TLR2/6 and TLR4-activated macrophages contribute to islet inflammation and impair beta cell insulin gene expression via IL-1 and IL-6
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Inflammation contributes to pancreatic beta cell dysfunction in type 2 diabetes. Toll-like receptor (TLR)-2 and -4 ligands are increased systemically in recently diagnosed type 2 diabetes patients, and TLR2- and TLR4-deficient mice are protected from the metabolic consequences of a high-fat diet. Here we investigated the role of macrophages in TLR2/6- and TLR4-mediated effects on islet inflammation and beta cell function.
Genetic and pharmacological approaches were used to determine the effects of TLR2/6 and TLR4 ligands on mouse islets, human islets and purified rat beta cells. Islet macrophages were depleted and sorted by flow cytometry and the effects of TLR2/6- and TLR4-activated bone-marrow-derived macrophages (BMDMs) on beta cell function were assessed.
Macrophages contributed to TLR2/6- and TLR4-induced islet Il1a/IL1A and Il1b/IL1B mRNA expression in mouse and human islets and IL-1β secretion from human islets. TLR2/6 and TLR4 ligands also reduced insulin gene expression; however, this occurred in a non-beta cell autonomous manner. TLR2/6- and TLR4-activated BMDMs reduced beta cell insulin secretion partly via reducing Ins1, Ins2, and Pdx1 mRNA expression. Antagonism of the IL-1 receptor and neutralisation of IL-6 completely reversed the effects of activated macrophages on beta cell gene expression.
We conclude that islet macrophages are major contributors to islet IL-1β secretion in response to TLR2/6 and TLR4 ligands. BMDMs stimulated with TLR2/6 and TLR4 ligands reduce insulin secretion from pancreatic beta cells, partly via IL-1β- and IL-6-mediated decreased insulin gene expression.
KeywordsBeta cell Diabetes Inflammation Pancreatic islet Toll-like receptor 2 Toll-like receptor 4
Chemokine (C-C motif) ligand 2
Danger-associated molecular patterns
Glucose-stimulated insulin secretion
Pathogen-associated molecular patterns
We thank L. Xu and M. Komba for technical assistance provided by the CFRI FACS core and islet isolation core facilities, respectively.
This work was supported by funding from the Child and Family Research Institute (JAE), the University of British Columbia (JAE), the Canadian Institutes of Health Research (PCN-110793 and PNI-120292; JAE), the European Research Council (KM), the Diabetes Competence Network KKNDm supported by the Federal Ministry of Germany (BMBF; KM), and a collaborative research agreement with Servier (JAE, KM). JAE has salary support from a Child and Family Research Institute Investigator Award and a Canadian Diabetes Association scholar award. DN is supported by a UBC Transplantation Training Program and a CIHR-Vanier Canada Graduate Scholarship. CW-R is supported by a CIHR-Vanier Canada Graduate Scholarship.
Duality of interest
CS-K and BG are employees of Servier, France. All other authors declare that there is no duality of interest associated with their contribution to this manuscript.
DN, MD, WH, RK, AS, SR, CW-R, AC, MS designed and performed experiments, and analysed data. KM designed experiments and CS-K and BG contributed to the conception and design of the study. All authors edited the manuscript and approved the final version. JAE supervised the study, designed and performed experiments, analysed data and wrote the manuscript. JAE is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
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