Decrease in the number of human Ap and Ad spermatogonia and in the Ap/ Ad ratio with advancing age. New data on the...

Area of Science:

• Reproductive biology
• Gerontology
• Human spermatogenesis

Background:

• Spermatogonial stem cells (SSCs) are crucial for continuous sperm production.
• Ap and Ad spermatogonia are distinct SSC populations in the human testis.
• Age-related changes in SSCs are not fully understood.

Purpose of the Study:

• To quantify age-related changes in Ap and Ad spermatogonia numbers in healthy adult males.
• To compare the timing of involution for Ap and Ad spermatogonia.

Main Methods:

• Autopsy specimens from young and elderly men without testicular pathology were analyzed.
• Numbers of Ap and Ad spermatogonia per testis section were calculated.

Main Results:

• Ap spermatogonia numbers decreased starting in the 6th decade of life.
• Ad spermatogonia numbers decreased starting in the 8th decade of life.
• Involution of Ap spermatogonia precedes that of Ad spermatogonia, contrary to expectations based on sensitivity to noxious agents.

Conclusions:

• Ap spermatogonia undergo age-related decline earlier than Ad spermatogonia in humans.
• These findings contribute novel information to the understanding of human spermatogonial stem cell biology and aging.
• The differential timing of involution suggests distinct regulatory mechanisms for Ap and Ad spermatogonia populations.