Follistatin-like 1 (Fstl1) is a bone morphogenetic protein (BMP) 4 signaling antagonist in controlling mouse lung development

Effects of FSTL1 on cell proliferation in breast cancer cell line MDA‑MB‑231 and its brain metastatic variant MDA‑MB‑231‑BR

In the past decades, altered Follistatin-like 1 (FSTL1) expression has been documented in a variety of cancers, while its functional roles are poorly understood. Particularly in breast cancer, the expression of FSTL1 and its signaling pathway remain to be determined. In the present study, an elevated FSTL1 expression and a supressed cell proliferation were detected in a specific brain metastatic cell line MDA-MB-231-BR (231-BR), compared with its parental cell line MDA-MB-231. However, this protein was hardly detected in the other three breast cancer cell lines. Next, lentiviral vectors encoding FSTL1 or FSTL1 specific shRNAs were used to overexpress or knock down FSTL1 in MDA-MB-231 or 231-BR, respectively (MDA-MB-231^FSTL1 or 231-BR^{sh FSTL1}). Results showed that overexpression of FSTL1 inhibited MDA-MB-231 cell proliferation, while knockdown of FSTL1 in 231-BR cells promotes cell proliferation, compared with their corresponding control groups. These results were further confirmed in nude mouse xenografts. The tumor volume in 231-BR cell-bearing mice was significantly smaller than that of MDA-MB-231 group, and reduction of tumor volume was detected in MDA-MB-231^FSTL1 cell-bearing mice compared with the control group. Previous studies revealed that TGF-β-Smad2/3 signaling pathway was activated in 231-BR and MDA-MB-231^FSTL1 cells, which may contribute to the inhibited cell proliferation. In addition, Smad3 knockdown could restore the inhibition of cell proliferation induced by FSTL1 overexpression in MDA-MB-231^FSTL1 cells, indicating that the anti-proliferative effect of FSTL1 overexpression may be associated with Smad3 involved TGF-β signaling pathway regulation. This study identified FSTL1 as an inhibitor of cell proliferation in MDA-MB-231 and 231-BR cell lines, which may provide new insights into the development and management of breast cancer.

FSTL1 Promotes Metastasis and Chemoresistance in Esophageal Squamous Cell Carcinoma through NFκB-BMP Signaling Cross-talk

Esophageal squamous cell carcinoma (ESCC) has a generally poor prognosis, and molecular markers to improve early detection and predict outcomes are greatly needed. Here, we report that the BMP-binding follistatin-like protein FSTL1 is overexpressed in ESCCs, where it correlates with poor overall survival. Genetic amplification of FSTL1 or chromosome 3q, where it is located, occurred frequently in ESCC, where FSTL1 copy number correlated positively with higher FSTL1 protein expression. Elevating FSTL1 levels by various means was sufficient to drive ESCC cell proliferation, clonogenicity, migration, invasion, self-renewal, and cisplatin resistance in vitro and tumorigenicity and distant metastasis in vivo Conversely, FSTL1 attenuation by shRNA or neutralizing antibody elicited the opposite effects in ESCC cells. mRNA profiling analyses suggested that FSTL1 drives ESCC oncogenesis and metastasis through various pathways, with deregulation of NFκB and BMP signaling figuring prominently. Cross-talk between the NFκB and BMP pathways was evidenced by functional rescue experiments using inhibitors of NFκB and TLR4. Our results establish the significance of FSTL1 in driving oncogenesis and metastasis in ESCC by coordinating NFκB and BMP pathway control, with implications for its potential use as a diagnostic or prognostic biomarker and as a candidate therapeutic target in this disease setting. Cancer Res; 77(21); 5886-99. ©2017 AACR.

Effects of FSTL1 on the proliferation and motility of breast cancer cells and vascular endothelial cells

Background

Treatments that prevent the motility of breast cancer cells and inhibit formation of new capillary vessels are urgently needed. FSTL1 is a secreted protein that has been implicated in maintaining the normal physiological function of the cardiovascular system, in addition to a variety of other biological functions. We investigated the role of FSTL1 in the proliferation and migration of breast cancer and vascular endothelial cells.

Methods

Human umbilical vein endothelial cells and human breast cancer BT‐549 cells were used to test the effects of FSTL1 and the N‐terminal domain of FSTL1. Immunofluorescence microscopy and 3‐(4, 5‐dimethylthiazolyl‐2)‐2,5‐diphenyltetrazolium bromide, transwell invasion, and wound healing assays were conducted.

Results

Different doses of the N‐terminal fragment of FSTL1 (FSTL‐N) have variable effects on the migration of these cells. However, FSTL1 does not significantly affect tube formation in vitro from vascular endothelial cells. FSTL1‐FL and FSTL1‐N have modest effects on the invasion of breast cancer and vascular endothelial cells. Interestingly, FSTL1‐FL, but not FSTL‐N, modulates vascular endothelial cell polarization.

Conclusion

FSTL1 modestly affects the proliferation of breast cancer cells and vascular endothelial cells. Our findings improve our understanding of the functions of FSTL1 in breast cancer development and angiogenesis.

BBS4 regulates the expression and secretion of FSTL1, a protein that participates in ciliogenesis and the differentiation of 3T3-L1

Bardet-Biedl syndrome is a model ciliopathy. Although the characterization of BBS proteins has evidenced their involvement in cilia, extraciliary functions for some of these proteins are also being recognized. Importantly, understanding both cilia and cilia-independent functions of the BBS proteins is key to fully dissect the cellular basis of the syndrome. Here we characterize a functional interaction between BBS4 and the secreted protein FSTL1, a protein linked to adipogenesis and inflammation among other functions. We show that BBS4 and cilia regulate FSTL1 mRNA levels, but BBS4 also modulates FSTL1 secretion. Moreover, we show that FSTL1 is a novel regulator of ciliogenesis thus underscoring a regulatory loop between FSTL1 and cilia. Finally, our data indicate that BBS4, cilia and FSTL1 are coordinated during the differentiation of 3T3-L1 cells and that FSTL1 plays a role in this process, at least in part, by modulating ciliogenesis. Therefore, our findings are relevant to fully understand the development of BBS-associated phenotypes such as obesity.

Decrease of FSTL1-BMP4-Smad signaling predicts poor prognosis in lung adenocarcinoma but not in squamous cell carcinoma

Follistatin-related protein 1 (FSTL1) plays a critical role in lung development through regulating BMP4-p-Smad1/5/8-Smad4 pathway. Regarding that many developmental pathways in embryogenesis are dysregulated in cancer, we aim to unravel the role of FSTL1-BMP4-Smad pathway in lung cancer. Our results showed low FSTL1 immunoexpression was significantly correlated with poor prognosis while patients with low BMP4 or low Smad4 immunoexpression showed a trend toward poor prognosis. When stratified by different histological types, low FSTL1, BMP4, and Smad4 expression retained their trends in predicting poor prognosis in lung adenocarcinoma (LUAD) but not in lung squamous cell carcinoma (SCC). Low FSTL1, BMP4, and Smad4 expression were more frequently observed in LUAD patients with smoking history. To determine smoking effect on FSTL1, normal cell BEAS2B and lung cancer cell lines was treated with nicotine and the results showed nicotine increased the proliferation of these cells. Interestingly, FSTL1 attenuated nicotine-induced BEAS2B and lung cancer cell line proliferation. Altogether, low FSTL1, BMP4, and Smad4 expression significantly correlated with poor prognosis in LUAD but not in SCC. Frequent decrease of FSTL1 expression in smokers LUAD further indicates its importance and therapeutic potential for lung cancer patients with specific subtypes. FSTL1 may prevent nicotine-induced lung cancer cell proliferation.

HOXA5 plays tissue-specific roles in the developing respiratory system

Hoxa5 is essential for development of several organs and tissues. In the respiratory system, loss of Hoxa5 function causes neonatal death due to respiratory distress. Expression of HOXA5 protein in mesenchyme of the respiratory tract and in phrenic motor neurons of the central nervous system led us to address the individual contribution of these Hoxa5 expression domains using a conditional gene targeting approach. Hoxa5 does not play a cell-autonomous role in lung epithelium, consistent with lack of HOXA5 expression in this cell layer. In contrast, ablation of Hoxa5 in mesenchyme perturbed trachea development, lung epithelial cell differentiation and lung growth. Further, deletion of Hoxa5 in motor neurons resulted in abnormal diaphragm innervation and musculature, and lung hypoplasia. It also reproduced the neonatal lethality observed in null mutants, indicating that the defective diaphragm is the main cause of impaired survival at birth. Thus, Hoxa5 possesses tissue-specific functions that differentially contribute to the morphogenesis of the respiratory tract.

The Correlation between FSTL1 Expression and Airway Remodeling in Asthmatics

Background

Asthma is characterized by airway remodeling. Follistatin-like protein 1 (FSTL1) is an extracellular glycoprotein. Recent studies suggest that FSTL1 may participate in the pathogenesis of asthma.

Objectives

To analyze the association between FSTL1 and some parameters and inspect the role of FSTL1 in asthma.

Methods

We examined FSTL1 levels in 32 asthmatics and 25 controls. All subjects enrolled had routine blood tests, spirometry, and impulse oscillometry performed. Additionally, 15 of the 32 asthmatics underwent fibre optic bronchoscopy. Spearman rank analysis was performed to detect the correlation between FSTL1 and other parameters.

Results

Plasma FSTL1 levels were higher in asthmatics (130.762 ± 46.029 ng/mL) than in controls (95.408 ± 33.938 ng/mL) (p = 0.009). Plasma FSTL1 levels were associated with fibrosis levels around the airways (rs = 0.529, p = 0.043) and α-smooth muscle actin (α-SMA) (rs = 0.554, p = 0.032). FSTL1 levels in bronchoalveolar lavage fluid were associated with collagen I (rs = 0.536, p = 0.040), α-SMA (rs = 0.561, p = 0.029), fibrosis levels (rs = 0.779, p = 0.001), and the thickness of the airway reticular basement membrane (RBM) (rs = 0.660, p = 0.007).

Conclusions

FSTL1 levels in asthmatics were linked with increased smooth muscle mass and thickened RBM. FSTL1 may contribute to airway remodeling in asthmatics.

Deletion of Fstl1 (Follistatin-Like 1) From the Endocardial/Endothelial Lineage Causes Mitral Valve Disease

OBJECTIVE

Fstl1 (Follistatin-like 1) is a secreted protein that is expressed in the atrioventricular valves throughout embryonic development, postnatal maturation, and adulthood. In this study, we investigated the loss of Fstl1 in the endocardium/endothelium and their derived cells.

APPROACH AND RESULTS

We conditionally ablated Fstl1 from the endocardial lineage using a transgenic Tie2-Cre mouse model. These mice showed a sustained Bmp and Tgfβ signaling after birth. This resulted in ongoing proliferation and endocardial-to-mesenchymal transition and ultimately in deformed nonfunctional mitral valves and a hypertrophic dilated heart. Echocardiographic and electrocardiographic analyses revealed that loss of Fstl1 leads to mitral regurgitation and left ventricular diastolic dysfunction. Cardiac function gradually deteriorated resulting in heart failure with preserved ejection fraction and death of the mice between 2 and 4 weeks after birth.

CONCLUSIONS

We report on a mouse model in which deletion of Fstl1 from the endocardial/endothelial lineage results in deformed mitral valves, which cause regurgitation, heart failure, and early cardiac death. The findings provide a potential molecular target for the clinical research into myxomatous mitral valve disease.

Follistatin like-1 (Fstl1) is required for the normal formation of lung airway and vascular smooth muscle at birth

Fstl1, a secreted protein of the BMP antagonist class, has been implicated in the regulation of lung development and alveolar maturation. Here we generated a Fstl1-lacZ reporter mouse line as well as a Fstl1 knockout allele. We localized Fstl1 transcript in lung smooth muscle cells and identified Fstl1 as essential regulator of lung smooth muscle formation. Deletion of Fstl1 in mice led to postnatal death as a result of respiratory failure due to multiple defects in lung development. Analysis of the mutant phenotype showed impaired airway smooth muscle (SM) manifested as smaller SM line in trachea and discontinued SM surrounding bronchi, which were associated with decreased transcriptional factors myocardin/serum response factor (SRF) and impaired differentiation of SM cells. Fstl1 knockout mice also displayed abnormal vasculature SM manifested as hyperplasia SM in pulmonary artery. This study indicates a pivotal role for Fstl1 in early stage of lung airway smooth muscle development.

TGF-β1 induces Fstl1 via the Smad3-c-Jun pathway in lung fibroblasts

Transforming growth factor (TGF)-β1 has long been regarded as a central mediator of tissue fibrosis. Follistatin-like 1 (Fstl1) is a crucial profibrotic glycoprotein that is upregulated in fibrotic lung tissues, and it promotes fibrogenesis via facilitating TGF-β signaling. Here we examined the signaling pathway by which TGF-β1 upregulates Fstl1 expression in mouse pulmonary fibroblasts. TGF-β1 regulated Fstl1 expression at both the transcriptional and translational levels. Although TGF-β1 rapidly activated the Smad, MAPK, and Akt pathways in lung fibroblasts, only Smad2/3 inhibition eliminated TGF-β1-induced Fstl1 expression. Analysis of the luciferase reporter activity identified a functional c-Jun transcription site in the Fstl1 promoter. Our results suggested a critical role for the Smad3-c-Jun pathway in the regulation of Fstl1 expression by TGF-β1 during fibrogenesis.

Autophagy plays a role in FSTL1-induced epithelial mesenchymal transition and airway remodeling in asthma

Asthma is a chronic disease related to airway hyperresponsiveness and airway remodeling. Airway remodeling is the important reason of refractory asthma and is associated with differentiation of airway epithelia into myofibroblasts via epithelial-mesenchymal transition (EMT) to increase the process of subepithelial fibrosis. There is growing evidence that autophagy modulates remodeling. However, the underlying molecular mechanisms of these effects are still unclear. In this study, we hypothesized that Follistatin-like 1 (FSTL1) promotes EMT and airway remodeling by intensifying autophagy. With the use of transmission electron microscopy (TEM), double-membrane autophagosomes were detected in the airways of patients and mice. More autophagosomes were in patients with asthma and OVA-challenged mice compared with healthy controls. The expression of FSTL1 and beclin-1 was upregulated in the airways of patients with asthma and OVA-challenged mice, accompanied by airway EMT and remodeling. In OVA-challenged Fstl1^+/- mice, the degree of airway remodeling and autophagy was decreased compared with control mice. The effects of FSTL1 on autophagy and EMT were also tested in 16HBE cells in vitro. Additionally, inhibition of autophagy by using LY-294002 and siRNA-ATG5 reduced the FSTL1-induced EMT in 16HBE cells, as measured by E-cadherin, N-cadherin, and vimentin expression. In line herewith, administration of LY-294002 reduced the expression of autophagy, EMT, and airway remodeling markers in FSTL1-challenged WT mice. Taken together, our study suggests that FSTL1 may induce EMT and airway remodeling by activating autophagy. These findings may provide novel avenues for therapeutic research targeting the autophagy and FSTL1 pathway, which may be beneficial to patients with refractory asthma.

Follistatin-like 1 expression is decreased in the alveolar epithelium of hypoplastic rat lungs with nitrofen-induced congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Pulmonary hypoplasia (PH), characterized by incomplete alveolar development, remains a major therapeutic challenge associated with congenital diaphragmatic hernia (CDH). Follistatin-like 1 (Fstl1) is a crucial regulator of alveolar formation and maturation, which is strongly expressed in distal airway epithelium. Fstl1-deficient mice exhibit reduced airspaces, impaired alveolar epithelial cell differentiation, and insufficient production of surfactant proteins similar to PH in human CDH. We hypothesized that pulmonary Fstl1 expression is decreased during alveolarization in the nitrofen-induced CDH model.

METHODS

Timed-pregnant rats received nitrofen or vehicle on gestational day 9 (D9). Fetal lungs were harvested on D18 and D21 and divided into control-/nitrofen-exposed specimens. Alveolarization was assessed using morphometric analysis techniques. Pulmonary gene expression of Fstl1 was determined by qRT-PCR. Immunofluorescence-double-staining for Fstl1 and alveolar epithelial marker surfactant protein C (SP-C) was performed to evaluate protein expression/localization.

RESULTS

Radial alveolar count was significantly reduced in hypoplastic lungs of nitrofen-exposed fetuses with significant down regulation of Fstl1 mRNA expression on D18 and D21 compared to controls. Confocal-laser-scanning-microscopy revealed strikingly diminished Fstl1 immunofluorescence and SP-C expression in distal alveolar epithelium of nitrofen-exposed fetuses with CDH-associated PH on D18 and D21 compared to controls.

CONCLUSIONS

Decreased expression of Fstl1 in alveolar epithelium may disrupt alveolarization and pulmonary surfactant production, thus contributing to the development of PH in the nitrofen-induced CDH model.

LEVEL OF EVIDENCE

2b (Centre for Evidence-Based Medicine, Oxford).

Follistatin-like protein 1 modulates IL-17 signaling via IL-17RC regulation in stromal cells

Follistatin-like protein 1 (FSTL-1) possesses several newly identified roles in mammalian biology, including IL-17 driven inflammation, though the mechanism underlying FSTL-1 influence on IL-17 mediated cytokine production is unknown. Using parallel in vitro bone marrow stromal cell models of FSTL-1 suppression we employed unbiased microarray analysis to identify FSTL-1 regulated genes and pathways that could influence IL-17 dependent production of IL-6 and G-CSF. We discovered that FSTL-1 modulates Il17rc gene expression. Specifically, FSTL-1 was necessary for Il17rc gene transcription, IL-17RC surface protein expression and IL-17-dependent cytokine production. This work identifies a mechanism by which FSTL-1 influences IL-17 driven inflammatory signalingin vitro and reveals a novel function for FSTL-1, as a modulator of gene expression. Thus, enhanced understanding of the interplay between FSTL-1 and IL-17 mediated inflammation may provide insight into potential therapeutic targets of IL-17 mediated diseases and warrants ongoing study of in vivo models and clinical scenarios of FSTL-1-influenced diseases.

Up-Regulation of Follistatin-Like 1 By the Androgen Receptor and Melanoma Antigen-A11 in Prostate Cancer

BACKGROUND

High affinity androgen binding to the androgen receptor (AR) activates genes required for male sex differentiation and promotes the development and progression of prostate cancer. Human AR transcriptional activity involves interactions with coregulatory proteins that include primate-specific melanoma antigen-A11 (MAGE-A11), a coactivator that increases AR transcriptional activity during prostate cancer progression to castration-resistant/recurrent prostate cancer (CRPC).

METHODS

Microarray analysis and quantitative RT-PCR were performed to identify androgen-regulated MAGE-A11-dependent genes in LAPC-4 prostate cancer cells after lentivirus shRNA knockdown of MAGE-A11. Chromatin immunoprecipitation was used to assess androgen-dependent AR recruitment, and immunocytochemistry to localize an androgen-dependent protein in prostate cancer cells and tissue and in the CWR22 human prostate cancer xenograft.

RESULTS

Microarray analysis of androgen-treated LAPC-4 prostate cancer cells indicated follistatin-like 1 (FSTL1) is up-regulated by MAGE-A11. Androgen-dependent up-regulation of FSTL1 was inhibited in LAPC-4 cells by lentivirus shRNA knockdown of AR or MAGE-A11. Chromatin immunoprecipitation demonstrated AR recruitment to intron 10 of the FSTL1 gene that contains a classical consensus androgen response element. Increased levels of FSTL1 protein in LAPC-4 cells correlated with higher levels of MAGE-A11 relative to other prostate cancer cells. FSTL1 mRNA levels increased in CRPC and castration-recurrent CWR22 xenografts in association with predominantly nuclear FSTL1. Increased nuclear localization of FSTL1 in prostate cancer was suggested by predominantly cytoplasmic FSTL1 in benign prostate epithelial cells and predominantly nuclear FSTL1 in epithelial cells in CRPC tissue and the castration-recurrent CWR22 xenograft. AR expression studies showed nuclear colocalization of AR and endogenous FSTL1 in response to androgen.

CONCLUSION

AR and MAGE-A11 cooperate in the up-regulation of FSTL1 to promote growth and progression of CRPC. Prostate 77:505-516, 2017. © 2016 Wiley Periodicals, Inc.

Follistatin-like 1 protects against hypoxia-induced pulmonary hypertension in mice

Pulmonary hypertension (PH) remains a life-limiting disease characterized by pulmonary vascular remodelling due to aberrant proliferation and migration of pulmonary artery smooth muscle cells (PASMCs), thus leading to raised pulmonary arterial pressure and right ventricular hypertrophy. Secreted glycoprotein follistatin-like 1 (FSTL1) has been reported to ameliorate tissue remodelling in cardiovascular injuries. However, the role of FSTL1 in deranged pulmonary arteries remains elusive. We found that there were higher serum levels of FSTL1 in patients with PH related to chronic obstructive pulmonary diseases (COPD) and in mice model of hypoxia-induced PH (HPH). Haploinsufficiency of Fstl1 in mice contributed to an exacerbated HPH, as demonstrated by increased right ventricular systolic pressure, pulmonary arterial muscularization and right ventricular hypertrophy index. Conversely, FSTL1 administration attenuated HPH. In cultured human PASMCs, hypoxia-promoted cellular viability, DNA synthesis and migration were suppressed by exogenous FSTL1 but enhanced by small interfering RNA targeting FSTL1. Additionally, FSTL1 inhibited the proliferation and migration of PASMCs via extracellular regulated kinase (ERK) signal pathway. All these findings indicate that FSTL1 imposed a protective modulation on pulmonary vascular remodelling, thereby suggesting its role in the regulation of HPH.

Follistatin like-1 aggravates silica-induced mouse lung injury

Occupational inhalation of dust, such as crystalline silica, for prolonged periods in the workplace leads to fibrotic lung diseases worldwide. The mechanisms underlying the diseases are unknown, so that no effective treatment exists for these conditions. We found elevated levels of follistatin like 1 (FSTL1) in serum from patients with silicosis and in lungs from silica-induced mouse model. The induced Fstl1 regulated inflammation response via activation of nod-like receptor family, pyrin domain containing 3v (NLRP3) inflammasome-mediated IL-1β production from macrophages. Meanwhile, Fstl1 promoted fibrosis via positive regulation of TGF-β1 signaling. Haploinsufficiency of Fstl1 or blockage of FSTL1 with a neutralizing antibody was protective from silica-induced lung injury in mice in vivo. Our data suggest that Fstl1 plays an important role in lung fibrosis, and may serve as a novel therapeutic target for treatment of silicosis.

Endothelial follistatin-like-1 regulates the postnatal development of the pulmonary vasculature by modulating BMP/Smad signaling

Bone morphogenetic protein (BMP) signaling regulates vascular smooth muscle maturation, endothelial cell proliferation, and tube formation. The endogenous BMP antagonist Follistatin-like 1 (Fstl1) is highly expressed in pulmonary vascular endothelium of the developing mouse lung, suggesting a role in pulmonary vascular formation and vascular homeostasis. The aim of this study was to investigate the role of Fstl1 in the pulmonary vascular endothelium. To this aim, Fstl1 was conditionally deleted from endothelial and endothelial-derived cells using Tie2-cre driven Fstl1-KO mice (Fstl1-eKO mice). Endothelial-specific Fstl1 deletion was postnatally lethal, as ∼70% of Fstl1-eKO mice died at three weeks after birth. Deletion of Fstl1 from endothelium resulted in a reduction of right ventricular output at three weeks after birth compared with controls. This was associated with pulmonary vascular remodeling, as the percentage of actin-positive small pulmonary vessels was increased at three weeks in Fstl1-eKO mice compared with controls. Endothelial deletion of Fstl1 resulted in activation of Smad1/5/8 signaling and increased BMP/Smad-regulated gene expression of Jagged1, Endoglin, and Gata2 at one week after birth compared with controls. In addition, potent vasoconstrictor Endothelin-1, the expression of which is driven by Gata2, was increased in expression, both on the mRNA and protein levels, at one week after birth compared with controls. At three weeks, Jagged1 was reduced in the Fstl1-eKO mice whereas Endoglin and Endothelin-1 were unchanged. In conclusion, loss of endothelial Fstl1 in the lung is associated with elevated BMP-regulated genes, impaired small pulmonary vascular remodeling, and decreased right ventricular output.

A novel embryo culture media supplement that improves pregnancy rates in mice

The preimplantation embryoinvivois exposed to numerous growth factors in the female reproductive tract, which are not recapitulated in embryo culture mediain vitro. The IGF2 and plasminogen activator systems facilitate blastocyst development. We hypothesized that the addition of IGF2 in combination with urokinase plasminogen activator (uPA) and plasminogen could improve rates of blastocyst hatching and implantation in mice. B6BcF1 and CBAB6F2 mouse embryos were divided into one of four supplemented culture media treatment groups: (1) control (media only); (2) 12.5 nM IGF2; (3) 10 µg/mL uPA and 5 µg/mL plasminogen; or (4) a combination of IGF2, uPA and plasminogen treatments. Embryo development to blastocyst stage and hatching were assessed before transfer to pseudopregnant recipient females and implantation, pregnancy rates and postnatal growth were assessed. After 90.5 h of culture, IGF2 + U + P treatment increased the percentage of B6BcF1 embryos that were hatching/hatched and percentage developing to blastocyst stage compared with controls (P < 0.02). Following B6BcF1 embryo transfer, IGF2 + U + P treatment increased implantation sites at day 8 of pregnancy compared with controls (P < 0.05). Replication in the CBAB6F2 mouse strain showed significant improvements in pregnancy rates at days 8 and 18 but not in blastocyst development. No adverse effects were seen on gestational age, litter size or birthweight, or the reproductive capacity of offspring of IGF2 + U + P treated embryos. For embryos susceptible to detrimental effects ofin vitroculture, IGF2, uPA and plasminogen supplementation of culture media can improve pregnancy success, but the effect of treatment is dependent on the mouse strain.

Mitotic cell death caused by follistatin-like 1 inhibition is associated with up-regulated Bim by inactivated Erk1/2 in human lung cancer cells

Follistatin-like 1 (FSTL1) was identified as a novel pro-inflammatory protein showing high-level expression in rheumatoid arthritis. The protective effect of FSTL1 via the inhibition of apoptosis was reported in myocardial injury. However, the functional mechanism of FSTL1 in cancer is poorly characterized, and its proliferative effects are ambiguous. Here, we examined the effects of FSTL1 on cellular proliferation and cell cycle checkpoints in lung cancer cells. FSTL1 inhibition induced the cellular portion of G2/M phase in human lung cancer cells via the accumulation of regulators of the transition through the G2/M phase, including the cyclin-dependent kinase 1 (Cdk1)-cyclin B1 complex. An increase in histone H3 phosphorylation (at Ser10), another hallmark of mitosis, indicated that the knockdown of FSTL1 in lung cancer cells stimulated a mitotic arrest. After that, apoptosis was promoted by the activation of caspase-3 and -9. Protein level of Bim, a BH3 domain-only, pro-apoptotic member and its isoforms, BimL, BimS, and BimEL were up-regulated by FSTL1 inhibition. Degradation of Bim was blocked in FSTL1-knockdown cells by decreased phosphorylation of Bim. Increased BimEL as well as decreased phosphorylated Erk1/2 is essential for cell death by FSTL1 inhibition in NCI-H460 cells. Taken together, our results suggest that the knockdown of FSTL1 induces apoptosis through a mitotic arrest and caspase-dependent cell death. FSTL1 plays the important roles in cellular proliferation and apoptosis in lung cancer cells, and thus can be a new target for lung cancer treatment.

A holistic approach to dissecting SPARC family protein complexity reveals FSTL-1 as an inhibitor of pancreatic cancer cell growth

SPARC is a matricellular protein that is involved in both pancreatic cancer and diabetes. It belongs to a wider family of proteins that share structural and functional similarities. Relatively little is known about this extended family, but evidence of regulatory interactions suggests the importance of a holistic approach to their study. We show that Hevin, SPOCKs, and SMOCs are strongly expressed within islets, ducts, and blood vessels, suggesting important roles for these proteins in the normal pancreas, while FSTL-1 expression is localised to the stromal compartment reminiscent of SPARC. In direct contrast to SPARC, however, FSTL-1 expression is reduced in pancreatic cancer. Consistent with this, FSTL-1 inhibited pancreatic cancer cell proliferation. The complexity of SPARC family proteins is further revealed by the detection of multiple cell-type specific isoforms that arise due to a combination of post-translational modification and alternative splicing. Identification of splice variants lacking a signal peptide suggests the existence of novel intracellular isoforms. This study underlines the importance of addressing the complexity of the SPARC family and provides a new framework to explain their controversial and contradictory effects. We also demonstrate for the first time that FSTL-1 suppresses pancreatic cancer cell growth.

Repair Injured Heart by Regulating Cardiac Regenerative Signals

Cardiac regeneration is a homeostatic cardiogenic process by which the sections of malfunctioning adult cardiovascular tissues are repaired and renewed employing a combination of both cardiomyogenesis and angiogenesis. Unfortunately, while high-quality regeneration can be performed in amphibians and zebrafish hearts, mammalian hearts do not respond in kind. Indeed, a long-term loss of proliferative capacity in mammalian adult cardiomyocytes in combination with dysregulated induction of tissue fibrosis impairs mammalian endogenous heart regenerative capacity, leading to deleterious cardiac remodeling at the end stage of heart failure. Interestingly, several studies have demonstrated that cardiomyocyte proliferation capacity is retained in mammals very soon after birth, and cardiac regeneration potential is correspondingly preserved in some preadolescent vertebrates after myocardial infarction. There is therefore great interest in uncovering the molecular mechanisms that may allow heart regeneration during adult stages. This review will summarize recent findings on cardiac regenerative regulatory mechanisms, especially with respect to extracellular signals and intracellular pathways that may provide novel therapeutics for heart diseases. Particularly, both in vitro and in vivo experimental evidences will be presented to highlight the functional role of these signaling cascades in regulating cardiomyocyte proliferation, cardiomyocyte growth, and maturation, with special emphasis on their responses to heart tissue injury.

Agonists and Antagonists of TGF-β Family Ligands

The discovery of the transforming growth factor β (TGF-β) family ligands and the realization that their bioactivities need to be tightly controlled temporally and spatially led to intensive research that has identified a multitude of extracellular modulators of TGF-β family ligands, uncovered their functions in developmental and pathophysiological processes, defined the mechanisms of their activities, and explored potential modulator-based therapeutic applications in treating human diseases. These studies revealed a diverse repertoire of extracellular and membrane-associated molecules that are capable of modulating TGF-β family signals via control of ligand availability, processing, ligand-receptor interaction, and receptor activation. These molecules include not only soluble ligand-binding proteins that were conventionally considered as agonists and antagonists of TGF-β family of growth factors, but also extracellular matrix (ECM) proteins and proteoglycans that can serve as "sink" and control storage and release of both the TGF-β family ligands and their regulators. This extensive network of soluble and ECM modulators helps to ensure dynamic and cell-specific control of TGF-β family signals. This article reviews our knowledge of extracellular modulation of TGF-β growth factors by diverse proteins and their molecular mechanisms to regulate TGF-β family signaling.

Whole-Genome Sequencing of Native Sheep Provides Insights into Rapid Adaptations to Extreme Environments

Global climate change has a significant effect on extreme environments and a profound influence on species survival. However, little is known of the genome-wide pattern of livestock adaptations to extreme environments over a short time frame following domestication. Sheep (Ovis aries) have become well adapted to a diverse range of agroecological zones, including certain extreme environments (e.g., plateaus and deserts), during their post-domestication (approximately 8–9 kya) migration and differentiation. Here, we generated whole-genome sequences from 77 native sheep, with an average effective sequencing depth of ∼5× for 75 samples and ∼42× for 2 samples. Comparative genomic analyses among sheep in contrasting environments, that is, plateau (>4,000 m above sea level) versus lowland (<100 m), high-altitude region (>1500 m) versus low-altitude region (<1300 m), desert (<10 mm average annual precipitation) versus highly humid region (>600 mm), and arid zone (<400 mm) versus humid zone (>400 mm), detected a novel set of candidate genes as well as pathways and GO categories that are putatively associated with hypoxia responses at high altitudes and water reabsorption in arid environments. In addition, candidate genes and GO terms functionally related to energy metabolism and body size variations were identified. This study offers novel insights into rapid genomic adaptations to extreme environments in sheep and other animals, and provides a valuable resource for future research on livestock breeding in response to climate change.

Apical Secretion of FSTL1 in the Respiratory Epithelium for Normal Lung Development

Follistatin-like 1 (FSTL1) is a secreted bone morphogenetic protein (BMP) antagonist, and it plays a crucial role in normal lung development. Deletion of Fstl1 leads to postnatal death in mice due to respiratory failure. To further explore the role of FSTL1 in mouse lung development, we created a transgene SFTPC-Fstl1 allele mouse displaying significant epithelial overexpression of Fstl1 in all stages of lung development. However, epithelial overexpression of Fstl1 did not alter lung morphogenesis, epithelial differentiation and lung function. Moreover, we found that FSTL1 function was blocked by the epithelial polarization, which was reflected by the remarkable apical secretion of FSTL1 and the basolateral BMP signaling. Taken together, this study demonstrates that tightly spatial interaction of FSTL1 and BMP signaling plays an essential role in lung development.

Bone Morphogenetic Protein 4 Signalling in Neural Stem and Progenitor Cells during Development and after Injury

Substantial progress has been made in identifying the extracellular signalling pathways that regulate neural stem and precursor cell biology in the central nervous system (CNS). The bone morphogenetic proteins (BMPs), in particular BMP4, are key players regulating neuronal and glial cell development from neural precursor cells in the embryonic, postnatal, and injured CNS. Here we review recent studies on BMP4 signalling in the generation of neurons, astrocytes, and oligodendroglial cells in the CNS. We also discuss putative mechanisms that BMP4 may utilise to influence glial cell development following CNS injury and highlight some questions for further research.

Progressive Differentiation and Instructive Capacities of Amniotic Fluid and Cerebrospinal Fluid Proteomes following Neural Tube Closure

After neural tube closure, amniotic fluid (AF) captured inside the neural tube forms the nascent cerebrospinal fluid (CSF). Neuroepithelial stem cells contact CSF-filled ventricles, proliferate, and differentiate to form the mammalian brain, while neurogenic placodes, which generate cranial sensory neurons, remain in contact with the AF. Using in vivo ultrasound imaging, we quantified the expansion of the embryonic ventricular-CSF space from its inception. We developed tools to obtain pure AF and nascent CSF, before and after neural tube closure, and to define how the AF and CSF proteomes diverge during mouse development. Using embryonic neural explants, we demonstrate that age-matched fluids promote Sox2-positive neurogenic identity in developing forebrain and olfactory epithelia. Nascent CSF also stimulates SOX2-positive self-renewal of forebrain progenitor cells, some of which is attributable to LIFR signaling. Our Resource should facilitate the investigation of fluid-tissue interactions during this highly vulnerable stage of early brain development.

Expression of histone deacetylase 3 instructs alveolar type I cell differentiation by regulating a Wnt signaling niche in the lung

The commitment and differentiation of the alveolar type I (AT1) cell lineage is a critical step for the formation of distal lung saccules, which are the primitive alveolar units required for postnatal respiration. How AT1 cells arise from the distal lung epithelial progenitor cells prior to birth and whether this process depends on a developmental niche instructed by mesenchymal cells is poorly understood. We show that mice lacking histone deacetylase 3 specifically in the developing lung mesenchyme display lung hypoplasia including decreased mesenchymal proliferation and a severe impairment of AT1 cell differentiation. This is correlated with a decrease in Wnt/β-catenin signaling in the lung epithelium. We demonstrate that inhibition of Wnt signaling causes defective AT1 cell lineage differentiation ex vivo. Importantly, systemic activation of Wnt signaling at specific stages of lung development can partially rescue the AT1 cell differentiation defect in vivo. These studies show that histone deacetylase 3 expression generates an important developmental niche in the lung mesenchyme through regulation of Wnt signaling, which is required for proper AT1 cell differentiation and lung sacculation.

Hoxa5: A Key Player in Development and Disease

A critical position in the developmental hierarchy is occupied by the Hox genes, which encode transcription factors. Hox genes are crucial in specifying regional identity along the embryonic axes and in regulating morphogenesis. In mouse, targeted mutations of Hox genes cause skeletal transformations and organ defects that can impair viability. Here, we present the current knowledge about the Hoxa5 gene, a paradigm for the function and the regulation of Hox genes. The phenotypic survey of Hoxa5-/- mice has unveiled its critical role in the regional specification of the skeleton and in organogenesis. Most Hoxa5-/- mice die at birth from respiratory distress due to tracheal and lung dysmorphogenesis and impaired diaphragm innervation. The severity of the phenotype establishes that Hoxa5 plays a predominant role in lung organogenesis versus other Hox genes. Hoxa5 also governs digestive tract morphogenesis, thyroid and mammary glands development, and ovary homeostasis. Deregulated Hoxa5 expression is reported in cancers, indicating Hoxa5 involvement in tumor predisposition and progression. The dynamic Hoxa5 expression profile is under the transcriptional control of multiple cis-acting sequences and trans-acting regulators. It is also modulated by epigenetic mechanisms, implicating chromatin modifications and microRNAs. Finally, lncRNAs originating from alternative splicing and distal promoters encompass the Hoxa5 locus.

Functional screen identifies regulators of murine hematopoietic stem cell repopulation

Holmfeldt et al. perform a transplant-based screen to identify regulators of HSPC engraftment and report that Foxa3 is critical for optimal HSC function after transplant.

Understanding the molecular regulation of hematopoietic stem and progenitor cell (HSPC) engraftment is paramount to improving transplant outcomes. To discover novel regulators of HSPC repopulation, we transplanted >1,300 mice with shRNA-transduced HSPCs within 24 h of isolation and transduction to focus on detecting genes regulating repopulation. We identified 17 regulators of HSPC repopulation: Arhgef5, Armcx1, Cadps2, Crispld1, Emcn, Foxa3, Fstl1, Glis2, Gprasp2, Gpr56, Myct1, Nbea, P2ry14, Smarca2, Sox4, Stat4, and Zfp521. Knockdown of each of these genes yielded a loss of function, except in the cases of Armcx1 and Gprasp2, whose loss enhanced hematopoietic stem cell (HSC) repopulation. The discovery of multiple genes regulating vesicular trafficking, cell surface receptor turnover, and secretion of extracellular matrix components suggests active cross talk between HSCs and the niche and that HSCs may actively condition the niche to promote engraftment. We validated that Foxa3 is required for HSC repopulating activity, as Foxa3^−/− HSC fails to repopulate ablated hosts efficiently, implicating for the first time Foxa genes as regulators of HSPCs. We further show that Foxa3 likely regulates the HSC response to hematologic stress. Each gene discovered here offers a window into the novel processes that regulate stable HSPC engraftment into an ablated host.

HDAC3-Dependent Epigenetic Pathway Controls Lung Alveolar Epithelial Cell Remodeling and Spreading via miR-17-92 and TGF-β Signaling Regulation

The terminal stages of pulmonary development, called sacculation and alveologenesis, involve both differentiation of distal lung endoderm progenitors and extensive cellular remodeling of the resultant epithelial lineages. These processes are coupled with dramatic expansion of distal airspace and surface area. Despite the importance of these late developmental processes and their relation to neonatal respiratory diseases, little is understood about the molecular and cellular pathways critical for their successful completion. We show that a histone deacetylase 3 (Hdac3)-mediated epigenetic pathway is critical for the proper remodeling and expansion of the distal lung saccules into primitive alveoli. Loss of Hdac3 in the developing lung epithelium leads to a reduction of alveolar type 1 cell spreading and a disruption of lung sacculation. Hdac3 represses miR-17-92 expression, a microRNA cluster that regulates transforming growth factor β (TGF-β) signaling. De-repression of miR-17-92 in Hdac3-deficient lung epithelium results in decreased TGF-β signaling activity. Importantly, inhibition of TGF-β signaling and overexpression of miR-17-92 can phenocopy the defects observed in Hdac3 null lungs. Conversely, loss of miR-17-92 expression rescues many of the defects caused by loss of Hdac3 in the lung. These studies reveal an intricate epigenetic pathway where Hdac3 is required to repress miR-17-92 expression to allow for proper TGF-β signaling during lung sacculation.

Altered Expression of Bone Morphogenetic Protein Accessory Proteins in Murine and Human Pulmonary Fibrosis

Idiopathic pulmonary fibrosis is a chronic, progressive fibrotic disease with a poor prognosis. The balance between transforming growth factor β1 and bone morphogenetic protein (BMP) signaling plays an important role in tissue homeostasis, and alterations can result in pulmonary fibrosis. We hypothesized that multiple BMP accessory proteins may be responsible for maintaining this balance in the lung. Using the bleomycin mouse model for fibrosis, we examined an array of BMP accessory proteins for changes in mRNA expression. We report significant increases in mRNA expression of gremlin 1, noggin, follistatin, and follistatin-like 1 (Fstl1), and significant decreases in mRNA expression of chordin, kielin/chordin-like protein, nephroblastoma overexpressed gene, and BMP and activin membrane-bound inhibitor (BAMBI). Protein expression studies demonstrated increased levels of noggin, BAMBI, and FSTL1 in the lungs of bleomycin-treated mice and in the lungs of idiopathic pulmonary fibrosis patients. Furthermore, we demonstrated that transforming growth factor β stimulation resulted in increased expression of noggin, BAMBI, and FSTL1 in human small airway epithelial cells. These results provide the first evidence that multiple BMP accessory proteins are altered in fibrosis and may play a role in promoting fibrotic injury.

Bone morphogenetic protein signaling in bone homeostasis

Bone morphogenetic proteins (BMPs) are cytokines belonging to the transforming growth factor-β (TGF-β) superfamily. They play multiple functions during development and tissue homeostasis, including regulation of the bone homeostasis. The BMP signaling pathway consists in a well-orchestrated manner of ligands, membrane receptors, co-receptors and intracellular mediators, that regulate the expression of genes controlling the normal functioning of the bone tissues. Interestingly, BMP signaling perturbation is associated to a variety of low and high bone mass diseases, including osteoporosis, bone fracture disorders and heterotopic ossification. Consistent with these findings, in vitro and in vivo studies have shown that BMPs have potent effects on the activity of cells regulating bone function, suggesting that manipulation of the BMP signaling pathway may be employed as a therapeutic approach to treat bone diseases. Here we review the recent advances on BMP signaling and bone homeostasis, and how this knowledge may be used towards improved diagnosis and development of novel treatment modalities. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Methylation-mediated BMPER expression in fibroblast activation in vitro and lung fibrosis in mice in vivo

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease. Although the pathogenesis is poorly understood, evidence suggests that genetic and epigenetic alterations, such as DNA methylation, may play a key role. Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-β (TGF-β) superfamily and are important regulators in IPF. Here we identified BMP endothelial cell precursor-derived regulator (BMPER) as a key regulator of fibroblast activation. BMPER is a secreted glycoprotein that binds directly to BMPs and may regulate TGF-β/BMP signaling, but its role in lung fibrosis is not clear. BMPER is highly expressed in human IPF lung fibroblasts compared to normal lung fibroblasts. Demethylation agent 5′-azacytidine decreased BMPER expression in fibroblasts, and attenuated the invasion and migration of IPF lung fibroblasts. Furthermore, siRNA-mediated reduction of BMPER in the human lung fibroblasts impaired cell migration and invasion. 5′-azacytidine treatment additionally regulated BMPER expression and reduced lung fibrosis in mice in vivo. These findings demonstrate that methylation of specific genes in fibroblasts may offer a new therapeutic strategy for IPF by modulating fibroblast activation.

Fstl1 is involved in the regulation of radial glial scaffold development

Background

Radial glial cells (RGCs), the instructive scaffolds for neuronal migration, are well characterized by their unique morphology and polarization; these cells extend elongated basal processes to the pial basement membrane (BM) and parallel to one another. However, little is known about the mechanisms that underlie the developmental regulation and maintenance of this unique morphology.

Results

Here, by crossing Fstl1^fl/fl mice with an EIIa-Cre line, we identified a new role for the secreted glycoprotein Follistatin like-1 (FSTL1). The ablation of Fstl1 in both of its cortical expression domains, the ventricular zone (VZ) and the pia mater, resulted in RGC morphologic disruption; basal processes were not parallel to each other, and endfeet exhibited greater density and branching. However, Fstl1 deletion in only the VZ in the Emx1^IREScre; Fstl1^fl/fl line did not affect RGC morphology, indicating that FSTL1 derived from the pia mater might be more important for RGC morphology. In addition, upper-layer projection neurons, not deeper-layer projection neurons, failed to reach their appropriate positions. We also found that BMP, AKT/PKB, Cdc42, GSK3β, integrin and reelin signals, which have previously been reported to regulate RGC development, were unchanged, indicating that Fstl1 may function through a unique mechanism.

Conclusions

In the present study, we identified a new role for FSTL1 in the development of radial glial scaffolds and the neuronal migration of upper-layer projection neurons. Our findings will improve understanding of the regulation of RGC development and neuronal migration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-015-0144-8) contains supplementary material, which is available to authorized users.

The expression and post-transcriptional regulation of FSTL1 transcripts in placental trophoblasts

INTRODUCTION

Follistatin-like-1 (FSTL1) is a widely expressed secreted protein with diverse but poorly understood functions. Originally described as a pro-inflammatory molecule, it has recently been reported to play a role in signaling pathways that regulate development and homeostasis. Distinctively, FSTL1 harbors within its 3'-UTR the sequence encoding microRNA-198 (miR-198), shown to be inversely regulated relative to FSTL1 expression and to exhibit opposite actions on cellular processes such as cell migration. We sought to investigate the expression of FSTL1 and to assess its interplay with miR-198 in human trophoblasts.

METHODS

We used a combination of northern blot analyses, quantitative PCR, small RNA sequencing, western blot and immunohistochemistry to characterize FSTL1 and miR-198 expression in placental trophoblasts. We also used reporter assays to examine the post-transcriptional regulation of FSTL1 and assess its putative regulation by miR-198.

RESULTS

We detected the expression of FSTL1 transcript in both the human extravillous trophoblast line HTR-8/SVneo and in primary term human villous trophoblasts. We also found that the expression of FSTL1 was largely restricted to extravillous trophoblasts. Hypoxia enhanced the expression of FSTL1 protein in cultured primary villous trophoblasts. Interestingly, we did not detect any evidence for expression or function of mature miR-198 in human trophoblasts.

DISCUSSION

Our data indicate that placental FSTL1 is expressed particularly in extravillous trophoblasts. We also found no evidence for placental expression of miR-198, or for its regulation of FSTL1, implying that the post-transcriptional regulation of FSTL1 by miR-198 is tissue specific.

Follistatin-like 1 attenuates differentiation and survival of erythroid cells through Smad2/3 signaling

Hematopoiesis is a complex process tightly controlled by sets of transcription factors in a context-dependent and stage-specific manner. Smad2/3 transcription factor plays a central role in differentiation and survival of erythroid cells. Here we report that follistatin-like 1 (FSTL1) treatment impairs hemin-induced erythroid differentiation and cell survival. FSTL1 differentially regulates transforming growth factor beta (TGF-β) and bone morphogenetic protein (BMP) signaling. Blockade of Smad2/3 signaling with the ALK5/type I TGF-βR kinase inhibitor, SB-525334, was efficacious for rescue of erythroid differentiation blockage and apoptosis. Reversely, activation of Smad1/5/8 signaling with BMP4 cannot rescue FSTL1-mediated erythroid differentiation blockage and apoptosis. Collectively, these data provide mechanistic insight into the regulation of erythropoiesis by FSTL1 signaling and lay a foundation for exploring FSTL1 signaling as a therapeutic target for anemia.

Fstl1 Promotes Asthmatic Airway Remodeling by Inducing Oncostatin M

Chronic asthma is associated with airway remodeling and decline in lung function. In this article, we show that follistatin-like 1 (Fstl1), a mediator not previously associated with asthma, is highly expressed by macrophages in the lungs of humans with severe asthma. Chronic allergen-challenged Lys-Cre(tg) /Fstl1(Δ/Δ) mice in whom Fstl1 is inactivated in macrophages/myeloid cells had significantly reduced airway remodeling and reduced levels of oncostatin M (OSM), a cytokine previously not known to be regulated by Fstl1. The importance of the Fstl1 induction of OSM to airway remodeling was demonstrated in murine studies in which administration of Fstl1 induced airway remodeling and increased OSM, whereas administration of an anti-OSM Ab blocked the effect of Fstl1 on inducing airway remodeling, eosinophilic airway inflammation, and airway hyperresponsiveness, all cardinal features of asthma. Overall, these studies demonstrate that the Fstl1/OSM pathway may be a novel pathway to inhibit airway remodeling in severe human asthma.

Transforming growth factor-β superfamily in obstructive lung diseases. more suspects than TGF-β alone

Asthma and chronic obstructive pulmonary disease are respiratory disorders and a major global health problem with increasing incidence and severity. Genes originally associated with lung development could be relevant in the pathogenesis of chronic obstructive pulmonary disease/asthma, owing to either an early-life origin of adult complex diseases or their dysregulation in adulthood upon exposure to environmental stressors (e.g., smoking). The transforming growth factor (TGF)-β superfamily is conserved through evolution and is involved in a range of biological processes, both during development and in adult tissue homeostasis. TGF-β1 has emerged as an important regulator of lung and immune system development. However, considerable evidence has been presented for a role of many of the other ligands of the TGF-β superfamily in lung pathology, including activins, bone morphogenetic proteins, and growth differentiation factors. In this review, we summarize the current knowledge on the mechanisms by which activin, bone morphogenetic protein, and growth differentiation factor signaling contribute to the pathogenesis of obstructive airway diseases.

The Bone Morphogenetic Proteins and Their Antagonists

The bone morphogenetic proteins (BMPs) and the growth and differentiation factors comprise a single family of some 20 homologous, dimeric cytokines which share the cystine-knot domain typical of the TGF-β superfamily. They control the differentiation and activity of a range of cell types, including many outside bone and cartilage. They serve as developmental morphogens, but are also important in chronic pathologies, including tissue fibrosis and cancer. One mechanism for enabling tight spatiotemporal control of their activities is through a number of antagonist proteins, including Noggin, Follistatin, Chordin, Twisted gastrulation (TSG), and the seven members of the Cerberus and Dan family. These antagonists are secreted proteins that bind selectively to particular BMPs with high affinity, thereby blocking receptor engagement and signaling. Most of these antagonists also possess a TGF-β cystine-knot domain. Here, we discuss current knowledge and understanding of the structures and activities of the BMPs and their antagonists, with a particular focus on the latter proteins. Recent advances in structural biology of BMP antagonists have begun the process of elucidating the molecular basis of their activity, displaying a surprising variety between the modes of action of these closely related proteins. We also discuss the interactions of the antagonists with the glycosaminoglycan heparan sulfate, which is found ubiquitously on cell surfaces and in the extracellular matrix.

Strategies of Manipulating BMP Signaling in Microgravity to Prevent Bone Loss

Bone structure and function is shaped by gravity. Prolonged exposure to microgravity leads to 1-2% bone loss per month in crew members compared to 1% bone loss per year in postmenopausal women. Exercise countermeasures developed to date are ineffective in combating bone loss in microgravity. The search is on for alternate therapies to prevent bone loss in space. Microgravity is an ideal stimulus to understand bone interactions at different levels of organizations. Spaceflight experiments are limited by high costs and lack of opportunity. Ground-based microgravity analogs have proven to simulate biological responses in space. Mice experiments have given important signaling clues in microgravity-associated bone loss, but are restricted by numbers and human application. Cell-based systems provide initial clues to signaling changes; however, the information is simplistic and limited to the cell type. There is a need to integrate information at different levels and provide a complete picture which will help develop a unique strategy to prevent bone weakening. Limited exposure to simulated microgravity using random positioning machine induces proliferation and differentiation of bipotential murine oval liver stem cells. Bone morphogenetic proteins (BMPs) are the prototypal osteogenic signaling molecule with multitude of bone protective functions. In this chapter, we discuss the basic BMP structure, its significance in bone repair, and stem cell differentiation in microgravity. Based on the current information, we propose a model for BMP signaling in space. Development of new technologies may help osteoporosis patients, bedridden people, spinal injuries, or paralytic patients.

Follistatin-like protein 1 and its role in inflammation and inflammatory diseases

Follistatin-like protein 1 (FSTL1) is a secreted glycoprotein produced mainly by cells of mesenchymal origin. FSTL1 has been shown to play an important role during embryogenesis; FSTL1-deficient mice die at birth from multiple developmental abnormalities. In the last decade, FSTL1 has been identified as a novel inflammatory protein, enhancing synthesis of proinflammatory cytokines and chemokines by immune cells in vitro and in vivo. FSTL1 mediates proinflammatory events in animal models of inflammatory diseases, particularly in collagen-induced arthritis in mice. FSTL1 is elevated in various inflammatory conditions and decreased during the course of treatment. FSTL1 may therefore be a valuable biomarker for such diseases. Moreover, a variety of experiments suggest that targeting of FSTL1 may be useful in the treatment of diseases in which inflammation plays a central role.

Large genomic fragment deletions and insertions in mouse using CRISPR/Cas9

ZFN, TALENs and CRISPR/Cas9 system have been used to generate point mutations and large fragment deletions and insertions in genomic modifications. CRISPR/Cas9 system is the most flexible and fast developing technology that has been extensively used to make mutations in all kinds of organisms. However, the most mutations reported up to date are small insertions and deletions. In this report, CRISPR/Cas9 system was used to make large DNA fragment deletions and insertions, including entire Dip2a gene deletion, about 65kb in size, and β-galactosidase (lacZ) reporter gene insertion of larger than 5kb in mouse. About 11.8% (11/93) are positive for 65kb deletion from transfected and diluted ES clones. High targeting efficiencies in ES cells were also achieved with G418 selection, 46.2% (12/26) and 73.1% (19/26) for left and right arms respectively. Targeted large fragment deletion efficiency is about 21.4% of live pups or 6.0% of injected embryos. Targeted insertion of lacZ reporter with NEO cassette showed 27.1% (13/48) of targeting rate by ES cell transfection and 11.1% (2/18) by direct zygote injection. The procedures have bypassed in vitro transcription by directly co-injection of zygotes or co-transfection of embryonic stem cells with circular plasmid DNA. The methods are technically easy, time saving, and cost effective in generating mouse models and will certainly facilitate gene function studies.

In vitro reconstruction of branched tubular structures from lung epithelial cells in high cell concentration gradient environment

We have succeeded in developing hollow branching structure in vitro commonly observed in lung airway using primary lung airway epithelial cells. Cell concentration gradient is the key factor that determines production of the branching cellular structures, as optimization of this component removes the need for heterotypic culture. The higher cell concentration leads to the more production of morphogens and increases the growth rate of cells. However, homogeneous high cell concentration does not make a branching structure. Branching requires sufficient space in which cells can grow from a high concentration toward a low concentration. Simulation performed using a reaction-diffusion model revealed that long-range inhibition prevents cells from branching when they are homogeneously spread in culture environments, while short-range activation from neighboring cells leads to positive feedback. Thus, a high cell concentration gradient is required to make branching structures. Spatial distributions of morphogens, such as BMP-4, play important roles in the pattern formation. This simple yet robust system provides an optimal platform for the further study and understanding of branching mechanisms in the lung airway, and will facilitate chemical and genetic studies of lung morphogenesis programs.

Blocking follistatin-like 1 attenuates bleomycin-induced pulmonary fibrosis in mice

Follistatin-like 1 (Fstl1) is induced in response to lung injury and promotes the accumulation of myofibroblasts and subsequent fibrosis via regulation of TGF-β and BMP. Reducing Fstl1 in mice reduces bleomycin-induced fibrosis in vivo, offering a potential therapeutic target for progressive lung fibrosis.

Progressive tissue fibrosis is a cause of major morbidity and mortality. Pulmonary fibrosis is an epithelial-mesenchymal disorder in which TGF-β1 plays a central role in pathogenesis. Here we show that follistatin-like 1 (FSTL1) differentially regulates TGF-β and bone morphogenetic protein signaling, leading to epithelial injury and fibroblast activation. Haplodeletion of Fstl1 in mice or blockage of FSTL1 with a neutralizing antibody in mice reduced bleomycin-induced fibrosis in vivo. Fstl1 is induced in response to lung injury and promotes the accumulation of myofibroblasts and subsequent fibrosis. These data suggest that Fstl1 may serve as a novel therapeutic target for treatment of progressive lung fibrosis.