MSX1 Regulates Goat Endometrial Function by Altering the Plasma Membrane Transformation of Endometrial Epithelium Cells during Early Pregnancy

MSX1 is an important member of the muscle segment homeobox gene (Msh) family and acts as a transcription factor to regulate tissue plasticity, yet its role in goat endometrium remodeling remains elusive. In this study, an immunohistochemical analysis showed that MSX1 was mainly expressed in the luminal and glandular epithelium of goat uterus, and the MSX1 expression was upregulated in pregnancy at days 15 and 18 compared with pregnancy at day 5. In order to explore its function, goat endometrial epithelial cells (gEECs) were treated with 17 &beta:-estrogen (E2), progesterone (P4), and/or interferon-tau (IFN&tau:), which were used to mimic the physiological environment of early pregnancy. The results showed that MSX1 was significantly upregulated with E2- and P4-alone treatment, or their combined treatment, and IFN&tau: further enhanced its expression. The spheroid attachment and PGE2/PGF2&alpha: ratio were downregulated by the suppression of MSX1. The combination of E2, P4, and IFN&tau: treatment induced the plasma membrane transformation (PMT) of gEECs, which mainly showed the upregulation of N-cadherin (CDH2) and concomitant downregulation of the polarity-related genes (ZO-1, &alpha:-PKC, Par3, Lgl2, and SCRIB). The knockdown of MSX1 partly hindered the PMT induced by E2, P4, and IFN&tau: treatment, while the upregulation of CDH2 and the downregulation of the partly polarity-related genes were significantly enhanced when MSX1 was overexpressed. Moreover, MSX1 regulated the CDH2 expression by activating the endoplasmic reticulum (ER) stress-mediated unfolded protein response (UPR) pathway. Collectively, these results suggest that MSX1 was involved in the PMT of the gEECs through the ER stress-mediated UPR pathway, which affects endometrial adhesion and secretion function.