Spermatogenesis is the process by which undifferentiated germ cells in the testis divide and mature. Continuous function of this process, which produces millions of spermatozoa daily, is required for sustained male fertility. Spermatogonial stem cells (SSCs), precursors of the spermatogonial lineage, have both self-renewal and differentiation abilities, and are tightly controlled in the stem cell niche.
However, biology of SSCs is difficult to study due to complexity of the microenvironment and because these cells are rare in the testis. Spermatogonial stem cells are generally similar to other stem cells. They are a rare, relatively quiescent population situated in a protected region of the testis among support cells, which may regulate their behavior. As with haematopoietic stem cells, mammalian SSCs can be transplanted and have the ability to expand the stem cell pool and regenerate an entire depleted spermatogenic lineage.
Fertility Center, CHA University, Seoul, Korea has reported that SSC-like cells could be isolated from testicular tissue of non-obstructive azoospermic (NOA) patients using modified stem cell culture conditions, but could not be maintained in vitro for more than a few passages. However, these same cells differentiated into haploid germ cells and produced embryos, confirming their developmental potential.
The Korean research group successfully isolated human testicular SSC-like cells from some NOA patients and confirmed identity and developmental potential of these cells by chromosome haploidy and embryo production. These cells proliferated slowly as colonies on autologous somatic cells, but could not be maintained for more than five passages. In addition, the number of spermatids produced in vitro from the few SSC-like cells was extremely small, and no progression into spermiogenesis was seen.
Isolated SSCs from OA and NOA patients expressed well-characterized SSC markers, and exhibited high-survival and low-apoptosis rates. In fact, SSCs were isolated and could be proliferated from 42.1% of NOA patients, including those with sertoli cells only and maturation arrest.
Culture of spermatogonial stem cells from non-obstructive azoospermia
In summary, recent results indicate that Spermatogonial stem cells present in the testes of non-obstructive azoospermia patients can be isolated and made to propagate in vitro using the highly efficient culture system described here. Furthermore, these derived SSCs were shown to produce differentiating germ cells with developmental potential.
In conclusion, non-obstructive azoospermia patients have active stem cells inside the testis but they blocked and cannot divide to produce sperm. the fact that these stem cell are still in the testis give us the hope to generate sperm.