The role of FMR1-associated miR-323a and its impact on SMAD-signaling pathway in relation to the regulation of ovarian function

Abstract Study question Is FMR1 (Fragile-X-Mental Retardation 1 Gene)-targeting miR-323a related to poor ovarian response and what impact does it have on the folliculogenesis-regulating SMAD-signaling pathway? Summary answer In poor ovarian responders, miR-323a is significantly upregulated, FMRP – downregulated. Human granulosa cells, transfected with a miR-323a mimic, show an upregulation of SMAD proteins. What is known already Folliculogenesis is a complex process, regulated, among others, by FMR1 and its protein FMRP. MicroRNAs are involved in translational repression, controlling ovarian function and follicular development. miR-323a suppresses FMR1 in tumor cells, but their relationship has not been evaluated in the human ovary. miR-323a also interacts with components of SMAD pathways, which regulate cell proliferation, differentiation and apoptosis. SMADs belong to the downstream signaling of bone morphogenetic protein-receptor-2, and our previous data shows that its expression is affected by FMRP. Thus, researching miR-323a together with its target molecules may provide more insight into the pathogenesis of poor ovarian response. Study design, size, duration For ex vivo experiments, we investigated human granulosa cell (HGC) samples of poor (POR, N = 22) and normal (NOR, N = 32) ovarian responders, with an ongoing sample collection which began in 2013. Our in vitro experiments were performed on COV434 cell line, transfected with a microRNA-323a-3p mimic. RNA extraction and RT-qPCR were performed to determine the relative expression levels of the targets, with NOR serving as the control group ex vivo and non-transfected COV434 cells in vitro. Participants/materials, setting, methods 54 patients who underwent IVF/ICSI treatments were recruited and divided into two groups based on their ovarian response according to the Bologna criteria. HGCs were collected during oocyte retrieval, and COV434 cell line was used for miRNA mimic transfection experiments. Briefly, we performed RNA extraction, cDNA synthesis and TaqMan RT-PCR, as well as protein extraction and ELISA. The collected data was analysed using the 2–ΔΔCtmethod and Student’s t-test. Main results and the role of chance We found that miR-323a was significantly upregulated in HGCs of POR (p = 0.0324). FMR1 expression in this patient group showed a slight downregulation that did not reach statistical significance (p = 0.1054). Protein expression level analysis of 22 patients from this collective (NNOR=11, NPOR=10) demonstrated a significant downregulation of FMRP in POR (p = 0.0373), suggesting its participation in the pathogenesis of poor ovarian response. Additionally, in vitro upregulation of miR-323a resulted in altered expressions of SMAD-signaling pathway components. Namely, SMAD3 expression increased by 5.7 fold, SMAD4 – 1.6 fold, SMAD5 – 2.5 fold, and SMAD8 – 4.1 fold, compared to non-transfected COV434 cells, with SMAD3 results requiring further investigation due to an unexpected 2 fold elevation of its expression in the negative control (scramble) sample. FMR1 and SMAD1 expression levels remained stable between transfected cells and control samples. These findings show that FMR1-targeting miR-323a may play a critical role in regulating the SMAD pathways, thus affecting folliculogenesis, HGC proliferation and, ultimately, ovarian reserve, which is reduced in case of poor ovarian response. Limitations, reasons for caution Larger patient sample size is needed to confirm the current results. An age-related influence cannot be ruled out because of the existing difference between the groups. More repeats of miR-323a-3p mimic transfection and miR-323a-3p inhibitor transfection should be carried out to support the in vitro findings. Wider implications of the findings For the first time, we researched the expression levels of miR-323a in HGCs. Our results suggest that miR-323a, which, like FMRP, is downregulated in POR, is involved in the FMR1/FMRP regulatory loop, and its upregulation affects the SMAD-signaling pathway, deepening our understanding of the pathogenesis of poor ovarian response. Trial registration number not applicable