Sperm cell / Credit: Anna Tanczos. Wellcome Images

Researchers from Washington State University have discovered a promising new technique for preserving sperm stem cells from prepubescent boys undergoing cancer treatment. The study, published in Stem Cell Reports, may have implications in other fields for long term storage of biological samples.

“I think it’s going to become the standard by which everybody cultures their cells, including trying to develop conditions for human cells,” said Jon Oatley, Ph.D., Associate Professor at the WSU School of Molecular Biosciences and Director of the Centre for Reproductive Biology.

Less than 1% of cancer cases in the USA are found in children, but this accounts for just over 10,000 children under the age of 15 in 2016 alone. More than 80% of these cases will have a survival rate of longer than five years, however many prepubescent boys are at risk of developing azoospermia, a lack of viable sperm.

“After the cancer is controlled, the quality of life, which often includes the ability to have a normal child, becomes a major issue,” said Marvin Meistrich, an oncologist from the University of Texas when writing in Pediatric Blood & Cancer.

Radiotherapy and chemotherapy, both mainline treatments for a range of cancers, have been shown to render sperm infertile permanently. At present, adult men can have sperm samples frozen before they begin their treatment and thus be able to have biological children in the future, but prepubescent boys have not yet developed sperm to donate. Instead, they can only have sperm stem cells removed and frozen in the hopes that a technology in the future will be developed to culture the cells successfully and reinsert them into the patient to produce sperm.

If successful, these stem cells would be able to differentiate into sperm. On average, a mature, fertile man is able to produce around 1,300 sperm cells with every heartbeat, and a single stem cell is responsible for producing 5,000 sperm when it differentiates.

To better understand the process by which these stem cells differentiate, the team from WSU observed prepubescent mouse pups by fusing a fluorescent tag to a stem cell-specific gene. The tag allowed them to track the processes by which the stem cell differentiated into the progenitor cells which ultimately develop into functional sperm.

Their results detailed how the stem cells used two different methods for producing energy: glycolysis, followed by oxidative phosphorylation. While glycolysis is a common, safe way for cells to produce energy, oxidative phosphorylation can result in the formation of free radicals, highly reactive species which can badly damage a cell’s DNA.

“If you’re a stem cell that is going to give rise to sperm essentially through the whole lifetime of an individual, you want to have a pristine genome,” said Dr. Oatley. “You don’t want it damaged by reactive oxygen species. That’s why we think glycolysis is important for the stem cell. So we tried to change the culture environment to favour glycolysis.”

As the name suggests, oxidative phosphorylation relies on the presence of oxygen in the surrounding area, so the team attempted to lower the oxygen concentration in their samples. They found that by adding Nitrogen instead, they were able to more than halve the level of oxygen and this resulted in a dramatic improvement in the number of viable stem cells. Previously only around 5% of the stem cells were able to produce sperm when reintroduced to the testes, whereas Oatley and his team saw roughly 40% that remained viable, an 8-fold improvement.

These results are very promising but there is a lot more work to further the investigation. One part of that is beginning collaboration with researchers at the University of Pennsylvania to observe any changes to the epigenome in the cultured cells. The team are also hoping to investigate whether their technique is transferable to human tissues or not.

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