Primordial follicle activation in the ovary of Ames dwarf mice

Abstract

BackgroundThe 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.MethodsFor 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.ResultsThe 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.ConclusionsIn 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 Prop1df mutation causes delayed ovarian aging.

Ovarian aging and the activation of the primordial follicle reserve in the long-lived Ames dwarf and the short-lived bGH transgenic mice

“…We also observed that df/df mice had increased pFoxO3a level in primordial follicle oocytes, but this increase was proportional to the increase in FoxO3a total protein. In a previous study we observed that pFoxO3a protein levels in primordial/primary follicles were lower in 12 mo old df/df compared to N/df mice, despite no difference in total FoxO3a protein levels (Schneider et al, 2014), which can suggest an age-dependent FoxO3a regulation in the ovary. FoxO3a and pFoxO3a were not different in primordial follicles of bGH and normal mice.…”

“…Only oocytes enclosed in follicles classified as primordial/in transition (n=108; n=18/group) and primary (n=108; n=18/group) were used. Protein quantification was performed by image analysis software (Image J®) and the most common value (the mode) of each area (oocyte) was registered by the 32-bit histogram application, using a scale ranging from 0 (the greatest staining intensity) to 255 (no staining) that was converted to a scale from 0 (no staining) to 4 (greatest staining) (Moreira et al, 2013; Schneider et al, 2014). …”

“…Hyperphosphorylation of FoxO3a results in its nuclear exclusion, culminating in the global activation of primordial follicles and premature ovarian failure (Castrillon et al, 2003). We have previously shown that oocytes enclosed in primordial/primary follicles from df/df mice have lower levels of pFoxO3a (Schneider et al, 2014). The reduced activation of the FoxO pathway by both insulin and IGF-I seems to have a central role in the extended longevity phenotype observed in the df/df and GHRKO mice (Bartke, 2008).…”

Growth hormone actions during development influence adult phenotype and longevity

“…Correlation between the age of female sexual maturation and circulating IGF-1 levels (a GH-dependent trait) was detected on analysis of multiple inbred mouse strains in which IGF-1 levels are negatively related to longevity [31]. Interestingly, delayed sexual maturation and reduced fecundity in long-lived GH-related mouse mutants [24–27] is associated with various indices of a delay in reproductive aging [66,67, and unpublished observations]. It could be argued that correcting the delay in sexual maturation in Ames dwarf mice by early GH treatment may account for or contribute to their reduced longevity.…”

The somatotropic axis and aging: Benefits of endocrine defects

“…Importantly, in both GH-resistant (GHRKO) and GH-deficient [hypopituitary Ames dwarf (Prop1 df ) and Snell dwarf (Pit1 dw )] mice, extension of average, median and maximal longevity is associated with improved maintenance of physical and cognitive function, resistance to oxidative stress, as well as reduced incidence and/or delayed onset of neoplasms and other age-related pathologies [4–6]. Trade-offs include major decreases in growth rate and adult body size, delayed maturation and reduced fertility [4, 6, 5, 7] which appears to be partially offset by a delay in reproductive aging [8, 9]. …”