysis of the np 14459 mutant complex I revealed that the Vmax of the enzyme was reduced while the Km remained the same as that of wild type. Furthermore, specific activity was inhibited by increasing concentrations of the reduced coenzyme Q analog decylubiquinol. These observations suggest that the np 14459 mutation may alter the coenzyme Q-binding site of complex I.

42]Assessment of mitochondrial oxidative phosphorylation in patient muscle biopsies, lymphoblasts, and transmitochondrial cell lines

Publisher Summary This chapter discusses the methods of assessment of mitochondrial oxidative phosphorylation in patient muscle biopsies, lymphoblasts, and transmitochondrial cell lines. Investigation of oxidative phosphorylation (OX-PHOS) in mitochondrial diseases has traditionally focused on the muscle biopsy. Skeletal muscle biopsy remains a valuable resource for biochemical studies as it is an easily accessed tissue and milligram quantities of mitochondria can be isolated for a wide range of OX-PHOS investigations. However, in mitochondrial diseases, the postmitotic muscle fibers commonly show secondary OX-PHOS defects that may hinder investigations of primary defects. Transformed cell lines expressing OX-PHOS defects provide a powerful model system for further genetic and biochemical characterization of nuclear and mitochondrial DNA (mtDNA) mutants and the design and testing of therapeutic approaches. The approach to OX-PHOS investigation combines the identification of patients with OX-PHOS defects using more sensitive muscle biopsy studies followed by further biochemical characterization of primary defects in Epstein–Barr virus-transformed lymphoblasts. The chapter presents novel methods for the production of transmitochondrial cybrids using lymphoblastoid and osteosarcoma ρO cells as recipients. Suspension enucleation of cells combined with electrofusion allows the use of any cell type, including lymphoblasts, as mitochondrial donors in fusions with either lymphoblastoid or osteosarcoma ρo cells.

Glucose-Induced Changes in Turnover of Na+/H+ Exchanger of Immortalized Lymphoblasts From Type I Diabetic Patients With Nephropathy

Increased cellular Na+/H+ exchanger (NHE) activity has been demonstrated in type I diabetic patients with nephropathy. Such patients also have a previous history of poor glycemic control. The interaction between hyperglycemia and changes in NHE activity remains obscure. Therefore, we examined the effects of media containing 5 and 25 mmol/l glucose on the increased NHE activity and turnover number in Epstein-Barr virus-transformed lymphoblasts from patients with diabetic nephropathy compared with normoalbuminuric diabetic and nondiabetic control subjects. NHE activity was determined fluorometrically, and NHE isoform 1 (NHE-1) density was measured with specific polyclonal antibodies. In the presence of 5 mmol/l glucose, cells from patients with diabetic nephropathy exhibited higher NHE activity with intracellular pH clamped to 6.0 compared with diabetic and nondiabetic control subjects (P < 0.005 for both), due to a higher turnover number of NHE-1. Incubation in 25 mmol/l glucose for 48 h caused an increase in NHE activity (P < 0.001) and turnover number (P < 0.01) in the diabetic nephropathy group only, with no significant change in the diabetic or nondiabetic control groups. The rate constants for cell proliferation and NHE activity or turnover number were correlated when cells were cultured in 5 mmol/l glucose (r = 0.34 and 0.32, respectively; P < 0.05) or 25 mmol/l glucose media (r = 0.66 and 0.65, respectively; P < 0.001). We conclude that only lymphoblasts from the diabetic nephropathy group show an increase in NHE activity and turnover number under conditions mimicking hyperglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Activity and density of the Na+/H+ antiporter in normal and transformed human lymphocytes and fibroblasts.

The turnover number for the sodium-hydrogen exchanger isoform 1 (NHE-1) has been determined in human lymphocytes and MRC5 fibroblasts and in their virally transformed counterparts. Using fluorometric methods, we have determined the intracellular pH and Na+/H+ antiport activity of these cells. Intracellular pH was elevated in both lines of transformed cells. In contrast, Na+/H+ antiport activity was apparently unchanged in simian virus 40-transformed MRC5 fibroblasts (MRC5 SV1 TV1 28.9 +/- 5.2 mM/min compared with MRC5 fibroblasts 26.5 +/- 5.3 mM/min) but slightly increased in Epstein-Barr virus-transformed lymphoblasts (16.7 +/- 1.0 mM/min compared with lymphocytes 13.5 +/- 2.3 mM/min, P < 0.05). With the use of specific antisera to NHE-1, viral transformation was associated with a decreased number of NHE-1 molecules per cell in fibroblasts (from 441,504 +/- 53,428 to 64,745 +/- 7,151 sites/cell, P < 0.001) but an increased number in lymphocytes (from 14,066 +/- 3,100 to 22,474 +/- 4,050 sites/cell, P < 0.01). The NHE-1 density per cell yielded very similar turnover numbers for NHE-1 in the untransformed cells (lymphocytes, 3,161 +/- 833 cycles/s; MRC5 fibroblasts, 3,026 +/- 441 cycles/s), which were significantly elevated in the transformed cells (lymphoblasts, 8,471 +/- 1,177 cycles/s; MRC5 SV1 TV1, 10,521 +/- 2,299 cycles/s, P < 0.001 compared with untransformed cells). We conclude that viral transformation has different effects on Na+/H+ antiport activity and NHE-1 density per cell in different cell types, but the turnover number of NHE-1 is significantly increased after viral transformation, which correlates with the increased proliferation rate of these transformed cells.

Abnormal Na+/H+ antiporter phenotype and turnover of immortalized lymphoblasts from type 1 diabetic patients with nephropathy.

Cellular Na+/H+ exchanger (NHE) activity is elevated in type 1 diabetic patients with nephropathy and patients with essential hypertension. The characteristics of this NHE phenotype in hypertension (raised Vmax and a lowered Hill coefficient) are preserved in Epstein-Barr virus-transformed lymphoblasts from hypertensive patients. In this study, we have determined NHE kinetics in cultured lymphoblasts from diabetic patients with and without nephropathy, with nondiabetic controls, using fluorometry with the pH indicator 2,7'-bis-(carboxyethyl)-5,6-carboxyfluorescein and estimation of NHE isoform 1 (NHE-1) density with specific polyclonal antibodies. The Vmax of NHE was elevated significantly, and the Hill coefficient for internal H+ binding was lowered in cells from patients with diabetic nephropathy compared with both normal controls and normoalbuminuric diabetic patients. NHE-1 density as measured by Western blotting was similar in all groups. The turnover number of NHE-1 was thus elevated in cells from nephropathy patients. This phenotype in cells from diabetic nephropathy patients resembles that in essential hypertension and suggests that such patients may have a predisposition to hypertension. Moreover, as these changes persist in cultured lymphoblasts in vitro, these cells should provide a cell culture model to further define the basic mechanisms leading to NHE activation in diabetic nephropathy.