Background: Chronic activation of the innate immune system drives inflammation and contributes directly to atherosclerosis. Previously, we showed that macrophages in the atherogenic plaque undergo RIPK3-MLKL-dependent programmed necroptosis in response to sterile ligands such as oxidized LDL and damage-associated patterns (DAMPs) and necroptosis is active in advanced atherosclerotic plaques. Upstream of the RIPK3-MLKL necroptotic machinery lies RIPK1, which acts as a master switch that controls whether the cell undergoes NFκB-dependent inflammation, caspase-dependent apoptosis or necroptosis in response to extracellular stimuli. We therefore set out to investigate the role of RIPK1 in the development of atherosclerosis, which is largely driven by NFκB-dependent inflammation at early stages. We hypothesize that, unlike RIPK3 and MLKL, RIPK1 primarily drives NFκB-dependent inflammation in early atherogenic lesions and knocking down RIPK1 will reduce inflammatory cell activation and protect against the progression of atherosclerosis. Methods: We examined expression of RIPK1 protein and mRNA in both human and mouse atherosclerotic lesions, and using loss-of-function approaches in vitro in macrophages and endothelial cells to measure inflammatory responses. We administered weekly injections of RIPK1 anti-sense oligonucleotides (ASO) to Apoe -/- mice fed a cholesterol-rich (Western) diet for 8 weeks. Results: We find RIPK1 expression is abundant in early-stage atherosclerotic lesions in both humans and mice. Treatment with RIPK1 ASOs led to a reduction in aortic sinus and en face lesion areas (47.2% or 58.8% decrease relative to control, p<0.01) and plasma inflammatory cytokines (IL-1α, IL-17A, p<0.05) compared to controls. RIPK1 knockdown in macrophages decreased inflammatory genes (NFκB, TNFα, IL-1α) and in vivo LPS- and atherogenic diet-induced NF-κB activation. In endothelial cells, knockdown of RIPK1 prevented NF-κB translocation to the nucleus in response to TNFα, where accordingly there was a reduction in gene expression of IL1B, E-selectin and monocyte attachment. Conclusions: We have identified RIPK1 as a central driver of inflammation in atherosclerosis by its ability to activate the NF-κB pathway and promote inflammatory cytokine release. Given the high levels of RIPK1 expression in human atherosclerotic lesions, our study suggests RIPK1 as a future therapeutic target to reduce residual inflammation in patients at high risk of coronary artery disease.

The healthy heart comprises many different cell types that work together to preserve optimal function. However, in a diseased heart the function of one or more cell types is compromised which can lead to many adverse events, one of which is myocardial infarction (MI). Immediately after MI, the cardiac environment is characterized by excessive cardiomyocyte death and inflammatory signals leading to the recruitment of macrophages to clear the debris. Proliferating fibroblasts then invade, and a collagenous scar is formed to prevent rupture. Better functional restoration of the heart is not achieved due to the limited regenerative capacity of cardiac tissue. To address this, biomaterial therapy is being investigated as an approach to improve regeneration in the infarcted heart, as they can possess the potential to control cell function in the infarct environment and limit the adverse compensatory changes that occur post-MI. Over the past decade, there has been considerable research into the development of biomaterials for cardiac regeneration post-MI; and various effects have been observed on different cell types depending on the biomaterial that is applied. Biomaterial treatment has been shown to enhance survival, improve function, promote proliferation, and guide the mobilization and recruitment of different cells in the post-MI heart. This review will provide a summary on the biomaterials developed to enhance cardiac regeneration and remodeling post-MI with a focus on how they control macrophages, cardiomyocytes, fibroblasts, and endothelial cells. A better understanding of how a biomaterial interacts with the different cell types in the heart may lead to the development of a more optimized biomaterial therapy for cardiac regeneration.

Abstract-We analyze the dynamics of advance reservation (AR) games: games in which customers compete for limited resources and can reserve resources for a fee. We introduce and analyze two different learning models. In the first model, called strategylearning, customers are informed of the strategy adopted in the previous iteration, while in the second model, called actionlearning, customers estimate the strategy by observing previous actions. We prove that in the strategy-learning model, convergence to equilibrium is guaranteed. In contrast, in the actionlearning model, the system converges only if an equilibrium in which none of the customers makes AR exists. Based on those results, we show that if the provider is risk-averse and sets the AR fee low enough, action-learning yields on average greater profit than strategy-learning. However, if the provider is risk-taking and sets a high AR fee, action-learning provably yields zero profit in the long term in contrast to strategy-learning.

IntroductionChronic activation of the innate immune system drives inflammation and contributes directly to obesity, insulin resistance and atherosclerosis. Previously we showed that necroptosis, a pro‐inflammatory form of programmed cell death, is activated in the vessel wall and drives atherosclerosis via activation of RIP3 and MLKL. We sought to determine upstream genetic regulators of necroptosis in atherosclerosis and metabolic disease, and hypothesized that gene expression of RIP1, a key regulatory kinase upstream of NFkB activation, apoptosis and necroptosis, drives macrophage inflammation in cardiometabolic diseases.MethodsRIP1 anti‐sense oligonucleotides (ASOs, 2 unique sequences) were used to reduce RIP1 expression in 2 mouse models: i) atherosclerotic model [ApoE−/− mice fed a western diet for 8wks] and ii) diet‐induced obesity (DIO) model [C57Bl/6 male mice fed a high fat diet for 24 wks]. Mice were given weekly injections of RIP1 ASOs (50 or 100mg/kg) or control ASO (non‐targeting).ResultsRIP1 ASO treated ApoE−/− mice had a marked reduction in aortic sinus and en face lesion areas (47.2% or 58.8% decrease relative to control, p<0.01) and plasma inflammatory cytokines (IL‐1a, IL‐17A, p<0.05). RIP1 knockdown in macrophages decreased inflammatory gene expression (NFkB, TNFa, IL‐1a) and in vivo LPS‐induced NFkB activation. In obese mice, RIP1 ASOs strikingly decreased body weight (25% decrease versus control p<0.001) and total fat mass (50–65% decrease versus control, p<0.001). Further, insulin resistance was improved in RIP1 ASO treated mice (fasted blood glucose: 10.9mM in control versus 8.5±mM in RIP1 ASO, p<0.001; GTT and ITT both p<0.001). In humans, we identified 5 novel SNPs in strong linkage disequilibrium in or nearby RIP1 gene exon 5. Notably, in a cohort of >1,800 people, individuals carrying the minor allele of these RIP1 SNPs have a 75–89% increase in the risk of developing obesity (adjusted odds ratios: 1.75–1.89, p<10−5) and a significant increase in RIP1 mRNA expression in adipose tissue (eQTL association in METSIM cohort, p=10−23).Conclusions: We have identified RIP1 as central a driver of insulin resistance, obesity, and atherosclerosis and demonstrate the potential of RIP1 as a novel therapeutic target.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

No abstract