The role of Klotho in an ovine model of ovarian aging

Ovarian aging encompasses the age-related decline in the quantity and quality of oocytes, affecting fertility. Delayed childbearing and ovarian pathological conditions have highlighted the need for therapies to protect reproductive lifespan. This thesis aimed to evaluate the role of Klotho, a proposed anti-aging protein, in the ovaries using sheep as a physiologically relevant model for human ovarian aging.
A systematic literature review of ovarian aging mechanisms highlighted oxidative stress and DNA mutation as main instigators of ovarian aging. Molecular analysis of the ovarian compartments showed Klotho gene (KLS) expression to be localised to granulosa cells from large (>5-8mm) follicles, with no significant changes with age. The suggested mechanism of action of Klotho was through the KLS-FGFR3c/FGFR4 pathway. Follicular fluid Klotho protein concentration was 3.8x higher in adult than prepubertal follicles (16.20 ± 6.90 ng/ml vs 4.24 ± 1.63 ng/ml), p>0.05). While no significant differences were observed in follicular fluid Klotho levels from adult sheep aged 1-9 years, concentrations significantly increased with follicles size 2-8mm diameter (prepubertal R2=0.245, p=0.014; adult R2= 0.236, p=0.019; adult aged 1-9 years R2=0.83; p=0.001).
The impact of Klotho on oocyte developmental competence was evaluated by exposure of cumulus enclosed oocytes to 25 and 50 ng/ml of recombinant Klotho protein over 18h of oocyte maturation in vitro in the presence or absence of oxidative stress induced by a 6h exposure to 40µM H2O2. Oocyte maturation, cumulus expansion, embryo cleavage and blastocyst production were evaluated. Outcome measures were lower after Klotho + H2O2 treatment compared to Klotho only treatment. While Klotho only treatment did enhance antioxidant defence mechanisms, response was insufficient to counteract oxidative stress induced by H2O2 treatment. These preliminary findings suggest that Klotho may impact oocyte quality. Further research is needed to determine whether Klotho may be a useful therapy for ovarian aging.