Inflammasome assembly is required for intracellular formation of β2-microglobulin amyloid fibrils, leading to IL-1β secretion

INTRODUCTION: Dialysis-related amyloidosis (DRA) caused by β2-microgloblin (B2M) fibrils is a serious complication for patients with kidney failure on long-term dialysis. Deposition of B2M amyloid fibrils is thought to be due not only to serum extracellular B2M but also to infiltrating inflammatory cells, which may have an important role in B2M amyloid deposition in osteoarticular tissues in patients with DRA. Here, we asked whether B2M amyloid fibrils activate the inflammasome and contribute to formation and deposition of amyloid fibrils in cells. METHODS: Amyloid formation was confirmed by a thioflavin T (ThT) spectroscopic assay and scanning electron microscopy (SEM). Activation of inflammasomes was assessed by detecting interleukin (IL)-1β in culture supernatants from human embryonic kidney (HEK) 293T cells ectopically expressing inflammasome components. IL-1β secretion was measured by enzyme-linked immunosorbent assay. Expression and co-localization were analyzed by immunohistochemistry and dual immunofluorescence microscopy. RESULTS: B2M amyloid fibrils interacted directly with NLRP3/Pyrin and to activate the NLRP3/Pyrin inflammasomes, resulting in IL-1β secretion. When HEK293T cells were transfected with inflammasome components NLRP3 or Pyrin, along with ASC, pro-caspase-1, pro-IL-1β, and B2M, ThT fluorescence intensity increased. This was accompanied by IL-1β secretion, which increased in line with the amount of transfected B2M. In this case, morphological glowing of amyloid fibrils was observed by SEM. In the absence of ASC, there was no increase in ThT fluorescence intensity or IL-1β secretion, or any morphological glowing of amyloid fibrils. NLRP3 or Pyrin and B2M were co-localized in a “speck” in HEK293T cells, and co-expressed in infiltrated monocytes/macrophages in the osteoarticular synovial tissues in a patient with DRA. CONCLUSION: Taken together, these data suggest that inflammasome assembly is required for the subsequent triggering of intracellular formation of B2M amyloid fibrils, which may contribute to osteoarticular deposition of B2M amyloid fibrils and inflammation in patients with DRA.