Immunohistochemical localization of activin A and follistatin in human tissues

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

Serum Follistatin Is Increased in Thyroid Cancer and Is Associated With Adverse Tumor Characteristics in Humans

CONTEXT

Obesity and classical growth factors are associated with thyroid cancer (TC). However, less is known regarding novel hormones such as follistatins and activins. We hypothesized that serum follistatin but not activins would be increased in TC.

OBJECTIVE

This work aimed to assess circulating levels of follistatins, activins, and growth factors in patients with a history of TC vs patients with nonmalignant thyroid diseases.

METHODS

A hospital-based, unmatched case-control study was conducted with 170 thyroidectomized patients due to well-differentiated TC and 106 thyroidectomized patients without history of malignancy. Anthropometric, biochemical, and histological parameters were recorded. Serum samples were collected in the steady state 45 days after surgery. Multivariate models were used to adjust for baseline differences of the unmatched variables. Serum levels of follistatin (FST), follistatin like-3, activin A, activin B, bioactive insulin-like growth factor-1, and stanniocalcin-2 were assayed with novel, highly specific ELISA kits.

RESULTS

In unmatched univariate models, TC patients had higher FST serum levels compared to cancer-free individuals, independently of histological subtype. In multivariate models adjusting for covariates, individuals in the highest tertile of FST levels were associated with an increased risk for the presence of any type of TC or specific histological subtypes, including papillary, follicular and Hürthle-cell carcinoma, and medullary TC. Higher postoperative FST concentrations were found in patients with vascular invasion and distant metastases and associated with TNM staging at diagnosis.

CONCLUSION

FST serum levels are increased in TC patients and correlate with advanced tumor aggressiveness. Future longitudinal studies are needed to confirm and extend our observations.

A Decade Later: Revisiting the TGFβ Family's Role in Diabetes

In 2010, we published a review summarizing the role of the transforming growth factor-beta (TGFβ) family of proteins in diabetes. At that time there were still many outstanding questions that needed to be answered. In this updated review, we revisit the topic and provide new evidence that supports findings from previous studies included in the 2010 review and adds to the knowledge base with new findings and information. The most substantial contributions in the past 10 years have been in the areas of human data, the investigation of TGFβ family members other than activin [e.g., bone morphogenetic proteins (BMPs), growth and differentiation factor 11 (GDF11), nodal], and the expansion of β-cell number through various mechanisms including transdifferentiation, which was previously believed to not be possible.

Renal Cell Carcinoma With Hemangioma-Like Features: Diagnostic Implications and Review of the Literature

Renal cell carcinoma (RCC) with clear cell morphology may show a prominent delicate vascularity. In this article, we report the morphologic and immunohistochemical features of a clear cell papillary RCC mimicking hemangioblastoma and a clear cell RCC mimicking hemangioma. Case 1 showed tubular and papillary growth of clear cells with distinctive areas of capillary proliferation and admixed stromal-like cells resembling a hemangioblastoma. Case 2 consisted of homogeneously delicate microvascular proliferations resembling a capillary hemangioma with scattered inconspicuous clear cells. The clear cells of Case 1 were PAX8(+), CK7(diffuse+), CA9(diffuse+, cup-shaped), and inhibin A(−). The hemangioblastoma-like areas were PAX8(+), CK7(−), CA9(diffuse+), and inhibin A(diffuse+). Case 2 showed PAX8(+), CK7(−), and CA9(diffuse+). They can be diagnostically challenging, and it is important to recognize that a pure hemangioma or hemangioblastoma of the kidneys is very rare, and that RCCs with clear cell morphology rarely exhibit hemangioma-like characteristics.

Activin A in Mammalian Physiology

Activins are dimeric glycoproteins belonging to the transforming growth factor beta superfamily and resulting from the assembly of two beta subunits, which may also be combined with alpha subunits to form inhibins. Activins were discovered in 1986 following the isolation of inhibins from porcine follicular fluid, and were characterized as ovarian hormones that stimulate follicle stimulating hormone (FSH) release by the pituitary gland. In particular, activin A was shown to be the isoform of greater physiological importance in humans. The current understanding of activin A surpasses the reproductive system and allows its classification as a hormone, a growth factor, and a cytokine. In more than 30 yr of intense research, activin A was localized in female and male reproductive organs but also in other organs and systems as diverse as the brain, liver, lung, bone, and gut. Moreover, its roles include embryonic differentiation, trophoblast invasion of the uterine wall in early pregnancy, and fetal/neonate brain protection in hypoxic conditions. It is now recognized that activin A overexpression may be either cytostatic or mitogenic, depending on the cell type, with important implications for tumor biology. Activin A also regulates bone formation and regeneration, enhances joint inflammation in rheumatoid arthritis, and triggers pathogenic mechanisms in the respiratory system. In this 30-yr review, we analyze the evidence for physiological roles of activin A and the potential use of activin agonists and antagonists as therapeutic agents.

Leydig cell insufficiency in hypospermatogenesis: a paracrine effect of activin-inhibin signaling?

Clinical findings and a variety of experimental models indicate that Leydig cell dysfunction accompanies damage to the seminiferous tubules with increasing severity. Most studies support the idea that intratesticular signaling from the seminiferous tubules to Leydig cells regulates steroidogenesis, which is disrupted when hypospermatogenesis occurs. Sertoli cells seem to play a pivotal role in this process. In this review, we summarize relevant clinical and experimental observations and present evidence to support the hypothesis that testicular activin signaling and its regulation by testicular inhibin may link seminiferous tubular dysfunction to reduced testosterone biosynthesis.

Serum Levels of Follistatin Are Positively Associated With Serum-Free Thyroxine Levels in Patients With Hyperthyroidism or Euthyroidism

Follistatin is a glycoprotein with various biologic functions that plays a role in adipocyte differentiation, muscle stimulation, anti-inflammation, and energy homeostasis. Thyroid hormones influence energy expenditure, glucose, and lipid metabolism. The association between serum follistatin level and thyroid function statuses has seldom been evaluated.The objectives of this study were to compare serum follistatin concentrations in different thyroid function statuses and to evaluate the associations between serum follistatin and free thyroxine (fT4) levels.In this study, 30 patients with hyperthyroidism (HY group) and 30 euthyroid individuals (EU group) were recruited. The patients of HY group were treated with antithyroid regimens as clinically indicated, whereas no medication was given to EU group. The demographic and anthropometric characteristics, biochemical data, serum levels of follistatin, and thyroid function of both groups at baseline and at the 6th month were compared. Data of all patients were pooled for the analysis of the associations between the levels of follistatin and fT4.At baseline, the HY group had significantly higher serum follistatin levels than the EU group (median [Q1, Q3]: 1.81 [1.33, 2.78] vs 1.13 [0.39, 1.45] ng/mL, P < 0.001). When treated with antithyroid regimens, the follistatin serum levels in HY group decreased to 1.54 [1.00, 1.88] ng/mL at the 6th month. In all patients, the serum levels of follistatin were positively associated with fT4 levels at baseline (β = 0.54, P = 0.005) and at the 6th month (β = 0.59, P < 0.001). The association between follistatin and fT4 levels remained significant in the stepwise multivariate regression analysis, both initially and at the 6th month.In comparison to the EU group, patients with hyperthyroidism had higher serum follistatin levels, which decreased after receiving antithyroid treatment. In addition, the serum follistatin concentrations were positively associated with serum fT4 levels in patients with hyperthyroidism or euthyroidism.

Inhibin at 90: from discovery to clinical application, a historical review

When it was initially discovered in 1923, inhibin was characterized as a hypophysiotropic hormone that acts on pituitary cells to regulate pituitary hormone secretion. Ninety years later, what we know about inhibin stretches far beyond its well-established capacity to inhibit activin signaling and suppress pituitary FSH production. Inhibin is one of the major reproductive hormones involved in the regulation of folliculogenesis and steroidogenesis. Although the physiological role of inhibin as an activin antagonist in other organ systems is not as well defined as it is in the pituitary-gonadal axis, inhibin also modulates biological processes in other organs through paracrine, autocrine, and/or endocrine mechanisms. Inhibin and components of its signaling pathway are expressed in many organs. Diagnostically, inhibin is used for prenatal screening of Down syndrome as part of the quadruple test and as a biochemical marker in the assessment of ovarian reserve. In this review, we provide a comprehensive summary of our current understanding of the biological role of inhibin, its relationship with activin, its signaling mechanisms, and its potential value as a diagnostic marker for reproductive function and pregnancy-associated conditions.

SMAD2 disruption in mouse pancreatic beta cells leads to islet hyperplasia and impaired insulin secretion due to the attenuation of ATP-sensitive K+ channel activity

AIMS/HYPOTHESIS

The TGF-β superfamily of ligands provides important signals for the development of pancreas islets. However, it is not yet known whether the TGF-β family signalling pathway is required for essential islet functions in the adult pancreas.

METHODS

To identify distinct roles for the downstream components of the canonical TGF-β signalling pathway, a Cre-loxP system was used to disrupt SMAD2, an intracellular transducer of TGF-β signals, in pancreatic beta cells (i.e. Smad2β knockout [KO] mice). The activity of ATP-sensitive K(+) channels (KATP channels) was recorded in mutant beta cells using patch-clamp techniques.

RESULTS

The Smad2βKO mice exhibited defective insulin secretion in response to glucose and overt diabetes. Interestingly, disruption of SMAD2 in beta cells was associated with a striking islet hyperplasia and increased pancreatic insulin content, together with defective glucose-responsive insulin secretion. The activity of KATP channels was decreased in mutant beta cells.

CONCLUSIONS/INTERPRETATION

These results suggest that in the adult pancreas, TGF-β signalling through SMAD2 is crucial for not only the determination of beta cell mass but also the maintenance of defining features of mature pancreatic beta cells, and that this involves modulation of KATP channel activity.

Effects of activin A on survival, function and gene expression of pancreatic islets from non-diabetic and diabetic human donors

Emerging evidence suggests that activin with its associated receptors, second messengers, and antagonists would be excellent targets for therapeutic drug development in the treatment of diabetes. We undertook the current study to investigate the ability to extrapolate findings from rodent studies to human islets in which data thus far has been scarce. We tested the hypothesis that human islets synthesize activin and that activin participates in the regulation of islet β-cells. Human islets from 33 separate isolations were categorized based on functional status, culture status and diabetic status. Statistical comparisons were made by ANOVA with Tukey post-hoc adjustment for multiple comparisons. Experiments investigating activin utilized qPCR, FACS cell sorting, immunofluorescent antibody staining, functionality assays, viability assays and protein secretion assays. We have defined the transcript expression patterns of activin and the TGFβ superfamily in human islets. We found INHBA (the gene encoding activin A) to be the most highly expressed of the superfamily in normal, cultured islets. We elucidated a link between the islet microenvironment and activin A. We found differential ligand expression based on diabetic, culture and functional status. Further, this is also the first report that links direct effects of activin A with the ability to restore glucose-stimulated insulin secretion in human islets from type 2 diabetic donors thereby establishing the relevance of targeting activin for therapeutic drug development.

Bimodal impact of skeletal muscle on pancreatic β-cell function in health and disease

Diabetes is a complex disease that affects many organs directly or indirectly. Type 2 diabetes mellitus is characterized by insulin resistance with a relative deficiency in insulin secretion. It has become apparent that inter-organ communication is of great importance in the pathophysiology of diabetes. Far from being an inert tissue in terms of inter-organ communication, it is now recognized that skeletal muscle can secrete so-called myokines that can impact on the function of distant organs/tissues both favourably and unfavourably. We have proposed that communication between insulin-resistant skeletal muscle and β-cells occurs in diabetes. This is a novel route of communication that we further suggest is modified by the prevailing degree of insulin resistance of skeletal muscle. This review focuses on the various myokines [interleukin-6 (IL-6), tumor necrosis factor-α, CXCL10, follistatin and IL-8] which have been identified either after different types of exercise or in the secretome from control and insulin-resistant human skeletal myotubes. We will also summarize studies on the impact of several myokines on pancreatic β-cell proliferation, survival and function.

Regulation of activin and inhibin in the adult testis and the evidence for functional roles in spermatogenesis and immunoregulation

Activin A provides a unique link between reproduction and immunity, which is especially significant in the adult testis. This cytokine, together with inhibin B and follistatin acting as regulators of activin A activity, is fundamentally involved in the regulation of spermatogenesis and testicular steroidogenesis. However, activin A also has a much broader role in control of inflammation, fibrosis and immunity. In the Sertoli cell, activin A is regulated by signalling pathways that normally regulate stress and inflammation, signalling pathways that intersect with the classical hormonal regulatory pathways mediated by FSH. Modulation of activin A production and activity during spermatogenesis is implicated in the fine control of the cycle of the seminiferous epithelium. The immunoregulatory properties of activin A also suggest that it may be involved in maintaining testicular immune privilege. Consequently, elevated activin A production within the testis during inflammation and infection may contribute to spermatogenic failure, fibrosis and testicular damage.

Acute regulation of activin A and its binding protein, follistatin, in serum and tissues following lipopolysaccharide treatment of adult male mice

Activin A, a member of the transforming growth factor-β family, increases in the circulation within 1 h after administration of bacterial LPS. To clarify the origins of this rapid increase, the distribution of activin A and its binding protein, follistatin, and their production following LPS treatment, were assessed in adult male mice. In untreated mice, activin A was detectable in all 23 tissues examined, with highest mRNA expression (as measured by quantitative RT-PCR) was found in the liver, and the largest concentration of activin A protein (by ELISA) was found in the bone marrow. Likewise, follistatin mRNA and protein were present in all tissues, with highest expression in the vas deferens. Activin A and follistatin mRNA did not increase significantly in any tissue within the first hour after LPS, but activin A protein decreased by 35% in the bone marrow and increased 5-fold in the lung. No significant changes were observed in any other tissue. Activin A reached a peak in the circulation 1 h following LPS, and then declined. Cycloheximide, an inhibitor of protein translation, reduced this increase of activin A by more than 50%. Actinomycin D, an inhibitor of mRNA transcription, had no effect. Circulating follistatin did not increase until 4 h after LPS and was not affected by either inhibitor. These data indicate that the rapid increase in circulating activin A during LPS-induced inflammation is regulated at the posttranscriptional level, apparently from newly translated and stored protein, and implicate bone marrow-derived cells, and, in particular, neutrophils, as a significant source of this preformed activin A.

Expression of inhibin/activin proteins and receptors in the human hypothalamus and basal forebrain

The inhibin/activin family of proteins is known to have a broad distribution of synthesis and expression in many species, as well as a variety of functions in reproductive and other physiological systems. Yet, our knowledge regarding the production and function of inhibin and activin in the central nervous system is relatively limited, especially in humans. The present study aimed to explore the distribution of inhibin/activin protein subunits and receptors in the adult human brain. The human hypothalamus and surrounding basal forebrain was examined using post-mortem tissues from 29 adults. Immunocytochemical studies were conducted with antibodies directed against the inhibin/activin α, βA, and βB subunits, betaglycan and the activin type IIA and IIB receptors. An immunoassay was also utilised to measure dimeric inhibin A and B levels in tissue homogenates of the infundibulum of the hypothalamus. Robust βA subunit immunoreactivity was present in the paraventricular, supraoptic, lateral hypothalamic, infundibular, dorsomedial and suprachiasmatic nuclei of the hypothalamus, in the basal ganglia, and in the nucleus basalis of Meynert. A similar staining distribution was noted for the βB subunit, betaglycan and the type II receptor antibodies, whereas α subunit staining was not detected in any of the major anatomical regions of the human brain. Inhibin B immunoreactivity was present in all tissues, whereas inhibin A levels were below detectable limits. These studies show for the first time that the inhibin/activin protein subunits and receptors can be co-localised in the human brain, implicating potential, diverse neural functions.

Testicular somatic cells, not gonocytes, are the major source of functional activin A during testis morphogenesis

Proper development of the seminiferous tubules (or testis cords in embryos) is critical for male fertility. Sertoli cells, somatic components of the seminiferous tubules, serve as nurse cells to the male germline, and thus their numbers decide the quantity of sperm output in adulthood. We previously identified activin A, the protein product of the activin βA (Inhba) gene, as a key regulator of murine Sertoli cell proliferation and testis cord expansion during embryogenesis. Although our genetic studies implicated fetal Leydig cells as the primary producers of testicular activin A, gonocytes are another potential source. To investigate the relative contribution of gonocyte-derived activin A to testis morphogenesis, we compared testis development in the Inhba global knockout mouse, which lacks activin A production in all cells (including the gonocytes), and a steroidogenic factor 1 (Sf1)-specific conditional knockout model in which activin A expression in testicular somatic cells is disrupted but gonocyte expression of activin A remains intact. Surprisingly, testis development was comparable in these two models of activin A insufficiency, with similar reductions in Sertoli cell proliferation and minor differences in testis histology. Thus, our findings suggest activin A from male gonocytes is insufficient to promote Sertoli cell proliferation and testis cord expansion in the absence of somatic cell-derived activin A. Evaluation of adult male mice with fetal disruption of activin A revealed reduced testis size, lowered sperm production, altered testicular histology, and elevated plasma FSH levels, defects reminiscent of human cases of androgen-sufficient idiopathic oligozoospermia.

Activin A levels are associated with abnormal glucose regulation in patients with myocardial infarction: potential counteracting effects of activin A on inflammation

OBJECTIVE

On the basis of the role of activin A in inflammation, atherogenesis, and glucose homeostasis, we investigated whether activin A could be related to glucometabolic abnormalities in patients with acute myocardial infarction (MI).

RESEARCH DESIGN AND METHODS

Activin A measurement and oral glucose tolerance tests (OGTTs) were performed in patients (n = 115) with acute MI, without previously known diabetes, and repeated after 3 months. Release of activin A and potential anti-inflammatory effects of activin A were measured in human endothelial cells. Activin A effects on insulin secretion and inflammation were tested in human pancreatic islet cells.

RESULTS

1) In patients with acute MI, serum levels of activin A were significantly higher in those with abnormal glucose regulation (AGR) compared with those with normal glucose regulation. Activin A levels were associated with the presence of AGR 3 months later (adjusted odds ratio 5.1 [95% CI 1.73-15.17], P = 0.003). 2) In endothelial cells, glucose enhanced the release of activin A, whereas activin A attenuated the release of interleukin (IL)-8 and enhanced the mRNA levels of the antioxidant metallothionein. 3) In islet cells, activin A attenuated the suppressive effect of inflammatory cytokines on insulin release, counteracted the ability of these inflammatory cytokines to induce mRNA expression of IL-8, and induced the expression of transforming growth factor-β.

CONCLUSIONS

We found a significant association between activin A and newly detected AGR in patients with acute MI. Our in vitro findings suggest that this association represents a counteracting mechanism to protect against inflammation, hyperglycemia, and oxidative stress.

The synthesis and secretion of inhibins

Inhibin A and B, dimeric glycoproteins comprising an α- and β((A/B))-subunit, negatively regulate follicle stimulating hormone (FSH) synthesis by the pituitary. The expression of α- and β-subunits within Sertoli cells of the testis and granulosa cells of the ovary is controlled by a range of transcription factors, including CREB, SP-1, Smads, and GATA factors. The inhibin α- and β-subunits are synthesized as precursor molecules consisting of an N-terminal propeptide and a C-terminal mature domain. Recently, we showed that hydrophobic residues within the propeptides of the α- and β-subunits interact noncovalently with their mature domains, maintaining the molecules in a conformation competent for dimerization. Dimeric precursors are cleaved by proprotein convertases and mature inhibins are secreted from the cell noncovalently associated with their propeptides. Propeptides may increase the half-life of inhibin A and B in circulation, but they are readily displaced in the presence of the high-affinity receptors, betaglycan, and ActRII.

Activin receptor-like kinase and the insulin gene

The biological responses of the transforming growth factor-β (TGF-β) superfamily, which includes Activins and Nodal, are induced by activation of a receptor complex and Smads. A type I receptor, which is a component of the complex, is known as an activin receptor-like kinase (ALK); currently seven ALKs (ALK1-ALK7) have been identified in humans. Activins signaling, which is mediated by ALK4 and 7 together with ActRIIA and IIB, plays a critical role in glucose-stimulated insulin secretion, development/neogenesis, and glucose homeostatic control of pancreatic endocrine cells; the insulin gene is regulated by these signaling pathways via ALK7, which is a receptor for Activins AB and B and Nodal. This review discusses signal transduction of ALKs in pancreatic endocrine cells and the role of ALKs in insulin gene regulation.

Reciprocal modulation of adult beta cell maturity by activin A and follistatin

AIMS/HYPOTHESIS

The functional maturity of pancreatic beta cells is impaired in diabetes mellitus. We sought to define factors that can influence adult beta cell maturation status and function.

METHODS

MIN6 cells labelled with a Pdx1 monomeric red fluorescent protein-Ins1 enhanced green fluorescent protein dual reporter lentivirus were used to screen candidate growth and/or differentiation factors using image-based approaches with confirmation by real-time RT-PCR and assays of beta cell function using primary mouse islets.

RESULTS

Activin A strikingly decreased the number of mature beta cells and increased the number of immature beta cells. While activins are critical for pancreatic morphogenesis, their role in adult beta cells remains controversial. In primary islets and MIN6 cells, activin A significantly decreased the expression of insulin and several genes associated with beta cell maturity (e.g. Pdx1, Mafa, Glut2 [also known as Slc2a2]). Genes found in immature beta cells (e.g. Mafb) tended to be upregulated by activin A. Insulin secretion was also reduced by activin A. In addition, activin A-treated MIN6 cells proliferated faster than non-treated cells. The effects of endogenous activin A on beta cells were completely reversed by exogenous follistatin.

CONCLUSIONS/INTERPRETATION

These results suggest that autocrine and/or paracrine activin A signalling exerts a suppressive effect on adult beta cell maturation and function. Thus, the maturation state of adult beta cells can be modulated by external factors in culture. Interventions inhibiting activin or its signalling pathways may improve beta cell function. Understanding of maturation and plasticity of adult pancreatic tissue has significant implications for islet regeneration and for in vitro generation of functional beta cells.

Emerging roles for the TGFbeta family in pancreatic beta-cell homeostasis

Loss of functional beta-cells is the primary cause of type 2 diabetes, so that there is an acute need to understand how beta-cell number and function are regulated in the adult under normal physiological conditions. Recent studies suggest that members of the transforming growth factor (TGF)-beta family regulate beta-cell function and glucose homeostasis. These factors are also likely to influence beta-cell proliferation and/or the incorporation of new beta-cells from progenitors in adults. Soluble TGFbeta antagonists also appear to have important roles in maintaining homeostasis, and the coordinated activity of TGFbeta family members is likely to regulate the differentiation and function of adult beta-cells, raising the possibility of developing new diabetes therapies based on TGFbeta agonists or antagonists.

A new 'total' activin B enzyme-linked immunosorbent assay (ELISA): development and validation for human samples

BACKGROUND AND OBJECTIVE

There are currently no sensitive and specific assays for activin B that could be utilized to study human biological fluids. The aim of this project was to develop and validate a 'total' activin B ELISA for use with human biological fluids and establish concentrations of activin B in the circulation and fluids from the reproductive organs.

DESIGN

The new ELISA was validated and then used to measure activin B levels in the circulation of healthy participants, IVF patients, pregnant women and in ovarian follicular fluid and seminal plasma.

PATIENTS AND MEASUREMENTS

Healthy adult subjects (n = 143), subjects from an IVF clinic (n = 27) and pregnancy groups (n = 29) were sampled.

RESULTS

The sensitivity of the assay was 0.019 ng/ml. Validation of the activin B ELISA showed good recovery (90.7 +/- 9.8%) and linearity in biological fluid and cell culture media and low cross-reactivity with related analytes (inhibin B = 0.077% and activin A = 0.0034%). There was a negative correlation between activin B concentration (r = -0.281, P < 0.011) and females with increasing age. Patients attending IVF clinics had significantly lower levels of activin B compared with gender-matched control subjects. Ovarian follicular fluid and seminal plasma had 50-80 fold higher levels of activin B (mean = 5.35 and 3.66 ng/ml respectively) than sera (mean = 0.071 ng/ml).

CONCLUSIONS

This fully validated ELISA for activin B offers a tremendous utility for measuring this protein in a variety of normal physiological processes and in various clinical pathologies.

Follistatin gene expression by gonadotropin-releasing hormone: a role for cyclic AMP and mitogen-activated protein kinase signaling pathways in clonal gonadotroph LbetaT2 cells

The purpose of the present study was to examine the signal transduction pathways involved in follistatin gene expression induced by GnRH in the LbetaT2 cell line. The LHbeta-subunit was predominantly increased by high frequency GnRH pulses (30 min interval); whereas low frequency pulses (120 min) increased FSHbeta. In a static culture, follistatin expression was significantly increased at 12 h (2.35 +/- 0.80-fold) after the addition of GnRH. Following pulsatile stimulation, follistatin mRNA was increased by high frequency GnRH pulses, but not by low frequency pulses. In a static culture, GnRH maximally activated extracellular signal-regulated kinase (ERK) 10 min (3.2 +/- 0.55-fold) after treatment. In addition, intracellular cAMP accumulated up to 2.1 +/- 0.76-fold. Follistatin promoter activity was significantly increased following transfection with either a constitutively active cAMP dependent protein kinase (PKA) or a constitutively active MEK kinase (MEKK). The induction of follistatin gene expression by GnRH was completely inhibited by H89, a protein kinase A inhibitor, and U0126, a MEK inhibitor. Follistatin gene expression was also activated by both PACAP and CPT-cAMP under static culture conditions. Maximal ERK activation levels were nearly identical regardless of GnRH pulse frequency; however, high frequency GnRH pulses elevated both the intracellular cAMP level as well as cAMP-response element (Cre) promoter activity. These results suggest that both the PKA and ERK pathways are necessary for the induction of the follistatin promoter. Furthermore, the intracellular cAMP level, but not ERK activity, determined whether follistatin was induced following high frequency GnRH pulses.

The biology of activin: recent advances in structure, regulation and function

Activin was discovered in the 1980s as a gonadal protein that stimulated FSH release from pituitary gonadotropes and was thought of as a reproductive hormone. In the ensuing decades, many additional activities of activin were described and it was found to be produced in a wide variety of cell types at nearly all stages of development. Its signaling and actions are regulated intracellularly and by extracellular antagonists. Over the past 5 years, a number of important advances have been made that clarify our understanding of the structural basis for signaling and regulation, as well as the biological roles of activin in stem cells, embryonic development and in adults. These include the crystallization of activin in complex with the activin type II receptor ActRIIB, or with the binding proteins follistatin and follistatin-like 3, as well as identification of activin's roles in gonadal sex development, follicle development, luteolysis, beta-cell proliferation and function in the islet, stem cell pluripotency and differentiation into different cell types and in immune cells. These advances are reviewed to provide perspective for future studies.

Activin subunit and receptor expression in normal and cleft human fetal palate tissues

Craniofacial malformations, such as cleft palate, present serious complications in the newborn and are often of unknown etiology. Activin BA subunit deletion leads to cleft palate in mice, but the expression of this protein in the human palate has not been explored. Our goal was to determine the spatial and temporal expression of inhibin/activin subunits; the binding protein, follistatin; and activin receptors in the human fetal palate. Residual human fetal palate tissues, with or without cleft, were collected during routine autopsy at Women and Infants Hospital. Inhibin/activin alpha and beta subunits, follistatin, and activin receptor protein and mRNA expression were studied by immunocytochemistry and reverse-transcriptase polymerase chain reaction (RT-PCR) experiments, respectively. Dimeric activin A levels were compared in cleft and normal palate tissue homogenates by immunoassay. Activin BA, follistatin, and activin receptor type IIA proteins were observed in normal and cleft palate tissues throughout pregnancy (gestational weeks 11 to 40). Proteins were predominantly found in developing bone cells, with no significant group differences. Inhibin/activin BA subunit, follistatin, and activin receptor mRNAs were also detected in normal and cleft fetal palate tissues, but inhibin alpha and BB subunit were absent. Inhibin/activin BA subunit expression was consistent with the presence of dimeric activin A, but levels did not differ significantly between cleft and control tissues. Inhibin/activin BA subunit, follistatin, and activin receptor proteins and mRNAs are present in the human fetal palate. These data suggest that activin signalling has the potential to be associated with human palate development.

FSTL3 deletion reveals roles for TGF-beta family ligands in glucose and fat homeostasis in adults

Activin and myostatin are related members of the TGF-beta growth factor superfamily. FSTL3 (Follistatin-like 3) is an activin and myostatin antagonist whose physiological role in adults remains to be determined. We found that homozygous FSTL3 knockout adults developed a distinct group of metabolic phenotypes, including increased pancreatic islet number and size, beta cell hyperplasia, decreased visceral fat mass, improved glucose tolerance, and enhanced insulin sensitivity, changes that might benefit obese, insulin-resistant patients. The mice also developed hepatic steatosis and mild hypertension but exhibited no alteration of muscle or body weight. This combination of phenotypes appears to arise from increased activin and myostatin bioactivity in specific tissues resulting from the absence of the FSTL3 antagonist. Thus, the enlarged islets and beta cell number likely result from increased activin action. Reduced visceral fat is consistent with a role for increased myostatin action in regulating fat deposition, which, in turn, may be partly responsible for the enhanced glucose tolerance and insulin sensitivity. Our results demonstrate that FSTL3 regulation of activin and myostatin is critical for normal adult metabolic homeostasis, suggesting that pharmacological manipulation of FSTL3 activity might simultaneously reduce visceral adiposity, increase beta cell mass, and improve insulin sensitivity.

Activin A concentrations in human cerebrospinal fluid are age-dependent and elevated in meningitis

OBJECTIVE

Activin A, and its binding protein, follistatin (FS), are expressed in the central nervous system (CNS). We have previously shown elevated concentrations of FS in the cerebrospinal fluid (CSF) of patients with meningitis and increased concentrations of activin A in the CSF of rabbits with bacterial meningitis.

METHODS

We measured CSF and serum concentrations of activin A and FS in normal subjects and in patients with various neurological diseases using previously validated immunoassays specific for activin A or FS.

RESULTS

In healthy persons, serum concentrations of both activin A and FS were age-dependent. In CSF, concentrations of activin A ranged from 0.03 to 0.33 ng/ml and were strongly correlated with age in both sexes, whereas FS CSF concentrations were below the assay detection limit in most of the patients. Activin A concentrations in CSF of patients with various neurological diseases, including meningitis, chronic inflammatory CNS diseases, neurodegenerative diseases, tumors in the CNS, cerebral ischemia, intracerebral/subarachnoid hemorrhages, subdural hemorrhages and epileptic seizures, were compared with age- and sex-matched control patients. The comparisons revealed significantly elevated concentrations of activin A in patients with meningitis (P=0.017). Serum concentrations of activin A or FS were not affected by any of the neurological diseases examined.

CONCLUSIONS

Our results show for the first time that in normal subjects concentrations of activin A in CSF are correlated with age, and furthermore, that activin A CSF concentrations are elevated in patients with meningitis. The latter underlines a role for activin A in acute inflammatory processes within the CNS.

Functional roles of the bone morphogenetic protein system in thyrotropin signaling in porcine thyroid cells

We uncovered a new regulation of thyrocyte function by bone morphogenetic protein (BMP) under the influence of thyrotropin (TSH) using primary culture of porcine thyrocytes. The BMP type I receptors, ALK-2 (ActRIA), -3 (BMPRIA), and -6 (BMPRIB), were expressed in porcine thyrocytes, while ALK-6 was not detected in human thyroid. Treatment with BMP-2, -4, -6, -7, and TGF-beta1 exhibited a dose-dependent suppression of DNA synthesis by porcine thyrocytes. BMP-2, -4, -6, -7, and TGF-beta1 suppressed TSH receptor mRNA expression on thyrocytes, which was consistent with their suppressive effect on TSH-induced cAMP synthesis and TSH-induced insulin-like growth factor-1 expression. Activin exhibited minimal suppression of thyrocyte DNA synthesis and did not exhibit suppressive effects on TSH receptor mRNA expression. Phosphorylated Smad1/5/8 was detected in the lysates of porcine thyrocytes treated with BMP-2, -4, -6, and -7. However, in the presence of TSH, BMP-6 and -7 failed to activate Smad1/5/8 phosphorylation and 3TP-reporter activity, whereas BMP-2 and -4 maintained clear activation of the BMP signaling regardless of the presence of TSH. This diverged regulation of thyroid BMP system by TSH is most likely due to the reduction of ALK-6 expression caused by TSH. Thus, the thyroid BMP system is functionally linked to TSH actions through modulating TSH receptor expression and TSH, in turn, selectively inhibits BMP signaling. Given that BMP system is present in human thyroid and the expression pattern of ALK-2 and BMPRII is different between follicular adenomas and normal thyroid tissues, the endogenous BMP system may be involved in regulating thyrocyte growth and TSH sensitivity of human thyroid adenomas.

Cell-specific expression of betaC-activin in the rat reproductive tract, adrenal and liver

betaC-activin expression was assessed in rat tissues, using reverse transcription and real-time polymerase chain reaction, Western blotting and immunohistochemistry with a specific monoclonal antibody. betaC-activin mRNA was predominantly expressed in liver, but significant amounts were found in rat whole pituitary extracts (n = 5), and in three of five extracts of ovary, testis, and adrenal gland. Specific betaC-activin immunoreactivity was demonstrated in the cytoplasm of hepatocytes, neurosecretory cell terminals in posterior pituitary, ovarian primordial follicles, theca interna, large luteal cells and rete ovarii, spermatogonia, pachytene spermatocytes and Leydig cells of the testis, uterine endometrium, oviduct epithelium and zona glomerulosa of the adrenal. The observation of stage-specific expression in gonadal cells suggests this activin subunit has specific roles, different from those of other activin/inhibin subunits. Small amounts of mRNA in the presence of significant betaC-activin protein highlights the importance of examining betaC-activin expression at both the mRNA and protein level.

Analysis of site-specific glycosylation in recombinant human follistatin expressed in Chinese hamster ovary cells

Follistatin (FS), a glycoprotein, plays an important role in cell growth and differentiation through the neutralization of the biological activities of activins. In this study, we analyzed the glycosylation of recombinant human FS (rhFS) produced in Chinese hamster ovary cells. The results of SDS-PAGE and MALDI-TOF MS revealed the presence of both non-glycosylated and glycosylated forms. FS contains two potential N-glycosylation sites, Asn95 and Asn259. Using mass spectrometric peptide/glycopeptide mapping and precursor-ion scanning, we found that both N-glycosylation sites were partially glycosylated. Monosaccharide composition analyses suggested the linkages of fucosylated bi- and triantennary complex-type oligosaccharides on rhFS. This finding was supported by mass spectrometric oligosaccharide profiling, in which the m/z values and elution times of some of the oligosaccharides from rhFS were in good agreement with those of standard oligosaccharides. Site-specific glycosylation was deduced on the basis of the mass spectra of the glycopeptides. It was suggested that biantennary oligosaccharides are major oligosaccharides located at both Asn95 and Asn259, whereas the triantennary structures are present mainly at Asn95.

Localization of inhibins and activins in normal endocrine cells and endocrine tumors of the gut and pancreas: an immunohistochemical and in situ hybridization study

Activins and inhibins, which belong to the TGF beta family, are composed of different combinations of alpha-, betaA-, and betaB-subunits, resulting in inhibin A (alphabetaA), inhibin B (alphabetaB), activin A (betaAbetaA), activin B (betaBbetaB), and activin AB (betaAbetaB). They regulate several cell functions, acting as paracrine/autocrine factors. Their actions, which depend on binding to specific receptors, are also modulated by follistatin. Gastroenteropancreatic (GEP) endocrine cells and endocrine tumors (ETs) produce several growth factors, but it is not well known whether they express follistatin and the various inhibin/activin subunits. We studied their expression in 65 GEP ETs using immunohistochemistry (IHC) and in situ hybridization (ISH). The alpha-subunit and follistatin were not identified in normal GEP endocrine cells and were poorly expressed in ETs. A betaA-subunit immunoreactivity (IR) was detected in A-, G-, EC-, and GIP-cells, while betaB-chain IR was present only in D-cells. The mRNAs encoding for these molecules were poorly expressed in normal tissues. BetaA- and betaB-subunits were identified in several ETs by both IHC and ISH: betaA-subunit mainly in G-cell and A-cell ETs, and betaB-subunit in D-cell, A-cell, and EC-cell ETs. Our results demonstrate a differential expression of activin/inhibin subunits among different types of GEP endocrine cells and related tumors, suggesting a role in modulation of biological functions of these normal and neoplastic endocrine cells.

Inhibin alpha distinguishes hemangioblastoma from clear cell renal cell carcinoma

Inhibin alpha subunit (inhibin A) expression in hemangioblastomas has not been previously reported in the literature. We analyzed the expression of inhibin A in 25 hemangioblastomas from 22 patients. Eleven cases were from 8 patients with von Hippel-Lindau disease, and these tumors were multicentric and/or recurrent. The remaining 14 cases from 14 patients were sporadic. The male-to-female ratio was 8:3, and the age at presentation ranged from 19 to 78 years (mean 35 years; median 45 years). Eighteen tumors were located in the cerebellum/posterior fossa, 1 in the medulla, 1 in the occipital lobe, and 5 in the spinal cord. Four metastatic renal cell carcinomas in brain, 10 renal cell carcinomas from 8 patients with von Hippel-Lindau disease, and 5 sporadic clear cell renal cell carcinomas were also included. Two patients with von Hippel-Lindau disease had both renal cell carcinoma and hemangioblastoma. The stromal cells of all 25 cases of hemangioblastoma expressed inhibin A. Strong, moderate, and weak cytoplasmic immunoreactivity was noted in 17, 5, and 3 cases, respectively. In contrast, none of the 19 renal cell carcinomas, primary as well as metastatic, expressed inhibin A. There was no difference in the inhibin A staining pattern between the sporadic hemangioblastoma and those associated with VHL. These findings demonstrate inhibin A to be a useful marker in distinguishing hemangioblastoma from metastatic clear cell renal cell carcinoma. While the diagnostic importance is evident, the pathophysiology of inhibin A expression by the stromal cells of hemangioblastoma remains unknown and further investigation is required.

Activin signaling through type IB activin receptor stimulates aromatase activity in the ovarian granulosa cell-like human granulosa (KGN) cells

In addition to a stimulatory effect on FSH production by the pituitary gland, activin is thought to have a paracrine or autocrine role in follicular development in the ovary, where it is produced. Recently, we established a human ovarian granulosa tumor cell line, KGN, which possesses in vivo characteristics of granulosa cells, namely the expression of functional FSH receptors and cytochrome P-450 aromatase. Here, we have demonstrated the activin signaling pathway and its role in KGN cells. A series of transient transfection experiments revealed that activin type IB receptor (ActRIB) is an essential component of the activin signaling pathway in KGN cells. Smad2 was found to act downstream of ActRIB as an intracellular signal transmitter. Smad7, but not Smad6, was an inhibitory Smad in the pathway. Finally, we show that FSH receptor expression and cytochrome P-450 (P-450) aromatase activity was up-regulated by activin stimulation through ActRIB in KGN cells. These results show that we have clarified the signaling mechanisms and the roles of activin in the human granulosa cell line, KGN. Activin signaling mediated by ActRIB-Smad2 system in the ovary may thus be essential for the regulation of follicular differentiation.

Activin betaB expression in rat experimental goiter and human thyroid tumors

Activins are dimeric proteins of the transforming growth factor beta superfamily, which exhibit multiple functions in gonadal and extragonadal tissues. Expression of activin A, composed of two betaA subunits, has been shown in the thyroid, whereas there has been no study regarding activin B (betaBbetaB) in this gland. In other tissues, such as the gonads, pancreas, and adrenal cortex, expression of both activin betaA and activin betaB has been described. In this study, we detected activin betaB mRNA and protein expression using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry in rat experimental goiter and in human thyroid, including multinodular goiter, follicular adenoma, papillary carcinoma, and follicular carcinoma. Activin betaA mRNA and protein expression was also investigated in rat and human thyroid tissue. The expression of both activin betaB and activin betaA was highest in rat methimazole-induced goiter and in human follicular adenoma, and papillary and follicular carcinomas when compared with multinodular goiter and normal thyroid tissue. The increased expression of activin betaB as well as activin betaA, observed in this study, suggests that activin B and activin A may be involved in the proliferative and neoplastic processes of the thyroid.

Role of H1-calponin in pancreatic AR42J cell differentiation into insulin-producing cells

Basic or h1-calponin is a smooth muscle-specific, actin-binding protein that is involved in the regulation of smooth muscle contractile activity. We found in this study the expression of mRNA and protein for h1-calponin in AR42J-B13 cells, which is a useful model for investigating islet beta-cell differentiation from pancreatic common precursor cells. Following treatment of AR42J cells with activin A and hepatocyte growth factor, the protein levels of h1-calponin decreased in a time-dependent manner during the course of the cell differentiation. When h1-calponin was continuously overexpressed by utilizing recombinant adenovirus-mediated gene transfer, the percentage of cell differentiation in h1-calponin overexpressing cells was markedly suppressed as compared with that in the cells without overexpression (6.7 +/- 2.5 vs. 28.6 +/- 3.2%, P < 0.001, Student's t test). Finally, overexpression of h1-calponin (65.6 +/- 3.4), or that lacking actin-binding domain (55.9 +/- 3.4%), significantly (P < 0.001) suppressed the activin A-stimulated transcriptional activity of activin responsive element (ARE), whereas calponin homology-domain disruption mutant did not (100.6 +/- 1.9%). These results suggest that regulation of h1-calponin is involved in the regulation of differentiation of AR42J cells into insulin-producing cells at least partly through modulating ARE transcriptional activity.

Serum activin A levels in different thyroid disorders

Activin A belongs to the transforming growth factor-beta superfamily that exerts a wide range of biologic activities on cellular proliferation and differentiation. Although it was suggested that gonadal tissue is the primary site of activin production, several extragonadal sources have subsequently been identified, including human thyrocytes. The goal of the present study was to evaluate serum activin A levels in a series of patients with different thyroid disorders during the active state of the diseases and after recovery. Serum activin A levels were evaluated in 60 healthy subjects (controls), 8 with multinodular nontoxic goiter (MNG), 30 hyperthyroid (15 with Graves' disease (GD), 12 with autonomous hyperfunctioning adenoma (ATA), and 3 with thyrotropin (TSH)-secreting pituitary adenoma, 16 hypothyroid (11 with Hashimoto's thyroiditis and 5 after total thyroidectomy), and 9 patients with resistance to thyroid hormone (RTH) by commercial enzyme-linked immunosorbent assay (ELISA) kit. Patients with GD and ATA showed activin A levels higher than those found in controls and similar to those observed in MNG (GD, 0.74 +/- 0.3 ng/mL; ATA, 0.86 +/- 0.4; and MNG; 1.0 +/- 0.2 vs. controls: 0.39 +/- 0.5, p < 0.001), while in patients with Hashimoto's thyroiditis, total thyroidectomy or RTH activin A levels were similar to those of controls. In conclusion, this study demonstrates that thyroid hyperplasia and hyperfunction result in increased levels of activin A, although the normal levels observed in thyroidectomized patients clearly demonstrate that the thyroid gland is not the predominant source of activin A in normal conditions. Because activin A may exert negative action on thyrocyte proliferation, it is conceivable that activin A hypersecretion in thyroid disorders might represent a counteracting mechanism.

Expression of activin/inhibin receptor and binding protein genes and regulation of activin/inhibin peptide secretion in human adrenocortical cells

Activins and inhibins are glycoprotein hormones produced mainly in gonads but also in other organs. They are believed to be important para/autocrine regulators of various cell functions. We investigated activin/inhibin receptor and binding protein gene expression and the regulation of activin/inhibin secretion in human adrenal cells. RT-PCR revealed inhibin/activin alpha-, betaA/B-subunit, follistatin, activin type I/II receptor, and inhibin receptor (betaglycan and inhibin-binding protein) mRNA expression in fetal and adult adrenals and cultured adrenocortical cells. Cultured cells secreted activin A and inhibin A/B as determined by specific ELISAs. ACTH stimulated inhibin A/B secretion in fetal (1.8- and 1.8-fold of control, respectively) and in adult cells (3.4- and 1.7-fold of control, respectively) without significant effect on activin A. 8-bromoadenosine cAMP (protein kinase A activator) increased activin A and inhibin A/B secretion in the human adrenocortical NCI-H295R cell line (32-, 17-, and 3-fold of control, respectively). 12-O-tetradecanoyl phorbol-13-acetate (protein kinase C activator) stimulated both activin A and inhibin A secretion (764- and 32-fold of control, respectively), and activin treatment increased inhibin B secretion in these cells (25-fold of control). In conclusion, human adrenocortical cells produce dimeric activins and inhibins. ACTH stimulates inhibin secretion and decreases activin/inhibin secretion ratio, probably via the protein kinase A signal transduction pathway. This, together with the adrenocortical activin/ inhibin receptor and binding protein expression, suggests a physiological role for activins and inhibins in the human adrenal gland.

Differential gene expression of TGF-beta family members and osteopontin in breast tumor tissue: analysis by real-time quantitative PCR

Several cytokines including members of the transforming growth factor-beta (TGF-beta) and tumor necrosis factor (TNF) families have been implicated in the homing mechanism of breast cancer metastasis. We hypothesize that primary breast tumor tissues differentially express modulators of bone cell function and that this expression pattern contributes to their aggressive and metastatic potential and to their capacity to establish and grow in bone. We, therefore, examined the gene expression pattern of the TGF-beta family members (inhibin/activin betaA subunit (activin betaA), inhibin alpha subunit, and bone morphogenetic protein-2 (BMP-2)), the TNF family members (receptor activator of NF-KB ligand (RANKL) and osteoprotegerin (OPG)), and osteopontin (OPN) in normal, non-invasive, invasive, and metastatic human breast cancer specimens. The mRNA transcript levels of these genes were quantified by reverse transcription (RT) and fluorescent-based kinetic PCR in 18 normal breast tissues, five ductal carcinoma in situ (DCIS). 24 primary breast tumor tissue, and five distant metastases. The mRNA transcript level of each gene was normalized to the amount of beta-actin present in the samples. We observed differential gene expression of the selected TGF-beta family members as well as OPN in breast cancer progression. The average gene expression of the putative tumor suppressor, inhibin alpha, did not significantly change in any of the tumor tissues examined compared to normal breast tissue. The mRNA level of BMP-2, a protein with anti-proliferative effects in breast cancer cell lines and involved in bone formation, significantly decreased in non-invasive, invasive, and liver metastatic breast tumor tissue compared to normal breast tissue. The gene expression of activin betaA, a protein involved in cell proliferation and osteoclast induction, increased in invasive and bone metastatic tumor tissue compared to normal breast tissue. The mRNA level of OPN, a bone matrix protein associated with enhanced malignancy, increased in non-invasive, invasive, and liver and bone metastatic breast tumor tissue compared to normal breast tissue. In contrast, the average gene expressions of the TNF family members, RANKL and OPG, proteins involved in the regulation of osteoclastogenesis, were only slightly if at all changed in the different stage breast tumor tissues. These results suggest that differential gene expression of bone-related proteins, especially OPN, activin betaA, and BMP-2, by primary breast tumor tissues may play a significant role in the invasiveness and metastatic potential of breast cancer.

Localization of an activin/activin receptor system in the porcine ovary

The aim of this study was to locate a possible activin/activin receptor system within porcine ovaries containing functional corpora lutea. In situ hybridization was used to assess the gene expression of beta(A)- and beta(B)-activin subunits, and immunohistochemical studies were done to detect activin-A protein and activin receptor type II. mRNA expression of the beta(A)- and beta(B)-activin subunits was found in the granulosa from the unilaminar follicle stage onward, in the developing thecal layer of multilaminar and small antral follicles, in the theca interna of mid-sized antral follicles, in corpora lutea, and in the ovarian surface epithelium. Immunoreactive activin A protein could be detected at the same ovarian sites, but in thecal tissue of small antral follicles only. This protein was also demonstrated at the peripheral zone of oocytes from multilaminar and antral follicles. A positive immunoreaction for activin receptor was found in granulosa cells from multilaminar and older follicles and in oocytes from the earliest stages of follicular development onward. In late multilaminar follicles and in antral follicles, the oolemma was stained. Except for small antral follicles, a positive activin receptor immunoreaction was absent in the follicular theca. Activin receptor immunoreaction was furthermore present in corpora lutea and in the ovarian surface epithelium. It is concluded that, within porcine ovaries containing functional corpora lutea, an activin/activin receptor system is present in all intact follicles, the corpora lutea and the surface epithelium. Within follicles, granulosa and theca cells are the main sites of activin synthesis, while oocytes and granulosa cells are the main activin binding sites.

Interleukin-1 beta enhances and interferon-gamma suppresses activin A actions by reciprocally regulating activin A and follistatin secretion from bone marrow stromal fibroblasts

Activin A is a multi-functional cytokine with a potent stimulation on erythroid cell differentiation in the bone marrow. The actions of activin A are determined by a balance of the levels of activin A and its inhibitor, follistatin (FS). However, the regulation of its actions in the bone marrow has been unclear. Here we show that bone marrow-derived stromal fibroblasts are the major source of activin A and FS in the bone marrow, and that the production of activin A is enhanced by interleukin-1beta (IL-1beta) and lipopolysaccharide (LPS), whereas interferon-gamma (IFN-gamma) inhibits the secretion of activin A by stromal fibroblasts. Concomitantly, IL-1beta as well as LPS inhibits and IFN-gamma stimulates FS secretion from stromal fibroblasts. Thus, these cytokines potently regulate activin A actions by reciprocal modulation of activin A and FS secretion from stromal fibroblasts. Because activin A exhibits anti-inflammatory effects in various tissues, up-regulation of activin A actions by IL-1beta and endotoxin in the bone marrow may play a protective role against inflammatory processes as well as anaemia. The present results also suggest that the inhibitory effect of IFN-gamma on erythropoiesis is mediated at least in part by a suppression of activin A actions in bone marrow.

In vitro release of activin A from human normal and pathological thyroid tissues

Activin A is a dimeric glycoprotein belonging to the transforming growth factor beta (TGF-beta) superfamily characterized by the ability to affect FSH secretion. Activin A was originally indicated as a gonadal product but the expression of activin A has been successively identified in several different tissues, including the thyroid gland. The aim of this study was to evaluate the release of activin A from human normal and pathological thyroid tissues in culture. Activin A concentration was evaluated in media obtained from primary culture of perinodular normal tissues (no.=2), hyperplastic hyperfunctioning thyroid tissues due to Graves' disease (no.=3) and autonomous thyroid adenomas (no.=3). Detectable levels of activin A were found in the incubation media from all tissues, without significant differences between normal and pathological samples. We conclude that activin A is secreted by follicle thyroid cells in normal and pathological conditions.

Pituitary follistatin and activin gene expression, and the testicular regulation of FSH in the adult Rhesus monkey (Macaca mulatta)

In rats, FSHbeta gene expression and FSH secretion are increased and decreased, respectively, by pituitary activin and follistatin. Because little information is available on the paracrine control of FSH secretion in the primate, follistatin and activin/inhibin beta(B) messenger RNA (mRNA) levels were measured in pituitaries of adult male rhesus monkeys 6 weeks after castration or sham surgery (n = 5/group). Follistatin mRNA was determined by quantitative RT-PCR assay using oligonucleotide primers designed to span exons 3-5 of the human follistatin gene. Activin/inhibin beta(B) mRNA levels were measured by ribonuclease protection. Orchidectomy resulted in a 100-fold increase in plasma FSH concentrations and a 60-fold rise in those of LH. In castrated monkeys, levels of mRNA encoding FSHbeta, LHbeta, alpha- subunit, and GnRH receptor (GnRH-R) were increased 21-, 2.1-, 1.7-, and 1.7-fold, respectively (P < 0.01). Levels of pituitary follistatin and activin/inhibin beta(B) mRNAs, however, were similar in castrated and intact animals. These data suggest that the paracrine control of FSH secretion in the male differs substantially in primates and rodents. Specifically, the relatively greater postcastration rise in FSHbeta gene expression and FSH secretion in the adult male monkey may result because in this species pituitary follistatin gene expression does not increase after orchidectomy, as it does in the rat.

Localization of inhibin/activin subunits in normal pituitary and in pituitary adenomas

The localization of inhibin/activin (I/A) subunits was investigated in human normal adenohypophysial cells and in 87 pituitary adenomas of different types, using immunohistochemistry. Monoclonal antibodies directed against alpha, beta A and beta B subunits of I/A were employed. In normal pituitary, alpha subunit of inhibin was detected only in FSH-positive gonadotrophs, while beta A subunit of I/A was expressed in FSH-positive gonadotrophs, GH-cells and in a few PRL-cells. beta B subunit was found in FSH-positive gonadotrophs, TSH-cells and a few LH-positive gonadotrophs. The three subunits of I/A were detected in the majority of nonfunctioning tumors, while functioning adenomas showed a significantly lower expression. This study shows that alpha, beta A and beta B subunits of I/A are expressed by specific adenohypophysial cell types and that they are characteristically present in nonfunctioning adenomas. These results suggest that inhibins and activins may play a role in the local regulation of pituitary hormonal secretion both in normal adenohypophysial cells and in pituitary adenomas.

A role for activin A and betacellulin in human fetal pancreatic cell differentiation and growth

Activin A (Act.A), a member of the transforming growth factor beta family of secreted proteins, has been implicated in the regulation of growth and differentiation of various cell types. Betacellulin (BTC), a member of the epidermal growth factor family, converts exocrine AR42J cells to insulin-expressing cells when combined with Act.A. We have used primary cultures of human fetal pancreatic tissue to identify the effects of Act.A and/or BTC on islet development and growth. Exposure to Act.A resulted in a 1.5-fold increase in insulin content (P < 0.005) and a 2-fold increase in the number of cells immunopositive for insulin (P < 0.005). The formation of islet-like cell clusters, containing mainly epithelial cells, during a 5-day culture, was stimulated 1.4-fold by BTC (P < 0.05). BTC alone caused a 2.6-fold increase in DNA synthesis (P < 0.005). These data suggest that Act.A induces endocrine differentiation, whereas BTC has a mitogenic effect on human undifferentiated pancreatic epithelial cells.

Activin A stimulates insulin secretion in cultured human pancreatic islets

Activin A is a dimeric glycoprotein showing a high sequence homology with transforming growth factor-beta (TGF-beta) and playing autocrine/paracrine actions in reproductive tissues. However, since the synthesis of activin is ubiquitous it may have a role in regulating cell growth and differentiation in several tissues. Previous studies showed that activin A is expressed by insulin-positive B cells of human pancreatic islets, and women with gestational diabetes have higher serum activin A levels than healthy pregnant women at the same gestational age. The present study aimed to evaluate the effect of activin A on insulin secretion from cultured human pancreatic islets. With this purpose human pancreatic islets were incubated with varying concentrations of activin A (0.1 to 10.0 nM). In absence of glucose, activin A did not modify insulin secretion at the different concentrations used. In absence of activin A, 8.3 mM and 16.7 mM glucose significantly increased insulin secretion, with a dose-dependent pattern. In presence of a non stimulatory concentration of glucose (3.3 mM), activin A significantly increased insulin secretion starting from low concentration (0.1 nM). Furthermore, the addition of activin A to 8.3 mM and 16.7 mM glucose induced an additional effect of the dose-dependent glucose-mediated insulin secretion (p<0.001). The present data could support a role for activin A in human endocrine pancreas in modulating insulin response to different glucose concentrations.

Expression of activin A and follistatin core proteins by human prostate tumor cell lines

Activin and follistatin (FS) messenger RNA and protein are expressed and localized to human prostate tissue from men with high grade cancer and to human prostate tumor cell lines LNCaP, DU145, and PC3. Although activin A induces apoptosis and inhibits cell proliferation in LNCaP cells, PC3 cells are insensitive to the effect of exogenous addition of activin A. The results of this study show that activin A and FS are produced and can be measured by specific enzyme-linked immunosorbent assays in PC3 cells and media but are not detectable in LNCaP cells. Over 10 days in culture, the production of activin A by PC3 cells declines and is inversely correlated (r = -0.779) to FS288 production, which steadily increases and is significantly elevated compared with Day 1 of culture. The presence of FS288 and FS315 proteins was confirmed by immunocytochemistry and showed that only PC3 cells produced the FS288 isoform. Western blotting of PC3 cell media confirmed the presence of the FS288 isoform. Blockade of FS288 activity with a neutralizing antibody rendered PC3 cells responsive to activin A, as measured by inhibition of proliferation. Collectively, these results suggest that PC3 tumor cells are insensitive to activin A because they produce measurable amounts of activin ligand and FS288 protein, which is capable of blocking the autocrine response of these cells to activin A.

Expression of transforming growth factor-beta1, activin A, and their receptors in thyroid follicle cells: negative regulation of thyrocyte growth and function

Thyroid growth and function are intricately regulated by both positive and negative factors. In the present study, we have investigated the expression of transforming growth factor-beta (TGF-beta) super-family members and their receptors in normal porcine thyroid follicle cells. In tissue sections of porcine thyroids, we observed an expression of TGF-beta1, activin A, and bone morphogenetic protein (BMP)-7 proteins. The staining was localized to the follicular epithelium. In affinity cross-linking experiments, TGF-beta1 was found to bind to heteromeric complexes of TGF-beta type I and type II receptors, and activin A bound most efficiently to heteromeric complexes of activin type IB and type II receptors. We were unable to detect any BMP receptors (BMPRs) in attempts to perform affinity cross-linking with BMP-7. However, expression of BMPR-IA and BMPR-II messenger RNA (mRNA) was detected by Northern blot analysis. Both TGF-beta1 and activin A, but not BMP-7, increased the phosphorylation of Smad2, induced nuclear translocation of Smad2, Smad3, and Smad4, and inhibited thyrocyte cell growth as well as TSH-stimulated cAMP response. TGF-beta1 was more potent, compared with activin A, to induce these cellular responses. Taken together, our findings indicate a role for several members of the TGF-beta family in regulation of thyroid growth and function.