Regulation of (alpha)2-Macroglobulin Expression in Rat Sertoli Cells and Hepatocytes by Germ Cells In Vitro

Germ cells isolated from rat testes by trypsinization have been shown to yield unwanted artifacts in biological assays, since conditioned media derived from these germ cells (germ cell-conditioned media [GCCM]) can modulate Sertoli cell secretory function because of the presence of residual trypsin. To determine whether germ cells themselves can modulate Sertoli cell function, we isolated germ cells from tubules by a mechanical procedure and assessed the effect of these cells on Sertoli cell (alpha)2-macroglobulin ((alpha)2-MG) steady-state mRNA level. It was found that germ cells indeed could stimulate Sertoli cell (alpha)2-MG expression. This effect is probably mediated by a soluble factor(s) released from germ cells, since GCCM fractionated by HPLC contained multiple fractions that can stimulate Sertoli cell (alpha)2-MG expression dose-dependently. These results illustrate that germ cells play a role in regulating testicular (alpha)2-MG expression. Since Sertoli cells synthesize and secrete many of the serum proteins behind the blood-testis barrier that are also produced by hepatocytes, we sought to ascertain whether germ cells can affect hepatic (alpha)2-MG expression. When germ cells were cocultured with hepatocytes isolated from adult rats, the hepatocyte (alpha)2-MG steady-state mRNA level was shown to be stimulated by germ cells dose-dependently. Using different pools of fractions derived from GCCM after their fractionation by a preparative anion-exchange HPLC column, GCCM was found to contain a factor(s) that stimulated hepatocyte (alpha)2-MG expression dose-dependently. More importantly, the fractions that stimulated hepatocyte (alpha)2-MG expression had a retention time different from that of the factor(s) that affected Sertoli cell (alpha)2-MG expression. These data illustrate that germ cells secrete multiple biological factors capable of regulating (alpha)2-MG expression in the testis and the liver. In summary, this study reveals a possible physiological link between the testis and the liver in that germ cells may release a factor(s) capable of modulating (alpha)2-MG expression in both organs.