1998 Global Conference Proceeding

March 02 - 04, 1998

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Conference: 1998 Global Conference
Title: Chemical Chaperones as a Novel Therapeutic Strategy for NDI
Author: Verkman, Alan S.
Institution: University of California, S.F.
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Abstract • Translation

My presentation will briefly summarize new information on the urinary concentrating mechanism that has come from studies on transgenic mice, and then provide evidence that chemical chaperones might provide a clinically-useful approach to treat NDI.

1. Evidence for 'proximal-type NDI'. Transgenic knockout mice were generated that lack AQP1 and AQP4. The AQP4 knockout mice have a mild defect in urinary concentrating ability, despite a 4-fold decrease in inner medullary collecting duct water permeability. It is thus likely that other water channels, including AQP3, are important in basolateral membrane water exit in more proximal segments of collecting duct. In contrast, AQP1 knockout mice become severely dehydrated and hyperosmolar in response to water deprivation, and are unable to concentrate their urine. Except for polyuria/polydipsia, the mice are grossly normal when not fluid-deprived. Absence of AQP1 (Colton null phenotype) thus produces a 'proximal-type' NDI with distinctly different physiology from existing forms of 'distal-type' NDI.

2.Chemical chaperones and NDI. A series of AQP2 mutants causing NDI in humans were characterized in transfected mammalian cells. Defects in protein targeting, protein function and/or protein turnover were identified; in some cases the primary defect was one of cellular processing with retention in the endoplasmic reticulum. We reasoned that NDI caused by such mutations might be treated with agents that facilitate protein processing and plasma membrane targeting of mutant AQP2 proteins. A series of 'chemical chaperones' including glycerol, trimethylamine oxide, DMSO and others, we were able to correct the NDI defect. Treatment of transfected cells with these agents produced a redistribution of mutant AQP2 from and ER to an endosomal/plasma membrane pattern, resulting in increased cell membrane water permeability. Pharmacology studies in mice indicated the potential feasibility of in vivo therapy with chemical chaperones.

A line of mice was bred to lack certain water-transporting proteins called aquaporins (AQP) that play an important role in urine regulation. There are different types of aquaporins. Mice lacking AQP4 show only a slight reduction of their ability to concentrate urine, whereas those lacking AQP1 show a complete lack of ability to concentrate urine. In fact, the absence of AQP1 produces a distinct form of nephrogenic diabetes insipidus (NDI) with different physical processes than other forms of NDI. A cell line generated to have mutant AQP2 showed defects in the aquaporin's ability to process proteins and travel to its work place, the plasma membranes. The researchers reasoned that if they treated the mutated AQP2 cells with agents which facilitate protein processing and traveling to plasma membranes such as glycerol, trimethylamine oxide and DMSO, these agents would be able to escort the mutated protein to its work site and therefore repair the abnormality in the disease. The researchers were correct; the treatment corrected the NDI defect. This finding points to the potential feasibility of using these agents, dubbed "chemical chaperones", to treat NDI patients.