Corneal lymphatic valve formation in relation to lymphangiogenesis

Lymphatic muscle cells contribute to dysfunction of the synovial lymphatic system in inflammatory arthritis in mice

BACKGROUND

Our previous studies reveal that impaired draining function of the synovial lymphatic vessel (LV) contributes to the pathogenesis of inflammatory arthritis, but the cellular and molecular mechanisms involved are not fully understood.

OBJECTIVE

To investigate the involvement of lymphatic muscle cells (LMCs) in mediating impaired LV function in inflammatory arthritis.

METHODS

TNF transgenic (TNF-Tg) arthritic mice were used. The structure and function of the LVs that drained the hind limbs were examined by whole-mount immunofluorescence staining, electron microscopy, and near-infrared lymphatic imaging. Primary LMCs were treated with TNF, and the changes in proliferation, apoptosis, and functional gene expression were assessed. The roles of the herbal drug, Panax notoginseng saponins (PNS), in arthritis and LVs were studied.

RESULTS

TNF-Tg mice developed ankle arthritis with age, which was associated with abnormalities of LVs: (1) dilated capillary LVs with few branch points, (2) mature LVs with reduced LMC coverage and draining function, and (3) degenerative and apoptotic appearance of LMCs. TNF caused LMC apoptosis, reduced expression of muscle functional genes, and promoted the production of nitric oxide (NO) by lymphatic endothelial cells (LECs). PNS attenuated arthritis, restored LMC coverage and draining function of mature LVs, inhibited TNF-mediated NO expression, and reduced LMC apoptosis.

CONCLUSION

The impaired draining function of LVs in TNF-Tg mice involves LMC apoptosis. TNF promotes LMC death directly and indirectly via NO production by LECs. PNS attenuates arthritis, improves LVs, and prevents TNF-induced LMC apoptosis by inhibiting NO production of LECs. LMCs contribute to the dysfunction of synovial LVs in inflammatory arthritis.

Aqueous humor induces lymphatic regression on the ocular surface

PURPOSE

This study is to investigate the potential effect of aqueous humor on already formed lymphatic vessels of the ocular surface including the conjunctiva and the cornea.

METHODS

Aqueous humor harvested from fresh bovine or murine eyeballs were used in the study. It was injected into the subconjunctival space of Prox-1-GFP (green fluorescent protein) transgenic mice. Pre-existing conjunctival lymphatics were observed in vivo using our advanced live imaging system. Additionally, ex vivo tissue cultures were performed in aqueous humor with normal conjunctival tissues or inflamed corneas with newly formed lymphatic vessels. Time lapse images were taken by an advanced live cell imaging system with an incubator. Moreover, human primary microdermal lymphatic endothelial cell culture system was employed to evaluate the effect of aqueous humor on lymphatic tube regression in vitro.

RESULTS

Aqueous humor induced lymphatic regression in both normal conjunctiva and inflamed corneas. It also led to the regression of formed lymphatic tubes by the lymphatic endothelial cells in vitro.

CONCLUSIONS

This study provides the first direct and real time live imaging evidence showing that aqueous humor induces lymphatic regression. Further investigation promises for divulging new mechanisms and therapeutic strategies to treat lymphatic diseases that occur both inside and outside the eye.

Phase-specific functions of macrophages determine injury-mediated corneal hem- and lymphangiogenesis

Macrophages are critical mediators of injury-associated corneal hemangiogenesis (HA) and lymphangiogenesis (LA). Yet, molecular regulators of the hem- and lymphangiogenic potential of corneal wound macrophages are poorly understood. Using two different mouse models of acute (perforating corneal incision injury) and chronic (corneal suture placement model) corneal injury, here we identified distinct functions of early- versus late-phase corneal wound macrophages in corneal HA and LA. Whereas early-phase wound macrophages are essential for initiation and progression of injury-mediated corneal HA and LA, late-phase wound macrophages control maintenance of established corneal lymphatic vessels, but not blood vessels. Furthermore, our findings reveal that the hem- and lymphangiogenic potential of corneal wound macrophages is controlled by the type of the corneal damage. Whereas perforating corneal incision injury induced primarily wound macrophages with lymphangiogenic potential, corneal suture placement provoked wound macrophages with both hem- and lymphangiogenic potential. Our findings highlight a previously unrecognized injury-context dependent role of early- versus late-phase corneal wound macrophages with potential clinical impact on therapy development for sight-threatening corneal neovascular diseases.

Integrin Alpha 9 Blockade Suppresses Lymphatic Valve Formation and Promotes Transplant Survival

Purpose

The lymphatic pathway mediates transplant rejection. We recently reported that lymphatic vessels develop luminal valves in the cornea during lymphangiogenesis, and these valves express integrin alpha 9 (Itga-9) and play a critical role in directing lymph flow. In this study, we used an allogeneic corneal transplantation model to investigate whether Itga-9 blockade could suppress valvulogenesis after transplantation, and how this effect would influence the outcomes of the transplants.

Methods

Orthotopic corneal transplantation was performed between fully mismatched C57BL/6 (donor) and BALB/c (recipient) mice. The recipients were randomized to receive subconjunctival injections of either Itga-9 blocking antibody or isotype control twice a week for 8 weeks. Corneal grafts were assessed in vivo by ophthalmic slit-lamp biomicroscopy and analyzed using Kaplan-Meier survival curves. Additionally, whole-mount full-thickness corneas were evaluated ex vivo by immunofluorescent microscopy on both lymphatic vessels and valves.

Results

Anti–Itga-9 treatment suppressed lymphatic valvulogenesis after transplantation. Our treatment did not affect lymphatic vessel formation or their nasal polarized distribution in the cornea. More importantly, Itga-9 blockade led to a significant promotion of graft survival.

Conclusions

Lymphatic valvulogenesis is critically involved in transplant rejection. Itga-9 targeting may offer a new and effective strategy to interfere with the immune responses and promote graft survival.

Inhibition of lymphangiogenesis in vitro and in vivo by the multikinase inhibitor nintedanib

Purpose

To investigate the feasibility of nintedanib, a novel triple angiokinase inhibitor, for inhibiting lymphatic endothelial cell (LEC)-induced lymphangiogenesis in vitro and inflammatory corneal lymphangiogenesis in vivo.

Materials and methods

Methylthiazolyldiphenyl-tetrazolium bromide (MTT) test, transwell system, and tube-formation assay were used to evaluate the effects of nintedanib on the proliferation, migration, and tube formation of LECs stimulated by vascular endothelial growth factor-C (VEGF-C), basic fibroblast growth factor (bFGF), or platelet-derived growth factor-BB (PDGF-BB). The murine model of suture-induced corneal neovascularization was used to assess the anti-hemangiogenic and anti-lymphangiogenic effects of nintedanib via systemic and topical applications. Corneal flatmounts were stained with lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) and CD31, and the areas of involved blood and lymph vessels were analyzed morphometrically. Corneal cryosections were stained with F4/80 to evaluate inflammatory cell recruitment.

Results

We observed a significant enhanced effect of LEC proliferation, migration, and tube formation with the administration of VEGF-C, PDGF-BB, and bFGF, respectively, which was diminished by nintedanib. Both topical and systemic applications of nintedanib inhibited suture-induced hemangiogenesis and lymphangiogenesis in the murine cornea. A reduction in F4/80⁺ cell infiltration was observed at day 14 after corneal suture for both systemic and topical applications of nintedanib. In comparison with controls, 61% of F4/80⁺ cell recruitment was inhibited via the systemic application of nintedanib, while 49% of F4/80⁺ cell recruitment was inhibited with the topical application of nintedanib.

Conclusion

Nintedanib was shown to inhibit in vitro lymphangiogenesis stimulated by VEGF-C, bFGF, and PDGF-BB. Applied topically or systemically, it effectively inhibited corneal hemangiogenesis and lymphangiogenesis, accompanied by reduced inflammatory cell recruitment, which represents a new promising treatment for graft rejection after penetrating keratoplasty.

Intravital Imaging Reveals Dynamics of Lymphangiogenesis and Valvulogenesis

Lymphatic research signifies a field of rapid progression in recent years. Though lymphatic dysfunction has been found in a myriad of disorders, to date, few effective treatments are available for lymphatic diseases. It is therefore urgent to develop new experimental approaches and therapeutic protocols. The cornea offers an ideal site for lymphatic research due to its transparent nature, accessible location, and lymphatic-free but -inducible features. Moreover, we have recently discovered that corneal lymphatic vessels develop luminal valves as lymphangiogenesis proceeds. This tissue thus provides an optimal tool to study both lymphangiogenesis and valvulogenesis upon a pathological insult. In this paper, we show that the modified Prox-1-GFP mice carrying wildtype C57BL/6 background provide a valuable tool for intravital imaging of corneal lymphatic vessels and valves and can be used to study pathological lymphangiogenesis induced by various insults. Further, we demonstrate the multifaceted dynamics of lymphangiogenesis and valvulogenesis associated with transplantation, from the initiation to regression phases, and report several novel and critical phenomena and mechanisms that cannot be detected by conventional ex vivo approaches. Further investigation holds the great potential for divulging new mechanisms and therapeutic strategies for lymphangiogenesis and lymphangiogenesis-related diseases at various stages and inside or outside the eye.

Integrin Alpha-9 Mediates Lymphatic Valve Formation in Corneal Lymphangiogenesis

PURPOSE

We recently reported that corneal lymphatic vessels develop integrin alpha-9 (Itga-9)-positive valves during inflammatory lymphangiogenesis. The purpose of this study was to further investigate the role of Itga-9 in corneal lymphatic valve formation in vivo and lymphatic endothelial cell (LEC) functions in vitro.

METHODS

Standard murine suture placement model was used to study the effect of Itga-9 blockade on lymphatic valve formation in vivo using Itga-9 neutralizing antibody. Whole-mount corneas were harvested for immunofluorescent microscopic analysis. Additionally, human LEC culture system was used to examine the effect of Itga-9 gene knockdown on cell functions using small interfering RNAs (siRNAs).

RESULTS

Itga-9 blockade in vivo significantly reduced the number of lymphatic valves formed in the inflamed cornea. Moreover, Itga-9 gene knockdown in human LECs suppresses cell functions of proliferation, adhesion, migration, and tube formation.

CONCLUSIONS

Itga-9 is critically involved in corneal lymphatic valve formation. Further investigation of the Itga-9 pathway may provide novel strategies to treat lymphatic-related diseases occurring both inside and outside the eye.