Date: Saturday, May 30, 2020
Session Name: Innate Immunity; Chemokines, Cytokines, Complement
Session Time: 3:15pm-4:45pm
Presentation Time: 3:39pm-3:51pm
*Purpose: Sequestered self-molecules, such as HMGB1 or haptoglobin, are appreciated to stimulate the pro-inflammatory response of infiltrating innate immune cells by targeting TLR4 after their release during tissue injury. We have recently established that IL-33, a protein sequestered in the nucleus or exosome-like vesicles, acts instead as a regulatory factor that limits chronic rejection after heart transplantation by restraining the generation of pro-inflammatory macrophages in the graft. The purpose of this study was to identify the molecular mechanism underlying the regulatory capacity of IL-33 on macrophages.
*Methods: Bioenergetics of wildtype (WT) C57BL/6 (B6) macrophages exposed to IL-33 were compared to macrophages stimulated with LPS, known to generate pro-inflammatory macrophages, or IL-4, which instead generates regulatory/reparative macrophages using a Seahorse XF96e Analyzer. Macrophages from WT B6 and B6 il1rl1-/- mice, which lack the IL-33 receptor, were assessed by RNAseq, qRT-PCR, and Western blot following treatment with IL-33, LPS, or IL-4. Macrophage functional phenotypes were also compared to mitochondrial mass, potential, and uptake of glucose and fatty acids by flow cytometry.
*Results: Unlike macrophages that responded to LPS by shifting their metabolic activity towards aerobic glycolysis, IL-33 augmented macrophage oxidative phosphorylation (OXPHOS). IL-33-stimulated macrophages also displayed increase mitochondrial potential and increased fatty acid uptake (FAU). RNAseq analysis revealed that IL-33 was a potent negative regulator of nos2, which is the message for inducible nitric oxide synthase (iNOS). Follow up studies established both that macrophage exposure to IL-33 blocked TLR4-mediated up-regulation of iNOS.
*Conclusions: Nitric oxide (NO) generated by iNOS in TLR4-stimulated macrophages has long been appreciated as a cytotoxic effector molecule, however, NO has emerged as an important regulator of mitochondrial metabolism. NO disrupts mitochondrial complex functions to generate metabolites that contribute to macrophage pro-inflammatory activity. This disruption requires macrophages to shift their metabolic activity to glycolysis. We now show that IL-33, instead blocks TLR4-induced iNOS induction and generates reparative/regulatory macrophage with augmented OXPHOS and FAU. Our data indicate that macrophage function in the graft can be shaped by local injury signals that orchestrate their metabolism.
To cite this abstract in AMA style:Li T, Zhang Z, Liu Q, Bartolacci J, Velayutham M, Hussey G, Dziki J, Mathews L, Lee Y, Dwyer G, Dai H, Roessing A, Shiva S, Oberbarnscheidt M, Badylak S, Turnquist H. IL-33 is a Potent Injury Signal That Programs Graft Macrophage Metabolism Toward That Required for Reparative and Regulatory Functions [abstract]. Am J Transplant. 2020; 20 (suppl 3). https://atcmeetingabstracts.com/abstract/il-33-is-a-potent-injury-signal-that-programs-graft-macrophage-metabolism-toward-that-required-for-reparative-and-regulatory-functions/. Accessed October 21, 2020.
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