Participation of the Fas-signaling system in the initiation of germ cell apoptosis in young rat testes after exposure to mono-(2-ethylhexyl) phthalate

The Fas-signaling system is composed of the interacting proteins Fas (CD95/ APO-1) and Fas ligand (FasL, CD95L, APO-1L) and is proposed to act in the t estis as a paracrine signaling mechanism by which Fast-expressing Sertoli c ells initiate apoptosis of Fas-bearing germ cells. Here we describe alterat ions in the expression of Fas and Fast in the testis after the intimate phy sical association between Sertoli cells and germ cells is disrupted by expo sure to the Sertoli cell toxicant mono-2-(ethylhexyl) phthalate (MEHP). You ng, 28-day-old Fisher rats were treated with MEHP (2 g/kg po) and killed 0, 3, 6, and 12 h after exposure. Immunohistochemical analyses revealed a sig nificant increase in the numbers of Fas-positive germ cells as well as incr eases in the expression of Sertoli cell Fast. Western blot analysis demonst rated a time-dependent increase in the production of the soluble form of Fa st after MEHP exposure and suggests that it may participate in triggering a poptosis in germ cells that have lost their intimate association with the S ertoli cells. Measurement of Fas in cytosolic and membrane fractions of tes tis homogenates by Western blot analysis revealed a significant shift of Fa s expression into the membrane fraction after MEHP exposure. Taken together , these observations indicate that the Fas-mediated paracsine signaling mec hanism participates in triggering apoptosis of germ cells despite the loss of their close physical association with Sertoli cells. A working model is presented to explain the involvement of the Fas-system in stimulating germ cell apoptosis after MEHP exposure. (C) 1999 Academic Press.