Mouse spermatozoa express a pH-dependent K⁺current (KSper) thought to be composed of subunits encoded by theSlo3gene. However, the equivalence of KSper andSlo3-dependent current remains uncertain, because heterologous expression ofSlo3results in currents that are less effectively activated by alkalization than are native KSper currents. Here, we show that genetic deletion ofSlo3abolishes all pH-dependent K⁺current at physiological membrane potentials in corpus epididymal sperm. A residual pH-dependent outward current (I_Kres) is observed inSlo3^−/−sperm at potentials of >0 mV. Differential inhibition of KSper/Slo3 andI_Kresby clofilium reveals that the amplitude ofI_Kresis similar in both wild-type (wt) andSlo3^−/−sperm. The properties ofI_Kressuggest that it likely represents outward monovalent cation flux through CatSper channels. Thus, KSper/Slo3 may account for essentially all mouse sperm K⁺current and is the sole pH-dependent K⁺conductance in these sperm. With physiological ionic gradients, alkalization depolarizesSlo3^−/−spermatozoa, presumably from CatSper activation, in contrast to Slo3/KSper-mediated hyperpolarization in wt sperm.Slo3^−/−male mice are infertile, butSlo3^−/−sperm exhibit some fertility within in vitro fertilization assays.Slo3^−/−sperm exhibit a higher incidence of morphological abnormalities accentuated by hypotonic challenge and also exhibit deficits in motility in the absence of bicarbonate, revealing a role of KSper under unstimulated conditions. Together, these results show that KSper/Slo3 is the primary spermatozoan K⁺current, that KSper may play a critical role in acquisition of normal morphology and sperm motility when faced with hyperosmotic challenges, and that Slo3 is critical for fertility.

Embryo implantation is a highly synchronized event between an activated blastocyst and a receptive endometrium. The success of this process relies on the dynamic interplay of estrogen (E₂) and progesterone (P₄), however, the details of this interaction are not entirely clear. Recent data implicate E₂ and P₄ in the regulation of glucose utilization by affecting facilitative glucose transporter (GLUT) expression. In this study we examine GLUT1 expression in murine and human endometrial stromal cells (ESCs) using a primary culture system. We show that expression of GLUT1 is increased during ESC decidualization in vitro. P₄ up-regulates, whereas E₂ down-regulates, GLUT1 expression. In addition, P₄ increases and E₂ decreases glucose uptake in ESCs, suggesting that GLUT1 may be a major player in glucose utilization in these cells. Moreover, GLUT1 expression is increased in human ESCs when decidualized in vitro with P₄ and dibutyryl cAMP, suggesting a similar role for P₄ in human endometrium. In conclusion, an imbalance between P₄ and E₂ seen in patients with polycystic ovary syndrome, luteal phase defect, and recurrent pregnancy loss may have a critical impact on glucose utilization in the endometrial stroma, and, thus, may be responsible for endometrial dysfunction and failure of embryo implantation in these patient populations. GLUT1 expression increases during decidualization of endometrial stromal cells in vitro. Progesterone upregulates and estrogen downregulates GLUT1 expression and glucose uptake in these cells.

The objective of this study was to determine whether sperm quality, fertilization capacity, and subsequent embryo development are altered in diabetic male mice and whether differences in facilitative glucose transporter (GLUT; now known as solute carrier family 2, SLC2A) expression in the testis and sperm exist. Using two type 1 diabetic mouse models, SLC2A expression in the testis and sperm was determined by western immunoblotting and immunofluorescence staining. To address sperm quality and fertilization capacity, computer-assisted sperm analysis and in vitro fertilization were performed. SLC2A1, SLC2A3, and SLC2A5 did not change in expression in the testes or sperm between diabetic and non-diabetic mice. SLC2A8 and SLC2A9b were less expressed in the testes of both diabetic models versus controls. SLC2A9a was not expressed in the Akita testis or sperm when compared with strain-matched controls. 3β-hydroxysteroid dehydrogenase (HSD3B) expression was significantly decreased in the Leydig cells from the diabetic mice. Sperm concentration and motility were significantly lower in both the diabetics when compared with the control. These parameters normalized in Akita diabetic males treated with insulin. In addition, fertilization rates were significantly lower in the Akita group (17.9%) and the streptozotocin (STZ)-injected male group (43.6%) when compared with the normal group (88.8%). Interestingly, of the fertilized zygotes, embryo developmental rates to the blastocyst stage were lower in both diabetic models (7.1% Akita and 50.0% STZ) when compared with controls (71.7%). Male diabetes may cause male subfertility by altering steroidogenesis, sperm motility, and SLC2A expression. This is the first study to link a paternal metabolic abnormality to a sperm effect on cell division and subsequent embryonic development.

Adiponectin (Adipoq), a protein secreted by adipocytes in inverse proportion to the adipose mass present, modulates energy homeostasis and increases insulin sensitivity. Tissue Adipoq signaling decreases in settings of maternal diabetes, polycystic ovary syndrome (PCOS) and endometriosis, conditions which are associated with reproductive difficulty. Our objective was to define the expression and hormonal regulation of Adipoq and its receptors in the mouse preimplantation embryo and uterus. By real-time quantitative PCR, mRNA transcripts for Adipoq, AdipoR1, AdipoR2, Ppara, Ppard, FATP1 (SLC27A1) and acyl CoA oxidase (Acox1) were identified in mouse 2-cell and 8-cell embryos, while blastocyst stage embryos and trophoblast stem (TS) cells expressed mRNA for all genes except Adipoq. Protein expression of Adipoq, AdipoR1, AdipoR2, the insulin sensitive transporters GLUT8 (Slc2A8), GLUT12 (Slc2A12) and p-PRKAA1 was identified by immunofluorescence staining in all stages of preimplantation embryos including the blastocyst. In situ hybridization demonstrated the presence of Adipoq, AdipoR1 and AdipoR2 mRNA in the mouse decidual cells of the implantation site and in artificially decidualized cells, and the expression of these proteins was confirmed by western blotting. Flow cytometry confirmed cell surface expression of AdipoR1 and AdipoR2 in TS cells and decidual cells. These results suggest for the first time that Adipoq signaling may play an important role in preimplantation embryo development and uterine receptivity by autocrine and paracrine methods in the mouse. Implantation failures and pregnancy loss, specifically those experienced in women with maternal metabolic conditions such as diabetes, obesity and PCOS, may be the result of aberrant Adipoq and AdipoR1 and AdipoR2 expression and suboptimal decidualization in the uterus.