One of the first events of mammalian sperm capacitation is the activation of the soluble adenyl cyclase/cAMP/protein kinase A (SACY/cAMP/PKA) pathway. Here, we evaluated whether the increase in PKA activity at the onset of human sperm capacitation is responsible for the activation of the sperm proteasome and whether this activation is required for capacitation progress. Viable human sperm were incubated with inhibitors of the SACY/cAMP/PKA pathway. The chymotrypsin-like activity of the sperm proteasome was evaluated using a fluorogenic substrate. Sperm capacitation status was evaluated using the chlortetracycline assay and tyrosine phosphorylation. To determine whether proteasomal subunits were phosphorylated by PKA, the proteasome was immunoprecipitated and tested on a western blot using an antibody against phosphorylated PKA substrates. Immunofluorescence microscopy analysis and co-immunoprecipitation (IPP) were used to investigate an association between the catalytic subunit alpha of PKA (PKA-Cα) and the proteasome. The chymotrypsin-like activity of the sperm proteasome significantly increased after 5 min of capacitation (P < 0.001) and remained high for the remaining incubation time. Treatment with H89, KT5720 or KH7 significantly decreased the chymotrypsin-like activity of the proteasome (P < 0.001). IPP experiments indicated that PKA inhibition significantly modified phosphorylation of proteasome subunits. In addition, PKA-Cα colocalized with the proteasome in the equatorial segment and in the connecting piece, and co-immunoprecipitated with the proteasome. This is the first demonstration of sperm proteasome activity being directly regulated by SACY/PKA-Cα. This novel discovery extends our current knowledge of sperm physiology and may be used to manage sperm capacitation during assisted reproductive technology procedures.

During mating, males provide not only the spermatozoa to fertilize the oocyte but also other stimuli that are essential for initiating and maintaining the reproductive programme in females. In the mammalian oviduct, mating regulates sperm storage, egg transport, fertilization, early embryonic development, and oestradiol metabolism. However, the main molecules underlying these processes are poorly understood. Using microarray analyses, we identified 58 genes that were either induced or repressed by mating in the endosalpinx at 3 h post-stimulus. RT-qPCR confirmed that mating downregulated the expression of the Oas1h and Prim1 genes and upregulated the expression of the Ceacam1, Chad, Chst10, Slc5a3 and Slc26a4 genes. The functional category “cell-to-cell signalling and interaction” was overrepresented in this gene list. Network modelling identified tumour necrosis factor (TNF) and all-trans retinoic acid (RA) as upstream regulators of the mating-induced transcriptional response, which was confirmed by intraoviductal injection of TNF or RA in unmated rats. It partially mimicked the transcriptional effect of mating in the rat endosalpinx. Furthermore, mating decreased RA levels in oviductal fluid, and RA-receptor-gamma (RARG) exhibited a nuclear location in oviductal epithelium in both unmated and mated rats, indicating RA-RARG transcriptional activity. In conclusion, the early transcriptional response regulated by mating in the rat endosalpinx is mediated by TNF and RA. These signalling molecules regulate a cohort of genes involved in “cell-to-cell signalling and interactions” and merit further studies to understand the specific processes activated in the endosalpinx to sustain the events that occur in the mammalian oviduct early after mating.

Previously, we reported that mating induces an early transcriptional response in the oviductal mucosa of rats. The functional category ‘cell-to-cell signaling and interaction’ was overrepresented in this gene list. Therefore, in the present study, we describe the role of one of these genes, carbohydrate sulfotransferase 10 (Chst10), in the oviductal mucosa. CHST10 participates in the synthesis of the carbohydrate moiety human natural killer-1 (HNK-1), which mediates cell-to-cell interactions. When using one-dimensional Western blot and sulfotransferase analyses, we found that mating increased the protein level and activity of CHST10 in the oviductal mucosa at 3 h after stimulation. A two-dimensional Western blot analysis and mass spectrometry were used to identify the novel HNK-1 glycoproteins aldehyde dehydrogenase 9 family, member A1 (ALDH9A1), fructose bisphosphate aldolase A (ALDOA), and four and a half LIM domains protein 1 (FHL1) in the oviductal mucosa, and we found that mating induces the synthesis of their acidic variants. Interestingly, in the utero-tubal junction (UTJ), acrosome-reacted sperm apparently were interacting with regions in which ALDH9A1 and HNK-1 signals overlap. Furthermore, vaginocervical stimulation applied to unmated rats increased the mRNA level of Chst10 in the oviductal mucosa. In conclusion, mating increases the activity of CHST10 in the oviductal mucosa, which in turn induces the synthesis of acidic variants of ALDH9A1 and FHL1 via HNK-1 glycosylation. ALDH9A1, HNK-1-ALDH9A1, and/or other HNK-1 glycoproteins could participate in the negative selection of sperm in the UTJ, since we detected acrosome-reacted sperm apparently interacting with regions where these proteins are located. Finally, the sensorial component of mating could regulate early events (e.g., sperm transport and selection) occurring in the oviductal mucosa after mating.

Previously, we reported that mating induces an early transcriptional response in the oviductal mucosa of rats. The functional category ‘cell-to-cell signaling and interaction’ was overrepresented in this gene list. Therefore, in the present study, we describe the role of one of these genes, carbohydrate sulfotransferase 10 (Chst10), in the oviductal mucosa. CHST10 participates in the synthesis of the carbohydrate moiety HNK-1, which mediates cell-to-cell interactions. Using 1D western blot and sulfotransferase assays, we showed that mating increased the protein level and activity of CHST10 in the oviductal mucosa at 3 h after stimulation. A 2D western blot assay and mass spectrometry were used to identify the novel HNK-1 glycoproteins ALDH9A1, ALDOA and FHL1 in the oviductal mucosa, and we showed that mating induces the synthesis of their acidic variants. Interestingly, in the utero-tubal junction (UTJ), acrosome-reacted sperm are in close contact with HNK-1-ALDH9A1 regions, and acrosome-intact sperm are in close contact with other regions in which HNK-1 and ALDH9A1 do not colocalize. Furthermore, vaginocervical stimulation applied to unmated rats increases the mRNA level of Chst10 in the oviductal mucosa. In conclusion, mating increases the activity of CHST10 in the oviductal mucosa, which in turn induces the synthesis of acidic variants of ALDH9A1 and FHL1 via HNK-1 glycosylation. In the UTJ, HNK-1-ALDH9A1 can control the quality of the sperm arriving at the fertilization site, since we detected acrosome-reacted sperm in close contact with this glycoprotein, a finding that merits further research to propose the use of HNK-1-ALDH9A1 in the selection of sperm in procedures of assisted reproduction. Finally, the sensorial component of mating could regulate events occurring in the oviductal mucosa early after mating.