Transforming growth factor beta2 is released from PC12 cells via the regulated pathway of secretion

Effect of TGF-beta1 on long-term synaptic plasticity and distribution of AMPA receptors in the CA1 field of the hippocampus

Using the methods of electrophysiology and immunohistochemistry, the effect of the transforming factor beta-1(TGF-β1), an anti-inflammatory cytokine, on the long-term post-tetanic potentiation (LTP) in CA1 field hippocampal slices and the distribution of the GluR1 subunit of the AMPA receptor has been studied. It was shown that TGF-β1 at a concentration of 10 ng/ml did not significantly affect the initial stage of LTP and substantially changed the distribution of synaptic AMPA receptors in response to tetanic stimulation. Twenty five minutes after the tetanization, the main pool of AMPA receptors (90%) was due to the postsynaptic density (PSD). By contrast, LTP in the presence of TGF-β1 was accompanied by less pronounced changes in the distribution of AMPA receptors. Their localization in both pre- and postsynaptic regions remained nearly the same as that in the control. It may be suggested that the normal distribution of AMPA receptors in spinous synapses promotes the stabilization of potentiated synapses, thereby retaining LTP for longer terms.

The ELAV family of RNA-binding proteins in synaptic plasticity and long-term memory

The mechanisms of de novo gene expression and translation of specific gene transcripts have long been known to support long-lasting changes in synaptic plasticity and behavioral long-term memory. In recent years, it has become increasingly apparent that gene expression is heavily regulated not only on the level of transcription, but also through post-transcriptional gene regulation, which governs the subcellular localization, stability, and likelihood of translation of mRNAs. Specific families of RNA-binding proteins (RBPs) bind transcripts which contain AU-rich elements (AREs) within their 3' UTR and thereby govern their downstream fate. These post-transcriptional gene regulatory mechanisms are coordinated through the same cell signaling pathways that play critical roles in long-term memory formation. In this review, we discuss recent results that demonstrate the roles that these ARE-binding proteins play in LTM formation.

A key role for TGF-β1 in hippocampal synaptic plasticity and memory

Transforming Growth Factor β1 (TGF-β1) is a well-known neuroprotective and neurotrophic factor demonstrated to play a role in synaptic transmission. However, its involvement in physiological mechanisms underlying synaptic plasticity and memory at hippocampal level has not been thoroughly investigated. Here, we examine the role of TGF-β1 in hippocampal long-term potentiation (LTP) and memory in adult wild type mice. Our data provide evidence that administration of exogenous TGF-β1 is able to convert early-phase-LTP into late-phase-LTP. Furthermore, we show that the block of the endogenous TGF-β1 signaling pathway by the specific TGF-β1 inhibitor SB431542, impairs LTP and object recognition memory. The latter impairment was rescued by administration of exogenous TGF-β1, suggesting that endogenously produced TGF-β1 plays a role in physiological mechanisms underlying LTP and memory. Finally, TGF-β1 functional effect correlates with an increased expression of the phosphorylated transcription factor cAMP-Responsive Element Binding protein.

Crimpy enables discrimination of presynaptic and postsynaptic pools of a BMP at the Drosophila neuromuscular junction

Distinct pools of the bone morphogenetic protein (BMP) Glass bottom boat (Gbb) control structure and function of the Drosophila neuromuscular junction. Specifically, motoneuron-derived Gbb regulates baseline neurotransmitter release, whereas muscle-derived Gbb regulates neuromuscular junction growth. Yet how cells differentiate between these ligand pools is not known. Here we present evidence that the neuronal Gbb-binding protein Crimpy (Cmpy) permits discrimination of pre- and postsynaptic ligand by serving sequential functions in Gbb signaling. Cmpy first delivers Gbb to dense core vesicles (DCVs) for activity-dependent release from presynaptic terminals. In the absence of Cmpy, Gbb is no longer associated with DCVs and is not released by activity. Electrophysiological analyses demonstrate that Cmpy promotes Gbb's proneurotransmission function. Surprisingly, the Cmpy ectodomain is itself released upon DCV exocytosis, arguing that Cmpy serves a second function in BMP signaling. In addition to trafficking Gbb to DCVs, we propose that Gbb/Cmpy corelease from presynaptic terminals defines a neuronal protransmission signal.

Anterograde Activin signaling regulates postsynaptic membrane potential and GluRIIA/B abundance at the Drosophila neuromuscular junction

Members of the TGF-β superfamily play numerous roles in nervous system development and function. In Drosophila, retrograde BMP signaling at the neuromuscular junction (NMJ) is required presynaptically for proper synapse growth and neurotransmitter release. In this study, we analyzed whether the Activin branch of the TGF-β superfamily also contributes to NMJ development and function. We find that elimination of the Activin/TGF-β type I receptor babo, or its downstream signal transducer smox, does not affect presynaptic NMJ growth or evoked excitatory junctional potentials (EJPs), but instead results in a number of postsynaptic defects including depolarized membrane potential, small size and frequency of miniature excitatory junction potentials (mEJPs), and decreased synaptic densities of the glutamate receptors GluRIIA and B. The majority of the defective smox synaptic phenotypes were rescued by muscle-specific expression of a smox transgene. Furthermore, a mutation in actβ, an Activin-like ligand that is strongly expressed in motor neurons, phenocopies babo and smox loss-of-function alleles. Our results demonstrate that anterograde Activin/TGF-β signaling at the Drosophila NMJ is crucial for achieving normal abundance and localization of several important postsynaptic signaling molecules and for regulating postsynaptic membrane physiology. Together with the well-established presynaptic role of the retrograde BMP signaling, our findings indicate that the two branches of the TGF-β superfamily are differentially deployed on each side of the Drosophila NMJ synapse to regulate distinct aspects of its development and function.

CEH-28 activates dbl-1 expression and TGF-β signaling in the C. elegans M4 neuron

M4 is a multifunctional neuron in the Caenorhabditis elegans pharynx that can both stimulate peristaltic contractions of the muscles in the pharyngeal isthmus and function systemically to regulate an enhanced sensory response under hypoxic conditions. Here we identify a third function for M4 that depends on activation of the TGF-β family gene dbl-1 by the homeodomain transcription factor CEH-28. dbl-1 is expressed in M4 and a subset of other neurons, and we show CEH-28 specifically activates dbl-1 expression in M4. Characterization of the dbl-1 promoter indicates that CEH-28 targets an M4-specific enhancer within the dbl-1 promoter region, while expression in other neurons is mediated by separate regulatory sequences. Unlike ceh-28 mutants, dbl-1 mutants do not exhibit M4 synaptic and signaling defects. Instead, both ceh-28 and dbl-1 mutants exhibit morphological defects in the g1 gland cells located adjacent to M4 in the pharynx, and these defects can be partially rescued by M4-specific expression of dbl-1 in these mutants. Identical gland cell defects are observed in sma-6 and daf-4 mutants defective in the receptor for DBL-1, but they are not observed in sma-2 and sma-3 mutants lacking the R-Smads functioning downstream of this receptor. Together these results identify a novel neuroendocrine function for M4 and provide evidence for an R-Smad-independent mechanism for DBL-1 signaling in C. elegans.

Growth factors in synaptic function

Synapses are increasingly recognized as key structures that malfunction in disorders like schizophrenia, mental retardation, and neurodegenerative diseases. The importance and complexity of the synapse has fuelled research into the molecular mechanisms underlying synaptogenesis, synaptic transmission, and plasticity. In this regard, neurotrophic factors such as netrin, Wnt, transforming growth factor-β (TGF-β), tumor necrosis factor-α (TNF-α), and others have gained prominence for their ability to regulate synaptic function. Several of these factors were first implicated in neuroprotection, neuronal growth, and axon guidance. However, their roles in synaptic development and function have become increasingly clear, and the downstream signaling pathways employed by these factors have begun to be elucidated. In this review, we will address the role of these factors and their downstream effectors in synaptic function in vivo and in cultured neurons.

Expression and function of the Transforming Growth Factor-b system in the human and rat enteric nervous system

BACKGROUND

Transforming growth factor-betas (TGF-bs) are pleiotropic growth factors exerting neurotrophic functions upon various neuronal populations of the central nervous system. In contrast, the role of TGF-b isoforms in the enteric nervous system (ENS) is largely unknown. We therefore analyzed the gene expression pattern of the TGF-b system in the human colon and in rat myenteric plexus, and smooth muscle cell cultures and determined the effect of TGF-b isoforms on neuronal differentiation.

METHODS

Human colonic samples as well as cultured rat myenteric plexus, and smooth muscle cells were assessed for mRNA expression levels of the TGF-b system (TGF-b1-3, TbR-1-3) by qPCR. The colonic wall was separated into mucosa and tunica muscularis and enteric ganglia were isolated by laser microdissection (LMD) to allow site-specific gene expression analysis. Effects of TGF-b isoforms on neurite outgrowth and branching pattern of cultured myenteric neurons were monitored.

KEY RESULTS

mRNA expression of the TGF-b system was detected in all compartments of the human colonic wall as well as in LMD-isolated myenteric ganglia. Cultured myenteric neurons and smooth muscle cells of rat intestine also showed mRNA expression of all ligands and receptors. Transforming growth factor-b2 treatment increased neurite length and branching pattern in cultured myenteric neurons.

CONCLUSIONS & INFERENCES

The TGF-b system is abundantly expressed in the human and rat ENS arguing for an auto-/paracrine function of this system on enteric neurons. Transforming growth factor-b2 promotes neuronal differentiation and plasticity characterizing this molecule as a relevant neurotrophic factor for the ENS.

Adenosine A2B receptor-mediated leukemia inhibitory factor release from astrocytes protects cortical neurons against excitotoxicity

Background

Neuroprotective and neurotrophic properties of leukemia inhibitory factor (LIF) have been widely reported. In the central nervous system (CNS), astrocytes are the major source for LIF, expression of which is enhanced following disturbances leading to neuronal damage. How astrocytic LIF expression is regulated, however, has remained an unanswered question. Since neuronal stress is associated with production of extracellular adenosine, we investigated whether LIF expression in astrocytes was mediated through adenosine receptor signaling.

Methods

Mouse cortical neuronal and astrocyte cultures from wild-type and adenosine A_2B receptor knock-out animals, as well as adenosine receptor agonists/antagonists and various enzymatic inhibitors, were used to study LIF expression and release in astrocytes. When needed, a one-way analysis of variance (ANOVA) followed by Bonferroni post-hoc test was used for statistical analysis.

Results

We show here that glutamate-stressed cortical neurons induce LIF expression through activation of adenosine A_2B receptor subtype in cultured astrocytes and require signaling of protein kinase C (PKC), mitogen-activated protein kinases (MAPKs: p38 and ERK1/2), and the nuclear transcription factor (NF)-κB. Moreover, LIF concentration in the supernatant in response to 5′-N-ethylcarboxamide (NECA) stimulation was directly correlated to de novo protein synthesis, suggesting that LIF release did not occur through a regulated release pathway. Immunocytochemistry experiments show that LIF-containing vesicles co-localize with clathrin and Rab11, but not with pHogrin, Chromogranin (Cg)A and CgB, suggesting that LIF might be secreted through recycling endosomes. We further show that pre-treatment with supernatants from NECA-treated astrocytes increased survival of cultured cortical neurons against glutamate, which was absent when the supernatants were pre-treated with an anti-LIF neutralizing antibody.

Conclusions

Adenosine from glutamate-stressed neurons induces rapid LIF release in astrocytes. This rapid release of LIF promotes the survival of cortical neurons against excitotoxicity.

More than being protective: functional roles for TGF-β/activin signaling pathways at central synapses

It is becoming increasingly clear that members of the transforming growth factor-β (TGF-β) family have roles in the central nervous system that extend beyond their well-established roles as neurotrophic and neuroprotective factors. Recent findings have indicated that the TGF-β signaling pathways are involved in the modulation of both excitatory and inhibitory synaptic transmission in the adult mammalian brain. In this review, we discuss how TGF-β, bone morphogenetic protein and activin signaling at central synapses modulate synaptic plasticity, cognition and affective behavior. We also discuss the implications of these findings for the molecular understanding and potential treatment of neuropsychiatric diseases, such as anxiety, depression and other neurological disorders.

Klf10 and Klf11 as mediators of TGF-beta superfamily signaling

Klf10 and Klf11 belong to the family of Sp1/Krüppel-like zinc finger transcription factors that play important roles in a variety of cell types and tissues. Although Klf10 and Klf11 were initially introduced as transforming growth factor-beta (TGF-beta)-inducible genes, several studies have described their upregulation by a plethora of growth factors, cytokines and hormones. Here, we review the current knowledge of the inductive cues for Klf10 and Klf11 and focus on their transcriptional regulation by members of the TGF-beta superfamily. We further summarize their involvement in the regulation of the TGF-beta signaling pathway and discuss their possible role as molecules mediating crosstalk between various signaling pathways. Finally, we provide an overview of the pro-apoptotic and anti-proliferative functions of Klf10 and Klf11.

Competitive enhancement of HGF-induced epithelial scattering by accessory growth factors

HGF signaling induces epithelial cells to disassemble cadherin-based adhesion and increase cell motility and invasion, a process termed epithelial-mesenchymal transition (EMT). EMT plays a major role in cancer metastasis, allowing individual cells to detach from the primary tumor, invade local tissue, and colonize distant tissues with new tumors. While invasion of vascular and lymphatic networks is the predominant route of metastasis, nerves also can act as networks for dissemination of cancer cell to distant sites in a process termed perineual invasion (PNI). Signaling between nerves and invasive cancer cells remains poorly understood, as does cellular decision making that selects the specific route of invasion. Here we examine how HGF signaling contributes to PNI using reductionist culture model systems. We find that TGFβ, produced by PC12 cells, enhances scattering in response to HGF stimulation, increasing both cell-cell junction disassembly and cell migration. Further, gradients of TGFβ induce migratory mesenchymal cells to undergo chemotaxis towards the source of TGFβ. Interestingly, VEGF suppresses TGFβ-induced enhancement of scattering. These results have broad implications for how combinatorial growth factor signaling contributes to cancer metastasis, suggesting that VEGF and TGFβ might modulate HGF signaling to influence route selection during cancer progression.

Expression of CXCL10 in cultured cortical neurons

Chemokines expressed in neurons are important mediators in neuron-neuron and neuron-glia signaling. One of these chemokines is CCL21 that activates microglia via the chemokine receptor CXCR3. As neurons also express CXCL10, a main ligand for CXCR3, we have thus investigated in detail the expression pattern of CXCL10 in neurons. We show that CXCL10 is constitutively expressed by neurons, is stored in large dense-core vesicles and is not regulated by neuronal injury or stress. Neuronal CXCL10 release occurred constitutively at low level. In vivo CXCL10 expression was found in the developing brain at various embryonic stages and its peak expression correlates with the presence of CD11b- and GFAP-positive cells expressing CXCR3. These results suggest a possible role of neuronal CXCL10 in recruitment and homing of glial cells during embryogenesis.

Impaired dense core vesicle maturation in Caenorhabditis elegans mutants lacking Rab2

Uncoordinated movement in Rab2 mutants is caused by impaired retention of cargo on dense core vesicles, not by defective synaptic vesicle release. (Also see the companion article by Sumakovic et al. in this issue.)

Despite a key role for dense core vesicles (DCVs) in neuronal function, there are major gaps in our understanding of DCV biogenesis. A genetic screen for Caenorhabditis elegans mutants with behavioral defects consistent with impaired DCV function yielded five mutations in UNC-108 (Rab2). A genetic analysis showed that unc-108 mutations impair a DCV function unrelated to neuropeptide release that, together with neuropeptide release, fully accounts for the role of DCVs in locomotion. An electron microscopy analysis of DCVs in unc-108 mutants, coupled with quantitative imaging of DCV cargo proteins, revealed that Rab2 acts in cell somas during DCV maturation to prevent the loss of soluble and membrane cargo. In Rab2 null mutants, two thirds of these cargoes move to early endosomes via a PI(3)P-dependent trafficking pathway, whereas aggregated neuropeptides are unaffected. These results reveal how neurons solve a challenging trafficking problem using the most highly conserved animal Rab.

Pheochromocytoma-induced cardiomyopathy is modulated by the synergistic effects of cell-secreted factors

BACKGROUND

Pheochromocytomas are rare tumors derived from the chromaffin cells of the adrenal medulla. Although these tumors have long been postulated to induce hypertension and cardiomyopathy through the hypersecretion of catecholamines, catecholamines alone may not fully explain the profound myocardial remodeling induced by these tumors. We sought to determine whether changes in myocardial function in pheochromocytoma-induced cardiomyopathy result solely from catecholamines secretion or from multiple pheochromocytoma-derived factors.

METHODS AND RESULTS

Isolated cardiomyocytes incubated with pheochromocytoma-conditioned growth media contracted at a higher frequency than cardiomyocytes incubated with norepinephrine (NE) only. Sprague-Dawley rats and black-6 mice were implanted with agarose-encapsulated pheochromocytoma (PC12) cells, dihydroxyphenylalanine decarboxylase knock-out PC12 cells deficient in NE (PC12-KO), or NE-secreting pumps. PC12 cell implantation increased left ventricular dilation by 35+/-6% and 9.6+/-1.4% and reduced left ventricular fractional shortening by 20+/-3% and 28+/-4% in rats and mice compared with animals dosed only with NE, respectively. Elimination of NE secretion in PC12-KO cells induced neither cardiac dilation (3.9%+/-1.8% increase versus control) nor changes in (1.9%+/-0.4% reduction) fractional shortening compared to controls.

CONCLUSIONS

Pheochromocytomas induce a greater degree of cardiomyopathy than equivalent doses of NE, suggesting pheochromocytoma-induced cardiomyopathy is not solely mediated by NE, rather pheochromocytoma secretory factors in combination with catecholamines act synergistically to induce greater cardiac damage than catecholamines alone.

Expression, transport, and axonal sorting of neuronal CCL21 in large dense-core vesicles

Neurons are highly polarized cells, and neuron-neuron communication is based on directed transport and release of neurotransmitters, neuropeptides, and neurotrophins. Directed communication may also be attributed to neuron-microglia signaling, since neuronal damage can induce a microglia reaction at specific sites only. However, the mechanism underlying this site-specific microglia reaction is not yet understood. Neuronal CCL21 is a microglia-activating chemokine, which in brain is solely found in endangered neurons and is therefore a candidate for neuron-microglia signaling. Here we present that neuronal CCL21 is sorted into large dense-core vesicles, the secretory granules of the regulated release pathway of neurons. Live-cell imaging studies show preferential sorting of CCL21-containing vesicles into axons, indicating its directed transport. Thus, mouse neurons express and transport a microglia activating factor very similar to signaling molecules used in neuron-neuron communication. These data show for the first time the directed transport of a microglia activating factor in neurons and corroborate the function of neuronal CCL21 in directed neuron-microglia communication.

Antidepressant drugs modulate growth factors in cultured cells

BACKGROUND

Different classes of antidepressant drugs are used as a treatment for depression by activating the catecholinergic system. In addition, depression has been associated with decrease of growth factors, which causes insufficient axonal sprouting and reduced neuronal damage repair. In this study, antidepressant treatments are analyzed in a cell culture system, to study the modulation of growth factors.

RESULTS

We quantified the transcription of several growth factors in three cell lines after application of antidepressant drugs by real time polymerase chain reaction. Antidepressant drugs counteracted against phorbolester-induced deregulation of growth factors in PMA-differentiated neuronal SY5Y cells. We also found indications in a pilot experiment that magnetic stimulation could possibly modify BDNF in the cell culture system.

CONCLUSION

The antidepressant effects antidepressant drugs might be explained by selective modulation of growth factors, which subsequently affects neuronal plasticity.

Pertussis toxin B-oligomer suppresses human immunodeficiency virus-1 Tat-induced neuronal apoptosis through feedback inhibition of phospholipase C-beta by protein kinase C

Human immunodeficiency virus (HIV)-1 Tat is a multifunctional protein involved in viral replication, inflammation and apoptosis. Tat activates phospholipase C-beta (PLC-beta), presumably via a pertussis toxin (PTX) sensitive G(i) protein, which is critical for neuronal apoptosis. In this study, we show that Tat-mediated intracellular Ca(2+) release in rat pheochromocytoma (PC-12) cells and rat primary cortical neuronal cultures was abrogated by pretreatment with either pertussis toxin and/or its B-oligomer subunit (PTX-B), devoid of ADP ribosyltransferase activity. PTX-B pretreatment also inhibited intracellular Ca(2+) release by bradykinin and 2,4,6-trimethyl-N-(m-3-trifluoromethylphenyl) benzenesulfonamide (m-3M3FBS), a director activator of phospholipase C. Activation of protein kinase C (PKC) by phorbol 12,13-dibutyrate (PdBu) mimicked the PTX-B-mediated inhibition of m-3M3FBS-stimulated intracellular Ca(2+) increase, while inhibition of PKC by bisindolylmaleimide I hydrochloride (BIM) reversed the inhibitory action of PTX-B. Functionally, PTX-B reduced Tat-induced Bax and caspase-3 proteins and reduced cell apoptosis. We conclude that PTX inhibition of Tat-mediated intracellular Ca(2+) release is independent of ADP ribosylation of the G(i) protein via the A protomer, but mediated by the B-oligomer. Furthermore, PTX-B suppresses HIV-1 Tat-mediated apoptosis by reducing its activation of PLC-beta through a PKC activation pathway.

Morphological alteration of Golgi apparatus and subcellular compartmentalization of TGF-beta1 in Golgi apparatus in gerbils following transient forebrain ischemia

Golgi apparatus (GA) is a very important organelle involved in the metabolism of numerous proteins. TGF-beta1 plays an important role in supporting neuronal survival after ischemic insults. Little is known, however, about the morphological alteration of GA and subcellular compartmentalization of TGF-beta1 in brain after ischemia. Therefore, our present study was designed to check for GA morphological alterations and TGF-beta1 subcellular localization. GA immunoreactivities were examined in the somatosensory cortex of gerbils after 10 min transient forebrain ischemia. Confocal Immunofluorographs of TGF-beta1 and TGN38 were also taken. Results indicated that no fragmentation of GA was found in gerbils of norm, shams and 6, 24 and 72 h postocclusion, but some of the cortical cells showed fragmentation of GA in gerbils 7 days postocclusion. TGF-beta1 was colocalized with TGN38, a marker molecule for the GA. We conclude that there was morphological alterations of GA and TGF-beta1 was present in GA in the somatosensory cortex after 10 min ischemia.

Constitutive secretion of protease nexin-1 by glial cells and its regulation by G-protein-coupled receptors

Extracellular serine proteases and their inhibitors (serpins) play a key role for synaptic plasticity in the developing and adult CNS. Serpins also counteract the extravasated proteases during brain injury. We studied the mechanisms by which one of the most important serpins, serpinE2 or protease nexin-1 (PN-1), is secreted by glial cells and how its secretion is regulated by extracellular signals. Using time-lapse videomicroscopy and biochemical methods, we demonstrate that PN-1 is constitutively secreted through small vesicles animated by a discontinuous movement using microtubules as tracks. The F-actin network underneath the plasma membrane acting as a barrier hindered PN-1 vesicle exocytosis. Vasointestinal/pituitary adenylate cyclase peptides and the G-protein activator mastoparan increased PN-1 secretion by disrupting the F-actin barrier. The receptor-mediated regulation of PN-1 constitutive secretion may be an important mechanism adapting extracellular proteolytic activity to synaptic activity.

Pioglitazone induces vascular smooth muscle cell apoptosis through a peroxisome proliferator-activated receptor-gamma, transforming growth factor-beta1, and a Smad2-dependent mechanism

Thiazolidinediones, such as pioglitazone, seem to exert direct antiatherosclerotic and antirestenotic effects on type 2 diabetes, in part due to an induction of vascular smooth muscle cell (VSMC) apoptosis. We aimed to study the role of transforming growth factor (TGF)-beta in rat aortic VSMC. Pioglitazone at 100 micromol/l increased apoptosis without affecting DNA synthesis, and this effect was reversed by an anti-TGF-beta1 antibody. Extracellular TGF-beta1 levels were rapidly increased after treatment with pioglitazone in a peroxisome proliferator-activated receptor (PPAR)-gamma-dependent mechanism because this secretion was blocked by the PPAR-gamma inhibitor GW9662. Pioglitazone subsequently increased the nuclear recruitment of phospho-Smad2, without any effect on protein expression. According to our results, we propose that the apoptotic effect of pioglitazone on VSMC depends on the following sequence: PPAR-gamma activation, TGF-beta1 release, and selective phospho-Smad2 nuclear recruitment. Management of Smad signaling on VSMC might provide future clinical benefits in vascular diseases.

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.