An early steroidogenic defect in hormone-induced Leydig cell desensitization

Integration of metabolomics and transcriptomics data to aid biomarker discovery in type 2 diabetes

Type 2 diabetes (T2D), one of the most common diseases in the western world, is characterized by insulin resistance and impaired beta-cell function but currently it is difficult to determine the precise pathophysiology in individual T2D patients. Non-targeted metabolomics technologies have the potential for providing novel biomarkers of disease and drug efficacy, and are increasingly being incorporated into biomarker exploration studies. Contextualization of metabolomics results is enhanced by integration of study data from other platforms, such as transcriptomics, thus linking known metabolites and genes to relevant biochemical pathways. In the current study, urinary NMR-based metabolomic and liver, adipose, and muscle transcriptomic results from the db/db diabetic mouse model are described. To assist with cross-platform integration, integrative pathway analysis was used. Sixty-six metabolites were identified in urine that discriminate between the diabetic db/db and control db/+ mice. The combined analysis of metabolite and gene expression changes revealed 24 distinct pathways that were altered in the diabetic model. Several of these pathways are related to expected diabetes-related changes including changes in lipid metabolism, gluconeogenesis, mitochondrial dysfunction and oxidative stress, as well as protein and amino acid metabolism. Novel findings were also observed, particularly related to the metabolism of branched chain amino acids (BCAAs), nicotinamide metabolites, and pantothenic acid. In particular, the observed decrease in urinary BCAA catabolites provides direct corroboration of previous reports that have inferred that elevated BCAAs in diabetic patients are caused, in part, by reduced catabolism. In summary, the integration of metabolomics and transcriptomics data via integrative pathway mapping has facilitated the identification and contextualization of biomarkers that, presuming further analytical and biological validation, may be useful in future T2D clinical studies by identifying patient populations that share common disease pathophysiology and therefore may identify those patients that may respond better to a particular class of anti-diabetic drugs.

Prolactin and Leydig cells: biphasic effects of prolactin on LH-, T3- and GH-induced testosterone/oestradiol secretion by Leydig cells in pubertal rats

The effect of rat prolactin (rPRL) on basal and LH-, GH- and T3-mediated testosterone and oestradiol secretion was studied in pubertal rat Leydig cells. Purified Leydig cells were cultured for 24 h at 37 degrees C in a medium containing 4% foetal calf serum (FCS). The medium was then replaced with fresh medium containing different concentrations of rPRL (5-400 ng/mL) for 48 h at 34 degrees C without FCS. rPRL increased testosterone secretion by Leydig cells at doses of 50-400 ng and maximum stimulation was observed at a dose of 200 ng. Oestradiol secretion was parallel to that of testosterone except at low doses (5-50 ng/mL). To assess the modulatory effect of rPRL on LH-, GH- and T3-induced Leydig cell testosterone and oestradiol secretion, minimum (50 ng) and maximum (200 ng) effective doses of rPRL were co-administered with LH (25/100 ng), GH (10/50 ng) and T3 (25/50 ng). Co-administration of rPRL (50/100 ng) with T3 (25/50 ng) decreased testosterone secretion. While co-administration of T3 (25 ng) decreased rPRL-induced oestradiol secretion, the latter was unaltered at a dose of 50 ng T3. A minimum effective dose of rPRL (50 ng) plus LH (25 ng) stimulated both testosterone and oestradiol secretion. While a maximum effective dose of rPRL (200 ng) did not alter LH (25 ng)-induced testosterone and oestradiol secretion, it inhibited testosterone secretion induced by 100 ng LH and increased oestradiol secretion. Both doses of rPRL (50, 200 ng) plus GH (10/50 ng) inhibited testosterone secretion when compared with testosterone secretion induced by either GH or PRL alone and stimulated oestradiol secretion. The present in vitro study indicates that rPRL stimulates both testosterone and oestradiol secretion by Leydig cells and that this effect can be modulated by LH, GH and T3.

Acquisition of hormone-mediated mechanisms regulating testicular steroidogenesis during development

Our studies have demonstrated that in the fetal rat Leydig cell, estradiol causes an up-regulation of its receptor and an induction of the regulatory mechanism (late steroidogenic lesion) that is similar to that observed in the adult rat Leydig cell. The absence of this regulation in fetal life is due to a very low level of aromatization capacity, with lack of up-regulation and/or induction of estrogen receptor by estradiol. Higher doses or frequent administration of LH is able to elevate aromatase activity and consequent E2-receptor-mediated action for the induction of gonadotropin-mediated desensitization in fetal cells. Our studies have revealed a small population of adult-like Leydig cells in the fetal testis and the emergence of a functional adult-like population from the fetal Leydig cell induced by gonadotropin treatment. The in vitro fetal Leydig cell culture system has permitted the analysis of cellular actions of gonadotropin with particular reference to the role of tropic hormone and estrogen in the development of late steroidogenic lesions during Leydig cell maturation. Future research with this system will help to clarify further the modulatory mechanisms responsible for emergence of the adult cell population.

Specific binding and steroidogenetic effects of atrial natriuretic factor (ANF) in Leydig cells of rats

Atrial natriuretic factors (ANF) may influence testicular steroidogenesis. This study was conducted to evaluate the presence of specific ANF-binding on isolated adult rat Leydig cells and the effects of ANF on testosterone production. Indirect immunofluorescence technique demonstrates that adult rat Leydig cells possess specific ANF-binding and that rAP-II strongly stimulates the testosterone production. rAP-II exerts its maximal stimulatory effect on the testosterone secretion at low doses (10(-11) M), corresponding at the physiological plasmatic concentration in the adult normal rat. High doses (10(-9)-10(-7) M) of rAP-II show a decline in the stimulatory effect on testosterone secretion. Our data suggest that rAP-II influences the testicular steroidogenesis by a receptorial mechanism; the biphasic effect of rAP-II on the testosterone production may be related to an acute receptorial desensitization phenomena.

Progesterone and relaxin secretion in relation to the ultrastructure of human luteal cells in culture: effects of human chorionic gonadotropin

This report describes the first study to correlate the ultrastructure of long-term monolayer cultures of human luteal cells with their secretion of relaxin and progesterone under basal and human chorionic gonadotropin-stimulated conditions. In culture from 14 to 28 days, cells from both corpora lutea of the menstrual cycle and corpora lutea of pregnancy took on characteristics of granulosa luteal cells, particularly after exposure to human chorionic gonadotropin. Relaxin was detectable in the luteal cell cultures only at early time points. The effect of human chorionic gonadotropin on media relaxin levels differed in cells of the cycle and cells of pregnancy. In the cells of the cycle, relaxin was detectable only on day 2 and was decreased by human chorionic gonadotropin (p less than 0.01). In cells of pregnancy, relaxin was detectable for the first 4 days of culture and was not affected by human chorionic gonadotropin. Progesterone was detectable in all the luteal cell cultures and was enhanced by human chorionic gonadotropin (10 and 50 IU/ml) after 24 days of exposure. At earlier time points in both the luteal cells of the cycle and the luteal cells of pregnancy, the human chorionic gonadotropin-induced increases in progesterone levels were not as consistent. However, in all cases of progesterone enhancement, smooth-surfaced endoplasmic reticulum was increased in the human chorionic gonadotropin-treated cells compared with corresponding controls, consistent with more active steroid production. In addition, gap junctions, considered to be responsive to trophic hormones, were increased in the treated cells. In conclusion, this long-term monolayer culture of human luteal cells, as monitored by ultrastructural and hormonal changes, retained the differentiated function of progesterone secretion and exhibited responsiveness to human chorionic gonadotropin. Therefore, morphologic and functional aspects of progesterone secretion may be investigated more closely with use of this long-term luteal cell culture system.

Differential down-regulation and induction responses of testicular steroidogenic cytochromes P-450(cscc) and P-450(C17 alpha) to human choriogonadotropin

Evidence is presented that the regulation of the cytochrome P-450(C17 alpha) of the steroid-17 alpha-monooxygenase and of the cytochrome P-450(cscc) of the cholesterol-monooxygenase by human choriogonadotropin (hCG) in vivo is mediated by differential mechanisms in the adult rat testis. An initial down-regulation of the cytochrome P-450(C17 alpha) but not of the P-450(cscc) can be demonstrated. Furthermore, induction of the cytochrome P-450(cscc) requires exposure to higher hCG doses (32% of the maximal induction rate of 43.7 pmol/(testis x d) are achieved with 4IU hCG/single dose) than induction of the P-450(C17 alpha) (59% of the maximal induction rate of 48.4 pmol/(testis x d) with 4IU hCG/single dose). Finally, induction of cytochrome P-450(cscc) starts faster after initiation of hCG treatment than induction of P-450(C17 alpha).