Plasminogen Improves Mouse IVF by Interactions with Inner Acrosomal Membrane-Bound MMP2 and SAMP14

Area of Science:

• Reproductive biology and biochemistry
• Sperm-egg interaction mechanisms
• Enzyme function in fertilization

Background:

• Spermatozoa require penetration of oocyte investments (cumulus oophorus, zona pellucida) for fertilization.
• Matrix metalloproteinase (MMP) 2, located on the sperm's inner acrosomal membrane, may be activated by oviductal fluid factors.
• Plasminogen, present in oviductal fluid, is known to activate MMP2 in other tissues.

Purpose of the Study:

• To investigate plasminogen interactions with sperm-bound plasminogen activator receptor (SAMP14) and MMP2.
• To confirm plasminogen's presence at the fertilization site.
• To establish plasminogen's role in facilitating fertilization.

Main Methods:

• Sperm extracts were analyzed using zymography to assess MMP2 activity with plasminogen.
• Immunohistochemistry and immunofluorescence localized plasminogen in ovarian and oviductal tissues.
• In vitro fertilization (IVF) assays were modified to mimic natural conditions, using reduced sperm concentration and assessing cumulus-intact vs. denuded oocytes.

Main Results:

• Plasminogen accelerated MMP2 activity in sperm extracts at low concentrations.
• Plasminogen was detected in oocytes, oviductal epithelium, around the zona pellucida, and within cumulus cells.
• Addition of plasminogen significantly improved IVF rates, while MMP2 or SAMP14 antibodies inhibited fertilization and cumulus dispersal.

Conclusions:

• Plasminogen directly enhances sperm's ability to penetrate oocyte investments.
• Plasminogen acts, at least partly, through an MMP2-dependent mechanism involving SAMP14.
• These findings highlight plasminogen's crucial role in natural fertilization processes.