Loss of Smad4 in Sertoli and Leydig Cells Leads to Testicular Dysgenesis and Hemorrhagic Tumor Formation in Mice1

Abstract

As the central component of canonical TGFbeta superfamily signaling, SMAD4 is a critical regulator of organ development, patterning, tumorigenesis, and many other biological processes. Because numerous TGFbeta superfamily ligands are expressed in developing testes, there may exist specific requirements for SMAD4 in individual testicular cell types. Previously, we reported that expansion of the fetal testis cords requires expression of SMAD4 by the Sertoli cell lineage. To further uncover the role of Smad4 in murine testes, we produced conditional knockout mice lacking Smad4 in either Leydig cells or in both Sertoli and Leydig cells simultaneously. Loss of Smad4 concomitantly in Sertoli and Leydig cells led to underdevelopment of the testis cords during fetal life and mild testicular dysgenesis in young adulthood (decreased testis size, partially dysgenic seminiferous tubules, and low sperm production). When the Sertoli/Leydig cell Smad4 conditional knockout mice aged (56- to 62-wk old), the testis phenotypes became exacerbated with the appearance of hemorrhagic tumors, Leydig cell adenomas, and a complete loss of spermatogenesis. In contrast, loss of Smad4 in Leydig cells alone did not appreciably alter fetal and adult testis development. Our findings support a cell type-specific requirement of Smad4 in testis development and suppression of testicular tumors.

Multiple signaling pathways in Sertoli cells: recent findings in spermatogenesis

“…Although Smad1, 3, 5, 6, 7, 8 express discriminately at birth, stages V, VII, VIII, XV, and adult based on immunohistochemical detection and RT-PCR results, Smad4 are distributed within SCs at all ages in mice and domestic fowl [60][61][62][63] . When Smad4 was conditionally deleted in mouse Sertoli cells, the fertility of mutant mouse was impaired with smaller testis size and decreased sperm production at adult 64 . The various trends of Smad expression and deleted phenotype demonstrate that the TGF-β/Smad signaling pathway occupies a continuous crucial position for SCs function during spermatogenesis, while different members of the TGF-β superfamily may perform their functions at different stages ( Fig.…”

“…Smad4, the Co-Smad in the TGF-β/Smad signaling pathway, may serve as a key mediator in Leydig cell adenomas. When Smad4 was conditionally knocked out in mouse Sertoli cells and Leydig cells, 87.5% of the mutant mice exhibited Leydig cell adenomas at 56-62 weeks of age 64 . After the BR-SMADs (Smad1, 5) in mice SCs is deleted via tissuespecific ablation, all male Smad1/Smad5 KO mice (14 samples) developed Sertoli-Leydig tumors after 28 weeks of age with 100% metastases to lymph and peritonea, implicating the role of the BR-SMAD signaling pathway as a tumor suppressor in testis 155 .…”

Novel Targets for the Transcription Factors MEF2 in MA-10 Leydig Cells1

“…SMAD4 (mothers against decapentaplegic homolog 4) belongs to the SMAD family of transcription factors that are induced by members of the TGFb superfamily of growth factors, several of which are essential for testis development (reviewed in [34]). Smad4 knockout in Sertoli and Leydig cells leads to abnormal formation of testis cords, seminiferous tubules, and vasculature during embryogenesis [35]. In aging Sertoli/Leydig-specific Smad4 knockout mice, the testes hemorrhage, develop tumors, including Leydig cell adenoma, and spermatogenesis is arrested [35].…”

“…Smad4 knockout in Sertoli and Leydig cells leads to abnormal formation of testis cords, seminiferous tubules, and vasculature during embryogenesis [35]. In aging Sertoli/Leydig-specific Smad4 knockout mice, the testes hemorrhage, develop tumors, including Leydig cell adenoma, and spermatogenesis is arrested [35]. Overexpression of SMAD4 also leads to testis defects and fertility issues, and these mice exhibit Leydig cell hyperplasia [36].…”

Establishment of fetal Sertoli cells and their role in testis morphogenesis

“…Early Sertoli cell proliferation and testis morphogenesis programs rely heavily on signals from the Sertoli cells themselves (i.e., FGF9); however, the so-called second wave of Sertoli cell proliferation that underlies testis cord elongation is dependent on signals produced by fetal Leydig cells. Interestingly, the cord defects of conditional Smad4 knockout fetal testes became more severe as the animals aged and manifested as stromal cell testicular tumors in a high portion of animals by 1 year of age [149]. Sertoli cell proliferation was reduced in mutant embryos at E19.5 and testis cords exhibited abnormal coiling.…”