Epigenetics and Infertility: The Link Between Nature & Nurture
You know who Charles Darwin is, right? One seriously influential figure in human history, Darwin’s famous natural selection theory is an easily digestible way to explain evolution. Makes sense: giraffes with longer necks can reach higher into trees to eat and survive. Advantage passed on to long-necked offspring. And so on, until poof! You have the modern giraffe.
But have you ever heard of Jean Baptiste Lamarck? Also a naturalist, he was a generation older than Darwin. And he also had a theory of how organisms evolve, which was familiar to Darwin. And since it’s unlikely that you’ve heard of him, you can guess that his theory of “soft inheritance” didn’t make the cut. That’s show business.
But alas, Lamarck imagined the unimagined. Darwin pictured evolution occurring in rather large, generational “steps” but had no clue as to exactly how it happens. Lamarck though believed that offspring inherited smaller, environmentally induced changes acquired by parents over their lives. In essence, he outlined a pathway for evolution to occur that involved passing things along that were gained from simply living and surviving. In essence, the giraffe developed a long neck because it spent its life constantly reaching higher and higher for leaves. And that lifelong effort was rewarded in offspring having longer necks.
So why all this noodling about old science? Because it matters now more than ever. In modern thought, this is the nature (Darwin) vs. nurture (Lamarck) issue. What really makes you who you are: your genes or your environment? And the answer is clearer than ever: Both. And the bridge between the two is epigenetics, my friends, which governs the way in which our genes interact with the environment. So, Lamarck was really onto something.
The Missing Link
This babbling has a point. In the field of human fertility, we have known for years that a man’s sperm count can be genetically or environmentally determined. Messed up Y chromosome genes will cause low or no sperm counts. And there are things in the environment like hot baths, tobacco and chemotherapy that will certainly kill sperm. But many men have low sperm counts and none of the above. Enter stage left: Lamarck…and epigenetics.
We are presenting a paper at the American Society of Reproductive Medicine that suggests that epigenetics can also explain semen quality. We examined the DNA methylation profiles of 480,000 CpG sites in semen in over 200 infertile men. When comparing semen samples with normal and low sperm counts, normal and low motilities and normal and abnormal shapes (morphology), we found large differences in epigenetic marks on sperm DNA in literally hundreds of genes. Furthermore, when we drilled down on the affected genes, many were found to have roles in infertile animal models, lending credence to the analysis.
This is exciting because it means that epigenetics could explain a large chunk of male infertility that is currently unexplained. From a Lamarckian viewpoint, and even more thrilling to me, is that knowing the epigenetics of infertility may allow us to pinpoint exactly what environmental issues are influencing things. And that, my friends, could be a very good thing for a species that is threatened with falling sperm counts.