Approximately 13.4% of women between the ages of 15 and 49 in the United States are infertile. Infertility treatments include fertility drugs that can stimulate the ovaries to release an egg; yet, these treatments are not free of negative side effects. Ovarian hyperstimulation syndrome (OHSS) is one side effect thought to be caused by hyperactivity of the human follicle-stimulating hormone receptor (hFSHR). OHSS leads to painful growth of the ovaries, blood clots, nausea, and an increased risk of miscarriage. Normal hFSHR functioning is regulated through the deactivation of the receptor through internalization after receptor signaling, a process mediated by the protein beta-arrestin. We hypothesized that reducing beta-arrestin would result in hyperactivity of the hFSHR, which would mimic the condition that leads to OHSS. Hyperactivity of the hFSHR would be shown through reduced extracellular signal-regulated kinase (ERK) phosphorylation and increased cyclic adenosine monophosphate (cAMP) compared to wild-type (WT).
We used small interfering RNA (siRNA) to decrease the levels of beta-arrestin 2 in human embryonic kidney (HEK) 293 cells expressing hFSHR prior to FSH stimulation. Using western blot analysis, we found that ERK phosphorylation was reduced following FSH stimulation in HEK 293 cells transfected with β-arrestin 2 siRNA. This suggested that internalization of the receptor was reduced in the KO cells compared to WT cells. However, when evaluating cAMP signaling there was a reduction compared to WT following a five-hour FSH treatment, which does not correlate with our initial hypothesis.
Understanding normal internalization of the hFSHR will provide insights into the pathology of OHSS due to the potential contribution of hFSHR hyperactivity. Studies like this will further research into interventions to improve in vitro fertilization outcomes by preventing OHSS.