Interleukin-18 is expressed in rat testis and may promote germ cell growth

The role of death receptor signaling pathways in mouse Sertoli cell avoidance of apoptosis during LPS- and IL-18-induced inflammatory conditions

Lipopolysaccharide (LPS) triggers infectious acute inflammation, and interleukin (IL)-18 is an inflammasome-mediated cytokine. We previously demonstrated that endogenous IL-18 induces testicular germ cell apoptosis during acute inflammation when plasma IL-18 levels are high. Additionally, high-dose recombinant IL-18 (rIL-18) induced Leydig cell apoptosis. The blood-testis barrier formed by Sertoli cells protects testicular germ cells from both exogenous and endogenous harmful substances. However, the impact of LPS and IL-18 on Sertoli cells remained unclear. We stimulated TM4 cells, a mouse Sertoli cell line, with LPS (200 or 1000 ng/mL) or rIL-18 (0.1-100 ng/mL) at levels that induced Leydig cell apoptosis in our previous study and assessed caspase 3 cleavage and the mRNA expression of inflammatory cytokines and markers of apoptotic pathways (Tnfr1, Fasl, Fas, Fadd) after stimulation. Il6 mRNA was increased by LPS stimulation. Tnfα mRNA was increased by 200 ng/mL LPS but not 1000 ng/mL LPS. Fas was increased, but Fasl was decreased, by LPS. LPS had little influence on Tnfr1 or Fadd mRNA expression and did not induce apoptosis. Il18 mRNA was not increased, and Il18r1 was significantly decreased following LPS treatment. Treatment with rIL-18 increased Il18r1 mRNA and induced inflammation, but decreased Tnfr1 and had little influence on apoptosis, as indicated by Tnfα, Fasl, Fas, Fadd and cleaved caspase 3. These results suggested that Sertoli cells do not easily undergo apoptosis despite strong inflammatory stimuli. Additionally, Sertoli cells may resist inflammation and play a larger role in protecting testicular homeostasis than other component cells of the testis.

Interleukin-18 levels and mouse Leydig cell apoptosis during lipopolysaccharide-induced acute inflammatory conditions

Interleukin (IL)-18 is an inflammasome-mediated cytokine produced by germ cells, Leydig cells, and resident macrophages that is indispensable in the maintenance of homeostasis in the testis. We previously demonstrated that endogenous IL-18 induces testicular germ cell apoptosis during acute inflammation when plasma IL-18 levels are very high. However, the impact of acute inflammation and IL-18 on Leydig cells remained unclear. TM3 cells, a mouse Leydig cell line, and RAW264.7 cells, a mouse macrophage cell line, were stimulated with lipopolysaccharide (LPS) or recombinant IL-18 (rIL-18). We assessed the expression of inflammatory cytokines, caspase cleavage, and markers of apoptotic pathways. In Leydig cells, caspase 3 cleavage was increased and death-receptor-mediated apoptotic pathways were activated after LPS stimulation. However, LPS stimulation did not increase IL-18 expression in the Leydig cell line. When high-dose rIL-18 was administered to the Leydig cell line to mimic levels seem after inflammation, rIL-18 upregulated Tnf-α mRNA, Fadd mRNA, and Fas protein, promoted cleavage of caspase-8 and caspase-3, and induced apoptosis. Low-dose rIL-18 did not stimulate apoptosis. To determine if the high level of IL-18 seen in the testes after inflammation was derived from immune cells, we examined IL-18 protein expression in a macrophage cell line, RAW264.7. In contrast to the TM3 cells, IL-18 was significantly increased in RAW264.7 cells after LPS stimulation. These results suggest that high-dose IL-18 derived from macrophages is harmful to Leydig cells. Reducing the overexpression of IL-18 could be a new therapeutic approach to prevent Leydig cell apoptosis as a result of acute inflammation.

Endogenous interleukin 18 regulates testicular germ cell apoptosis during endotoxemia

Orchitis (testicular swelling) often occurs during systemic inflammatory conditions, such as sepsis. Interleukin 18 (IL18) is a proinflammatory cytokine and is an apoptotic mediator during endotoxemia, but the role of IL18 in response to inflammation in the testes was unclear. WT and IL18 knockout (KO) mice were injected lipopolysaccharide (LPS) to induce endotoxemia and examined 12 and 48  h after LPS administration to model the acute and recovery phases of endotoxemia. Caspase activation was assessed using immunohistochemistry. Protein and mRNA expression were examined by western blot and quantitative real-time RT-PCR respectively. During the acute phase of endotoxemia, apoptosis (as indicated by caspase-3 cleavage) was increased in WT mice but not in IL18 KO mice. The death receptor-mediated and mitochondrial-mediated apoptotic pathways were both activated in the WT mice but not in the KO mice. During the recovery phase of endotoxemia, apoptosis was observed in the IL18 KO mice but not in the WT mice. Activation of the death-receptor mediated apoptotic pathway could be seen in the IL18 KO mice but not the WT mice. These results suggested that endogenous IL18 induces germ cell apoptosis via death receptor mediated- and mitochondrial-mediated pathways during the acute phase of endotoxemia and suppresses germ cell apoptosis via death-receptor mediated pathways during recovery from endotoxemia. Taken together, IL18 could be a new therapeutic target to prevent orchitis during endotoxemia.

Antimicrobial responses in the male reproductive tract of lipopolysaccharide challenged rats

PROBLEM

Innate immune machinery including the Toll-like receptors (TLRs) confers the first line of defense mechanisms to counter pathogenic microorganisms that enter the body. The male reproductive tract is vulnerable to infection and the role of TLRs and the antimicrobial responses that operate to counter infections in this organ system are poorly understood.

METHOD OF STUDY

Caput and cauda epididymides, testes and seminal vesicles were collected at 0, 3, 6, 9, 12, 15 and 24 h from rats injected intraperitoneally with a single dose of LPS. Plasma testosterone was measured using ELISA. Expression pattern of defensins and Spag11 isoforms were analysed using RT-PCR. Immunohistochemical analyses was performed to determine SPAG11E protein expression following LPS treatment.

RESULTS

We provide the first line of evidence that the male reproductive tract induces the expression of Sperm Associated Antigen 11 (Spag11) mRNA variants and defensins when challenged with lipopolysaccharide (LPS) with a concomitant increase in protein expression. However, there was an inverse relationship between induction of antimicrobial gene expression and plasma testosterone. An increase in the mRNA levels of proinflammatory cytokines was observed parallel to the induction of Spag11 variants and majority of defensin expression in the male reproductive tract.

CONCLUSION

The increase in Spag11 and defensin mRNA in response to LPS administration demonstrates their importance in protecting the male reproductive tract during infection. Results of this study help to understand male reproductive tract innate immune defense mechanisms and to design novel peptide antibiotics to prevent sexually transmitted diseases.

Immunology of the Testis and Male Reproductive Tract

A large body of evidence points to the existence of a close, dynamic relationship between the immune system and the male reproductive tract, which has important implications for our understanding of both systems. The testis and the male reproductive tract provide an environment that protects the otherwise highly immunogenic spermatogenic cells and sperm from immunological attack. At the same time, secretions of the testis, including androgens, influence the development and mature functions of the immune system. Activation of the immune system has negative effects on both androgen and sperm production, so that systemic or local infection and inflammation compromise male fertility. The mechanisms underlying these interactions have begun to receive the attention from reproductive biologists and immunologists that they deserve, but many crucial details remain to be uncovered. A complete picture of male reproductive tract function and its response to toxic agents is contingent upon continued exploration of these interactions and the mechanisms involved.

Inflammatory networks in the control of spermatogenesis : chronic inflammation in an immunologically privileged tissue?

Spermatogenesis is a complex, organized process involving intimate interactions between the developing germ cells and supporting Sertoli cells. The process is also highly regulated. Studies suggest that regulation in the seminiferous epithelium involves molecules normally associated with either immune or inflammatory processes; in particular, interleukin 1a (IL1a), IL6, tumor necrosis factor (TNFa), activin A and nitric oxide (NO). While there is considerable evidence that these inflammatory mediators have effects on spermatogonial and spermatocyte development as well as critical supportive functions of the Sertoli cells, which are undoubtedly of considerable importance during testicular inflammation, there remains some skepticism regarding the significance of these molecules with respect to normal testicular function. Nonetheless, it is evident that expression of these regulators varies across the cycle of the seminiferous epithelium in a consistent manner, with major changes in production coinciding with key events within the cycle. This review summarizes the evidence supporting the hypothesis that inflammatory cytokines play a role in normal testicular spermatogenesis, as well as in the etiology of inflammation induced sub-fertility. The balance of data leads to the striking conclusion that the cycle of the seminiferous epithelium resembles a chronic inflammatory event. This appears to be a somewhat paradoxical assertion, since the testis is an immunologically privileged tissue based on its well-established ability to support grafts with minimal rejection responses. However, it may be argued that local immunoregulatory mechanisms, which confer protection from immunity on both transplanted tissues and the developing spermatogenic cells, are equally necessary to prevent local inflammation responses associated with the spermatogenic process from activating the adaptive immune response.

Constitutive expression of IL-18 and IL-18R in differentiated IEC-6 cells: effect of TNF-alpha and IFN-gamma treatment

The multifunctional cytokine interleukin-18 (IL-18) is an important mediator in intestinal inflammatory processes. The aim of this study was to evaluate the constitutive expression of IL-18 and its receptors (IL-18Ralpha and IL-18Rbeta) in intestinal epithelial cells (IEC) stimulated by tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). In addition, cellular proliferation and evaluation of brush border enzymes as differentiation markers were studied. Nontransformed rat intestinal epithelial IEC-6 cells were grown on an extracellular matrix (ECM) in medium with or without TNF-alpha, IFN-gamma, or a combination of both. Gene expression of IL-18, its receptors and apoptotic markers was evaluated using real-time PCR. Expression of IL-18Ralpha protein was demonstrated by flow cytometry and Western blot. Enzymatic activities of brush border enzymes and caspase-1 were determined. The constitutive expression of IL-18, IL-18Ralpha and IL-18Rbeta mRNAs and proteins were detected in IEC-6 cells. The biologically active form of IL-18 was released in response to TNF-alpha and IFN-gamma treatment. Exogenous IL-18 had no effect on cellular proliferation, brush border enzyme activities, and gene expression of apoptotic markers. However, the addition of IL-18 stimulated production and release of the chemokine IL-8. These data suggest that IEC-6 cells may be not only a source of IL-18 but also a target for its action.

Interleukin-1 superfamily genes expression in normal or impaired human spermatogenesis

Interleukin-1 (IL-1) is a pleiotropic cytokine that may play a role in contributing to the specific immune environment of mammalian testis and in regulating cell differentiation. We have determined the transcription activity of the IL-1 gene family (using real-time polymerase chain reaction (PCR)) in two main functional testicular compartments (interstitial and intratubular ones), and in tissue homogenates obtained from patients with fertility disorders (spermatogenic arrest and testicular tumors). We observed the prominent expression of gene coding for IL-1 receptor antagonist (IL-1RA) in a purified fraction of gametogenic cells (normal gonad). Caspase-1 (ICE - IL-1beta-converting enzyme) was highly expressed (on mRNA level) in interstitial compartments as well in testicular tumors (immune enhancement?). In addition we found, that the activity of IL-1RA gene decreased along spermatogenic alteration in an inversely related manner with IL-1alpha (from normal gonad through spermatogenic arrest to Sertoli cell only syndrome). Therefore, the quotient value of IL-1alpha/IL-1RA could potentially serve as the diagnostic molecular probe for spermatogenesis assessment. The precise level of mRNA for IL-1-IL-18 cytokines and their receptors, and specifically of the receptor antagonist in immune privileged gonad, could be one of the main factors responsible for maintaining testicular homeostasis, thus enabling generation of the mature spermatozoa.

The high mobility group box chromosomal protein 1 is expressed in the human and rat testis where it may function as an antibacterial factor

BACKGROUND

The high mobility group box chromosomal protein 1 (HMGB1) was originally shown to be a nuclear DNA-binding protein that activates transcription and promotes differentiation. More recently, there have been reports that HMGB1 may also function as a pro-inflammatory and antibacterial factor. The aim of this study was to investigate the testicular expression and antibacterial functions of HMGB1 to elucidate a possible role of HMGB1 in the testicular barrier defence against infections.

METHODS AND RESULTS

RT-PCR and in situ hybridization revealed high-level testicular expression of HMGB1 mRNA and localization of this expression to the Sertoli cells and germ cells of the human and rat testis. In addition, immunohistochemical examination demonstrated the presence of the corresponding protein in Sertoli cells and spermatogonia in human and rat testes. Western blotting detected abundant amounts of the HMGB1 protein in the interstitial and intratubular fluids of the intact adult rat testis. Finally, the HMGB1 protein purified from both human and rat testis by reversed-phase high-performance liquid chromatography (HPLC) exerted antibacterial activity towards Bacillus megaterium in an inhibition zone assay.

CONCLUSION

HMGB1 is expressed by Sertoli cells and germ cells in the mammalian testis. In addition, purified testicular HMGB1 shows antibacterial activity, indicating that this protein may function as a paracrine host defence factor in the testis.