Ldlr Knockout Research Articles

Abstract Tu016: Alleviating Aortic Valve Calcification By Blocking TNFα Receptors

Background: Tumor Necrosis Factor-alpha (TNFα) is a key inflammatory cytokine involved in calcific aortic valve disease (CAVD). Following mechanical stress, activated monocytes, macrophages induce TNFα signaling in aortic valve (AoV). The activated TNFα binds to its own receptors, TNFR1 and TNFR2, in which TNFR1 has a death domain likely to cause cell death in AoV. Subsequently, the release of extracellular vesicles (calcium and inorganic phosphates) following inflammatory process results in valve calcification and stenosis. Hypothesis: Blocking TNFα-mediated inflammation by genetic knockout of Tnfr1/Tnfr2 slowdown CAVD progression in mice. Methods and Results: Using a mouse model of CAVD with deletion of Ldlr, low-density lipoprotein receptor, we compared the disease progression in mice fed with standard and high fat diet. To get better understanding on the role of TNFα in CAVD, Ldlr -/- mice (3 months old) on the TNFR1 and TNFR2 knockout background, were also fed with high fat diet for 3 months ( Ldlr -/- ; Tnfr1 -/- : Tnfr2 -/- ). Aortic valve function was analyzed by using echocardiogram and it showed decreased AoV velocity and increased ejection fraction in Ldlr -/- ; Tnfr1 -/- : Tnfr2 -/- compared to Ldlr -/- ; Tnfr1 +/- : Tnfr2 +/- group. The pathological changes such as fibrosis, calcium and collagen deposition seen under routine and specialized histological staining methods were reduced in TNF receptors knockout group. Next, using customized designed for PCR arrays, we examined the expression of 62 candidate genes involved in inflammation, apoptosis, extracellular matrix remodeling or aortic valve stenosis pathways. The top downregulated genes in the Ldlr -/- ; Tnfr1 -/- : Tnfr2 -/- group compared to Ldlr -/- ; Tnfr1 +/- : Tnfr2 +/- group are (Col3a1, MMp7, Klk1) whereas the top upregulated gene are (Igf1r and MMp14). We are currently validating these findings by using qPCR and immunofluorescence. Conclusion: Our findings reveal blocking TNFα signaling receptors downregulate the genes related to inflammatory cytokine activation and aortic valve stenosis in the Ldlr knockout mice fed with high fat diet. Blockage of TNFα likely reduces apoptosis and inflammation while improves extracellular matrix remodeling to slowdown CAVD progression. Our findings thus suggest a new therapeutic strategy for CAVD.

Novel Mouse Model of Myocardial Infarction, Plaque Rupture, and Stroke Shows Improved Survival With Myeloperoxidase Inhibition.

Thromboembolic events, including myocardial infarction (MI) or stroke, caused by the rupture or erosion of unstable atherosclerotic plaques are the leading cause of death worldwide. Although most mouse models of atherosclerosis develop lesions in the aorta and carotid arteries, they do not develop advanced coronary artery lesions. Moreover, they do not undergo spontaneous plaque rupture with MI and stroke or do so at such a low frequency that they are not viable experimental models to study late-stage thrombotic events or to identify novel therapeutic approaches for treating atherosclerotic disease. This has stymied the development of more effective therapeutic approaches for reducing these events beyond what has been achieved with aggressive lipid lowering. Here, we describe a diet-inducible mouse model that develops widespread advanced atherosclerosis in coronary, brachiocephalic, and carotid arteries with plaque rupture, MI, and stroke. We characterized a novel mouse model with a C-terminal mutation in the scavenger receptor class B, type 1 (SR-BI), combined with Ldlr knockout (designated SR-BI∆CT/∆CT/Ldlr-/-). Mice were fed Western diet (WD) for 26 weeks and analyzed for MI and stroke. Coronary, brachiocephalic, and carotid arteries were analyzed for atherosclerotic lesions and indices of plaque stability. To validate the utility of this model, SR-BI∆CT/∆CT/Ldlr-/- mice were treated with the drug candidate AZM198, which inhibits myeloperoxidase, an enzyme produced by activated neutrophils that predicts rupture of human atherosclerotic lesions. SR-BI∆CT/∆CT/Ldlr-/- mice show high (>80%) mortality rates after 26 weeks of WD feeding because of major adverse cardiovascular events, including spontaneous plaque rupture with MI and stroke. Moreover, WD-fed SR-BI∆CT/∆CT/Ldlr-/- mice displayed elevated circulating high-sensitivity cardiac troponin I and increased neutrophil extracellular trap formation within lesions compared with control mice. Treatment of WD-fed SR-BI∆CT/∆CT/Ldlr-/- mice with AZM198 showed remarkable benefits, including >90% improvement in survival and >60% decrease in the incidence of plaque rupture, MI, and stroke, in conjunction with decreased circulating high-sensitivity cardiac troponin I and reduced neutrophil extracellular trap formation within lesions. WD-fed SR-BI∆CT/∆CT/Ldlr-/- mice more closely replicate late-stage clinical events of advanced human atherosclerotic disease than previous models and can be used to identify and test potential new therapeutic agents to prevent major adverse cardiac events.

Abstract 115: Scavenger Receptor-BI Mediates Endothelial Uptake Of Lipoprotein(a)

Elevated levels of lipoprotein(a) [Lp(a)], an apoB100-containing lipoprotein, are an independent risk factor for atherosclerotic cardiovascular disease, even in the setting of effective reduction of plasma low-density lipoprotein (LDL) cholesterol. To date, the mechanisms whereby Lp(a) exerts its atherogenic effects remain poorly understood, and no treatments aimed at lowering Lp(a) have been approved. Two receptors - scavenger receptor-BI (SR-BI) and activin receptor-like kinase 1 (ALK1) - have been proposed to bind apoB100 and mediate the atherogenic uptake and transcytosis of LDL across the endothelial cell (EC) barrier. EC-specific SR-BI knockout reduces atherosclerosis in both apoE and LDLR knockout mice. We have shown that SR-BI also mediates EC uptake of nascent chylomicrons. Although binding of ALK1 to apoB is believed to occur through the N-terminus of apoB, the receptor is not involved in the uptake of chylomicrons. We assessed which if any of these receptors are involved in Lp(a) uptake by ECs. Despite the presence of apoB100, EC uptake of Lp(a), like apoB48 chylomicrons, was reduced by SR-BI, but not ALK1, knockdown. We then used a series of small N terminal apoB peptides (apoB3-apoB18, with sequences comprising the 3%, 8%, 12%, 15%, and 18% N terminus of apoB) to compete with Lp(a) uptake. Both chylomicron and Lp(a) uptake was inhibited by apoB15 and apoB18, whereas LDL uptake was additionally inhibited by apoB12. These observations suggest that a) the binding sequence to SR-BI is between residues 547-684 of apoB, and b) an additional sequence between residues 365-547 participates in apoB binding to ALK1. Our findings suggest that apo(a) alters the structure of apoB to make it a better ligand for SR-BI uptake by ECs. Because this uptake pathway leads to transcytosis, we hypothesize that the greater atherogenicity of Lp(a) is mediated by its increased binding to and uptake by ECs.

Abstract 14517: apoE Receptor-2-R952Q Variant in Macrophages Potentiates Hyperlipidemia and Atherosclerosis in LDL Receptor-Knockout Mice via Increased Secretion of Soluble LDL Receptor-Related Protein-1

Introduction and objective: Apolipoprotein E Receptor-2 (apoER2) is a type I transmembrane receptor in the LDLR family expressed in vascular smooth muscle cells (VSMC), endothelium, and macrophages. An apoER2 mutation referred to as apoER2-R952Q (R952Q) is associated with elevated plasma triglyceride levels and increased risk of premature coronary artery disease and myocardial infarction in humans. This study investigated the role of the R952Q mutation of apoER2 in modulating disease development. Methods and Results: We generated R952Q-expressing mice using a CRISPR-directed approach. This mouse line was crossed with the LDLR knockout mouse line and the progenies were fed a high cholesterol diet for 16 or 24 weeks. Results showed that unlike apoER2 knockout, the accelerated atherosclerosis R952Q variant mice exhibited was linked to increased plasma lipid levels. Considering apoER2's expression, which is notably absent in hepatocytes, we investigated the impact of R952Q myeloid cells on disease progression via bone marrow transplant. Results showed that wildtype apoER2 mouse recipients of R952Q bone marrow recapitulated the elevated plasma lipid level phenotype while R952Q mouse recipients of wildtype apoER2 bone marrow did not. Due to the absence of LDLR in our model, we investigated LRP1’s role in the context of myeloid-specific R952Q and found an increase in the production of hypercholesterolemia-associated soluble LRP1 (sLRP1) in the plasma of high cholesterol diet-fed mice with myeloid-specific R952Q. sLRP1 may compete with cell-surface LRP1 in lipoprotein clearance, suggesting a novel mechanism by which the R952Q mutation in macrophages may increase plasma lipid levels, thereby accelerating atherosclerosis. Conclusion: The R952Q mutation in apoER2 accelerates atherosclerosis via overproduction of soluble LRP1, a gain-of-function mechanism in macrophages resulting in hypercholesterolemia.

Transcriptome analysis of T cells from Ldlr−/− mice and effects of in vitro vitamin D treatment

Vitamin D is known for its immunosuppressive effects on T cells, suppressing Th1 and Th17 and promoting Treg differentiation. Th1 cells contribute to inflammatory responses such as inflammatory cytokine production and macrophage activation, which accelerate the progression of atherosclerosis. However, the mechanisms underlying the modulation of T cell functions by vitamin D in atherosclerosis have not been investigated. This study analyzed the gene expression profiles of T cells, using RNA-seq transcriptome analysis, to investigate the effects of in vitro vitamin D treatment on T cell differentiation and signal transduction pathways in Ldlr knock-out (Ldlr−/−) mice. C57BL/6 mice were randomly assigned to two groups and fed a control diet (CON) or a Western diet (WD) for 16 weeks, while Ldlr−/- mice (LDLR−/−) were fed a Western diet. Splenic T cells were isolated and stimulated with anti-CD3e and anti-CD28 mAb for 48 h with or without 10 nM 1,25(OH)2D3. RNA sequencing was performed, followed by KEGG and GO enrichment analyses. Populations of T cell subsets and cytokine production were measured to assess T cell lineage differentiation. The JAK-STAT, HIF-1, and calcium signaling pathways of Ldlr−/− mice significantly differed from those of control mice, and 1,25(OH)2D3 treatment affected MAPKKK binding molecular function of Ldlr−/− mice. Percentages of Th1 cells and IL-17 production were significantly reduced by 1,25(OH)2D3 treatment in all three mouse groups. These results suggest that 1,25(OH)2D3 has anti-inflammatory effects in atherosclerosis and is involved in cell signaling pathways that could prevent disease progression by regulating T cell differentiation and effector functions.

Tanshinone IIA alleviates atherosclerosis in LDLR-/- mice by regulating efferocytosis of macrophages.

Background: Tanshinone IIA (TIIA) is the major lipid-soluble active ingredient of the traditional Chinese medicine Salvia miltiorrhiza, which slows down atherosclerosis (AS). However, it remains unclear whether TIIA has the potential to enhance macrophage efferocytosis and thereby improve atherosclerosis. Objective: The focus of this examination was to determine if TIIA could reduce lipid accumulation and treat AS by enhancing efferocytosis. Methods: Firstly, we conducted in vivo experiments using LDLR knockout (LDLR-/-) mice for a period of 24weeks, using histopathological staining, immunofluorescence and Western blot experiments to validate from the efficacy and mechanism parts, respectively; in addition, we utilized cells to validate our study again in vitro. The specific experimental design scheme is as follows: In vivo, Western diet-fed LDLR-/- mice for 12weeks were constructed as an AS model, and normal diet-fed LDLR-/- mice were taken as a blank control group. The TIIA group and positive control group (atorvastatin, ATO) were intervened for 12weeks by intraperitoneal injection (15mg/kg/d) and gavage (1.3mg/kg/d), respectively. In vitro, RAW264.7 cells were cultured with ox-LDL (50ug/mL) or ox-LDL (50ug/mL) + TIIA (20uM/L or 40uM/L). Pathological changes in aortic plaques and foam cell formation in RAW264.7 cells were evaluated using Masson and Oil Red O staining, respectively. Biochemical methods were used to detect lipid levels in mice. The immunofluorescence assay was performed to detect apoptotic cells and efferocytosis-related signal expression at the plaques. RT-qPCR and Western blot were carried out to observe the trend change of efferocytosis-related molecules in both mouse aorta and RAW264.7 cells. We also used the neutral red assay to assess RAW264.7 cells' phagocytic capacity. Results: Compared with the model group, TIIA decreased serum TC, TG, and LDL-C levels (p < 0.01), reduced the relative lumen area of murine aortic lipid-rich plaques (p < 0.01), enhanced the stability of murine aortic plaques (p < 0.01), reduced ox-LDL-induced lipid build-up in RAW264.7 cells (p < 0.01), and upregulated efferocytosis-related molecules expression and enhance the efferocytosis rate of ox-LDL-induced RAW264.7 cells. Conclusion: TIIA might reduce lipid accumulation by enhancing the efferocytosis of macrophages and thus treat AS.

Abstract 023: Prior Sflt1 Induced Preeclampsia Exacerbates Post-partum Hypertension-mediated Aortic Stiffness And Hypercholesterolemia-induced Atherosclerotic Inflammation

Preeclampsia (PE) is new high blood pressure (BP) and organ damage occurring late in pregnancy in association with increased soluble VEGF receptor (sFlt1). PE survivors have increased risk of future hypertension and myocardial infarction/stroke. We hypothesized that exposure to high sFlt1 during pregnancy exacerbates hypertension and atherosclerosis post-partum. PE was induced by transient adenoviral expression of sFlt1 compared to control virus in pregnant mice. PE mice had elevated sFlt1, BP and kidney damage during pregnancy which resolve post partum. Two months post-partum, prior PE mice had significantly increased BP response to high salt diet. After high BP stimuli, we studied large and small artery function. Prior PE mice had diminished nitric oxide-mediated vasodilation and stiffer aortas with more fibrosis as measured by pulse wave velocity (Con:3.7 vs sFlt:5.9 mm/ms, p&lt;0.0001) and trichrome staining (Con:13.7% vs sFlt:33.9%, p=0.0009). Atherosclerosis studies exposed LDLR knockout mice to PE followed by high fat diet feeding for 8 weeks. Body weight, fasting glucose and cholesterol were not altered by prior PE. Aortic roots were histologically analyzed for plaque size and composition. Aortic root plaque size (Con:73.3 vs sFlt:78.0 AU, p=0.60) and necrotic core were not different between groups. Aortic arch plaque inflammation was quantified via flow cytometry showing significantly increased plaque CD45+ leukocytes (sFlt:1.6 fold, p=0.036) and T cells (sFlt:1.8 fold, p=0.031) from mice with prior PE. Atheroprone mice with prior PE had significantly increased aortic expression of CCL22 (sFlt:1.5 fold, p=0.047), providing a potential mechanism for increased T cell infiltration into atherosclerotic plaques. Experimental PE produces a state of enhanced sensitivity to hypertensive stimuli and increased vascular inflammation in atherosclerotic plaques supporting the concept that PE directly exacerbates hypertension, vascular stiffness, and atherosclerotic inflammation independent of pre-existing risk factors.

Abstract P3198: Spermidine Ameliorates Aortic Valve Degenerations By Improving Mitochondrial Biogenesis

Aortic stenosis is the most common heart valve disease in the elderly, and aging is a leading factor. However, there is no medical treatment yet except for an operation. We investigated that mitochondrial function deteriorated in isolated human aortic valve interstitial cells (hAVICs) from the patients who had aortic stenosis (Figure A, B). We examined the therapeutic effect of spermidine (SPD) which is known to enhance mitochondrial function in the treatment of diseased hAVICs. As a result, we showed the expression of fibrosis, inflammation, and calcification markers decreased after the SPD treatment. Using the LDLR knockout mice model fed a high-fat diet, we found that the mitochondrial function in mouse AVICs improved after the SPD treatment, and the thickening, inflammation, and calcification of aortic valve leaflets significantly decreased in the SPD-fed mice (Figure C, D). Ingenuity pathway analysis from proteomic data in this animal model suggested the IRS2-AKT-TP53-SIRT1-DNMT1 pathway as a treatment mechanism and we could confirm that TP53, SIRT1, and PPARG increased while IRS2, AKT and DNMT1 were inhibited by the treatment of SPD in ex-vivo and in vitro experiments. In addition, we found that 5-azacytidine, as a DNMT1 inhibitor, induces the mitochondrial biogenesis-related genes by lowering mtDNA hypermethylation in hAVICs. In conclusion, spermidine ameliorates the mitochondrial function through the IRS-AKT-TP53-SIRT1-DNMT1 pathway in AVICs and the inhibition of DNMT1 and mtDNA hypermethylation improves mitochondrial biogenesis which can be a treatment mechanism for aortic stenosis.

Abstract 708: Murine Atherosclerosis Data Integration: The Sum Is Greater Than The Parts

Translation of murine atherosclerosis studies to human disease has limited reproducibility. Our prior work showed that aggregated data from one mouse atherosclerosis model identified etiologic pathways and networks associated with human atherosclerotic cardiovascular disease (ASCVD). Therefore, we extracted data from 991 ApoE knockout (KO) manuscripts and 544 LDLR KO manuscripts to identify 405 unique genes associated with significant changes in plaque size in mice. The impact of each gene on plaque size was analyzed using Ingenuity Pathway Analysis to contextualize the gene data. The most significantly activated pathways for genes that increased plaque size were neuroinflammation (p=3.02 E-55) and hepatic fibrosis signaling (p=2.25 E-52), while the LXR/RXR pathway was the most significantly downregulated (p=1.32 E-37). We then performed association analyses from Vanderbilt University Medical Center’s BioVU using genetically predicted gene expression of the individual genes from these datasets. Neither the aggregated genes identified in each individual mouse model nor the genes directly studied in the murine models that mapped to the top pathways were significantly enriched for association with ASCVD in humans. However, when homologous human gene sets derived from the top identified murine pathways were considered as a whole, they were highly significantly enriched for association with ASCVD (Fig 1). Further, this method identified human genes significantly associated with ASCVD that were not directly studied in mice. For example, in the neuroinflammation pathway, the genes studied in mice were not enriched for ASCVD, yet 61/117 genes (52%) in the global pathway were associated with ASCVD (p=0.00017), 43 of which were not directly studied in mice. Thus, integration of murine data identifies novel pathways significantly associated with human ASCVD thereby providing mechanistic insight into human disease only possible through contextualization.

Abstract 15473: A New Metabolic Phenotype in a Mouse Model of Chronic Kidney Disease and Atherosclerosis

Introduction: Patients with chronic kidney disease (CKD) experience significant cardiovascular morbidity and mortality. Vascular calcification is a hallmark of CKD and a strong predictor of atherosclerotic cardiovascular disease. Hypothesis: We hypothesize that CKD-induced vascular calcification potentiates atherosclerosis. Methods: First, wished to conduct a pilot study to confirm that a co-treatment of the low-density protein receptor mutant mice (Ldlr whc ) with a 0.2% adenine in a western diet will produce accelerated atherosclerosis, consistent with a well-known phenotype in the 5/6 nephrectomy model on an ApoE or Ldlr knockout background. Then we developed a two-step non-surgical mouse model in which the induction of calcification by a 0.2% adenine treatment was followed by western diet-induced hyperlipidemia. Results: Contrary to expected, the adenine and western diet (W+A) co-treatment resulted in a striking reduction of plasma triglycerides (TG), aortic root atherosclerosis, and liver lipids despite a fully penetrant CKD phenotype with tubulointerstitial damage, increased blood urea nitrogen, hyperphosphatemia, polyuria, vascular calcification, and osteoporosis. The two-step induction of CKD and atherosclerosis demonstrated partially normalized but reduced plasma triglycerides and liver lipid content, polyurea, and polydipsia in CKD mice, and there was no difference in atherosclerotic burden or plaque calcification between the groups. Interestingly we observed an increase in food and calorie intake and 24-hour glucose excretion in the urine in the pre-treated group compared with mice on a western diet without pre-treatment, while plasma glucose levels were not different between the groups. Conclusion: The paradoxical lack of dyslipidemia in mice treated with adenine provides an insight into the potential effects of tubulointerstitial kidney disease and nephrogenic diabetes incipits on lipid metabolism and atherosclerosis. 1

LncRNA MDRL Mitigates Atherosclerosis through miR-361/SQSTM1/NLRP3 Signaling.

Objective Long non-coding RNAs (lncRNAs) play many important roles in gene regulation and disease pathogenesis. Here, we sought to determine that mitochondrial dynamic related lncRNA (MDRL) modulates NLRP3 inflammasome activation and apoptosis of vascular smooth muscle cells (VSMCs) and protects arteries against atherosclerosis. Methods In vivo experiments, we applied LDLR knockout (LDLR−/−) mice fed the high-fat diet to investigate the effects of MDRL on atherosclerosis. In vitro experiments, we applied mouse aortic smooth muscle cells to determine the mechanism of MDRL in abrogating NLRP3 inflammasome and inhibiting cell apoptosis through miR-361/sequentosome 1 (SQSTM1) by TUNEL staining, quantitative RT-PCR, western blot, microribonucleoprotein immunoprecipitation, and luciferase reporter assay. Results Downregulated MDRL and increased NLRP3 were observed in mouse atherosclerotic plaques, accompanied with the increase of miR-361. The results showed that MDRL overexpression significantly attenuated the burden of atherosclerotic plaque and facilitated plaque stability through inhibiting NLRP3 inflammasome activation and cell apoptosis, and vice versa. Mechanically, MDRL suppressed NLRP3 inflammasome activation and VSMC apoptosis via suppressing miR-361. Furthermore, miR-361 directly bound to the 3'UTR of SQSTM1 and inhibited its translation, subsequently activating NLRP3 inflammasome. Systematic delivery of miR-361 partly counteracted the beneficial effects of MDRL overexpression on atherosclerotic development in LDLR−/− mice. Conclusions In summary, MDRL alleviates NLRP3 inflammasome activation and apoptosis in VSMCs through miR-361/SQSTM1/NLRP3 pathway during atherogenesis. These data indicate that MDRL and inhibition of miR-361 represent potential therapeutic targets in atherosclerosis-related diseases.

Crocin mitigates atherosclerotic progression in LDLR knockout mice by hepatic oxidative stress and inflammatory reaction reduction, and intestinal barrier improvement and gut microbiota modulation

Crocin has a protective effect on neurodegenerative disease, but whether crocin can prevent atherosclerosis remains unclear. The present study aimed to explore the possible anti-atherosclerotic mechanism of crocin in LDLR-/- mice. Mice were fed an atherogenic high-fat/cholesterol diet and concomitantly treated by intragastric administration with normal saline (Model) or 20 or 40 mg/(kg.bw.day) crocin for 8 weeks. Pathological results showed that Model group exhibited a marked atherosclerotic plaque, while crocin significantly reduced atherosclerotic plaque, accompanied by a small amount of denatured collagen fiber and foam cells. Mechanistically, crocin, especially high-dose suppressed the formation of atherosclerotic plaques via enhancing hepatic antioxidant capacity. Besides, crocin effectively inhibited NLRP3 inflammasome and blocked TLR4 signal, through reducing oxidative stress based on Nrf2/Keap1 pathway, and increasing intestinal tight junction proteins and improving gut microbiota composition. These results suggest that crocin can ameliorate inflammation and attenuate atherosclerotic progression by oxidative stress reduction and intestinal barrier improvement.

Liver injury in non-alcoholic fatty liver disease is associated with urea cycle enzyme dysregulation

The main aim was to evaluate changes in urea cycle enzymes in NAFLD patients and in two preclinical animal models mimicking this entity. Seventeen liver specimens from NAFLD patients were included for immunohistochemistry and gene expression analyses. Three-hundred-and-eighty-two biopsy-proven NAFLD patients were genotyped for rs1047891, a functional variant located in carbamoyl phosphate synthetase-1 (CPS1) gene. Two preclinical models were employed to analyse CPS1 by immunohistochemistry, a choline deficient high-fat diet model (CDA-HFD) and a high fat diet LDLr knockout model (LDLr −/−). A significant downregulation in mRNA was observed in CPS1 and ornithine transcarbamylase (OTC1) in simple steatosis and NASH-fibrosis patients versus controls. Further, age, obesity (BMI > 30 kg/m2), diabetes mellitus and ALT werefound to be risk factors whereas A-allele from CPS1 was a protective factor from liver fibrosis. CPS1 hepatic expression was diminished in parallel with the increase of fibrosis, and its levels reverted up to normality after changing diet in CDA-HFD mice. In conclusion, liver fibrosis and steatosis were associated with a reduction in both gene and protein expression patterns of mitochondrial urea cycle enzymes. A-allele from a variant on CPS1 may protect from fibrosis development. CPS1 expression is restored in a preclinical model when the main trigger of the liver damage disappears.

Investigating the Complex Interplay Between Genotype and High Fat Diet Feeding in the Lactating Mammary Gland using the Tph1and Ldlr knockout models

Investigating the Complex Interplay Between Genotype and High Fat Diet Feeding in the Lactating Mammary Gland using the Tph1and Ldlr knockout models

Sitagliptin attenuates arterial calcification by downregulating oxidative stress-induced receptor for advanced glycation end products in LDLR knockout mice

Diabetes is a complex disease characterized by hyperglycemia, dyslipidemia, and insulin resistance. Plasma advanced glycation end products (AGEs) activated the receptor for advanced glycation end products (RAGE) and the activation of RAGE is implicated to be the pathogenesis of type 2 diabetic mellitus (T2DM) patient vascular complications. Sitagliptin, a dipeptidyl peptidase-4 (DPP4) inhibitor, is a new oral hypoglycemic agent for the treatment of T2DM. However, the beneficial effects on vascular calcification remain unclear. In this study, we used a high-fat diet (HFD)-fed low-density lipoprotein receptor deficiency (LDLR−/−) mice model to investigate the potential effects of sitagliptin on HFD-induced arterial calcification. Mice were randomly divided into 3 groups: (1) normal diet group, (2) HFD group and (3) HFD + sitagliptin group. After 24 weeks treatment, we collected the blood for chemistry parameters and DPP4 activity measurement, and harvested the aorta to evaluate calcification using immunohistochemistry and calcium content. To determine the effects of sitagliptin, tumor necrosis factor (TNF)-α combined with S100A12 was used to induce oxidative stress, activation of nicotinamide adenine dinucleotide phosphate (NADPH), up-regulation of bone markers and RAGE expression, and cell calcium deposition on human aortic smooth muscle cells (HASMCs). We found that sitagliptin effectively blunted the HFD-induced artery calcification and significantly lowered the levels of fasting serum glucose, triglyceride (TG), nitrotyrosine and TNF-α, decreased the calcium deposits, and reduced arterial calcification. In an in-vitro study, both S100A12 and TNF-α stimulated RAGE expression and cellular calcium deposits in HASMCs. The potency of S100A12 on HASMCs was amplified by the presence of TNF-α. Sitagliptin and Apocynin (APO), an NADPH oxidase inhibitor, inhibited the TNF-α + S100A12-induced NADPH oxidase and nuclear factor (NF)-κB activation, cellular oxidative stress, RAGE expression, osteo transcription factors expression and calcium deposition. In addition, treatment with sitagliptin, knockdown of RAGE or TNF-α receptor blunted the TNF-α + S100A12-induced RAGE expression. Our findings suggest that sitagliptin may suppress the initiation and progression of arterial calcification by inhibiting the activation of NADPH oxidase and NF-κB, followed by decreasing the expression of RAGE.

Abstract 103: Smooth Muscle Cell Specific Overexpression Of Adamts7 Drives Atherosclerosis Development Through The Remodeling Of The Extracellular Matrix

Genome-wide association studies in humans link ADAMTS7 with coronary artery disease. Subsequent studies in mice showed ADAMTS7 to be proatherogenic, as whole-body knockout (KO) reduced atherosclerosis independent of lipid-lowering. Further studies show that Adamts7 expression is temporarily induced in response to vascular injury, and Adamts7 KO reduces primary smooth muscle cell (SMC) migration ex vivo. However, both the mechanism through which ADAMTS7 influences atherosclerosis progression and the responsible cell type remain unclear. As ADAMTS7 is secreted, we sought to determine its cleavage targets. We generated an immortalized human SMC line with doxycycline-inducible expression of GFP or ADAMTS7. We analyzed conditioned media from these cells via terminal amine isotopic labeling of substrates (TAILS) proteomics. This method labels new protein N termini, enabling the identification of cleavage products. Overexpression of Adamts7 enriched extracellular matrix (ECM) peptides such as Col1a1, Col1a2, Col4a2, and fibronectin. Furthermore, KEGG analysis identified ECM receptor interaction and focal adhesion formation as highly enriched pathways in the dataset. These results suggest ADAMTS7 alters SMCs by modulating signaling between cell and ECM. To examine the cell type that confers the proatherogenic effects of Adamts7, we generated a conditional transgenic ADAMTS7 mouse on the Ldlr knockout background. Given previously described roles for ADAMTS7 in SMC migration and vascular reendothelialization, we crossed these mice to either the Tie2-Cre or Myh11-CreERT2 to overexpress ADAMTS7 in endothelial and SMCs respectively. We found &gt;3-fold increase (p = 0.0002) in plaque burden by en face staining in overexpression of Adamts7 in SMCs compared to controls. In contrast, transgenic overexpression of Adamts7 in endothelial cells is embryonic or perinatally lethal (Chi-squared = 0.0018). In summary, our transgenic study affirms the proatherogenic effect of increased Adamts7 expression in SMCs in vivo. Furthermore, our TAILS data suggests a dynamic role of ADAMTS7 in cleaving ECM. These studies fill critical knowledge gaps in our understanding of ADAMTS7 biology and help inform potential therapeutic avenues to targeting this enzyme.

Abstract MP35: Single-cell Analysis Uncovers Multiple Adventitial Fibroblast Populations With Expression Of CAD GWAS Genes In Murine Atherosclerosis

The arterial adventitia is a layer of cells outside the external lamina of blood vessels that contribute to the progression of coronary artery disease (CAD) like atherosclerosis. Adventitial fibroblasts are known regulators of vascular remodeling through their deposition of collagen fibrils around vessels during atherosclerotic lesion development. However, the molecular identity and function of the participating fibroblasts have not been well studied. We used single cell RNA sequencing (scRNA-seq) to characterize the transcriptome of adventitial fibroblasts and other cell types at multiple timepoints during atherogenesis in hyperlipidemic Ldlr knockout mice. Specifically, scRNA-seq was applied to Ldlr KO aortic adventitia after 0, 9, and 16 weeks of western diet (WD) feeding. Unbiased clustering analysis uncovered 9 different cell clusters, including 5 different fibroblast populations (Fibro1-5), and a single cluster each of macrophages, T cells, SMCs, and ECs. We observed that, as atherosclerosis progressed from 9 to 16 weeks of feedings, the proportion of total cells that were Fibro1, 3, and 4 decreased (33, 40, and 13%), while populations of Fibro2 and 5 slightly increased (13 and 18%). All of non-fibroblast populations (Macrophage, T cells, SMCs and ECs) increased from 9-16wks of diet. Next, we asked whether genes associated with coronary artery disease by human genome-wide association studies (GWAS) are expressed in different adventitial fibroblast clusters. We determined the expression of 266 genes implicated in CAD by GWAS and found 201 genes (76%) were expressed in adventitial cells at either/both 9 or 16wks. 34 genes displayed large changes in expression from 9 to 16wks. We identified five genes that were highly expressed in the adventitial Fibro5 cluster specifically, and additional other CAD GWAS genes specifically expressed in adventitial macrophages, SMCs, and ECs. In summary, we present here a cell atlas defined by scRNA-seq that reveals the heterogeneity amongst the fibroblasts in adventitial cells during atherogenesis. Additionally, we find that many CAD GWAS genes are expressed in adventitial cell populations, raising the intriguing possibility that CAD GWAS are identifying adventitial mechanisms that contribute to CAD.

Apolipoprotein E, low-density lipoprotein receptor, and immune cells control blood-brain barrier penetration by AAV-PHP.eB in mice.

Rationale: The blood-brain barrier (BBB) prevents the effective delivery of therapeutic molecules to the central nervous system (CNS). A recently generated adeno-associated virus (AAV)-based vector, AAV-PHP.eB, has been found to penetrate the BBB more efficiently than other vectors including AAV-PHP.B. However, little is known about the mechanisms. In this study, we investigated how AAV-PHP.eB penetrates the BBB in mice.Methods: We injected AAV-PHP.eB into the bloodstream of wild-type C57BL/6 and BALB/c mice as well as mouse strains carrying genetic mutation in apolipoprotein E gene (Apoe) or low-density lipoprotein receptor gene (Ldlr), or lacking various components of the immune system. Then, we evaluated AAV-PHP.eB transduction to the brain and spinal cord in these mice.Results: We found that the transduction to the CNS of intravenous AAV-PHP.eB was more efficient in C57BL/6 than BALB/c mice, and significantly reduced in Apoe or Ldlr knockout C57BL/6 mice compared to wild-type C57BL/6 mice. Moreover, poor CNS transduction in BALB/c mice was dramatically increased by B-cell or natural killer-cell depletion.Conclusions: Our findings demonstrate that the ApoE-LDLR pathway underlies the CNS tropism of AAV-PHP.eB and that the immune system contributes to the strain specificity of AAV-PHP.eB.

Investigating the Complex Interplay Between Genotype and High Fat Diet Feeding in the Lactating Mammary Gland using the Tph1and Ldlr knockout models

Investigating the Complex Interplay Between Genotype and High Fat Diet Feeding in the Lactating Mammary Gland using the Tph1and Ldlr knockout models

Reversing Clonal Hematopoiesis and Associated Atherosclerotic Disease By Targeted Antibody-Drug-Conjugate (ADC) Conditioning and Transplant

Cardiovascular disease (CVD) is the leading cause of death worldwide. Recently, age-related clonal hematopoiesis (CH) has been recognized as a risk factor for CVD of comparable magnitude to smoking, hypertension and hypercholesteremia. While these other risk factors can be mitigated by pharmacological intervention or lifestyle changes, there are no such strategies in place for CH. As CH is initiated by mutations in hematopoietic stem cells (HSCs), a hematopoietic stem cell transplantat (HSCT) could serve as a curative therapy. However, stem cell transplantation is associated with significant toxicity due in part from current conditioning regimens. There is also no evidence that depletion of the disease-driving clones impacts established atherosclerosis. We developed an antibody drug conjugate (ADC) targeting murine CD45. In the context of stem cell transplantation, the CD45-ADC efficiently depletes endogenous HSCs as well as mature leukocytes while enabling rapid engraftment of an infused stem cell graft. In addition, the CD45-ADCs are not based on broad-acting genotoxic agents that lead to long-lasting health risks. We decided to test if CD45-ADC and HSCT could halt atherosclerosis progression through elimination Tet2 knockout HSCs and their disease propagating myeloid progeny. To model CH associated atherosclerosis, LDLR knockout mice were transplanted with 20% CFP labeled wild-type (WT) or Tet2 knockout bone marrow. A single dose of isotype- or CD45-ADC was delivered after 6 weeks of atherosclerosis development and was followed by an infusion of WT CD45.1 bone marrow. As has been reported before, we observed in the isotype-ADC treated animals that Tet2 deficiency leads to a competitive advantage over WT cells. Tet2 knockout cells contributed to peripheral blood chimerism at successively increasing levels and mice harboring the knockout graft showed a significant expansion of their HSC population. Despite their obvious advantage, Tet2 deficient HSC were as efficiently depleted as their WT counterparts upon CD45-ADC and HSCT. Peripheral blood and bone marrow chimerism were similar in WT and Tet2 knockout hosts and the expanded HSC pool was successfully curbed 6 weeks following the intervention. More importantly, CD45-ADC also depleted cells in the atherosclerotic plaques as efficiently as in blood in both WT and Tet2 mutant recipients. This resulted in a significant reduction of myeloid cell infiltration in CD45-ADC conditioned and transplanted knockout hosts and ultimately lead to drastically reduced plaque size in these animals. In conclusion, these data demonstrate that CD45-ADC and HSCT efficiently replaces the disease driving myeloid cells in the atherosclerosis plaques leading to an overall reduction in disease burden. CD45-ADC and transplantation may thus offer a novel therapy for CH and its associated morbidities. Disclosures Palchaudhuri: Magenta Therapeutics: Current Employment. Hyzy:Magenta Therapeutics: Current Employment, Current equity holder in publicly-traded company. Proctor:Magenta Therapeutics: Current Employment. Gillard:Magenta Therapeutics: Current Employment. Boitano:Magenta Therapeutics: Ended employment in the past 24 months, Patents &amp; Royalties. Cooke:Magenta Therapeutics: Ended employment in the past 24 months. Scadden:Magenta Therapeutics: Consultancy, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees.