Project description:Elevated plasma levels of High Density Lipoprotein (HDL) are associated with decreased risk of cardiovascular disease (CVD). The protective role of HDL in atherosclerosis has been attributed primarily to its ability to remove excess cholesterol from lipid-laden macrophages (foam cells) within the arterial walls. However, clinical trials that raise HDL cholesterol levels have failed to show a benefit casting doubts on our basic understanding of HDL function. Atherosclerosis is a chronic inflammatory condition underlying CVD and driven in part by the recognition of metabolic danger signals by innate immune receptors on macrophages. A potential feature that could contribute to HDL’s protective effects in CVD could be HDL's anti-inflammatory nature, such as its ability to reduce endothelial cell activation. However, the molecular mechanisms by which HDL reduces inflammatory macrophage responses remain poorly understood and difficult to separate from its cholesterol depleting activity. Here we show that HDL protects against Toll like receptor (TLR)-induced inflammation both in vivo and in vitro under normocholesteremic conditions by suppressing the transcription of inflammatory cytokines in a manner independent of its ability to remove cellular cholesterol. We identify Activating Transcription Factor 3 (ATF3), a transcriptional repressor of the CREB family of basic leucine zipper transcription factors, as a HDL-inducible regulator of macrophage activation. HDL’s ability to down modulate TLR responses was severely compromised in ATF3-deficient cells demonstrating that ATF3 mediates HDL's anti-inflammatory effects and may explain the broad anti-inflammatory functions of HDL. Bone marrow-derived macrophages (BMDMs) were obtained by culturing bone marrow cells from 6 to 8 week old wildtype C57BL/6 mice in DMEM supplemented with 10% FCS, 10 mg ml-1 Ciprobay-500 and 40 ng ml-1 M-CSF (R & D Systems). BMDMs of wt mice were pretreated for 6 h with HDL (2 mg ml-1 ) then stimulated with CpG (100 nM) for 4 h. Further wild type or Atf3-deficient BMDMs were pretreated with 2 mg ml-1 HDL for 6 h and subsequently stimulated with CpG (100 nM) or P3C (50 ng ml-1) for 4 h. For carotid artery injury approximately 12-week old male WT and Atf3-deficient mice were anesthetized with i.p. injection of 150 mg/kg ketaminehydrochloride (Ketanest, Pharmacia) and 0.1 mg/kg xylazinehydrochloride (Rompun 2%, Bayer). A small incision from the cranial apex of the sternum to just below the mandible was made. After careful preparation of an approximately 6 mm long segment proximal of the bifurcation, the common carotid artery was electrically denuded. A 4 mm long lesion was made by applying two serial 5 second bursts of 2 Watt using 2 mm wide forceps. The skin was then sutured and the mice allowed to recover in individual cages before returning to their littermates. Three hours later the mice received a single 200 ?l i.v. injection of 20 mg/kg HDL or PBS.

Project description:Chronic Kidney Disease (CKD) is associated with markedly increased cardiovascular (CV) morbidity and mortality. Chronic inflammation, a hallmark of both CKD and CV diseases (CVD), is believed to drive this association. Pro-inflammatory TLR agonists, Damage-Associated Molecular Patterns (DAMPs), have been found elevated in CKD patients’ plasma and suggested to promote CVD, however, confirmation of their involvement, the underlying mechanism(s), the extent to which individual DAMPs contribute to vascular pathology in CKD and the evaluation of potential therapeutic strategies, have remained largely undescribed. A multi-TLR inhibitor, soluble TLR2, abrogated chronic vascular inflammatory responses and the increased aortic atherosclerosis-associated gene expression observed in nephropathic mice, without compromising infection clearance. Mechanistically, we confirmed elevation of 4 TLR DAMPs in CKD patients’ plasma, namely Hsp70, Hyaluronic acid, HMGB-1 and Calprotectin, which displayed different abilities to promote key cellular responses associated with vascular inflammation and worsening of atherosclerosis in a TLR-dependent manner. These included loss of trans-endothelial resistance, enhanced monocyte migration, increased cytokine production, and foam cell formation by macrophages, the latter via cholesterol efflux inhibition. Calprotectin and Hsp70 most consistently affected these functions. Calprotectin was further elevated in CVD-diagnosed CKD patients and strongly correlated with the predictor of CV events CRP. In nephropathic mice, Calprotectin blockade robustly reduced vascular chronic inflammatory responses and pro-atherosclerotic gene expression. Taken together, these findings demonstrated the critical extent to which the DAMP-TLR pathway contributes to vascular inflammatory and atherogenic responses in CKD, revealed the mechanistic contribution of specific DAMPs and described two alternatives therapeutic approaches to reduce chronic vascular inflammation and lower CV pathology in CKD.

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The anti-inflammatory nature of HDL in macrophages is mediated by ATF3

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