Cytosolic sodium accumulation is a cellular danger signal triggering endocytic dysfunction and NLRP3 inflammasome activation

Detection of internalized bacterial toxins and particulate matter within the endo/lysosomal system is essential for the response to cellular intoxication and damage. We reveal that large clostridial toxins, including toxin B from Clostridioides difficile, monosodium urate and silica crystals, activate the NLRP3 inflammasome by enabling translocation of sodium from the endo/lysosomal system to the cytosol in human macrophages. Sodium accumulation activates NLRP3 through two distinct mechanisms: Sodium triggers cell swelling and subsequent potassium efflux, while concurrently, it inhibits endocytic trafficking by preventing osmotic resolution of endocytic vesicles. As cytosolic sodium influx and inhibition of endocytic trafficking were also mediated by non-particulate NLRP3 activators ATP and ouabain, our findings illustrate that accumulation of cytosolic sodium is a common danger signal to activate the NLRP3 inflammasome.