Stem Cell Therapy for Infertility! What’s new?
What are Stem Cells?
Stem cells, by definition, have the potentials of both self-renewal and differentiation into specialized cell types.
Currently, there are three major stem cell sources for generating male differentiated germ cells: the embryonic stem cells, the induced pluripotent stem cells, and spermatogonial stem cells.
Embryonic stem cells are divided from five to seven-day old blastocysts that are precursor to embryos. They are pluripotent in nature and capable of generating any cell in the body, any kind of tissue.
Collectively, derivation of male germ cells from embryonic stem cells has promising applications for male infertility treatment and provides an ideal platform for elucidating molecular mechanisms of male germ cell development. However, in regard of fertility treatment, gametes derive from embryonic stem cell lines would be genetically unrelated to the patient Furthermore, there are ethical problems concerned with the use of human embryonic stem cells and sources of human embryonic stem cells are limited.
One of the exciting breakthroughs in stem cell research is the establishment of the induced pluripotent stem cells from somatic cells via overexpressing one or more transcription factors. The induced pluripotent stem cells are very similar to embryonic stem cells in many aspects.
Compared with human embryonic stem cells, induced pluripotent stem cells have some advantages:
- there is no ethical issue for using human induced pluripotent stem cells;
- the source for obtaining human induced pluripotent stem cells is more abundant;
- male gametes derived from patients’ own induced pluripotent stem cells have genetic information.
Due to human induced pluripotent stem cells can be generated from patients’ somatic cells, a large number of patient-specific human induced pluripotent stem cell lines have been established and might be used for reproductive medicine.
Male germ cells derived from human induced pluripotent stem cells may not be used for treating male infertility due to tumor-forming risks, which might result from cancer-formation risks and their genetic instability. Therefore, more attention has been paid to generate male gametes from human spermatogonial stem cells.
Unlike other stem cells, spermatogonial stem cells are unique in that they are the stem cells that transmit genetic information to subsequent generations. Spermatogenesis is a complex differentiation process in which spermatogonial stem cells self-renew and differentiate into spermatozoa with the support of different cells inside the testis. Therefore, researchers have a long way to recapitulate the process in vitro, including the mechanism and the conditions for spermatogenesis. great efforts have been made to achieve spermatogenesis in vitro using animal models but the generation of functional haploid spermatids from human spermatogonial stem cells in vitro has not been achieved yet.
In short, we have addressed the advancements on differentiation of male differentiated germ cells from various kinds of stem cells. Nevertheless, the use of stem cells to generate male gametes in vitro remains an avenue of research which is still in its infancy. Although several questions remain to be answered before the stem cell-derived spermatozoa can be used successfully in clinical therapies, exciting progress has been made. More and more researchers are dedicated to the study of kinds of stem cells for generating mature and functional spermatozoa. The rapid development of stem cell research, particularly with respect to induced pluripotent stem cells and spermatogonial stem cells, lays a solid basis for offering an invaluable source of functional male gametes for treating male infertility with their own genetics.
For more detalis read: https://www.ncbi.nlm.nih.gov/pubmed/24534952