Corneal scarring from trauma and inflammation disrupts vision for millions worldwide, but corneal transplantation, the primary therapy for corneal blindness, is unavailable to many affected individuals. In this study, stem cells isolated from adult human corneal stroma were examined for the ability to correct stromal opacity in a murine model by direct injection of cells into the corneal stroma. In wild-type mice, injected human stem cells remained viable for months without fusing with host cells or eliciting an immune T-cell response. Human corneal-specific extracellular matrix, including the proteoglycans lumican and keratocan, accumulated in the treated corneas. Lumican-null mice have corneal opacity similar to that of scar tissue as a result of disruption of stromal collagen organization. After injection with human stromal stem cells, stromal thickness and collagen fibril defects in these mice were restored to that of normal mice. Corneal transparency in the treated mice was indistinguishable from that of wild-type mice. These results support the immune privilege of adult stem cells and the ability of stem cell therapy to regenerate tissue in a manner analogous to organogenesis and clearly different from that of normal wound healing. The results suggest that cell-based therapy can be an effective approach to treatment of human corneal blindness.

Lumican is an extracellular matrix glycoprotein widely distributed in mammalian connective tissues. Corneal lumican modified with keratan sulfate constitutes one of the major proteoglycans of the stroma. Lumican-null mice exhibit altered collagen fibril organization and loss of corneal transparency. A closely related protein, keratocan, carries the remaining keratan sulfate of the cornea, but keratocan-null mice exhibit a less severe corneal phenotype. In the current study, we examined the effect of lumican overexpression in corneas of wild type mice. These mice showed no alteration in collagen organization or transparency but had increased keratocan expression at both protein and mRNA levels. Corneas of lumican-null mice showed decreased keratocan. This coupling of keratocan expression with lumican also was observed after intrastromal injection of a lumican expression minigene into the corneal stroma of Lum ؊/؊ mice. Small interfering RNA knockdown of lumican in vitro reduced keratocan expression, whereas co-injection of a lumican-expressing minigene with a ␤-galactosidase reporter driven by the keratocan promoter demonstrated an increase of keratocan transcriptional activity in response to lumican expression in Lum ؊/؊ corneas in vivo. These observations demonstrate that lumican has a novel regulatory role in keratocan expression at the transcriptional level. Such results help provide an explanation for the differences in severity of corneal manifestation found in Lum ؊/؊ and Kera ؊/؊ mice. The results also suggest a critical level of small proteoglycans to be essential for collagen organization but that overabundance is not detrimental to extracellular matrix morphogenesis.

Retinopathies are major causes of visual impairment. We used a model of ischemic retinopathy to examine the role of CD40 in the pathogenesis of retinal injury. Retinal inflammation, loss of ganglion cells, and capillary degeneration were markedly attenuated in ischemic retinas of CD40−/− mice. Up-regulation of NOS2 and COX2 after retinal ischemia were blunted in CD40−/− mice. NOS2-COX-2 up-regulation in ischemic retinas from wild-type mice was at least in part explained by recruitment of NOS2+COX-2+ leukocytes. Up-regulation of KC/CXCL1 and ICAM-1 also required CD40. Retinal endothelial and Muller cells expressed CD40. Stimulation of these cells through CD40 caused ICAM-1 up-regulation and KC/CXCL1 production. Bone marrow transplant experiments revealed that leukocyte infiltration, ganglion cell loss, and up-regulation of proinflammatory molecules after retinal ischemia were dependent on CD40 expression in the retina and not peripheral blood leukocytes. These studies identified CD40 as a regulator of retinal inflammation and neurovascular degeneration. They support a model in which CD40 stimulation of endothelial and Muller cells triggers adhesion molecule up-regulation and chemokine production, promoting the recruitment of leukocytes that express NOS2/COX-2, molecules linked to neurovascular degeneration.