Ovarian cortical tissue cryopreservation is a relatively novel approach to preserving fertility in women diagnosed with cancer. However, the effects of freezing-thawing are not fully understood, mainly due to the lack of suitable methods to assess tissue’s survival after thawing. Disparities in steroid production have been associated with ovarian failure by disrupting folliculogenesis, ovulation and oocyte apoptosis. Moreover, specific miRNAs, identified in human ovarian follicles, are thought to play a fundamental role in folliculogenesis. In this study, we investigated the possible interplay between the ovarian steroidal production and miRNA expression patterns in spent culture media, as potential non-invasive markers for ovarian tissue damage after cryopreservation. Cryopreservation of ovarian cortical tissue decreased (P < 0.05) both steroid production (oestradiol and progesterone) and expression of miRNA-193b and 320A in spent culture media over 5 days; however, expression of miRNA-24 increased (P < 0.05). The number of primordial follicles was also reduced (P < 0.05) in fresh-cultured and cryopreserved-cultured cortical tissues when compared with fresh tissues. Downregulation of miRNA-193b and miRNA-320A together with upregulation of miRNA-24 could have a synergistic role in cell apoptosis, and consequently leading to reduced oestradiol and progesterone production. Thus, there appears to be an interplay between these miRNAs, ovarian steroid production and cell damage, which can be further explored as novel non-invasive markers of cell damage following cryopreservation.

The primary aims of this study were to utilize a specialized culture system to further elucidate the functional significance of pericellular hypoxia within the granulosa cell (GC) compartment of growing follicles, and to clarify its effects on the production of vascular endothelial growth factor (VEGF)-A isoforms and steroid hormones. Multilaminar clusters formed rapidly in ovine GCs seeded at high density (HD), and Hypoxyprobe-1 protein adducts appeared markedly more abundant and HIF-1 activation significantly (P < 0.001) greater than in cells seeded at low density (LD). Four proangiogenic VEGF mRNA transcript variants were identified in cultured GCs. Most abundant were VEGF120 and VEGF164, but VEGF182 and VEGF188 were also detected. Total VEGF mRNA was shown to be up-regulated transiently in the HD cells (P < 0.001) and VEGF164 mRNA appeared to contribute most to this. The hypoxia mimetic cobalt chloride also induced marked increases in HIF-1 activation (P < 0.01) and total VEGF mRNA (P < 0.01) production. HD cells increased levels of HIF-1alpha (P < 0.001) and VEGF receptor type 1 (P < 0.05), but not VEGF receptor type 2 mRNA, compared to LD cells or cells grown under chemically induced hypoxia. Both 17beta-estradiol (E2) and progesterone (P4) were markedly lower (P < 0.001) in the HD, cells but though cobalt chloride treatment accompanied significantly reduced P4 production (P < 0.05), E2 levels remained similar to those in untreated cells. These outcomes suggest that pericellular hypoxia may be an important mediator of VEGF production in the GCs of growing follicles, but that local regulation is complex and may involve multiple mechanisms such as mediation by steroid hormones and differential variant mRNA production.

Natriuretic peptides (NPs) have been reported to have critical roles in follicular development and oocyte maturation in rodents. This study aimed to extend our current understanding of NP-mediated signalling pathways and mechanisms of action in the follicles of a monovulatory species. Ovine granulosa cells (GCs) and theca cells (TCs) were cultured under conditions designed to allow gonadotrophin-stimulated cell differentiation. Gene expression analysis was performed by qualitative (q)PCR for NPs and NPRs (between 16 and 96 h of culture) and VEGF120 and VEGF164 (between 16 and 144 h of culture). A qualitative analysis of the production of NP/NPR family members and NP ligand/receptor associations was carried out utilising a highly sensitive immunological approach known as ‘proximity ligation assay’ (PLA). All NPRs were observed in GCs, while NPRA was absent in TCs. In GCs, gene expression of NPRA, NPRB and NPRC was apparent but only active BNP and CNP and not ANP, were detected. Also in GCs, ANP but not CNP was able to significantly (P < 0.05) reduce oestradiol and increase (P < 0.05) progesterone. Inhibition of VEGF164 by ANP and CNP (P < 0.01) after 48 h of culture preceded up-regulation of VEGF120 by ANP (P < 0.01) after 144 h, but not CNP. Taken together, these findings appear to demonstrate that NP responsiveness in the GC compartment of sheep follicles is multi-facilitated, utilising both autocrine and paracrine stimulation pathways.