Human resistin is critical to activation of the NLRP3 inflammasome in macrophages

Abstract

Elevated levels of human resistin (hResistin) have been associated with diverse inflammatory diseases, but the precise mechanisms through which hResistins many inflammatory effects contribute to the progression of these diseases remain poorly understood. NLRP3 inflammasome activation is essential in many of these inflammatory conditions; however, there is an unmet explanation connecting hResistin with the NLRP3 inflammatory pathway. Here we describe a unique role of hResistin and its rodent homolog, resistin-like molecule alpha (RELM) in priming and activating the NLRP3 inflammasome. Through qPCR and western blot analysis, we found that hResistin-dependent expression and secretion of high mobility group box 1 (HMGB1) in human macrophages primes the expression of NLRP3, pro-capsase-1, pro-interleukin(IL)-1{beta}, and pro-IL-18. Co-immunoprecipitation showed that hResistin binds to Brutons tyrosine kinase (BTK), which causes the kinase to autophosphorylate, allowing BTK to phosphorylate NLRP3, leading to its assembly and activation with subsequent cleavage of pro-caspase-1, pro-IL-1{beta}, and pro-IL-18, causing initiation of the inflammasome cascade. The hResistin-dependent activation and secretion of IL-1{beta} and IL-18 was critical to the proliferation of human pulmonary vascular smooth muscle cells. For confirmation in vivo, we studied rodent and human pulmonary hypertension (PH). Chronic hypoxia-induced PH in wild-type and RELM KO mice showed RELM-dependent upregulation of HMGB1, BTK, and NLRP3 in mouse lung and was linked to vascular remodeling pathways. Immunohistochemistry revealed that the majority of NLRP3-expressing cells were macrophages and the colocalization of hResistin, BTK, and NLRP3 in macrophages was increased in PH patients lungs. Our work reveals a novel immune mechanism demonstrating hResistin is essential to the priming and activation of NLRP3. Inhibiting NLRP3 activation by blocking hResistin with a human monoclonal antibody suggests a likely therapeutic pathway for NLRP3-driven inflammatory diseases.