Hepcidin-ferroportin axis controls toll-like receptor 4 dependent macrophage inflammatory responses in human atherosclerotic plaques.

OBJECTIVES: Toll-like Receptor 4 (TLR4) is implicated in modulating inflammatory cytokines though its role in atherosclerosis remains uncertain. We have recently described a non-foam cell macrophage phenotype driven by ingestion of hemoglobin:haptoglobin complexes (HH), via the scavenger receptor CD163, characterized by reduced inflammatory cytokine production. In this study, we examined the role of iron metabolism in modulating TLR4 signaling in these cells. METHODS AND RESULTS: Areas in human atherosclerotic plaque with non-foam cell, CD163 positive macrophages demonstrated reduced expression of tumor necrosis factor alpha (TNF-α) and interferon-beta (INF-ß) compared to foam cells. Human macrophages differentiated in hemoglobin:haptoglobin (HH) complexes expressed the CD163 positive non-foam cell phenotype and demonstrated significantly less TNF-α and INF-ß compared to control macrophages when exposed to oxidized LDL (oxLDL) or lipopolysaccharide (LPS). LPS stimulated expression of TNF-α and INF-ß could be restored in HH macrophages by pretreatment with hepcidin, an endogenous suppressor of ferroportin1 (FPN), or by genetic suppression of FPN in macrophages derived from myeloid specific FPN knockout mice. LPS stimulated control macrophages demonstrated increase in TLR4 trafficking to lipid rafts; this response was suppressed in HH macrophages but was restored upon pretreatment with hepcidin. Using a pharmacologic hepcidin suppressor, we observed a decrease in cytokine expression and TLR4-lipid raft trafficking in LPS-stimulated in a murine macrophage model. CONCLUSION: TLR4 dependent macrophage signaling is controlled via hepcidin-ferroportin1 axis by influencing TLR4-lipid raft interactions. Pharmacologic manipulation of iron metabolism may represent a promising approach to limiting TLR4-mediated inflammatory responses.

CD163 interacts with TWEAK to regulate tissue regeneration after ischaemic injury.

Macrophages are an essential component of the immune response to ischaemic injury and play an important role in promoting inflammation and its resolution, which is necessary for tissue repair. The type I transmembrane glycoprotein CD163 is exclusively expressed on macrophages, where it acts as a receptor for haemoglobin:haptoglobin complexes. An extracellular portion of CD163 circulates in the blood as a soluble protein, for which no physiological function has so far been described. Here we show that during ischaemia, soluble CD163 functions as a decoy receptor for TWEAK, a secreted pro-inflammatory cytokine of the tumour necrosis factor family, to regulate TWEAK-induced activation of canonical nuclear factor-κB (NF-κB) and Notch signalling necessary for myogenic progenitor cell proliferation. Mice with deletion of CD163 have transiently elevated levels of TWEAK, which stimulate muscle satellite cell proliferation and tissue regeneration in their ischaemic and non-ischaemic limbs. These results reveal a role for soluble CD163 in regulating muscle regeneration after ischaemic injury.

CHADS(2) score is predictive of left atrial thrombus on precardioversion transesophageal echocardiography in atrial fibrillation.

OBJECTIVE: The goals of this study were to determine: 1) if the CHADS(2) score correlates with left atrial (LA) or left atrial appendage (LAA) thrombus on pre-cardioversion transesophageal echocardiography (TEE) in nonvalvular atrial fibrillation (NVAF); and 2) what, if any, components of the CHADS(2) score are most important in predicting LA/LAA thrombus. BACKGROUND: It is unknown if CHADS(2) score, a marker of thromboembolic risk in NVAF, accurately predicts LA/LAA thrombus on pre-cardioversion TEE. METHODS: We retrospectively studied patients undergoing precardioversion TEE for NVAF at a tertiary hospital. TEE reports were reviewed for presence of LA/LAA thrombus. Using medical records and an ICD-9 coding database, a CHADS(2) score was derived, and the association between CHADS(2) and thrombus was evaluated with Mantel-Haenszel Chi-Square. The relation between the singular components of CHADS(2) and thrombus were analyzed using Pearson's Chi-Square. RESULTS: In 643 consecutive patients undergoing pre-cardioversion TEE, LA/LAA thrombus was identified in 46 (7.2 %). A strong association was present between CHADS(2)score and LA/LAA thrombus (p = 0.0005). No thrombi were identified in patients with CHADS(2) = 0. Among 46 patients with thrombus, all (100%) had CHF. Of the singular components, CHF was the only factor independently associated with thrombus (p < 0.0001). CONCLUSIONS: In non-valvular atrial fibrillation, CHADS(2) is strongly associated with LA thrombus on TEE. Our findings suggest pre-cardioversion TEE may be unnecessary if the CHADS(2) score = 0. Of the components of the CHADS(2) score, CHF was the only independently associated risk factor which correlated with LA/LAA thrombus.