Researching treatments for inherited corneal dystrophy

Overview

The cornea is the clear front surface of the eye. It protects the eye and helps to focus light, which means it needs to be clear or light can’t get through.

In a group of conditions known as corneal dystrophies, people inherit a faulty gene that means the cornea becomes cloudy. The gene is usually only inherited from one parent (known as ‘dominant inheritance’). Meesmann epithelial corneal dystrophy is one that affects the cornea’s outer layer (the epithelial layer).

In this project the team is testing two approaches to treating dominantly inherited corneal dystrophy. The first approach ‘silences’ the faulty gene inherited from one parent and leaves the healthy version from the other parent untouched to take over. The team will first test mice engineered to make the cornea glow. They’ll know whether the treatment is good at silencing the target gene if the eye stops glowing. Once they have a good formula they will test it on mice that have a human-like version of Meesmann corneal dystrophy.

The second approach is to use gene replacement therapy to silence both copies of the gene and replace them with a healthy version that’s been engineered so that it can’t be silenced.

At the end of the project the team will know if it’s possible to make a gene-silencing cream or ointment that could go on to human trials. They’ll also know more about whether gene-replacement therapy can work for this type of inherited eye disorder.

Publications
Courtney DG, Atkinson SD, Allen EHA, Moore JE, Walsh CP, Pedrioli DML, et al. siRNA silencing of the mutant keratin 12 allele in corneal limbal epithelial cells grown from patients with Meesmann’s epithelial corneal dystrophy. Invest Ophthalmol Vis Sci. 2014 May;55(5):3352–60.
Research update

The team has shown that injecting a targeted ‘silencer’ into the mouse cornea can stop the faulty protein from being made for up to 7 days. This is an exciting first step, and they’re now working on ways to apply it as an eye drop or cream that also works.
Scientific summary

In vivo proof-of-concept for two gene silencing technologies in the dominantly inherited corneal dystrophies

Corneal dystrophy (CD) is a heterogeneous group of hereditary eye disorders. Common, severe CD is caused by dominant-negative mutations in the TGFBI gene. Meesmann epithelial corneal dystrophy (MECD) is due to dominant-negative mutations in keratins K3 or K12. MECD is an ideal model disorder for therapy development because the keratin protein aggregates are short-lived and confined to the epithelium, whereas TGFBI aggregates develop slowly and are secreted into the stroma. Two alternative strategies could treat dominant-negative disorders like CD. These are (i) mutation-specific siRNA (in vivo approach); or (ii) a vector-expressed shRNA knockout-replacement system (ex vivo strategy).

The team has developed potent, specific allele-specific siRNA for common and severe K12 mutations. They have also developed all components of an shRNA-based knockout replacement system targeting K12. They recently developed two mouse models to facilitate CD gene therapy development and testing in vivo. These are: (i) a K12-luc mouse expressing luciferase in the corneal epithelium; and (ii) a humanized K12 mouse model of MECD.

Here they exploit live-animal imaging of the K12-luc mice to develop corneal delivery of therapeutic siRNA using a library of ocular surface formulations. The optimised formulation will be used to reverse the phenotype in the humanized MECD mouse. Similarly, a transgenic mouse expressing their knockout-replacement therapeutic gene will be crossed into the MECD mouse to see if this system can also rescue the phenotype. Together, these studies will provide a compelling in vivo data package to attract major funding and take these therapies into human trials.