Role of platelet-derived growth factors in the testis.

Normal development and function of the testis are controlled by endocrine and paracrine signaling pathways. Platelet-derived growth factors (PDGFs) are growth factors that mediate epithelial-mesenchymal interactions in various tissues during normal and abnormal processes such as embryo development, wound healing, tissue fibrosis, vascular disorders, and cancer. PDGFs and their receptors (PDGFRs) have emerged as key players in the regulation of embryonic and postnatal development of the male gonad. Cells that express PDGFs and PDGFRs are found in the testis of mammals, birds, and reptiles, and their distribution, regulation, and function vary across species. Testicular PDGFs and PDGFRs appear after the process of sex determination in animals that use either genetic sex determination or environmental sex determination. Sertoli cells are the main PDGF-producing cells during the entire period of prenatal and postnatal testis development. Fetal Leydig cells and their precursors, adult Leydig cells and their stem cell precursors, peritubular myoid cells, cells of the blood vessels, and gonocytes are the testicular cell types expressing PDGFRs. Genetically targeted deletions of PDGFs, PDGFRs, PDGFR target genes or pharmacological silencing of PDGF signaling produce profound damage on the target cells that, depending on the developmental period, are under direct or indirect control of PDGF. PDGF signaling may also serve diverse functions outside of the realm of testis development, including testicular tumors. In this review, we provide a framework of the current knowledge to clarify the useful information regarding how PDGFs function in individual cells of the testis.