Yangluowa Qu

Short ragweed pollen triggers allergic inflammation through Toll-like receptor 4-dependent thymic stromal lymphopoietin/OX40 ligand/OX40 signaling pathways.

BACKGROUND Allergic diseases affect a large population. Pollen, an ubiquitous allergen, is the trigger of seasonal rhinitis, conjunctivitis, and asthma, as well as an exacerbating factor of atopic dermatitis. However, the underlying mechanism by which pollen induces thymic stromal lymphopoietin (TSLP)-triggered allergic inflammation through epithelial innate immunity is largely unknown. OBJECTIVE We sought to explore whether short ragweed (SRW) pollen induces TSLP/OX40 ligand (OX40L)/OX40 signaling through Toll-like receptor (TLR) 4-dependent pathways in patients with allergic disease. METHODS Three models were used for this study, a well-characterized murine model of allergic conjunctivitis induced by SRW pollen, a topical challenge model on the murine ocular surface, and a culture model of primary human corneal epithelium exposed to aqueous extract of defatted SRW pollen (SRWe). RESULTS The topical challenges with SRW pollen generated typical allergic conjunctivitis in BALB/c mice. Clinical signs, stimulated TSLP/OX40L/OX40 signaling, and T(H)2 cytokine levels in the ocular mucosa and draining cervical lymph nodes were significantly reduced or eliminated in TLR4-deficient (Tlr4-d) or myeloid differentiation primary response gene 88 (MyD88) knockout (MyD88(-/-)) mice compared with those seen in their wild-type littermates. SRWe stimulated TSLP production by ocular epithelia in wild-type but not Tlr4-d or MyD88(-/-) mice. SRWe-stimulated TSLP was blocked by TLR4 antibody and nuclear factor κB inhibitor in murine and human corneal epithelia. CONCLUSION For the first time, we have shown that SRW pollen, acting as a functional TLR4 agonist, initiates TLR4-dependent TSLP/OX40L/OX40 signaling, which triggers T(H)2-dominant allergic inflammation. These findings shed light on the understanding of mucosal epithelial innate immunity and create new therapeutic targets to cure allergic diseases.

Netrin-1 Simultaneously Suppresses Corneal Inflammation and Neovascularization

PURPOSE To investigate the effect of netrin-1 on alkali burn-induced corneal inflammation and neovascularization. METHODS The expression of netrin-1 and its receptors UNC5A, UNC5B, UNC5C, UNC5D, adenosine 2b receptor (A2BAR), deleted in colorectal cancer (DCC), and neogenin in normal and alkali-burned rat cornea were determined by RT-PCR and/or Western blot analysis, or immunostaining. Topical netrin-1 protein was applied to treat rat corneal alkali-burn injury for 14 consecutive days, started right after the injury or 10 days postinjury. Corneal inflammation and neovascularization were observed under slit lamp microscope. The apoptosis of corneal cells was determined by terminal deoxynucleotidyl transferase-mediated nick end labeling assay. Corneal inflammatory cell infiltration was evaluated by immunostaining of anti-PMN and anti-ED1 antibodies. The expression of epidermal growth factor (EGF), vascular epidermal growth factor (VEGF), and pigment epithelium-derived factor (PEDF) in rat cornea was determined by Western blot analysis. RESULTS Netrin-1 and its receptor UNC5B were expressed in normal rat corneal epithelium and stromal cells, and their expression decreased after corneal alkali burn. Exogenous netrin-1 administered on rat ocular surfaces resolved alkali burn-induced corneal inflammation, and also suppressed corneal neovascularization. Furthermore, netrin-1 could reverse neovascularization in alkali-burned cornea. The authors found that netrin-1 executed the functions through various mechanisms, including upregulating EGF expression, accelerating epithelial wound healing, inhibiting neutrophil and macrophage infiltration, reducing corneal cell apoptosis, and restoring the equilibrium of VEGF and PEDF in the wounded cornea. CONCLUSIONS Netrin-1 could dampen inflammation, inhibit, and reverse neovascularization in alkali-burned cornea.

Transcription Factor TCF4 Maintains the Properties of Human Corneal Epithelial Stem Cells

TCF4, a key transcription factor of Wnt signaling system, has been recently found to be essential for maintaining stem cells. However, its signaling pathway is not well elucidated. This study was to explore the functional roles and signaling pathway of TCF4 in maintaining adult stem cell properties using human corneal epithelial stem cells as a model. With immunofluorescent staining and real‐time polymerase chain reaction, we observed that TCF4 was exclusively expressed in the basal layer of human limbal epithelium where corneal epithelial stem cells reside. TCF4 was found to be well colocalized with ABCG2 and p63, two recognized epithelial stem/progenitor cell markers. Using in vitro culture models of primary human corneal epithelial cells, we revealed that TCF4 mRNA and protein were upregulated by cells in exponential growth stage, and RNA interference by small interfering RNA‐TCF4 (10‐50 nM) transfection blocked TCF4 signaling and suppressed cell proliferation as measured by WST‐1 assay. TCF4 silence was found to be accompanied by downregulated proliferation‐associated factors p63 and survivin, as well as upregulated cyclin‐dependent kinase inhibitor 1C (p57). By creating a wound healing model in vitro, we identified upregulation and activation of β‐catenin/TCF4 with their protein translocation from cytoplasm to nuclei, as evaluated by reverse transcription‐quantitative real‐time polymerase chain reaction, immunostaining, and Western blotting. Upregulated p63/survivin and downregulated p57 were further identified to be TCF4 downstream molecules that promote cell migration and proliferation in wound healing process. These findings demonstrate that transcription factor TCF4 plays an important role in determining or maintaining the phenotype and functional properties of human corneal epithelial stem cells. STEM CELLS 2012; 30:753–761

Identification of Human Fibroblast Cell Lines as a Feeder Layer for Human Corneal Epithelial Regeneration

There is a great interest in using epithelium generated in vitro for tissue bioengineering. Mouse 3T3 fibroblasts have been used as a feeder layer to cultivate human epithelia including corneal epithelial cells for more than 3 decades. To avoid the use of xeno-components, we evaluated human fibroblasts as an alternative feeder supporting human corneal epithelial regeneration. Five human fibroblast cell lines were used for evaluation with mouse 3T3 fibroblasts as a control. Human epithelial cells isolated from fresh corneal limbal tissue were seeded on these feeders. Colony forming efficiency (CFE) and cell growth capacity were evaluated on days 5–14. The phenotype of the regenerated epithelia was evaluated by morphology and immunostaining with epithelial markers. cDNA microarray was used to analyze the gene expression profile of the supportive human fibroblasts. Among 5 strains of human fibroblasts evaluated, two newborn foreskin fibroblast cell lines, Hs68 and CCD1112Sk, were identified to strongly support human corneal epithelial growth. Tested for 10 passages, these fibroblasts continually showed a comparative efficiency to the 3T3 feeder layer for CFE and growth capacity of human corneal epithelial cells. Limbal epithelial cells seeded at 1×104 in a 35-mm dish (9.6 cm2) grew to confluence (about 1.87–2.41×106 cells) in 12–14 days, representing 187–241 fold expansion with over 7–8 doublings on these human feeders. The regenerated epithelia expressed K3, K12, connexin 43, p63, EGFR and integrin β1, resembling the phenotype of human corneal epithelium. DNA microarray revealed 3 up-regulated and 10 down-regulated genes, which may be involved in the functions of human fibroblast feeders. These findings demonstrate that commercial human fibroblast cell lines support human corneal epithelial regeneration, and have potential use in tissue bioengineering for corneal reconstruction.

Oxygen Tension Affects Terminal Differentiation of Corneal Limbal Epithelial Cells

Oxygen concentration has been shown to be crucial in the proliferation and differentiation of various types of cells, while the impact of oxygen tension on the lineage commitment of epithelial cells remains elusive. In this study, we investigated the effect of hypoxia on the differentiation of corneal limbal epithelium using an ex vivo squamous metaplasia model. Under normoxic conditions when exposed to air, the hyperproliferation and abnormal epidermal‐like differentiation of human corneal limbal epithelium was induced, whereas when exposed to air under hypoxic conditions, although we observed augmented proliferation, the abnormal differentiation was inhibited. The Notch signaling pathway was activated in hypoxic cultures, whereas the p38 MAPK signaling pathway was downregulated. The addition of Notch inhibitor under hypoxic conditions restored the activation of p38 MAPK and resulted in the recidivation of limbal epithelial cells to epidermal‐like differentiation. Moreover, the epidermal‐like differentiation of rabbit limbal epithelial cells was also blocked under hypoxic conditions in corneal epithelial cell sheets engineered ex vivo. We concluded that hypoxia can prevent abnormal differentiation while enhancing the proliferation of corneal limbal epithelial cells. Hypoxia coupled with air exposure can be used in the tissue engineering of corneal limbal epithelium. J. Cell. Physiol. 226: 2429–2437, 2011.

Amniotic membrane inhibits squamous metaplasia of human conjunctival epithelium

Squamous metaplasia is a common pathological process that occurs in the ocular surface epithelium. At present, there is no effective treatment for this abnormality. In the current study, we established an ex vivo conjunctival squamous metaplasia model by culturing human conjunctival tissues at an air-liquid interface for durations of up to 12 days. We then investigated the effects of amniotic membrane (AM) on squamous metaplasia through coculture of conjunctival tissues with AM or AM extract. We found that metaplasia features such as hyperproliferation and abnormal epidermal differentiation of conjunctival epithelium could be inhibited by AM or its extract. In addition, existing squamous metaplasia of conjunctival epithelium could be reversed to a nearly normal phenotype by AM. The mechanism by which AM prevents squamous metaplasia may involve downregulation of p38 mitogen-activated protein kinase and Wnt signaling pathways, which were activated in conjunctival explants cultured with an airlift technique. In conclusion, AM can inhibit and reverse squamous metaplasia of conjunctival epithelium. This finding may shed new light on prevention and treatment of diseases that involve epithelial squamous metaplasia.

Therapeutic effects of topical netrin-4 inhibits corneal neovascularization in alkali-burn rats.

Netrins are secreted molecules involved in axon guidance and angiogenesis. However, the role of netrins in the vasculature remains unclear. Netrin-4 and netrin-1 have been found to be either pro- or antiangiogenic factors. Previously, we found that netrin-1 acts as an anti-angiogenic factor in rats by inhibiting alkali burn-induced corneal neovascularization. Here, we further investigate the effects of netrin-4, another member of the same netrin family, on neovascularization in vitro and in vivo. We found that netrin-4 functions similarly as netrin-1 in angiogenesis. In vitro angiogenesis assay shows that netrin-4 affected human umbilical vein endothelial cell (HUVEC) tube formation, viability and proliferation, apoptosis, migration, and invasion in a dose-dependent manner. Netrin-4 was topically applied in vivo to alkali-burned rat corneas on day 0 (immediately after injury) and/or day 10 post-injury. Netrin-4 subsequently suppressed and reversed corneal neovascularization. Netrin-4 inhibited corneal epithelial and stromal cell apoptosis, inhibited vascular endothelial growth factor (VEGF), but promoted pigment epithelium-derived factor (PEDF) expression, decreased NK-KB p65 expression, and inhibits neutrophil and macrophage infiltration. These results indicate that netrin-4 shed new light on its potential roles in treatmenting for angiogenic diseases that affect the ocular surface, as well as other tissues.

An Ultra-thin Amniotic Membrane as Carrier in Corneal Epithelium Tissue-Engineering

Amniotic membranes (AMs) are widely used as a corneal epithelial tissue carrier in reconstruction surgery. However, the engineered tissue transparency is low due to the translucent thick underlying AM stroma. To overcome this drawback, we developed an ultra-thin AM (UAM) by using collagenase IV to strip away from the epithelial denuded AM (DAM) some of the stroma. By thinning the stroma to about 30 μm, its moist and dry forms were rendered acellular, optically clear and its collagen framework became compacted and inerratic. Engineered rabbit corneal epithelial cell (RCEC) sheets generated through expansion of limbal epithelial cells on UAM were more transparent and thicker than those expanded on DAM. Moreover, ΔNp63 and ABCG2 gene expression was greater in tissue engineered cell sheets expanded on UAM than on DAM. Furthermore, 2 weeks after surgery, the cornea grafted with UAM based cell sheets showed higher transparency and more stratified epithelium than the cornea grafted with DAM based cell sheets. Taken together, tissue engineered corneal epithelium generated on UAM has a preferable outcome because the transplanted tissue is more transparent and better resembles the phenotype of the native tissue than that obtained by using DAM for this procedure. UAM preserves compact layer of the amniotic membrane and maybe an ideal substrate for corneal epithelial tissue engineering.

Unique Expression Pattern and Functional Role of Periostin in Human Limbal Stem Cells

Periostin is a non-structural matricellular protein. Little is known about periostin in human limbal stem cells (LSCs). This study was to explore the unique expression pattern and functional role of periostin in maintaining the properties of human LSCs. Fresh donor corneal tissues were used to make cryosections for evaluation of periostin expression on ex vivo tissues. Primary human limbal epithelial cells (HLECs) were generated from limbal explant culture. In vitro culture models for proliferation and epithelial regeneration were performed to explore functional role of periostin in LSCs. The mRNA expression was determined by reverse transcription and quantitative real-time PCR (RT-qPCR), and the protein production and localization were detected by immunofluorescent staining and Western blot analysis. Periostin protein was found to be exclusively immunolocalized in the basal layer of human limbal epithelium. Periostin localization was well matched with nuclear factor p63, but not with corneal epithelial differentiation marker Keratin 3. Periostin transcripts was also highly expressed in limbal than corneal epithelium. In primary HLECs, periostin expression at mRNA and protein levels was significantly higher in 50% and 70% confluent cultures at exponential growth stage than in 100% confluent cultures at slow growth or quiescent condition. This expression pattern was similar to other stem/progenitor cell markers (p63, integrin β1 and TCF4). Periostin expression at transcripts, protein and immunoreactivity levels increased significantly during epithelial regeneration in wound healing process, especially in 16-24 hours at wound edge, which was accompanied by similar upregulation and activation of p63, integrin β1 and TCF4. Our findings demonstrated that periostin is exclusively produced by limbal basal epithelium and co-localized with p63, where limbal stem cells reside. Periostin promotes HLEC proliferation and regeneration with accompanied activation of stem/progenitor cell markers p63, integrin β1 and TCF4, suggesting its novel role in maintaining the phenotype and functional properties of LSC.

Air Exposure Induced Characteristics of Dry Eye in Conjunctival Tissue Culture

There are several animal models illustrating dry eye pathophysiology. Current study would like to establish an ex vivo tissue culture model for characterizing dry eye. Human conjunctival explants were cultured under airlift or submerged conditions for up to 2 weeks, and only airlifted conjunctival cultures underwent increased epithelial stratification. Starting on day 4, the suprabasal cells displayed decreased K19 expression whereas K10 keratin became evident in airlift group. Pax6 nuclear expression attenuated already at 2 days, while its perinuclear and cytoplasmic expression gradually increased. MUC5AC and MUC19 expression dramatically decreased whereas the full thickness MUC4 and MUC16 expression pattern disappeared soon after initiating the airlift condition. Real time PCR showed K16, K10 and MUC16 gene up-regulated while K19, MUC5AC, MUC19 and MUC4 down-regulated on day 8 and day 14. On day 2 was the appearance of apoptotic epithelial and stromal cells appeared. The Wnt signaling pathway was transiently activated from day 2 to day 10. The inflammatory mediators IL-1β, TNF-α, and MMP-9 were detected in the conditioned media after 6 to 8 days. In conclusion, airlifted conjunctival tissue cultures demonstrated Wnt signaling pathway activation, coupled with squamous metaplasia, mucin pattern alteration, apoptosis and upregulation of proinflammatory cytokine expression. These changes mimic the pathohistological alterations described in dry eye. This correspondence suggests that insight into the pathophysiology of dry eye may be aided through the use of airlifted conjunctival tissue cultures.