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Scholarly Works (5 results)

  • Article
  • Peer Reviewed
UC Irvine Previously Published Works (2021)
Oocyte mitochondria are unique organelles that establish a founder population in primordial germ cells (PGCs). As the oocyte matures in the postnatal mammalian ovary during folliculogenesis it increases exponentially in volume, and the oocyte mitochondria population proliferates to about 100 000 mitochondria per healthy, mature murine oocyte. The health of the mature oocyte and subsequent embryo is highly dependent on the oocyte mitochondria. Mitochondria are especially sensitive to toxic insults, as they are a major source of reactive oxygen species (ROS), they contain their own DNA (mtDNA) that is unprotected by histone proteins, they contain the electron transport chain that uses electron donors, including oxygen, to generate ATP, and they are important sensors for overall cellular stress. Here we review the effects that toxic insults including chemotherapeutics, toxic metals, plasticizers, pesticides, polycyclic aromatic hydrocarbons (PAHs), and ionizing radiation can have on oocyte mitochondria. This is very clearly a burgeoning field, as our understanding of oocyte mitochondria and metabolism is still relatively new, and we contend much more research is needed to understand the detrimental impacts of exposure to toxicants on oocyte mitochondria. Developing this field further can benefit our understanding of assisted reproductive technologies and the developmental origins of health and disease (DOHaD).
    Cover page: Toxicant effects on mammalian oocyte mitochondria†
    • Thesis
    • Peer Reviewed
    UC Irvine Electronic Theses and Dissertations (2022)

    Polycyclic aromatic hydrocarbons (PAHs) are ovotoxicants. Benzo[a]pyrene (BaP) is a PAH that depletes the ovarian reserve when females are exposed directly or in utero. Oocyte quality is developmental competence acquired through folliculogenesis. Among the attributes of the oocyte that determine its competence include mitochondria, lipid droplets (LDs), and small antioxidant molecules such as glutathione (GSH). Whether the developing germ cells in the embryo are more sensitive to BaP exposure during proliferation or meiosis has been unexplored. Further, how gestational BaP exposure and persistent oxidative stress impact the developmental competence of the oocyte remains unclear.

    C57BL/6J female mice were mated with males and orally dosed with 0 or 2 mg/kg/day of BaP from either embryonic day (E)6.5-11.5 (proliferative phase, BaP6.5 and Oil6.5) or E12.5-17.5 (meiotic phase, BaP12.5 and Oil 12.5). F1 pubertal ovaries were examined for follicle counts and persistent oxidative stress. BaP6.5 and BaP12.5 had statistically significant depletion in primordial, primary, and secondary follicles as well as increased lipid peroxidation compared with controls. Oocytes from F1 BaP6.5 and Oil6.5 females were examined and BaP6.5 oocytes were observed to have increased levels of superoxide while significantly decreased mitochondrial membrane potential and LD volume.

    We exposed female mice to concentrated air particulates at 2.5 µm or less (PM2.5) in aerodynamic diameter using a Versatile Air Concentration Enrichment System (VACES) for 6 h/ day, 5 days/ week, for 12 weeks. With our collaborators, I developed and validated an extraction and HPLC-MS/MS method to measure ovarian 17β-estradiol concentrations. The concentration of 17β-estradiol did not differ among exposure groups. However, the 17β-estradiol content of ovaries from wild-type, unexposed mice were significantly higher than either exposure group of the transgenic mouse model (Apoe -/-) that were used in this study.

    GSH deficiency reduction mature oocyte developmental competence was explored. Using a transgenic mouse model, deleting the modifier subunit of the rate-limiting enzyme in GSH synthesis, glutamate cysteine ligase (Gclm), we demonstrated that Gclm -/- oocytes have increased levels of ROS, superoxide and decreased mitochondrial membrane potential. Additionally, Gclm -/- oocytes had decreased LD content compared with Gclm +/+ oocytes. The data in this work demonstrate that the developing ovary is sensitive to BaP exposure across the entirety of its development resulting in F1 ovarian follicular depletion, and persistent F1 ovarian oxidative stress which reduces oocyte developmental competence through disrupted redox homeostasis and lipid dysregulation, and that BaP has similar effects on the ovary as PM2.5.

    • 2 supplemental PDFs
    Cover page: The Roles of Oxidative Stress, Mitochondria, and Lipid Droplets in Glutathione Deficiency and Benzo(a)pyrene-induced Germ Cell Death and Reduced Oocyte Developmental Competence
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2022)
    Glutathione (GSH) is a tripeptide thiol antioxidant that has been shown to be important to overall reproductive health. Glutamate cysteine ligase, the rate-limiting enzyme in GSH synthesis consists of a catalytic and a modifier (GCLM) subunit. We previously showed that oxidative stress in the ovary and oocytes of Gclm-/- mice is associated with accelerated age-related decline in ovarian follicles and decreased female fertility due to preimplantation embryonic mortality. Mammalian preimplantation development is a highly regulated and energy-intensive process that primarily relies on coordination between lipid droplets (LDs) and mitochondria to maintain cellular homeostasis. In this study, we hypothesized that GSH deficiency in oocytes increases oxidative stress, leading to increased mitochondrial dysfunction and decreased LD consumption, thereby decreasing oocyte developmental competence. We observed that Gclm-/- oocytes have increased oxidative stress, primarily in the form of mitochondrial superoxide and decreased subcortical mitochondrial clusters. Further, Gclm-/- oocytes have decreased mitochondrial membrane potential (ΔΨm) compared with Gclm+/+. We surmise this is likely due to the decreased availability of LDs, as we observed a significant decrease in LD content in Gclm-/- oocytes compared with Gclm+/+. The decreased oocyte LD content is likely related to an altered serum lipidome, with Gclm-/- serum having relatively lower unsaturated fatty acids and triglycerides than that of Gclm+/+ and Gclm+/- females. Altogether these data support that decreased LDs and increased oxidative stress are primary drivers of decreased oocyte developmental competence in GSH-deficient oocytes.
      Cover page: Glutathione deficiency decreases lipid droplet stores and increases reactive oxygen species in mouse oocytes†
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2022)
      Polycyclic aromatic hydrocarbons, including benzo[a]pyrene (BaP), are products of incomplete combustion. In female mouse embryos primordial germ cells proliferate before and after arriving at the gonadal ridge around embryonic (E) 10 and begin entering meiosis at E13.5. Now oocytes, they arrest in the first meiotic prophase beginning at E17.5. We previously reported dose-dependent depletion of ovarian follicles in female mice exposed to 2 or 10 mg/kg-day BaP E6.5-15.5. We hypothesized that embryonic ovaries are more sensitive to gestational BaP exposure during the mitotic developmental window, and that this exposure results in persistent oxidative stress in ovaries and oocytes of exposed F1 female offspring. We orally dosed timed-pregnant female mice with 0 or 2 mg/kg-day BaP in oil from E6.5-11.5 (mitotic window) or E12.5-17.5 (meiotic window). Cultured E13.5 ovaries were utilized to investigate the mechanism of BaP-induced germ cell death. We observed statistically significant follicle depletion and increased ovarian lipid peroxidation in F1 pubertal ovaries following BaP exposure during either prenatal window. Culture of E13.5 ovaries with BaP induced germ cell DNA damage and release of cytochrome c from the mitochondria in oocytes, confirming that BaP exposure induced apoptosis via the mitochondrial pathway. Mitochondrial membrane potential, oocyte lipid droplet (LD) volume, and mitochondrial-LD colocalization were decreased and mitochondrial superoxide levels were increased in the MII oocytes of F1 females exposed gestationally to BaP. Results demonstrate similar sensitivity to germ cell depletion and persistent oxidative stress in F1 ovaries and oocytes following gestational BaP exposure during mitotic or meiotic windows.
        Cover page: Gestational Benzo[a]pyrene Exposure Destroys F1 Ovarian Germ Cells Through Mitochondrial Apoptosis Pathway and Diminishes Surviving Oocyte Quality
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2023)
        People are widely exposed to polycyclic aromatic hydrocarbons, like benzo[a]pyrene (BaP). Prior studies showed that prenatal exposure to BaP depletes germ cells in ovaries, causing earlier onset of ovarian senescence post-natally; developing testes were affected at higher doses than ovaries. Our primary objective was to determine if prenatal BaP exposure results in transgenerational effects on ovaries and testes. We orally dosed pregnant germ cell-specific EGFP-expressing mice (F0) with 0.033, 0.2, or 2 mg/kg-day BaP or vehicle from embryonic day (E) 6.5-11.5 (F1 offspring) or E6.5-15.5 (F2 and F3). Ovarian germ cells at E13.5 and follicle numbers at postnatal day 21 were significantly decreased in F3 females at all doses of BaP; testicular germ cell numbers were not affected. E13.5 germ cell RNA-sequencing revealed significantly increased expression of male-specific genes in female germ cells across generations and BaP doses. Next, we compared the ovarian effects of 2 mg/kg-day BaP dosing to wild type C57BL/6J F0 dams from E6.5-11.5 or E12.5-17.5. We observed no effects on F3 ovarian follicle numbers with either of the shorter dosing windows. Our results demonstrate that F0 BaP exposure from E6.5-15.5 decreased the number of and partially disrupted transcriptomic sexual identity of female germ cells transgenerationally.
          Cover page: Prenatal exposure to benzo[a]pyrene depletes ovarian reserve and masculinizes embryonic ovarian germ cell transcriptome transgenerationally
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