Cell death induced by zinc and cadmium is mediated by clusterin in cultured mouse seminiferous tubules

Abstract

Sertoli cells, lining the walls of the seminiferous tubules, are in close contact with and regulate all aspects of the development of the germ cells. Clusterin, is a glycoprotein produced abundantly by Sertoli cells, and associated with either apoptosis or cell survival. Zinc is present in high concentrations in the testis and required for sperm development by an as yet unknown mechanism. Permeation of zinc into cells via voltage-gated calcium channels (VGCCs), however, is suggested to induce cell death. We examined the possibility that Zn(2+) acts via clusterin to regulate germ cell survival. Employing an ex vivo model of mouse testis, we have assessed the role of permeation of heavy metal ions on clusterin production and secretion. Up-regulation of clusterin expression and its secretion was observed after a short exposure to zinc or to cadmium under depolarizing conditions. Expression of zinc transporter-1 (ZnT-1), previously shown to regulate Zn(2+) influx, increased following prolonged application of zinc or cadmium to the explants and prevented clusterin up-regulation by subsequent exposure to these ions. Inhibition of the MAPK and PI3K pathways reduced the up-regulation of clusterin following the intracellular rise of Zn(2+) or Cd(2+). Neutralization of secreted clusterin by an antibody or attenuation of clusterin up-regulation by inhibition of Zn(2+) permeation via the LTCC, reduced cell death in cultured seminiferous tubule cells. Taken together, our results indicate that Zn(2+) and Cd(2+) influx induce expression and secretion of clusterin, thereby linking metal homeostasis and germ cell fate.