Inhibitors of c-Jun phosphorylation impede ovine primordial follicle activation

Abstract

Study hypothesis: Is the c-Jun-N-terminal kinase (JNK) pathway implicated in primordial follicle activation?

Study finding: Culture of ovine ovarian cortex in the presence of two different c-Jun phosphorylation inhibitors impeded pre-antral follicle activation.

What is known already: Despite its importance for fertility preservation therapies, the mechanisms of primordial follicle activation are poorly understood. Amongst different signalling pathways potentially involved, the JNK pathway has been previously shown to be essential for cell cycle progression and pre-antral follicle development in mice.

Study design, samples/materials, methods: Ovine ovarian cortex pieces were cultured with varying concentrations of SP600125, JNK inhibitor VIII or anti-Mullerian hormone (AMH) in the presence of FSH for 9 days. Follicular morphometry and immunohistochemistry for proliferating cell nuclear antigen (PCNA), apoptosis and follicle activation (Foxo3a) were assessed.

Main results and the role of chance: Inhibition of primordial follicle activation occurred in the presence of SP600125, JNK inhibitor VIII and AMH when compared with controls (all P < 0.05) after 2 days of culture. However, only in the highest concentrations used was the inhibition of activation associated with induction of follicular apoptosis (P < 0.05). In growing follicles, PCNA antigen expression was reduced when the JNK inhibitors or AMH were used (P < 0.05 versus control), indicating reduced proliferation of the somatic compartment.

Limitations, reasons for caution: Although we evaluated the effects of inhibition of c-Jun phosphorylation on primordial follicle development, we did not determine the cellular targets and mechanism of action of the inhibitors.

Wider implications of the findings: These results are the first to implicate the JNK pathway in primordial follicle activation and could have significant consequences for the successful development of fertility preservation strategies and our understanding of primordial follicle activation.

Large scale data: n/a.

Study funding and competing interests: Dr Michael J. Bertoldo and the laboratories involved in the present study were supported by a grant from 'Région Centre' (CRYOVAIRE, Grant number #320000268). There are no conflicts of interest to declare.

Keywords: Foxo3a; anti-Mullerian hormone; c-Jun-N-terminal kinase; fertility preservation; in vitro ovarian tissue culture; primordial follicle activation.