Essential role of aralar in the transduction of small Ca2+ signals to neuronal mitochondria

Aralar, the neuronal Ca2+-binding mitochondrial aspartate-glutamate carrier, has Ca2+ binding domains facing the extramitochondrial space and functions in the malate-aspartate NADH shuttle (MAS). Here we showed that MAS activity in brain mitochondria is stimulated by extramitochondrial Ca2+ with an S0.5 of 324 nM. By employing primary neuronal cultures from control and aralar-deficient mice and NAD(P)H imaging with two-photon excitation microscopy, we showed that lactate utilization involves a substantial transfer of NAD(P)H to mitochondria in control but not aralar-deficient neurons, in agreement with the lack of MAS activity associated with aralar deficiency. The increase in mitochondrial NAD(P)H was greatly potentiated by large [Ca2+]i signals both in control and aralar-deficient neurons, showing that these large signals activate the Ca2+ uniporter and mitochondrial dehydrogenases but not MAS activity. On the other hand, small [Ca2+]i signals potentiate the increase in mitochondrial NAD(P)H only in control but not in aralar-deficient neurons. We concluded that neuronal MAS activity is selectively activated by small Ca2+ signals that fall below the activation range of the Ca2+ uniporter and plays an essential role in mitochondrial Ca2+ signalingThisworkwassupportedinpartbyDireccio´nGeneraldeInvestigacio´ndelMinisterio deCienciayTecnologı´aGrantBMC2002-02072,ComunidaddeMadridGrant08.5/ 0024/2003,FondodeInvestigacionesSanitariasdelMinisteriodeSanidadyConsumo 01/0395(toJ.S.),aninstitutionalgrant fromtheFundacio´nRamo´nArecestothe CentrodeBiologı´aMolecular ‘SeveroOchoa,‘ andbyaGrant-in-aidforScientific Research16390100fromtheJapanSocietyforthePromotionofScience(toK.K.).The costsofpublicationof thisarticleweredefrayedinpartbythepaymentofpage charges.Thisarticlemustthereforebeherebymarked“advertisement”inaccordance with18U.S.C.Section1734solelytoindicatethisfac

Ca2+ activation kinetics of the two aspartate-glutamate mitochondrial carriers, aralar and citrin: Role in the heart malate-aspartate NADH shuttle

Ca2+ regulation of the Ca2+ binding mitochondrial carriers for aspartate/glutamate (AGCs) is provided by their N-terminal extensions, which face the intermembrane space. The two mammalian AGCs, aralar and citrin, are members of the malate-aspartate NADH shuttle. We report that their N-terminal extensions contain up to four pairs of EF-hand motifs plus a single vestigial EF-hand, and have no known homolog. Aralar and citrin contain one fully canonical EF-hand pair and aralar two additional half-pairs, in which a single EF-hand is predicted to bind Ca2+. Shuttle activity in brain or skeletal muscle mitochondria, which contain aralar as the major AGC, is activated by Ca2+ with S0.5 values of 280-350 nM; higher than those obtained in liver mitochondria (100-150 nM) that contain citrin as the major AGC. We have used aralar- and citrin-deficient mice to study the role of the two isoforms in heart, which expresses both AGCs. The S0.5 for Ca 2+ activation of the shuttle in heart mitochondria is about 300 nM, and it remains essentially unchanged in citrin-deficient mice, although it undergoes a drastic reduction to about 100 nM in aralar-deficient mice. Therefore, aralar and citrin, when expressed as single isoforms in heart, confer differences in Ca2+ activation of shuttle activity, probably associated with their structural differences. In addition, the results reveal that the two AGCs fully account for shuttle activity in mouse heart mitochondria and that no other glutamate transporter can replace the AGCs in this pathwayThis work was supported in part by grants from the Ministerio de Educacio´ n y Ciencia (BFU2005-C02-01, GEN2003-20235-C05-03/NAC), Instituto de Salud Carlos III del Ministerio de Sanidad (PI042457), European Union (LSHM-CT-2006-518153) (to J. S.), by Grant SAF2004-06843-C03 from the Ministerio de Educacio´ n y Ciencia (to P. G.-P.), by an institutional grant from the Fundacio´ n Ramo´ n Areces to the CBMSO, and by Grants-in-Aid for Scientific Research (16390100) from the Japan Society for the Promotion of Science (to K. K.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fac

Karyotypic analysis in the process of immortalization of human cells treated with 4-nitroquinoline 1-oxide

The establishment of a model system of neoplastic transformation of normal human cells has been attempted with a chemical carcinogen, 4-nitroquinoline 1-oxide (4NQO). In the course of these experiments, it was noticed that immortalization of human cells is a multi-step process involving several mutational genetic events. Thus, chromosomal changes which occurred during the process of immortalization of human fibroblasts were examined. To accomplish immortalization, fibroblasts obtained from an embryo were repeatedly treated with 10-6M4NQO from primary culture to passage 51 (59 treatments in total). Before immortalization, some chromosomes (especially, chromosomes 2, 6, 8, 10, 11, 12, 15, 19, and 20), were lost at a relatively high frequency. After immortalization, the chromosomes distributed so broadly in the triploid to hypotetraploid region without a distinct modal number or without marker chromosomes that it was difficult to identify the specific chromosomes related to the immortalization of human cells. No specific structural chromosomal changes were detected. Although the significance of such chromosome changes in relation to immortalization is not clear, the loss of some specific chromosomes suggests that genes which are involved in cellular aging and which suppress immortalization may have been lost in the immortalization process.</p

Aberrant methylation of the TDMR of the GTF2A1L promoter does not affect fertilisation rates via TESE in patients with hypospermatogenesis

Increasing evidence shows a relationship between epigenetic regulation and male infertility. The GTF2A1L gene promoter contains the DNA methylation site of a tissue-specific differentially methylated region (TDMR). Eighty-six patients with non-obstructive azoospermia were assessed for the DNA methylation state of CpG islands in the GTF2A1L promoter using testicular genomic DNA. Based on histological criteria, 26 of the 86 patients had normal spermatogenesis (controls), 17 had hypospermatogenesis and 26 had a Sertoli cell-only phenotype or tubular sclerosis. GTF2A1L TDMR methylation was significantly lower in testes DNA from control samples than from hypospermatogenic samples (P=0.029). Patients with hypospermatogenesis were divided into two subgroups: high DNA methylation (HM, n=5) and low DNA methylation (LM, n=12). The GTF2A1L TDMR methylation rate differed significantly between the HM and LM groups (P=0.0019), and GTF2A1L expression was significantly higher among the LM than in the HM patients (P=0.023). High TDMR methylation was correlated with low GTF2A1L gene expression levels. Both groups demonstrated relatively good outcomes with respect to sperm retrieval, fertilisation, pregnancy and childbirth rates. We observed that aberrant GTF2A1L gene expression was not correlated with fertilisation rates. The testicular sperm extraction (TESE) technique may be used to overcome male infertility due to aberrant TDMR methylation. © 2013 AJA, SIMM & SJTU. All rights reserved

Comparison of testosterone fractions between Framingham Heart Study participants and Japanese participants

Objectives: To determine testosterone fractions in Japanese men and to compare these values with those of Framingham Heart Study participants. Methods: We enrolled 498 healthy Japanese men. Total testosterone was assayed by liquid chromatography tandem mass spectrometry, sex hormone-binding globulin was assayed by immunoassay and free testosterone was calculated by a laboratory at the Boston Medical Center. Analog-based free testosterone and immunoassay-based total testosterone were determined by immunoassay. We compared mass spectrometry assay-based total testosterone and calculated free testosterone values in the Japanese participants with values in the American Framingham Heart Study third generation cohort. Results: The mean serum mass spectrometry assay-based total testosterone, sex hormone-binding globulin, and calculated free testosterone values were 439.4±167ng/dL, 65.34±30.61nmol/L, and 58.75±20.0pg/mL, respectively. The correlation coefficients with age for mass spectrometry assay-based total testosterone, sex hormone-binding globulin, and calculated free testosterone were 0.0010, 0.5041, and -0.496, respectively. There were no age-related changes in mass spectrometry assay-based total testosterone values in healthy men (P=0.981), whereas sex hormone-binding globulin and calculated free testosterone levels showed similar age-related changes (P<0.0001). Serum analog-based free testosterone levels (8.24±2.9pg/mL) showed age-related changes (P<0.0001) regardless of immunoassay-based total testosterone levels (P=0.828). Serum immunoassay-based total testosterone values (486.1±162.5ng/dL) correlated with serum mass spectrometry assay-based total testosterone values (r=0.740, 95% confidence interval 0.6965-0.7781, P<0.0001). Similarly, analog-based free testosterone and calculated free testosterone values showed a highly significant correlation (r=0.706, 95% confidence interval 0.6587-0.7473, P<0.0001). The analog-based free testosterone values were approximately 10% of the calculated free testosterone values. Conclusions: In contrast to the Framingham Heart Study cohort, total testosterone values in Japanese men are not associated with advancing age; thus, they cannot be used to diagnose late-onset hypogonadism in Japan. The analog-based free testosterone value can be considered instead as a suitable biochemical determinant for diagnosing late-onset hypogonadism syndrome. © 2014 The Japanese Urological Association

New molecular diagnostic kit to assess Y-chromosome deletions in the Japanese population

Objectives: Deletions in the azoospermia factor regions are the most common known molecular genetic cause of human male infertility involving spermatogenetic failure. Testing for these deletions in Japanese DNA samples using conventional sequence-tagged site probes occasionally lead to considerable non-specific or faint products in the Japanese population. The aim of the present study was to evaluate the sensitivity and specificity of a newly developed kit for the detection of azoospermia factor microdeletions in the Japanese population. Methods: Sequence-tagged site probes were reselected and the Luminex suspension array assay was carried out. Validation was retrospectively carried out with 2014 DNA sequences with known microdeletions, which were divided into four categories. Results: Category1 deletions that corresponded to the conventional classification of azoospermia factor deletion were present in 83 men (4.2%), which can result in intrachromosomal homologous recombination. Kit data confirmed the presence of deletions of this type in DNA sequences known to harbor the azoospermia factor deletions. Category2 deletions involved cytogenetic abnormalities in 28 men (1.4%), whereas category3 deletions in 759 men (37.7%) were atypical classifications including the gr/gr deletion. As these deletions are thought to be a result of palindromic units and non-homologous recombination, these microdeletions might impact in the interpretation of some clinical findings. The rest of the 1145 cases (56.8%) were assigned to category4 as normal variants (polymorphism/no deletion). Conclusions: The present findings show that this new kit offers good sensitivity and specificity with the advantage of saving in terms of cost and time. © 2014 The Japanese Urological Association

A novel y chromosome microdeletion with the loss of an endogenous retrovirus related, testis specific transcript in AZFb region

Purpose: We identified the endogenous retroviruses associated with TTYs (testis specific transcripts linked to the Y) in the AZFb region. We evaluated the relationship between endogenous retroviruses, and TTY expression patterns and function in spermatogenesis. Materials and Methods: We identified family members of TTYs in the AZFb region using computational screening. After investigating the relationship between the endogenous retrovirus genome and TTY expression patterns we screened genomic polymerase chain reaction products from TTY13 amplified from 790 Japanese men, including 275 with azoospermia, 285 with oligozoospermia and 230 who were fertile. Results: Computational screening revealed that 3 members of the TTY family, TTY9, 10 and 13, were regulated by endogenous retroviruses in the AZFb region. Homologous recombination between long terminal repeat of the TTY13 associated human endogenous retrovirus-K14C resulted in TTY13 deletion events. These deletions were more common in patients with azoospermia and oligozoospermia than in fertile males. Specifically 15.63% of the azoospermia group, 10.88% of the oligozoospermia group and 0% of fertile controls had only the deletion variant, indicating an association between the homologous recombination rate and the severity of spermatogenesis failure that was statistically significant (p <0.05). Conclusions: Because of the finding of what are to our knowledge novel microdeletions due to endogenous retrovirus in the AZFb region, our study raises the possibility that specific variations in genomic structure may contribute to some forms of human idiopathic male infertility. © 2011 American Urological Association Education and Research, Inc

Reduced N-acetylaspartate levels in mice lacking aralar, a brain- and muscle-type mitochondrial aspartate-glutamate carrier

Aralar is a mitochondrial calcium-regulated aspartate-glutamate carrier mainly distributed in brain and skeletal muscle, involved in the transport of aspartate from mitochondria to cytosol, and in the transfer of cytosolic reducing equivalents into mitochondria as a member of the malate-aspartate NADH shuttle. In the present study, we describe the characteristics of aralar-deficient (Aralar-/-) mice, generated by a gene-trap method, showing no aralar mRNA and protein, and no detectable malate-aspartate shuttle activity in skeletal muscle and brain mitochondria. Aralar-/- mice were growth-retarded, exhibited generalized tremoring, and had pronounced motor coordination defects along with an impaired myelination in the central nervous system. Analysis of lipid components showed a marked decrease in the myelin lipid galactosyl cerebroside. The content of the myelin lipid precursor, N-acetylaspartate, and that of aspartate are drastically decreased in the brain of Aralar-/- mice. The defect in N-acetylaspartate production was also observed in cell extracts from primary neuronal cultures derived from Aralar-/- mouse embryos. These results show that aralar plays an important role in myelin formation by providing aspartate for the synthesis of N-acetylaspartate in neuronal cell