Divergent cell-specific effects of activin-A on thymocyte proliferation stimulated by phytohemagglutinin, and interleukin 1beta or interleukin 6 in vitro

Preeclampsia and Its Impact on Human Milk Activin A Concentration

BACKGROUND

It is known that preeclampsia affects lactogenesis. However, data on the effects of this pathology on human milk neurobiomarker composition are not available. The aim of this study is to investigate the effects of this gestational pathology on activin A levels, a neurobiomarker known to play an important role in the development and protection of the central nervous system.

METHODS

The women recruited were divided in two different study groups: preeclamptic or normotensive women. All the human milk samples were collected using the same procedure. Activin A was quantified using an Enzyme-linked immunosorbent assay (ELISA) test. To investigate the effect of preeclampsia on the activin A concentration in the three lactation phases, a mixed linear model with a unistructural covariance structure, with the mother as the random effect, and fixed effects were performed.

RESULTS

Activin A was detected in all samples. There were no significant differences between preeclamptic and normotensive women. The only significant effect is related to the lactation phase: the difference between colostrum and mature milk (p < 0.01) was significant. In conclusion, these results allow us to affirm that breast milk's beneficial properties are maintained even if preeclampsia occurs.

Clinical and Therapeutic Implications of Follistatin in Solid Tumours

Follistatin (FST), as a single-chain glycosylated protein, has two major isoforms, FST288 and FST315. The FST315 isoform is the predominant form whilst the FST288 variant accounts for less than 5% of the encoded mRNA. FST is differentially expressed in human tissues and aberrant expression has been observed in a variety of solid tumours, including gonadal, gastric and lung cancer, hepatocellular carcinoma, basal cell carcinoma and melanoma. Based on the current evidence, FST is an antagonist of transforming growth factor beta family members, such as activin and bone morphogenetic proteins (BMPs). FST plays a role in tumourigenesis, metastasis and angiogenesis of solid tumours through its interaction with activin and BMPs, thus resulting in pathophysiological function. In terms of diagnosis, prognosis and therapy, FST has shown strong promise. Through a better understanding of its biological functions, potential clinical applications may yet emerge.

The Effect of Holder Pasteurization on Activin A Levels in Human Milk

INTRODUCTION

There is evidence that mother's own milk is the best nutrient in terms of multiorgan protection and infection prevention. However, when maternal milk is scarce, the solution can be represented by donor milk (DM), which requires specific storage procedures such as Holder Pasteurization (HoP). HoP is not free from side effects since it is widely known that it causes qualitative/quantitative changes in milk composition, particularly in the protein content. Therefore, the aim of this study is to investigate the effects of HoP on Activin A, a neurobiomarker known to play an important role in the development and protection of the central nervous system.

METHODS

In 24 mothers who delivered preterm (n = 12) and term (n = 12) healthy newborns, we conducted a pretest/test study where the milk donors acted as their own controls. Each sample was divided into two parts: the first was frozen at -80°C (Group 1); the second was Holder-pasteurized before freezing at -80°C (Group 2). Activin A was quantified using an ELISA test.

RESULTS

Activin A was detected in all samples. There were no significant differences (p > 0.05) between the two groups, also when the analysis was stratified for gestational age at delivery and milk maturation degree (p > 0.05, for both).

CONCLUSION

The present findings on the absence of any side effects of HoP on the milk concentration of Activin A offer additional support to the efficacy of HoP in DM storage. Our data open up to further investigations on neurobiomarkers' assessment in human milk and their preanalytical stability according to storage procedures.

Serum activin-A as a predictive and prognostic marker in critically ill patients with sepsis

BACKGROUND AND OBJECTIVE

There are limited data regarding serum activin-A as a biomarker for sepsis. We examined whether serum activin-A concentration could predict sepsis severity and prognosis in the management of critically ill patients with sepsis.

METHODS

The subjects were adult patients suspected of having sepsis and admitted to intensive care unit (ICU) from January 2013 to March 2014. Serum activin-A concentration was measured in blood sampled within 48 h after ICU admission. The primary and secondary outcomes were the diagnostic value of serum activin-A concentration as a biomarker of sepsis and the prognostic value for predicting the clinical outcomes of sepsis, respectively.

RESULTS

One hundred and thirty patients who had clinically suspected sepsis were included. Most (66.2%) were male; their median age was 65 years, and their Acute Physiology and Chronic Health Evaluation II score was 22.3. Serum activin-A concentration tended to increase with sepsis severity and differed significantly between those with non-sepsis and severe sepsis and between those with severe sepsis and septic shock. The risks of sepsis, severe sepsis and septic shock were significantly higher in patients with a serum activin-A concentration of 251, 319 and 432 pg/mL or greater, respectively. Serum activin-A concentration was significantly associated with the Acute Physiology and Chronic Health Evaluation II score, Sequential Organ Failure Assessment score, Charlson comorbidity index and ICU mortality.

CONCLUSION

Serum activin-A was a predictor of sepsis severity and a prognostic marker in critically ill patients with sepsis. Serum activin-A concentration in the early phase of sepsis was associated with prognostic indexes on ICU admission and with ICU mortality.

The activins and their binding protein, follistatin-Diagnostic and therapeutic targets in inflammatory disease and fibrosis

The activins, as members of the transforming growth factor-β superfamily, are pleiotrophic regulators of cell development and function, including cells of the myeloid and lymphoid lineages. Clinical and animal studies have shown that activin levels increase in both acute and chronic inflammation, and are frequently indicators of disease severity. Moreover, inhibition of activin action can reduce inflammation, damage, fibrosis and morbidity/mortality in various disease models. Consequently, activin A and, more recently, activin B are emerging as important diagnostic tools and therapeutic targets in inflammatory and fibrotic diseases. Activin antagonists such as follistatin, an endogenous activin-binding protein, offer considerable promise as therapies in conditions as diverse as sepsis, liver fibrosis, acute lung injury, asthma, wound healing and ischaemia-reperfusion injury.

The roles of activin A and its binding protein, follistatin, in inflammation and tissue repair

Activin A, a member of the transforming growth factor-β superfamily of cytokines, is a critical controller of inflammation, immunity and fibrosis. It is rapidly released into the blood following a lipopolysaccharide challenge in experimental animals, through activation of the Toll-like receptor 4 signalling pathway. Blocking activin action by pre-treatment with its binding protein, follistatin, modifies the inflammatory cytokine cascade, and reduces the severity of the subsequent inflammatory response and mortality. Likewise, high serum levels of activin A are predictive of death in patients with septicaemia. However, activin A has complex immunomodulatory actions. It is produced by inflammatory macrophages, but can regulate either pro- or anti-inflammatory responses in these cells, depending on their prior activation status. Activin A is also produced by Th2 cells, and stimulates antibody production by B cells and the development of regulatory T cells. Production of activin A during inflammatory responses stimulates fibrosis and tissue remodelling, and follistatin inhibits these actions of activin A. The modulation of activin by follistatin may represent an important therapeutic target for the modulation and amelioration of inflammatory and fibrotic disorders.

The regulation and functions of activin and follistatin in inflammation and immunity

The activins are members of the transforming growth factor β superfamily with broad and complex effects on cell growth and differentiation. Activin A has long been known to be a critical regulator of inflammation and immunity, and similar roles are now emerging for activin B, with which it shares 65% sequence homology. These molecules and their binding protein, follistatin, are widely expressed, and their production is increased in many acute and chronic inflammatory conditions. Synthesis and release of the activins are stimulated by inflammatory cytokines, Toll-like receptor ligands, and oxidative stress. The activins interact with heterodimeric serine/threonine kinase receptor complexes to activate SMAD transcription factors and the MAP kinase signaling pathways, which mediate inflammation, stress, and immunity. Follistatin binds to the activins with high affinity, thereby obstructing the activin receptor binding site, and targets them to cell surface proteoglycans and lysosomal degradation. Studies on transgenic mice and those with gene knockouts, together with blocking studies using exogenous follistatin, have established that activin A plays critical roles in the onset of cachexia, acute and chronic inflammatory responses such as septicemia, colitis and asthma, and fibrosis. However, activin A also directs the development of monocyte/macrophages, myeloid dendritic cells, and T cell subsets to promote type 2 and regulatory immune responses. The ability of both endogenous and exogenous follistatin to block the proinflammatory and profibrotic actions of activin A has led to interest in this binding protein as a potential therapeutic for limiting the severity of disease and to improve subsequent damage associated with inflammation and fibrosis. However, the ability of activin A to sculpt the subsequent immune response as well means that the full range of effects that might arise from blocking activin bioactivity will need to be considered in any therapeutic applications.

Value of serum and synovial fluid activin A and inhibin A in some rheumatic diseases

AIM

The purpose of the study is to measure serum and synovial fluid levels of activin A and inhibin A in patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and osteoarthritis (OA) and correlate them with disease activity parameters.

SUBJECTS AND METHODS

This study included 60 patients with various rheumatic diseases (20 with RA, 20 with SLE and 20 with OA), as well as 10 healthy controls. All of them were subjected to complete history-taking, examination and estimation of disease activity index. The following investigations were done for all subjects: serum and synovial activin A, inhibin A, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), anti-dsDNA and complements 3 and 4.

RESULTS

Serum levels of activin A were significantly higher in RA, SLE and OA than controls and in RA and SLE versus OA The mean values of serum inhibin A were significantly higher in all studied groups than controls. Synovial activin A and inhibin A were significantly higher in RA than OA. Positive correlations were found between serum activin A and disease activity parameters of RA. In SLE, positive correlations were found between serum activin A and inhibin A with ESR and SLE Disease Activity Index.

CONCLUSIONS

Serum activin A and inhibin A were significantly higher in RA and SLE. Serum levels correlated positively with disease activity parameters of RA and SLE. However, synovial levels were significantly higher in RA than OA but showed no correlation or negative correlation with disease activity. We recommend further studies to detect the exact role of activin A and inhibin A in these conditions.

Role of activin in bacterial infections: a potential target for immunointervention?

Severe bacterial infections such as sepsis and meningitis still kill or severely injure people despite the use of bactericidal antibiotics. Therefore, new strategies for a better therapy are needed. Activin A, a member of the TGF-β superfamily and its binding protein follistatin (FS) are released by various cell types during acute and chronic inflammatory processes. Until now, a clear definition of conditions in which activin A exerts either its pro- or anti-inflammatory functions is lacking. The activin/FS-system participates in the fine-tuning of the host’s inflammatory response upon infectious stimuli. This response is on the one hand necessary for fighting pathogens, but on the other hand can negatively affect the host. This article focuses on the role of activin A and FS in infection and after acute inflammatory stimuli. The therapeutic potentials of blocking or promoting activin actions are discussed.

Activin and related proteins in inflammation: not just interested bystanders

Activin A, a member of the transforming growth factor-beta superfamily, is released rapidly into the circulation during inflammation. This review examines the evidence that activin is a critical mediator of inflammation and immunity. Activin modulates several aspects of the inflammatory response, including release of pro-inflammatory cytokines, nitric oxide production and immune cell activity. Crucially, inhibiting activin with follistatin, a high affinity binding protein, alters the pattern of cytokines released and improves survival in a mouse model of endotoxic shock. Serum and tissue concentrations of activin are elevated in a wide range of pathological conditions. The utility of activin as a diagnostic marker of clinical inflammation and the use of follistatin to block activin actions therapeutically are also discussed.

Activins and inhibins: novel regulators of thymocyte development

Activins and inhibins are members of the transforming growth factor-beta superfamily that act on different cell types and regulate a broad range of cellular processes including proliferation, differentiation, and apoptosis. Here, we provide the first evidence that activins and inhibins regulate specific checkpoints during thymocyte development. We demonstrate that both activin A and inhibin A promote the DN3-DN4 transition in vitro, although they differentially control the transition to the DP stage. Whereas activin A induces the accumulation of a CD8+CD24(hi)TCRbeta(lo) intermediate subpopulation, inhibin A promotes the differentiation of DN4 to DP. In addition, both activin A and inhibin A appear to promote CD8+SP differentiation. Moreover, inhibin alpha null mice have delayed in vitro T cell development, showing both a decrease in the DN-DP transition and reduced thymocyte numbers, further supporting a role for inhibins in the control of developmental signals taking place during T cell differentiation in vivo.

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.

Activin-A: a novel dendritic cell–derived cytokine that potently attenuates CD40 ligand–specific cytokine and chemokine production

Activin-A is a transforming growth factor-β (TGF-β) superfamily member that plays a pivotal role in many developmental and reproductive processes. It is also involved in neuroprotection, apoptosis of tumor and some immune cells, wound healing, and cancer. Its role as an immune-regulating protein has not previously been described. Here we demonstrate for the first time that activin-A has potent autocrine effects on the capacity of human dendritic cells (DCs) to stimulate immune responses. Human monocyte-derived DCs (MoDCs) and the CD1c+ and CD123+ peripheral blood DC populations express both activin-A and the type I and II activin receptors. Furthermore, MoDCs and CD1c+ myeloid DCs rapidly secrete high levels of activin-A after exposure to bacteria, specific toll-like receptor (TLR) ligands, or CD40 ligand (CD40L). Blocking autocrine activin-A signaling in DCs using its antagonist, follistatin, enhanced DC cytokine (IL-6, IL-10, IL-12p70, and tumor necrosis factor-α [TNF-α]) and chemokine (IL-8, IP-10, RANTES, and MCP-1) production during CD40L stimulation, but not TLR-4 ligation. Moreover, antagonizing DC-derived activin-A resulted in significantly enhanced expansion of viral antigen-specific effector CD8+ T cells. These findings establish an immune-regulatory role for activin-A in DCs, highlighting the potential of antagonizing activin-A signaling in vivo to enhance vaccine immunogenicity.

Activin A is a critical component of the inflammatory response, and its binding protein, follistatin, reduces mortality in endotoxemia

Activin A is a member of the transforming growth factor-beta superfamily, which we have identified as having a role in inflammatory responses. We show that circulating levels of activin increase rapidly after LPS-induced challenge through activation of Toll-like receptor 4 and the key adaptor protein, MyD88. Treatment with the activin-binding protein, follistatin, alters the profiles of TNF, IL-1beta, and IL-6 after LPS stimulation, indicating that activin modulates the release of several key proinflammatory cytokines. Further, mice administered one 10-mug dose of follistatin to block activin effects have increased survival after a lethal dose of LPS, and the circulating levels of activin correlate with survival outcome. These findings demonstrate activin A's crucial role in the inflammatory response and show that blocking its actions by the use of follistatin has significant therapeutic potential to reduce the severity of inflammatory diseases.

Activin A suppresses interleukin-1-induced matrix metalloproteinase 3 secretion in human chondrosarcoma cells

The objective was to investigate the effect of activin A on matrix metalloproteinase 3 (MMP-3) production and to identify the role of activin A in chondroprotection. SW1353 cells, a human chondrosarcoma cell line, were stimulated with interleukin (IL) 1alpha and tumor necrosis factor (TNF) alpha, and the concentrations of activin A, follistatin, and MMP-3 secreted into the culture media were measured by enzyme-linked immunosorbent assay (ELISA). Activin A was added to cell cultures in the presence of IL-1alpha or TNFalpha to determine its effect on the production of MMP-3 and sulfated glycosaminoglycan (sGAG) (measured by Alcian blue assay). To study the mechanism responsible for the chondroprotective effects of activin A, the production of IL-1 receptor antagonist (IL-1ra) and tissue inhibitor for metalloproteinases 1 (TIMP-1) was examined by ELISA. Addition of IL-1alpha did not affect the production of activin A by cultured SW1353 cells. IL-1alpha and activin A inhibited the production of follistatin. Stimulation of SW1353 cells with activin A suppressed IL-1alpha-induced, but not TNFalpha-induced, MMP-3 expression. Activin A had no effect on the production of sGAG, IL-1ra, or TIMP-1, although it suppressed the induction of TIMP-1 and IL-1ra by IL-1alpha. This novel finding of MMP-3 inhibition by activin A suggests a new role of activin A in cartilage remodeling. Activin A may have therapeutic potential for preventing cartilage degradation.

Integrated morphogen signal inputs in gammadelta versus alphabeta T-cell differentiation

Morphogens, a class of secreted proteins that regulate gene expression in a concentration-dependent manner, are responsible for directing nearly all lineage fate choices during embryogenesis. In the thymus, morphogen signal pathways consisting of WNT, Hedgehog, and the transforming growth factor-beta superfamily are active and have been implicated in various developmental processes including proliferation, survival, and differentiation of maturing thymocytes. Intriguingly, it has been inferred that some of these morphogen signal pathways differentially affect gammadelta and alphabeta T-cell development or maintenance, but their role in T-cell lineage commitment has not been directly probed. We have recently identified a modulator of morphogen signaling that significantly influences binary gammadelta versus alphabeta T-cell lineage diversification. In this review, we summarize functions of morphogens in the thymus and provide a highly speculative model of integrated morphogen signals, potentially directing the gammadelta versus alphabeta T-cell fate determination process.

The role of TGF-beta superfamily during T cell development: new insights

Members of the transforming growth factor beta (TGF-beta) superfamily are soluble factors that regulate a variety of functional responses including proliferation, differentiation, apoptosis and cell cycle, among others, depending not only on the cell type and its differentiation state, but also on the milieu of cytokines present. All three members of this superfamily: TGF-betas, bone morphogenetic proteins (BMPs) and Activins, have been shown to be expressed in the thymus suggesting their potential role as regulators of the T lymphocyte differentiation process. Although initial reports described the role of TGF-beta in controlling specific checkpoints during thymocyte development, recent data has provided new evidence on the role of BMPs and Activins in this process. This review provides new insights on the function of members of the TGF-beta superfamily at different stages of thymocyte development.

Dissociation of Angiogenesis and Tumorigenesis in Follistatin- and Activin-Expressing Tumors

The transforming growth factor-beta superfamily member activin and its antagonist, follistatin, act as a pleiotropic growth factor system that controls cell proliferation, differentiation, and apoptosis. Activin inhibits fibroblast growth factor 2-induced sprouting angiogenesis in vitro (spheroidal angiogenesis assay) and in vivo (Matrigel assay). To further study the role of the activin/follistatin system during angiogenesis and tumor progression, activin- and follistatin-expressing R30C mammary carcinoma cells were studied in mouse tumor experiments. Surprisingly, activin-expressing tumors grew much faster than follistatin-expressing tumors although they failed to induce increased angiogenesis (as evidenced by low microvessel density counts). Conversely, follistatin-expressing tumors were much smaller but had a dense network of small-diameter capillaries. Qualitative angioarchitectural analyses (mural cell recruitment, perfusion) revealed no major functional differences of the tumor neovasculature. Analysis of activin- and follistatin-expressing R30C cells identified a cell autonomous role of this system in controlling tumor cell growth. Whereas proliferation of R30C cells was not altered, follistatin-expressing R30C cells had an enhanced susceptibility to undergo apoptosis. These findings in experimental tumors are complemented by an intriguing case report of a human renal cell carcinoma that similarly shows a dissociation of angiogenesis and tumorigenesis during tumor progression. Collectively, the data shed further light into the dichotomous stimulating and inhibiting roles that the activin/follistatin system can exert during angiogenesis and tumor progression. Furthermore, the experiments provide a critical proof-of-principle example for the dissociation of angiogenesis and tumorigenesis, supporting the concept that tumor growth may not be dependent on increased angiogenesis as long as a minimal intratumoral microvessel density is maintained.

The relationship between immunosuppressive activity and immunoregulatory cytokines in seminal plasma: influence of sperm autoimmunity and seminal leukocytes

While the contributions of prostasomes, polyamines and prostaglandins to the immunosuppressive activity (ISA) of human seminal plasma have been well-characterised, the contribution of immunoregulatory cytokines found in seminal plasma has received relatively little attention. Semen samples were collected from adult men displaying normospermic parameters, sperm antibodies or substantially elevated seminal leukocytes. Samples were processed through ultracentrifugation and dialysis (<3500Da) to remove prostasomes, polyamines and prostaglandins, and then assayed for ISA by an in vitro T lymphocyte inhibition assay, as well as by specific immunoassays for transforming growth factor beta(1) (TGFbeta(1)), interleukin-10 (IL-10), activin A and the activin-binding protein, follistatin. Seminal plasma from all groups retained substantial ISA following processing. Compared with normospermic men, this 'large' molecular weight ISA fraction was significantly increased in a subset of men with sperm antibodies, but was not altered in the group with elevated leukocytes. There was no relationship between ISA and any cytokine examined, and only TGFbeta(1) was present at levels sufficient to contribute to ISA. Inhibition with a TGFbeta-specific antibody reduced ISA in seminal plasma by approximately 50%. Across all patients, TGFbeta(1) levels were positively correlated with sperm numbers in the ejaculate and with activin A, but not with follistatin or IL-10. Activin A and IL-10 also displayed a positive relationship, and elevated leukocytes was associated with a significant elevation of IL-10 and activin A, but not TGFbeta(1). It is concluded that 'large' molecular weight molecules, the most important of which appears to be TGFbeta(1), make a significant contribution to immunosuppression by human seminal plasma.

Inhibins are the major activin ligands expressed during early thymocyte development

Activins are members of the transforming growth factor-beta (TGFbeta) superfamily, which regulate cell differentiation processes. Here we report the first quantitative analysis of the expression of Activin/Inhibin ligands, type I and II receptors, as well as Smad proteins in fetal (E14-E16) and adult thymic subpopulations. Our data showed that Alk4, ActRIIA, ActRIIB, and Smads 2, 3, and 4, are expressed in fetal thymus (E14 > E15 > E16) and in thymocytes from adult mice (mostly in the double negative [DN] subpopulation). Ligand expression analysis showed that betaA, betaB, and alpha subunits were mainly detected in thymic stromal cells. Interestingly, alpha subunits were expressed at much higher levels compared to betaA and betaB subunits, demonstrating for the first time the potential role of Inhibins as important mediators during early T cell development. Our data indicate that Activin/Inhibin signaling could regulate the process of thymus organogenesis and early thymocyte differentiation, as it has been demonstrated for other members of the TGF-beta superfamily.

Activin A and follistatin in systemic inflammation

Inflammation is a complex process regulated by a cascade of cytokines and growth factors. This review summarizes the emerging evidence implicating activin A and follistatin in the inflammatory process. Our recent studies have highlighted that activin A is released early in the process as part of the circulatory cytokine cascade during acute systemic inflammation. This release occurs concurrently with tumor necrosis factor (TNF)-alpha and prior to that of interleukin (IL)-6 and follistatin. Although, the cellular source(s) of activin A are yet to be established, circulating blood cells and the vascular endothelium are candidates for this rapid release of activin A into the circulation. The release of activin A and follistatin is also observed in the clinical setting, in particular in sepsis. Furthermore activin A is released into cerebrospinal fluid in a model of meningitis in rabbits. The role of activin A in the inflammatory response is poorly understood, however, in vitro data has highlighted that activin A can have both pro- and anti-inflammatory actions on key mediators of the inflammatory response such as TNF-alpha, IL-1beta and IL-6. Furthermore, emerging data would suggest that activin A induction is restricted to certain types of inflammation and its release is dependant upon the inflammatory setting.

Activin A induces cell proliferation of fibroblast-like synoviocytes in rheumatoid arthritis

OBJECTIVE

To investigate the expression of activin A and its receptors in rheumatoid arthritis (RA) synovial tissues, and to determine the effect of activin A on cultured fibroblast-like synoviocytes (FLS).

METHODS

The localization of activin A and activin type II receptor (ARII) in synovial tissues of RA patients was analyzed by immunohistochemistry. The expression of activin A and activin receptors in human cultured FLS was examined by reverse transcriptase-polymerase chain reaction and Western blotting. Enzyme-linked immunosorbent assay was used to measure activin A in culture supernatants. The cell growth of FLS was determined by (3)H-thymidine incorporation and MTT assay.

RESULTS

Immunohistochemical analysis confirmed the up-regulation of activin A in rheumatoid synovium as compared with osteoarthritis or normal joint tissues. CD68+ macrophage-lineage cells and vimentin-positive FLS were identified as activin-producing cells in rheumatoid synovium. Both cell types also expressed ARII. The expression of activin A and ARII on cultured FLS was confirmed at the protein and messenger RNA levels. Interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha, and transforming growth factor beta activated FLS to secrete activin A. Recombinant activin A accelerated the proliferation of FLS, while follistatin, an endogenous activin antagonist, partially inhibited FLS proliferation induced by IL-1 beta.

CONCLUSION

These results suggest that activin A acts as a growth factor of FLS in RA.

The role of activin a in regulation of hemopoiesis

Activin A, a cytokine member of the transforming growth factor-beta superfamily, is expressed locally by the mesenchymal component of the hemopoietic microenvironment. Its expression is regulated on the mRNA level by different cytokines, and the biological activity of the protein is tightly controlled by several inhibitory molecules. Activin A affects hemopoietic cells of various lineages, as evidenced by in vitro studies of leukemia and lymphoma cell lines, which were used to elucidate the mechanism of its action. In the B-cell lineage, activin A is a cell cycle inhibitor, a mediator of apoptosis, and a cytokine antagonist. Limited information is available on the effects of activin A on normal hemopoietic cells. Recent studies suggest that it might be a negative regulator of normal B lymphopoiesis. Whereas the functions of activin A in vitro are well established, further research tools are needed to elucidate its role within specific hemopoietic microenvironments in vivo.

Evidence for activin A and follistatin involvement in the systemic inflammatory response

The inflammatory cascade is a multifactorial process regulated by interwoven cytokine and growth factor networks. This review summarizes the emerging evidence that implicate activin A and follistatin in inflammatory processes. Our recent studies have determined that activin A is released early in the cascade of circulatory cytokines during systemic inflammatory episodes, roughly coincident with tumour necrosis factor (TNF)-alpha and before interleukin (IL)-6 and follistatin. The source(s) of this activin A are not yet established, but prime candidates are monocytes/macrophages, other immune cell types or vascular endothelial cells. Clinical data are limited, but activin beta(A) subunit mRNA or activin A protein is elevated in inflammatory bowel diseases and inflammatory arthropathies, and circulating concentrations of follistatin are elevated in patients with sepsis. In more mechanistic approaches, in vitro studies show that activin A can have both pro- and anti-inflammatory actions on key inflammatory mediators such as TNFalpha, IL-1beta and IL-6. Furthermore, there is emerging understanding of how the intracellular signaling pathway for activin A, incorporating Smads, may interact with and be modulated by other key regulatory cytokines and growth factors.