Ischemic Muscle Tissue Research Articles

Abstract Tu023: The VEGF-A splice variants as a mechanism of impaired Inflammatory Angiogenesis in the context of advanced aging.

Background and Objectives: Aging and age-related diseases like peripheral artery disease (PAD) is associated with impairment of angiogenesis responses to injury. Critical ischemic limb and wound injury animal models have shown impact of monocytes/macrophages as a major source of angiogenic mediators leading to new arterial growth. Aging has also been associated with impairment of blood flow recovery and reduced VEGF-A expression in animals. However, recombinant VEGF-A administration or clinical trials involving VEGF-A have not fully overcome the foot perfusion and prevent limb/leg amputation. We sought to understand molecular mechanisms of reduced VEGF-A expression which remain incomplete in the context of advanced aging. Results: Firstly, in hindlimb ischemia mouse model, our data from liposomes containing-clodronate treated mice (12-weeks C57Bl6 with macrophage depletion model ) ( Fig. 1a ) demonstrate impairment of blood flow recovery compared to Control group. On day 3 post-surgery, VEGF-A and VEGF-A isoforms expression (VEGF-A 165 a and VEGF-A 165 b, respectively) were reduced in ischemic muscle. Fluorescence staining showed a reduction of macrophages (CD68 + ) was also associated with reduced endothelial cells (CD31 + ). Using a myeloid-specific and inducible deleted VEGF fl/fl mice, we then have shown a key role of early inflammatory macrophages stage as a major source of VEGF-A required for angiogenesis in young mice (Fig. 1b). Secondly, bone marrow-derived-macrophages (BMDMs) from C57Bl6 104-weeks mice also demonstrate reduced VEGF-A expression. Aged BMDMs demonstrate reduced VEGF-A 165 a while VEGF-A 165 b was highly increased. Polarized BMDMs from 12-weeks demonstrate increased VEGFR1 in “M2" macrophages while VEGFR2 was increased in “M1” macrophages. On the other hand, BMDMs from 104-weeks demonstrate reduced VEGFR2 expression while VEGFR1 was unaffected compared to young. Lastly, 104-weeks mice also demonstrate severe impairment of blood flow recovery ( Fig. 2 ) after surgery and reduced VEGF-A and VEGF-A 165 a in ischemic muscle tissue. VEGF-A 165 b was increased and both receptors, VEGF-R1/R2 levels ( Fig. 3 ) were also reduced. Fluorescence staining on day 3 post ligation demonstrates reduced endothelial cells recruitment in muscle tissue while macrophage (CD68+) number was similar. Conclusion: Our investigations will contribute to define mechanisms whereby vascular injury is associated with VEGF-A isoforms specific switch in the context of advanced aging.

Reduction of oxidative stress response and protection of liver and renal cell functions by reduced glutathione in lower limb arterial ischemia–reperfusion in New Zealand white rabbits with high triglyceride levels

ObjectiveAcute liver and kidney injury is the most common complication after aortic surgery, which seriously affects the survival and safety of perioperative patients. The presence of chronic preoperative liver and renal insufficiency, presence of preoperative blood inflammation indicators, duration of intraoperative extracorporeal circulation, and volume of red blood cell transfusion are the main influencing factors for acute postoperative liver and kidney injuries. In recent years, with the research progress on oxidative stress, a growing body of evidence has demonstrated that oxidative stress may cause tissue damage after ischemia–reperfusion (IR). However, the impact of the oxidative stress of distal tissues caused by IR on liver and renal cells after arterial surgeries has not yet been elucidated. MethodsNew Zealand white rabbits were used for the experiments and were divided into three groups. Among them, two groups were fed high-fat feed to establish a white rabbit model of hypertriglyceridemia, whereas the control group was provided with ordinary feed. In the experiment, white rabbits were subjected to occlusion of the infrarenal aorta abdominalis to simulate IR of the lower limbs. The effects of high triglyceride levels after the arterial IR of the lower limbs were investigated using the contents of reactive oxygen species (ROS) and malondialdehyde (MDA), a fat metabolite, in ischemic muscle tissues and blood tissues. One of the groups receiving high-fat feed received intervention with reduced glutathione (GSH) before IR of the lower limbs. Pathological studies were performed to identify the expression levels of inflammatory factors and inflammatory cells in liver and renal cells as well as cell apoptosis. The effects of GSH administration before IR on reducing the oxidative stress in adipose tissues and alleviating liver and kidney damage after stress response were investigated. ResultsAfter IR, the increases in ROS and MDA in ischemic muscle tissues and blood tissues were higher in white rabbits with high triglyceride levels than in those that only received ordinary feed or received intervention with GSH. In addition, for white rabbits with high triglyceride levels, the TNF-α expression levels in the liver increased after IR. Moreover, a considerable increase in the expression of TNF-α, IL-6, macrophages, and T lymphocytes were observed in renal cells. A large number of inflammatory cells and the formation of immune complexes were also noted in the glomeruli; in addition, cell apoptosis was promoted. ConclusionThis study showed that high triglyceride levels enhanced the oxidative stress response and increased ROS production in New Zealand white rabbits after arterial IR of the lower limbs. High ROS levels activated the expression of inflammatory factors and inflammatory cells in the liver and kidney, which affected cell functions and promoted apoptosis. At high triglyceride levels, GSH downregulated ROS production in oxidative stress after IR, thereby protecting liver and kidney functions.

UFM1 inhibits hypoxia-induced angiogenesis via promoting proteasome degradation of HIF-1α.

Angiogenesis is crucial for blood flow recovery and ischemic tissue repair of peripheral artery disease (PAD). Exploration of new mechanisms underlying angiogenesis will shed light on the treatment of PAD. Ubiquitin-fold modifier 1 (UFM1), a newly identified ubiquitin-like molecule, has been discovered to be involved in various pathophysiological processes. However, the role of UFM1 in the pathogenesis of PAD, especially in endothelial angiogenesis remains obscure, and we aimed to clarify this issue in this study. We initially found UFM1 was significantly upregulated in gastrocnemius muscles of PAD patients and hind limb ischemia mice. And UFM1 was mainly colocalized with endothelial cells in ischemic muscle tissues. Further, elevated expression of UFM1 was observed in hypoxic endothelial cells. Subsequent genetic inhibition of UFM1 dramatically enhanced migration, invasion, adhesion, and tube formation of endothelial cells under hypoxia. Mechanistically, UFM1 reduced the stability of hypoxia-inducible factor-1α (HIF-1α) and promoted the von Hippel-Lindau-mediated K48-linked ubiquitin-proteasome degradation of HIF-1α, which in turn decreased angiogenic factor VEGFA expression and suppressed VEGFA related signaling pathway. Consistently, overexpression of UFM1 inhibited the angiogenesis of endothelial cells under hypoxic conditions, whereas overexpression of HIF-1α reversed this effect. Collectively, our data reveal that UFM1 inhibits the angiogenesis of endothelial cells under hypoxia through promoting ubiquitin-proteasome degradation of HIF-1α, suggesting UFM1 might serve as a potential therapeutic target for PAD.

Mesenchymal stem cell-derived extracellular vesicles exert pro-angiogenic and pro-lymphangiogenic effects in ischemic tissues by transferring various microRNAs and proteins including ITGa5 and NRP1

Mesenchymal stem cells/stromal cells (MSCs)-derived extracellular vesicles (EVs) mediate pro-regenerative effects in damaged ischemic tissues by regulating angiogenesis. MSCs-EVs modulate functions of cells including endogenous mature cells, progenitors and stem cells, resulting in restoration of blood flow. However, the mechanisms underlying such MSC-EV activity still remain poorly understood. The present study analyzes biological effects of bone marrow (BM) MSC-EVs on endothelial cells (ECs) in ischemic tissues both in in vitro and in vivo conditions and elucidates the molecular mechanisms underlying the tissue repair. MSC-EVs were isolated from murine BM-derived MSCs and their morphological, antigenic and molecular composition regarding protein and microRNA levels were evaluated to examine their properties. Global proteomic analysis demonstrated the presence in MSC-EVs of proteins regulating pro-regenerative pathways, including integrin α5 (Itgα5) and neuropilin-1 (NRP1) involved in lymphangiogenesis. MSC-EVs were also enriched in microRNAs regulating angiogenesis, TGF-β signaling and processes guiding cellular adhesion and interactions with extracellular matrix. The functional effects of MSC-EVs on capillary ECs in vitro included the increase of capillary-like tube formation and cytoprotection under normal and inflammatory conditions by inhibiting apoptosis. Notably, MSC-EVs enhanced also capillary-like tube formation of lymphatic ECs, which may be regulated by Itgα5 and NRP1. Moreover, in a mouse model of critical hind limb ischemia, MSC-EVs increased the recovery of blood flow in ischemic muscle tissue, which was accompanied with increased vascular density in vivo. This pro-angiogenic effect was associated with an increase in nitric oxide (NO) production via endothelial NO-synthase activation in ischemic muscles. Interestingly, MSC-EVs enhanced lymphangiogenesis, which has never been reported before. The study provides evidence on pro-angiogenic and novel pro-lymphangiogenic role of MSC-EVs on ECs in ischemic tissue mediated by their protein and miRNA molecular cargos. The results highlight Itgα5 and NRP1 carried by MSC-EVs as potential therapeutic targets to boost lymphangiogenesis.Graphical

A Circular Network of Coregulated L-Threonine and L-Tryptophan Metabolism Dictates Acute Lower Limb Ischemic Injury.

Lower limb ischemia is characterized by reduced arterial perfusion in the lower limbs, leading to tissue ischemia and cell death. It is primarily caused by thrombosis and the rupture of arterial plaques, resulting in damage to ischemic muscle tissues. Metabolic processes are crucial in its development. Herein we combined single-cell data with metabolomics data to explore the pathways and mechanisms influencing lower limb ischemia. We analyzed single-cell and metabolomics data. In single-cell analysis, we identified different cell subpopulations and key regulatory genes, and biological enrichment analysis was performed to understand their functions and relationships. For metabolomics, mass spectrometry and chromatography techniques were employed to analyze metabolites in clinical samples. We performed differential analysis, correlation analysis, and Mendelian randomization to determine the relationships between key metabolites and genes. Nebl, Dapl1, Igfbp4, Lef1, Klrd1, Ciita, Il17f, Cd8b1, Il17a, Cd180, Il17re, Trim7, and Slc6a19 were identified to play a crucial role in lower limb ischemia. Important metabolites included L-threonine and L-tryptophan. The metabolism of L-threonine and L-tryptophan is linked to lower limb ischemia and thrombosis. B0AT1, encoded by SLC6A19, is closely related to these metabolites and appears to play a key role in lower limb ischemia development. Our analysis revealed the roles of key genes and metabolites in lower limb ischemia. These findings enhance our understanding of the pathogenesis of lower limb ischemia and provide new insights into its prevention and treatment.

Abstract 18998: Deletion of the Duffy Antigen Receptor for Chemokines Impairs Blood Flow Recovery in the Mouse Hindlimb Ischemia Model: Role of CCL11

Introduction: Peripheral Artery Disease (PAD) is characterized by obstruction of the arteries in the lower extremities. Impaired angiogenesis plays a major role in the progression of PAD. Pro-angiogenic and anti-angiogenic chemokines are modulated by binding to the Duffy antigen receptor for chemokines (DARC), a non-signaling receptor expressed primarily on erythrocytes. Incidence and severity of PAD is greater in Blacks, ~70% of whom do not express DARC on their erythrocytes due to a common gene variant. Here, we tested the hypothesis that hematopoietic-specific deletion of DARC impairs blood flow recovery in mouse hindlimb ischemia model. Methods: Twelve week old female DARC Flox/Vav1-Cre+ (DARC HKO ) and littermate Vav1-Cre- (wild type, WT) mice underwent unilateral femoral artery ligation and excision. Ischemic muscle tissue and plasma were analyzed at early ischemic phase (day three post ligation) and late ischemic phase (day fourteen post ligation). Blood flow recovery was measured weekly via laser Doppler imaging. Results: DARC HKO mice had poor blood flow recovery compared to WT mice (p<0.05), along with reduced capillary formation and increased inflammation, necrosis and fibrosis in the ischemic gastrocnemius muscles. Amongst the various DARC-bound chemokines assayed, levels of CCL11 (a pro-angiogenic strong DARC-bound chemokine) were significantly reduced in the plasma of DARC HKO mice, both at early and late ischemic phases (p<0.01). CCL11 levels strongly correlated with capillary formation in ischemic hindlimb. CCL11 levels in ischemic muscle tissue were significantly reduced in the DARC HKO mice in the early, but not late, ischemic phase. Conclusions: Loss of DARC on hematopoietic cells has a negative impact on the recovery of perfusion and angiogenesis in the murine hindlimb ischemia model, possibly due to reduced levels of CCL11 consequent to DARC deletion. These findings may be relevant to ethnic differences in susceptibility to PAD and suggest that therapies directed towards increasing CCL11 may be beneficial in Blacks with PAD.

Neutrophils for Revascularization Require Activation of CCR6 and CCL20 by TNFα.

Activation of immune-inflammatory pathways involving TNFα (tumor necrosis factor alpha) signaling is critical for revascularization and peripheral muscle tissue repair after ischemic injury. However, mechanisms of TNFα-driven inflammatory cascades directing recruitment of proangiogenic immune cells to sites of ischemia are unknown. Muscle tissue revascularization after permanent femoral artery ligation was monitored in mutant mice by laser Doppler imaging and light sheet fluorescence microscopy. TNFα-mediated signaling and the role of the CCL20 (C-C motif chemokine ligand 20)-CCR6 (C-C chemokine receptor 6) axis for formation of new vessels was studied in vitro and in vivo using bone marrow transplantation, flow cytometry, as well as biochemical and molecular biological techniques. TNFα-mediated activation of TNFR (tumor necrosis factor receptor) 1 but not TNFR2 was found to be required for postischemic muscle tissue revascularization. Bone marrow-derived CCR6+ neutrophil granulocytes were identified as a previously undescribed TNFα-induced population of proangiogenic neutrophils, characterized by increased expression of VEGFA (vascular endothelial growth factor A). Mechanistically, postischemic activation of TNFR1 induced expression of the CCL20 in vascular cells and promoted translocation of the CCL20 receptor CCR6 to the cell surface of neutrophils, essentially conditioning VEGFA-expressing proangiogenic neutrophils for CCL20-dependent recruitment to sites of ischemia. Moreover, impaired revascularization of ischemic peripheral muscle tissue in diabetic mice was associated with reduced numbers of proangiogenic neutrophils and diminished CCL20 expression. Administration of recombinant CCL20 enhanced recruitment of proangiogenic neutrophils and improved revascularization of diabetic ischemic skeletal muscles, which was sustained by sequential treatment with fluvastatin. We demonstrate that site-specific activation of the CCL20-CCR6 axis via TNFα recruits proangiogenic VEGFA-expressing neutrophils to sites of ischemic injury for initiation of muscle tissue revascularization. The findings provide an attractive option for tissue revascularization, particularly under diabetic conditions.

SUV39H1 Inhibits Angiogenesis in Limb Ischemia of Mice

Peripheral arterial disease (PAD), characterized by atherosclerosis of the peripheral arteries or even amputation, has threatened public life and health. However, the underlying mechanism remains largely obscure. SUV39H1, a histone methyltransferase, could specifically methylate lysine 9 of histone H3 and act as a repressor in transcriptional activity. The study aimed to investigate the role of SUV39H1 in limb ischemia. C57BL/6 male mice were randomly divided into Sham or Model groups to investigate the expression of SUV39H1 in the ischemic limbs. Then, pharmaceutical inhibition or genetic deletion of SUV39H1 in the limb ischemia mice model was performed to confirm its effect on limb ischemia. The blood perfusion was quantified by laser speckle contrast imaging (LSCI). Capillary density and muscle edema were measured by CD31 immunohistochemical staining and HE staining. The expressions of SUV39H1 and Catalase were confirmed by western blot. Transcriptome sequencing of siSUV39H1 in human umbilical vein endothelial cells (HUVECs) was used to explore the regulation mechanism of SUV39H1 on angiogenesis. The results showed that SUV39H1 was highly expressed in the ischemic muscle tissue of the mice. Pharmaceutical inhibition or genetic deletion of SUV39H1 significantly improved blood perfusion, capillary density, and angiogenesis in ischemic muscle tissue. Cell experiments showed that SUV39H1 knockdown promoted cell migration, tube formation, and mitochondrial membrane potential in endothelial cells under oxidative stress. The transcriptome sequencing results unmasked mechanisms of the regulation of angiogenesis induced by SUV39H1. Finally, Salvianolic acid B and Astragaloside IV were identified as potential drug candidates for the improvement of endothelial function by repressing SUV39H1. Our study reveals a new mechanism in limb ischemia. Targeting SUV39H1 could improve endothelial dysfunction and thus prevent limb ischemia.

Intravenous infusion of bone marrow-derived mesenchymal stem cells improves tissue perfusion in a rat hindlimb ischemia model

Intravenous infusion of stem cells is a minimally invasive cellular delivery method, though a few have been reported in a critical limb-threatening ischemia (CLTI) animal model or patients. In the present study, we hypothesized that intravenous infusion of bone-marrow derived mesenchymal stem cells (MSCs) improves tissue perfusion in a rat hindlimb ischemia model. Hindlimb ischemia was generated in Sprague–Dawley rats by femoral artery removal, then seven days after ischemic induction intravenous infusion of 1 × 106 MSCs (cell group) or vehicle (control group) was performed. As compared with the control, tissue perfusion was significantly increased in the cell group. Histological findings showed that capillary density was significantly increased in the cell group, with infused green fluorescent protein (GFP)-MSCs distributed in the ischemic limb. Furthermore, gene expression of vascular endothelial growth factor (VEGF) was significantly increased in ischemic hindlimb muscle tissues of rats treated with MSC infusion. In conclusion, intravenous infusion of bone-marrow derived MSCs improved tissue perfusion in ischemic hindlimbs through angiogenesis, suggesting that intravenous infusion of MSCs was a promising cell delivery method for treatment of CLTI.

Recovery of Ischemic Limb and Femoral Artery Endothelial Function Are Preserved in Mice with Dextran Sodium Sulfate-Induced Chronic Colitis

Simple SummaryThe present study examines the effect of experimental inflammatory bowel disease on femoral artery endothelial function and limb ischemia recovery in female mice using a chronic colitis model induced by dextran sodium sulfate exposure. As expected, plasma levels of proinflammatory cytokines, including interleukin-6, interleukin-17, tumor necrosis factor alpha, and chemokine ligand 1, were significantly increased in the chronic colitis model. However, ROS levels in the ischemic muscle tissues were not significantly increased in mice with colitis as compared to controls. There were no significant changes in endothelium-dependent or -independent vasodilation of femoral artery between the colitis model and the control. Recovery of function and blood flow of the ischemic limb and capillary density in the ischemic muscle were preserved in the colitis model as compared with the control.Inflammatory bowel disease (IBD) produces significant systemic inflammation and increases the risk of endothelial dysfunction and peripheral artery disease. Our recent study demonstrated that abdominal aortic endothelial cell function was impaired selectively in female mice with chronic colitis. This study aimed to test the hypothesis that experimental colitis leads to femoral artery endothelial cell dysfunction and impairs limb ischemia recovery in female mice. An experimental chronic colitis model was created in female C57BL/6 mice with dextran sodium sulfate (DSS) treatment. Unilateral hind limb ischemia was produced by femoral artery ligation. Limb blood perfusion, vascular density, tissue ROS levels, and plasma levels of proinflammatory cytokines were assessed. Femoral artery endothelium-dependent and -independent vasodilation of the contralateral limb were evaluated ex vivo using acetylcholine and nitroglycerin, respectively. As expected, the plasma levels of proinflammatory cytokines, including tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, and IL-17, were significantly increased in the DSS-induced colitis model. However, ROS levels in the ischemic muscle tissues were not significantly increased in colitis model as compared to the controls. There were no significant changes in endothelium-dependent or -independent vasodilation of the femoral artery between colitis model and the control. Recovery of function and blood flow in the ischemic limb and capillary density in the ischemic gastrocnemius muscle were preserved in the colitis model as compared with the control. The data demonstrated that DSS-induced chronic colitis had no significant impact on femoral artery endothelial function or ischemic limb recovery in female mice.

Selective delivery of pitavastatin-loaded nanoparticles induces arteriogenesis upon chronic myocardial ischemia

Recent evidence has depicted nanoparticles (NPs) targeted delivery of statin facilitates neovascularization. Herein, we aimed to examine the impact of pitavastatin carrying NPs (pitavastatin-NPs) on collateral arteries and myocardial ischemia (MI). After establishment of MI model and preparation of nanomaterials, the animals were administered pitavastatin-NPs, pitavastatin or Fluorescein isothiocyanate-NP (FITC-NP) at concentration of 0.05, 0.15 and 0.5 mg/kg through intramuscular injection. Capillary and arteriole density was measured through immunofluorescence and angiogenesis was assessed by angiography. Human endothelial cells were also treated with pitavastatin or pitavastatin-NPs, followed by detection of angiogenic activity. Pitavastatin-NPs (0.5 mg/kg) promoted endothelial cell arteriogenesis and growth of collateral arteries in the rabbit with myocardial ischemia, exerting greater efficacy than NPs, FITC-NP, or PBS. For up to 4 weeks, FITC-NPs were mainly detected in the ischemic muscle tissue. Pitavastatin-NPs induced arteriogenesis and improved exercise-induced ischemic symptoms with enhancement in angiography score. Collectively, pitavastatin-NPs enhance arteriogenesis and alleviate MI as presence of nanocarriers improve the efficacy of pitavastatin. This evidence indicates pitavastatin-NPs as a promising treatment strategy and may contribute to development of nanotechnology to promote the formation of new blood vessels.

Depletion of γδ T Cells Leads to Reduced Angiogenesis and Increased Infiltration of Inflammatory M1-like Macrophages in Ischemic Muscle Tissue

γδ T cells, a small subset of T cells in blood, play a substantial role in influencing immunoregulatory and inflammatory processes. The functional impact of γδ T cells on angiogenesis in ischemic muscle tissue has never been reported and is the topic of the present work. Femoral artery ligation (FAL) was used to induce angiogenesis in the lower leg of γδ T cell depleted mice and wildtype and isotype antibody-treated control groups. Gastrocnemius muscle tissue was harvested 3 and 7 days after FAL and assessed using (immuno-)histological analyses. Hematoxylin and Eosin staining showed an increased area of tissue damage in γδ T cell depleted mice 7 days after FAL. Impaired angiogenesis was demonstrated by lower capillary to muscle fiber ratio and decreased number of proliferating endothelial cells (CD31+/BrdU+). γδ T cell depleted mice showed an increased number of total leukocytes (CD45+), neutrophils (MPO+) and neutrophil extracellular traps (NETs) (MPO+/CitH3+), without changes in the neutrophils to NETs ratio. Moreover, the depletion resulted in a higher macrophage count (DAPI/CD68+) caused by an increase in inflammatory M1-like macrophages (CD68+/MRC1−). Altogether, we show that depletion of γδ T cells leads to increased accumulation of leukocytes and M1-like macrophages, along with impaired angiogenesis.

The Absence of Extracellular Cold-Inducible RNA-Binding Protein (eCIRP) Promotes Pro-Angiogenic Microenvironmental Conditions and Angiogenesis in Muscle Tissue Ischemia.

Extracellular Cold-inducible RNA-binding protein (eCIRP), a damage-associated molecular pattern, is released from cells upon hypoxia and cold-stress. The overall absence of extra- and intracellular CIRP is associated with increased angiogenesis, most likely induced through influencing leukocyte accumulation. The aim of the present study was to specifically characterize the role of eCIRP in ischemia-induced angiogenesis together with the associated leukocyte recruitment. For analyzing eCIRPs impact, we induced muscle ischemia via femoral artery ligation (FAL) in mice in the presence or absence of an anti-CIRP antibody and isolated the gastrocnemius muscle for immunohistological analyses. Upon eCIRP-depletion, mice showed increased capillary/muscle fiber ratio and numbers of proliferating endothelial cells (CD31+/CD45−/BrdU+). This was accompanied by a reduction of total leukocyte count (CD45+), neutrophils (MPO+), neutrophil extracellular traps (NETs) (MPO+CitH3+), apoptotic area (ascertained via TUNEL assay), and pro-inflammatory M1-like polarized macrophages (CD68+/MRC1−) in ischemic muscle tissue. Conversely, the number of regenerative M2-like polarized macrophages (CD68+/MRC1+) was elevated. Altogether, we observed that eCIRP depletion similarly affected angiogenesis and leukocyte recruitment as described for the overall absence of CIRP. Thus, we propose that eCIRP is mainly responsible for modulating angiogenesis via promoting pro-angiogenic microenvironmental conditions in muscle ischemia.

C3 Deficiency Leads to Increased Angiogenesis and Elevated Pro-Angiogenic Leukocyte Recruitment in Ischemic Muscle Tissue.

The complement system is a potent inflammatory trigger, activator, and chemoattractant for leukocytes, which play a crucial role in promoting angiogenesis. However, little information is available about the influence of the complement system on angiogenesis in ischemic muscle tissue. To address this topic and analyze the impact of the complement system on angiogenesis, we induced muscle ischemia in complement factor C3 deficient (C3−/−) and wildtype control mice by femoral artery ligation (FAL). At 24 h and 7 days after FAL, we isolated the ischemic gastrocnemius muscles and investigated them by means of (immuno-)histological analyses. C3−/− mice showed elevated ischemic damage 7 days after FAL, as evidenced by H&E staining. In addition, angiogenesis was increased in C3−/− mice, as demonstrated by increased capillary/muscle fiber ratio and increased proliferating endothelial cells (CD31+/BrdU+). Moreover, our results showed that the total number of leukocytes (CD45+) was increased in C3−/− mice, which was based on an increased number of neutrophils (MPO+), neutrophil extracellular trap formation (MPO+/CitH3+), and macrophages (CD68+) displaying a shift toward an anti-inflammatory and pro-angiogenic M2-like polarized phenotype (CD68+/MRC1+). In summary, we show that the deficiency of complement factor C3 increased neutrophil and M2-like polarized macrophage accumulation in ischemic muscle tissue, contributing to angiogenesis.

Absence of Cold-Inducible RNA-Binding Protein (CIRP) Promotes Angiogenesis and Regeneration of Ischemic Tissue by Inducing M2-Like Macrophage Polarization.

Cold-inducible RNA-binding protein (CIRP) is an intracellular RNA-chaperone and extracellular promoter of inflammation, which is increasingly expressed and released under conditions of hypoxia and cold stress. The functional relevance of CIRP for angiogenesis and regeneration of ischemic muscle tissue has never been investigated and is the topic of the present study. We investigated the role of CIRP employing CIRP deficient mice along with a hindlimb model of ischemia-induced angiogenesis. 1 and 7 days after femoral artery ligation or sham operation, gastrocnemius muscles of CIRP-deficient and wildtype mice were isolated and processed for (immuno-) histological analyses. CIRP deficient mice showed decreased ischemic tissue damage as evidenced by Hematoxylin and Eosin staining, whereas angiogenesis was enhanced as demonstrated by increased capillary/muscle fiber ratio and number of proliferating endothelial (CD31+/BrdU+) cells on day 7 after surgery. Moreover, CIRP deficiency resulted in a reduction of total leukocyte count (CD45+), neutrophils (myeloperoxidase, MPO+), neutrophil extracellular traps (NETs) (MPO+/CitH3+), and inflammatory M1-like polarized macrophages (CD68+/MRC1-), whereas the number of tissue regenerating M2-like polarized macrophages (CD68+/MRC1-) was increased in ischemic tissue samples. In summary, we show that the absence of CIRP ameliorates angiogenesis and regeneration of ischemic muscle tissue, most likely by influencing macrophage polarization in direction to regenerative M2-like macrophages.

Ultrasound-Mediated Microbubble Cavitation Transiently Reverses Acute Hindlimb Tissue Ischemia through Augmentation of Microcirculation Perfusion via the eNOS/NO Pathway

Ultrasound-mediated microbubble cavitation improves perfusion in chronic limb and myocardial ischemia. The purpose of this study was to determine the effects of ultrasound-mediated microbubble cavitation in acute limb ischemia and investigate the mechanism of action. The animal with acute hindlimb ischemia was established using male Sprague-Dawley rats. The rats were randomly divided into three groups: intermittent high-mechanical-index ultrasound pulses combined with microbubbles (ultrasound [US] + MB group), US alone (US group) and MB alone (MB group). Both hindlimbs were treated for 10 min. Contrast ultrasound perfusion imaging of both hindlimbs was performed immediately and 5, 10, 15, 20 and 25 min after treatment. The role of the nitric oxide (NO) pathway in increasing blood flow in acutely ischemic tissue was evaluated by inhibiting endothelial nitric oxide synthase (eNOS) with Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME). In the US + MB group, microvascular blood volume and microvascular blood flow of the ischemic hindlimb were significantly increased after treatment (both p values <0.05), while the microvascular flux rate (β) increased, but not significantly (p > 0.05). The increases were observed immediately after treatment, and had dissipated by 25 min. Changes in the US and MB groups were minimal. Inhibitory studies indicated cavitation increased phospho-eNOS concentration in ischemic hindlimb muscle tissue, and the increase was significantly inhibited by L-NAME (p < 0.05). Ultrasound-mediated microbubble cavitation transiently increases local perfusion in acutely ischemic tissue, mainly by improving microcirculatory perfusion. The eNOS/NO signaling pathway appears to be an important mediator of the effect.

RNase A Treatment Interferes With Leukocyte Recruitment, Neutrophil Extracellular Trap Formation, and Angiogenesis in Ischemic Muscle Tissue.

Background: RNase A (the bovine equivalent to human RNase 1) and RNase 5 (angiogenin) are two closely related ribonucleases. RNase 5 is described as a powerful angiogenic factor. Whether RNase A shares the same angiogenic characteristic, or interferes with vessel growth as demonstrated for arteriogenesis, has never been investigated and is the topic of this present study.Methods and Results: To investigate whether RNase A shows a pro‐ or anti-angiogenic effect, we employed a murine hindlimb model, in which femoral artery ligation (FAL) results in arteriogenesis in the upper leg, and, due to provoked ischemia, in angiogenesis in the lower leg. C57BL/6J male mice underwent unilateral FAL, whereas the contralateral leg was sham operated. Two and seven days after the surgery and intravenous injection of RNase A (50 μg/kg dissolved in saline) or saline (control), the gastrocnemius muscles of mice were isolated from the lower legs for (immuno-) histological analyses. Hematoxylin and Eosin staining evidenced that RNase A treatment resulted in a higher degree of ischemic tissue damage. This was, however, associated with reduced angiogenesis, as evidenced by a reduced capillary/muscle fiber ratio. Moreover, RNase A treatment was associated with a significant reduction in leukocyte infiltration as shown by CD45+ (pan-leukocyte marker), Ly6G+ or MPO+ (neutrophils), MPO+/CitH3+ [neutrophil extracellular traps (NETs)], and CD68+ (macrophages) staining. CD68/MRC1 double staining revealed that RNase A treated mice showed a reduced percentage of M1-like polarized (CD68+/MRC1−) macrophages whereas the percentage of M2-like polarized (CD68+/MRC1+) macrophages was increased.Conclusion: In contrast to RNase 5, RNase A interferes with angiogenesis, which is linked to reduced leukocyte infiltration and NET formation.

MicroRNA‑210 improves perfusion recovery following hindlimb ischemia via suppressing reactive oxygen species

In peripheral arterial disease (PAD), angiogenesis is a major process involved in repairing the microvasculature in the ischemic lower limb. MicroRNA-210 (miR-210) is a microRNA that is substantially increased in patients with PAD. However, the effects of miR-210 on angiogenesis following PAD remain elusive. In the present study, mice with hindlimb ischemia (HLI) were generated as an animal model of PAD, and miR-210 levels were overexpressed in the ischemic limb. The overexpression of miR-210 using microRNA mimics greatly improved angiogenesis and perfusion recovery; in contrast, the knockdown of miR-210 impaired perfusion recovery 28 days after HLI. Ischemic muscle tissue was harvested 7 days after experimental PAD in order to perform biochemical tests, and miR-210 antagonism resulted in increased malondialdehyde levels. In cultured endothelial cells under simulated ischemia, miR-210 mimic improved endothelial cell viability and enhanced tube formation; and a miR-210 inhibitor decreased cell survival, reduced tube formation and increased reactive oxygen species (ROS) levels. Furthermore, miR-210 antagonism increased the protein disulfide-isomerase levels in cultured endothelial cells. These results demonstrate that ischemia-induced miR-210 elevation is adaptive in PAD, and that miR-210 improves angiogenesis at least partially through decreasing ROS production.

Effects of electroacupuncture on skeletal muscle and blood glucose in rats with diabetic amyotrophy

To explore the effects of electroacupuncture (EA) on skeletal muscle and blood glucose in rats with diabetic amyotrophy. Among 40 SD rats, 10 rats were randomly selected into the control group and received no treatment. The remaining 30 rats were treated with intraperitoneal injection of streptozotocin (STZ, 60 mg/kg) to establish diabetes mellitus (DM) model, and then the rats were treated with vascular ligation at right posterior limb to establish amyotrophy model. The rats with diabetic amyotrophy were randomly divided into a model group and an EA group, 10 rats in each group (10 rats were excluded due to unsuccessful model establishment and death). The rats in the EA group was treated with EA at right-side "Yishu (EX-B 3)" "Shenshu (BL 23)" "Zusanli (ST 36)" and "Sanyinjiao (SP 6)", disperse-dense wave, 2 Hz/ 15 Hz, 20 minutes each time, once a day for 3 weeks. Before and after EA treatment, the blood sample was collected from inner canthus and the "glucose oxidase-peroxidase" method was used to detect fasting blood glucose level; ELISA method was used to detect insulin content. At the end of the treatment, HE staining method was used to observe the morphology of ischemic skeletal muscle in the right hindlimb; the real-time PCR method was used to detect the mRNA expression of muscle atrophy F-box (MAFbx), muscle ring finger-1 (MuRF1) and forkhead box O3a (FOXO3a) in the ischemic skeletal muscle tissue of right hindlimb. Before the treatment, the body mass in the model group and EA group was lower than that in the control group (P<0.01); after the treatment, the body mass in the control group was increased, while the body mass in the model group and EA group was decreased (P<0.01). Compared with the control group, the fasting blood glucose was significantly increased and insulin content was significantly decreased in the model group (P<0.01); compared with the model group, the fasting blood glucose was significantly decreased and the insulin content was significantly increased in the EA group after treatment (P<0.01). The muscle fibers of the model group were obviously broken, the number of the nuclei decreased, and the nuclei shrinked or even dissolved; the morphology of the muscle tissue of the EA group after intervention was improved compared with the model group. Compared with the control group, the cross-sectional area of ischemic skeletal muscle cells in the right hindlimb in the model group was decreased (P<0.01); compared with the model group, the cross-sectional area of ischemic skeletal muscle cells in the right hindlimb was increased in EA group (P<0.05). Compared with the control group, the levels of MAFbx, MuRF1 and FOXO3a mRNA in the right hindlimb ischemic skeletal muscle in the model group were increased significantly (P<0.01, P<0.05); compared with the model group, the levels of MAFbx, MuRF1 and FOXO3a mRNA in the EA group were decreased significantly (P<0.05, P<0.01). EA may play a role in the treatment of diabetic amyotrophy by inducing FOXO3a to reduce the transcription of MAFbx and MuRF1.

Local Mast Cell Activation Promotes Neovascularization.

Mast cells have been associated with arteriogenesis and collateral formation. In advanced human atherosclerotic plaques, mast cells have been shown to colocalize with plaque neovessels, and mast cells have also been associated with tumor vascularization. Based on these associations, we hypothesize that mast cells promote angiogenesis during ischemia. In human ischemic muscle tissue from patients with end-stage peripheral artery disease, we observed activated mast cells, predominantly located around capillaries. Also, in mouse ischemic muscles, mast cells were detected during the revascularization process and interestingly, mast cell activation status was enhanced up to 10 days after ischemia induction. To determine whether mast cells contribute to both arteriogenesis and angiogenesis, mast cells were locally activated immediately upon hind limb ischemia in C57Bl/6 mice. At day 9, we observed a 3-fold increase in activated mast cell numbers in the inguinal lymph nodes. This was accompanied by an increase in the amount of Ly6Chigh inflammatory monocytes. Interestingly, local mast cell activation increased blood flow through the hind limb (46% at day 9) compared to that in non-activated control mice. Histological analysis of the muscle tissue revealed that mast cell activation did not affect the number of collaterals, but increased the collateral diameter, as well as the number of CD31+ capillaries. Together, these data illustrate that locally activated mast cell contribute to arteriogenesis and angiogenesis.