NCBI Summary:
L-glutamate dehydrogenase (EC 1.4.1.3) has a central role in nitrogen metabolism in plants and animals. Glutamate dehydrogenase is found in all organisms and catalyzes the oxidative deamination of 1-glutamate to 2-oxoglutarate (Smith et al., 2001 [PubMed 11254391]). Glutamate, the main substrate of GLUD, is present in brain in concentrations higher than in other organs. In nervous tissue, GLUD appears to function in both the synthesis and the catabolism of glutamate and perhaps in ammonia detoxification (Mavrothalassitis et al., 1988 [PubMed 3368458]).[supplied by OMIM]
General function
Comment
Cellular localization
Mitochondrial
Comment
Ovarian function
Comment
Mitochondrial SIRT3 and its target glutamate dehydrogenase are altered in follicular cells of women with reduced ovarian reserve or advanced maternal age. Pacella-Ince L 2014 et al.
STUDY QUESTION
Is the activity of sirtuin 3 (SIRT3) altered in granulosa and cumulus cells from young women with reduced ovarian reserve or women of advanced maternal age?
SUMMARY ANSWER
SIRT3 mRNA and active protein in granulosa and cumulus cells were decreased in women with reduced ovarian reserve and advanced maternal age.
WHAT IS KNOWN ALREADY
Young women with reduced ovarian reserve or women of advanced maternal age have reduced oocyte viability, possibly due to altered granulosa and cumulus cell metabolism. The mitochondrial SIRT3 protein may be implicated in these processes as it is able to sense the metabolic state of the cell and alter mitochondrial protein function post-translationally.
STUDY DESIGN, SIZE, DURATION
This is a prospective cohort study, in which women (n = 72) undergoing routine IVF/ICSI were recruited and allocated to one of three cohorts based on age and ovarian reserve (as assessed by serum anti-Mullerian hormone level). Women were classified as young (=35 years) or of advanced maternal age (=40 years).
PARTICIPANTS/MATERIALS, SETTING, METHODS
Granulosa and cumulus cells were collected. SIRT3 mRNA and protein levels and protein activity was analysed in granulosa and cumulus cells via quantitative PCR, immunohistochemistry and western blotting, and deacetylation activity, respectively. Activity of the glutamate dehydrogenase (GDH) enzyme, a known target of SIRT3, was assessed, and acetylated proteins in mitochondria isolated from granulosa and cumulus cells were separated by immunoprecipitation and acetylation of GDH assessed by western blotting. Data for women with good prognosis (young women with normal ovarian reserve) were compared with those from young women with reduced ovarian reserve and those of advanced maternal age.
MAIN RESULTS AND THE ROLE OF CHANCE
SIRT3 mRNA and active protein were present in granulosa and cumulus cells and co-localized to the mitochondria. SIRT3 mRNA in granulosa cells was decreased in young women with reduced ovarian reserve and advanced maternal age versus young women with normal ovarian reserve (P < 0.05). SIRT3 mRNA in cumulus cells was decreased in women of advanced maternal age versus young women with normal ovarian reserve only (P < 0.05). Granulosa cell GDH activity was decreased in young women with reduced ovarian reserve and in women of advanced maternal age (P < 0.05), whereas cumulus cell GDH activity was reduced in the advanced maternal age group only (P < 0.05). The acetylation profile of GDH in mitochondria revealed increased acetylation of GDH in granulosa and cumulus cells from women of advanced maternal age (P < 0.05) while young women with reduced ovarian reserve had increased GDH acetylation in granulosa cells only (P < 0.05).
LIMITATIONS, REASONS FOR CAUTION
Although patients were allocated to groups based on maternal age and ovarian reserve and matched for BMI, other maternal factors may also alter the 'molecular health' of ovarian cells.
WIDER IMPLICATIONS OF THE FINDINGS
Our data suggest that SIRT3 post-translational modification of mitochondrial enzymes in human granulosa and cumulus cells may regulate GDH activity, thus altering the metabolic milieu surrounding the developing oocyte. Owing to the association between the decline in oocyte quality and pregnancy rates in women of advanced maternal age and the possible association with reduced ovarian reserve, knowledge of perturbed SIRT3 function in granulosa and cumulus cells may lead to novel therapies to improve mitochondrial metabolism in the oocyte and follicular cells in women undergoing IVF treatment.
STUDY FUNDING/COMPETING INTEREST(S)
No conflicts of interest to declare. Research was funded by an NHMRC project grant.
/////////////////////////
Expression regulated by
Comment
Ovarian localization
Oocyte, Cumulus, Granulosa, Luteal cells
Comment
Bostrom M, et al 2004 reported detailed analytical subcellular fractionation of non-pregnant porcine corpus luteum reveals peroxisomes of normal size and significant UDP-glucuronosyltransferase activity in the high-speed supernatant.
A detailed subfractionation of the non-pregnant porcine corpus luteum (CL) was performed employing differential centrifugation. Marker enzyme assays (i.e., lactate dehydrogenase for the cytosol, NADPH-cytochrome P450 reductase for the endoplasmatic reticulum, catalase (CAT) for peroxisomes, glutamate dehydrogenase for the mitochondrial matrix and acid phosphatase for lysosomes) in all subfractions obtained exhibited a pattern of distribution similar to that observed with rat liver. These subfractions should be useful in connection with many types of future studies.In disagreement with previous biochemical and morphological studies, peroxisomes (identified on the basis of catalase activity and by Western blotting of catalase and of the major peroxisomal membrane protein (PMP-70)) sedimented together with mitochondria (i.e., at 5000xg(av) for 10min) and not in the post-mitochodrial fraction prepared at 30,000xg(av) for 20min by Peterson and Stevensson [Biochim. Biophys. Acta 1135 (1992) 207]. No other classical peroxisomal enzymes were detectable in the porcine ovary, raising questions concerning the function of peroxisomes in this organ.Furthermore, UDP-glucuronosyltransferase (UGT), generally considered to be an integral membrane protein anchored in the endoplasmatic reticulum, was recovered in both the cytosolic (i.e., the supernatant after centrifugation at 50,000xg(av) for 1h) and the microsomal fraction of the porcine corpus luteum, even upon further centrifugation of the former. In contrast, UGT sediments exclusively in the microsomal fraction upon subfractionation of the liver and ovary from rat.
Follicle stages
Corpus luteum
Comment
Maternal gene transcription in mouse oocytes: genes implicated in oocyte maturation and fertilization. Cui XS et al. Maternal gene expression is an important biological process in oocyte maturation and early cleavage. To gain insights into oocyte maturation and early embryo development, we used microarray analysis to compare the gene expression profiles of germinal vesicle (GV)- and metaphase II (MII)-stage oocytes. The differences in spot intensities were normalized and grouped using the Avadis Prophetic software platform. Of the 12164 genes examined, we found 1682 genes with more highly expression in GV-stage oocytes than in MII-stage oocytes, while 1936 genes were more highly expressed in MII-stage oocytes (P<0.05). The genes were grouped on the basis of the Panther classification system according to their involvement in particular biological processes. The genes that were up-regulated in GV oocytes were more likely to be involved in protein metabolism and modification, the mitotic cell cycle, electron transport, or fertilization or belong to the microtubule/cytoskeletal protein family. The genes specifically upregulated in the MII oocytes were more likely to be involved in DNA replication, amino acid metabolism, or expression of G protein-coupled receptors and signaling molecules. Identification of genes that are preferentially expressed at particular oocyte maturation stages provides insights into the complex gene regulatory networks that drive oocyte maturation and fertilization. Expression higher in MII than GV oocytes.