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

Abstract

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.

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

“…In order to avoid introducing variation due to stage of the estrous cycle, all ovaries were collected on Day 2 of diestrus with a maximum lag in tissue collection of 3 days post-cessation of DMBA exposure. This experimental paradigm was previously observed to have a basal impact of obesity on primary, preantral, and corpora lutea numbers which were reduced [ 53 ]. A differential response to DMBA was also reported with a tendency for a reduced primordial follicle number in lean mice and an increased primary follicle number in obese mice as a result of DMBA exposure [ 53 ].…”

“…This experimental paradigm was previously observed to have a basal impact of obesity on primary, preantral, and corpora lutea numbers which were reduced [ 53 ]. A differential response to DMBA was also reported with a tendency for a reduced primordial follicle number in lean mice and an increased primary follicle number in obese mice as a result of DMBA exposure [ 53 ]. There was also evidence of DNA damage induction due to DMBA exposure, with both phosphorylated histone 2AX (γH2AX) and breast cancer 1 (BRCA1) classic DNA repair proteins being observed albeit decreased in some follicle stages by DMBA exposure [ 53 ].…”

“…When an ~30% weight difference was determined between the HPL and HPO mice, they received either corn oil as vehicle control (C) or DMBA (D; 1 mg/Kg/day) via intraperitoneal injection for 7 days. This exposure paradigm and route of exposure was determined to result in a tendency to increase time spent in proestrus and to reduce primordial follicle number in lean mice [ 53 ]. In obese mice, DMBA exposure decreased uterine weight and increased primary follicle number [ 53 ].…”

“…This exposure paradigm and route of exposure was determined to result in a tendency to increase time spent in proestrus and to reduce primordial follicle number in lean mice [ 53 ]. In obese mice, DMBA exposure decreased uterine weight and increased primary follicle number [ 53 ]. Obese mice had reduced primary, preantral, and corpora lutea number [ 53 ].…”

“…In obese mice, DMBA exposure decreased uterine weight and increased primary follicle number [ 53 ]. Obese mice had reduced primary, preantral, and corpora lutea number [ 53 ]. Thus, there was evidence of ovotoxicity without a complete depletion of ovarian follicles.…”