Phil Bach*, Anna Mielnik, Alexander Bolyakov, Bobby Najari, Peter Schlegel, Darius Paduch, New York, NY
INTRODUCTION AND OBJECTIVES:
Sertoli cell-only syndrome (SCOS) is one of the most severe forms of male factor infertility and is classically thought to be devoid of germ cells.
However, evidence from microsurgical testicular sperm extractions (TESE) on patients with SCOS has revealed the presence of rare focal areas of spermatogenesis, thereby suggesting the presence of spermatogonial stem cells (SSC) in at least some patients with SCOS.
We hypothesize that SSCs are present in most patients with SCOS and that it is abnormal differentiation of the SSC into spermatogonia (SPG) A and/or B that leads to SCOS.
Testicular samples were obtained from 5 men with pure SCOS on biopsy during TESE and from 5 cadaveric men with normal spermatogenesis.
Specimens were assessed for mRNA markers of SSC, SPG A, and SPG B by RNA sequencing. Immuno- fluorescence was then used to visualize SSCs and SPG A in the testicular samples.
Finally, flow cytometry using known markers for SSC (SSEA4) and SPG A (GFRa1) was used to provide quantitative evidence of cellular presence in testicular samples.
On RNA sequencing, mRNA markers for SSC and SPG A are expressed in similar numbers in men with normal spermatogenesis and in those with SCOS. On the other hand, there was a dramatic overexpression of mRNA markers for differentiated cells, such as spermatocytes, in men with normal spermatogenesis (Table 1).
Immunofluorescence showed increased expression of GFRa1 in the testes of men with SCOS when compared to the testes of men with normal spermatogenesis.
Flow cytometry analysis of four testicular samples from men with SCOS and four samples from those with normal spermatogenesis showed a similar number of SSEA4+ cells (0.11%), but a nearly four-fold increase in the number of GFRa1+ cells in men with SCOS compared to those with normal spermatogenesis (0.7% versus 0.18%, respectively).
These findings suggest that SSCs are present in patients with SCOS in similar numbers as in those with normal spermatogenesis.
However, there is a surprising accumulation of SPG in SCOS patients. Rather than differentiating and proceeding down the spermatogenesis pathway, the SSCs proliferate, but remain undifferentiated.
The azoospermia seen in men with SCOS appears to be secondary to a defect in SSC differentiation and entry into meiosis.