NLRP3 inflammasome activation in macrophages is mechanosensitive

Abstract Macrophages are innate immune cells that activate the NLRP3 inflammasome to induce inflammatory cytokine IL-1b production and pyroptotic cell death to combat infections. Dysregulated NLRP3 activation escalates inflammatory diseases under mechanical stress, such as ventilator induced injury (VLI), liver fibrosis, acute lung injury (ALI), and idiopathic pulmonary fibrosis (IPF). Macrophages reside in tissues via anchoring to the extracellular matrix (ECM), and change in adhesiveness tunes their inflammatory response via a process known as “mechanotransduction”. However, the underlying mechanism of how mechanical signaling regulates the NLRP3 inflammasome is not fully known. We have found that the NLRP3 inflammasome pathway in macrophages is sensitive to altered stiffness of the culture surface. We cultured bone-marrow derived macrophages (BMDMs) on collagen-coated polyacrylamide gels or silicone gels mimicking physiological tissue stiffness. We observed that NLRP3-induced IL-1b release was smallest on the softest gel (elastic moduli 0.2 kPa) and increased with a stiffer gel (64 kPa). Additionally, macrophages displayed increased adhesiveness and spreading on stiffer gels, indicating enhanced mechanical force. Further examination of how adhesion based-mechanotransduction modulates NLRP3 signaling will help in understanding inflammatory diseases associated with changing adhesive microenvironments such as lung fibrosis. We propose that increased stiffness during lung fibrosis exerts mechanical stress on macrophages and may promote NLRP3 inflammasome activation. Elucidating the mechanosensitivity of the NLRP3 inflammasome will aid in identifying treatment for such inflammatory diseases.