Inclusion bodies enriched for p62 and polyubiquitinated proteins in macrophages protect against atherosclerosis

Fucoidan Inhibits NLRP3 Inflammasome Activation by Enhancing p62/SQSTM1-Dependent Selective Autophagy to Alleviate Atherosclerosis

NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome activation contributes to the progression of atherosclerosis, and autophagy inhibits inflammasome activation by targeting macrophages. We investigated whether fucoidan, a marine sulfated polysaccharide derived from brown seaweeds, could reduce NLRP3 inflammasome activation by enhancing sequestosome 1 (p62/SQSTM1)-dependent selective autophagy to alleviate atherosclerosis in high-fat-fed ApoE-/- mice with partial carotid ligation and differentiated THP-1 cells incubated with oxidized low-density lipoprotein (oxLDL). Fucoidan significantly ameliorated lipid accumulation, attenuated progression of carotid atherosclerotic plaques, deregulated the expression of NLRP3 inflammasome, autophagy receptor p62, and upregulated microtubule-associated protein light chain 3 (LC3)-II/I levels. Transmission electron microscopy and GFP-RFP-LC3 lentivirus transfection further demonstrated that fucoidan could activate autophagy. Mechanistically, fucoidan remarkably inhibited NLRP3 inflammasome activation, which was mostly dependent on autophagy. The inhibitory effects of fucoidan on NLRP3 inflammasome were enhanced by autophagy activator rapamycin (Rapa) and alleviated by autophagy inhibitor 3-methyladenine (3-MA). Fucoidan promoted the colocalization of NLRP3 and p62. Knockdown of p62 and ATG5 by small interfering RNA significantly reduced the inhibitory effects of fucoidan treatment on NLRP3 inflammasome. The data suggest that fucoidan can inhibit NLRP3 inflammasome activation by enhancing p62/SQSTM1-dependent selective autophagy to alleviate atherosclerosis.

PDLIM7 Synergizes With PDLIM2 and p62/Sqstm1 to Inhibit Inflammatory Signaling by Promoting Degradation of the p65 Subunit of NF-κB

Activation of NF-κB transcription factors is critical for innate immune cells to induce inflammation and fight against microbial pathogens. On the other hand, the excessive and prolonged activation of NF-κB causes massive inflammatory damage to the host, suggesting that regulatory mechanisms to promptly terminate NF-κB activation are important to prevent immunopathology. We have previously reported that PDLIM2, a PDZ-LIM domain-containing protein, is a nuclear ubiquitin E3 ligase that targets the p65 subunit of NF-κB for degradation, thereby suppressing NF-κB activation. Here we show that PDLIM7, another member of LIM protein family, is also a ubiquitin E3 ligase that inhibits NF-κB-mediated inflammatory responses. PDLIM7 directly polyubiquitinates p65 and promotes its proteasomal degradation. Moreover, PDLIM7 heterodimerizes with PDLIM2 to promote synergistic PDLIM2-mediated degradation of p65. Mechanistically, PDLIM7 promotes K63-linked ubiquitination of PDLIM2 and then the proteasome/autophagosome cargo protein p62/Sqstm1 binds to both polyubiquitinated PDLIM2 and the proteasome, thereby facilitating the delivery of the NF-κB-PDLIM2 complex to the proteasome and subsequent p65 degradation. Consistently, double knockdown of PDLIM7 and either PDLIM2 or p62/Sqstm1 results in augmented proinflammatory cytokine production compared to control cells or single knockdown cells. These data delineate a new role for PDLIM7 and p62/Sqstm1 in the regulation of NF-κB signaling by bridging a ubiquitin E3 ligase and the proteasome.

Mitochondrial Dysfunction and DNA Damage in the Context of Pathogenesis of Atherosclerosis

Atherosclerosis is a multifactorial disease of the cardiovascular system associated with aging, inflammation, and oxidative stress. An important role in the development of atherosclerosis play elevated plasma lipoproteins. A number of external factors (smoking, diabetes, infections) can also contribute to the development of the disease. For a long time, atherosclerosis remains asymptomatic, therefore, the search for early markers of the disease is critical for the timely management and better outcomes for patients. Mitochondrial dysfunction and mitochondrial DNA (mtDNA) damage appear to connect different aspects of atherosclerosis pathogenesis. To date, multiple lines of research have demonstrated the strong association of mitochondrial dysfunction with the development of various human diseases. Therapies aimed at restoring the mitochondrial function are being actively developed, and are expected to broaden the therapeutic possibilities for several chronic human diseases. The development of such therapies depends on our understanding of the functional roles of different mtDNA variants associated with one or another disorder, and the molecular mechanisms linking mitochondrial dysfunction with a given pathological feature. These questions are, however, challenging and require future intensive research. This review summarizes the recent studies and describes the central processes of the development of atherosclerosis, and shows their relationship with mitochondrial dysfunction. One of the promising therapeutic approaches for future atherosclerosis treatments is the use of mitochondria-targeted antioxidants. Future studies should focus on characterizing the mechanisms of mitochondrial involvement in cardiovascular pathologies to better direct the search for novel therapies.

SQSTM1/p62 and PPARGC1A/PGC-1alpha at the interface of autophagy and vascular senescence

Defective macroautophagy/autophagy and mitochondrial dysfunction are known to stimulate senescence. The mitochondrial regulator PPARGC1A (peroxisome proliferator activated receptor gamma, coactivator 1 alpha) regulates mitochondrial biogenesis, reducing senescence of vascular smooth muscle cells (VSMCs); however, it is unknown whether autophagy mediates PPARGC1A-protective effects on senescence. Using ppargc1a-/- VSMCs, we identified the autophagy receptor SQSTM1/p62 (sequestosome 1) as a major regulator of autophagy and senescence of VSMCs. Abnormal autophagosomes were observed in VSMCs in aortas of ppargc1a-/- mice. ppargc1a-/- VSMCs in culture presented reductions in LC3-II levels; in autophagosome number; and in the expression of SQSTM1 (protein and mRNA), LAMP2 (lysosomal-associated membrane protein 2), CTSD (cathepsin D), and TFRC (transferrin receptor). Reduced SQSTM1 protein expression was also observed in aortas of ppargc1a-/- mice and was upregulated by PPARGC1A overexpression, suggesting that SQSTM1 is a direct target of PPARGC1A. Inhibition of autophagy by 3-MA (3 methyladenine), spautin-1 or Atg5 (autophagy related 5) siRNA stimulated senescence. Rapamycin rescued the effect of Atg5 siRNA in Ppargc1a+/+ , but not in ppargc1a-/- VSMCs, suggesting that other targets of MTOR (mechanistic target of rapamycin kinase), in addition to autophagy, also contribute to senescence. Sqstm1 siRNA increased senescence basally and in response to AGT II (angiotensin II) and zinc overload, two known inducers of senescence. Furthermore, Sqstm1 gene deficiency mimicked the phenotype of Ppargc1a depletion by presenting reduced autophagy and increased senescence in vitro and in vivo. Thus, PPARGC1A upregulates autophagy reducing senescence by a SQSTM1-dependent mechanism. We propose SQSTM1 as a novel target in therapeutic interventions reducing senescence.

ABBREVIATIONS

3-MA: 3 methyladenine; ACTA2/SM-actin: actin, alpha 2, smooth muscle, aorta; ACTB/β-actin: actin beta; AGT II: angiotensin II; ATG5: autophagy related 5; BECN1: beclin 1; CAT: catalase; CDKN1A: cyclin-dependent kinase inhibitor 1A (P21); Chl: chloroquine; CTSD: cathepsin D; CYCS: cytochrome C, somatic; DHE: dihydroethidium; DPBS: Dulbecco's phosphate-buffered saline; EL: elastic lamina; EM: extracellular matrix; FDG: fluorescein-di-β-D-galactopyranoside; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; γH2AFX: phosphorylated H2A histone family, member X, H2DCFDA: 2',7'-dichlorodihydrofluorescein diacetate; LAMP2: lysosomal-associated membrane protein 2; MASMs: mouse vascular smooth muscle cells; MEF: mouse embryonic fibroblast; NBR1: NBR1, autophagy cargo receptor; NFKB/NF-κB: nuclear factor of kappa light polypeptide gene enhancer in B cells; MTOR: mechanistic target of rapamycin kinase; NFE2L2: nuclear factor, erythroid derived 2, like 2; NOX1: NADPH oxidase 1; OPTN: optineurin; PFA: paraformaldehyde; PFU: plaque-forming units; PPARGC1A/PGC-1α: peroxisome proliferator activated receptor, gamma, coactivator 1 alpha; Ptdln3K: phosphatidylinositol 3-kinase; RASMs: rat vascular smooth muscle cells; ROS: reactive oxygen species; SA-GLB1/β-gal: senescence-associated galactosidase, beta 1; SASP: senescence-associated secretory phenotype; SIRT1: sirtuin 1; Spautin 1: specific and potent autophagy inhibitor 1; SQSTM1/p62: sequestosome 1; SOD: superoxide dismutase; TEM: transmission electron microscopy; TFEB: transcription factor EB; TFRC: transferrin receptor; TRP53/p53: transformation related protein 53; TUBG1: tubulin gamma 1; VSMCs: vascular smooth muscle cells; WT: wild type.

Functional Genetic Variant in ATG5 Gene Promoter in Acute Myocardial Infarction

Coronary artery disease (CAD) including acute myocardial infarction (AMI) is an inflammatory and metabolic disease mainly caused by atherosclerosis. Dysfunctional autophagy has been associated with abnormal lipid metabolism and inflammation. In previous studies, we have reported altered autophagic activity in AMI patients. As autophagy-related protein 5 (ATG5) is a core protein in autophagy, we speculated that altered ATG5 level may contribute to CAD and AMI development. In this study, the promoter of the ATG5 gene was genetically and functionally investigated in large groups of AMI patients (n = 378) and ethnic-matched healthy controls (n = 386). The results showed that a total of 15 genetic variants including 6 single-nucleotide polymorphisms (SNPs) in the ATG5 gene promoter were found in this study population. A novel deletion variant (g.106326168_70delTCT) and an SNP [g.106325757C > G (rs190825454)] were found in one 66-year-old male patient with non-ST-segment elevated AMI, but in none of controls. In cultured HEK-293 and H9c2 cells, the deletion variant significantly decreased the transcriptional activity of the ATG5 gene promoter (P < 0.01). In contrast, the genetic variants either identified only in controls or found in both AMI patients and controls did not affect the transcriptional activity of the ATG5 gene promoter (P > 0.05). Furthermore, an electrophoretic mobility shift assay showed that the deletion variant evidently affected the binding of a transcription factor. Therefore, the genetic variant identified in AMI may affect the activity of the ATG5 gene promoter and change the ATG5 level, contributing to AMI as a rare risk factor.

Mitophagy in Cardiovascular Diseases

Cardiovascular diseases are one of the leading causes of death. Increasing evidence has shown that pharmacological or genetic targeting of mitochondria can ameliorate each stage of these pathologies, which are strongly associated with mitochondrial dysfunction. Removal of inefficient and dysfunctional mitochondria through the process of mitophagy has been reported to be essential for meeting the energetic requirements and maintaining the biochemical homeostasis of cells. This process is useful for counteracting the negative phenotypic changes that occur during cardiovascular diseases, and understanding the molecular players involved might be crucial for the development of potential therapies. Here, we summarize the current knowledge on mitophagy (and autophagy) mechanisms in the context of heart disease with an important focus on atherosclerosis, ischemic heart disease, cardiomyopathies, heart failure, hypertension, arrhythmia, congenital heart disease and peripheral vascular disease. We aim to provide a complete background on the mechanisms of action of this mitochondrial quality control process in cardiology and in cardiac surgery by also reviewing studies on the use of known compounds able to modulate mitophagy for cardioprotective purposes.

Macrophage-Based Therapies for Atherosclerosis Management

Atherosclerosis (AS), a typical chronic inflammatory vascular disease, is the main pathological basis of ischemic cardio/cerebrovascular disease (CVD). Long-term administration was characterized with low efficacy and serious side effects, while the macrophages with attractive intrinsic homing target have great potential in the efficient and safe management of AS. In this review, we focused on the systematical summary of the macrophage-based therapies in AS management, including macrophage autophagy, polarization, targeted delivery, microenvironment-triggered drug release, and macrophage- or macrophage membrane-based drug carrier. In conclusion, macrophage-based therapies have great promise to effectively manage AS in future research and clinic translation.

Myeloid atg5 deletion impairs n-3 PUFA-mediated atheroprotection

BACKGROUND AND AIMS

Dietary long-chain (≥20 carbons) n-3 polyunsaturated fatty acids (PUFAs) reduce atherosclerosis and enhance macrophage autophagy activation. How macrophage autophagy impacts atherosclerotic progression, particularly when comparing dietary n-3 PUFA supplementation vs. saturated fat feeding, is unknown.

METHODS

We generated myeloid-specific autophagy-deficient and control mice in the Ldlr^-/- background by transplanting bone marrow from myeloid-specific autophagy-related (atg) 5 knockout mice and wild type controls into irradiated Ldlr^-/- recipients. After 7 weeks for recovery from radiation, mice were fed an atherogenic diet containing 0.2% cholesterol and 20% calories as palm oil (PO diet), or 10% calories as PO plus 10% calories as fish oil (FO diet) for 16 weeks.

RESULTS

Compared to PO, FO significantly reduced plasma cholesterol, triglyceride, hepatic neutral lipid, and aortic caspase-1 cleavage, but increased aortic efferocytosis, leading to attenuated atherosclerosis in Ldlr^-/- mice receiving wild type bone marrow. Myeloid atg5 deletion had little impact on plasma lipid concentrations and hepatic neutral lipid content, regardless of diet. Myeloid atg5 deletion increased aortic caspase-1 cleavage, decreased aortic efferocytosis and worsened atherosclerosis only in the FO-fed Ldlr^-/- mice.

CONCLUSIONS

Deficient myeloid autophagy significantly attenuated FO-induced atheroprotection, suggesting that dietary n-3 PUFAs reduce atherosclerosis, in part, by activation of macrophage autophagy.

High-protein diets increase cardiovascular risk by activating macrophage mTOR to suppress mitophagy

High protein diets are commonly utilized for weight loss, yet have been reported to raise cardiovascular risk. The mechanisms underlying this risk are unknown. Here, we show that dietary protein drives atherosclerosis and lesion complexity. Protein ingestion acutely elevates amino acid levels in blood and atherosclerotic plaques, stimulating macrophage mTOR signaling. This is causal in plaque progression as the effects of dietary protein are abrogated in macrophage-specific Raptor-null mice. Mechanistically, we find amino acids exacerbate macrophage apoptosis induced by atherogenic lipids, a process that involves mTORC1-dependent inhibition of mitophagy, accumulation of dysfunctional mitochondria, and mitochondrial apoptosis. Using macrophage-specific mTORC1- and autophagy-deficient mice we confirm this amino acid-mTORC1-autophagy signaling axis in vivo. Our data provide the first insights into the deleterious impact of excessive protein ingestion on macrophages and atherosclerotic progression. Incorporation of these concepts in clinical studies will be important to define the vascular effects of protein-based weight loss regimens.

p62 /SQSTM1 coding plasmid prevents age related macular degeneration in a rat model

P62/SQSTM1, a multi-domain protein that regulates inflammation, apoptosis, and autophagy, has been linked to age-related pathologies. For example, previously we demonstrated that administration of p62/SQSTM1-encoding plasmid reduced chronic inflammation and alleviated osteoporosis and metabolic syndrome in animal models. Herein, we built upon these findings to investigate effect of the p62-encoding plasmid on an age-related macular degeneration (AMD), a progressive neurodegenerative ocular disease, using spontaneous retinopathy in senescence-accelerated OXYS rats as a model. Overall, the p62DNA decreased the incidence and severity of retinopathy. In retinal pigment epithelium (RPE), p62DNA administration slowed down development of the destructive alterations of RPE cells, including loss of regular hexagonal shape, hypertrophy, and multinucleation. In neuroretina, p62DNA prevented gliosis, retinal thinning, and significantly inhibited microglia/macrophages migration to the outer retina, prohibiting their subretinal accumulation. Taken together, our results suggest that the p62DNA has a strong retinoprotective effect in AMD.

TPM2 as a potential predictive biomarker for atherosclerosis

Cardiac-cerebral vascular disease (CCVD), is primarily induced by atherosclerosis, and is a leading cause of mortality. Numerous studies have investigated and attempted to clarify the molecular mechanisms of atherosclerosis; however, its pathogenesis has yet to be completely elucidated. Two expression profiling datasets, GSE43292 and GSE57691, were obtained from the Gene Expression Omnibus (GEO) database. The present study then identified the differentially expressed genes (DEGs), and functional annotation of the DEGs was performed. Finally, an atherosclerosis animal model and neural network prediction model was constructed to verify the relationship between hub gene and atherosclerosis. The results identified a total of 234 DEGs between the normal and atherosclerosis samples. The DEGs were mainly enriched in actin filament, actin binding, smooth muscle cells, and cytokine-cytokine receptor interactions. A total of 13 genes were identified as hub genes. Following verification of animal model, the common DEG, Tropomyosin 2 (TPM2), was found, which were displayed at lower levels in the atherosclerosis models and samples. In summary, DEGs identified in the present study may assist clinicians in understanding the pathogenesis governing the occurrence and development of atherosclerosis, and TPM2 exhibits potential as a promising diagnostic and therapeutic biomarker for atherosclerosis.

p62/SQSTM1 and Selective Autophagy in Cardiometabolic Diseases

Significance: p62/SQSTM1 is a multifunctional scaffolding protein involved in the regulation of various signaling pathways as well as autophagy. In particular, p62/SQSTM1 serves as an essential adaptor to identify and deliver specific organelles and protein aggregates to autophagosomes for degradation, a process known as selective autophagy. Critical Issues: With the emergence of autophagy as a critical process in cellular metabolism and the development of cardiometabolic diseases, it is increasingly important to understand p62's role in the integration of signaling and autophagic pathways. Recent Advances: This review first discusses the features that make p62/SQSTM1 an ideal chaperone in integrating signaling pathways with autophagy and details the current understanding of its diverse roles in selective autophagy processes. Distinct and overlapping roles of other chaperones with similar functions are then discussed in the context of p62/SQSTM1. Finally, the recent literature focusing on p62 and selective autophagy in metabolism and the spectrum of cardiometabolic diseases including atherosclerosis, fatty liver disease, and obesity is evaluated. Future Directions: A comprehensive understanding of the nuanced roles p62/SQSTM1 plays in mediating distinct autophagy pathways would provide new insights into the mechanisms of this critical degradative pathway. This will, in turn, facilitate our understanding of cardiovascular and cardiometabolic disease pathology and the development of novel autophagy-modulating therapeutic strategies.

Knockdown of LSD1 meliorates Ox-LDL-stimulated NLRP3 activation and inflammation by promoting autophagy via SESN2-mesiated PI3K/Akt/mTOR signaling pathway

AIMS

To explore the mechanism of how LSD1 regulates autophagy and the correlation between LSD1 and Ox-LDL-induced inflammation.

MAIN METHODS

RAW264.7 cells were used during the whole study. Firstly, the effect of Ox-LDL-stimulation on LSD1 expression was detected. Through loss-of-function assay, the associations between LSD1 interference and SESN2 expression, autophagy, NLRP3 inflammasome and inflammatory cytokines were explored. Finally, the function of LSD1 exerted on activation of PI3K/Akt/mTOR signal pathway was detected using western blotting assay.

KEY FINDINGS

The expression of LSD1 was significantly elevated in Ox-LDL-treated RAW264.7 cells. Inhibition of LSD1 promoted autophagy, inhibited inflammation and activated NLRP3 inflammasome. SESN2 was elevated by LSD1 inhibition, and thus activate the PI3K/Akt/mTOR signal pathway. What' more, Knockdown of SESN2 or deactivate the PI3K/Akt/mTOR signal pathway partly reversed the effect of LSD1 inhibition on autophagy.

SIGNIFICANCE

Our present study drew the finding that the knockdown of LSD1 meliorated Ox-LDL-stimulated NLRP3 activation and inflammation through promoting autophagy via SESN2-mediated PI3K/Akt/mTOR pathway.

Effect of typhaneoside on ventricular remodeling and regulation of PI3K/Akt/mTOR pathway

Background

This study aimed to investigate the effect of typhaneoside on ventricular remodeling and regulation of the PI3K/Akt/mTOR autophagy transduction pathway in rats with heart failure after myocardial infarction.

Methods

The effects of typhaneoside on the general condition of rats were observed in vivo using a rat model of heart failure after myocardial infarction had been established. The expression of serum N‑terminal pro-brain natriuretic peptide (NT-proBNP), matrix lysin 2 (ST2), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), matrix metalloproteinase 2 (MMP-2), and MMP-9 was detected via ELISA. A hypoxia/reoxygenation model was established to analyze the number and morphology of autophagosomes in vitro by transmission electron microscopy. Light chain 3 (LC3) variations were detected by immunofluorescence. Western blotting was used to assess LC3-II/LC3-I and p62 expression as well as p‑Akt/Akt, p‑mTOR/mTOR ratios.

Results

Compared with the sham group, the general condition scores of the rats in the model group decreased significantly, while the expression of serum NT-proBNP, ST2, IL-6, TNF-α, MMP-2, and MMP-9 increased. The number of autophagosomes in the drug-containing serum group was significantly reduced and the ratio of LC3-II/LC3-I was significantly decreased. The expression of P62 protein was increased, and the ratios of p‑Akt/Akt and p‑mTOR/mTOR were significantly increased.

Conclusion

Typhaneoside regulates IL-6 and TNF-α as well as MMP-2 and MMP-9 in rats with heart failure after myocardial infarction. Typhaneoside can improve cardiac morphological structure and myocardial remodeling and enhance heart function. It may mediate autophagy inhibition in the cardiomyocyte anoxia/reoxygenation (A/R) pathway through the PI3K/Akt/mTOR autophagy transduction pathway.

p62/mTOR/LXRα pathway inhibits cholesterol efflux mediated by ABCA1 and ABCG1 during autophagy blockage

OBJECTIVE

Atherosclerosis is a disease characterized by abnormal lipid metabolism, and the formation of foam cells is considered an early event of atherosclerosis. Intracellular cholesterol efflux mediated by ABCA1 and ABCG1 helps to reduce lipid accumulation in foam cells. Related studies have shown that autophagy and mTOR are involved in cholesterol efflux, but the role of p62, an autophagy substrate protein, has not been evaluated.

METHODS

THP-1 derived macrophages were incubated with ox-LDL to establish a foam cell model and treated with different autophagy inducers. The effects of p62 on cholesterol efflux were investigated using overexpression vectors, gene silencing and western blotting.

RESULTS

This study showed a blockage of autophagy and decreased expression of ABCA1 and ABCG1 under the stress of excess ox-LDL in a concentration-dependent manner in THP-1 cells. Furthermore, the activation of autophagy led to increased expression of ABCA1 and ABCG1, as well as their upstream transcription factor LXRα, thereby promoting cholesterol efflux from foam cells. We also demonstrated that accumulated p62 played an important role during autophagy blockage, which was achieved by activating mTOR and then inhibited the expression of LXRα and its downstream target proteins ABCA1 and ABCG1.

CONCLUSION

In conclusion, our experiments demonstrated that a p62/mTOR/LXRα signaling pathway was involved in cholesterol efflux mediated by ABCA1 and ABCG1 when autophagy blockage occurred. Our study offers a rationale for the development of autophagy and p62 as a new target for the treatment of atherosclerosis.

p62/SQSTM1 - steering the cell through health and disease

SQSTM1 (also known as p62) is a multifunctional stress-inducible scaffold protein involved in diverse cellular processes. Its functions are tightly regulated through an extensive pattern of post-translational modifications, and include the isolation of cargos degraded by autophagy, induction of the antioxidant response by the Keap1-Nrf2 system, as well as the regulation of endosomal trafficking, apoptosis and inflammation. Accordingly, malfunction of SQSTM1 is associated with a wide range of diseases, including bone and muscle disorders, neurodegenerative and metabolic diseases, and multiple forms of cancer. In this Review, we summarize current knowledge regarding regulation, post-translational modifications and functions of SQSTM1, as well as how they are dysregulated in various pathogenic contexts.

Autophagy in Metabolic Age-Related Human Diseases

Autophagy is a highly conserved homeostatic cellular mechanism that mediates the degradation of damaged organelles, protein aggregates, and invading pathogens through a lysosome-dependent pathway. Over the last few years, specific functions of autophagy have been discovered in many tissues and organs; however, abnormal upregulation or downregulation of autophagy has been depicted as an attribute of a variety of pathologic conditions. In this review, we will describe the current knowledge on the role of autophagy, from its regulation to its physiological influence, in metabolic age-related disorders. Finally, we propose to discuss the therapeutic potential of pharmacological and nutritional modulators of autophagy to treat metabolic diseases.

The autophagy receptor SQSTM1/p62 mediates anti-inflammatory actions of the selective NR3C1/glucocorticoid receptor modulator compound A (CpdA) in macrophages

Glucocorticoids are widely used to treat inflammatory disorders; however, prolonged use of glucocorticoids results in side effects including osteoporosis, diabetes and obesity. Compound A (CpdA), identified as a selective NR3C1/glucocorticoid receptor (nuclear receptor subfamily 3, group C, member 1) modulator, exhibits an inflammation-suppressive effect, largely in the absence of detrimental side effects. To understand the mechanistic differences between the classic glucocorticoid dexamethasone (DEX) and CpdA, we looked for proteins oppositely regulated in bone marrow-derived macrophages using an unbiased proteomics approach. We found that the autophagy receptor SQSTM1 but not NR3C1 mediates the anti-inflammatory action of CpdA. CpdA drives SQSTM1 upregulation by recruiting the NFE2L2 transcription factor to its promoter. In contrast, the classic NR3C1 ligand dexamethasone recruits NR3C1 to the Sqstm1 promoter and other NFE2L2-controlled gene promoters, resulting in gene downregulation. Both DEX and CpdA induce autophagy, with marked different autophagy characteristics and morphology. Suppression of LPS-induced Il6 and Ccl2 genes by CpdA in macrophages is hampered upon Sqstm1 silencing, confirming that SQSTM1 is essential for the anti-inflammatory capacity of CpdA, at least in this cell type. Together, these results demonstrate how off-target mechanisms of selective NR3C1 ligands may contribute to a more efficient anti-inflammatory therapy.

Classical and alternative roles for autophagy in lipid metabolism

PURPOSE OF REVIEW

Intracellular lipid metabolism is a complex interplay of exogenous lipid handling, trafficking, storage, lipolysis, and export. Recent work has implicated the cellular degradative process called autophagy in several aspects of lipid metabolism. We will discuss both the classical and novel roles of autophagy and the autophagic machinery in this setting.

RECENT FINDINGS

The delivery of lipid droplets to lysosomes for hydrolysis, named lipophagy, was the first described functional role for autophagy in lipid metabolism. The molecular machinery and regulation of this selective form of macroautophagy is beginning to be discovered and has the potential to shed enormous light on intracellular lipolysis. Yet, the autophagic machinery appears to also be coopted for alternative roles that include interaction with cytosolic lipolysis pathways, supply and expansion of lipid droplets, and lipoprotein trafficking. Additionally, lesser studied forms of autophagy called microautophagy and chaperone-mediated autophagy have distinct roles in lipid handling that also intersect with classical macroautophagy. The integration of current knowledge in these areas into a holistic understanding of intracellular lipid metabolism will be a goal of this review.

SUMMARY

As the field of autophagy has evolved and expanded to include functional roles in various aspects of cellular degradation, so has its role in intracellular lipid metabolism. Understanding the mechanisms underlying these classical and alternative roles of autophagy will not only enhance our knowledge in lipid biology but also provide new avenues of translation to human lipid disorders.

Atorvastatin Inhibits Inflammatory Response, Attenuates Lipid Deposition, and Improves the Stability of Vulnerable Atherosclerotic Plaques by Modulating Autophagy

Atherosclerosis is a chronic disease comprising intima malfunction and arterial inflammation. Recent studies have demonstrated that autophagy could inhibit inflammatory response in atherosclerosis and exert subsequent atheroprotective effects. Our previous study also demonstrated the role of autophagy in the inhibition of inflammation by atorvastatin in vitro. Therefore, in the present study, we aimed to determine whether atorvastatin could upregulate autophagy to inhibit inflammatory cytokines secretion, lipid accumulation, and improve vulnerable plaque stability, both in vitro and in vivo. First, we established a vulnerable atherosclerotic plaque mouse model through partial ligation of left common carotid artery and left renal artery to explore the effect of atorvastatin on vulnerable plaques. The results showed that atorvastatin could enhance the stability of vulnerable atherosclerotic plaques and reduce the lesion area in the aorta. Atorvastatin could also inhibit NLRP3 inflammasome activation and inflammatory cytokines, such as IL-1β, TNF-α, and IL-18 secretion in vivo. Atorvastatin treatment upregulated the expression of autophagy-related protein microtubule-associated protein light chain (LC3B) and downregulated the expression of SQSTM1/p62, which suggested that autophagy was activated in vulnerable plaques. Transmission electron microscopy further demonstrated the atorvastatin-induced increase in autophagy activity in vulnerable atherosclerotic plaques. We employed oxidized low-density lipoprotein (ox-LDL) to stimulate RAW264.7 cells with atorvastatin, which showed that atorvastatin could attenuate lipid deposition, ameliorate inflammation, inhibit NLRP3 inflammasome activation, and enhance autophagy in vitro. All these beneficial effects were abolished by 3-methyladenine treatment, an autophagy inhibitor. Atorvastatin also significantly inhibited the phosphorylation of mTOR, which strongly suggested the involvement of the mTOR pathway. Our study proposed a new role for atorvastatin as an autophagy inducer to exert anti-inflammatory and atheroprotective effects, to stabilize vulnerable atherosclerotic plaques.

Defective Autophagy in Atherosclerosis: To Die or to Senesce?

Autophagy is a subcellular process that plays an important role in the degradation of proteins and damaged organelles such as mitochondria (a process termed “mitophagy”) via lysosomes. It is crucial for regulating protein and mitochondrial quality control and maintaining cellular homeostasis, whereas dysregulation of autophagy has been implicated in a wide range of diseases including atherosclerosis. Recent evidence has shown that the autophagic process becomes dysfunctional during the progression of atherosclerosis, regardless of whether there are many autophagy-stimulating factors (e.g., reactive oxygen species, oxidized lipids, and cytokines) present within the atherosclerotic plaque. This review highlights the recent insights into the causes and consequences of defective autophagy in atherosclerosis, with a special focus on the role of autophagy and mitophagy in plaque macrophages, vascular smooth muscle cells (VSMCs), and endothelial cells (ECs). It has been shown that defective autophagy can promote apoptosis in macrophages but that it accelerates premature senescence in VSMCs. In the ECs, defective autophagy promotes both apoptosis and senescence. We will discuss the discrepancy between these three cell types in their response to autophagy deficiency and underline the cell type-dependent role of autophagy, which may have important implications for the efficacy of autophagy-targeted treatments for atherosclerosis.

Cell-Based High Content Analysis of Cell Proliferation and Apoptosis

High content imaging-based cell cycle analysis allows multiplexing of various parameters including DNA content, DNA synthesis, cell proliferation, and other cell cycle markers such as phosho-histone H3. 5'-Ethynyl-2'-deoxyuridine (EdU) incorporation is a thymidine analog that provides a sensitive method for the detection of DNA synthesis in proliferating cells that is a more convenient method than the traditional BrdU detection by antibody. Caspase 3 is activated in programmed cell death induced by both intrinsic (mitochondrial) and extrinsic factors (death ligand). Cell cycle and apoptosis are common parameters studied in the phenotypic analysis of compound toxicity and anti-cancer drugs. In this chapter, we describe methods for the detection of s-phase cell cycle progression by EdU incorporation, and caspase 3 activation using the CellEvent caspase 3/7 detection reagent.

Protein aggregation, cardiovascular diseases, and exercise training: Where do we stand?

Cells ensure their protein quality control through the proteostasis network. Aging and age-related diseases, such as neurodegenerative and cardiovascular diseases, have been associated to the reduction of proteostasis network efficiency and, consequently, to the accumulation of protein misfolded aggregates. The decline in protein homeostasis has been associated with the development and progression of atherosclerotic cardiovascular disease, cardiac hypertrophy, cardiomyopathies, and heart failure. Exercise training is a key component of the management of patients with cardiovascular disease, consistently improving quality of life and prognosis. In this review, we give an overview on age-related protein aggregation, the role of the increase of misfolded protein aggregates on cardiovascular pathophysiology, and describe the beneficial or deleterious effects of the proteostasis network on the development of cardiovascular disease. We subsequently discuss how exercise training, a key lifestyle intervention in those with cardiovascular disease, could restore proteostasis and improve disease status.

Multifunctional p62 Effects Underlie Diverse Metabolic Diseases

p62, a protein capable of binding both ubiquitin and autophagy substrates, is well established as a key regulator in cancer and neurodegenerative diseases. Recently, there has been accumulating evidence that p62 is also a pivotal regulator in metabolic diseases, such as obesity, T2DM, NAFLD, metabolic bone disease, gout and thyroid disease. This review summarizes the emerging role of p62 on these diseases by considering its functional domains, phenotypes in genetically modified animals, clinically observed alterations, and its effects on downstream metabolic signaling pathways. At the same time, we highlight the need to explore the roles played by p62 in the gastrointestinal environment and immune system, and the extent to which its elevated expression may confer protection against metabolic disorders.

Potential role of IL-37 in atherosclerosis

IL-37 is a member of the IL-1 family, but unlike most other members of this family of cytokines, it has wide-ranging anti-inflammatory properties. Initially shown to bind IL-18 binding protein and prevent IL-18-mediated inflammation, its known role has been expanded to include distinct pathways, both intracellular involving the transcription factor Smad3, and extracellular via binding to the orphan receptor IL-1R8. A number of recent publications investigating the role of IL-37 in atherosclerosis and ischemic heart disease have revealed promising therapeutic value of the cytokine. Although research concerning the role of IL-37 and its mechanism in atherosclerosis is relatively scant, there are a number of well-known atherosclerotic processes that this cytokine can mediate with the potential of modulating the disease progression itself. This review will probe in detail the effects of IL-37 on important pathological processes such as inflammation, dysregulated lipid metabolism, and apoptosis, by analyzing existing data as well as exploring the potential of this cytokine to influence these properties.

N-3 PUFAs induce inflammatory tolerance by formation of KEAP1-containing SQSTM1/p62-bodies and activation of NFE2L2

Inflammation is crucial in the defense against infections but must be tightly controlled to limit detrimental hyperactivation. Our diet influences inflammatory processes and omega-3 polyunsaturated fatty acids (n-3 PUFAs) have known anti-inflammatory effects. The balance of pro- and anti-inflammatory processes is coordinated by macrophages and macroautophagy/autophagy has recently emerged as a cellular process that dampens inflammation. Here we report that the n-3 PUFA docosahexaenoic acid (DHA) transiently induces cytosolic speckles of the autophagic receptor SQSTM1/p62 (sequestosome 1) (described as SQSTM1/p62-bodies) in macrophages. We suggest that the formation of SQSTM1/p62-bodies represents a fast mechanism of NFE2L2/Nrf2 (nuclear factor, erythroid 2 like 2) activation by recruitment of KEAP1 (kelch like ECH associated protein 1). Further, the autophagy receptor TAX1BP1 (Tax1 binding protein 1) and ubiquitin-editing enzyme TNFAIP3/A20 (TNF α induced protein 3) could be identified in DHA-induced SQSTM1/p62-bodies. Simultaneously, DHA strongly dampened the induction of pro-inflammatory genes including CXCL10 (C-X-C motif chemokine ligand 10) and we suggest that formation of SQSTM1/p62-bodies and activation of NFE2L2 leads to tolerance towards selective inflammatory stimuli. Finally, reduced CXCL10 levels were related to the improved clinical outcome in n-3 PUFA-supplemented heart-transplant patients and we propose CXCL10 as a robust marker for the clinical benefits mobilized by n-3 PUFA supplementation.

Exploiting macrophage autophagy-lysosomal biogenesis as a therapy for atherosclerosis

Macrophages specialize in removing lipids and debris present in the atherosclerotic plaque. However, plaque progression renders macrophages unable to degrade exogenous atherogenic material and endogenous cargo including dysfunctional proteins and organelles. Here we show that a decline in the autophagy–lysosome system contributes to this as evidenced by a derangement in key autophagy markers in both mouse and human atherosclerotic plaques. By augmenting macrophage TFEB, the master transcriptional regulator of autophagy–lysosomal biogenesis, we can reverse the autophagy dysfunction of plaques, enhance aggrephagy of p62-enriched protein aggregates and blunt macrophage apoptosis and pro-inflammatory IL-1β levels, leading to reduced atherosclerosis. In order to harness this degradative response therapeutically, we also describe a natural sugar called trehalose as an inducer of macrophage autophagy–lysosomal biogenesis and show trehalose's ability to recapitulate the atheroprotective properties of macrophage TFEB overexpression. Our data support this practical method of enhancing the degradative capacity of macrophages as a therapy for atherosclerotic vascular disease.

Dysfunction of autophagy in plaque macrophages aggravates atherosclerosis. Here the authors show that induction of macrophage autophagy–lysosomal biogenesis either genetically by overexpression of the master transcriptional regulator of this process, TFEB, or pharmacologically with trehalose is atheroprotective.

SIRT1 inhibition promotes atherosclerosis through impaired autophagy

SIRT1, a highly conserved NAD⁺-dependent protein deacetylase, plays a pivotal role in the pathogenesis and therapy of atherosclerosis (AS). The aim of this study is to investigate the potential effects of SIRT1 on AS in ApoE^-/- mice and the underlying mechanisms of autophagy in an ox-LDL-stimulated human monocyte cell line, THP-1. In vivo, the accelerated atherosclerotic progression of mice was established by carotid collar placement; then, mice were treated for 4 weeks with a SIRT1-specific inhibitor, EX-527. The atherosclerotic lesion size of EX-527-treated mice was greatly increased compared to that of the mice in the control group. Immunostaining protocols confirmed that the inhibition of SIRT1 during plaque initiation and progression enhanced the extent of intraplaque macrophage infiltration and impaired the autophagy process. In vitro cultured THP-1 macrophages exposed to ox-LDL were utilized to study the link between the SIRT1 function, autophagy flux, pro-inflammatory cytokine secretion, and foam cell formation using different methods. Our data showed that ox-LDL markedly suppressed SIRT1 protein expression and the autophagy level, while it elevated the MCP-1 production and lipid uptake. Additionally, the application of the SIRT1 inhibitor EX-527 or SIRT1 siRNA further attenuated ox-LDL-induced autophagy inhibition. In conclusion, our results show that the inhibition of SIRT1 promoted atherosclerotic plaque development in ApoE^-/- mice by increasing the MCP-1 expression and macrophage accumulation. In particular, we demonstrate that blocking SIRT1 can exacerbate the acetylation of key autophagy machinery, the Atg5 protein, which further regulates the THP-1 macrophage-derived foam cell formation that is triggered by ox-LDL.

Understanding cell cycle and cell death regulation provides novel weapons against human diseases

Cell division, cell differentiation and cell death are the three principal physiological processes that regulate tissue homoeostasis in multicellular organisms. The growth and survival of cells as well as the integrity of the genome are regulated by a complex network of pathways, in which cell cycle checkpoints, DNA repair and programmed cell death have critical roles. Disruption of genomic integrity and impaired regulation of cell death may both lead to uncontrolled cell growth. Compromised cell death can also favour genomic instability. It is becoming increasingly clear that dysregulation of cell cycle and cell death processes plays an important role in the development of major disorders such as cancer, cardiovascular disease, infection, inflammation and neurodegenerative diseases. Research achievements in these fields have led to the development of novel approaches for treatment of various conditions associated with abnormalities in the regulation of cell cycle progression or cell death. A better understanding of how cellular life-and-death processes are regulated is essential for this development. To highlight these important advances, the Third Nobel Conference entitled 'The Cell Cycle and Cell Death in Disease' was organized at Karolinska Institutet in 2016. In this review we will summarize current understanding of cell cycle progression and cell death and discuss some of the recent advances in therapeutic applications in pathological conditions such as cancer, neurological disorders and inflammation.

The walking dead: macrophage inflammation and death in atherosclerosis

PURPOSE OF REVIEW

To highlight recent studies that describe novel inflammatory and signaling mechanisms that regulate macrophage death in atherosclerosis.

RECENT FINDINGS

Macrophages contribute to all stages of atherosclerosis. The traditional dogma states that in homeostatic conditions, macrophages undergo apoptosis and are efficiently phagocytosed to be cleared by a process called efferocytosis. In advanced atherosclerosis, however, defective efferocytosis results in secondary necrosis of these uncleared apoptotic cells, which ultimately contributes to the formation of the characteristic necrotic core and the vulnerable plaque. Here, we outline the different types of lesional macrophage death: apoptosis, autophagic and the newly defined necroptosis (i.e. a type of programmed necrosis). Recent discoveries demonstrate that macrophage necroptosis directly contributes to necrotic core formation and plaque instability. Further, promoting the resolution of inflammation using preresolving mediators has been shown to enhance efferocytosis and decrease plaque vulnerability. Finally, the canonical 'don't eat me' signal CD47 has recently been described as playing an important role in atherosclerotic lesion progression by impairing efficient efferocytosis. Although we have made significant strides in improving our understanding of cell death and clearance mechanisms in atherosclerosis, there still remains unanswered questions as to how these pathways can be harnessed using therapeutics to promote lesion regression and disease stability.

SUMMARY

Improving our understanding of the mechanisms that regulate macrophage death in atherosclerosis, in particular apoptosis, necroptosis and efferocytosis, will provide novel therapeutic opportunities to resolve atherosclerosis and promote plaque stability.

Target acquired: Selective autophagy in cardiometabolic disease

The accumulation of damaged or excess proteins and organelles is a defining feature of metabolic disease in nearly every tissue. Thus, a central challenge in maintaining metabolic homeostasis is the identification, sequestration, and degradation of these cellular components, including protein aggregates, mitochondria, peroxisomes, inflammasomes, and lipid droplets. A primary route through which this challenge is met is selective autophagy, the targeting of specific cellular cargo for autophagic compartmentalization and lysosomal degradation. In addition to its roles in degradation, selective autophagy is emerging as an integral component of inflammatory and metabolic signaling cascades. In this Review, we focus on emerging evidence and key questions about the role of selective autophagy in the cell biology and pathophysiology of metabolic diseases such as obesity, diabetes, atherosclerosis, and steatohepatitis. Essential players in these processes are the selective autophagy receptors, defined broadly as adapter proteins that both recognize cargo and target it to the autophagosome. Additional domains within these receptors may allow integration of information about autophagic flux with critical regulators of cellular metabolism and inflammation. Details regarding the precise receptors involved, such as p62 and NBR1, and their predominant interacting partners are just beginning to be defined. Overall, we anticipate that the continued study of selective autophagy will prove to be informative in understanding the pathogenesis of metabolic diseases and to provide previously unrecognized therapeutic targets.

SNAPIN is critical for lysosomal acidification and autophagosome maturation in macrophages

We previously observed that SNAPIN, which is an adaptor protein in the SNARE core complex, was highly expressed in rheumatoid arthritis synovial tissue macrophages, but its role in macrophages and autoimmunity is unknown. To identify SNAPIN's role in these cells, we employed siRNA to silence the expression of SNAPIN in primary human macrophages. Silencing SNAPIN resulted in swollen lysosomes with impaired CTSD (cathepsin D) activation, although total CTSD was not reduced. Neither endosome cargo delivery nor lysosomal fusion with endosomes or autophagosomes was inhibited following the forced silencing of SNAPIN. The acidification of lysosomes and accumulation of autolysosomes in SNAPIN-silenced cells was inhibited, resulting in incomplete lysosomal hydrolysis and impaired macroautophagy/autophagy flux. Mechanistic studies employing ratiometric color fluorescence on living cells demonstrated that the reduction of SNAPIN resulted in a modest reduction of H⁺ pump activity; however, the more critical mechanism was a lysosomal proton leak. Overall, our results demonstrate that SNAPIN is critical in the maintenance of healthy lysosomes and autophagy through its role in lysosome acidification and autophagosome maturation in macrophages largely through preventing proton leak. These observations suggest an important role for SNAPIN and autophagy in the homeostasis of macrophages, particularly long-lived tissue resident macrophages.

Post-translational regulation of inflammasomes

Inflammasomes play essential roles in immune protection against microbial infections. However, excessive inflammation is implicated in various human diseases, including autoinflammatory syndromes, diabetes, multiple sclerosis, cardiovascular disorders and neurodegenerative diseases. Therefore, precise regulation of inflammasome activities is critical for adequate immune protection while limiting collateral tissue damage. In this review, we focus on the emerging roles of post-translational modifications (PTMs) that regulate activation of the NLRP3, NLRP1, NLRC4, AIM2 and IFI16 inflammasomes. We anticipate that these types of PTMs will be identified in other types of and less well-characterized inflammasomes. Because these highly diverse and versatile PTMs shape distinct inflammatory responses in response to infections and tissue damage, targeting the enzymes involved in these PTMs will undoubtedly offer opportunities for precise modulation of inflammasome activities under various pathophysiological conditions.