Alternation in the Abundance and Phosphorylation Status of Aquaporin-2 in the Serum Exosome of Patients with Chronic Kidney Disease

Background: Exosomes, which are vesicles ranging from 40 to 160 nm in size, are released from cellular membranes and serve as a means of cell-to-cell communication by delivering their contents, such as microRNA and protein, to recipient cells. These extracellular vesicles are present in human blood and urine and their composition can be altered in specific pathogenic conditions. Aquaporin-2 (AQP2) is a critical aquaporin involved in water homeostasis and has been identified as an important biomarker in chronic kidney disease. However, it is unclear whether AQP2 is transported via exosomes. Method: This study included 16 participants with chronic kidney disease and 11 healthy volunteers. Serum exosomes were isolated through polymer precipitation and imaged using transmission electron microscopy. The diameter of purified serum exosomes was measured via flow cytometry, and their identity was further confirmed by identifying exosome markers through immunoblotting. Additionally, the participants’ hepatic B and C virus infection status was determined using chemiluminescent microparticle immunoassay. Results: The precipitation method was utilized to isolate serum exosomes, and successful purification was confirmed through transmission electron microscopy imaging. Size estimation was conducted via flow cytometry, and the presence of exosome markers CD63, TSG101, CD9, and CD81 was confirmed through immunoblotting. Furthermore, the presence of AQP2 was detected in serum exosomes, and its abundance was found to significantly decrease in patients with chronic kidney disease. However, despite the decreased abundance, the percentage of phosphorylated AQP2 at serine 256 was significantly increased. Conclusion: Our findings suggest that changes in the abundance and phosphorylation status of AQP2 on serum exosomes are associated with the development of chronic kidney disease, and could potentially serve as a signal for exosome transport.