PCSK9 in Liver Cancers at the Crossroads between Lipid Metabolism and Immunity.

Metabolic rewiring and defective immune responses are considered to be the main driving forces sustaining cell growth and oncogenesis in many cancers. The atypical enzyme, proprotein convertase subtilisin/kexin type 9 (PCSK9), is produced by the liver in large amounts and plays a major role in lipid metabolism via the control of the low density lipoprotein receptor (LDLR) and other cell surface receptors. In this context, many clinical studies have clearly demonstrated the high efficacy of PCSK9 inhibitors in treating hyperlipidemia and cardiovascular diseases. Recent data implicated PCSK9 in the degradation of major histocompatibility complex I (MHC-I) receptors and the immune system as well as in other physiological activities. This review highlights the complex crosstalk between PCSK9, lipid metabolism and immunosuppression and underlines the latest advances in understanding the involvement of this convertase in other critical functions. We present a comprehensive assessment of the different strategies targeting PCSK9 and show how these approaches could be extended to future therapeutic options to treat cancers with a main focus on the liver.

Targeting PCSK9 in Liver Cancer Cells Triggers Metabolic Exhaustion and Cell Death by Ferroptosis.

Deregulated lipid metabolism is a common feature of liver cancers needed to sustain tumor cell growth and survival. We aim at taking advantage of this vulnerability and rewiring the oncogenic metabolic hub by targeting the key metabolic player pro-protein convertase subtilisin/kexin type 9 (PCSK9). We assessed the effect of PCSK9 inhibition using the three hepatoma cell lines Huh6, Huh7 and HepG2 and validated the results using the zebrafish in vivo model. PCSK9 deficiency led to strong inhibition of cell proliferation in all cell lines. At the lipid metabolic level, PCSK9 inhibition was translated by an increase in intracellular neutral lipids, phospholipids and polyunsaturated fatty acids as well as a higher accumulation of lipid hydroperoxide. Molecular signaling analysis involved the disruption of the sequestome 1/Kelch-like ECH-associated protein 1/nuclear factor erythroid 2-related factor 2 (p62/Keap1/Nrf2) antioxidative axis, leading to ferroptosis, for which morphological features were confirmed by electron and confocal microscopies. The anti-tumoral effects of PCSK9 deficiency were validated using xenograft experiments in zebrafish. The inhibition of PCSK9 was effective in disrupting the oncometabolic process, inducing metabolic exhaustion and enhancing the vulnerability of cancer cells to iron-triggered lipid peroxidation. We provide strong evidence supporting the drug repositioning of anti-PCSK9 approaches to treat liver cancers.

Rewiring Lipid Metabolism by Targeting PCSK9 and HMGCR to Treat Liver Cancer.

Alterations in lipid handling are an important hallmark in cancer. Our aim here is to target key metabolic enzymes to reshape the oncogenic lipid metabolism triggering irreversible cell breakdown. We targeted the key metabolic player proprotein convertase subtilisin/kexin type 9 (PCSK9) using a pharmacological inhibitor (R-IMPP) alone or in combination with 3-hydroxy 3-methylglutaryl-Coenzyme A reductase (HMGCR) inhibitor, simvastatin. We assessed the effect of these treatments using 3 hepatoma cell lines, Huh6, Huh7 and HepG2 and a tumor xenograft in chicken choriorallantoic membrane (CAM) model. PCSK9 deficiency led to dose-dependent inhibition of cell proliferation in all cell lines and a decrease in cell migration. Co-treatment with simvastatin presented synergetic anti-proliferative effects. At the metabolic level, mitochondrial respiration assays as well as the assessment of glucose and glutamine consumption showed higher metabolic adaptability and surge in the absence of PCSK9. Enhanced lipid uptake and biogenesis led to excessive accumulation of intracellular lipid droplets as revealed by electron microscopy and metabolic tracing. Using xenograft experiments in CAM model, we further demonstrated the effect of anti-PCSK9 treatment in reducing tumor aggressiveness. Targeting PCSK9 alone or in combination with statins deserves to be considered as a new therapeutic option in liver cancer clinical applications.

Immuno-Metabolic Modulation of Liver Oncogenesis by the Tryptophan Metabolism.

Metabolic rewiring in tumor cells is a major hallmark of oncogenesis. Some of the oncometabolites drive suppressive and tolerogenic signals from the immune system, which becomes complicit to the advent and the survival of neoplasia. Tryptophan (TRP) catabolism through the kynurenine (KYN) pathway was reported to play immunosuppressive actions across many types of cancer. Extensive debate of whether the culprit of immunosuppression was the depletion of TRP or rather KYN accumulation in the tumor microenvironment has been ongoing for years. Results from clinical trials assessing the benefit of inhibiting key limiting enzymes of this pathway such as indoleamine 2,3-dioxygenase (IDO1) or tryptophan 2,3-dioxygenase (TDO2) failed to meet the expectations. Bearing in mind the complexity of the tumoral terrain and the existence of different cancers with IDO1/TDO2 expressing and non-expressing tumoral cells, here we present a comprehensive analysis of the TRP global metabolic hub and the driving potential of the process of oncogenesis with the main focus on liver cancers.

Hepatocellular Carcinoma and Statins.

HMG-CoA reductase inhibitors (known as statins) are commonly prescribed worldwide for the management of coronary heart disease and the underlying dyslipidemia. This class of drugs has been shown to infer a significant decrease in the risk of cardiovascular morbidity and mortality. Only recently though have the beneficial effects of statins in other diseases such as non-alcoholic steatohepatitis been highlighted. Importantly, also, multiple studies have revealed that statin use was associated with lower cancer-associated mortality across multiple types of cancers. This work aims to review those studies with a particular focus on liver cancer. We also provide a review of the proposed mechanisms of action describing how statins can induce chemo-preventive and antitumor effects.

Targeting Lipid Metabolism in Liver Cancer.

Cancer cells are highly dependent on different metabolic pathways for sustaining their survival, growth, and proliferation. Lipid metabolism not only provides the energetic needs of the cells but also provides the raw material for cellular growth and the signaling molecules for many oncogenic pathways. Mainly processed in the liver, lipids play an essential role in the physiology of this organ and in the pathological progression of many diseases such as metabolic syndrome and hepatocellular carcinoma (HCC). The progression of HCC is associated with inflammation and complex metabolic reprogramming, and its prognosis remains poor because of the lack of effective therapies despite many years of dedicated research. Defects in hepatic lipid metabolism induce abnormal gene expression and rewire many cellular pathways involved in oncogenesis and metastasis, implying that interfering with lipid metabolism within the tumor and the surrounding microenvironment may be a novel therapeutic approach for treating liver cancer patients. Therefore, this review focuses on the latest advances in drugs targeting lipid metabolism and leading to promising outcomes in preclinical studies and some ongoing clinical trials.

Tracking cellular and molecular changes in a species-specific manner during experimental tumor progression in vivo.

Hepatoblastoma (HBL) is a pediatric liver cancer with defined molecular alterations driving its progression. Here, we describe an animal model for HBL on the chick chorioallantoic membrane (CAM), which recapitulates relevant features of HBL in patients. Expression of classic tumor-associated proteins such as ß-catenin, EpCAM and CK19 was maintained in acini-like organized tumors on CAM, as was synthesis of AFP, a tumor marker used for monitoring patient response. RNA sequencing revealed an unexpected molecular evolution of HBL cells on the CAM, with significant deregulation of more than 6,000 genes including more than half of all HOX genes. Bioinformatic analysis distinguish between tumor cell-expressed genes and chick genes, thereby shedding new light on the complex interactions taking place during HBL progression. Importantly, human tumor suppressive ribosomal genes were downregulated after implantation, whereas mitochondrial genes encoding for anti-apoptotic peptides were strongly induced in vivo. Meprin-1α expression was increased during evolution of CAM tumors and confirmed by immunohistochemistry. Cisplatin, a commonly used chemotherapeutic agent for HBL, showed significant anti-tumoral effects. Our results broaden the understanding of the molecular adaptation process of human cancer cells to the microenvironment and might help to elaborate novel therapeutic concepts for the treatment of this pediatric liver tumor.

Vitiligo therapy: restoring immune privilege?

The therapeutic hypothesis proposed by Speeckaert and van Geel in this issue (1) is based on the dramatic effects of the new drugs targeting immune privilege checkpoints (PD1/PDL, CTLA4) in current advanced melanoma therapy as major inductors of vitiligo changes in the skin. Such striking clinical manifestations cannot be classified as mere side effects without considering possible consequences for spontaneously occurring vitiligo."

Specific autoantigens in experimental autoimmunity-associated atherosclerosis.

Higher cardiovascular morbidity in patients with a wide range of autoimmune diseases highlights the importance of autoimmunity in promoting atherosclerosis. Our purpose was to investigate the mechanisms of accelerated atherosclerosis and identified vascular autoantigens targeted by autoimmunity. We created a mouse model of autoimmunity-associated atherosclerosis by transplanting bone marrow from FcγRIIB knockout (FcRIIB(-/-)) mice into LDL receptor knockout mice. We characterized the cellular and molecular mechanisms of atherogenesis and identified specific aortic autoantigens using serologic proteomic studies. En face lesion area analysis showed more aggressive atherosclerosis in autoimmune mice compared with control mice (0.64 ± 0.12 vs 0.32 ± 0.05 mm(2); P < 0.05, respectively). At the cellular level, FcRIIB(-/-) macrophages showed significant reduction (46-72%) in phagocytic capabilities. Proteomic analysis revealed circulating autoantibodies in autoimmune mice that targeted 25 atherosclerotic lesion proteins, including essential components of adhesion complex, cytoskeleton, and extracellular matrix, and proteins involved in critical functions and pathways. Microscopic examination of atherosclerotic plaques revealed essential colocalization of autoantibodies with endothelial cells, their adherence to basement membranes, the internal elastica lamina, and necrotic cores. The new vascular autoimmunosome may be a useful target for diagnostic and immunotherapeutic interventions in autoimmunity-associated diseases that have accelerated atherosclerosis.-Merched, A. J., Daret, D., Li, L., Franzl, N., Sauvage-Merched, M. Specific autoantigens in experimental autoimmunity-associated atherosclerosis.

Sonic hedgehog mediates a novel pathway of PDGF-BB-dependent vessel maturation.

Recruitment of mural cells (MCs), namely pericytes and smooth muscle cells (SMCs), is essential to improve the maturation of newly formed vessels. Sonic hedgehog (Shh) has been suggested to promote the formation of larger and more muscularized vessels, but the underlying mechanisms of this process have not yet been elucidated. We first identified Shh as a target of platelet-derived growth factor BB (PDGF-BB) and found that SMCs respond to Shh by upregulating extracellular signal-regulated kinase 1/2 and Akt phosphorylation. We next showed that PDGF-BB-induced SMC migration was reduced after inhibition of Shh or its signaling pathway. Moreover, we found that PDGF-BB-induced SMC migration involves Shh-mediated motility. In vivo, in the mouse model of corneal angiogenesis, Shh is expressed by MCs of newly formed blood vessels. PDGF-BB inhibition reduced Shh expression, demonstrating that Shh is a target of PDGF-BB, confirming in vitro experiments. Finally, we found that in vivo inhibition of either PDGF-BB or Shh signaling reduces NG2(+) MC recruitment into neovessels and subsequently reduces neovessel life span. Our findings demonstrate, for the first time, that Shh is involved in PDGF-BB-induced SMC migration and recruitment of MCs into neovessels and elucidate the molecular signaling pathway involved in this process.

Nutrigenetics and nutrigenomics of atherosclerosis.

The latest genome-wide association studies (GWAS) have re-energized our effort to understand the genetic basis of atherosclerotic cardiovascular disease. Although the knowledge generated by GWAS has confirmed that mediators of inflammation and perturbed lipid metabolism are major players in cardiovascular disease (CVD) development, much of individual disease heritability remains unexplained by the variants identified through GWAS. Moreover, results from interventions that aim at the pharmaceutical modification of lipid parameters fall short of expectation. These elusive treatment goals based on heritability studies highlight a key supportive, and perhaps even primary, role of nutritional therapy to achieve better health outcomes. Nonetheless, effective and specific interventions for CVD prevention using principles of "personalized" nutrition require a better knowledge of gene-diet interactions, an area that remains poorly explored. Dietary fatty acids such as omega-3 polyunsaturated fatty acids (PUFAs) are an excellent example of a widely studied "environment" that interacts with the genetic makeup in relation to CVD. A thorough exploration of the nutrigenomics and nutrigenetics of omega-3 PUFAs is key to understanding the etiology, and developing effective preventive measures. In this review, we will summarize the current state of knowledge of genetic interactions with omega-3 PUFAs in modulating lipid metabolism and inflammation, and defining health outcomes. Nutrigenetics and nutrigenomics are still in their infancy with respect to CVD prediction and therapy. Integration of the progress in the omics, including metabolomics, lipidomics, transcriptomics, and proteomics, coupled with advances in nutrigenomic and nutrigenetic research will move us towards personalized medicine as the ultimate paradigm of responsible clinical practice.

Nutrigenetic disruption of inflammation-resolution homeostasis and atherogenesis.

BACKGROUND/AIM: Pro-resolving and anti-inflammatory mediator products of murine 12/15-lipoxygenase (LOX) exhibit potent actions on vascular inflammation and protect against the progression of atherosclerosis. The present study was designed to determine whether augmenting dietary lipids modulates the body's endogenous anti-inflammatory pro-resolving mechanisms and promotes atherosclerosis. METHODS/RESULTS: We investigated the biometabolic consequences of variations in lipid mediator biosynthesis using genetic knockout and overexpression models of 12/15-LOX mice fed the commonly used 'Western diet'. Unexpectedly, this high-fat diet annulled the protective actions of 12/15-LOX, and the combination of a Western diet and 12/15-LOX overexpression paradoxically promoted inflammation leading to production of diet-related and 12/15-LOX-dependent blood mediators that differentially activated endothelial cells via expression of ICAM-1. Hyperlipidemia not only affected the biosynthesis of lipoxin A4, a key pro-resolving mediator, but also disrupted the protective pro-resolving function of 12/15-LOX products, and the enzyme pathway no longer protected against atherosclerosis in vivo. CONCLUSION: We uncovered a novel mechanism whereby a high-fat diet as well as hyperlipidemia disrupt the homeostasis of inflammation resolution. These findings underscore the importance of dietary essential PUFAs and LOX-derived lipid mediators in combination with lipid-lowering agents in the prevention and treatment of atherosclerotic cardiovascular diseases.

Beta2 integrins modulate the initiation and progression of atherosclerosis in low-density lipoprotein receptor knockout mice.

AIMS: Beta2 integrin-mediated adhesion is thought to be a key event in cardiovascular disease. However, results of clinical trials targeting these molecules have been disappointing. Here, we investigated the effect of inactivation of beta2 integrins at different stages of atherosclerosis by timed bone marrow transplantation (BMT) of CD18(-/-) cells in low-density lipoprotein receptor knockout (LDLR(-/-)) mice. METHODS AND RESULTS: Early BMT before fatty streak formation revealed a short-term protective effect of CD18 (34% atherosclerotic lesion reduction). Once fatty streak lesions had developed (5-week atherogenic diet) before BMT, beta2 integrin expression did not affect lesion progression. However, after the establishment of more mature lesions (pre-feeding mice the atherogenic diet for 10 weeks), CD18(+/+) BMT enhanced atherosclerosis (36%) lesion progression compared with CD18(-/-) BMT. Furthermore, beta2 integrins modulated the capacity of isolated peritoneal macrophages to take up acetylated LDL and native LDL and to phagocytose apoptotic cells, possibly via CD18-dependent mitogen-activated protein kinase signalling. Gene expression profile of CD18(-/-) and CD18(+/+) macrophages revealed significant differences in putative protective as well as atherogenic functions. CONCLUSION: beta2 integrin-mediated interaction between leucocytes and the vessel wall is a time-dependent and dynamic process. During the initiation phase, it protects against atherosclerotic lesion formation. However, with the evolution of the lesion and chronic exposure to dyslipidaemia, beta2 integrins' pro-atherogenic action becomes dominant, accelerating the atherosclerotic process.

Atherosclerosis: evidence for impairment of resolution of vascular inflammation governed by specific lipid mediators.

Atherosclerosis is now recognized as an inflammatory disease involving the vascular wall. Recent results indicate that acute inflammation does not simply passively resolve as previously assumed but is actively terminated by a homeostatic process that is governed by specific lipid-derived mediators initiated by lipoxygenases. Experiments with animals and humans support a proinflammatory role for the 5-lipoxygenase system. In contrast, results from animal experiments show a range of responses with the 12/15-lipoxygenase pathways in atherosclerosis. To date, the only two clinical epidemiology human studies both support an antiatherogenic role for 12/15-lipoxygenase downstream actions. We tested the hypothesis that atherosclerosis results from a failure in the resolution of local inflammation by analyzing apolipoprotein E-deficient mice with 1) global leukocyte 12/15-lipoxygenase deficiency, 2) normal enzyme expression, or 3) macrophage-specific 12/15-lipoxygenase overexpression. Results from these indicate that 12/15-lipoxygenase expression protects mice against atherosclerosis via its role in the local biosynthesis of lipid mediators, including lipoxin A(4), resolvin D1, and protectin D1. These mediators exert potent agonist actions on macrophages and vascular endothelial cells that can control the magnitude of the local inflammatory response. Taken together, these findings suggest that a failure of local endogenous resolution mechanisms may underlie the unremitting inflammation that fuels atherosclerosis.

Mechanical stretch inhibits oxidized low density lipoprotein-induced apoptosis in vascular smooth muscle cells by up-regulating integrin alphavbeta3 and stablization of PINCH-1.

To determine the mechanisms involved in regulating the balance between apoptosis and survival in vascular smooth muscle cells (VSMC), we studied anti-apoptotic stimuli that can counteract pro-apoptotic events in the process of early atherosclerotic lesions formation. Such a process involves VSMC accumulation even in the presence of oxidized low density lipoprotein (Ox-LDL). In the arch of the aorta, we find that integrin beta3 is higher than in descending arteries. In the advanced atherosclerosis lesion, we found an inverse correlation between the level of integrin beta3 and apoptosis (deoxynucleotidyltransferase-mediated dUTP nick end labeling-positive). We also found an increase in integrin alphaVbeta3 (but not integrin beta1) expression in VSMC that are subjected to cyclic stretch. VSMC subjected to stretch as well as VSMC with forced expression of alphaVbeta3 were demonstrated to be resistant to Ox-LDL-induced cytoskeleton disruption and apoptosis. The anti-apoptotic effect of stretch was abolished by treatment of VSMC with small interfering RNA against integrin beta3 as well as VSMC isolated from integrin beta3 knock-out mice. Disruption of the cytoskeleton abolished the protective effect of stretch or alphaVbeta3 overexpression on Ox-LDL-induced activation of Bax and apoptosis. We also demonstrated that stretch-mediated protection of Ox-LDL-induced apoptosis involved stabilization of PINCH-1; Ox-LDL decreased the level of PINCH-1, but the application of mechanical stretch or overexpression of either integrin beta1 or integrin beta3 prevented its down-regulation. In the arteries of integrin beta3 null mice, there were lower levels of PINCH-1 and ILK-1. Moreover, deletion of integrin beta3 in VSMC abolished the stretch protective effect on PINCH-1. Small interfering RNA-mediated knockdown of PINCH-1 disrupted the cytoskeleton and caused apoptosis of VSMC. These findings provided experimental evidence that mechanical stretch acted as a survival factor in the arches of aortas. Furthermore, mechanical stretch prevented VSMC from apoptosis via a mechanism that involves alphaVbeta3 integrin expression, stabilization of PINCH-1, and remodeling of the cytoskeleton.

Nicotine induces proinflammatory responses in macrophages and the aorta leading to acceleration of atherosclerosis in low-density lipoprotein receptor(-/-) mice.

OBJECTIVE: We investigated the molecular mechanism of nicotine-accelerated atherosclerosis in a hyperlipidemic low-density lipoprotein receptor(-/-) mouse model. METHODS AND RESULTS: Low-density lipoprotein receptor(-/-) mice received time-release nicotine or placebo pellets for 90 days. Aortic lesion size was 2.5 times larger in nicotine-treated than in placebo-treated mice (P<0.001). A mild increase in lipids was seen in treated mice. We quantified 18 different serum cytokines and found a significant increase of tumor necrosis factor alpha, interleukin 1beta, and keratinocyte-derived chemokine in nicotine-treated mice. Among 107 nuclear factor kappaB (NF-kappaB) target genes screened from the aorta, we found that nicotine treatment upregulated only 4 atherogenic genes including vascular adhesion molecule 1 and cyclooxygenase 2 on day 60 and platelet-derived growth factor B and platelet 12-lipoxygenase on day 90. At the cellular level, nicotine induced tumor necrosis factor alpha and inducible nitric oxide synthase expression in RAW264.7 cells via the nicotinic acetylcholine receptors. Induction was confirmed in peritoneal macrophages isolated from nicotine-treated mice. Finally, we showed that preconditioned medium from nicotine-treated RAW264.7 cells activated NF-kappaB in human smooth muscle cells and vascular endothelial cells as evidenced by nuclear localization and electromobility shift assay. CONCLUSIONS: Chronic nicotine exposure augments atherosclerosis by enhancing the production of proinflammatory cytokines by macrophages, which, in turn, activate atherogenic NF-kappaB target genes in the aortic lesions.

Absence of p21Waf1/Cip1/Sdi1 modulates macrophage differentiation and inflammatory response and protects against atherosclerosis.

BACKGROUND: The tumor suppressor p53 protects against atherosclerosis progression in several different mouse models. A major target of p53 is p21, the cyclin-dependent kinase inhibitor that regulates entry into the cell cycle of different types of cells, including stem cells. p21 is also involved in the maturation and differentiation of monocytes into macrophages. METHODS AND RESULTS: We studied the effect of p21Waf1 inactivation on atherosclerosis development in apolipoprotein E-deficient mice (apoE-/-). Contrary to previous data suggesting a protective role for p21, we found that absence of p21, either globally or in bone marrow-derived cells, protects against atherosclerosis. Atherosclerotic lesions of p21-/-/apoE-/- mice exhibit a more stable phenotype, with increased apoptosis and reduced inflammatory vascular cell adhesion molecule-1 immunostaining but no difference in cellular proliferation compared with lesions of p21+/+/apoE-/- mice. Because bone marrow-derived cells mediate many of the effects of p21, we examined the expression profile of 23 genes in macrophages using real-time polymerase chain reaction. Compared with their p21+/+ counterparts, peritoneal macrophages of p21-/- mice express lower levels of proinflammatory markers, including macrophage inflammatory proteins 1 and 2 and interleukin-1alpha, and higher levels of putative protective genes, such as scavenger receptor type B-I and LDL receptor-related protein. Furthermore, we found that, in comparison with p21+/+ macrophages, p21-/- macrophages displayed increased phagocytic activity toward fluorescent latex microspheres as well as apoptotic cells, thus uncovering a novel mechanism of the antiinflammatory activity of p21-/- macrophages. CONCLUSIONS: Loss of p21 protects against atherosclerosis in apoE-/- mice. The data underscore the important role of p21 in macrophage function and inflammation and provide insight into the mechanism of the proatherogenic effect of p21.