Zebrafish carbohydrate sulfotransferase 6 (chst6) mutants provide a preclinical model for macular corneal dystrophy

Macular corneal dystrophy (MCD) is a rare congenital disease caused by mutations in the carbohydrate sulfotransferase 6 (chst6) gene. Patients suffer from opaque aggregates in the cornea leading to bilateral progressive vision loss by 4th decade of life. Corneal transplantation is the only available treatment, which is invasive, not available to every patient and recurrence of the symptoms is common. Keratocytes in the cornea express the chst6 gene, which encodes a golgi enzyme that is essential for sulfation of the keratan sulfate proteoglycans (KSPG). The loss of KS sulfation leads to defects in collagen fibril organization and aggregate formation in the corneal extracellular matrix. Lack of preclinical disease models is a major limitation for the development of accessible treatment strategies. Attempts to develop mouse MCD models have failed due to lack of chst6 gene in mice and difference in proteoglycan composition of the mouse cornea. The zebrafish chst6 gene has not been studied previously. Zebrafish cornea structure is highly similar to humans, containing high levels of keratan sulfate proteoglycans in the stroma. Here, loss of function chst6 mutant zebrafish were generated with CRISPR/Cas9 mediated gene editing. Several chst6 alleles were obtained, and loss of KSPG sulfation in the eye stroma was shown. Mutant zebrafish developed age-dependent, alcian blue positive, opaque accumulates in the cornea. Degeneration of corneal structure and changes in epithelial thickness were observed. The zebrafish MCD model developed here is the first in vivo model of the disease and opens up possibilities to develop and screen treatment strategies. Significance StatementFirst in vivo model of macular corneal dystrophy (MCD) is reported in this study. Zebrafish model developed here paves the way for modeling of other corneal dystrophies in this aquatic vertebrate which is easy to apply therapeutics and image in vivo. The clinical symptoms of MCD are well reproduced in the zebrafish MCD model. Moreover, the authors showed that chst6 gene function is not restricted to cornea, and a fraction of mutant larvae have morphological defects. The mutants developed here provide a genetic model for understanding the highly complex roles of keratan sulfate proteoglycans.