Mechanism of NCX1-mediated calcium ions influx in podocyte injury

  Background  The glomerular filtration barrier is composed of podocytes and slit diaphragm. Under pathological condition, the structure of slit diaphragm has been damaged during podocytes injury, resulting in changes in glomerular filtration function and proteinuria. As a Ca²⁺ channel, sodium-calcium exchanger 1 (NCX1) plays an important role in regulating calcium homeostasis and maintaining cell structure.

  Objective  To confirm the role of NCX1 in podocyte injury and analyze a new mechanism of proteinuria.

  Methods  A Passive Hyman Nephritis (PHN) rat model was established and the expression of NCX1 was detected in the animal model. Mouse podocytes were cultured and a complement injured podocyte model was established. The intracellular Ca²⁺ level of podocytes was detected with a Ca²⁺ fluorescence probe fluo-3. Immunofluorescence was used to confirm the changes of podocyte injury and cytoskeleton structure rearrangement and the downstream signaling pathway proteins were analyzed by Western blot. NCX1 reverse mode inhibitor KB-R7943 was applied to the complement injured podocyte model to observe whether the podocytes injury was effectively reduced.

  Results  NCX1 expression in PHN rat model decreased gradually with time and reached the minimum level at 21 d. Meanwhile, in complement injured podocytes we also found the decreased expression of NCX1. The concentration of Ca²⁺ increased significantly, and the protein expression of RhoA, ROCK1 and ROCK2 also increased. NCX1 reverse mode was activated to promote Ca²⁺ influx and RhoA/ROCK signaling pathway was activated. The expression of podocyte markers Nephrin and Synaptopodin decreased with F-actin rearragement. The podocytes injury could be significantly reduced by KB-R7943.

  Conclusion  NCX1 regulates calcium influx to active RhoA/ROCK signaling pathway mediated podocyte injury with cytoskeleton structure rearragement, thus leading to proteinuria.