Specificity of a new lipid mediator produced by testicular and peritoneal macrophages on steroidogenesis

Pathogenic role of 25-hydroxycholesterol in cancer development and progression

Cholesterol is an essential lipid that serves several important functions, including maintaining the homeostasis of cells, acting as a precursor to bile acid and steroid hormones and preserving the stability of membrane lipid rafts. 25-hydroxycholesterol (25-HC) is a cholesterol derivative that may be formed from cholesterol. 25-HC is a crucial component in various biological activities, including cholesterol metabolism. In recent years, growing evidence has shown that 25-HC performs a critical function in the etiology of cancer, infectious diseases and autoimmune disorders. This review will summarize the latest findings regarding 25-HC, including its biogenesis, immunomodulatory properties and role in innate/adaptive immunity, inflammation and the development of various types of cancer.

Immune Cells as Critical Regulators of Steroidogenesis in the Testis and Beyond

Steroidogenesis is an essential biological process for embryonic development, reproduction, and adult health. While specific glandular cells, such as Leydig cells in the testis, are traditionally known to be the principal players in steroid hormone production, there are other cell types that contribute to the process of steroidogenesis. In particular, immune cells are often an important component of the cellular niche that is required for the production of steroid hormones. For several decades, studies have reported that testicular macrophages and Leydig cells are intimately associated and exhibit a dependency on the other cell type for their proper development; however, the mechanisms that underlie the functional relationship between macrophages and Leydig cells are unclear. Beyond the testis, in certain instances immune cells themselves, such as certain types of lymphocytes, are capable of steroid hormone production, thus highlighting the complexity and diversity that underlie steroidogenesis. In this review we will describe how immune cells are critical regulators of steroidogenesis in the testis and in extra-glandular locations, as well as discuss how this area of research offers opportunities to uncover new insights into steroid hormone production.

Regulation of Human Spermatogenesis

Human spermatogenesis (HS) is an intricate network of sequential processes responsible for the production of the male gamete, the spermatozoon. These processes take place in the seminiferous tubules (ST) of the testis, which are small tubular structures considered the functional units of the testes. Each human testicle contains approximately 600-1200 STs [1], and are capable of producing up to 275 million spermatozoa per day [2].

Building the mammalian testis: origins, differentiation, and assembly of the component cell populations

Development of testes in the mammalian embryo requires the formation and assembly of several cell types that allow these organs to achieve their roles in male reproduction and endocrine regulation. Testis development is unusual in that several cell types such as Sertoli, Leydig, and spermatogonial cells arise from bipotential precursors present in the precursor tissue, the genital ridge. These cell types do not differentiate independently but depend on signals from Sertoli cells that differentiate under the influence of transcription factors SRY and SOX9. While these steps are becoming better understood, the origins and roles of many testicular cell types and structures-including peritubular myoid cells, the tunica albuginea, the arterial and venous blood vasculature, lymphatic vessels, macrophages, and nerve cells-have remained unclear. This review synthesizes current knowledge of how the architecture of the testis unfolds and highlights the questions that remain to be explored, thus providing a roadmap for future studies that may help illuminate the causes of XY disorders of sex development, infertility, and testicular cancers.

Physiologic interactions between macrophages and Leydig cells

The purpose of this minireview is to present information concerning the morphologic and functional relationship between testicular macrophages and Leydig cells. Although data concerning the negative influence of macrophage-derived products on testicular Leydig cells exist, this review is focused on the stimulatory influences thought to be involved in the physiologic interactions between these two diverse cell types.

HLDF-6 peptide affects behavioral reactions and organism functions dependent on androgen hormones in normal and castrated male mice

The hexapeptide Thr-Gly-Glu-Asn-His-Arg (HLDF-6), which was first identified as an active fragment of the human leukemia differentiation factor (HLDF) molecule, displays differentiation-inducing, neuroprotective and anti-drug abuse activities. Most of its in vivo effects were revealed only on male animals. We have studied HLDF-6 effects on a variety of organism functions and behavioral reactions, which are known to be dependent on androgen steroid hormones, both on castrated and normal (sham-operated) animals. Male NMRI mice were castrated or sham-operated at the age of 55 days (after puberty). After that, HLDF-6 peptide was injected daily during 3 weeks, followed by behavioral, morphological and biochemical testing. HLDF-6 increased testosterone level (1.5- to 2-fold) both in sham-operated and castrated animals. Sexual activity and pain sensitivity, which are strongly reduced in castrates, were completely or partially recovered by HLDF-6. At the same time, the peptide caused some effects similar to castration in sham-operated animals: aggression and locomotor activity were decreased; oral grooming was prolonged. Morphological studies of accessory sex glands showed that HLDF-6 partially normalizes the morphology and functional activity of seminal vesicles in castrates, but it does not prevent castration-induced apoptosis of prostate epithelial cells. Based on these observations, we can assume that HLDF-6 peptide displays at least two effects on androgen hormones metabolism in males: it stimulates testosterone biosynthesis by both testes and adrenals and simultaneously inhibits its conversion to dihydrotestosterone (DHT), most probably by diminution of 5alpha-reductase isoform 1 mRNA expression.

Testosterone regulates 25-hydroxycholesterol production in testicular macrophages

Recently, we found that testicular macrophages produce 25-hydroxycholesterol (25-HC) and express 25-hydroxylase, the enzyme that converts cholesterol to 25-HC. In addition, 25-HC may be an important paracrine factor mediating the known interactions between macrophages and neighboring Leydig cells, because it is efficiently converted to testosterone by Leydig cells. The purpose of the present study was to determine if testosterone can regulate the production of 25-HC in rat testicular macrophages, representing a potential negative-feedback loop from Leydig cells. We found that expression of 25-hydroxylase mRNA and production of 25-HC by cultured testicular macrophages were significantly inhibited by testosterone at 10 micro g/ml. This dose of testosterone did not have an effect on cell viability and did not change the rate of mRNA degradation in the presence of actinomycin D. These studies indicate that production of 25-HC is negatively regulated by testosterone, which may be representative of a paracrine negative-feedback loop.

Number, distribution pattern, and identification of macrophages in the testes of infertile men

OBJECTIVE

To investigate the number, location, and secretory products of macrophages in human testes showing normal and abnormal spermatogenesis.

DESIGN

Evaluation of testicular biopsies with the use of immunohistochemistry, laser capture microdissection, and reverse transcriptase polymerase chain reaction.

SETTING

University research and clinical institutes.

PATIENT(S)

Infertile men with germ cell arrest (n = 10), Sertoli cell only (n = 8), or mixed atrophy (n = 7) syndromes, and with cases of idiopathic infertility showing normal spermatogenesis (n = 8).

INTERVENTION(S)

Diagnostic testicular biopsy was performed on participants.

MAIN OUTCOME MEASURE(S)

We recorded the location, number, distribution, and cytokine expression of human testicular macrophages.

RESULT(S)

CD68-positive macrophages were found in the testes of all groups analyzed. These macrophages expressed the genes for interleukin 1 and tumor necrosis factor-alpha, and were located in the interstitium, tubular wall, and tubular lumen. In Sertoli cell only and germ cell arrest syndromes, the overall macrophage number was increased over twofold. In all pathologic states, there was a significant shift of these cells from the interstitium to the tubules.

CONCLUSION(S)

Our study suggests that increased numbers of CD68-positive macrophages directly (via phagocytosis) or indirectly (via paracrine actions exerted through their secretory products) are involved in the regulation of steroidogenesis, Sertoli cell activity, germ cell survival, and, in consequence, in the pathogenesis or maintenance of infertility states in the human testes.

25-hydroxycholesterol is produced by testicular macrophages during the early postnatal period and influences differentiation of Leydig cells in vitro

Leydig cells develop inappropriately in animals lacking testicular macrophages. We have recently found that macrophages from adult animals produce 25-hydroxycholesterol, an oxysterol involved in the differentiation of hepatocytes and keratinocytes. Therefore, we hypothesized that testicular macrophages also produce 25-hydroxycholesterol during the early postnatal period and that this oxysterol plays a role in the differentiation of Leydig cells. We assessed the production of 25-hydroxycholesterol and 25-hydroxylase mRNA by cultured testicular macrophages from rats at 10, 20, and 40 days of age. We also tested the long-term effects of 25-hydroxycholesterol on basal and LH-stimulated testosterone production, and 3beta-hydroxysteroid dehydrogenase activity as end points of Leydig cell differentiation in vitro. We found that testicular macrophages from animals at all ages produced both 25-hydroxycholesterol and 25-hydroxylase mRNA, with macrophages from 10-day-old animals having the highest steady-state levels of message. We also found that chronic exposure of Leydig cells to 25-hydroxycholesterol increased basal production of testosterone but decreased LH-stimulated steroidogenesis at all ages. Finally, 25-hydroxycholesterol increased 3beta-hydroxysteroid dehydrogenase activity in both progenitor and immature Leydig cells. These findings support the hypothesis that testicular macrophages play an important role in the differentiation of Leydig cells through the secretion of 25-hydroxycholesterol.

Production of 25-hydroxycholesterol by testicular macrophages and its effects on Leydig cells

Testicular macrophages secrete 25-hydroxycholesterol, which can be converted to testosterone by neighboring Leydig cells. The purposes of the present studies were to determine the mode of production of this oxysterol and its long-term effects on Leydig cells. Because oxysterols are produced both enzymatically and by auto-oxidation, we first determined if testicular macrophages possess cholesterol 25-hydroxylase mRNA and/or if macrophage-secreted products oxidize cholesterol extracellularly. Rat testicular macrophages had 25-hydroxylase mRNA and converted 14C-cholesterol to 14C-25-hydroxycholesterol; however, radiolabeled cholesterol was not converted to 25-hydroxycholesterol when incubated with medium previously exposed to testicular macrophages. Exposure of Leydig cells to 10 microg/ml of 25-hydroxycholesterol, a dose within the range known to result in high basal production of testosterone when tested from 1 to 6 h, completely abolished LH responsiveness after 2 days of treatment. Because 25-hydroxycholesterol is toxic to many cell types at 1-5 microg/ml, we also studied its influence on Leydig cells during 4 days in culture using a wide range of doses. Leydig cells were highly resistant to the cytotoxic effects of 25-hydroxycholesterol, with no cells dying at 10 microg/ml and only 50% of cells affected at 100 microg/ml after 2 days of treatment. Similar conditions resulted in 100% death of a control lymphocyte cell line. These results demonstrate that 1) testicular macrophages have mRNA for cholesterol 25-hydroxylase and can convert cholesterol into 25-hydroxycholesterol, 2) macrophage-conditioned medium is not capable of auto-oxidation of cholesterol, 3) Leydig cells are highly resistant to the cytotoxic influences of 25-hydroxycholesterol, and 4) long-term treatment with high doses of 25-hydroxycholesterol results in loss of LH responsiveness. These results support the concept that testicular macrophages enzymatically produce 25-hydroxycholesterol that not only is metabolized to testosterone by Leydig cells when present at putative physiological levels but also may exert inhibitory influences on Leydig cells when present for extended periods at very high concentrations that may occur under pathological conditions.