Stem cell-based peripheral vascular regeneration

Effect of acidosis on adipose-derived stem cell impairment and gene expression

Based on disappointing results of stem cell-based application in clinical trials for patients with critical limb ischemia, we hypothesized that the acidic environment might be the key factor limiting cell survival and function. In the present study, we used microdialysis to determine presence of acidosis and metabolic imbalance in critical ischemia. Moreover, we explored the effect of extracellular acidosis on adipose-derived stem cells (ADSCs) at molecular and transcriptional level. Our data demonstrate that low pH negatively regulates cell proliferation and survival, also, it results in cell cycle arrest, mitochondrial dynamics disorder, DNA damage as well as the impairment of proangiogenic function in a pH-dependent manner. Further transcriptome profiling identified the pivotal signaling pathways and hub genes in response to acidosis. Collectively, these findings provide strong evidences for a critical role of acidosis in ADSCs impairment with ischemic condition and suggest treatments focus on tissue pH balance and acidosis-mediated hub genes may have therapeutic potential in stem cell-based application.

The Impact of Modern Anti-Diabetic Treatment on Endothelial Progenitor Cells

Diabetes is one of the leading chronic diseases globally with a significant impact on mortality. This condition is associated with chronic microvascular and macrovascular complications caused by vascular damage. Recently, endothelial progenitor cells (EPCs) raised interest due to their regenerative properties. EPCs are mononuclear cells that are derived from different tissues. Circulating EPCs contribute to regenerating the vessel's intima and restoring vascular function. The ability of EPCs to repair vascular damage depends on their number and functionality. Diabetic patients have a decreased circulating EPC count and impaired EPC function. This may at least partially explain the increased risk of diabetic complications, including the increased cardiovascular risk in these patients. Recent studies have confirmed that many currently available drugs with proven cardiovascular benefits have beneficial effects on EPC count and function. Among these drugs are also medications used to treat different types of diabetes. This manuscript aims to critically review currently available evidence about the ways anti-diabetic treatment affects EPC biology and to provide a broader context considering cardiovascular complications. The therapies that will be discussed include lifestyle adjustments, metformin, sulphonylureas, gut glucosidase inhibitors, thiazolidinediones, dipeptidyl peptidase 4 inhibitors, glucagon-like peptide 1 receptor analogs, sodium-glucose transporter 2 inhibitors, and insulin.

Different methods of bone marrow harvesting influence cell characteristics and purity, affecting clinical outcomes

Background

Bone marrow (BM)-derived stem cells were implanted to induce angiogenesis in patients with no-option critical limb-threatening ischemia. Considering the potential for this therapy, conflicting results related to BM harvesting methods have been reported that could affect stem cell concentrations and quality.

Methods

A total of 75 patients with no-option critical limb-threatening ischemia were treated with BM implantation. For 58 patients, BM was harvested using a BM aspirate concentrate system (Harvest Technologies; group HT) with a standard aspiration needle, followed by an automated centrifugation process, to produce BM aspirate concentrate. For 17 patients, BM was harvested using the Marrow Cellution system (Aspire Medical Innovation; group MC). CD34+ cells/mL, CD117+ cells/mL, CD133+ cells/mL, CD309+ cells/mL, hematocrit, and BM purity were compared between the two BM preparations.

Results

The retrospective analysis of a subset group after adjustment for age shows that the quality of BM obtained using the Marrow Cellution system is better, in terms of purity, than the classic harvesting method before centrifugation. Harvested BM before centrifugation is characterized by a higher percentage of CD133+ cells compared with BM after centrifugation. In contrast, the MC aspirate had a larger amount of very small embryonic-like cells, as indicated by the higher percentage of CD133+, CD34+, and CD45- cells. These differences translated into an increased occurrence of leg amputations in group HT than in group MC and an increase in transcutaneous oxygen pressure in patients treated with BM aspirated using MC.

Conclusions

BM manipulation, such as centrifugation, affects the quality and number of stem cells, with detrimental consequences on clinical outcomes, as reflected by the different amputation rates between the two groups.

Reoxygenation Modulates the Adverse Effects of Hypoxia on Wound Repair

Hypoxia is a major stressor and a prominent feature of pathological conditions, such as bacterial infections, inflammation, wounds, and cardiovascular defects. In this study, we investigated whether reoxygenation has a protective effect against hypoxia-induced acute injury and burn using the C57BL/6 mouse model. C57BL/6 mice were exposed to hypoxia and treated with both acute and burn injuries and were in hypoxia until wound healing. Next, C57BL/6 mice were exposed to hypoxia for three days and then transferred to normoxic conditions for reoxygenation until wound healing. Finally, skin wound tissue was collected to analyze healing-related markers, such as inflammation, vascularization, and collagen. Hypoxia significantly increased inflammatory cell infiltration and decreased vascular and collagen production, and reoxygenation notably attenuated hypoxia-induced infiltration of inflammatory cells, upregulation of pro-inflammatory cytokine levels (IL-6 and TNF-α) in the wound, and remission of inflammation in the wound. Immunofluorescence analysis showed that reoxygenation increased the expression of the angiogenic factor α-SMA and decreased ROS expression in burn tissues compared to hypoxia-treated animals. Moreover, further analysis by qPCR showed that reoxygenation could alleviate the expression of hypoxic-induced inflammatory markers (IL-6 and TNF), increase angiogenesis (SMA) and collagen synthesis (Col I), and thus promote wound healing. It is suggested that oxygen can be further evaluated in combination with oxygen-releasing materials as a supplementary therapy for patients with chronic hypoxic wounds.

Emerging roles of mesenchymal stem cell therapy in patients with critical limb ischemia

Critical limb ischemia (CLI), the terminal stage of peripheral arterial disease (PAD), is characterized by an extremely high risk of amputation and vascular issues, resulting in severe morbidity and mortality. In patients with severe limb ischemia with no alternative therapy options, such as endovascular angioplasty or bypass surgery, therapeutic angiogenesis utilizing cell-based therapies is vital for increasing blood flow to ischemic regions. Mesenchymal stem cells (MSCs) are currently considered one of the most encouraging cells as a regenerative alternative for the surgical treatment of CLI, including restoring tissue function and repairing ischemic tissue via immunomodulation and angiogenesis. The regenerative treatments for limb ischemia based on MSC therapy are still considered experimental. Despite recent advances in preclinical and clinical research studies, it is not recommended for regular clinical use. In this study, we review the immunomodulatory features of MSC besides the current understanding of different sources of MSC in the angiogenic treatment of CLI subjects and their potential applications as therapeutic agents. Specifically, this paper concentrates on the most current clinical application issues, and several recommendations are provided to improve the efficacy of cell therapy for CLI patients.

Autophagy-Sirtuin1(SIRT1) Alleviated the Coronary Atherosclerosis (AS)in Mice through Regulating the Proliferation and Migration of Endothelial Progenitor Cells (EPCs) via wnt/β-catenin/GSK3β Signaling Pathway

BACKGROUND AND PURPOSE

SIRT1 was associated with AS risk and EPCs were reported to participate in the endothelial repair in Coronary Atherosclerosis (CAS). In this study, we explored the role of SIRT1 in AS mice and also its modulation in EPCs.

METHODS AND MATERIALS

ApoE-/-mice were fed on high-fat and high-glucose diet to establish the AS animal model with the normally-raised C57BL/6 mice as a control group. SIRT1 activator, SRT 2104 was injected intravenously into 5 ApoE-/-mice and its inhibitor Nicotinamide was injected in tail in another 5 ApoE-/-mice. Weight changes were recorded. Blood samples were taken from posterior orbital venous plexus and were detected by automatic biochemical analyzer. HE staining displayed the pathological conditions while Immunohistochemistry (IHC) evaluated the CD34+/VEGFR2+ relative density in the aorta tissues. EPCs were isolated from bone marrow and verified using immunofluorescence staining (IFS). The modulatory mechanism of SIRT1 in EPCs were studied by using RT-PCR, MTT, Western Blot and colony formation, scratch methods.

RESULTS

SIRT1 activator negatively regulated the weight and TC, TG and LDL levels, alleviated the lesion conditions and decreased the CD34+/VEGFR2+ density compared to the AS control. In vitro, SIRT1 activator promoted the proliferation and migration of EPCs and activated wnt/β-catenin/GSK3β signaling pathway. SIRT1 activator also inhibited the autophagy biomarkers ATG1 and LC3II. Furthermore, inhibitor of autophagy promoted SIRT1 expression and induced EPC proliferation, migration and activated wnt/β-catenin/GSK3β pathway. The suppression of the wnt/β-catenin/GSK3β pathway inhibited SIRT1 expression in EPCs, attenuated the proliferation and migration and promoted autophagy of EPCs.

CONCLUSION

SIRT1 activation might be protective in AS mice through autophagy inhibition in EPCs via wnt/β-catenin/GSK3β signaling pathway.

Implantation of Hypoxia-Induced Mesenchymal Stem Cell Advances Therapeutic Angiogenesis

Hypoxia preconditioning enhances the paracrine abilities of mesenchymal stem cells (MSCs) for vascular regeneration and tissue healing. Implantation of hypoxia-induced mesenchymal stem cells (hi-MSCs) may further improve limb perfusion in a murine model of hindlimb ischemia. This study is aimed at determining whether implantation of hi-MSCs is an effective modality for improving outcomes of treatment of ischemic artery diseases. We evaluated the effects of human bone marrow-derived MSC implantation on limb blood flow in an ischemic hindlimb model. hi-MSCs were prepared by cell culture under 1% oxygen for 24 hours prior to implantation. A total of 1 × 10⁵ MSCs and hi-MSCs and phosphate-buffered saline (PBS) were intramuscularly implanted into ischemic muscles at 36 hours after surgery. Restoration of blood flow and muscle perfusion was evaluated by laser Doppler perfusion imaging. Blood perfusion recovery, enhanced vessel densities, and improvement of function of the ischemia limb were significantly greater in the hi-MSC group than in the MSC or PBS group. Immunochemistry revealed that hi-MSCs had higher expression levels of hypoxia-inducible factor-1 alpha and vascular endothelial growth factor A than those in MSCs. In addition, an endothelial cell-inducing medium showed high expression levels of vascular endothelial growth factor, platelet endothelial cell adhesion molecule-1, and von Willebrand factor in hi-MSCs compared to those in MSCs. These findings suggest that pretreatment of MSCs with a hypoxia condition and implantation of hi-MSCs advances neovascularization capability with enhanced therapeutic angiogenic effects in a murine hindlimb ischemia model.

CircHIPK3 Plays Vital Roles in Cardiovascular Disease

Circular RNAs (circRNAs) are covalently closed RNAs that function in various physiological and pathological processes. CircRNAs are widely involved in the development of cardiovascular disease (CVD), one of the leading causes of morbidity and mortality worldwide. CircHIPK3 is generated from the second exon of the HIPK3 gene, a corepressor of homeodomain transcription factors. As an exonic circRNA (ecRNA), circHIPK3 is produced through intron-pairing driven circularization facilitated by Alu elements. In the past 5 years, a growing number of studies have revealed the multifunctional roles of circHIPK3 in different diseases, such as cancer and CVD. CircHIPK3 mainly participates in CVD pathogenesis through interacting with miRNAs. This paper summarizes the current literature on the biogenesis and functions of circHIPK3, elucidates the role of circHIPK3 in different CVD patterns, and explores future perspectives.

Antioxidative and Angiogenic Hyaluronic Acid-Based Hydrogel for the Treatment of Peripheral Artery Disease

Peripheral arterial disease (PAD) is a progressive atherosclerotic disorder characterized by blockages of the arteries supplying the lower extremities. Ischemia initiates oxidative damage and mitochondrial dysfunction in the legs of PAD patients, causing injury to the tissues of the leg, significant decline in walking performance, leg pain while walking, and in the most severe cases, nonhealing ulcers and gangrene. Current clinical trials based on cells/stem cells, the trophic factor, or gene therapy systems have shown some promising results for the treatment of PAD. Biomaterial matrices have been explored in animal models of PAD to enhance these therapies. However, current biomaterial approaches have not fully met the essential requirements for minimally invasive intramuscular delivery to the leg. Ideally, a biomaterial should present properties to ameliorate oxidative stress/damage and failure of angiogenesis. Recently, we have created a thermosensitive hyaluronic acid (HA) hydrogel with antioxidant capacity and skeletal muscle-matching stiffness. Here, we further optimized HA hydrogels with the cell adhesion peptide RGD to facilitate the development of vascular-like structures in vitro. The optimized HA hydrogel reduced intracellular reactive oxygen species levels and preserved vascular-like structures against H₂O₂-induced damage in vitro. HA hydrogels also provided prolonged release of the vascular endothelial growth factor (VEGF). After injection into rat ischemic hindlimb muscles, this VEGF-releasing hydrogel reduced lipid oxidation, regulated oxidative-related genes, enhanced local blood flow in the muscle, and improved running capacity of the treated rats. Our HA hydrogel system holds great potential for the treatment of the ischemic legs of patients with PAD.

Construction of transplantable artificial vascular tissue based on adipose tissue-derived mesenchymal stromal cells by a cell coating and cryopreservation technique

Prevascularized artificial three-dimensional (3D) tissues are effective biomaterials for regenerative medicine. We have previously established a scaffold-free 3D artificial vascular tissue from normal human dermal fibroblasts (NHDFs) and umbilical vein-derived endothelial cells (HUVECs) by layer-by-layer cell coating technique. In this study, we constructed an artificial vascular tissue constructed by human adipose tissue-derived stromal cells (hASCs) and HUVECs (ASCVT) by a modified technique with cryopreservation. ASCVT showed a higher thickness with more dense vascular networks than the 3D tissue based on NHDFs. Correspondingly, 3D-cultured ASCs showed higher expression of several angiogenesis-related factors, including vascular endothelial growth factor-A and hepatic growth factor, compared to that of NHDFs. Moreover, perivascular cells in ASCVT were detected by pericyte markers, suggesting the differentiation of hASCs into pericyte-like cells. Subcutaneous transplantation of ASCVTs to nude mice resulted in an engraftment with anastomosis of host's vascular structures at 2 weeks after operation. In the engrafted tissue, the vascular network was surrounded by mural-like structure-forming hASCs, in which some parts developed to form vein-like structures at 4 weeks, suggesting the generation of functional vessel networks. These results demonstrated that cryopreserved human cells, including hASCs, could be used directly to construct the artificial transplantable tissue for regenerative medicine.

The Immunomodulatory Properties of Mesenchymal Stem Cells Play a Critical Role in Inducing Immune Tolerance after Liver Transplantation

Although liver transplantation is considered to be the best choice for patients with end-stage liver diseases, postoperative immune rejection still cannot be overlooked. Patients with liver transplantation have to take immunosuppressive drugs for a long time or even their entire lives, in which heavy economic burden and side effects caused by the drugs have become the major impediment for liver transplantation. There is a growing body of evidences indicating that mesenchymal stem cell (MSC) transplantation, a promising tool in regenerative medicine, can be used as an effective way to induce immune tolerance after liver transplantation based on their huge expansion potential and unique immunomodulatory properties. MSCs have been reported to inhibit innate immunity and adaptive immunity to induce a tolerogenic microenvironment. In in vitro studies, transplanted MSCs show plasticity in immune regulation by altering their viability, migration, differentiation, and secretion in the interactions with the surrounding host microenvironment. In this review, we aim to provide an overview of the current understanding of immunomodulatory properties of MSCs in liver transplantation, to elucidate the potential mechanisms behind MSCs regulating immune response, especially in vivo and the influence of the microenvironment, and ultimately to discuss the feasible strategies to improve the clinical prognosis of liver transplantation. Only after exhaustive understanding of potential mechanisms of the MSC immunomodulation can we improve the safety and effectiveness of MSC treatment and achieve better therapeutic effects.

Long Term Response to Circulating Angiogenic Cells, Unstimulated or Atherosclerotic Pre-Conditioned, in Critical Limb Ischemic Mice

Critical limb ischemia (CLI), the most severe form of peripheral artery disease, results from the blockade of peripheral vessels, usually correlated to atherosclerosis. Currently, endovascular and surgical revascularization strategies cannot be applied to all patients due to related comorbidities, and even so, most patients require re-intervention or amputation within a year. Circulating angiogenic cells (CACs) constitute a good alternative as CLI cell therapy due to their vascular regenerative potential, although the mechanisms of action of these cells, as well as their response to pathological conditions, remain unclear. Previously, we have shown that CACs enhance angiogenesis/arteriogenesis from the first days of administration in CLI mice. Also, the incubation ex vivo of these cells with factors secreted by atherosclerotic plaques promotes their activation and mobilization. Herein, we have evaluated the long-term effect of CACs administration in CLI mice, whether pre-stimulated or not with atherosclerotic factors. Remarkably, mice receiving CACs and moreover, pre-stimulated CACs, presented the highest blood flow recovery, lower progression of ischemic symptoms, and decrease of immune cells recruitment. In addition, many proteins potentially involved, like CD44 or matrix metalloproteinase 9 (MMP9), up-regulated in response to ischemia and decreased after CACs administration, were identified by a quantitative proteomics approach. Overall, our data suggest that pre-stimulation of CACs with atherosclerotic factors might potentiate the regenerative properties of these cells in vivo.

Mussel patterned with 4D biodegrading elastomer durably recruits regenerative macrophages to promote regeneration of craniofacial bone

Crosstalk between bone marrow mesenchymal stem cells (BMSCs) and macrophages plays vital role in bone healing. By investigating the mechanism of collagen membrane-guided bone regeneration, we found compact structure and rapid membrane degradation compromised the duration of M2 macrophages influx, which restricts the recruitment of BMSCs that is essential for bone healing. To tackle this issue, a biodegrading elastomeric compound consisting of poly(glycerol sebacate) (PGS) and polycaprolactone (PCL) was fabricated into hierarchically porous membrane. The rational design of 3D microstructure enabled sufficient polydopamine (PDA) coating. Without any addition of growth factors, the 3D-patterned PDA membrane enables early and durable influx of M2 macrophages, which in turn promotes BMSCs recruitment and osteogenic differentiation. Furthermore, 4D-morphing of the membrane fully regenerates the dome shaped calvarial bone as well as arc-shape bone in peri-implant alveolar defect without filling xenogenous substitute. This study revealed the superiority of 3D printed microstructures in immunomodulatory materials. The availability of 4D-morphing for PGS/PCL construct expanded their advantages in reconstructing craniofacial bone.

Intravascular Application of Labelled Cell Spheroids: An Approach for Ischemic Peripheral Artery Disease

Mesenchymal stem cells (MSC) are known for their vascular regeneration capacity by neoangiogenesis. Even though, several delivery approaches exist, particularly in the case of intravascular delivery, only limited number of cells reach the targeted tissue and are not able to remain on site. Applicated cells exhibit poor survival accompanied with a loss of functionality. Moreover, cell application techniques lead to cell death and impede the overall MSC function and survival. 3D cell spheroids mimic the physiological microenvironment, thus, overcoming these limitations. Therefore, in this study we aimed to evaluate and assess the feasibility of 3D MSCs spheroids for endovascular application, for treatment of ischemic peripheral vascular pathologies. Multicellular 3D MSC spheroids were generated at different cell seeding densities, labelled with ultra-small particles of iron oxide (USPIO) and investigated in vitro in terms of morphology, size distribution, mechanical stability as well as ex vivo with magnetic resonance imaging (MRI) to assess their trackability and distribution. Generated 3D spheroids were stable, viable, maintained stem cell phenotype and were easily trackable and visualized via MRI. MSC 3D spheroids are suitable candidates for endovascular delivery approaches in the context of ischemic peripheral vascular pathologies.

Combined NOX/ROS/PKC Signaling Pathway and Metabolomic Analysis Reveals the Mechanism of TRAM34-Induced Endothelial Progenitor Cell Senescence

It has been shown that the KCa3.1 channel-specific blocker, TRAM34, is a promising antiatherosclerosis (AS) agent, but its side effects restrict its clinical application. Notably, its effect on endothelial progenitor cells (EPCs) is unclear. We aim to unravel the effect of TRAM34 on EPCs and identify the underlying mechanism. Rats were injected intraperitoneally with TRAM34, and EPCs were isolated from bone marrow. The gene and protein levels of corresponding factors were detected by real-time PCR, enzyme-linked immunosorbent assay, western blotting, and fluorescence-activated cell sorting. Liquid chromatography-tandem mass spectrometry (LC-MS) was applied to detect metabolite differences. We showed that when rats were treated with TRAM34 in vivo, colony formation and proliferation of early EPCs were reduced, but their senescence and apoptosis were enhanced. Moreover, TRAM34 enhanced NOX activity, promoted an increase in intracellular ROS levels, increased PKC expression, and subsequently promoted EPC senescence, which is unfavorable for EPC angiogenesis in vivo and in vitro. Combining these results with LC-MS data, we found that TRAM34 significantly promoted pyrimidine and purine metabolism, leading to cellular senescence. Furthermore, the NOX inhibitor, Setanaxib, enhanced antioxidant metabolic pathways, especially S-adenosylmethioninamine (SAM) metabolism, to exert an antisenescence effect. Finally, we confirmed that SAM alleviates TRAM34-induced cellular senescence, suggesting an efficient approach to improve the quality of endogenous EPCs. This study reveals the mechanism of TRAM34-induced EPC senescence, providing a solution for the extended application of KCa3.1 inhibitor in AS.

Hydrogel-based therapeutic angiogenesis: An alternative treatment strategy for critical limb ischemia

Critical limb ischemia (CLI) is the most severe clinical manifestation of peripheral arterial disease (PAD), resulting in the total or partial loss of limb function. Although the conventional treatment strategy of CLI (e.g., medical treatment and surgery) can improve blood perfusion and restore limb function, many patients are unsuitable for these strategies and they still face the threats of amputation or death. Therapeutic angiogenesis, as a potential solution for these problems, attempts to manipulate blood vessel growth in vivo for augment perfusion without the help of extra pharmaceutics and surgery. With the rise of interdisciplinary research, regenerative medicine strategies provide new possibilities for treating many clinical diseases. Hydrogel, as an excellent biocompatibility material, is an ideal candidate for delivering bioactive molecules and cells for therapeutic angiogenesis. Besides, hydrogel could precisely deliver, control release, and keep the bioactivity of cargos, making hydrogel-based therapeutic angiogenesis a new strategy for CLI therapy. In this review, we comprehensively discuss the approaches of hydrogel-based strategy for CLI treatment as well as their challenges, and future directions.

A low-temperature-printed hierarchical porous sponge-like scaffold that promotes cell-material interaction and modulates paracrine activity of MSCs for vascularized bone regeneration

Mesenchymal stem cells (MSCs) secrete paracrine trophic factors that are beneficial for tissue regeneration. In this study, a sponge-like scaffold with hierarchical and interconnected pores was developed using low-temperature deposition modeling (LDM) printing. Its effects on the cellular behavior, especially on the paracrine secretion patterns of MSCs, were comprehensively investigated. We found that compared with the scaffolds printed via the fused deposition modeling (FDM) technique, the LDM-printed sponges enhanced the adhesion, retention, survival, and ingrowth of MSCs and promoted cell-material interactions. Moreover, the paracrine functions of the cultured MSCs on the LDM-printed sponges were improved, with significant secretion of upregulated immunomodulatory, angiogenic, and osteogenic factors. MSCs on the LDM-printed sponges exert beneficial paracrine effects on multiple regenerative processes, including macrophage polarization, tube formation, and osteogenesis, verifying the enhanced immunomodulatory, angiogenic, and osteogenic potential. Further protein function assays indicated that focal adhesion kinase (FAK), downstream AKT, and yes-associated-protein (YAP) signaling might participate in the required mechanotransductive pathways, through which the hierarchical porous structures stimulated the paracrine effects of MSCs. In a rat distal femoral defect model, the MSC-laden LDM-printed sponges significantly promoted vascularized bone regeneration. The results of the present study demonstrate that the hierarchical porous biomimetic sponges prepared via LDM printing have potential applications in tissue engineering based on their cell-material interaction promotion and MSC paracrine function modulation effects. Furthermore, our findings suggest that the optimization of biomaterial properties to direct the paracrine signaling of MSCs would enhance tissue regeneration.

Therapeutic Biomaterial Approaches to Alleviate Chronic Limb Threatening Ischemia

Chronic limb threatening ischemia (CLTI) is a severe condition defined by the blockage of arteries in the lower extremities that leads to the degeneration of blood vessels and is characterized by the formation of non-healing ulcers and necrosis. The gold standard therapies such as bypass and endovascular surgery aim at the removal of the blockage. These therapies are not suitable for the so-called "no option patients" which present multiple artery occlusions with a likelihood of significant limb amputation. Therefore, CLTI represents a significant clinical challenge, and the efforts of developing new treatments have been focused on stimulating angiogenesis in the ischemic muscle. The delivery of pro-angiogenic nucleic acid, protein, and stem cell-based interventions have limited efficacy due to their short survival. Engineered biomaterials have emerged as a promising method to improve the effectiveness of these latter strategies. Several synthetic and natural biomaterials are tested in different formulations aiming to incorporate nucleic acid, proteins, stem cells, macrophages, or endothelial cells in supportive matrices. In this review, an overview of the biomaterials used alone and in combination with growth factors, nucleic acid, and cells in preclinical models is provided and their potential to induce revascularization and regeneration for CLTI applications is discussed.

Oxygen-release microspheres capable of releasing oxygen in response to environmental oxygen level to improve stem cell survival and tissue regeneration in ischemic hindlimbs

Stem cell transplantation has been extensively explored to promote ischemic limb vascularization and skeletal muscle regeneration. Yet the therapeutic efficacy is low due to limited cell survival under low oxygen environment of the ischemic limbs. Therefore, continuously oxygenating the transplanted cells has potential to increase their survival. During tissue regeneration, the number of blood vessels are gradually increased, leading to the elevation of tissue oxygen content. Accordingly, less exogenous oxygen is needed for the transplanted cells. Excessive oxygen may induce reactive oxygen species (ROS) formation, causing cell apoptosis. Thus, it is attractive to develop oxygen-release biomaterials that are responsive to the environmental oxygen level. Herein, we developed oxygen-release microspheres whose oxygen release was controlled by oxygen-responsive shell. The shell hydrophilicity and degradation rate decreased as the environmental oxygen level increased, leading to slower oxygen release. The microspheres were capable of directly releasing molecular oxygen, which are safer than those oxygen-release biomaterials that release hydrogen peroxide and rely on its decomposition to form oxygen. The released oxygen significantly enhanced mesenchymal stem cell (MSC) survival without inducing ROS production under hypoxic condition. Co-delivery of MSCs and microspheres to the mouse ischemic limbs ameliorated MSC survival, proliferation and paracrine effects under ischemic conditions. It also significantly accelerated angiogenesis, blood flow restoration, and skeletal muscle regeneration without provoking tissue inflammation. The above results demonstrate that the developed microspheres have potential to augment cell survival in ischemic tissues, and promote ischemic tissue regeneration in a safer and more efficient manner.

Exosomes: Biomarkers and Therapeutic Targets of Diabetic Vascular Complications

Diabetic vascular complications (DVC) including macrovascular and microvascular lesions, have a significant impact on public health, and lead to increased patient mortality. Disordered intercellular cascades play a vital role in diabetic systemic vasculopathy. Exosomes participate in the abnormal signal transduction of local vascular cells and mediate the transmission of metabolic disorder signal molecules in distant organs and cells through the blood circulation. They can store different signaling molecules in the membrane structure and release them into the blood, urine, and tears. In recent years, the carrier value and therapeutic effect of exosomes derived from stem cells have garnered attention. Exosomes are not only a promising biomarker but also a potential target and tool for the treatment of DVC. This review explored changes in the production process of exosomes in the diabetic microenvironment and exosomes' early warning role in DVC from different systems and their pathological processes. On the basis of these findings, we discussed the future direction of exosomes in the treatment of DVC, and the current limitations of exosomes in DVC research.

REX-001, a BM-MNC Enriched Solution, Induces Revascularization of Ischemic Tissues in a Murine Model of Chronic Limb-Threatening Ischemia

Background: Bone Marrow Mononuclear Cells (BM-MNC) constitute a promising alternative for the treatment of Chronic Limb-Threatening ischemia (CLTI), a disease characterized by extensive blockade of peripheral arteries, clinically presenting as excruciating pain at rest and ischemic ulcers which may lead to gangrene and amputation. BM-MNC implantation has shown to be efficient in promoting angiogenesis and ameliorating ischemic symptoms in CLTI patients. However, the variability seen between clinical trials makes necessary a further understanding of the mechanisms of action of BM-MNC, and moreover, to improve trial characteristics such as endpoints, inclusion/exclusion criteria or drug product compositions, in order to implement their use as stem-cell therapy.

Materials: Herein, the effect of REX-001, a human-BM derived cell suspension enriched for mononuclear cells, granulocytes and CD34+ cells, has been assessed in a murine model of CLTI. In addition, a REX-001 placebo solution containing BM-derived red blood cells (BM-RBCs) was also tested. Thus, 24 h after double ligation of the femoral artery, REX-001 and placebo were administrated intramuscularly to Balb-c nude mice (n:51) and follow-up of ischemic symptoms (blood flow perfusion, motility, ulceration and necrosis) was carried out for 21 days. The number of vessels and vascular diameter sizes were measured within the ischemic tissues to evaluate neovascularization and arteriogenesis. Finally, several cell-tracking assays were performed to evaluate potential biodistribution of these cells.

Results: REX-001 induced a significant recovery of blood flow by increasing vascular density within the ischemic limbs, with no cell translocation to other organs. Moreover, cell tracking assays confirmed a decrease in the number of infused cells after 2 weeks post-injection despite on-going revascularization, suggesting a paracrine mechanism of action.

Conclusion: Overall, our data supported the role of REX-001 product to improve revascularization and ischemic reperfusion in CLTI.

Rejuvenation of Senescent Endothelial Progenitor Cells by Extracellular Vesicles Derived From Mesenchymal Stromal Cells

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EVs derived from young, but not aged, MSCs rejuvenate senescent EPCs in vitro, recapitulating the effect of MSC transplantation.

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Aged MSCs can be genetically modified to produce tailored EVs with increased EPC rejuvenation capacity in vitro and increased angiogenesis capacity following ischemic event in vivo.

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EVs represent a promising platform to develop an acellular therapeutic approach in regenerative medicine for cardiovascular diseases.

Mesenchymal stromal cell (MSC) transplantation is a form of the stem-cell therapy that has shown beneficial effects for many diseases. The use of stem-cell therapy, including MSC transplantation, however, has limitations such as the tumorigenic potential of stem cells and the lack of efficacy of aged autologous cells. An ideal therapeutic approach would keep the beneficial effects of MSC transplantation while circumventing the limitations associated with the use of intact stem cells. This study provides proof-of-concept evidence that MSC-derived extracellular vesicles represent a promising platform to develop an acellular therapeutic approach that would just do that. Extracellular vesicles are membranous vesicles secreted by MSCs and contain bioactive molecules to mediate communication between different cells. Extracellular vesicles can be taken up by recipient cells, and once inside the recipient cells, the bioactive molecules are released to exert the beneficial effects on the recipient cells. This study, for the first time to our knowledge, shows that extracellular vesicles secreted by MSCs recapitulate the beneficial effects of MSCs on vascular repair and promote blood vessel regeneration after ischemic events. Furthermore, MSCs from aged donors can be engineered to produce extracellular vesicles with improved regenerative potential, comparable to MSCs from young donors, thus eliminating the need for allogenic young donors for elderly patients.

[Problems and prospects of cell therapy for critical ischaemia of lower limbs]

BACKGROUND

Cell therapy was proposed as a procedure of indirect revascularization for patients with critical ischaemia of lower extremities for whom endovascular and surgical revascularization is impossible. We present herein a review of the state of the art of studies in the field of cell therapy of this cohort of patients.

BASIC PROVISIONS

Cell therapy has proved safe, however, the results of studies of efficacy are relatively ambiguous and unconvincing. The number of patients in separately taken clinical trials is minimal. The reviewed studies differed not only by heterogeneity of the cell types used but by the routes of administration of cells (cells were delivered either intramuscularly (predominantly) or intraarterially) and the duration of follow up (time of assessment and duration of follow up varied from 1 month to 2 years). One of the problems became the lack of the routine study of the angiogenic potential of stem cells prior to their clinical application. It is known that the angiogenic activity of multipotent cells of apparently healthy patients may differ from that of patients suffering from atherosclerosis, chronic renal failure, diabetes.

CONCLUSIONS

It is supposed that treatment with stem cells or precursor cells is more efficient as compared to protein or gene therapy not only owing to direct vasculogenic properties but a paracrine action through excretion of proangiogenic biologically active substances. More studies with larger cohorts are necessary to provide stronger safety and efficacy data on cell therapy. Besides, a promising trend in the field of cellular approaches is modulation of regenerative capability of stem cells, which may help overcome difficulties in understanding the place of cell therapy in therapeutic angiogenesis.

Chemerin enhances the adhesion and migration of human endothelial progenitor cells and increases lipid accumulation in mice with atherosclerosis

Background

The role of adipokines in the development of atherosclerosis (AS) has received increasing attention in recent years. This study aimed to explore the effects of chemerin on the functions of human endothelial progenitor cells (EPCs) and to investigate its role in lipid accumulation in ApoE-knockout (ApoE−/−) mice.

Methods

EPCs were cultured and treated with chemerin together with the specific p38 mitogen-activated protein kinase (MAPK) inhibitor SB 203580 in a time- and dose-dependent manner. Changes in migration, adhesion, proliferation and the apoptosis rate of EPCs were detected. ApoE−/− mice with high-fat diet-induced AS were treated with chemerin with or without SB 203580. Weights were recorded, lipid indicators were detected, and tissues sections were stained.

Results

The data showed that chemerin enhanced the adhesion and migration abilities of EPCs, and reduced the apoptosis ratio and that this effect might be mediated through the p38 MAPK pathway. Additionally, chemerin increased the instability of plaques. Compared with the control group and the inhibitor group, ApoE−/− mice treated with chemerin protein had more serious arterial stenosis, higher lipid contents in plaques and decreased collagen. Lipid accumulation in the liver and kidney and inflammation in the hepatic portal area were enhanced by treatment with chemerin, and the size of adipocytes also increased after chemerin treatment. In conclusion, chemerin can enhance the adhesion and migration abilities of human EPCs and reduce the apoptosis ratio. In animals, chemerin can increase lipid accumulation in atherosclerotic plaques and exacerbate plaques instability. At the same time, chemerin can cause abnormal lipid accumulation in the livers and kidneys of model animals. After specifically blocking the p38 MAPK pathway, the effect of chemerin was reduced.

Conclusions

In conclusion, this study showed that chemerin enhances the adhesion and migration abilities of EPCs and increases the instability of plaques and abnormal lipid accumulation in ApoE−/− mice. Furthermore, these effects might be mediated through the p38 MAPK pathway.

Synthesis and characterization of a hyaluronic acid-based hydrogel with antioxidative and thermosensitive properties

Peripheral arterial disease (PAD) is initiated by progressive atherosclerotic blockages of the arteries supplying the lower extremities. The most common presentation of PAD is claudication (leg pain and severe walking limitation), with many patients progressing to limb threatening ischemia and amputation. Biomaterial approaches are just beginning to be explored in the therapy of PAD with different materials now being evaluated for the delivery of cells or growth factors in animal models of PAD. A biomaterial matrix optimized for minimally invasive injection in the ischemic leg muscles of patients with PAD is urgently needed. There are several important requirements for optimal delivery, retention, and performance of a biomaterial matrix in the mechanically, histologically, and biochemically dynamic intramuscular environment of the PAD leg. Ideally, the material should have mechanical properties matching those of the recipient muscle, undergo minimal swelling, and should introduce properties that can ameliorate the mechanisms operating in PAD like oxidative stress and damage. Here we have developed an injectable, antioxidative, and thermosensitive hydrogel system based on hyaluronic acid (HA). We first synthesized a unique crosslinker of disulfide-modified poloxamer F127 diacrylate. This crosslinker led to the creation of a thermosensitive HA hydrogel with minimal swelling and muscle-matching mechanical properties. We introduced unique disulfide groups into hydrogels which functioned as an effective reactive oxygen species scavenger, exhibited hydrogen peroxide (H2O2)-responsive degradation, and protected cells against H2O2-induced damage. Our antioxidative thermosensitive HA hydrogel system holds great potential for the treatment of the ischemic legs of patients with PAD.

A nitric oxide-releasing hydrogel for enhancing the therapeutic effects of mesenchymal stem cell therapy for hindlimb ischemia

Therapeutic angiogenesis with mesenchymal stem cells (MSCs) is promising for the clinical treatment of peripheral artery disease (PAD). However, the heterogeneous proangiogenic nature of MSCs is a key challenge in developing more effective treatments with MSCs for therapeutic angiogenesis purposes. Here, we propose to enhance the therapeutic function of human placenta-derived MSCs (hP-MSCs) in hindlimb ischemia therapy by using nitric oxide (NO)-releasing chitosan hydrogel (CS-NO). Our data showed that the co-transplantation of CS-NO hydrogel with hP-MSCs remarkably improved the grafting of hP-MSCs and ameliorated the functional recovery of ischemic hindlimbs. Moreover, we found that the neovascularization of damaged hindlimbs was significantly increased after co-transplanting CS-NO hydrogel and hP-MSCs, as confirmed by bioluminescence imaging (BLI). Further analysis revealed an endothelial-like status transformation of hP-MSCs in the presence of NO, which was identified as a potential mechanism contributing to the enhanced endothelium-protective and proangiogenic capacities of hP-MSCs that promote angiogenesis in mouse models of hindlimb ischemia. In conclusion, this study provides a promising approach for using NO hydrogel to improve the proangiogenic potency of MSCs in ischemic diseases, and the strategy used here facilitates the development of controlled-release scaffolds for enhancing the therapeutic efficiency of MSCs in angiogenic therapy. STATEMENT OF SIGNIFICANCE: The heterogeneous proangiogenic nature of mesenchymal stem cells (MSCs) is a key challenge in developing more effective treatments with MSCs for therapeutic angiogenesis purposes. In this study, we investigated whether nitric oxide (NO)-releasing chitosan hydrogel (CS-NO) could improve the proangiogenic potency of MSCs in ischemic diseases. Our results revealed an endothelial-like status transformation of human placenta-derived MSCs (hP-MSCs) in the presence of NO, which was identified as a potential mechanism contributing to the enhanced endothelium-protective and proangiogenic capacities of hP-MSCs that promote angiogenesis in mouse models of hindlimb ischemia. The strategy for enhancing the pro-angiogenic activity of MSCs with biomaterials provides a practical idea for overcoming the challenges associated with the clinical application of MSCs in therapeutic angiogenesis.

Adipose-derived mesenchymal stromal cells promote corneal wound healing by accelerating the clearance of neutrophils in cornea

The dome-shaped cornea is a transparent, non-vascularized, and epithelialized highly organized tissue. Physical and chemical injuries may trigger corneal wound healing (CWH) response and result in neovascularization that impairs the visual function. CWH involves not only migration, proliferation, and differentiation of the cells in different layers of cornea, but also the mobilization of immune cells. We demonstrated here that human adipose-derived mesenchymal stromal cells (ADSCs) could effectively inhibit neovascularization during ethanol-induced injury in mouse cornea. Importantly, we found that while neutrophils are essential for CWH, excessive and prolonged neutrophil retention during the granulation stage contributes to neovascularization. ADSCs were found to promote the clearance of neutrophils in the cornea during the granulation stage, likely via increasing the reverse transendothelial cell migration of CXCR4high neutrophils from cornea to the lung. Our results demonstrate that ADSCs are effective in treating CWH-induced neovascularization and modulation of neutrophil clearance could be novel strategies for better vision recovery after injury.

Combined Transplantation of Adipose Tissue-Derived Stem Cells and Endothelial Progenitor Cells Improve Diabetic Erectile Dysfunction in a Rat Model

Erectile dysfunction (ED) is a common complication in men suffered with diabetic mellitus. Stem cell transplantation is a promising strategy for the treatment of diabetic ED (DED). In this study, we evaluated whether combined transplantation of adipose tissue-derived stem cells (ADSCs) and endothelial progenitor cells (EPCs) could improve the erectile function of the DED rat model. DED rats were induced via intraperitoneal injection of streptozotocin (50 mg/kg), and ED was screened by apomorphine (100 mg/kg). DED rats were divided into 4 groups (n = 14 each): DED, ADSC, EPC, and ADSC/EPC group. Another 14 age-matched male SD rats with normal erectile function were served as the normal group. The normal group and the DED group were received intracavernous injection with phosphate-buffered saline (PBS). And the other groups were received intracavernous injection with ADSCs (1 × 10⁶), EPCs (1 × 10⁶), and ADSCs/EPCs (0.5 × 10⁶/0.5 × 10⁶), respectively. The total intracavernous pressure (ICP) and mean arterial pressure (MAP) were recorded at day 28 after injection. The endothelium, smooth muscle, and penile dorsal nerves were assessed within cavernoursal tissue. On day 28 after injection, the ADSC/EPC group displayed more significantly enhanced ICP and ICP/MAP than the DED or ADSC or EPC group (p < 0.05). Immunofluorescent analysis and western blot demonstrated that the improvement of erectile function in the ADSC/EPC5 group was associated with increased expression of endothelial marker (CD31) and the correction of eNOS-cGMP-NO signaling. More 5-ethynyl-2′-deoxyuridine- (EdU-) positive EPCs could be found lining in the cavernous endothelial layer in the ADSC/EPC group than the EPC group, which was attributed to the paracrine of vascular endothelial growth factor (VEGF) and stromal-derived factor-1 (SDF-1) by ADSCs. Combined transplantation of ADSCs and EPCs has a synergic effect in repairing the endothelial function of DED rats, and the underlying mechanism might be the paracrine of VEGF and SDF-1 by ADSCs, which improves the recruitment and proliferation of EPCs in the cavernosum.

Atherosclerotic Pre-Conditioning Affects the Paracrine Role of Circulating Angiogenic Cells Ex-Vivo

In atherosclerosis, circulating angiogenic cells (CAC), also known as early endothelial progenitor cells (eEPC), are thought to participate mainly in a paracrine fashion by promoting the recruitment of other cell populations such as late EPC, or endothelial colony-forming cells (ECFC), to the injured areas. There, ECFC replace the damaged endothelium, promoting neovascularization. However, despite their regenerative role, the number and function of EPC are severely affected under pathological conditions, being essential to further understand how these cells react to such environments in order to implement their use in regenerative cell therapies. Herein, we evaluated the effect of direct incubation ex vivo of healthy CAC with the secretome of atherosclerotic arteries. By using a quantitative proteomics approach, 194 altered proteins were identified in the secretome of pre-conditioned CAC, many of them related to inhibition of angiogenesis (e.g., endostatin, thrombospondin-1, fibulins) and cell migration. Functional assays corroborated that healthy CAC released factors enhanced ECFC angiogenesis, but, after atherosclerotic pre-conditioning, the secretome of pre-stimulated CAC negatively affected ECFC migration, as well as their ability to form tubules on a basement membrane matrix assay. Overall, we have shown here, for the first time, the effect of atherosclerotic factors over the paracrine role of CAC ex vivo. The increased release of angiogenic inhibitors by CAC in response to atherosclerotic factors induced an angiogenic switch, by blocking ECFC ability to form tubules in response to pre-conditioned CAC. Thus, we confirmed here that the angiogenic role of CAC is highly affected by the atherosclerotic environment.

The neovascularization effect of dedifferentiated fat cells

Mature adipocyte-derived dedifferentiated fat (DFAT) cells can be prepared efficiently and with minimal invasiveness to the donor. They can be utilized as a source of transplanted cells during therapy. Although the transplantation of DFAT cells into an ischemic tissue enhances angiogenesis and increases vascular flow, there is little information regarding the mechanism of the therapeutic angiogenesis. To further study this, mice ischemic hindlimb model was used. It was confirmed that in comparison with the adipose derived stem cells and fibroblasts, the transplantation of DFAT cells led to a significant improvement in the blood flow and increased mature blood vessel density. The ability of DFAT cells to secrete angiogenic factors in hypoxic conditions and upon co-culture with vascular endothelial cells was then examined. Furthermore, we examined the possibility that DFAT cells differentiating into pericytes. The therapeutic angiogenic effects of DFAT cells were observed by the secretion of angiogenic factors and pericyte differentiation by transforming growth factor β1 signalling via Smad2/3. DFAT cells can be prepared with minimal invasiveness and high efficiency and are expected to become a source of transplanted cells in the future of angiogenic cell therapy.

Identification of the initial molecular changes in response to circulating angiogenic cells-mediated therapy in critical limb ischemia

Background

Critical limb ischemia (CLI) constitutes the most aggressive form of peripheral arterial occlusive disease, characterized by the blockade of arteries supplying blood to the lower extremities, significantly diminishing oxygen and nutrient supply. CLI patients usually undergo amputation of fingers, feet, or extremities, with a high risk of mortality due to associated comorbidities.

Circulating angiogenic cells (CACs), also known as early endothelial progenitor cells, constitute promising candidates for cell therapy in CLI due to their assigned vascular regenerative properties. Preclinical and clinical assays with CACs have shown promising results. A better understanding of how these cells participate in vascular regeneration would significantly help to potentiate their role in revascularization.

Herein, we analyzed the initial molecular mechanisms triggered by human CACs after being administered to a murine model of CLI, in order to understand how these cells promote angiogenesis within the ischemic tissues.

Methods

Balb-c nude mice (n:24) were distributed in four different groups: healthy controls (C, n:4), shams (SH, n:4), and ischemic mice (after femoral ligation) that received either 50 μl physiological serum (SC, n:8) or 5 × 10⁵ human CACs (SE, n:8). Ischemic mice were sacrificed on days 2 and 4 (n:4/group/day), and immunohistochemistry assays and qPCR amplification of Alu-human-specific sequences were carried out for cell detection and vascular density measurements. Additionally, a label-free MS-based quantitative approach was performed to identify protein changes related.

Results

Administration of CACs induced in the ischemic tissues an increase in the number of blood vessels as well as the diameter size compared to ischemic, non-treated mice, although the number of CACs decreased within time. The initial protein changes taking place in response to ischemia and more importantly, right after administration of CACs to CLI mice, are shown.

Conclusions

Our results indicate that CACs migrate to the injured area; moreover, they trigger protein changes correlated with cell migration, cell death, angiogenesis, and arteriogenesis in the host. These changes indicate that CACs promote from the beginning an increase in the number of vessels as well as the development of an appropriate vascular network.

Graphical abstract

Ophiopogonin D promotes bone regeneration by stimulating CD31hi EMCNhi vessel formation

Objectives

CD31^hiEMCN^hi vessels (CD31, also known as PECAM1 [platelet and endothelial cell adhesion molecule 1]; EMCN, endomucin), which are strongly positive for CD31 and endomucin, couple angiogenesis and osteogenesis. However, the role of CD31^hiEMCN^hi vessels in bone regeneration remains unknown. In the present study, we investigated the role of CD31^hiEMCN^hi vessels in the process of bone regeneration.

Materials and Methods

We used endothelial‐specific Krüppel like factor 3 (Klf3) knockout mice and ophiopogonin D treatment to interfere with CD31^hiEMCN^hi vessel formation. We constructed a bone regeneration model by surgical ablation of the trabecular bone. Immunofluorescence and micro‐computed tomography (CT) were used to detect CD31^hiEMCN^hi vessels and bone formation.

Results

CD31^hiEMCN^hi vessels participate in the process of bone regeneration, such that endothelial‐specific Klf3 knockout mice showed increased CD31^hiEMCN^hi vessels and osteoprogenitors in the bone regeneration area, and further accelerated bone formation. We also demonstrated that the natural compound, ophiopogonin D, acts as a KLF3 inhibitor to promote vessels formation both in vitro and in vivo. Administration of ophiopogonin D increased the abundance of CD31^hiEmcn^hi vessels and accelerated bone healing.

Conclusions

Our findings confirmed the important role of CD31^hiEmcn^hi vessels in bone regeneration and provided a new target to treat bone fracture or promote bone regeneration.

Exosomal circHIPK3 Released from Hypoxia-Pretreated Cardiomyocytes Regulates Oxidative Damage in Cardiac Microvascular Endothelial Cells via the miR-29a/IGF-1 Pathway

Background/Aims

Circular RNAs (circRNAs) are a class of endogenous noncoding RNAs that regulate gene expression in eukaryotes. Recently, exosomes from cardiomyocytes (CMs) have been found to facilitate cell proliferation and survival by transporting various bioactive molecules, including circRNA. However, the functions of exosomal circRNAs are not clear. The present research is aimed at determining whether circHIPK3 released from hypoxia-pretreated CMs is transferred into cardiac microvascular endothelial cells (CMVECs) by exosomes and becomes functionally active in the CMVECs under oxidative stress conditions.

Methods

Quantitative polymerase chain reactions were conducted to detect the expression pattern of circHIPK3 in CMVECs under oxidative stress. Annexin V-FITC/propidium iodide (PI) staining assays, TUNEL assays, ROS assays, and Western blot analysis were conducted to detect the role of exosomal circHIPK3 in CMVEC function in vitro. Luciferase activity assays and RNA immunoprecipitation studies were conducted in vitro to reveal the mechanism of circHIPK3-mediated CMVEC function.

Results

circHIPK3 expression was significantly upregulated in hypoxic exosomes (HPC-exos) compared with normoxic exosomes (Nor-exos). Moreover, HPC-exos induced stronger antioxidant effects than Nor-exos. The silencing or overexpression of circHIPK3 changed CMVEC survival under oxidative conditions in vitro. Furthermore, circHIPK3 silencing in HPC-exos abrogated the protective effects of HPC-exos in CMVECs, as shown by increased levels of apoptosis, ROS, MDA, and proapoptotic proteins. circHIPK3 acted as an endogenous miR-29a sponge to sequester and inhibit miR-29a activity, which led to increased IGF-1 expression. The ectopic expression of miR-29a mimicked the effect of circHIPK3 silencing in CMVECs in vitro.

Conclusions

circHIPK3 in HPC-exos plays a role in CMVECs under oxidative conditions through miR-29a-mediated IGF-1 expression, leading to a decrease in oxidative stress-induced CMVECs dysfunction. These data suggest that the exosomal circRNA in CMs is a potential target to control CMVECs dysfunction under oxidative conditions.

Human Umbilical Cord-Derived Mesenchymal Stem Cells Relieve Hind Limb Ischemia by Promoting Angiogenesis in Mice

Chronic critical limb ischemia (CLI) represents a clinical end stage of peripheral arterial disease. Many CLI patients are ineligible for conventional revascularization therapies; thus, it is urgent to explore an alternative strategy to rescue the ischemic limb. Recent stem cell studies have greatly developed the field of therapeutic angiogenesis, which aims to significantly improve the limb blood supply. In our study, bone marrow mesenchymal stem cells (BMMSCs) served as the control to evaluate the function of umbilical cord mesenchymal stem cells (UCMSCs) in enhancing angiogenesis. We compared gene expression between BMMSCs and UCMSCs, and a bioinformatics analysis indicated that both UCMSCs and BMMSCs could stimulate angiogenesis and angiogenesis-related factors were upregulated in UCMSCs. In vitro assays indicated that both BMMSCs and UCMSCs promoted human umbilical vein endothelial cell proliferation, migration, and tube formation, and the effects of UCMSCs were more obvious. Consistent with in vitro results, both UCMSCs and BMMSCs improved the limb blood supply in a mouse model of hind limb ischemia, in which UCMSCs promoted angiogenesis more significantly. Finally, we found that activation of ERK and PI3K-Akt pathways might be the mechanism by which UCMSCs promote angiogenesis. These results indicate that UCMSCs play an important role in therapeutic angiogenesis to improve limb blood perfusion.

Research Status of Mesenchymal Stem Cells in Liver Transplantation

Liver transplantation has been deemed the best choice for end-stage liver disease patients but immune rejection after surgery is still a serious problem. Patients have to take immunosuppressive drugs for a long time after liver transplantation, and this often leads to many side effects. Mesenchymal stem cells (MSCs) gradually became of interest to researchers because of their powerful immunomodulatory effects. In the past, a large number of in vitro and in vivo studies have demonstrated the great potential of MSCs for participation in posttransplant immunomodulation. In addition, MSCs also have properties that may potentially benefit patients undergoing liver transplantation. This article aims to provide an overview of the current understanding of the immunomodulation achieved by the application of MSCs in liver transplantation, to discuss the problems that may be encountered when using MSCs in clinical practice, and to describe some of the underlying capabilities of MSCs in liver transplantation. Cell–cell contact, soluble molecules, and exosomes have been suggested to be critical approaches to MSCs’ immunoregulation in vitro; however, the exact mechanism, especially in vivo, is still unclear. In recent years, the clinical safety of MSCs has been proven by a series of clinical trials. The obstacles to the clinical application of MSCs are decreasing, but large sample clinical trials involving MSCs are still needed to further study their clinical effects.

Critical limb ischemia: Current and novel therapeutic strategies

Critical limb ischemia (CLI) is the advanced stage of peripheral artery disease spectrum and is defined by limb pain or impending limb loss because of compromised blood flow to the affected extremity. Current conventional therapies for CLI include amputation, bypass surgery, endovascular therapy, and pharmacological approaches. Although these conventional therapeutic strategies still remain as the mainstay of treatments for CLI, novel and promising therapeutic approaches such as proangiogenic gene/protein therapies and stem cell-based therapies have emerged to overcome, at least partially, the limitations and disadvantages of current conventional therapeutic approaches. Such novel CLI treatment options may become even more effective when other complementary approaches such as utilizing proper bioscaffolds are used to increase the survival and engraftment of delivered genes and stem cells. Therefore, herein, we address the benefits and disadvantages of current therapeutic strategies for CLI treatment and summarize the novel and promising therapeutic approaches for CLI treatment. Our analyses also suggest that these novel CLI therapeutic strategies show considerable advantages to be used when current conventional methods have failed for CLI treatment.

Mesenchymal Stem Cells for Regenerative Medicine

In recent decades, the biomedical applications of mesenchymal stem cells (MSCs) have attracted increasing attention. MSCs are easily extracted from the bone marrow, fat, and synovium, and differentiate into various cell lineages according to the requirements of specific biomedical applications. As MSCs do not express significant histocompatibility complexes and immune stimulating molecules, they are not detected by immune surveillance and do not lead to graft rejection after transplantation. These properties make them competent biomedical candidates, especially in tissue engineering. We present a brief overview of MSC extraction methods and subsequent potential for differentiation, and a comprehensive overview of their preclinical and clinical applications in regenerative medicine, and discuss future challenges.

Targeting Early Atherosclerosis: A Focus on Oxidative Stress and Inflammation

Atherosclerosis is a chronic vascular inflammatory disease associated to oxidative stress and endothelial dysfunction. Oxidation of low-density lipoprotein (LDL) cholesterol is one of the key factors for the development of atherosclerosis. Nonoxidized LDL have a low affinity for macrophages, so they are not themselves a risk factor. However, lowering LDL levels is a common clinical practice to reduce oxidation and the risk of major events in patients with cardiovascular diseases (CVD). Atherosclerosis starts with dysfunctional changes in the endothelium induced by disturbed shear stress which can lead to endothelial and platelet activation, adhesion of monocytes on the activated endothelium, and differentiation into proinflammatory macrophages, which increase the uptake of oxidized LDL (oxLDL) and turn into foam cells, exacerbating the inflammatory signalling. The atherosclerotic process is accelerated by a myriad of factors, such as the release of inflammatory chemokines and cytokines, the generation of reactive oxygen species (ROS), growth factors, and the proliferation of vascular smooth muscle cells. Inflammation and immunity are key factors for the development and complications of atherosclerosis, and therefore, the whole atherosclerotic process is a target for diagnosis and treatment. In this review, we focus on early stages of the disease and we address both biomarkers and therapeutic approaches currently available and under research.

Human umbilical cord mesenchymal stem cells pretreated with Angiotensin-II attenuate pancreas injury of rats with severe acute pancreatitis

Mesenchymal stem cells (MSCs) pretreatment is an effective route for improving cell-based therapy of endothelial cell survival, vascular stabilization, and angiogenesis. We hypothesized that the application of human umbilical cord-MSCs (hUC-MSCs) pretreated with angiotensin-II (Ang-II) might be a potential therapeutic approach for severe acute pancreatitis (SAP). Therefore, the effect of Ang-II pretreated hUC-MSCs on SAP was investigated in vitro and in vivo.

METHODS

In the present study, human umbilical cord-derived MSCs pretreated with or without Ang-II were delivered through the tail vein of rats 12 h after induction of SAP. Pancreatitis severity scores and serum lipase levels, as well as the levels of VEGF and VEGFR2 were evaluated.

RESULTS

We found that the administration of Ang-II-MSCs significantly inhibited pancreatic injury, as reflected by reductions of pancreatitis severity scores, serum amylase and serum lipase levels. Furthermore, the reduced apoptotic rate and increased tube formation in human umbilical vein endothelial Cells (HUVEC) were found resulting from the administration of Ang-II-MSC-CM. Moreover, knockdown of VEGFR2 can block the effect of Ang-II-MSC-CM on preventing HUVEC from apoptosis, as well as the capacity of tube formation was also suppressed. In addition, the expression of increased Bcl-2 and alleviated caspase-3 were observed in HUVEC and HUVEC transfectants exposure to Ang-II-MSC-CM.

CONCLUSION

Collectively, these results elucidated that the pretreatment of hUC-MSCs with Ang-II improved the outcome of MSC-based therapy for SAP via enhancing angiogenesis and ameliorating endothelial cell dysfunction in a VEGFR2 dependent manner.

Local pharmacological induction of angiogenesis: Drugs for cells and cells as drugs

The past decades have seen significant advances in pro-angiogenic strategies based on delivery of molecules and cells for conditions such as coronary artery disease, critical limb ischemia and stroke. Currently, three major strategies are evolving. Firstly, various pharmacological agents (growth factors, interleukins, small molecules, DNA/RNA) are locally applied at the ischemic region. Secondly, preparations of living cells with considerable bandwidth of tissue origin, differentiation state and preconditioning are delivered locally, rarely systemically. Thirdly, based on the notion, that cellular effects can be attributed mostly to factors secreted in situ, the cellular secretome (conditioned media, exosomes) has come into the spotlight. We review these three strategies to achieve (neo)angiogenesis in ischemic tissue with focus on the angiogenic mechanisms they tackle, such as transcription cascades, specific signalling steps and cellular gases. We also include cancer-therapy relevant lymphangiogenesis, and shall seek to explain why there are often conflicting data between in vitro and in vivo. The lion's share of data encompassing all three approaches comes from experimental animal work and we shall highlight common technical obstacles in the delivery of therapeutic molecules, cells, and secretome. This plethora of preclinical data contrasts with a dearth of clinical studies. A lack of adequate delivery vehicles and standardised assessment of clinical outcomes might play a role here, as well as regulatory, IP, and manufacturing constraints of candidate compounds; in addition, completed clinical trials have yet to reveal a successful and efficacious strategy. As the biology of angiogenesis is understood well enough for clinical purposes, it will be a matter of time to achieve success for well-stratified patients, and most probably with a combination of compounds.

VEGFR endocytosis regulates the angiogenesis in a mouse model of hindlimb ischemia

Background

The regulation of angiogenesis in the treatment of cardiovascular diseases has been widely studied and the vascular endothelial growth factor (VEGF) families and VEGF receptor (VEGFR) have been proven to be one of the key regulators. The VEGFR endocytosis has been recently proved to be involved in the regulation of angiogenesis. Our previous study showed that the upregulation of VEGFR endocytosis enhanced angiogenesis in vitro. In this research, we utilized mice with induced hindlimb ischemia, as a model to investigate the role of VEGFR endocytosis in the regulation of angiogenesis in vivo. Our goal was to observe the effect of revascularization with different degrees of VEGFR endocytosis after injecting atypical protein kinase C inhibitor (αPKCi) and dynasore, which could respectively promote and inhibit the VEGFR endocytosis.

Methods

We induced the hindlimb ischemia in adult male mice by ligating the hindlimb artery. By directly injecting the ischemic muscles with endothelial progenitor cells (EPCs) alone or EPCs + αPKCi/EPCs + dynasore or control medium (sham group), we divided the mice into four groups and detected lower limb blood flow using a laser Doppler blood perfusion imager. We also measured the immunohistochemistry (IHC) of markers for angiogenesis, such as CD31 and alpha smooth muscle actin (α-SMA) in the ischemic hindlimb tissues.

Results

We demonstrated VEGFR endocytosis played an important role in the angiogenesis of the ischemic hindlimb model in vivo. By using atypical PKC inhibitor that increase the VEGFR endocytosis, the angiogenesis in the mice model was promoted. Treatment with EPCs + αPKCi showed greater effects on blood perfusion recovery and increased the α-SMA-positive vessels.

Conclusions

The regulation of VEGFR endocytosis represents a valuable method of improving angiogenesis and thus revascularization in ischemic disease model.

Silica-coated magnetic nanoparticles labeled endothelial progenitor cells alleviate ischemic myocardial injury and improve long-term cardiac function with magnetic field guidance in rats with myocardial infarction

Low retention of endothelial progenitor cells (EPCs) in the infarct area has been suggested to be responsible for the poor clinical efficacy of EPC therapy for myocardial infarction (MI). This study aimed to evaluate whether magnetized EPCs guided through an external magnetic field could augment the aggregation of EPCs in an ischemia area, thereby enhancing therapeutic efficacy. EPCs from male rats were isolated and labeled with silica‐coated magnetic iron oxide nanoparticles to form magnetized EPCs. Then, the proliferation, migration, vascularization, and cytophenotypic markers of magnetized EPCs were analyzed. Afterward, the magnetized EPCs (1 × 10⁶) were transplanted into a female rat model of MI via the tail vein at 7 days after MI with or without the guidance of an external magnet above the infarct area. Cardiac function, myocardial fibrosis, and the apoptosis of cardiomyocytes were observed at 4 weeks after treatment. In addition, EPC retention and the angiogenesis of ischemic myocardium were evaluated. Labeling with magnetic nanoparticles exhibited minimal influence to the biological functions of EPCs. The transplantation of magnetized EPCs guided by an external magnet significantly improved the cardiac function, decreased infarction size, and reduced myocardial apoptosis in MI rats. Moreover, enhanced aggregations of magnetized EPCs in the infarcted border zone were observed in rats with external magnet‐guided transplantation, accompanied by the significantly increased density of microvessels and upregulated the expression of proangiogenic factors, when compared with non‐external‐magnet‐guided rats. The magnetic field‐guided transplantation of magnetized EPCs was associated with the enhanced aggregation of EPCs in the infarcted border zone, thereby improving the therapeutic efficacy of MI.

Cell therapy of critical limb ischemia-problems and prospects

Cell therapy is proposed for indirect revascularization for the patient's incurable by endovascular or surgical revascularization. The therapy with stem cells (SCs) or progenitor cells is assumed to be more efficient as compared with protein or gene therapy not only because of their direct vasculogenic properties, but also thanks to their paracrine effect via secretion of manifold biologically active substances. This review gives an overview of the potential of SC-based therapy for critical limb ischemia (CLI), putative mechanism underlying cell therapy, and comparison of cell therapy to angiogenesis gene therapy in CLI treatment. Human trial data and meta-analysis, as well as some problems of clinical trials and considerations for future SC-based therapy in CLI are also discussed.

Diabetic endothelial colony forming cells have the potential for restoration with glycomimetics

Endothelial colony forming progenitor cell (ECFC) function is compromised in diabetes, leading to poor vascular endothelial repair, which contributes to impaired diabetic foot ulcer healing. We have generated novel glycomimetic drugs with protective effects against endothelial dysfunction. We investigated the effect of glycomimetic C3 on the functional capacity of diabetic ECFCs. ECFCs were isolated from healthy controls and patients with diabetes with neuroischaemic (NI) or neuropathic (NP) foot ulcers. Functionally, diabetic ECFCs demonstrated delayed colony formation (p < 0.02), differential proliferative capacity (p < 0.001) and reduced NO bioavailability (NI ECFCs; p < 0.05). Chemokinetic migration and angiogenesis were also reduced in diabetic ECFCs (p < 0.01 and p < 0.001), and defects in wound closure and tube formation were apparent in NP ECFCs (p < 0.01). Differential patterns in mitochondrial activity were pronounced, with raised activity in NI and depressed activity in NP cells (p < 0.05). The application of glycomimetic improved scratch wound closure in vitro in patient ECFCs (p < 0.01), most significantly in NI cells (p < 0.001), where tube formation (p < 0.05) was also improved. We demonstrate restoration of the deficits in NI cells but not NP cells, using a novel glycomimetic agent, which may be advantageous for therapeutic cell transplantation or as a localised treatment for NI but not NP patients.

Thermosensitive, fast gelling, photoluminescent, highly flexible, and degradable hydrogels for stem cell delivery

Stem cell therapy is a promising approach to regenerate ischemic cardiovascular tissues yet experiences low efficacy. One of the major causes is inferior cell retention in tissues. Injectable cell carriers that can quickly solidify upon injection into tissues so as to immediately increase viscosity have potential to largely improve cell retention. A family of injectable, fast gelling, and thermosensitive hydrogels were developed for delivering stem cells into heart and skeletal muscle tissues. The hydrogels were also photoluminescent with low photobleaching, allowing for non-invasively tracking hydrogel biodistribution and retention by fluorescent imaging. The hydrogels were polymerized by N-isopropylacrylamide (NIPAAm), 2-hydroxyethyl methacrylate (HEMA), 1-vinyl-2-pyrrolidinone (VP), and acrylate-oligolactide (AOLA), followed by conjugation with hypericin (HYP). The hydrogel solutions had thermal transition temperatures around room temperature, and were readily injectable at 4 °C. The solutions were able to quickly solidify within 7 s at 37 °C. The formed gels were highly flexible possessing similar moduli as the heart and skeletal muscle tissues. In vitro, hydrogel fluorescence intensity decreased proportionally to weight loss. After being injected into thigh muscles, the hydrogel can be detected by an in vivo imaging system for 4 weeks. The hydrogels showed excellent biocompatibility in vitro and in vivo, and can stimulate mesenchymal stem cell (MSC) proliferation and paracrine effects. The fast gelling hydrogel remarkably increased MSC retention in thigh muscles compared to slow gelling collagen, and non-gelling PBS. These hydrogels have potential to efficiently deliver stem cells into tissues. Hydrogel degradation can be non-invasively and real-time tracked. STATEMENT OF SIGNIFICANCE: Low cell retention in tissues represents one of the major causes for limited therapeutic efficacy in stem cell therapy. A family of injectable, fast gelling, and thermosensitive hydrogels that can quickly solidify upon injection into tissues were developed to improve cell retention. The hydrogels were also photoluminescent, allowing for non-invasively and real-time tracking hydrogel biodistribution and retention by fluorescent imaging.

Platelet-rich plasma enhances adipose-derived stem cell-mediated angiogenesis in a mouse ischemic hindlimb model

AIM

To evaluate the angiogenic effect of platelet-rich plasma (PRP)-preconditioned adipose-derived stem cells (ADSCs) both in vitro and in a mouse ischemic hindlimb model.

METHODS

ADSCs were divided based on culture medium: 2.5% PRP, 5% PRP, 7.5% PRP, and 10% PRP. Cell proliferation rate was analyzed using the MTS assay. The gene expression of CD31, vascular endothelial growth factor, hypoxia-inducible factors, and endothelial cell nitric oxide synthase was analyzed using reverse transcription polymerase chain reaction. Cell markers and structural changes were assessed through immunofluorescence staining and the tube formation assay. Subsequently, we studied the in vivo angiogenic capabilities of ADSCs by a mouse ischemic hindlimb model.

RESULTS

The proliferation rate of ADSCs was higher in the 2.5%, 5%, and 7.5% PRP groups. The expression of hypoxia-inducible factor, CD31, vascular endothelial growth factor, and endothelial cell nitric oxide synthase in the 5% and 7.5% PRP groups increased. The 5%, 7.5%, and 10% PRP groups showed higher abilities to promote both CD31 and vascular endothelial growth factor production and tubular structure formation in ADSCs. According to laser Doppler perfusion scan, the perfusion ratios of ischemic limb to normal limb were significantly higher in 5% PRP, 7.5% PRP, and human umbilical vein endothelial cells groups compared with the negative control and fetal bovine serum (FBS) groups (0.88 ± 0.08, 0.85 ± 0.07 and 0.81 ± 0.06 for 5%, 7.5% PRP and human umbilical vein endothelial cells compared with 0.42 ± 0.17 and 0.54 ± 0.14 for the negative control and FBS, P < 0.01).

CONCLUSION

PRP-preconditioned ADSCs presented endothelial cell characteristics in vitro and significantly improved neovascularization in ischemic hindlimbs. The optimal angiogenic effect occurred in 5% PRP- and 7.5% PRP-preconditioned ADSCs.

Conversion of human adipose-derived stem cells into functional and expandable endothelial-like cells for cell-based therapies

Background

Ischemic vascular diseases are the major cause of death worldwide. In recent years, endothelial cell (EC)-based approaches to vascular regeneration are increasingly viable strategies for treating ischemic diseases, but their applications are challenged by the difficulties in their efficient generation and stable maintenance. Here, we show an alternative protocol that facilitates the generation of functional and expandable ETS variant 2 (ETV2)-induced endothelial-like cells (EiECs) from human adipose-derived stem cells (hADSCs), providing a potential source of cells for autologous ECs to treat ischemic vascular diseases.

Methods

hADSCs were obtained from fresh human adipose tissue. Passage 3 hADSCs were transduced with doxycycline (DOX)-inducible ETV2 transcription factor; purified ETV2-hADSCs were induced into endothelial-like cells using a two-stage induction culture system composed of small molecule compounds and cell factors. EiECs were evaluated for their surface markers, proliferation, gene expression, secretory capacity, and effects on vascular regeneration in vivo.

Results

We found that short-term ETV2 expression combined with TGF-β inhibition is sufficient for the generation of kinase insert domain receptor (KDR)+ cells from hADSCs within 10 days. KDR+ cells showed immature endothelial characteristics, and they can gradually mature in a chemically defined induction medium at the second stage of induction. Futher studies showed that KDR+ cells deriving EC-like cells could stably self-renew and expand about 10⁶-fold in 1 month, and they exhibited expected genome-wide molecular features of mature ECs. Functionally, these EC-like cells significantly promoted revascularization in a hind limb ischemic model.

Conclusions

We isolated highly purified hADSCs and effectively converted them into functional and expandable endothelial-like cells. Thus, the study may provide an alternative strategy to obtain functional EC-like cells with potential for biomedical and pharmaceutical applications.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1088-6) contains supplementary material, which is available to authorized users.

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