The Y227N mutation affects bestrophin-1 protein stability and impairs sperm function in a mouse model of Best vitelliform macular dystrophy.

Human bestrophin-1 (BEST1) is an integral membrane protein known to function as a Ca-activated and volume-regulated chloride channel. The majority of disease-associated mutations in constitute missense mutations and were shown to lead to a reduction in mutant protein half-life causing Best disease (BD), a rare autosomal dominant macular dystrophy. To further delineate BEST1-associated pathology and to provide an animal model useful to explore experimental treatment efficacies, we have generated a knock-in mouse line (Best1). Heterozygous and homozygous mutants revealed no significant ocular abnormalities up to 2 years of age. In contrast, knock-in animals demonstrated a severe phenotype in the male reproductive tract. In heterozygous Best1 males, Best1 protein was significantly reduced in testis and almost absent in homozygous mutant mice, although mRNA transcription of wild-type and knock-in allele is present and similar in quantity. Degradation of mutant Best1 protein in testis was associated with adverse effects on sperm motility and the capability to fertilize eggs. Based on these results, we conclude that mice carrying the Y227N mutation reveal a reproducible pathologic phenotype and thus provide a valuable tool to evaluate efficacy of drug therapies aimed at restoring Best1 protein stability and function.