T Cells Mediate Kidney Tubular Injury via Impaired PDHA1 and Autophagy in Type 1 Diabetes

CONTEXT

Nephropathy is a severe complication of type 1 diabetes (T1DM). However, the interaction between the PDHA1-regulated mechanism and CD4+ T cells in the early stage of kidney tubular injury remains unknown.

OBJECTIVE

To evaluate the role of PDHA1 in the regulation of tubular cells and CD4+ T cells and further to study its interaction in tubular cell injury in T1DM.

METHODS

Plasma and total RNA were collected from T cells of T1DM patients (n = 35) and healthy donors (n = 33) and evaluated for neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1, PDHA1, and biomarkers of CD4+ T cells including T helper 1 cells (Th1) and regulatory T cells (Treg) markers. HK-2 cells cocultured with CD4+ T cells from T1DM patients or healthy donors (HDs) to evaluate the interaction with CD4+ T cells.

RESULTS

Increased PDHA1 gene expression levels in CD4+ T cells were positively associated with the plasma level of NGAL in T1DM patients and HDs. Our data demonstrated that the Th1/Treg subsets skewed Th1 in T1DM. Knockdown of PDHA1 in kidney tubular cells decreased ATP/ROS production, NAD/NADH ratio, mitochondrial respiration, and cell apoptosis. Furthermore, PDHA1 depletion induced impaired autophagic flux. Coculture of tubular cells and T1DM T cells showed impaired CPT1A, upregulated FASN, and induced kidney injury.

CONCLUSION

Our findings indicate that Th1 cells induced tubular cell injury through dysregulated metabolic reprogramming and autophagy, thereby indicating a new therapeutic approach for kidney tubular injury in T1DM.

Creatine Monohydrate Supplementation Increases White Adipose Tissue Mitochondrial Markers in Male and Female Rats in a Depot Specific Manner

White adipose tissue (WAT) is a dynamic endocrine organ that can play a significant role in thermoregulation. WAT has the capacity to adopt structural and functional characteristics of the more metabolically active brown adipose tissue (BAT) and contribute to non-shivering thermogenesis under specific stimuli. Non-shivering thermogenesis was previously thought to be uncoupling protein 1 (UCP1)-dependent however, recent evidence suggests that UCP1-independent mechanisms of thermogenesis exist. Namely, futile creatine cycling has been identified as a contributor to WAT thermogenesis. The purpose of this study was to examine the efficacy of creatine supplementation to alter mitochondrial markers as well as adipocyte size and multilocularity in inguinal (iWAT), gonadal (gWAT), and BAT. Thirty-two male and female Sprague-Dawley rats were treated with varying doses (0 g/L, 2.5 g/L, 5 g/L, and 10 g/L) of creatine monohydrate for 8 weeks. We demonstrate that mitochondrial markers respond in a sex and depot specific manner. In iWAT, female rats displayed significant increases in COXIV, PDH-E1alpha, and cytochrome C protein content. Male rats exhibited gWAT specific increases in COXIV and PDH-E1alpha protein content. This study supports creatine supplementation as a potential method of UCP1-independant thermogenesis and highlights the importance of taking a sex-specific approach when examining the efficacy of browning therapeutics in future research.

Design, Synthesis, and Antifungal Activity of 2,6-Dimethyl-4-aminopyrimidine Hydrazones as PDHc-E1 Inhibitors with a Novel Binding Mode

A series of novel 2,6-dimethyl-4-aminopyrimidine hydrazones 5 were rationally designed and synthesized as pyruvate dehydrogenase complex E1 (PDHc-E1) inhibitors. Compounds 5 strongly inhibited Escherichia coli (E. coli) PDHc-E1 (IC₅₀ values 0.94-15.80 μM). As revealed by molecular docking, site-directed mutagenesis, enzymatic, and inhibition kinetic analyses, compounds 5 competitively inhibited PDHc-E1 and bound in a "straight" pattern at the E. coli PDHc-E1 active site, which is a new binding mode. In in vitro antifungal assays, most compounds 5 at 50 μg/mL showed more than 80% inhibition against the mycelial growth of six tested phytopathogenic fungi, including Botrytis cinerea, Monilia fructigena, Colletotrichum gloeosporioides, andBotryosphaeria dothidea. Notably, 5f and 5i were 1.8-380 fold more potent against M. fructigena than the commercial fungicides captan and chlorothalonil. In vivo, 5f and 5i controlled the growth of M. fructigena comparably to the commercial fungicide tebuconazole. Thus, 5f and 5i have potential commercial value for the control of peach brown rot caused by M. fructigena.

Four weeks one-leg training and high fat diet does not alter PPARalpha protein or mRNA expression in human skeletal muscle

Fatty acid metabolism is influenced by training and diet with exercise training mediating this through activation of nuclear hormone receptor peroxisome proliferator-activated receptor alpha (PPARalpha) in skeletal muscle. This study investigated the effect of training and high fat or normal diet on PPARalpha expression in human skeletal muscle. Thirteen men trained one leg (T) four weeks (31.5 h in total), while the other leg (UT) served as control. During the 4 weeks six subjects consumed high fat (FAT) diet and seven subjects maintained a normal (CHO) diet. Biopsies were obtained from vastus lateralis muscle in both legs before and after training. After the biopsy, one-leg extension exercise was performed in random order with both legs 30 min at 95% of workload max. A training effect was evident as citrate synthase activity increased (P < 0.05) by 15% in the trained, but not the control leg in both groups. During exercise respiratory exchange ratio was lower in FAT (0.86 +/- 0.01, 0.83 +/- 0.01, mean +/- SEM) than CHO (0.96 +/- 0.02, 0.94 +/- 0.03) and in UT than T legs, respectively. The PPARalpha protein (144 +/- 44, 104 +/- 28, 79 +/- 15, 79 +/- 14, % of pre level) and PPARalpha mRNA (69 +/- [2, 2], 78 +/- [7, 6], 92 +/- [22, 18], 106 +/- [21, 18], % of pre level, geometric mean +/- SEM) expression remained unchanged by diet and training in FAT (UT, T) and CHO (UT, T), respectively. After the training and diet CS, HAD, PPARalpha, UCP2, UCP3 and mFABP mRNA content remained unchanged, whereas GLUT4 mRNA was lower in both groups and LDHA mRNA was lower (P < 0.05) only in FAT.

IN CONCLUSION

4 weeks one leg knee extensor training did not affect PPARalpha protein or mRNA expression. Furthermore, higher fat oxidation during exercise after fat rich diet was not accompanied by an increased PPARalpha protein or mRNA expression after 4 weeks.

Atrophic corpus gastritis and Helicobacter pylori infection in primary biliary cirrhosis

Chronic atrophic corpus gastritis, termed as autoimmune corpus gastritis or type A gastritis, and primary biliary cirrhosis (PBC) are characterized by a common immunological process against the exocrine glandular structures of both the stomach and bile duct. However, there has been controversy over whether atrophic corpus gastritis is associated with PBC. Recently, it has been suggested that Helicobacter pylori plays an important role in the early stage of atrophic corpus gastritis due to the induction of autoantibodies that are reactive with a protein in the gastric parietal cells. One hypothesis is that molecular mimicry, possibly resulting from H. pylori infection, might be responsible for initiating an autoimmune response in a predisposed host due to cross-reactivity among gastric mucosal, bile ductular, and bacterial antigens. The aim of this study is to assess whether atrophic changes of the gastric corpus could affect patients with PBC, and to determine the correlation with H. pylori infection. Sixteen patients with PBC were enrolled in this study. All patients were examined by serological studies of anti-pyruvate dehydrogenase (PDH) antibody, anti-H. pylori antibody, gastrin and vitamin B12. Gastroscopy was performed on all patients in order to verify the histological findings and to microscopically identify H. pylori. Atrophic corpus gastritis was found in 2 of 16 patients with PBC (12.5%), one of whom was confirmed to have pernicious anemia, a developed stage of atrophic corpus gastritis. H. pylori infection in the gastric corpus and the anti-H. pylori antibody were found in 7 (43.8%) and 11 (68.8%) of 16 patients, respectively. Anti-H. pylori antibody was confirmed to be positive in both of the patients with atrophic corpus gastritis, although H. pylori was absent in the gastric biopsy specimen. There was a positive correlation between anti-PDH antibodies and anti-H. pylori antibodies in sera from patients with PBC. Atrophic corpus gastritis is not frequently involved in PBC. However, H. pylori is a possible pathogenic factor in atrophic corpus gastritis in PBC patients because of the presence of anti-H. pylori antibody. A positive correlation between the titer of anti-PDH antibodies and the titer of anti-H. pylori antibodies was confirmed. Consequently, H. pylori infection could induce autoimmune responses in the development of both PBC and atrophic corpus gastritis. H. pylori infection associated with PBC requires further study.

Effects of bezafibrate on beta-cell function of rat pancreatic islets

Bezafibrate is an activator of peroxisome proliferator-activated receptors (PPAR) alpha. The present study was performed to investigate the effects of bezafibrate and the PPAR alpha activator, 4-Cholro-6-(2.3-xylidino)-2-pyrimidin-ylthio acetic acid (WY14643), on the beta-cell function of rat pancreatic islets in vitro. In islets cultured with 300 microM bezafibrate or WY14643 for 8 h, a low glucose concentration induced insulin release and increased the levels of mRNA for PPAR alpha, acyl CoA oxidase, carnitine palmitoyl transferase-1, pyruvate dehydrogenase E1 alpha or pyruvate carboxylase. In contrast, after a 48-h culture period, a high glucose concentration induced insulin release and islet insulin content, but decreased the levels of mRNA for glucose transporter-2 (GLUT-2), preproinsulin or pancreatic/duodenal homeobox-1. Diazoxide, the KATP channel opener, restored these responses. We conclude that bezafibrate enhances insulin release through the activation of PPAR alpha gene expression during a short culture period, whereas it may contribute to beta-cell dysfunction through the mechanism of "excessive stimulation" during longer culture periods.

Human populations show reduced DNA sequence variation at the Factor IX locus

Levels and patterns of human DNA sequence variation vary widely among loci. However, some of this variation may be due to the different populations used in different studies. So far, few studies of diverse human populations have compared different genetic loci for the same samples of populations and individuals. Here, we present new polymorphism data from intron 4 of the Factor IX gene (FIX) sequenced in diverse Old World populations. An explicit comparison is made with another X-linked gene, PDHA1, for which the sampling of individuals was very similar. Despite having a similar amount of divergence from chimpanzees, as do other nuclear genes, FIX has comparatively much less DNA sequence variation among humans. Nucleotide diversity at FIX is the lowest among the existing non-Y chromosome nuclear gene datasets and is less than 10% of the diversity found at PDHA1. Estimates of effective population size based on FIX are 8,558, about half of the value obtained for PDHA1, and the time to the most recent common ancestry among human FIX gene copies (282,000 years) is one of the most recent estimates reported for human genes. Analyses presented here suggest a history for the FIX region that includes recent positive directional selection, or background, selection. The general conclusion emerging is that very large variations can exist between the histories of similar genomic regions, even when sampling differences are minimized.

Congenital lactic acidosis: evaluation of the properties of the a199t natural variant of human pyruvate dehydrogenase e1alpha by in vitro mutation

One cause of congenital lactic acidosis is a mutation in the E1 alpha-subunit of the pyruvate dehydrogenase multienzyme complex. Little is known about the consequences of these mutations at the enzymatic level. Here we study the A199T mutation by expressing the protein in Escherichia coli. The specific activity is 25% of normal and the K(m) for pyruvate is elevated by 10-fold. Inhibitors of lactate dehydrogenase might be a useful therapy for patients with such mutations.

Analysis of exonic mutations leading to exon skipping in patients with pyruvate dehydrogenase E1 alpha deficiency

The pyruvate dehydrogenase (PDH) complex is situated at a key position in energy metabolism and is responsible for the conversion of pyruvate to acetyl CoA. In the literature, two unrelated patients with a PDH complex deficiency and splicing out of exon 6 of the PDH E1 alpha gene have been described, although intronic/exonic boundaries on either side of exon 6 were completely normal. Analysis of exon 6 in genomic DNA of these patients revealed two exonic mutations, a silent and a missense mutation. Although not experimentally demonstrated, the authors in both publications suggested that the exonic mutations were responsible for the exon skipping. In this work, we were able to demonstrate, by performing splicing experiments, that the two exonic mutations described in the PDH E1 alpha gene lead to aberrant splicing. We observed a disruption of the predicted wild-type pre-mRNA secondary structure of exon 6 by the mutated sequences described. However, when we constructed mutations that either reverted or disrupted the wild-type predicted pre-mRNA secondary structure of exon 6, we were unable to establish a correlation between the aberrant splicing and disruption of the predicted structure. The mutagenic experiments described here and the silent mutation found in one of the patients suggest the presence of an exonic splicing enhancer in the middle region of exon 6 of the PDH E1alpha gene.

Tetrameric assembly and conservation in the ATP-binding domain of rat branched-chain alpha-ketoacid dehydrogenase kinase

We showed previously that the rat branched-chain alpha-ketoacid dehydrogenase (BCKD) kinase is capable of autophosphorylation. However, despite its sequence similarity to bacterial histidine protein kinases, BCKD kinase does not function as a histidine protein kinase. In the present study, we report that the rat BCKD kinase exists as a homotetramer of M(r) = 185,000, based on results of gel filtration and dynamic light scattering. This is in contrast to the related mammalian pyruvate dehydrogenase kinase isozymes that occur as homodimers. The tetrameric assembly of BCKD kinase was confirmed by the presence of four 5'-adenylyl-imidodiphosphate-binding sites (K(D) = 4.1 x 10(-6)m) per molecule of the kinase. Incubation of the BCKD kinase with increasing concentrations of urea resulted in dissociation of the tetramer to dimers and eventually to monomers as separated on a sucrose density gradient. Both tetramers and dimers, but not the monomer, maintained the conformation capable of binding ATP and undergoing autophosphorylation. BCKD kinase depends on a fully lipoylated transacylase for maximal activity, but the interaction between the kinase and the transacylase is impeded in the presence of high salt concentrations. Alterations of conserved residues in the ATP-binding domain led to a marked reduction or complete loss in the catalytic efficiency of the BCKD kinase. The results indicate that BCKD kinase, similar to pyruvate dehydrogenase kinase isozymes, belongs to the superfamily of ATPase/kinase.

Effects of X chromosome number and parental origin on X-linked gene expression in preimplantation mouse embryos

Diploid androgenetic mouse embryos, possessing two sets of paternally inherited chromosomes, and control fertilized embryos were used to examine the relative effects of X chromosome number and parental chromosome origin on androgenone viability and X-linked gene expression. A significant difference in efficiency of blastocyst formation was observed between XX and XY androgenones in some experiments, but this difference was not uniformly observed. Significant effects of both X chromosome number and parental origin on X-linked gene expression were observed. Male and female control embryos expressed the XIST: RNA initially. This expression was followed by a preferential reduction in XIST: RNA abundance in male embryos, indicating that dosage compensation for the X chromosome may normally require the downregulation of XIST: RNA expression in male embryos, in conjunction with the production of stable XIST: transcripts in female embryos. By the late blastocyst stage, XX control embryos expressed significantly more XIST: RNA than did XY embryos. Unlike their normal counterparts, XX androgenones did not express significantly more XIST: RNA than did XY androgenones at the late blastocyst stage. Androgenones exhibited severe repression of the Pgk1 gene, but during development to the late blastocyst stage Pgk1 mRNA expression increased in XX androgenones and decreased in XY androgenones. Thus, the initial repression of the Pgk1 gene in XX androgenones was lost as the XIST: RNA declined in abundance, and this loss was correlated with a failure of XX androgenones to express significantly more XIST: RNA than did XY androgenones. These results indicate that androgenones may lack a factor that is expressed from the maternal genome and required for dosage compensation in preimplantation embryos. The results also indicate that early dosage compensation in preimplantation embryos may normally be reversible, thus providing flexibility to meet different developmental requirements of the embryonic and extraembryonic lineages.

Pisum sativum mitochondrial pyruvate dehydrogenase can be assembled as a functional alpha(2)beta(2) heterotetramer in the cytoplasm of Pichia pastoris

Pea (Pisum sativum) mitochondrial pyruvate dehydrogenase (E1) was produced by coexpression of the mature alpha and beta subunits in the cytoplasm of the yeast Pichia pastoris. Size-exclusion chromatography of recombinant E1, using a Superose 12 column, yielded a peak at M(r) 160,000 that contained both alpha and beta subunits as well as E1 activity. This corresponds to the size of native alpha(2)beta(2) E1. Recombinant E1 alpha (His(6))-E1 beta was purified by affinity chromatography using immobilized Ni(+), with a yield of 2.8 mg L(-1). The pyruvate-decarboxylating activity of recombinant E1 was dependent upon added Mg(2+) and thiamin-pyrophosphate and was enhanced by the oxidant potassium ferricyanide. Native pea mitochondrial E1-kinase catalyzed phosphorylation of Ser residues in the alpha-subunit of recombinant E1, with concomitant loss of enzymatic activity. Thus, mitochondrial pyruvate dehydrogenase can be assembled in the cytoplasm of P. pastoris into an alpha(2)beta(2) heterotetramer that is both catalytically active and competent for regulatory phosphorylation.

Methylation-dependent silencing of the testis-specific Pdha-2 basal promoter occurs through selective targeting of an activating transcription factor/cAMP-responsive element-binding site

In this study, we demonstrate that methylation-dependent repression of the Pdha-2 core promoter is mediated regionally through a consensus activating transcription factor/cAMP-responsive element-binding site located between nucleotides -54 and -62 upstream of the major transcriptional start site. Targeting of the CpG dinucleotide within this cis-element significantly disrupts the ability of this basal promoter to activate gene expression in vitro and completely abolishes promoter activity in vivo. DNase I footprinting experiments indicated that availability of the nuclear factor(s) binding this element is limiting in sexually immature mouse testis, and as such, these factors may play an important role in the coordinate activation of early spermatogenic gene expression. Interestingly, CpG dinucleotides associated with the hypersensitive region flanking the activating transcription factor/cAMP-responsive element-binding site appear to confer some conformational structure on the promoter since mutations at these specific CpG dinucleotides result in elevated basal levels of transcription. This raises the possibility of a potential bifunctional role for CpG dinucleotides in either methylation-dependent or -independent processes. Our data support the notion that hypomethylation and transcription factor recruitment are necessary events that precede gene activation at the early stages of spermatogenesis.

Arginine 302 mutations in the pyruvate dehydrogenase E1alpha subunit gene: identification of further patients and in vitro demonstration of pathogenicity

Three further patients with mutations in the codon for arginine 302 of the E1alpha subunit of the pyruvate dehydrogenase complex have been identified. Mutations in this codon have now been found in nine patients with pyruvate dehydrogenase deficiency in seven unrelated families, in sharp contrast to the great majority of other PDH E1alpha mutations which have been described in single individuals only. Because of the relatively high frequency of this mutation and because very few PDH E1alpha mutations have been demonstrated to be causative, we have established a system for analysing the consequences of defined mutations using transfection of normal and mutant PDH E1alpha cDNA into transformed human fibroblasts which have no endogenous E1alpha mRNA or protein. Using this test system, we have demonstrated that the R302C mutation results in the production of PDH E1alpha protein which is devoid of enzymic activity.

Import, processing, and assembly of the alpha- and beta-subunits of chloroplast pyruvate dehydrogenase

Sequence comparisons were used to identify cDNAs potentially encoding the alpha- and beta-subunits of chloroplast pyruvate dehydrogenase. Coupled in-vitro transcription plus translation was used to synthesize radiolabeled pyruvate dehydrogenase alpha- and beta-subunit precursor proteins. When the precursors were incubated with intact pea (Pisum sativum L.) seedling chloroplasts in the presence of ATP, they were imported and proteolytically processed. In contrast, there was no import or processing of the precursors by isolated, intact pea seedling mitochondria. Monospecific antibodies to the recombinant pyruvate dehydrogenase alpha-subunit were additionally able to co-precipitate radiolabeled pyruvate dehydrogenase beta-subunit, indicating association between subunits after import and processing. Furthermore, size-exclusion chromatography was used to identify an alphabeta heterodimer that is an intermediate in the assembly of the native alpha2beta2 heterotetrameric enzyme.

Mutations in the X-linked pyruvate dehydrogenase (E1) alpha subunit gene (PDHA1) in patients with a pyruvate dehydrogenase complex deficiency

Defects in the pyruvate dehydrogenase (PDH) complex are an important cause of primary lactic acidosis, a frequent manifestation of metabolic disease in children. Clinical symptoms can vary considerably in patients with PDH complex deficiencies, and almost equal numbers of affected males and females have been identified, suggesting an autosomal recessive mode of inheritance of the disease. However, the great majority of PDH complex deficiencies result from mutations in the X-linked pyruvate dehydrogenase (E1) alpha subunit gene (PDHA1). The major factors that contribute to the clinical variation in E1alpha deficiency and its resemblance to a recessive disease are developmental lethality in some males with severe mutations and the pattern of X-inactivation in females. To date, 37 different missense/nonsense and 39 different insertion/deletion mutations have been identified in the E1alpha subunit gene of 130 patients (61 females and 69 males) from 123 unrelated families. Insertion/deletion mutations occur preferentially in exons 10 and 11, while missense/nonsense mutations are found in all exons. In males, the majority of missense/nonsense mutations are found in exons 3, 7, 8 and 11, and three recurrent mutations at codons R72, R263 and R378 account for half of these patients with missense/nonsense mutations (25 of 50). A significantly lower number of females is found with missense/nonsense mutations (25). However, 36 females out of 55 affected patients have insertion/deletion mutations. The total number of female and male patients is thus almost the same, although a difference in the distribution of the type of mutations is evident between both sexes. In many families, the parents of the affected patients were studied for the presence of the PDHA1 mutation. The mutation was never present in the somatic cells of the father; in 63 mothers studied, 16 were carriers (25%). In four families, the origin of the new mutation was determined to be twice paternal and twice maternal.

Sequential deletion of C-terminal amino acids of the E(1)alpha component of the pyruvate dehydrogenase (PDH) complex leads to reduced steady-state levels of functional E(1)alpha(2)beta(2) tetramers: implications for patients with PDH deficiency

Human pyruvate dehydrogenase (PDH) complex deficiency is an extremely heterogeneous disease in its presentation and clinical course. We have characterized novel mutations that affect the C-terminal portion of the PDH-E(1)alpha-coding sequence. Although the molecular defects underlying these mutations are different, both effectively produce a stop codon prematurely three amino acids from the C-terminus. The clinical and biochemical consequences of these mutations are unusual in that the affected individuals are very long-term survivors with PDH complex deficiency despite having low (<20%) activity in skin fibroblasts. These findings prompted us to investigate the C-terminus of E(1)alpha in greater detail. We constructed and expressed a series of PDH-E(1)alpha deletion mutants in a cell line with zero PDH complex activity due to a null E(1)alpha allele. Sequential deletion of the C-terminus by one, two, three and four amino acids resulted in PDH complex activities of 100, 60, 36 and 14%, respectively, compared with wild-type E(1)alpha expressed in PDH complex-deficient cells. The immunodetectable protein was decreased by the same amount as the activity, suggesting that the stability and/or assembly of the E(1)alpha(2)beta(2)heterotetramer might depend on the intactness of the PDH-E(1)alpha C-terminus. In addition, we compared the somatic and the testis-specific isoforms of E(1)alphaand concluded that they are biochemically equivalent.

Staphylococcal protein A as a fusion partner directs secretion of the e1alpha and e1beta subunits of pea mitochondrial pyruvate dehydrogenase by Bacillus subtilis

Staphylococcal protein A (SPA)-based vectors were constructed to direct secretion of the E1alpha and E1beta subunits of Pisum sativum mitochondrial pyruvate dehydrogenase from Bacillus subtilis. These proteins were not exported when the signal peptide from levansucrase (SacBSP) was fused to their N-termini. Both SacBSP-E1alpha and SacBSP-E1beta fusion proteins were insoluble in the cytoplasm. However, when the SPA open-reading frame was inserted between SacBSP and E1alpha or E1beta, corresponding fusion proteins were secreted from the cells. The first (E) IgG-binding domain of SPA was sufficient to direct low level secretion of both fusion proteins (SacBSP-E-E1alpha and SacBSP-E-E1beta). Adding the second (D) IgG-binding domain improved extracellular protein yields 3- to 4-fold over E alone, but was not as efficient as secretion of the full-length (EDABC) SPA-fusion proteins. All constructs were based on the pUB110-derived multicopy plasmid pWB705. Separate B. subtilis strains transformed with SacBSP-E-E1alpha-His(6) or SacBSP-E1beta were cocultivated in the presence of Ni-NTA agarose. The native pyruvate dehydrogenase alpha2beta2 structure was bound to the affinity matrix, demonstrating assembly after secretion. The use of SPA as a fusion partner during expression of heterologous proteins by B. subtilis provides the basis of a versatile system that can be used to study both secretion and protein:protein interactions.

Histidine modifying agents abolish pyruvate dehydrogenase kinase activity

Pyruvate dehydrogenase kinase (PDK) specifically phosphorylates the E1alpha subunit of the pyruvate dehydrogenase complex (PDC). Sequence analysis of cloned PDKs led to the proposal that they are mechanistically related to prokaryotic 2-component His-kinases. The reaction mechanism of protein His-kinases involves autophosphorylation of a specific His residue followed by phosphotransfer to an Asp residue. Treatment of recombinant Arabidopsis thaliana PDK with the His-directed reagents diethyl pyrocarbonate (DEPC) and dichloro-(2,2':6', 2"-terpyridine)-platinum(II) dihydrate led to a marked inhibition of autophosphorylation. In addition, DEPC treatment abolished the ability of PDK to trans-phosphorylate and inactivate PDC. These results validate the prediction that PDKs require His residues for activity.

Concomitant administration of sodium dichloroacetate and thiamine in west syndrome caused by thiamine-responsive pyruvate dehydrogenase complex deficiency

We treated a female patient with West syndrome caused by thiamine-responsive pyruvate dehydrogenase complex (PDHC) deficiency. Infantile spasms occurred in association with elevated blood and CSF lactate concentrations; these symptoms disappeared when lactate concentrations had been lowered by treatment with concomitant sodium dichloroacetate (DCA) and high dose thiamine. Sequencing the patient's PDHC E(1)alpha subunit revealed a substitution of serine for glycine at position 89 in exon 3 (G89S). This mutation must be a de novo mutation because it was not found in either parents' genome DNA. To our knowledge, five previously described patients with PDHC deficiency have displayed the West syndrome. All six known patients, including our own, were female, even though an approximately equal number of males and females have been identified with PDHC deficiency and overall West syndrome occurs somewhat more frequently in males. These results indicated that West syndrome occurred more frequently in female patients with PDHC deficiency. It is suggested that lactate concentration should be measured in patients with West syndrome for potential PDHC deficiency, especially in females.

Characterization of the regulatory region of the human testis-specific form of the pyruvate dehydrogenase alpha-subunit (PDHA-2) gene

The alpha-subunit of human pyruvate dehydrogenase (E(1)) is encoded by two separate genes. The gene located on chromosome X (PDHA-1) is expressed in somatic tissues, whereas the second gene (PDHA-2), located on chromosome 4, is expressed only in post-meiotic spermatogenic cells. A genomic fragment harboring the human gene encoding PDHA-2 has been isolated and approximately 800 nucleotides of the promoter region have been characterized. Functional studies of the promoter indicate the presence of both enhancer and repressor elements that are common to other genes that are only expressed in mature sperm.

Cerebral palsy and pyruvate dehydrogenase deficiency: identification of two new mutations in the E1alpha gene

Pyruvate dehydrogenase (PDH) complex deficiency, a common cause of congenital lactic acidosis, is mostly due to mutations in the X-linked gene coding for the E1alpha subunit of the complex. We have studied two unrelated girls presenting a static encephalopathy with spastic quadriplegia, microcephaly and seizures and in one girl, hypocalcaemia, a new finding in PDH complex deficiency. PDH deficiency was diagnosed in adolescence and both girls had low PDH complex activity in muscle but normal amounts of all subunits on Western blotting, and a normal lactate/pyruvate ratio in blood and CSF. Mutation analysis of the E1alpha gene at the cDNA or DNA level revealed an arginine to histidine substitution at amino acid position 288 (R288H) in the girl with hypocalcaemia and a 12 bp insertion, predicting a four amino acid duplication at the c-terminal end of the protein in the second girl. They both carried a normal and a mutated E1alpha gene and X-inactivation studies showed skewed patterns.

CONCLUSION

Mutation identification in pyruvate dehydrogenase complex deficiency remains important especially for the determination of the recurrence risk and for reliable genetic counselling in couples with an affected child.

Involvement of alpha-cysteine-62 and beta-tryptophan-135 in human pyruvate dehydrogenase catalysis

Pyruvate dehydrogenase (E1), a heterotetramer (alpha(2)beta(2)), is the first catalytic component of the mammalian pyruvate dehydrogenase complex (PDC). To investigate the roles of cysteine-62 of E1alpha (alphaC62) and tryptophan-135 of E1beta (betaW135) (identified previously as active site residues using chemical modifications) in E1 catalysis, two recombinant human E1 mutants were generated using site-directed mutagenesis: alphaC62A and betaW135L. Compared to wild-type, k(cat) values for alphaC62A and betaW135L measured by PDC assay were markedly reduced to 7.2 and 11. 6%, respectively. Apparent K(m) values for thiamin pyrophosphate (TPP) were increased approximately sixfold for both mutants, resulting in catalytic efficiency for TPP of only 1-2% of the wild-type E1. K(m) values for pyruvate increased only moderately (twofold). The alphaC62A and betaW135L mutants were less thermostable than wild-type E1. The conformations of the mutant apo-E1s determined by spectral analysis were different from that of the wild-type apo-E1. CD spectral analysis indicated that TPP binding was affected for both the alphaC62A and betaW135L mutant E1s. The substrate analogs, fluoropyruvate and bromopyruvate, were shown to be active site-directed inhibitors of human E1; in the absence of TPP, bromopyruvate (but not fluoropyruvate) inhibited human E1 due to SH-group modification. Pyruvate induced inactivation of human E1 could be restored by thiol reagents. Cysteine-62 (and maybe another group) is proposed to be involved in E1 inhibition by the substrate and substrate analogs. Taken together these results indicate that alphaC62 and betaW135 facilitate coenzyme binding, and alphaC62 could be near the substrate-binding site.

Exceptional characteristics of heterotetrameric (alpha 2 beta 2) E1p of the pyruvate dehydrogenase complex from Zymomonas mobilis: expression from an own promoter and a lipoyl domain in E1 beta

In the pyruvate dehydrogenase complex (PDHC) of Zymomonas mobilis the beta subunit of the pyruvate dehydrogenase (E1p) as well as the acetyltransferase (E2p) contain an N-terminal lipoyl domain. Both lipoyl domains were acetylated in vitro using 2-14C-pyruvate as a substrate, demonstrating that both lipoyl domains can accept acetyl groups from the E1 component. As previously shown the structural genes (pdhA alpha beta, pdhB, lpd) encoding the pyruvate dehydrogenase complex of Z. mobilis are located in two distinct gene clusters, pdhA alpha beta and pdhB-orf2-lpd (U. Neveling et al. (1998) J. Bacteriol. 180, 1540-1548). Analysis of pdh gene expression using lacZ fusions revealed that the DNA fragments upstream of pdhA alpha, pdhB and lpd each have promoter activities. These pdh promoter activities were 7-30-fold higher in Z. mobilis than in Escherichia coli.

Cloning and characterization of a 5.9 kb promoter region of the human pyruvate dehydrogenase alpha subunit gene

A human genomic clone containing a 5.9 kb promoter region of the human pyruvate dehydrogenase (E1) alpha subunit gene (PDHA1) was isolated from a human X-chromosome library. The nucleotide sequence showed two Alu repeats at the -2880 and -2200 bp regions. Comparison between the -1400 bp E1alpha promoter and the -1241 bp E1beta promoter revealed a 57% homology, with a high degree of homology at the putative protein binding regions in these two promoters. Computer-aided transcription factor binding consensus sequence analysis revealed the presence of PPAR, HOXD, MyoD and other tissue-specific transcription factor binding sites. Promoter function analysis using the chloramphenicol acetyltransferase reporter gene indicated that the -2.2 kb/-1.7 kb and -5.9 kb/-5.2 kb regions of the E1alpha promoter may possess negative regulatory elements which are likely to function in a tissue-specific manner.

X chromosome evidence for ancient human histories

Diverse African and non-African samples of the X-linked PDHA1 (pyruvate dehydrogenase E1 alpha subunit) locus revealed a fixed DNA sequence difference between the two sample groups. The age of onset of population subdivision appears to be about 200 thousand years ago. This predates the earliest modern human fossils, suggesting the transformation to modern humans occurred in a subdivided population. The base of the PDHA1 gene tree is relatively ancient, with an estimated age of 1.86 million years, a late Pliocene time associated with early species of Homo. PDHA1 revealed very low variation among non-Africans, but in other respects the data are consistent with reports from other X-linked and autosomal haplotype data sets. Like these other genes, but in conflict with microsatellite and mitochondrial data, PDHA1 does not show evidence of human population expansion.

Identification of the catalytic glutamate in the E1 component of human pyruvate dehydrogenase

The pyruvate dehydrogenase complex catalyzes the conversion of pyruvate to acetyl-CoA. The first component (E1) converts pyruvate to bound acetaldehyde using thiamine diphosphate (ThDP) and Mg2+ as cofactors. There is no 3D structure of E1 available but those of other ThDP-dependent enzymes show some similarities including a glutamate residue that assists in ThDP activation. Eukaryotic E1 has an alpha2beta2 structure and the conserved Glu89 of the beta-subunit was identified as a possible catalytic residue by sequence alignment. Human E1 was expressed in Escherichia coli and purified. Mutating Glu89 to glutamine, aspartate and alanine markedly reduces catalytic activity and the affinity for ThDP, consistent with a role as the catalytic glutamate.

Longitudinal study of tissue- and subunit-specific obesity-induced regulation of the pyruvate dehydrogenase complex

The tissue-specific expression of the mitochondrial pyruvate dehydrogenase complex (PDHc) has been studied in an animal model of obesity with hyperinsulinemia, the obese (fa/fa) Zucker rat. Liver and heart were obtained from 4 and 8 week-old obese rats and age-matched lean animals, and in each tissue the following parameters were analyzed: (1) total activity of the mitochondrial PDHc; (2) abundance of the mitochondrial PDHc subunits on Western blots; and (3) abundance of the E1alpha and E1beta subunit mRNAs on Northern blots and semi-quantitative RT-PCR. Regardless of age, obese rats showed an increase in liver total PDHc activity and a coordinate increase in liver E1alpha and E1beta PDHc subunit abundance. At 4 weeks, obese rats also showed an increase in liver PDH E1alpha mRNA level, but regardless of age E1beta mRNA level was unchanged. In contrast, neither total PDHc activity nor the concentration of its protein subunits were increased in heart of obese rats. Thus, obese Zucker rats display a liver-specific early increase in PDHc which results from a selective up-regulation of the E1alpha gene expression.

The pyruvate dehydrogenase multi-enzyme complex from Gram-negative bacteria

Pyruvate dehydrogenase multi-enzyme complexes from Gram-negative bacteria consists of three enzymes, pyruvate dehydrogenase/decarboxylase (E1p), dihydrolipoyl acetyltransferase (E2p) and dihydrolipoyl dehydrogenase (E3). The acetyltransferase harbors all properties required for multi-enzyme catalysis: it forms a large core of 24 subunits, it contains multiple binding sites for the E1p and E3 components, the acetyltransferase catalytic site and mobile substrate carrying lipoyl domains that visit the active sites. Today, the Azotobacter vinelandii complex is the best understood oxo acid dehydrogenase complex with respect to structural details. A description of multi-enzyme catalysis starts with the structural and catalytic properties of the individual components of the complex. Integration of the individual properties is obtained by a description of how the many copies of the individual enzymes are arranged in the complex and how the lipoyl domains couple the activities of the respective active sites by way of flexible linkers. These latter aspects are the most difficult to study and future research need to be aimed at these properties.

Expression of pyruvate dehydrogenase isoforms during the aerobic/anaerobic transition in the development of the parasitic nematode Ascaris suum: altered stoichiometry of phosphorylation/inactivation

The pyruvate dehydrogenase complex (PDC) plays a key role in the anaerobic metabolism of the parasitic nematode Ascaris suum. Two isoforms of the alpha-subunit of pyruvate dehydrogenase (E1) have been identified: alpha I is most abundant in anaerobic adult muscle and alpha II in aerobic larvae. Both isoforms have been expressed as alpha 2 beta 2 tetramers with a muscle-specific beta-subunit, purified to apparent homogeneity, reconstituted with E1-deficient adult A. suum muscle PDC, and assayed for PDC and E1 kinase activity. Recombinant alpha II is a poor substrate for the adult E1 kinase, but its stoichiometry of phosphorylation/inactivation is similar to that reported for the human E1. Initially, inactivation parallels the incorporation of about 1 mol 32P/mol E1 and at maximal phosphorylation about 2.4 32P/mol E1 is incorporated. In contrast, recombinant alpha I (r alpha I) is phosphorylated rapidly, and substantially more phosphorylation accompanies inactivation. To examine this altered pattern of phosphorylation, the two phosphorylation sites in each E1 alpha subunit of the r alpha I (site 1 and site 2) were changed either individually or together from Ser to Ala by site-directed mutagenesis. Site 1 was phosphorylated more rapidly than site 2, but the phosphorylation of either site resulted in inactivation, and the phosphorylation of only a single E1 alpha subunit of the tetramer was necessary for inactivation. However, both E1 alpha subunits of the tetramer were phosphorylated, based on the incorporation of about 3.5 mol 32P/mol E1 at maximal phosphorylation and the altered mobility of most of the E1 alpha subunits during SDS-PAGE. These observations suggest that the regulation of both E1 isoforms is modified to maintain PDC activity during the transition to anaerobiosis.

Purification of the pyruvate dehydrogenase multienzyme complex of Zymomonas mobilis and identification and sequence analysis of the corresponding genes

The pyruvate dehydrogenase (PDH) complex of the gram-negative bacterium Zymomonas mobilis was purified to homogeneity. From 250 g of cells, we isolated 1 mg of PDH complex with a specific activity of 12.6 U/mg of protein. Analysis of subunit composition revealed a PDH (E1) consisting of the two subunits E1alpha (38 kDa) and E1beta (56 kDa), a dihydrolipoamide acetyltransferase (E2) of 48 kDa, and a lipoamide dehydrogenase (E3) of 50 kDa. The E2 core of the complex is arranged to form a pentagonal dodecahedron, as shown by electron microscopic images, resembling the quaternary structures of PDH complexes from gram-positive bacteria and eukaryotes. The PDH complex-encoding genes were identified by hybridization experiments and sequence analysis in two separate gene regions in the genome of Z. mobilis. The genes pdhAalpha (1,065 bp) and pdhAbeta (1,389 bp), encoding the E1alpha and E1beta subunits of the E1 component, were located downstream of the gene encoding enolase. The pdhB (1,323 bp) and lpd (1,401 bp) genes, encoding the E2 and E3 components, were identified in an unrelated gene region together with a 450-bp open reading frame (ORF) of unknown function in the order pdhB-ORF2-lpd. Highest similarities of the gene products of the pdhAalpha, pdhAbeta, and pdhB genes were found with the corresponding enzymes of Saccharomyces cerevisiae and other eukaryotes. Like the dihydrolipoamide acetyltransferases of S. cerevisiae and numerous other organisms, the product of the pdhB gene contains a single lipoyl domain. The E1beta subunit PDH was found to contain an amino-terminal lipoyl domain, a property which is unique among PDHs.

Transfection screening for primary defects in the pyruvate dehydrogenase E1alpha subunit gene

In a significant number of patients with biochemical evidence of a defect in the E1 (pyruvate dehydrogenase) component of the pyruvate dehydrogenase complex, it has not proved possible to identify a mutation in the gene coding regions. To assess the need for more extensive genetic analysis in these patients and to establish a test system in which to study the biochemical consequences of mutations in the E1alpha subunit gene (which is responsible for the great majority of defined cases of pyruvate dehydrogenase deficiency), we have developed a method to screen for E1alpha gene defects based on complementation of the enzyme deficiency in transformed fibroblast cell lines following transfection and expression of the normal cDNA. Using this system, cell lines from patients with a variety of different defined mutations in the E1alpha gene show restoration of enzyme activity. A number of patients have been identified in whom deficient enzyme activity is not restored by expression of the normal cDNA indicating that an alternative explanation for the enzyme defect must be sought.

Biochemical and genetic studies of four patients with pyruvate dehydrogenase E1 alpha deficiency

We report studies of four patients with pyruvate dehydrogenase complex (PDH) deficiency caused by mutations in the E1 alpha subunit. Two unrelated male patients presented with Leigh syndrome and a R263G missense mutation in exon 8. This mutation has previously been described in males with the same phenotype. The two other patients had different novel mutations: (1) an 8-bp deletion at the C-terminus (exon 11) was found in one allele of a young girl suffering from microcephaly and (2) a C88S missense mutation (exon 3) in a boy who only presented with motor neuropathy. These mutations were not found in the mothers of any of the four cases. Immunoblot analysis revealed decreased immunoreactivity for the E1 alpha and E1 beta subunits in three out of the four patients. These findings confirm that: (1) PDH deficiencies are genetically heterogeneous, (2) the R263G mutation is more frequent in male cases than are other mutations and this amino acid is a hot spot for gene mutations, (3) the last eight amino acids may be important for the conformation of the tetrameric E1-PDH enzyme, and (4) the amino acids at positions 88, 263 and 382-387 are essential for the linking of the alpha subunit with the beta subunit and for the activity of the holoenzyme.

Regulation of Pdha-2 expression is mediated by proximal promoter sequences and CpG methylation

Spermatogenesis is a complex process requiring the coordinate expression of a number of testis-specific genes. One of these, Pdha-2, codes for the murine spermatogenesis-specific isoform of the E1a subunit of the pyruvate dehydrogenase complex. To begin to delineate the mechanisms regulating its expression in vivo, we have generated transgenic mice lines carrying Pdha-2 promoter deletion constructs. Here we report that transgenic mice harboring a construct containing only 187 bp of promoter and upstream sequences (core promoter) is sufficient for directing the testis-specific expression of a chloramphenicol acetyltransferase (CAT) reporter gene. Like the endogenous Pdha-2, the CAT gene is expressed in testis in a stage-specific manner. Our studies also show a correlation between CpG methylation within the core promoter and its capacity to regulate transcription. In NIH 3T3 cell lines stably transfected with the Pdha-2 core promoter-CAT construct, high levels of CAT reporter expression are observed, whereas the endogenous Pdha-2 gene is repressed. In these cells, the CpG dinucleotides residing within the transfected promoter are hypomethylated whereas those residing in the endogenous promoter are methylated. Furthermore, promoter activity can be abated by the in vitro methylation of its CpG dinucleotides. DNase I footprint analysis indicates that at least one site for the methylation-mediated repression may occur through the ATF/cyclic AMP response element binding element located within the core promoter. Mutations within this element reduces activity to approximately 50% of the wild-type promoter activity. These results suggest that tissue-specific gene expression may be modulated by other mechanisms in addition to specific transcription factor availability and cooperativity. We propose that methylation may be a mechanism by which repression of the testis-specific Pdha-2 gene is established in somatic tissue.

Mitochondrial and nuclear genes present conflicting portraits of human origins

Human mitochondrial DNA (mtDNA) sequences reveal an abundance of polymorphic sites in which the frequencies of the segregating bases are very different. A typical polymorphism involves one base at low frequency and the other base at high frequency. In contrast, nuclear gene data sets tend to show an excess of polymorphisms in which both segregating bases are at intermediate frequencies. A new statistical test of this difference finds significant differences between mtDNA and nuclear gene data sets reported in the literature. However, differences in the polymorphism patterns could be caused by different sample origins for the different data sets. To examine the mtDNA-nuclear difference more closely, DNA sequences were generated from a portion of the X-linked pyruvate dehydrogenase E1 alpha subunit (PDHA1) locus and from a portion of mitochondrial control region I (CRI) from each of eight individuals, four from sub-Saharan Africa. The two genes revealed a significant difference in the site frequency distribution of polymorphic sites. PDHA1 revealed an excess of intermediate-frequency polymorphisms, while CRI showed an excess of sites with the low-high frequency pattern. The discrepancy suggests that mitochondrial variation has been shaped by natural selection, and may not be ideal for some questions on human origins.

Refined localization of the pyruvate dehydrogenase E1 alpha gene (PDHA1) by linkage analysis

Pyruvate dehydrogenase (PDH) E1 alpha is a key component in the PDH complex which catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA. Defects in the gene coding for PDH E1 alpha (PDHA1) are associated with a variety of clinical symptoms, often of a severe character. In the present study, the segregation of three polymorphic CA repeats located in PDHA1 was followed in the 40 CEPH reference pedigrees. Using these data, multipoint linkage analysis was carried out, refining the genetic location of PDHA1. The 16-point map presented locates PDHA1 in an approximately 3-cM interval between DXS999 and DXS365 with odds of more than 1000:1. From known physical localizations of the flanking marker loci, PDHA1 could be regionally assigned to Xp22.1-p22.2. The information provided should be of value in clinical settings.

Effect of substitutions in the thiamin diphosphate-magnesium fold on the activation of the pyruvate dehydrogenase complex from Escherichia coli by cofactors and substrate

The homotropic regulation of the Escherichia coli pyruvate dehydrogenase multienzyme complex (PDHc) by its coenzyme thiamin diphosphate and its substrate pyruvate was re-examined with complexes containing three and one lipoyl domains per E2 chain, and several variants of the latter, containing substitutions in the putative thiamin diphosphate fold of E1 (G231A, G231S, C259S, C259N, and N258Q). It was found that all of the E1 variants had significantly reduced specific activities, as reported elsewhere (Russell, G. C., Machado, R. S., and Guest, J. R. (1992) Biochem. J. 287, 611-619). In addition, extensive kinetic studies were performed in an attempt to determine the effects of the amino acid substitutions on the Hill coefficients with respect to thiamin diphosphate and pyruvate. All but one of the variants were incapable of being saturated with thiamin diphosphate, even at concentrations > 5 mM. Most importantly, the striking activation lag phase lasting for many seconds in the parental complexes containing three and one lipoyl domains per E2 chain was totally eliminated in the variants. Furthermore, activation by the coenzyme was localized to the E1 subunit, because resolved E1 exhibits virtually the same behavior during the activation lag phase as does the complex. In the parental complexes two distinct lag phases could be resolved, the duration of both decreases with increasing ThDP concentration. A mechanism that is consistent with all of the kinetic data on the parental complexes involves rapid equilibration of the first ThDP with the E1 dimer, followed by a slow conformational equilibration, that in turn is followed by slow addition of the second ThDP to form the fully activated dimer. When the diphosphate site is badly impaired, the binding affinity is very much reduced, this perhaps eliminates the slow step leading to the activated dimer form of the E1.

Antibodies to E1 and E2/Protein X components of pyruvate dehydrogenase complex in sera of patients with primary biliary cirrhosis

AIMS/METHODS

Using purified E1 component of pyruvate dehydrogenase complex (PDC) from bovine heart, we measured the levels of anti-E1 antibodies in PBC sera using ELISA and determined the degree of inhibition that these antibodies exerted on E1 enzyme activity. We also estimated levels of anti-E2/Protein X (Pro-X) antibodies in PBC sera using purified E2 and Pro-X of PDC which were copurified with E1.

RESULTS/CONCLUSIONS

Anti-E1 antibodies were detected in 87.5% (35/40) of PBC sera. Some of these sera inhibited E1 enzyme activity but inhibition did not correlate with levels of anti-E1 antibodies. A high positive correlation (r = 0.918) was found between levels of anti-E1 and anti-E2/Pro-X antibodies, suggesting that anti-PDC antibody production was stimulated by PDC itself. Levels of IgG class anti-E2/Pro-X antibodies were significantly higher in sera of symptomatic PBC patients than in those of asymptomatic PBC patients. It was also found that patients who were positive for only IgM class anti-E2/Pro-X antibodies had early-stage PBC.

Antisense and sense poly(A)-RNAs from the Xenopus laevis pyruvate dehydrogenase gene loci are regulated with message production during embryogenesis

The structure and temporal expression of two Xenopus cDNAs encoding the beta subunit of pyruvate dehydrogenase (XPdhE1 beta) have been determined. XPdhE1 beta was 88% homologous to mature human PdhE1 beta, but the putative N-terminal mitochondrial signal peptide was poorly conserved. Zygotic expression of XPdhE1 beta mRNA was detected at neural tube closure and increased until stage 40. RT-PCR cloning identified a short homology to a protein kinase open reading frame within the 3' non-coding sequence of the XPdhE1 beta cDNAs. This homology, which occurred on the antisense cDNA strand, was shown by strand specific RT-PCR to be transcribed in vivo as part of an antisense RNA. Northern analysis showed that this RNA formed part of an abundant and heterogeneous population of antisense and sense poly(A)-RNAs transcribed from the XPdhE1 beta loci and coordinately regulated with message production.

Evolution of mammalian X-linked and autosomal Pgk and Pdh E1 alpha subunit genes

The phylogeny and substitution rates of the mammalian X chromosome-located and autosomal phosphoglycerate kinase and pyruvate dehydrogenase genes were investigated. Compatibility analysis was used to show reticulate evolution in these genes. Analysis of the marsupial, mouse, and human phosphoglycerate kinase genes suggests that at least two recombination events have taken place, one occurring about the time of the placental-marsupial split involving exons 1-5 and the other before the primate-rodent split involving exons 9-10. Similar analysis of the pyruvate dehydrogenase genes indicates a recombination event involving exons 2-3 at a time before the primate-rodent split and a gene conversion between exons 3-4 in the human somatic and testis-specific pyruvate dehydrogenase genes after the primate-rodent split. This demonstrates that genetic exchange can occur between paralogous genes at widely separated chromosomal locations. Estimation of nucleotide substitution rates in these genes confirmed a higher substitution rate in the pyruvate dehydrogenase genes. In the phosphoglycerate kinase genes, there is no difference between the substitution rates in mice and humans and between the X chromosome- and autosome-located genes. A greater substitution rate was noted in the mouse autosomal pyruvate dehydrogenase gene when compared with the other mouse and human genes. This may be a result of either directional natural selection or a relaxation of functional constraint at this specific gene.

Ursodeoxycholic acid treatment lowers the serum level of antibodies against pyruvate dehydrogenase and influences their inhibitory capacity for the enzyme complex in patients with primary biliary cirrhosis

A two-year randomized, double-blind, placebo-controlled clinical trial used paired serum samples from 122 patients with primary biliary cirrhosis to compare the effect of ursodeoxycholic acid and colchicine on their immune parameters. IgG antibodies to pyruvate dehydrogenase, the major autoantigen in primary biliary cirrhosis, were determined by enzyme-linked immunosorbent assay and immunoblot; enzyme inhibition assay against pyruvate dehydrogenase was used to test the changes of the functional reactivity of the serum autoantibodies. Treatment with ursodeoxycholic acid decreased both the level of IgG antibodies to pyruvate dehydrogenase (P < 0.01) and the inihibitory titer of the sera for pyruvate dehydrogenase (P < 0.01). Treatment with colchicine or placebo showed no statistically significant changes in either the antibody levels or the inhibitory titers. Ursodeoxycholic acid thus alters the immune parameters of patients with primary biliary cirrhosis. The mechanism of these changes needs further investigation.

Mutation analysis of the pyruvate dehydrogenase E1 alpha gene in eight patients with a pyruvate dehydrogenase complex deficiency

Most of the mutations causing deficiency of the pyruvate dehydrogenase (PDH) complex are in the X-linked E1 alpha gene. We have developed a rapid screening method for the detection of mutations in this gene using reverse transcription of total RNA, polymerase chain reaction amplification of the whole coding region of the gene and single-strand conformation polymorphism (SSCP) analysis. With this method, we studied eight patients with a PDH complex deficiency, using cultured fibroblasts. In all patients, aberrant SSCP patterns were found and, after sequencing of the corresponding fragments, we were able to identify six new mutations and two mutations already described previously. The mutations are point mutations leading to amino acid substitutions (5) and direct repeat insertions (3). The presence of the mutations was confirmed in genomic fibroblast DNA. The 4 female patients were shown to carry both a normal and a mutated E1 alpha gene.

Mutations in the X-linked E1 alpha subunit of pyruvate dehydrogenase: exon skipping, insertion of duplicate sequence, and missense mutations leading to the deficiency of the pyruvate dehydrogenase complex

Human pyruvate dehydrogenase (PDH)-complex deficiency is an inborn error of metabolism that is extremely heterogeneous in its presentation and clinical course. In a study of 14 patients (7 females and 7 males), we have found a mutation in the coding region of the E1 alpha gene in all 14 patients. Two female patients had the same 7-bp deletion at nt 927; another female patient had a 3-bp deletion at nt 931. Another female patient was found to have a deletion of exon 6 in her cDNA. Two other female patients were found to have insertions, one of 13 bp at nt 981 and one of 46 bp at nucleotide 1078. Two male patients were found to have a 4-bp insertion at nucleotide 1163. The remaining six patients all had missense mutations. A male patient and a female patient both had an A1133G mutation. The other missense mutations were C214T, C615A, and C787G (two patients). Five of these mutations are novel mutations, five have been previously reported in other patients, and two were published observations in other patients in an E1 alpha-mutation summary. In the four cases where parent DNA was available, only one mother was found to be a carrier of the same mutation as her child.