Transferrin-2, partial

CP-2/cathepsin L mRNA is expressed primarily by rat Sertoli cells within stage VI-VIII seminiferous tubules. To test whether germ cells regulated this expression, we examined if separating Sertoli cells from specific germ cells affected expression of this transcript in Sertoli cells. First, Sertoli cells were isolated from adult (90-day-old) and immature (25-day-old) rats and levels of this transcript measured immediately or after 1, 3 and 5 days in culture. Results demonstrated that immediately upon isolation, CP-2/cathepsin L mRNA levels were significantly higher in mature cells. However, after 1 day in culture, the levels of this transcript increased in immature cells and remained high in mature cells. We therefore conclude that in vivo, a subset of germ cells inhibit the expression of CP-2/cathepsin L mRNA by immature Sertoli cells. Second, to examine the effect of specific germ cells on CP-2/cathepsin L mRNA expression, we exposed the testes of mature rats to 3 Gy of gamma-radiation and analyzed stage-specific expression of this transcript at varying times during maturation depletion and subsequent germ cell restoration. Loss of spermatogonia or spermatocytes was without effect. However, when pachytene spermatocytes through step 14 spermatids were depleted, expression at stages VI-VIII was reduced by half and expression at stages IX-I was increased 14-fold. These changes resulted in the loss of stage-specific expression of CP-2/cathepsin L mRNA by Sertoli cells. Finally, stage VI-VIII tubules, depleted primarily in step 15-19 spermatids, had levels of CP-2/cathepsin L mRNA that were 60% of control. However, stage-specific expression of this transcript was detected in these tubules. In contrast to what we noted with CP-2/cathepsin L mRNA, loss and restoration of germ cells had no effect on Sertoli cell levels of SGP-2 mRNA, indicating that testicular irradiation had no overall effect on Sertoli cell function. Taken together, these data suggest that the stage-specific expression of the CP-2/cathepsin L gene results from the sequential stimulation and inhibition of Sertoli cells by germ cells, that pachytene spermatocytes through step 14 spermatids are required for this stage-specific expression and that step 18 and 19 spermatids amplify this expression at stages VI-VIII.

Using multiple high-performance liquid chromatography (HPLC) steps and high-performance electrophoresis chromatography (HPEC) in conjunction with an [125I]collagen film assay to identify inhibitors of metalloproteases, we have purified a 22-kDa polypeptide to apparent homogeneity from primary Sertoli cell-enriched culture medium. Partial N-terminal amino acid sequence analysis revealed that this protein is similar to the human tissue inhibitor of metalloproteases-2 (TIMP-2). To determine the similarity of rat testicular TIMP-2 to the human homolog, a full-length cDNA coding for rat testicular TIMP-2 was isolated from a rat Sertoli cell cDNA expression library and sequenced. Analysis of the nucleotide sequence and the deduced amino acid sequence of the rat testicular TIMP-2 cDNA revealed an 84 and 98% homology with the human TIMP-2 nucleotide and amino acid sequences, respectively. A survey of its mRNA transcripts in different tissues by northern blots revealed the presence of two mRNA species of 3.7 and 1.3 kb in the testis and brain but not in the kidney, spleen, epididymis, and liver in adult male rats. Studies using polymerase chain reaction (PCR) and Southern blot to detect the TIMP-2 mRNA using total RNA isolated from germ cells, Sertoli cells, and Leydig cells have shown that only Sertoli and Leydig cells expressed TIMP-2 mRNA. These results indicate that Sertoli cells are the major source of TIMP-2 in the testis behind the blood-testis barrier (seminiferous tubule barrier). During testicular development from 3 to 60 days of age, the testicular steady-state TIMP-2 mRNA level increased steadily with an advancement of age. Such an increase in the steady-state testicular TIMP-2 mRNA level apparently is not the result of an up-regulation by germ cells because germ cells cocultured with Sertoli cells failed to elicit an increase in the Sertoli cell steady-state TIMP-2 mRNA level. The results of this study suggest that TIMP-2 secreted by Sertoli cells may play a role in tissue restructuring and germ cell migration during spermatogenesis.

The present study investigated the time course of the onset of the abnormalities in spermatogenesis following spinal cord injury, and their relationship to changes in the pituitary testicular hormonal axis and Sertoli cell function. Spinal cord injury (SCI) was induced in adult male rats by surgical transection of the spinal cord at the level of T9 and L1 vertebrae. Animals were killed 3, 7, and 14 days after the operation. As early as 3 days following SCI, abnormalities in spermatogenesis, including delayed spermiation and vacuolization of the nucleus of spermatids, were noted in both the T9 and L1 animals. By 14 days, other lesions, including phagocytosis of mature spermatids, incomplete cellular associations, and total regression of seminiferous epithelium, became apparent. Concurrently a transient but significant (P < 0.05) suppression of serum follicle-stimulating hormone (FSH) occurred in the T9 animals, and a suppression of serum luteinizing hormone (LH) occurred in both the T9 and the L1 animals 3 days after the surgery. This was accompanied by a suppression of testicular and serum testosterone levels (P < 0.05, P < 0.01, respectively). Most of the hormonal parameters had recovered and were not different from those of sham-operated animals by 14 days (P > 0.10). Northern blot analysis of testicular poly(A)+ RNA revealed a transient but significant reduction in the steady-state level of the 2.7-kilobase (kb) Sertoli cell transferrin mRNA transcript in both the T9 and the L1 animals 3 days after the operation (P < 0.05). On the other hand, the 1.7-kb androgen binding protein (ABP) mRNA remained unaffected during the 2-week study period. The steady-state level of mRNA transcripts for spermatogenic cell-specific hemiferrin and spermatid specific transition protein 2 and protamine 1 also remained unchanged. These results suggest that spinal cord injury will result in a temporary, but profound, effect on the pituitary-testicular hormone axis. These changes may impair certain aspects of Sertoli cell function that could render these cells incapable of supporting normal spermatogenesis. However, the severity of spermatogenic lesions and the disparate responses of the two major Sertoli cell proteins make it unlikely that hormone deficiency is the only mechanism responsible for the impaired spermatogenesis following spinal cord injury.