Role of protein kinase C δ in ER stress and apoptosis induced by oxidized LDL in human vascular smooth muscle cells

PKCδ regulates the vascular biology in diabetic atherosclerosis

Diabetes mellitus, known for its complications, especially vascular complications, is becoming a globally serious social problem. Atherosclerosis has been recognized as a common vascular complication mechanism in diabetes. The diacylglycerol (DAG)-protein kinase C (PKC) pathway plays an important role in atherosclerosis. PKCs can be divided into three subgroups: conventional PKCs (cPKCs), novel PKCs (nPKCs), and atypical PKCs (aPKCs). The aim of this review is to provide a comprehensive overview of the role of the PKCδ pathway, an isoform of nPKC, in regulating the function of endothelial cells, vascular smooth muscle cells, and macrophages in diabetic atherosclerosis. In addition, potential therapeutic targets regarding the PKCδ pathway are summarized. Video Abstract.

Acovenoside A as a novel therapeutic approach to boost taxol and carboplatin apoptotic and antiproliferative activities in NSCLC: Interplay of miR-630/miR-181a and apoptosis genes

The aim of the present study is to explore the potential anticancer effect of the cardenolide; acovenoside A against non-small cell lung cancer (NSCLC), understand its molecular mechanism in inducing apoptosis and show the effect of its combination with carboplatin and taxol. MTT assay showed that the combination of acovenoside A with taxol and carboplatin caused 78.9% cytotoxicity reflecting the synergistic effect. The triple combination showed the best growth inhibition efficiency where the number of cells at the G2/M phase was decreased and boosted up apoptotic and necrotic activity. The combination also showed the most remarkable increase in gene expression of Bax and p53 and the least level of Bcl2. The gene expression of miRNA181a and miRNA630 was significantly upregulated in cell lines treated with the combination. The present study has proven that the underlying mechanism of acovenoside A is partially attributed to the upregulation of miR-630 and miR-181a gene expressions which in turn targets the intrinsic apoptosis genes as p53, Bax and Bcl2 as well as caspase 3. The present study is the first to address the valuable effect of using acovenoside A together with carboplatin and taxol in the treatment of NSCLC via exerting apoptotic, antiproliferative, and cytotoxic effects..

Effect of Photobiomodulation on Protein Kinase Cδ, Cytochrome C, and Mitochondria in U87 MG Cells

Photobiomodulation (PBM) therapy is a relatively new modality for the combined treatment of cancer. Pre-treatment of certain types of cancer cells with PBM potentiates the treatment efficacy of photodynamic therapy (PDT). The mechanism of action of this synergetic effect is not yet fully understood. In the present study, we focused on protein kinase Cδ (PKCδ) as a proapoptotic agent that is highly expressed in U87MG cells. The distribution of PKCδ in the cytoplasm was changed and its concentration was increased by PBM using radiation at 808 nm (15 mW/cm², 120 s). This process was accompanied by the organelle specific phosphorylation of PKCδ amino acids (serine/tyrosine). Enhanced phosphorylation of serine 645 in the catalytic domain of PKCδ was found in the cytoplasm, whereas the phosphorylation of tyrosine 311 was mainly localized in the mitochondria. Despite a local increase in the level of oxidative stress, only a small amount of cytochrome c was released from the mitochondria to cytosol. Although a partial inhibition of mitochondrial metabolic activity was induced in PBM-exposed cells, apoptosis was not observed. We hypothesized that PBM-induced photodamage of organelles was neutralized by autophagy maintained in these cells. However, photodynamic therapy may effectively exploit this behaviour to generate apoptosis in cancer treatment, which may increase the treatment efficacy and open up prospects for further applications.

Global research trends in atherosclerosis: A bibliometric and visualized study

Background

Increasing evidence has spurred a considerable evolution of concepts related to atherosclerosis, prompting the need to provide a comprehensive view of the growing literature. By retrieving publications in the Web of Science Core Collection (WoSCC) of Clarivate Analytics, we conducted a bibliometric analysis of the scientific literature on atherosclerosis to describe the research landscape.

Methods

A search was conducted of the WoSCC for articles and reviews serving exclusively as a source of information on atherosclerosis published between 2012 and 2022. Microsoft Excel 2019 was used to chart the annual productivity of research relevant to atherosclerosis. Through CiteSpace and VOSviewer, the most prolific countries or regions, authors, journals, and resource-, intellectual-, and knowledge-sharing in atherosclerosis research, as well as co-citation analysis of references and keywords, were analyzed.

Results

A total of 20,014 publications were retrieved. In terms of publications, the United States remains the most productive country (6,390, 31,93%). The most publications have been contributed by Johns Hopkins Univ (730, 3.65%). ALVARO ALONSO produced the most published works (171, 0.85%). With a betweenness centrality of 0.17, ERIN D MICHOS was the most influential author. The most prolific journal was identified as Atherosclerosis (893, 4.46%). Circulation received the most co-citations (14,939, 2.79%). Keywords with the ongoing strong citation bursts were “nucleotide-binding oligomerization (NOD), Leucine-rich repeat (LRR)-containing protein (NLRP3) inflammasome,” “short-chain fatty acids (SCFAs),” “exosome,” and “homeostasis,” etc.

Conclusion

The research on atherosclerosis is driven mostly by North America and Europe. Intensive research has focused on the link between inflammation and atherosclerosis, as well as its complications. Specifically, the NLRP3 inflammasome, interleukin-1β, gut microbiota and SCFAs, exosome, long non-coding RNAs, autophagy, and cellular senescence were described to be hot issues in the field.

Unfolded Protein Response Differentially Modulates the Platelet Phenotype

BACKGROUND

Unfolded protein response (UPR) is a multifaceted signaling cascade that alleviates protein misfolding. Although well studied in nucleated cells, UPR in absence of transcriptional regulation has not been described. Intricately associated with cardiovascular diseases, platelets, despite being anucleate, respond rapidly to stressors in blood. We investigate the UPR in anucleate platelets and explore its role, if any, on platelet physiology and function.

METHODS

Human and mouse platelets were studied using a combination of ex vivo and in vivo experiments. Platelet lineage-specific knockout mice were generated independently for each of the 3 UPR pathways, PERK (protein kinase RNA [PKR]-like endoplasmic reticulum kinase), XBP1 (X-binding protein), and ATF6 (activating transcription factor 6). Diabetes patients were prospectively recruited, and platelets were evaluated for activation of UPR under chronic pathophysiological disease conditions.

RESULTS

Tunicamycin induced the IRE1α (inositol-requiring enzyme-1alpha)-XBP1 pathway in human and mouse platelets, while oxidative stress predominantly activated the PERK pathway. PERK deletion significantly increased platelet aggregation and apoptosis and phosphorylation of PLCγ2, PLCβ3, and p38 MAPK. Deficiency of XBP1 increased platelet aggregation, with higher PLCβ3 and PKCδ activation. ATF6 deletion mediated a relatively modest effect on platelet phenotype with increased PKA (protein kinase A). Platelets from diabetes patients exhibited a positive correlation between disease severity, platelet activation, and protein aggregation, with only IRE1α-XBP1 activation. Moreover, IRE1α inhibition increased platelet aggregation, while clinically approved chemical chaperone, sodium 4-phenylbutyrate reduced the platelet hyperactivation.

CONCLUSIONS

We show for the first time, that UPR activation occurs in platelets and can be independent of genomic regulation, with selective induction being specific to the source and severity of stress. Each UPR pathway plays a key role and can differentially modulate the platelet activation pathways and phenotype. Targeting the specific arms of UPR may provide a new antiplatelet strategy to mitigate thrombotic risk in diabetes and other cardiovascular diseases.

Senescence in Vascular Smooth Muscle Cells and Atherosclerosis

Vascular smooth muscle cells (VSMCs) are the primary cell type involved in the atherosclerosis process; senescent VSMCs are observed in both aged vessels and atherosclerotic plaques. Factors associated with the atherosclerotic process, including oxidative stress, inflammation, and calcium-regulating factors, are closely linked to senescence in VSMCs. A number of experimental studies using traditional cellular aging markers have suggested that anti-aging biochemical agents could be used to treat atherosclerosis. However, doubt has recently been cast on such potential due to the increasingly apparent complexity of VSMCs status and an incomplete understanding of the role that these cells play in the atherosclerosis process, as well as a lack of specific or spectrum-limited cellular aging markers. The utility of anti-aging drugs in atherosclerosis treatment should be reevaluated. Promotion of a healthy lifestyle, exploring in depth the characteristics of each cell type associated with atherosclerosis, including VSMCs, and development of targeted drug delivery systems will ensure efficacy whilst evaluation of the safety and tolerability of drug use should be key aims of future anti-atherosclerosis research. This review summarizes the characteristics of VSMC senescence during the atherosclerosis process, the factors regulating this process, as well as an overview of progress toward the development and application of anti-aging drugs.

Mechanism of Endoplasmic Reticulum Stress Pathway in the Osteogenic Phenotypic Transformation of Aortic Valve Interstitial Cells

BACKGROUND AND PURPOSE

Calcific Aortic Valve Disease (CAVD) is a crucial component of degenerative valvular disease in old age and with the increasing prevalence of the aging population. we hope that by modeling valvular osteogenesis and intervening with endoplasmic reticulum stress inhibitor TUDCA to observe the effect of endoplasmic reticulum stress on valve osteogenesis.

METHODS

In this study, rabbit heart valvular interstitial cells (VICs) were isolated and cultured. They treated with ox-LDL (Oxidized Low Density Lipoprotein) stimulation to establish a model of valvular osteogenic transformation. BMP2 (Bone Morphogenetic Protein 2), PERK (Protein kinase R-like endoplasmic reticulum kinase), CHOP (CCAAT/enhancer-binding protein homologous protein) and transcriptional regulatory factor ATF4 (Activating Transcription Factor 4 )were recorded after intervention with ER stress inhibitor TUDCA. The effects of er stress on valvular osteogenic transformation were analyzed.

RESULT

After stimulation of VICs with ox-LDL, the expression levels of BMP2, PERK, CHOP, and ATF4 increased. However, TUDCA treatment can alleviate the increased expression levels of BMP2, PERK ATF4, and CHOP under ox-LDL stimulation to a certain extent.

CONCLUSION

The endoplasmic reticulum stress signaling pathway is involved in ox-LDL-induced calcification of rabbit valve interstitial cells. Inhibition of endoplasmic reticulum stress using TUDCA can improve the progression of rabbit aortic valve calcification.

Antioxidant and Cytoprotective Properties of Polyphenol-Rich Extracts from Antirhea borbonica and Doratoxylon apetalum against Atherogenic Lipids in Human Endothelial Cells

The endothelial integrity is the cornerstone of the atherogenic process. Low-density lipoprotein (LDL) oxidation occurring within atheromatous plaques leads to deleterious vascular effects including endothelial cell cytotoxicity. The aim of this study was to evaluate the vascular antioxidant and cytoprotective effects of polyphenol-rich extracts from two medicinal plants from the Reunion Island: Antirhea borbonica (A. borbonica), Doratoxylon apetalum (D. apetalum). The polyphenol-rich extracts were obtained after dissolving each dry plant powder in an aqueous acetonic solution. Quantification of polyphenol content was achieved by the Folin–Ciocalteu assay and total phenol content was expressed as g gallic acid equivalent/100 g plant powder (GAE). Human vascular endothelial cells were incubated with increasing concentrations of polyphenols (1–50 µM GAE) before stimulation with oxidized low-density lipoproteins (oxLDLs). LDL oxidation was assessed by quantification of hydroperoxides and thiobarbituric acid reactive substances (TBARS). Intracellular oxidative stress and antioxidant activity (catalase and superoxide dismutase) were measured after stimulation with oxLDLs. Cell viability and apoptosis were quantified using different assays (MTT, Annexin V staining, cytochrome C release, caspase 3 activation and TUNEL test). A. borbonica and D. apetalum displayed high levels of polyphenols and limited LDL oxidation as well as oxLDL-induced intracellular oxidative stress in endothelial cells. Polyphenol extracts of A. borbonica and D. apetalum exerted a protective effect against oxLDL-induced cell apoptosis in a dose-dependent manner (10, 25, and 50 µM GAE) similar to that observed for curcumin, used as positive control. All together, these results showed significant antioxidant and antiapoptotic properties for two plants of the Reunion Island pharmacopeia, A. borbonica and D. apetalum, suggesting their therapeutic potential to prevent cardiovascular diseases by limiting LDL oxidation and protecting the endothelium.

Procyanidins inhibit fine particulate matter-induced vascular smooth muscle cells apoptosis via the activation of the Nrf2 signaling pathway

The functional role of procyanidins (PC) in PM2.5-induced cardiovascular diseases (CVD) is largely unexplored. This study aimed to explore the protective effect of PC against PM2.5-induced vascular smooth muscle cells (VSMCs) apoptosis and underlying mechanisms. Sprague Dawley rats were pretreated with three doses of PC (50, 100, and 200 mg/kg) and exposed to 10 mg/kg PM2.5 by intratracheal instillation three times a week. VSMCs were exposed to 5, 10, and 20 μM PC before the addition of 100 μg/mL PM2.5. In vivo, the PM2.5 exposure induced apoptosis in the thoracic aorta of rats. The PM2.5 exposure significantly elevated the reactive oxygen species (ROS) and malondialdehyde (MDA) levels and decreased the superoxide dismutase activity. Also, PC supplementation increased the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), and its downstream antioxidant genes, i.e., NAD(P)H dehydrogenase (quinine) 1 and heme oxygenase 1, attenuated oxidative stress and vascular apoptosis. In vitro, PM2.5 induced cytotoxicity in VSMCs in a dose-dependent manner. Besides, PC abolished the PM2.5-induced cytotoxicity by activating the Nrf2 signal pathway, alleviating oxidative stress, and decreasing apoptosis. In conclusion, this work is the first study to demonstrate that PC can suppress the PM2.5-induced VSMCs apoptosis via the activation of the Nrf2 signal pathway.

Potential Role of Protein Kinase C in the Pathophysiology of Diabetes-Associated Atherosclerosis

Diabetes mellitus is a metabolic syndrome that affects millions of people worldwide. Recent studies have demonstrated that protein kinase C (PKC) activation plays an important role in hyperglycemia-induced atherosclerosis. PKC activation is involved in several cellular responses such as the expression of various growth factors, activation of signaling pathways, and enhancement of oxidative stress in hyperglycemia. However, the role of PKC activation in pro-atherogenic and anti-atherogenic mechanisms remains controversial, especially under hyperglycemic condition. In this review, we discuss the role of different PKC isoforms in lipid regulation, oxidative stress, inflammatory response, and apoptosis. These intracellular events are linked to the pathogenesis of atherosclerosis in diabetes. PKC deletion or treatment with PKC inhibitors has been studied in the regulation of atherosclerotic plaque formation and evolution. Furthermore, some preclinical and clinical studies have indicated that PKCβ and PKCδ are potential targets for the treatment of diabetic vascular complications. The current review summarizes these multiple signaling pathways and cellular responses regulated by PKC activation and the potential therapeutic targets of PKC in diabetic complications.

PKC Delta Activation Promotes Endoplasmic Reticulum Stress (ERS) and NLR Family Pyrin Domain-Containing 3 (NLRP3) Inflammasome Activation Subsequent to Asynuclein-Induced Microglial Activation: Involvement of Thioredoxin-Interacting Protein (TXNIP)/Thioredoxin (Trx) Redoxisome Pathway

A classical hallmark of Parkinson's disease (PD) pathogenesis is the accumulation of misfolded alpha-synuclein (αSyn) within Lewy bodies and Lewy neurites, although its role in microglial dysfunction and resultant dopaminergic (DAergic) neurotoxicity is still elusive. Previously, we identified that protein kinase C delta (PKCδ) is activated in post mortem PD brains and experimental Parkinsonism and that it participates in reactive microgliosis; however, the relationship between PKCδ activation, endoplasmic reticulum stress (ERS) and the reactive microglial activation state in the context of α-synucleinopathy is largely unknown. Herein, we show that oxidative stress, mitochondrial dysfunction, NLR family pyrin domain containing 3 (NLRP3) inflammasome activation, and PKCδ activation increased concomitantly with ERS markers, including the activating transcription factor 4 (ATF-4), serine/threonine-protein kinase/endoribonuclease inositol-requiring enzyme 1α (p-IRE1α), p-eukaryotic initiation factor 2 (eIF2α) as well as increased generation of neurotoxic cytokines, including IL-1β in aggregated αSyn_agg-stimulated primary microglia. Importantly, in mouse primary microglia-treated with αSyn_agg we observed increased expression of Thioredoxin-interacting protein (TXNIP), an endogenous inhibitor of the thioredoxin (Trx) pathway, a major antioxidant protein system. Additionally, αSyn_agg promoted interaction between NLRP3 and TXNIP in these cells. In vitro knockdown of PKCδ using siRNA reduced ERS and led to reduced expression of TXNIP and the NLRP3 activation response in αSyn_agg-stimulated mouse microglial cells (MMCs). Additionally, attenuation of mitochondrial reactive oxygen species (mitoROS) via mito-apocynin and amelioration of ERS via the eIF2α inhibitor salubrinal (SAL) reduced the induction of the ERS/TXNIP/NLRP3 signaling axis, suggesting that mitochondrial dysfunction and ERS may act in concert to promote the αSyn_agg-induced microglial activation response. Likewise, knockdown of TXNIP by siRNA attenuated the αSyn_agg-induced NLRP3 inflammasome activation response. Finally, unilateral injection of αSyn preformed fibrils (αSyn_PFF) into the striatum of wild-type mice induced a significant increase in the expression of nigral p-PKCδ, ERS markers, and upregulation of the TXNIP/NLRP3 inflammasome signaling axis prior to delayed loss of TH⁺ neurons. Together, our results suggest that inhibition of ERS and its downstream signaling mediators TXNIP and NLRP3 might represent novel therapeutic avenues for ameliorating microglia-mediated neuroinflammation in PD and other synucleinopathies.

SUMO wrestling in the cellular dohyō: crosstalk between phosphorylation and SUMOylation of PKCδ regulates oxidative cell damage

The novel PKCδ isoform has been shown to mediate a pro-apoptotic function in response to oxidative stressors. Siman Gao and colleagues performed an in-depth biochemical and molecular analysis of factors that regulate PKCδ function. They demonstrated convincingly that PKCδ is regulated by an interplay between SUMOylation and phosphorylation. They also showed that these events are critical for hydrogen peroxide induced apoptosis, thus identifying potentially novel mechanisms that may be harnessed for cell protection.

Pathological Crosstalk Between Oxidized LDL and ER Stress in Human Diseases: A Comprehensive Review

The oxidative modification of the major cholesterol carrying lipoprotein, oxLDL, is a biomarker as well as a pathological factor in cardiovascular diseases (CVD), type 2 diabetes mellitus (T2DM), obesity and other metabolic diseases. Perturbed cellular homeostasis due to physiological, pathological and pharmacological factors hinder the proper functioning of the endoplasmic reticulum (ER), which is the major hub for protein folding and processing, lipid biosynthesis and calcium storage, thereby leading to ER stress. The cellular response to ER stress is marked by a defensive mechanism called unfolded protein response (UPR), wherein the cell adapts strategies that favor survival. Under conditions of excessive ER stress, when the survival mechanisms fail to restore balance, UPR switches to apoptosis and eliminates the defective cells. ER stress is a major hallmark in metabolic syndromes such as diabetes, non-alcoholic fatty liver disease (NAFLD), neurological and cardiovascular diseases. Though the pathological link between oxLDL and ER stress in cardiovascular diseases is well-documented, its involvement in other diseases is still largely unexplored. This review provides a deep insight into the common mechanisms in the pathogenicity of diseases involving oxLDL and ER stress as key players. In addition, the potential therapeutic intervention of the targets implicated in the pathogenic processes are also explored.

Compartmentalized Proteomic Profiling Outlines the Crucial Role of the Classical Secretory Pathway during Recombinant Protein Production in Chinese Hamster Ovary Cells

Different cellular processes that contribute to protein production in Chinese hamster ovary (CHO) cells have been previously investigated by proteomics. However, although the classical secretory pathway (CSP) has been well documented as a bottleneck during recombinant protein (RP) production, it has not been well represented in previous proteomic studies. Hence, the significance of this pathway for production of RP was assessed by identifying its own proteins that were associated to changes in RP production, through subcellular fractionation coupled to shot-gun proteomics. Two CHO cell lines producing a monoclonal antibody with different specific productivities were used as cellular models, from which 4952 protein groups were identified, which represent a coverage of 59% of the Chinese hamster proteome. Data are available via ProteomeXchange with identifier PXD021014. By using SAM and ROTS algorithms, 493 proteins were classified as differentially expressed, of which about 80% was proposed as novel targets and one-third were assigned to the CSP. Endoplasmic reticulum (ER) stress, unfolded protein response, calcium homeostasis, vesicle traffic, glycosylation, autophagy, proteasomal activity, protein synthesis and translocation into ER lumen, and secretion of extracellular matrix components were some of the affected processes that occurred in the secretory pathway. Processes from other cellular compartments, such as DNA replication, transcription, cytoskeleton organization, signaling, and metabolism, were also modified. This study gives new insights into the molecular traits of higher producer cells and provides novel targets for development of new sub-lines with improved phenotypes for RP production.

Characterization of Signalling Pathways That Link Apoptosis and Autophagy to Cell Death Induced by Estrone Analogues Which Reversibly Depolymerize Microtubules

The search for novel anti-cancer compounds which can circumvent chemotherapeutic drug resistance and limit systemic toxicity remains a priority. 2-Ethyl-3-O-sulphamoyl-estra-1,3,5(10)15-tetraene-3-ol-17one (ESE-15-one) and 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) are sulphamoylated 2-methoxyestradiol (2-ME) analogues designed by our research team. Although their cytotoxicity has been demonstrated in vitro, the temporal and mechanistic responses of the initiated intracellular events are yet to be determined. In order to do so, assays investigating the compounds' effects on microtubules, cell cycle progression, signalling cascades, autophagy and apoptosis were conducted using HeLa cervical- and MDA-MB-231 metastatic breast cancer cells. Both compounds reversibly disrupted microtubule dynamics as an early event by binding to the microtubule colchicine site, which blocked progression through the cell cycle at the G₁/S- and G₂/M transitions. This was supported by increased pRB and p27^Kip1 phosphorylation. Induction of apoptosis with time-dependent signalling involving the p-JNK, Erk1/2 and Akt/mTOR pathways and loss of mitochondrial membrane potential was demonstrated. Inhibition of autophagy attenuated the apoptotic response. In conclusion, the 2-ME analogues induced a time-dependent cross-talk between cell cycle checkpoints, apoptotic signalling and autophagic processes, with an increased reactive oxygen species formation and perturbated microtubule functioning appearing to connect the processes. Subtle differences in the responses were observed between the two compounds and the different cell lines.

Cholesterol-Induced Phenotypic Modulation of Smooth Muscle Cells to Macrophage/Fibroblast-like Cells Is Driven by an Unfolded Protein Response

OBJECTIVE

Vascular smooth muscle cells (SMCs) dedifferentiate and initiate expression of macrophage markers with cholesterol exposure. This phenotypic switching is dependent on the transcription factor Klf4 (Krüppel-like factor 4). We investigated the molecular pathway by which cholesterol induces SMC phenotypic switching. Approach and Results: With exposure to free cholesterol, SMCs decrease expression of contractile markers, activate Klf4, and upregulate a subset of macrophage and fibroblast markers characteristic of modulated SMCs that appear with atherosclerotic plaque formation. These phenotypic changes are associated with activation of all 3 pathways of the endoplasmic reticulum unfolded protein response (UPR), Perk (protein kinase RNA-like endoplasmic reticulum kinase), Ire (inositol-requiring enzyme) 1α, and Atf (activating transcription factor) 6. Blocking the movement of cholesterol from the plasma membrane to the endoplasmic reticulum prevents free cholesterol-induced UPR, Klf4 activation, and upregulation of the majority of macrophage and fibroblast markers. Cholesterol-induced phenotypic switching is also prevented by global UPR inhibition or specific inhibition of Perk signaling. Exposure to chemical UPR inducers, tunicamycin and thapsigargin, is sufficient to induce these same phenotypic transitions. Finally, analysis of published single-cell RNA sequencing data during atherosclerotic plaque formation in hyperlipidemic mice provides preliminary in vivo evidence of a role of UPR activation in modulated SMCs.

CONCLUSIONS

Our data demonstrate that UPR is necessary and sufficient to drive phenotypic switching of SMCs to cells that resemble modulated SMCs found in atherosclerotic plaques. Preventing a UPR in hyperlipidemic mice diminishes atherosclerotic burden, and our data suggest that preventing SMC transition to dedifferentiated cells expressing macrophage and fibroblast markers contributes to this decreased plaque burden.

MicroRNAs are critical in regulating smooth muscle cell mineralization and apoptosis during vascular calcification

Vascular calcification refers to the pathological deposition of calcium and phosphate minerals into the vasculature. It is prevalent in atherosclerosis, ageing, type 2 diabetes mellitus and chronic kidney disease, thus, increasing morbidity and mortality from these conditions. Vascular calcification shares similar mechanisms with bone mineralization, with smooth muscle cells playing a critical role in both processes. In the last decade, a variety of microRNAs have been identified as key regulators for the differentiation, phenotypic switch, proliferation, apoptosis, cytokine production and matrix deposition in vascular smooth muscle cells during vascular calcification. Therefore, this review mainly discusses the roles of microRNAs in the pathophysiological mechanisms of vascular calcification in smooth muscle cells and describes several interventions against vascular calcification by regulating microRNAs. As the exact mechanisms of calcification remain not fully elucidated, having a better understanding of microRNA involvement in vascular calcification may give impetus to development of novel therapeutics for the control and treatment of vascular calcification.

The pro-apoptotic actions of 2-methoxyestradiol against ovarian cancer involve catalytic activation of PKCδ signaling

Background: 2-methoxyestradiol (2MeOE₂) is a natural metabolite of estradiol, which is generated by the action of CYP1A1 enzyme in the liver. We have previously shown that a flaxseed-supplemented diet decreases both the incidence and severity of ovarian cancer in laying hens, also induces CYP1A1 expression in liver. Recently, we have shown that as a biologically derived active component of flax diet, 2MeOE₂ induces apoptosis in ovarian cancer cells which is partially dependent on p38 MAPK. The objective of this study was to elucidate the molecular mechanism of actions of 2MeOE₂, a known microtubule disrupting agent, in inducing apoptosis in ovarian tumors.

Results: 2MeOE₂ induces γH2Ax expression and apoptotic histone modifications in ovarian cancer cells, which are predicted downstream targets of protein kinase Cδ (PKCδ) during apoptosis. Overexpressing full length PKCδ alone does not induce apoptosis but potentiates 2MeOE₂-mediated apoptosis. C3-domain mutated dominant-negative PKCδ (PKCδ^DN) significantly reduces 2MeOE₂-induced caspase-3 cleavage and apoptotic histone modification. Silencing PKCδ diminishes 2MeOE₂-mediated apoptosis. The catalytic fragment of PKCδ (PKCδ^CAT) evokes pro-apoptotic effects which are principally dependent on p38 MAPK phosphorylation.

Conclusions: The pro-apoptotic actions of 2MeOE₂ are in part dependent on catalytic activation of PKCδ. Catalytic activation of PKCδ accelerates the 2MeOE₂-induced apoptotic cascade. This study describes a novel molecular action of flaxseed diet in ovarian cancer.

Searching for combination therapy by clustering methods: Stimulation of PKC in Golgi apparatus combined with hypericin induced PDT

Cancer cell metabolism is a very attractive target for anticancer treatments. This work focuses on protein kinase C (PKC) signaling in the U87 MG glioma. By means of western blot, fluorescence and time-resolved fluorescence microscopy the correlation between the Golgi apparatus (GA), lysosomes and mitochondria were evaluated. The known regulators of PKC were applied to cancer cells. Phorbol myristate acetate (PMA) was chosen as the activator of PKC. Gö6976, hypericin and rottlerin, the inhibitors of PKCα and PKCδ were selected as well. Stabilization, destabilization processes occurring in cells allow classification of observations into several groups. Multiple versions of hierarchical cluster analysis have been applied and similarities have been found between organelles and PKC regulators. The method identified GA as an extraordinary organelle whose functionality is significantly influenced by PKC regulators as well as oxidative stress. Therefore, combination therapy has been designed according to the results of the cluster analysis. Furthermore, the efficacy of photodynamic therapy mediated by hypericin, and the consequent apoptosis, was significantly increased during the treatment. To our knowledge, this is the first demonstration of the effectiveness of the clustering in the given area.

Kefir peptides alleviate high-fat diet-induced atherosclerosis by attenuating macrophage accumulation and oxidative stress in ApoE knockout mice

In the past decade, the high morbidity and mortality of atherosclerotic disease have been prevalent worldwide. High-fat food consumption has been suggested to be an overarching factor for atherosclerosis incidence. This study aims to investigate the effects of kefir peptides on high-fat diet (HFD)-induced atherosclerosis in apolipoprotein E knockout (ApoE^−/−) mice. 7-week old male ApoE^−/− and normal C57BL/6 mice were randomly divided into five groups (n = 8). Atherosclerotic lesion development in ApoE^−/− mice was established after fed the HFD for 12 weeks compared to standard chow diet (SCD)-fed C57BL/6 and ApoE^−/− control groups. Kefir peptides oral administration significantly improved atherosclerotic lesion development by protecting against endothelial dysfunction, decreasing oxidative stress, reducing aortic lipid deposition, attenuating macrophage accumulation, and suppressing the inflammatory immune response compared with the HFD/ApoE^−/− mock group. Moreover, the high dose of kefir peptides substantially inhibited aortic fibrosis and restored the fibrosis in the aorta root close to that observed in the C57BL/6 normal control group. Our findings show, for the first time, anti-atherosclerotic progression via kefir peptides consumption in HFD-fed ApoE^−/− mice. The profitable effects of kefir peptides provide new perspectives for its use as an anti-atherosclerotic agent in the preventive medicine.

Atorvastatin inhibits endoplasmic reticulum stress through AMPK signaling pathway in atherosclerosis in mice

Effect of atorvastatin inhibition of endoplasmic reticulum stress and amelioration of atherosclerosis through AMPK pathway were studied. Eight-week-old male apolipoprotein E-deficient (ApoE^-/^-) mice were fed with high-fat diet for 2 weeks and randomly divided into two groups: Atorvastatin treatment group was given atorvastatin (5 mg/kg/day) injection for a total of 6 weeks; control group was given the same dose of PBS through intraperitoneal injection for a total of 6 weeks. H&E staining was used to detect plaque size; immunohistochemical staining was used to detect T cells, macrophages and phospho-protein kinase-like ER kinase (phospho-PERK) in localized plaques. Proteins were extracted from mouse thoracic and abdominal aortic tissues. Western blot analysis was used to detect the protein expression levels of endoplasmic reticulum stress-related molecules phospho-eukaryotic initiation factor-2α (p-eIF2α), eukaryotic initiation factor (eIF2a), and sliced x-box binding protein 1 (sXBP-1). Cultured human umbilical vein endothelial cells (HUVECs), induced endoplasmic reticulum stress with human oxidized low density lipoprotein (ox-LDL), were treated with atorvastatin, AMPK agonist 5-amino-4-imidazolecarboxamide riboside-I-β-D-ribofuranoside (AICAR) and AMPK-DN that expressed a dominant-negative mutant of AMPK. Western blot analysis was used to test the expression levels of endoplasmic reticulum stress-related molecules p-elF2a and sXBP-1. The area of aortic plaques in atorvastatin group was obviously decreased, and the infiltrations of CD3⁺ T cells and macrophages in the localized plaques were reduced. The endoplasmic reticulum stress-related proteins sXBP-1 and p-eIF2a were significantly reduced. The results of immunohistochemistry also showed a significant decrease in the level of phospho-PERK (p-PERK) in atorvastatin group. The results in ox-LDL-induced HUVECs showed that atorvastatin inhibited ox-LDL-induced endoplasmic reticulum stress, and the AMPK agonist AICAR also had the same effect, which was offset by DN-AMPK treatment. Atorvastatin inhibits ER stress both in vitro and in vivo and this protective effect is mediated by AMPK activation.

Vascular smooth muscle cell death, autophagy and senescence in atherosclerosis

In the present review, we describe the causes and consequences of loss of vascular smooth muscle cells (VSMCs) or their function in advanced atherosclerotic plaques and discuss possible mechanisms such as cell death or senescence, and induction of autophagy to promote cell survival. We also highlight the potential use of pharmacological modulators of these processes to limit plaque progression and/or improve plaque stability. VSMCs play a pivotal role in atherogenesis. Loss of VSMCs via initiation of cell death leads to fibrous cap thinning and promotes necrotic core formation and calcification. VSMC apoptosis is induced by pro-inflammatory cytokines, oxidized low density lipoprotein, high levels of nitric oxide and mechanical injury. Apoptotic VSMCs are characterized by a thickened basal lamina surrounding the cytoplasmic remnants of the VSMC. Inefficient clearance of apoptotic VSMCs results in secondary necrosis and subsequent inflammation. A critical determinant in the VSMC stress response and phenotypic switching is autophagy, which is activated by various stimuli, including reactive oxygen and lipid species, cytokines, growth factors and metabolic stress. Successful autophagy stimulates VSMC survival, whereas reduced autophagy promotes age-related changes in the vasculature. Recently, an interesting link between autophagy and VSMC senescence has been uncovered. Defective VSMC autophagy accelerates not only the development of stress-induced premature senescence but also atherogenesis, albeit without worsening plaque stability. VSMC senescence in atherosclerosis is likely a result of replicative senescence and/or stress-induced premature senescence in response to DNA damaging and/or oxidative stress-inducing stimuli. The finding that VSMC senescence can promote atherosclerosis further illustrates that normal, adequate VSMC function is crucial in protecting the vessel wall against atherosclerosis.

The Multifunctional Sorting Protein PACS-2 Controls Mitophagosome Formation in Human Vascular Smooth Muscle Cells through Mitochondria-ER Contact Sites

Mitochondria-associated ER membranes (MAMs) are crucial for lipid transport and synthesis, calcium exchange, and mitochondrial functions, and they also act as signaling platforms. These contact sites also play a critical role in the decision between autophagy and apoptosis with far reaching implications for cell fate. Vascular smooth muscle cell (VSMC) apoptosis accelerates atherogenesis and the progression of advanced lesions, leading to atherosclerotic plaque vulnerability and medial degeneration. Though the successful autophagy of damaged mitochondria promotes VSMC survival against pro-apoptotic atherogenic stressors, it is unknown whether MAMs are involved in VSMC mitophagy processes. Here, we investigated the role of the multifunctional MAM protein phosphofurin acidic cluster sorting protein 2 (PACS-2) in regulating VSMC survival following a challenge by atherogenic lipids. Using high-resolution confocal microscopy and proximity ligation assays, we found an increase in MAM contacts as in PACS-2-associated MAMs upon stimulation with atherogenic lipids. Correspondingly, the disruption of MAM contacts by PACS-2 knockdown impaired mitophagosome formation and mitophagy, thus potentiating VSMC apoptosis. In conclusion, our data shed new light on the significance of the MAM modulatory protein PACS-2 in vascular cell physiopathology and suggest MAMs may be a new target to modulate VSMC fate and favor atherosclerotic plaque stability.

An integrated PKD1-dependent signaling network amplifies IRE1 prosurvival signaling

Following the accumulation of improperly folded proteins in the endoplasmic reticulum (ER), a condition known as ER stress in this compartment triggers an adaptive signaling pathway referred to as the unfolded protein response (UPR). The UPR aims at restoring ER homeostasis; if the ER stress cannot be resolved, apoptosis is triggered. However, the mechanisms responsible for regulating the balance between cell life and death decisions that occur after exposure to ER stress remain unclear. Protein kinase D1 (PKD1) has been reported to initiate protective signaling against oxidative stress or ischemia, two conditions that impinge on the induction of ER stress. In addition, the high levels of expression of PKD1, observed in highly proliferative cancers and tumors with poor prognosis, contribute to enhanced resistance to chemotherapy. In this study, we show that the ER stress inducers tunicamycin and thapsigargin lead to the activation of PKD1 in human prostate cancer PC-3 cells and in hepatoma HepG2 cells through a PKCδ-dependent mechanism. Moreover, our data indicate that PKD1 is required for the stabilization of inositol-requiring enzyme 1 (IRE1) and the subsequent regulation of its activity. PKD1 activation contributes to the phosphorylation of mitogen-activated protein kinase phosphatase 1, resulting in decreased IRE1-mediated c-Jun N-terminal kinase activation. This study unveils the existence of a novel PKD1-dependent prosurvival mechanism that is activated upon ER stress and selectively enhances IRE1 prosurvival signaling.

MiR-210 inhibits hypoxia-induced apoptosis of smooth muscle cells via targeting MEF2C

BACKGROUND

Vascular smooth muscle cell (VSMC) apoptosis plays an important role in vascular remodeling and atherosclerotic plaque instability. Growing evidence suggests that microRNAs (miRNAs) play a critical role in VSMC function, however, the underlying mechanism remains unclear.

METHODS

This study used a hypoxic-induced VSMC apoptosis model. Expression of miR-210, its target MEF2C, and other key factors of apoptosis were detected and measured by real-time PCR and western blot. Luciferase reporter assay was performed to detect the miR-210 target. The function of miR-210 in apoptosis was determined using flow cytometric cell apoptosis assays. The relationship between miR-210 and MEF2C was confirmed and key apoptosis factors were detected.

RESULTS

The restoration of miR-210 function in cells transfected with a miR-210 mimic inhibited VSMC apoptosis compared to control. MiR-210 overexpression inhibited the expression of Bax, Bad, cleaved Caspase-3, and promoted the expression of Bcl-2, Caspase-3, Caspase-9 and mitochondrial cytochrome c at both the mRNA and protein levels. Results also found that MEF2C was a direct target of miR-210 in hypoxic VSMCs. Further, miR-210 suppressed MEF2C expression by directly binding to its 3'-untranslated region and the expression of miR-210 was negatively correlated with MEF2C mRNA levels.

CONCLUSIONS

Results from this study provide the first evidence that miR-210 can inhibit apoptosis by targeting MEF2C in hypoxic VSMCs and may support the development of new biomarkers and therapeutic targets for atherosclerosis.

PPARδ: A Potential Therapeutic Target for the Treatment of Metabolic Hypertension

High blood pressure and its associated cardiovascular diseases have been major risks for public health. Multiple metabolic risk factors can cause the vascular dysfunction and vascular lesion, and the hypertension due to metabolic disturbances was defined as metabolic hypertension. The members of a subfamily of the nuclear receptors, peroxisome proliferator-activated receptors (PPARs), were found to be key regulators of metabolism and vascular function. We provide up-to-date knowledge on the role of subtype PPARδ in the regulation of metabolism and vascular function and the effect of its intervention on the metabolic hypertension management. We hope to give some insights into the development of more effective treatments of metabolic hypertension and its main complications.

Calcium Signaling As a Therapeutic Target for Liver Steatosis

Hepatic steatosis, the first step in nonalcoholic fatty liver disease (NAFLD), can arise from various pathophysiological conditions. While lipid metabolism in the liver is normally balanced such that there is no excessive lipid accumulation, when this homeostasis is disrupted lipid droplets (LDs) accumulate in hepatocytes resulting in cellular toxicity. The mechanisms underlying this accumulation and the subsequent hepatocellular damage are multifactorial and poorly understood, with the result that there are no currently approved treatments for NAFLD. Impaired calcium signaling has recently been identified as a cause of increased endoplasmic reticulum (ER) stress contributing to hepatic lipid accumulation. This review highlights new findings on the role of impaired Ca²⁺ signaling in the development of steatosis and discusses potential new approaches to NAFLD treatment based on these new insights.

PLOD3 suppression exerts an anti-tumor effect on human lung cancer cells by modulating the PKC-delta signaling pathway

Current lung cancer treatments are far from satisfactory; thus, finding novel treatment targets is crucial. We recently identified procollagen-lysine, 2-oxoglutarate 5-dioxygenase 3 (PLOD3), which is involved in fibrosis and tissue remodeling as a radioresistance-related protein in lung cancer cells; however, its mechanism is unclear. In this study, we designed human PLOD3-specific short interfering (si)RNAs and tested their effects on tumor growth inhibition in vitro and in vivo. PLOD3 knockdown overcame chemoresistance and decreased radioresistance by inducing caspase-3-dependent apoptosis in lung cancer cells. Furthermore, PLOD3 interacted with PKCδ to activate caspase-2,4-dependent apoptosis through ER-stress-induced IRE1α activation and the downstream unfolded-protein response pathway. In a mouse xenograft model, PLOD3 knockdown promoted radiation-induced tumor growth inhibition, without side effects. Moreover, lung cancer patients with high PLOD3 expression showed poorer prognosis than those with low PLOD3 expression upon radiotherapy, suggesting that PLOD3 promotes tumor growth. Therefore, PLOD3 siRNA suppresses radioresistance and chemoresistance by inducing apoptosis and renders PLOD3 as a candidate lung cancer biomarker. PLOD3 gene therapy might enhance the efficacy of radiotherapy or chemotherapy in lung cancer patients.

The protein S-nitrosylation of splicing and translational machinery in vascular endothelial cells is susceptible to oxidative stress induced by oxidized low-density lipoprotein

Oxidized low-density lipoprotein (ox-LDL) can impair endothelial function and lead to the atherosclerosis development. Protein S-nitrosylation is sensitive to cellular redox state and acts as a crucial regulator and executor of nitric oxide (NO) signaling pathways. Aberrant S-nitrosylation contributes to the pathogenesis of cardiovascular and cerebrovascular diseases. However, the effect of ox-LDL on S-nitrosylation and its significance for endothelial dysfunction have not been studied at proteome level. Herein, the combined quantitative analysis of proteome and S-nitrosoproteome was performed using an integrated biotin switch and iTRAQ labeling approach in EA.hy926 cell line derived from human umbilical vein endothelial cell (HUVEC) treated with ox-LDL. A total of 2204 S-nitrosylated (SNO) peptides of 1318 SNO-proteins were quantified. Notably, 352 SNO-peptides of 262 SNO-proteins were significantly regulated after excluding S-nitrosylation changes caused by protein expression alterations. Many of them belonged to mRNA splicing, ribosomal structure and translational regulatory proteins, covering the entire translation process. The results indicated that S-nitrosylation of the splicing and translational machinery in vascular endothelial cells was susceptible to ox-LDL. Abnormal protein S-nitrosylation may be one pivotal mechanism underlying endothelial dysfunction induced by ox-LDL. This study potentially enriches the present understanding of pro-atherogenic effect of ox-LDL from the perspective of S-nitrosylation. SIGNIFICANCE: The role of ox-LDL in endothelial dysfunction and atherosclerosis development has been recognized from the aspect of impaired NO production. However, its effect on S-nitrosylation, which is directly related to NO signaling pathway, still remains largely unexplored. Our work initially provided a systematic characterization of S-nitrosoproteome in ox-LDL-treated endothelial cells after ruling out the changes of S-nitrosylation modification caused by protein expression alone. MS-based approach coupled with iTRAQ technique indicated 262 SNO-proteins were significantly regulated. Functional enrichment and interaction network analysis revealed that proteins involved in mRNA splicing and translational machinery were susceptible to abnormal S-nitrosylation under ox-LDL treatment. This achievement suggested one potential mechanism underlying endothelial dysfunction induced by ox-LDL from the perspective of S-nitrosoproteome.

Intracellular albumin overload elicits endoplasmic reticulum stress and PKC-delta/p38 MAPK pathway activation to induce podocyte apoptosis

Podocyte injury is closely related to proteinuria and the progression of chronic kidney disease (CKD). Currently, there is no conclusive understanding about the mechanisms involved in albumin overload and podocyte apoptosis response. In this study, we sought to explore the ways by which intracellular albumin can mediate podocyte apoptosis. Here, immortalized mouse podocytes were treated with bovine serum albumin (BSA) at different times and concentrations, in the presence or absence of SB203580 (0.1 µM, inhibitor of mitogen-activated-protein kinase – p38MAPK). Using immunofluorescence images, flow cytometry and immunoblotting, we observed a time-dependent intracellular accumulation of fluorescent albumin-FITC-BSA, followed by concentration-and time-dependent effect of intracellular albumin overload on podocyte apoptosis, which was mediated by increased expression of the chaperone glucose-regulated-protein 78 (GRP 78) and phosphorylated inositol-requiring enzyme 1 alpha (pIRE1-α), as well as protein kinase C delta (PKC-δ), p38MAPK and cleaved caspase 12 expression. SB203580 prevented the cleavage of caspase 12 and the albumin-mediated podocyte apoptosis. These results suggest that intracellular albumin overload is associated with endoplasmic reticulum (ER) stress and upregulation of PKC-δ/p38MAPK/caspase 12 pathway, which may be a target for future therapeutic of albumin-induced podocyte apoptosis.

Angiotensin II-induced podocyte apoptosis is mediated by endoplasmic reticulum stress/PKC-δ/p38 MAPK pathway activation and trough increased Na+/H+ exchanger isoform 1 activity

Background

Angiotensin II (Ang II) contributes to the progression of renal diseases associated with proteinuria and glomerulosclerosis mainly by inducing podocyte apoptosis. In the present study, we investigated whether the chronic effects of Ang II via AT1 receptor (AT1R) would result in endoplasmic reticulum (ER) stress/PKC-delta/p38 MAPK stimulation, and consequently podocyte apoptosis.

Methods

Wistar rats were treated with Ang II (200 ng·kg⁻¹·min⁻¹, 42 days) and or losartan (10 mg·kg⁻¹·day⁻¹, 14 days). Immortalized mouse podocyte were treated with 1 μM Ang II and/or losartan (1 μM) or SB203580 (0.1 μM) (AT1 receptor antagonist and p38 MAPK inhibitor) for 24 h. Kidney sections and cultured podocytes were used to evaluate protein expression by immunofluorescence and immunoblotting. Apoptosis was evaluated by flow cytometry and intracellular pH (pHi) was analyzed using microscopy combined with the fluorescent probe BCECF/AM.

Results

Compared with controls, Ang II via AT1R increased chaperone GRP 78/Bip protein expression in rat glomeruli (p < 0.001) as well as in podocyte culture (p < 0.01); increased phosphorylated eIf2-α (p < 0.05), PKC-delta (p < 0.01) and p38 MAPK (p < 0.001) protein expression. Furthermore, Ang II induced p38 MAPK-mediated late apoptosis and increased the Bax/Bcl-2 ratio (p < 0.001). Simultaneously, Ang II via AT1R induced p38 MAPK-NHE1-mediated increase of pHi recovery rate after acid loading.

Conclusion

Together, our results indicate that Ang II-induced podocyte apoptosis is associated with AT1R/ER stress/PKC-delta/p38 MAPK axis and enhanced NHE1-mediated pHi recovery rate.

Ox-LDL induces endothelial cell apoptosis and macrophage migration by regulating caveolin-1 phosphorylation

Oxidative low-density lipoprotein (ox-LDL) is a risk factor for atherosclerosis. Ox-LDL leads to endothelial injury in the initial stage of atherosclerosis. In this study, we investigated the role of ox-LDL in endothelial injury and macrophage recruitment. We demonstrated that ox-LDL promoted a dose-dependent phosphorylation of caveolin-1 in human umbilical vein endothelial cells. Phosphorylated caveolin-1 increased ox-LDL uptake. Intracellular accumulation of ox-LDL induced NF-κB p65 phosphorylation, promoted HMGB1 translocation from nucleus to cytoplasm and cytochrome C release from mitochondria to cytoplasm, and activated caspase 3, resulting in cell apoptosis. NF-κB activation also facilitated cavolin-1 phosphorylation and HMGB1 expression. In addition, caveolin-1 phosphorylation favored HMGB1 release and nuclear translocation of EGR1. Nuclear translocation of EGR1 contributed to cytoplasmic translocation of HMGB1. The extracellular HMGB1 induced the migration of PMBC-derived macrophages toward HUVECs in a TLR4-dependent manner. Our results suggested that ox-LDL promoted HUVECs apoptosis and macrophage recruitment by regulating caveolin-1 phosphorylation.

Mitophagy acts as a safeguard mechanism against human vascular smooth muscle cell apoptosis induced by atherogenic lipids

Mitophagy is a critical cellular process that selectively targets damaged mitochondria for autophagosomal degradation both under baseline conditions and in response to stress preventing oxidative damage and cell death. Recent studies have linked alterations in mitochondria function and reduced autophagy with the development of age-related pathologies. However, the significance of mitochondrial autophagy in vessel wall in response to atherogenic lipid stressors is not known. In the present study, we investigated the role of mitophagy on human vascular smooth muscle cells (VSMC) apoptosis induced by oxidized low-density lipoproteins (LDL). We reported for the first time that the engulfment of defective mitochondria by autophagosomes occurred in human VSMC in response to oxidized LDL. The molecular mechanism mediating mitophagy in human VSMC involved dynamin-related protein 1 (Drp1)-mediated mitochondrial fission, accumulation of PTEN-induced putative kinase 1 (PINK1) and the recruitment of the E3 ubiquitin ligase Parkin to mitochondria. Likewise, we found increased voltage-dependent anion channel 1 (VDAC1) and mitofusin 2 (Mnf2) mitochondrial proteins ubiquitination and LC3 association to mitochondria. Using flow cytometry in the presence of lysosomal inhibitors, we showed that PINK1 and Parkin silencing impaired mitophagy flux and enhanced oxidized LDL-induced VSMC apoptosis. In addition, overexpression of PINK1 and Parkin were protective by limiting cell death. Moreover, reduced Bax levels found in VSMC-overexpressing Parkin indicated cross talk among mitophagy and mitochondrial apoptotic signalling pathways. Altogether these data demonstrate that mitophagy is a safeguard mechanism against human VSMC apoptosis induced by atherogenic stressors and highlight mitophagy as a potential target to stabilize atherosclerotic plaque.

Deficiency of CCAAT/enhancer-binding protein homologous protein (CHOP) prevents diet-induced aortic valve calcification in vivo

Aortic valve (AoV) calcification is common in aged populations. Its subsequent aortic stenosis has been linked with increased morbidity, but still has no effective pharmacological intervention. Our previous data show endoplasmic reticulum (ER) stress is involved in AoV calcification. Here, we investigated whether deficiency of ER stress downstream effector CCAAT/enhancer-binding protein homology protein (CHOP) may prevent development of AoV calcification. AoV calcification was evaluated in Apoe-/- mice (n = 10) or in mice with dual deficiencies of ApoE and CHOP (Apoe-/- CHOP-/- , n = 10) fed with Western diet for 24 weeks. Histological and echocardiographic analysis showed that genetic ablation of CHOP attenuated AoV calcification, pro-calcification signaling activation, and apoptosis in the leaflets of Apoe-/- mice. In cultured human aortic valvular interstitial cells (VIC), we found oxidized low-density lipoprotein (oxLDL) promoted apoptosis and osteoblastic differentiation of VIC via CHOP activation. Using conditioned media (CM) from oxLDL-treated VIC, we further identified that oxLDL triggered osteoblastic differentiation of VIC via paracrine pathway, while depletion of apoptotic bodies (ABs) in CM suppressed the effect. CM from oxLDL-exposed CHOP-silenced cells prevented osteoblastic differentiation of VIC, while depletion of ABs did not further enhance this protective effect. Overall, our study indicates that CHOP deficiency protects against Western diet-induced AoV calcification in Apoe-/- mice. CHOP deficiency prevents oxLDL-induced VIC osteoblastic differentiation via preventing VIC-derived ABs releasing.

Oxidative Stress-Mediated Atherosclerosis: Mechanisms and Therapies

Atherogenesis, the formation of atherosclerotic plaques, is a complex process that involves several mechanisms, including endothelial dysfunction, neovascularization, vascular proliferation, apoptosis, matrix degradation, inflammation, and thrombosis. The pathogenesis and progression of atherosclerosis are explained differently by different scholars. One of the most common theories is the destruction of well-balanced homeostatic mechanisms, which incurs the oxidative stress. And oxidative stress is widely regarded as the redox status realized when an imbalance exists between antioxidant capability and activity species including reactive oxygen (ROS), nitrogen (RNS) and halogen species, non-radical as well as free radical species. This occurrence results in cell injury due to direct oxidation of cellular protein, lipid, and DNA or via cell death signaling pathways responsible for accelerating atherogenesis. This paper discusses inflammation, mitochondria, autophagy, apoptosis, and epigenetics as they induce oxidative stress in atherosclerosis, as well as various treatments for antioxidative stress that may prevent atherosclerosis.

Chronic Intermittent Hypobaric Hypoxia Improves Cardiac Function through Inhibition of Endoplasmic Reticulum Stress

We investigated the role of endoplasmic reticulum stress (ERS) in chronic intermittent hypobaric hypoxia (CIHH)-induced cardiac protection. Adult male Sprague-Dawley rats were exposed to CIHH treatment simulating 5000 m altitude for 28 days, 6 hours per day. The heart was isolated and perfused with Langendorff apparatus and subjected to 30-min ischemia followed by 60-min reperfusion. Cardiac function, infarct size, and lactate dehydrogenase (LDH) activity were assessed. Expression of ERS molecular chaperones (GRP78, CHOP and caspase-12) was assayed by western blot analysis. CIHH treatment improved the recovery of left ventricular function and decreased cardiac infarct size and activity of LDH after I/R compared to control rats. Furthermore, CIHH treatment inhibited over-expression of ERS-related factors including GRP78, CHOP and caspase-12. CIHH-induced cardioprotection and inhibition of ERS were eliminated by application of dithiothreitol, an ERS inducer, and chelerythrine, a protein kinase C (PKC) inhibitor. In conclusion CIHH treatment exerts cardiac protection against I/R injury through inhibition of ERS via PKC signaling pathway.

Perpetual change: autophagy, the endothelium, and response to vascular injury

Current studies of vascular health, aging, and autophagy emphasize how the endothelium adapts to stress and contributes to disease. The endothelium is far from an inert barrier to blood-borne cells, pathogens, and chemical signals; rather, it actively translates circulating mediators into tissue responses, changing rapidly in response to physiologic stressors. Macroautophagy-the cellular ingestion of effete organelles and protein aggregates to provide anabolic substrates to fuel bioenergetics in times of stress-plays an important role in endothelial cell homeostasis, vascular remodeling, and disease. These roles include regulating vascular tone, sustaining or limiting cell survival, and contributing to the development of atherosclerosis secondary to infection, inflammation, and angiogenesis. Autophagy modulates these critical functions of the endothelium in a dynamic and perpetual response to tissue and intravascular cues.

Endoplasmic Reticulum Stress in Arterial Smooth Muscle Cells: A Novel Regulator of Vascular Disease

Cardiovascular disease continues to be the leading cause of death in industrialised societies. The idea that the arterial smooth muscle cell (ASMC) plays a key role in regulating many vascular pathologies has been gaining importance, as has the realisation that not enough is known about the pathological cellular mechanisms regulating ASMC function in vascular remodelling. In the past decade endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) have been recognised as a stress response underlying many physiological and pathological processes in various vascular cell types. Here we summarise what is known about how ER stress signalling regulates phenotypic switching, trans/dedifferentiation and apoptosis of ASMCs and contributes to atherosclerosis, hypertension, aneurysms and vascular calcification.

Melanoma Differentiation-associated Gene 7/IL-24 Exerts Cytotoxic Effects by Altering the Alternative Splicing of Bcl-x Pre-mRNA via the SRC/PKCδ Signaling Axis

Melanoma differentiation-associated gene 7 (MDA-7/IL-24) exhibits cytotoxic effects on tumor cells while sparing untransformed cells, and Bcl-x(L) is reported to efficiently block the induction of cell death by MDA-7/IL-24. The expression of Bcl-x(L) is regulated at the level of RNA splicing via alternative 5' splice site selection within exon 2 to produce either the pro-apoptotic Bcl-x(s) or the anti-apoptotic Bcl-x(L). Our laboratory previously reported that Bcl-x RNA splicing is dysregulated in a large percentage of human non-small cell lung cancer (NSCLC) tumors. Therefore, we investigated whether the alternative RNA splicing of Bcl-x pre-mRNA was modulated by MDA-7/IL-24, which would suggest that specific NSCLC tumors are valid targets for this cytokine therapy. Adenovirus-delivered MDA-7/IL-24 (Ad.mda-7) reduced the viability of NSCLC cells of varying oncogenotypes, which was preceded by a decrease in the ratio of Bcl-x(L)/Bcl-x(s) mRNA and Bcl-x(L) protein expression. Importantly, both the expression of Bcl-x(L) and the loss of cell viability were "rescued" in Ad.mda-7-treated cells incubated with Bcl-x(s) siRNA. In addition, NSCLC cells ectopically expressing Bcl-x(s) exhibited significantly reduced Bcl-x(L) expression, which was again restored by Bcl-x(s) siRNA, suggesting the existence of a novel mechanism by which Bcl-x(s) mRNA restrains the expression of Bcl-x(L). In additional mechanistic studies, inhibition of SRC and PKCδ completely ablated the ability of MDA-7/IL-24 to reduce the Bcl-x(L)/(s) mRNA ratio and cell viability. These findings show that Bcl-x(s) expression is an important mediator of MDA-7/IL-24-induced cytotoxicity requiring the SRC/PKCδ signaling axis in NSCLC cells.

Role of PKCδ in Enhanced Expression of Gqα/PLCβ1 Proteins and VSMC Hypertrophy in Spontaneously Hypertensive Rats

Gqα signaling has been implicated in cardiac hypertrophy. In addition, angiotensin II (Ang II) was also shown to induce its hypertrophic effect through Gqα and PKCδ activation. We recently showed the role of enhanced expression of Gqα/PLCβ1 proteins in vascular smooth muscle cell (VSMC) hypertrophy, however, the role of PKCδ in VSMC hypertrophy in animal model is still lacking. The present study was therefore undertaken to examine the role of PKCδ and the associated signaling mechanisms in VSMC hypertrophy using 16-week-old spontaneously hypertensive rats (SHR). VSMC from 16-week-old SHR exhibited enhanced phosphorylation of PKCδ-Tyr311 and increased protein synthesis, marker of hypertrophy, as compared to WKY rats which was attenuated by rottlerin, an inhibitor of PKCδ. In addition, knocking down of PKCδ by PKCδ-siRNA also attenuated enhanced protein synthesis in VSMC from SHR. Furthermore, rottlerin attenuated the increased production of superoxide anion, NAD(P)H oxidase activity, increased expression of Gqα, phospholipase C (PLC)β1, insulin like growth factor-1 receptor (IGF-1R) and epidermal growth factor receptor (EGFR) proteins in VSMC from SHR. In addition, the enhanced phosphorylation of c-Src, PKCδ-Tyr311, IGF-1R, EGFR and ERK1/2 exhibited by VSMC from SHR was also attenuated by rottlerin. These results suggest that VSMC from SHR exhibit enhanced activity of PKCδ and that PKCδ is the upstream molecule of reactive oxygen species (ROS) and contributes to the enhanced expression of Gqα and PLCβ1 proteins and resultant VSMC hypertrophy involving c-Src, growth factor receptor transactivation and MAP kinase signaling.

Distinctive roles of PKC delta isozyme in platelet function

Platelet activation is a complex balance of positive and negative signaling pathways. Several protein kinase C (PKC) isoforms are expressed in human platelets. They are a major regulator of platelet granule secretion, activation and aggregation activity. One of those isoforms is the PKCδ isozyme, it has a central yet complex role in platelets such as opposite signaling functions depending on the nature of the agonist, it concentration and pathway. In fact, it has been shown that PKCδ has an overall negative influence on platelet function in response to collagen, while, following PAR stimulation, PKCδ has a positive effect on platelet function. Understanding the crucial role of PKCδ in platelet functions is recently emerging in the literature, therefore, further investigations should shed light into its specific role in hemostasis. In this review, we focus on the different roles of PKCδ in platelet activation, aggregation and thrombus formation.

TRAF3IP2 mediates atherosclerotic plaque development and vulnerability in ApoE(-/-) mice

BACKGROUND AND AIMS

Atherosclerosis is a major cause of heart attack and stroke. Inflammation plays a critical role in the development of atherosclerosis. Since the cytoplasmic adaptor molecule TRAF3IP2 (TRAF3-Interacting Protein 2) plays a causal role in various autoimmune and inflammatory diseases, we hypothesized that TRAF3IP2 mediates atherosclerotic plaque development.

METHODS

TRAF3IP2/ApoE double knockout (DKO) mice were generated by crossing TRAF3IP2(-/-) and ApoE(-/-) mice. ApoE(-/-) mice served as controls. Both DKO and control mice were fed a high-fat diet for 12 weeks. Plasma lipids were measured by ELISA, atherosclerosis by en face analysis of aorta and plaque cross-section measurements at the aortic valve region, plaque necrotic core area, collagen and smooth muscle cell (SMC) content by histomorphometry, and aortic gene expression by RT-qPCR.

RESULTS

The plasma lipoprotein profile was not altered by TRAF3IP2 gene deletion in ApoE(-/-) mice. While total aortic plaque area was decreased in DKO female, but not male mice, the plaque necrotic area was significantly decreased in DKO mice of both genders. Plaque collagen and SMC contents were increased significantly in both female and male DKO mice compared to respective controls. Aortic expression of proinflammatory cytokine (Tumor necrosis factor α, TNFα), chemokine (Chemokine (C-X-C motif) Ligand 1, CXCL1) and adhesion molecule (Vascular cell adhesion molecule 1, VCAM1; and Intercellular adhesion molecule 1, ICAM1) gene expression were decreased in both male and female DKO mice. In addition, the male DKO mice expressed markedly reduced levels of extracellular matrix (ECM)-related genes, including TIMP1 (Tissue inhibitor of metalloproteinase 1), RECK (Reversion-Inducing-Cysteine-Rich Protein with Kazal Motifs) and ADAM17 (A Disintegrin And Metalloproteinase 17).

CONCLUSIONS

TRAF3IP2 plays a causal role in atherosclerotic plaque development and vulnerability, possibly by inducing the expression of multiple proinflammatory mediators. TRAF3IP2 could be a potential therapeutic target in atherosclerotic vascular diseases.

The anti-hypertensive drug prazosin inhibits glioblastoma growth via the PKCδ-dependent inhibition of the AKT pathway

A variety of drugs targeting monoamine receptors are routinely used in human pharmacology. We assessed the effect of these drugs on the viability of tumor-initiating cells isolated from patients with glioblastoma. Among the drugs targeting monoamine receptors, we identified prazosin, an α1- and α2B-adrenergic receptor antagonist, as the most potent inducer of patient-derived glioblastoma-initiating cell death. Prazosin triggered apoptosis of glioblastoma-initiating cells and of their differentiated progeny, inhibited glioblastoma growth in orthotopic xenografts of patient-derived glioblastoma-initiating cells, and increased survival of glioblastoma-bearing mice. We found that prazosin acted in glioblastoma-initiating cells independently from adrenergic receptors. Its off-target activity occurred via a PKCδ-dependent inhibition of the AKT pathway, which resulted in caspase-3 activation. Blockade of PKCδ activation prevented all molecular changes observed in prazosin-treated glioblastoma-initiating cells, as well as prazosin-induced apoptosis. Based on these data, we conclude that prazosin, an FDA-approved drug for the control of hypertension, inhibits glioblastoma growth through a PKCδ-dependent mechanism. These findings open up promising prospects for the use of prazosin as an adjuvant therapy for glioblastoma patients.

Lysophosphatidic acid receptor 1 antagonist ki16425 blunts abdominal and systemic inflammation in a mouse model of peritoneal sepsis

Lysophosphatidic acid (LPA) is a bioactive lipid mediator of inflammation via the LPA receptors 1-6. We and others have previously described proinflammatory and profibrotic activities of LPA signaling in bleomycin- or lipopolysaccharide (LPS)-induced pulmonary fibrosis or lung injury models. In this study, we investigated if LPA signaling plays a role in the pathogenesis of systemic sepsis from an abdominal source. We report here that antagonism of the LPA receptor LPA1 with the small molecule ki16425 reduces the severity of abdominal inflammation and organ damage in the setting of peritoneal endotoxin exposure. Pretreatment of mice with intraperitoneal ki16425 eliminates LPS-induced peritoneal neutrophil chemokine and cytokine production, liver oxidative stress, liver injury, and cellular apoptosis in visceral organs. Mice pretreated with ki16425 are also protected from LPS-induced mortality. Tissue myeloperoxidase activity is not affected by LPA1 antagonism. We have shown that LPA1 is associated with LPS coreceptor CD14 and the association is suppressed by ki16425. LPS-induced phosphorylation of protein kinase C δ (PKCδ) and p38 mitogen-activated protein kinase (p38 MAPK) in liver cells and interleukin 6 production in Raw264 cells are likewise blunted by LPA1 antagonism. These studies indicate that the small molecule inhibitor of LPA1, ki16425, suppresses cytokine responses and inflammation in a peritoneal sepsis model by blunting downstream signaling through the LPA1-CD14-toll-like receptor 4 receptor complex. This anti-inflammatory effect may represent a therapeutic strategy for the treatment of systemic inflammatory responses to infection of the abdominal cavity.

Ethambutol induces impaired autophagic flux and apoptosis in the rat retina

Ethambutol (EMB), an effective first-line antituberculosis agent, can cause serious visual impairment or irreversible vision loss in a significant number of patients. However, the mechanism underlying this ocular cytotoxicity remains to be elucidated. In this study, we found that there were statistically significant dose- and time-dependent increases in the number of cytoplasmic vacuoles and the level of cell death in EMB-treated RGC-5 cells (retinal ganglion cells). The protein kinase C (PKC)δ inhibitor rottlerin markedly reduced the EMB-induced activation of caspase-3 and the subsequent apoptosis of RGC-5 cells. Western blot analysis revealed that the expression levels of class III PI3K, Beclin-1, p62 and LC3-II were upregulated, and LC3 immunostaining results showed activation of the early phase and inhibition of the late stage of autophagy in retinas of the EMB-intraperitoneal (IP)-injected rat model. We further demonstrated that exposure to EMB induces autophagosome accumulation, which results from the impaired autophagic flux that is mediated by a PKCδ-dependent pathway, inhibits the PI3K/Akt/mTOR signaling pathway and leads to apoptotic death in retina neuronal cells. These results indicate that autophagy dysregulation in retinal neuronal cells might play a substantial role in EMB-induced optic neuroretinopathy.

Summary: This study provides the first evidence that EMB induces autophagosome accumulation, which results from the impaired autophagic flux that is mediated by a PKCδ-dependent pathway, and leads to apoptotic death in retina neuronal cells.

Cantharidin Induces Apoptosis Through the Calcium/PKC-Regulated Endoplasmic Reticulum Stress Pathway in Human Bladder Cancer Cells

Bladder cancer is a common malignancy worldwide. However, there is still no effective therapy for bladder cancer. In this study, we investigated the cytotoxic effects of cantharidin [a natural toxin produced (pure compound) from Chinese blister beetles (Mylabrisphalerata or Mylabriscichorii) and Spanish flies (Cantharis vesicatoria)] in human bladder cancer cell lines (including: T24 and RT4 cells). Treatment of human bladder cancer cells with cantharidin significantly decreased cell viability. The increase in the expressions of caspase-3 activity and cleaved form of caspase-9/-7/-3 were also increased in cantharidin-treated T24 cells. Furthermore, cantharidin increased the levels of phospho-eIF2α and Grp78 and decreased the protein expression of procaspase-12, which was accompanied by the increase in calpain activity in T24 cells. Cantharidin was capable of increasing the intracellular Ca 2+ and the phosphorylation of protein kinase C (PKC) in T24 cells. The addition of BAPTA/AM (a Ca 2+ chelator) and RO320432 (a selective cell-permeable PKC inhibitor) effectively reversed the increase in caspase-3 and calpain activity, the phosphorylation levels of PKC and eIF2α and Grp78 protein expression, and the decrease in procaspase-12 expression induced by cantharidin. Importantly, cantharidin significantly decreased the tumor volume (a dramatic 71% reduction after 21 days of treatment) in nude mice xenografted with T24 cells. Taken together, these results indicate cantharidin induced human bladder cancer cell apoptosis through a calcium/PKC-regulated ER stress pathway. These findings suggest that cantharidin may be a novel and potential anticancer agent targeting on bladder cancer cells.