Steroid metabolism by purified adult rat Leydig cells in primary culture

Identification and functional characterization of microRNAs in rat Leydig cells during development from the progenitor to the adult stage

The aim of the present study was to identify microRNAs (miRNAs) that regulate the proliferation and differentiation of Leydig cells (LCs) of rat. Three small RNA libraries derived from progenitor LCs (PLCs), immature LCs (ILCs) and adult LCs (ALCs) were analyzed by microarrays. In total, 68 differentially expressed miRNAs (DEMs) were identified. Based on the trend of DEM expression from PLCs to ALCs, primary LCs were transfected with miRNA mimics or inhibitors. Five miRNAs (miR-30a-5p, miR-3585-5p, miR-212-3p, miR-369-5p and miR-434-3p) promoted PLC proliferation, and 3 miRNAs (miR-17-5p, miR-532-3p and miR-329-3p) activated caspase-3, which triggered LC apoptosis. For steroidogenesis, 18 miRNAs could elevate or inhibit androsterone release at the PLC stage. Eleven and 9 miRNAs inhibited the production of 5α-androstane-3α,17β-diol in ILCs and testosterone in ALCs, respectively. miR-17-5p, miR-29a-3p and miR-299a-5p decreased androgen production by LCs at all developmental stages. Furthermore, the miR-299a-5p-mediated decrease in androgen production by the LC lineage was primarily achieved by downregulating the expression of luteinizing hormone/choriogonadotropin receptor (LHCGR) and 3β-hydroxysteroid dehydrogenase 1 (HSD3B1). These findings provide insights into the regulatory roles of miRNAs during the postnatal development of LCs and suggest potential strategies for the treatment of steroid-related disorders.

Disruption of NHE8 expression impairs Leydig cell function in the testes

Multiple sodium/hydrogen exchanger (NHE) isoforms are expressed in the testes, and they play various roles in cell volume regulation, intracellular pH regulation, and fluid absorption. NHE8, the most recently characterized NHE family member, is detected in the Leydig cells in humans and mice in great abundance by immunohistochemistry in the current study. Male mice lacking NHE8 expression were infertile. Despite having intact male reproductive organs, male NHE8-/- mice have smaller testes and lacked spermatozoon in the seminiferous tubules and the epididymis. At the age of 39 wk, few spermogonia were seen in the testis in NHE8-/- mice. Although male NHE8-/- mice have normal serum levels of luteinizing hormone and follicle-stimulating hormone, serum testosterone level was significantly reduced. These mice have decreased expression of luteinizing hormone receptor in the testes. In NHE8 small-interfering RNA-transfected mouse Leydig cells (MLTC-1), silencing of NHE8 decreased the expression of luteinizing hormone receptor by ∼70%. Moreover, loss of NHE8 function in Leydig cells resulted in disorganized luteinizing hormone receptor membrane distribution. Therefore, male infertility in NHE8-/- mice is at least partially due to the disruption of luteinizing hormone receptor distribution and consequent low testosterone production, which leads to Sertoli cell dysfunction. Our work identified a novel role of NHE8 in male fertility through its effect on modifying luteinizing hormone receptor function.

Simple approach to measure metabolic pathways of steroids in living cells

A simple, rapid approach to the study of conversion rates and metabolic patterns of the steroids testosterone and estradiol is presented. It includes an optimized isocratic high-performance liquid chromatographic procedure in the reversed-phase mode and radioactive on-line detection. The purpose was to estimate the activity of key enzymes of steroid pathways, such as 17 beta-hydroxysteroid dehydrogenase and 5 alpha-reductase, in in vivo conditions. Using this system, we obtained good efficiency and linearity of radio detection, under continuous flow conditions. Sensitivity limits were of the order of 50 and 70 cpm for [3H]estradiol and [14C]estrone, respectively, even though the efficiency was quite dissimilar (17.3% versus 56.2%). The applicability of this approach to studies of steroid metabolic pathways in growing cancer cells in culture is illustrated with examples of the conversion rates of both testosterone and estradiol. The high reproducibility (coefficients of variation of 2.7 and 5.1% for 3H and 14C, respectively) and good extraction efficiency (ranging from 86 to 94%) indicate the feasibility and reliability of this approach.

The effects of reduced O2 and antioxidants on steroidogenic capacity of cultured rat Leydig cells

We have examined the effects of reduced O2 tension and the antioxidant dimethylsulfoxide (DMSO) to determine if O2-derived free radicals are the cause of decreased steroidogenic capacity (testosterone and progesterone production) of cultured rat Leydig cells. Rat Leydig cells were initially cultured under standard conditions of 5% CO2, 95% air (19% O2) with or without DMSO. Addition of DMSO resulted in increased basal testosterone production on days 2, 3 and 4 of culture. hCG (10 mIU)-stimulated testosterone secretion was 2-3 times greater on days 2 and 3 in the presence of DMSO. Lowering the O2 concentration to 5% in the presence of DMSO resulted in even greater hCG-stimulated testosterone production on days 1 to 3. However, the effect of DMSO or low O2 and DMSO were not seen after 5 days. The reduced O2 concentration resulted in an increase in hCG (10 mIU)-stimulated progesterone synthesis throughout the culture, particularly on days 4 to 8. Also, when total steroid (progesterone and testosterone) was determined, cells cultured under reduced O2 conditions responded with increased steroid production on days 1 to 8 in comparison to controls (19% O2). These results demonstrate that lowered O2 concentration and DMSO provide a protective effect resulting in the maintenance of testosterone production and an increase in progesterone synthesis. These findings suggest that free radical-mediated damage of enzymes may result in decreased steroidogenic capacity of cultured Leydig cells.

[3H]Oestradiol metabolism by 18-day rat interstitial cells in culture and the effect of FSH: presence of 16 alpha-hydroxylase

The metabolism of [3H]oestradiol by interstitial cells in culture prepared from 18-day old rat testes was investigated. Interstitial cells were able to convert [3H]oestradiol to [3H]oestriol as confirmed by recrystallization of oestriol to constant specific activity from samples containing cells and not from controls. This demonstrated for the first time the presence of 16 alpha-hydroxylase in rat testicular interstitial cells. The effect of in vitro FSH treatment on the cells in culture was also investigated. FSH failed to affect 16 alpha-hydroxylase activity since we could not demonstrate a significant difference between treated and untreated preparations. The 16 alpha-hydroxylation of phenolic steroids is widely regarded as the major pathway of oestrogen metabolism in mammals. This metabolic step significantly reduces the biological activity of oestradiol. The presence of 16 alpha-hydroxylase in interstitial cells suggests that it may play a role in inactivating the oestradiol that is produced in the Leydig cells and thus prevent its intracellular accumulation. Such activity may conceivably play a role in the overall local "fine tuning" of androgen biosynthesis.