Targeting IRE1 with small molecules counteracts progression of atherosclerosis

Abstract

Metaflammation, an atypical, metabolically induced, chronic lowgrade inflammation, plays an important role in the development of obesity, diabetes, and atherosclerosis. An important primer for metaflammation is the persistent metabolic overloading of the endoplasmic reticulum (ER), leading to its functional impairment. Activation of the unfolded protein response (UPR), a homeostatic regulatory network that responds to ER stress, is a hallmark of all stages of atherosclerotic plaque formation. The most conserved ERresident UPR regulator, the kinase/endoribonuclease inositol-requiring enzyme 1 (IRE1), is activated in lipid-laden macrophages that infiltrate the atherosclerotic lesions. Using RNA sequencing in macrophages, we discovered that IRE1 regulates the expression of many proatherogenic genes, including several important cytokines and chemokines. We show that IRE1 inhibitors uncouple lipid-induced ER stress from inflammasome activation in both mouse and human macrophages. In vivo, these IRE1 inhibitors led to a significant decrease in hyperlipidemia-induced IL-1β and IL-18 production, lowered T-helper type-1 immune responses, and reduced atherosclerotic plaque size without altering the plasma lipid profiles in apolipoprotein E-deficient mice. These results show that pharmacologic modulation of IRE1 counteracts metaflammation and alleviates atherosclerosis.endoplasmic reticulum stress | unfolded protein response | metaflammation | lipotoxicity | atherosclerosis C omplex molecular interactions between environment, diet, and genetics that take place at the metabolic and immune interface provoke a low-grade, chronic inflammatory responsemetaflammation-that engages cells of the immune system (macrophages, neutrophils, and lymphocytes) and metabolic tissues (adipocytes, hepatocytes, and pancreatic cells) (1). An important primer for metaflammation is chronic metabolic overloading of organelles, such as the endoplasmic reticulum (ER) and mitochondria, which results in impairment of their functions (2).The ER serves essential cellular functions that include the synthesis and folding of secreted and transmembrane proteins, calcium storage, and lipid synthesis for membrane biogenesis or energy storage. Disruption of any of these functions leads to ER stress and the subsequent activation of an elaborate network of adaptive responses, collectively known as the unfolded protein response (UPR) (3). The UPR reestablishes homeostasis through both transcriptional and translational layers of control. The UPR signals through three mechanistically distinct branches that are initiated by the ER-resident protein folding sensors inositolrequiring enzyme 1 (IRE1), protein kinase RNA-like endoplasmic reticulum kinase (PERK), and activating transcription factor 6 (ATF6) (3).IRE1 controls the phylogenetically most conserved branch of the UPR found from fungi to metazoans. It has an ER-lumenal sensor domain that recognizes unfolded peptides and cytosolic kinase and endoribonuclease (RNase) domains that relay the information to downstrea...

High Mobility Group B-1 (HMGB-1) Promotes Apoptosis of Macrophage-Derived Foam Cells by Inducing Endoplasmic Reticulum Stress

“…Accumulating evidence illustrated that severe ERS plays a critical role in foam cell formation and the development of atherosclerosis [15,16]. Furthermore, ERS induced C/EBP-homologous protein (CHOP)-related apoptotic signaling pathway in macrophages of advanced atherosclerotic plaques and promoted the rupture formation of plaques [2].…”

Snapshots: Endoplasmic Reticulum Stress in Lipid Metabolism and Cardiovascular Disease

“…Tufanli and colleagues reported that IRE1 inhibitors uncouple lipid-induced ERS from inflammasome activation in both mouse and human macrophages, which leads to a significant decrease in hyperlipidemia-induced IL-1β and IL-18 production, lowers T-helper type-1 immune responses, and reduces atherosclerotic plaque size without altering the plasma lipid profiles in apolipoprotein E-deficient mice. These results reveal that pharmacologic modulation of IRE1 alleviates ERS, lipid metabolic disorders, and atherosclerosis (Tufanli et al, 2017 expressed within human and mouse atherosclerotic lesions, and is activated by necrotic lesion extracts. Clec4e induces UPR in macrophages, promotes cholesterol accumulation and plaque instability whereas CHOP and IRE1a deficiencies significantly limit Clec4e-dependent effects (Clement et al, 2016).…”

“…ERS, proposed by Gajkowska et al in 2001, is the disturbance of ER homeostasis in a stressful environment, such as inflammation, oxidative stress, and hyperlipidemia. During ERS, three upstream proteins, IRE1 (inositol requiring 1, the most conserved ER-resident UPR regulator) (Tufanli et al, 2017), activating transcription factor 6 (ATF6), and PERK (RNA-dependent protein kinaselike endoplasmic reticulum kinase) are activated and trigger the unfolded protein response (UPR), usually activated in response to accumulation of unfolded or misfolded proteins in the lumen of the ER (BlondElguindi et al, 1993;Xu et al, 2005;Ron et al, 2007;Jiang et al, 2015). Numerous key lipogenic molecules and pathways are located in the ER, and determine the regulatory effects of ER in lipid (Fagone et al, 2009;Morgan et al, 2016).…”

CAMKIIγ suppresses an efferocytosis pathway in macrophages and promotes atherosclerotic plaque necrosis

“…Elevated ER stress, particularly increased expression of mediators of the unfolded protein response (UPR), is another feature of advanced human and mouse plaques (22,25,26). Using laser capture microdissection (LCM) of aortic root sections followed by quantitative real-time quantitative PCR (RT-qPCR), we found significantly less expression of mRNAs encoding 3 genes that are induced by the UPR: Ddit3 (encoding CHOP), spliced Xbp1, and Dnajb9 (encoding ERdj4) (Supplemental Figure 4, A-C).…”

“…First, suppression of the UPR may decrease lesional cell apoptosis (above). For example, genetic targeting of CHOP in atherosclerosis-prone mice leads to less lesional apoptosis and smaller necrotic cores (22,52,53), as does treatment with an IRE1 inhibitor or with ER stress-relieving "chemical chaperones" (26,(54)(55)(56). Moreover, higher expression of CHOP in human coronary artery sections is associated with symptomatic, necrotic plaques (25).…”