Effects of age on DNA double-strand breaks and apoptosis in human sperm*

Male factor

Effects of age on DNA double-strand breaks and apoptosis in human sperm*1

Narendra P. Singh M.B.B.S., M.S.a, , , Charles H. Muller Ph.D.b and Richard E. Berger M.D.b
a Bioengineering, University of Washington, Seattle, Washington, USA
b Department of Urology, University of Washington, Seattle, Washington, USA
Received 6 February 2003; revised 30 April 2003; accepted 30 April 2003. ;

Available online 3 December 2003.

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Source: University Of Washington
Date: November 27, 2002
More on: Fertility, Stem Cells, Brain Injury, Prostate Cancer, Pregnancy and Childbirth, Nervous System

Research Reveals A Cellular Basis For A Male Biological Clock
Science Daily — Researchers at the University of Washington have discovered a cellular basis for what many have long suspected: Men, as well as women, have a reproductive clock that ticks down with age.



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A recent study revealed that sperm in men older than 35 showed more DNA damage than that of men in the younger age group. In addition, the older men's bodies appeared less efficient at eliminating the damaged cells, which could pass along problems to offspring.

"When you talk about having children, there has been a lot of focus on maternal age," said Narendra Singh, research assistant professor in the UW Department of Bioengineering and lead researcher on the study. "I think our study shows that paternal age is also relevant."

Charles Muller, with the UW Department of Urology and a collaborator on the study, recently presented the findings at the annual meeting of the American Society for Reproductive Medicine in Seattle.

In the study, researchers recruited 60 men, age 22 to 60, from laboratory and clinical groups. A computerized semen analysis was performed for each of the subjects, looking for breaks in sperm cell DNA and evidence of apoptosis, or cell suicide. Normally, when something goes irreparably wrong in a cell, that cell is programmed to kill itself as a means of protecting the body.

The researchers found that men over age 35 had sperm with lower motility and more highly damaged DNA in the form of DNA double-strand breaks. The older group also had fewer apoptotic cells an important discovery, Singh said.

"A really key factor that differentiates sperm from other cells in the body is that they do not repair their DNA damage," he said. "Most other cells do."

As a result, the only way to avoid passing sperm DNA damage to a child is for the damaged cells to undergo apoptosis, a process that the study indicates declines with age.

"So in older men, the sperm are accumulating more damage, and those severely damaged sperm are not being eliminated," Singh said. "That means some of that damage could be transmitted to the baby." More research is needed to determine just what the risks are. Other reseachers in the study included Richard E. Berger, UW professor of urology. The work was supported by the Paul G. Allen Foundation for Medical Research.


Note: This story has been adapted from a news release issued by University Of Washington






Abstract

Objective

This study was designed to explore the relationship between men's age and DNA damage and apoptosis in human spermatozoa.

Design

Semen samples were collected from men between the ages of 20 and 57 years. Sperm DNA double-strand breaks were assessed using the neutral microgel electrophoresis (comet) assay, and apoptosis was estimated using the DNA diffusion assay.

Setting

Academic medical center.

Patient(s)

Sixty-six men aged 20 to 57 years were recruited from infertility laboratory and general populations and consented to donate a semen sample. Recruitment was determined by time and day of analysis; the only exclusions were for azoospermia, prostatitis, or prior cancer therapy.

Intervention(s)

None.

Main outcome measure(s)

DNA damage and apoptosis in human sperm.

Result(s)

Age correlated with an increasing percentage of sperm with highly damaged DNA (range: 0–83%) and tended to inversely correlate with percentage of apoptotic sperm (range: 0.3%–23%). For example, percentage of sperm with highly damaged DNA, comet extent, DNA break number, and other comet measures was statistically significantly higher in men aged 36–57 years than in those aged 20–35 years, but percentage apoptosis was statistically significantly lower in the older group. Semen analysis showed percentage motility to be significantly higher in younger age groups.

Conclusion(s)

This study clearly demonstrates an increase in sperm double-stranded DNA breaks with age. Our findings also suggest for the first time an age-related decrease in human sperm apoptosis. These novel findings may indicate deterioration of healthy sperm cell selection process with age.

Author Keywords: DNA double-strand breaks; apoptosis; human sperm; aging; Comet assay


Corresponding author. Reprint requests: Narendra P. Singh, M.B.B.S., M.S., Department of Bioengineering, Box 357962, University of Washington, , Seattle, Washington 98195-7962, , USA (FAX: 206-685-2060).

*1 Supported by the Paul G. Allen Foundation for Medical Research.

Authors Singh, Muller, and Berger contributed equally to this work.