Lipid environment induces ER stress, TXNIP expression and inflammation in immune cells of individuals with type 2 diabetes
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Obesity and type 2 diabetes are concomitant with low-grade inflammation affecting insulin sensitivity and insulin secretion. Recently, the thioredoxin interacting protein (TXNIP) has been implicated in the activation process of the NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome. In this study, we aim to determine whether the expression of TXNIP is altered in the circulating immune cells of individuals with type 2 vs type 1 diabetes and whether this can be related to specific causes and consequences of inflammation.
The expression of TXNIP, inflammatory markers, markers of the unfolded protein response (UPR) to endoplasmic reticulum (ER) stress and enzymes involved in sphingolipid metabolism was quantified by quantitative reverse transcription real-time PCR (qRT-PCR) in peripheral blood mononuclear cells (PBMCs) of 13 non-diabetic individuals, 23 individuals with type 1 diabetes and 81 with type 2 diabetes. A lipidomic analysis on the plasma of 13 non-diabetic individuals, 35 individuals with type 1 diabetes and 94 with type 2 diabetes was performed. The effects of ER stress or of specific lipids on TXNIP and inflammatory marker expression were analysed in human monocyte-derived macrophages (HMDMs) and THP-1 cells.
The expression of TXNIP and inflammatory and UPR markers was increased in the PBMCs of individuals with type 2 diabetes when compared with non-diabetic individuals or individuals with type 1 diabetes. TXNIP expression was significantly correlated with plasma fasting glucose, plasma triacylglycerol concentrations and specific UPR markers. Induction of ER stress in THP-1 cells or cultured HMDMs led to increased expression of UPR markers, TXNIP, NLRP3 and IL-1β. Conversely, a chemical chaperone reduced the expression of UPR markers and TXNIP in PBMCs of individuals with type 2 diabetes. The lipidomic plasma analysis revealed an increased concentration of saturated dihydroceramide and sphingomyelin in individuals with type 2 diabetes when compared with non-diabetic individuals and individuals with type 1 diabetes. In addition, the expression of specific enzymes of sphingolipid metabolism, dihydroceramide desaturase 1 and sphingomyelin synthase 1, was increased in the PBMCs of individuals with type 2 diabetes. Palmitate or C2 ceramide induced ER stress in macrophages as well as increased expression of TXNIP, NLRP3 and IL-1β.
In individuals with type 2 diabetes, circulating immune cells display an inflammatory phenotype that can be linked to ER stress and TXNIP expression. Immune cell ER stress can in turn be linked to the specific exogenous and endogenous lipid environment found in type 2 diabetes.
KeywordsCeramide Diabetes mellitus Endoplasmic reticulum stress Inflammasome Macrophages NLRP3 Peripheral blood mononuclear cells Sphingolipids TXNIP
ER stress activated transcription factor 6
Bone marrow-derived macrophages
Chemokine ligand 2
Carbohydrate response element binding protein
Human monocyte-derived macrophage
Inositol requiring enzyme 1
NOD-like receptor family, pyrin domain containing 3
Peripheral blood mononuclear cell
Protein kinase R-like endoplasmic reticulum kinase
Quantitative reverse transcription real-time PCR
Thioredoxin interacting protein
Unfolded protein response
X box binding protein 1
We are grateful to the donors for allowing us to use the blood samples and to the animal platform of the Centre de Recherche des Cordeliers for taking care of the animals. We thank H. Le Stunff (University Denis Diderot) for useful discussions, F. Fumeron (University Denis Diderot) for his help with statistical methods and F. Alzaïd (Centre de Recherche des Cordeliers) for editing the manuscript.
The data supporting the results reported in the article are available on request from the corresponding author.
This work was supported by a grant from the ‘Fondation pour la Recherche Médicale’ Equipe FRM DEQ20140329504.
Duality of interest
CB is and AK was an employee of Servier Pharmaceutical. AS received a grant from Servier Pharmaceutical during the conduct of this study. All other authors declare that there is no duality of interest associated with their contribution to this manuscript.
AS contributed to the experimental design and data acquisition and wrote the manuscript. IH and AFB contributed to the experimental design and data acquisition and reviewed/edited the manuscript. NV contributed to the experimental design, interpretation of data and reviewed/edited the manuscript. AC, JFG and OB assisted in the collection of human specimens at Lariboisière and Pitié-Salpêtrière hospitals, interpretation of data and reviewed/edited the manuscript. OB also contributed to the conception and design of the study. EH contributed to interpretation of data and reviewed/edited the manuscript. CB and AK contributed to the experimental design and reviewed/edited the manuscript. PF contributed to the experimental design and data interpretation and wrote the manuscript. FF contributed to the experimental design and data analysis and interpretation, wrote the manuscript and is the guarantor of this work and, as such, had full access to all the data in the study. She takes responsibility for the integrity of the data and the accuracy of the data analysis. All authors approved the final version of the manuscript.
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