The yeast Sir2 protein regulates epigenetic gene silencing and, as a possible antiaging effect, suppresses
recombination of rDNA. Studies involving cobB, a bacterial Sir2-like gene, have suggested that Sir2 may encode a pyridine
nucleotide transferase. By in silico and PCR-cloning techniques, Frye (1999) obtained cDNA sequences encoding 5 human
Sir2-like genes, which they called sirtuin-1 to -5 (SIRT1 to SIRT5). Recombinant human
SIRT2 was able to cause radioactivity to be transferred from (32P)NAD to bovine serum albumin (BSA). When a conserved
histidine within SIRT2 was converted to tyrosine, the mutant recombinant protein was unable to transfer radioactivity from
(32P)NAD to BSA. These results suggested that the sirtuins may function via mono-ADP-ribosylation of proteins.
NCBI Summary:
This gene encodes a member of the sirtuin family of proteins, homologs to the yeast Sir2 protein. Members of the sirtuin family are characterized by a sirtuin core domain and grouped into four classes. The functions of human sirtuins have not yet been determined; however, yeast sirtuin proteins are known to regulate epigenetic gene silencing and suppress recombination of rDNA. Studies suggest that the human sirtuins may function as intracellular regulatory proteins with mono-ADP-ribosyltransferase activity. The protein encoded by this gene is included in class I of the sirtuin family. Several transcript variants are resulted from alternative splicing of this gene. [provided by RefSeq, Jul 2010]
The human Sir2 ortholog, SIRT2, is an NAD+-dependent tubulin deacetylase. North BJ et al. The silent information regulator 2 protein (Sir2p) of Saccharomyces cerevisiae is an NAD-dependent histone deacetylase that plays a critical role in transcriptional silencing. Here, we report that a human ortholog of Sir2p, sirtuin type 2 (SIRT2), is a predominantly cytoplasmic protein that colocalizes with microtubules. SIRT2 deacetylates lysine-40 of alpha-tubulin both in vitro and in vivo. Knockdown of SIRT2 via siRNA results in tubulin hyperacetylation. SIRT2 colocalizes and interacts in vivo with HDAC6, another tubulin deacetylase. Enzymatic analysis of recombinant SIRT2 in comparison to a yeast homolog of Sir2 protein (Hst2p) shows a striking preference of SIRT2 for acetylated tubulin peptide as a substrate relative to acetylated histone H3 peptide. These observations establish SIRT2 as a bona fide tubulin deacetylase.
Cellular localization
Cytoplasmic
Comment
Melatonin ameliorates the advanced maternal age-associated meiotic defects in oocytes through the SIRT2-dependent H4K16 deacetylation pathway. Li C et al. (2020) It has been widely reported that advanced maternal age impairs oocyte quality. To date, various molecules have been discovered to be involved in this process. However, prevention of fertility issues associated with maternal age is still a challenge. In the present study, we find that both in vitro supplement and in vivo administration of melatonin are capable of alleviating the meiotic phenotypes of aged oocytes, specifically the spindle/chromosome disorganization and aneuploidy generation. Furthermore, we identify SIRT2 as a critical effector mediating the effects of melatonin on meiotic structure in old oocytes. Candidate screening shows that SIRT2-controlled deacetylation of histone H4K16 is essential for maintaining the meiotic apparatus in oocytes. Importantly, non-acetylatable-mimetic mutant H4K16R partially rescues the meiotic deficits in oocytes from reproductive aged mice. In contrast, overexpression of acetylation-mimetic mutant H4K16Q abolishes the beneficial effects of melatonin on the meiotic phenotypes in aged oocytes. To sum up, our data uncover that melatonin alleviates advanced maternal aged-associated meiotic defects in oocytes through the SIRT2-depenendet H4K16 deacetylation pathway.//////////////////
Ovarian function
Oocyte maturation
Comment
A novel role of SIRT2 in regulating gap junction communications via connexin-43 in bovine cumulus-oocyte complexes. Xu D et al. (2020) SIRT2, the predominantly cytosolic sirtuin, plays important role in multiple biological processes, including metabolism, stress response, and aging. However, the function of SIRT2 in gap junction intercellular communications (GJICs) of cumulus-oocyte complexes (COCs) is not yet known. The purpose of the present study was to evaluate the effect and underlining mechanism of SIRT2 on GJICs in COCs. Here, we found that treatment with SIRT2 inhibitors (SirReal2 or TM) inhibited bovine oocyte nuclear maturation. Further analysis revealed that SIRT2 inactivation disturbed the GJICs of COCs during in vitro maturation. Correspondingly, both the Cx43 phosphorylation levels and MEK/MER signaling pathways were induced by SIRT2 inhibition. Importantly, SIRT2-mediated Cx43 phosphorylation was completely abolished by treatment with MEK1/2 inhibitor (Trametinib). Furthermore, treatment with SIRT2 inhibitors resulted in the high levels of MEK1/2 acetylation. Functionally, downregulating the MER/ERK pathways with inhibitors (Trametinib or SCH772984) could attenuate the closure of GJICs caused by SIRT2 inactivation in partly. In addition, inhibition of SIRT2 activity significantly decreased the membrane and zona pellucida localization of Cx43 by upregulating the levels of Cx43 acetylation. Taken together, these results demonstrated a novel role that SIRT2 regulates GJICs via modulating the phosphorylation and deacetylation of Cx43 in COCs.//////////////////
Sirt2-BubR1 acetylation pathway mediates the effects of advanced maternal age on oocyte quality. Qiu D et al. (2017) The level of Sirt2 protein is reduced in oocytes from aged mice, while exogenous expression of Sirt2 could ameliorate the maternal age-associated meiotic defects. To date, the underlying mechanism remains unclear. Here, we confirmed that specific depletion of Sirt2 disrupts maturational progression and spindle/chromosome organization in mouse oocytes, with compromised kinetochore-microtubule attachments. Candidate screening revealed that acetylation state of lysine 243 on BubR1 (BubR1-K243, an integral part of the spindle assembly checkpoint complex) functions during oocyte meiosis, and acetylation-mimetic mutant BubR1-K243Q results in the very similar phenotypes as Sirt2-knockdown oocytes. Furthermore, we found that nonacetylatable-mimetic mutant BubR1-K243R partly prevents the meiotic deficits in oocytes depleted of Sirt2. Importantly, BubR1-K243R overexpression in oocytes derived from aged mice markedly suppresses spindle/chromosome anomalies and thereupon lowers the incidence of aneuploid eggs. In sum, our data suggest that Sirt2-dependent BubR1 deacetylation involves in the regulation of meiotic apparatus in normal oocytes and mediates the effects of advanced maternal age on oocyte quality.//////////////////
Nicotinamide impairs entry into and exit from meiosis I in mouse oocytes. Riepsamen A et al. (2015) Following exit from meiosis I, mammalian oocytes immediately enter meiosis II without an intervening interphase, accompanied by rapid reassembly of a bipolar spindle that maintains condensed chromosomes in a metaphase configuration (metaphase II arrest). Here we study the effect of nicotinamide (NAM), a non-competitive pan-sirtuin inhibitor, during meiotic maturation in mouse oocytes. Sirtuins are a family of seven NAD+-dependent deacetylases (Sirt1-7), which are involved in multiple cellular processes and are emerging as important regulators in oocytes and embryos. We found that NAM significantly delayed entry into meiosis I associated with delayed accumulation of the Cdk1 co-activator, cyclin B1. GVBD was also inhibited by the Sirt2-specific inhibitor, AGK2, and in a very similar pattern to NAM, supporting the notion that as in somatic cells, NAM inhibits sirtuins in oocytes. NAM did not affect subsequent spindle assembly, chromosome alignment or the timing of first polar body extrusion (PBE). Unexpectedly, however, in the majority of oocytes with a polar body, chromatin was decondensed and a nuclear structure was present. An identical phenotype was observed when flavopiridol was used to induce Cdk1 inactivation during late meiosis I prior to PBE, but not if Cdk1 was inactivated after PBE when metaphase II arrest was already established, altogether indicating that NAM impaired establishment rather than maintenance of metaphase II arrest. During meiosis I exit in NAM-treated medium, we found that cyclin B1 levels were lower and inhibitory Cdk1 phosphorylation was increased compared with controls. Although activation of the anaphase-promoting complex-Cdc20 (APC-Cdc20) occurred on-time in NAM-treated oocytes, Cdc20 levels were higher in very late meiosis I, pointing to exaggerated APC-Cdc20-mediated proteolysis as a reason for lower cyclin B1 levels. Collectively, therefore, our data indicate that by disrupting Cdk1 regulation, NAM impairs entry into meiosis I and the establishment of metaphase II arrest.//////////////////
Sirt2 functions in spindle organization and chromosome alignment in mouse oocyte meiosis. Zhang L 2013 et al.
Sirtuins have been widely reported to be involved in multiple biological processes; however, their function in oocyte meiosis has not been. Here, by confocal scanning and quantitative analysis, we show that specific depletion of Sirt2 in mouse oocytes results in spindle defects and chromosome disorganization (35.58.7 vs. 9.63.8% control; P<0.05), with impaired microtubule-kinetochore interaction. Moreover, knockdown and overexpression experiments reveal that Sirt2 modulates the acetylation status of histone H4K16 and a-tubulin in oocytes, which may in part mediate the defective phenotypes described above by influencing microtubule dynamics and kinetochore function. Finally, we find lower Sirt2 protein level in oocytes from aged mice by immunoblotting and that maternal age-associated meiotic defects can be ameliorated through overexpression of Sirt2 (33.25.1% old vs.12.75.2% old+Sirt2; P<0.05), providing support for the hypothesis that decreased Sirt2 is one of a number of factors contributing to oocyte age-dependent deficits. In summary, our data indicate a role for Sirt2 during oocyte meiosis and uncover a striking beneficial effect of increased Sirt2 expression on aged oocytes.-Zhang, L., Hou, X., Ma, R., Moley, K., Schedl, T., Wang, Q. Sirt2 functions in spindle organization and chromosome alignment in mouse oocyte meiosis.
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Expression regulated by
Comment
Ovarian localization
Oocyte, Cumulus
Comment
The expression of Sirtuin2 goes down during oocyte develoment.//////ournal of Mammalian Ova Research 30(1):24-29. 2013
doi: http://dx.doi.org/10.1274/jmor.30.24
Effects of Maternal Aging on Expression of Sirtuin Genes in Ovulated Oocyte and Cumulus Cells
Naoki Okamoto 1,3, Kazuhiro Kawamura 1,*, Nanami Kawamura 2, Chie Nishijima 1, Bunpei Ishizuka 2, Nao Suzuki 1 and Kazuaki Hirata 3
1 Department of Obstetrics and Gynecology
2 Department of Advanced Reproductive Medicine
3 Department of Anatomy, St. Marianna University School of Medicine, Kanagawa 216-8512, Japan
* To whom corresponding should be addressed. e-mail: kawamurak@marianna-u.ac.jp
Abstract:
Sirtuins, a family of NAD+-dependent protein deacetylases, regulate important physiological events including aging and cell metabolism, mainly by protecting cells/tissues from oxidative damage. Ovarian aging decreases the quality of oocytes through induction of mitochondrial dysfunction and increases in DNA strand breaks by accumulation of reactive oxygen species. However, involvement of sirtuins in regulating oocyte quality with aging has not been determined. Here, we found the expression of sirtuin genes (Sirt1?7) in mouse ovaries and isolated oocytes and cumulus cells in a cell-specific manner. Based on real-time RT-PCR, all seven sirtuin genes were detected in the ovary with Sirt2 transcript levels showing the highest abundance. Oocyte expressed high levels of Sirt6, whereas the expressions of Sirt1, Sirt2, Sirt4, and Sirt6 were high in cumulus cells. When comparing samples from young and aged mice, oocyte levels of Sirt1?7 mRNA were not different. However, Sirt2 and Sirt6 transcript levels were decreased in cumulus cells of aged mice. Our findings suggest a possible association of Sirt2 and Sirt6 transcript levels in cumulus cells with impaired oocyte quality in aged mice. Further understanding the roles of these sirtuins in cumulus cell and oocyte could provide a better strategy to minimize aging-related decline in oocyte quality.
Follicle stages
Comment
Phenotypes
Mutations
2 mutations
Species: mouse
Mutation name: type: null mutation fertility: fertile Comment: 3 Female infertility is a common and devastating condition with life-long health, emotional and
4 social consequences. There is currently no pharmacological therapy for preserving oocyte
5 quality during aging, which is the strongest risk factor for infertility. This leads to an age
6 dependent decline in natural conception and IVF success rates (1). Here, we show that this is
7 due in part to declining levels of the metabolic cofactor nicotinamide adenine dinucleotide
8 (NAD+), and that restoring NAD+ levels with its metabolic precursor nicotinamide
9 mononucleotide (NMN) rejuvenates oocyte quality and quantity in aged animals, leading to
10 improved fertility. These benefits extend to the developing embryo, where NMN
11 supplementation in embryo culture media following IVF enhances blastocyst formation in
12 older mice. The NAD+ dependent deacylase SIRT2 is sufficient, but not essential, to
13 recapitulate the benefits of in vivo NMN treatment, and transgenic overexpression of SIRT2
14 maintains oocyte spindle assembly, accurate chromosome segregation, decreased oxidative
15 stress and overall fertility with ageing. Pharmacological elevation of NAD+ may be an
16 effective, non-invasive strategy for restoring and maintaining female fertility during ageing,
17 and for improving the success of IVF.
Species: mouse
Mutation name: type: null mutation fertility: subfertile Comment: NAD+ Repletion Rescues Female Fertility during Reproductive Aging. Bertoldo MJ et al. (2020) Reproductive aging in female mammals is an irreversible process associated with declining oocyte quality, which is the rate-limiting factor to fertility. Here, we show that this loss of oocyte quality with age accompanies declining levels of the prominent metabolic cofactor nicotinamide adenine dinucleotide (NAD+). Treatment with the NAD+ metabolic precursor nicotinamide mononucleotide (NMN) rejuvenates oocyte quality in aged animals, leading to restoration in fertility, and this can be recapitulated by transgenic overexpression of the NAD+-dependent deacylase SIRT2, though deletion of this enzyme does not impair oocyte quality. These benefits of NMN extend to the developing embryo, where supplementation reverses the adverse effect of maternal age on developmental milestones. These findings suggest that late-life restoration of NAD+ levels represents an opportunity to rescue female reproductive function in mammals.//////////////////