Prolonged Hyperoxygenation Treatment Improves Vein Graft Patency and Decreases Macrophage Content in Atherosclerotic Lesions in ApoE3*Leiden Mice

Myeloid PHD2 Conditional Knockout Improves Intraplaque Angiogenesis and Vascular Remodeling in a Murine Model of Venous Bypass Grafting

BACKGROUND

Intraplaque angiogenesis occurs in response to atherosclerotic plaque hypoxia, which is driven mainly by highly metabolically active macrophages. Improving plaque oxygenation by increasing macrophage hypoxic signaling, thus stimulating intraplaque angiogenesis, could restore cellular function and neovessel maturation, and decrease plaque formation. Prolyl hydroxylases (PHDs) regulate cellular responses to hypoxia. We therefore aimed to elucidate the role of myeloid PHD2, the dominant PHD isoform, on intraplaque angiogenesis in a murine model for venous bypass grafting.

METHODS AND RESULTS

Myeloid PHD2 conditional knockout (PHD2cko) and PHD2 wild type mice on an Ldlr-/- background underwent vein graft surgery (n=11-15/group) by interpositioning donor caval veins into the carotid artery of genotype-matched mice. At postoperative day 28, vein grafts were harvested for morphometric and compositional analysis, and blood was collected for flow cytometry. Myeloid PHD2cko induced and improved intraplaque angiogenesis by improving neovessel maturation, which reduced intraplaque hemorrhage. Intima/media ratio was decreased in myeloid PHD2cko vein grafts. In addition, PHD2 deficiency prevented dissection of vein grafts and resulted in an increase in vessel wall collagen content. Moreover, the macrophage proinflammatory phenotype in the vein graft wall was attenuated in myeloid PHD2cko mice. In vitro cultured PHD2cko bone marrow-derived macrophages exhibited an increased proangiogenic phenotype compared with control.

CONCLUSIONS

Myeloid PHD2cko reduces vein graft disease and ameliorates vein graft lesion stability by improving intraplaque angiogenesis.

Effect of thermophilic bacterium HB27 manganese superoxide dismutase in a rat model of chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS)

We investigated the therapeutic effects of superoxide dismutase (SOD) from thermophilic bacterium HB27 on chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) and its underlying mechanisms. A Sprague–Dawley rat model of CP/CPPS was prepared and then administered saline or Thermus thermophilic (Tt)-SOD intragastrically for 4 weeks. Prostate inflammation and fibrosis were analyzed by hematoxylin and eosin staining, and Masson staining. Alanine transaminase (ALT), aspartate transaminase (AST), serum creatinine (CR), and blood urea nitrogen (BUN) levels were assayed for all animals. Enzyme-linked immunosorbent assays (ELISA) were performed to analyze serum cytokine concentrations and tissue levels of malondialdehyde, nitric oxide, SOD, catalase, and glutathione peroxidase. Reactive oxygen species levels were detected using dichlorofluorescein diacetate. The messenger ribonucleic acid (mRNA) expression of tissue cytokines was analyzed by reverse transcription polymerase chain reaction (RT-PCR), and infiltrating inflammatory cells were examined using immunohistochemistry. Nuclear factor-κB (NF-κB) P65, P38, and inhibitor of nuclear factor-κBα (I-κBα) protein levels were determined using western blot. Tt-SOD significantly improved histopathological changes in CP/CPPS, reduced inflammatory cell infiltration and fibrosis, increased pain threshold, and reduced the prostate index. Tt-SOD treatment showed no significant effect on ALT, AST, CR, or BUN levels. Furthermore, Tt-SOD reduced inflammatory cytokine expression in prostate tissue and increased antioxidant capacity. This anti-inflammatory activity correlated with decreases in the abundance of cluster of differentiation 3 (CD3), cluster of differentiation 45 (CD45), and macrophage inflammatory protein 1α (MIP1α) cells. Tt-SOD alleviated inflammation and oxidative stress by reducing NF-κB P65 and P38 protein levels and increasing I-κBα protein levels. These findings support Tt-SOD as a potential drug for CP/CPPS.

PFKFB3 gene deletion in endothelial cells inhibits intraplaque angiogenesis and lesion formation in a murine model of venous bypass grafting

Vein grafting is a frequently used surgical intervention for cardiac revascularization. However, vein grafts display regions with intraplaque (IP) angiogenesis, which promotes atherogenesis and formation of unstable plaques. Graft neovessels are mainly composed of endothelial cells (ECs) that largely depend on glycolysis for migration and proliferation. In the present study, we aimed to investigate whether loss of the glycolytic flux enzyme phosphofructokinase-2/fructose-2,6-bisphosphatase 3 (PFKFB3) in ECs inhibits IP angiogenesis and as such prevents unstable plaque formation. To this end, apolipoprotein E deficient (ApoE^−/−) mice were backcrossed to a previously generated PFKFB3^fl/fl Cdh5^iCre mouse strain. Animals were injected with either corn oil (ApoE^−/−PFKFB3^fl/fl) or tamoxifen (ApoE^−/−PFKFB3^ECKO), and were fed a western-type diet for 4 weeks prior to vein grafting. Hereafter, mice received a western diet for an additional 28 days and were then sacrificed for graft assessment. Size and thickness of vein graft lesions decreased by 35 and 32%, respectively, in ApoE^−/−PFKFB3^ECKO mice compared to controls, while stenosis diminished by 23%. Moreover, vein graft lesions in ApoE^−/−PFKFB3^ECKO mice showed a significant reduction in macrophage infiltration (29%), number of neovessels (62%), and hemorrhages (86%). EC-specific PFKFB3 deletion did not show obvious adverse effects or changes in general metabolism. Interestingly, RT-PCR showed an increased M2 macrophage signature in vein grafts from ApoE^−/−PFKFB3^ECKO mice. Altogether, EC-specific PFKFB3 gene deletion leads to a significant reduction in lesion size, IP angiogenesis, and hemorrhagic complications in vein grafts. This study demonstrates that inhibition of endothelial glycolysis is a promising therapeutic strategy to slow down plaque progression.

Endothelial Barrier Function and Leukocyte Transmigration in Atherosclerosis

The vascular endothelium is a highly specialized barrier that controls passage of fluids and migration of cells from the lumen into the vessel wall. Endothelial cells assist leukocytes to extravasate and despite the variety in the specific mechanisms utilized by different leukocytes to cross different vascular beds, there is a general principle of capture, rolling, slow rolling, arrest, crawling, and ultimately diapedesis via a paracellular or transcellular route. In atherosclerosis, the barrier function of the endothelium is impaired leading to uncontrolled leukocyte extravasation and vascular leakage. This is also observed in the neovessels that grow into the atherosclerotic plaque leading to intraplaque hemorrhage and plaque destabilization. This review focuses on the vascular endothelial barrier function and the interaction between endothelial cells and leukocytes during transmigration. We will discuss the role of endothelial dysfunction, transendothelial migration of leukocytes and plaque angiogenesis in atherosclerosis.

Establishment of a Novel Mouse Model for Atherosclerotic Vulnerable Plaque

Background and Aims: Acute coronary syndrome (ACS) is a group of clinical syndromes characterized by rupture or erosion of atherosclerotic unstable plaques. Effective intervention for vulnerable plaques (VP) is of great significance to reduce adverse cardiovascular events.

Methods: Fbn1^C1039G+/− mice were crossbred with LDLR^−/− mice to obtain a novel model for atherosclerotic VP. After the mice were fed with a high-fat diet (HFD) for 12 or 24 weeks, pathological staining and immunohistochemistry analyses were employed to evaluate atherosclerotic lesions.

Results: Compared to control mice, Fbn1^C1039G+/−LDLR^−/− mice developed more severe atherosclerotic lesions, and the positive area of oil red O staining in the aortic sinus was significantly increased after 12 weeks (21.7 ± 2.0 vs. 6.3 ± 2.1) and 24 weeks (32.6 ± 2.5 vs. 18.7 ± 2.6) on a HFD. Additional vulnerable plaque characteristics, including significantly larger necrotic cores (280 ± 19 vs. 105 ± 7), thinner fiber caps (14.0 ± 2.8 vs. 32.6 ± 2.7), apparent elastin fiber fragmentation and vessel dilation (3,010 ± 67 vs. 1,465 ± 49), a 2-fold increase in macrophage number (8.5 ± 1.0 vs. 5.0 ± 0.6), obviously decreased smooth muscle cell number (0.6 ± 0.1 vs. 2.1 ± 0.2) and an ~25% decrease in total collagen content (33.6 ± 0.3 vs. 44.9 ± 9.1) were observed in Fbn1^C1039G+/−LDLR^−/− mice compared with control mice after 24 weeks. Furthermore, spontaneous plaque rupture, neovascularization, and intraplaque hemorrhage were detected in the model mouse plaque regions but not in those of the control mice.

Conclusions: Plaques in Fbn1^C1039G+/−LDLR^−/− mice fed a HFD show many features of human advanced atherosclerotic unstable plaques. These results suggest that the Fbn1^C1039G+/−LDLR^−/− mouse is a novel model for investigating the pathological and physiological mechanisms of advanced atherosclerotic unstable plaques.

A Multichamber Gas System to Examine the Effect of Multiple Oxygen Conditions on Cell Culture

The classic bone tissue engineering model for bone regeneration combines three elements: scaffolds, biomaterials, and mesenchymal stem cells (MSCs). Incorporation of MSCs and growth factors into a scaffold implanted into the area of bone injury is a proven strategy to achieve successful bone regeneration as demonstrated in the literature. However, a major limitation of using bone grafts or scaffolds is oxygen (O₂) deprivation in the inner sections of the construct, due to lack of adequate vascularization. To address this limitation, we proposed two treatment strategies for MSC-seeded constructs or adipose tissue scaffolds before implantation: (1) O₂ enrichment and (2) acclimation to hypoxia. Based on previous studies, the significance of the different O₂ concentrations on MSC biological characteristics remains controversial. Therefore, the optimal O₂ condition for engineered bone tissues should be determined. Thus, we designed an innovative multichamber gas system aimed to simultaneously assess the effects of different O₂ levels on cell culture. This system was assembled using three isolated chambers integrated into a single incubator. To explore the efficacy of our method, we investigated the effect of hyperoxia, normoxia, and hypoxia, (50-60%, 21%, and 5-7.5% O₂, respectively) on the biological characteristics of human adipose-derived MSCs: immunophenotyping, adhesion, proliferation, and osteogenic, and angiogenic differentiation. Our findings demonstrated that hypoxic adipose-derived mesenchymal stem cells (ASCs) conditions exhibited significantly lower levels of CD34 (p = 0.014), with significantly higher osteogenic and angiogenic differentiation capacities (p = 0.023 and p = 0.0042, respectively) than normoxia. Conversely, hyperoxia-cultured ASCs demonstrated significantly higher levels of CD73 and CD90 expression than both normoxic ASCs (p = 0.006 and p = 0.025, respectively) and hypoxic ASCs (p = 0.003 and p = 0.003, respectively). In addition, hyperoxic ASCs showed significantly reduced proliferation capacity by day 11 (p = 0.032) and significantly enhanced migration rates after 48 h (p = 0.044). The newly developed controllable multichamber gas system was cost-effective and easy to use. Different assays can be performed concurrently while preserving all other conditions identical, and the use of other ranges of O₂ concentrations is feasible and also necessary to determine the ideal O₂ concentration. Furthermore, the multichamber gas system has the potential for wide application, including other cell cultures, grafts, or scaffolds for in vitro and in vivo experimentation. This study was approved by the Galilee Medical Center Helsinki Committee (No. 0009-19-NHR). Impact statement The introduced multichamber gas system provides a custom-made setup for simultaneous control of three oxygen (O₂) levels in a single incubator. The use of our innovative multichamber gas system is essential to determine the ideal O₂ levels for engineered tissues by examining multiple O₂ concentrations on cells in vitro. The determined ideal O₂ concentration will then be used through this system to investigate the engrafted cell survival ex vivo, to ensure successful integration of the engineered tissues and tissue regeneration in vivo. Use of this method may promote a therapeutic tool for a major limitation in tissue engineering due to the problematic O₂ insufficiency in tissue scaffolds.

bFGF blockade reduces intraplaque angiogenesis and macrophage infiltration in atherosclerotic vein graft lesions in ApoE3*Leiden mice

Intraplaque angiogenesis increases the chance of unstable atherosclerotic plaque rupture and thrombus formation leading to myocardial infarction. Basic Fibroblast Growth Factor (bFGF) plays a key role in angiogenesis and inflammation and is involved in the pathogenesis of atherosclerosis. Therefore, we aim to test K5, a small molecule bFGF-inhibitor, on remodelling of accelerated atherosclerotic vein grafts lesions in ApoE3*Leiden mice. K5-mediated bFGF-signalling blockade strongly decreased intraplaque angiogenesis and intraplaque hemorrhage. Moreover, it reduced macrophage infiltration in the lesions by modulating CCL2 and VCAM1 expression. Therefore, K5 increases plaque stability. To study the isolated effect of K5 on angiogenesis and SMCs-mediated intimal hyperplasia formation, we used an in vivo Matrigel-plug mouse model that reveals the effects on in vivo angiogenesis and femoral artery cuff model to exclusively looks at SMCs. K5 drastically reduced in vivo angiogenesis in the matrigel plug model while no effect on SMCs migration nor proliferation could be seen in the femoral artery cuff model. Moreover, in vitro K5 impaired endothelial cells functions, decreasing migration, proliferation and tube formation. Our data show that K5-mediated bFGF signalling blockade in hypercholesterolemic ApoE3*Leiden mice reduces intraplaque angiogenesis, haemorrhage and inflammation. Therefore, K5 is a promising candidate to stabilize advanced atherosclerotic plaques.