Role of the long noncoding RNA H19 in TGF-β1-induced Tenon's capsule fibroblast proliferation and extracellular matrix deposition

Abstract

Glaucoma filtration surgery (GFS) is a classic surgical method used to treat glaucoma, the second leading cause of blindness. Scar formation caused by excessive Tenon's capsule fibroblast activation leads to surgical failure. However, the mechanism underlying this activation is largely unknown. In this study, we first isolated primary human Tenon's capsule fibroblasts (HTFs) and found that TGF-β promoted the viability, proliferation and extracellular matrix (ECM) deposition of HTFs. Then, we showed that TGF-β promoted the expression of H19 in HTFs and that suppression of H19 inhibited the effect of TGF-β on HTFs. Furthermore, we revealed that H19 exerted its effects by interacting with miR-200a in TGF-β-treated HTFs. Additionally, we showed that β-catenin was a target of miR-200a in TGF-β-treated HTFs. We also demonstrated that H19 acted by modulating the H19/miR-200a/β-catenin regulatory axis in TGF-β-treated HTFs. Ultimately, we found that the components of the H19/miR-200a/β-catenin regulatory axis were aberrantly expressed in a rat model of GFS. Our results show that H19 indeed acts by modulating β-catenin expression via miR-200a in TGF-β-treated HTFs, thus providing a novel rationale for the development of H19-based strategies to attenuate scar formation after GFS.

Introduction

The World Health Organization reports that glaucoma is the second most common cause of blindness [1]. Currently, approximately 66.8 million people suffer from glaucoma; unfortunately, the incidence is predicted to increase to 80 million by 2020 [2]. The primary goal of glaucoma treatment is to reduce the intraocular pressure (IOP) to a level considered safe to maintain the visual function of the optic nerve. Currently, glaucoma filtration surgery (GFS) is among the classic and effective surgical methods used to treat glaucoma in patients who cannot tolerate medical management and laser surgery [3]. However, approximately 15–25% of GFSs fail due to post-operative scar formation in the filtering blebs [4]. It has been reported that fibroblast repopulation and the associated extracellular matrix (ECM) production are the main reasons for scar formation [5]. However, the mechanism underlying scar formation in the filtering blebs after GFS is only partially understood.

The excessive activation of Tenon's capsule fibroblasts, which leads to cell proliferation and migration and ECM synthesis, is the primary reason for scar formation [6]. Previous studies have demonstrated that fibroblast activation is caused by the stimulatory effect of chemokines and cytokines, which are commonly produced under the conjunctiva during the wound healing response [7]. The cytokine transforming growth factor beta (TGF-β) plays a pivotal role in mediating wound healing by driving the conversion of fibroblasts to myofibroblasts [8]. The resident cells at the wound site produce TGF-β, which may contribute to scar formation. In the stromal connective tissue of scarred filtering blebs, TGF-β1 and TGF-β2 are differentially expressed, but TGF-β1 is the primary form expressed [9,10]. In particular, TGF-β1 has been implicated in tissue fibrosis and scarring [11]. In addition, previous studies have reported that TGF-β1 is expressed in primary human ocular fibroblast subpopulations [12]. Thus, a better understanding of the TGF-β1-mediated regulation of human Tenon's capsule fibroblast (HTF) activation and collagen expression and the underlying mechanism is crucial for the development of therapeutic strategies for GFS.

Recently, a growing number of long noncoding RNAs (lncRNAs) have been discovered and explained. LncRNAs belong to a new class of RNA transcripts that are more than 200 nucleotides in length and are evolutionarily conserved and lack protein coding ability [13,14]. Previous studies have shown that lncRNAs are roughly separated into five classical biological types, including bidirectional, sense, antisense, intergenic and intronic [15]. Although once thought to be only “transcriptional noise”, lncRNAs are currently viewed as biologically active molecules involved in various cellular processes, such as angiogenesis, growth, cell proliferation, cell cycle progression, migration, invasion, and carcinogenesis by modulating the expression of various genes during processes such as transcription, post-transcriptional modification, RNA editing, RNA transport and translation [[16], [17], [18], [19]]. Studies have increasingly found that lncRNAs, such as H19, PVT1, SNHG7, MALTA1 NEAT1, and UCA1, are related to the role of TGF-β [[20], [21], [22]]. Wang and colleagues demonstrated that decreased lncRNA-MEG3 expression attenuated cell proliferation and viability and contributed to Nrf 2 protein upregulation in TGF-β2-stimulated granulation tissue fibroblasts (GTFs) [23]. However, the function and potential mechanism of lncRNAs in TGF-β1-stimulated HTFs are largely unclear.

H19, which was the first identified lncRNA, is highly expressed in fetal tissues but is expressed after birth in only a few tissues, such as skeletal muscle and the heart [24]. The function of H19 remains controversial; some evidence indicates that H19 could act as an oncogene, whereas other evidence indicates that H19 acts as a tumor suppressor [[25], [26], [27]]. In addition to its role in tumors, H19 participates in several other physiological conditions and noncancerous disease states, such as vascular biology and disease, preeclampsia pathogenesis, cardiac remodeling, and glucose metabolism [[28], [29], [30], [31]]. Furthermore, some studies have focused on the function of H19 in TGF-β stimulation [20]. However, the biological role of H19 in the effect on TGF-β-induced HTFs remains unknown.

Thus, we attempted to analyze the role of H19 in mediating the effect of TGF-β1 on HTFs. We isolated and cultured primary HTFs, demonstrated the role and mechanism of H19 in TGF-β1-treated HTFs and revealed the aberrant expression of H19/miR-200a/β-catenin regulatory axis components in a rat model of GFS. Taken together, these results indicate that H19 plays a role in modulating the H19/miR-200a/β-catenin axis and suggest that H19 and this pathway may be novel therapeutic targets for attenuating scar formation after GFS.