Uterine miR-877-3p and let-7a-5p are increased during simulated menstruation in a mouse model.

Heavy periods are common and debilitating, but we do not fully understand how they are caused. Increased understanding of menstrual bleeding could result in new treatments for problematic periods. Low oxygen levels are present in the womb lining during a period. These low oxygen levels help trigger the repair process required to stop menstrual bleeding. MicroRNAs (miRNAs) are small molecules that can affect cell function, and some are regulated by oxygen levels. We examined whether such miRNAs were present in the womb lining during a period. To overcome the variability present in humans, we studied the womb of mice given hormones to mimic the human menstrual cycle. We revealed that two miRNAs known to be regulated by oxygen levels were increased in the womb during menstruation. These miRNAs may help regulate menstrual blood loss and merit further study as a potential target for future treatments for heavy periods.