Thiol oxidation by nitrosative stress: Cellular localization in human spermatozoa.

Area of Science:

• Reproductive Biology
• Oxidative Stress Research
• Spermatozoa Physiology

Background:

• Peroxynitrite (ONOO(-)) is a reactive nitrogen species (RNS) implicated in impaired sperm function and decreased semen quality.
• Thiol groups in sperm proteins are susceptible to oxidation by peroxynitrite, but their subcellular localization of damage is unknown.
• Nitrosative stress from peroxynitrite is a significant factor affecting male fertility.

Purpose of the Study:

• To determine the subcellular localization of peroxynitrite-induced nitrosative stress on thiol groups in human spermatozoa.
• To investigate the relationship between thiol oxidation and sperm motility.

Main Methods:

• Human spermatozoa were exposed in vitro to 3-morpholinosydnonimine (SIN-1) to generate peroxynitrite.
• Fluorescent probes dihydrorhodamine 123 (DHR) and monobromobimane (mBBr) were used to detect peroxynitrite and reduced thiol groups, respectively.
• Confocal microscopy, flow cytometry, and Computer-Aided Sperm Analysis (CASA) were employed to assess peroxynitrite levels, thiol redox state, sperm viability, and motility.

Main Results:

• Peroxynitrite exposure led to increased thiol oxidation, predominantly localized in the sperm head and principal piece.
• Thiol oxidation in these regions was significantly associated with a loss of sperm motility.
• Sperm viability remained largely unaffected, indicating specific damage to motile structures.

Conclusions:

• Peroxynitrite-induced thiol oxidation in human spermatozoa is primarily localized to the head and principal piece.
• This localized oxidation directly correlates with impaired sperm motility.
• The high susceptibility of sperm thiol groups to peroxynitrite explains the negative impact of RNS on sperm function.