Expression of ASC in renal tissues of familial mediterranean fever patients with amyloidosis: postulating a role for ASC in AA type amyloid deposition

Abstract

Familial Mediterranean fever (FMF) is characterized by recurrent attacks of fever and serositis; in some cases, ensuing amyloidosis results in kidney damage. Treatment with colchicine reduces the frequency and severity of FMF attacks and prevents amyloidosis, although the mechanisms behind these effects are unknown. Pyrin, the protein product of the MEFV gene, interacts with ASC, a key molecule in apoptotic and inflammatory processes. ASC forms intracellular speck-like aggregates that presage cell death. Here we show that cell death after ASC speck formation is much slower in nonmyeloid cells than in myeloid cells. Additionally, we demonstrate that colchicine prevents speck formation and show that specks can survive in the extracellular space after cell death. Because we also found that ASC is expressed in renal glomeruli of patients with FMF but not in those of control patients, we posit that high local ASC expression may result in speck formation and that specks from dying cells may persist in the extracellular space where they have the potential (perhaps in association with pyrin) to nucleate amyloid. The fact that speck formation requires an intact microtubule network as shown here could potentially account for the ability of prophylactic colchicine to prevent or reverse amyloidosis in patients with FMF.