Primordial follicle activation in the ovary of Ames dwarf mice

The insulin receptor substrate 1 (IRS1), phosphoinositide 3-kinase (Pi3k), protein kinase B (Akt1), Forkhead Box O3a (FOXO3a) pathway is directly involved in aging and ovarian activation of follicle growth. Therefore, the aim of this work was to measure the expression of genes related to the ovarian pathway for activation of primordial follicles and FOXO3a protein phosphorylation between young and old female Ames dwarf (df/df) and normal (N) mice.

For this study ovaries from N (n = 10) and df/df (n = 10) female mice were collected at 5-6 months of age and at 21-22 months of age. For immunohistochemistry ovaries from 12 month-old and df/df mice were used.

The expression of Irs1, Pi3k, Akt1, mammalian target of rapamycin (Mtor), suppressor of cytokine signaling -2 (Socs2), Socs3 was lower (P < 0.05) in older than younger N mice and not different (P > 0.05) between young and old df/df mice. The expression of Foxo3a was also lower (P < 0.05) in old than younger N and df/df mice and was higher (P < 0.05) in old df/df than N mice. Expression of Amh was lower (P < 0.05) in old than young N and df/df mice and was higher (P = 0.0009) in df/df than N mice. Imunnostaining for p-FOXO3 was lower in df/df than N mice (P < 0.001), although FOXO3 immunostaining was not different (P > 0.05) between df/df and N mice.

In sum, the present study indicates that lower expression of Irs1, Socs2, Socs3, Akt1, Pi3k, Mtor and Foxo3a mRNA in the ovaries of older mice of both genotypes is associated to a reduced ovarian activity revealed by lower expression of Amh mRNA. At the same time, ovaries of old df/df mice maintained higher expression of Foxo3a mRNA, which was associated to higher ovarian activity. We have shown that df/df females have a lower level of p-FOXO3 in oocytes from primordial/primary follicles, an important activator of follicular growth. Therefore, this study strongly indicates that Prop1(df) mutation causes delayed ovarian aging.