Hypotonic stress induces fast, reversible degradation of the vimentin cytoskeleton via intracellular calcium release

Abstract

The dynamic response of the cell to osmotic changes is critical to its physiology and has been widely exploited for cell manipulation. Using 3D-STORM super-resolution microscopy, here we examine the hypotonic stress-induced ultrastructural changes of the cytoskeleton of a common fibroblast cell type. Unexpectedly, we observe a fast, yet reversible dissolution of the vimentin intermediate filament system that precedes ultrastructural changes of the supposedly more dynamic actin and tubulin cytoskeletal systems, as well as changes in cell morphology. In combination with calcium imaging and biochemical analysis, we next show that the vimentin-specific fast cytoskeletal degradation under hypotonic stress is due to proteolysis by the calcium-dependent protease calpain. We find the process to be activated by the hypotonic stress-induced calcium release from intracellular stores, and so is efficiently suppressed by inhibiting any part of the IP3-Ca2+-calpain pathway we establish. Together, our findings highlight an unexpected, fast degradation mechanism for the vimentin cytoskeleton in response to the external stimuli, and point to the significant, yet previously overlooked physiological impacts of hypotonic stress-induced intracellular calcium release on cell ultrastructure and function.