Saturated fatty acids activate caspase-4/5 in human monocytes, triggering IL-1β and IL-18 release.
Obesity is associated with metabolic tissue infiltration by monocyte-derived macrophages. Saturated fatty acids contribute to proinflammatory gene induction in tissue-embedded immune cells. However, it is unknown how circulating monocytes, the macrophage precursors, react to high-fat environments. In macrophages, saturated fatty acids activate inflammatory pathways and, notably, prime caspase-associated inflammasomes. Inflammasome-activated IL-1β contributes to type 2 diabetes. We hypothesized that 1) human monocytes from obese patients show caspase activation, and 2) fatty acids trigger this response and consequent release of IL-1β/IL-18. Human peripheral blood monocytes were sorted by flow cytometry, and caspase activity was measured with a FLICA dye-based assay. Blood monocytes from obese individuals exhibited elevated caspase activity. To explore the nature and consequence of this activity, human THP1 monocytes were exposed to saturated or unsaturated fatty acids. Caspase activity was revealed by isoform-specific cleavage and enzymatic activity; cytokine expression/release was measured by qPCR and ELISA. Palmitate, but not palmitoleate, increased caspase activity in parallel to the release of IL-1β and IL-18. Palmitate induced eventual monocyte cell death with features of pyroptosis (an inflammation-linked cell death program involving caspase-4/5), scored through LDH release, vital dye influx, cell volume changes, and nuclear morphology. Notably, selective gene silencing or inhibition of caspase-4/5 reduced palmitate-induced release of IL-1β and IL-18. In summary, monocytes from obese individuals present elevated caspase activity. Mechanistically, palmitate activates a pyroptotic program in monocytes through caspase-4/5, causing inflammatory cytokine release, additional to inflammasomes. These caspases represent potential, novel, therapeutic targets to taper obesity-associated inflammation.
Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
Nicolas J
NJ
Pillon
Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
Kenny L
KL
Chan
Department of Immunology, Key Laboratory of Immuno Microenvironment and Disease of the Educational Ministry of China, Tianjin Medical University, Tianjin, China; and.
Shitian
S
Zhang
Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
Marios
M
Mejdani
Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
Maya R
MR
Jacobson
Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
Alexandre
A
Ducos
Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
Philip J
PJ
Bilan
Department of Immunology, Key Laboratory of Immuno Microenvironment and Disease of the Educational Ministry of China, Tianjin Medical University, Tianjin, China; and.|Key Laboratory of Hormones and Development (Ministry of Health), Metabolic Diseases Hospital and Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin, China.
Wenyan
W
Niu
Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada; amira@sickkids.ca.
Amira
A
Klip
D000328:Adult; D061945:Caspase Inhibitors / Q000494:pharmacology; D020169:Caspases / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D053471:Caspases, Initiator / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005227:Fatty Acids / Q000494:pharmacology*; D005229:Fatty Acids, Monounsaturated / Q000494:pharmacology; D005260:Female; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D020868:Gene Silencing; D006801:Humans; D015151:Immunoblotting; D020382:Interleukin-18 / Q000378:metabolism; D053583:Interleukin-1beta / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000187:drug effects* / Q000378:metabolism; D009765:Obesity / Q000378:metabolism*; D050177:Overweight / Q000150:complications / Q000378:metabolism*; D010168:Palmitates / Q000494:pharmacology; D010865:Pilot Projects; D016133:Polymerase Chain Reaction; D000069292:Pyroptosis / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism
D061945:Caspase Inhibitors; D005227:Fatty Acids; D005229:Fatty Acids, Monounsaturated; C508585:IL1B protein, human; D020382:Interleukin-18; D053583:Interleukin-1beta; D010168:Palmitates; D012333:RNA, Messenger; C008757:palmitoleic acid; C093516:CASP4 protein, human; C099217:CASP5 protein, human; D020169:Caspases; D053471:Caspases, Initiator
THP-1; caspase; fatty acids; inflammation; interleukin-1β; monocytes; palmitate; pyroptosis