Multiplatform analysis of DCT-specific mechanisms during low dietary potassium intake
Authors: Assmus Adrienne , Wu Qi , Little Robert , Poulsen Søren , Fenton Robert 
Published: May 2023

Western diets are typically high in sodium, widely regarded to increase blood pressure (BP). They are also characterised by a relatively low potassium (K) intake, also linked to higher BP. Previous studies have shown that the ability of low dietary K to increase BP is almost fully accounted for by an increase in the abundance and activity of the thiazide-sensitive sodium-chloride transporter (NCC) in the kidney distal convoluted tubule (DCT). This study aims to increase our understanding of the specific effects of low K intake on the molecular landscape of the DCT. Hypothesis: During low dietary K intake unique DCT specific mechanisms account both for the higher NCC abundance and underlie the DCT remodelling processes leading to DCT hypertrophy. Methods: Due to the relatively low abundance of DCT cells vs. whole kidney, many DCT-specific changes are undetectable when analysing whole kidney or cortex samples. To uncover DCT-specific mechanisms, Parvalbumin-GFP+ mice (GFP expressed only in DCT) were fed control (1% K) or a low K (0.2%K, n=7) diet for 4 days. Kidneys were collected on day 5, a single cell suspension prepared and GFP- and GFP+ cells separated using FACs. Cells were prepared for both bulk RNAseq and protein mass spectrometry. In parallel, kidney samples were embedded in paraffin, tubules were isolated using a laser microdissection system (LMD) and a protocol optimized to analyse these samples with mass spectrometry. Results: Compared to control diets, mice on 0.2%K intake had increased NCC (+44%) and phosphorylated NCC (+51%), and decreased expression of α-ENaC (-20%) and cleaved γ-ENaC (-10%). Mice on 0.2%K also had higher BP by tail cuff plethysmography (SBP 121.4 ± 2.1 vs. 110.8 ± 1.1 mmHg), reduced urine volume and reduced urinary K excretion (5.5-fold). Plasma K was slightly decreased compared to control diets (4.06 vs. 4.35mmol/l). FACs of living GFP+ cells was optimized to 95±2% purity and enrichment of DCT cells confirmed at protein and RNA level for DCT specific genes of interest. RNAseq and mass spectrometry studies of these samples are ongoing. For LMD samples, mass spectrometry detected ~1400 proteins from ~40 tubules. Samples from specific segments were enriched for proteins known to be expressed in these regions. Ongoing studies are addressing the proteomes of proximal tubule, DCT and collecting duct cells subsequent to 0.2% K+ intake. Perspectives: Understanding the mechanisms of K handling and their effects on BP may offer new targets for prevention or treatment of hypertension, both through drug and dietary intervention. We have developed a multiplatform approach to study DCT cells by proteomics, transcriptomics and coupled it to functional studies. We have also developed a protocol for processing LMD samples that allows for a good recovery of proteins from a low number of tubules, opening up the possibilities to process a large number of already existing samples from a range of different studies. Novo Nordisk Foundation (NNF21OC0067647), Leducq Foundation (17CVD05). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.