Cold-induced loss of interaction with HSC70 triggers inflammasome activity of familial cold autoinflammatory syndrome-causing mutants of NLRP3.

Abstract

NLRP3 is a cytoplasmic receptor protein, which initiates caspase-1 mediated inflammatory immune response upon detection of invading pathogen or a wide array of internal distress signals. Several gain-of function mutations of NLRP3 cause hereditary disorder of cold-induced hyper-inflammation known as familial cold autoinflammatory syndrome-1 (FCAS1). Although, caspase-1 activation and downstream interleukin-1β/interleukin-18 maturation are common effectors in pathophysiology of this disorder, molecular mechanisms of how exposure to subnormal temperature triggers mutant NLRP3-inflammsome activity is not understood. Here, we show that endogenous NLRP3 is in complex with HSC70 (HSPA8), and this interaction is reduced upon exposure to cold. FCAS-causing NLRP3-L353P and NLRP3-R260W mutants show enhanced interaction with HSC70. Upon exposure to subnormal temperature, NLRP3-L353P and NLRP3-R260W show enhanced inflammasome formation, increased caspase-1 activation and reduced interaction with HSC70. Knockdown of HSC70 results in increased inflammasome formation by L353P and R260W mutants of NLRP3. Our results suggest that interaction with HSC70 suppresses inflammasome formation by FCAS-causing NLRP3 mutants at physiological temperature, and loss of this inhibitory association at subnormal temperature causes aggravated inflammasome formation and caspase-1 activation leading to interleukin-1β maturation. These results provide evidence for HSC70 being a cold-sensor and a temperature-dependent regulator of inflammatory signaling by FCAS-causing NLRP3 mutants.