Maturation promoting factor destabilization facilitates postovulatory aging-mediated abortive spontaneous egg activation in rat

Follicular oocyte as a potential target for severe acute respiratory syndrome coronavirus 2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was reported in December 2019 and rapidly became a pandemic as coronavirus disease 2019 (COVID-19). Apart from other organs, presence of specific receptor angiotensin-converting enzyme (ACE2) and corresponding proteases such as transmembrane serine protease 2, basigin and cysteine protease cathepsin L make follicular somatic cells as well as oocyte as potential targets for SARS-CoV-2 infection. The SARS-CoV-2 causes inflammation and hypoxia that generate reactive oxygen species (ROS) in critically ill patients. In addition, a large number of casualties and insecurity of life due to repeated waves of SARS-CoV-2 infection generate psychological stress and cortisol resulting in the further generation of ROS. The excess levels of ROS under physiological range cause meiotic instability, while high levels result in oxidative stress that trigger various death pathways and affect number as well as quality of follicular oocytes. Although, emerging evidence suggests that the SARS-CoV-2 utilises cellular machinery of ovarian follicular cells, generates ROS and impairs quality of follicular oocytes, the underlying mechanism of viral entry into host cell and its negative impact on the follicular oocyte remains poorly understood. Therefore, this review summarises emerging evidence on the presence of cellular machinery for SARS-CoV-2 in ovarian follicles and the potential negative impact of viral infection on the follicular oocytes that affect ovarian functions in critically ill and stressed women.

Reactive oxygen species signalling in the deterioration of quality of mammalian oocytes cultured in vitro: Protective effect of antioxidants

The in vitro fertilization (IVF) is the first choice of infertile couples worldwide to plan for conception. Besides having a significant advancement in IVF procedure, the success rate is still poor. Although several approaches have been tested to improve IVF protocol, minor changes in culture conditions, physical factors and/or drug treatment generate reactive oxygen species (ROS) in oocytes. Due to large size and huge number of mitochondria, oocyte is more susceptible towards ROS-mediated signalling under in vitro culture conditions. Elevation of ROS levels destabilize maturation promoting factor (MPF) that results in meiotic exit from diplotene as well as metaphase-II (M-II) arrest in vitro. Once meiotic exit occurs, these oocytes get further arrested at metaphase-I (M-I) stage or metaphase-III (M-III)-like stage under in vitro culture conditions. The M-I as well as M-III arrested oocytes are not fit for fertilization and limits IVF outcome. Further, the generation of excess levels of ROS cause oxidative stress (OS) that initiate downstream signalling to initiate various death pathways such as apoptosis, autophagy, necroptosis and deteriorates oocyte quality under in vitro culture conditions. The increase of cellular enzymatic antioxidants and/or supplementation of exogenous antioxidants in culture medium protect ROS-induced deterioration of oocyte quality in vitro. Although a growing body of evidence suggests the ROS and OS-mediated deterioration of oocyte quality in vitro, their downstream signalling and related mechanisms remain poorly understood. Hence, this review article summarizes the existing evidences concerning ROS and OS-mediated downstream signalling during deterioration of oocyte quality in vitro. The use of various antioxidants against ROS and OS-mediated impairment of oocyte quality in vitro has also been explored in order to increase the success rate of IVF during assisted reproductive health management.

Association between F-box-only protein 43 overexpression and hepatocellular carcinoma pathogenesis and prognosis

BACKGROUND

Despite great advances in the prevention, diagnosis, treatment, and management regarding hepatocellular carcinoma (HCC), the overall prognosis of HCC remains unfavorable. The expression profile, prognostic role, and biological functions of F-box-only protein 43 (FBXO43) in HCC remain unclear. Here, we determine the expression profile and prognostic value of FBXO43 in patients with HCC.

MATERIALS AND METHODS

A total of 467 HCC patients and their clinicopathological data were collected from the Second Affiliated Hospital of Jiaxing University, the Cancer Genome Atlas (TCGA), and Genotype-Tissue Expression (GTEx) databases. The expression profile, prognostic value, biological functions, and underlying mechanism of its involvement of FBXO43 were explored based on TCGA, Gene Expression Omnibus (GEO), LinkedOmics, and Cancer Dependency Map (DepMap). The expression of FBXO43 in 93 paired liver tissues was investigated via immunohistochemical staining, tissue microarray analysis, and Western blot. The prognostic value was assessed using survival analysis.

RESULTS

FBXO43 RNA was upregulated in HCC liver tissues and was associated with an unfavorable prognosis (p < 0.05). Furthermore, FBXO43 protein was overexpressed in HCC liver tissues compared with that in paired normal liver tissues. Overexpression of FBXO43 protein was significantly associated with advanced TNM stage, large tumor size, lymphatic invasion, distant metastasis, earlier cancer recurrence, and decreased overall survival after radical surgery (p < 0.05). Cox regression analysis showed that FBXO43 had significant prognostic value in HCC. Importantly, FBXO43 and its co-expressed genes were mainly involved in cell cycle regulation, DNA replication, metabolic regulation, and so on. FBXO43 knockdown could significantly affect the HCC cell lines growth and proliferation.

CONCLUSIONS

We first revealed that FBXO43 was overexpressed in liver HCC tissues at the RNA and protein levels and served as an independent prognostic factor for HCC patients. Therefore, FBXO43 is worth investigating as a potential HCC treatment target.

Cilostamide, a phosphodiesterase 3A inhibitor, sustains meiotic arrest of rat oocytes by modulating cyclic adenosine monophosphate level and the key regulators of maturation promoting factor

Cilostamide, a phosphodiesterase 3A (Pde3A) inhibitor, is known to increase intraoocyte cyclic adenosine monophosphate (cAMP) level which is involved in sustaining meiotic arrest of the oocytes. To explore the mechanisms involved in the cilostamide-mediated meiotic arrest of the oocytes, the present study describes the effects of cilostamide on cAMP level and related factors involved in maturation of the oocytes at its different meiotic stages; diplotene, metaphase I (MI) and metaphase II (MII). The oocytes from these three stages were collected from rat ovary and incubated with 10 µM cilostamide for 3 h in CO₂ incubator. The levels of cAMP, cyclic guanosine monophosphate (cGMP) and the key players of maintaining meiotic arrest during oocyte maturation; Emi2, Apc, Cyclin B1, and Cdk1, were analyzed in diplotene, MI and MII stages. Pde3A was found to be expressed at all three stages but with the lowest level in MI oocyte. As compared to the control sets, the cAMP concentration was found to be highest in MII whereas cGMP was highest in the diplotene stage of cilostamide-treated group. The treated group showed declined reactive oxygen species level as compared with the control counterparts. Relatively increased levels of the Emi2, Cyclin B1, and phosphorylated thr161 of Cdk1 versus declined levels of phosphorylated thr14/tyr15 of Cdk1 in diplotene and MII stage oocytes are known to be involved in maintaining meiotic arrest and all these factors were found to undergo similar pattern of change due to the treatment with cilostamide. The findings thus suggest that cilostamide treatment promotes meiotic arrest by Pde3A inhibition led increase of both cAMP and cGMP level vis-a-vis modulation of the related regulatory factors such as Emi2, CyclinB1, and phosphorylated status of Cdk1 in diplotene and MII stage oocytes. Such a mechanism of meiotic arrest could allow the oocyte to prepare itself for meiotic maturation and thereby to improve oocyte quality.

Exploration of the Cytoplasmic Function of Abnormally Fertilized Embryos via Novel Pronuclear-Stage Cytoplasmic Transfer

In regular IVF, a portion of oocytes exhibit abnormal numbers of pronuclei (PN) that is considered as abnormal fertilization, and they are routinely discarded. However, it is known that abnormal ploidy still does not completely abandon embryo development and implantation. To explore the potential of cytoplasm from those abnormally fertilized oocytes, we developed a novel technique for the transfer of large cytoplasm between pronuclear-stage mouse embryos, and assessed its impact. A large volume of cytoplast could be efficiently transferred in the PN stage using a novel two-step method of pronuclear-stage cytoplasmic transfer (PNCT). PNCT revealed the difference in the cytoplasmic function among abnormally fertilized embryos where the cytoplasm of 3PN was developmentally more competent than 1PN, and the supplementing of fresh 3PN cytoplasm restored the impaired developmental potential of postovulatory “aged” oocytes. PNCT-derived embryos harbored significantly higher mitochondrial DNA copies, ATP content, oxygen consumption rate, and total cells. The difference in cytoplasmic function between 3PN and 1PN mouse oocytes probably attributed to the proper activation via sperm and may impact subsequent epigenetic events. These results imply that PNCT may serve as a potential alternative treatment to whole egg donation for patients with age-related recurrent IVF failure.

Meiotic Instability Generates a Pathological Condition in Mammalian Ovum

Maintenance of metaphase-II (M-II) arrest in ovum is required to present itself as a right gamete for successful fertilization in mammals. Surprisingly, instability of meiotic cell cycle results in spontaneous exit from M-II arrest, chromosomal scattering and incomplete extrusion of second polar body (PB-II) without forming pronuclei so called abortive spontaneous ovum activation (SOA). It remains unclear what causes meiotic instability in freshly ovulated ovum that results in abortive SOA. We propose the involvement of various signal molecules such as reactive oxygen species (ROS), cyclic 3',5' adenosine monophosphate (cAMP) and calcium (Ca²⁺) in the induction of meiotic instability and thereby abortive SOA. These signal molecules through their downstream pathways modulate phosphorylation status and activity of cyclin dependent kinase (cdk1) as well as cyclin B1 level. Changes in phosphorylation status of cdk1 and its activity, dissociation and degradation of cyclin B1 destabilize maturation promoting factor (MPF). The premature MPF destabilization and defects in other cell cycle regulators possibly cause meiotic instability in ovum soon after ovulation. The meiotic instability results in a pathological condition of abortive SOA and deteriorates ovum quality. These ova are unfit for fertilization and limit reproductive outcome in several mammalian species including human. Therefore, global attention is required to identify the underlying causes in greater details in order to address the problem of meiotic instability in ova of several mammalian species icluding human. Moreover, these activated ova may be used to create parthenogenetic embryonic stem cell lines in vitro for the use in regenerative medicine.Graphical abstract.

Roles of Resveratrol in Improving the Quality of Postovulatory Aging Oocytes In Vitro

After ovulation, mammalian oocytes will undergo a time-dependent process of aging if they are not fertilized. This postovulatory aging (POA) seriously affects the oocyte quality and then impairs the subsequent fertilization and early embryo development, which should be avoided especially in assisted reproductive technology (ART). Resveratrol is an antioxidant substance that can scavenge free radicals and is effective in improving ovary functions. Here, mouse oocytes were used to investigate the effects and mechanisms of resveratrol on POA oocytes in vitro. With 1.0 µM resveratrol treatment during aging process, the rates of fertilization and blastocyst in POA oocytes increased significantly compared with those in the POA group. Resveratrol can reduce the loss of sperm binding sites by stabilizing Juno. Resveratrol can maintain the normal morphology of spindle and mitochondrion distribution and alleviate the levels of ROS and early apoptosis. Additionally, resveratrol can reduce the changes of H3K9me2. Therefore, resveratrol can significantly improve the quality of POA oocytes in vitro to enhance the rates of fertilization and blastocyst, which may be very helpful during the ART process.

Journey of oocyte from metaphase-I to metaphase-II stage in mammals

In mammals, journey from metaphase-I (M-I) to metaphase-II (M-II) is important since oocyte extrude first polar body (PB-I) and gets converted into haploid gamete. The molecular and cellular changes associated with meiotic cell cycle progression from M-I to M-II stage and extrusion of PB-I remain ill understood. Several factors drive oocyte meiosis from M-I to M-II stage. The mitogen-activated protein kinase3/1 (MAPK3/1), signal molecules and Rho family GTPases act through various pathways to drive cell cycle progression from M-I to M-II stage. The down regulation of MOS/MEK/MAPK3/1 pathway results in the activation of anaphase-promoting complex/cyclosome (APC/C). The active APC/C destabilizes maturation promoting factor (MPF) and induces meiotic resumption. Several signal molecules such as, c-Jun N-terminal kinase (JNK2), SENP3, mitotic kinesin-like protein 2 (MKlp2), regulator of G-protein signaling (RGS2), Epsin2, polo-like kinase 1 (Plk1) are directly or indirectly involved in chromosomal segregation. Rho family GTPase is another enzyme that along with cell division cycle (Cdc42) to form actomyosin contractile ring required for chromosomal segregation. In the presence of origin recognition complex (ORC4), eccentrically localized haploid set of chromosomes trigger cortex differentiation and determine the division site for polar body formation. The actomyosin contractile activity at the site of division plane helps to form cytokinetic furrow that results in the formation and extrusion of PB-I. Indeed, oocyte journey from M-I to M-II stage is coordinated by several factors and pathways that enable oocyte to extrude PB-I. Quality of oocyte directly impact fertilization rate, early embryonic development, and reproductive outcome in mammals.

Maturation promoting factor destabilization mediates human chorionic gonadotropin induced meiotic resumption in rat oocytes

Human chorionic gonadotropin (hCG) mimics the action of luteinizing hormone (LH) and triggers meiotic maturation and ovulation in mammals. The mechanism by which hCG triggers meiotic resumption in mammalian oocytes remains poorly understood. We aimed to find out the impact of hCG surge on morphological changes, adenosine 3',5'-cyclic monophosphate (cAMP), guanosine 3',5'-cyclic monophosphate (cGMP), cell division cycle 25B (Cdc25B), Wee1, early mitotic inhibitor 2 (Emi2), anaphase-promoting complex/cyclosome (APC/C), meiotic arrest deficient protein 2 (MAD2), phosphorylation status of cyclin-dependent kinase 1 (Cdk1), its activity and cyclin B1 expression levels during meiotic resumption from diplotene as well as metaphase-II (M-II) arrest in cumulus oocyte complexes (COCs). Our data suggest that hCG surge increased cyclic nucleotides level in encircling granulosa cells but decreased their level in oocyte. The reduced intraoocyte cyclic nucleotides level is associated with the decrease of Cdc25B, Thr161 phosphorylated Cdk1 and Emi2 expression levels. On the other hand, hCG surge increased Wee1, Thr14/Tyr15 phosphorylated Cdk1, APC/C as well as MAD2 expression levels. The elevated APC/C activity reduced cyclin B1 level. The changes in phosphorylation status of Cdk1 and reduced cyclin B1 level might have resulted in maturation promoting factor (MPF) destabilization. The destabilized MPF finally triggered resumption of meiosis from diplotene as well as M-II arrest in rat oocytes.

Increased Telomerase Reverse Transcriptase Expression Associates with Spontaneous Exit from M-II Arrest in Rat Eggs

In mammals, postovulatory egg aging deteriorates egg quality possibly by mediating spontaneous exit from metaphase-II (M-II) arrest and/or inducing apoptosis. To test this possibility, present study was designed to investigate telomerase reverse transcriptase (TERT) expression, Bcl2 expression, and DNA fragmentation during postovulatory egg aging in vivo, as well as in vitro. Results suggest that postovulatory egg aging induced a time-dependent increase in the number of eggs undergoing spontaneous exit from M-II arrest in vivo, as well as in vitro. However, rate of spontaneous exit from M-II arrest was high in eggs cultured in vitro compared to in vivo aging. A time-dependent increase of TERT expression was associated with postovulatory aging-mediated spontaneous exit from M-II arrest in vivo, as well as in vitro. The Bcl2 level did not reduce and DNA fragmentation was not detected until 7 hours of in vivo, as well as in vitro, postovulatory egg aging. Taken together these data suggest that the eggs undergo postovulatory aging as evidenced by increased TERT expression without having any decrease of Bcl2 level or increase of DNA fragmentation until 7 hours of in vivo, as well as in vitro egg aging.

Calcium Signaling During Meiotic Cell Cycle Regulation and Apoptosis in Mammalian Oocytes

Calcium (Ca⁺⁺ ) is one of the major signal molecules that regulate various aspects of cell functions including cell cycle progression, arrest, and apoptosis in wide variety of cells. This review summarizes current knowledge on the differential roles of Ca⁺⁺ in meiotic cell cycle resumption, arrest, and apoptosis in mammalian oocytes. Release of Ca⁺⁺ from internal stores and/or Ca⁺⁺ influx from extracellular medium causes moderate increase of intracellular Ca⁺⁺ ([Ca⁺⁺ ]i) level and reactive oxygen species (ROS). Increase of Ca⁺⁺ as well as ROS levels under physiological range trigger maturation promoting factor (MPF) destabilization, thereby meiotic resumption from diplotene as well as metaphase-II (M-II) arrest in oocytes. A sustained increase of [Ca⁺⁺ ]i level beyond physiological range induces generation of ROS sufficient enough to cause oxidative stress (OS) in aging oocytes. The increased [Ca⁺⁺ ]i triggers Fas ligand-mediated oocyte apoptosis. Further, OS triggers mitochondria-mediated oocyte apoptosis in several mammalian species. Thus, Ca⁺⁺ exerts differential roles on oocyte physiology depending upon its intracellular concentration. A moderate increase of [Ca⁺⁺ ]i as well as ROS mediate spontaneous resumption of meiosis from diplotene as well as M-II arrest, while their high levels cause meiotic cell cycle arrest and apoptosis by operating both mitochondria- as well as Fas ligand-mediated apoptotic pathways. Indeed, Ca⁺⁺ regulates cellular physiology by modulating meiotic cell cycle and apoptosis in mammalian oocytes. J. Cell. Physiol. 232: 976-981, 2017. © 2016 Wiley Periodicals, Inc.

S-nitroso-N-acetyl penicillamine inhibits spontaneous exit from metaphase-II arrest in rat eggs cultured in vitro

BACKGROUND

Present study was designed to investigate the in vitro effects of nitric oxide (NO) donor such as S-nitroso-N-acetyl penicillamine (SNAP) on spontaneous exit from metaphase-II arrest (SEM-II) in rat eggs cultured in vitro.

METHODS

Ovulated eggs were denuded and then exposed to various concentrations (0.0, 0.01, 0.1 and 1.0mM) of SNAP for 3h under in vitro culture conditions. The percentage of SEM-II, specific and total phosphorylated cyclin-dependent kinase-1 (Cdk1), cyclin B1 and anaphase promoting complex/cyclosome (APC/C) levels as well as Cdk1 activity were analyzed.

RESULTS

The SEM-II was associated with a decrease of Thr-161 phosphorylated Cdk1 as well as cyclin B1 levels and increase of Thr-14/Tyr-15 phosphorylated Cdk1, APC/C levels and Cdk1 activity in aged eggs cultured in vitro. On the other hand, SNAP treatment prevented a decrease of Thr-161 phosphorylated Cdk1 as well as cyclin B1 levels and increase of Thr-14/Tyr-15 phosphorylated Cdk1, Cdk1 activity that finally prevented SEM-II in a concentration-dependent manner. However, APC/C level was not affected by SNAP during the course of treatment in vitro.

CONCLUSIONS

Present data suggest that SNAP prevented SEM-II possibly by increasing high level of NO and thereby maturation promoting factor (MPF) stabilization in rat eggs cultured in vitro. Hence, SNAP could be used to prevent SEM-II that reduces reproductive outcome in several mammalian species.