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

Comprehensive profiling of extracellular vesicles in uveitis and scleritis enables biomarker discovery and mechanism exploration

BACKGROUND

Uveitis and posterior scleritis are sight-threatening diseases with undefined pathogenesis and accurate diagnosis remains challenging.

METHODS

Two plasma-derived extracellular vesicle (EV) subpopulations, small and large EVs, obtained from patients with ankylosing spondylitis-related uveitis, Behcet's disease uveitis, Vogt-Koyanagi-Harada syndrome, and posterior scleritis were subjected to proteomics analysis alongside plasma using SWATH-MS. A comprehensive bioinformatics analysis was performed on the proteomic profiles of sEVs, lEVs, and plasma. Candidate biomarkers were validated in a new cohort using ELISA. Pearson correlation analysis was performed to analyze the relationship between clinical parameters and proteomic data. Connectivity map database was used to predict therapeutic agents.

RESULTS

In total, 3,668 proteins were identified and over 3000 proteins were quantified from 278 samples. When comparing diseased group to healthy control, the proteomic profiles of the two EV subgroups were more correlated with disease than plasma. Comprehensive bioinformatics analysis highlighted potential pathogenic mechanisms for these diseases. Potential biomarker panels for four diseases were identified and validated. We found a negative correlation between plasma endothelin-converting enzyme 1 level and mean retinal thickness. Potential therapeutic drugs were proposed, and their targets were identified.

CONCLUSIONS

This study provides a proteomic landscape of plasma and EVs involved in ankylosing spondylitis-related uveitis, Behcet's disease uveitis, Vogt-Koyanagi-Harada syndrome, and posterior scleritis, offers insights into disease pathogenesis, identifies valuable biomarker candidates, and proposes promising therapeutic agents.

Follistatin-Like Proteins: Structure, Functions and Biomedical Importance

Main forms of cellular signal transmission are known to be autocrine and paracrine signaling. Several cells secrete messengers called autocrine or paracrine agents that can bind the corresponding receptors on the surface of the cells themselves or their microenvironment. Follistatin and follistatin-like proteins can be called one of the most important bifunctional messengers capable of displaying both autocrine and paracrine activity. Whilst they are not as diverse as protein hormones or protein kinases, there are only five types of proteins. However, unlike protein kinases, there are no minor proteins among them; each follistatin-like protein performs an important physiological function. These proteins are involved in a variety of signaling pathways and biological processes, having the ability to bind to receptors such as DIP2A, TLR4, BMP and some others. The activation or experimentally induced knockout of the protein-coding genes often leads to fatal consequences for individual cells and the whole body as follistatin-like proteins indirectly regulate the cell cycle, tissue differentiation, metabolic pathways, and participate in the transmission chains of the pro-inflammatory intracellular signal. Abnormal course of these processes can cause the development of oncology or apoptosis, programmed cell death. There is still no comprehensive understanding of the spectrum of mechanisms of action of follistatin-like proteins, so the systematization and study of their cellular functions and regulation is an important direction of modern molecular and cell biology. Therefore, this review focuses on follistatin-related proteins that affect multiple targets and have direct or indirect effects on cellular signaling pathways, as well as to characterize the directions of their practical application in the field of biomedicine.

Regulation of Pulmonary Bacterial Immunity by Follistatin-Like Protein 1

Klebsiella pneumoniae is a common cause of antibiotic-resistant pneumonia. Follistatin-like protein 1 (FSTL-1) is highly expressed in the lung and is critical for lung homeostasis. The role of FSTL-1 in immunity to bacterial pneumonia is unknown. Wild-type (WT) and FSTL-1 hypomorphic (Hypo) mice were infected with Klebsiella pneumoniae to determine infectious burden, immune cell abundance, and cytokine production. FSTL-1 Hypo/TCRδ^-/- and FSTL-1 Hypo/IL17ra^-/- were also generated to assess the role of γδT17 cells in this model. FSTL-1 Hypo mice had reduced K. pneumoniae lung burden compared with that of WT controls. FSTL-1 Hypo mice had increased Il17a/interleukin-17A (IL-17A) and IL-17-dependent cytokine expression. FSTL-1 Hypo lungs also had increased IL-17A⁺ and TCRγδ⁺ cells. FSTL-1 Hypo/TCRδ^-/- displayed a lung burden similar to that of FSTL-1 Hypo and reduced lung burden compared with the TCRδ^-/- controls. However, FSTL-1 Hypo/TCRδ^-/- mice had greater bacterial dissemination than FSTL-1 Hypo mice, suggesting that gamma delta T (γδT) cells are dispensable for FSTL-1 Hypo control of pulmonary infection but are required for dissemination control. Confusing these observations, FSTL-1 Hypo/TCRδ^-/- lungs had an increased percentage of IL-17A-producing cells compared with that of TCRδ^-/- mice. Removal of IL-17A signaling in the FSTL-1 Hypo mouse resulted in an increased lung burden. These findings identify a novel role for FSTL-1 in innate lung immunity to bacterial infection, suggesting that FSTL-1 influences type-17 pulmonary bacterial immunity.

FSTL-1 Attenuation Causes Spontaneous Smoke-Resistant Pulmonary Emphysema

Rationale: The role of FSTL-1 (follistatin-like 1) in lung homeostasis is unknown.Objectives: We aimed to define the impact of FSTL-1 attenuation on lung structure and function and to identify FSTL-1-regulated transcriptional pathways in the lung. Further, we aimed to analyze the association of FSTL-1 SNPs with lung disease.Methods: FSTL-1 hypomorphic (FSTL-1 Hypo) mice underwent lung morphometry, pulmonary function testing, and micro-computed tomography. Fstl1 expression was determined in wild-type lung cell populations from three independent research groups. RNA sequencing of wild-type and FSTL-1 Hypo mice identified FSTL-1-regulated gene expression, followed by validation and mechanistic in vitro examination. FSTL1 SNP analysis was performed in the COPDGene (Genetic Epidemiology of Chronic Obstructive Pulmonary Disease) cohort.Measurements and Main Results: FSTL-1 Hypo mice developed spontaneous emphysema, independent of smoke exposure. Fstl1 is highly expressed in the lung by mesenchymal and endothelial cells but not immune cells. RNA sequencing of whole lung identified 33 FSTL-1-regulated genes, including Nr4a1, an orphan nuclear hormone receptor that negatively regulates NF-κB (nuclear factor-κB) signaling. In vitro, recombinant FSTL-1 treatment of macrophages attenuated NF-κB p65 phosphorylation in an Nr4a1-dependent manner. Within the COPDGene cohort, several SNPs in the FSTL1 region corresponded to chronic obstructive pulmonary disease and lung function.Conclusions: This work identifies a novel role for FSTL-1 protecting against emphysema development independent of smoke exposure. This FSTL-1-deficient emphysema implicates regulation of immune tolerance in lung macrophages through Nr4a1. Further study of the mechanisms involving FSTL-1 in lung homeostasis, immune regulation, and NF-κB signaling may provide additional insight into the pathophysiology of emphysema and inflammatory lung diseases.

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.

Downregulation of FSTL‑1 attenuates the inflammation injury during Streptococcus pneumoniae infection by inhibiting the NLRP3 and TLR4/NF‑κB signaling pathway

Streptococcus pneumoniae‑induced pneumonia is a common disease and major cause of community‑acquired pneumonia. Previous studies have shown that Follistatin‑like protein 1 (FSTL‑1) serves important roles in regulating the inflammatory response. The present study aimed to investigate the effect of FSTL‑1 on the inflammatory response during S. pneumoniae infection using in vitro and in vivo models. ELISAs were used to detect the production of interleukin (IL)‑1β, tumor necrosis factor‑α and IL‑6. Western blotting and reverse transcription‑quantitative PCR were performed to determine the protein and mRNA expression of these factors. The results of the present study indicated that S. pneumoniae infection triggered a strong proinflammatory response and a high level of FSTL‑1 expression in mouse bone marrow‑derived macrophages. Moreover, FSTL‑1 may be required for the production of inflammatory factors during S. pneumoniae infection by regulating nucleotide oligomerization domain‑like receptor protein 3 in vitro and in vivo. In addition, it was found that the Toll‑like receptor 4/nuclear factor‑κB signaling pathway was involved in the inflammatory response regulated by FSTL‑1. The findings of the present study suggested that FSTL‑1 plays an important role in the inflammatory response during S. pneumoniae infection, providing a potential therapeutic target for reducing morbidity and mortality in patients with pneumonia.

Potential role of the IL17RC gene in the thoracic ossification of the posterior longitudinal ligament

The thoracic ossification of the posterior longitudinal ligament (T-OPLL) can cause thoracic spinal stenosis, which results in intractable myelopathy and radiculopathy. Our previous whole-genome sequencing study first reported rs199772854 in the interleukin 17 receptor C (IL17RC) gene as a potentially pathogenic loci for T-OPLL. The aim of the present study was to examine the effects of the IL17RC gene rs199772854A site mutation on osteogenesis by establishing a model of osteogenic differentiation. IL17RC gene mutation site and wild-type site mouse embryonic osteoblast (3T3-E1) models were constructed in order to induce the differentiation of the cells into osteoblasts. Whether the mutation site causes the abnormal expression of the IL17RC gene and osteogenic markers was analyzed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis. The IL17RC gene rs199772854A site mutation was demonstrated to play a biological role through the overexpression of its own gene, and also to significantly increase the expression levels of osteogenic markers. Furthermore, the mutation upregulated the expression of the key proteins, tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) and nuclear factor (NF)-κB, in the interleukin (IL)-17 signaling axis. On the whole, the findings of this study suggest that the IL17RC gene rs199772854A loci mutation propels mouse embryonic osteoblasts towards osteogenic differentiation and may play an important role in the pathogenesis of T-OPLL. The IL17RC gene may promote osteogenesis through the IL-17 signaling pathway and may thus be involved in the process of ectopic osteogenesis in T-OPLL.

Hepatic expression profiling identifies steatosis-independent and steatosis-driven advanced fibrosis genes

Chronic liver disease (CLD) is associated with tissue-destructive fibrosis. Considering that common mechanisms drive fibrosis across etiologies, and that steatosis is an important cofactor for pathology, we performed RNA sequencing on liver biopsies of patients with different fibrosis stages, resulting from infection with hepatitis C virus (HCV) (with or without steatosis) or fatty liver disease. In combination with enhanced liver fibrosis score correlation analysis, we reveal a common set of genes associated with advanced fibrosis, as exemplified by those encoding the transcription factor ETS-homologous factor (EHF) and the extracellular matrix protein versican (VCAN). We identified 17 fibrosis-associated genes as candidate EHF targets and demonstrated that EHF regulates multiple fibrosis-associated genes, including VCAN, in hepatic stellate cells. Serum VCAN levels were also elevated in advanced fibrosis patients. Comparing biopsies from patients with HCV with or without steatosis, we identified a steatosis-enriched gene set associated with advanced fibrosis, validating follistatin-like protein 1 (FSTL1) as an exemplar of this profile. In patients with advanced fibrosis, serum FSTL1 levels were elevated in those with steatosis (versus those without). Liver Fstl1 mRNA levels were also elevated in murine CLD models. We thus reveal a common gene signature for CLD-associated liver fibrosis and potential biomarkers and/or targets for steatosis-associated liver fibrosis.