Stem cells prodded toward turning into sperm

U. PITTSBURGH (US) — Scientists have turned two types of stem cells into precursor sperm cells—and say one day it could be possible to restore sterile men’s fertility with just skin samples.

Researchers at the University of Pittsburgh School of Medicine report their findings today in the online version of Cell Reports.

Infertility can be a side effect of some cancer treatments because the drugs work by destroying rapidly-dividing cells, which includes sperm precursor cells, explains the study’s lead author Charles Easley, formerly a post-doctoral fellow in the Department of Obstetrics, Gynecology, and Reproductive Sciences, and now a faculty member at Emory University.

“Sperm can be banked for future artificial insemination procedures, but that does not help some patients, such as pre-pubertal boys,” Easley says. “There are procedures to store testicular tissue prior to cancer therapy, but men who didn’t have the opportunity to save tissue are permanently sterile, and so far there are no cures for their sterility.”

There is growing research evidence that adult somatic cells, such as those of the skin, can be induced or biologically prodded to return to a more primitive state and then redirected to become different cell types.

To see if it was possible to derive sperm cells, Easley and his colleagues cultured lab-grade human induced pluripotent stem cells (hiPSCs) from commercially available skin samples, as well as Human embryonic stem cells (hESCs) from established cell lines, in conditions typically used to sustain spermatogonial stem cells.

They found that both kinds of stem cells were able to generate key cells, including the spermatogonial stem cells, spermatocytes containing a full complement of chromosomes prior to cell division known as meiosis, then post-meiotic spermatocytes with half the chromosome number, and round spermatids, which are precursors to sperm.

Testing of certain chromosome sites showed correct parent-of-origin genomic imprints in these haploid cells as well, the researchers note.

“No one has been able to make human sperm from pluripotent stem cells in the lab, but this research indicates it might be possible,” Easley says.

“This model also gives us a unique opportunity to study the molecular signals that govern the process, allowing us to learn much more about how sperm are made. Perhaps one day this will lead to new ways of diagnosing and treating male infertility.”

Co-authors of the paper, funded by the National Institutes of Health, include researchers from the Department of Obstetrics, Gynecology, and Reproductive Sciences at Pitt School of Medicine, the Magee-Womens Research Institute, the University of Texas, San Antonio, and University of California, Los Angeles.

Source: University of Pittsburgh