CRISPR/Cas9 holds immense potential to treat a range of genetic disorders. Allele-specific gene disruption induced by non-homologous end-joining (NHEJ) DNA repair offers a potential treatment option for autosomal dominant disease. Here, we successfully delivered a plasmid encoding S. pyogenes Cas9 and sgRNA to the corneal epithelium by intrastromal injection and acheived long-term knockdown of a corneal epithelial reporter gene, demonstrating gene disruption via NHEJ in vivo. In addition, we used TGFBI corneal dystrophies as a model of autosomal dominant disease to assess the use of CRISPR/Cas9 in two allele-specific systems, comparing cleavage using a SNP-derived PAM to a guide specific approach. In vitro, cleavage via a SNP-derived PAM was found to confer stringent allele-specific cleavage, while a guide-specific approach lacked the ability to distinguish between the wild-type and mutant alleles. The failings of the guide-specific approach highlights the necessity for meticulous guide design and assessment, as various degrees of allele-specificity are achieved depending on the guide sequence employed. A major concern for the use of CRISPR/Cas9 is its tendency to cleave DNA non-specifically at “off-target” sites. Confirmation that S. pyogenes Cas9 lacks the specificity to discriminate between alleles differing by a single base-pair regardless of the position in the guide is demonstrated.

PURPOSE.To identify an allele-specific short interfering RNA (siRNA), against the common KRT12 mutation Arg135Thr in Meesmann epithelial corneal dystrophy (MECD) as a personalized approach to treatment.METHODS. siRNAs against the K12 Arg135Thr mutation were evaluated using a dual luciferase reporter gene assay and the most potent and specific siRNAs were further screened by Western blot. Off-target effects on related keratins were assessed and immunological stimulation of TLR3 was evaluated by RT-PCR. A modified 5 0 rapid amplification of cDNA ends method was used to confirm siRNA-mediated mutant knockdown. Allele discrimination was confirmed by quantitative infrared immunoblotting.RESULTS. The lead siRNA, with an IC 50 of thirty picomolar, showed no keratin off-target effects or activation of TLR3 in the concentration ranges tested. We confirmed siRNA-mediated knockdown by the presence of K12 mRNA fragments cleaved at the predicted site. A dual tag infrared immunoblot showed knockdown to be allele-specific, with 70% to 80% silencing of the mutant protein. CONCLUSIONS.A potent allele-specific siRNA against the K12 Arg135Thr mutation was identified. In combination with efficient eyedrop formulation delivery, this would represent a personalized medicine approach, aimed at preventing the pathology associated with MECD and other ocular surface pathologies with dominant-negative or gain-of-function pathomechanisms. (Invest Ophthalmol Vis Sci. 2013;54:494-502)

Transforming growth factor-β-induced protein (TGFBIp), an extracellular matrix protein, is the second most abundant protein in the corneal stroma. In this review, we summarize the current knowledge concerning the expression, molecular structure, binding partners, and functions of human TGFBIp. To date, 74 mutations in the transforming growth factor-β-induced gene (TGFBI) are associated with amyloid and amorphous protein deposition in TGFBI-linked corneal dystrophies. We discuss the current understanding of the biochemical mechanisms of TGFBI-linked corneal dystrophies and propose that mutations leading to granular corneal dystrophy (GCD) decrease the solubility of TGFBIp and affect the interactions between TGFBIp and components of the corneal stroma, whereas mutations associated with lattice corneal dystrophy (LCD) lead to a destabilization of the protein that disrupts proteolytic turnover, especially by the serine protease HtrA1. Future research should focus on TGFBIp function in the cornea, confirmation of the biochemical mechanisms in vivo, and the development of disease models. Future therapies for TGFBI-linked corneal dystrophies might include topical agents that regulate protein aggregation or gene therapy that targets the mutant allele by CRISPR/Cas9 technology.