EZH2 as a major histone methyltransferase in PDGF-BB-activated orbital fibroblast in the pathogenesis of Graves' ophthalmopathy

Graves' ophthalmopathy (GO) is an extra-thyroidal complication of Graves' disease which can lead to vision loss in severe cases. Currently, treatments of GO are not sufficiently effective, so novel therapeutic strategies are needed. As platelet-derived growth factor (PDGF)-BB induces several effector mechanisms in GO orbital fibroblasts including cytokine production and myofibroblast activation, this study aims to investigate the roles of histone lysine methyltransferases (HKMTs) in PDGF-BB-activated GO orbital fibroblasts by screening with HKMTs inhibitors library. From the total of twelve selective HKMT inhibitors in the library, EZH2, G9a and DOT1L inhibitors, DZNeP, BIX01294 and Pinometostat, respectively, prevented PDGF-BB-induced proliferation and hyaluronan production by GO orbital fibroblasts. However, only EZH2 inhibitor, DZNeP, significantly blocked pro-inflammatory cytokine production. For the HKMTs expression in GO orbital fibroblasts, PDGF-BB significantly and time-dependently induced EZH2, G9a and DOT1L mRNA expression. To confirm the role of EZH2 in PDGF-BB-induced orbital fibroblast activation, EZH2 silencing experiments revealed suppression of PDGF-BB-induced collagen type I and α-SMA expression along with decreasing histone H3 lysine 27 trimethylation (H3K27me3) level. In a more clinically relevant model than orbital fibroblast culture experiments, DZNeP treated GO orbital tissues significantly reduced pro-inflammatory cytokine production while slightly reduced ACTA2 mRNA expression. Our data is the first to demonstrate that among all HKMTs EZH2 dominantly involved in the expression of myofibroblast markers in PDGF-BB-activated orbital fibroblast from GO presumably via H3K27me3. Thus, EZH2 may represent a novel therapeutics target for GO.

Lutein targeting orbital fibroblasts attenuates fibrotic and inflammatory effects in thyroid-associated ophthalmopathy

Lutein (LU) is a carotenoid that has recently been implicated in multiple roles in fibrosis, inflammation, and oxidative stress. Thyroid-associated ophthalmopathy (TAO) is particularly relevant to these pathological changes. We thus aim to probe the potential therapeutic effects of TAO in an in vitro model. We used LU pre-treating OFs derived from patients with TAO or not, then treated with TGF-β1(or IL-1β)to induce fibrosis (or inflammation). We analyzed the different expressions of related genes and proteins, and the molecular mechanism pathway on TAO OFs was screened by RNA sequencing, which is identified in vitro. We found that LU attenuates fibrotic and inflammatory effects in TAO. LU inhibited ACTA2, COL1A1, FN1, and CTGF mRNA expression and suppressed α-SMA, and FN1 protein expression induced by TGF-β1. Besides, LU suppressed OFs migration. Besides, it is shown that LU suppressed inflammation-related genes, such as IL-6, IL-8, CXCL1, and MCP-1. Moreover, LU inhibited oxidative stress induced by IL-1β, which is analyzed by DHE fluorescent probe staining. RNA sequencing suggested ERK/AP-1 pathway may be the molecular mechanism of LU protective effect on TAO, which is identified by RT-qPCR and western-blot. In summary, this study provides the first evidence that LU significantly attenuates the pathogenic manifestations of TAO by inhibiting the expression of fibrotic and inflammation-related genes and ROS produced by OFs. These data suggested that LU may be a potential medicine for TAO.

Botox-A improve the thyroid-associated ophthalmopathy (TAO) orbital fibroblast activation through inhibiting the TGF-β/Smad signaling

The activation of orbital fibroblasts can result in fibrosis, finally contributing to thyroid-associated ophthalmopathy (TAO) progression. Although the effect of BTX-A on the treatment of TAO-related strabismus and upper eyelid retraction has long been recognized in clinical work, the underlying mechanism of BTX-A improving TAO-related strabismus and upper eyelid retraction has not been uncovered yet. In the present study, we successfully isolated and authenticated normal and TAO orbital fibroblasts. Compared with PBS, BTX-A and TACA exerted similar inhibitory effects on TAO orbital fibroblast proliferation and ECM production. TGF-β stimulation induced the proliferation and ECM production by TAO orbital fibroblast, which was significantly inhibited by BTX-A or TACA treatment. Under TGF-β stimulation, the inhibitory effects of BTX-A or TACA treatment on TAO orbital fibroblast proliferation and ECM production were reversed by TGF-β/Smad signaling agonist SRI-011381. Collectively, BTX-A inhibited TGF-β-induced TAO orbital fibroblast activation through inhibiting the TGF-β/Smad signaling. Considering that TACA shows no satisfactory curative effects on symptoms closely related to the function of extraocular muscles, such as eye movement and diplopia, BTX-A might be a promising agent in TAO treatment.

Transforming growth factor-β1 suppress pentraxin-3 in human orbital fibroblasts

PURPOSE

Transforming growth factor-β (TGF-β), recognized as a crucial factor in regulating fibrosis and tissue remodeling, plays a role in thyroid-associated ophthalmopathy (TAO). Pentraxin-3 (PTX3), a member of pentraxins, was recently implicated in many autoimmune and fibrotic diseases. Thus, we hypothesize if there is a potential correlation between TGF-β and PTX3 in orbital fibroblasts (OFs).

METHODS

Several strains of OFs obtained from patients with TAO (n = 8) and healthy donors (n = 3) were established as the study model. Recombinant TGF-β1 was exerted as an intervention and the expression of PTX3 was detected. To uncover the underlying mechanism, specific inhibitors of TGF-β and siRNA knockdown of Smads were utilized.

RESULTS

We found that TGF-β1 can reduce PTX3 protein expression in OFs. We also demonstrated that this downregulation was mediated at a pretranslational level, and PTX3 mRNA was inhibited in a time- and concentration-dependent manner by TGF-β1. Interestingly, the basic level of PTX3 and the magnitude of suppression were not significantly different between TAO and control groups. Furthermore, the TGF-β receptor complex (type I:type II) and the Smad2/3-Smad4-dependent pathway are essential for TGF-mediated PTX3 repression.

CONCLUSION

These findings indicated that TGF-β1 can inhibit PTX3 expression in human OFs, which may participate in inflammation and fibrosis in patients with TAO and provide a potential target for the antifibrotic treatment.

[Antifibrotic effect of pirfenidone on orbital fibroblasts in patients with thyroid-associated ophthalmopathy and its mechanisms]

Objective: To investigate the effects of pirfenidone on orbital fibroblasts (OFs) from patients with thyroid-associated ophthalmopathy (TAO) and its underlying mechanisms. Methods: OFs from patients with TAO were isolated and cultured in DMEM. Cells were divided into four groups and treated with 0, 250, 500 and 1 000 μg/ml pirfenidone for 24, 48 or 72 hours, respectively. Cell proliferation was detected by tetramethyl azo salt (MTT) assay, and cell viability was determined by trypan blue. Transforming growth factor (TGF) β1 mRNA level was determined by real-time fluorescence quantitative PCR (RT-qPCR). Type Ⅰ and type Ⅲ collagen secreted from cultured cells were measured by enzyme-linked immuno sorbent assay (ELISA). Results: (1) The primary cultured OFs had typical fibroblast spindle-like morphology. (2) MTT assay showed that pirfenidone treatment significantly inhibited the proliferation of OFs in a dose-dependent manner (P<0.05) with the proliferation rates of pirfenidone treated groups of -15.31%, -24.92%, -48.53% from 250, 500, 1 000 μg/ml after 72 h, respectively, in which the inhibition effect of 1 000 μg/ml pirfenidone was significantly different from the other two treated groups (P<0.05). There were no significant differences in the inhibitory effect of the same concentration group among different time points at 24 h, 48 h and 72 h (P>0.05). Trypan blue showed that the survival rate of OFs in different concentrations of pirfenidone from 0,250, 500, 1 000 μg/ml at 72 h were 78.37%, 79.21%, 78.24% and 76.28%, respectively. There were no significant differences between each drug treated and the control group (P>0.05). (3) RT-qPCR results showed that the mRNA expression levels of TGFβ1 at 250, 500, 1 000 μg/ml pirfenidone treated groups at 72 h were 0.760±0.010, 0.440±0.006, and 0.290±0.002, respectively. Compared with the control group (0.950±0.014), the differences were statistically significant (all P<0.05). Moreover, TGFβ1 mRNA expression level in 1 000 μg/ml pirfenidone treated group was significantly lower than those in the other two treated groups (all P<0.05). The secretion of type Ⅰ collagen (0.633±0.006, 0.527±0.003 and 0.402±0.008) and type Ⅲ collagen (0.511±0.003, 0.439±0.007 and 0.223±0.006) in 250, 500 and 1 000 μg/ml pirfenidone treated groups at 72 h were significantly lower than those in the control group (0.794±0.005, 0.527±0.007, all P<0.05). Type Ⅰ and type Ⅲ collagen secretion in 1 000 μg/ml pirfenidone treated group were significantly lower than those in the other two groups (P<0.05). Conclusions: Pirfenidone inhibits the cell proliferation, TGFβ1 expression and collagen secretion of OFs, which may contribute to the anti-fibrotic effect of pirfenidone.

Basic FGF and PDGF-BB synergistically stimulate hyaluronan and IL-6 production by orbital fibroblasts

Orbital fibroblast activation is a central pathologic feature of Graves' Ophthalmopathy (GO). Basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) have been proposed to contribute to GO, but their effects on orbital fibroblasts are largely unknown. We found that bFGF stimulated proliferation and hyaluronan production, but not IL-6 production by orbital fibroblasts, while VEGF hardly affected orbital fibroblast activity. Remarkably, co-stimulation of orbital fibroblasts with bFGF and PDGF-BB synergistically enhanced IL-6 and hyaluronan production and displayed an additive effect on proliferation compared to either bFGF or PDGF-BB stimulation. Nintedanib, a FGF- and PDGF-receptor targeting drug, more efficiently blocked bFGF + PDGF-BB-induced IL-6 and hyaluronan production than dasatinib that only targets PDGF-receptor. In conclusion, bFGF may contribute to orbital inflammation and tissue remodeling in GO, especially through synergistic interaction with PDGF-BB. Multi-target therapy directed at the bFGF and PDGF pathways may potentially be of interest for the treatment of GO.

Histamine induces NF-κB controlled cytokine secretion by orbital fibroblasts via histamine receptor type-1

Mast cells and their products are likely to be involved in regulating orbital fibroblast activity in Graves' Ophthalmopathy (GO). Histamine is abundantly present in granules of mast cells and is released upon mast cell activation. However, the effect of histamine on orbital fibroblasts has not been examined so far. Orbital tissues from GO patients and controls were analyzed for the presence of mast cells using toluidine blue staining and immunohistochemical detection of CD117 (stem cell factor receptor). Orbital fibroblasts were cultured from GO patients and healthy controls, stimulated with histamine and cytokines (IL-6, IL-8, CCL2, CCL5, CCL7, CXCL10 and CXCL11) were measured in culture supernatants. Also hyaluronan levels were measured in culture supernatants and hyaluronan synthase (HAS) and hyaluronidase (HYAL) gene expression levels were determined. In addition, histamine receptor subtype gene expression levels were examined as well as the effect of the histamine receptor-1 (HRH1) antagonist loratadine and NF-κB inhibitor SC-514 on histamine-induced cytokine production. Mast cell numbers were increased in GO orbital tissues. Histamine stimulated the production of IL-6, IL-8 and CCL2 by orbital fibroblasts, while it had no effect on the production of CCL5, CCL7, CXCL10, CXCL11 and hyaluronan. Orbital fibroblasts expressed HRH1 and loratadine and SC-514 both blocked histamine-induced IL-6, IL-8 and CCL2 production by orbital fibroblasts. In conclusion, this study demonstrates that histamine can induce the production of NF-κB controlled-cytokines by orbital fibroblasts, which supports a role for mast cells in GO.

Current perspectives on the role of orbital fibroblasts in the pathogenesis of Graves' ophthalmopathy

Graves' ophthalmopathy (GO) is an extra-thyroidal complication of Graves' disease (GD; Graves' hyperthyroidism) characterized by orbital tissue inflammation, expansion, remodeling and fibrosis. Although the initiating trigger of GO is still indistinct, excessive orbital fibroblast activity is at the heart of its pathogenesis. Orbital fibroblasts are activated by cellular interactions with immune cells and the soluble factors they secrete. Orbital fibroblasts, especially from GO patients, express the thyrotropin receptor (TSH-receptor; TSHR), and activation of the orbital fibroblast population by stimulatory autoantibodies directed against the TSHR may provide an important link between GD and GO. Furthermore, stimulatory autoantibodies directed against the insulin-like growth factor-1 receptor have been proposed to contribute to orbital fibroblast activation in GO. Activated orbital fibroblasts produce inflammatory mediators thereby contributing to the orbital inflammatory process in GO. Moreover, orbital fibroblasts exhibit robust proliferative activity and extracellular matrix (especially hyaluronan) synthesizing capacity and can differentiate into adipocytes and myofibroblasts with disease progression, thereby contributing to tissue expansion/remodeling and fibrosis in GO. Orbital fibroblasts, especially those from GO patients, exhibit a hyper-responsive phenotype when compared to fibroblasts from other anatomical regions, which may further contribute to GO pathogenesis. Fibrocytes have been identified as additional source of orbital fibroblasts in GO, where they may contribute to orbital tissue inflammation, adipogenesis and remodeling/fibrosis. This review addresses our current view on the role that orbital fibroblasts fulfill in GO pathogenesis and both established as well as less established not fully crystallized concepts that need future studies will be discussed.

Platelet-derived growth factor: a key factor in the pathogenesis of graves' ophthalmopathy and potential target for treatment

Activation of orbital fibroblasts resulting in excessive proliferation, cytokine and hyaluronan production and differentiation into adipocytes, is a main determinant of orbital tissue inflammation and tissue expansion in Graves' ophthalmopathy (GO). During the last years we have shown that the platelet-derived growth factor (PDGF) isoforms PDGF-AA, PDGF-AB and PDGF-BB are increased in orbital tissue from GO patients with active and inactive disease. These PDGF isoforms exhibit the capacity to stimulate proliferation, hyaluronan and cytokine/chemokine production by orbital fibroblasts. Moreover, PDGF-AB and PDGF-BB increase thyroid stimulating hormone receptor (TSHR) expression by orbital fibroblasts, which enhances the orbital fibroblast activating capacity of the THSR stimulatory autoantibodies present in Graves' disease (GD) patients. Of these PDGF isoforms PDGF-BB exhibits the strongest orbital fibroblast activating effects, which is likely related to its ability to bind both the PDGF-receptor (PDGF-R)α and PDGF-Rβ chains. Thus the PDGF-system fulfills important roles in orbital fibroblast activation in both active and inactive GO, which supports a therapeutic rationale for blocking PDGF signaling in GO. Tyrosine kinase inhibitors (TKIs) may be candidates to target PDGF signaling. Of several TKIs tested dasatinib exhibited the highest potency to block PDGF-R signaling in orbital fibroblasts and may represent a promising compound for the treatment of GO as it was effective at low dosage and is associated with less side effects compared to imatinib mesylate and nilotinib. In this review the contribution of PDGF to the pathophysiology of GO as well as therapeutic approaches to target this PDGF-system will be addressed.