Molecular mechanisms of cataract and glaucoma induced by mutations in the Na-HCO3 cotransporter

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Proximal renal tubular acidosis (pRTA) associated with ocular abnormalities such as band keratopathy, cataracts, and glaucoma is caused by mutations in the Na-HCO3 cotransporter (NBC1). To clarify the mechanism by which NBC1 mutations lead to such ocular abnormalities, we performed immunohistochemical analysis of rat and human eyes. The results demonstrated both kidney-type (kNBC1) and a pancreatic type (pNBC1) transporter is present in the corneal endothelium, lens epithelium, and trabecular meshwork cells. We also detected the Na-HCO3 cotransport activity in human lens epithelial (HLE) cells, which was largely inhibited by specific ribozyme against NBC1. These results indicate that the normal transport activity of NBC1 is indispensable for the homeostasis in cornea and lens. NBC1 may also play an important role in regulation of aqueous humor outflow. In the subsequent studies we revealed the transport activity of Na-independent C1/HCO3 exchange activity in HLE cells, which seemed to be related to anion exchanger Aes.