REGULATION BY THYROID-HORMONE OF THE EXPRESSION OF BASEMENT-MEMBRANE COMPONENTS IN RAT PREPUBERTAL SERTOLI CELLS

The present study reports the modulation of basement membrane (BM) com ponents, laminin, entactin, and type IV collagen, expression in prepub ertal rat Sertoli cell by the thyroid hormone T-3. Immunocytochemical studies of permeabilized Sertoli cells in culture showed that T-3 trea tment (10(-7) M for 24 h) increased the number of cells staining posit ive for laminin and/or entactin (from 58 +/- 5.3% to 86.4 +/- 6.5%, P < 0.01). In contrast, a strong inhibition of type IT collagen immunopo sitivity was observed. Western blot analysis of Sertoli cell-condition ed media indicated that T-3 treatment significantly (P < 0.01) increas ed the level of secreted entactin by 60-65% without affecting the leve ls of laminin A and B-1/B-2 chains. Moreover, thyroid hormone treatmen t of Sertoli cells significantly reduced type IV collagen secretion by 62% (P < 0.05). Slot blot analysis of poly-A RNA demonstrated a signi ficant (P < 0.01) increase in the level of entactin messenger RNA (mRN A) by 140% (P < 0.01) and a 50% reduction of type SV collagen al chain mRNA after thyroid hormone treatment. No effect of the hormone was ob served on the accumulation of the laminin B1 and B2 chain mRNAs in Ser toli cell cultures. These effects cannot be ascribed to changes in the degradation of BM components, because no effect of thyroid hormone wa s observed on plasminogen activators or metalloproteinase secretion by Sertoli cells. These observations indicate the Sertoli cell as a sour ce of entactin within the testis, demonstrate the ability of T-3 to di fferentially regulate the expression of BM components, and can be rega rded as a part of the integrated mechanism by which thyroid hormone af fects testicular development and differentiation.