Psychiatric patients treated with lithium (Li+) may develop nephrogenic diabetes insipidus (NDI). Although the etiology of Li+-induced NDI (Li-NDI) is poorly understood, it occurs partially due to reduced aquaporin-2 (AQP2) expression in the kidney collecting ducts. A mechanism postulated for this is that Li+ inhibits adenylyl cyclase (AC) activity, leading to decreased cAMP, reduced AQP2 abundance, and less membrane targeting. We hypothesized that Li-NDI would not develop in mice lacking AC6. Whole-body AC6 knockout (AC6–/–) mice and potentially novel connecting tubule/principal cell–specific AC6 knockout (AC6loxloxCre) mice had approximately 50% lower urine osmolality and doubled water intake under baseline conditions compared with controls. Dietary Li+ administration increased water intake and reduced urine osmolality in control, AC6–/–, and AC6loxloxCre mice. Consistent with AC6–/– mice, medullary AQP2 and pS256-AQP2 abundances were lower in AC6loxloxCre mice compared with controls under standard conditions, and levels were further reduced after Li+ administration. AC6loxloxCre and control mice had a similar increase in the numbers of proliferating cell nuclear antigen–positive cells in response to Li+. However, AC6loxloxCre mice had a higher number of H+-ATPase B1 subunit–positive cells under standard conditions and after Li+ administration. Collectively, AC6 has a minor role in Li-NDI development but may be important for determining the intercalated cell–to–principal cell ratio.
Søren Brandt Poulsen, Tina Bøgelund Kristensen, Heddwen L. Brooks, Donald E. Kohan, Timo Rieg, Robert A. Fenton
Li+ reduces urine osmolality and increases water intake in AC6–/– and WT mice.