Deficiency of Follistatin-Like Protein 1 Accelerates the Growth of Breast Cancer Cells at Lung Metastatic Sites

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.

The Association between Serum Follistatin-like Proteins and Cardiovascular Diseases: A Systematic Review and Meta-analysis

BACKGROUND

Follistatin-like proteins (FSTLs) are adipomyokines secreted by adipocytes and myocytes. Previous studies have reported an increase in circulating FSTL1 levels in response to cardiovascular injuries. In this study, we conducted a systematic review and metaanalysis to assess the association between circulating FSTLs and Cardiovascular Diseases (CVDs).

METHODS

We performed a comprehensive literature search using PubMed, Web of Science, Scopus, and Embase databases. After screening the articles, we selected eligible studies, extracted relevant data, and calculated the pooled Standardized Mean Difference (SMD). We also conducted a sensitivity analysis to identify sources of heterogeneity and assessed publication bias.

RESULTS

Among the 577 articles initially retrieved, we included 5 studies comprising a total of 941 cases with CVDs and 446 controls. All included studies measured FSTL1 levels. The pooled SMD analysis revealed a significant difference in circulating FSTL1 levels between subjects with CVDs and control groups (SMD = 0.853, 95% CI = 0.158-1.548, P = 0.016). Heterogeneity was primarily attributed to a single study that measured FSTL1 levels in heart failure patients with preserved ejection fraction. No publication bias was observed.

CONCLUSION

Our findings demonstrate significantly higher levels of FSTL1 in patients with CVD compared to control subjects. This suggests that FSTL1 may have potential as a diagnostic and prognostic biomarker in CVDs. However, further well-designed studies are needed to validate its clinical utility.

FSTL1 Suppresses Triple-Negative Breast Cancer Lung Metastasis by Inhibiting M2-like Tumor-Associated Macrophage Recruitment toward the Lungs

Immune cell infiltration into the tumor microenvironment is associated with cancer prognosis. Tumor-associated macrophages play essential roles in tumor initiation, progression, and metastasis. Follistatin-like protein 1 (FSTL1), a widely expressed glycoprotein in human and mouse tissues, is a tumor suppressor in various cancers and a regulator of macrophage polarization. However, the mechanism by which FSTL1 affects crosstalk between breast cancer cells and macrophages remains unclear. By analyzing public data, we found that FSTL1 expression was significantly low in breast cancer tissues compared to normal breast tissues, and high expression of FSTL1 in patients indicated prolonged survival. Using flow cytometry, we found that total and M2-like macrophages dramatically increased in the metastatic lung tissues during breast cancer lung metastasis in Fstl1+/- mice. Transwell assay in vitro and q-PCR experimental results showed that FSTL1 inhibited macrophage migration toward 4T1 cells by decreasing CSF1, VEGF-α, and TGF-β secretion in 4T1 cells. We demonstrated that FSTL1 inhibited M2-like tumor-associated macrophage recruitment toward the lungs by suppressing CSF1, VEGF-α, and TGF-β secretion in 4T1 cells. Therefore, we identified a potential therapeutic strategy for triple-negative breast cancer.

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.

Follistatin-like 1 deficiency impairs T cell development to promote lung metastasis of triple negative breast cancer

Our study aims to detect the underlying mechanism of the suppressive effect of Follistatin-like 1 (FSTL1) on lung metastasis of triple negative breast cancer (TNBC). We found that FSTL1 had no effect on the proliferation and metastasis of 4T1 cells in vitro, while in the tumor-bearing Fstl1 heterozygous (Fstl1^+/-) mice, the number of anti-tumor T lymphocytes in the lung was significantly reduced with the increase in lung metastasis. Impaired development of T cells can cause dysfunction of adaptive immune system, which promotes cancer metastasis. Therefore the effect of FSTL1 on T cell development was further investigated. Lower population of T cells in periphery and decreased proliferation of CD4^- CD8^- double negative (DN) thymocytes and impairment development of T cells were found in Fstl1^+/- mice. Furthermore, high expression of FSTL1 in medullary thymus epithelial (mTEC) cells and decreased mRNA expression of inducible costimulator on activated T-cell ligand (Icosl) in mTEC^{sh Fstl1} were detected. Combining other studies that the generation of ICOSL by mTEC cells promotes CD4⁺ single positive (SP) thymocytes to produce IL-2, which promotes T cell development. Our results indicate FSTL1 deficiency in mTEC cells impairs T cell development to promote the lung metastasis of TNBC.

The glycoprotein follistatin-like 1 promotes brown adipose thermogenesis

OBJECTIVES

The thermogenic brown adipose tissue (BAT) has been proposed as a potential target to prevent or treat obesity and related metabolic diseases. BAT secretes adipokines to regulate the thermogenic program in an autocrine or paracrine manner. Follistatin-like 1 (FSTL1), a glycoprotein involved in adipogenesis and obesity, however, the function of FSTL1 in BAT thermogenesis and in the regulation of systemic energy homeostasis are not fully understood.

METHODS

Whole-body ablation Fstl1 heterozygous mice (Fstl1^+/-) and its littermates control were injected with CL316,243 to assess energy balance. A series of FSTL1 overexpression and knockdown experiments were carried out to evaluate its function in regulating thermogenic gene expression in brown adipocytes.

RESULTS

FSTL1 expression was induced upon BAT activation during cold challenge or β3-adrenergic activation. FSTL1 haploinsufficiency in mice led to reduced thermogenic gene expression, impaired BAT recruitment, and decreased heat production. FSTL1 cell-autonomously promoted the β3-adrenergic signaling, which was required to upregulate PPARγ and UCP1 in brown adipocytes. Furthermore, only glycosylated FSTL1 could be secreted from brown adipocytes to induce the β3-adrenergic activation.

CONCLUSIONS

Our results suggest FSTL1 as a novel stimulator of the β-adrenergic signaling and BAT thermogenesis.

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.