miR-205 Expression Elevated With EDS Treatment and Induced Leydig Cell Apoptosis by Targeting RAP2B via the PI3K/AKT Signaling Pathway

Leydig cells (LCs) are thought to differentiate from spindle-shaped precursor cells that exhibit some aspects of differentiated function, including 3beta-hydroxysteroid dehydrogenase (3betaHSD) activity. The precursor cells ultimately derive from undifferentiated stem LCs (SLCs), which are postulated to be present in testes before the onset of precursor cell differentiation. We searched for cells in the neonatal rat testis with the abilities to: (i) proliferate and expand indefinitely in vitro (self renew); (ii) differentiate (i.e., 3betaHSD and ultimately synthesize testosterone); and (iii) when transplanted into host rat testes, colonize the interstitium and subsequently differentiate in vivo. At 1 week postpartum, spindle-shaped cells were seen in the testicular interstitium that differed from the precursor cells in that they were 3betaHSD-negative, luteinizing hormone (LH) receptor (LHR)-negative, and platelet-derived growth factor receptor alpha (PDGFR alpha)-positive. These cells were purified from the testes of 1-week-old rats. The cells contained proteins known to be involved in LC development, including GATA4, c-kit receptor, and leukemia inhibitory factor receptor. The putative SLCs expanded over the course of 6 months while remaining undifferentiated. When treated in media that contained thyroid hormone, insulin-like growth factor I, and LH, 40% of the putative SLCs came to express 3betaHSD and to synthesize testosterone. When transplanted into host rat testes from which LCs had been eliminated, the putative SLCs colonized the interstitium and subsequently expressed 3betaHSD, demonstrating their ability to differentiate in vivo. We conclude that these cells are likely to be the sought-after SLCs.

Leydig cells are the testosterone-producing cells of the testis. The adult Leydig cell population ultimately develops from undifferentiated mesenchymal-like stem cells present in the interstitial compartment of the neonatal testis. Four distinct stages of adult Leydig cell development have been identified and characterized: stem Leydig cells, progenitor Leydig cells, immature Leydig cells and adult Leydig cells. The stem Leydig cells are undifferentiated cells that are capable of indefinite self-renewal, differentiation, and replenishment of the Leydig cell niche. Progenitor Leydig cells are derived from the stem Leydig cells. These spindle-shaped cells are luteinizing hormone (LH) receptor positive, have high mitotic activity, and produce little testosterone but rather testosterone metabolites. The progenitor Leydig cells give rise to immature Leydig cells which are round, contain large amounts of smooth endoplasmic reticulum, and produce some testosterone but also very high levels of testosterone metabolites. A single division of these cells produces adult Leydig cells, which are terminally differentiated cells that produce high levels of testosterone. As men age, serum testosterone levels decline, and this is associated with alterations in body composition, energy level, muscle strength, physical, sexual and cognitive functions, and mood. In the Brown Norway rat, used extensively as a model for male reproductive aging, age-related reductions in serum testosterone result from significant decline in the ability of aged Leydig cells to produce testosterone in response to LH stimulation. This review describes Leydig cell development and aging. Additionally, the molecular mechanisms by which testosterone synthesis declines with aging are discussed.