Role of TSH (Thyroid Stimulating Hormone) in the maintenance and functioning of the human corpus luteum

Study question: Is Thyroid Stimulating Hormone (TSH) able to interfere with the vitality and functionality of the human corpus luteum (CL)? Summary answer: TSH does not influence steroidogenesis but negatively affects granulosa-luteal (hGL) cell viability. What is known already: One of the most common endocrine diseases in women of childbearing age is thyroid dysfunction. Hypothyroidism, characterized by elevated serum TSH levels, affects female reproductive function because it is associated with menstrual cycle disturbances and an increased risk of miscarriage. Thyroid hormones have been shown to exert an anti-apoptotic effect on granulosa cells (GC) and CL. The CL is a transient endocrine gland that secretes progesterone which is essential for the maintenance of pregnancy. Evidence of the presence of receptors for TSH on hGL cells and bovine CL suggests that TSH may directly affect the CL. Study design, size, duration: GCs obtained from follicular fluid of women undergoing in vitro fertilization (IVF) treatment, can be induced to luteinization in vitro. As it happens during the luteinization process in vivo, these cells respond to the treatment with luteinizing hormone (LH) by increasing progesterone production and decreasing their replication rate. Therefore, they can be used as an experimental model for the study of CL. Participants/materials, setting, methods: GCs were isolated from follicular aspirates derived from patients undergoing IVF treatment at a private IVF clinic, without any thyroid disorder (serum TSH 0.5-2 mU/L). Cells were cultured at 37°C in DMEM, supplemented with 5% FBS. The cells were treated with 1nM LH and increasing concentrations of TSH. At the end of culture, conditioned medium and cells were collected to analyze progesterone production, cell viability, and mRNA levels of genes involved in the steroidogenesis process. Main results and the role of chance: We observed by PCR the presence of the TSH receptor in hGL cells, which has already been described as present in bovine CL and human ovarian tissue. Next, we analyzed the possible effects of TSH on progesterone secretion by evaluating the progesterone secreted by cells in the culture medium following treatment with increasing concentrations of TSH and the expression of genes involved in the steroidogenesis process. Our results show that TSH does not modulate progesterone production by hGL cells and does not affect mRNA levels of genes such as p450scc and HSD3b 1/2. On the other hand, we observed a significant decrease in cell number in response to increasing doses of TSH. To investigate if the reduction in cell number was due to increased cell death associated with DNA fragmentation, we performed TUNEL assay. We found a significant dose-dependent increase in cell death percentage, which correlated well with their lower growth rate. Finally, we focused on LH and TSH co-treatment's effect on cell viability and steroidogenesis. Our data show that TSH does not affect LH-induced P4 production, and LH cannot revert TSH action on cell death. Limitations, reasons for caution: This is an in vitro study where an experimental model mimicking the human corpus luteum was used. To date, it is difficult to access human luteal tissue. In addition, it was complicated to obtain large sample sizes with the inclusivity criteria selected for this study. Wider implications of the findings: We conclude that elevated TSH levels in hypothyroid women may be associated with impaired CL functioning and maintenance. These findings open a new line of research for the importance of the treatment of women with thyroid dysfunction that could contribute to the onset of infertility. Trial registration number: Not required.