Spermatozoa are not mature until they transit the
epididymis where they acquire motility and the
ability to fertilize an
egg through sequential modifications. The
epididymis has three functional regions, caput, corpus, and cauda, and the
luminal proteins of the
epididymis play important
roles in the above modifications. However, the
proteins with differential enrichment between the caput and cauda are still largely unknown. To reveal the functions of the caput and cauda during
sperm maturation,
luminal proteins from caput and cauda of
mice were analyzed by isobaric tag for relative and absolute quantitation (iTRAQ). Overall, 128 differentially enriched
proteins were found, of which 46 were caput enriched and 82 were cauda enriched.
Bioinformatic analysis showed that
lipid metabolism was active in the caput; while
anion- and
cation-binding activity and
phosphorus and
organophosphate metabolism were active in the cauda. A new epididymal
luminal protein, the caput-enriched
PDZ domain containing 1 (Pdzk1), also named Na+/H+ exchange regulatory cofactor 3 (NHERF3), which
plays a critical
role in
cholesterol metabolism and
carnitine transport, was found in the
lipid metabolism.
Western blotting and
immunofluorescence analyses showed that Pdzk1 was expressed in the
epididymis but not in the
testis, and localized at the middle piece of the
sperm tail. Pdzk1
protein level was also reduced in the
spermatozoa in case of asthenozoospermic
patients compared with that in normozoospermic
men, suggesting that Pdzk1 may participate in
sperm maturation regulation and may be associated with
male infertility. These results may provide new insights into the mechanisms of
sperm maturation and
male infertility.