TGF-β-induced activation of conjunctival fibroblasts is modulated by FGF-2 and substratum stiffness

Lysophosphatidic Acid Modulates TGF-β2-Induced Biological Phenotype in Human Conjunctival Fibroblasts

BACKGROUND

Although lysophosphatidic acid (LPA) is known to have multiple pathophysiological roles, its contributions to ocular tissues, especially conjunctival fibrogenesis, remain to be elucidated.

METHODS

To study this issue, the effects of LPA on transforming growth factor-β2 (TGF-β2)-induced fibrogenesis of two-dimensional (2D) and three-dimensional (3D) cultures of human conjunctival fibroblasts (HconF) were examined by the following analyses: (1) planar proliferation determined by transepithelial electrical resistance (TEER) and fluorescein isothiocyanate (FITC)-dextran permeability measurements, (2) real-time metabolic analyses, (3) measurements of the size and stiffness of 3D spheroids, and (4) mRNA expression of extracellular matrix (ECM) molecules and their modulators.

RESULTS

LPA had no effect on TGF-β2-induced increase in the planar proliferation of HconF cells. LPA induced a more quiescent metabolic state in 2D HconF cells, but this metabolic suppression by LPA was partially blunted in the presence of TGF-β2. In contrast, LPA caused a substantial decrease in the hardness of 3D HconF spheroids independently of TGF-β2. In agreement with these different LPA-induced effects between 2D and 3D cultured HconF cells, mRNA expressions of ECM and their modulators were differently modulated.

CONCLUSION

The findings that LPA induced the inhibition of both TGF-β2-related and -unrelated subepithelial proliferation of HconF cells may be clinically applicable.

Pharmacological Stimulation of Soluble Guanylate Cyclase Counteracts the Profibrotic Activation of Human Conjunctival Fibroblasts

Conjunctival fibrosis is a serious clinical concern implicated in a wide spectrum of eye diseases, including outcomes of surgery for pterygium and glaucoma. It is mainly driven by chronic inflammation that stimulates conjunctival fibroblasts to differentiate into myofibroblasts over time, leading to abnormal wound healing and scar formation. Soluble guanylate cyclase (sGC) stimulation was found to suppress transforming growth factor β (TGFβ)-induced myofibroblastic differentiation in various stromal cells such as skin and pulmonary fibroblasts, as well as corneal keratocytes. Here, we evaluated the in vitro effects of stimulation of the sGC enzyme with the cell-permeable pyrazolopyridinylpyrimidine compound BAY 41-2272 in modulating the TGFβ1-mediated profibrotic activation of human conjunctival fibroblasts. Cells were pretreated with the sGC stimulator before challenging with recombinant human TGFβ1, and subsequently assayed for viability, proliferation, migration, invasiveness, myofibroblast marker expression, and contractile properties. Stimulation of sGC significantly counteracted TGFβ1-induced cell proliferation, migration, invasiveness, and acquisition of a myofibroblast-like phenotype, as shown by a significant downregulation of FAP, ACTA2, COL1A1, COL1A2, FN1, MMP2, TIMP1, and TIMP2 mRNA levels, as well as by a significant reduction in α-smooth muscle actin, N-cadherin, COL1A1, and FN-EDA protein expression. In addition, pretreatment with the sGC stimulator was capable of significantly dampening TGFβ1-induced acquisition of a contractile phenotype by conjunctival fibroblasts, as well as phosphorylation of Smad3 and release of the proinflammatory cytokines IL-1β and IL-6. Taken together, our findings are the first to demonstrate the effectiveness of pharmacological sGC stimulation in counteracting conjunctival fibroblast-to-myofibroblast transition, thus providing a promising scientific background to further explore the feasibility of sGC stimulators as potential new adjuvant therapeutic compounds to treat conjunctival fibrotic conditions.

Altered actin dynamics is possibly implicated in the inhibition of mechanical stimulation-induced dermal fibroblast differentiation into myofibroblasts

The formation of hypertrophic scars and keloids is strongly associated with mechanical stimulation, and myofibroblasts are known to play a major role in abnormal scar formation. Wounds in patients with neurofibromatosis type 1 (NF1) become inconspicuous and lack the tendency to form abnormal scars. We hypothesized that there would be a unique response to mechanical stimulation and subsequent scar formation in NF1. To test this hypothesis, we investigated the molecular mechanisms of differentiation into myofibroblasts in NF1-derived fibroblasts and neurofibromin-depleted fibroblasts and examined actin dynamics, which is involved in fibroblast differentiation, with a focus on the pathway linking LIMK2/cofilin to actin dynamics. In normal fibroblasts, expression of α-smooth muscle actin (α-SMA), a marker of myofibroblasts, significantly increased after mechanical stimulation, whereas in NF1-derived and neurofibromin-depleted fibroblasts, α-SMA expression did not change. Phosphorylation of cofilin and subsequent actin polymerization did not increase in NF1-derived and neurofibromin-depleted fibroblasts after mechanical stimulation. Finally, in normal fibroblasts treated with Jasplakinolide, an actin stabilizer, α-SMA expression did not change after mechanical stimulation. Therefore, when neurofibromin was dysfunctional or depleted, subsequent actin polymerization did not occur in response to mechanical stimulation, which may have led to the unchanged expression of α-SMA. We believe this molecular pathway can be a potential therapeutic target for the treatment of abnormal scars.

Fibroblast growth factor 2 acts as an upstream regulator of inhibition of pulmonary fibroblast activation

Fibroblast growth factor (FGF) signaling plays a crucial role in lung development and repair. Fibroblast growth factor 2 (FGF2) can inhibit fibrotic gene expression and suppress the differentiation of pulmonary fibroblasts (PFs) into myofibroblasts in vitro, suggesting that FGF2 is a potential target for inhibiting pulmonary fibrosis. To gain deeper insights into the molecular mechanism underlying FGF2-mediated regulation of PFs, we performed mRNA sequencing analysis to systematically and globally uncover the regulated genes and biological functions of FGF2 in PFs. Gene Ontology analysis revealed that the differentially expressed genes regulated by FGF2 were enriched in multiple cellular functions including extracellular matrix (ECM) organization, cytoskeleton formation, β-catenin-independent Wnt signaling pathway, supramolecular fiber organization, epithelial cell proliferation, and cell adhesion. Gene Set Enrichment Analysis and cellular experiments confirmed that FGF2 can suppress ECM and actin filament organization and increase PFs proliferation. Taken together, these findings indicate that FGF2 acts as an upstream regulator of the inhibition of PFs activation and may play a regulatory role in pulmonary fibrosis.

TGF-β Isoforms Affect the Planar and Subepithelial Fibrogenesis of Human Conjunctival Fibroblasts in Different Manners

Three highly homologous isoforms of TGF-β, TGF-β-1~3, are involved in the regulation of various pathophysiological conditions such as wound healing processes in different manners, despite the fact that they bind to the same receptors during their activation. The purpose of the current investigation was to elucidate the contributions of TGF-β-1 ~3 to the pathology associated with conjunctiva. For this purpose, the biological effects of these TGF-β isoforms on the structural and functional properties of two-dimensional (2D) and three-dimensional (3D) cultured human conjunctival fibroblasts (HconF) were subjected to the following analyses: 1) transendothelial electrical resistance (TEER), a Seahorse cellular metabolic measurement (2D), size and stiffness measurements of the 3D HTM spheroids, and the qPCR gene expression analyses of extracellular matrix (ECM) components (2D and 3D). The TGF-β isoforms caused different effects on the proliferation of the HconF cell monolayer evaluated by TEER measurements. The differences included a significant increase in the presence of 5 ng/mL TGF-β-1 and -2 and a substantial decrease in the presence of 5 ng/mL TGF-β-3, although there were no significant differences in the response to the TGF-β isoforms for cellular metabolism among the three groups. Similar to planar proliferation, the TGF-β isoforms also induced diverse effects toward the mechanical aspects of 3D HconF spheroids, where TGF-β-1 increased stiffness, TGF-β-2 caused no significant effects, and TGF-β-3 caused the downsizing of the spheroids and stiffness enhancement. The mRNA expression of the ECMs were also modulated in diverse manners by the TGF-β isoforms as well as the culture conditions for the 2D vs. 3D isoforms. Many of these TGF-β-3 inducible effects were markedly different from those caused by TGF-β1 and TGF-β-2. The findings presented herein suggest that the three TGF-β isoforms induce diverse and distinctly different effects on cellular properties and the expressions of ECM molecules in HconF and that these changes are independent of cellular metabolism, thereby inducing different effects on the epithelial and subepithelial proliferation of human conjunctiva.

Prostanoid FP and EP2 Receptor Agonists Induce Epithelial and Subepithelial Fibrogenetic Changes in Human Conjunctival Fibroblasts in Different Manners

Purpose: To examine the effects of prostanoid FP and EP2 receptor agonists, PGF2α and Omidenepag (OMD), respectively, on the transforming growth factor beta (TGF-β2) induced conjunctival fibrogenesis. Methods: Two-dimension (2D) and three-dimension (3D) cultures of these fibroblasts were subjected to following analyses: (1) planar proliferation evaluated by transendothelial electron resistance (TEER) measurements, (2) real-time metabolic analyses, (3) subepithelial proliferation evaluated by 3D spheroid' size and stiffness measurements, and (4) the mRNA expression of extracellular matrix (ECM) molecules and their modulators. Results: TGF-β2 induced increase in the planar proliferation was significantly decreased or enhanced by PGF2α or OMD, respectively. The proportion of oxygen consumption required to drive ATP synthesis compared with that driving proton leakage was increased by PGF2α and OMD independently with TGF-β2. In contrast, maximal mitochondrial respiration was decreased by PGF2α and OMD, and the OMD-induced effect was further enhanced by the presence of TGF-β2. In addition, the TGF-β2 dependent increase in the glycolytic capacity was cancelled by PGF2α and/or OMD. Alternatively, subepithelial proliferation, as evidenced by the stiffness of the 3D spheroids, was substantially increased by both PGF2α and OMD, and these were differently modulated by TGF-β2. The expression of several related factors as above fluctuated among the conditions for both 2D and 3D and TGF-β2 untreated or treated cultures. Conclusion: The present findings indicate that the prostanoid FP or the EP2 receptor agonist may solely and differently induce the planar and subepithelial proliferation of HconF cells and these were also modulated by TGF-β2.

Fibroblasts at the curtain call: from ensemble to principal dancers in immunometabolism and inflammaging

Inflammation is a necessary step in response to injuries, being vital in restoring homeostasis and facilitating tissue healing. Among the cells that play a crucial role in inflammatory responses, stromal cells, including fibroblasts, have an undeniable significance in fine-tuning the magnitude of mediators that directly affect hyper-inflammatory responses and tissue destruction. Fibroblasts, the dominant cells in the gingival connective tissue, are a very heterogeneous population of cells, and more recently they have been receiving well deserved attention as central players and often the 'principal dancers' of many pathological processes ranging from inflammation and fibrosis to altered immunity and cancer. The goal of the current investigation is to dive into the exact role of the stromal fibroblast and the responsible mechanistic factors involved in both regulation and dysregulation of the inflammatory responses. This article reviews the most recent literature on how fibroblasts, in their different activation states or subtypes, play a crucial role in contributing to inflammatory outcomes. We will focus on recent findings on inflammatory diseases. We will also provide connections regarding the stromal-immune relationship, which supports the idea of fibroblast coming out from the 'ensemble' of cell types to the protagonist role in immunometabolism and inflammaging. Additionally, we discuss the current advances in variation of fibroblast nomenclature and division into clusters with their own suggested function and particularities in gene expression. Here, we provide a perspective for the periodontal implications, discussing the fibroblast role in the infection-driven and inflammatory mediated diseases such as periodontitis.

A ROCK inhibitor suppresses the transforming growth factor-beta-2-induced endothelial-mesenchymal transition in Schlemm's canal endothelial cells

In the normal eye, most of the aqueous humor drains through the trabecular meshwork (TM) and Schlemm's canal (SC). The concentration of transforming growth factor beta 2 (TGF-β2) is increased in the aqueous humor of primary open angle glaucoma patients. TGF-β2 increases outflow resistance by affecting the TM and SC, and endothelial-mesenchymal transition (EndMT) of SC cells is involved in these changes. Here, we investigated the effect of a ROCK inhibitor on TGF-β2-induced EndMT in SC cells. The ROCK inhibitor Y-27632 suppressed the TGF-β2-induced increase in the trans-endothelial electrical resistance (TER) and proliferation of SC cells. Y-27632 suppressed the expression of α-SMA, N-cadherin, and Snail, which are upregulated by TGF-β2. Moreover, TGF-β2 decreased mRNA levels of bone morphogenetic protein (BMP) 4 and increased those of the BMP antagonist gremlin (GREM1), but Y-27632 significantly suppressed these changes. Y-27632 also inhibited TGF-β2-induced phosphorylation of p-38 mitogen-activated protein kinase (MAPK). BMP4 and the p-38 MAPK inhibitor SB203580 suppressed the TGF-β2-induced TER elevation in SC cells. Moreover, SB203580 suppressed TGF-β2-induced upregulation of fibronectin, Snail, and GREM1. These results indicate that a ROCK inhibitor inhibited the TGF-β2-induced EndMT in SC cells, implying the involvement of p38 MAPK and BMP4 signaling.

FGF-2 enhances fibrogenetic changes in TGF-β2 treated human conjunctival fibroblasts

The objective of the current study was to examine the effects of fibroblast growth factor-2 (FGF-2) on conjunctival fibrogenesis that was induced by the presence of transforming growth factor-β2 (TGF-β2). Two-dimension (2D) and three-dimension (3D) cultured human conjunctival fibroblasts (HconF) were used for this purpose. The 2D and 3D cultured HconF were characterized by transendothelial electrical resistance (TEER) and FITC dextran permeability measurements (2D), real-time metabolic analyses (2D), size and stiffness measurements (3D), and the mRNA expression of extracellular matrix molecules, their modulators, Tissue inhibitor of metalloproteinases and matrix metalloproteinases and ER-stress related genes (2D and 3D). FGF-2 significantly increased planar proliferation, as evidenced by TEER values and FITC dextran permeability, and shifted glucose metabolism to the energetic phenotype of 2D HconF cells, and the stiffness of the 3D spheroids, and these effects were further enhanced in the presence of TGF-β2. Analyses of the expression of possible candidate molecules involved in cell architecture and stress indicated that some additive effects caused by both factors were also recognized in some of these molecules. The findings reported herein indicate that the FGF-2, either along or additively with TGF- β2 increased the fibrogenetic changes on the plane as well as in the spatial space of HconF cells.

Pathophysiology of Pulmonary Fibrosis in the Context of COVID-19 and Implications for Treatment: A Narrative Review

Pulmonary fibrosis (PF) is a feared outcome of many pulmonary diseases which results in a reduction in lung compliance and capacity. The development of PF is relatively rare, but it can occur secondary to viral pneumonia, especially COVID-19 infection. While COVID-19 infection and its complications are still under investigation, we can look at a similar outbreak in the past to gain better insight as to the expected long-term outcomes of COVID-19 patient lung function. In the current article, we review the literature relative to PF via PubMed. We also performed a literature search for COVID-related pathological changes in the lungs. Finally, the paper was reviewed and summarized based on the studies’ integrity, relative, or power calculations. This article provides a narrative review that endeavors to elucidate the current understanding of the pathophysiological mechanisms underlying PF and therapeutic strategies. We also discussed the potential for preventing progression to the fibrotic state within the context of the COVID-19 pandemic. With the massive scale of the COVID-19 pandemic, we expect there should more instances of PF due to COVID-19 infection. Patients who survive severe COVID-19 infection may suffer from a high incidence of PF.

Anti-fibrotic effects of pharmacologic FGF-2: a review of recent literature

Fibrosis is a process of pathological tissue repair that replaces damaged, formerly functional tissue with a non-functional, collagen-rich scar. Complications of fibrotic pathologies, which can arise in numerous organs and from numerous conditions, result in nearly half of deaths in the developed world. Despite this, therapies that target fibrosis at its mechanistic roots are still notably lacking. The ubiquity of the occurrence of fibrosis in myriad organs emphasizes the fact that there are shared mechanisms underlying fibrotic conditions, which may serve as common therapeutic targets for multiple fibrotic diseases of varied organs. Thus, study of the basic science of fibrosis and of anti-fibrotic modalities is critical to therapeutic development and may have potential to translate across organs and disease states. Fibroblast growth factor 2 (FGF-2) is a broadly studied member of the fibroblast growth factors, a family of multipotent cytokines implicated in diverse cellular and tissue processes, which has previously been recognized for its anti-fibrotic potential. However, the mechanisms underlying this potential are not fully understood, nor is the potential for its use to ameliorate fibrosis in diverse pathologies and tissues. Presented here is a review of recent literature that sheds further light on these questions, with the hopes of inspiring further research into the mechanisms underlying the anti-fibrotic activities of FGF-2, as well as the disease conditions for which pharmacologic FGF-2 might be a useful option in the future.

The Stiffness of Cardiac Fibroblast Substrates Exerts a Regulatory Influence on Collagen Metabolism via α2β1 Integrin, FAK and Src Kinases

Information about mechanical strain in the extracellular space is conducted along collagen fibers connected with integrins and then transmitted within cells. An aim of the study is to verify the hypothesis that the stiffness of cardiac human fibroblast substrates exerts a regulatory effect on collagen metabolism via integrin α2β1 and downstream signaling. The experiments were performed on human cardiac fibroblasts cultured on stiff or soft polyacrylamide gels. Extracellular and intracellular collagen content, metalloproteinase-1 (MMP-1), metalloproteinase-9 (MMP-9) and expression of the α1 chain of the procollagen type I gene (Col1A1) were elevated in cultures settled on soft substrate. The substrate stiffness did not modify tissue inhibitors of matrix metalloproteinase capacity (TIMPs 1–4). Integrin α2β1 inhibition (TC-I 15) or α2 subunit silencing resulted in augmentation of collagen content within the culture. Expression of Col1A1 and Col3A1 genes was increased in TC-I 15-treated fibroblasts. Total and phosphorylated levels of both FAK and Src kinases were elevated in fibroblasts cultured on stiff substrate. Inhibition of FAK (FAK kinase inhibitor 14) or Src kinase (AZM 47527) increased collagen content within the culture. The substrate stiffness exerted a regulatory influence on collagen metabolism via integrin α2β1 and its downstream signaling (FAK and Src kinases) in cardiac fibroblasts.

Novel Bacterial Cellulose Membrane to Reduce Fibrosis Following Trabeculectomy

PURPOSE

The aim was to evaluate the effectiveness of bacterial cellulose membrane (BCM) in preventing fibrosis in trabeculectomy and the biocompatibility of BCM with conjunctiva and sclera.

MATERIALS AND METHODS

Twenty-one eyes of 21 adult rabbits underwent fornix-based trabeculectomy. Standard surgery was done to control group (CG, n=7). Mitomycin-C (MMC) (0.3 mg/mL, 3 min) was applied to MMC group only (MMCG, n=7). BCM (~100 µm thick, 10×10 mm, single layer) was covered on the sclerotomy area before conjunctiva was closed in BCM group (BCMG, n=7). Intraocular pressures (IOP) were measured before, and 7, 14, 28, and 45 days after surgery (IOP-POD7, POD14, POD28, POD45). The IOP decrease were expressed as DIOP%-POD7, DIOP%-POD14, DIOP%-POD28, and DIOP%-POD45. The rabbits were sacrificed on the 45th day. Conjunctival vessel number, degrees of fibrosis, total inflammation, foreign body reaction, inflammatory cell types (B cells, T cells, plasma cells), macrophages, bleb spaces and the expression of α-smooth muscle actin were studied using histopathology and immunohistochemistry techniques. The groups were compared using nonparametric tests.

RESULTS

There was no statistically significant difference between the groups regarding baseline IOP and DIOP%-POD7 (P>0.05). While DIOP%-POD14, 28 and 45 were similar between BCMG and MMCG, they were significantly lower in CG (P<0.05). The lowest conjunctival vessel number was detected in the MMCG but the difference was not significant. There was no difference between BCMG and CG with regard to the numbers of B cells, T cells, and macrophages, however, these cells were significantly lower in MMCG (P<0.05). Five cases had mild and 2 cases had moderate foreign body reaction in the BCMG. There was mild to moderate inflammation in all BCM cases. While fibrosis and α-smooth muscle actin staining were higher in the CG (P<0.001), they were minimal in the BCM and MMCGs.

CONCLUSIONS

BCM showed good biocompatibility and provided better control of IOP with minimal fibrosis at the trabeculectomy site compared with the control group.

Backstage players of fibrosis: NOX4, mTOR, HDAC, and S1P; companions of TGF-β

The fibrotic process could be easily defined as a pathological excess of extracellular matrix deposition, leading to disruption of tissue architecture and eventually loss of function; however, this process involves a complex network of several signal transduction pathways. Virtually almost all organs could be affected by fibrosis, the most affected are the liver, lung, skin, kidney, heart, and eyes; in all of them, the transforming growth factor-beta (TGF-β) has a central role. The canonical and non-canonical signal pathways of TGF-β impact the fibrotic process at the cellular and molecular levels, inducing the epithelial-mesenchymal transition (EMT) and the induction of profibrotic gene expression with the consequent increase in proteins such as alpha-smooth actin (α-SMA), fibronectin, collagen, and other extracellular matrix proteins. Recently, it has been reported that some molecules that have not been typically associated with the fibrotic process, such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4), mammalian target of rapamycin (mTOR), histone deacetylases (HDAC), and sphingosine-1 phosphate (S1P); are critical in its development. In this review, we describe and discuss the role of these new players of fibrosis and the convergence with TGF-β signaling pathways, unveiling new insights into the panorama of fibrosis that could be useful for future therapeutic targets.

Suberoylanilide hydroxamic acid (SAHA) inhibits transforming growth factor-beta 2-induced increases in aqueous humor outflow resistance

Transforming growth factor-beta 2 (TGF-β2) is highly concentrated in the aqueous humor of primary open-angle glaucoma patients. TGF-β2 causes fibrosis of outflow tissues, such as the trabecular meshwork (TM), and increases intraocular pressure by increasing resistance to aqueous humor outflow. Recently, histone deacetylase (HDAC) activity was investigated in fibrosis in various tissues, revealing that HDAC inhibitors suppress tissue fibrosis. However, the effect of HDAC inhibitors on fibrosis in the eye was not determined. Here, we investigated the effect of suberoylanilide hydroxamic acid (SAHA), an HDAC inhibitor, on TGF-β2-induced increased resistance to aqueous humor outflow. We found that SAHA suppressed TGF-β2-induced outflow resistance in perfused porcine eyes. Moreover, SAHA cotreatment suppressed TGF-β2-induced ocular hypertension in rabbits. The permeability of monkey TM (MTM) and Schlemm’s canal (MSC) cell monolayers was decreased by TGF-β2 treatment. SAHA inhibited the effects of TGF-β2 on the permeability of these cells. TGF-β2 also increased the expression of extracellular matrix proteins (fibronectin and collagen type I or IV) in MTM, MSC, and human TM (HTM) cells, while SAHA inhibited TGF-β2-induced extracellular matrix protein expression in these cells. SAHA also inhibited TGF-β2-induced phosphorylation of Akt and ERK, but did not inhibit Smad2/3 phosphorylation, the canonical pathway of TGF-β signaling. Moreover, SAHA induced the expression of phosphatase and tensin homolog, a PI3K/Akt signaling factor, as well as bone morphogenetic protein 7, an endogenous antagonist of TGF-β. These results imply that SAHA prevents TGF-β2-induced increases in outflow resistance and regulates the non-Smad pathway of TGF-β signaling in TM and MSC cells.