Mechanical Stimulation of Piezo1 Induced Protein Expression and Intracellular Trafficking of Aquaporin‐2 in IMCD Cells

Pressure and shear stress‐induced stretch of tubular epithelial cells is relevant to both physiological and diseased kidney. Piezo1 is a mechanically‐activated cation channel stimulated by membrane tension and stretch; it is highly expressed in the inner medulla of the kidney. Aquaporin‐2 (AQP2) is located in the principal cells of the collecting ducts in the kidney, which is a key aquaporin determining final urine output. The current study aims to investigate whether activation of Piezo1 induces AQP2 expression in the collecting duct principal cells. In human kidney biopsy specimen, Piezo1 was found expressed mainly in the collecting ducts where it co‐localized with AQP2. Upon treating primary cultured rat inner medullary collecting duct (IMCD) cells with Piezo1 activator Yoda1 (0.01μM to 1μM), the protein expression of AQP2 was markedly increased. Activation of Piezo1 by Yoda1 was also associated with intracellular F‐actin depolymerization and dramatically increased accumulation of AQP2 on the apical plasma membrane of IMCD cells. Upregulation of AQP2 protein was also observed when Piezo1 was stimulated with mechanical cyclic tensile strain at 5% elongation, 1Hz for 3hour in IMCD cells, which was markedly inhibited by GsMTx4 (0.1μM to 5μM), a Piezo1 antagonist. Both stretch and Yoda1 treatment induced elevation of intracellular calcium levels and upregulation of calpain2 protein expression (calcium‐activated non‐lysosomal thiol‐proteases) as well as phosphorylation of Akt protein in rat IMCD cells. Dehydration for 24h (which is presumably leading to the swelling of principal cells, Chou CL, Am J Physiol Renal Physiol, 2008) in mice was associated with increased levels of piezo1 mRNA and protein expression in the kidney inner medulla. In conclusion, activation of Piezo1 by mechanical stretch or activators increased protein expression and intracellular trafficking of AQP2 in rat IMCD cells, which was associated with F‐actin depolymerizing and elevated intracellular calcium levels. These studies indicate that piezo1 may play a functional role in the regulation of urinary osmolarity in pressure‐induced stretch of principal cells relevant to both physiological and pathophysiological conditions.