Changes in gene expression associated with vitamin A metabolism in the corpora lutea and endometria during day 15 of the estrous cycle and throughout gestation in gilts

Retinoids (i.e., vitamin A and metabolites) have biological importance for functions involved in growth and development, immunity, and reproduction. Previous studies involving retinoids have demonstrated positive associations with increased luteal progesterone (P4) concentrations, and similarly, progesterone has been implicated in the regulation of uterine secretion of retinol-binding protein (RBP), warranting further investigation. Therefore, the aim of this study was to identify the expression of various enzymes and binding proteins involved in vitamin A metabolism in corpora lutea (CL) and endometria during day 15 of the estrous cycle and throughout various points of gestation in gilts. Sexually mature, crossbred gilts were ovariohysterectomized on days 11, 15, 60, or 90 of pregnancy, or day 15 of the estrous cycle (cyclic day 15). Plasma was collected for P4 and vitamin A analysis. Corpora luteal and endometrial tissues were analyzed for mRNAs associated with vitamin A metabolism. There were no differences in CL count, P4 concentrations, or vitamin A concentrations by cyclic or gestational day (P > 0.05). Corpora lutea expression of aldehyde dehydrogenase 1 family member A1 (ALDH1A1) and RBP4 mRNAs were greater on day 15 of pregnancy compared cyclic day 15 gilts (P < 0.05). Moreover, corpora lutea mRNA expression of ALDH1A1 (P = 0.0003), RBP2 (P = 0.02), and alcohol dehydrogenase 1C (ADH1C, P = 0.07) were greater on day 11 of pregnancy. Corpora lutea expression of lecithin retinol acyltransferase (LRAT) mRNA were not different (P > 0.05). Endometrial mRNA expression of ALDH1A1 was greater on cyclic day 15 compared to day 15 of pregnancy (P = 0.002). Endometrial mRNA expression of ALDH1A1 and LRAT were greater on days 60 and 90 of pregnancy compared to days 11 and 15 of pregnancy (P ≤ 0.0001). Endometrial expression of RBP4 mRNA was greater on days 11 and 60 compared to day 90, and greater on day 60 compared to day 15 (P = 0.01). Endometrial expression of ADH1C and RBP2 mRNAs were not different (P > 0.05). These results suggest that genes encoding enzymes involved in vitamin A metabolism (ALDH1A1, ADH1C, RBP2, and RBP4) are elevated in the CL during the period of early gestation when the anti-luteolytic mechanism of maternal recognition of pregnancy is occurring. Additionally, certain genes encoding enzymes involved in vitamin A metabolism (ALDH1A1 and LRAT) are elevated mid- to late-gestation in the endometrium of pregnant pigs.