BioWorld International Correspondent
LONDON - Stem cells can be isolated from the testes of adult mice and turned into many types of cells depending on how they are cultured, a team of researchers in Germany showed.
When the stem cells are injected into a blastocyst, they contribute to all organs in the fetus that develops, confirming their pluripotent characteristics, the scientists said.
Gerd Hasenfuss, chair of the department of cardiology and pneumonology at Georg-August-University of Göttingen in Germany, told BioWorld International: "If we can transfer what we have done to the human situation, we will have many new possibilities for treating severe human diseases, and we would have resolved the ethical problems associated with using embryonic stem cells, which exist in many countries."
The team already has successfully induced the adult murine stem cells it obtained to differentiate into neurons, contracting cardiomyocytes, liver cells, skin cells, muscular cells and vascular cells. Hasenfuss said the diseases that could be treated using that approach include myocardial infarction, Parkinson's disease, diabetes and diseases of skeletal muscle such as muscular dystrophy.
Hasenfuss and his colleagues reported their findings in the March 24, 2006, issue of Nature in a letter titled "Pluripotency of spermatogonial stem cells from adult mouse testis."
Hasenfuss's involvement in the study began with his interest in developing cells that could be used to repair heart defects. Researchers at the Institute of Human Genetics in Göttingen, led by Wolfgang Engel, already were studying spermatogonial stem cells - the cells which manufacture sperm - from the testes of mice, in the hope of finding novel ways to treat male infertility.
The interests of the two groups converged when Engel's group developed a transgenic mouse that had added DNA: It encoded a protein called Stra8, which is expressed only in spermatogonial stem cells, coupled to the gene encoding green fluorescent protein. The existence of the mouse made it possible to identify cells that activated the Stra8 promoter.
"We extracted these cells," Hasenfuss said, "and we were then able to reprogram them in culture, so that they gained the pluripotency of embryonic stem cells. Using existing culture techniques, we were able to induce them to differentiate into different tissue-specific cells. In addition, when we returned the cells back to the testicular environment, they were again able to generate sperm. Finally, we showed that when we injected the cells into a blastocyst and put this into the uterus of a pseudopregnant mouse, the labelled cells contributed to all the fetal organs."
The ultimate goal is to make the technique work using human spermatogonial stem cells. Already, the team has started working on testicular biopsy material taken from men for diagnostic or treatment purposes. Spermatogonial stem cells can be selected using specific cell-surface markers. The researchers are adjusting the culture conditions to encourage the cells to become pluripotent.
Hasenfuss predicted that this strategy would solve the ethical problems associated with use of embryonic stem cells to treat human disease. "For the man who donated the spermatogonial stem cells, you would also resolve the immunological problem that you would have if you used embryonic stem cells to treat his disease, because, of course, the cells used for treatment would be genetically identical to his. For other men, and for women, the immunological problem would remain, but this is just the same as you would have if you used embryonic stem cells, because they are never genetically identical with the recipient," he said.
In related news, at a conference on Therapeutic Potential of Stem Cells In Reproductive Medicine held in Valencia, Spain, last week, researchers from PrimeGen Biotech LLC, of Irvine, Calif., announced that they developed human adult therapeutic germ stem cells. They took adult stem cells from the testis and transformed them, through culturing in specific growth media, into cardiomyocytes, neurons, osteocytes and chondrocytes. The work is being submitted for publication.
The company says it is reviewing an earlier study, which showed that, contrary to popular belief, female germ cells do exist after birth. A spokeswoman for the company said: "We are developing a female model to attempt to reproduce the results achieved using male germ line stem cells."