Sperm Maturation (Capacitation) but not Progesterone Reduces the Abundance of a Receptor for Oviduct Glycans

Abstract Text:  As sperm travel through the female reproductive tract they bind to glycan motifs on cells lining the oviduct lumen, forming a sperm reservoir.  Near the time of ovulation, sperm are released and travel to the site of fertilization.  Our lab has found that a boar sperm protein called lactadherin binds to an oviduct trisaccharide, Lewis^x, to mediate sperm binding to oviduct cells.  It has been suggested that sperm release from the oviduct reservoir is partially mediated by an increase in progesterone concentration in the oviductal fluid that would affect sperm capacitation and promote release from oviduct Lewis^x, perhaps by releasing sperm lactadherin.  We tested this hypothesis in experiments to define the effect of sperm capacitation and progesterone exposure on sperm lactadherin abundance.  Sperm from fertile boars were washed using a Percoll™ cushion.  Treatments consisted of 1) sperm capacitation for 4 hours using mTALP medium containing BSA and sodium bicarbonate and 2) sperm treatment with increasing concentrations of progesterone (0, 80, 800nM) for 30min in mTALP.  After treatment, sperm protein was extracted using a 0.1% NP40 lysis buffer and samples were submitted to western blot analysis.  Experiments were repeated at least twice.  Based on western blotting with a lactadherin antibody, two protein bands migrating at 35 kDa and 47 kDa were identified.  The greater signal was present at 47 kDa and, based on its migration, it is recognized as lactadherin.  The 47 kDa signal (lactadherin) was higher in sperm prior to capacitation than after capacitation.  Based on western blot results, lactadherin concentration was not affected by progesterone treatment; the abundance of the 47kDa band did not change.  In conclusion, two bands were detected by the lactadherin antibody suggesting the presence of two protein isoforms.  Lactadherin abundance on the sperm surface was reduced after sperm capacitation but progesterone did not affect the abundance of lactadherin.  The reduction in lactadherin during capacitation may contribute to sperm release from the oviduct.  This project was supported by Agriculture and Food Research Initiative Competitive Grant no. 2011-67015-20099 from the USDA National Institute of Food and Agriculture. 

Keywords: sperm, capacitation, oviduct