Corneal Stromal PDGF Receptor Expression, PDGF Blockade and Modulation of Myofibroblast Development

Abstract

Purpose: : To analyze platelet-derived growth factor (PDGF) receptor expression in myofibroblasts and the effect of PDGF receptor blockade on the development of myofibroblasts associated with development of stromal haze in response to -9 diopter photorefractive keratectomy in rabbits.

Methods: : Immunohistochemistry for PDGF receptor- (PDGFR-) was performed in rabbit corneas at one month after haze generating -9 diopter photorefractive keratectomy (PRK). Rabbits that had - 9 diopter PRK in one eye were also divided into three different groups: stromal application of plasmid pCMV.PDGFRB.23KDEL expressing a subunit of PDGF receptor β (domains 2-3, which bind PDGF-β), stromal application of empty plasmid pCMV, or stromal application of balanced salt solution (BSS). The plasmids (at a concentration 1000 ng/µl) or BSS were applied to the exposed stroma immediately after surgery and every 24 hours for 4-5 days until the epithelium healed. At 4 weeks after surgery corneas were graded for haze at the slit lamp and myofibroblast density in corneal sections was determined by immunohistochemistry for smooth muscle actin (SMA).

Results: : PDGF receptors were expressed at high levels in myofibroblasts. After gene transfer, the group treated with pCMV.PDGFRB.23KDEL plasmid showed low SMA+ myofibroblast density in the anterior stroma compared to either control group (P≤ 0.001). Although there was also lower corneal haze at the slit lamp at one month after surgery, the difference in haze after PDGF-β blockade was not statistically significant compared to either control group.

Conclusions: : PDGF receptor is expressed in corneal myofibroblasts. Stromal PDGF-β blockade during the early postoperative period following PRK profoundly decreases stromal SMA+ myofibroblast generation. However, since significant haze is still present, we hypothesize that PDGF modulates later events in myofibroblast development, such as the transition from vimentin+ to SMA+ myofibroblast.

Keywords: cornea: stroma and keratocytes • cytokines/chemokines • gene transfer/gene therapy