Obesity-induced oocyte mitochondrial defects are partially prevented and rescued by supplementation with co-enzyme Q10 in a mouse model

Abstract

Study question: Does supplementation with co-enzyme Q10 (CoQ10) improve the oocyte mitochondrial abnormalities associated with obesity in mice?

Summary answer: In an obese mouse model, CoQ10 improves the mitochondrial function of oocytes.

What is known already: Obesity impairs oocyte quality. Oocytes from mice fed a high-fat/high-sugar (HF/HS) diet have abnormalities in mitochondrial distribution and function and in meiotic progression.

Study design, size, duration: Mice were randomly assigned to a normal, chow diet or an isocaloric HF/HS diet for 12 weeks. After 6 weeks on the diet, half of the mice receiving a normal diet and half of the mice receiving a HF/HS diet were randomly assigned to receive CoQ10 supplementation injections for the remaining 6 weeks.

Participants/materials, setting, methods: Dietary intervention was initiated on C57Bl6 female mice at 4 weeks of age, CoQ10 versus vehicle injections were assigned at 10 weeks, and assays were conducted at 16 weeks of age. Mice were super-ovulated, and oocytes were collected and stained to assess mitochondrial distribution, quantify reactive oxygen species (ROS), assess meiotic spindle formation, and measure metabolites. In vitro fertilization was performed, and blastocyst embryos were transferred into control mice. Oocyte number, fertilization rate, blastulation rate and implantation rate were compared between the four cohorts. Bivariate statistics were performed appropriately.

Main results and the role of chance: HF/HS mice weighed significantly more than normal diet mice (29 versus 22 g, P< 0.001). CoQ10 supplementation did not influence weight. Levels of ATP, citrate, and phosphocreatine were lower and ROS levels were higher in HF/HS mice than in controls (P< 0.001). CoQ10 supplementation significantly increased the levels of metabolites and decreased ROS levels in oocytes from normal diet mice but not in oocytes from HF/HS mice. However, CoQ10 completely prevented the mitochondrial distribution abnormalities observed in the HF/HS mice. Overall, CoQ10 supplementation significantly increased the percentage of normal spindle and chromosome alignment (92.3 versus 80.2%, P= 0.039). In the sub-analysis by diet, the difference did not reach statistical significance. When undergoing IVF, there were no statistically significant differences in the number of mature oocytes, the fertilization rate, blastocyst formation rates, implantation rates, resorption rates or litter size between HF/HS mice receiving CoQ10 or vehicle injections.

Limitations, reasons for caution: Experiments were limited to one species and strain of mice. The majority of experiments were performed after ovulation induction, which may not represent natural cycle fertility.

Wider implications of the findings: Improvement in oocyte mitochondrial distribution and function of normal, chow-fed mice and HF/HS-fed mice demonstrates the importance of CoQ10 and the efficiency of the mitochondrial respiratory chain in oocyte competence. Clinical studies are now needed to evaluate the therapeutic potential of CoQ10 in women's reproductive health.

Study funding/competing interests: C.E.B. received support from the National Research Training Program in Reproductive Medicine sponsored by the National Institute of Health (T32 HD040135-13) and the Scientific Advisory Board of Vivere Health. K.H.M received support from the American Diabetes Association and the National Institute of Health (R01 HD083895). There are no conflicts of interest to declare.

Trial registration number: This study is not a clinical trial.

Keywords: antioxidant; co-enzyme Q10; electron transport complex; mitochondria; obesity; oocyte quality; spindle and chromosome alignment.

Figure 1

Metabolic phenotype: (A) mice (n = 200, 50 per group) were on the high-fat/high-sugar (HF/HS) diet or a normal diet for 12 weeks and received subcutaneous, injections of co-enzyme Q10 (CoQ10, 22 mg/kg) or vehicle (Veh) for the latter 6 weeks. (B) Weekly weights (n = 50 per group) were obtained starting at 4 weeks until 16 weeks. (C) Prior to sacrifice at 16 weeks, body composition (n = 73) was assessed by EchoMRI. (D) Glucose levels (n = 50) were measured using venous tail blood after 4–5 h of fasting at 4 weeks, prior to diet exposure and again at 16 weeks. (E) Serum cholesterol (n = 40) concentration was obtained at 10 and 16 weeks. Values are represented as mean with error bars indicating+SEM. Statistical analyses were performed using Student's t-test or one-way ANOVA. *P < 0.05.

Figure 2

Metabolites (A–C) were measured from single GV oocytes using microanalytical assays as described in the Materials and Methods section. Sixty oocytes from 5 mice per group were used to quantify levels of ATP, citrate and Creatine phosphate (PhosphCr). Mean metabolite levels are expressed as millimoles/kilograms wet weight (mmol/kg wet wt.). (D) Depiction of citric acid cycle and its metabolites. Statistical analyses were performed using Student's t-test or one-way ANOVA. *P< 0.05. Error bars indicate + SEM. HF/HS, high-fat/high-sugar; CoQ10, co-enzyme q10.

Figure 3

Mitochondria: (A) MitoTracker Red CMXRos (red) probes were used to localize mitochondria in germinal vesicle (GV) oocytes and 4′,6′-diamidino-2-phenylindole (DAPI, blue) to stain DNA. Oocytes were imaged with fluorescence microscopy. Distribution was blindly categorized as perinuclear (normal), homogenous (abnormal) or aggregating (abnormal) in 340 oocytes from 20 mice (five per group). Statistical analyses were performed using χ² test. *Significantly different from normal and HF/HS + CoQ10, P < 0.05. (B) Reactive oxygen species levels were quantified by MitoSOX Red staining and live imaging of 438 GV oocytes from 20 mice (5 per group) using a confocal microscope. Mean signal intensity was adjusted for oocyte size and expressed as mean gray value. Student's t-test and one-way ANOVA were utilized for statistical analyses. *P < 0.05. Error bars indicate + SEM. (C) Mature, ovulated oocytes were immunolabeled with anti-α tubulin antibody (green) and counterstained with DAPI (blue). A blind, qualitative analysis of confocal images was performed to assess the proportion of normally aligned spindles and chromosomes (n = 146 oocytes from 20 mice [5per group]). Statistical analyses were performed using χ² test. *P < 0.05.