Biology subjects

Linton, M. F.

Publications and source records attributed to Linton, M. F..

11 recordsLinked to original sources

bioRxiv2026

N-aldehyde modified phosphatidylethanolamines formed by lipid peroxidation inhibit efferocytosis.

Objective: Impairments in efferocytosis, the phagocytic clearance of apoptotic cells, contribute to the development of chronic inflammation and promote the formation of large necrotic cores within atherosclerotic plaques. A better understanding of the factors that impair efferocytosis could lead to improved interventions. Many chronic inflammatory conditions feature excessive lipid peroxidation, which generates reactive lipid aldehydes that can potentially form N-aldehyde-modified phosphatidylethanolamines (NAMPs). We therefore investigated the extent to which levels of NAMPs are elevated under conditions of oxidative stress and whether exposure of macrophages to NAMPs inhibit efferocytosis. Approach and Results: The effects of synthetic NAMPs and lipid peroxidation on efferocytosis were measured using the Incucyte Live-Cell Analysis System to monitor rate of ingestion of CypHer-labeled apoptotic cells by cultured bone marrow-derived macrophages in real time. The extent of NAMP formation under various conditions was examined using liquid chromatography coupled with mass spectrometry. Several representative species of NAMPs (N-isolevuglandin-phosphatidylethanolamine, N-IsoLG-PE; N-4-hydroxynonenal-phosphatidylethanolamine, N-HNE-PE; and N-azeloyl-phosphatidylethanolamine, N-Aze-PE) inhibited efferocytosis in a concentration-dependent manner. Hydrolysis of NAMPs by recombinant N-acyl phosphatidylethanolamine hydrolyzing phospholipase D (NAPE-PLD) abolished their inhibitory activity, whereas genetic deletion of macrophage NAPE-PLD enhanced NAMP-mediated inhibition of efferocytosis. Blocking the inhibitor of lipid peroxidation, glutathione peroxidase 4 (GPX4), increased macrophage NAMP concentrations and impaired efferocytosis. Unmodified high-density lipoprotein (HDL) promoted efferocytosis, but exposing HDL to reactive lipid aldehydes or peroxidizing agents markedly increased NAMPs and this modified HDL inhibited efferocytosis. HDL isolated from subjects with familial hypercholesterolemia had elevated levels of multiple NAMP species. NAMPs impaired macrophage cholesterol efflux, which is required for continual efferocytosis. Conclusion: NAMPs accumulate under conditions associated with lipid peroxidation and inhibit the ability of macrophages to carry out efferocytosis.

immunology↗

bioRxiv2024

Post-transcriptional modifications on tRNA fragments confer functional changes to high-density lipoproteins in atherosclerosis

Epitranscriptomic modifications on RNA play critical roles in stability, processing, and function, partly by influencing interactions with RNA-binding proteins and receptors. The role of post-transcriptional RNA modifications on cell-free non-coding small RNA (sRNA) remains poorly understood in disease contexts. High-density lipoproteins (HDL), which transport sRNAs, can lose their beneficial properties in atherosclerosis cardiovascular disease (ASCVD). We hypothesize that changes to regulatory modifications on HDL-sRNAs contribute to this dysfunction. To assess changes in HDL-sRNA modification status, HDL-derived RNA from healthy subjects and those with atherosclerotic lesion development were analyzed using LC-MS/MS and AlkB-facilitated RNA (de)Methylation Sequencing. ASVD-HDL showed an enrichment in modified nucleosides including m1A tRNA-derived sRNAs (tDRs), particularly tDR-ArgACG-1. Functional studies revealed that ASCVD-HDL induced cell adhesion genes, including TMEM123, in primary macrophages. Recombinant HDL loaded with m1A-tDR-ArgACG-1 induced immune signaling, and similarly upregulated TMEM123. These findings suggest HDL-delivered-m1A-tDR-ArgACG-1 act on adhesion genes and immune pathways, promoting macrophage activation.

cell biology↗

bioRxiv2022

Targeting Epsins to Inhibit FGF Signaling while Potentiating TGF-β Signaling Constrains Endothelial-to-Mesenchymal-Transition in Atherosclerosis

BACKGROUNDEpsin endocytic adaptor proteins are implicated in the progression of atherosclerosis; however, the underlying molecular mechanisms have not yet been fully defined. In this study, we determined how epsins enhance endothelial-to-mesenchymal transition (EndoMT) in atherosclerosis and assessed the efficacy of a therapeutic peptide in a preclinical model of this disease. METHODSUsing single cell RNA sequencing (scRNA-seq), combined with molecular, cellular, and biochemical analyses, we investigated the role of epsins in stimulating EndoMT using knock-out mouse models. The therapeutic efficacy of a synthetic peptide targeting atherosclerotic plaques was then assessed in Apoe-/- mice. RESULTSScRNA-seq and lineage tracing revealed that epsins 1 and 2 promote EndoMT, and the loss of endothelial epsins inhibits EndoMT marker expression as well as transforming growth factor-beta signaling in vitro and in atherosclerotic mice, which is associated with smaller lesions in Apoe-/- mouse model. Mechanistically, the loss of endothelial cell epsins results in increased fibroblast growth factor receptor-1 (FGFR1) expression that inhibits TGF-{beta} signaling and EndoMT. Epsins directly bind ubiquitinated FGFR1 through their ubiquitin-interacting motif (UIM), which results in endocytosis and degradation of this receptor complex. Consequently, administration of a synthetic UIM-containing peptide API significantly attenuates EndoMT and progression of atherosclerosis. CONCLUSIONSWe conclude that epsins potentiate EndoMT during atherogenesis by increasing TGF-{beta} signaling through FGFR1 internalization and degradation. Inhibition of EndoMT by reducing epsin-FGFR1 interaction with a therapeutic peptide may represent a novel treatment strategy for atherosclerosis.

cell biology↗

bioRxiv2022

Targeting Epsins by nanotherapy regulates lipid metabolism and promotes 1 ABCG1-mediated cholesterol efflux to fortify atheroma regression

BACKGROUNDExcess cholesterol accumulation in lesional macrophages elicits complex responses in atherosclerosis. Epsins, a family of endocytic adaptors, fuel the progression of atherosclerosis; however, the underlying mechanism and therapeutic potential of targeting Epsins remains unknown. In this study, we determined the role of Epsins in macrophage-mediated metabolic regulation. We then developed an innovative method to therapeutically-target macrophage Epsins with specially-designed S2P-conjugated lipid nanoparticles (NPs), which encapsulate small interfering RNAs to suppress Epsins. METHODSWe used single cell RNA sequencing (scRNA-seq) with our newly developed algorithm MEBOCOST to study cell-cell communications mediated by metabolites from sender cells and sensor proteins on receiver cells. Biomedical, cellular and molecular approaches were utilized to investigate the role of macrophage Epsins in regulating lipid metabolism and transport. We performed this study using myeloid-specific Epsin double knockout (LysM-DKO) mice and mice with a genetic reduction of ABCG1 (LysM-DKO-ABCG1fl/+). The NPs targeting lesional macrophages were developed to encapsulate interfering RNAs to treat atherosclerosis. RESULTSWe revealed that Epsins regulate lipid metabolism and transport in atherosclerotic macrophages. Inhibiting Epsins by nanotherapy halts inflammation and accelerates atheroma resolution. Harnessing lesional macrophage-specific NP delivery of Epsin siRNAs, we showed that silencing of macrophage Epsins markedly diminished atherosclerotic plaque size and promoted plaque regression. Mechanistically, we demonstrated that Epsins bound to CD36 to facilitate lipid uptake by enhancing CD36 endocytosis and recycling. Conversely, Epsins promoted ABCG1 degradation via lysosomes and hampered ABCG1-mediated cholesterol efflux and reverse cholesterol transport. In a LysM-DKO-ABCG1fl/+ mouse model, enhanced cholesterol efflux and reverse transport due to Epsin deficiency was suppressed by the reduction of ABCG1. CONCLUSIONSOur findings suggest that targeting Epsins in lesional macrophages may offer therapeutic benefits for advanced atherosclerosis by reducing CD36-mediated lipid uptake and increasing ABCG1-mediated cholesterol efflux. Novelty and SignificanceO_ST_ABSWHAT IS KNOWN?C_ST_ABSO_LIEpsin endocytic adaptor proteins are upregulated in human and mouse atherosclerotic lesions C_LIO_LILesional macrophages internalize lipids primarily through scavenger receptor-mediated endocytosis such as CD36 and SR-A C_LIO_LIMacrophage-mediated cholesterol efflux and reverse cholesterol transport is crucial to atheroma resolution C_LI WHAT NEW INFORMATION DOES THIS ARTICLE CONTRIBUTE?O_LIScRNA-seq combined with the newly-developed algorithm MEBOCOST reveals that Epsins are involved in macrophage-mediated lipid metabolic regulation C_LIO_LIMacrophage epsins promote lipid uptake by targeting CD36 endocytosis and membrane recycling via the Epsin ENTH domain C_LIO_LIEpsins bind ubiquitinated ABCG1--resulting in the endocytosis and lysosomal degradation of this cholesterol transporter, which reduces cholesterol efflux. C_LIO_LIMacrophage-specific, nanoparticle-mediated RNAi delivery exhibits a therapeutic benefit for the treatment of atherosclerosis C_LIO_LIAtherosclerotic plaque regression using this nanoparticle delivery platform represents a clinically-relevant approach for the treatment of advance atherosclerosis C_LI BRIEF SUMMARYDespite the development of new cholesterol-lowering therapies, including the recently approved PCSK9 small interfering RNA (siRNA) antagonists, patients still face a tremendous risk of developing major acute cardiovascular events resulting from chronic inflammation in the plaque. We employed a novel nanomedicine platform containing a stabilin-2 targeting peptide (S2P) to deliver Epsin-specific siRNAs to lesional macrophages. We discovered that inhibition of these adaptor proteins in lesional macrophages significantly diminished plaque size and necrotic core area, increased fibrous cap thickness, and promoted plaque regression.

cell biology↗

bioRxiv2021

Physico-chemical principles of HDL-small RNA binding interactions.

Extracellular small RNAs (sRNA) are abundant in many biofluids, but little is known about their mechanisms of transport and stability in RNase-rich environments. We previously reported that high-density lipoproteins (HDL) of mice were enriched with multiple classes of sRNA derived from the endogenous transcriptome, but also exogenous organisms. Here, we show that human HDL transports tRNA-derived sRNAs (tDRs) from host and non-host species which were found to be altered in human atherosclerosis. We hypothesized that HDL binds to tDRs through apolipoprotein A-I (apoA-I) and these interactions are conferred by RNA-specific features. We tested this using microscale thermophoresis and electrophoretic mobility shift assays and found that HDL bind tDRs and other single-stranded sRNAs with strong affinity, but not doublestranded RNA or DNA. Natural and synthetic RNA modifications influenced tDR binding to HDL. Reconstituted HDL bound tDRs only in the presence of apoA-I and purified apoA-I alone was sufficient for binding sRNA. Conversely, phosphatidylcholine vesicles did not bind tDRs. In summary, HDL preferentially binds to single-stranded sRNAs likely through non-ionic interactions with apoA-I. These studies highlight binding properties that likely enable extracellular RNA communication and provide a foundation for future studies to manipulate HDL-sRNA for therapeutic approaches to prevent or treat disease.

molecular biology↗

bioRxiv2019

4-oxo-2-nonenal Adducts In HDL Are Elevated In Familial Hypercholesterolemia: Identification Of Modified Sites And Functional Consequences

The lipid aldehyde 4-oxo-2-nonenal (ONE) derived from peroxidation of n-6 polyunsaturated fatty acids and generated in parallel to 4-hydroxynonenal (HNE) is a highly reactive protein crosslinker. Crosslinking of proteins in high-density lipoprotein (HDL) by lipid peroxidation products causes HDL dysfunction and contributes to atherogenesis. While HNE is relatively well studied, the relevance of ONE in atherosclerosis and in modifying HDL has not been examined. In the present study, we found a significant increase in ONE-ketoamide (lysine) adducts in HDL derived from patients with familial hypercholesterolemia (FH) (1620 {+/-} 985.4 pmol/mg) compared to healthy controls (664 {+/-} 219.5 pmol/mg). ONE crosslinked apoA-I on HDL at a concentration of >3 mol ONE per 10 mol apoA-I (0.3 eq), which is 100-fold lower than HNE but comparable to the potent protein crosslinker, isolevuglandin. ONE-modified HDL partially inhibited the ability of HDL to protect against LPS-induced TNF and IL-1{beta} mRNA expression in murine macrophages. At 3 eq., ONE dramatically decreased the ability of apoA-I to exchange from HDL, from ~46.5% to only ~18.4% (P<0.001). Surprisingly, ONE-modification of HDL or apoA-I did not alter macrophage cholesterol efflux capacity. LC/MS/MS analysis showed modification of Lys12, Lys23, Lys96, and Lys226 of apoA-I by ONE-ketoamide adducts. Compared to other dicarbonyl scavengers, pentylpyridoxamine (PPM) was most efficacious at blocking ONE-induced protein crosslinking in HDL. Our studies show that ONE HDL adducts are elevated in FH who have severe hypercholesterolemia and atherosclerosis and causes HDL dysfunction. We demonstrate the use of PPM in preferentially scavenging ONE in biological systems.

biochemistry↗

bioRxiv2019

Scavenging dicarbonyls with 5'-O-pentyl-pyridoxamine improves insulin sensitivity and reduces atherosclerosis through modulating inflammatory Ly6Chi monocytosis and macrophage polarization

ObjectiveOxidative stress contributes to the development of insulin resistance (IR) and atherosclerosis. Peroxidation of lipids produces reactive dicarbonyls such as Isolevuglandins (IsoLG) and malondialdehyde (MDA) that covalently bind plasma/cellular proteins, phospholipids, and DNA leading to altered function and toxicity. We examined whether scavenging reactive dicarbonyls with 5-O-pentyl-pyridoxamine (PPM) protects against the development of IR and atherosclerosis in Ldlr-/- mice. MethodsMale or female Ldlr-/- mice were fed a western diet (WD) for 16 weeks and treated with PPM versus vehicle alone. Plaque extent, dicarbonyl-lysyl adducts, efferocytosis, apoptosis, macrophage inflammation, and necrotic area were measured. Plasma MDA-LDL adducts and the in vivo and in vitro effects of PPM on the ability of HDL to reduce macrophage cholesterol were measured. Blood Ly6Chi monocytes and ex vivo 5-ethynyl-2-deoxyuridine (EdU) incorporation into bone marrow CD11b+ monocytes and CD34+ hematopoietic stem and progenitor cells (HSPC) were also examined. IR was examined by measuring fasting glucose/insulin levels and tolerance to insulin/glucose challenge. ResultsPPM reduced the proximal aortic atherosclerosis by 48% and by 46% in female and male Ldlr-/- mice, respectively. PPM also decreased IR and hepatic fat and inflammation in male Ldlr-/- mice. Importantly, PPM decreased plasma MDA-LDL adducts and prevented the accumulation of plaque MDA- and IsoLG-lysyl adducts in Ldlr-/- mice. In addition, PPM increased the net cholesterol efflux capacity of HDL from Ldlr-/- mice and prevented both the in vitro impairment of HDL net cholesterol efflux capacity and apoAI crosslinking by MPO generated hypochlorous acid. Moreover, PPM decreased features of plaque instability including decreased proinflammatory M1-like macrophages, IL-1{beta} expression, myeloperoxidase, apoptosis, and necrotic core. In contrast, PPM increased M2-like macrophages, Tregs, fibrous cap thickness, and efferocytosis. Furthermore, PPM reduced inflammatory monocytosis as evidenced by decreased blood Ly6Chi monocytes and proliferation of bone marrow monocytes and HSPC from Ldlr-/- mice. ConclusionsPPM has pleotropic atheroprotective effects in a murine model of familial hypercholesterolemia, supporting the therapeutic potential of reactive dicarbonyl scavenging in the treatment of IR and atherosclerotic cardiovascular disease.

pharmacology and toxicology↗

bioRxiv2019

Reactive Dicarbonyl Scavenging Effectively Reduces MPO-Mediated Oxidation of HDL and Preserves HDL Atheroprotective Functions

High-density lipoprotein (HDL) is atheroprotective by mediating cholesterol efflux, anti-inflammatory, and anti-oxidation functions. Atheroprotective functions of HDL are related to the activity of HDL-associated enzymes such as paraoxonase 1 (PON1). We examined the impact of inhibition of myeloperoxidase (MPO)-mediated HDL oxidation by PON1 on HDL malondialdehyde (MDA) content and HDL function. In the presence of PON1, crosslinking of apoAI in response to MPO-mediated oxidation of HDL was abolished and MDA-HDL adduct levels were decreased. In addition, PON1 prevented the impaired cholesterol efflux capacity of MPO-oxidized HDL from Apoe-/- macrophages. Direct modification of HDL with MDA increased apoAI crosslinking and reduced the cholesterol efflux capacity in a dose dependent manner. In addition, MDA modification of HDL reduced its anti-inflammatory function compared to native HDL as the expression of IL-1{beta} and IL6 increased by 3-(p<0.05) and 1.8-fold (p<0.05) in Apoe-/- macrophages in response to LPS. MDA-HDL also had impaired ability to increase PON1 activity. Importantly, HDL from subjects with familial hypercholesterolemia (FH-HDL) versus controls had increased MDA-apoAI adducts, and normalization of the PON1 activity to PON1 mass revealed a 24 % (p<0.05) decrease in specific activity indicating that PON1 activity is also impaired in FH. Consistent with the impaired PON1 activity and increased MDA-apoAI, FH-HDL induced a pro-inflammatory response in Apoe-/- macrophages compared to incubation with LPS alone. FH-HDL versus control HDL also had an impaired ability to promote cholesterol efflux from Apoe-/- macrophages. Interestingly, reactive dicarbonyl scavengers effectively abolished MPO-mediated apoAI crosslinking, MDA adduct formation, and improved cholesterol efflux capacity. Importantly, in vivo treatment of hypercholesterolemic mice with reactive dicarbonyl scavengers effectively reduced MDA-HDL adduct formation and increased PON1 activity and HDL cholesterol efflux capacity, supporting a therapeutic potential of reactive carbonyl scavenging in maintaining HDL function.

pharmacology and toxicology↗

bioRxiv2019

Scavenging of reactive dicarbonyls with 2-hydroxybenzylamine reduces atherosclerosis in hypercholesterolemic Ldlr-/- mice

The pathogenesis of atherosclerosis may be accelerated by oxidative stress, which produces lipid peroxidation. Among the products of lipid peroxidation are highly reactive dicarbonyls including isolevuglandins (IsoLGs) and malondialdehyde (MDA) that covalently modify proteins. We investigated the impact of treatment with the dicarbonyl scavenger, 2-hydroxybenzylamine (2-HOBA) on HDL function and atherosclerosis in hyperlipidemic Ldlr-/- mice, a model of familial hypercholesterolemia (FH). Compared to mice treated with vehicle, 2-HOBA significantly decreased atherosclerosis in hypercholesterolemic Ldlr-/- mice by 31% in the proximal aortas and 60% in en face aortas, in the absence of changes in blood lipid levels. 2-HOBA reduced MDA content in HDL and LDL. Consuming a western diet increased plasma MDA-apoAI adduct levels in Ldlr-/- mice. 2-HOBA inhibited MDA-apoAI formation and increased the capacity of the mouse HDL to reduce macrophage cholesterol stores. Importantly, 2-HOBA reduced the MDA- and IsoLG-lysyl content in atherosclerotic aortas in Ldlr-/- mice. Furthermore, 2-HOBA diminished oxidative stress-induced inflammatory responses in macrophages, reduced the number of TUNEL-positive cells in atherosclerotic lesions by 72%, and decreased serum proinflammatory cytokines. Furthermore, 2-HOBA enhanced efferocytosis and promoted characteristics of stable plaque formation in mice as evidenced by a 69% (p<0.01) reduction in necrotic core and by increased collagen content (2.7-fold) and fibrous cap thickness (2.1-fold). HDL from patients with FH had increased MDA content resulting in a reduced ability of FH-HDL to decrease macrophage cholesterol content versus controls. Our results demonstrate that dicarbonyl scavenging with 2-HOBA has multiple atheroprotective effects on lipoproteins and reduces atherosclerosis in a murine model of FH, supporting its potential as a novel therapeutic approach for the prevention and treatment of human atherosclerotic cardiovascular disease.\n\nAbbreviations2-HOBA, 2-hydroxybenzylamine; 4-HOBA, 4-hydroxybenzylamine; MDA, malondialdehyde; 4-HNE, 4-hydroxynonenal; IsoLGs, isolevuglandins; HDL, high-density lipoproteins; LDL, lowdensity lipoprotein; LDLR, low-density lipoprotein receptor; ApoAI, apolipoprotein AI; ApoB, apolipoprotein B; ROS, reactive oxygen species; IL, interleukin.

pharmacology and toxicology↗

bioRxiv2019

Genetic risk for major depressive disorder and loneliness in gender-specific associations with coronary artery disease

ImportanceEpidemiological evidence indicates that major depressive disorder (MDD) and loneliness both reduce life expectancies, but mechanisms underlying the excess morbidity are unclear. Electronic health records (EHRs) linked to genetic data offer new opportunities to address this knowledge gap.\n\nObjectiveTo determine the medical morbidity pattern associated with genetic risk factors for MDD and loneliness, two common psychological traits with adverse health outcomes.\n\nDesignPhenome-wide association study using EHRs spanning 1990 to 2017 from the Vanderbilt University Medical Center biobank, BioVU. Top associations with coronary artery disease (CAD) were replicated in the Atherosclerosis Risk in Communities (ARIC) cohort.\n\nSettingHospital-based EHR study, with replication in a population-based cohort study.\n\nParticipants18,385 genotyped adult patients in BioVU. Replication in ARIC included 7,197 genotyped participants. All participants were of European ancestry.\n\nExposuresPolygenic scores for MDD and loneliness were developed for each individual using previously published meta-GWAS summary statistics.\n\nMain Outcomes and MeasuresThe phenome-wide association study included 882 clinical diagnoses ascertained via billing codes in the EHR. ARIC included 1598 incident CAD cases.\n\nResultsBioVU patients had a median EHR length of 9.91 years. In the phenome-wide association study, polygenic scores for MDD and loneliness were significantly associated with psychiatric and cardiac phenotypes. Targeted analyses of CAD in 3,893 cases and 4,197 controls in BioVU found odds ratios of 1.11 (95% CI, 1.04-1.18; P=8.43x10-4) and 1.13 (95% CI, 1.07-1.20; P=4.51x10-6) per 1-SD increase in the polygenic scores for MDD and loneliness, respectively. Comparable hazard ratios in ARIC were 1.07 (95% CI, 0.99-1.14; P=0.07) and 1.07 (1.01-1.15; P=0.03). Across both studies, the increased risk persisted in women after adjusting for multiple conventional risk factors, a polygenic score for CAD, and psychiatric symptoms (available in BioVU). Controlling for genetic risk factors shared between MDD and loneliness, the polygenic score for loneliness conditioned on MDD remained associated with CAD risk, but the polygenic score for MDD conditioned on loneliness did not.\n\nConclusions and RelevanceGenetic risk factors for MDD and loneliness act pleiotropically to increase CAD risk in women. Continued research into the biological and clinical connections between the heart and mind is warranted.

genetics↗

bioRxiv2018

Bioinformatic analysis of endogenous and exogenous small RNAs on lipoproteins

To comprehensively study extracellular small RNAs (sRNA) by sequencing (sRNA-seq), we developed a novel pipeline to overcome current limitations in analysis entitled, \"Tools for Integrative Genome analysis of Extracellular sRNAs (TIGER)\". To demonstrate the power of this tool, sRNA-seq was performed on mouse lipoproteins, bile, urine, and liver samples. A key advance for the TIGER pipeline is the ability to analyze both host and non-host sRNAs at genomic, parent RNA, and individual fragment levels. TIGER was able to identify approximately 60% of sRNAs on lipoproteins, and >85% of sRNAs in liver, bile, and urine, a significant advance compared to existing software. Results suggest that the majority of sRNAs on lipoproteins are non-host sRNAs derived from bacterial sources in the microbiome and environment, specifically rRNA-derived sRNAs from Proteobacteria. Collectively, TIGER facilitated novel discoveries of lipoprotein and biofluid sRNAs and has tremendous applicability for the field of extracellular RNA.

bioinformatics↗