Activin signal transduction pathways

Activin receptors in human cancer: Functions, mechanisms, and potential clinical applications

Activins are members of the transforming growth factor-β (TGF-β) superfamily and act as key regulators in various physiological processes, such as follicle and embryonic development, as well as in multiple human diseases, including cancer. They have been established to signal through three type I and two type II serine/threonine kinase receptors, which, upon ligand binding, form a final signal-transducing receptor complex that activates downstream signaling and governs gene expression. Recent research highlighted the dysregulation of the expression or activity of activin receptors in multiple human cancers and their critical involvement in cancer progression. Furthermore, expression levels of activin receptors have been associated with clinicopathological features and patient outcomes across different cancers. However, there is currently a paucity of comprehensive systematic reviews of activin receptors in cancer. Thus, this review aimed to consolidate existing knowledge concerning activin receptors, with a primary emphasis on their signaling cascade and emerging biological functions, regulatory mechanisms, and potential clinical applications in human cancers in order to provide novel perspectives on cancer prognosis and targeted therapy.

Production of Mature Recombinant Human Activin A in Transgenic Rice Cell Suspension Culture

Activin A belongs to the transforming growth factor (TGF) family member, which exhibits a wide range of biological activities, including the regulation of cellular proliferation and differentiation and the promotion of neuronal survival. The isolation of AA from natural sources can only produce limited quantities of this bioactive protein. In this study, the whole gene of the precursor form of recombinant human activin A (rhAA) contains a signal peptide, and a pro-region and a mature region were cloned into an expression vector under the control of the rice α-amylase 3D (RAmy3D) promoter. To obtain the mature (active) form of rhAA, an enterokinase cleavage site was inserted between the pro-region and mature region of rhAA. The rice seed (Oryza sativa L. cv. Dongjin) was transformed with recombinant vectors by the Agrobacterium-mediated method, and the integration of the target gene into the plant genome was confirmed by genomic PCR. The transcript expression of rhAA in transgenic rice calli was confirmed by a Northern blot analysis of mRNA. The production of rhAA was verified by Western blot analysis and ELISA. The accumulation of secreted rhAA in the culture medium was purified by Ni2+-NTA. The mature form of AA was released from the precursor form of rhAA after proteolytically processing with enterokinase. Western blot shows that the mature AA was split into monomer and homodimer with molecular weights of 14 kDa and 28 kDa under reducing and non-reducing conditions, respectively. These results suggest that the mature form of rhAA could be produced and purified using transgenic rice cell suspension culture.

Molecular Mechanisms Determining Mammalian Oocyte Quality with the Treatment of Cancer Therapy

Cancer is a global public health issue and remains one of the leading causes of death in the United States (Siegel et al. CA Cancer J Clin. 72:7-33, 2022). It is estimated in the US in 2022, about 935,000 new cases of cancer will be diagnosed in women, and the probability of developing invasive cancer is 5.8% for females younger than 50 years old (Siegel et al. CA Cancer J Clin. 72:7-33, 2022). However, advances in screening programs, diagnostic methods, and therapeutic options have greatly increased the five-year survival rate in reproductive-age women with a variety of cancers. Given the clinical consequences of gonadotoxic cancer therapies, young, female cancer survivors may face compromised fertility, premature ovarian insufficiency, early-onset menopause, and endocrine dysregulation (Bedoschi et al. Future Oncol. 12:2333-44, 2016). Gonadotoxic side effects may include decreased oocyte quality within surviving follicles, loss of ovarian follicles, and impaired ovarian function. In reproductive-age women, oocyte quality is an important element for successful clinical pregnancies and healthy offspring as poor-quality oocytes may be a cause of infertility (McClam et al. Biol Reprod. 106:328-37, 2022; Marteil et al. Reprod Biol. 9:203-24, 2009; Krisher. J Anim Sci. 82: E14-E23, 2004). Thus, it is critical to determine the quantity and quality of surviving follicles in the ovary after cancer treatment and to assess oocyte quality within those surviving follicles as these are markers for determining the capacity for ovarian function restoration and future fertility, especially for young cancer survivors (Xu et al. Nat Med. 17:1562-3, 2011). The long-term effects of cancer therapeutics on oocyte quality are influenced by factors including, but not limited to, individual patient characteristics (e.g. age, health history, comorbidities, etc.), disease type, or treatment regimen (Marci et al. Reprod Biol Endocrinol. 16:1-112, 2018). These effects may translate clinically into an impaired production of viable oocytes and compromised fertility (Garutti et al. ESMO Open. 6:100276, 2021).

Activin A marks a novel progenitor cell population during fracture healing and reveals a therapeutic strategy

Insufficient bone fracture repair represents a major clinical and societal burden and novel strategies are needed to address it. Our data reveal that the transforming growth factor-β superfamily member Activin A became very abundant during mouse and human bone fracture healing but was minimally detectable in intact bones. Single-cell RNA-sequencing revealed that the Activin A-encoding gene Inhba was highly expressed in a unique, highly proliferative progenitor cell (PPC) population with a myofibroblast character that quickly emerged after fracture and represented the center of a developmental trajectory bifurcation producing cartilage and bone cells within callus. Systemic administration of neutralizing Activin A antibody inhibited bone healing. In contrast, a single recombinant Activin A implantation at fracture site in young and aged mice boosted: PPC numbers; phosphorylated SMAD2 signaling levels; and bone repair and mechanical properties in endochondral and intramembranous healing models. Activin A directly stimulated myofibroblastic differentiation, chondrogenesis and osteogenesis in periosteal mesenchymal progenitor culture. Our data identify a distinct population of Activin A-expressing PPCs central to fracture healing and establish Activin A as a potential new therapeutic tool.

Direct contact with endothelial cells drives dental pulp stem cells toward smooth muscle cells differentiation via TGF-β1 secretion

AIM

Prevascularization is vital to accelerate functional blood circulation establishment in transplanted engineered tissue constructs. Mesenchymal stem cells (MSCs) or mural cells could promote the survival of implanted endothelial cells (ECs) and enhance the stabilization of newly formed blood vessels. However, the dynamic cell-cell interactions between MSCs, mural cells and ECs in the angiogenic processes remain unclear. This study aimed to explore the interactions of human umbilical vein ECs (HUVECs) and dental pulp stem cells (DPSCs) in an in vitro cell coculture model.

METHODOLOGY

Human umbilical vascular ECs and DPSCs were directly cocultured or indirectly cocultured with transwell inserts in endothelial basal media-2 (EBM-2) supplemented with 5% FBS for 6 days. Expression of SMC-specific markers in DPSCs monoculture and HUVEC+DPSC cocultures was assessed by western blot and immunofluorescence. Activin A and transforming growth factor-beta 1 (TGF-β1) in conditioned media (CM) of HUVECs monoculture (E-CM), DPSCs monoculture (D-CM) and HUVEC+DPSC cocultures (E+D-CM) were analysed by enzyme-linked immunosorbent assay. TGF-β RI kinase inhibitor VI, SB431542, was used to block TGF-β1/ALK5 signalling in DPSCs.

RESULTS

The expression of SMC-specific markers, α-SMA, SM22α and Calponin, were markedly increased in HUVEC+DPSC direct cocultures compared to that in DPSCs monoculture, while no differences were demonstrated between HUVEC+DPSC indirect cocultures and DPSCs monoculture. E+D-CM significantly upregulated the expression of SMC-specific markers in DPSCs compared to E-CM and D-CM. Activin A and TGF-β1 were considerably higher in E+D-CM than that in D-CM, with upregulated Smad2 phosphorylation in HUVEC+DPSC cocultures. Treatment with activin A did not change the expression of SMC-specific markers in DPSCs, while treatment with TGF-β1 significantly enhanced these markers' expression in DPSCs. In addition, blocking TGF-β1/ALK5 signalling inhibited the expression of α-SMA, SM22α and Calponin in DPSCs.

CONCLUSIONS

TGF-β1 was responsible for DPSC differentiation into SMCs in HUVEC+DPSC cocultures, and TGF-β1/ALK5 signalling pathway played a vital role in this process.

Gastrointestinal pharmacology activins in liver health and disease

Activins are a subgroup of the TGFβ superfamily of growth and differentiation factors, dimeric in nature and consisting of two inhibin beta subunits linked via a disulfide bridge. Canonical activin signaling occurs through Smad2/3, with negative feedback initiated by Smad6/7 following signal transduction, which binds activin type I receptor preventing phosphorylation of Smad2/3 and activation of downstream signaling. In addition to Smad6/7, other inhibitors of activin signaling have been identified as well, including inhibins (dimers of an inhibin alpha and beta subunit), BAMBI, Cripto, follistatin, and follistatin-like 3 (fstl3). To date, activins A, B, AB, C, and E have been identified and isolated in mammals, with activin A and B having the most characterization of biological activity. Activin A has been implicated as a regulator of several important functions of liver biology, including hepatocyte proliferation and apoptosis, ECM production, and liver regeneration; the role of other subunits of activin in liver physiology are less understood. There is mounting data to suggest a link between dysregulation of activins contributing to various hepatic diseases such as inflammation, fibrosis, and hepatocellular carcinoma, and emerging studies demonstrating the protective and regenerative effects of inhibiting activins in mouse models of liver disease. Due to their importance in liver biology, activins demonstrate utility as a therapeutic target for the treatment of hepatic diseases such as cirrhosis, NASH, NAFLD, and HCC; further research regarding activins may provide diagnostic or therapeutic opportunity for those suffering from various liver diseases.

Activin A and pathologies of pregnancy: a review

Activin A is a two-subunit protein belonging to the transforming growth factor β superfamily. First discovered almost three decades ago, it has since been implicated in diverse physiological roles, ranging from wound repair to reproduction. After 30 years of research, altered activin A levels are now understood to be associated with the development of various diseases, making activin A a potential therapeutic target. In pregnancy, the placenta and fetal membranes are major producers of activin A, with significantly enhanced serum concentrations now recognised as a contributor to numerous gestational disorders. Evidence now suggests that circulating levels of activin A may be clinically relevant in the early detection of pregnancy complications, including miscarriage and preeclampsia. This review aims to summarise our current understanding of activin A as a potential diagnostic marker in common pregnancy pathologies.

The expression and phosphorylation of SMAD3 protein in microglia and astrocytes of the rat hippocampus after transient global cerebral ischemia

SMAD3 protein transduces signals from TGF-β and activins. In vitro studies have shown that SMAD3 plays an important role in regulating of micoglia and astrocytic function. However, there is little information on the association between SMAD3 signaling and the pathophysiology of the glial cells in the post-ischemic hippocampus. In this study, we examined the time-course changes in the expression and phosphorylation of SMAD3 in the rat hippocampus using a rat model of global cerebral ischemia. Most pyramidal neuronal cells in the CA1 region died within 7 days after ischemia. The number of SMAD3- or phosphorylated SMAD3 (p-SMAD3)-immunopositive microglia or astrocytes increased in the CA1 region 7 days after ischemia. Real-time PCR analysis showed an increase in the level of TGF-β1 mRNA in the hippocampus after ischemia. Intracerebroventricular injection of SB525334, a selective inhibitor of TGF-β receptor I kinase (ALK5), reduced the ischemia-induced p-SMAD3 immunoreactivity in the microglia and astrocytes. By contrast, intracerebroventricular injection of SB525334 did not affect the ischemia-induced neuronal cell death. These results suggest that ischemia-induced SMAD3 phosphorylation in the microglia and astrocytes of post-ischemic hippocampi is associated with tissue repair and not neuroprotection.

Distinct gene expression dynamics in germ line and somatic tissue during ovariole morphogenesis in Drosophila melanogaster

The survival and evolution of a species is a function of the number of offspring it can produce. In insects, the number of eggs that an ovary can produce is a major determinant of reproductive capacity. Insect ovaries are made up of tubular egg-producing subunits called ovarioles, whose number largely determines the number of eggs that can be potentially laid. Ovariole number in Drosophila is directly determined by the number of cellular structures called terminal filaments, which are stacks of cells that assemble in the larval ovary. Elucidating the developmental and regulatory mechanisms of terminal filament formation is thus key to understanding the regulation of insect reproduction through ovariole number regulation. We systematically measured mRNA expression of all cells in the larval ovary at the beginning, middle, and end of terminal filament formation. We also separated somatic and germ line cells during these stages and assessed their tissue-specific gene expression during larval ovary development. We found that the number of differentially expressed somatic genes is highest during the late stages of terminal filament formation and includes many signaling pathways that govern ovary development. We also show that germ line tissue, in contrast, shows greater differential expression during early stages of terminal filament formation, and highly expressed germ line genes at these stages largely control cell division and DNA repair. We provide a tissue-specific and temporal transcriptomic dataset of gene expression in the developing larval ovary as a resource to study insect reproduction.

Activin a inhibits foam cell formation and up-regulates ABCA1 and ABCG1 expression through Alk4-Smad signaling pathway in RAW 264.7 macrophages

BACKGROUND

Activin A has been reported to play important roles in the pathogenesis of atherosclerosis. The purpose of this study is to investigate the effects of activin A on oxidized low-density lipoprotein (ox-LDL)-induced foam cell formation and explore the underlying molecular mechanisms in murine macrophage-like cell line RAW 264.7.

METHODS

The effects of activin A on Dil-labeled ox-LDL uptake were examined by confocal microscopy and flow cytometry analysis. The mRNA and protein levels of cholesterol receptors were analyzed by RT-qPCR and western blot analysis, respectively. To investigate whether activin receptor-like kinase 4 (Alk4) is required for activin A-mediated cellular effects, cells were pre-treated with SB-431542. The involvement of Smad2, Smad3 and Smad4 was confirmed by transfection with specific small interfering RNAs (siRNAs).

RESULTS

Activin A inhibits ox-ldl-induced foam cell formation and class A scavenger receptors (SR-A) expression, while up-regulates ATP-binding cassette transporter A1 (ABCA1) and ABCG1 expression in RAW 264.7 macrophages. Pre-treatment with SB-431542 abolished activin A-mediated anti-atherogenic effect. Knockdown of Smad2 reversed activin A-induced inhibition of ox-LDL uptake and SR-A expression. However, knockdown of Smad3 or Smad4 did not have such effect. Meanwhile, knockdown of either Smad2, Smad3 or Smad4 reversed the activin A-induced up-regulation of ABCA1 and ABCG1.

CONCLUSIONS

Our study provides novel evidence that activin A may exert anti-atherogenic effects through Alk4-Smad signaling pathway in RAW 264.7 macrophages.

Fibroblasts: Origins, definitions, and functions in health and disease

Fibroblasts are diverse mesenchymal cells that participate in tissue homeostasis and disease by producing complex extracellular matrix and creating signaling niches through biophysical and biochemical cues. Transcriptionally and functionally heterogeneous across and within organs, fibroblasts encode regional positional information and maintain distinct cellular progeny. We summarize their development, lineages, functions, and contributions to fibrosis in four fibroblast-rich organs: skin, lung, skeletal muscle, and heart. We propose that fibroblasts are uniquely poised for tissue repair by easily reentering the cell cycle and exhibiting a reversible plasticity in phenotype and cell fate. These properties, when activated aberrantly, drive fibrotic disorders in humans.

Circulating activin A during equine gestation and immunolocalization of its receptors system in utero-placental tissues and fetal gonads

Although equine gestation is unique from the standpoint of fetal gonadal enlargement and regression, the activator of this process is still unknown. The present study aimed to show a possible role of activin during equine gestation. In the first experiment, weekly plasma samples from six pregnant mares were used to measure activin A. In the second experiment, eight pregnant mares carrying female (gestational days 110, 140, 180, and 270) and male fetuses (gestational days 120, 180, 225, and 314) were used for immunohistochemistry of activin receptors (IA, IB, IIA, IIB), and their intracellular mediators (Smad2, Smad3, Smad4). Activin A levels in maternal circulation remained low until fourth weeks of gestation, thereafter, started to increase, and peaked first at 11 weeks of gestation. The second significant peak was observed on the day of parturition. Activin receptors type IA, IB, IIA, and IIB were immunostained in interstitial and germ cells of fetal ovaries and testes along with utero-placental tissues. Smad2, Smad3, and Smad4 were also immunolocalized in all these organs. These results demonstrated the activin-producing capacity of utero-placental tissues, and also evidenced the existence of activin receptors and functional signaling molecules in these organs. The first increment in circulating activin A in maternal circulation coinciding with the timing of initiation of fetal gonadal enlargement suggests that activin from the utero-placental tissues may have a stimulatory role in fetal gonad enlargement and utero-placental development in mares, whereas the second peak could be important to follicular development in the maternal ovary for foal heat.

Identification of Molecules from Coffee Silverskin That Suppresses Myostatin Activity and Improves Muscle Mass and Strength in Mice

Coffee has been shown to attenuate sarcopenia, the age-associated muscle atrophy. Myostatin (MSTN), a member of the TGF-β growth/differentiation factor superfamily, is a potent negative regulator of skeletal muscle mass, and MSTN-inhibition increases muscle mass or prevents muscle atrophy. This study, thus, investigated the presence of MSTN-inhibitory capacity in coffee extracts. The ethanol-extract of coffee silverskin (CSE) but not other extracts demonstrated anti-MSTN activity in a pGL3-(CAGA)₁₂-luciferase reporter gene assay. CSE also blocked Smad3 phosphorylation induced by MSTN but not by GDF11 or Activin A in Western blot analysis, demonstrating its capacity to block the binding of MSTN to its receptor. Oral administration of CSE significantly increased forelimb muscle mass and grip strength in mice. Using solvent partitioning, solid-phase chromatography, and reverse-phase HPLC, two peaks having MSTN-inhibitory capacity were purified from CSE. The two peaks were identified as ^βN-arachinoyl−5-hydroxytryptamide (C₂₀−5HT) and ^βN-behenoyl−5-hydroxytryptamide (C₂₂−5HT) using mass spectrometry and NMR analysis. In summary, the results show that CSE has the MSTN-inhibitory capacity, and C₂₀−5HT and C₂₂−5HT are active components of CSE-suppressing MSTN activity, suggesting the potential of CSE, C₂₀−5HT, and C₂₂−5HT being developed as agents to combat muscle atrophy and metabolic syndrome.

Changes in Smad1/5/9 expression and phosphorylation in astrocytes of the rat hippocampus after transient global cerebral ischemia

Smad proteins are known to transduce the actions of the transforming growth factor-β (TGF-β) family including TGF-βs, activins, and bone morphogenetic proteins (BMPs). We previously reported that Smad1/5/9 immunoreactivity was observed in astrocytes of various rat brain regions including the hippocampus, suggesting that Smad1/5/9 may be associated with the physiology of astrocytes. However, the Smad1/5/9 expression and activation in the hippocampal astrocytes after global cerebral ischemia has not been yet elucidated. In this study, we examined temporal changes in the expression and phosphorylation of Smad1/5/9 in the hippocampus using a rat model of global cerebral ischemia. Furthermore, we examined the candidate ligand involved in the phosphorylation of Smad1/5/9 in the hippocampus after ischemia. Pyramidal neuronal cell death in the CA1 regions was visible at 3 days, and maximum death occurred within 7 days after ischemia. At 7 days after ischemia, astrocytes that showed strong immunoreactivity for Smad1/5/9 were frequently observed in the CA1 region. Additionally, there was an increase in phosphorylated Smad1/5/9 (phospho-Smad1/5/9) -immunopositive astrocytes in the CA1 region 7 days after ischemia. Real-time PCR analysis showed an increase in the expression level of TGF-β1 mRNA in the hippocampus after ischemia. Intracerebroventricular injection of SB525334, an inhibitor of TGF-β/Smad signaling, reduced immunoreactivity for phospho-Smad1/5/9 in astrocytes. These results suggest that TGF-β1 may be a key molecule for ischemia-induced Smad1/5/9 phosphorylation in astrocytes, and TGF-β1-Smad1/5/9 signaling may play a role in post-ischemic events, including brain inflammation or tissue repair rather than neuroprotection of the hippocampus.

The role of glycogen synthase kinase 3 (GSK3) in cancer with emphasis on ovarian cancer development and progression: A comprehensive review

Glycogen synthase kinase 3 (GSK3) is a monomeric serine-threonine kinase discovered in 1980 in a rat skeletal muscle. It has been involved in various cellular processes including embryogenesis, immune response, inflammation, apoptosis, autophagy, wound healing, neurodegeneration, and carcinogenesis. GSK3 exists in two different isoforms, GSK3α and GSK3β, both containing seven antiparallel beta-plates, a short linking part and an alpha helix, but coded by different genes and variously expressed in human tissues. In the current review, we comprehensively appraise the current literature on the role of GSK3 in various cancers with emphasis on ovarian carcinoma. Our findings indicate that the role of GSK3 in ovarian cancer development cannot be decisively determined as the currently available data support both prooncogenic and tumor-suppressive effects. Likewise, the clinical impact of GSK3 expression on ovarian cancer patients and its potential therapeutic implications are also limited. Further studies are needed to fully elucidate the pathophysiological and clinical implications of GSK3 activity in ovarian cancer.

The complexity of TGFβ/activin signaling in regeneration

The role of transforming growth factor β TGFβ/activin signaling in wound repair and regeneration is highly conserved in the animal kingdom. Various studies have shown that TGF-β/activin signaling can either promote or inhibit different aspects of the regeneration process (i.e., proliferation, differentiation, and re-epithelialization). It has been demonstrated in several biological systems that some of the different cellular responses promoted by TGFβ/activin signaling depend on the activation of Smad-dependent or Smad-independent signal transduction pathways. In the context of regeneration and wound healing, it has been shown that the type of R-Smad stimulated determines the different effects that can be obtained. However, neither the possible roles of Smad-independent pathways nor the interaction of the TGFβ/activin pathway with other complex signaling networks involved in the regenerative process has been studied extensively. Here, we review the important aspects concerning the TGFβ/activin signaling pathway in the regeneration process. We discuss data regarding the role of TGF-β/activin in the most common animal regenerative models to demonstrate how this signaling promotes or inhibits regeneration, depending on the cellular context.

Activin type IIA decoy receptor and intermittent parathyroid hormone in combination overturns the bone loss in disuse-osteopenic mice

Damage of the lower motor neuron cell bodies or their axons results in reduced or abolished voluntary movement accompanied by a substantial loss of bone and muscle mass. Intermittent parathyroid hormone 1-34 (PTH) (teriparatide) is one of the most potent bone-anabolic treatment regimens. ActRIIA-mFc is an activin type IIA decoy receptor that increases bone mass mediated by inhibition of the activin receptor signaling pathway. We investigated whether PTH or ActRIIA-mFc alone or in combination could prevent loss of bone and muscle mass induced by injecting botulinum toxin A (BTX) into the right hind limb in mice. Seventy-two 16-week-old female C57BL/6 mice were allocated to the following groups: Baseline, Control, BTX, BTX + ActRIIA-mFc (10 mg/kg), BTX + PTH (100 μg/kg), and BTX + ActRIIA-mFc + PTH. The mice were sacrificed after three weeks of disuse and treatment. In contrast to monotherapy with PTH, ActRIIA-mFc alone or in combination with PTH was able partly or completely to prevent disuse-induced loss of whole femoral bone mass, trabecular thickness, and bone strength. Moreover, an additive effect of ActRIIA-mFc and PTH on areal bone mineral density and trabecular bone volume was found. In summary, ActRIIA-mFc and PTH in combination were more effective in preventing disuse-induced bone loss and deterioration of trabecular micro-architecture than either treatment alone.

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.

Activin A increases human trophoblast invasion by upregulating integrin β1 through ALK4

Activin A promotes human trophoblast invasion during the first trimester of pregnancy and is associated with preeclampsia and pregnancy-induced hypertension (PE/PIH) in naturally conceived pregnancies. However, whether integrin β1 mediates activin A-increased trophoblast invasion remains unknown and the evidence is limited regarding the predictive value of activin A for PE/PIH in women receiving in vitro fertilization (IVF) treatment. Here, we studied the role and underlying molecular mechanisms of integrin β1 in activin A-promoted invasion in immortalized (HTR8/SVneo) and primary human extravillous trophoblast (EVT) cells. A nest case-control study was designed to investigate the predictive/diagnostic value of activin A in IVF pregnancies. Results showed that integrin β1 expression increased after activin A treatment and knockdown of integrin β1 significantly decreased both basal and activin A-increased HTR8/SVneo cell invasion. SB431542 (TGF-β type I receptors inhibitor) abolished activin A-induced SMAD2/SMAD3 phosphorylation and integrin β1 overexpression. Activin A-upregulated integrin β1 expression was attenuated after the depletion of ALK4 or SMAD4 in both HTR8/SVneo and primary EVT cells. Furthermore, we found similar first-trimester activin A levels in IVF patients with or without subsequent PE/PIH. These results reveal that integrin β1 mediates activin A-promoted trophoblast invasion through ALK4-activated SMAD2/3-SMAD4 pathway, and the predictive/diagnostic value of first-trimester maternal serum activin A for hypertensive disorders of pregnancy might be different in IVF population.

Automated Hypothesis Generation to Identify Signals Relevant in the Development of Mammalian Cell and Tissue Bioprocesses, With Validation in a Retinal Culture System

We have developed an accessible software tool (receptoR) to predict potentially active signaling pathways in one or more cell type(s) of interest from publicly available transcriptome data. As proof-of-concept, we applied it to mouse photoreceptors, yielding the previously untested hypothesis that activin signaling pathways are active in these cells. Expression of the type 2 activin receptor (Acvr2a) was experimentally confirmed by both RT-qPCR and immunochemistry, and activation of this signaling pathway with recombinant activin A significantly enhanced the survival of magnetically sorted photoreceptors in culture. Taken together, we demonstrate that our approach can be easily used to mine publicly available transcriptome data and generate hypotheses around receptor expression that can be used to identify novel signaling pathways in specific cell types of interest. We anticipate that receptoR (available at https://www.ucalgary.ca/ungrinlab/receptoR) will enable more efficient use of limited research resources.

Neuroendocrine, autocrine, and paracrine control of follicle-stimulating hormone secretion

Follicle-stimulating hormone (FSH) is a glycoprotein hormone produced by gonadotropes in the anterior pituitary that plays a central role in controlling ovarian folliculogenesis and steroidogenesis in females. Moreover, recent studies strongly suggest that FSH exerts extragonadal actions, particularly regulating bone mass and adiposity. Despite its crucial role, the mechanisms regulating FSH secretion are not completely understood. It is evident that hypothalamic, ovarian, and pituitary factors are involved in the neuroendocrine, paracrine, and autocrine regulation of FSH production. Large animal models, such as the female sheep, represent valuable research models to investigate specific aspects of FSH secretory processes. This review: (i) summarizes the role of FSH controlling reproduction and other biological processes; (ii) discusses the hypothalamic, gonadal, and pituitary regulation of FSH secretion; (iii) considers the biological relevance of the different FSH isoforms; and (iv) summarizes the distinct patterns of FSH secretion under different physiological conditions.

Specification of BMP Signaling

Bone Morphogenetic Proteins (BMPs) together with the Growth and Differentiation Factors (GDFs) form the largest subgroup of the Transforming Growth Factor (TGF)β family and represent secreted growth factors, which play an essential role in many aspects of cell communication in higher organisms. As morphogens they exert crucial functions during embryonal development, but are also involved in tissue homeostasis and regeneration in the adult organism. Their involvement in maintenance and repair processes of various tissues and organs made these growth factors highly interesting targets for novel pharmaceutical applications in regenerative medicine. A hallmark of the TGFβ protein family is that all of the more than 30 growth factors identified to date signal by binding and hetero-oligomerization of a very limited set of transmembrane serine-threonine kinase receptors, which can be classified into two subgroups termed type I and type II. Only seven type I and five type II receptors exist for all 30plus TGFβ members suggesting a pronounced ligand-receptor promiscuity. Indeed, many TGFβ ligands can bind the same type I or type II receptor and a particular receptor of either subtype can usually interact with and bind various TGFβ ligands. The possible consequence of this ligand-receptor promiscuity is further aggravated by the finding that canonical TGFβ signaling of all family members seemingly results in the activation of just two distinct signaling pathways, that is either SMAD2/3 or SMAD1/5/8 activation. While this would implicate that different ligands can assemble seemingly identical receptor complexes that activate just either one of two distinct pathways, in vitro and in vivo analyses show that the different TGFβ members exert quite distinct biological functions with high specificity. This discrepancy indicates that our current view of TGFβ signaling initiation just by hetero-oligomerization of two receptor subtypes and transduction via two main pathways in an on-off switch manner is too simplified. Hence, the signals generated by the various TGFβ members are either quantitatively interpreted using the subtle differences in their receptor-binding properties leading to ligand-specific modulation of the downstream signaling cascade or additional components participating in the signaling activation complex allow diversification of the encoded signal in a ligand-dependent manner at all cellular levels. In this review we focus on signal specification of TGFβ members, particularly of BMPs and GDFs addressing the role of binding affinities, specificities, and kinetics of individual ligand-receptor interactions for the assembly of specific receptor complexes with potentially distinct signaling properties.

The first two Chinese Myhre syndrome patients with the recurrent SMAD4 pathogenic variants: Functional consequences and clinical diversity

Myhre syndrome is a rare autosomal dominant multi-organ disorder characterized by growth retardation, skeletal anomalies, muscular hypertrophy, joint stiffness, facial dysmorphism, deafness, cardiovascular disease, and abnormal sexual development. Here we described the first two Chinese Myhre syndrome patients diagnosed by whole-exome sequencing. They both had de novo c.1498A > G (p.Ile500Val) variant in SMAD4 and presented with key characteristics of Myhre syndrome but also revealed uncommon features (polydactyly in the girl and precocious puberty in the boy). We performed functional analysis on four previously reported SMAD4 pathogenic variants in Myhre syndrome patients using dual-luciferase assay. Our results revealed that the pathogenic variants resulted in a variable degree of increased transcription activity of target genes that contain the minimal SMAD binding elements in their promoter regions. The boy responded to the recombinant human growth hormone treatment with improved height but also led to hyperinsulinemia and advanced bone age. Because of his precocious puberty, we subsequently combined the recombinant human growth hormone and gonadotrophin-releasing hormone agonist treatments, which resulted in overall improved height. We reviewed the sexual features of reported Myhre syndrome cases and discussed the possible mechanism of SMAD4 variants in Myhre syndrome that lead to the abnormal hypothalamic-pituitary-gonadal axis.

Activin-A in the regulation of immunity in health and disease

The TGF-β superfamily of cytokines plays pivotal roles in the regulation of immune responses protecting against or contributing to diseases, such as, allergy, autoimmunity and cancer. Activin-A, a member of the TGF-β superfamily, was initially identified as an inducer of follicle-stimulating hormone secretion. Extensive research over the past decades illuminated fundamental roles for activin-A in essential biologic processes, including embryonic development, stem cell maintenance and differentiation, haematopoiesis, cell proliferation and tissue fibrosis. Activin-A signals through two type I and two type II receptors which, upon ligand binding, activate their kinase activity, phosphorylate the SMAD2 and 3 intracellular signaling mediators that form a complex with SMAD4, translocate to the nucleus and activate or silence gene expression. Most immune cell types, including macrophages, dendritic cells (DCs), T and B lymphocytes and natural killer cells have the capacity to produce and respond to activin-A, although not in a similar manner. In innate immune cells, including macrophages, DCs and neutrophils, activin-A exerts a broad range of pro- or anti-inflammatory functions depending on the cell maturation and activation status and the spatiotemporal context. Activin-A also controls the differentiation and effector functions of Th cell subsets, including Th9 cells, T_FH cells, Tr1 Treg cells and Foxp3⁺ Treg cells. Moreover, activin-A affects B cell responses, enhancing mucosal IgA secretion and inhibiting pathogenic autoantibody production. Interestingly, an array of preclinical and clinical studies has highlighted crucial functions of activin-A in the initiation, propagation and resolution of human diseases, including autoimmune diseases, such as, systemic lupus erythematosus, rheumatoid arthritis and pulmonary alveolar proteinosis, in allergic disorders, including allergic asthma and atopic dermatitis, in cancer and in microbial infections. Here, we provide an overview of the biology of activin-A and its signaling pathways, summarize recent studies pertinent to the role of activin-A in the modulation of inflammation and immunity, and discuss the potential of targeting activin-A as a novel therapeutic approach for the control of inflammatory diseases.

Activin B Stimulates Mouse Vibrissae Growth and Regulates Cell Proliferation and Cell Cycle Progression of Hair Matrix Cells through ERK Signaling

Activins and their receptors play important roles in the control of hair follicle morphogenesis, but their role in vibrissae follicle growth remains unclear. To investigate the effect of Activin B on vibrissae follicles, the anagen induction assay and an in vitro vibrissae culture system were constructed. Hematoxylin and eosin staining were performed to determine the hair cycle stages. The 5-ethynyl-2′-deoxyuridine (EdU) and Cell Counting Kit-8 (CCK-8) assays were used to examine the cell proliferation. Flow cytometry was used to detect the cell cycle phase. Inhibitors and Western blot analysis were used to investigate the signaling pathway induced by Activin B. As a result, we found that the vibrissae follicle growth was accelerated by 10 ng/mL Activin B in the anagen induction assay and in an organ culture model. 10 ng/mL Activin B promoted hair matrix cell proliferation in vivo and in vitro. Moreover, Activin B modulates hair matrix cell growth through the ERK–Elk1 signaling pathway, and Activin B accelerates hair matrix cell transition from the G1/G0 phase to the S phase through the ERK–Cyclin D1 signaling pathway. Taken together, these results demonstrated that Activin B may promote mouse vibrissae growth by stimulating hair matrix cell proliferation and cell cycle progression through ERK signaling.

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.

Identification of genes involved in gonadal sex differentiation and the dimorphic expression pattern in Takifugu rubripes gonad at the early stage of sex differentiation

Quantifying the expression of mRNAs in the gonads at the critical stage of molecular sex differentiation stage might help to clarify the regulatory network during early sex differentiation and provide new information on the role of sex-related genes in gonadal function. In this study, transcriptomic analysis of sex-related genes expression profiles in fugu gonads at 60 and 90 days after hatching (dah) was conducted firstly, and a total of 112,504,991 clean reads, encompassing 28.35 Gb of sequences were retrieved. Twenty-three thousand eight hundred ten genes were found to be expressed in juvenile fugu gonads, and we mainly focused on the differentially expressed genes that have the potential to be involved in the gonadal sex differentiation. For 60-dah juveniles, we identified 1014 genes that were upregulated in the ovary and 1570 that were upregulated in the testis. For 90-dah juveniles, we identified 1287 genes that were upregulated in the ovary and 1500 that were upregulated in the testis. The dimorphic expression patterns of 15 genes in gonads at 30 and 40 dah were further investigate using qPCR. Cyp11b and star were expressed at higher levels in XY than in XX, while cyp11a1 and cyp19a1a were expressed at higher levels in XX than in XY at 30 dah. At 40 dah, the levels of gsdf, dmrt1, dmrt3, cyp11c1, star, and hsd3b expression were higher in XY, while the levels of foxl2, cyp19a1a, wnt9b, and foxD4 expression were higher in XX. Sox9, cyp11a1, cyp17a1, cyp17a2, and nr5a2 were expressed at similar levels in XX and XY at 40 dah. This is the first report of gonadal transcriptome of fugu at early sex differentiation stage, and our results provide an archive for further study on molecular mechanism underlying sex differentiation in this species.

ActivinA: a new leukemia-promoting factor conferring migratory advantage to B-cell precursor-acute lymphoblastic leukemic cells

B-cell precursor-acute lymphoblastic leukemia modulates the bone marrow (BM) niche to become leukemia-supporting and chemo-protective by reprogramming the stromal microenvironment. New therapies targeting the interplay between leukemia and stroma can help improve disease outcome. We identified ActivinA, a TGF-β family member with a well-described role in promoting several solid malignancies, as a factor favoring leukemia that could represent a new potential target for therapy. ActivinA resulted over-expressed in the leukemic BM and its production was strongly induced in mesenchymal stromal cells after culture with leukemic cells. Moreover, MSCs isolated from BM of leukemic patients showed an intrinsic ability to secrete higher amounts of ActivinA compared to their normal counterparts. The pro-inflammatory leukemic BM microenvironment synergized with leukemic cells to induce stromal-derived ActivinA. Gene expression analysis of ActivinA-treated leukemic cells showed that this protein was able to significantly influence motility-associated pathways. Interestingly, ActivinA promoted random motility and CXCL12-driven migration of leukemic cells, even at suboptimal chemokine concentrations, characterizing the leukemic niche. Conversely, ActivinA severely impaired CXCL12-induced migration of healthy CD34⁺ cells. This opposite effect can be explained by the ability of ActivinA to increase intracellular calcium only in leukemic cells, boosting cytoskeleton dynamics through a higher rate of actin polymerization. Moreover, by stimulating the invasiveness of the leukemic cells, ActivinA was found to be a leukemia-promoting factor. Importantly, the ability of ActivinA to enhance BM engraftment and the metastatic potential of leukemic cells was confirmed in a xenograft mouse model of the disease. Overall, ActivinA was seen to be a key factor in conferring a migratory advantage to leukemic cells over healthy hematopoiesis within the leukemic niche.

Expression of activin receptors in the equine uteroplacental tissue: an immunohistochemical analysis

Activin is secreted from equine uterine glands and plays important roles in establishment and maintenance of pregnancy in mares. This study aimed to localize activin receptors (ActRs) IA/B and IIA/B using immunohistochemistry in the uteroplacental tissues of seven pregnant Thoroughbred mares. At the time of tissue collection, the mares were at the following days of pregnancy: 88, 120, 161, 269, 290, 313, and 335 days. We fixed the uteroplacental tissues in 4% paraformaldehyde and obtained serial sections that were subsequently stained for analysis. All four isoforms of ActR were expressed in the uteroplacental tissues, including the endometrial epithelium, uterine glands, trophoblasts, and myometrium, throughout pregnancy. Our results suggested the potential role of activin in the uteroplacental tissues.

A soluble activin type IIA receptor mitigates the loss of femoral neck bone strength and cancellous bone mass in a mouse model of disuse osteopenia

Disuse causes a rapid and substantial bone loss distinct in its pathophysiology from the bone loss associated with cancers, age, and menopause. While inhibitors of the activin-receptor signaling pathway (IASPs) have been shown to prevent ovariectomy- and cancer-induced bone loss, their application in a model of disuse osteopenia remains to be tested. Here, we show that a soluble activin type IIA receptor (ActRIIA-mFc) increases diaphyseal bone strength and cancellous bone mass, and mitigates the loss of femoral neck bone strength in the Botulinum Toxin A (BTX)-model of disuse osteopenia in female C57BL/6J mice. We show that ActRIIA-mFc treatment preferentially stimulates a dual-effect (anabolic-antiresorptive) on the periosteal envelope of diaphyseal bone, demonstrating in detail the effects of ActRIIA-mFc on cortical bone. These observations constitute a previously undescribed feature of IASPs that mediates at least part of their ability to mitigate detrimental effects of unloading on bone tissue. The study findings support the application of IASPs as a strategy to combat bone loss during disuse.

Identification and Evolution of TGF-β Signaling Pathway Members in Twenty-Four Animal Species and Expression in Tilapia

Transforming growth factor β (TGF-β) signaling controls diverse cellular processes during embryogenesis as well as in mature tissues of multicellular animals. Here we carried out a comprehensive analysis of TGF-β pathway members in 24 representative animal species. The appearance of the TGF-β pathway was intrinsically linked to the emergence of metazoan. The total number of TGF-β ligands, receptors, and smads changed slightly in all invertebrates and jawless vertebrates analyzed. In contrast, expansion of the pathway members, especially ligands, was observed in jawed vertebrates most likely due to the second round of whole genome duplication (2R) and additional rounds in teleosts. Duplications of TGFB2, TGFBR2, ACVR1, SMAD4 and SMAD6, which were resulted from 2R, were first isolated. Type II receptors may be originated from the ACVR2-like ancestor. Interestingly, AMHR2 was not identified in Chimaeriformes and Cypriniformes even though they had the ligand AMH. Based on transcriptome data, TGF-β ligands exhibited a tissue-specific expression especially in the heart and gonads. However, most receptors and smads were expressed in multiple tissues indicating they were shared by different ligands. Spatial and temporal expression profiles of 8 genes in gonads of different developmental stages provided a fundamental clue for understanding their important roles in sex determination and reproduction. Taken together, our findings provided a global insight into the phylogeny and expression patterns of the TGF-β pathway genes, and hence contribute to the greater understanding of their biological roles in the organism especially in teleosts.

Genetic Approaches in Preeclampsia

Preeclampsia (PE) is a serious hypertensive disorder that affects up to 8% of all pregnancies annually. An established risk factor for PE is family history, clearly demonstrating an underlying genetic component to the disorder. To date, numerous genetic studies, using both the candidate gene and genome-wide approach, have been undertaken to tease out the genetic basis of PE and understand its origins. Such studies have identified some promising candidate genes such as STOX1 and ACVR2A. Nevertheless, researchers face ongoing challenges of replicating these genetic associations in different populations and performing the functional validation of identified genetic variants to determine their causality in the disorder. This chapter will review the genetic approaches used in the study of PE, discuss their limitations and possible confounders, and describe current strategies.

Dynamics of miRNA transcriptome during gonadal development of zebrafish

Studies in non-teleost vertebrates have found microRNAs (miRNAs) to be essential for proper gonadal development. However, comparatively little is known about their role during gonadal development in teleost fishes. So far in zebrafish, a model teleost, transcript profiling throughout gonadal development has not been established because of a tiny size of an organ in juvenile stages and its poor distinguishability from surrounding tissues. We performed small RNA sequencing on isolated gonads of See-Thru-Gonad line, from the undifferentiated state at 3 weeks post fertilization (wpf) to fully mature adults at 24 wpf. We identified 520 gonadal mature miRNAs; 111 of them had significant changes in abundance over time, while 50 miRNAs were either testis- or ovary-enriched significantly in at least one developmental stage. We characterized patterns of miRNA abundance over time including isomiR variants. We identified putative germline versus gonadal somatic miRNAs through differential small RNA sequencing of isolated gametes versus the whole gonads. This report is the most comprehensive analysis of the miRNA repertoire in zebrafish gonads during the sexual development to date and provides an important database from which functional studies can be performed.

SMAD3 Regulates Follicle-stimulating Hormone Synthesis by Pituitary Gonadotrope Cells in Vivo

Pituitary follicle-stimulating hormone (FSH) is an essential regulator of fertility in females and of quantitatively normal spermatogenesis in males. Pituitary-derived activins are thought to act as major stimulators of FSH synthesis by gonadotrope cells. In vitro, activins signal via SMAD3, SMAD4, and forkhead box L2 (FOXL2) to regulate transcription of the FSHβ subunit gene (Fshb). Consistent with this model, gonadotrope-specific Smad4 or Foxl2 knock-out mice have greatly reduced FSH and are subfertile. The role of SMAD3 in vivo is unresolved; however, residual FSH production in Smad4 conditional knock-out mice may derive from partial compensation by SMAD3 and its ability to bind DNA in the absence of SMAD4. To test this hypothesis and determine the role of SMAD3 in FSH biosynthesis, we generated mice lacking both the SMAD3 DNA binding domain and SMAD4 specifically in gonadotropes. Conditional knock-out females were hypogonadal, acyclic, and sterile and had thread-like uteri; their ovaries lacked antral follicles and corpora lutea. Knock-out males were fertile but had reduced testis weights and epididymal sperm counts. These phenotypes were consistent with those of Fshb knock-out mice. Indeed, pituitary Fshb mRNA levels were nearly undetectable in both male and female knock-outs. In contrast, gonadotropin-releasing hormone receptor mRNA levels were significantly elevated in knock-outs in both sexes. Interestingly, luteinizing hormone production was altered in a sex-specific fashion. Overall, our analyses demonstrate that SMAD3 is required for FSH synthesis in vivo.

Mouse Models for the Study of Synthesis, Secretion, and Action of Pituitary Gonadotropins

Gonadotropins play fundamental roles in reproduction. More than 30years ago, Cga transgenic mice were generated, and more than 20years ago, the phenotypes of Cga null mice were reported. Since then, numerous mouse strains have been generated and characterized to address several questions in reproductive biology involving gonadotropin synthesis, secretion, and action. More recently, extragonadal expression, and in some cases, functions of gonadotropins in nongonadal tissues have been identified. Several genomic and proteomic approaches including novel mouse genome editing tools are available now. It is anticipated that these and other emerging technologies will be useful to build an integrated network of gonadotropin signaling pathways in various tissues. Undoubtedly, research on gonadotropins will continue to provide new knowledge and allow us transcend from benchside to the bedside.

The crucial role of Activin A on the formation of primordial germ cell-like cells from skin-derived stem cells in vitro

Primordial germ cells (PGCs) are founder cells of the germ cell lineage, and can be differentiated from stem cells in an induced system in vitro. However, the induction conditions need to be optimized in order to improve the differentiation efficiency. Activin A (ActA) is a member of the TGF-β super family and plays an important role in oogenesis and folliculogenesis. In the present study, we found that ActA promoted PGC-like cells (PGCLCs) formation from mouse skin-derived stem cells (SDSCs) in both embryoid body-like structure (EBLS) differentiation and the co-culture stage in a dose dependent manner. ActA treatment (100 ng/ml) during EBLS differentiation stage and further co-cultured for 6 days without ActA significantly increased PGCLCs from 53.2% to 82.8%, and as well as EBLS differentiation without ActA followed by co-cultured with 100 ng/ml ActA for 4 to 12 days with the percentage of PGCLCs increasing markedly in vitro. Moreover, mice treated with ActA at 100 ng/kg body weight from embryonic day (E) 5.5-12.5 led to more PGCs formation. However, the stimulating effects of ActA were interrupted by Smad3 RNAi, and in an in vitro cultured Smad3(-/-) mouse skin cells scenario. SMAD3 is thus likely a key effecter molecule in the ActA signaling pathway. In addition, we found that the expression of some epiblast cell markers, Fgf5, Dnmt3a, Dnmt3b and Wnt3, was increased in EBLSs cultured for 4 days or PGCLCs co-cultured for 12 days with ActA treatment. Interestingly, at 16 days of differentiation, the percentage of PGCLCs was decreased in the presence of ActA, but the expression of meiosis-relative genes, such as Stra8, Dmc1, Sycp3 and Sycp1, was increased. In conclusion, our data here demonstrated that ActA can promote PGCLC formation from SDSCs in vitro, at early stages of differentiation, and affect meiotic initiation of PGCLCs in later stages.

Studying the Functions of TGF-β Signaling in the Ovary

In mammals, ovulation is a multistep physiological process that includes preovulatory follicle growth, oocyte meiotic maturation, cumulus-oocyte complex (COC) expansion, follicle rupture, and luteinization. TGF-β signaling pathway has multiple functions in mammalian ovary, as its complexity in ovarian function has been demonstrated by mouse models with knockouts of TGF-β receptors and SMADs. We describe the protocol that we use to study functions of TGF-β signaling pathway in follicle development and ovulation. Because total knockout of TGF-β pathway components often causes embryonic lethality, which prevents further investigation of these genes in ovarian functions, people have generated ovarian cell type-specific knockout mouse strains for TGF-β signaling pathway genes. These mouse models are also described.

Vascular Endothelial Growth Factor-A (VEGF-A) Mediates Activin A-Induced Human Trophoblast Endothelial-Like Tube Formation

Remodeling of maternal spiral arteries during pregnancy requires a subpopulation of extravillous cytotrophoblasts (EVTs) to differentiate into endovascular EVTs. Activin A, which is abundantly expressed at the maternal-fetal interface, has been shown to promote trophoblast invasion, but its role in endovascular differentiation remains unknown. Vascular endothelial growth factor-A (VEGF-A) is well recognized as a key regulator in trophoblast endovascular differentiation. Whether and how activin A might regulate VEGF-A production in human trophoblasts and its relationship to endovascular differentiation have yet to be determined. In the present study, we found that activin A increased VEGF-A production in primary and immortalized (HTR8/SVneo) human EVT cells. In addition, activin A enhanced HTR8/SVneo endothelial-like tube formation, and these effects were attenuated by pretreatment with small interfering RNA targeting VEGF-A or the VEGF receptor 1/2 inhibitor SU4312. Pretreatment with the activin/TGF-β type 1 receptor (ALK4/5/7) inhibitor SB431542 abolished the stimulatory effects of activin A on phosphorylated mothers against decapentaplegic (SMAD)-2/3 phosphorylation, VEGF-A production, and endothelial-like tube formation. Moreover, small interfering RNA-mediated down-regulation of SMAD2, SMAD3, or common SMAD4 abolished the effects of activin A on VEGF-A production and endothelial-like tube formation. In conclusion, activin A may promote human trophoblast cell endothelial-like tube formation by up-regulating VEGF-A production in an SMAD2/3-SMAD4-dependent manner. These findings provide insight into the cellular and molecular events regulated by activin A during human implantation.

Follistatin Gene Therapy Improves Ambulation in Becker Muscular Dystrophy

Follistatin is a ubiquitous secretory propeptide that functions as a potent inhibitor of the myostatin pathway, resulting in an increase in skeletal muscle mass. Its ability to interact with the pituitary activin-inhibin axis and suppress the secretion of follicle-stimulating hormone (FSH) called for caution in its clinical applicability. This limitation was circumvented by the use of one of the alternatively spliced follistatin variants, FS344, undergoing post-translational modification to FS315. This follistatin isoform is serum-based, and has a 10-fold lower affinity to activin compared to FS288. Preclinical studies of intramuscular delivery of the follistatin gene demonstrated safety and efficacy in enhancing muscle mass. We herein review the evidence supporting the utility of follistatin as a genetic enhancer to improve cellular performance. In addition, we shed light on the results of the first clinical gene transfer trial using the FS344 isoform of follistatin in subjects with Becker muscular dystrophy as well as the future directions for clinical gene therapy trials using follistatin.

Chronic Noise Exposure Acts Cumulatively to Exacerbate Alzheimer's Disease-Like Amyloid-β Pathology and Neuroinflammation in the Rat Hippocampus

A putative etiological association exists between noise exposure and Alzheimer’s disease (AD). Amyloid-β (Aβ) pathology is thought to be one of the primary initiating factors in AD. It has been further suggested that subsequent dysregulation of Aβ may play a mechanistic role in the AD-like pathophysiology associated with noise exposure. Here, we used ELISA, immunoblotting, cytokine arrays, and RT-PCR, to examine both hippocampal Aβ pathology and neuroinflammation in rats at different time points after noise exposure. We found that chronic noise exposure significantly accelerated the progressive overproduction of Aβ, which persisted for 7 to 14 days after the cessation of exposure. This effect was accompanied by up-regulated expression of amyloid precursor protein (APP) and its cleavage enzymes, β- and γ-secretases. Cytokine analysis revealed that chronic noise exposure increased levels of tumor necrosis factor-α and the receptor for advanced glycation end products, while decreasing the expression of activin A and platelet-derived growth factor- AA. Furthermore, we found persistent elevations of glial fibrillary acidic protein and ionized calcium-binding adapter molecule 1 expression that closely corresponded to the noise-induced increases in Aβ and neuroinflammation. These studies suggest that lifelong environmental noise exposure may have cumulative effects on the onset and development of AD.

Inhibition of transforming growth factor β (TGF-β) signaling can substitute for Oct4 protein in reprogramming and maintain pluripotency

Mouse pluripotent stem cells (PSCs), such as ES cells and induced PSCs (iPSCs), are an excellent system to investigate the molecular and cellular mechanisms involved in early embryonic development. The signaling pathways orchestrated by leukemia inhibitor factor/STAT3, Wnt/β-catenin, and FGF/MEK/ERK play key roles in the generation of pluripotency. However, the function of TGF-β signaling in this process remains elusive. Here we show that inhibiting TGF-β signaling with its inhibitor SB431542 can substitute for Oct4 during reprogramming. Moreover, inhibiting TGF-β signaling can sustain the pluripotency of iPSCs and ES cells through modulating FGF/MEK/ERK signaling. Therefore, this study reveals a novel function of TGF-β signaling inhibition in the generation and maintenance of PSCs.

Activin B Promotes BMSC-Mediated Cutaneous Wound Healing by Regulating Cell Migration via the JNK—ERK Signaling Pathway

Bone marrow-derived mesenchymal stem cells (BMSCs) are able to differentiate into various types of skin cells and participate in skin regeneration and repair. Activin signaling can regulate wound healing and reepithelialization. The present study assessed the impact of activin B on BMSC-mediated cutaneous wound healing in rats and explored the possible mechanism involved. We found that CFSE-labeled BMSCs participated in wound healing in vivo, and compared to administration with PBS, activin B, or BMSCs, activin B plus BMSCs significantly promoted wound healing and hair follicle regeneration. Activin B induced actin stress fiber formation and cell migration in BMSCs in vitro. Activation of JNK and ERK, but not p38, was required for activin B-induced actin stress fiber formation and BMSC migration. These results show that activin B may promote BMSC-mediated wound healing by inducing actin stress fiber formation and BMSC migration via the ERK and JNK signal pathways. Combined administration of BMSCs and cytokines may be a promising therapeutic strategy for the management of skin wounds.

Acute modulation of synaptic plasticity of pyramidal neurons by activin in adult hippocampus

Activin A is known as a neuroprotective factor produced upon acute excitotoxic injury of the hippocampus (in pathological states). We attempt to reveal the role of activin as a neuromodulator in the adult male hippocampus under physiological conditions (in healthy states), which remains largely unknown. We showed endogenous/basal expression of activin in the hippocampal neurons. Localization of activin receptors in dendritic spines (=postsynapses) was demonstrated by immunoelectron microscopy. The incubation of hippocampal acute slices with activin A (10 ng/mL, 0.4 nM) for 2 h altered the density and morphology of spines in CA1 pyramidal neurons. The total spine density increased by 1.2-fold upon activin treatments. Activin selectively increased the density of large-head spines, without affecting middle-head and small-head spines. Blocking Erk/MAPK, PKA, or PKC prevented the activin-induced spinogenesis by reducing the density of large-head spines, independent of Smad-induced gene transcription which usually takes more than several hours. Incubation of acute slices with activin for 2 h induced the moderate early long-term potentiation (moderate LTP) upon weak theta burst stimuli. This moderate LTP induction was blocked by follistatin, MAPK inhibitor (PD98059) and inhibitor of NR2B subunit of NMDA receptors (Ro25-6981). It should be noted that the weak theta burst stimuli alone cannot induce moderate LTP. These results suggest that MAPK-induced phosphorylation of NMDA receptors (including NR2B) may play an important role for activin-induced moderate LTP. Taken together, the current results reveal interesting physiological roles of endogenous activin as a rapid synaptic modulator in the adult hippocampus.

Follicle-stimulating hormone synthesis and fertility are intact in mice lacking SMAD3 DNA binding activity and SMAD2 in gonadotrope cells

The activin/inhibin system regulates follicle-stimulating hormone (FSH) synthesis and release by pituitary gonadotrope cells in mammals. In vitro cell line data suggest that activins stimulate FSH β-subunit (Fshb) transcription via complexes containing the receptor-regulated SMAD proteins SMAD2 and SMAD3. Here, we used a Cre-loxP approach to determine the necessity for SMAD2 and/or SMAD3 in FSH synthesis in vivo. Surprisingly, mice with conditional mutations in both Smad2 and Smad3 specifically in gonadotrope cells are fertile and produce FSH at quantitatively normal levels. Notably, however, we discovered that the recombined Smad3 allele produces a transcript that encodes the entirety of the SMAD3 C-terminal Mad homology 2 (MH2) domain. This protein behaves similarly to full-length SMAD3 in Fshb transcriptional assays. As the truncated protein lacks the N-terminal Mad homology 1 (MH1) domain, these results show that SMAD3 DNA-binding activity as well as SMAD2 are dispensable for normal FSH synthesis in vivo. Furthermore, the observation that deletion of proximal exons does not remove all SMAD3 function may facilitate interpretation of divergent phenotypes previously described in different Smad3 knockout mouse lines.

Increased decidual mRNA expression levels of candidate maternal pre-eclampsia susceptibility genes are associated with clinical severity

INTRODUCTION

Pre-eclampsia (PE) has a familial association, with daughters of women who had PE during pregnancy having more than twice the risk of developing PE themselves. Through genome-wide linkage and genetic association studies in PE-affected families and large population samples, we previously identified the following as positional candidate maternal susceptibility genes for PE; ACVR1, INHA, INHBB, ERAP1, ERAP2, LNPEP, COL4A1 and COL4A2. The aims of this study were to determine mRNA expression levels of previously identified candidate maternal pre-eclampsia susceptibility genes from normotensive and severe PE (SPE) pregnancies and correlate mRNA expression levels with the clinical severity of SPE.

METHODS

Third trimester decidual tissues were collected from both normotensive (n = 21) and SPE pregnancies (n = 24) and mRNA expression levels were determined by real-time PCR. Gene expression was then correlated with several parameters of clinical severity in SPE. Statistical significance was determined by Mann-Whitney U test and Spearman's Correlation.

RESULTS

The data demonstrate significantly increased decidual mRNA expression levels of ACVR1, INHBB, ERAP1, ERAP2, LNPEP, COL4A1 and COL4A2 in SPE (p < 0.05). Increased mRNA expression levels of several genes - INHA, INHBB, COL4A1 and COL4A2 were correlated with earlier onset of PE and earlier delivery of the fetus (p < 0.05).

CONCLUSION

These results suggest altered expression of maternal susceptibility genes may play roles in PE development and the course of disease severity.

Temporal and regional patterns of Smad activation in the rat hippocampus following global ischemia

In this study, we examined the temporal and regional patterns of Smad activation in the rat hippocampus following global ischemia. We also examined the association between Smad activation and ischemia-induced pathology in the hippocampus. We found that 1) Smad1, -2, -3, and -5 proteins were detected in the rat hippocampus by means of western blot and immunohistochemistry; 2) after 5 min of ischemia, Smad2 and Smad3 proteins accumulated in the nuclei of pyramidal cells in the CA1 region, which is vulnerable to ischemia; 3) after 3 min of ischemia, which was non-lethal, there was no such nuclear accumulation of Smad2 and Smad3 in the CA1 region; 4) following injection of activin A, nuclear accumulation of Smad2 and Smad3 was induced not only in pyramidal cells of the CA1 region, but also in pyramidal cells of the CA3 region as well as in granule cells of the DG region; 5) activin A-induced nuclear accumulation of Smad2 and Smad3 neither caused degeneration of hippocampal neurons nor prevented degeneration induced by ischemia. These results suggest that in the hippocampus, ischemia-induced activation of Smad2 and Smad3 is associated with the response to stress but is not related to neuronal survival or death.

15-deoxy-Δ12,14 -prostaglandin J 2 Down-Regulates Activin-Induced Activin Receptor, Smad, and Cytokines Expression via Suppression of NF- κ B and MAPK Signaling in HepG2 Cells

15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) and activin are implicated in the control of apoptosis, cell proliferation, and inflammation in cells. We examined both the mechanism by which 15d-PGJ₂ regulates the transcription of activin-induced activin receptors (ActR) and Smads in HepG2 cells and the involvement of the nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) pathways in this regulation. Activin A (25 ng/mL) inhibited HepG2 cell proliferation, whereas 15d-PGJ₂ (2 μM and 5 μM) had no effect. Activin A and 15d-PGJ₂ showed different regulatory effects on ActR and Smad expression, NF-κB p65 activity and MEK/ERK phosphorylation, whereas they both decreased IL-6 production and increased IL-8 production. When co-stimulated with 15d-PGJ₂ and activin, 15d-PGJ₂ inhibited the activin-induced increases in ActR and Smad expression, and decreased activin-induced IL-6 production. However, it increased activin-induced IL-8 production. In addition, 15d-PGJ₂ inhibited activin-induced NF-κB p65 activity and activin-induced MEK/ERK phosphorylation. These results suggest that 15d-PGJ₂ suppresses activin-induced ActR and Smad expression, down-regulates IL-6 production, and up-regulates IL-8 production via suppression of NF-κB and MAPK signaling pathway in HepG2 cells. Regulation of ActR and Smad transcript expression and cytokine production involves NF-κB and the MAPK pathway via interaction with 15d-PGJ₂/activin/Smad signaling.