BACKGROUND: Fertilization in mammals comprises the sequential interactions of the sperm with the cumulus oophorus, zona pellucida, and oocyte plasma membrane. Here we investigate proteasome activity in human sperm and its possible involvement during the fertilization process. METHODS: Proteasome activity was measured in intact sperm and in sperm extracts using the fluorogenic substrate Suc‐Leu‐Leu‐Val‐Tyr‐AMC, in the presence or absence of the specific proteasome inhibitor, clasto‐lactacystin β‐lactone. The participation of the proteasome was evaluated during (i) sperm–zona binding using the hemizona assay; (ii) zona pellucida‐induced acrosome reactions with a pulse and chase design; (iii) progesterone‐induced acrosome reactions incubating overnight capacitated sperm with progesterone; and (iv) progesterone‐induced Ca²⁺ influx using fura‐2AM. RESULTS: Intact sperm and sperm extracts possessed proteasome activity, which was susceptible to inhibition by clasto‐lactacystin β‐lactone. Sperm–zona binding was not inhibited by clasto‐lactacystin β‐lactone. However, both zona pellucida‐ and progesterone‐induced acrosome reactions were inhibited by clasto‐lactacystin β‐lactone. The proteasome inhibitor also blocked the sustained phase of the Ca²⁺ influx provoked by progesterone but not the peak. CONCLUSION: The human sperm proteasome is involved in the exocytosis of the acrosome, perhaps in events upstream of the plateau phase of the Ca²⁺ influx.

Oxidative stress produces macromolecules dysfunction and cellular damage. Renal ischemia-reperfusion injury (IRI) induces oxidative stress, inflammation, epithelium and endothelium damage, and cessation of renal function. The IRI is an inevitable process during kidney transplantation. Preliminary studies suggest that aminoguanidine (AG) is an antioxidant compound. In this study, we investigated the antioxidant effects of AG (50 mg/kg, intraperitoneal) and its association with molecular pathways activated by IRI (30 min/48 h) in the kidney. The antioxidant effect of AG was studied measuring GSSH/GSSG ratio, GST activity, lipoperoxidation, iNOS, and Hsp27 levels. In addition, we examined the effect of AG on elements associated with cell survival, inflammation, endothelium, and mesenchymal transition during IRI. AG prevented lipid peroxidation, increased GSH levels, and recovered the GST activity impaired by IRI. AG was associated with inhibition of iNOS, Hsp27, endothelial activation (VE-cadherin, PECAM), mesenchymal markers (vimentin, fascin, and HSP47), and inflammation (IL-1β, IL-6, Foxp3, and IL-10) upregulation. In addition, AG reduced kidney injury (NGAL, clusterin, Arg-2, and TFG-β1) and improved kidney function (glomerular filtration rate) during IRI. In conclusion, we found new evidence of the antioxidant properties of AG as a renoprotective compound during IRI. Therefore, AG is a promising compound to treat the deleterious effect of renal IRI.