Corneal stromal cell responses to traumatic wounds and topical treatments

Abstract: Background. The cornea has unique anatomic, cellular, molecular, and functional features that lead to important mechanistic differences in the process of repair in comparison with what occurs in skin and other organs. The first observable stromal response in corneal wound healing is keratocyte apoptosis. Shortly thereafter, remaining keratocytes in adjacent areas obtain a fibroblastic phenotype and begin to proliferate and to migrate, transforming into myofibroblasts, a phenotype associated with remodeling of stromal collagen. Return to normalcy following wound healing includes elimination of myofibroblasts and restoration of the quiescent state of the keratocytes. Often, however, a wound healing response results in the persistence of myofibroblasts and their subsequent production of fibrous scar tissue.Aims. The overall aim is to understand the role of keratocytes, and their phenotypic variations in a cornea subjected to various types of trauma or treatments. More specific aims are to define expression pattern of alpha-smooth muscle actin (α-SMA) and chaperonin containing T-complex polypeptide 1 (CCT) in ultraviolet radiation wound model, to evaluate the effect of biglycan and platelet rich plasma (PRP) treatment during wound healing after corneal incision, and to characterize the structure of the bioengineered porcine construct and its interaction with stromal cells after implantation.Methods. CCT and α-SMA expression level was evaluated by reverse transcription polymerase chain reaction (RT-PCR) in rabbit corneas subjected to ultraviolet radiation (UVR). Effect of biglycan and PRP on keratocyte phenotype and survival was evaluated by immunohistochemistry, and real time PCR using rat corneas after  incisional wounding. Bioengineered porcine construct (BPC) was implanted into rabbit corneas using femtosecond laser-enabled intrastromal keratoplasty (FLISK) and characterized by means of immunohistochemistry, electron microscopy, and in vivo confocal microscopy (IVCM).Results and conclusions. In a mild wound, the expression of α-SMA mRNA is followed by expression of mRNA of at least one subunit of the complex folding α-SMA. At protein level, α-SMA is detected in the front line of repopulating keratocytes. Expression levels for both mRNAs decline as the stroma repopulation process progresses.Biglycan appears to accelerate corneal wound healing in vivo by modulating myofibroblast apoptosis, resulting in removal of myofibroblasts that may otherwise compromise corneal transparency.PRP treatment resulted in suppressed stromal cell apoptosis followed by SMAD3 activation and a greater proportion of myofibroblasts present at the wound site. Suppression of stromal cell apoptosis after corneal wounding by use of a growth factor rich formulation may lead to myofibroblast accumulation by modulation of the TGF-β pathway.A cost-effective BPC extracellular matrix equivalent can incorporate cells passively to initiate normal regenerative healing of the corneal stroma.Taken together, results present an interesting possibility to combine BPC implantation and topical biglycan treatment to improve surgical outcome in future studies.