Leptin secretion by human ejaculated spermatozoa.
BACKGROUND
Leptin action is a dynamic area of investigation that continues to broaden beyond the basic lipostatic model originally envisaged. Here, we show that leptin is expressed in and secreted from human ejaculated spermatozoa.


METHODS
By RT-PCR, Western blot, and immunofluorescence techniques, we have demonstrated that human sperm express leptin. RIA method evidenced leptin secretion. Phosphatidyl-inositol-kinase-3 (PI3K)/Akt pathway was examined by PI3K activity assay and Western blot. Leptin and insulin regulation of glycogen synthesis was evaluated by glycogen synthase activity (GSA).


RESULTS
The large differences of leptin secretion between uncapacitated and capacitated sperm suggest a functional role for leptin in capacitation. Indeed, in uncapacitated sperm, leptin enhances both cholesterol efflux and protein tyrosine phosphorylation. In uncapacitated sperm, both insulin and leptin increased PI3K activity, Akt S473, and glycogen synthase kinase-3 S9 phosphorylation. Interestingly, during capacitation, concomitantly to the massive release of both hormones, we observed a strong reduction in the phosphorylation of glycogen synthase kinase-3 S9, kinase downstream of Akt that regulates the glycogen synthase. Our results from GSA showed that the enzymatic activity was significantly higher in uncapacitated than in capacitated sperm. Particularly, in uncapacitated sperm, GSA appeared to depend on the hormones concentration, because the enzymatic activity was stimulated at low doses, whereas it was inhibited at high doses. Moreover, both leptin and insulin regulate in autocrine fashion sperm glycogen synthesis.


CONCLUSIONS
Leptin secretion by sperm suggests that the male gamete may be able to modulate its metabolism independently by systemic leptin. These data open new considerations about leptin significance in male fertility.
Aquila
Saveria
S
Department of Pharmaco-Biology, Faculty of Pharmacy, University of Calabria, Arcavacata-Rende (Cosenza) 87036, Italy. aquisav@libero.it
Gentile
Mariaelena
M
Middea
Emilia
E
Catalano
Stefania
S
Morelli
Catia
C
Pezzi
Vincenzo
V
Andò
Sebastiano
S
D015139:Blotting, Southern; D015153:Blotting, Western; D002784:Cholesterol / Q000378:metabolism; D004542:Ejaculation; D006801:Humans; D007328:Insulin / Q000378:metabolism; D020738:Leptin / Q000235:genetics* / Q000378:metabolism*; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D013094:Spermatozoa / Q000378:metabolism* / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism
D002784:Cholesterol; D007328:Insulin; D020738:Leptin; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D014443:Tyrosine; C494918:AKT1 protein, human