Mouse Model Of Hindlimb Ischemia Research Articles

L-theanine promotes angiogenesis in limb ischemic mice by modulating NRP1/VEGFR2 signaling.

Peripheral artery disease (PAD), primarily caused by atherosclerosis, leads to the narrowing or blockage of arteries that supply blood to the limbs. This study explores the pro-angiogenic effects of L-theanine and its underlying mechanisms in a mouse model of hindlimb ischemia (HLI). To evaluate L-theanine's pro-angiogenic effects, human umbilical vein endothelial cells (HUVECs) were subjected to tube formation, migration, sprouting, and proliferation assays. In vivo, C57BL/6 mice with induced HLI were treated with L-theanine. Blood flow recovery was measured via Doppler ultrasound, and vascular density was analyzed using immunofluorescence staining. RNA sequencing identified neuropilin-1 (NRP1) as a key regulator, and the expression levels of NRP1 and VEGFR2 were examined through qPCR and Western blotting. L-theanine significantly enhanced angiogenesis in HUVECs, as demonstrated by improved tube formation, migration, sprouting, and proliferation. In mice, L-theanine treatment resulted in increased vessel density and improved blood flow recovery. Furthermore, L-theanine was found to activate the NRP1/VEGFR2 signaling pathway in both HUVECs and the HLI mouse model. These findings indicate that L-theanine can promote angiogenesis and activate key pathways involved in vascular repair, suggesting its potential as a therapeutic agent for treating vascular defects associated with PAD.

Signal regulatory protein α dynamically mediates macrophage polarization facilitated alleviation of ischemic diseases

Backgroundmacrophage-targeting therapy of ischemic disease has made progress in clinic trial. However, the role and underlying mechanism of pro-inflammatory or anti-inflammatory polarized macrophages in modulating ischemic diseases remain incompletely understood.Resultshere we examine the effect of pro-inflammatory (LPS) and anti-inflammatory (IL-4) macrophage on ischemic diseases in a mouse ischemic hindlimb and heart model, and identify that signal regulatory protein α (Sirpα) modulates macrophage polarization induced angiogenesis via promoting phagocytosis or activating HIF1α nucleus relocation in macrophages, respectively. More importantly, the therapeutic effect of polarized macrophages is controlled by Sirpα in a time-dependent manner. Downregulation of macrophage Sirpα at the early-stage or upregulation of macrophage Sirpα at the late-stage of ischemic disease enhances the therapeutic effect. In contrast, increasing Sirpα at the early-stage or decreasing it at the late-stage leads to failure of inducing ischemic disease resilience. Mechanistically, we find that signal transducer and activator of transcription 3 and 6 (Stat3 and Stat6) mediate downregulation (pro-inflammatory polarization) or upregulation (anti-inflammatory polarization) of Sirpα, respectively.ConclusionOur results reveal that dynamic regulation of macrophage by Sirpα plays a critical role in alleviating ischemic diseases.

Microbubble enhanced ultrasound with low mechanical index promotes therapeutic angiogenesis in hind limb ischemia mouse model.

Microbubble enhanced ultrasound (MEUS) can augment tissue perfusion by angiogenesis yet the best treatment ultrasound power in the initial ischemia period is uncertain. Considering the mechanical index (MI) is the most commonly used parameter for regulating diagnostic ultrasound power, here, we explored the effects of MEUS mediated by different MI on perfusion and sought to characterize the angiogenesis in the early stage of ischemia. Experiments were conducted on hind limb ischemia mouse model (HLI) and MEUS was administrated in the first week every other day following induction of HLI for four times. MEUS was conducted with a modified diagnostic ultrasound in combination with a lipid microbubble at 3MHz and 21 cycles employing MI 0.3 (0.8MPa), 0.7 (1.32MPa) and 1.3 (2.78MPa), respectively. Semi-quantitative visual score and blood perfusion quantitation by contrast-enhanced ultrasound were performed before each treatment. Hematoxylin-eosin staining and immunohistochemistry with CD31 were performed after four times treatment. The results showed HLI mice in MI 0.3 mediated MEUS group longitudinally exhibited more blood perfusion in calf muscle and less visible necrosis compared to other experimental groups in the early stage. Additionally, diffused inflammatory cells with greater number of vessels in calf muscle were observed in MI 0.3 group. Low MI mediated MEUS had significantly greater effects on augmenting muscle blood perfusion and reducing necrosis in the initial period after HLI surgery. These effects are most likely mediated by angiogenesis stimulated by low MI mediated MEUS.

Circadian Dysfunction in the Skeletal Muscle Impairs Limb Perfusion and Muscle Regeneration in Peripheral Artery Disease.

Peripheral artery disease (PAD), caused by atherosclerosis, leads to limb ischemia, muscle damage, and impaired mobility in the lower extremities. Recent studies suggest that circadian rhythm disruptions can hinder vascular repair during ischemia, but the specific tissues involved and the impact on muscle health remain unclear. This study investigates the role of the skeletal muscle circadian clock in muscle adaptation to ischemic stress using a surgical mouse model of hindlimb ischemia. We performed secondary analysis of publicly available RNA-sequencing data sets derived from patients with PAD to identify the differential expression of circadian-related genes in endothelial cells and ischemic limb skeletal muscles. We used mice with specific genetic loss of the circadian clock activator, BMAL1 (brain and muscle ARNT-like 1), in adult skeletal muscle tissues (Bmal1muscle). Bmal1muscle mice and controls underwent femoral artery ligation surgery to induce hindlimb ischemia. Laser Doppler imaging was used to assess limb perfusion at various time points after the surgery. Muscle tissues were analyzed with RNA sequencing and histological examination to investigate PAD-related muscle pathologies. Additionally, we studied the role of BMAL1 in muscle fiber adaptation to hypoxia using RNA and assay for transposase-accessible chromatin with sequencing analyses in primary myotube culture model. Disrupted expression of circadian rhythm-related genes was observed in existing RNA-sequencing data sets from endothelial cells and ischemic limb skeletal muscles derived from patients with PAD. Genetic loss of Bmal1 specifically in adult mouse skeletal muscle tissues delayed reperfusion recovery following induction of hindlimb ischemia. Histological examination of muscle tissues showed reduced regenerated myofiber number and a decreased proportion of type IIB fast-twitch myofibers in Bmal1muscle mouse muscles in the ischemic limbs but not in their contralateral nonischemic limbs. Transcriptomic analysis revealed abrogated metabolic, angiogenic, and myogenic pathways relevant to hypoxia adaptation in Bmal1muscle mouse muscles. These changes were corroborated in Bmal1-deficient cultured primary myotubes cultured under hypoxic conditions. Circadian clock in skeletal muscle is crucial for the muscle's response to hypoxia during hindlimb ischemia. Targeting the muscle circadian clock may have therapeutic potential for enhancing muscle response to reduced blood flow and promoting recovery in conditions such as PAD.

Berbamine Promotes the Repair of Lower Limb Muscle Damage in Chronic Limb-Threatening Ischemia by Inhibiting Local Inflammation and NF-κB Nuclear Translocation.

Background/Objectives: Chronic Limb-Threatening Ischemia (CLTI) is a chronic limb ischemic disease caused by vascular lesions, characterized by pain, ulcers, and gangrene, which can be life-threatening in severe cases. The objective of this study is to explore whether Berbamine (BBM) can protect against and repair ischemic muscle tissue in the lower limbs; Methods: Using a mouse hindlimb ischemia (HLI) model, 36 C57BL6 mice were divided into sham, HLI, and HLI+BBM treatment groups. Results: Our findings indicate that BBM can restore motor function and muscle tissue pathology in mice, potentially by inhibiting the nuclear translocation of nuclear factor kappa-B (NF-κB), thereby alleviating tissue inflammation caused by chronic ischemia, reducing muscle cell apoptosis, inhibiting M1 macrophage polarization, and promoting angiogenesis. Conclusions: Our research suggests that BBM has the potential to protect against ischemic damage in lower limb muscle tissue, providing a new approach to the treatment of CLTI.

The Systemic Effect of Ischemia Training and Its Impact on Bone Marrow-Derived Monocytes.

Monocytes are innate immune cells that play a central role in inflammation, an essential component during neovascularization. Our recent publication demonstrated that ischemia training by 24 h unilateral occlusion of the femoral artery (FA) can modify bone marrow-derived monocytes (BM-Mono), allowing them to improve collateral remodeling in a mouse model of hindlimb ischemia. Here, we expand on our previous findings, investigating a potential systemic effect of ischemia training and how this training can impact BM-Mono. BM-Mono from mice exposed to ischemia training (24 h) or Sham (same surgical procedure without femoral artery occlusion-ischemia training) procedures were used as donors in adoptive transfer experiments where recipients were subjected to hindlimb ischemia. Donor cells were divided corresponding to the limb from which they were isolated (left-limb previously subjected to 24 h ischemia and right-contralateral limb). Recipients who received 24 h ischemic-trained monocytes isolated from either limb had remarkable blood flow recovery compared to recipients with Sham monocytes (monocytes isolated from Sham group-no ischemia training). Since these data suggested a systemic effect of ischemic training, circulating extracellular vesicles (EVs) were investigated as potential players. EVs were isolated from both groups, 24 h-trained and Sham, and the former showed increased expression of histone deacetylase 1 (HDAC1), which is known to downregulate 24-dehydrocholesterol reductase (Dhcr24) gene expression. Since we previously revealed that ischemia training downregulates Dhcr24 in BM-Mono, we incubated EVs from 24 h-trained and Sham groups with wild-type (WT) BM-Mono and demonstrated that WT BM-Mono incubated with 24 h-trained EVs had lower gene expression of Dhcr24 and an HDAC1 inhibitor blunted this effect. Next, we repeated the adoptive transfer experiment using Dhcr24 KO mice as donors of BM-Mono for WT mice subjected to hindlimb ischemia. Recipients who received Dhcr24 KO BM-Mono had greater limb perfusion than those who received WT BM-Mono. Further, we focused on the 24 h-trained monocytes (which previously showed downregulation of Dhcr24 gene expression and higher desmosterol) to test the expression of a few genes downstream of the desmosterol pathway, confirm the Dhcr24 protein level and assess its differentiation in M2-like macrophage phenotype. We found that 24 h-trained BM-Mono had greater expression of key genes in the desmosterol pathway, such as liver X receptors (LXRs) and ATP-binding cassette transporter (ABCA1), and we confirmed low protein expression of Dhcr24. Further, we demonstrated that ischemic-trained BM-Mono polarized towards an anti-inflammatory M2 macrophage phenotype. Finally, we demonstrated that 24 h-trained monocytes adhere less to endothelial cells, and the same pattern was shown by WT BM-Mono treated with Dhcr24 inhibitor. Ischemia training leads to a systemic effect that, at least in part, involves circulating EVs and potential epigenetic modification in BM-Mono. These ischemic-trained BM-Mono demonstrated an anti-inflammatory phenotype towards M2 macrophage differentiation and less ability to adhere to endothelial cells, which is associated with the downregulation of Dhcr24 in those cells. These data together suggest that Dhcr24 might be an important target within monocytes to improve the outcomes of hindlimb ischemia.

Insulin-like growth factor-2 mRNA-binding protein 2 facilitates post-ischemic angiogenesis by increasing the stability of fibroblast growth factor 2 mRNA and its protein expression

BackgroundPost-ischemic angiogenesis is crucial for reestablishing blood flow in conditions such as peripheral artery disease (PAD). The role of insulin-like growth factor-2 mRNA-binding protein 2 (IGF2BP2) in post-transcriptional RNA metabolism and its involvement in post-ischemic angiogenesis remains unclear. MethodsUsing a human GEO database and a hind-limb ischemia (HLI) mouse model, the predominant isoform IGF2BP2 in ischemic gastrocnemius tissue was identified. Adeno-associated virus with the Tie1 promoter induced IGF2BP2 overexpression in the HLI model, evaluating the expression of vascular structural proteins (CD31 and α-SMA) and blood flow recovery after HLI. In vitro experiments with human umbilical vein endothelial cells (HUVECs) demonstrated that lentivirus-mediated IGF2BP2 overexpression upregulates cell proliferation, migration, and tube formation. GeneCards, RNAct databases, and subsequent reverse transcription quantitative polymerase chain reaction (RT-qPCR) predicted IGF2BP2 interactions with fibroblast growth factor 2 (FGF2) mRNA, and actinomycin D treatment, binding site predictions and CLIP-seq data further confirmed this interaction. Furthermore, western blotting, enzyme-linked immunosorbent assay, and RNA immunoprecipitation followed by RT-qPCR were performed to validate IGF2BP2's interaction with FGF2 mRNA and to assess its role in stabilizing FGF2 mRNA, as well as its impact on FGF2 protein expression. ResultsHLI reduced IGF2BP2 expression in the gastrocnemius tissue, which gradually increased during blood flow recovery. IGF2BP2 overexpression in HLI mice accelerated blood flow recovery and increased capillary and small artery densities. The overexpression of IGF2BP2 in HUVECs stimulated proliferation, migration, and tube formation by interacting with FGF2 mRNA to increase its stability. This interaction resulted in increased levels of FGF2 protein and secretion, ultimately promoting angiogenesis. ConclusionsIGF2BP2 contributes to blood flow restoration post-ischemia in vivo and promotes angiogenesis in HUVECs by enhancing FGF2 mRNA stability and FGF2 protein expression and secretion. These findings underscore IGF2BP2's therapeutic potential in ischemic conditions, such as PAD.

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.

Targeting TXNIP in endothelial progenitors mitigates IL-8-induced neutrophil recruitment under metabolic stress

BackgroundThis study explores the potential role of Thioredoxin-interacting protein (TXNIP) silencing in endothelial colony-forming cells (ECFCs) within the scope of age-related comorbidities and impaired vascular repair. We aim to elucidate the effects of TXNIP silencing on vasculogenic properties, paracrine secretion, and neutrophil recruitment under conditions of metabolic stress.MethodsECFCs, isolated from human blood cord, were transfected with TXNIP siRNA and exposed to a high glucose and β-hydroxybutyrate (BHB) medium to simulate metabolic stress. We evaluated the effects of TXNIP silencing on ECFCs’ functional and secretory responses under these conditions. Assessments included analyses of gene and protein expression profiles, vasculogenic properties, cytokine secretion and neutrophil recruitment both in vitro and in vivo. The in vivo effects were examined using a murine model of hindlimb ischemia to observe the physiological relevance of TXNIP modulation under metabolic disorders.ResultsTXNIP silencing did not mitigate the adverse effects on cell recruitment, vasculogenic properties, or senescence induced by metabolic stress in ECFCs. However, it significantly reduced IL-8 secretion and consequent neutrophil recruitment under these conditions. In a mouse model of hindlimb ischemia, endothelial deletion of TXNIP reduced MIP-2 secretion and prevented increased neutrophil recruitment induced by age-related comorbidities.ConclusionsOur findings suggest that targeting TXNIP in ECFCs may alleviate ischemic complications exacerbated by metabolic stress, offering potential clinical benefits for patients suffering from age-related comorbidities.

Selective Enrichment of Angiomirs in Extracellular Vesicles Released from Ischemic Skeletal Muscles: Potential Role in Angiogenesis and Neovascularization.

MicroRNAs (miRs) regulate physiological and pathological processes, including ischemia-induced angiogenesis and neovascularization. They can be transferred between cells by extracellular vesicles (EVs). However, the specific miRs that are packaged in EVs released from skeletal muscles, and how this process is modulated by ischemia, remain to be determined. We used a mouse model of hindlimb ischemia and next generation sequencing (NGS) to perform a complete profiling of miR expression and determine the effect of ischemia in skeletal muscles, and in EVs of different sizes (microvesicles (MVs) and exosomes) released from these muscles. Ischemia significantly modulated miR expression in whole muscles and EVs, increasing the levels of several miRs that can have pro-angiogenic effects (angiomiRs). We found that specific angiomiRs are selectively enriched in MVs and/or exosomes in response to ischemia. In silico approaches indicate that these miRs modulate pathways that play key roles in angiogenesis and neovascularization, including HIF1/VEGF signaling, regulation of actin cytoskeleton and focal adhesion, NOTCH, PI3K/AKT, RAS/MAPK, JAK/STAT, TGFb/SMAD signaling and the NO/cGMP/PKG pathway. Thus, we show for the first time that angiomiRs are selectively enriched in MVs and exosomes released from ischemic muscles. These angiomiRs could be targeted in order to improve the angiogenic function of EVs for potential novel therapeutic applications in patients with severe ischemic vascular diseases.

An Endocellulase-Triggered NO Targeted-Release Enzyme-Prodrug Therapy System and Its Application in Ischemia Injury.

Nitric oxide (NO) is a crucial gaseous signaling molecules in regulating cardiovascular, immune, and nervous systems. Controlled and targeted NO delivery is imperative for treating cancer, inflammation, and cardiovascular diseases. Despite various enzyme-prodrug therapy (EPT) systems facilitating controlled NO release, their clinical utility is hindered by nonspecific NO release and undesired metabolic consequence. In this study, a novel EPT system is presented utilizing a cellobioside-diazeniumdiolate (Cel2-NO) prodrug, activated by an endocellulase (Cel5A-h38) derived from the rumen uncultured bacterium of Hu sheep. This system demonstrates nearly complete orthogonality, wherein Cel2-NO prodrug maintains excellent stability under endogenous enzymes. Importantly, Cel5A-h38 efficiently processes the prodrug without recognizing endogenous glycosides. The targeted drug release capability of the system is vividly illustrated through an in vivo near-infrared imaging assay. The precise NO release by this EPT system exhibits significant therapeutic potential in a mouse hindlimb ischemia model, showcasing reductions in ischemic damage, ambulatory impairment, and modulation of inflammatory responses. Concurrently, the system enhances tissue repair and promotes function recovery efficacy. The novel EPT system holds broad applicability for the controlled and targeted delivery of essential drug molecules, providing a potent tool for treating cardiovascular diseases, tumors, and inflammation-related disorders.

A subpopulation of tissue remodeling monocytes stimulates revascularization of the ischemic limb.

Despite decades of effort aimed at developing clinically effective cell therapies, including mixed population mononuclear cells, to revascularize the ischemic limb, there remains a paucity of patient-based studies that inform the function and fate of candidate cell types. In this study, we showed that circulating proangiogenic/arteriogenic monocytes (PAMs) expressing the FcγIIIA receptor CD16 were elevated in patients with chronic limb-threatening ischemia (CLTI), and these amounts decreased after revascularization. Unlike CD16-negative monocytes, PAMs showed large vessel remodeling properties in vitro when cultured with endothelial cells and smooth muscle cells and promoted salvage of the ischemic limb in vivo in a mouse model of hindlimb ischemia. PAMs showed a propensity to migrate toward and bind to ischemic muscle and to secrete angiogenic/arteriogenic factors, vascular endothelial growth factor A (VEGF-A) and heparin-binding epidermal growth factor. We instigated a first-in-human single-arm cohort study in which autologous PAMs were injected into the ischemic limbs of five patients with CLTI. Greater than 25% of injected cells were retained in the leg for at least 72 hours, of which greater than 80% were viable, with evidence of enhanced large vessel remodeling in the injected muscle area. In summary, we identified up-regulation of a circulatory PAM subpopulation as an endogenous response to limb ischemia in CLTI and tested a potentially clinically relevant therapeutic strategy.

Biomimetic nanocomposite cryogel with enhanced peptide binding promotes therapeutic angiogenesis and bone regeneration

The effective regeneration of large bone defects faces a significant hurdle, primarily due to inadequate vascularization. This study explores the potential of enhancing vascularization and bone regeneration by incorporating whitlockite nanoparticles (nWH; Ca18Mg2(HPO4)2(PO4)12) and WKYMVm (W) peptide into a gelatin-sulfated hyaluronic acid (WH10-W) cryogel. The developed cryogels showed an average pore size of 70 μm. Further, they were characterized for degradation rate, swelling ratio, mechanical and rheological properties. The WH10-W group exhibited sustained release of the W peptide, in contrast to the rapid release observed from gelatin-hyaluronic acid. In silico binding studies revealed that the binding of the W peptide was dependent on the sulfation degree in hyaluronic acid. The prepared cryogels were cytocompatible. The combinatorial group (WH10-W) demonstrated superior pro-angiogenic compared to cryogel with only nWH or W peptide, as seen from tube formation assay, scratch test and gene expression studies. In addition, WH10-W enhanced the osteogenic differentiation as seen from the osteogenic gene expression, ALP and alizarin red s staining. Finally, mouse hind limb ischemia model demonstrated enhanced angiogenic potential, while a mouse cranial defect study showed increased new bone formation in the WH10-W group compared to all other groups. These findings suggest a promising strategy for addressing large non-load bearing bone defects.

Senescence induces miR-409 to down-regulate CCL5 and impairs angiogenesis in endothelial progenitor cells.

This study explores the impact of senescence on autocrine C-C motif chemokine ligand 5 (CCL5) in human endothelial progenitor cell (EPCs), addressing the poorly understood decline in number and function of EPCs during ageing. We examined the effects of replication-induced senescence on CCL5/CCL5 receptor (CCR5) signalling and angiogenic activity of EPCs invitro and invivo. We also explored microRNAs controlling CCL5 secretion in senescent EPCs, its impact on EPC angiogenic activity, and validated our findings in humans. CCL5 secretion and CCR5 levels in senescent EPCs were reduced, leading to attenuated angiogenic activity. CCL5 enhanced EPC proliferation via the CCR5/AKT/P70S6K axis and increased vascular endothelial growth factor (VEGF) secretion. Up-regulation of miR-409 in senescent EPCs resulted in decreased CCL5 secretion, inhibiting the angiogenic activity, though these negative effects were counteracted by the addition of CCL5 and VEGF. In a mouse hind limb ischemia model, CCL5 improved the angiogenic activity of senescent EPCs. Analysis involving 62 healthy donors revealed a negative association between CCL5 levels, age and Framingham Risk Score. These findings propose CCL5 as a potential biomarker for detection of EPC senescence and cardiovascular risk assessment, suggesting its therapeutic potential for age-related cardiovascular disorders.

Abstract 1142: Effect Of Chronic E-cigarette Nicotine Exposure On A Mouse Model Of Hind-limb Ischemia

Background: The rise of e-cigarette use in the United States has been rapid, yet its impact on peripheral artery disease (PAD) remains largely unexplored. This study investigates the relationship between e-cigarette use and PAD using a mouse ischemic hindlimb model. Method: Mice aged 6-8 weeks were divided into four groups. Three groups inhaled e-cigarette vapor continuously for 14, 20, or 28 days prior, and for 28 days after hindlimb ischemia (HLI) surgery, using an InExpose system (Figure 1). A control group was exposed to room air (RA) before and after HLI. Laser-Doppler perfusion imaging tracked hindlimb blood flow, and functional deficits were assessed using the modified ischemia scale. Figure 1: Methodology Results: Blood perfusion in the ischemic hindlimb of the e-cigarette groups (EC-14, EC-20, EC-28) was significantly lower than the non-vaping group at 21 days post-surgery. In the EC-14 group, perfusion improved after 10 days of vaping cessation (Figure 2). Additionally, there was a reduction in platelet and leukocyte counts in the e-cigarette groups compared to RA, with no difference in red blood cells. Necrosis and claw damage were observed in EC-20 and EC-28 groups but not in non-vaping mice. Figure 2: Representative images of perfusion recovery measured by LDPI. Conclusion: Chronic e-cigarette nicotine exposure impairs blood flow recovery and causes necrosis in mice with hind limb ischemia, potentially due to perturbed angiogenesis and arteriogenesis. This study highlights the detrimental effects of e-cigarette nicotine on vascular health.

Abstract 2005: Interrogating The Cross-talk: Endothelial-Macrophage Interactions In Diabetic Vascular Dysfunction

Cardiovascular disease (CVD) occurs 15 years earlier in diabetics compared to those without, but the underlying mechanisms driving diabetes-accelerated CVDs (DACVDs) pathogenesis remains incompletely understood. Endothelial cells (ECs) and macrophages (MΦ) are key players in vascular wall and their crosstalk is crucial in DACVD. In diabetes, ECs activation enables monocytes recruitment, which transmigrate across the intima and differentiate into macrophages (MΦ). Beyond this established diapedesis model, EC-MΦ interplay is highly intricate and heterogenous. Here, we leveraged human mesenteric arteries of varied diabetic state and used single cell (sc)- and spatial transcriptome mapping to interrogate the functional crosstalk between MΦ subtypes and ECs in diabetes. We identified diabetes-induced EC-MΦ interactions and explored their consequences in vitro and in vivo, in peripheral artery disease (PAD), a prominent DACVD. Integrative scRNA-seq and spatial transcriptome (Visium) profiling identified a remarkable increase of MΦ subtype expressing triggering receptor expressed on myeloid cells (TREM2) with concomitant increased EC-derived TREM2 ligands in human diabetic vs non-diabetic vessels. Such induction of TREM2 MΦ was consistently observed in arteries from type I and II diabetes mouse models. Compared to the condition medium from MΦ cultured under normal glucose, that from MΦ cultured under high glucose conditions reduced EC migration and increased inflammatory markers, which were reversed by the medium from MΦ with TREM2-knockdown. We further evaluated the functional importance of EC-TREM2 interaction in vivo in a mouse hindlimb ischemia (HLI) model. In diabetic mice under HLI, a TREM2 neutralizing antibody promoted tissue recovery and perfusion. Finally, we showed that TREM2 was increased, especially in proximity to ECs, in ischemic sites, as compared to non-ischemic regions in limb muscles from human PAD patients.Taken together, our study presents a diabetic artery atlas and identifies EC-TREM2 interaction as a crucial event in DACVDs, such as PAD. Our findings provide novel insights into the EC-MΦ interplay in diabetes and vascular inflammation and how these cellular interactions may be targeted to ameliorate DACVD.

Role of toll-like receptor 4 in skeletal muscle damage in chronic limb-threatening ischemia

ObjectiveToll-like receptors (TLRs) are key pattern recognition receptors in the innate immune system. In particular, the TLR4-mediated immune response has been implicated in ischemia-induced tissue injury. Mounting evidence supports a detrimental role of the innate immune system in the pathophysiology of skeletal muscle damage in patients with chronic limb-threatening ischemia (CLTI), in whom patient-oriented functional outcomes are poor. The overall aim of this study was to investigate the potential role of TLR4 in skeletal muscle dysfunction and damage in CLTI. MethodsThe role of TLR4 in ischemic muscle was investigated by (1) studying TLR4 expression and distribution in human gastrocnemius muscle biopsies, (2) evaluating the functional consequences of TLR4 inhibition in myotubes derived from human muscle biopsies, and (3) assessing the therapeutic potential of modulating TLR4 signaling in ischemic muscle in a mouse hindlimb ischemia model. ResultsTLR4 was found to be expressed in human muscle biopsies, with significant upregulation in samples from patients with CLTI. In vitro studies using cultured human myotubes demonstrated upregulation of TLR4 in ischemia, with activation of the downstream signaling pathway. Inhibition of TLR4 before ischemia was associated with reduced ischemia-induced apoptosis. Upregulation of TLR4 also occurred in ischemia in vivo and TLR4 inhibition was associated with decreased inflammatory cell infiltration and diminished apoptosis in the ischemic limb. ConclusionsTLR4 is upregulated and activated in ischemic skeletal muscle in patients with CLTI. Modulating TLR4 signaling in vitro and in vivo was associated with attenuation of ischemia-induced skeletal muscle damage. This strategy could be explored further for potential clinical application.

Adipose-Derived Mesenchymal Stem Cells Protect Endothelial Cells from Hypoxic Injury by Suppressing Terminal UPR In Vivo and In Vitro.

Adipose-derived stem cells (ASCs) have been used as a therapeutic intervention for peripheral artery disease (PAD) in clinical trials. To further explore the therapeutic mechanism of these mesenchymal multipotent stromal/stem cells in PAD, this study was designed to test the effect of xenogeneic ASCs extracted from human adipose tissue on hypoxic endothelial cells (ECs) and terminal unfolded protein response (UPR) in vitro and in an atherosclerosis-prone apolipoprotein E-deficient mice (ApoE-/- mice) hindlimb ischemia model in vivo. ASCs were added to Cobalt (II) chloride-treated ECs; then, metabolic activity, cell migration, and tube formation were evaluated. Fluorescence-based sensors were used to assess dynamic changes in Ca2+ levels in the cytosolic- and endoplasmic reticulum (ER) as well as changes in reactive oxygen species. Western blotting was used to observe the UPR pathway. To simulate an acute-on-chronic model of PAD, ApoE-/- mice were subjected to a double ligation of the femoral artery (DLFA). An assessment of functional recovery after DFLA was conducted, as well as histology of gastrocnemius. Hypoxia caused ER stress in ECs, but ASCs reduced it, thereby promoting cell survival. Treatment with ASCs ameliorated the effects of ischemia on muscle tissue in the ApoE-/- mice hindlimb ischemia model. Animals showed less muscle necrosis, less inflammation, and lower levels of muscle enzymes after ASC injection. In vitro and in vivo results revealed that all ER stress sensors (BIP, ATF6, CHOP, and XBP1) were activated. We also observed that the expression of these proteins was reduced in the ASCs treatment group. ASCs effectively alleviated endothelial dysfunction under hypoxic conditions by strengthening ATF6 and initiating a transcriptional program to restore ER homeostasis. In general, our data suggest that ASCs may be a meaningful treatment option for patients with PAD who do not have traditional revascularization options.

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.

FNIP1 abrogation promotes functional revascularization of ischemic skeletal muscle by driving macrophage recruitment

Ischaemia of the heart and limbs attributable to compromised blood supply is a major cause of mortality and morbidity. The mechanisms of functional angiogenesis remain poorly understood, however. Here we show that FNIP1 plays a critical role in controlling skeletal muscle functional angiogenesis, a process pivotal for muscle revascularization during ischemia. Muscle FNIP1 expression is down-regulated by exercise. Genetic overexpression of FNIP1 in myofiber causes limited angiogenesis in mice, whereas its myofiber-specific ablation markedly promotes the formation of functional blood vessels. Interestingly, the increased muscle angiogenesis is independent of AMPK but due to enhanced macrophage recruitment in FNIP1-depleted muscles. Mechanistically, myofiber FNIP1 deficiency induces PGC-1α to activate chemokine gene transcription, thereby driving macrophage recruitment and muscle angiogenesis program. Furthermore, in a mouse hindlimb ischemia model of peripheral artery disease, the loss of myofiber FNIP1 significantly improved the recovery of blood flow. Thus, these results reveal a pivotal role of FNIP1 as a negative regulator of functional angiogenesis in muscle, offering insight into potential therapeutic strategies for ischemic diseases.