Modeling of Aniridia-Related Keratopathy by CRISPR/Cas9 Genome Editing of Human Limbal Epithelial Cells and Rescue by Recombinant PAX6 Protein.

Heterozygous PAX6 gene mutations leading to haploinsufficiency are the main cause of congenital aniridia, a rare and progressive panocular disease characterized by reduced visual acuity. Up to 90% of patients suffer from aniridia-related keratopathy (ARK), caused by a combination of factors including limbal epithelial stem cell (LSC) deficiency, impaired healing response and abnormal differentiation of the corneal epithelium. It usually begins in the first decade of life, resulting in recurrent corneal erosions, sub-epithelial fibrosis, and corneal opacification. Unfortunately, there are currently no efficient treatments available for these patients and no in vitro model for this pathology. We used CRISPR/Cas9 technology to introduce into the PAX6 gene of LSCs a heterozygous nonsense mutation found in ARK patients. Nine clones carrying a p.E109X mutation on one allele were obtained with no off-target mutations. Compared with the parental LSCs, heterozygous mutant LSCs displayed reduced expression of PAX6 and marked slow-down of cell proliferation, migration and detachment. Moreover, addition to the culture medium of recombinant PAX6 protein fused to a cell penetrating peptide was able to activate the endogenous PAX6 gene and to rescue phenotypic defects of mutant LSCs, suggesting that administration of such recombinant PAX6 protein could be a promising therapeutic approach for aniridia-related keratopathy. More generally, our results demonstrate that introduction of disease mutations into LSCs by CRISPR/Cas9 genome editing allows the creation of relevant cellular models of ocular disease that should greatly facilitate screening of novel therapeutic approaches. Stem Cells 2018;36:1421-1429.

Human aniridia limbal epithelial cells lack expression of keratins K3 and K12.

Aniridia is a rare disease of the eye that affects the iris, lens and the cornea. In about 90% of the cases, patients showed a loss of PAX6 function. Patients with aniridia often develop aniridia-related keratopathy (ARK), due to limbal stem cell insufficiency. The aim of this study was to determine the differentiation status of limbal epithelial cells (LECs) in patients with ARK. Epithelial cells were isolated from the limbus region of two patients with aniridia and cultured in KSFM medium supplemented with EGF and BPE. Normal cells were obtained from limbus region of cadaveric control patients. Cells were analyzed with RT-PCR, qPCR and Western blot to evaluate expression of the developmental transcription factor, PAX6, potential stem cell markers, ΔNp63α and ABCG2, and corneal differentiation markers, keratin 12 (K12) and K3. Conjunctival differentiation markers, keratin 13 (K13) and K19 were also investigated. Cells were immunostained to evaluate K3, PAX6, and p63α protein expression. Protein coding sequence of PAX6 from patient LEC-cDNA was cloned and sequenced. RT-PCR showed that K3 and K12 transcripts were absent from patient cells, but present in healthy control preparations. Transcription levels of PAX6, ABCG2, and p63α of aniridia patients show no differences compared to normal control cells. Western blot showed reduced PAX6, protein levels in aniridia-LECs compared to control-LECs. Immunostaining also showed reduced PAX6 and K3 expression in aniridia-LECs compared to control-LECs. One aniridia patient showed a loss of stop codon in half of the cloned transcripts. In the second aniridia patient mRNA degradation through nonsense mediated decay seems to be very likely since we could not identify the mutation c.174C > T (Refseq. NM_000280), or misspliced transcripts in cDNA. We identified decreased PAX6 protein levels in aniridia patients in addition to decreased K12 mRNA levels compared to control cells. This result indicates an altered differentiation of limbal epithelial cells of aniridia patients. Further studies are necessary to evaluate the mechanism of differentiation of limbal epithelial cells in aniridia.

PAX6 mutation in association with ptosis, cataract, iris hypoplasia, corneal opacification and diabetes: a new variant of familial aniridia?

BACKGROUND: We report a family with ptosis, cataract, iris hypoplasia and gradual corneal opacification occurring in association with a PAX6 mutation. DESIGN: Case-series. PARTICIPANTS: Fourteen family members - 8 affected, 6 unaffected controls. METHODS: All participants underwent ophthalmological assessment, including best-corrected visual acuity, slit-lamp-examination, pachymetry, endothelial cell-count, tonometry and dilated fundoscopy. All subjects underwent anthropometry and assessment of glycaemic status. Genetic analysis of the PAX6 gene was performed. MAIN OUTCOME MEASURES: Presence of ptosis, corneal, iris and lenticular changes, gycaemic and PAX6 status. RESULTS: All eight affected subjects had ptosis with reduced levator function, anterior polar cataracts, and corneal changes of variable severity - two patients had undergone penetrating keratoplasties, with graft histology revealing conjunctival cells on the cornea and severe fibroinflammatory change. Five patients had iris hypoplasia. One patient had aphakic glaucoma and another had hypoplastic optic discs. Four of the six controls had no ocular features of this syndrome, and two had isolated mild ptosis. There was no difference in height or body mass index between cases and family controls (p > 0.05), but Haemoglobin A1c was greater in the cases (median [interquartile range] 5.6(0.8) vs 5.1(0.3), p = 0.028). Genetic analysis confirmed a pathogenic PAX6 mutation in exon 12 (c1439delC) in all eight patients, but none of the controls. CONCLUSION: This is the first report of this particular constellation of ocular signs occurring in association with a PAX6 mutation. There was no association with anthropometric features, but affected subjects had worse glycaemia than controls, which may be related to the known role of PAX6 in development of the pancreas.

Corneal transplantation in aniridia-related keratopathy with a two-year follow-up period, an uncommon disease with precarious course.

PURPOSE: The purpose of this study is to study the frequency, surgical transplantation technique and outcome in patients with aniridia-related keratopathy (ARK) with two-year follow-up period. METHODS: A retrospective registry-study including all ARK cases performed in Sweden and Denmark between 2001 and 2016 and registered in the Swedish Cornea Transplant Registry. RESULTS: A total of 36 eyes of 26 patients were subjected to corneal transplantation due to ARK during 2001 to 2016. Penetrating keratoplasty (PK) was the procedure of choice in 58.3% (n = 21) of the eyes, followed by a combination of PK and limbal stem cell transplantation in 13.9% (n = 5) and keratolimbal allograft in 13.9% (n = 5). Boston keratoprosthesis was used in 8.3% (n = 3), and anterior lamellar keratoplasty in 5.6% (n = 2). Thirteen of the procedures (36.1%) were retransplantations. Two years after surgery 26 cases were available to follow-up of which 16 of the grafts were functioning (61.5%). The median visual acuity showed a trend of improvement from hand motion to counting fingers. CONCLUSIONS: A majority of the ARK cases (61.5%) had a graft providing useful vision for the patient 2 years after corneal transplantation, but the visual gain was modest at best. Longer follow-up time is required to evaluate functional graft outcomes. Despite the introduction of limbal stem cell transplantation as a suitable treatment, PK was the most common surgical method in the present study.