Glycogen Synthase Kinase-3 Isoform Variants and Their Inhibitory Phosphorylation in Human Testes and Spermatozoa

Area of Science:

• Reproductive Biology
• Molecular Endocrinology
• Cell Signaling

Background:

• Glycogen synthase kinase-3 (GSK3) is a key regulator of cellular processes.
• GSK3 exists as α and β isoforms with potential distinct functions.
• Understanding GSK3 isoform expression in human testes and spermatozoa is crucial for reproductive health.

Purpose of the Study:

• To investigate the expression and localization of glycogen synthase kinase-3 (GSK3) α and β isoforms and their phosphorylated forms in human testes and spermatozoa.
• To elucidate the functional significance of GSK3 isoforms in germ cell development, Sertoli cell function, and sperm capacitation.

Main Methods:

• Analysis of GSK3 isoform variants in testicular biopsies from normospermic and Sertoli cell-only (SCO) individuals.
• Immunohistochemical examination of GSK3α, GSK3β, and their phosphorylated forms (p-GSK3α/β) in testicular tissues and spermatozoa.
• Correlation of GSK3 expression and phosphorylation with germ cell stages, Sertoli cell status, and sperm capacitation.

Main Results:

• GSK3α and GSK3β variants were detected in normospermic testes, with decreased levels in SCO testes.
• GSK3β was prominent in spermatogonia, while GSK3α dominated meiotic germ cells.
• Increased inhibitory phosphorylation of GSK3α (p-GSK3α(Ser)) was observed during sperm capacitation, correlating with enhanced motility.

Conclusions:

• GSK3 isoform switching from GSK3β to GSK3α during meiotic entry suggests specific roles in spermatogonial stemness and meiosis.
• Downregulation of GSK3 activity via inhibitory phosphorylation may occur in dormant Sertoli cells of SCO testes.
• Inhibitory phosphorylation of GSK3α in spermatozoa is linked to motility activation during capacitation.