Dietary saturated fatty acids prime the NLRP3 inflammasome via TLR4 in dendritic cells-implications for diet-induced insulin resistance.
METHODS
Inflammasome-mediated inflammation is a critical regulator of obesity-induced insulin resistance (IR). We hypothesized that saturated fatty acids (SFA) directly prime the NLRP3 inflammasome via TLR4 concurrent with IR. We focused on dendritic cells (DCs) (CD11c(+) CD11b(+) F4/80(-) ), which are recruited into obese adipose tissue following high-fat diet (HFD) challenge and are a key cell in inflammasome biology.


RESULTS
C57BL/6 mice were fed HFD for 16 weeks (45% kcal palm oil), glucose homeostasis was monitored by glucose and insulin tolerance tests. Stromal vascular fraction (SVF) cells were isolated from adipose and analyzed for CD11c(+) CD11b(+) F480(-)  DC. Following coculture with bone marrow derived DC (BMDC) insulin-stimulated (3) H-glucose transport into adipocytes, IL-1β secretion and caspase-1 activation was monitored. BMDCs primed with LPS (100 ng/mL), linoleic acid (LA; 200 μM), or palmitic acid (PA; 200 μM) were used to monitor inflammasome activation. We demonstrated significant infiltration of DCs into adipose after HFD. HFD-derived DCs reduce adipocyte insulin sensitivity upon coculture co-incident with enhanced adipocyte caspase-1 activation/IL-1β secretion. HFD-derived DCs are skewed toward a pro-inflammatory phenotype with increased IL-1β secretion, IL-1R1, TLR4, and caspase-1 expression. Complementary in vitro experiments demonstrate that TLR4 is critical in propagating SFA-mediated inflammasome activation.


CONCLUSIONS
SFA represent metabolic triggers priming the inflammasome, promoting adipocyte inflammation/IR, suggesting direct effects of SFA on inflammasome activation via TLR4.
Nutrigenomics Research Group, UCD Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland.
Clare M
CM
Reynolds
Fiona C
FC
McGillicuddy
Karen A
KA
Harford
Orla M
OM
Finucane
Kingston H G
KH
Mills
Helen M
HM
Roche
D041721:3T3-L1 Cells; D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D020170:Caspase 1 / Q000378:metabolism; D018920:Coculture Techniques; D016207:Cytokines / Q000378:metabolism; D003713:Dendritic Cells / Q000187:drug effects* / Q000378:metabolism; D059305:Diet, High-Fat / Q000009:adverse effects; D004041:Dietary Fats / Q000494:pharmacology; D005227:Fatty Acids / Q000494:pharmacology*; D058847:Inflammasomes / Q000187:drug effects* / Q000378:metabolism; D007333:Insulin Resistance / Q000502:physiology*; D053583:Interleukin-1beta / Q000378:metabolism; D019787:Linoleic Acid / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
D002352:Carrier Proteins; D016207:Cytokines; D004041:Dietary Fats; D005227:Fatty Acids; D058847:Inflammasomes; D053583:Interleukin-1beta; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D019787:Linoleic Acid; D020170:Caspase 1