Role of adenylyl cyclase 6 in the development of lithium-induced nephrogenic diabetes insipidus
Søren Brandt Poulsen, … , Timo Rieg, Robert A. Fenton
Søren Brandt Poulsen, … , Timo Rieg, Robert A. Fenton
Published April 6, 2017
Citation Information: JCI Insight. 2017;2(7):e91042. https://doi.org/10.1172/jci.insight.91042.
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Research Article Cell biology

Role of adenylyl cyclase 6 in the development of lithium-induced nephrogenic diabetes insipidus

Abstract

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.

Authors

Søren Brandt Poulsen, Tina Bøgelund Kristensen, Heddwen L. Brooks, Donald E. Kohan, Timo Rieg, Robert A. Fenton

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Figure 2

AC6loxloxCre mice have greater water intake and lower urine osmolality under baseline conditions.

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AC6loxloxCre mice have greater water intake and lower urine osmolality u...
A mouse model with deletion of adenylyl cyclase 6 (AC6) in aquaporin-2–expressing (AQP2-expressing) cells (AC6loxloxCre) was generated as described in Methods. (A) AC6 was detected using immunoblotting as a broad smear in cortex homogenates from WT mice, whereas no signal was detectable in mice lacking AC6 (AC6–/– mice), confirming antibody specificity. (B) Under baseline conditions, AC6 protein signal was approximately 50% less intense in inner medulla (IM) homogenates from AC6loxloxCre mice compared with AC6loxlox control mice, whereas no significant reductions could be observed in cortex or outer medulla (OM)/cortex homogenates. The samples were used for immunoblotting on Figure 5. (C–F) Cre recombinase IHC showed clear nuclear labeling in cortical and IM collecting ducts of AC6loxloxCre mice. Scale bar: 50 μm. (G) Under baseline conditions, AC6loxloxCre mice had lower urine osmolality and higher water intake than AC6loxlox mice, while no significant differences were found in food intake or plasma osmolality. Values are mean ± SEM. Numbers in parentheses indicate sample sizes. Statistical comparisons were performed using Student’s 2-tailed t tests (B [cortex and OM/cortex homogenates] and G [water intake, food intake, and plasma osmolality]) and Satterthwaite’s 2-tailed unequal variance t test (B [IM homogenate] and G [urine osmolality]). *P < 0.05. Data on urine osmolality and water intake are equivalent to baseline data presented in Figure 3 and Supplemental Figure 1. Plasma osmolality data originate from a different cohort of mice.