Proteomic analysis of lithium-induced nephrogenic diabetes insipidus: Mechanisms for aquaporin 2 down-regulation and cellular proliferation

Abstract

Lithium is a commonly prescribed mood-stabilizing drug. However, chronic treatment with lithium induces numerous kidney-related side effects, such as dramatically reduced aquaporin 2 (AQP2) abundance, altered renal function, and structural changes. As a model system, inner medullary collecting ducts (IMCD) isolated from rats treated with lithium for either 1 or 2 weeks were subjected to differential 2D gel electrophoresis combined with mass spectrometry and bioinformatics analysis to identify (i) signaling pathways affected by lithium and (ii) unique candidate proteins for AQP2 regulation. After 1 or 2 weeks of lithium treatment, we identified 6 and 74 proteins with altered abundance compared with controls, respectively. We randomly selected 17 proteins with altered abundance caused by lithium treatment for validation by immunoblotting. Bioinformatics analysis of the data indicated that proteins involved in cell death, apoptosis, cell proliferation, and morphology are highly affected by lithium. We demonstrate that members of several signaling pathways are activated by lithium treatment, including the PKB/Akt-kinase and the mitogen-activated protein kinases (MAPK), such as extracellular regulated kinase (ERK), c-Jun NH2-terminal kinase (JNK), and p38. Lithium treatment increased the intracellular accumulation of ␤-catenin in association with increased levels of phosphorylated glycogen synthase kinase type 3␤ (GSK3␤). This study provides a comprehensive analysis of the proteins affected by lithium treatment in the IMCD and, as such, provides clues to potential lithium targets in the brain.L ithium administration is the most popular therapeutic approach to treat bipolar disorders, with 0.1% of the population receiving lithium (1, 2). In 50% of these patients, chronic lithium treatment is associated with altered renal function and nephrogenic diabetes insipidus (NDI) characterized by a defective urinary concentrating mechanism that manifests in polyuria, increased sodium excretion, and hypercholoremic metabolic acidosis (3). The polyuria is largely explained by decreased abundances of the vasopressin (AVP)-regulated aquaporin 2 and aquaporin 3 (AQP2 and AQP3) water channels in the collecting duct (4, 5). The renal sodium loss is likely to be caused by reduced expression of the epithelial sodium channel (ENaC) in the cortical and outer medullary collecting duct (6, 7). In addition, lithium induces increased expression of important acid-base transporting proteins including the H ϩ -ATPase and the anion exchanger type 1 (AE1) in the collecting duct (8). These changes may be, at least in part, attributable to an increase in the proportion of intercalated cells compared with principal cells (9), which is associated with increased cell proliferation and apoptosis of principal cells (10). Additionally, further ''remodeling'' of the kidney can occur with lithium treatment, including major structural changes such as medullary tubular cysts and tubular atrophy, resulting in tubulointerstitial fibrosis and renal failure (11)....

Phosphoproteomic Profiling Reveals Vasopressin-Regulated Phosphorylation Sites in Collecting Duct

“…Although involvement of ␤-catenin in the embryonic development of the collecting duct has been well studied, [31][32][33] there is only indirect evidence regarding its relationship to vasopressin signaling in the mature collecting duct. 23 The amino acid sequence surrounding Ser-552 of ␤-catenin (…QRRTS 552 MGGT…) is consistent with a PKA motif. 27 Through 32 P labeling and site-directed mutagenesis, it has been shown previously that PKA can phosphorylate Ser-552.…”

“…Because ␤-catenin has been proposed to play a role in regulation of aquaporin-2, 23 we investigated this response further using a phosphospecific antibody. Figure 5A shows an immunoblot performed on protein isolates from the same five pairs of animals used in our large-scale quantitation experiment.…”

Quantitative Proteomics Identifies Vasopressin-Responsive Nuclear Proteins in Collecting Duct Cells

“…18 Prior studies showed that b-catenin phosphorylation at Ser-552 is regulated by vasopressin. [19][20][21] However, none of these studies addressed changes in subcellular localization.…”

“…There is an emerging recognition of a role for b-catenin in vasopressin signaling in the renal collecting duct. [17][18][19][20][21] b-catenin is a multifunctional protein acting in at least three ways: (1) as a transcriptional coregulator, (2) as a component of the Wnt signaling network, and (3) as a component of adherens junctions. We also identified numerous proteins that putatively interact with b-catenin in collecting duct nuclei such as Cdh, Vcl, Scrib, Crebbp, Ep300, Tcf7l2, and Tax1bp3.…”

Role of aquaporins in cell proliferation: What else beyond water permeability?

“…99 In skin, AQP3 is important for the phosphorylation of p38, ERK and JNK in keratinocyte, and less phosphorylation of p38 and JNK was observed in epidermis from AQP3-null mice which exhibit clearly impaired wound healing capacity compared to wild-type animals. 14 Further, the activation of GSK-3b, ERK, JNK, and p38 MAPK pathways has been associated with levels of AQP2 and proliferation in kidney collecting duct cells treated with lithium; 101,102 while the antiproliferative and anti-metastasis activity of anti-prostate cancer compounds such as Rg3 was associated with p38 MAPK-mediated downregulation of AQP1. 103 On the other hand, NF-kb seems to be the key transcription factor to which the actions of AQPs converge to produce a more proliferative phenotype.…”