Attenuation of early atherogenesis in low-density lipoprotein receptor-deficient mice by proteasome inhibition

Targeting endothelial vascular cell adhesion molecule-1 in atherosclerosis: drug discovery and development of vascular cell adhesion molecule-1-directed novel therapeutics

Vascular cell adhesion molecule-1 (VCAM-1) has been well established as a critical contributor to atherosclerosis and consequently as an attractive therapeutic target for anti-atherosclerotic drug candidates. Many publications have demonstrated that disrupting the VCAM-1 function blocks monocyte infiltration into the sub-endothelial space, which effectively prevents macrophage maturation and foam cell transformation necessary for atherosclerotic lesion formation. Currently, most VCAM-1-inhibiting drug candidates in pre-clinical and clinical testing do not directly target VCAM-1 itself but rather down-regulate its expression by inhibiting upstream cytokines and transcriptional regulators. However, the pleiotropic nature of these regulators within innate immunity means that optimizing dosage to a level that suppresses pathological activity while preserving normal physiological function is extremely challenging and oftentimes infeasible. In recent years, highly specific pharmacological strategies that selectively inhibit VCAM-1 function have emerged, particularly peptide- and antibody-based novel therapeutics. Studies in such VCAM-1-directed therapies so far remain scarce and are limited by the constraints of current experimental atherosclerosis models in accurately representing the complex pathophysiology of the disease. This has prompted the need for a comprehensive review that recounts the evolution of VCAM-1-directed pharmaceuticals and addresses the current challenges in novel anti-atherosclerotic drug development.

Targeting VCAM-1: a therapeutic opportunity for vascular damage

INTRODUCTION

The vascular cell adhesion molecule (VCAM-1) is a transmembrane sialoglycoprotein detected in activated endothelial and vascular smooth muscle cells involved in the adhesion and transmigration of inflammatory cells into damaged tissue. Widely used as a pro-inflammatory marker, its potential role as a targeting molecule has not been thoroughly explored.

AREAS COVERED

We discuss the current evidence supporting the potential targeting of VCAM-1 in atherosclerosis, diabetes, hypertension and ischemia/reperfusion injury.

EXPERT OPINION

There is emerging evidence that VCAM-1 is more than a biomarker and may be a promising therapeutic target for vascular diseases. While there are neutralizing antibodies that allow preclinical research, the development of pharmacological tools to activate or inhibit this protein are required to thoroughly assess its therapeutic potential.

Effect of bortezomib on fatty liver in a rat model of atherosclerosis

Introduction and Aim: Fatty liver is associated with atherosclerosis even though the exact mechanism remains unknown. Fatty liver and atherosclerosis correlate with inflammation. Interleukin 6 (IL-6) is recognized as an inflammatory marker. Bortezomib is a proteasome inhibitor that will inhibit the proteasome pathway and is expected to inhibit inflammation in atherosclerosis. The current research aimed to investigate the effect of bortezomib on the fatty liver of atherosclerosis rats and to analyze its correlation with serum IL-6 concentration.   Materials and Methods: Experimental subjects were 18 male Wistar rats (Rattus novergicus) divided into three treatment groups, namely atherosclerosis group (I), atherosclerosis + bortezomib group (II), and control group (III). Bortezomib (50 ?g/kg BW) was given twice intraperitoneally, on day 1 and day 3. The presence of fatty liver was evaluated using the percentage system. Serum IL-6 concentrations were measured using enzyme-linked immunosorbent assay kits.   Results: The highest amount of fatty liver was found in the atherosclerosis group (group I) (38.33%), while the lowest was in the control group (group III) (5.83%). There was a decreasing fatty liver percentage due to bortezomib administration (group II) (29.17%), and it was statistically significant. There is a significant correlation between the degree of fatty liver and serum IL-6 concentration.   Conclusion: The administration of bortezomib 50 ?g/kg BW in atherosclerosis model rats can reduce the occurrence of fatty liver by reducing the inflammatory process.

Effect of Proteasome Inhibitor on Vascular Cell Adhesion Molecule-1 (VCAM-1) and Intercellular Adhesion Molecule-1 (ICAM-1) Expressions in Rat Model of Atherosclerosis

BACKGROUND

The effect of proteasome inhibitors on atherosclerosis is known to vary depending on the atherosclerosis stage. Previous studies have shown that the highest proteasome expression in atherosclerotic lesions is at the progression stage. Adhesion molecules play a role in the progression stage of atherosclerosis, but no studies have analyzed the effect of proteasome inhibitors on the expression of adhesion molecules at this stage.

METHODS

This experimental study aimed to analyze the effect of a proteasome inhibitor, namely bortezomib, on the vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule1 (ICAM-1) expressions in blood vessels of rat model of atherosclerosis at the progression stage. This study used 18 male Wistar rats divided into three groups, i.e. group I that is the control group given standard feed, group II induced by atherosclerosis, and group III induced by atherosclerosis and given bortezomib. Atherosclerosis induction was performed using vitamin D3 (700,000 IU/kg) orally by gastric intubation on the 1st day and atherogenic feed given for four days. Bortezomib 50 µg/kgBW/day was administered intra-peritoneally. The expression of VCAM-1 and ICAM-1 molecules was measured using immunohistochemistry and analyzed quantitatively using Adobe Photoshop software.

RESULTS

The statistical test showed differences in VCAM-1 expression between atherosclerosis + Bortezomib group and atherosclerosis group, but there were no differences in the expression of ICAM-1 and atherosclerotic lesions between the groups.

CONCLUSION

Administration of bortezomib 50μg/kg for four days in progressive atherosclerosis model rats can inhibit VCAM-1 expression, although it does not affect ICAM-1 expression and cannot inhibit atherosclerotic lesion formation.

Bortezomib alleviates myocardial ischemia reperfusion injury via enhancing of Nrf2/HO-1 signaling pathway

Bortezomib is a classical proteasome inhibitor and previous researches have reported its roles of anti-oxidation and anti-inflammatory functions in various diseases. However, the role of Bortezomib in myocardial ischemia reperfusion injury (MIRI) is unclear. Thus, our research seeks to reveal the protective effects of Bortezomib pretreatment in the mice model of MIRI. First, by the optimization of Bortezomib concentration and pretreatment timepoints, we found that 0.5 mg/kg Bortezomib pretreatment 2 h before MIRI significantly attenuated pathological damage and neutrophil infiltration. Then we found that pretreatment with Bortezomib obviously increased myocardial systolic function ((left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS)) and decreased infarct size, as well as serum Troponin T levels. Meanwhile, Bortezomib pretreatment also remarkably augmented oxidative stress related protein levels of Superoxide dismutase [Cu-Zn] (SOD1), Catalase (CAT) and Glutathione (GSH), while reactive oxygen species (ROS) contents and Malonaldehyde (MDA) protein level were significantly reduced. Mechanistically, Bortezomib pretreatment significantly promoted nuclear translocation of transcriptional factor nuclear factor erythroid 2-related factor 2(Nrf2) and Heme Oxygenase 1(HO-1) expression. Interestingly, co-treatment with ML-385, a new type and selective Nrf2 inhibitor, counteracted antioxidative effects induced by Bortezomib pretreatment. In conclusion, Bortezomib pretreatment mitigates MIRI by inhibiting oxidative damage which is regulated by Nrf2/HO-1 signaling pathway.

Deficiency of LMP10 Attenuates Diet-Induced Atherosclerosis by Inhibiting Macrophage Polarization and Inflammation in Apolipoprotein E Deficient Mice

Macrophage polarization and inflammation are key factors for the onset and progression of atherosclerosis. The immunoproteasome complex consists of three inducible catalytic subunits (LMP2, LMP10, and LMP7) that play a critical role in the regulation of these risk factors. We recently demonstrated that the LMP7 subunit promotes diet-induced atherosclerosis via inhibition of MERTK-mediated efferocytosis. Here, we explored the role of another subunit of LMP10 in the disease process, using ApoE knockout (ko) mice fed on an atherogenic diet (ATD) containing 0.5% cholesterol and 20% fat for 8 weeks as an in vivo atherosclerosis model. We observed that ATD significantly upregulated LMP10 expression in aortic lesions, which were primarily co-localized with plaque macrophages. Conversely, deletion of LMP10 markedly attenuated atherosclerotic lesion area, CD68⁺ macrophage accumulation, and necrotic core expansion in the plaques, but did not change plasma metabolic parameters, lesional SM22α⁺ smooth muscle cells, or collagen content. Myeloid-specific deletion of LMP10 by bone marrow transplantation resulted in similar phenotypes. Furthermore, deletion of LMP10 remarkably reduced aortic macrophage infiltration and increased M2/M1 ratio, accompanied by decreased expression of pro-inflammatory M1 cytokines (MCP-1, IL-1, and IL-6) and increased expression of anti-inflammatory M2 cytokines (IL-4 and IL-10). In addition, we confirmed in cultured macrophages that LMP10 deletion blunted macrophage polarization and inflammation during ox-LDL-induced foam cell formation in vitro, which was associated with decreased IκBα degradation and NF-κB activation. Our results show that the immunoproteasome subunit LMP10 promoted diet-induced atherosclerosis in ApoE ko mice possibly through regulation of NF-κB-mediated macrophage polarization and inflammation. Targeting LMP10 may represent a new therapeutic approach for atherosclerosis.

Immunoproteasome subunit β5i regulates diet-induced atherosclerosis through altering MERTK-mediated efferocytosis in Apoe knockout mice

The immunoproteasome contains three catalytic subunits (β1i, β2i and β5i) that are important modulators of immune cell homeostasis. A previous study showed a correlation between β5i and human atherosclerotic plaque instability; however, the causative role of β5i in atherosclerosis and the underlying mechanisms remain unknown. Here we explored this issue in apolipoprotein E (Apoe) knockout (eKO) mice with genetic deletion or pharmacological inhibition of β5i. We found that β5i expression was upregulated in lesional macrophages after an atherogenic diet (ATD). β5i/Apoe double KO (dKO) mice fed on the ATD had a significant decrease in both lesion area and necrotic core area, compared with eKO controls. Moreover, dKO mice had less caspase-3⁺ apoptotic cell accumulation but enhanced efferocytosis of apoptotic cells and increased expression of Mer receptor tyrosine kinase (MERTK). Consistently, similar phenotypes were observed in eKO mice transplanted with dKO bone marrow or treated with β5i-specific inhibitor PR-957. Mechanistic studies in vitro revealed that β5i deletion reduced IκBα degradation and inhibited NF-κB activation, promoting Mertk transcription and efferocytosis, thereby attenuating apoptotic cell accumulation. In conclusion, we demonstrate that β5i plays an important role in diet-induced atherosclerosis by altering MERTK-mediated efferocytosis. β5i might be a potential pharmaceutical target against atherosclerosis. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Impact of Dysfunctional Protein Catabolism on Macrophage Cholesterol Handling

Protein catabolism in macrophages, which is accomplished mainly through autophagy- lysosomal degradation, ubiquitin-proteasome system, and calpains, is disturbed in atheroprone vessels. Moreover, growing evidence suggests that defects in protein catabolism interfere with cholesterol handling in macrophages. Indeed, decreases in autophagy facilitate the deposition of cholesterol in atheroprone macrophages and the subsequent development of vulnerable atherosclerotic plaques due to impaired catabolism of lipid droplets and limited efferocytic clearance of dead cells. The proteasome is responsible for the degradation of ATP-binding cassette transporters, which leads to impaired cholesterol efflux from macrophages. Overactivation of conventional calpains contributes to excessive processing of functional proteins, thereby accelerating receptor-mediated uptake of oxidized low-density lipoproteins (LDLs) and slowing cholesterol efflux. Furthermore, calpain-6, an unconventional nonproteolytic calpain in macrophages, potentiates pinocytotic uptake of native LDL and attenuates the efferocytic clearance of dead cells. Herein, we focus on recent progress in understanding how defective protein catabolism is associated with macrophage cholesterol handling and subsequent atherogenesis.

Proteasome biology and therapeutics in cardiac diseases

The ubiquitin proteasome system (UPS) is the major pathway for intracellular protein degradation in most organs, including the heart. UPS controls many fundamental biological processes such as cell cycle, cell division, immune responses, antigen presentation, apoptosis, and cell signaling. The UPS not only degrades substrates but also regulates activity of gene transcription at the post-transcription level. Emerging evidence suggests that impairment of UPS function is sufficient to cause a number of cardiac diseases, including heart failure, cardiomyopathies, hypertrophy, atrophy, ischemia-reperfusion, and atherosclerosis. Alterations in the expression of UPS components, changes in proteasomal peptidase activities and increased ubiquitinated and oxidized proteins have also been detected in diabetic cardiomyopathy (DCM). However, the pathophysiological role of the UPS in DCM has not been examined. Recently, in vitro and in vivo studies have proven highly valuable in assessing effects of various stressors on the UPS and, in some cases, suggesting a causal link between defective protein clearance and disease phenotypes in different cardiac diseases, including DCM. Translation of these findings to human disease can be greatly strengthened by corroboration of discoveries from experimental model systems using human heart tissue from well-defined patient populations. This review will summarize the general role of the UPS in different cardiac diseases, with major focus on DCM, and on recent advances in therapeutic development.

Cardiovascular oncology: exploring the effects of targeted cancer therapies on atherosclerosis

PURPOSE OF REVIEW

Targeted cancer therapies have revolutionized the treatment of cancer in the past decade, but cardiovascular toxicity is a rising problem in cancer patients. Here we discuss the effects of targeted cancer therapies on atherosclerosis. Increasing the awareness of these adverse effects will promote the development of evidence-based preventive strategies in the emerging field of cardiovascular oncology.

RECENT FINDINGS

Vascular endothelial growth factor inhibitors, immunomodulatory imide drugs, tyrosine kinase inhibitors and immune checkpoint inhibitors are successfully used as treatment for many types of solid and hematologic malignancies. However, clinical and experimental studies have demonstrated that these drugs can drive atherosclerosis, thereby causing adverse cardiovascular events such as myocardial infarction, stroke and peripheral arterial occlusive diseases.

SUMMARY

In this review, we discuss how on-target and off-target effects of novel cancer drugs may affect atherosclerosis and we postulate how these cardiovascular adverse events can be prevented in the future.

Defective Protein Catabolism in Atherosclerotic Vascular Inflammation

Vascular inflammation in atheroprone vessels propagates throughout the arterial tree in dyslipidemic patients, thereby accelerating atherosclerotic progression. To elucidate the mechanism of vascular inflammation, most previous studies have focused on inflammation-related signals that are sent in response to vasoactive stimuli. However, it is also important to understand how normal blood vessels become defective and start degenerating. Growing evidence suggests that major protein catabolism pathways, including the ubiquitin-proteasome, autophagy, and calpain systems, are disturbed in atheroprone vessels and contribute to the pathogenesis of atherosclerosis. Indeed, dysregulation of ubiquitin-proteasome pathways results in the accumulation of defective proteins in blood vessels, leading to vascular endothelial dysfunction and apoptosis in affected cells. Impaired autophagy-lysosomal degradation affects smooth muscle cell transformation and proliferation, as well as endothelial integrity and phagocytic clearance of cellular corpses. Dysregulation of the calpain system confers proatherogenic properties to endothelial cells, smooth muscle cells, and macrophages. In this review article, we will discuss the current information available on defective protein catabolism in atheroprone vessels and its potential interrelation with inflammation-related signals.

Immunoproteasome subunit ß5i/LMP7-deficiency in atherosclerosis

Management of protein homeostasis by the ubiquitin-proteasome system is critical for atherosclerosis development. Recent studies showed controversial results on the role of immunoproteasome (IP) subunit β5i/LMP7 in maintenance of protein homeostasis under cytokine induced oxidative stress. The present study aimed to investigate the effect of β5i/LMP7-deficiency on the initiation and progression of atherosclerosis as a chronic inflammatory, immune cell driven disease. LDLR-/-LMP7-/- and LDLR-/- mice were fed a Western-type diet for either 6 or 24 weeks to induce early and advanced stage atherosclerosis, respectively. Lesion burden was similar between genotypes in both stages. Macrophage content and abundance of polyubiquitin conjugates in aortic root plaques were unaltered by β5i/LMP7-deficiency. In vitro experiments using bone marrow-derived macrophages (BMDM) showed that β5i/LMP7-deficiency did not influence macrophage polarization or accumulation of polyubiquitinated proteins and cell survival upon hydrogen peroxide and interferon-γ treatment. Analyses of proteasome core particle composition by Western blot revealed incorporation of standard proteasome subunits in β5i/LMP7-deficient BMDM and spleen. Chymotrypsin-, trypsin- and caspase-like activities assessed by using short fluorogenic peptides in BMDM whole cell lysates were similar in both genotypes. Taken together, deficiency of IP subunit β5i/LMP7 does not disturb protein homeostasis and does not aggravate atherogenesis in LDLR-/- mice.

The Effect of Low-Dose Proteasome Inhibition on Pre-Existing Atherosclerosis in LDL Receptor-Deficient Mice

Dysfunction of the ubiquitin-proteasome system (UPS) has been implicated in atherosclerosis development. However, the nature of UPS dysfunction has been proposed to be specific to certain stages of atherosclerosis development, which has implications for proteasome inhibition as a potential treatment option. Recently, low-dose proteasome inhibition with bortezomib has been shown to attenuate early atherosclerosis in low-density lipoprotein receptor-deficient (LDLR^−/−) mice. The present study investigates the effect of low-dose proteasome inhibition with bortezomib on pre-existing advanced atherosclerosis in LDLR^−/− mice. We found that bortezomib treatment of LDLR^−/− mice with pre-existing atherosclerosis does not alter lesion burden. Additionally, macrophage infiltration of aortic root plaques, total plasma cholesterol levels, and pro-inflammatory serum markers were not influenced by bortezomib. However, plaques of bortezomib-treated mice exhibited larger necrotic core areas and a significant thinning of the fibrous cap, indicating a more unstable plaque phenotype. Taking recent studies on favorable effects of proteasome inhibition in early atherogenesis into consideration, our data support the hypothesis of stage-dependent effects of proteasome inhibition in atherosclerosis.

Inhibition of Proteasome Activity by Low-dose Bortezomib Attenuates Angiotensin II-induced Abdominal Aortic Aneurysm in Apo E(-/-) Mice

Abdominal aortic aneurysm (AAA) is a leading cause of sudden death in aged people. Activation of ubiquitin proteasome system (UPS) plays a critical role in the protein quality control and various diseases. However, the functional role of UPS in AAA formation remains unclear. In this study, we found that the proteasome activities and subunit expressions in AAA tissues from human and angiotensin II (Ang II)-infused apolipoprotein E knockout (Apo E^−/−) mice were significantly increased. To investigate the effect of proteasome activation on the AAA formation, Apo E^−/− mice were cotreated with bortezomib (BTZ) (a proteasome inhibitor, 50 μg/kg, 2 times per week) and Ang II (1000 ng/kg/min) up to 28 days. Ang II infusion significantly increased the incidence and severity of AAA in Apo E^−/− mice, whereas BTZ treatment markedly inhibited proteasome activities and prevented AAA formation. Furthermore, BTZ treatment significantly reduced the inflammation, inhibited the metal matrix metalloprotease activity, and reversed the phenotypic SMC modulation in AAA tissue. In conclusion, these results provide a new evidence that proteasome activation plays a critical role in AAA formation through multiple mechanisms, and suggest that BTZ might be a novel therapeutic target for treatment of AAA formation.

Ageing induced vascular smooth muscle cell senescence in atherosclerosis

Atherosclerosis is a disease of ageing in that its incidence and prevalence increase with age. However, atherosclerosis is also associated with biological ageing, manifest by a number of typical hallmarks of ageing in the atherosclerotic plaque. Thus, accelerated biological ageing may be superimposed on the effects of chronological ageing in atherosclerosis. Tissue ageing is seen in all cells that comprise the plaque, but particularly in vascular smooth muscle cells (VSMCs). Hallmarks of ageing include evidence of cell senescence, DNA damage (including telomere attrition), mitochondrial dysfunction, a pro-inflammatory secretory phenotype, defects in proteostasis, epigenetic changes, deregulated nutrient sensing, and exhaustion of progenitor cells. In this model, initial damage to DNA (genomic, telomeric, mitochondrial and epigenetic changes) results in a number of cellular responses (cellular senescence, deregulated nutrient sensing and defects in proteostasis). Ultimately, ongoing damage and attempts at repair by continued proliferation overwhelm reparative capacity, causing loss of specialised cell functions, cell death and inflammation. This review summarises the evidence for accelerated biological ageing in atherosclerosis, the functional consequences of cell ageing on cells comprising the plaque, and the causal role that VSMC senescence plays in atherogenesis.

Modulatory effects of bortezomib on host immune cell functions

Bortezomib is an inhibitor of the ubiquitin-proteasome proteolytic pathway responsible for intracellular protein turnover. Cellular proteins controlled by this pathway represent a diverse group of potential therapeutic targets, particularly in cancer cells, which exploit this proteasomal pathway to promote their growth and diminish apoptosis. Along with inhibiting the proteasome and thus sensitizing tumor cells to apoptosis, bortezomib may also have multiple effects on the host immune responses. This review summarizes the effects that bortezomib may play on immune cell subsets in various disease states in modifying lymphocyte receptors, ligands, the expression of various cytokines and chemokines and their downstream signaling. We also propose steps that can be taken to refine combinatorial strategies that include bortezomib to improve current immunotherapeutic approaches.

Targeting the ubiquitin-proteasome system in atherosclerosis: status quo, challenges, and perspectives

SIGNIFICANCE

Atherosclerosis is a vascular disease of worldwide significance with fatal complications such as myocardial infarction, stroke, and peripheral artery disease. Atherosclerosis is recognized as a chronic inflammatory disease leading to arterial plaque formation and vessel narrowing in different vascular beds. Besides the strong inflammatory nature of atherosclerosis, it is also characterized by proliferation, apoptosis, and enhanced oxidative stress. The ubiquitin-proteasome system (UPS) is the major intracellular degradation system in eukaryotic cells. Besides its essential role in the degradation of dysfunctional and oxidatively damaged proteins, it is involved in many processes that influence disease progression in atherosclerosis. Hence, it is logical to ask whether targeting the proteasome is a reasonable and feasible option for the treatment of atherosclerosis.

RECENT ADVANCES

Several lines of evidence suggest stage-specific dysfunction of the UPS in atherogenesis. Regulation of key processes by the proteasome in atherosclerosis, as well as the modulation of these processes by proteasome inhibitors in vascular cells, is outlined in this review. The treatment of atherosclerotic animal models with proteasome inhibitors yielded partly opposing results, the potentially underlying reasons of which are discussed here.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Targeting UPS function in atherosclerosis is a promising but challenging option. Limitations of current proteasome inhibitors, dose dependency, and the cell specificity of effects, as well as the potential of future therapeutics are discussed. A stage-specific in-depth exploration of UPS function in atherosclerosis in the future will help identify targets and windows for beneficial intervention.

Targeting the ubiquitin-proteasome system in heart disease: the basis for new therapeutic strategies

SIGNIFICANCE

Novel therapeutic strategies to treat heart failure are greatly needed. The ubiquitin-proteasome system (UPS) affects the structure and function of cardiac cells through targeted degradation of signaling and structural proteins. This review discusses both beneficial and detrimental consequences of modulating the UPS in the heart.

RECENT ADVANCES

Proteasome inhibitors were first used to test the role of the UPS in cardiac disease phenotypes, indicating therapeutic potential. In early cardiac remodeling and pathological hypertrophy with increased proteasome activities, proteasome inhibition prevented or restricted disease progression and contractile dysfunction. Conversely, enhancing proteasome activities by genetic manipulation, pharmacological intervention, or ischemic preconditioning also improved the outcome of cardiomyopathies and infarcted hearts with impaired cardiac and UPS function, which is, at least in part, caused by oxidative damage.

CRITICAL ISSUES

An understanding of the UPS status and the underlying mechanisms for its potential deregulation in cardiac disease is critical for targeted interventions. Several studies indicate that type and stage of cardiac disease influence the dynamics of UPS regulation in a nonlinear and multifactorial manner. Proteasome inhibitors targeting all proteasome complexes are associated with cardiotoxicity in humans. Furthermore, the type and dosage of proteasome inhibitor impact the pathogenesis in nonuniform ways.

FUTURE DIRECTIONS

Systematic analysis and targeting of individual UPS components with established and innovative tools will unravel and discriminate regulatory mechanisms that contribute to and protect against the progression of cardiac disease. Integrating this knowledge in drug design may reduce adverse effects on the heart as observed in patients treated with proteasome inhibitors against noncardiac diseases, especially cancer.

MG132, a proteasome inhibitor, enhances LDL uptake in HepG2 cells in vitro by regulating LDLR and PCSK9 expression

AIM

Expression of liver low-density lipoprotein receptor (LDLR), a determinant regulator in cholesterol homeostasis, is tightly controlled at multiple levels. The aim of this study was to examine whether proteasome inhibition could affect LDLR expression and LDL uptake in liver cells in vitro.

METHODS

HepG2 cells were examined. Real-time PCR and Western blot analysis were used to determine the mRNA and protein levels, respectively. DiI-LDL uptake assay was used to quantify the LDLR function. Luciferase assay system was used to detect the activity of proprotein convertase subtilisin/kexin type 9 (PCSK9, a major protein mediating LDLR degradation) promoter. Specific siRNAs were used to verify the involvement of PCSK9.

RESULTS

Treatment of HepG2 cells with the specific proteasome inhibitor MG132 (0.03-3 μmol/L) dose-dependently increased LDLR mRNA and protein levels, as well as LDL uptake. Short-term treatment with MG132 (0.3 μmol/L, up to 8 h) significantly increased both LDLR mRNA and protein levels in HepG2 cells, which was blocked by the specific PKC inhibitors GF 109203X, Gö 6983 or staurosporine. In contrast, a longer treatment with MG132 (0.3 μmol/L, 24 h) did not change LDLR mRNA, but markedly increased LDLR protein by reducing PCSK9-mediated lysosome LDLR degradation. Furthermore, MG132 time-dependently suppressed PCSK9 expression in the HepG2 cells through a SREBP-1c related pathway. Combined treatment with MG132 (0.3 μmol/L) and pravastatin (5 μmol/L) strongly promoted LDLR expression and LDL uptake in HepG2 cells, and blocked the upregulation of PCSK9 caused by pravastatin alone.

CONCLUSION

Inhibition of proteasome by MG132 in HepG2 cells plays dual roles in LDLR and PCSK9 expression, and exerts a beneficial effect on cholesterol homeostasis.

Bortezomib protects from varicose-like venous remodeling

Despite the high prevalence of venous diseases that are associated with and based on the structural reorganization of the venous vessel wall, not much is known about their mechanistic causes. In this context, we demonstrated that the quantity of myocardin, a transcriptional regulator of the contractile and quiescent smooth muscle cell phenotype, was diminished in proliferating synthetic venous smooth muscle cells (VSMCs) of human and mouse varicose veins by 51 and 60%, respectively. On the basis of the relevance of proteasomal activity for such phenotypic changes, we hypothesized that the observed VSMC activation is attenuated by the proteasome inhibitor bortezomib. This drug fully abolished VSMC proliferation and loss of myocardin in perfused mouse veins and blocked VSMC invasion in collagen gels by almost 80%. In line with this, topical transdermal treatment with bortezomib diminished VSMC proliferation by 80%, rescued 90% of VSMC myocardin abundance, and inhibited varicose-like venous remodeling by 67 to 72% in a mouse model. Collectively, our data indicate that the proteasome plays a pivotal role in VSMC phenotype changes during venous remodeling processes. Its inhibition protects from varicose-like vein remodeling in mice and may thus serve as a putative therapeutic strategy to treat human varicose veins.

Therapeutic effect of MG132 on the aortic oxidative damage and inflammatory response in OVE26 type 1 diabetic mice

The present study tested whether MG132 increases vascular nuclear factor E2-related factor-2 (Nrf2) expression and transcription to provide a therapeutic effect on diabetes-induced pathogenic changes in the aorta. To this end, three-month-old OVE26 diabetic and age-matched control mice were intraperitoneally injected with MG-132, 10 μg/kg daily for 3 months. OVE26 transgenic type 1 diabetic mice develop hyperglycemia at 2-3 weeks of age and exhibit albuminuria at 3 months of age with mild increases in TNF-α expression and 3-NT accumulation in the aorta. Diabetes-induced significant increases in the wall thickness and structural derangement of aorta were found in OVE26 mice with significant increases in aortic oxidative and nitrosative damage, inflammation, and remodeling at 6 months of diabetes, but not at 3 months of diabetes. However, these pathological changes seen at the 6 months of diabetes were abolished in OVE26 mice treated with MG-132 for 3 months that were also associated with a significant increase in Nrf2 expression in the aorta as well as transcription of downstream genes. These results suggest that chronic treatment with low-dose MG132 can afford an effective therapy for diabetes-induced pathogenic changes in the aorta, which is associated with the increased Nrf2 expression and transcription.