Induction of apoptosis by 25-hydroxycholesterol in adult rat Leydig cells: protective effect of 17beta-estradiol.

Testicular macrophages can convert cholesterol into 25-hydroxycholesterol which strongly stimulates Leydig cell testosterone production. We demonstrated that 25-hydroxycholesterol reduced cholesterol biosynthesis in adult rat Leydig cells. This oxysterol can also be cytotoxic. As hydroxylated cholesterol can induce apoptosis in various cells, we investigated cell death produced by 25-hydroxycholesterol. Apoptosis was characterized by TUNEL assay and by DAPI test. Addition of 25-hydroxycholesterol, during 24h, induced a dose dependent increase of apoptosis. This effect was reduced by a treatment with a caspase-3 inhibitor (Ac-DEVD-CHO). 25-Hydroxycholesterol is known to stimulate testosterone production, but an increase of intracellular or culture medium testosterone level does not modify significantly the percentage of apoptotic cells. In contrast, addition of 17beta-estradiol (2 nM) induced a decrease of apoptotic cells. These data suggested that this oxysterol can be used by rat Leydig cells in culture for sterol metabolism, but also induces apoptosis which could be inhibited by 17beta-estradiol.