Proceedings of the National Academy of Sciences | 2019
Calpain drives pyroptotic vimentin cleavage, intermediate filament loss, and cell rupture that mediates immunostimulation
Abstract
Significance Pyroptosis is a form of inflammatory cell death. It is driven by plasma membrane pore formation that is thought to rupture cells through osmotic influx, thereby releasing intracellular content that initiates an inflammatory response to fight acute infection and tissue damage. However, when chronic or unregulated, this process can drive autoimmune disease and cancer. Here, we show that pyroptotic cells do not undergo rupture in culture. Instead, the calcium-dependent protease calpain destroys intermediate filaments, which provide mechanical resilience to cells. As a result, cells are susceptible to rupture by mechanical disruption from shear stress or compression as occurs in the blood stream or within tissues. Thus, our data reveal potential targets for the therapeutic intervention of autoimmune diseases and cancer. Pyroptosis is an inflammatory form of programmed cell death following cellular damage or infection. It is a lytic process driven by gasdermin D-mediated cellular permeabilization and presumed osmotic forces thought to induce swelling and rupture. We found that pyroptotic cells do not spontaneously rupture in culture but lose mechanical resilience. As a result, cells were susceptible to rupture by extrinsic forces, such as shear stress or compression. Cell analyses revealed that all major cytoskeleton components were disrupted during pyroptosis and that sensitivity to rupture was calpain-dependent and linked with cleavage of vimentin and loss of intermediate filaments. Moreover, while release of lactate dehydrogenase (LDH), HMGB1, and IL-1β occurred without rupture, rupture was required for release of large inflammatory stimuli—ASC specks, mitochondria, nuclei, and bacteria. Importantly, supernatants from ruptured cells were more immunostimulatory than those from nonruptured cells. These observations reveal undiscovered cellular events occurring during pyroptosis, define the mechanisms driving pyroptotic rupture, and highlight the immunologic importance of this event.