Six percent of women under 44 are infertile, 12% have difficulty getting pregnant or carrying pregnancies to term, and over 75% of failed pregnancies involve implantation defects. Endometriosis, afflicting more than 10% of women of reproductive age, is a major cause of infertility, but its etiology is unclear. Therefore, identification of mechanisms involved in the pathogenesis of endometriosis-related infertility are critical. We have evidence that HDAC3 attenuation is implicated in infertile women with endometriosis. Induced endometriosis animal models involving baboons and mice showed a significant reduction of HDAC3 during the progression of endometriosis. Uterine-specific Hdac3 knock-out mice were sterile due to a defect of implantation and decidualization. In this proposal, our central hypothesis is that HDAC3 maintains steroid hormone regulation for endometrial functions, and HDAC3 loss causes infertility due to defects of implantation and decidualization. Our objective is to help solve infertility and endometrial diseases by revealing how HDAC3 functions in the uterus, and how epigenetic regulation and ovarian steroid hormone signaling are correlated. First, we will determine the pathophysiological role of HDAC3. Second, we will determine the effects of HDAC3 loss on endometriosis-related infertility. The proposed study will motivate the development of preclinical drug therapies for infertility and endometriosis and provide evidence of the molecular link between HDAC3 and steroid hormone signaling in order to accelerate evaluation of an emerging therapy against early pregnancy loss.