Glucose Regulated Protein 78 Phosphorylation in Sperm Undergoes Dynamic Changes during Maturation

Area of Science:

• Biochemistry
• Reproductive Biology
• Proteomics

Background:

• Glucose-regulated protein 78 (GRP78) is an endoplasmic reticulum chaperone found in human sperm.
• Previous studies indicated reduced GRP78 phosphorylation in asthenozoosperm (low sperm motility).

Purpose of the Study:

• To investigate GRP78 phosphorylation changes during epididymal maturation in rats.
• To compare GRP78 phosphoforms in asthenozoospermic versus normozoospermic human sperm.

Main Methods:

• Differential gel electrophoresis (DIGE) to analyze GRP78 phosphorylation.
• Immunoprecipitation with specific antibodies for GRP78 and phospho-residues (serine, threonine, tyrosine).
• Phosphatase assays and nanofluidic proteomic immunoassay (NIA) to identify GRP78 phosphoforms.

Main Results:

• GRP78 is phosphorylated at serine, threonine, and tyrosine residues in rat and human sperm.
• Rat sperm show three GRP78 phosphoforms (GP4.96, GP4.94, GP4.85) in mature sperm versus two (GP4.96, GP4.94) in immature sperm.
• Human asthenozoospermic sperm exhibit significantly reduced levels of GP4.94 and GP5.04 phosphoforms.

Conclusions:

• Sperm GRP78 phosphorylation undergoes spatial reorganization during epididymal maturation.
• Altered GRP78 phosphorylation patterns in asthenozoosperm suggest a role in sperm function and potential clinical significance for male infertility.