Hyperosmolarity-induced activation of PIEZO1 engages detrimental calcium/oxidative stress signaling and adaptive catalase response in renal inner medullary collecting duct (mIMCD3) cells

The collecting duct (CD) is the final segment of the renal nephron and is involved in the fine regulation of osmotic and ionic homeostasis. Its medullary segment is continuously exposed to a wide spectrum of osmotic gradients and resultant osmotic stress. Strikingly, the expression of the mechanically activated non-selective cationic and CA²⁺-permeable transduction ion channel PIEZO1 is most prominent in inner medullary CD (IMCD) cells, yet its functions there are still not well understood. We hypothesized increased PIEZO1 expression in the IMCD could be linked to its hyperosmotic stress environment. Using the mouse mIMCD₃ cell line, which has been used to characterize hyperosmotic stress-induced cell death, we demonstrate twice as much PIEZO1 expression compared to proximal tubule (WKPT-0293 Cl.2) or cortical CD (mCCD(cl.1)) cell lines. Hyperosmolarity/-tonicity by addition of NaCl ± urea to the culture medium (+ 100-300 mosmol/l) or PIEZO1 agonist Yoda1 (20 μmol/l) decreased mIMCD₃ cell viability assayed by MTT, which were antagonized by PIEZO1 inhibitors GsMTx4 (2.5 μmol/l) and salvianolic acid (SalB, 10 μmol/l). PIEZO1 activation by hyperosmolarity and agonists (Yoda1, Jedi1) increased CA²⁺ influx, downstream Reactive Oxygen Species (ROS), in particular mitochondrial superoxide (O₂^•-) formation, and subsequent adaptive ROS-decomposing catalase expression and activity that were sensitive to PIEZO1 antagonists (GsMTx4, SalB). Hence, the data demonstrate hyperosmolarity/-tonicity of the kidney elicits PIEZO1 activation, mitochondrial ROS formation and cell death that are partially countered by catalase-mediated stress adaptation.

Apoptosis; Mechanosensing; Regulatory volume increase; Superoxide dismutase; Tonicity-responsive-enhancer-binding-protein/nuclear factor of activated T-cells 5.