#111 RNAseq of microdissected collecting ducts revealing the early signaling mediating the loss of aquaporin 2 after K+ deprivation

Abstract

Abstract Background and Aims Potassium (K+) deficiency could cause a reduction in urinary concentrating ability, resulting in nephrogenic diabetes insipidus (NDI), but the detailed mechanism remains unclear. Recently, transcriptomic and proteomic data from acquired NDI models reveal that oxidative stress, apoptosis, and inflammatory signaling are associated with AQP2 loss. We aim to explore the early signaling after K+ deprivation in collecting ducts. Method Immunoblotting of kidney lysate were performed at 0, 12, 24, and 48 hours after K+ deprivation in rats. Serum and urine biochemistry were also recorded. Based on immunoblotting, cortical collecting ducts (CCDs) were microdissected from rats at 6 hrs after K+ deprivation versus time controls. Small samples RNA-Seq was carried out independently in K+ deprivation rats versus controls (n = 4). Results Immunoblotting of bulk kidney showed a decreased in AQP2 protein abundance at 12 hours of K+ deprivation diet, and urine osmolality was significantly decreased at 24 hours, confirming the animal model of K+ deprivation-induced NDI. Small samples RNA-Seq data of CCDs at 6 hrs after K+ deprivation showed Aqp2, Aqp3, and Atp1a1 were significantly downregulated. It also revealed that chemokine transcripts (Ccl20 and Ccl28) were increased significantly. We also carried out analysis of Gene Ontology Biological Process terms that are statistically over-represented in the list of 88 “Increased Transcripts” at 6 hrs of K+ deprivation in CCDs, and many of the terms are related to glutathione metabolic process, cell chemotaxis, cellular response to lipopolysaccharide, consistent with an inflammatory response. Conclusion Our small samples RNA-Seq from microdissected CCDs in rats showed early cellular signaling changes in activation of oxidative stress and inflammatory signaling causing loss of aquaporin-2 in K+ deficiency induced NDI.