Oocyte Health and Quality: Implication of Mitochondria-related Organelle Interactions.

Among factors like hormonal imbalance and uterine condition, oocyte quality is regarded as one of the key factors involved in age-related decline in the reproductive capacity. Here, are discussions about the functions played by organelles within the oocyte in forming the next generation that is more suitable for survival. Many insights on the adaptation to aging and maintenance of quality can be obtained from: interactions between mitochondria and other organelles that enable the long life of primordial oocytes; characteristics of organelle interactions after breaking dormancy from primary oocytes to mature oocytes; and characteristics of interactions between mitochondria and other organelles of aged oocytes collected during the ovulatory cycle from elderly individuals and animals. This information would potentially be beneficial to the development of future therapeutic methods or agents.

Behavior of Assembled Promyelocytic Leukemia Nuclear Bodies upon Asymmetric Division in Mouse Oocytes.

Promyelocytic leukemia (PML) nuclear bodies (PML-NBs) are core-shell-type membrane-less organelles typically found in the nucleus of mammalian somatic cells but are absent in mouse oocytes. Here, we deliberately induced the assembly of PML-NBs by injecting mRNA encoding human PML protein (hPML VI -sfGFP) into oocytes and investigated their impact on fertilization in which oocyte/embryos undergo multiple types of stresses. Following nuclear membrane breakdown, preassembled hPML VI -sfGFP mRNA-derived PML-NBs (hmdPML-NBs) persisted in the cytoplasm of oocytes, forming less-soluble debris, particularly under stress. Parthenogenetic embryos that successfully formed pronuclei were capable of removing preassembled hmdPML-NBs from the cytoplasm while forming new hmdPML-NBs in the pronucleus. These observations highlight the beneficial aspect of the PML-NB-free nucleoplasmic environment and suggest that the ability to eliminate unnecessary materials in the cytoplasm of metaphase oocytes serves as a potential indicator of the oocyte quality.

Promyelocytic leukemia nuclear body-like structures can assemble in mouse oocytes.

Promyelocytic leukemia (PML) nuclear bodies (PML-NBs), a class of membrane-less cellular organelles, participate in various biological activities. PML-NBs are known as the core-shell-type nuclear body, harboring 'client' proteins in their core. Although multiple membrane-less organelles work in the oocyte nucleus, PML-NBs have been predicted to be absent from oocytes. Here, we show that some well-known PML clients (but not endogenous PML) co-localized with small ubiquitin-related modifier (SUMO) protein in the nucleolus and peri-centromeric heterochromatin of maturing oocytes. In oocytes devoid of PML-NBs, endogenous PML protein localized in the vicinity of chromatin. During and after meiotic resumption, PML co-localized with SUMO gathering around chromosomes. To examine the benefit of the PML-NB-free intranuclear milieu in oocytes, we deliberately assembled PML-NBs by microinjecting human PML-encoding plasmids into oocytes. Under conditions of limited SUMO availability, assembled PML-NBs tended to cluster. Upon proteotoxic stress, SUMO delocalized from peri-centromeric heterochromatin and co-localized with SC35 (a marker of nuclear speckles)-positive large compartments, which was disturbed by pre-assembled PML-NBs. These observations suggest that the PML-NB-free intranuclear environment helps reserve SUMO for emergent responses by redirecting the flux of SUMO otherwise needed to maintain PML-NB dynamics.

Effects of arsenic on the topology and solubility of promyelocytic leukemia (PML)-nuclear bodies.

Promyelocytic leukemia (PML) proteins are involved in the pathogenesis of acute promyelocytic leukemia (APL). Trivalent arsenic (As3+) is known to cure APL by binding to cysteine residues of PML and enhance the degradation of PML-retinoic acid receptor α (RARα), a t(15;17) gene translocation product in APL cells, and restore PML-nuclear bodies (NBs). The size, number, and shape of PML-NBs vary among cell types and during cell division. However, topological changes of PML-NBs in As3+-exposed cells have not been well-documented. We report that As3+-induced solubility shift underlies rapid SUMOylation of PML and late agglomeration of PML-NBs. Most PML-NBs were toroidal and granular dot-like in GFPPML-transduced CHO-K1 and HEK293 cells, respectively. Exposure to As3+ and antimony (Sb3+) greatly reduced the solubility of PML and enhanced SUMOylation within 2 h in the absence of changes in the number and size of PML-NBs. However, the prolonged exposure to As3+ and Sb3+ resulted in agglomeration of PML-NBs. Exposure to bismuth (Bi3+), another Group 15 element, did not induce any of these changes. ML792, a SUMO activation inhibitor, reduced the number of PML-NBs and increased the size of the NBs, but had little effect on the As3+-induced solubility change of PML. These results warrant the importance of As3+- or Sb3+-induced solubility shift of PML for the regulation intranuclear dynamics of PML-NBs.

SUMOylation regulates the number and size of promyelocytic leukemia-nuclear bodies (PML-NBs) and arsenic perturbs SUMO dynamics on PML by insolubilizing PML in THP-1 cells.

The functional roles of protein modification by small ubiquitin-like modifier (SUMO) proteins are not well understood compared to ubiquitination. Promyelocytic leukemia (PML) proteins are good substrates for SUMOylation, and PML-nuclear bodies (PML-NBs) may function as a platform for the PML SUMOylation. PML proteins are rapidly modified both with SUMO2/3 and SUMO1 after exposure to arsenite (As3+) and SUMOylated PML are further ubiquitinated and degraded by proteasomes. However, effects of As3+ on SUMO dynamics on PML-NBs are not well investigated. In the present study, we report that (1) the number and size of PML-NBs were regulated by SUMO E1-activating enzyme, (2) SUMO2/3 co-localized with PML irrespective of As3+ exposure and was restricted to PML-nuclear bodies (PML-NBs) via covalent binding in response to As3+, and (3) As3+-induced biochemical changes in PML were not modulated by ubiquitin-proteasome system (UPS) in THP-1 cells. Undifferentiated and differentiated THP-1 cells responded to As3+ similarly and PML proteins were changed from the detergent soluble to the insoluble form and further SUMOylated with SUMO2/3 and SUMO1. ML792, a SUMO E1 inhibitor, decreased the number of PML-NBs and reciprocally increased the size irrespective of exposure to As3+, which itself slightly decrease both the number and size of PML-NBs. TAK243, a ubiquitin E1 inhibitor, did not change the PML-NBs, while SUMOylated proteins accumulated in the TAK243-exposed cells. Proteasome inhibitors did not change the As3+-induced SUMOylation levels of PML. Co-localization and further restriction of SUMO2/3 to PML-NBs were confirmed by PML-transfected CHO-K1 cells. Collectively, SUMOylation regulates PML-NBs and As3+ restricts SUMO dynamics on PML by changing its solubility.

Mitochondrial dynamics and interorganellar communication in the development and dysmorphism of mammalian oocytes.

Mitochondria play many critical roles in cells, not only by supplying energy, but also by supplying metabolites, buffering Ca2+ levels and regulating apoptosis. During oocyte maturation and subsequent embryo development, mitochondria change their morphology by membrane fusion and fission, and coordinately undergo multiple cellular events with the endoplasmic reticulum (ER) closely apposed. Mitochondrial fusion and fission, known as mitochondrial dynamics, are regulated by family members of dynamin GTPases. Oocytes in animal models with these regulators artificially altered exhibit morphological abnormalities in nearby mitochondria and at the ER interface that are reminiscent of major cytoplasmic dysmorphisms in human assisted reproductive technology, in which a portion of mature oocytes retrieved from patients contain cytoplasmic dysmorphisms associated with mitochondria and ER abnormal morphologies. Understanding organelle morpho-homeostasis in oocytes obtained from animal models will contribute to the development of novel methods for determining oocyte health and for how to deal with dysmorphic oocytes.

Proposed Key Characteristics of Female Reproductive Toxicants as an Approach for Organizing and Evaluating Mechanistic Data in Hazard Assessment.

BACKGROUND: Identification of female reproductive toxicants is currently based largely on integrated epidemiological and in vivo toxicology data and, to a lesser degree, on mechanistic data. A uniform approach to systematically search, organize, integrate, and evaluate mechanistic evidence of female reproductive toxicity from various data types is lacking. OBJECTIVE: We sought to apply a key characteristics approach similar to that pioneered for carcinogen hazard identification to female reproductive toxicant hazard identification. METHODS: A working group of international experts was convened to discuss mechanisms associated with chemical-induced female reproductive toxicity and identified 10 key characteristics of chemicals that cause female reproductive toxicity: 1) alters hormone receptor signaling; alters reproductive hormone production, secretion, or metabolism; 2) chemical or metabolite is genotoxic; 3) induces epigenetic alterations; 4) causes mitochondrial dysfunction; 5) induces oxidative stress; 6) alters immune function; 7) alters cell signal transduction; 8) alters direct cell­cell interactions; 9) alters survival, proliferation, cell death, or metabolic pathways; and 10) alters microtubules and associated structures. As proof of principle, cyclophosphamide and diethylstilbestrol (DES), for which both human and animal studies have demonstrated female reproductive toxicity, display at least 5 and 3 key characteristics, respectively. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), for which the epidemiological evidence is mixed, exhibits 5 key characteristics. DISCUSSION: Future efforts should focus on evaluating the proposed key characteristics against additional known and suspected female reproductive toxicants. Chemicals that exhibit one or more of the key characteristics could be prioritized for additional evaluation and testing. A key characteristics approach has the potential to integrate with pathway-based toxicity testing to improve prediction of female reproductive toxicity in chemicals and potentially prevent some toxicants from entering common use. https://doi.org/10.1289/EHP4971.

Solubility changes of promyelocytic leukemia (PML) and SUMO monomers and dynamics of PML nuclear body proteins in arsenite-treated cells.

Promyelocytic leukemia (PML) and a suite of other proteins form nuclear bodies (NBs) where SUMOylation of PML and tumor suppression events occur in response to arsenite (As3+) treatment. Soluble PML is rapidly modified to the insoluble form in response to As3+, yet the relationship between the solubility change and nuclear localization of PML and PML-nuclear body (PML-NB) proteins remained elusive. We have investigated differences in the solubility change of well-known PML-NB proteins such as death-associated protein 6 (DAXX), SUMO, and PML in genetically engineered HEK293, and Jurkat and HL60 cells. The solubility of PML and SUMO2/3 monomers in RIPA solution decreased in 2 h in response to As3+. Live image analysis of GFP-PML revealed that extranuclear PML was insoluble in RIPA irrespective of the As3+-treatment and PML in PML-NBs, which was soluble in the untreated cells, was converted to insoluble forms by As3+. The solubility of DAXX was not changed by As3+, even though PML and DAXX co-localized completely in the subcellular compartments. Murine double mutant 2 (MDM2), which is known to interacts with intranuclear PML, did not affect the As3+-induced solubility change of PML. These results indicate that As3+ selectively reorganizes PML and SUMO2/3 monomers into insoluble forms in PML-NBs, and then PML SUMOylation proceeds.

Effects of diesel exhaust-derived secondary organic aerosol (SOA) on oocytes: Potential risks to meiotic maturation.

Particulate air pollution (PM 2.5) is a worldwide concern. Growing epidemiological evidence has shown pathophysiological effects of PM 2.5, not only on cardiovascular system but also on reproductive performance. The composition and physicochemical properties of PM 2.5 vary depending on the emission sources, climate conditions, and complex chemical reactions in the air. These factors make it difficult to understand the cause and mechanistic details of the adverse health effects of PM 2.5. Here, we show potential impacts of PM 2.5 on oocyte maturation in mice by utilizing diesel exhaust-derived secondary organic aerosol (SOA), a major component of urban PM 2.5. We found that the SOA destabilized microtubules of mouse oocytes and p-benzoquinone is one of the candidates for the microtubule-destabilizing compounds. We propose that some biologically reactive components of PM 2.5 should be prioritized for the regulation of atmospheric quality.

Pharmacodynamics of S-dimethylarsino-glutathione, a putative metabolic intermediate of inorganic arsenic, in mice.

Inorganic arsenicals are well-known carcinogens, whereas arsenite (iAsIII) compounds are now recognized as potent therapeutic agents for several leukemias, and arsenic trioxide has been used for the treatment of recurrent acute promyelocytic leukemia (APL). However, recent clinical trials revealed that arsenite is not always effective for non-APL malignancies. Another arsenical, S-dimethylarsino-glutathione ([DMAIII(GS)]), which is a putative metabolic intermediate in the hepatic metabolism of iAsIII, shows promise for treating several types of lymphoma. However, the metabolism of [DMAIII(GS)] has not been well investigated, probably because [DMAIII(GS)] is not stable in biological fluids where the concentration of glutathione is low. In the present study, we injected [DMAIII(GS)] intravenously into mice and compared the tissue distribution and metabolic dynamics of [DMAIII(GS)] with those of sodium arsenite (NaAsO2). We found a unique organ preference for the distribution of [DMAIII(GS)] to the lung and brain in comparison to NaAsO2. Furthermore, [DMAIII(GS)] appeared to bind to serum albumin by exchanging its glutathione moiety quickly after administration, providing novel insights into the longer retention of [DMAIII(GS)] in plasma.

Solubility shift and SUMOylaltion of promyelocytic leukemia (PML) protein in response to arsenic(III) and fate of the SUMOylated PML.

Promyelocytic leukemia (PML), which is a tumor suppressor protein that nevertheless plays an important role in the maintenance of leukemia initiating cells, is known to be biochemically modified by As(3+). We recently developed a simple method to evaluate the modification of PML by As(3+) resulting in a change in solubility and the covalent binding of small ubiquitin-like modifier (SUMO). Here we semi-quantitatively investigated the SUMOylation of PML using HEK293 cells which were stably transfected with PML-VI (HEK-PML). Western blot analyses indicated that PML became insoluble in cold RadioImmunoPrecipitation Assay (RIPA) lysis buffer and was SUMOylated by both SUMO2/3 and SUMO1 by As(3+). Surprisingly SUMO1 monomers were completely utilized for the SUMOylation of PML. Antimony (Sb(3+)) but not bismuth (Bi(3+)), Cu(2+), or Cd(2+) biochemically modified PML similarly. SUMOylated PML decreased after removal of As(3+) from the culture medium. However, unSUMOylated PML was still recovered in the RIPA-insoluble fraction, suggesting that SUMOylation is not requisite for changing the RIPA-soluble PML into the RIPA-insoluble form. Immunofluorescence staining of As(3+)-exposed cells indicated that SUMO2/3 was co-localized with PML in the nuclear bodies. However, some PML protein was present in peri-nuclear regions without SUMO2/3. Functional Really Interesting New Gene (RING)-deleted mutant PML neither formed PML nuclear bodies nor was biochemically modified by As(3+). Conjugation with intracellular glutathione may explain the accessibility of As(3+) and Sb(3+) to PML in the nuclear region evading chelation and entrapping by cytoplasmic proteins such as metallothioneins.

Mitochondrial fission factor Drp1 maintains oocyte quality via dynamic rearrangement of multiple organelles.

Mitochondria are dynamic organelles that change their morphology by active fusion and fission in response to cellular signaling and differentiation. The in vivo role of mitochondrial fission in mammals has been examined by using tissue-specific knockout (KO) mice of the mitochondria fission-regulating GTPase Drp1, as well as analyzing a human patient harboring a point mutation in Drp1, showing that Drp1 is essential for embryonic and neonatal development and neuronal function. During oocyte maturation and aging, structures of various membrane organelles including mitochondria and the endoplasmic reticulum (ER) are changed dynamically, and their organelle aggregation is related to germ cell formation and epigenetic regulation. However, the underlying molecular mechanisms of organelle dynamics during the development and aging of oocytes have not been well understood. Here, we analyzed oocyte-specific mitochondrial fission factor Drp1-deficient mice and found that mitochondrial fission is essential for follicular maturation and ovulation in an age-dependent manner. Mitochondria were highly aggregated with other organelles, such as the ER and secretory vesicles, in KO oocyte, which resulted in impaired Ca(2+) signaling, intercellular communication via secretion, and meiotic resumption. We further found that oocytes from aged mice displayed reduced Drp1-dependent mitochondrial fission and defective organelle morphogenesis, similar to Drp1 KO oocytes. On the basis of these findings, it appears that mitochondrial fission maintains the competency of oocytes via multiorganelle rearrangement.

Oligo-astheno-teratozoospermia in mice lacking ORP4, a sterol-binding protein in the OSBP-related protein family.

Oligo-astheno-teratozoospermia (OAT), a condition that includes low sperm number, low sperm motility and abnormal sperm morphology, is the commonest cause of male infertility. Because genetic analysis is frequently impeded by the infertility phenotype, the genetic basis of many of OAT conditions has been hard to verify. Here, we show that deficiency of ORP4, a sterol-binding protein in the oxysterol-binding protein (OSBP)-related protein family, causes male infertility due to severe OAT in mice. In ORP4-deficient mice, spermatogonia proliferation and subsequent meiosis occurred normally, but the morphology of elongating and elongated spermatids was severely distorted, with round-shaped head, curled back head or symplast. Spermatozoa derived from ORP4-deficient mice had little or no motility and no fertilizing ability in vitro. In ORP4-deficient testis, postmeiotic spermatids underwent extensive apoptosis, leading to a severely reduced number of spermatozoa. At the ultrastructural level, nascent acrosomes appeared to normally develop in round spermatids, but acrosomes were detached from the nucleus in elongating spermatids. These results suggest that ORP4 is essential for the postmeiotic differentiation of germ cells.

LPIAT1 regulates arachidonic acid content in phosphatidylinositol and is required for cortical lamination in mice.

Dietary arachidonic acid (AA) has roles in growth, neuronal development, and cognitive function in infants. AA is remarkably enriched in phosphatidylinositol (PI), an important constituent of biological membranes in mammals; however, the physiological significance of AA-containing PI remains unknown. In an RNA interference-based genetic screen using Caenorhabditis elegans, we recently cloned mboa-7 as an acyltransferase that selectively incorporates AA into PI. Here we show that lysophosphatidylinositol acyltransferase 1 (LPIAT1, also known as MBOAT7), the closest mammalian homologue, plays a crucial role in brain development in mice. Lpiat1(-/-) mice show almost no LPIAT activity with arachidonoyl-CoA as an acyl donor and show reduced AA contents in PI and PI phosphates. Lpiat1(-/-) mice die within a month and show atrophy of the cerebral cortex and hippocampus. Immunohistochemical analysis reveals disordered cortical lamination and delayed neuronal migration in the cortex of E18.5 Lpiat1(-/-) mice. LPIAT1 deficiency also causes disordered neuronal processes in the cortex and reduced neurite outgrowth in vitro. Taken together, these results demonstrate that AA-containing PI/PI phosphates play an important role in normal cortical lamination during brain development in mice.