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Role of Tissue Inhibitor of Metalloproteases-1 in Junction Dynamics in the Testis

From the Population Council, Center for Biomedical Research, New York, New York.

Correspondence to: Dolores D. Mruk, Ph.D., Population Council, Center for Biomedical Research, 1230 York Avenue, New York, NY 10021.

Using multiple high-performance liquid chromatography steps, we have identified and purified a polypeptide to apparent homogeneity from primary Sertoli cell conditioned culture medium that consisted of 2 molecular variants of 31 and 29 kDa when electrophoresed on a sodium dodecyl sulfate–polyacrylamide gel run under reducing conditions. Partial N-terminal amino acid sequence analysis of these 2 proteins revealed a sequence of NH₂-IKMAKMLKGFDAVGNATG, which is homologous to tissue inhibitor of metalloproteases-1 (TIMP-1). Studies by semiquantitative reverse transcription-polymerase chain reaction using a primer pair specific to rat TIMP-1 demonstrated that both Sertoli and germ cells express TIMP-1. During maturation, the steady-state TIMP-1 mRNA level in the testis increased significantly from 40 to 60 days of age, which suggests its role in the restructuring of the epithelium during spermiation. This increase in testicular TIMP-1 expression was apparently not due to the increase in germ cell number, because TIMP-1 expression decreased approximately fivefold in germ cells isolated from testes of aging rats. Using Sertoli cells cultured at low (0.05 x 10⁶ cells/cm²) and high (0.5 x 10⁶ cells/cm²) densities, it was found that TIMP-1 expression increased transiently but significantly during junction assembly. A similar induction of TIMP-1 mRNA was also detected in Sertoli–germ cell cocultures during germ cell adhesion onto Sertoli cells. More important, the inclusion of either ₂-macroglobulin (a protease inhibitor produced by Sertoli cells) or aprotinin (a serine protease inhibitor) into an in vitro germ cell adhesion assay facilitated the attachment of fluorescently labeled germ cells onto the Sertoli cell epithelium when compared to control, which suggests that the assembly of adherens junctions may involve protease inhibitors.

     Key words: Protease inhibitor, Sertoli cell, germ cell, tight junction, adherens junction

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