Role of fluid shear stress in cytoskeleton reorganization of mouse proximal tubule epithelium

Our previous studies of microperfused single mouse proximal tubule (mPT) have demonstrated that flow‐dependent Na and HCO 3 reabsorption is due to a change of NHE3 and H‐ATPase activity. Actin cytoskeleton was indicated to provide a structural framework for PT cells to transmit mechanical forces and subsequently modulate cellular functions. However, how the cytoskeleton and other structural components respond to fluid shear is still elusive. Using a parallel plate flow chamber, mPT cells grown on collagen substrate were subjected to 5h of shear stress (1 dyne/cm 2 ) to investigate the organization aspects of F‐actin, ZO‐1 (tight junction protein), E‐cadherin (adherens junction protein), and vinculin (a marker protein located at focal adhesion plaques). Immunostaining showed a reinforcement of peripheral actin networks with disappearance of cytosolic stress fibers after shear stress. Continuous ZO‐1 at cell‐cell contacts was observed under dynamic situation but not in control. Similar adherens junction‐like structure was also found only after flow. Shear stress further caused increased vinculin expression both at cell border and the base. Our results showed that shear‐induced cytoskeleton reorganization in mPT cells is exactly opposite to that observed in endothelial cells. We therefore built a conceptual model for epithelial cytoskeleton remodeling to explain this strikingly different response.