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) components, laminin, entactin, and type IV collagen, expression in prepubertal rat Sertoli cell by the thyroid hormone T-3. Immunocytochemical studies of permeabilized Sertoli cells in culture showed that T-3 treatment (10(-7) M for 24 h) increased the number of cells staining positive 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 immunopositivity was observed. Western blot analysis of Sertoli cell-conditioned media indicated that T-3 treatment significantly (P < 0.01) increased the level of secreted entactin by 60-65% without affecting the levels of laminin A and B-1/B-2 chains. Moreover, thyroid hormone treatment of Sertoli cells significantly reduced type IV collagen secretion by 62% (P < 0.05). Slot blot analysis of poly-A RNA demonstrated a significant (P < 0.01) increase in the level of entactin messenger RNA (mRNA) 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 observed on the accumulation of the laminin B1 and B2 chain mRNAs in Sertoli cell cultures. These effects cannot be ascribed to changes in the degradation of BM components, because no effect of thyroid hormone was observed on plasminogen activators or metalloproteinase secretion by Sertoli cells. These observations indicate the Sertoli cell as a source of entactin within the testis, demonstrate the ability of T-3 to differentially regulate the expression of BM components, and can be regarded as a part of the integrated mechanism by which thyroid hormone affects testicular development and differentiation.