Knockdown of heme oxygenase-2 impairs corneal epithelial cell wound healing

Heme oxygenase (HO) represents an intrinsic cytoprotective system based on its anti-oxidative and anti-inflammatory properties mediated via its products biliverdin/bilirubin and carbon monoxide (CO). We showed that deletion of HO-2 results in impaired corneal wound healing with associated chronic inflammatory complications. This study was undertaken to examine the role of HO activity and the contribution of HO-1 and HO-2 to corneal wound healing in an in vitro epithelial scratch injury model. A scratch wound model was established using human corneal epithelial (HCE) cells. These cells expressed both HO-1 and HO-2 proteins. Injury elicited a rapid and transient increase in HO-1 and HO activity; HO-2 expression was unchanged. Treatment with biliverdin or CORM-A1, a CO donor, accelerated wound closure by 10% at 24 h. Inhibition of HO activity impaired wound closure by more than 50%. However, addition of biliverdin or CORM-A1 reversed the effect of HO inhibition on wound healing. Moreover, knockdown of HO-2 expression, but not HO-1, significantly impaired wound healing. These results indicate that HO activity is required for corneal epithelial cell migration. Inhibition of HO activity impairs wound healing while amplification of its activity restores and accelerates healing. Importantly, HO-2, which is highly expressed in the corneal epithelium, appears to be critical for the wound healing process in the cornea. The mechanisms by which it contributes to cell migration in response to injury may reside in the cytoprotective properties of CO and biliverdin.

Biliverdin Rescues the HO-2 Null Mouse Phenotype of Unresolved Chronic Inflammation Following Corneal Epithelial Injury

PURPOSE. The heme oxygenase system (HO-1 and HO-2) represents an intrinsic cytoprotective and anti-inflammatory pathway based on its ability to modulate leukocyte migration and to inhibit the expression of inflammatory cytokines and proteins by its products biliverdin/bilirubin and carbon monoxide. Corneal injury in HO-2 null mice leads to impaired healing and chronic inflammatory complications, including ulceration and neovascularization. The authors examined whether topically administered biliverdin can counteract the effects of HO deficiency in a corneal epithelial injury model. METHODS. HO-2 null mice were treated with biliverdin 1 hour before epithelial injury and twice a day thereafter. Reepithelialization and neovascularization were assessed by fluorescein staining and vital microscopy, respectively, and were quantified by image analysis. Inflammation was quantified by histology and Gr-1-specific immunofluorescence, and oxidative stress was assessed by DHE fluorescence. RESULTS. Treatment with biliverdin accelerated wound closure, inhibited neovascularization and reduced epithelial defects. It also reduced inflammation, as evidenced by a reduction in the appearance of inflammatory cells and the expression levels of inflammatory and oxidant proteins, including KC and NOXs. CONCLUSIONS. The results clearly show that biliverdin, directly or through its metabolism to bilirubin by biliverdin reductase-the expression of which is increased after injury-rescues the aberrant inflammatory phenotype, further underscoring the importance of the HO system in the cornea for the execution of an ordered inflammatory and reparative response.

Targeted suppression of HO-2 gene expression impairs the innate anti-inflammatory and repair responses of the cornea to injury

PURPOSE

Heme oxygenase (HO)-2 is highly expressed in the corneal epithelium and is a component of the heme oxygenase system that represents an intrinsic cytoprotective and anti-inflammatory system based on its ability to modulate leukocyte migration and to inhibit expression of inflammatory cytokines and proteins via its products biliverdin/bilirubin and carbon monoxide (CO). We have shown that in HO-2 null mice epithelial injury leads to unresolved corneal inflammation and chronic inflammatory complications including ulceration, perforation and neovascularization. In this study, we explore whether a localized corneal suppression of HO-2 is sufficient for disrupting the innate anti-inflammatory and repair capability of the cornea.

METHODS

Silencing hairpin RNA (shRNA) against HO-2 was administered subconjunctivally (100 ng/eye) as well as topically (100 ng/eye) starting one day before corneal epithelial debridement and once daily, thereafter. The corneal epithelium was removed using an Alger Brush in anesthetized mice. Re-epithelialization was assessed by fluorescein staining using a dissecting microscope and image analysis. Inflammatory response was quantified by myeloperoxidase activity. Levels of mRNA were measured by RT-PCR.

RESULTS

Local injection of HO-2-specific shRNA led to a 50% reduction in corneal HO-2 mRNA. Administration of HO-2-specific shRNA delayed corneal re-epithelialization when compared with the control shRNA-treated group by 14%, 20%, and 12% at days 3, 4, and 7 after injury, respectively (n=18-24). The observed delay in the wound repair process in HO-2 shRNA treated mice was accompanied by a threefold and 3.5 fold increase in the neovascular response at days 4 and 7 after injury. Further, local knockdown of HO-2 lead to an aberrant chronic inflammatory response, as shown by presence of high numbers of inflammatory cells still present in the cornea at day 7 after injury; 1.04±0.45×10(6) in HO-2 knockdown mice versus 0.14±0.03×10(6) inflammatory cells in control mice. Matrix metalloproteinase-2 (MMP-2) but not MMP-9 increased following injury and remained elevated in the injured corneas of the HO-2 shRNA-treated eyes.

CONCLUSIONS

Corneal knockdown of HO-2 via local administration of HO-2-specific shRNA leads to delayed re-epithelialization, increased neovascularization and an aberrant inflammatory response similar to what is observed in the HO-2 null mouse. The elevated MMP-2 expression may contribute to the increase in neovascularization in corneas in which HO-2 expression is suppressed.

Neuroprotectin D1 inhibits retinal ganglion cell death following axotomy

Neuroprotectin D1 (NPD1), a docosahexaenoic acid-derived autacoid, is an endogenous neuroprotective and anti-inflammatory mediator that is generated in the retina and brain. The effects of exogenous NPD1 on retinal ganglion cell (RGC) apoptosis and the role of 12/15-lipoxygenase (Alox15) in retina were evaluated after optic nerve transection (ONT). Treatment with NPD1 was associated with significant protection against RGC death. The percentage of RGC survival in NPD1-treated group was 30% at 2 weeks after ONT as compared with 12% of RGC survival in the ONT group without treatment. Endogenous NPD1 was a predominant lipid autocoid in uninjured and axotomized retinas. Alox15 mRNA expression was upregulated in retinas following ONT suggesting that amplification of 12/15-lipoxygenase (12/15-LOX) may represent a neuroprotective response in the rat retina. The density of RGCs was higher in the normal retina of 12/15-LOX-deficient mice as compared with congenic controls. Hence, the resident NPD1 has a potential role in the physiological and pathophysiological responses of the retina.

Exacerbated corneal inflammation and neovascularization in the HO-2 null mice is ameliorated by biliverdin

Heme oxygenase (HO-1 and HO-2) represents an intrinsic cytoprotective and anti-inflammatory system based on its ability to modulate leukocyte migration and to inhibit expression of inflammatory cytokines and proteins. HO-2 deletion leads to unresolved corneal inflammation and chronic inflammatory complications including ulceration, perforation and neovascularization. We examined the consequences of HO-2 deletion on hemangiogenesis and lymphangiogenesis in the model of suture-induced inflammatory neovascularization. An 8.0 silk suture was placed at the corneal apex of wild type and HO-2 null mice. Neovascularization was assessed by vital microscopy and quantified by image analysis. Hemangiogenesis and lymphangiogenesis were determined by immunofluorescence staining using anti-CD31 and anti-LYVE-1 antibodies, respectively. Inflammation was quantified by histology and myeloperoxidase activity. The levels of HO-1 expression and inflammatory cytokines were determined by real time PCR and ELISA, respectively. Corneal sutures produced a consistent inflammatory response and a time-dependent neovascularization. The response in HO-2 null mice was associated with a greater increase compared to the wild type in the number of leukocytes (827,600+/-129,000 vs. 294,500+/-57,510; p<0.05), neovessels measured by vital microscopy (21.91+/-1.05 vs. 12.77+/-1.55 mm; p<0.001) 4 days after suture placement. Hemangiogenesis but not lymphangiogenesis was more pronounced in HO-2 null mice compared to wild type mice. Induction of HO-1 in sutured corneas was greatly attenuated in HO-2 null corneas and treatment with biliverdin diminished the exaggerated inflammatory and neovascular response in HO-2 null mice. The demonstration that the inflammatory responses, including expression of proinflammatory proteins, inflammatory cell influx and hemangiogenesis are exaggerated in HO-2 knockout mice strongly supports the notion that the HO system is critical for controlling the inflammatory and neovascular response in the cornea. Hence, pharmacological amplification of this system may constitute a novel therapeutic strategy for the treatment of corneal disorders associated with excessive inflammation and neovascularization.

Dorzolamide and timolol saves retinal ganglion cells in glaucomatous adult rats

PURPOSE

This study was designed to evaluate the effects of a dorzolamide-timolol combination or dorzolamide on retinal ganglion cell (RGC) density and intraocular pressure (IOP) in glaucomatous eyes of adult rats.

METHODS

Glaucoma was induced in the right eye of adult Wistar rats by episcleral venous occlusion. One experimental group was administered dorzolamide 2%-timolol 0.5% combination eye drops, while the other experimental group was administered dorzolamide 2% eye drops. Control groups had surgery without drug administration. Drug application was initiated either 2 weeks before surgery (Group A), from the day of surgery (Group B), 2 weeks after surgery (Group C), or 4 weeks after surgery (Group D). RGCs were labeled by intratectal Fluorogold injections and counted from flat-mount preparations, and IOP was measured using Tonopen.

RESULTS

Both dorzolamide-timolol combination and dorzolamide, when applied topically, significantly reduced IOP and improved RGC densities in experimental eyes when compared to control eyes. Earlier initiation, as well as longer duration of drug application, resulted in higher RGC densities.

CONCLUSIONS

Topical application of a dorzolamide-timolol combination or dorzolamide saved RGCs to a significant extent and reduced IOP in glaucomatous rat eyes.