Follicle Loss and Apoptosis in Cyclophosphamide-Treated Mice: What’s the Matter?

Abstract

With increasing numbers of young female cancer survivors following chemotherapy, chemotherapy-induced fertility loss must be considered. Menstrual disorder and infertility are of particular concern in female cancer patients. We showed that treatment with the alkylating agent cyclophosphamide (CTX) could cause severe primordial follicle loss and growing follicle apoptosis, resulting in loss of ovarian reserve. SPF C57BL/6 female mice were treated with a single dose of 120 mg/kg of CTX or saline as a control, and both sides of ovaries were collected three or seven days after injection. Following CTX treatment, the ovaries were mostly composed of collapsed oocytes and presented marked cortical fibrosis and a reduced number of follicles, especially primordial follicles. The loss of primordial follicles was confirmed by primordial follicle counting, immunohistochemistry and Western blot detection of DDx4/MVH. Follicle apoptosis was tested by a TUNEL assay and the number of TUNEL-positive follicle cells increased, as expected, in CTX-treated mice. Furthermore, expression of APAF-1 and cleaved caspase-3 was also increased after CTX treatment. Analysis of the PI3K/Akt/mTOR signaling pathway showed that CTX increased phosphorylation of Akt, mTOR and downstream proteins without affecting total levels. These results demonstrated that the CTX treatment led to the hyperactivation of the PI3K/Akt/mTOR signaling pathway in ovaries which may be related to primordial follicle loss and growing follicle apoptosis.

AMH prevents primordial ovarian follicle loss and fertility alteration in cyclophosphamide‐treated mice

“…Our results are in accordance with the burnout effect because we showed, using Western blot analyses of whole ovaries, an increase in the phosphorylation of key proteins of the PI3K pathway in mice treated with Cy. Others have also confirmed this mechanism, with Cy or with other chemotherapeutic agents (29)(30)(31).…”

Ovarian Fibrosis

“…Chemotherapy and radiotherapy[ 55 ] lead to ovarian damage and can cause POF. Cyclophosphamide[ 56 ] induces the hyperactivation of the phosphatidylinositol-3-kinase/protein kinase B/the mammalian target of rapamycin signaling pathway in ovaries, which leads to primordial follicle loss and increased follicle apoptosis. Although firm evidence is lacking, dioxin[ 54 ] exposure may also influence the ovarian reserve, and cigarette smoke[ 57 ] induces dysfunction of mitochondrial repair mechanisms, leading to autophagy-mediated follicle death.…”

<p>The Protective Effect of Testosterone on the Ovarian Reserve During Cyclophosphamide Treatment</p>

“…[7][8][9] Previous studies have demonstrated follicular decline after cyclophosphamide treatment, and have indicated that apoptotic changes in granulosa and theca cells are the mechanism that leads to follicle loss. 10 In previous reports, testosterone was shown to be essential for normal follicular development; it enhances follicular recruitment, 11 promotes follicular growth and development, 12 increases the insulin-like growth factor 1 expression in the primate ovary to induce follicular development, 13 and increases follicular sensitivity to follicle-stimulating hormone via the androgen receptor. 14,15 However, high concentrations of testosterone inhibit follicle development through the regulation of the folliclestimulating hormone signaling pathway.…”