Proliferative Activity In Vitro and DNA Repair Indicate that Adult Mouse and Human Sertoli Cells Are Not Terminally Differentiated, Quiescent Cells1

Abstract

Sertoli cells isolated from the adult mouse and human testis resume proliferation in culture. After 20 days of culture in Dulbecco modified Eagle medium/Ham F12 (DMEM/F12) medium containing 5%% fetal calf serum, about 36%% of the mouse Sertoli cells, identified by their immunohistochemical staining for the Sertoli cell marker vimentin, incorporated bromodeoxyuridine (BrdU). The renewed proliferation was associated with a 70%% decrease in expression of the cell cycle inhibitor CDKN1B (P27(kip1)) and a 2-fold increase in the levels of the proliferation inducer ID2. In vivo, the balance between cell cycle inhibitors and inducers probably is such that the cells remain quiescent, whereas in culture the balance is disturbed such that Sertoli cells start to proliferate again. The renewed proliferative activity of Sertoli cells in culture was further confirmed by double staining for BrdU and the Sertoli cell marker clusterin (CLU), showing about 25%% of the CLU-positive Sertoli cells to be also positive for BrdU after 13 days of culture. Radiobiologically, Sertoli cells are also different from other quiescent somatic cells in the testis because they express several DNA repair proteins (XRCC1, PARP1, and others). Indeed, a comet assay on irradiated Sertoli cells revealed a 70%% reduction in tail length and tail moment at 20 h after irradiation. Hence, Sertoli cells repair DNA damage, whereas other quiescent somatic testicular cells do not. This repair may be accomplished by nonhomologous end joining via XRCC1 and PARP1. In conclusion, cell kinetic and radiobiological data indicate that Sertoli cells more resemble arrested proliferating cells than the classic postmitotic and terminally differentiated somatic cells that they have always been assumed to be.

Ku70 and non-homologous end joining protect testicular cells from DNA damage

“…Furthermore, it is possible that the action of reactive oxygen species might have induced accumulation of DNA damage in this cell type. However, because other NHEJ-deficient testicular cells did not display such large DNA damage foci, we consider it likely that these damage foci result from replication stress during the prepuberal Sertoli proliferation that remains irreparable in absence of NHEJ, the major repair pathway of cell cyclearrested Sertoli cells (Ahmed et al, 2009;Ahmed et al, 2007).…”

Microbiota and the control of blood-tissue barriers

“…22 Thus, in adult mammals the number of Sertoli cells is thought to remain relatively constant, 19,22 although there are reports that these cells can proliferate and divide in adult rodents under experimental conditions 23 and even under physiological conditions in humans. 24 The number of Sertoli cells determines the number of germ cells that can be supported during spermatogenesis and thus sperm production and the sperm count in adulthood. 21,22 Sertoli cells are highly dynamic, changing their 3-dimensional structure during the course of spermatogenesis and spermiogenesis.…”

17β-estradiol signaling and regulation of Sertoli cell function

“…52 The Sertoli cell population remains relatively constant in adult mammals, and each Sertoli cell supports approximately 30-50 germ cells at different stages of development in the seminiferous epithelium. 53 However, recent studies have shown that Sertoli cells are capable of dividing even in adult animals, including rats, 54 mice 55 and humans, 55,56 under experimental and even physiological conditions.…”