Expression and regulation of transforming growth factor beta1 mRNA and protein in rat fetal testis in vitro

The Fate of Leydig Cells in Men with Spermatogenic Failure

The steroidogenic cells in the testicle, Leydig cells, located in the interstitial compartment, play a vital role in male reproductive tract development, maintenance of proper spermatogenesis, and overall male reproductive function. Therefore, their dysfunction can lead to all sorts of testicular pathologies. Spermatogenesis failure, manifested as azoospermia, is often associated with defective Leydig cell activity. Spermatogenic failure is the most severe form of male infertility, caused by disorders of the testicular parenchyma or testicular hormone imbalance. This review covers current progress in knowledge on Leydig cells origin, structure, and function, and focuses on recent advances in understanding how Leydig cells contribute to the impairment of spermatogenesis.

Apolipoprotein(a) stimulates vascular endothelial cell growth and migration and signals through integrin alphaVbeta3

Elevated plasma concentrations of Lp(a) [lipoprotein(a)] are an emerging risk factor for atherothrombotic disease. Apo(a) [apolipoprotein(a)], the unique glycoprotein component of Lp(a), contains tandem repeats of a plasminogen kringle (K) IV-like domain. In the light of recent studies suggesting that apo(a)/Lp(a) affects endothelial function, we evaluated the effects of apo(a)/Lp(a) on growth and migration of cultured HUVECs (human umbilical-vein endothelial cells). Two full-length r-apo(a) [recombinant apo(a)] variants (12K and 17K), as well as Lp(a), were able to stimulate HUVEC growth and migration to a comparable extent; 17K r-apo(a) also decreased the levels of total and active transforming growth factor-beta secreted by these cells. Using additional r-apo(a) variants corresponding to deletions and/or site-directed mutants of various kringle domains in the molecule, we were able to determine that the observed effects of full-length r-apo(a) on HUVECs were dependent on the presence of a functional lysine-binding site(s) in the apo(a) molecule. With respect to signalling events elicited by apo(a) in HUVECs, we found that 17K treatment of the cells increased the phosphorylation level of FAK (focal adhesion kinase) and MAPKs (mitogen-activated protein kinases), including ERK (extracellular-signal-regulated kinase), p38 and JNK (c-Jun N-terminal kinase). In addition, we showed that LM609, the function-blocking antibody to integrin alphaVbeta3, abrogated the effects of 17K r-apo(a) and Lp(a) on HUVECs. Taken together, the results of the present study suggest that the apo(a) component of Lp(a) signals through integrin alphaVbeta3 to activate endothelial cells.

Ontogeny of gonadal sex steroids

Sex steroids are crucial hormones for the proper development and function of the body; they regulate sexual differentiation, the secondary sex characteristics, and sexual behaviour patterns. Gonads are the major sources of sex steroids, although adrenal cortex, placenta, and to a lesser extent other tissues contribute to their production in adult life and at various phases of development. Steroidogenesis of gonadal sex hormones is by definition sexually dimorphic, and involves differences not only in hormonal action but also in regulation and temporal patterns of production. This review focuses on the ontogeny and developmental regulation of steroid hormones in the gonads, with an attempt to detail these processes in humans.

Alteration of transforming growth factor-beta signaling system expression in adult rat germ cells with a chronic apoptotic cell death process after fetal androgen disruption

In utero exposure to chemicals with antiandrogen activity induces undescended testis, hypospadias, and sub- or infertility. The hypospermatogenesis observed in the adult rat testis exposed in utero to the antiandrogen flutamide has been reported to be a result of a long-term apoptotic cell death process in mature germ cells. However, little if anything is known about the upstream signaling mechanisms controlling this apoptosis. In the present study, we have investigated the possibility that the TGF-beta signaling pathway may be at play in this control of the apoptotic germ cell death process. By using a model of adult rat exposed in utero to 0, 0.4, 2, or 10 mg/kg.d flutamide, we observed that pro-TGF-beta signaling members, such as the three isoforms of TGF-beta ligands (TGF-beta1-3), the two TGF-beta receptors (TGF-betaRI and -RII) and the R-Smads Smad 1, Smad 2, Smad 3, and Smad 5 were inhibited at the mRNA and protein levels, whereas the anti-TGF-beta signaling member Smad 7 was overexpressed. Furthermore, we report that the overexpression of Smad 7 mRNA could induce an activation of c-Jun N-terminal kinase, because of the observed c-Jun overexpression, activation, and nuclear translocation leading to an increase in the transcription of the proapoptotic factor Fas-L. Together, the alterations of TGF-beta signaling may represent upstream mechanisms underlying the adult germ cell apoptotic process evidenced in adult rat testis exposed in utero to antiandrogenic compounds such as flutamide.

Macrophage migration inhibitory factor suppresses transforming growth factor-β2 secretion in cultured rat testicular peritubular cells

Cytokines have direct effects on testicular cell functions and a number of cytokines are produced constitutively within the testis, even in the absence of immune-activation events. There is clear evidence that cytokines play a dual role as important regulatory factors in the normal function of the testis, as well as in testicular inflammation. The pro-inflammatory cytokine macrophage migration inhibitory factor (MIF) is expressed locally in the testis and has direct effects on peritubular cells, which, in turn, produce anti-inflammatory mediators, including transforming growth factor (TGF)-β2. In the present study, we investigated the function of MIF by examining its effect on the secretion of TGF-β2 in peritubular cells. Expression of TGF-β2 mRNA was shown by reverse transcription–polymerase chain reaction in peritubular cells isolated from 19-day-old rat testis. The addition of recombinant MIF to cultured peritubular cells resulted in a dose-dependent decrease in TGF-β2 secretion up to 52% of control levels after 48 h, which was significant for all doses investigated (10–100 ng mL−1 MIF). Inhibition of TGF-β2 secretion was sustained for 72 h for the highest dose of MIF used (100 ng mL−1). No effect of MIF was observed on TGF-β2 mRNA expression levels, as shown by real-time polymerase chain reaction. These results suggest that the pro-inflammatory cytokine MIF can shift the cytokine balance from the immunosuppressive state towards an inflammatory reaction, potentially through the inhibition of TGF-β2 secretion by peritubular cells.

Differential expression of transforming growth factor-? in the interstitial tissue of testis during aging

Transforming growth factor-betas (TGF-betas) have significant effects on testis development. The pattern of TGF-beta expression in aging testis has not been established to date. We examined age-related changes in the expression of TGF-beta and its receptors in the testis using Western blot analysis. TGF-beta1 expression increased continuously in aging rat testis, whereas no age-associated changes were observed for TGF-beta3. Strong expression of TGF-beta2, as well as type I and II receptors was observed in 12-month-old testis, but following this time, expression decreased dramatically. Interestingly, TGF-beta2 and -beta3 displayed strong and similar expression patterns in liver, regardless of age, suggesting that the down-regulation of TGF-beta2 is testis-specific. We observed significant induction of p53 and p21WAF1 in 18-month-old testis that appeared to correspond with aging. Moreover, caloric restriction (CR) prevented age-related decrease in TGF-beta2 expression. Using immunohistochemistry, we showed that all TGF-beta1, -beta2, and -beta3 proteins are expressed primarily in interstitial cells, which are located in the space between adjoining seminiferous tubules. Our data collectively indicate that aging in the testis is regulated by differential expression of TGF-beta proteins, and decreased levels of TGF-beta2 contribute to the aging process.

Immune-endocrine interactions and Leydig cell function: the role of cytokines

Inflammatory disease is known to affect male reproductive function and fertility. Male accessory gland infections (MAGI) account for almost 15% of all cases of male infertility seen in infertility clinics. Infections of the male accessory glands are associated with increased counts of white blood cells in semen and elevated levels of pro-inflammatory cytokines in the semen and the testis. Numerous studies have underscored the importance of cytokines in the regulation of testicular and glandular function during pathophysiological events as well as under normal physiological conditions when cytokines act as growth and differentiation factors. The purpose of this paper is to particularly review the role of cytokines in the regulation of Leydig cell function in the testis primarily under pathophysiological conditions, and also considers clinical investigations that help to improve the evaluation and treatment of male infertility.

Defining the actions of transforming growth factor beta in reproduction

Members of the transforming growth factor beta (TGFbeta) family are pleiotropic cytokines with key roles in tissue morphogenesis and growth. TGFbeta1, TGFbeta2 and TGFbeta3 are abundant in mammalian reproductive tissues, where development and cyclic remodelling continue in post-natal and adult life. Potential roles for TGFbeta have been identified in gonad and secondary sex organ development, spermatogenesis and ovarian function, immunoregulation of pregnancy, embryo implantation and placental development. However, better tools must now be employed to map more precisely essential functions and the regulatory networks governing their activity. Gene ablation and transgenic models are expected to provide novel insights into distinct physiological activities for each TGFbeta isoform in normal reproductive function and reproductive pathologies. It is also necessary to consider the mechanisms controlling TGFbeta activation from latent precursor forms, and receptor and binding protein expression. Smad intracellular signalling circuitry and modulation by environmental stimuli through cross-talk with other signal transduction pathways will further constrain TGFbeta action. This review examines existing evidence for TGFbeta1, TGFbeta2 and TGFbeta3 regulation of male and female reproductive biology, and highlights prospects for future research.

Cadmium- and mercury-induced intercellular adhesion molecule-1 expression in immortalized proximal tubule cells: evidence for a role of decreased transforming growth factor-beta1

A definitive association between the aberrant expression of cytokines and adhesion molecules in renal failure has been established. In this regard a relationship between cytokine and adhesion molecule expression is suggested but has not been shown in models of proximal tubular cell injury. To investigate the impact of acute injury on the relationship between transforming growth factor-beta 1 (TGF-beta1) and intercellular adhesion molecule-1 (ICAM-1) expression, two immortalized mouse proximal tubular epithelial cell lines were exposed to cadmium chloride or mercuric chloride (0-50 microM) for 0-8 h. ELISA and Western blot measured expression of secreted and intercellular TGF-beta1, respectively. Direct cellular ELISA or Western blot was used to assess ICAM-1 expression. Challenge with cadmium caused a greater loss of cell viability than did mercury. Interestingly, cadmium significantly decreased the amount of TGF-beta1 in the conditioned media. Although a similar trend was seen in mercury-challenged cells, no significant differences were observed. The decrease in TGF-beta1 in the culture media was not due to decreased expression of this cytokine, as intercellular levels were not affected by metal-induced injury. Significant increases in ICAM-1 protein expression were observed following cadmium and mercury challenge. The increase in ICAM-1 appears to be due to increased mRNA, as Northern blot analysis demonstrated increased message expression following a 4-h cadmium or mercury challenge. Supplementation of the culture media with exogenous TGF-beta1 decreased basal ICAM-1 expression and attenuated the cadmium-induced increase. These data suggest that metal-induced injury is associated with increased ICAM-1 expression. The mechanism of this induction may involve the decreased TGF-beta1 in the conditioned media following metal challenge. Taken together, these studies suggest a link between cytokine and adhesion molecule expression in renal injury.

Role of cytokines in testicular function

Inflammatory disease has been established to affect male reproductive function and fertility. Relevant inflammatory diseases include general and chronic infectious diseases as well as localized acute or chronic infections of the male genitourinary tract. Male accessory gland infections account for almost 15% of all cases of male infertility seen in infertility clinics while fertility usually is not a clinical objective among patients with acute systemic infections such as Gram-negative sepsis. Infections of the male accessory glands frequently are associated with increased counts of white blood cells in semen and elevated levels of proinflammatory cytokines in semen and the testis. There is a mounting body of evidence that demonstrates the importance of cytokines and chemokines in the regulation of testicular and glandular function during pathophysiological states as well as under normal physiological conditions when cytokines act as growth and differentiation factors. The purpose of this review is to examine the role of cytokines in the regulation of steroidogenesis and spermatogenesis in the testis under physiological and pathophysiological conditions and considers clinical investigations that help to improve the evaluation and treatment of male infertility.

Autocrine regulation of Leydig cell differentiated functions by insulin-like growth factor I and transforming growth factor beta

The expression and the maintenance of specific differentiated function of Leydig cells are regulated not only by gonadotropin but by locally produced factors, which may act as autocrine regulators. Many factors, in particular growth factors, have been postulated to have such a type of effect on testicular cells, but very few fulfilled the three criteria required to establish a paracrine/autocrine role: (a) presence of receptors and biological action on local cells; (b) local secretion regulated by physiological signals; and (c) blockade of the factor or its receptors must modify the function of local cells. In the present work we demonstrate that two factors, insulin-like growth factor 1 (IGF-I) and transforming growth factor beta1 (TGFbeta1) fulfilled the three criteria: (a) IGF-I stimulates the transcription of the genes encoding Leydig cell differentiated function, leading to an enhanced steroidogenic responsiveness to LH/hCG; (b) Leydig cells (LC) express and secrete IGF-I and this secretion is enhanced by hCG; and (c) incubation of LC with IgG anti-IGF-I, but not with IgG-control, markedly reduced the steroidogenic responsiveness to LH/hCG. In contrast to IGF-I, TGFbeta is a potent inhibitor of LC differentiated function. Moreover, LC express TGFbeta1 mRNA and secrete this peptide. To prove that the locally produced TGFbeta has an autocrine role, LC were transfected with 10 microM of an antisense oligonucleotide (AON) complementary to the translation initiation region of TGFbeta1 mRNA. Transfection with AON but not with sense deoxynucleotide induces a complete disappearance of TGFbeta immunoreactivity in LC and an enhanced hCG-induced testosterone production by LC. This increased steroidogenic responsiveness was associated with a significant enhancement of both LH/hCG receptor mRNA and P450c17 mRNA. Taken together, the above results show that both factors play an autocrine role, although opposite, on Leydig cell function.