TNIK regulation of interferon signaling and endothelial cell response to virus infection

Background

Traf2 and Nck-interacting kinase (TNIK) is known for its regulatory role in various processes within cancer cells. However, its role within endothelial cells (ECs) has remained relatively unexplored.

Methods

Leveraging RNA-seq data and Ingenuity Pathway Analysis (IPA), we probed the potential impact of TNIK depletion on ECs.

Results

Examination of RNA-seq data uncovered more than 450 Differentially Expressed Genes (DEGs) in TNIK-depleted ECs, displaying a fold change exceeding 2 with a false discovery rate (FDR) below 0.05. IPA analysis unveiled that TNIK depletion leads to the inhibition of the interferon (IFN) pathway [-log (p-value) >11], downregulation of IFN-related genes, and inhibition of Hypercytokinemia/Hyperchemokinemia [-log (p-value) >8]. The validation process encompassed qRT-PCR to evaluate mRNA expression of crucial IFN-related genes, immunoblotting to gauge STAT1 and STAT2 protein levels, and ELISA for the quantification of IFN and cytokine secretion in siTNIK-depleted ECs. These assessments consistently revealed substantial reductions upon TNIK depletion. When transducing HUVECs with replication incompetent E1-E4 deleted adenovirus expressing green fluorescent protein (Ad-GFP), it was demonstrated that TNIK depletion did not affect the uptake of Ad-GFP. Nonetheless, TNIK depletion induced cytopathic effects (CPE) in ECs transduced with wild-type human adenovirus serotype 5 (Ad-WT).

Summary

Our findings suggest that TNIK plays a crucial role in regulating the EC response to virus infections through modulation of the IFN pathway.

Heterozygous Kmt2d loss diminishes enhancers to render medulloblastoma cells vulnerable to combinatory inhibition of lysine demethylation and oxidative phosphorylation

The histone H3 lysine 4 (H3K4) methyltransferase KMT2D (also called MLL4) is one of the most frequently mutated epigenetic modifiers in medulloblastoma (MB) and other types of cancer. Notably, heterozygous loss of KMT2D is prevalent in MB and other cancer types. However, what role heterozygous KMT2D loss plays in tumorigenesis has not been well characterized. Here, we show that heterozygous Kmt2d loss highly promotes MB driven by heterozygous loss of the MB suppressor gene Ptch in mice. Heterozygous Kmt2d loss upregulated tumor-promoting programs, including oxidative phosphorylation and G-protein-coupled receptor signaling, in Ptch-mutant-driven MB genesis. Mechanistically, both downregulation of the transcription-repressive tumor suppressor gene NCOR2 by heterozygous Kmt2d loss and upregulation of the oncogene MycN by heterozygous Ptch loss increased the expression of tumor-promoting genes. Moreover, heterozygous Kmt2d loss extensively diminished enhancer signals (e.g., H3K27ac) and H3K4me3 signature, including those for tumor suppressor genes (e.g., Ncor2). Combinatory pharmacological inhibition of oxidative phosphorylation and the H3K4 demethylase LSD1 drastically reduced tumorigenicity of MB cells bearing heterozygous Kmt2d loss. These findings reveal the mechanistic basis underlying the MB-promoting effect of heterozygous KMT2D loss, provide a rationale for a therapeutic strategy for treatment of KMT2D-deficient MB, and have mechanistic implications for the molecular pathogenesis of other types of cancer bearing heterozygous KMT2D loss.

Premature senescence and cardiovascular disease following cancer treatments: mechanistic insights

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality, especially among the aging population. The "response-to-injury" model proposed by Dr. Russell Ross in 1999 emphasizes inflammation as a critical factor in atherosclerosis development, with atherosclerotic plaques forming due to endothelial cell (EC) injury, followed by myeloid cell adhesion and invasion into the blood vessel walls. Recent evidence indicates that cancer and its treatments can lead to long-term complications, including CVD. Cellular senescence, a hallmark of aging, is implicated in CVD pathogenesis, particularly in cancer survivors. However, the precise mechanisms linking premature senescence to CVD in cancer survivors remain poorly understood. This article aims to provide mechanistic insights into this association and propose future directions to better comprehend this complex interplay.

Aerobic Exercise Alters the Melanoma Microenvironment and Modulates ERK5 S496 Phosphorylation

Exercise changes the tumor microenvironment by remodeling blood vessels and increasing infiltration by cytotoxic immune cells. The mechanisms driving these changes remain unclear. Herein, we demonstrate that exercise normalizes tumor vasculature and upregulates endothelial expression of VCAM1 in YUMMER 1.7 and B16F10 murine models of melanoma but differentially regulates tumor growth, hypoxia, and the immune response. We found that exercise suppressed tumor growth and increased CD8+ T-cell infiltration in YUMMER but not in B16F10 tumors. Single-cell RNA sequencing and flow cytometry revealed exercise modulated the number and phenotype of tumor-infiltrating CD8+ T cells and myeloid cells. Specifically, exercise caused a phenotypic shift in the tumor-associated macrophage population and increased the expression of MHC class II transcripts. We further demonstrated that ERK5 S496A knock-in mice, which are phosphorylation deficient at the S496 residue, "mimicked" the exercise effect when unexercised, yet when exercised, these mice displayed a reversal in the effect of exercise on tumor growth and macrophage polarization compared with wild-type mice. Taken together, our results reveal tumor-specific differences in the immune response to exercise and show that ERK5 signaling via the S496 residue plays a crucial role in exercise-induced tumor microenvironment changes. See related Spotlight by Betof Warner, p. 1158.

Endothelial activation and fibrotic changes are impeded by laminar flow-induced CHK1-SENP2 activity through mechanisms distinct from endothelial-to-mesenchymal cell transition

Background

The deSUMOylase sentrin-specific isopeptidase 2 (SENP2) plays a crucial role in atheroprotection. However, the phosphorylation of SENP2 at T368 under disturbed flow (D-flow) conditions hinders its nuclear function and promotes endothelial cell (EC) activation. SUMOylation has been implicated in D-flow-induced endothelial-to-mesenchymal transition (endoMT), but the precise role of SENP2 in counteracting this process remains unclear.

Method

We developed a phospho-specific SENP2 S344 antibody and generated knock-in (KI) mice with a phospho-site mutation of SENP2 S344A using CRISPR/Cas9 technology. We then investigated the effects of SENP2 S344 phosphorylation under two distinct flow patterns and during hypercholesteremia (HC)-mediated EC activation.

Result

Our findings demonstrate that laminar flow (L-flow) induces phosphorylation of SENP2 at S344 through the activation of checkpoint kinase 1 (CHK1), leading to the inhibition of ERK5 and p53 SUMOylation and subsequent suppression of EC activation. We observed a significant increase in lipid-laden lesions in both the aortic arch (under D-flow) and descending aorta (under L-flow) of female hypercholesterolemic SENP2 S344A KI mice. In male hypercholesterolemic SENP2 S344A KI mice, larger lipid-laden lesions were only observed in the aortic arch area, suggesting a weaker HC-mediated atherogenesis in male mice compared to females. Ionizing radiation (IR) reduced CHK1 expression and SENP2 S344 phosphorylation, attenuating the pro-atherosclerotic effects observed in female SENP2 S344A KI mice after bone marrow transplantation (BMT), particularly in L-flow areas. The phospho-site mutation SENP2 S344A upregulates processes associated with EC activation, including inflammation, migration, and proliferation. Additionally, fibrotic changes and up-regulated expression of EC marker genes were observed. Apoptosis was augmented in ECs derived from the lungs of SENP2 S344A KI mice, primarily through the inhibition of ERK5-mediated expression of DNA damage-induced apoptosis suppressor (DDIAS).

Summary

In this study, we have revealed a novel mechanism underlying the suppressive effects of L-flow on EC inflammation, migration, proliferation, apoptosis, and fibrotic changes through promoting CHK1-induced SENP2 S344 phosphorylation. The phospho-site mutation SENP2 S344A responds to L-flow through a distinct mechanism, which involves the upregulation of both mesenchymal and EC marker genes.

An ERK5-NRF2 Axis Mediates Senescence-Associated Stemness and Atherosclerosis

BACKGROUND

ERK5 (extracellular signal-regulated kinase 5) is a dual kinase transcription factor containing an N-terminal kinase domain and a C-terminal transcriptional activation domain. Many ERK5 kinase inhibitors have been developed and tested to treat cancer and inflammatory diseases. However, recent data have raised questions about the role of the catalytic activity of ERK5 in proliferation and inflammation. We aimed to investigate how ERK5 reprograms myeloid cells to the proinflammatory senescent phenotype, subsequently leading to atherosclerosis.

METHODS

A ERK5 S496A (dephosphorylation mimic) knock in (KI) mouse model was generated using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated 9), and atherosclerosis was characterized by hypercholesterolemia induction. The plaque phenotyping in homozygous ERK5 S496A KI and wild type (WT) mice was studied using imaging mass cytometry. Bone marrow-derived macrophages were isolated from hypercholesterolemic mice and characterized using RNA sequencing and functional in vitro approaches, including senescence, mitochondria reactive oxygen species, and inflammation assays, as well as by metabolic extracellular flux analysis.

RESULTS

We show that atherosclerosis was inhibited in ERK5 S496A KI mice. Furthermore, ERK5 S496 phosphorylation mediates both senescence-associated secretory phenotype and senescence-associated stemness by upregulating AHR (aryl hydrocarbon receptor) in plaque and bone marrow-derived macrophages isolated from hypercholesterolemic mice. We also discovered that ERK5 S496 phosphorylation could induce NRF2 (NFE2-related factor 2) SUMOylation at a novel K518 site to inhibit NRF2 transcriptional activity without altering ERK5 catalytic activity and mediates oxidized LDL (low-density lipoprotein)-induced senescence-associated secretory phenotype. Specific ERK5 kinase inhibitors (AX15836 and XMD8-92) also inhibited ERK5 S496 phosphorylation, suggesting the involvement of ERK5 S496 phosphorylation in the anti-inflammatory effects of these ERK5 kinase inhibitors.

CONCLUSIONS

We discovered a novel mechanism by which the macrophage ERK5-NRF2 axis develops a unique senescence-associated secretory phenotype/stemness phenotype by upregulating AHR to engender atherogenesis. The finding of senescence-associated stemness phenotype provides a molecular explanation to resolve the paradox of senescence in proliferative plaque by permitting myeloid cells to escape the senescence-induced cell cycle arrest during atherosclerosis formation.

Possible molecular mechanisms underlying the development of atherosclerosis in cancer survivors

Cancer survivors undergone treatment face an increased risk of developing atherosclerotic cardiovascular disease (CVD), yet the underlying mechanisms remain elusive. Recent studies have revealed that chemotherapy can drive senescent cancer cells to acquire a proliferative phenotype known as senescence-associated stemness (SAS). These SAS cells exhibit enhanced growth and resistance to cancer treatment, thereby contributing to disease progression. Endothelial cell (EC) senescence has been implicated in atherosclerosis and cancer, including among cancer survivors. Treatment modalities for cancer can induce EC senescence, leading to the development of SAS phenotype and subsequent atherosclerosis in cancer survivors. Consequently, targeting senescent ECs displaying the SAS phenotype hold promise as a therapeutic approach for managing atherosclerotic CVD in this population. This review aims to provide a mechanistic understanding of SAS induction in ECs and its contribution to atherosclerosis among cancer survivors. We delve into the mechanisms underlying EC senescence in response to disturbed flow and ionizing radiation, which play pivotal role in atherosclerosis and cancer. Key pathways, including p90RSK/TERF2IP, TGFβR1/SMAD, and BH4 signaling are explored as potential targets for cancer treatment. By comprehending the similarities and distinctions between different types of senescence and the associated pathways, we can pave the way for targeted interventions aim at enhancing the cardiovascular health of this vulnerable population. The insights gained from this review may facilitate the development of novel therapeutic strategies for managing atherosclerotic CVD in cancer survivors.

Radiation therapy induces immunosenescence mediated by p90RSK

Radiation therapy (RT) to the chest increases the patients' risk of cardiovascular disease (CVD). A complete understanding of the mechanisms by which RT induces CVD could lead to specific preventive, therapeutic approaches. It is becoming evident that both genotoxic chemotherapy agents and radiation induce mitochondrial dysfunction and cellular senescence. Notably, one of the common phenotypes observed in cancer survivors is accelerated senescence, and immunosenescence is closely related to both cancer risk and CVD development. Therefore, suppression of immunosenescence can be an ideal target to prevent cancer treatment-induced CVD. However, the mechanism(s) by which cancer treatments induce immunosenescence are incompletely characterized. We isolated peripheral blood mononuclear cells (PBMCs) before and 3 months after RT from 16 thoracic cancer patients. We characterized human immune cell lineages and markers of senescence, DNA damage response (DDR), efferocytosis, and determinants of clonal hematopoiesis of indeterminant potential (CHIP), using mass cytometry (CyTOF). We found that the frequency of the B cell subtype was decreased after RT. Unsupervised clustering of the CyTOF data identified 138 functional subsets of PBMCs. Compared with baseline, RT increased TBX21 (T-bet) expression in the largest B cell subset of Ki67-/DNMT3a+naïve B cells, and T-bet expression was correlated with phosphorylation of p90RSK expression. CD38 expression was also increased in naïve B cells (CD27-) and CD8+ effector memory CD45RA T cells (TEMRA). In vitro, we found the critical role of p90RSK activation in upregulating (1) CD38+/T-bet+ memory and naïve B, and myeloid cells, (2) senescence-associated β-gal staining, and (3) mitochondrial reactive oxygen species (ROS) after ionizing radiation (IR). These data suggest the crucial role of p90RSK activation in immunosenescence. The critical role of p90RSK activation in immune cells and T-bet induction in upregulating atherosclerosis formation has been reported. Furthermore, T-bet directly binds to the CD38 promoter region and upregulates CD38 expression. Since both T-bet and CD38 play a significant role in the process of immunosenescence, our data provide a cellular and molecular mechanism that links RT-induced p90RSK activation and the immunosenescence with T-bet and CD38 induction observed in thoracic cancer patients treated by RT and suggests that targeting the p90RSK/T-bet/CD38 pathway could play a role in preventing the radiation-associated CVD and improving cancer prognosis by inhibiting immunosenescence.

MAGI1 inhibits interferon signaling to promote influenza A infection

We have shown that membrane-associated guanylate kinase with inverted domain structure-1 (MAGI1), a scaffold protein with six PSD95/DiscLarge/ZO-1 (PDZ) domains, is involved in the regulation of endothelial cell (EC) activation and atherogenesis in mice. In addition to causing acute respiratory disease, influenza A virus (IAV) infection plays an important role in atherogenesis and triggers acute coronary syndromes and fatal myocardial infarction. Therefore, the aim of this study is to investigate the function and regulation of MAGI1 in IAV-induced EC activation. Whereas, EC infection by IAV increases MAGI1 expression, MAGI1 depletion suppresses IAV infection, suggesting that the induction of MAGI1 may promote IAV infection. Treatment of ECs with oxidized low-density lipoprotein (OxLDL) increases MAGI1 expression and IAV infection, suggesting that MAGI1 is part of the mechanistic link between serum lipid levels and patient prognosis following IAV infection. Our microarray studies suggest that MAGI1-depleted ECs increase protein expression and signaling networks involve in interferon (IFN) production. Specifically, infection of MAGI1-null ECs with IAV upregulates expression of signal transducer and activator of transcription 1 (STAT1), interferon b1 (IFNb1), myxovirus resistance protein 1 (MX1) and 2'-5'-oligoadenylate synthetase 2 (OAS2), and activate STAT5. By contrast, MAGI1 overexpression inhibits Ifnb1 mRNA and MX1 expression, again supporting the pro-viral response mediated by MAGI1. MAGI1 depletion induces the expression of MX1 and virus suppression. The data suggests that IAV suppression by MAGI1 depletion may, in part, be due to MX1 induction. Lastly, interferon regulatory factor 3 (IRF3) translocates to the nucleus in the absence of IRF3 phosphorylation, and IRF3 SUMOylation is abolished in MAGI1-depleted ECs. The data suggests that MAGI1 inhibits IRF3 activation by maintaining IRF3 SUMOylation. In summary, IAV infection occurs in ECs in a MAGI1 expression-dependent manner by inhibiting anti-viral responses including STATs and IRF3 activation and subsequent MX1 induction, and MAGI1 plays a role in EC activation, and in upregulating a pro-viral response. Therefore, the inhibition of MAGI1 is a potential therapeutic target for IAV-induced cardiovascular disease.

Abstract 278: Aerobic exercise suppresses melanoma tumor growth via upregulating ERK5 S496 phosphorylation

Hypoxia, immune cell infiltration, and drug delivery are key elements of therapeutic efficacy in solid tumors. Each are strongly influenced by the tumor microenvironment. Identification of novel methods to change the microenvironment is needed to improve the response of solid tumors, including melanoma, to therapies like immune checkpoint blockade. We and others have demonstrated that aerobic exercise remodels tumor microenvironment in multiple tumor types. Here, we present data to suggest that this exercise-induced remodeling of the tumor microenvironment is partially dependent on modulation of ERK5 in both tumor endothelium and infiltrating immune cells. The depletion of ERK5 in tumor-associated macrophages inhibits the growth of melanoma and lung carcinoma in mouse models, and the depletion of ERK5 in keratocytes prevents tumorigenesis promoted by inflammation. Multiple reports have shown the potential therapeutic approach of both ERK5 knockdown and pharmacological kinase inhibition in regulating inflammation and tumorigenesis. Here we identify the role of ERK5 S496 phosphorylation, known to promote inflammatory signaling, as a novel mediator of exercise induced tumor microenvironment alterations. Utilizing two melanoma models, we found that aerobic exercise suppresses the growth of YUMMER 1.7 tumors but not B16F10 in mice. Consistent with this, single cell RNA sequencing revealed reductions in myeloid derived suppressor cells and a shift in T cell populations favoring a non-exhausted phenotype in YUMMER 1.7. Flow cytometry evaluation demonstrated significantly more CD8+ T cells in YUMMER 1.7, but not in B16F10, tumors from exercised mice. Interestingly, we found increased phosphorylation of ERK5 at the S496 residue when ECs were treated with serum from exercised mice ex vivo. We also found the crucial role of ERK5 S496 phosphorylation in promoting both inflammation and proliferation in ERK5 TEY motif phosphorylation (kinase activity) and transactivation-independent manner in both ECs and macrophages. We generated ERK5 S496A knock-in mice, and found that the ability of exercise to suppress YUMMER 1.7 tumor growth was completely lost in ERK5 S496A knock-in mice, suggesting that ERK5 S496 phosphorylation is a key in exercise-induced tumor growth suppression. We are currently evaluating immune cell infiltration into tumors with or without exercise in the ERK5 S496A knock-in model relative to wild type mice. Our data suggest that ERK5 S496 phosphorylation is a critical mediator of the tumor microenvironment. The often neglected role of ERK5 S496 signaling should be carefully considered in the interpretation of prior reports of ERK5 knockdown and pharmacological kinase inhibition relative to tumorigenesis.

Citation Format: Hannah Savage, Sumedha Pareek, Jonghae Lee, Riccardo Ballaro, Venkatasubrahman Samanthapudi, Kyung Ae Ko, Masaki Imanishi, Sivareddy Kotla, Jun-ichi Abe, Keri Schadler. Aerobic exercise suppresses melanoma tumor growth via upregulating ERK5 S496 phosphorylation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 278.

Abstract 518: Erk5 S496 Phosphorylation, But Not Erk5 Kinase Or Transcriptional Activity, Is Responsible For Promoting Macrophage Inflammation And Mitochondrial Dysfunction Via Upregulating Novel Site Of Nrf2 K518 Sumoylation

ERK5 is a dual kinase-transcription factor, which contains two transcriptional transactivation domains in the C-terminus and a kinase domain in the N-terminus. Many ERK5 kinase inhibitors have been developed, and are being tested in clinical studies for cancer and inflammatory diseases. Recent data has raised questions regarding the functional role of these ERK5 kinase inhibitors. Specifically, the possible link between blockade of pro-inflammatory ERK5 S496 phosphorylation and the anti-inflammatory effects of ERK5-specific kinase inhibitors has largely been neglected. In this study, we aimed to study the role and regulatory mechanisms of ERK5 S496 phosphorylation on macrophage inflammation and the impact of ERK5-specific kinase inhibitors. ATP binding site deletion mutant of ERK5b (a kinase-dead mutant) inhibited KLF2 induction but not oxidized LDL (oxLDL)-induced ERK5 S496 phosphorylation and TNFα expression. In contrast, both specific ERK5 kinase inhibitors (AX15836 and XMD8-92) and a dual phosphorylation site mutant of ERK5 (AEF) inhibited not only KLF2 but also oxLDL-induced ERK5 S496 phosphorylation and TNFα induction. These data suggested that ERK5 S496 phosphorylation, but not ERK5 kinase activity, plays a crucial role in ERK5-mediated pro-inflammatory effects. We also discovered a key effect of ERK5 S496 phosphorylation on SUMOylation at a novel site of NRF2 (i.e., K518), which inhibited NRF2 transcriptional activity without affecting ERK5 kinase activity, and antagonized oxLDL-induced macrophage inflammation. The role of NRF2 activation on the efficiency of oxidative phosphorylation (OXPHOS) and ATP synthesis had previously been reported, and we found that both ERK5 S496A and NRF2 K518R mutants abolished oxLDL-induced reduction of OXPHOS, ATP, and NAD + levels. In summary, we discovered a novel mechanism in which ERK5 S496 phosphorylation directly inhibited NRF2 activity via SUMOylation of NRF2 at K518 and thereby induced macrophage inflammation and mitochondrial dysfunction. The often-neglected role of ERK S496 signaling should be carefully considered in the interpretation of prior reports of ERK5 knockdown and pharmacological kinase inhibition relative to cellular inflammation and mitochondrial dysfunction.

Abstract 503: Multiparameter Mass Cytometry Reveals The Unique Response Of NaïVe B Cell Cd27 - Subset With The Increase Of T-bet And Cd38 Expression After Radiation Therapy In Thoracic Cancer Patients

Cancer Radiation therapy (RT) induces cardiovascular disease (CVD) even when the heart is shealed or not irradiated, but there is a paucity of available preventive measures for RT-induced CVD. Ionizing radiation (IR) induces senescence, which was originally discovered to suppress tumorigenesis by inducing cell cycle blockade and necrosis, and positioned IR as pro-senescence cancer therapy. IR-induced senescence cells secrete cytokines, growth factors, and reactive oxygen species (ROS), becoming so called senescence associated secretory phenotype (SASP), and we hypothesize that SASP induction in immune cells cause CVD after RT. Although the involvement of DNA damage response (DDR), efferocytosis, and clonal hematopoiesis drivers (CHD) to SASP induction has been suggested, the exact mechanisms through which RT induces SASP in a specific cell type remains unclear. We characterize most of the major human immune cell lineages in a single assay using mass cytometery (CyTOF). We generated a CyTOF panel which includes antibodies against various senescence phenotype, DDR, efferocytosis, and CHD. We isolated peripheral blood mononuclear cells (PBMCs) before and 3 month after RT from 16 thoracic cancer patients. First, we found the frequency of only B cell subtype was decreased after RT. Second, we obtained 138 functional profiling subsets by unsupervised clustering with our antibody set, and found that T-bet expression was increased in the largest B cell subset of naïve B Cell (CD27 - ) Ki67 lo CD38 lo DNMT3a hi after RT, which showed the good correlation with p-p90RSK expression in the samples from pre-RT and post-RT. Lastly, the significant increase of CD38 expression in the subsets of naïve B cell (CD27 - ) and CD8 + T cell (EMRA) was detected. These data suggest the unique response of naïve B cell (CD27-) to RT with the increase of CD38 expression, and T-bet in the subset of B Cell (CD27 - ) Ki67 lo CD38 lo DNMT3a hi , and also the potential role of p90RSK activation in IR-induced T-bet expression. T-bet plays a role in developing the age-associated B cell (ABC), and the increase of CD38 expression promotes aging-related events. Therefore, the induction of T-bet and CD38 in naïve B (CD27 - ) cell after RT supports the novel role of naïve B cell in IR-induced SASP and subsequent CVD.

Abstract 226: Novel Athero-protective Role Of Chk1-induced Senp2 S344 Phosphorylation Under Laminar Flow

Atherosclerosis (AthS) tends to form at arterial regions exposed to disturbed (DF) but not laminar (LF) flow. Previously, we reported the significant role of SUMOylation in DF-induced endothelial (EC) activation and subsequent AthS formation via upregulating p53 and ERK5 SUMOylation. LF can inhibit the basal levels of p53 and ERK5 SUMOylation, but how LF inhibits SUMOylation remains unknown. A chemical genetics approach with high-resolution mass spectrometry revealed that the cell-cycle checkpoint kinases CHK1 can phosphorylate SENP2 S344 site, but the functional role remains largely unknown. We aimed to study the functional role of CHK1 in SENP2 function and subsequent AthS. First, we generated phospho-specific SENP2 S344 antibody, and found that LF, but not DF, increases SENP2 S344 phosphorylation. We found the increase of CHK1 S280 phosphorylation (related to nuclear translocation) after LF, suggesting LF-induced nuclear translocation of CHK1. The CHK1 specific inhibitor of GDC0575 and the depletion of CHK1 inhibited LF-induced SENP2 S344 phsophorylation and increased both p53 and ERK5 SUMOylation in ECs. These data suggested the crucial role of CHK1 in LF-induced SENP2 S344 phosphorylation and upregulating de-SUMOylation activity. Next, we generated CRISPR/Cas9-induced Senp2 S344A knock-in (KI) and found that the mutation of SENP2 S344A accelerated p53 and ERK5 SUMOylation. LF-induced reduction of p21, cleaved caspase 3, and ICAM-1 were all reversed by SENP2 S344A mutation. Lastly, we found that the significant acceleration of AthS formation in both ascending aorta/arch (DF area) and descending aorta (LF area) in KI mice compared to wild type (WT) mice after receiving AAV-PCSK9 and high fat diet. We also performed bone marrow transplantation (BMT) after 13 Gy whole body radiation, and larger AthS but only in the aortic arch was observed in BMT mice from WT donor to KI recipient, but not in BMT mice from WT donor to WT recipient, supporting the role of endothelial SENP2 S344 phosphorylation on AthS. The radiation reduced CHK1 expression in ECs, which may explain the different regulatory pattern under BMT or non-BMT. Taken together, these results suggest the critical role of CHK1-mediated SENP2 S344 phosphorylation on LF-induced anti-AthS effects.

Abstract 244: Differentially Expressed Genes Mediated By Erk5 S496 Phosphorylation In Hypercholesterolemia-induced Macrophage Reprogramming

The crucial role of ERK5 S496 phosphorylation in reprogramming macrophage phenotype to pro-inflammatory senescent phenotype (PISP) has been reported, but the exact molecular mechanism remains unclear. This study focused on identifying the dysregulated molecular pathways and core genes that are differentially regulated in bone marrow derived macrophage (BMDMs) isolated from wild type and ERK5 S549A knock-in (KI) mice under normal or hypercholesterolemia (HC) after high-fat diet (HFD) and AAV-PCSK9 injection. The extent of atherosclerosis was inhibited in ERK5 S496A KI mice. We sequenced RNA-seq for wild type and ERK5 S549A KI mice and used Top Hat program (v2.0.12) with default parameters to map all reads to the mouse genome (Mus musculus GRCm38). Gene expression and significance of differential expression were calculated by Cuffdiff (v2.0.12). Differentially expressed genes (DEGs) were defined by Cuffdiff according to Q value ≤0.05 as a threshold. Hallmark analysis was performed by Gene Set Enrichment Analysis (GSEA v4.2.1). We used the R package “GOplot” to perform GO bubble plot, GO circle plot, and GO chord plot. We identified 784 DEGs regulated by HC-induced ERK5 S496 phosphorylation, and the GO analysis revealed that they are involved in critical senescent processes including cell cycle, cellular response to DNA damage stimulus, protein transport, and negative regulation of apoptotic process. Gene-annotation enrichment analysis (GOCircle) showed that Z-scores of both cell cycle and cellular response to DNA damage stimulus were negative in ERK5 S496A KI mice, suggesting the role of cell cycle and DNA damage response in inducing PISP. Interestingly, we only found 40 DEGs in BMDMs isolated from normal chow diet and HFD-fed wild type mice, and 15 out of 40 DEGs were significantly regulated by ERK5 S496 phosphorylation, supporting the critical role of ERK5 S496 phosphorylation in HC-mediated macrophage reprogramming. Our study identified 10 core genes (Ahr, Gclm, H3C3, H4c11, Lpar1, Megf9, Nfe2, Ppih, Rpl22l1, and Tpt1) that are regulated by HC-mediated ERK5 S496 phosphorylation, which might be crucial for HC-induced PISP. However, functional analysis is further needed to validate their roles in PISP induction.

Abstract 390: Influenza A Virus Infection Increases Magi1 Expression In Endothelial Cells And Its Depletion Inhibits Virus Replication Through Increased Expression Of Mx1

When influenza virus infects cells, it changes cellular metabolism in such a way that allows virus particles to replicate efficiently. This metabolic engineering takes place soon after virus infects cells, for which the PSD95/DiscLarge/ZO-1 (PDZ) domain of certain proteins is known to play a role. Membrane-associated guanylate kinase with inverted domain structure-1 (MAGI1) is a scaffold protein with 6 PDZ domains, and we have shown that it is involved in the regulation of endothelial cell (EC) activation and atherosclerosis in mice. Since recent studies indicate that the vascular endothelium can be infected by influenza A virus (IAV) and plays a role in the influenza-induced pathogenesis and cardiovascular disease (CVD), we investigated the role of MAGI1 in IAV infection using cultured human umbilical vein endothelial cells (HUVECs) as well as human lung microvascular endothelial cells (HULECs). We found increased MAGI1 mRNA expression in IAV-infected cells. Conversely, when MAGI1 depleted ECs were infected with IAV, virus infection and replication was greatly suppressed. Our microarray studies revealed that depletion of MAGI1 in HUVECs increased the protein expression and signaling networks involved in interferon production. Specifically, we found that the MAGI1 null condition induced expression of anti-viral response genes including interferon-induced GTP-binding protein MX1, an antiviral protein, interferon beta1, a cytokine promotor STAT1 (signal transducer and activator of transcription 1), and also increased protein expression levels of STAT1, phosphorylated STAT5 and MX1. Co-transfection of HUVECs with siMX1 and siMAGI1 impaired MAGI1 depletion-induced suppression of IAV infection. Furthermore, we found nuclear localization of interferon regulatory factor 3 (IRF3) in MAGI1 depleted cells, indicating that MAGI1 depletion elicits the interferon production and signaling. Taken together, we conclude that IAV infection and replication occurs in ECs in a MAGI1 expression dependent manner. Thus, MGAI1 depletion in ECs suppresses IAV replication, and this suppression is due to increased MX1 expression, which induces IRF3 activation and interferon production. MAGI1 can be a potential therapeutic target for influenza-induced CVD.

Cancer treatment-induced NAD+ depletion in premature senescence and late cardiovascular complications

Numerous studies have revealed the critical role of premature senescence induced by various cancer treatment modalities in the pathogenesis of aging-related diseases. Senescence-associated secretory phenotype (SASP) can be induced by telomere dysfunction. Telomeric DNA damage response induced by some cancer treatments can persist for months, possibly accounting for long-term sequelae of cancer treatments. Telomeric DNA damage-induced mitochondrial dysfunction and increased reactive oxygen species production are hallmarks of premature senescence. Recently, we reported that the nucleus-mitochondria positive feedback loop formed by p90 ribosomal S6 kinase (p90RSK) and phosphorylation of S496 on ERK5 (a unique member of the mitogen-activated protein kinase family that is not only a kinase but also a transcriptional co-activator) were vital signaling events that played crucial roles in linking mitochondrial dysfunction, nuclear telomere dysfunction, persistent SASP induction, and atherosclerosis. In this review, we will discuss the role of NAD⁺ depletion in instigating SASP and its downstream signaling and regulatory mechanisms that lead to the premature onset of atherosclerotic cardiovascular diseases in cancer survivors.

Disturbed flow-induced FAK K152 SUMOylation initiates the formation of pro-inflammation positive feedback loop by inducing reactive oxygen species production in endothelial cells

Focal adhesion kinase (FAK) activation plays a crucial role in vascular diseases. In endothelial cells, FAK activation is involved in the activation of pro-inflammatory signaling and the progression of atherosclerosis. Disturbed flow (D-flow) induces endothelial activation and senescence, but the exact role of FAK in D-flow-induced endothelial activation and senescence remains unclear. The objective of this study is to investigate the role of FAK SUMOylation in D-flow-induced endothelial activation and senescence. The results showed that D-flow induced reactive oxygen species (ROS) production via NADPH oxidase activation and activated a redox-sensitive kinase p90RSK, leading to FAK activation by upregulating FAK K152 SUMOylation and the subsequent Vav2 phosphorylation, which in turn formed a positive feedback loop by upregulating ROS production. This feedback loop played a crucial role in regulating endothelial activation and senescence. D-flow-induced endothelial activation and senescence were significantly inhibited by mutating a FAK SUMOylation site lysine152 to arginine. Collectively, we concluded that FAK K152 SUMOylation plays a key role in D-flow-induced endothelial activation and senescence by forming a positive feedback loop through ROS production.

Senescence-Associated Secretory Phenotype as a Hinge Between Cardiovascular Diseases and Cancer

Overlapping risks for cancer and cardiovascular diseases (CVD), the two leading causes of mortality worldwide, suggest a shared biology between these diseases. The role of senescence in the development of cancer and CVD has been established. However, its role as the intersection between these diseases remains unclear. Senescence was originally characterized by an irreversible cell cycle arrest after a high number of divisions, namely replicative senescence (RS). However, it is becoming clear that senescence can also be instigated by cellular stress, so-called stress-induced premature senescence (SIPS). Telomere shortening is a hallmark of RS. The contribution of telomere DNA damage and subsequent DNA damage response/repair to SIPS has also been suggested. Although cellular senescence can mediate cell cycle arrest, senescent cells can also remain metabolically active and secrete cytokines, chemokines, growth factors, and reactive oxygen species (ROS), so-called senescence-associated secretory phenotype (SASP). The involvement of SASP in both cancer and CVD has been established. In patients with cancer or CVD, SASP is induced by various stressors including cancer treatments, pro-inflammatory cytokines, and ROS. Therefore, SASP can be the intersection between cancer and CVD. Importantly, the conventional concept of senescence as the mediator of cell cycle arrest has been challenged, as it was recently reported that chemotherapy-induced senescence can reprogram senescent cancer cells to acquire “stemness” (SAS: senescence-associated stemness). SAS allows senescent cancer cells to escape cell cycle arrest with strongly enhanced clonogenic growth capacity. SAS supports senescent cells to promote both cancer and CVD, particularly in highly stressful conditions such as cancer treatments, myocardial infarction, and heart failure. As therapeutic advances have increased overlapping risk factors for cancer and CVD, to further understand their interaction may provide better prevention, earlier detection, and safer treatment. Thus, it is critical to study the mechanisms by which these senescence pathways (SAS/SASP) are induced and regulated in both cancer and CVD.

Nucleus-mitochondria positive feedback loop formed by ERK5 S496 phosphorylation-mediated poly (ADP-ribose) polymerase activation provokes persistent pro-inflammatory senescent phenotype and accelerates coronary atherosclerosis after chemo-radiation

The incidence of cardiovascular disease (CVD) is higher in cancer survivors than in the general population. Several cancer treatments are recognized as risk factors for CVD, but specific therapies are unavailable. Many cancer treatments activate shared signaling events, which reprogram myeloid cells (MCs) towards persistent senescence-associated secretory phenotype (SASP) and consequently CVD, but the exact mechanisms remain unclear. This study aimed to provide mechanistic insights and potential treatments by investigating how chemo-radiation can induce persistent SASP. We generated ERK5 S496A knock-in mice and determined SASP in myeloid cells (MCs) by evaluating their efferocytotic ability, antioxidation-related molecule expression, telomere length, and inflammatory gene expression. Candidate SASP inducers were identified by high-throughput screening, using the ERK5 transcriptional activity reporter cell system. Various chemotherapy agents and ionizing radiation (IR) up-regulated p90RSK-mediated ERK5 S496 phosphorylation. Doxorubicin and IR caused metabolic changes with nicotinamide adenine dinucleotide depletion and ensuing mitochondrial stunning (reversible mitochondria dysfunction without showing any cell death under ATP depletion) via p90RSK-ERK5 modulation and poly (ADP-ribose) polymerase (PARP) activation, which formed a nucleus-mitochondria positive feedback loop. This feedback loop reprogramed MCs to induce a sustained SASP state, and ultimately primed MCs to be more sensitive to reactive oxygen species. This priming was also detected in circulating monocytes from cancer patients after IR. When PARP activity was transiently inhibited at the time of IR, mitochondrial stunning, priming, macrophage infiltration, and coronary atherosclerosis were all eradicated. The p90RSK-ERK5 module plays a crucial role in SASP-mediated mitochondrial stunning via regulating PARP activation. Our data show for the first time that the nucleus-mitochondria positive feedback loop formed by p90RSK-ERK5 S496 phosphorylation-mediated PARP activation plays a crucial role of persistent SASP state, and also provide preclinical evidence supporting that transient inhibition of PARP activation only at the time of radiation therapy can prevent future CVD in cancer survivors.

Abstract MP45: The Roles Of Telomeric Repeat Binding Factor 2-interacting Protein (TERF2IP) K240 Sumoylation In Endothelial Cells On Atherogenesis

Background and Objectives: It is not yet clear how the pro-atherogenic signaling events in endothelial cells (ECs) such as those that lead to EC senescence, apoptosis and activation are interconnected and promote atherosclerotic plaque formation in the area exposed to disturbed blood flow (d-flow). TERF2IP, a member of the shelterin complex of the telomere, regulates all three pathological events. We investigated the role of TERF2IP K240 SUMOylation in the process of d-flow-induced atherosclerotic plaque formation.

Methods and Results: We found that d-flow increased TERF2IP K240 SUMOylation in ECs and that it was suppressed by a p90RSK specific inhibitor, FMK-MEA. This SUMOylation was independent of TERF2IP S205 phosphorylation. The d-flow-induced senescence, DNA damage, and apoptosis were inhibited in ECs with TERF2IP depletion or point-mutated phosphorylation (S205A) and SUMOylation (K240R) sites. NF-κB activation induced by d-flow or overexpression of p90RSK was also significantly inhibited in ECs overexpressing the TERF2IP S205A phosphorylation mutant. However, cells overexpressing the TERF2IP K240R SUMOylation mutant showed no effect on the d-flow or p90RSK-medaited NF-κB activation. To determine the biological function of TERF2IP K240 SUMOylation, we generated TERF2IP K240R knock-in (KI) mice and examined d-flow-induced atherosclerotic plaque formation using partial left carotid ligation model mice fed a high-fat diet after AAV8-PCSK9 injection. We found no differences in body weights and cholesterol levels between TERF2IP K240R KI and wild type control (WT) mice, but plaque formation was significantly inhibited in the KI mice compared to WT animals (Oil Red O positive area (%): 19.0 +/- 12.5 (KI mice, n=8) vs 61.2 +/- 24.3 (WT mice, n=7), p = 0.0008). Bone marrow from WT mice were transplanted into KI and WT mice, which were then injected with AAV8-PCSK9 virus and fed a high-fat diet for 16 weeks, but we still found that plaque formation was inhibited in the KI mice.

Conclusion: TERF2IP SUMOylation plays a role in in EC senescence but not in activation. The significant inhibition of plaque formation in the TERF2IP K240R KI mice is due to downregulation of TERF2IP SUMOylation in ECs not in myeloid cells.

Abstract P184: Novel Model Of Ionizing Radiation-induced Mouse Coronary Arteriosclerosis, Which Was Attenuated By Precise Time Treatment Of Poly (adp-ribose) Polymerase (parp) Inhibitor

Background: It is well known that radiation therapy (RT) induces coronary artery disease (CAD). However, since we don’t have an adequate mouse model to evaluate CAD after RT, it has been difficult to perform pre-clinical study to detect the effective treatment. The inhibition of PARPs can prevent apoptosis and inflammation. Although PARP inhibitors have already been used as anti-tumor agents, their long-term use in CAD is not recommended because the inhibition of DNA damage response can cause DNA instability and eventually cancer. In this study, we restricted the use of PARP inhibitors to the time of IR exposure only and detected IR-induced atherosclerosis (AS).

Methods and Results: Marino et al. reported that thoracic aortic constriction (TAC) can exacerbate coronary artery stenosis and myocardial infarction in ApoE -/- mice. We tested this model in LDLR -/- mice that were fed a high fat (HFD) with or without IR (3, 5, and 10 Gy). We observed cardiac hypertrophy and dose-dependent reduction of fractional shortening (FS) after 4-5 weeks of TAC (FS%, 33.74 ± 7.35 (Non-IR, n=9), 26.59 ± 9.19 (3Gy, n=6), 28.49 ± 2.49 (5Gy, n=5), 22.62 ± 6.16 (10Gy, n=6), mean ± SD, p <0.05). Most importantly, we observed localized cardiac dysfunction and infarct only in mice exposed to 10 Gy (n = 2 out of 6), detected by transmural strain analysis with echocardiography. Next, the whole heart was sectioned, with sets of 11 consecutive sections of 5 μm collected every 450 μm interval. We also found the diffuse increase of vascular wall thickness at left anterior descending coronary artery in mice exposed to IR. We fed a HFD on LDLR -/- mice with Olaparib (10 mg/kg/day) or vehicle one day before & after, and the day of IR (5 Gy twice, total 6 days only), then performed TAC. The reduction of FS induced by IR (10 Gy) was significantly improved by the precise time treatment of Olaparib against IR.

Conclusion: These data suggested the usefulness of TAC-induced coronary AS mouse model to develop medical countermeasures against RT-induced CAD as pre-clinical study.

p90RSK-MAGI1 Module Controls Endothelial Permeability by Post-translational Modifications of MAGI1 and Hippo Pathway

Previously, we reported that post-translational modifications (PTMs) of MAGI1, including S741 phosphorylation and K931 de-SUMOylation, both of which are regulated by p90RSK activation, lead to endothelial cell (EC) activation. However, roles for p90RSK and MAGI1-PTMs in regulating EC permeability remain unclear despite MAGI1 being a junctional molecule. Here, we show that thrombin (Thb)-induced EC permeability, detected by the electric cell-substrate impedance sensing (ECIS) based system, was decreased by overexpression of dominant negative p90RSK or a MAGI1-S741A phosphorylation mutant, but was accelerated by overexpression of p90RSK, siRNA-mediated knockdown of magi1, or the MAGI1-K931R SUMOylation mutant. MAGI1 depletion also increased the mRNA and protein expression of the large tumor suppressor kinases 1 and 2 (LATS1/2), which inhibited YAP/TAZ activity and increased EC permeability. Because the endothelial barrier is a critical mediator of tumor hypoxia, we also evaluated the role of p90RSK activation in tumor vessel leakiness by using a relatively low dose of the p90RSK specific inhibitor, FMK-MEA. FMK-MEA significantly inhibited tumor vessel leakiness at a dose that does not affect morphology and growth of tumor vessels in vivo. These results provide novel insights into crucial roles for p90RSK-mediated MAGI1 PTMs and the Hippo pathway in EC permeability, as well as p90RSK activation in tumor vessel leakiness.

Single-cell RNA sequencing analysis of SARS-CoV-2 entry receptors in human organoids

Coronavirus disease‐2019 (COVID‐19) is a global pandemic and caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), which has resulted in millions of deaths worldwide. Reports denote SARS‐CoV‐2 uses angiotensin‐converting enzyme 2 (ACE2), transmembrane serine protease 2 (TMPRSS2) as its primary entry point into the host cell. However, understanding the biology behind this viral replication, disease mechanism and drug discovery efforts are limited due to the lack of a suitable experimental model. Here, we used single‐cell RNA sequencing data of human organoids to analyze expressions of ACE2 and TMPRSS2, in addition to an array of RNA receptors to examine their role in SARS‐CoV‐2 pathogenesis. ACE2 is abundant in all organoids, except the prostate and brain, and TMPRSS2 is omnipresent. Innate immune pathways are upregulated in ACE2(+) cells of all organoids, except the lungs. Besides this, the expression of low‐density lipoprotein receptor is highly enriched in ACE2(+) cells in intestinal, lung, and retinal organoids, with the highest expression in lung organoids. Collectively, this study demonstrates that the organoids can be used as an experimental platform to explore this novel virus disease mechanism and for drug development.

Senescent Phenotype Induced by p90RSK-NRF2 Signaling Sensitizes Monocytes and Macrophages to Oxidative Stress in HIV-Positive Individuals

BACKGROUND

The incidence of cardiovascular disease is higher in HIV-positive (HIV⁺) patients than it is in the average population, and combination antiretroviral therapy (cART) is a recognized risk factor for cardiovascular disease. However, the molecular mechanisms that link cART and cardiovascular disease are currently unknown. Our study explores the role of the activation of p90RSK, a reactive oxygen species-sensitive kinase, in engendering senescent phenotype in macrophages and accelerating atherogenesis in patients undergoing cART.

METHODS

Peripheral whole blood from cART-treated HIV⁺ individuals and nontreated HIV-negative individuals was treated with H₂O₂ (200 µmol/L) for 4 minutes, and p90RSK activity in CD14⁺ monocytes was measured. Plaque formation in the carotids was also analyzed in these individuals. Macrophage senescence was determined by evaluating their efferocytotic ability, antioxidation-related molecule expression, telomere length, and inflammatory gene expression. The involvement of p90RSK-NRF2 signaling in cART-induced senescence was assessed by p90RSK-specific inhibitor (FMK-MEA) or dominant-negative p90RSK (DN-p90RSK) and NRF2 activator (NRF2A). Further, the severity of atherosclerosis was determined in myeloid cell-specific wild-type and DN-p90RSK transgenic mice.

RESULTS

Monocytes from HIV⁺ patients exhibited higher levels of p90RSK activity and were also more sensitive to reactive oxygen species than monocytes from HIV-negative individuals. A multiple linear regression analysis involving cART, Reynolds cardiovascular risk score, and basal p90RSK activity revealed that cART and basal p90RSK activity were the 2 significant determinants of plaque formation. Many of the antiretroviral drugs individually activated p90RSK, which simultaneously triggered all components of the macrophage senescent phenotype. cART inhibited antioxidant response element reporter activity via ERK5 S496 phosphorylation. NRF2A reversed the H₂O₂-induced overactivation of p90RSK in cART-treated macrophages by countering the induction of senescent phenotype. Last, the data obtained from our gain- or loss-of-function mice conclusively showed the crucial role of p90RSK in inducing senescent phenotype in macrophages and atherogenesis.

CONCLUSIONS

cART increased monocyte/macrophage sensitivity to reactive oxygen species- in HIV⁺ individuals by suppressing NRF2-ARE activity via p90RSK-mediated ERK5 S496 phosphorylation, which coordinately elicited senescent phenotypes and proinflammatory responses. As such, our report underscores the importance of p90RSK regulation in monocytes/macrophages as a viable biomarker and therapeutic target for preventing cardiovascular disease, especially in HIV⁺ patients treated with cART.

Endothelial senescence-associated secretory phenotype (SASP) is regulated by Makorin-1 ubiquitin E3 ligase

BACKGROUND

Disturbed flow (d-flow)-induced senescence and activation of endothelial cells (ECs) have been suggested to have critical roles in promoting atherosclerosis. Telomeric repeat-binding factor 2 (TERF2)-interacting protein (TERF2IP), a member of the shelterin complex at the telomere, regulates the senescence-associated secretory phenotype (SASP), in which EC activation and senescence are engendered simultaneously by p90RSK-induced phosphorylation of TERF2IP S205 and subsequent nuclear export of the TERF2IP-TERF2 complex. In this study, we investigated TERF2IP-dependent gene expression and its role in regulating d-flow-induced SASP.

METHODS

A principal component analysis and hierarchical clustering were used to identify genes whose expression is regulated by TERF2IP in ECs under d-flow conditions. Senescence was determined by reduced telomere length, increased p53 and p21 expression, and increased apoptosis; EC activation was detected by NF-κB activation and the expression of adhesion molecules. The involvement of TERF2IP S205 phosphorylation in d-flow-induced SASP was assessed by depletion of TERF2IP and mutation of the phosphorylation site.

RESULTS

Our unbiased transcriptome analysis showed that TERF2IP caused alteration in the expression of a distinct set of genes, including rapamycin-insensitive companion of mTOR (RICTOR) and makorin-1 (MKRN1) ubiquitin E3 ligase, under d-flow conditions. In particular, both depletion of TERF2IP and overexpression of the TERF2IP S205A phosphorylation site mutant in ECs increased the d-flow and p90RSK-induced MKRN1 expression and subsequently inhibited apoptosis, telomere shortening, and NF-κB activation in ECs via suppression of p53, p21, and telomerase (TERT) induction.

CONCLUSIONS

MKRN1 and RICTOR belong to a distinct reciprocal gene set that is both negatively and positively regulated by p90RSK. TERF2IP S205 phosphorylation, a downstream event of p90RSK activation, uniquely inhibits MKRN1 expression and contributes to EC activation and senescence, which are key events for atherogenesis.

Endothelial senescence is induced by phosphorylation and nuclear export of telomeric repeat binding factor 2-interacting protein

The interplay among signaling events for endothelial cell (EC) senescence, apoptosis, and activation and how these pathological conditions promote atherosclerosis in the area exposed to disturbed flow (d-flow) in concert remain unclear. The aim of this study was to determine whether telomeric repeat-binding factor 2-interacting protein (TERF2IP), a member of the shelterin complex at the telomere, can regulate EC senescence, apoptosis, and activation simultaneously, and if so, by what molecular mechanisms. We found that d-flow induced p90RSK and TERF2IP interaction in a p90RSK kinase activity-dependent manner. An in vitro kinase assay revealed that p90RSK directly phosphorylated TERF2IP at the serine 205 (S205) residue, and d-flow increased TERF2IP S205 phosphorylation as well as EC senescence, apoptosis, and activation by activating p90RSK. TERF2IP phosphorylation was crucial for nuclear export of the TERF2IP-TRF2 complex, which led to EC activation by cytosolic TERF2IP-mediated NF-κB activation and also to senescence and apoptosis of ECs by depleting TRF2 from the nucleus. Lastly, using EC-specific TERF2IP-knockout (TERF2IP-KO) mice, we found that the depletion of TERF2IP inhibited d-flow-induced EC senescence, apoptosis, and activation, as well as atherosclerotic plaque formation. These findings demonstrate that TERF2IP is an important molecular switch that simultaneously accelerates EC senescence, apoptosis, and activation by S205 phosphorylation.

MAGI1 as a link between endothelial activation and ER stress drives atherosclerosis

The possible association between the membrane-associated guanylate kinase with inverted domain structure-1 (MAGI1) and inflammation has been suggested, but the molecular mechanisms underlying this link, especially during atherogenesis, remain unclear. In endothelial cells (ECs) exposed to disturbed flow (d-flow), p90 ribosomal S6 kinase (p90RSK) bound to MAGI1, causing MAGI1-S741 phosphorylation and sentrin/SUMO-specific protease 2 T368 phosphorylation-mediated MAGI1-K931 deSUMOylation. MAGI1-S741 phosphorylation upregulated EC activation via activating Rap1. MAGI1-K931 deSUMOylation induced both nuclear translocation of p90RSK-MAGI1 and ATF-6-MAGI1 complexes, which accelerated EC activation and apoptosis, respectively. Microarray screening revealed key roles for MAGI1 in the endoplasmic reticulum (ER) stress response. In this context, MAGI1 associated with activating transcription factor 6 (ATF-6). MAGI1 expression was upregulated in ECs and macrophages found in atherosclerotic-prone regions of mouse aortas as well as in the colonic epithelia and ECs of patients with inflammatory bowel disease. Further, reduced MAGI1 expression in Magi1-/+ mice inhibited d-flow-induced atherogenesis. In sum, EC activation and ER stress-mediated apoptosis are regulated in concert by two different types of MAGI1 posttranslational modifications, elucidating attractive drug targets for chronic inflammatory disease, particularly atherosclerosis.

Ponatinib Activates an Inflammatory Response in Endothelial Cells via ERK5 SUMOylation

Ponatinib is a multi-targeted third generation tyrosine kinase inhibitor (TKI) used in the treatment of chronic myeloid leukemia (CML) patients harboring the Abelson (Abl)-breakpoint cluster region (Bcr) T315I mutation. In spite of having superb clinical efficacy, ponatinib triggers severe vascular adverse events (VAEs) that significantly limit its therapeutic potential. On vascular endothelial cells (ECs), ponatinib promotes EC dysfunction and apoptosis, and inhibits angiogenesis. Furthermore, ponatinib-mediated anti-angiogenic effect has been suggested to play a partial role in systemic and pulmonary hypertension via inhibition of vascular endothelial growth factor receptor 2 (VEGFR2). Even though ponatinib-associated VAEs are well documented, their etiology remains largely unknown, making it difficult to efficiently counteract treatment-related adversities. Therefore, a better understanding of the mechanisms by which ponatinib mediates VAEs is critical. In cultured human aortic ECs (HAECs) treated with ponatinib, we found an increase in nuclear factor NF-kB/p65 phosphorylation and NF-kB activity, inflammatory gene expression, cell permeability, and cell apoptosis. Mechanistically, ponatinib abolished extracellular signal-regulated kinase 5 (ERK5) transcriptional activity even under activation by its upstream kinase mitogen-activated protein kinase kinase 5α (CA-MEK5α). Ponatinib also diminished expression of ERK5 responsive genes such as Krüppel-like Factor 2/4 (klf2/4) and eNOS. Because ERK5 SUMOylation counteracts its transcriptional activity, we examined the effect of ponatinib on ERK5 SUMOylation, and found that ERK5 SUMOylation is increased by ponatinib. We also found that ponatibib-mediated increased inflammatory gene expression and decreased anti-inflammatory gene expression were reversed when ERK5 SUMOylation was inhibited endogenously or exogenously. Overall, we propose a novel mechanism by which ponatinib up-regulates endothelial ERK5 SUMOylation and shifts ECs to an inflammatory phenotype, disrupting vascular homeostasis.

Abstract 223: Monocytes/macrophages Are Sensitized to Secondary Oxidative Insult by Cardiovascular Toxic Drugs via the P90rsk-erk5 S496 Phosphorylation Pathway, Aggrandizing Atherosclerotic Plaque Formation

Increased cardiovascular (CV) events in HIV patients and cancer survivors and the fact that combination antiretroviral therapy (cART) and chemotherapy induce similar unwanted CV effects are becoming evident, but the reason for this is unclear. In this study, we examined the role of p90RSK in the CV toxicity of cART and anti-cancer drugs. The level of p90RSK activation by H2O2 was higher in peripheral monocytes from cART-treated patients than in those from untreated patients. Multiple linear regression analysis involving HIV+/-, Reynolds CV risk score, and basal p90RSK activation revealed HIV+/- and basal p90RSK activation to be strong determinants for plaque formation when adjusted for other independent variables. In murine macrophages most of the cART and several chemotherapy agents activated p90RSK and reduced antioxidant molecule expression and telomere (TL) lengths. p90RSK-mediated ERK5 S496 phosphorylation inhibited transcriptional activity of ERK5 and NRF2, decreasing efferocytosis, antioxidant production and TL lengths. NRF2 activator normalized cART-induced sensitization of p90RSK to H2O2. Lastly, we generated myeloid cells-specific wild type (WT) and dominant negative (DN) p90RSK transgenic mice, and ERK5 S496A knock-in mice, crossed with Ldlr-/- mice or treated with a single injection of adeno-associated virus vector (AAV) encoding a gain-of-function mutant of PCSK9 and fed a high fat diet. Our animal studies showed the crucial role of p90RSK-mediated ERK5 S496 phosphorylation in suppressing effecrocytosis and antioxidant production, and up-regulating senescence and inflammation-related molecules expression, leading to atherogenesis. Our results taken together show that p90RSK is activated by anti-HIV and anti-cancer drugs, and this activation sensitizes the monocyte/macrophages to the secondary oxidative insult by reducing NRF2 transcriptional activity and TL length. The p90RSK activation also reduces macrophage efferocytosis and antioxidant capacity, and increases inflammation and senescence via up-regulating ERK5 S496 phosphorylation, thereby accelerating atherosclerosis. Monocyte/macrophage p90RSK-ERK5 S496 phosphorylation could be a good target to prevent drugs-induced CV diseases.

Abstract 451: Radiation Induced Atherosclerosis on Mice

Rationale: The high prevalence of cardiovascular disease (CVD) in cancer survivors after ionizing radiation (IR) therapy has long been recognized, but the mechanism for this is unknown. Previous studies reported that the plaques in IR therapy survivors exhibit characteristics of increased instability without changes in the plaque size.

Objective: To study the mechanism of IR induced CVD in humans, we decided to develop an IR mouse model that mimics human CV events.

Methods and Results: We fed LDLR-/- mice or C57 mice with a single injection of adeno -associated virus vector(AAV) encoding a gain-of function of PCSK9 with a high fat diet, then irradiated the mice with different doses of IR (2 Gy, 5 Gy, 10 Gy). Whole body radiation was given 2 Gy, while localized IR to the neck and thoracic area was given at 5 Gy (1 time) or 10Gy (weekly 5 Gy, twice).About 2~3 weeks after the IR treatment, we performed left partial carotid artery ligation (PCL), and 3 weeks later examined the extent of plaque formation and cardiac abnormality by comparing those detected in non-irradiated control mice. The lesion area ratio between the partially ligated left carotid artery (LCA) and the right carotid artery (RCA) was significantly increased in the IR-treated group compared to the non-IR-treated group (3.1 ± 0.3 vs.1.8 ± 0.4, n = 7-8, p = 0.03). In addition, the lesion in the IR-treated of mice had significantly larger necrotic cores with a thinner fibrous cap when compared to those in non-irradiate mice. Furthermore, IR-treated mice showed cardiac hypertrophy, in which we found a significant increase of the wall thickness of mid-to small sized arteries as well as perivascular fibrosis, which were not noticed in the non-IR-treated mice.

Conclusions: Our results demonstrate that IR not only increases atherosclerotic and vulnerable plaque formation but also cardiac hypertrophy with mid- and micro-vascular wall swelling. The increase of mid- and micro-vascular wall thickness may explain the heart failure preserved heart failure, which is observed in the majority of heart failure patients after IR treatment.

Developing a Reliable Mouse Model for Cancer Therapy-Induced Cardiovascular Toxicity in Cancer Patients and Survivors

Background

The high incidence of cardiovascular events in cancer survivors has long been noted, but the mechanistic insights of cardiovascular toxicity of cancer treatments, especially for vessel diseases, remain unclear. It is well known that atherosclerotic plaque formation begins in the area exposed to disturbed blood flow, but the relationship between cancer therapy and disturbed flow in regulating plaque formation has not been well studied. Therefore, we had two goals for this study; (1) Generate an affordable, reliable, and reproducible mouse model to recapitulate the cancer therapy-induced cardiovascular events in cancer survivors, and (2) Establish a mouse model to investigate the interplay between disturbed flow and various cancer therapies in the process of atherosclerotic plaque formation.

Methods and Results

We examined the effects of two cancer drugs and ionizing radiation (IR) on disturbed blood flow-induced plaque formation using a mouse carotid artery partial ligation (PCL) model of atherosclerosis. We found that doxorubicin and cisplatin, which are commonly used anti-cancer drugs, had no effect on plaque formation in partially ligated carotid arteries. Similarly, PCL-induced plaque formation was not affected in mice that received IR (2 Gy) and PCL surgery performed one week later. In contrast, when PCL surgery was performed 26 days after IR treatment, not only the atherosclerotic plaque formation but also the necrotic core formation was significantly enhanced. Lastly, we found a significant increase in p90RSK phosphorylation in the plaques from the IR-treated group compared to those from the non-IR treated group.

Conclusions

Our results demonstrate that IR not only increases atherosclerotic events but also vulnerable plaque formation. These increases were a somewhat delayed effect of IR as they were observed in mice with PCL surgery performed 26 days, but not 10 days, after IR exposure. A proper animal model must be developed to study how to minimize the cardiovascular toxicity due to cancer treatment.

Ionizing Radiation Induces Endothelial Inflammation and Apoptosis via p90RSK-Mediated ERK5 S496 Phosphorylation

Adverse cardiovascular events are a leading nonmalignant cause of morbidity and mortality among cancer survivors who have been exposed to ionizing radiation (IR), but the exact mechanism of the cardiovascular complications induced by IR remains unclear. In this study we investigated the potential role of the p90RSK-ERK5 module in regulating IR-induced endothelial cell inflammation and apoptosis.

Whole body radiation of mice with 2 Gy γ-ray significantly increased endothelial VCAM-1 expression; especially in the disturbed flow area in vivo. In vitro studies showed that IR increased p90RSK activation as well as subsequent ERK5 S496 phosphorylation in cultured human endothelial cells (ECs). A specific p90RSK inhibitor, FMK-MEA, significantly inhibited both p90RSK activation and ERK5 S496 phosphorylation, but it had no effect on IR-induced ERK5 TEY motif phosphorylation, suggesting that p90RSK regulates ERK5 transcriptional activity, but not its kinase activity. In fact, we found that IR-induced NF-kB activation and VCAM-1 expression in ECs were significantly inhibited by the over-expression of S496 phosphorylation site mutant of ERK5 (ERK5 S496A) compared to overexpression of wild type ERK5. Furthermore, when ECs were exposed to IR, the number of annexin V positive cells increased, and overexpression of ERK5 S496A, but not wild type ERK5, significantly inhibited this increase.

Our results demonstrate that IR augmented disturbed flow-induced VCAM-1 expression in vivo. Endothelial p90RSK was robustly activated by IR and subsequently up-regulated ERK5 S496 phosphorylation, inflammation, and apoptosis in ECs. The EC p90RSK-ERK5 signaling axis can be a good target to prevent cardiovascular events after radiation therapy in cancer patients.

Heterodimers of the transcriptional factors NFATc3 and FosB mediate tissue factor expression for 15(S)-hydroxyeicosatetraenoic acid-induced monocyte trafficking

Tissue factor (TF) is expressed in vascular and nonvascular tissues and functions in several pathways, including embryonic development, inflammation, and cell migration. Many risk factors for atherosclerosis, including hypertension, diabetes, obesity, and smoking, increase TF expression. To better understand the TF-related mechanisms in atherosclerosis, here we investigated the role of 12/15-lipoxygenase (12/15-LOX) in TF expression. 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE), the major product of human 15-LOXs 1 and 2, induced TF expression and activity in a time-dependent manner in the human monocytic cell line THP1. Moreover, TF suppression with neutralizing antibodies blocked 15(S)-HETE-induced monocyte migration. We also found that NADPH- and xanthine oxidase-dependent reactive oxygen species (ROS) production, calcium/calmodulin-dependent protein kinase IV (CaMKIV) activation, and interactions between nuclear factor of activated T cells 3 (NFATc3) and FosB proto-oncogene, AP-1 transcription factor subunit (FosB) are involved in 15(S)-HETE-induced TF expression. Interestingly, NFATc3 first induced the expression of its interaction partner FosB before forming the heterodimeric NFATc3-FosB transcription factor complex, which bound the proximal AP-1 site in the TF gene promoter and activated TF expression. We also observed that macrophages from 12/15-LOX-/- mice exhibit diminished migratory response to monocyte chemotactic protein 1 (MCP-1) and lipopolysaccharide compared with WT mouse macrophages. Similarly, compared with WT macrophages, monocytes from 12/15-LOX-/- mice displayed diminished trafficking, which was rescued by prior treatment with 12(S)-HETE, in a peritonitis model. These observations indicate that 15(S)-HETE-induced monocyte/macrophage migration and trafficking require ROS-mediated CaMKIV activation leading to formation of NFATc3 and FosB heterodimer, which binds and activates the TF promoter.

ROS via BTK-p300-STAT1-PPARγ signaling activation mediates cholesterol crystals-induced CD36 expression and foam cell formation

In understanding the mechanisms of cholesterol in the pathogenesis of atherosclerosis, previous studies from other laboratories have demonstrated that cholesterol crystals (CC) induce scavenger receptor CD36 expression and NLRP3-mediated inflammasome formation. In elucidating the mechanisms by which CC could enhance CD36 expression and foam cell formation, here we report that CC via NADPH and xanthine oxidases-mediated ROS production activates BTK, a non-receptor tyrosine kinase. In addition, CC induce p300 tyrosine phosphorylation and activation in a BTK-dependent manner, which in turn, leads to STAT1 acetylation and its interaction with PPARγ in CD36 expression, oxLDL uptake and foam cell formation. Furthermore, p300, STAT1 and PPARγ bound to a STAT binding site at −107 nt in CD36 promoter and enhanced its activity in ROS and BTK-dependent manner. Disruption of this STAT binding site by site-directed mutagenesis abolished CC-induced CD36 promoter activity. Together these results reveal for the first time that CC via producing ROS and activating BTK causes p300-mediated STAT1 acetylation and its interaction with PPARγ in CD36 expression, oxLDL uptake and foam cell formation.

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CC induces CD36 expression and foam cell formation by ROS-mediated BTK activation.

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STAT1 and PPARγ interactions are required for CC-induced CD36 expression.

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ROS-dependent BTK and p300 activation mediate STAT1 and PPARγ interactions.

Reactive Oxygen Species (ROS) Mediate p300-dependent STAT1 Protein Interaction with Peroxisome Proliferator-activated Receptor (PPAR)-γ in CD36 Protein Expression and Foam Cell Formation

Previously, we have demonstrated that 15(S)-hydroxyeicosatetranoic acid (15(S)-HETE) induces CD36 expression involving STAT1. Many studies have shown that peroxisome proliferator-activated receptor (PPAR)-γ mediates CD36 expression. Therefore, we asked the question whether these transcriptional factors interact with each other in the regulation of CD36 expression by 15(S)-HETE. Here, we show that STAT1 interacts with PPARγ in the induction of CD36 expression and foam cell formation by 15(S)-HETE. In addition, using molecular biological approaches such as EMSA, supershift EMSA, ChIP, re-ChIP, and promoter-reporter gene assays, we demonstrate that the STAT1 and PPARγ complex binds to the STAT-binding site at -107 nucleotides in the CD36 promoter and enhances its activity. Furthermore, the interaction of STAT1 with PPARγ depends on STAT1 acetylation, which is mediated by p300. In addition, our findings show that reactive oxygen species-dependent Syk and Pyk2 stimulation is required for p300 tyrosine phosphorylation and activation. Together, these results demonstrate that an interaction between STAT1, p300, and peroxisome proliferator-activated receptor-γ is required for 15(S)-HETE-induced CD36 expression, oxidized low density lipoprotein uptake, and foam cell formation, critical events underlying the pathogenesis of atherosclerosis.

PLCβ3 mediates cortactin interaction with WAVE2 in MCP1-induced actin polymerization and cell migration

Monocyte chemotactic protein 1 (MCP1) stimulates vascular smooth muscle cell (VSMC) migration in vascular wall remodeling. However, the mechanisms underlying MCP1-induced VSMC migration have not been understood. Here we identify the signaling pathway associated with MCP1-induced human aortic smooth muscle cell (HASMC) migration. MCP1, a G protein-coupled receptor agonist, activates phosphorylation of cortactin on S405 and S418 residues in a time-dependent manner, and inhibition of its phosphorylation attenuates MCP1-induced HASMC G-actin polymerization, F-actin stress fiber formation, and migration. Cortactin phosphorylation on S405/S418 is found to be critical for its interaction with WAVE2, a member of the WASP family of cytoskeletal regulatory proteins required for cell migration. In addition, the MCP1-induced cortactin phosphorylation is dependent on PLCβ3-mediated PKCδ activation, and siRNA-mediated down-regulation of either of these molecules prevents cortactin interaction with WAVE2, affecting G-actin polymerization, F-actin stress fiber formation, and HASMC migration. Upstream, MCP1 activates CCR2 and Gαq/11 in a time-dependent manner, and down-regulation of their levels attenuates MCP1-induced PLCβ3 and PKCδ activation, cortactin phosphorylation, cortactin-WAVE2 interaction, G-actin polymerization, F-actin stress fiber formation, and HASMC migration. Together these findings demonstrate that phosphorylation of cortactin on S405 and S418 residues is required for its interaction with WAVE2 in MCP1-induced cytoskeleton remodeling, facilitating HASMC migration.

Cyclic AMP Response Element Binding Protein Mediates Pathological Retinal Neovascularization via Modulating DLL4-NOTCH1 Signaling

Retinal neovascularization is the most common cause of moderate to severe vision loss in all age groups. Despite the use of anti-VEGFA therapies, this complication continues to cause blindness, suggesting a role for additional molecules in retinal neovascularization. Besides VEGFA and VEGFB, hypoxia induced VEGFC expression robustly. Based on this finding, we tested the role of VEGFC in pathological retinal angiogenesis. VEGFC induced proliferation, migration, sprouting and tube formation of human retinal microvascular endothelial cells (HRMVECs) and these responses require CREB-mediated DLL4 expression and NOTCH1 activation. Furthermore, down regulation of VEGFC levels substantially reduced tip cell formation and retinal neovascularization in vivo. In addition, we observed that CREB via modulating the DLL4-NOTCH1 signaling mediates VEGFC-induced tip cell formation and retinal neovascularization. In regard to upstream mechanism, we found that down regulation of p38β levels inhibited hypoxia-induced CREB-DLL4-NOTCH1 activation, tip cell formation, sprouting and retinal neovascularization. Based on these findings, it may be suggested that VEGFC besides its role in the regulation of lymphangiogenesis also plays a role in pathological retinal angiogenesis and this effect depends on p38β and CREB-mediated activation of DLL4-NOTCH1 signaling.

Disruption of p21-activated kinase 1 gene diminishes atherosclerosis in apolipoprotein E-deficient mice

Pak1 plays an important role in various cellular processes, including cell motility, polarity, survival and proliferation. To date, its role in atherogenesis has not been explored. Here we report the effect of Pak1 on atherogenesis using atherosclerosis-prone apolipoprotein E-deficient (ApoE^−/−) mice as a model. Disruption of Pak1 in ApoE^−/− mice results in reduced plaque burden, significantly attenuates circulating IL-6 and MCP-1 levels, limits the expression of adhesion molecules and diminishes the macrophage content in the aortic root of ApoE^−/− mice. We also observed reduced oxidized LDL uptake and increased cholesterol efflux by macrophages and smooth muscle cells of ApoE^−/−:Pak1^−/− mice as compared with ApoE^−/− mice. In addition, we detect increased Pak1 phosphorylation in human atherosclerotic arteries, suggesting its role in human atherogenesis. Altogether, these results identify Pak1 as an important factor in the initiation and progression of atherogenesis.

Atherogenesis involves coordinated action of different cell types and factors. Here the authors show that the kinase Pak1 represents a key pro-atherogenic factor affecting the function of macrophages and vascular smooth muscle cells, including their production of proinflammatory cytokine IL-6 and chemokine MCP-1, and retention of cholesterol.

12/15-Lipoxygenase-dependent ROS production is required for diet-induced endothelial barrier dysfunction

To understand the mechanisms of 15(S)-HETE-induced endothelial cell (EC) barrier dysfunction, we examined the role of xanthine oxidase (XO). 15(S)-HETE induced junction adhesion molecule A (JamA) phosphorylation on Y164, Y218, and Y280 involving XO-mediated reactive oxygen species production and Src and Pyk2 activation, resulting in its dissociation from occludin, thereby causing tight junction (TJ) disruption, increased vascular permeability, and enhanced leukocyte and monocyte transmigration in vitro using EC monolayer and ex vivo using arteries as models. The phosphorylation of JamA on Y164, Y218, and Y280 appears to be critical for its role in 15(S)-HETE-induced EC barrier dysfunction, as mutation of any one of these amino acid residues prevented its dissociation from occludin and restored TJ integrity and barrier function. In response to high-fat diet (HFD) feeding, WT, but not 12/15-lipoxygenase (LO)(-/-), mice showed enhanced XO expression and its activity in the artery, which was correlated with increased aortic TJ disruption and barrier permeability with enhanced leukocyte adhesion and these responses were inhibited by allopurinol. These observations provide novel insights on the role of XO in 12/15-LO-induced JamA tyrosine phosphorylation and TJ disruption leading to increased vascular permeability in response to HFD.

ROS-dependent Syk and Pyk2-mediated STAT1 activation is required for 15(S)-hydroxyeicosatetraenoic acid-induced CD36 expression and foam cell formation

15(S)-Hydroxyeicosatetraenoic acid (15(S)-HETE), the major 15-lipoxygenase 1/2 (15-LO1/2) metabolite of arachidonic acid (AA), induces CD36 expression through xanthine oxidase and NADPH oxidase-dependent ROS production and Syk and Pyk2-dependent STAT1 activation. In line with these observations, 15(S)-HETE also induced foam cell formation involving ROS, Syk, Pyk2, and STAT1-mediated CD36 expression. In addition, peritoneal macrophages from Western diet-fed ApoE(-/-) mice exhibited elevated levels of xanthine oxidase and NADPH oxidase activities, ROS production, Syk, Pyk2, and STAT1 phosphorylation, and CD36 expression compared to those from ApoE(-/-):12/15-LO(-/-) mice and these events correlated with increased lipid deposits, macrophage content, and lesion progression in the aortic roots. Human atherosclerotic arteries also showed increased 15-LO1 expression, STAT1 phosphorylation, and CD36 levels as compared to normal arteries. Together, these findings suggest that 12/15-LO metabolites of AA, particularly 12/15(S)-HETE, might play a crucial role in atherogenesis by enhancing foam cell formation.

Abstract 674: 15(S)-Hydroxyeicosatetraenoic Acid Induces Foam Cell Formation by Enhancing CD36 Expression via Activation of ROS-Syk-Pyk2-STAT1 Signaling

15(S)-Hydroxyeicosatetraenoic acid (15(S)-HETE), the major 15-lipoxygenase 1 (15-LO1) metabolite of arachidonic acid (AA), induces CD36 expression in xanthine oxidase and NADPH oxidase-dependent ROS production and Syk and Pyk2-dependent STAT1 activation. In line with these observations, 15(S)-HETE also induced foam cell formation involving ROS, Syk, Pyk2 and STAT1-mediated CD36 expression. In addition, peritoneal macrophages from high-fat diet-fed ApoE-/- mice exhibited elevated levels of xanthine oxidase and NADPH oxidase activities, ROS production, Syk, Pyk2, and STAT1 phosphorylation and CD36 expression compared to those from ApoE-/-:12/15-LO-/- mice and these events correlated well with increased lipid deposits and macrophage content in the aortic arches resulting in atherosclerotic plaque formation. These findings strongly suggest that 12/15-LO metabolites of AA such as 15(S)-HETE play a crucial role in atherogenesis by enhancing foam cell formation.