Potential role of corneal epithelial cell-derived exosomes in corneal wound healing and neovascularization

Abstract

Specific factors from the corneal epithelium underlying the stimulation of stromal fibrosis and myofibroblast formation in corneal wound healing have not been fully elucidated. Given that exosomes are known to transfer bioactive molecules among cells and play crucial roles in wound healing, angiogenesis, and cancer, we hypothesized that corneal epithelial cell-derived exosomes may gain access to the underlying stromal fibroblasts upon disruption of the epithelial basement membrane and that they induce signaling events essential for corneal wound healing. In the present study, exosome-like vesicles were observed between corneal epithelial cells and the stroma during wound healing after corneal epithelial debridement. These vesicles were also found in the stroma following anterior stromal keratectomy, in which surgical removal of the epithelium, basement membrane, and anterior stroma was performed. Exosomes secreted by mouse corneal epithelial cells were found to fuse to keratocytes in vitro and to induce myofibroblast transformation. In addition, epithelial cell-derived exosomes induced endothelial cell proliferation and ex vivo aortic ring sprouting. Our results indicate that epithelial cell-derived exosomes mediate communication between corneal epithelial cells and corneal keratocytes as well as vascular endothelial cells. These findings demonstrate that epithelial-derived exosomes may be involved in corneal wound healing and neovascularization, and thus, may serve as targets for potential therapeutic interventions.

Extracellular Vesicles and Cell–Cell Communication in the Cornea

“…We have previously demonstrated that EVs can be isolated from cultured corneal epithelial and stromal cells and identified by TEM (Han et al, ). To examine if the secretion of EVs can be visualized in a 3D in vivo ‐like culture, HCFs were cultivated in a VitC‐rich medium that stimulates extracellular matrix secretion and assembly.…”

“…To show that EVs are involved in signaling for corneal wound healing, we first needed to prove that EVs were present in the cornea. This was accomplished by Han et al (), who showed that EVs could be isolated from both human epithelial and stromal cells in culture. In the present study, we took the next step and examined if EVs could be observed in a more natural 3D environment.…”

“…In this concept, EVs released from epithelial cells migrating to cover a wound would promote transformation of the stromal cells to myofibroblasts. We have demonstrated a portion of this concept in a cell culture model (Han et al, ), and parts of this concept have been observed in kidney and cutaneous injuries (Tan et al, ; Than et al, ).…”

“…Azar and colleagues reported that EVs secreted by corneal fibroblasts could transport proteins to vascular endothelial cells demonstrating the important concept that cell–cell communication via EV is functional in the cornea (Han et al, ). In a second paper (Han et al, ), which was a collaboration between my lab and Dr. Azar's, we examined if EVs isolated from corneal epithelium interacted with corneal keratocytes/fibroblasts, and if these EVs stimulated fibrosis, as indicated by the expression of α‐smooth muscle actin (SMA). Important findings included that epithelial EVs interacted with keratocytes and stimulated SMA expression.…”

Recent advances of exosomes in immune-mediated eye diseases

“…Jangamreddy et al found that one kind of peptide analogs as alternatives to collagen promoted regeneration of corneal tissue by stimulating in-growing corneal epithelium cells to secrete EVs for generating matrix components [55]. During corneal wound healing, mouse corneal epithelial cell-derived exosomes induced fibroblast proliferation and transformation of keratocytes to myofibroblasts, mediating intercellular communication between the corneal epithelium and stroma [56]. Besides, exosomes derived from normal human corneal limbal keratocytes were found to greatly enhance proliferation and wound healing rates of primary limbal epithelial cells, likely via activating Akt signaling [57].…”