E2 regulates several germ cell genes via EREs (demonstrated by CHIP assays), including repressed transcripts TPs and P (demonstrated by real-time PCR) in PPT/DPN-treated rats, that are eventually stored in the chromatoid body 15, 16, 33, 70. Free T could enter Sertoli cells by diffusion but its lipophilic nature would limit intracellular bioavailability . Conventional mechanism of intravascular T action involving induction of Calcium influxes via non-genomic AR on Sertoli cells leading to CaM/CaMKIV/CREB activation 66-69. Leydig cells secrete lipophilic hormone T in peripheral circulation 64, 65. Development of mice lacking androgen-binding protein would be the ideal approach to study its role in iT retention and storage . For example, transcription factors including Krüppel-like factor 4 (KLF4) , nuclear factor (NF)-κB , and activator protein-1 (AP-1) are involved in the regulation of Sertoli cell differentiation by FSH. Furthermore, FSH targets functional factors and transcription factors through the cAMP/PKA pathway to affect Sertoli cell differentiation and apoptosis 76,77. The suppression of FSH in neonates reduces the number of final Sertoli cells by approximately 40% , which in turn affects the quantity of sperm. FSH-induced signal transduction is mediated by FSHR, and its function reliant on interactions with numerous intracellular effectors. Interestingly, the role of androgens in establishing normal reproductive tract development and the masculinization of anogenital distance (AGD) is limited to a specific developmental window, known as the "masculinization programming window" (MPW). In males, these are usual late pubertal effects, and occur in women after prolonged periods of heightened levels of free testosterone in the blood. Pubertal effects begin to occur when androgen has been higher than normal adult female levels for months or years. For postnatal effects in both males and females, these are mostly dependent on the levels and duration of circulating free testosterone. In general, androgens such as testosterone promote protein synthesis and thus growth of tissues with androgen receptors. As the metabolism of testosterone in males is more pronounced, the daily production is about 20 times greater in men. Once through the BTB, the germ cells continue to develop into spermatozoa in a defined, protected microenvironment. Sertoli cells contribute to the niche required to maintain the renewal of spermatogonial stem cells so that developing germ cells can be produced continuously. Spermatogenesis is supported by somatic Sertoli cells that surround and nurture the developing germ cells. At the tissue level, testosterone dissociates from albumin and quickly diffuses into the tissues. This binding plays an important role in regulating the transport, tissue delivery, bioactivity, and metabolism of testosterone. As a result, testosterone which is not bound to SHBG is called free testosterone. Specific proteins include sex hormone-binding globulin (SHBG), which binds testosterone, dihydrotestosterone, estradiol, and other sex steroids. Lipophilic hormones (soluble in lipids but not in water), such as steroid hormones, including testosterone, are transported in water-based blood plasma through specific and non-specific proteins. Fairer offers from test subjects with higher testosterone in the original study increase the likeliness of the offer being accepted by the negotiating partner, therefore decreasing the probability of both participants leaving without any money. Similarly, it has been described that T3 also stimulates the maturation of Sertoli cells in vitro implying that T3 can terminates Sertoli cell proliferation and favors the terminal maturation of Sertoli cells (132). Some studies demonstrated that T3 treatment can reduce Sertoli cell proliferation activity, as well as Sertoli cell proliferation period and Sertoli cell number (88, 128, 131). Interestingly, animal model studies with disrupted interleukin or tumor necrosis factors displayed no obvious alterations in testicular development. Notably, IL-1 activity in Sertoli cells can be specifically neutralized by IL-1α antiserum, implying that IL-1α is the major isoform of IL-1 in Sertoli cells (17). Furthermore, it was also noted that only IL-1, neither IL-6 nor TNF-α, enhanced lactate production and secretion during Sertoli cell proliferation (1).
