TNFα-induced NLRP3 inflammasome mediates adipocyte dysfunction and activates macrophages through adipocyte-derived lipocalin 2

초록

Background and aims: Obesity is a state of chronic low-grade systemic inflammation. Recent studies showed that NLRP3 inflammasome initiates metabolic dysregulation in adipose tissues, primarily through activation of adi-pose tissue infiltrated macrophages. However, the mechanism of NLRP3 activation and its role in adipocytes remains elusive. Therefore, we aimed to examine the activation of TNFa-induced NLRP3 inflammasome in ad-ipocytes and its role on adipocyte metabolism and crosstalk with macrophages. Methods: The effect of TNFa on adipocyte NLRP3 inflammasome activation was measured. Caspase-1 inhibitor (Ac-YVAD-cmk) and primary adipocytes from NLRP3 and caspase-1 knockout mice were utilized to block NLRP3 inflammasome activation. Biomarkers were measured by using real-time PCR, western blotting, immunofluo-rescence staining, and enzyme assay kits. Conditioned media from TNFa-stimulated adipocytes was used to establish the adipocyte-macrophage crosstalk. Chromatin immunoprecipitation assay was used to identify the role of NLRP3 as a transcription factor. Mouse and human adipose tissues were collected for correlation analysis.Results: TNFa treatment induced NLRP3 expression and caspase-1 activity in adipocytes, partly through auto-phagy dysregulation. The activated adipocyte NLRP3 inflammasome participated in mitochondrial dysfunction and insulin resistance, as evidenced by the amelioration of these effects in Ac-YVAD-cmk treated 3T3-L1 cells or primary adipocytes isolated from NLRP3 and caspase-1 knockout mice. Particularly, the adipocyte NLRP3 inflammasome was involved in glucose uptake regulation. Also, TNFa induced expression and secretion of lip-ocalin 2 (Lcn2) in a NLRP3-dependent manner. NLRP3 could bind to the promoter and transcriptionally regulate Lcn2 in adipocytes. Treatment with adipocyte conditioned media revealed that adipocyte-derived Lcn2 was responsible for macrophage NLRP3 inflammasome activation, working as a second signal. Adipocytes isolated from high-fat diet mice and adipose tissue from obese individuals showed a positive correlation between NLRP3 and Lcn2 gene expression.Conclusions: This study highlights the importance of adipocyte NLRP3 inflammasome activation and novel role of TNFa-NLRP3-Lcn2 axis in adipose tissue. It adds rational for the current development of NLRP3 inhibitors for treating obesity-induced metabolic diseases.

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