RNA-Seq and protein mass spectrometry in microdissected kidney tubules reveal signaling processes initiating lithium-induced nephrogenic diabetes insipidus

Purpose: Lithium salts, used for treatment of bipolar disorder, frequently induce nephrogenic diabetes insipidus (NDI), limiting therapeutic success. NDI is associated with loss of expression of the molecular water channel, aquaporin-2, in the renal collecting duct (CD). Here, we use the methods of systems biology in a well-established rat model of lithium-induced NDI to identify signaling pathways activated at the onset of polyuria. Methods: We carried out RNA-sequencing in cortical CDs microdissected from rats treated with lithium for 12-72 hours (vs. time controls). Administration of anti-inflammatory doses of dexamethasone to lithium-treated rats countered the loss of aquaporin-2 protein. Protein mass spectrometry in microdissected cortical CDs provided corroborative evidence, but also identified decreased abundance of several anti-oxidant proteins. Cortical thick ascending limbs of Henle were also microdissected for RNA-Seq at 72 hrs. We carried out RNA-Seq for 2-3 CCD sample per rat (1 lithium-treated rat versus 1 control at 12, 24, 36 hrs). Results and conclusion: Integration of new data with prior data about lithium effects at a molecular level leads to a signaling model in which lithium increases ERK activation leading to induction of NF-?B signaling and an inflammatory-like response that represses Aqp2 gene transcription. Overall design: We carried out RNA-sequencing and protein mass spectrometry in cortical CDs microdissected from rats treated with lithium. We identified signaling pathways that initiate Lithium-induced NDI using systems biology approaches.