Shear Stress Stimulated MSC Activities: Direct Changes of Membrane Tension or Cytoskeletal Stress?

Abstract

Fluid shear stress induced membrane transport such as Ca2+ influx and the activation of ion channels has been widely reported. The shear stress can be mediated by a direct change in bilipid membrane tension and/or by a change in cytoskeletal stress via binding proteins that link channels to actin, but how the shear stress is coupled to ion channels is unclear. Using narrow shear pulse stimuli generated by a pressure servo in a microfluidic chamber, we measured the changes of membrane tension and cytoskeletal protein stress simultaneously in astrocytes. The membrane tension was reported using molecular motor probes (2-carboxy-2-cyanovinyl)-julolidine farnesyl ester (FCVJ) and cytoskeletal tension reported by genetically encoded force probe actinin-cpst-FRET. Our results show that the changes of membrane tension are highly localized and the gradient is relevant to the flow directions. A shear stress pulse (23 dyn/cm2, 400 ms duration) caused a rapid increase in membrane tension at the front edge of the cell with respect to the flow and a decrease in tension (compression) at the distal edge. The rise time was less than 30 ms, and the tension dropped to the initial state within ∼30 ms post stimulus, showing a typical elastic behavior. In contrast, the same shear pulse generated profound and long-lasting tension in cytoskeletal cross-linking proteins α-actinin at the front edge of the cell, and the tension persisted for the entire experimental duration of 60 s. In situ Ca2+ imaging showed that the initial Ca2+ influx was strongly correlated with the region having high cytoskeletal tension, but weakly linked to the bilayer tension. The results suggest the cytoskeletal tension plays primary role in shear stress activated Ca2+ influx. This work was funded by NINDS.