Cofilin-1 promotes fibrocyte differentiation and contributes to pulmonary fibrosis
Introduction
Fibrocytes, which originate from bone marrow, can develop into different effector cells outside the circulation depending on the local tissue environment [1]. They can be identified by detecting the expression of CD34 and/or CD45 and collagen production [2]. Fibrocytes are important cells in the process of pulmonary fibrogenesis [3]. Heukels et al. found that fibrocytes were increased in lung tissues and peripheral blood from patients with idiopathic pulmonary fibrosis (IPF) [4]. Moeller et al. further confirmed that higher counts of circulating fibrocytes are indicators of worse prognosis in IPF patients [5]. Fibrocytes can promote pulmonary fibrosis by differentiating into myofibroblasts or inducing resident mesenchymal cells to differentiate into myofibroblasts [6]. They can also express mRNA encoding chains of collagens, especially collagen VI [7], which suggests that fibrocytes may accelerate pulmonary fibrosis by producing collagen directly. However, some studies have indicated that fibrocytes are not the main sources of collagen compared with myofibroblasts and fibroblasts [6,8]. Recently, Chen et al. demonstrated that exosomes released from fibrocytes could induce recipient cells to express collagen and α-SMA [9], which indicates a new mechanism in the fibrosis process. However, research thus far is still limited in providing a comprehensive picture of fibrocytes and their roles in the pathogenesis of pulmonary fibrosis, especially regarding their differentiation and related regulators.
Cofilin-1 (CFL-1), a small (∼18.5 kDa) ubiquitous protein of the ADF/Cofilin family, regulates actin dynamics by binding and severing actin filaments during cell migration [10], especially in the invasion and motility of tumor cells [11]. CFL-1 also participates in cell proliferation, phagocytosis, chemotactic movement and micropinocytosis [12,13]. CFL-1 has been identified as a novel biomarker for myofibroblasts and functionally contributes to extracellular matrix (ECM) remodeling in valve interstitial cells [14]. Additionally, CFL-1 is significantly upregulated in paraquat-induced lung fibrosis [15]. Therefore, CFL-1 probably plays a role in pulmonary fibrosis. The specific mechanism of CFL in the process of pulmonary fibrosis is unclear, and whether it is associated with fibrocyte differentiation needs exploration.
To investigate the role of CFL-1 in pulmonary fibrosis and study its effect on fibrocyte differentiation, we tested the expression of CFL-1 and measured the counts of fibrocytes in patients with IPF or connective tissue disease-associated interstitial lung disease (CTD-ILD) and in mice with pulmonary fibrosis induced by bleomycin. We then further confirmed the relationship between CFL-1 and fibrocyte differentiation by changing the expression of CFL-1 in vivo and in vitro. Our study may provide new insight toward a better understanding of the disease and suggest potential therapeutic targets.
Section snippets
Human subjects
All human studies were performed with approval from the Human Investigations Committee of the Second Xiangya Hospital of Central-South University. Diagnoses of patients with IPF or CTD-ILD were based on current consensus guidelines. Healthy, age-matched controls were recruited from the Hunan Province area. Participants provided written informed consent.
Reagents and antibodies
DMEM was purchased from HyClone (USA). Fetal bovine serum (FBS) was acquired from Gibco-BRL (USA). FITC mouse-anti-human CD45 and FITC
Expression of CFL-1 and the percentages of fibrocytes in PBMCs were increased in IPF and CTD-ILD patients
To determine the expression of CFL-1 in patients with pulmonary fibrosis, we performed ELISA, Western blotting, and RT-PCR on 28 pairs of IPF or CTD-ILD patients and healthy age-matched controls. The expression of CFL-1 was significantly increased in the plasma of IPF and CTD-ILD patients compared with the controls (Fig. 1A). Both the mRNA and protein levels of CFL-1 were significantly higher in the PBMCs from IPF and CTD-ILD patients than in those isolated from the controls (Fig. 1B and C),
Discussion
In this study, we found that the expression of CFL-1 was substantially increased in a cohort of human subjects with pulmonary fibrosis and in a mouse model of pulmonary fibrosis induced by bleomycin. Using both cell experiments and murine experiments with pulmonary fibrosis caused by bleomycin, we further found that reducing CFL-1 levels could impede the differentiation of peripheral blood monocytes into fibrocytes and alleviate pulmonary fibrosis.
Currently, the role of CFL-1 in the
Ethics statement
All human studies were performed with approval form the Human Investigations Committee of the Second Xiangya Hospital of Central-South University. Participants have provided with written informed consent. The animals studies were approved by Institutional Animal Care and Use committee of the Second Xiangya Hospital of Central-South University.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 81370164 and No. 81670062), the National Natural Science Foundation of Hunan Province (No. 2015JJ4087 and No. 2020JJ8070), the National key clinical specialist construction Programs of China, the Fundamental Research Funds for the Central Universities of Central South University (No. 2020zzts880), and the China Scholarship Council (No. 201906370238).
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These authors have contributed equally to this work and share first authorship.