Scientists from the University of Illinois at Chicago have identified the enzyme heparanase as the crucial factor involved in herpes simplex (HSV-1)-associated corneal inflammation. The heterodimer protein appears responsible for triggering multiple pathologies associated with infection. A drug that blocks heparanase, therefore, may treat long-term inflammation associated with HSV-1 infection.
Study design
The study used both in vitro and in vivo experiments to verify its findings. For the in vivo portion, investigators transfected mouse corneas with vectors containing the human HPSE gene to induce continuous overexpression of heparanase. Control mice were transfected with empty vectors. The team also modeled HSV infection with ex vivo porcine corneas. In vitro studies were performed using a human corneal cell line (HCE).
Outcomes
The findings consisted of 3 main parts:
- Overexpression of heparanase triggers pro-inflammatory disease conditions
Transfected mouse corneas displayed increased periorbital edema and erythema, as well as increased ocular discharge, all signs of worse herpetic disease. Additionally, the study mice had significantly higher numbers of cells in their ipsilateral draining lymph nodes, indicating a heightened inflammatory response. Together, these findings indicate that aberrant heparanase expression in the cornea drives pathological responses to ocular infection.
- Wound healing is defective in the presence of active heparanase
In corneal wound healing assays, heparanase overexpression in the absence of infection prevented closure of defects in the corneal epithelium in vivo. The findings were confirmed in an in vitro scratch assay, where the presence of heparanase delayed the wound healing of human corneal epithelial and HeLa cell monolayers. Additionally, the introduction of HSV-1 virus in the cell culture media caused a further delay in wound healing.
- Pharmacological inhibition of heparanase prevents spread of HSV-1 infection
To further verify that the control of pro-inflammatory factor expression is specific to heparanase, the authors used an HPSE inhibitor, OGT 2115. Treatment of HCE cells with OGT 2115 resulted in decreased expression of pro-inflammatory factors IL-1β, IL-6, and TNF-α. The compound also effectively decreased the spread of HSV-1 in cellular cultures, reducing the size of typical plaque formations. This suggests that inhibition of heparanse led to decreased passage of virus from infected to uninfected neighboring cells.
Limitations
Heparanase is found in low levels throughout the body and within the cornea, and triggers a host of cellular responses. Therefore, manipulating up- and down-regulation of heparanase is a complex challenge, and may have detrimental unintended effects. These findings are also very preliminary, as many animal studies do not translate to human clinical trials.
Clinical significance
The findings here clearly show that the active form of heparanase was involved in promoting and sustaining inflammation in the cornea through multiple channels. Heparanase may also be a key factor in other inflammatory disorders, including dry eye disease. A drug that blocks heparanase may represent a novel treatment for long-term inflammation associated with HSV-1 infection as well as other inflammatory disorders of the eye.