title: Macrophage specific caspase-1/11 deficiency protects against cholesterol crystallization and hepatic inflammation in hyperlipidemic mice.
abstract: OBJECTIVE
  While non-alcoholic steatohepatitis (NASH) is characterized by hepatic steatosis combined with inflammation, the mechanisms triggering hepatic inflammation are unknown. In Ldlr(-/-) mice, we have previously shown that lysosomal cholesterol accumulation in Kupffer cells (KCs) correlates with hepatic inflammation and cholesterol crystallization. Previously, cholesterol crystals have been shown to induce the activation of inflammasomes. Inflammasomes are protein complexes that induce the processing and release of pro-inflammatory cytokines IL-1b and IL-18 via caspase-1 activation. Whereas caspase-1 activation is independent of caspase-11 in the canonical pathway of inflammasome activation, caspase-11 was found to trigger caspase-1-dependent IL-1b and IL-18 in response to non-canonical inflammasome activators. So far, it has not been investigated whether inflammasome activation stimulates the formation of cholesterol crystals. We hypothesized that inflammasome activation in KCs stimulates cholesterol crystallization, thereby leading to hepatic inflammation.
  
  
  METHODS
  Ldlr (-/-) mice were transplanted (tp) with wild-type (Wt) or caspase-1/11(-/-) (dKO) bone marrow and fed either regular chow or a high-fat, high-cholesterol (HFC) diet for 12 weeks. In vitro, bone marrow derived macrophages (BMDM) from wt or caspase-1/11(-/-) mice were incubated with oxLDL for 24h and autophagy was assessed.
  
  
  RESULTS
  In line with our hypothesis, caspase-1/11(-/-)-tp mice had less severe hepatic inflammation than Wt-tp animals, as evident from liver histology and gene expression analysis in isolated KCs. Mechanistically, KCs from caspase-1/11(-/-)-tp mice showed less cholesterol crystals, enhanced cholesterol efflux and increased autophagy. In wt BMDM, oxLDL incubation led to disturbed autophagy activity whereas BMDM from caspase-1/11(-/-) mice had normal autophagy activity.
  
  
  CONCLUSIONS
  Altogether, these data suggest a vicious cycle whereby disturbed autophagy and decreased cholesterol efflux leads to newly formed cholesterol crystals and thereby maintain hepatic inflammation during NASH by further activating the inflammasome.
authors: Departments of Molecular Genetics, Electron Microscopy and Internal Medicine, Nutrition and Toxicology Research (NUTRIM) Institute of Maastricht and Maastricht University Medical Centre (MUMC), Maastricht University, Maastricht, The Netherlands.
authors: Tim
authors: T
authors: Hendrikx
authors: Veerle
authors: V
authors: Bieghs
authors: Sofie M A
authors: SM
authors: Walenbergh
authors: Patrick J
authors: PJ
authors: van Gorp
authors: Fons
authors: F
authors: Verheyen
authors: Mike L J
authors: ML
authors: Jeurissen
authors: Mandy M F
authors: MM
authors: Steinbusch
authors: Nathalie
authors: N
authors: Vaes
authors: Christoph J
authors: CJ
authors: Binder
authors: Ger H
authors: GH
authors: Koek
authors: Rinke
authors: R
authors: Stienstra
authors: Mihai G
authors: MG
authors: Netea
authors: Marten H
authors: MH
authors: Hofker
authors: Ronit
authors: R
authors: Shiri-Sverdlov
mesh_terms: D000818:Animals; D020170:Caspase 1 / Q000235:genetics / Q000378:metabolism*; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D053471:Caspases, Initiator; D002784:Cholesterol / Q000235:genetics / Q000378:metabolism; D004041:Dietary Fats / Q000009:adverse effects / Q000494:pharmacology; D006505:Hepatitis / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D006949:Hyperlipidemias / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D058847:Inflammasomes / Q000235:genetics / Q000378:metabolism; D020382:Interleukin-18 / Q000235:genetics / Q000378:metabolism; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism; D007728:Kupffer Cells / Q000201:enzymology* / Q000473:pathology; D008077:Lipoproteins, LDL / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout
chemical_list: D004041:Dietary Fats; D058847:Inflammasomes; D020382:Interleukin-18; D053583:Interleukin-1beta; D008077:Lipoproteins, LDL; C099252:oxidized low density lipoprotein; D002784:Cholesterol; C101136:Casp4 protein, mouse; D020169:Caspases; D053471:Caspases, Initiator; D020170:Caspase 1