Syndecan-1 regulates extracellular matrix expression in keloid fibroblasts via TGF-β1/Smad and MAPK signaling pathways

Highlights

• The overexpression of syndecan-1 in keloid tissues and fibroblasts.

• Knockdown of syndecan-1 could suppress cell proliferation in keloid fibroblasts.

• Extracellular matrix expression is positively correlated with syndecan-1 level in keloid fibroblasts.

• Syndecan-1 regulates extracellular matrix expression in keloid fibroblasts via TGF-β1/Smad and MAPK signaling pathway.

• Syndecan-1 is a potential target for treatment in keloid.

Abstract

Aims

The present study aimed to explore the effect of syndecan-1 on keloid fibroblasts.

Main methods

Immunohistochemistry and Western blot were employed to assess the expression of syndecan-1. Primary cultured keloid fibroblasts were transfected with syndecan-1 siRNA. The function of syndecan-1 on the proliferation of keloid fibroblasts was investigated through Cell Counting Kit-8 (CCK-8) and flow cytometry. Extracellular matrix, TGF-β1/Smad, and MAPK related proteins were evaluated by Western blot.

Key findings

Syndecan-1 was significantly overexpressed in both keloid tissues and fibroblasts. Moreover, the knockdown of syndecan-1 remarkably attenuated the proliferation of keloid fibroblasts and reduced the content of the extracellular matrix. Importantly, syndecan-1 regulates the expression of the extracellular matrix in keloid fibroblasts via TGF-β1/Smad and mitogen-activated protein kinase (MAPK) signaling pathways.

Significance

The current results revealed a crucial function for syndecan-1 in regulating the expression of extracellular matrix and cell proliferation, thereby designating syndecan-1 as a novel target for keloid.

Introduction

Despite sustainable development in the various fields of the dermatological diseases, management of keloid is challenging for the Dermatologist. Keloid is caused by cutaneous injury and characterized by the abnormal hyperplasia of the fibroblasts and excessive extracellular matrix secretion. The etiology includes genetic predisposition, hyperactive inflammation, tension alignment, and immunological conditions [[1], [2], [3]]. During keloid, the fibroblasts are activated and differentiated into myofibroblasts. Then, they start to proliferate and produce extracellular matrix (ECM) proteins, including collagen I, collagen III, fibronectin (FN), as well as matrix metalloproteinases (MMPs) and TIMPs [[2], [3], [4]]. This process involves several other factors, including growth factors and cytokines [1,2].

Transforming growth factor-β1 (TGF-β1) signaling involves the regulation of diverse EMT-relevant transcription factors and synthesis of ECM components. Epithelial-to-mesenchymal transition (EMT) is a dynamic process associated with the loss of polarity of epithelial cells and their development into mesenchymal cells with invasive and migratory properties. TGF-β1 activates not only the Smad-dependent signaling pathway but also Smad-independent signaling pathway [5]. TGF-β1 activates R-SMADs (Smad2 and 3) when signaling through type I TGF-β receptor (TGF-βRI), the common-mediator SMADs (co-Smads) complexes translocate to the nucleus and become a critical part of specific transcriptional complexes, which induce cell proliferation and inhibit cell apoptosis and regulate the transcription of target genes [5]. In addition, ISMADs (Smad7) functions to inhibit TGF-β signaling through specific mechanisms that regulate receptor recycling [6]. The specific mechanisms possibly include the SMAD7 acts on TβRI, thereby preventing the recruitment and phosphorylation of receptor-regulated SMADs (R-SMADs). Second, SMAD7 degrades SMAD2 and TβRI through the E3 ubiquitin ligase SMAD ubiquitination regulatory factors (SMURF) [7]. Smad-independent (non-canonical) pathway includes nuclear factor-κb (NF-κB), MAPK, GTPase Rho, Par6/RhoA, and PI3K/Akt signaling cascade [5].

Syndecan-1 was first described in mouse mammary gland epithelial cells [8] and rat liver plasma membranes [9]. Subsequently, it was also found in epithelial cells and plasma cells. It is a cell surface proteoglycan which carries three heparin sulfate and two chondroitin sulfate side chains. Moreover, the molecule is widely studied in various physiological and pathological processes, including cell proliferation, cell migration, cell invasion, cell differentiation, and cell adhesion [10,11]. Interestingly, syndecan-1 plays a major role in wound healing [12]. It is also reported to be present in neonatal scars, while the expression is lacking in scar-less fetal wound healing [12]. Furthermore, the expression level of syndecan-1 is significantly upregulated in a wounded region, which is associated with the proliferation and migration of epidermal cells [13]. Syndecan-1 overexpression transgenic mice exhibit hyperproliferation of epidermis that promotes epidermal differentiation as compared to the wild-type mice [14]. However, the role of syndecan-1 in the regulation of ECM and signaling pathways related with keloid remains largely unknown.

In this study, we investigate the expression of syndecan-1 in keloid tissues and fibroblasts and explore syndecan-1 in cell proliferation and expression of ECM. Recent studies have reported that syndecan-1 is highly expressed in organ fibrotic diseases. However, these studies focus on the syndecan-1 shedding, and there are few studies on cell surface syndecan-1. Thus, the present study aimed to explore the role of syndecan-1 in the keloids.