Leptin and leptin receptor in pig spermatozoa: evidence of their involvement in sperm capacitation and survival

Several studies have recently investigated the role of leptin, the adipocyte-secreted hormone, in the growth and reproduction of rodents,humans, and domestic animals. The present study was designed to explore the expression of leptin and its receptor in pig spermatozoa.Successful Western blot evidenced a 16 kDa band for leptin and six isoforms, ranging from 120 to 40 kDa, for the leptin receptor. Bothleptin and leptin receptor were interestingly located at sperm acrosomal level, suggesting their involvement in the oocyte fertilizationevents. In fact, both capacitation indexes and acrosin activity were enhanced by leptin, and these effects were reduced by the anti-leptinreceptor antibody. Afterwards, we investigated the main transduction pathways regulated by the hormone. Our results showed that, inpig sperm, leptin can trigger the signal transducer and activator of transcription 3, a classical component of cytokine signal transductionpathways, whose expression has not been previously reported in male gamete; in addition it was found constitutively activated. Besides,leptin was able to induce the activation of phosphatidylinositol phosphate kinase 3 and MAP kinase pathways as well as of BCL2, a knownantiapoptotic protein. These data address to a role of leptin and its receptor on pig sperm survival. The presence of leptin and its receptorin pig sperm suggests that they, through an autocrine short loop, may induce signal transduction and molecular changes associated withsperm capacitation and survival.