Obesity and age effect on oocyte in-vitro developmental competence

OBJECTIVE: Obesity reduces the ability to conceive but not many studies explored if obesity effect oocyte quality. The present study examines how obesity and aging effect oocyte gene expression and oocyte developmental potential. DESIGN: Avy mice used in the study have a spectrum of coat color and BMI which change in relation to the Agouti gene expression leading to the following fur color and body mass state: Yellow (obese), Mottled (lightly Mottled are obese), Agouti (lean) and Black, which are Agouti (lean). Lean and obese females were divided into three age groups: <12 weeks, 12-24 weeks and >24 weeks. Oocytes retrieved from females were either examined for global gene expression or inseminated with sperm from lean males. The development of zygotes to blastocysts in-vitro was monitored. MATERIALS AND METHODS: For ovulation induction females were injected with 10 IU PMSG and 10 IU hCG 48hrs later. Oocytes were retrieved 1-2hrs after ovulation and inseminated with sperm collected from mature lean Black males. The development of fertilized oocytes was examined every 24 hrs. For global gene expression mouse Codelink whole genome chips (Applied Microarrays, USA) was used and the data has been analyzed using Codelink and GeneSpring GX9.0 software. RESULTS: While BMI of Agouti and Black females stayed constant (2.8-2.9) with aging, BMI of Mottled and Yellow females increased significantly from 3.2 to 4.7 (p<0.01). The number of females responding to ovulation induction and the number of oocytes per ovulating females declined with age regardless of BMI. In addition, less mature and morphologically normal oocytes were obtained from aged females. At any age examined, higher proportions of zygotes developed to blastocysts when oocytes were obtained from lean females predominantly at the age group of 12-24 weeks. The proportions of blastocysts developed from lean females were 84% and 56% for Agouti and Yellow females, respectively (p<0.001). Gene array expression revealed significant differences in global expression. Currently the study is identifying to which physiological pathways this genes are related to. CONCLUSIONS: The data demonstrates that the obese environment effect the developmental potential of oocytes. Hence, when ART is suggested to assist obese females to conceive, it needs to be taken into consideration that oocyte quality may compromise the outcome.