Cloning of follistatin-related protein as a novel autoantigen in systemic rheumatic diseases

FSTL1: A double-edged sword in cancer development

Flolistatin-related protein 1 (FSTL1), a secreted glycoprotein that is involved in many physiological functions, has attracted much interest and has been implicated in a wide range of diseases, including heart diseases and inflammatory diseases. In recent years, the involvement of FSTL1 in cancer progression has been implicated and researched. FSTL1 plays a contradictory role in cancer, depending on the cancer type as well as the contents of the tumor microenvironment. As reviewed here, the structure and distribution of FSTL1 are first introduced. Subsequently, the expression and clinical significance of FSTL1 in various types of cancer as a tumor enhancer or inhibitor are addressed. Furthermore, we discuss the functional role of FSTL1 in various processes that involve tumor cell proliferation, metastasis, immune responses, stemness, cell apoptosis, and resistance to chemotherapy. FSTL1 expression is tightly controlled in cancer, and a multitude of cancer-related signaling cascades like TGF-β/BMP/Smad signaling, AKT, NF-κB, and Wnt-β-catenin signaling pathways are modulated by FSTL1. Finally, FSTL1 as a therapeutic target using monoclonal antibodies is stated. Herein, we review recent findings showing the double-edged characteristics and mechanisms of FSTL1 in cancer and elaborate on the current understanding of therapeutic approaches targeting FSTL1.

miR-125a-3p regulates the expression of FSTL1, a pro-inflammatory factor, during adipogenic differentiation, and inhibits adipogenesis in mice

Adipogenesis is tightly regulated by various factors, including genes and microRNAs. Excessive fat deposition is the key feature of obesity, which is a low-grade chronic inflammatory disease. Follistatin-like 1 (FSTL1) has been reported to be an important mediator involved in various inflammatory diseases. However, the underlying mechanism of FSTL1 in preadipocyte differentiation and inflammatory response is still unclear. The current study was designed to explore the biological function and potential mechanism of FSTL1 in mouse subcutaneous preadipocyte differentiation. We found that FSTL1 was highly expressed in the early stage of differentiation and subsequently decreased sharply, suggesting that FSTL1 played a possible role in adipogenesis. Meanwhile, the gain- and loss-of-function assays showed that FSTL1 was not only involved in the inflammatory response by inducing the expression of pro-inflammatory factors IL-1β and CCL2 but also significantly attenuated preadipocyte differentiation, as evidenced by the reduction of lipid accumulation and the levels of adipogenic genes, including PPARγ and FABP4. In addition, the target gene prediction and luciferase reporter assay validated that miR-125a-3p targeted the 3' UTR region of FSTL1. These results demonstrated that miR-125a-3p negatively regulated the expression of FSTL1 at the mRNA and protein levels. Furthermore, overexpressing miR-125a-3p in preadipocytes dramatically accelerated adipogenic differentiation and downregulated the levels of IL-1β and CCL2, which were in accordance with the knockdown of FSTL1. On the contrary, treatment with miR-125a-3p inhibitors attenuated adipogenesis but induced the expression of inflammatory genes. In summary, this study suggests a positive function of FSTL1 in adipocyte-induced inflammation and negatively regulates preadipocyte differentiation. Further studies demonstrated that miR-125a-3p could reverse the effect by targeting FSTL1, which might provide a better understanding of treating obesity-related inflammatory diseases.

Follistatin-like 1 and its paralogs in heart development and cardiovascular disease

Cardiovascular diseases (CVDs) are a group of disorders affecting the heart and blood vessels and a leading cause of death worldwide. Thus, there is a need to identify new cardiokines that may protect the heart from damage as reported in GBD 2017 Causes of Death Collaborators (2018) (The Lancet 392:1736-1788). Follistatin-like 1 (FSTL1) is a cardiokine that is highly expressed in the heart and released to the serum after cardiac injury where it is associated with CVD and predicts poor outcome. The action of FSTL1 likely depends not only on the tissue source but also post-translation modifications that are target tissue- and cell-specific. Animal studies examining the effect of FSTL1 in various models of heart disease have exploded over the past 15 years and primarily report a protective effect spanning from inhibiting inflammation via transforming growth factor, preventing remodeling and fibrosis to promoting angiogenesis and hypertrophy. A better understanding of FSTL1 and its homologs is needed to determine whether this protein could be a useful novel biomarker to predict poor outcome and death and whether it has therapeutic potential. The aim of this review is to provide a comprehensive description of the literature for this family of proteins in order to better understand their role in normal physiology and CVD.

Validation of the Diagnostic and Prognostic Values of ADAMTS5 and FSTL1 in Osteoarthritis Rat Model

OBJECTIVE

Osteoarthritis (OA) is a global public health problem and a leading cause of morbidity and disability. Due to lack of sensitive and specific tools for early OA diagnosis and predicting prognosis, the availability of new reliable and sensitive biomarkers is a widely appreciated need to identify patients at risk for incident disease or disease progression. Accordingly, our study was conducted to validate the usefulness of disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS5) and follistatin-like protein 1 (FSTL1) to achieve this goal.

DESIGN

Fifty-four male Wistar rats were randomized into 3 groups; 24 rats were subjected to medial meniscal tear (MMT) surgery on the right knee joint (OA group), 24 rats were subjected to sham surgery (sham group), and 6 healthy rats (negative control group). Six animals from each group were sacrificed every 2 weeks. At each time point, the right knee joint of each animal was visualized radiologically, a blood sample was collected, and cartilage tissues were isolated for histopathological and western blot analysis.

RESULTS

We found that the expression levels of ADAMTS5 and FSTL1 significantly increased with OA progression, especially at weeks 4, 6, and 8 after surgery. Notably, the serum levels of ADAMTS5 and FSTL1 showed significant positive correlations with each other and with the studied inflammatory markers.

CONCLUSIONS

Our findings suggest that ADAMTS5 and FSTL1 can serve as important and informative serological markers of disease activity in OA. However, further research is needed to validate their use for improving the diagnosis and prognosis of OA in humans.

Follistatin-Like 1 Attenuation Suppresses Intervertebral Disc Degeneration in Mice through Interacting with TNF-α and Smad Signaling Pathway

Background

Inflammation plays an important role in intervertebral disc degeneration (IDD). The protein follistatin-like 1 (FSTL1) plays a proinflammatory role in a variety of inflammatory diseases.

Objectives

The purpose of this study was to investigate whether IDD could be delayed by inhibiting FSTL-1 expression.

Methods

We established a puncture-induced IDD model in wild-type and FSTL-1+/- mice and collected intervertebral discs (IVDs) from the mice. Safranin O staining was used to detect cartilage loss of IVD tissue, and HE staining was used to detect morphological changes of IVD tissue. We measured the expression of FSTL-1 and related inflammatory indicators in IVD tissues by immunohistochemical staining, real-time PCR, and Western blotting.

Results

In the age-induced model of IDD, the level of FSTL-1 increased with the exacerbation of degeneration. In the puncture-induced IDD model, FSTL-1-knockdown mice showed a reduced degree of degeneration compared with that of wild-type mice. Further experiments showed that FSTL-1 knockdown also significantly reduced the level of related inflammatory factors in IVD. In vitro experiments showed that FSTL-1 knockdown significantly reduced TNF-α-induced inflammation. Specifically, the expression levels of the inflammatory factors COX-2, iNOS, MMP-13, and ADAMTS-5 were reduced. Knockdown of FSTL-1 attenuated inflammation by inhibiting the expression of P-Smad1/5/8, P-Erk1/2, and P-P65.

Conclusion

Knockdown of FSTL-1 attenuated inflammation by inhibiting the TNF-α response and Smad pathway activity and ultimately delayed IDD.

Signalling and putative therapeutic molecules on the regulation of synoviocyte signalling in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by symmetrical and chronic polyarthritis. Fibroblast-like synoviocytes are mainly involved in joint inflammation and cartilage and bone destruction by inflammatory cytokines and matrix-degrading enzymes in RA. Approaches that induce various cellular growth alterations of synoviocytes are considered as potential strategies for treating RA. However, since synoviocytes play a critical role in RA, the mechanism and hyperplastic modulation of synoviocytes and their motility need to be addressed. In this review, we focus on the alteration of synoviocyte signalling and cell fate provided by signalling proteins, various antioxidant molecules, enzymes, compounds, clinical candidates, to understand the pathology of the synoviocytes, and finally to achieve developed therapeutic strategies of RA.

Cite this article: Bone Joint Res 2021;10(4):285–297.

Follistatin-like protein 1 functions as a potential target of gene therapy in proliferative diabetic retinopathy

The degree of retinal fibrosis increased in proliferative diabetic retinopathy (PDR) patients after administration of anti-Vascular endothelial growth factor (VEGF) injections. Previous studies showed that the balance between connective tissue growth factor (CTGF) and VEGF plays an important role. Therefore, in a high-glucose state, an anti-VEGF and CTGFshRNA dual-target model was used to simulate clinical dual-target treatment in PDR patients, and RNA sequencing (RNA-Seq) technology was used for whole transcriptome sequencing. A hypoxia model was constructed to verify the sequencing results at the cellular level, and the vitreous humor and proliferative membranes were collected from patients for verification. All sequencing results included Follistatin-like protein 1 (FSTL1) and extracellular matrix (ECM) receptor pathway, indicated that anti-VEGF therapy may upregulate FSTL1 expression, while dual-target treatment downregulated FSTL1. Thus, we further studied the function of FSTL1 on the expression of VEGF and ECM factors by both overexpressing and silencing FSTL1. In conclusion, our results suggested that FSTL1 may be involved in the pathogenesis of PDR and is related to fibrosis caused by the anti-VEGF treatment, thus providing a potential target for gene therapy in PDR.

Identification of two genes potentially related to myogenesis and muscle growth in Fenneropenaeus chinensis: Activin receptor II and Follistatin-like protein

Activin receptor (ActR) and follistatin-like (FSTL) genes, which are involved in the Myostatin (Mstn) related TGF-β/Smad signaling pathway, play important roles in regulating the muscle generation, development and growth of muscle in vertebrate. Our previous studies have confirmed that Mstn negatively regulates muscle development and growth in Fenneropenaeus chinensis as that in vertebrate. However, the roles of ActR and FSTL in muscle development and growth in invertebrate remains unclear. In the present study, type II ActR(FcActRII) and FSTL (FcFSTL) genes from F. chinensis were cloned and characterized, and their functions on muscle development and growth were investigated. The full-length cDNAs of FcActRII and FcFSTL were 2366 bp that encoded 572 amino acids and 2474 bp that encoded 717 amino acids, respectively. Sequence analysis revealed that the overall protein sequences of the two genes shared 97% and 96% identities with Penaeus vannamei and 50%-59% and 35%-36% identities with vertebrates, respectively. In the early development stages, muscles firstly appeared in nauplius stage and developed gradually until post larval, and the mRNA expressions of FcActRII increased from gastrula to zoea stage and then decreased from zoea stage to post larval stage while that of FcFSTL was lowest in gastrula stage and increased rapidly in nauplius stage and then expressed stably from nauplius stage to post-larval stage. In the adult shrimp, the two genes were widely distributed in the examined tissues. The FcActRII expression in muscle of L group was significantly lower than that of S group, but the FcFSTL expression showed an opposite result. After down-regulating the expression of FcMstn by RNAi, FcActRII expression was significantly down-regulated while that of FcFSTL was up-regulated. The present study suggested that FcActRII and FcFSTL, regulated by FcMstn, might be involved in myogenesis and muscle growth.

Follistatin-like 1 (FSTL1) is a prognostic biomarker and correlated with immune cell infiltration in gastric cancer

Background

Follistatin-like 1 (FSTL1) plays a central role in the progression of tumor and tumor immunity. However, the effect of FSTL1 on the prognosis and immune infiltration of gastric cancer (GC) remains to be elucidated.

Methods

The expression of FSTL1 data was analyzed in Oncomine and TIMER databases. Analyses of clinical parameters and survival data were conducted by Kaplan-Meier plotter and immunohistochemistry. Western blot assay and real-time quantitative PCR (RT-qPCR) were used to analyze protein and mRNA expression, respectively. The correlations between FSTL1 and cancer immune infiltrates were analyzed by Tumor Immune Estimation Resource (TIME), Gene Expression Profiling Interactive Analysis (GEPIA), and LinkedOmics database.

Results

The expression of FSTL1 was significantly higher in GC tissues than in normal tissues, and bioinformatic analysis and immunohistochemistry (IHC) indicated that high FSTL1 expression significantly correlated with poor prognosis in GC. Moreover, FSTL1 was predicted as an independent prognostic factor in GC patients. Bioinformatics analysis results suggested that FSTL1 mainly involved in tumor progression and tumor immunity. And significant correlations were found between FSTL1 expression and immune cell infiltration in GC.

Conclusions

The study effectively revealed useful information about FSTL1 expression, prognostic values, potential functional networks, and impact of tumor immune infiltration in GC. In summary, FSTL1 can be used as a biomarker for prognosis and evaluating immune cell infiltration in GC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12957-020-02070-9.

FSTL1 Promotes Inflammatory Reaction and Cartilage Catabolism through Interplay with NFκB Signaling Pathways in an In Vitro ONFH Model

Osteonecrosis of the femoral head (ONFH) usually occurs in young people and is closely associated with autoimmune reactions. Follistatin-like 1 (FSTL1) was recently proven to participate in several inflammation-related diseases. The role of FSTL1 in ONFH is still unclear. Serum levels of FSTL1 were not significantly different in ONFH patients and healthy individuals. In contrast, elevated expression levels of FSTL1 were observed in degraded cartilage and synovial fluid in ONFH patients and in a cultured human primary chondrocyte model treated with interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α). Suppression of FSTL1 by FSTL1-siRNA downregulated the inflammatory response mediated by IL-1β or TNF-α in cultured human chondrocytes. In a human cartilage culture model, FSTL1 promoted the production of inflammatory cytokines and cartilage degradation enzymes. The activation of NFκB signaling pathway was detected in degenerated cartilage from ONFH patients and in FSTL1-treated chondrocytes. Additionally, administration of an NFκB inhibitor (JSH-23) significantly reduced the overexpression of inflammatory cytokines and protein degradation enzymes induced by FSTL1 and maintained the level of major cartilage matrix components (aggrecan and collagen II). In summary, FSTL1 was involved in the degeneration progression of the ONFH and might provide a novel direction for treating and curing ONFH.

Follistatin-like 1 in Cardiovascular Disease and Inflammation

Follistatin-like 1 (FSTL1), a secreted glycoprotein, has been shown to participate in regulating developmental processes and to be involved in states of disease and injury. Spatiotemporal regulation and posttranslational modifications contribute to its specific functions and make it an intriguing candidate to study disease mechanisms and potentially develop new therapies. With cardiovascular diseases as the primary cause of death worldwide, clarification of mechanisms underlying cardiac regeneration and revascularization remains essential. Recent findings on FSTL1 in both acute coronary syndrome and heart failure emphasize its potential as a target for cardiac regenerative therapy. With this review, we aim to shed light on the role of FSTL1 specifically in cardiovascular disease and inflammation.

Determination of follistatin-like protein 1 expression in colorectal cancer and its association with clinical outcomes

Background

Follistatin-like protein 1 (FSTL1) has been demonstrated to play a controversial role in cancer. In this study, we aimed to investigate the expression of FSTL1 and its characteristics in patients with colorectal cancer (CRC).

Methods

Gene expression microarray assays in 30 CRC patients and a real-time quantitative polymerase chain reaction (RT-qPCR) of 22 patients were performed to compare the mRNA level of FSTL1 in tumor lesions and paired normal tissues. Also, 332 consecutive patients with pathologically confirmed CRC were selected to detect FSTL1 expression by using immunohistochemistry (IHC). Enzyme-linked immunosorbent assay (ELISA) was also applied to determine the serum level of FSTL1 in 60 CRC patients, as well as 34 healthy donors.

Results

Gene expression microarray assays and RT-qPCR in CRC tissues, as well as ELISA in the serum all, revealed that the expression level of FSTL1 was higher in cancer tissue of CRC patients compared with paired normal tissue or healthy donors. The IHC results suggested that FSTL1 was also higher in tumor tissues than in its normal counterparts, however interestingly, a narrow scan focusing on the stromal region indicated that FSTL1 was significantly higher in normal tissues than in cancerous tissues. Besides, higher FSTL1 expression in cancer tissue, as well as lower FSTL1 expression in cancer stroma, both correlated with a worse prognosis, and the latter was an independent prognostic factor.

Conclusions

Our results provide novel insight into the role of FSTL1 in CRC, and it might be an essential factor in CRC development.

Structural and functional study of FK domain of Fstl1

Fstl1 is a TGF-β superfamily binding protein which involved in many pathological processes. The function of Fstl1 has been widely elucidated, but its structural characterization has not been explored. Here we solved the high-resolution crystal structure of FK domain of murine Fstl1, analyzed its unique characteristics, and investigated its contribution to the function of full-length Fstl1. We found that Fstl1-FK forms a stable dimer in both solution and crystal, which suggest that this protein may function as a dimer during its interaction with TGF-β, a molecule known to form dimer during activation process. We also found this FK domain is indispensable for the proper function of Fstl1 during the transduction of TGF-β signaling. These observations provide important insights into the understanding of Fstl1 and may facilitate the exploration of this molecule in clinical study.

Follistatin-like protein 1 (FSTL1) promotes chondrocyte expression of matrix metalloproteinase and inflammatory factors via the NF-κB pathway

Background

The expression of follistatin‐like protein 1 (FSTL1) is closely associated with diseases of the musculoskeletal system. However, despite being a well characterized inflammatory mediator, the effects of FSTL1 on chondrocytes are not completely understood. In this study, we investigated the effects of FSTL1 on the expression of inflammatory and catabolic factors in rat chondrocytes.

Methods

Rat chondrocytes were treated directly with various concentrations of FSTL1 in vitro. The levels of matrix metalloproteinases (MMPs), inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)‐2, interleukin (IL)‐1β, tumour necrosis factor (TNF)‐α and IL‐6 were measured by polymerase chain reaction, ELISA and Western blotting. In addition, activation of the nuclear factor kappa B (NF‐κB) pathway was explored to identify potential regulatory mechanisms.

Results

Follistatin‐like protein 1 directly increased the expression of MMP‐1, MMP‐13, iNOS, COX‐2, IL‐1β, TNF‐α and IL‐6 at both gene and protein level in a dose‐dependent manner. Activation of NF‐ κB and phosphorylation of p65 were also promoted by FSTL1 stimulation.

Conclusions

Follistatin‐like protein 1 exerts pro‐inflammatory and catabolic effects on cultured chondrocytes via activation of the NF‐κB signalling pathway. FSTL1 may therefore be a target in the treatment of OA.

Recent Advances in Research Regarding Autoantibodies in Connective Tissue Diseases and Related Disorders

Connective tissue diseases (CTDs), also known as systemic autoimmune diseases, involve a variety of autoantibodies against cellular components. An important factor regarding these autoantibodies is that each antibody is exclusively related to a certain clinical feature of the disease type, which may prove useful in clinical practice. Thus far, more than 100 types of autoantibodies have been found in CTDs, and most of their target antigens have been identified. Many of these autoantigens are enzymes or regulators involved in important cellular functions, such as gene replication, transcription, repair/recombination, RNA processing, and protein synthesis, as well as proteins that form complexes with RNA and DNA. This article reviews the autoantibodies for each CTD, along with an assessment of their clinical significance, and provides suggestions regarding their utilization for clinical practice.

Multi-omic analysis of signalling factors in inflammatory comorbidities

BACKGROUND

Inflammation is a core element of many different, systemic and chronic diseases that usually involve an important autoimmune component. The clinical phase of inflammatory diseases is often the culmination of a long series of pathologic events that started years before. The systemic characteristics and related mechanisms could be investigated through the multi-omic comparative analysis of many inflammatory diseases. Therefore, it is important to use molecular data to study the genesis of the diseases. Here we propose a new methodology to study the relationships between inflammatory diseases and signalling molecules whose dysregulation at molecular levels could lead to systemic pathological events observed in inflammatory diseases.

RESULTS

We first perform an exploratory analysis of gene expression data of a number of diseases that involve a strong inflammatory component. The comparison of gene expression between disease and healthy samples reveals the importance of members of gene families coding for signalling factors. Next, we focus on interested signalling gene families and a subset of inflammation related diseases with multi-omic features including both gene expression and DNA methylation. We introduce a phylogenetic-based multi-omic method to study the relationships between multi-omic features of inflammation related diseases by integrating gene expression, DNA methylation through sequence based phylogeny of the signalling gene families. The models of adaptations between gene expression and DNA methylation can be inferred from pre-estimated evolutionary relationship of a gene family. Members of the gene family whose expression or methylation levels significantly deviate from the model are considered as the potential disease associated genes.

CONCLUSIONS

Applying the methodology to four gene families (the chemokine receptor family, the TNF receptor family, the TGF- β gene family, the IL-17 gene family) in nine inflammation related diseases, we identify disease associated genes which exhibit significant dysregulation in gene expression or DNA methylation in the inflammation related diseases, which provides clues for functional associations between the diseases.

Follistatin-like 1 in development and human diseases

Follistatin-like 1 (FSTL1) is a secreted glycoprotein displaying expression changes during development and disease, among which cardiovascular disease, cancer, and arthritis. The cardioprotective role of FSTL1 has been intensively studied over the last years, though its mechanism of action remains elusive. FSTL1 is involved in multiple signaling pathways and biological processes, including vascularization and regulation of the immune response, a feature that complicates its study. Binding to the DIP2A, TLR4 and BMP receptors have been shown, but other molecular partners probably exist. During cancer progression and rheumatoid arthritis, controversial data have been reported with respect to the proliferative, apoptotic, migratory, and inflammatory effects of FSTL1. This controversy might reside in the extensive post-transcriptional regulation of FSTL1. The FSTL1 primary transcript also encodes for a microRNA (miR-198) in primates and multiple microRNA-binding sites are present in the 3'UTR. The switch between expression of the FSTL1 protein and miR-198 is an important regulator of tumour metastasis and wound healing. The glycosylation state of FSTL1 is a determinant of biological activity, in cardiomyocytes the glycosylated form promoting proliferation and the non-glycosylated working anti-apoptotic. Moreover, the glycosylation state shows differences between species and tissues which might underlie the differences observed in in vitro studies. Finally, regulation at the level of protein secretion has been described.

Follistatin-like protein 1 promotes inflammatory reactions in nucleus pulposus cells by interacting with the MAPK and NFκB signaling pathways

Objective

Follistatin-like protein 1 (FSTL1) is a well-known mediator of inflammation. Intervertebral disc disease is an inflammatory disorder. Here, we investigated the role of FSTL1 in the intervertebral discs inflammation.

Methods

Expression of FSTL1 in nucleus pulposus tissues from rats and human was determined by immunohistochemistry staining and western blot analysis. The expression levels of tumor necrosis factor-α (TNF-α), interleukin1-β (IL-1β) and matrix metalloproteinase 13 (MMP-13) in human and rat nucleus pulposus tissues were measured by immunohistochemistry staining. The mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NFκB) signaling pathways were detected by western blotting.

Results

FSTL1 serum levels were significantly increased in lumbar disc herniation patients and had a positive correlation with Visual Analogue Scores. Additionally, FSTL1 expression was significantly increased in extrusion group compared with protrusion and control groups. Furthermore, FSTL1 expression was significantly increased in intervertebral disc degeneration models of rats. Immunohistochemistry staining demonstrated that the levels of TNF-α, IL-1β and MMP-13 were increased in the pathogenesis of intervertebral disc disease. Recombinant human FSTL1 significantly increased the production of proinflammatory cytokines in vitro. In addition, FSTL1 promoted inflammation by activating c-Jun N-terminal kinase (JNK), extracellular regulated protein kinases 1/2(ERK1/2) and NFκB signaling.

Conclusions

These data imply that FSTL1 expression was increased in the pathogenesis of intervertebral disc disease. Importantly, FSTL1 promoted inflammatory catabolism in the nucleus pulposus by activating JNK, ERK 1/2/MAPK and NFκB signaling.

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.

Follistatin-like protein 1 suppressed pro-inflammatory cytokines expression during neuroinflammation induced by lipopolysaccharide

Follistain-like protein 1 (FSTL1), has been recently demonstrated to be involved in the embryo development of nervous system and glioblastoma. However, the role of FSTL1 in neuroinflammation remains unexplored. In this study, the expression of FSTL1 in astrocytes was verified and its role was studied in neuroinflammation induced by in vivo intracerebroventricular (ICV) injection of lipopolysaccharide (LPS) or LPS treatment to astrocytes in vitro. FSTL1 was significantly induced after ICV LPS injection or LPS treatment. FSTL1 suppressed upregulation of pro-inflammatory cytokines in astrocytes after LPS treatment. Moreover, FSTL1 downregulated expression of pro-inflammatory cytokines through suppressing MAPK/p-ERK1/2 pathway in astrocytes. Our results suggest that FSTL1 may play an anti-inflammatory role in neuroinflammation mediated by astrocytes.

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.

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.

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.

Follistatin-like 1 in vertebrate development

Follistatin-like 1 (Fstl1) is a member of the secreted protein acidic rich in cysteins (SPARC) family and has been implicated in many different signaling pathways, including bone morphogenetic protein (BMP) signaling. In many different developmental processes like, dorso-ventral axis establishment, skeletal, lung and ureter development, loss of function experiments have unveiled an important role for Fstl1. Fstl1 largely functions through inhibiting interactions with the BMP signaling pathway, although, in various disease models, different signaling pathways, like activation of pAKT, pAMPK, Na/K-ATPase, or innate immune responses, are linked to Fstl1. How Fstl1 inhibits BMP signaling remains unclear, although it is known that Fstl1 does not function through a scavenging mechanism, like the other known extracellular BMP inhibitors such as noggin. It has been proposed that Fstl1 interferes with BMP receptor complex formation and as such inhibits propagation of the BMP signal into the cell. Future challenges will encompass the identification of the factors that determine the mechanisms that underlie the fact that Fstl1 acts by interfering with BMP signaling during development, but through other signaling pathways during disease.

Impaired elastin deposition in Fstl1-/- lung allograft under the renal capsule

Lung alveolar development in late gestation is a process important to postnatal survival. Follistatin-like 1 (Fstl1) is a matricellular protein of the Bmp antagonist class, which is involved in the differentiation/maturation of alveolar epithelial cells during saccular stage of lung development. This study investigates the role of Fstl1 on elastin deposition in mesenchyme and subsequent secondary septation in the late gestation stage of terminal saccular formation. To this aim, we modified the renal capsule allograft model for lung organ culture by grafting diced E15.5 distal lung underneath the renal capsule of syngeneic host and cultured up to 7 days. The saccular development of the diced lung allografts, as indicated by the morphology, epithelial and vascular developments, occurred in a manner similar to that in utero. Fstl1 deficiency caused atelectatic phenotype companied by impaired epithelial differentiation in D3 Fstl1^−/− lung allografts, which is similar to that of E18.5 Fstl1^−/− lungs, supporting the role of Fstl1 during saccular stage. Inhibition of Bmp signaling by intraperitoneal injection of dorsomorphin in the host mice rescued the pulmonary atelectasis of D3 Fstl1^−/− allografts. Furthermore, a marked reduction in elastin expression and deposition was observed in walls of air sacs of E18.5 Fstl1^−/− lungs and at the tips of the developing alveolar septae of D7 Fstl1^−/− allografts. Thus, in addition to its role on alveolar epithelium, Fstl1 is crucial for elastin expression and deposition in mesenchyme during lung alveologenesis. Our data demonstrates that the modified renal capsule allograft model for lung organ culture is a robust and efficient technique to increase our understanding of saccular stage of lung development.

Follistatin-like 1: a potential mediator of inflammation in obesity

Obesity is associated with a state of chronic low-grade inflammation, which contributes to insulin resistance and type 2 diabetes. However, the molecular mechanisms that link obesity to inflammation are not fully understood. Follistatin-like 1 (FSTL1) is a novel proinflammatory cytokine that is expressed in adipose tissue and secreted by preadipocytes/adipocytes. We aimed to test whether FSTL1 could have a role in obesity-induced inflammation and insulin resistance. It was found that FSTL1 expression was markedly decreased during differentiation of 3T3-L1 preadipocytes but reinduced by TNF-α. Furthermore, a significant increase in FSTL1 levels was observed in adipose tissue of obese ob/ob mice, as well as in serum of overweight/obese subjects. Mechanistic studies revealed that FSTL1 induced inflammatory responses in both 3T3-L1 adipocytes and RAW264.7 macrophages. The expression of proinflammatory mediators including IL-6, TNF-α, and MCP-1 was upregulated by recombinant FSTL1 in a dose-dependent manner, paralleled with activation of the IKKβ-NFκB and JNK signaling pathways in the two cell lines. Moreover, FSTL1 impaired insulin signaling in 3T3-L1 adipocytes, as revealed by attenuated phosphorylation of both Akt and IRS-1 in response to insulin stimulation. Together, our results suggest that FSTL1 is a potential mediator of inflammation and insulin resistance in obesity.

Osteoarthritis year 2012 in review: biomarkers

PURPOSE

Biomarkers provide useful diagnostic information by detecting cartilage degradation in osteoarthritis (OA), reflecting disease-relevant biological activity and predicting the course of disease progression. They also serve as surrogate endpoints in the drug discovery process. The aim of this narrative review was to focus on OA biomarker-related papers published between the osteoarthritis research society international (OARSI) 2011 meeting in San Diego and the OARSI 2012 meeting in Barcelona.

METHODS

The PubMed/MEDLINE and SciVerse Scopus bibliographic databases were searched using the keywords: 'biomarker' and 'osteoarthritis' and/or 'biomarker' and 'proteomics'.

RESULTS

Ninety-eight papers were found with the keywords 'biomarker' and 'osteoarthritis'. Fifteen papers were found with the keywords 'biomarker' and 'proteomics'. Review articles were also included. The most relevant published studies focused on extracellular matrix (ECM) molecules in body fluids. Enrichment of the deamidated epitope of cartilage oligomeric matrix protein (D-COMP) suggests that OA disease progression is associated with post-translational modifications that may show specificity for particular joint sites. Fibulin-3 peptides (Fib3-1 and Fib3-2) have been proposed as potential biomarkers of OA along with follistatin-like protein 1 (FSTL1), a new serum biomarker with the capacity to reflect the severity of joint damage. The 'membrane attack complex' (MAC) component of complement has also been implicated in OA.

CONCLUSION

Novel OA biomarkers are needed for sub-clinical disease diagnosis. Proteomic techniques are beginning to yield useful data and deliver new OA biomarkers in serum and urine. Combining biochemical markers with tissue and cell imaging techniques and bioinformatics (i.e., machine learning, clustering, data visualization) may facilitate the development of biomarker combinations enabling earlier detection of OA.

Serum S100A8/A9, But Not Follistatin-like Protein 1 and Interleukin 18, May Be a Useful Biomarker of Disease Activity in Adult-onset Still’s Disease

Objective.

S100A8/A9, follistatin-like protein 1, and interleukin 18 (IL-18) have been suggested as biomarkers of disease activity in patients with systemic juvenile idiopathic arthritis or adult-onset Still’s disease (AOSD). We investigated the clinical significance of these factors in AOSD.

Methods.

Blood samples were collected from 36 patients with AOSD, 40 patients with rheumatoid arthritis (RA), and 33 healthy controls. Of the patients with AOSD, followup samples were collected from 16 patients after resolution of disease activity.

Results.

Serum levels of S100A8/A9 (11.77 ± 8.84 μg/ml) in AOSD patients were higher than those in RA patients (3.53 ± 3.43 μg/ml; p < 0.001) and controls (2.49 ± 1.83 μg/ml; p < 0.001). Follistatin-like protein 1 levels in AOSD were not different from those in RA and controls. IL-18 levels in AOSD (7560.3 ± 7577.6 pg/ml) were higher than those in RA (217.7 ± 292.1 pg/ml; p < 0.001) and controls (139.2 ± 86.2 pg/ml; p < 0.001). The sensitivity and specificity of IL-18 for diagnosing AOSD was highest with a cutoff value of 366.1 pg/ml. Serum S100A8/A9 correlated with leukocyte count, erythrocyte sedimentation rate, C-reactive protein, ferritin, and systemic disease score; however, IL-18 correlated only with ferritin and systemic disease score. S100A8/A9 was decreased after disease activity was resolved in followup of AOSD patients (9.96 ± 7.35 μg/ml in active AOSD vs 3.6 ± 4.77 μg/ml in resolved cases; p = 0.001). The change of S100A8/A9 was well correlated with that of systemic disease score.

Conclusion.

The data suggest that serum S100A8/A9 may be a useful biomarker for evaluating disease activity in patients with AOSD.

Follistatin-like protein 1: a serum biochemical marker reflecting the severity of joint damage in patients with osteoarthritis

Introduction

Follistatin-like protein 1 (FSTL1) is a secreted glycoprotein that has been implicated in arthritis pathogenesis in a mouse model. The aim of this study is to detect FSTL1 expression and to further assess its potential utility as a biomarker of joint damage in osteoarthritis (OA) patients.

Methods

FSTL1 expression was detected by real-time PCR, western blot and immunohistochemistry (IHC) in the synovial tissues (STs) and by IHC in the articular cartilage from OA patients and control trauma patients. The serum and synovial fluid (SF) FSTL1 concentrations were measured by ELISA in OA patients and control individuals. Linear regression analyses were used to assess correlations between the serum FSTL1 levels and the clinical characteristics in OA patients.

Results

The FSTL1 mRNA and protein levels were substantially elevated in the STs from OA patients compared with those from control trauma patients. The FSTL1 expression was strong in the cytoplasm of the synovial and capillary endothelial cells of the STs, but weak in the chondrocytes of the articular cartilage from OA patients. Furthermore, the serum and SF FSTL1 concentrations were significantly higher in OA patients than in respective control subjects. Interestingly, the serum and SF FSTL1 levels were markedly higher in female OA patients than in males. Importantly, bivariate regression analysis revealed that the serum FSTL1 levels in female OA patients had significant correlations with Kellgren and Lawrence (KL) grade, joint space narrowing (JSN) and the Western Ontario McMaster and Universities Osteoarthritis (WOMAC) stiffness subscale, an inverse correlation with height, and marginal correlations with the total WOMAC score and the WOMAC function subscale. Multivariate regression analysis revealed that the serum FSTL1 levels correlated independently with KL grade in female OA patients. Bivariate analysis also revealed that the serum FSTL1 levels correlated significantly with age and disease duration, and they correlated marginally with high sensitivity C-reactive protein (hs-CRP) and KL grade in male OA patients.

Conclusions

Increased FSTL1 expression may be a characteristic of OA patients. FSTL1 is a potential serum biomarker that may reflect the severity of joint damage, and further studies are required to evaluate its potential application for monitoring the course of the disease and the efficacy of therapies in OA patients.

Renal tubular dysgenesis and tubulointerstitial nephritis antigen in juvenile nephronophthisis

AIM

The relationship between abnormalities of tubular architecture and tubulointerstitial nephritis antigen (TIN-ag) in juvenile nephronophthisis (J-NPH) was evaluated.

METHODS

Sixteen J-NPH patients were examined. Nephrocystin-1, TIN-ag, type IV collagen, Fas antigen and the C5b-9 complement complex were stained by immunohistochemical methods.

RESULTS

Renal tubules of patients with J-NPH showed morphological abnormalities of tubular basement membranes (TBM) and frequent apoptosis of tubular epithelial cells. Additionally, the C5b-9 complement complex was deposited within the TBM in the absence of immunoglobulin deposition, suggesting complement-dependent TBM injury. Localization of TIN-ag in the TBM of J-NPH patients disclosed a partial defect or discontinuity in 14 of the 16 patients, while type IV collagen immunoreactivity was relatively preserved. These findings suggest that tubulogenesis is disturbed during nephronogenesis in J-NPH patients because of a defect in nephrocystin, an NPHP gene product. TBM defects induce further morphological abnormalities such as cystic dilation of tubules; as tubular function impairment advances, the incomplete tubules may be injured by C5b-9 complement complexes, followed by apoptotic cell death.

CONCLUSION

TIN-ag, which is important in early nephrogenesis, lacks normal activity, and vulnerable and incomplete tubules with deficient TIN-ag expression are formed. Removal of these defective tubules by apoptosis combined with the C5b-9 complement complex could be the primary reason for progression to end-stage renal disease in J-NPH patients.

FSTL1 promotes arthritis in mice by enhancing inflammatory cytokine/chemokine expression

OBJECTIVE

FSTL1 is a secreted glycoprotein that exacerbates murine arthritis and is overexpressed in human arthritis. The aim of this study was to determine the mechanism by which FSTL1 promotes arthritis.

METHODS

Collagen-induced arthritis was induced in mice hypomorphic for FSTL1, generated with a gene trap-targeted mutant embryonic stem cell line. Arthritis was assessed by measuring paw swelling and using a qualitative arthritis index. Bone marrow-derived mesenchymal stromal cells from hypomorphic mice, as well as mouse stromal ST2 cells transduced with short hairpin RNA to suppress FSTL1 expression, were stimulated with interleukin-1β (IL-1β), tumor necrosis factor α, and IL-17. The monocyte cell line U937, which does not express FSTL1, was transfected with a plasmid encoding FSTL1 and stimulated with phorbol myristate acetate and lipopolysaccharide. Cell supernatants were assayed for IL-6, IL-8, monocyte chemotactic protein 1 (MCP-1), and FSTL1 by enzyme-linked immunosorbent assay.

RESULTS

FSTL1 hypomorphic mice had reduced levels of FSTL1 compared to littermate controls. Following induction of arthritis, a significant correlation was observed between serum FSTL1 levels and both paw swelling and the arthritis index. Similar correlations were observed between the amount of FSTL1 produced by mesenchymal stromal cells, stromal ST2 cells, and monocytes and the secretion of IL-6, IL-8, and MCP-1.

CONCLUSION

These findings demonstrate that FSTL1 up-regulates proinflammatory mediators important in the pathology of arthritis, and that serum levels of FSTL1 correlate with severity of arthritis. The latter supports the possibility that FSTL1 might be a target for treatment of certain forms of arthritis.

Follistatin-like 1 suppresses sensory afferent transmission by activating Na+,K+-ATPase

Excitatory synaptic transmission is modulated by inhibitory neurotransmitters and neuromodulators. We found that the synaptic transmission of somatic sensory afferents can be rapidly regulated by a presynaptically secreted protein, follistatin-like 1 (FSTL1), which serves as a direct activator of Na(+),K(+)-ATPase (NKA). The FSTL1 protein is highly expressed in small-diameter neurons of the dorsal root ganglion (DRG). It is transported to axon terminals via small translucent vesicles and secreted in both spontaneous and depolarization-induced manners. Biochemical assays showed that FSTL1 binds to the α1 subunit of NKA and elevates NKA activity. Extracellular FSTL1 induced membrane hyperpolarization in cultured cells and inhibited afferent synaptic transmission in spinal cord slices by activating NKA. Genetic deletion of FSTL1 in small DRG neurons of mice resulted in enhanced afferent synaptic transmission and sensory hypersensitivity, which could be reduced by intrathecally applied FSTL1 protein. Thus, FSTL1-dependent activation of NKA regulates the threshold of somatic sensation.

Follistatin-like protein 1 is elevated in systemic autoimmune diseases and correlated with disease activity in patients with rheumatoid arthritis

Introduction

Follistatin-like protein 1 (FSTL1) is a proinflammation mediator implicated in arthritis in rodent animal models. The present study is aimed at assessing FSTL1 levels in systemic autoimmune diseases and correlating them with disease activity in patients with rheumatoid arthritis (RA).

Methods

Serum FSTL1 levels from 487 patients with systemic autoimmune diseases and 69 healthy individuals were measured by enzyme-linked immunosorbent assay (ELISA). FSTL1 expression in synovial fluid (SF) and synovial tissues (STs) was determined by ELISA, immunohistochemistry, real-time polymerase chain reaction (RT-PCR) and western blot analysis in RA patients and trauma controls. FSTL1 levels in fibroblast-like synoviocytes (FLSs) from RA patients were determined by real-time PCR and western blot analysis.

Results

Serum FSTL1 levels were significantly elevated in patients with RA, ulcerative colitis, systemic lupus erythematosus, Sjögren's syndrome (SS), systemic sclerosis and polymyositis/dermatomyositis. Serum FSTL1 levels in the RA and secondary SS patients were substantially higher than those in other patients. Serum FSTL1 levels were increased in early RA, rheumatoid factor (RF)- and anti-cyclic citrullinated peptide antibody (ACPA)-negative patients compared to healthy controls. Moreover, serum FSTL1 concentrations were significantly higher in long-standing RA patients than in early RA patients and in the RF- and ACPA-positive RA patients than in RF- and ACPA-negative RA patients. Elevated FSTL1 levels in the STs and SF of RA patients were also observed. FSTL1 levels in serum were markedly higher than those in SF in RA patients. The strongest FSTL1 staining was detected in the cytoplasm of synovial and capillary endothelial cells from RA synovium. Furthermore, FSTL1 was induced in FLSs by inflammatory mediators. Importantly, serum FSTL1 levels were correlated with several important biologic and clinical markers of disease activity, including erythrocyte sedimentation rate, C-reactive protein, RF, ACPA, swollen joint count, patient global visual analogue scale score and Disease Activity Score 28 in the adult RA patient population. Notably, serum FSTL1 levels were significantly diminished following successful treatment and clinical improvement.

Conclusions

Elevated FSTL1 levels reflect not only joint diseases but also inflammation and tissue degradation in systemic autoimmune diseases. Serum FSTL1 levels may thus serve as a serological inflammatory marker of disease activity in RA patients.

DIP2 disco-interacting protein 2 homolog A (Drosophila) is a candidate receptor for follistatin-related protein/follistatin-like 1--analysis of their binding with TGF-β superfamily proteins

Follistatin-related protein (FRP)/follistatin-like 1 (FSTL1) is a member of the follistatin protein family, all of which share a characteristic structure unit found in follistatin, called the FS domain. Developmental studies have suggested that FRP regulates organ tissue formation in embryos. Immunological studies showed that FRP modifies joint inflammation in arthritic disease, and modulates allograft tolerance. However, the principle physiological function of FRP is currently unknown. To address this issue, we cloned four FRP-associated proteins using a two-hybrid cloning method: disco-interacting protein 2 homolog A from Drosophila (DIP2A), CD14, glypican 1 and titin. Only DIP2A was expected to be a membrane receptor protein with intracellular regions. Over-expression of FLAG epitope-tagged DIP2A augmented the suppressive effect of FRP on FBJ murine osteosarcoma viral oncogene homolog (FOS) expression, and the Fab fragment of IgG to FLAG blocked this effect. Knockdown of Dip2a leaded to Fos gene up-regulation, and this was not affected by exogenous FRP. These in vitro experiments confirmed that DIP2A could be a cell-surface receptor protein and mediate a FOS down-regulation signal of FRP. Moreover, molecular interaction analyses using Biacore demonstrated that FRP bound to DIP2A and CD14, and also with proteins of the TGF-β superfamily, i.e. activin, TGF-β, bone morphogenetic protein 2/4 (BMP-2/4), their receptors and follistatin. FRP binding to DIP2A was blocked by CD14, follistatin, activin and BMP-2. FRP blocked the ligand-receptor binding of activin and BMP-2, but integrated itself with that of BMP-4. This multi-specific binding may reflect the broad physiological activity of FRP.

Follistatin-like 1 regulates renal IL-1β expression in cisplatin nephrotoxicity

Follistatin-like 1 (FSTL1) is a secreted protein with homology to both Follistatin and the SPARC/BM40 family of matricellular proteins. In this study, we sought to determine the expression patterns of Fstl1 and its cognate receptor Dip2a in the adult, and to assess the consequences of Fstl1 inactivation on development and homeostasis of the kidney. We find that FSTL1 circulates at high levels in both the human and the mouse and that it is also locally expressed in the loop of Henle in the kidney. To begin to understand the in vivo functions of Fstl1, we generated a mouse mutant using a genetrap approach. The hypomorphic Fstl1 genetrap strain displays a strong reduction in FSTL1 expression at the protein level, but it does not show overt developmental defects. FSTL1 has previously been implicated in diverse disease processes as a regulator of inflammatory cytokine expression, and we therefore evaluated the response of the genetrap strain to cisplatin-mediated acute kidney injury, a disease model with highly cytokine-dependent pathology. We find that although TNF-α and Il6 levels are unchanged relative to wild-type, renal Il-1β expression is increased in genetrap mice following cisplatin treatment. Furthermore, histopatological analysis, expression of the tissue injury marker Havcr1, and measurement of serum creatinine demonstrate that reduction of Fstl1 expression sensitizes the kidney to acute cisplatin nephrotoxicity, suggesting a role for FSTL1-mediated Il-1β suppression in protection of the kidney from acute nephrotoxic injury.

Follistatin-like protein 1 is a mesenchyme-derived inflammatory protein and may represent a biomarker for systemic-onset juvenile rheumatoid arthritis

OBJECTIVE

To examine both the source of follistatin-like protein 1 (FSTL-1) and the factors that induce its expression in arthritis, and to determine whether juvenile rheumatoid arthritis (JRA) is characterized by overexpression of FSTL-1.

METHODS

FSTL-1 expression patterns were analyzed by immunohistochemical staining of joint tissue derived from mice with collagen-induced arthritis. Induction of FSTL-1 secretion was assessed in osteoblasts, adipocytes, and human fibroblast-like synoviocytes in response to transforming growth factor beta (TGFbeta), interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNFalpha), and IL-6. In addition, sera and synovial fluid from children with oligoarticular, polyarticular, or systemic-onset JRA were assayed for FSTL-1 using a custom enzyme-linked immunosorbent assay. FSTL-1 concentrations in these patients were assessed for correlations with the erythrocyte sedimentation rate (ESR) and platelet count.

RESULTS

Immunohistochemical staining of murine joint sections demonstrated expression of FSTL-1 in all cell types of the mesenchymal lineage, including osteocytes, chondrocytes, adipocytes, and fibroblasts. FSTL-1 could be induced in osteoblasts, adipocytes, and human fibroblast-like synoviocytes by TGFbeta, IL-1beta, TNFalpha, and IL-6. The IL-1beta response was significantly greater than the TNFalpha response (P < 0.05). In human serum and synovial fluid, only those samples from children with the systemic-onset JRA subtype had elevated concentrations of FSTL-1. The synovial fluid concentrations of FSTL-1 were 2-3-fold higher than the serum concentrations. The elevation in serum FSTL-1 concentrations seen in children with systemic-onset JRA correlated closely with elevations in the ESR and platelet count.

CONCLUSION

These findings demonstrate that the arthritic joint matrix is a major source of FSTL-1 and that IL-1beta is a central mediator of FSTL-1 secretion. Furthermore, FSTL-1 may represent a useful biomarker of disease activity in systemic-onset JRA.

Downregulated expression of the secreted glycoprotein follistatin-like 1 (Fstl1) is a robust hallmark of preadipocyte to adipocyte conversion

Obesity is a public health crisis in the United States. Targeting preadipocyte to adipocyte conversion may be an effective approach to regulate adipose mass. Using differential screening we identified Fstl1, a secreted glycoprotein with roles in immunomodulation, cell growth, cardioprotection, and vascularization, as a "preadipokine". Fstl1 is highly expressed in 3T3-L1 preadipocytes and dramatically downregulated early in their differentiation to adipocytes. Northern blot analysis of murine tissues reveals white adipose tissue (WAT), lung and heart as primary sites of Fstl1 transcript expression. In WAT, Fstl1 transcript is restricted to the preadipocyte-containing stromal-vascular cell population. Time course studies in multiple adipogenesis models reveal downregulation of Fstl1 is a hallmark of white and brown adipocyte conversion. By Western blot, we show culture media of 3T3-L1 preadipocytes contains high levels of Fstl1 protein that rapidly decline in adipocyte conversion. Moreover, we observe a correlation between preadipocyte phenotype and Fstl1 expression in that TNFalpha-mediated de-differentiation of 3T3-L1 adipocytes is accompanied by re-expression of Fstl1 transcript and protein. Treatment of 3T3-L1 preadipocytes with a panel of 18 hormones and other agents revealed the demethylating agent 5-aza-cytidine decreases Fstl1 transcript and protein levels by approximately 90%. Furthermore, of 10 additional preadipocyte-expressed genes analyzed we find Pref-1, Col1A1, Sca-1/Ly6a, Lox and Thbs2, are also downregulated by 5-aza-cytidine. Using luciferase reporter constructs containing 791 or 3922 bp of the Fstl1 5' flanking region, we determine negative transcriptional regulation by Kruppel-like factor 15. Together, our data suggest downregulation of Fstl1 expression may be an important feature of preadipocyte to adipocyte conversion.

Circulating Concentrations of Follistatin-Like 1 in Healthy Individuals and Patients with Acute Coronary Syndrome as Assessed by an Immunoluminometric Sandwich Assay

Background: Follistatin-like 1 (FSTL1) is a 308–amino acid secreted glycoprotein. Tissue levels of FSTL1 are induced in animal models and patients with chronic inflammatory and cardiovascular disease. We hypothesized that FSTL1 can be measured in the human circulation and used as a biomarker in acute coronary syndrome (ACS).

Methods: We developed an immunoluminometric assay (ILMA), assessed the preanalytic characteristics of FSTL1, and determined circulating FSTL1 concentrations in 120 apparently healthy individuals and 216 patients with ACS.

Results: The assay had a limit of detection of 0.17 μg/L, limit of quantification of 1.02 μg/L, intraassay imprecision of ≤12.7%, and interassay imprecision of ≤15.4%. Selectivity was demonstrated with size-exclusion chromatography and lack of cross-reactivity with related proteins. The assay was not appreciably influenced by unrelated biological substances. FSTL1 in serum or whole blood was stable at room temperature for 48 h and was resistant to 4 freeze-thaw cycles. Measured FSTL1 concentrations in citrated plasma and heparin-treated plasma were 18% and 17% lower, respectively, than concentrations measured in serum. Apparently healthy individuals presented with a median FSTL1 serum concentration of 7.18 (range 1.06–18.49) μg/L. Serum FSTL1 concentrations were increased in ACS and related to the risk of all-cause mortality during follow-up.

Conclusions: The ILMA permits detection of FSTL1 in human serum and plasma. We expect that the favorable preanalytic characteristics of FSTL1 and the reference limits defined here for apparently healthy individuals will facilitate future studies of FSTL1 as a biomarker in various disease settings, including ACS.

Follistatin-like protein 1 promotes arthritis by up-regulating IFN-gamma

Follistatin-like protein-1 (FSTL-1) is a poorly characterized protein that is up-regulated in the early stage of collagen-induced arthritis and that exacerbates arthritis when delivered by gene transfer. The current study was designed to determine the mechanism by which FSTL-1 promotes arthritis. FSTL-1 was injected into mouse paws, resulting in severe paw swelling associated with up-regulation of IFN-gamma transcript and the IFN-gamma-induced chemokine, CXCL10. Mice depleted of T cells were protected. A central role for IFN-gamma was confirmed by the finding that mice deficient in IFN-gamma failed to exhibit paw swelling in response to injection of FSTL-1. Furthermore, IFN-gamma secretion from mouse spleen cells exposed to a weak TCR signal was increased 5-fold in the presence of FSTL-1. FSTL-1 could be induced by innate immune signals, including TLR4 agonists and the arthritogenic cytokine, IL-1beta, via an NFkappaB pathway. Finally, FSTL-1 was found to be overexpressed in human arthritis and its neutralization inhibited murine collagen-induced arthritis and suppressed IFN-gamma and CXCL10 production in arthritic joints. These findings demonstrate that FSTL-1 plays a critical role in arthritis by enhancing IFN-gamma signaling pathways and suggest a mechanism by which FSTL-1 bridges innate and adaptive immune responses.

miR-198 inhibits HIV-1 gene expression and replication in monocytes and its mechanism of action appears to involve repression of cyclin T1

Cyclin T1 is a regulatory subunit of a general RNA polymerase II elongation factor known as P-TEFb. Cyclin T1 is also required for Tat transactivation of HIV-1 LTR-directed gene expression. Translation of Cyclin T1 mRNA has been shown to be repressed in human monocytes, and this repression is relieved when cells differentiate to macrophages. We identified miR-198 as a microRNA (miRNA) that is strongly down-regulated when monocytes are induced to differentiate. Ectopic expression of miR-198 in tissue culture cells reduced Cyclin T1 protein expression, and plasmid reporter assays verified miR-198 target sequences in the 3′ untranslated region (3′UTR) of Cyclin T1 mRNA. Cyclin T1 protein levels increased when an inhibitor of miR-198 was transfected into primary monocytes, and overexpression of miR-198 in primary monocytes repressed the normal up-regulation of Cyclin T1 during differentiation. Expression of an HIV-1 proviral plasmid and HIV-1 replication were repressed in a monocytic cell line upon overexpression of miR-198. Our data indicate that miR-198 functions to restrict HIV-1 replication in monocytes, and its mechanism of action appears to involve repression of Cyclin T1 expression.

Monocytes do not support HIV-1 replication, in part because they do not express adequate levels of essential cellular cofactors that mediate steps in the viral replication cycle. Monocytes become permissive for viral replication upon differentiation to macrophages, indicating that cellular cofactors are induced during the differentiation process. One such cofactor is Cyclin T1, which is not expressed in monocytes and is expressed at high levels following macrophage differentiation. Cyclin T1 functions to greatly stimulate the amount of HIV-1 produced in the infected cell. We identified a microRNA (miRNA) named miR-198 that represses the expression of Cyclin T1 in monocytes. miRNAs block expression of proteins by binding to messenger RNAs and preventing their translation by ribosomes. The expression levels of miR-198 are greatly reduced in macrophages, and this appears to allow translation of Cyclin T1 mRNA and expression of Cyclin T1 protein. Our study indicates that this miRNA restricts HIV-1 replication in monocytes. We think that it is possible, if not likely, that additional miRNAs in monocytes also restrict HIV-1 replication by repressing other essential cellular cofactors.

An immunomodulatory role for follistatin-like 1 in heart allograft transplantation

Donor-specific tolerance to heart allografts in the rat can be achieved by donor-specific blood transfusions (DST) before transplantation. We have previously reported that this tolerance is associated with strong leukocyte infiltration, and that host CD8(+) T cells and TGFbeta are required. In order to identify new molecules involved in the induction phase of tolerance, we compared tolerated and rejected heart allografts (suppressive subtractive hybridization) 5 days after transplantation. We identified overexpression of Follistatin-like 1 (FSTL1) transcript in tolerated allografts compared to rejected allografts or syngeneic grafts. We show that FSTL1 is overexpressed during both the induction and maintenance phase of tolerance, and appears to be specific to the tolerance model induced by DST. Analysis of graft-infiltrating cells revealed predominant expression of FSTL1 in CD8(+) T cells from tolerated grafts, and depletion of these cells prior to transplantation abrogated FSTL1 expression and heart allograft survival. Moreover, overexpression of FSTL1 by adenovirus gene transfer in vivo significantly prolonged allograft survival in association with inhibition of the proinflammatory cytokines, IL6, IL17 A and IFNgamma. Taken together, these results suggest that FSTL1 could be an active component of the mechanisms mediating heart allograft tolerance.

Follistatin-like protein-1 is a novel proinflammatory molecule

While analyzing gene expression in collagen-induced arthritis, we discovered that a poorly characterized gene, follistatin-like protein 1 (FSTL-1), is highly overexpressed in mouse paws during early arthritis, especially at the interface of synovial pannus and eroding bone. In this study, we show that FSTL-1 is a novel proinflammatory molecule with a previously unrecognized role in inflammation. Transfection of FSTL-1 into macrophages and fibroblasts leads to up-regulation of proinflammatory cytokines, including IL-1beta, TNF-alpha, and IL-6. Overexpression of FSTL-1 in mouse paws by gene transfer results in severe paw swelling and arthritis.

Identification of a follistatin-related protein from the tick Haemaphysalis longicornis and its effect on tick oviposition

The identification of ovary-associated molecules will lead to a better understanding of the physiology of tick reproduction and vector-pathogen interactions. A gene encoding a follistatin-related protein (FRP) was obtained by random sequencing from the ovary cDNA library of the tick Haemaphysalis longicornis. The full-length cDNA is 1157 bp, including an intact ORF encoding an expected protein with 289 amino acids. Three distinct domains were present in the deduced amino acids, namely, the follistatin-like domain, KAZAL, and two calcium-binding motifs, EFh. The sequence shows homology with the follistatin-related protein (FRP), which was thought to play some roles in the negative regulation of cellular growth. RT-PCR showed that the gene was expressed throughout the developing stages and mainly in the ovary as well as in fat body, hemocytes, salivary glands, and midgut. This gene was expressed in GST-fused recombinant protein with an expected size. The mouse antiserum against the recombinant protein recognized a 56-kDa native protein in both tick ovary and hemolymph. The recombinant proteins were found to have binding activity for both activin A and bone morphogenetic protein-2 (BMP-2). Silencing of FRP by RNAi showed a decrease in tick oviposition, which is consistent with the effect of a recombinant protein vaccine on the adult tick. These results showed that the tick FRP might be involved in tick oviposition. This is the first report of a member of follistatin family proteins in Chelicerata, which include ticks, spiders, and scorpions.