Corneal stromal stem cells reduce corneal scarring by mediating neutrophil infiltration after wounding

Abstract

Corneal scarring limits vision for millions of individuals worldwide. Corneal transplantation (keratoplasty) is the standard of care for corneal opacity; however, it bears the risk of graft rejection and infection and is not universally available. Stem cell therapy holds promise as an alternative to keratoplasty. Stem cells from human corneal stroma (CSSC) induce regeneration of transparent corneal tissue in a mouse wound-healing model. In this study we investigated the mechanism by which CSSC prevent deposition of fibrotic tissue. Infiltration by CD11b+/Ly6G+ neutrophils and myeloperoxidase expression were increased in corneas 24 hr after corneal wounding but were reduced in CSSC-treated wounds. Secretion of TSG-6, a protein known to regulate neutrophil migration, was up-regulated in CSSC in response to TNFα and as CSSC differentiate to keratocytes. In vivo, wounded mouse corneas treated with CSSC contained human TSG-6. Inhibition of neutrophil infiltration into cornea by CSSC was reversed when TSG-6 expression was knocked down using siRNA. Silencing of TSG-6 expression in CSSC reduced their ability to block scarring and the expression of mRNA for fibrosis-associated proteins collagen III, tenascin C, and smooth muscle actin in wounded corneas. Neutropenic mice exhibited a significant reduction in corneal scarring and fibrotic mRNA expression 2 weeks after wounding. These results support the conclusion that neutrophil infiltration is an essential event in the fibrotic response to corneal damage and that prevention of scarring by CSSC is mediated by secretion of TSG-6 by these cells.

Mesenchymal Stem Cells Reduce Corneal Fibrosis and Inflammation via Extracellular Vesicle-Mediated Delivery of miRNA

“…Our previous studies demonstrated a reduction of corneal infiltration by neutrophil granulocytes resulting from treatment with CSSC after wounding. We assessed neutrophil infiltration at 24 hours after wounding by measurement of corneal myeloperoxidase, an enzyme highly expressed by neutrophils . Based on MPO expression, we found that treatment with CSSC EVs significantly reduced on neutrophil infiltration 24 hours after wounding (Fig.…”

“…Assessment of neutrophil infiltration was estimated as previously described by measurement of myeloperoxidase in corneas 24 hours after wounding . Mouse corneas were excised and dissected 24 hours after wounding, removing all residual iris and scleral tissues, and each cornea was incised radially.…”

Concise Review: Stem Cells for Corneal Wound Healing

“…) and contributed to the normal regeneration of stromal ECM with the structure similar to uninjured corneas . These limbal biopsy‐derived stromal cells inhibited neutrophil migration into the wounded stroma, suppressing fibrotic tissue deposition . Such cells also contributed to increased strength of adhesion of flaps created in the laser‐assisted in situ keratomileusis procedure in organ‐cultured corneas, which may be clinically important for flap integrity .…”

Compressed Collagen Enhances Stem Cell Therapy for Corneal Scarring

“…Addition of CSSC to the corneal surface in a fibrin gel immediately after wounding resulted in increased transparency, reduction of fibrotic matrix components and a reconstitution of a stromal lamellar organization. Subsequent studies revealed a significant role of tumor necrosis factor α‐stimulated gene 6 protein (TSG‐6), secreted by CSSC, in preventing neutrophil granulocytes to infiltrate the injured cornea .…”

“…To increase collagen gel stiffness without affecting its biocompatibility, Brown et al and others developed a technique to produce plastic compressed collagen gels (CCG) by dehydrating the gels using compression and passive absorption. These plastic CCG have greatly increased strength, stiffness and can be produced without cytotoxicity to embedded cells . Corneal stromal cells, including CSSC, have been successfully embedded in CCG and used as feeder layers for corneal epithelial cells.…”