Massimiliano Caprio

Leptin in reproduction

In mammals, the function of the reproductive system is dependent on the availability of energy in the environment. It is well established that acute modifications of energy balance modulate the hypothalamic-pituitary-gonadal axis. In several species, fasting and caloric restriction have been shown to cause the suppression of pulsatile luteinizing hormone secretion, via an inhibition of the gonadotropin-releasing hormone pulse generator. Such a mechanism probably prevents energy being wasted for reproduction. By contrast, excessive energy storage and obesity interfere with the correct regulation of the reproductive axis. The identification of leptin and leptin receptors, along with studies performed in animal models of leptin deficiency and resistance, has focused attention on the role of this molecule in reproduction, and disclosed new aspects of the relationship between energy stores, adipose tissue and reproductive function. Here, we discuss the central and peripheral effects of leptin on reproductive tissues, and try to fit a complex reality into a simplified model. In particular, the roles of leptin in reproduction at different anatomical levels and in various clinical and experimental settings are discussed.

Androgens and penile erection: evidence for a direct relationship between free testosterone and cavernous vasodilation in men with erectile dysfunction.

Androgens are essential in the maintenance of nitric oxide‐mediated erectile activity in the rat. The objective of the present study was to investigate the role of androgens in regulating trabecular smooth muscle relaxation in the corpus cavernosum in response to vasoactive challenge in men with erectile dysfunction (ED).

Functional Mineralocorticoid Receptors in Human Vascular Endothelial Cells Regulate Intercellular Adhesion Molecule-1 Expression and Promote Leukocyte Adhesion

In clinical trials, aldosterone antagonists decrease cardiovascular mortality and ischemia by unknown mechanisms. The steroid hormone aldosterone acts by binding to the mineralocorticoid receptor (MR), a ligand-activated transcription factor. In humans, aldosterone causes MR-dependent endothelial cell (EC) dysfunction and in animal models, aldosterone increases vascular macrophage infiltration and atherosclerosis. MR antagonists inhibit these effects without changing blood pressure, suggesting a direct role for vascular MR in EC function and atherosclerosis. Whether human vascular ECs express functional MR is not known. Here, we show that human coronary artery and aortic ECs express MR mRNA and protein and that EC MR mediates aldosterone-dependent gene transcription. Human ECs also express the enzyme 11-&bgr;-hydroxysteroid dehydrogenase-2 (11&bgr;HSD2), and inhibition of 11&bgr;HSD2 in aortic ECs enhances gene transactivation by cortisol, supporting that EC 11&bgr;HSD2 is functional. Furthermore, aldosterone stimulates transcription of the proatherogenic leukocyte–EC adhesion molecule intercellular adhesion molecule (ICAM)1 gene and protein expression on human coronary artery ECs, an effect inhibited by the MR antagonist spironolactone and by MR knock down with small interfering RNA. Cell adhesion assays demonstrate that aldosterone promotes leukocyte–EC adhesion, an effect that is inhibited by spironolactone and ICAM1 blocking antibody, supporting that aldosterone induction of EC ICAM1 surface expression via MR mediates leukocyte–EC adhesion. These data show that aldosterone activates endogenous EC MR and proatherogenic gene expression in clinically important human ECs. These studies describe a novel mechanism by which aldosterone may influence ischemic cardiovascular events and support a new explanation for the decrease in ischemic events in patients treated with aldosterone antagonists.

Cellular Models for Understanding Adipogenesis, Adipose Dysfunction, and Obesity

White adipose tissue (WAT) is no longer considered a depot for energy storage in the form of triglycerides, but is a secretory organ that releases factors, known as adipokines, capable of regulating several physiological processes. Alteration of WAT function with subsequent dysfunctional expression and secretion of adipokines plays a key role in the pathogenesis of obesity, diabetes, and other metabolic diseases. For this reason, a deeper understanding of the molecular mechanisms regulating adipocyte function is deemed necessary for planning strategies to treat and prevent obesity and its metabolic complications. This review examines cell culture models currently available for studying adipocyte biology. We focus on advantages, disadvantages and main differences between established preadipocyte cell lines and primary preadipocyte cultures. We revise protocols used to promote adipocyte differentiation and mature adipocytes dedifferentiation into preadipocytes. Finally, we briefly describe co‐cultures of adipocytes with other cell types and three‐dimensional adipocyte culture systems. These models allow investigation of cell–cell interactions with the cross‐talk physiologically occurring between adipocytes and other cell types residing within or outside adipose tissue. J. Cell. Biochem. 110: 564–572, 2010.

The role of the mineralocorticoid receptor in adipocyte biology and fat metabolism

Aldosterone controls blood pressure by binding to the mineralocorticoid receptor (MR), a ligand-activated transcription factor which regulates critical genes controlling salt and water homeostasis in the kidney. In recent years, inappropriate MR activation has been shown to trigger deleterious responses in various tissues, including vessels, heart and brain, hence promoting vascular inflammation, cardiovascular remodeling, endothelial dysfunction, and oxidative stress. Moreover, epidemiological studies have shown a clear association between aldosterone levels and the incidence of metabolic syndrome. In particular, recent work has revealed functional MRs in adipose tissue, where they mediate the effects of aldosterone and glucocorticoids, displaying important and specific functions involving adipose differentiation, expansion and proinflammatory capacity. This recent evidence finally moved MR out of the shadow of the glucocorticoid receptor (GR), which had previously been considered the only player mediating corticosteroid action in adipose tissue. This has opened a new era of research focusing on the complexity and selectivity of MR function in adipocyte biology. The aim of this review is to summarize the latest concepts on the role of MR in white and brown adipocytes, and to discuss the potential benefits of tissue-selective MR blockade in the treatment of obesity and metabolic syndrome.

Antiadipogenic Effects of the Mineralocorticoid Receptor Antagonist Drospirenone: Potential Implications for the Treatment of Metabolic Syndrome

The mineralocorticoid receptor (MR) mediates aldosterone- and glucocorticoid-induced adipocyte differentiation. Drospirenone (DRSP) is a potent synthetic antimineralocorticoid with progestogenic and antiandrogenic properties, which is widely used for contraception and hormone replacement therapy. We investigated its potential role on adipocyte differentiation. The effects of DRSP were studied in murine preadipocyte cell lines and primary cultures of human preadipocytes. Differentiation markers and mechanisms underlying phenotypic variations in response to DRSP were explored. Early exposure to DRSP during differentiation led to a marked dose-dependent inhibition of adipose differentiation and triglyceride accumulation in 3T3-L1 and 3T3-F442A cells. DRSP also markedly inhibited adipose conversion of human primary preadipocytes derived from visceral (mesenteric and epicardial) and subcutaneous fat. This effect was MR-dependent and did not involve the glucocorticoid, androgen, or progesterone receptors. DRSP inhibited clonal expansion of preadipocytes and decreased expression of PPARγ, a key transcriptional mediator of adipogenesis, but had no effect on lipolysis, glucose uptake, and PPARγ binding to its ligands. DRSP exerts a potent antiadipogenic effect that is related to an alteration of the transcriptional control of adipogenesis via an antagonistic effect on the MR. Selective MR blockade therefore has promise as a novel therapeutic option for the control of excessive adipose tissue deposition and its related metabolic complications.

Mineralocorticoid receptors in the metabolic syndrome

The mineralocorticoid receptor (MR) mediates aldosterone effects on salt homeostasis and blood pressure regulation. MR activation also promotes inflammation, cardiovascular remodelling and endothelial dysfunction, and affects adipose tissue differentiation and function. Some of these effects derive from MR activation by glucocorticoids. Recent epidemiological studies show that the incidence of metabolic syndrome increases across quartiles of aldosterone, implicating the MR as a central player in metabolic homeostasis, involving electrolyte, water and energy balance. This review summarizes the current understanding of MR-mediated effects in diverse tissues and the role of aldosterone as a cardiometabolic risk factor, and discusses the possible relationship between inappropriate MR activation (by both mineralocorticoids and glucocorticoids) and the development of metabolic syndrome.

ACTH and α-MSH inhibit leptin expression and secretion in 3T3-L1 adipocytes: model for a central–peripheral melanocortin-leptin pathway ☆

Leptin is the 167 amino-acid protein product of the Lep (obese) gene that is released predominantly from adipose tissue and circulates at levels related to the amount of fat. Leptin expression is hormonally regulated: insulin and glucocorticoids are stimulators, while inhibitors include beta-adrenergic agonists and testosterone. Recently, adenylate cyclase-coupled melanocortin receptors have been identified in murine adipose tissue, the 3T3-L1 adipocyte cell line, and in human fat tissue. These studies prompted us to evaluate the effects of pro-opiomelanocortin (POMC)-derived peptides on leptin production and expression in 3T3-L1 adipocytes in culture. 3T3-L1 pre-adipocytes differentiated by the insulin/indomethacin (I/I) method produced leptin at levels that were two times higher than those obtained in cells differentiated by the more traditional insulin/dexamethasone/isobutylmethylxanthine (I/D/M) method. By RT-PCR studies, 3T3-L1 cells expressed both the melanocortin 2 receptors (MC2-R) and melanocortin 5 receptors (MC5-R) isoforms of the melanocortin receptor at an early stage of differentiation. When I/I differentiated 3T3-L1 adipocytes were incubated with different concentrations of dibutyryl cAMP (db-cAMP) or POMC-derived peptides (ACTH and alpha-MSH), ACTH and alpha-MSH stimulated cAMP production after 30 min (2-fold increase) associated with a dose-dependent inhibition of leptin secretion (ACTHz.Gt;alpha-MSH; IC(50)=3.2+/-0.4 SE and 36+/-5 nM, respectively), maximal after 3 h of incubation (30% inhibition). In addition, 100 nM ACTH and alpha-MSH induced a 60% reduction in leptin expression by RT-PCR. Incubation of cells with 0.5 mM db-cAMP led to a more prominent inhibition of leptin expression and secretion (up to 80% at 1 and 24 h, respectively). The ACTH and alpha-MSH inhibitory effects on leptin secretion were mediated by activation of the MC2-R and MC5-R and were reversed by the MC-R antagonists ACTH(11-24) and ACTH(7-38). In summary, we have shown that POMC-peptides are potent inhibitors of leptin expression and production in 3T3-L1 adipocytes. The finding of ACTH/alpha-MSH receptor-induced inhibition of leptin production and expression in adipocytes support the possibility that there is a control mechanism for modulation of adipose tissue function via a melanocortin-leptin axis.

Ontogenesis of Leptin Receptor in Rat Leydig Cells

Abstract There are still many controversies about the role of leptin in reproductive function and sexual development. We recently demonstrated that leptin receptors are expressed in rodent Leydig cells and that leptin has inhibitory effects on hCG-stimulated testosterone production by adult rat Leydig cells in culture. In this study, we evaluated the expression of leptin receptor (Ob-R) in rat testes from gestational to adult age in comparison with the pattern of expression of relaxin-like factor (RLF), a specific marker of Leydig cell differentiation status. Immunohistochemical analysis showed that, in prenatal life, Ob-R immunoreactivity was absent at early embryonic ages (E14.5) and appeared at a late embryonic age (E19.5); in postnatal life, immunoreactivity was evident only after sexual maturation (35-, 60-, and 90-days old), whereas it was absent in testes from sexually immature rats (7-, 14-, and 21-days old). Immunoreaction was always confined to Leydig cells and no signal of Ob-R was detected within the tubules. The pattern of expression of Ob-R during testicular development was similar with that of RLF immunoreactivity, which was present in mature fetal as well as adult-type Leydig cells. In contrast with the findings in the testis, in the hypothalamus, the immunohistochemical pattern of Ob-R was very similar between pre- and postpubertal life. Reverse transcription-polymerase chain reaction studies showed that Ob-R expression was present in embryonic, prepubertal, and adult rat testes; semiquantitative analysis showed that mRNA levels were much higher in late versus early embryonic testes, as well as in mature adults versus sexually immature testes, with a gradual increase from younger to older ages. Functional studies showed that, while leptin (150 ng/ml) significantly inhibited hCG-stimulated testosterone production in adult rat Leydig cells (46% reduction; P > 0.01), it did not modify prepubertal rat Leydig cells steroidogenic function in vitro. In conclusion, we showed that, in rat testis, Ob-R expression is characteristic of mature Leydig cells (fetal and adult type) and it is functional in adult but not prepubertal life.

Mineralocorticoid receptor antagonism induces browning of white adipose tissue through impairment of autophagy and prevents adipocyte dysfunction in high-fat-diet-fed mice

The mineralocorticoid receptor (MR) controls adipocyte function, but its role in the conversion of white adipose tissue (WAT) into thermogenic fat has not been elucidated. We investigated responses to the MR antagonists spironolactone (spiro; 20 mg/kg/d) and drospirenone (DRSP; 6 mg/kg/d) in C57BL/6 mice fed a high‐fat (HF) diet for 90 d. DRSP and spiro curbed HF diet‐induced impairment in glucose tolerance, and prevented body weight gain and white fat expansion. Notably, either MR antagonist induced up‐regulation of brown adipocyte‐specific transcripts and markedly increased protein levels of uncoupling protein 1 (UCP1) in visceral and inguinal fat depots when compared with the HF diet group. Positron emission tomography and magnetic resonance spectroscopy confirmed acquisition of brown fat features in WAT. Interestingly, MR antagonists markedly reduced the autophagic rate both in murine preadipocytes in vitro (10‐5 M) and in WAT depots in vivo, with a concomitant increase in UCP1 protein expression. Moreover, the autophagy repressor bafilomycin A1 (10‐8 M) mimicked the effect of MR antagonists, increasing UCP1 protein expression in primary preadipocytes. Hence, we showed that adipocyte MR regulates brown remodeling of WAT through a modulation of autophagy. These results provide a rationale for the use of MR antagonists to prevent the adverse metabolic consequences of adipocyte dysfunction.—Armani, A., Cinti, F., Marzolla, V., Morgan, J., Cranston, G. A., Antelmi, A., Carpinelli, G., Canese, R., Pagotto, U., Quarta, C., Malorni, W., Matarrese, P., Marconi, M., Fabbri, A., Rosano, G., Cinti, S., Young, M. J., Caprio, M. Mineralocorticoid receptor antagonism induces browning of white adipose tissue through impairment of autophagy and prevents adipocyte dysfunction in high‐fat‐diet‐fed mice. FASEB J. 28, 3745–3757 (2014). www.fasebj.org