Extracellular Vesicle Transcriptomes in Human Urine Capture Kidney Adaptation to Sodium Intake

Urine extracellular vesicles (uEVs) originate from the genitourinary system, including the kidney's tubular epithelial cells. These cells control Na⁺ balance, e.g., by increased aldosterone-induced Na⁺ reabsorption in response to a low Na⁺ intake. We hypothesized that the uEV transcriptome reflects the physiological adaptation of tubular epithelial cells to variation in dietary Na⁺. Paired biobanked urine samples from healthy young men after 5 days on a low (70 mmol/day) and high (250 mmol/day) Na⁺ diet were analyzed by RNA sequencing. From 20 samples, 17 produced high-quality data, yielding quantitative data for >13,000 genes. The Na⁺ diets only significantly affected the uEV abundance of 10 gene transcripts; 5 decreased, and 5 increased, including SLC12A3, encoding the Na⁺, Cl^- transporter NCC, in low-Na⁺ diet sample uEVs. We used transcriptomic deconvolution to estimate the uEVs' tissue and cell-type origins. The uEVs were mainly derived from the kidneys and bladder. Compared to the high-Na⁺ diet samples, the low-Na⁺ diet samples had a ~30% higher kidney-derived uEV abundance. The estimated kidney-derived EV abundance was strongly correlated to plasma renin, plasma and urine aldosterone, and mean arterial blood pressure. At the kidney epithelial cell level, proximal tubule-derived EVs were most abundant. While most of the cell-type-specific uEV abundances were not different between Na⁺ diets, intercalated cell-derived EVs were significantly less abundant in low Na⁺ diet samples. Moreover, intercalated cell-uEV abundance estimates were negatively correlated with mean arterial pressure. In conclusion, uEV RNA analyses illuminate the pathways underlying physiological control of renal Na⁺ reabsorption in the human kidney.