OVARIAN AGING AND REPRODUCTIVE SENESCENCE IN MOUSE MODEL OF MITOCHONDRIAL DYSFUNCTION

Abstract

To evaluate the mechanisms of female reproductive aging and senescence induced by mitochondrial dysfunction in mice. Prospective cohort design study. 13 female mice with mitochondrial dysfunction (mtDNA-depleter) and 13 wild-type (WT) female mice were studied at three time points in their reproductive life cycle: 4-6, 8-10, and 11-12 months of age. A transgenic mouse model with an inducible gene for mitochondrial dysfunction (mtDNA-depleter) was previously created by our lab. All protocols were approved by our institutional IACUC. At each of the three time points, reproductive markers were assessed, including estrous cyclicity, plasma anti-Mullerian hormone (AMH), ovarian follicles, estrogen receptor staining, and uterine and vaginal atrophy. Breeding experiments were performed to assess fertility. Differences between the mtDNA-depleter and WT groups were evaluated by independent two-sample t-test. Twenty-six female mice were studied from 4 to 12 months of age. The estrous cycles in 4-6-month mtDNA-depleter mice were prolonged, 9.4 days (n = 7), versus 5.3 days in WT (n = 9), p-value of 0.021. By 11-12 months, both groups had prolonged estrous cycles consistent with physiologic aging. AMH levels in 4-6-month mtDNA-depleter mice were decreased, 84 (n = 4), versus 114 ng/mL in WT (n = 5), p-value of 0.013. AMH was reduced in older mice at 8-10 and 11-12 months, but there were no significant differences between groups. Looking at the data collectively for all three time points, there were fewer tertiary (early antral, antral, or pre-ovulatory) follicles in mtDNA-depleter mice than in WT, 3.5 versus 4.9 per cut section, respectively (p-value of 0.039). There were fewer corpora lutea in mtDNA-depleter mice than in WT, 0.90 versus 1.7 per cut section, respectively (p-value of 0.027). Collectively, average uterine weight in mtDNA-depleter mice was lower, 62.2, versus 92.3 mg in WT mice, p-value of 0.0028. Vaginal epithelium in 4-6-month mtDNA-depleter mice was thinner, 98 μm (n = 4), versus 200 μm in WT mice (n = 4), p-value of 0.035. In breeding experiments, mtDNA-depleter mice at age 3 and 5 months did not produce litters. Estrogen receptor levels were reduced in mtDNA-depleter mouse ovary relative to WT, evident from both immunofluorescence and semi-quantitative PCR analysis. Mitochondrial dysfunction in mice is associated with premature reproductive aging and senescence, as evidenced by early onset of prolonged estrous cycles, diminished ovarian reserve, uterine and vaginal atrophy, and sterility. Mitochondrial dysfunction is also associated with premature estrogen receptor down-regulation in the mouse ovary.