Differences in the TGF-{beta}1-induced profibrotic response of anterior and posterior corneal keratocytes in vitro

Repeated cell sorting ensures the homogeneity of ocular cell populations expressing a transgenic protein

Transgenic proteins can be routinely expressed in various mammalian cell types via different transgenic systems, but the efficiency of transgene expression is constrained by the complex interplay among factors such as the temporal consistency of expression and compatibility with specific cell types, including ocular cells. Here, we report a more efficient way to express an enhanced green fluorescent protein (EGFP) in human corneal fibroblasts, corneal epithelial cells, and conjunctival epithelial cells through a lentiviral expression system. The relative transducing unit criterion for EGFP-expressing pseudovirions was first determined in HEK-293T cells. Homogeneous populations of EGFP-positive and EGFP-negative cells could be isolated by cell sorting. The half-maximal inhibitory concentration (IC₅₀) value for puromycin was calculated according to viability curves for each cell type. The results revealed that cell types differed with respect to EGFP expression efficiency after transduction with the same amount of EGFP-encoding pseudovirions. Using a cell sorter, the homogeneity of EGFP-positive cells reached >95%. In the initial sorting stage, however, the efficiency of EGFP expression in the sorted cells was noticeably reduced after two rounds of sequential culture, but repeated sorting for up to four rounds yielded homogeneous EGFP-positive human corneal fibroblasts that could be maintained in continuous culture in vitro. The sorted EGFP-positive cells retained their proper morphology and cell type-specific protein expression patterns. Puromycin resistance was found to depend on cell type, indicating that the IC₅₀ for puromycin must be determined for each cell type to ensure the isolation of homogeneous EGFP-positive cells. Taken together, repeated cell sorting is an efficient means of obtaining homogeneous populations of ocular cells expressing a transgenic protein during continuous culture without the potential confounding effects of antibiotics.

More than Meets the Eye: The Aryl Hydrocarbon Receptor is an Environmental Sensor, Physiological Regulator and a Therapeutic Target in Ocular Disease

The aryl hydrocarbon receptor (AHR) is a ligand activated transcription factor originally identified as an environmental sensor of xenobiotic chemicals. However, studies have revealed that the AHR regulates crucial aspects of cell growth and metabolism, development and the immune system. The importance of the AHR and AHR signaling in eye development, toxicology and disease is now being uncovered. The AHR is expressed in many ocular tissues including the retina, choroid, cornea and the orbit. A significant role for the AHR in age-related macular degeneration (AMD), autoimmune uveitis, and other ocular diseases has been identified. Ligands for the AHR are structurally diverse organic molecules from exogenous and endogenous sources. Natural AHR ligands include metabolites of tryptophan and byproducts of the microbiome. Xenobiotic AHR ligands include persistent environmental pollutants such as dioxins, benzo (a) pyrene [B (a) P] and polychlorinated biphenyls (PCBs). Pharmaceutical agents including the proton pump inhibitors, esomeprazole and lansoprazole, and the immunosuppressive drug, leflunomide, activate the AHR. In this review, we highlight the role of the AHR in the eye and discuss how AHR signaling is involved in responding to endogenous and environmental stimuli. We also present the emerging concept that the AHR is a promising therapeutic target for eye disease.

Fibroblastic and bone marrow-derived cellularity in the corneal stroma

The unwounded, normal corneal stroma is a relatively simple, avascular tissue populated with quiescent keratocytes, along with corneal nerves and a few resident dendritic and monocyte/macrophage cells. In the past, the resting keratocytes were thought of as a homogenous cellular population, but recent work has shown local variations in vimentin and nestin expression, and responsiveness to transforming growth factor (TGF)-β1. Studies have also supported there being "stromal stem cells" in localized areas. After corneal wounding, depending on the site and severity of injury, profound changes in stromal cellularity occur. Anterior or posterior injuries to the epithelium or endothelium, respectively, trigger apoptosis of adjacent keratocytes. Many contiguous keratocytes transition to keratocan-negative corneal fibroblasts that are proliferative and produce limited amounts of disorganized extracellular matrix components. Simultaneously, large numbers of bone marrow-derived cells, including monocytes, neutrophils, fibrocytes and lymphocytes, invade the stroma from the limbal blood vessels. Ongoing adequate levels of TGFβ1, TGFβ2 and platelet-derived growth factor (PDGF) from epithelium, tears, endothelium and aqueous humor that penetrate defective or absent epithelial barrier function (EBF) and epithelial basement membrane (EBM) and/or Descemet's basement membrane (DBM) drive corneal fibroblasts and fibrocytes to differentiate into alpha-smooth muscle actin (SMA)-positive myofibroblasts. If the EBF, EBM and/or DBM are repaired or replaced in a timely manner, typically measured in weeks, then corneal fibroblast and fibrocyte progeny, deprived of requisite levels of TGFβ1 and TGFβ2, undergo apoptosis or revert to their precursor cell-types. If the EBF, EBM and/or DBM are not repaired or replaced, stromal levels of TGFβ1 and TGFβ2 remain elevated, and mature myofibroblasts are generated from corneal fibroblasts and fibrocyte precursors that produce prodigious amounts of disordered extracellular matrix materials associated with scarring fibrosis. This fibrotic stromal matrix persists, at least until the EBF, EBM and/or DBM are regenerated or replaced, and keratocytes remove and reorganize the affected stromal matrix.

Fiber reinforced GelMA hydrogel to induce the regeneration of corneal stroma

Regeneration of corneal stroma has always been a challenge due to its sophisticated structure and keratocyte-fibroblast transformation. In this study, we fabricate grid poly (ε-caprolactone)-poly (ethylene glycol) microfibrous scaffold and infuse the scaffold with gelatin methacrylate (GelMA) hydrogel to obtain a 3 D fiber hydrogel construct; the fiber spacing is adjusted to fabricate optimal construct that simulates the stromal structure with properties most similar to the native cornea. The topological structure (3 D fiber hydrogel, 3 D GelMA hydrogel, and 2 D culture dish) and chemical factors (serum, ascorbic acid, insulin, and β-FGF) are examined to study their effects on the differentiation of limbal stromal stem cells to keratocytes or fibroblasts and the phenotype maintenance, in vitro and in vivo tissue regeneration. The results demonstrate that fiber hydrogel and serum-free media synergize to provide an optimal environment for the maintenance of keratocyte phenotype and the regeneration of damaged corneal stroma.

Regeneration of corneal stroma has been a challenge due to its sophisticated structure and the easy transformation of the keratocyte. Here, the authors use a hydrogel reinforced with orthogonally aligned fibres and serum free medium to maintain keratocyte phenotype for the in vivo stromal regeneration.

Activation and Migration of Adventitial Fibroblasts Contributes to Vascular Remodeling

The rat carotid artery balloon injury model was used to prove the activation and migration of adventitial fibroblasts. We found that at day 7 after injury, adventitial fibroblasts proliferated, transformed into myofibroblasts under transmission electron microscopy in the model group. Simultaneously, we proved that the adventitial cells migrated to the media and intima on seventh day after injury by directly labeled the adventitial cells by the in vivo gene transfer technique. Moreover, we captured the precise moment when the adventitial fibroblasts migrated from the adventitia to the media through the external elastic plate under transmission electron microscope. This study provides direct evidences that adventitial fibroblasts activate and migrate to the media and intima, then actively take part in revascularization. Anat Rec, 301:1216-1223, 2018. © 2018 Wiley Periodicals, Inc.

Moxifloxacin modifies corneal fibroblast-to-myofibroblast differentiation

BACKGROUND AND PURPOSE

Fibroblast-to-myofibroblast differentiation is associated with scarring, an important issue in corneal surgery. Moxifloxacin (MOX), commonly applied to prevent post-operative infection, would benefit more if it modifies fibroblast-to-myofibroblast differentiation other than antimicrobial activity. Our purpose was to explore whether MOX has anti-fibrotic effect in human corneal fibroblasts (HCFs).

EXPERIMENTAL APPROACH

HCFs were incubated in MOX-containing medium concurrently with TGF-β1 (co-treatment), before (pretreatment) or after (post-treatment) adding TGF-β1. HCF contractility was evaluated with a type I collagen gel contraction assay. Expression of α-smooth muscle actin (α-SMA), Smad2, phospho-Smad2-Ser467, Smad4 and Smad7 was determined by immunoblotting. Formation of α-SMA-positive filaments and distribution of active Smad2 were observed under confocal microscopy. Expression of TGF-β receptor types I (TGFBR1) and II (TGFBR2) was assessed with flow cytometry.

KEY RESULTS

MOX did not affect gel contractility or α-SMA filament formation in HCFs without TGF-β1 stimulation. MOX did, however, retard HCF-containing gel contractility and α-SMA filament formation following TGF-β1 stimulation in the pretreatment and co-treatment groups but not in the post-treatment group. MOX blocked the expression of Smad2, phospho-Smad2-Ser467 and TGFBR1 under TGF-β1 incubation. Additionally, MOX enhanced Smad7 expression in TGF-β1-incubated HCFs, but did not interfere with TGF-β-triggered Smad2 nuclear translocation or Smad4 expression.

CONCLUSIONS AND IMPLICATIONS

MOX inhibited TGF-β-induced fibroblast-to-myofibroblast differentiation via blocking TGFBR1 and enhancing Smad7 expression. MOX should be used before or during surgery to achieve these effects. These results suggest a de novo mechanism by which MOX participates in corneal wound healing.

Ocular fibroblast diversity: implications for inflammation and ocular wound healing

PURPOSE

Various ocular and orbital tissues differ in their manifestations of inflammation, although the reasons for this are unclear. Such differences may be due to behaviors exhibited by resident cell types, including fibroblasts. Fibroblasts mediate immune function and produce inflammatory mediators. Chronic stimulation of ocular fibroblasts can lead to prolonged inflammation and, in turn, to impaired vision and blindness. Interleukin (IL)-1β, which is produced by various cells during inflammation, is a potent activator of fibroblasts and inducer of the expression of inflammatory mediators. The hypothesis for this study was that that human fibroblasts derived from distinct ocular tissues differ in their responses to IL-1β and that variations in the IL-1 signaling pathway account for these differences.

METHODS

Human fibroblasts were isolated from the lacrimal gland, cornea, and Tenon's capsule and treated with IL-1β in vitro. Cytokine and prostaglandin (PG)E(2) production were measured by ELISA and EIA. Cyclooxygenase (Cox)-2 expression was detected by Western blot. Components of the IL-1 signaling pathway were detected by flow cytometry, ELISA, Western blot, and immunofluorescence.

RESULTS

Cytokine and PGE(2) production and Cox-2 expression were greatest in corneal fibroblasts. VEGF production was greatest in Tenon's capsule fibroblasts. Variations in IL-1 receptor and receptor antagonist expression, IκBα degradation and p65 nuclear translocation, however, did not account for these differences, but overexpression of the NF-κB member RelB dampened Cox-2 expression in all three fibroblast types.

CONCLUSIONS

The results highlight the inherent differences between ocular fibroblast strains and provide crucial insight into novel, tissue-specific treatments for ocular inflammation and disease, such as RelB overexpression.

Yin yang 1 is a novel regulator of pulmonary fibrosis

RATIONALE

The differentiation of fibroblasts into myofibroblasts is a cardinal feature of idiopathic pulmonary fibrosis (IPF). The transcription factor Yin Yang 1 (YY1) plays a role in the proliferation and differentiation of diverse cell types, but its role in fibrotic lung diseases is not known.

OBJECTIVES

To elucidate the mechanism by which YY1 regulates fibroblast differentiation and lung fibrosis.

METHODS

Lung fibroblasts were cultured with transforming growth factor (TGF)-β or tumor necrosis factor-α. Nuclear factor (NF)-κB, YY1, and α-smooth muscle actin (SMA) were determined in protein, mRNA, and promoter reporter level. Lung fibroblasts and lung fibrosis were assessed in a partial YY1-deficient mouse and a YY1(f/f) conditional knockout mouse after being exposed to silica or bleomycin.

MEASUREMENTS AND MAIN RESULTS

TGF-β and tumor necrosis factor-α up-regulated YY1 expression in lung fibroblasts. TGF-β-induced YY1 expression was dramatically decreased by an inhibitor of NF-κB, which blocked I-κB degradation. YY1 is significantly overexpressed in both human IPF and murine models of lung fibrosis, including in the aggregated pulmonary fibroblasts of fibrotic foci. Furthermore, the mechanism of fibrogenesis is that YY1 can up-regulate α-SMA expression in pulmonary fibroblasts. YY1-deficient (YY1(+/-)) mice were significantly protected from lung fibrosis, which was associated with attenuated α-SMA and collagen expression. Finally, decreasing YY1 expression through instilled adenovirus-cre in floxed-YY1(f/f) mice reduced lung fibrosis.

CONCLUSIONS

YY1 is overexpressed in fibroblasts in both human IPF and murine models in a NF-κB-dependent manner, and YY1 regulates fibrogenesis at least in part by increasing α-SMA and collagen expression. Decreasing YY1 expression may provide a new therapeutic strategy for pulmonary fibrosis.