Trajectory of primordial follicle depletion is accelerated in obese mice in response to 7,12-dimethylbenz[a]anthracene exposure.

Both obesity and exposure to environmental genotoxicants, such as 7,12-dimethylbenz[a]anthracene (DMBA), negatively impair female reproductive health. Hyperphagic lean KK.Cg-a/a (n = 8) and obese KK.Cg-Ay/J (n = 10) mice were exposed to corn oil as vehicle control (CT) or DMBA (1 mg/kg/day) for 7d intraperitoneally, followed by a recovery period. Obesity increased liver and spleen weight (P < 0.05), and DMBA exposure decreased uterine weight (P < 0.05) in obese mice. Primordial follicle loss (P < 0.05) caused by DMBA exposure was observed in obese mice only. Primary (lean P < 0.1; obese P < 0.05) and secondary (lean P < 0.05, obese P < 0.1) follicle loss initiated by DMBA exposure continued across recovery. Reduced pre-antral follicle number in lean mice (P < 0.05), regardless of DMBA exposure, was evident with no effect on antral follicles or corpora lutea number. Immunofluorescence staining of DNA damage marker, γH2AX, did not indicate ongoing DNA damage but TRP53 abundance was decreased in follicles (P < 0.05) of DMBA-exposed obese mice. In contrast, increased (P < 0.05) superoxide dismutase was observed in the corpora lutea of DMBA-exposed obese mice and reduced (P < 0.05) TRP53 abundance was noted in preantral and antral follicles of DMBA-exposed obese mice. This study indicates that obesity influences ovotoxicity caused by a genotoxicant, potentially involving accelerated primordial follicle activation and hampering normal follicular dynamics.

Altered histone abundance as a mode of ovotoxicity during 7,12-dimethylbenz[a]anthracene exposure with additive influence of obesity†.

Histones are slowly evolving chromatin components and chromatin remodeling can incorporate histone variants differing from canonical histones as an epigenetic modification. Several identified histone variants are involved with the environmental stress-induced DNA damage response (DDR). Mechanisms of DDR in transcriptionally inactive, prophase-arrested oocytes and epigenetic regulation are under-explored in ovarian toxicology. The study objective was to identify ovarian proteomic and histone modifications induced by DMBA exposure and an influence of obesity. Post-pubertal wildtype (KK.Cg-a/a; lean) and agouti (KK.Cg-Ay/J; obese) female mice, were exposed to either corn oil (control; CT) or DMBA (1 mg/kg) for 7d via intraperitoneal injection (n = 10/treatment). Ovarian proteome analysis (LC-MS/MS) determined that obesity altered 225 proteins (P < 0.05) with histone 3 being the second least abundant (FC = -5.98, P < 0.05). Histone 4 decreased by 3.33-fold, histone variant H3.3 decreased by 3.05-fold, and H1.2, H1.4 and H1.1(alpha) variants increased by 1.59, 1.90 and 2.01-fold, respectively (P < 0.05). DMBA exposure altered 48 proteins in lean mice with no observed alterations in histones or histone variants. In obese mice, DMBA exposure altered 120 proteins and histone 2B abundance increased by 0.30-fold (P < 0.05). In DMBA-exposed mice, obesity altered the abundance of 634 proteins. Histones 4, 3 and 2A type 1-F decreased by 4.03, 3.71, 0.43-fold, respectively, whereas histone variant H1.2 and linker histone, H15 increased by 2.72- and 3.07-fold, respectively (P < 0.05). Thus, DMBA exposure alters histones and histone variants, and responsivity is more pronounced during obesity, potentially altering ovarian transcriptional regulation.

Obesity partially potentiates dimethylbenz[a]anthracene-exposed ovotoxicity by altering the DNA damage repair response in mice†.

Obesity adversely affects reproduction, impairing oocyte quality, fecundity, conception, and implantation. The ovotoxicant, dimethylbenz[a]anthracene, is biotransformed into a genotoxic metabolite to which the ovary responds by activating the ataxia telangiectasia mutated DNA repair pathway. Basal ovarian DNA damage coupled with a blunted response to genotoxicant exposure occurs in obese females, leading to the hypothesis that obesity potentiates ovotoxicity through ineffective DNA damage repair. Female KK.Cg-a/a (lean) and KK.Cg-Ay/J (obese) mice received corn oil or dimethylbenz[a]anthracene (1 mg/kg) at 9 weeks of age for 7 days via intraperitoneal injection (n = 10/treatment). Obesity increased liver weight (P < 0.001) and reduced (P < 0.05) primary, preantral, and corpora lutea number. In lean mice, dimethylbenz[a]anthracene exposure tended (P < 0.1) to increase proestrus duration and reduced (P = 0.07) primordial follicle number. Dimethylbenz[a]anthracene exposure decreased (P < 0.05) uterine weight and increased (P < 0.05) primary follicle number in obese mice. Total ovarian abundance of BRCA1, γH2AX, H3K4me, H4K5ac, H4K12ac, and H4K16ac (P > 0.05) was unchanged by obesity or dimethylbenz[a]anthracene exposure. Immunofluorescence staining demonstrated decreased (P < 0.05) abundance of γH2AX foci in antral follicles of obese mice. In primary follicle oocytes, BRCA1 protein was reduced (P < 0.05) by dimethylbenz[a]anthracene exposure in lean mice. Obesity also decreased (P < 0.05) BRCA1 protein in primary follicle oocytes. These findings support both a follicle stage-specific ovarian response to dimethylbenz[a]anthracene exposure and an impact of obesity on this ovarian response.