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D. Gagen, Z. Li, F. W. Lam, R. E. Rumbaut, C. W. Smith, A. R. Burns; Keratocyte Repopulation Following Corneal Epithelial Abrasion in the Mouse: A Role for Platelets. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3831.
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Central corneal epithelial abrasion results in inflammation and substantial anterior keratocyte death below the region of injury. During inflammation, neutrophils (PMNs) infiltrate the corneal stroma and their infiltration is coincident with platelet recruitment to the limbus. In the absence of CD18, a leukocyte-specific adhesion molecule, PMN recruitment to the injured cornea is delayed by 24h and this delay is associated with reduced limbal platelet accumulation and impaired epithelial wound healing, suggesting CD18-dependent platelet recruitment is necessary for efficient epithelial wound healing. Indeed, epithelial repair is significantly delayed in platelet-depleted wild type (WT) mice. The purpose of this study is to determine whether platelets also contribute to efficient keratocyte repopulation following corneal epithelial abrasion.
A 2 mm diameter central epithelial region was mechanically debrided from the corneas of male C57Bl/6 WT mice, CD18-/- mice, and WT mice injected (IP) with platelet-depleting antibody, anti-CD42b. Four days post-injury, corneas were immunostained with DAPI and a cocktail of FITC-conjugated leukocyte specific antibodies. Keratocyte nuclei were counted in the anterior central stroma; FITC stained cells were excluded from the counts. Eighteen and 36 hours post-injury, platelet counts were obtained from the limbal region of corneas labeled with PE CD41 (a platelet marker).
Compared to WT, platelet recruitment to the limbus was markedly reduced (by 65%) in CD18-/- mice. Prior to injury, anterior central keratocyte numbers were similar in WT and CD18-/- mice. Four days post-injury, WT keratocytes recovered to 80% of baseline value while keratocyte numbers recovered to only 50% of baseline in mice lacking CD18. Platelet depletion in WT mice effectively blunted keratocyte repopulation whereby the number of anterior central keratocytes at 4 days post-injury was only 30% of baseline.
Collectively, the data show platelet recruitment to the limbus is necessary for effective keratocyte repopulation and this recruitment is mediated, in part, by the PMN β2 integrin CD18. We suggest platelets may enhance limbal keratocyte proliferation through the release of platelet-derived growth factors (e.g., PDGF), but further studies are needed to evaluate this possibility.
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