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Immune responses to injury and their links to eye disease. Transl Res 2021; 236:52-71. [PMID: 34051364 PMCID: PMC8380715 DOI: 10.1016/j.trsl.2021.05.005] [Citation(s) in RCA: 72] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 05/12/2021] [Accepted: 05/24/2021] [Indexed: 12/31/2022]
Abstract
The eye is regarded as an immune privileged site. Since the presence of a vasculature would impair vision, the vasculature of the eye is located outside of the central light path. As a result, many regions of the eye evolved mechanisms to deliver immune cells to sites of dysgenesis, injury, or in response to the many age-related pathologies. While the purpose of these immune responses is reparative or protective, cytokines released by immune cells compromise visual acuity by inducing inflammation and fibrosis. The response to traumatic or pathological injury is distinct in different regions of the eye. Age-related diseases impact both the anterior and posterior segment and lead to reduced quality of life and blindness. Here we focus attention on the role that inflammation and fibrosis play in the progression of age-related pathologies of the cornea and the lens as well as in glaucoma, the formation of epiretinal membranes, and in proliferative vitreoretinopathy.
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Key Words
- 2ryERM
- A T-helper cell that expresses high levels of IL-17 which can suppress T-regulatory cell function
- A cytokine expressed early during inflammation that attracts neutrophils
- A cytokine expressed early during inflammation that attracts neutrophils, sometimes referred to as monocyte chemoattractant protein-1 (MCP-1))
- A mouse model that lacks functional T and B cells and used to study the immune response
- A pigmented mouse strain used for research and known to mount a primarily Th1 response to infection
- A protein encoded by the ADGRE1 gene that, in mice, is expressed primarily on macrophages
- A strain of pigmented mice used in glaucoma research
- ACAID
- APCs
- ASC
- An albino mouse strain used for research and known to mount a primarily Th2 response to infection
- Antigen Presenting Cells, this class includes dendritic cells and monocytes
- BALB/c
- BM
- C57BL6
- CCL2
- CD45
- CNS
- CXCL1
- Central Nervous System
- Cluster of differentiation 45 antigen
- DAMPs
- DBA/2J
- EBM
- ECM
- EMT
- ERM
- Epithelial Basement Membrane
- F4/80
- FGF2
- HA =hyaluronic acid
- HSK
- HSP
- HSPGs
- HSV
- ICN
- IL-20
- IL6
- ILM
- IOP
- Inner (or internal) limiting membrane
- Interleukin 6
- Interleukin-20
- MAGP1
- MHC-II
- Major histocompatibility complex type II, a class of MHC proteins typically found only on APCs
- Microfibril-associated glycoprotein 1
- N-cad
- N-cadherin
- NEI
- NK
- National Eye Institute
- Natural killer T cells
- PCO
- PDGF
- PDR
- PVD
- PVR
- Platelet derived growth factor
- Posterior capsular opacification
- RGC
- RPE
- RRD
- Rag1-/-
- Retinal ganglion cells
- Retinal pigment epithelial cells
- SMAD
- Sons of Mothers Against Decapentaplegic, SMADs are a class of molecules that mediate TGF and bone morphogenetic protein signaling
- T-helper cell 1 response, proinflammatory adaptive response involving interferon gamma and associated with autoimmunity
- T-helper cell 2 response involving IgE and interleukins 4,5, and 13, also induces the anti-inflammatory interleukin 10 family cytokines
- T-regulatory cell
- TG
- TGF1
- TM
- TNF
- Th1
- Th17
- Th2
- Transforming growth factor 1
- Treg
- Tumor necrosis factor a cytokine produced during inflammation
- VEGF
- Vascular endothelial growth factor
- WHO
- World Health Organization
- anterior chamber immune deviation
- anterior subcapsular cataracts
- basement membrane
- damage-associated molecular patterns
- epiretinal membrane
- epiretinal membrane secondary to disease pathology
- epithelial-mesenchymal transition
- extracellular matrix
- fibroblast growth factor 2, also referred to as basic FGF
- heat shock protein
- heparan sulfate proteoglycans
- herpes simplex virus
- herpes stromal keratitis
- iERM
- idiopathic epiretinal membrane
- intraepithelial corneal nerves
- intraocular pressure
- mTOR
- mechanistic target of rapamycin, a protein kinase encoded by the MTOR genes that regulates a variety of signal transduction events including cell growth, autophagy and actin cytoskeleton
- posterior vitreous detachment
- proliferative diabetic retinopathy
- proliferative vitreoretinopathy
- rhegmatogenous (rupture, tear) retinal detachment
- trabecular meshwork
- trigeminal ganglion
- αSMA
- α−Smooth muscle actin, a class of actin expressed in mesenchymal cells
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Macrophage recruitment in immune-privileged lens during capsule repair, necrotic fiber removal, and fibrosis. iScience 2021; 24:102533. [PMID: 34142044 PMCID: PMC8188486 DOI: 10.1016/j.isci.2021.102533] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 04/01/2021] [Accepted: 05/10/2021] [Indexed: 12/26/2022] Open
Abstract
Emerging evidence challenges the lens as an immune-privileged organ. Here, we provide a direct mechanism supporting a role of macrophages in lens capsule rupture repair. Posterior lens capsule rupture in a connexin 50 and aquaporin 0 double-knockout mouse model resulted in lens tissue extrusion into the vitreous cavity with formation of a “tail-like” tissue containing delayed regressed hyaloid vessels, fibrotic tissue and macrophages at postnatal (P) 15 days. The macrophages declined after P 30 days with M2 macrophages detected inside the lens. By P 90 days, the “tail-like” tissue completely disappeared and the posterior capsule rupture was sealed with thick fibrotic tissue. Colony-stimulating factor 1 (CSF-1) accelerated capsule repair, whereas inhibition of the CSF-1 receptor delayed the repair. Together, these results suggest that lens posterior rupture leads to the recruitment of macrophages delivered by the regression delayed hyaloid vessels. CSF-1-activated M2 macrophages mediate capsule rupture repair and development of fibrosis. Lens posterior rupture delays regression of the hyaloid vessels. Lens posterior rupture recruits macrophages delivered by the hyaloid vessels. Macrophages mediate necrotic fiber cell removal and capsule rupture sealing. CSF-1 activated M2 macrophages facilitate capsular rupture sealing by fibrosis.
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DeDreu J, Bowen CJ, Logan CM, Pal-Ghosh S, Parlanti P, Stepp MA, Menko AS. An immune response to the avascular lens following wounding of the cornea involves ciliary zonule fibrils. FASEB J 2020; 34:9316-9336. [PMID: 32452112 PMCID: PMC7384020 DOI: 10.1096/fj.202000289r] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 04/22/2020] [Accepted: 04/28/2020] [Indexed: 12/12/2022]
Abstract
The lens and central cornea are avascular. It was assumed that the adult lens had no source of immune cells and that the basement membrane capsule surrounding the lens was a barrier to immune cell migration. Yet, microfibril‐associated protein‐1 (MAGP1)‐rich ciliary zonules that originate from the vasculature‐rich ciliary body and extend along the surface of the lens capsule, form a potential conduit for immune cells to the lens. In response to cornea debridement wounding, we find increased expression of MAGP1 throughout the central corneal stroma. The immune cells that populate this typically avascular region after wounding closely associate with this MAGP1‐rich matrix. These results suggest that MAGP1‐rich microfibrils support immune cell migration post‐injury. Using this cornea wound model, we investigated whether there is an immune response to the lens following cornea injury involving the lens‐associated MAGP1‐rich ciliary zonules. Our results provide the first evidence that following corneal wounding immune cells are activated to travel along zonule fibers that extend anteriorly along the equatorial surface of the lens, from where they migrate across the anterior lens capsule. These results demonstrate that lens‐associated ciliary zonules are directly involved in the lens immune response and suggest the ciliary body as a source of immune cells to the avascular lens.
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Affiliation(s)
- JodiRae DeDreu
- Department of Pathology, Anatomy and Cell Biology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, USA
| | - Caitlin J Bowen
- Department of Pathology, Anatomy and Cell Biology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, USA
| | - Caitlin M Logan
- Department of Pathology, Anatomy and Cell Biology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, USA
| | - Sonali Pal-Ghosh
- Department of Anatomy and Cell Biology, George Washington University School of Medicine and Health Sciences, Washington, DC, USA
| | - Paola Parlanti
- George Washington University Nanofabrication and Imaging Center, George Washington University School of Medicine and Health Sciences, Washington, DC, USA
| | - Mary Ann Stepp
- Department of Anatomy and Cell Biology, George Washington University School of Medicine and Health Sciences, Washington, DC, USA.,Department of Ophthalmology, George Washington University School of Medicine and Health Sciences, Washington, DC, USA
| | - A Sue Menko
- Department of Pathology, Anatomy and Cell Biology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, USA.,Department of Ophthalmology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, USA
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Parlanti P, Pal-Ghosh S, Williams A, Tadvalkar G, Popratiloff A, Stepp MA. Axonal debris accumulates in corneal epithelial cells after intraepithelial corneal nerves are damaged: A focused Ion Beam Scanning Electron Microscopy (FIB-SEM) study. Exp Eye Res 2020; 194:107998. [PMID: 32209319 PMCID: PMC7697722 DOI: 10.1016/j.exer.2020.107998] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 02/13/2020] [Accepted: 03/07/2020] [Indexed: 12/15/2022]
Abstract
The intraepithelial corneal nerves (ICNs) that innervate the corneal epithelium are maintained through interactions with corneal epithelial cells and the extracellular matrix they produce. One to several axons bundle together within the basal cell layer and extend parallel to the ocular surface or branch and extend apically. Here we use 3-dimentional (3D) ultrastructural reconstructions of control and trephine injured mouse corneal epithelium and stroma produced using Focused Ion Beam Scanning Electron Microscope (FIB-SEM) to determine whether corneal epithelial or immune cells resident in the epithelium remove axonal debris and degrade it in their lysosomes after trephine injury to the cornea. We demonstrate that axonal fragments are internalized in the corneal epithelium and accumulate within electron dense structures consistent with lysosomes 3 h after trephine injury in both epithelial and immune cells located among the basal cells of the trephine injured cornea. Confocal imaging showed fewer CD45+ immune cells within the corneal epithelium after trephine injury compared to controls. The resolution obtained using FIB-SEM also allowed us to show that the presence of sensory axons at the basal aspect of the epithelial basal cells close to the anterior aspect of the epithelial basement membrane (EBM) is associated with a focal reduction in EBM thickness. In addition, we show using FIB-SEM and confocal imaging that superficial trephine injuries that do not penetrate the stroma, damage the integrity of anterior stromal nerves. These studies are the first to look at the mouse cornea following nerve injury using FIB-SEM.
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Affiliation(s)
- Paola Parlanti
- GW Nanofabrication and Imaging Center, The George Washington School of Medicine and Health Sciences, Washington DC, 20052, USA
| | - Sonali Pal-Ghosh
- Department of Anatomy and Cell Biology, The George Washington School of Medicine and Health Sciences, Washington DC, 20052, USA
| | - Alexa Williams
- Department of Anatomy and Cell Biology, The George Washington School of Medicine and Health Sciences, Washington DC, 20052, USA
| | - Gauri Tadvalkar
- Department of Anatomy and Cell Biology, The George Washington School of Medicine and Health Sciences, Washington DC, 20052, USA
| | - Anastas Popratiloff
- GW Nanofabrication and Imaging Center, The George Washington School of Medicine and Health Sciences, Washington DC, 20052, USA; Department of Anatomy and Cell Biology, The George Washington School of Medicine and Health Sciences, Washington DC, 20052, USA
| | - Mary Ann Stepp
- Department of Anatomy and Cell Biology, The George Washington School of Medicine and Health Sciences, Washington DC, 20052, USA; Department of Ophthalmology, The George Washington School of Medicine and Health Sciences, Washington DC, 20052, USA.
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Jiao H, Naranjo Golborne C, Dando SJ, McMenamin PG, Downie LE, Chinnery HR. Topographical and Morphological Differences of Corneal Dendritic Cells during Steady State and Inflammation. Ocul Immunol Inflamm 2019; 28:898-907. [PMID: 31429614 DOI: 10.1080/09273948.2019.1646775] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
PURPOSE We report novel differences in mouse corneal DC morphology and density during local and systemic inflammation. METHODS Local inflammation was induced by topical application of saline or TLR9 agonist CpG-ODN on abraded C57BL6J mouse corneas. Systemic inflammation was induced by intraperitoneal injection of lipopolysaccharide (LPS) in CD11c-YFP mice. Corneal epithelial DCs from uninjured, injured and contralateral eyes were analysed by confocal microscopy. RESULTS Following local CpG delivery on the injured cornea, the DC density and size increased in both central and peripheral regions. Contralateral uninjured eyes displayed enlarged DC morphology in the central cornea compared to naïve cohorts. After systemic LPS, the size of DCs in the central cornea was lower at 2 hours, returning to baseline after 24 hours. CONCLUSIONS Corneal DCs respond differently in terms of shape and distribution during local and systemic inflammation. These features can serve as in vivo indicators in ocular and systemic diseases.
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Affiliation(s)
- Haihan Jiao
- Department of Optometry and Vision Sciences, The University of Melbourne , Melbourne, Australia
| | - Cecilia Naranjo Golborne
- Monash Genome Modification Platform, Faculty of Medicine, Nursing and Health Sciences, Monash University , Melbourne, Australia
| | - Samantha J Dando
- School of Biomedical Sciences and Institute of Health and Biomedical Innovation, Queensland University of Technology , Brisbane, Australia.,Monash Biomedicine Discovery Institute and Department of Anatomy & Developmental Biology, Faculty of Medicine, Nursing and Health Sciences, Monash University , Melbourne, Australia
| | - Paul G McMenamin
- Monash Biomedicine Discovery Institute and Department of Anatomy & Developmental Biology, Faculty of Medicine, Nursing and Health Sciences, Monash University , Melbourne, Australia
| | - Laura E Downie
- Department of Optometry and Vision Sciences, The University of Melbourne , Melbourne, Australia
| | - Holly R Chinnery
- Department of Optometry and Vision Sciences, The University of Melbourne , Melbourne, Australia
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Menko AS, Walker JL, Stepp MA. Fibrosis: Shared Lessons From the Lens and Cornea. Anat Rec (Hoboken) 2019; 303:1689-1702. [PMID: 30768772 PMCID: PMC6697240 DOI: 10.1002/ar.24088] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Revised: 08/23/2018] [Accepted: 09/04/2018] [Indexed: 12/13/2022]
Abstract
Regenerative repair in response to wounding involves cell proliferation and migration. This is followed by the reestablishment of cell structure and organization and a dynamic process of remodeling and restoration of the injured cells' extracellular matrix microenvironment and the integration of the newly synthesized matrix into the surrounding tissue. Fibrosis in the lungs, liver, and heart can lead to loss of life and in the eye to loss of vision. Learning to control fibrosis and restore normal tissue function after injury repair remains a goal of research in this area. Here we use knowledge gained using the lens and the cornea to provide insight into how fibrosis develops and clues to how it can be controlled. The lens and cornea are less complex than other tissues that develop life‐threatening fibrosis, but they are well characterized and research using them as model systems to study fibrosis is leading toward an improved understanding of fibrosis. Here we summarize the current state of the literature and how it is leading to promising new treatments. Anat Rec, 2019. © 2019 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.
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Affiliation(s)
- A Sue Menko
- Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania
| | - Janice L Walker
- Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania
| | - Mary Ann Stepp
- Department of Anatomy and Cell Biology, George Washington University, Washington, District of Columbia
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Logan CM, Bowen CJ, Menko AS. Induction of Immune Surveillance of the Dysmorphogenic Lens. Sci Rep 2017; 7:16235. [PMID: 29176738 PMCID: PMC5701161 DOI: 10.1038/s41598-017-16456-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Accepted: 11/12/2017] [Indexed: 01/10/2023] Open
Abstract
The lens has been considered to be an immune privileged site not susceptible to the immune processes normally associated with tissue injury and wound repair. However, as greater insight into the immune surveillance process is gained, we have reevaluated the concept of immune privilege. Our studies using an N-cadherin lens-specific conditional knockout mouse, N-cadΔlens, show that loss of this cell-cell junctional protein leads to lens degeneration, necrosis and fibrotic change, postnatally. The degeneration of this tissue induces an immune response resulting in immune cells populating the lens that contribute to the development of fibrosis. Additionally, we demonstrate that the lens is connected to the lymphatic system, with LYVE(+) labeling reaching the lens along the suspensory ligaments that connect the lens to the ciliary body, providing a potential mechanism for the immune circulation. Importantly, we observe that degeneration of the lens activates an immune response throughout the eye, including cornea, vitreous humor, and retina, suggesting a coordinated protective response in the visual system to defects of a component tissue. These studies demonstrate that lens degeneration induces an immune response that can contribute to the fibrosis that often accompanies lens dysgenesis, a consideration for understanding organ system response to injury.
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Affiliation(s)
- Caitlin M Logan
- Thomas Jefferson University, Department of Pathology, Anatomy and Cell Biology, Philadelphia, Pennsylvania, 19107, United States
| | - Caitlin J Bowen
- Thomas Jefferson University, Department of Pathology, Anatomy and Cell Biology, Philadelphia, Pennsylvania, 19107, United States
| | - A Sue Menko
- Thomas Jefferson University, Department of Pathology, Anatomy and Cell Biology, Philadelphia, Pennsylvania, 19107, United States.
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Stepp MA, Tadvalkar G, Hakh R, Pal-Ghosh S. Corneal epithelial cells function as surrogate Schwann cells for their sensory nerves. Glia 2016; 65:851-863. [PMID: 27878997 DOI: 10.1002/glia.23102] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 10/30/2016] [Accepted: 11/02/2016] [Indexed: 12/13/2022]
Abstract
The eye is innervated by neurons derived from both the central nervous system and peripheral nervous system (PNS). While much is known about retinal neurobiology and phototransduction, less attention has been paid to the innervation of the eye by the PNS and the roles it plays in maintaining a functioning visual system. The ophthalmic branch of the trigeminal ganglion contains somas of neurons that innervate the cornea. These nerves provide sensory functions for the cornea and are referred to as intraepithelial corneal nerves (ICNs) consisting of subbasal nerves and their associated intraepithelial nerve terminals. ICNs project for several millimeters within the corneal epithelium without Schwann cell support. Here, we present evidence for the hypothesis that corneal epithelial cells function as glial cells to support the ICNs. Much of the data supporting this hypothesis is derived from studies of corneal development and the reinnervation of the ICNs in the rodent and rabbit cornea after superficial wounds. Corneal epithelial cells activate in response to injury via mechanisms similar to those induced in Schwann cells during Wallerian Degeneration. Corneal epithelial cells phagocytize distal axon fragments within hours of ICN crush wounds. During aging, the proteins, lipids, and mitochondria within the ICNs become damaged in a process exacerbated by UV light. We propose that ICNs shed their aged and damaged termini and continuously elongate to maintain their density. Available evidence points to new unexpected roles for corneal epithelial cells functioning as surrogate Schwann cells for the ICNs during homeostasis and in response to injury. GLIA 2017;65:851-863.
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Affiliation(s)
- Mary Ann Stepp
- Department of Anatomy and Regenerative Biology, George Washington University Medical School, Washington, DC
| | - Gauri Tadvalkar
- Department of Anatomy and Regenerative Biology, George Washington University Medical School, Washington, DC
| | - Raymond Hakh
- Department of Anatomy and Regenerative Biology, George Washington University Medical School, Washington, DC
| | - Sonali Pal-Ghosh
- Department of Anatomy and Regenerative Biology, George Washington University Medical School, Washington, DC
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Daull P, Feraille L, Elena PP, Garrigue JS. Comparison of the Anti-Inflammatory Effects of Artificial Tears in a Rat Model of Corneal Scraping. J Ocul Pharmacol Ther 2016; 32:109-18. [PMID: 26751507 PMCID: PMC4779975 DOI: 10.1089/jop.2015.0054] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Accepted: 10/19/2015] [Indexed: 01/10/2023] Open
Abstract
PURPOSE Artificial tears (ATs) are used routinely to alleviate the symptoms of mild to moderate dry eye. Preservative-free cationic emulsions (eg, Cationorm(®)) are an innovative approach for the management of signs and symptoms of dry eye. The aim of the present exploratory experiment was to evaluate the efficacy of this cetalkonium chloride (CKC)-containing cationic emulsion on debrided cornea and to characterize its effects on scraping-induced inflammation. METHODS Four ATs were assessed in a rat model of corneal scraping. The upper part of the corneal epithelium was scraped before a 5-day treatment, followed by clinical evaluations and fluorescein staining to evaluate cornea recovery. The anti-inflammatory efficacy of the ATs was assessed in vivo and in vitro. RESULTS In vivo confocal microscopy (IVCM) revealed a trend toward better corneal clinical signs (lower IVCM scores) for the animals treated with the unpreserved ATs. Benzalkonium chloride treatment decreased goblet cell count by 37.5%. While the soft-preserved Systane Balance(®) and Optive(®) and the preservative-free Vismed(®) had no effect on the goblet cell count, Cationorm increased this count by almost 40%. Interestingly, inflammatory cell infiltration in the stroma was at its lowest following treatment with the preservative-free Cationorm. Cationorm is also the only AT decreasing IL6- and IL8-stimulated secretion by 59% and 74%, respectively. CONCLUSION By restoring an adequately hydrated ocular surface environment, the different ATs promote corneal epithelium healing. These data position Cationorm as a promising AT for the management of signs and symptoms of dry eye in patients with mild to moderate dry eye disease presenting chronic subclinical levels of ocular inflammation.
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Partial denervation of sub-basal axons persists following debridement wounds to the mouse cornea. J Transl Med 2015; 95:1305-18. [PMID: 26280222 PMCID: PMC4626298 DOI: 10.1038/labinvest.2015.113] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Revised: 06/18/2015] [Accepted: 06/24/2015] [Indexed: 01/09/2023] Open
Abstract
Although sensory reinnervation occurs after injury in the peripheral nervous system, poor reinnervation in the elderly and those with diabetes often leads to pathology. Here we quantify sub-basal axon density in the central and peripheral mouse cornea over time after three different types of injury. The mouse cornea is highly innervated with a dense array of sub-basal nerves that form a spiral called the vortex at the corneal center or apex; these nerves are readily detected within flat mounted corneas. After anesthesia, corneal epithelial cells were removed using either a dulled blade or a rotating burr within an area demarcated centrally with a 1.5 mm trephine. A third wound type, superficial trephination, involved demarcating the area with the 1.5 mm trephine but not removing cells. By 7 days after superficial trephination, sub-basal axon density returns to control levels; by 28 days the vortex reforms. Although axon density is similar to control 14 days after dulled blade and rotating burr wounding, defects in axon morphology at the corneal apex remain. After 14 days, axons retract from the center leaving the sub-basal axon density reduced by 37.2 and 36.8% at 28 days after dulled blade and rotating burr wounding, respectively, compared with control. Assessment of inflammation using flow cytometry shows that persistent inflammation is not a factor in the incomplete reinnervation. Expression of mRNAs encoding 22 regeneration-associated genes involved in axon targeting assessed by QPCR reveals that netrin-1 and ephrin signaling are altered after wounding. Subpopulations of corneal epithelial basal cells at the corneal apex stop expressing ki67 as early as 7 days after injury and by 14 and 28 days after wounding, many of these basal cells undergo apoptosis and die. Although sub-basal axons are restored to their normal density and morphology after superficial trephination, sub-basal axon recovery is partial after debridement wounds. The increase in corneal epithelial basal cell apoptosis at the apex observed at 14 days after corneal debridement may destabilize newly reinnervated sub-basal axons and lead to their retraction toward the periphery.
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