Dysregulation of SGK1 in the endometrium causes endometrial receptivity defects and embryo implantation failure in diabetes

To investigate whether diabetes affects the natural events involved with successful implantation in female and to confirm the expression level of the serum- and glucocorticoid-inducible kinase SGK1 in the endometria of diabetics, furthermore to uncover the underlying mechanisms. Explore the morphological features of endometria from diabetics and control patients during the window of implantation, examine the JAr spheroid attachment rates in a model in vitro system of the human endometrial cancer (Ishikawa) cell line and detect the expression levels of SGK1 and other molecules associated with uterine receptivity and embryo implantation. The endometrial samples were obtained from diabetics and euglycemia women with male factor infertility (control) during the window of implantation. Scanning electron microscope examinations were performed to assess morphological features of uterine receptivity. Ishikawa cells were grown in steroid-depleted media administered with 5mM glucose(control group) or 25mM glucose(high glucose group).The effect of high glucose on implantation was examined via attachment assay of JAr spheroids to Ishikawa cells. The expression levels of molecules associated with uterine receptivity and embryo implantation were detected by qRT-PCR and Western blot. Nuclear-cytoplasmic localization of SGK1 after high glucose treatment was detected by laser scanning confocal microscopy in Ishikawa cells. There was a reduced number of mature uterodomes in the endometria of diabetics compared to control, shown as patches of luminal surface dominated by underdeveloped or immature microvilli. Treating Ishikawa cells with high glucose decreased JAr spheroid attachment rate, up-regulated the expression levels of SGK1 and ENACα, but significantly down-regulated the expression levels of LIF,HOXA10 and HBEGF. Furthermore high glucose treatment can also activate TGFβ1/Smad2 signaling pathway, which may lead to the increased expression of SGK1 directly. Those effects can be reversed by the TGFβR1 inhibitor SB431542. High glucose treatment also promoted the nuclear translocation of SGK1 in Ishikawa cells, and the activated SGK1 regulated the expression of a subset of genes that were involved in uterine receptivity, including ENACα, LIF, HOXA10,HBEGF. Diabetes may cause endometrial receptivity impairment and embryo implantation failure via increasing the expression level of SGK1 and promoting its activation, which may be due to a high glucose microenvironment in endometrium during the window of implantation.