Necroptosis promotes necrotic core and vulnerable atherosclerosis in humans and mice and is a prospective therapeutic and diagnostic tool.

During obesity, macrophage accumulation in adipose tissue propagates the chronic inflammation and insulin resistance associated with type 2 diabetes. The factors that regulate the accrual of macrophages in adipose are not well understood. Here we show that the neuroimmune guidance cue netrin-1 is highly expressed in obese, but not lean adipose tissue of humans and mice, where it directs the retention of macrophages. Expression of netrin-1 is induced in macrophages by the saturated fatty acid palmitate, and acts via its receptor Unc5b to block macrophage migration. In a mouse model of diet-induced obesity, we show that adipose tissue macrophages exhibit reduced migratory capacity, which can be restored by blocking netrin-1. Furthermore, hematopoietic deletion of Ntn1 facilitates adipose tissue macrophage emigration, reduces inflammation, and improves insulin sensitivity. Collectively, these findings identify netrin-1 as a macrophage retention signal in adipose tissue during obesity, which promotes chronic inflammation and insulin resistance.

Mitochondrial hyperfusion has recently been shown to function as a cellular stress response, providing transient protection against apoptosis and mitophagy. However, the mechanisms that mediate this response remain poorly understood. In this study, we demonstrate that oxidized glutathione (GSSG), the core cellular stress indicator, strongly induces mitochondrial fusion. Biochemical and functional experiments show that GSSG induces the generation of disulphide-mediated mitofusin oligomers, in a process that also requires GTP hydrolysis. Our data outline the molecular events that prime the fusion machinery, providing new insights into the coupling of mitochondrial fusion with the cellular stress response.Keywords: mitochondria; fusion; glutathione; stress; mitofusin EMBO reports (2012) 13, 909-915.

Differences in susceptibility to diabetic nephropathy (DN) between mouse strains with identical levels of hyperglycemia correlate with renal levels of oxidative stress, shown previously to play a central role in the pathogenesis of DN. Susceptibility to DN appears to be genetically determined, but the critical genes have not yet been identified. Overexpression of the enzyme glyoxalase 1 (Glo1), which prevents posttranslational modification of proteins by the glycolysis-derived α-oxoaldehyde, methylglyoxal (MG), prevents hyperglycemia-induced oxidative stress in cultured cells and model organisms. In this study, we show that in nondiabetic mice, knockdown of Glo1 increases to diabetic levels both MG modification of glomerular proteins and oxidative stress, causing alterations in kidney morphology indistinguishable from those caused by diabetes. We also show that in diabetic mice, Glo1 overexpression completely prevents diabetes-induced increases in MG modification of glomerular proteins, increased oxidative stress, and the development of diabetic kidney pathology, despite unchanged levels of diabetic hyperglycemia. Together, these data indicate that Glo1 activity regulates the sensitivity of the kidney to hyperglycemic-induced renal pathology and that alterations in the rate of MG detoxification are sufficient to determine the glycemic set point at which DN occurs.

Rationale Therapeutically targeting macrophage reverse cholesterol transport is a promising approach to treat atherosclerosis. Macrophage energy metabolism can significantly influence macrophage phenotype, but how this is controlled in foam cells is not known. Bioinformatic pathway analysis predicts that miR-33 represses a cluster of genes controlling cellular energy metabolism that may be important in macrophage cholesterol efflux. Objective We hypothesized that cellular energy status can influence cholesterol efflux from macrophages, and that miR-33 reduces cholesterol efflux via repression of mitochondrial energy metabolism pathways. Methods and Results In this study, we demonstrated that macrophage cholesterol efflux is regulated by mitochondrial ATP production, and that miR-33 controls a network of genes that synchronize mitochondrial function. Inhibition of mitochondrial ATP synthase markedly reduces macrophage cholesterol efflux capacity, and anti-miR33 required fully functional mitochondria to enhance ABCA1-mediated cholesterol efflux. Specifically, anti-miR33 de-repressed the novel target genes PGC-1α, PDK4 and SLC25A25 and boosted mitochondrial respiration and production of ATP. Treatment of atherosclerotic Apoe-/- mice with anti-miR33 oligonucleotides reduced aortic sinus lesion area compared to controls, despite no changes in HDL-C or other circulating lipids. Expression of miR-33a/b was markedly increased in human carotid atherosclerotic plaques compared to normal arteries, and there was a concomitant decrease in mitochondrial regulatory genes PGC-1α, SLC25A25, NRF1 and TFAM, suggesting these genes are associated with advanced atherosclerosis in humans. Conclusions This study demonstrates that anti-miR33 therapy de-represses genes that enhance mitochondrial respiration and ATP production, which in conjunction with increased ABCA1 expression, works to promote macrophage cholesterol efflux and reduce atherosclerosis.

EV-derived miRNAs from atherogenic macrophages, in particular miR-146a, may accelerate the development of atherosclerosis by decreasing cell migration and promoting macrophage entrapment in the vessel wall.

Rationale: Inflammation impairs macrophage cholesterol clearance from vascular tissues and promotes atherosclerosis. Inflammatory macrophages suppress expression of the transcription cofactor interferon regulatory factor 2–binding protein 2 (IRF2BP2), and genetic variants near IRF2BP2 associate with ischemic heart disease progression in humans. Objectives: To test whether IRF2BP2 in macrophages affects atherosclerosis in mice and humans. Methods and Results: We generated mice that delete IRF2BP2 in macrophages. IRF2BP2-deficient macrophages worsened atherosclerosis in irradiated low-density lipoprotein receptor null-recipient mice and in apolipoprotein E null mice. IRF2BP2-deficient macrophages were inflammatory and had impaired cholesterol efflux because of their inability to activate the cholesterol transporter ABCA1 in response to cholesterol loading. Their expression of the anti-inflammatory transcription factor Krüppel-like factor 2 was markedly reduced. Promoter studies revealed that IRF2BP2 is required for MEF2-dependent activation of Krüppel-like factor 2. Importantly, restoring Krüppel-like factor 2 in IRF2BP2-deficient macrophages attenuated M1 inflammatory and rescued M2 anti-inflammatory gene activation and improved the cholesterol efflux deficit by restoring ABCA1 activation in response to cholesterol loading. In a cohort of 1066 angiographic cases and 1011 controls, homozygous carriers of a deletion polymorphism (rs3045215) in the 3′ untranslated region sequence of human IRF2BP2 mRNA had a higher risk of coronary artery disease (recessive model, odds ratio [95% confidence interval]=1.560 [1.179–2.065], P =1.73E-03) and had lower IRF2BP2 (and Krüppel-like factor 2) protein levels in peripheral blood mononuclear cells. The effect of this deletion polymorphism to suppress protein expression was confirmed in luciferase reporter studies. Conclusion: Ablation of IRF2BP2 in macrophages worsens atherosclerosis in mice, and a deletion variant that lowers IRF2BP2 expression predisposes to coronary artery disease in humans.

OBJECTIVETo study whether modification of LDL by methylglyoxal (MG), a potent arginine-directed glycating agent that is increased in diabetes, is associated with increased atherogenicity.RESEARCH DESIGN AND METHODSHuman LDL was isolated and modified by MG in vitro to minimal extent (MGmin-LDL) as occurs in vivo. Atherogenic characteristics of MGmin-LDL were characterized: particle size, proteoglycan-binding, susceptibility to aggregation, LDL and non-LDL receptor–binding, and aortal deposition. The major site of modification of apolipoprotein B100 (apoB100) modification was investigated by mass spectrometric peptide mapping.RESULTSMGmin-LDL contained 1.6 molar equivalents of MG modification—mostly hydroimidazolone—as found in vivo. MGmin-LDL had decreased particle size, increased binding to proteoglycans, and increased aggregation in vitro. Cell culture studies showed that MGmin-LDL was bound by the LDL receptor but not by the scavenger receptor and had increased binding affinity for cell surface heparan sulfate–containing proteoglycan. Radiotracer studies in rats showed that MGmin-LDL had a similar fractional clearance rate in plasma to unmodified LDL but increased partitioning onto the aortal wall. Mass spectrometry peptide mapping identified arginine-18 as the hotspot site of apoB100 modification in MGmin-LDL. A computed structural model predicted that MG modification of apoB100 induces distortion, increasing exposure of the N-terminal proteoglycan–binding domain on the surface of LDL. This likely mediates particle remodeling and increases proteoglycan binding.CONCLUSIONSMG modification of LDL forms small, dense LDL with increased atherogenicity that provides a new route to atherogenic LDL and may explain the escalation of cardiovascular risk in diabetes and the cardioprotective effect of metformin.