Retinoic acid action is altered within endometrium of baboons affected with endometriosis

Objective: Using a baboon model, we determined the changing expression of Retinoic Acid (RA) target genes during the menstrual cycle and during disease progression. This change could explain the cellular response and changes characteristic of endometriosis. In previous studies, we established that endometriosis affects the CRABP2:FABP5 ratio in an in vitro environment, shifting toward apoptosis and differentiation with higher CRABP2, and anti-apoptosis with higher levels of FABP5. Intervention(s): Endometriosis was induced in female baboons with intraperitoneal inoculation of menstrual endometrium (n = 2–4). Tissue was harvested via endometrectomy during different stages of the menstrual cycle as well at 3, 6, and 12 month timepoints after inoculation with endometriosis. Main outcome measure(s): Real time PCR was used to quantify STRA6 (a gene responsible for retinol uptake), CRABP2 (a gene necessary for apoptotic and anti-apoptotic estrogenic RA effects), and FABP5 (a gene that mediates the anti-apoptotic actions of RA). Results: STRA6 and CRABP2 expression were highest in the proliferative phase and lowest in the late secretory phase. FABP5 expression remained stable throughout the 12 months following the induction of the disease, whereas STRA6 and CRABP2 continued to decrease during the same period. Conclusions: Our study confirms that a shift in the CRABP2:FABP5 ratio has similar in vivo effects as it does in vitro: changing RA expression with disease induction and progression. As CRABP2 may be important in determining cell fate in the endometrium, gene expression changes could contribute to the anti-apoptotic behavior of affected cells. As expression changes more during progression, earlier rather than later treatment becomes more critical in reducing the rate of disease progression.