AMPK Suppression Due to Obesity Drives Oocyte mtDNA Heteroplasmy via ATF5-POLG Axis

Due to the exclusive maternal transmission, oocyte mitochondrial dysfunction reduces fertility rates, affects embryonic development, and programs offspring to metabolic diseases. However, mitochondrial DNA (mtDNA) are vulnerable to mutations during oocyte maturation, leading to mitochondrial nucleotide variations (mtSNVs) within a single oocyte, referring to mtDNA heteroplasmy. Obesity (OB) accounts for more than 40% of women at the reproductive age in the USA, but little is known about impacts of OB on mtSNVs in mature oocytes. It is found that OB reduces mtDNA content and increases mtSNVs in mature oocytes, which impairs mitochondrial energetic functions and oocyte quality. In mature oocytes, OB suppresses AMPK activity, aligned with an increased binding affinity of the ATF5-POLG protein complex to mutated mtDNA D-loop and protein-coding regions. Similarly, AMPK knockout increases the binding affinity of ATF5-POLG proteins to mutated mtDNA, leading to the replication of heteroplasmic mtDNA and impairing oocyte quality. Consistently, AMPK activation blocks the detrimental impacts of OB by preventing ATF5-POLG protein recruitment, improving oocyte maturation and mitochondrial energetics. Overall, the data uncover key features of AMPK activation in suppressing mtSNVs, and improving mitochondrial biogenesis and oocyte maturation in obese females.

Estradiol cycling drives female obesogenic adipocyte hyperplasia

White adipose tissue (WAT) distribution is sex dependent. Adipocyte hyperplasia contributes to WAT distribution in mice driven by cues in the tissue microenvironment, with females displaying hyperplasia in subcutaneous and visceral WAT, while males and ovariectomized females have visceral WAT (VWAT)-specific hyperplasia. However, the mechanism underlying sex-specific hyperplasia remains elusive. Here, transcriptome analysis in female mice shows that high-fat diet (HFD) induces estrogen signaling in adipocyte precursor cells (APCs). Analysis of APCs throughout the estrous cycle demonstrates increased proliferation only when proestrus (high estrogen) coincides with the onset of HFD feeding. We further show that estrogen receptor α (ERα) is required for this proliferation and that estradiol treatment at the onset of HFD feeding is sufficient to drive it. This estrous influence on APC proliferation leads to increased obesity driven by adipocyte hyperplasia. These data indicate that estrogen drives ERα-dependent obesogenic adipocyte hyperplasia in females, exacerbating obesity and contributing to the differential fat distribution between the sexes.

Female obesity does not impact live birth rate after frozen-thawed blastocyst transfer

STUDY QUESTION

Does female obesity affect live birth rate after frozen-thawed blastocyst transfer?

SUMMARY ANSWER

Live birth rate was not statistically different between obese and normal weight patients after frozen-thawed blastocyst transfer (FBT).

WHAT IS KNOWN ALREADY

Obesity is a major health problem across the world, especially in women of reproductive age. It impacts both spontaneous fertility and clinical outcomes after assisted reproductive technology. However, the respective impact of female obesity on oocyte quality and endometrial receptivity remains unclear. While several studies showed that live birth rate was decreased in obese women after fresh embryo transfer in IVF cycle, only two studies have evaluated the effects of female body mass index (BMI) on pregnancy outcomes after frozen-thawed blastocyst transfer (FBT), reporting conflicting data.

STUDY DESIGN, SIZE, DURATION

This retrospective case control study was conducted in all consecutive frozen-thawed autologous blastocyst transfer (FBT) cycles conducted between 2012 and 2017 in a single university-based centre. A total of 1415 FBT cycles performed in normal weight women (BMI = 18.5-24.9 kg/m2) and 252 FBT cycles performed in obese women (BMI ≥ 30 kg/m2) were included in the analysis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Endometrial preparation was standard and based on hormonal replacement therapy. One or two blastocysts were transferred according to couple's history and embryo quality.

MAIN RESULTS AND THE ROLE OF CHANCE

Female and male age, smoking status, basal AMH level and type of infertility were comparable in obese and normal weight groups. Concerning FBT cycles, the duration of hormonal treatment, the stage and number of embryos (84% single blastocyst transfer and 16% double blastocysts transfer) used for transfer were comparable between both groups. Mean endometrium thickness was significantly higher in obese than in normal weight group (8.7 ± 1.8 vs 8.1 ± 1.6 mm, P < 0.0001). Concerning FBT cycle outcomes, implantation rate, clinical pregnancy rate and live birth rate were comparable in obese and in normal weight groups. Odds ratio (OR) demonstrated no association between live birth rate after FBT and female BMI (OR = 0.92, CI 0.61-1.38, P = 0.68).

LIMITATIONS, REASONS FOR CAUTION

Anthropometric parameters such as hip to waist ratio were not used. Polycystic ovarian syndrome status was not included in the analysis.

WIDER IMPLICATIONS OF THE FINDINGS

Our study showed that live birth rate after frozen-thawed blastocyst transfer was not statistically different in obese and in normal-weight women. Although this needs confirmation, this suggests that the impairment of uterine receptivity observed in obese women after fresh embryo transfer might be associated with ovarian stimulation and its hormonal perturbations rather than with oocyte/embryo quality.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was received. There are no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Female obesity is negatively associated with live birth rate following IVF: a systematic review and meta-analysis

BACKGROUND

A worldwide increase in the prevalence of obesity has been observed in the past three decades, particularly in women of reproductive age. Female obesity has been clearly associated with impaired spontaneous fertility, as well as adverse pregnancy outcomes. Increasing evidence in the literature shows that obesity also contributes to adverse clinical outcomes following in vitro fertilization (IVF) procedures. However, the heterogeneity of the available studies in terms of populations, group definition and outcomes prevents drawing firm conclusions. A previous meta-analysis published in 2011 identified a marginal but significant negative effect of increased female body mass index (BMI) on IVF results, but numerous studies have been published since then, including large cohort studies from national registries, highlighting the need for an updated review and meta-analysis.

OBJECTIVE AND RATIONALE

Our systematic review and meta-analysis of the available literature aims to evaluate the association of female obesity with the probability of live birth following IVF. Subgroup analyses according to ovulatory status, oocyte origin, fresh or frozen-embryo transfer and cycle rank were performed.

SEARCH METHODS

A systematic review was performed using the following key words: ('obesity', 'body mass index', 'live birth', 'IVF', 'ICSI'). Searches were conducted in MEDLINE, EMBASE, Cochrane Library, Eudract and clinicaltrial.gov from 01 January 2007 to 30 November 2017. Study selection was based on title and abstract. Full texts of potentially relevant articles were retrieved and assessed for inclusion by two reviewers. Subsequently, quality was assessed using the Newcastle-Ottawa Quality Assessment Scales for patient selection, comparability and assessment of outcomes. Two independent reviewers carried out study selection and data extraction according to Cochrane methods. Random-effect meta-analysis was performed using Review Manager software on all data (overall analysis), followed by subgroup analyses.

OUTCOMES

A total of 21 studies were included in the meta-analysis. A decreased probability of live birth following IVF was observed in obese (BMI ≥ 30 kg/m2) women when compared with normal weight (BMI 18.5-24.9 kg/m2) women: risk ratio (RR) (95% CI) 0.85 (0.82-0.87). Subgroups analyses demonstrated that prognosis was poorer when obesity was associated with polycystic ovary syndrome, while the oocyte origin (donor or non-donor) did not modify the overall interpretation.

WIDER IMPLICATIONS

Our meta-analysis clearly demonstrates that female obesity negatively and significantly impacts live birth rates following IVF. Whether weight loss can reverse this deleterious effect through lifestyle modifications or bariatric surgery should be further evaluated.

Identification of Genetic Variants for Female Obesity and Evaluation of the Causal Role of Genetically Defined Obesity in Polycystic Ovarian Syndrome

PURPOSE

Observational studies have demonstrated an increased risk of polycystic ovarian syndrome (PCOS) in obese women. This study aimed to identify genetic variants influencing obesity in females and to evaluate the causal association between genetically defined obesity and PCOS in Korean women.

METHODS

Two-stage GWAS was conducted to identify genetic variants influencing obesity traits (such as body mass index [BMI], waist-hip ratio [WHR], and waist circumference [WC]) in Korean women. Two-sample Mendelian randomization (MR) analysis was employed to evaluate the causal effect of variants as genetic instruments for female obesity on PCOS.

RESULTS

Meta-analysis of 9953 females combining discovery (N = 4658) and replication (N = 5295) stages detected four (rs11162584, rs6760543, rs828104, rs56137030), six (rs139702234, rs2341967, rs73059848, rs5020945, rs550532151, rs61971548), and two genetic variants (rs7722169, rs7206790) suggesting a highly significant association (P < 1×10^-6) with BMI, WHR, and WC, respectively. Of these, an intron variant rs56137030 in FTO achieved genome-wide significant association (P = 3.39×10^-8) with BMI in females. Using variants for female obesity, their effect on PCOS in 946 cases and 976 controls was evaluated by MR analysis. MR results indicated no significant association between genetically defined obesity and PCOS in Korean women.

CONCLUSION

This study, for the first time, revealed genetic variants for female obesity in the Korean population and reported no causal association between genetically defined obesity and PCOS in Korean women.

Weighing the impact of obesity on female reproductive function and fertility

Obesity in women is associated with serious reproductive sequelae. Given its prevalence among women of reproductive age, much recent attention has focused on the mechanisms by which obesity affects female reproductive function and fertility. This review summarizes the literature investigating the epidemiology and pathophysiology of obesity in women of reproductive age and proposes research strategies that may help inform approaches to improve reproductive function and outcomes among obese women.