Expression of Vascular Endothelial Growth Factor Receptor 1 in Bone Marrow-derived Mesenchymal Cells Is Dependent on Hypoxia-inducible Factor 1

Paracrine and Autocrine Effects of VEGF Are Enhanced in Human eMSC Spheroids

The mechanisms underlying the therapeutic potential of MSCs are the focus of intense research. We studied human MSCs isolated from desquamated endometrium (eMSCs), which, as previously shown, have high regenerative potential in various disease models. The aim was to evaluate the role of secreted VEGF in stimulating angiogenesis and maintaining eMSC viability and migration, which is important for improving the therapeutic properties of MSCs. We compared three eMSC cultures differing in the level of VEGF secretion: 3D spheroids, monolayer eMSCs, and monolayer eMSCs with VEGF knockdown. Spheroid eMSCs produced higher amounts of VEGF and had the strongest paracrine effect on HUVEC. eMSCs with VEGF knockdown did not stimulate angiogenesis. Monolayered eMSCs expressed VEGFR1, while spheroid eMSCs expressed both VEGFR1 and VEGFR2 receptors. The knockdown of VEGF caused a significant decrease in the viability and migration of eMSCs. eMSCs from 3D spheroids enhanced proliferation and migration in response to exogenous VEGF, in contrast to monolayered eMSCs. Our results suggest that the VEGF-VEGFR1 loop appears to be autocrine-involved in maintaining the viability of eMSCs, and VEGFR2 expression enhances their response to exogenous VEGF, so the angiogenic potential of eMSC can be up- or downregulated by intrinsic VEGF signals.

AKT-AMPKα-mTOR-dependent HIF-1α Activation is a New Therapeutic Target for Cancer Treatment: A Novel Approach to Repositioning the Antidiabetic Drug Sitagliptin for the Management of Hepatocellular Carcinoma

HIF-1α is a key factor promoting the development of hepatocellular carcinoma (HCC). As well, AKT-AMPKα-mTOR signaling is a promising target for cancer therapy. Yet, the AKT-AMPKα-mTOR-dependent activation of HIF-1α has not been studied in livers with HCC. In addition, the mechanisms underlying the potential antineoplastic effects of sitagliptin (STGPT), an antidiabetic agent, have not yet been elucidated. For that purpose, the N-nitrosodiethylamine (NDEA)-induced HCC mouse model was used in the present study using a dose of 100 mg/kg/week, i.p., for 8 weeks. NDEA-induced HCC mice received STGPT 20, 40, or 80 mg/kg starting on day 61 up to day 120. The present study revealed that STGPT inhibited HIF-1α activation via the interference with the AKT-AMPKα-mTOR axis and the interruption of IKKβ, P38α, and ERK1/2 signals as well. Accordingly, STGPT prolonged the survival, restored the histological features and improved liver function. Additionally, STGPT inhibited angiogenesis, as revealed by a significant downregulation in the VEGF and mRNA expression of CD309 with concomitant inhibition of tissue invasion was evident by an increased ratio of TIMP-1/MMP-2. STGPT exhibited apoptotic stimulatory effect as indicated upon calculating the BCL-2/Bax ratio and by the gene expression of p53. The decrease in AFP and liver index calculation, gene expression of Ki-67 confirmed the antiproliferative activity of STGPT. The anti-inflammatory potential was revealed by the decreased TNF-α level and the downregulation of MCP-1 gene expression. Moreover, an antifibrotic potential was supported by lower levels of TGF-β. These effects appear to be GLP1R-independent. The present study provides a potential basis for repurposing STGPT for the inhibition of HCC progression. Since STGPT is unlikely to cause hypoglycemia, it may be promising as monotherapy or adjuvant therapy to treat diabetic or even normoglycemic patients with HCC.

Empagliflozin adjunct with metformin for the inhibition of hepatocellular carcinoma progression: Emerging approach for new application

Hepatocellular carcinoma (HCC) is on the rise worldwide, and its incidence in diabetic patients is two to three times that of non-diabetics. Current therapeutic options fail to provide considerable survival benefits to patients with HCC. There is a strong possibility that the FDA-approved antidiabetic combination of empagliflozin and metformin could show complementary effects to control HCC progression. However, their multitarget effects have not yet been studied on HCC development. Therefore, the present study aims to evaluate the antitumorigenic activity of this combination in non-diabetic mice with diethylnitrosamine-induced HCC. Empagliflozin/metformin combination prolonged survival and improved histological features of mice livers. Additionally, Empagliflozin/metformin showed anti-inflammatory potential and relieved oxidative stress. On the one hand these effects are likely attributed to the ability of metformin to inactivate NF-κB in an AMPK-dependent mechanism and on the other hand to the ability of the empagliflozin to inhibit the MAPKs, p38 and ERK1/2. Empagliflozin also showed a less robust effect on AMPK than that of metformin. Moreover, empagliflozin enhanced the autophagy inducing activity of metformin. Furthermore, empagliflozin/metformin exhibited increased apoptotic potential. Consequently, empagliflozin augmented the antitumorigenic function of metformin by exerting better control of angiogenesis, and metastasis. To conclude, our findings suggest empagliflozin as an ideal adjunct to metformin for the inhibition of HCC progression. In addition, since the incidence of hypoglycemia is minimal due to insulin-independent mechanism of action of both treatments, empagliflozin/metformin could be a promising therapeutic modality for the management of diabetic patients with HCC; and even non diabetic ones.

HIF-1α promotes the migration and invasion of cancer-associated fibroblasts by miR-210

Metastasis is the major cause of death in colorectal cancer (CRC) patients. Inhibition of metastasis will prolong the survival of patients with CRC. Cancer cells bring their own soil, cancer-associated fibroblasts (CAFs), to metastasize together, promoting the survival and colonization of circulating cancer cells. However, the mechanism by which CAFs metastasize remains unclear. In this study, CAFs were derived from adipose mesenchymal stem cells (MSCs) after co-culture with CRC cell lines. Transwell assays showed that CAFs have stronger migration and invasion abilities than MSCs. In a nude mouse subcutaneous xenograft model, CAFs metastasized from the primary tumour to the lung and promoted the formation of CRC metastases. The expression of HIF-1α was upregulated when MSCs differentiated into CAFs. Inhibition of HIF-1α expression inhibited the migration and invasion of CAFs. Western blot and ChIP assays were used to identify the genes regulated by HIF-1α. HIF-1α regulated the migration and invasion of CAFs by upregulating miR-210 transcription. Bioinformatics analysis and luciferase reporter assays revealed that miR-210 specifically targeted the 3'UTR of VMP1 and regulated its expression. Downregulation of VMP1 enhanced the migration and invasion of CAFs. In vivo, inhibition of miR-210 expression in CAFs reduced the metastasis of CAFs and tumour cells. Therefore, the HIF-1α/miR-210/VMP1 pathway might regulate the migration and invasion of CAFs in CRC. Inhibition of CAF metastasis might reduce CRC metastasis.

Polydopamine-Coated Poly(l-lactide) Nanofibers with Controlled Release of VEGF and BMP-2 as a Regenerative Periosteum

The periosteum plays an important role in vascularization and ossification during bone repair. However, in most studies, an artificial periosteum cannot restore both functions of the periosteum concurrently. In this study, a novel nanofiber that can sustain the release of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2) was fabricated to enhance the durability of angiogenesis and osteogenesis during bone regeneration. A cell-free tissue engineered periosteum based on an electrospinning poly-l-lactic acid (PLLA) nanofiber was fabricated, on which VEGF and BMP-2 were immobilized through a polydopamine (PDA) coating conveniently and safely (BVP@PLLA membrane). The results indicated a significantly improved loading rate as well as a slow and sustained release of VEGF and BMP-2 with the help of the PDA coating. BMP-2 immobilized on nanofibers successfully induced the osteogenic differentiation of human bone marrow mesenchymal stem cells (BMSCs) in vitro with high expression of runt-related transcription factor 2 (Runx2), osteopontin (OPN), and alkaline phosphatase (ALP). Similarly, angiogenic differentiation of BMSCs with the expression of fetal liver kinase-1 (Flk-1) and vascular endothelial cadherin (VE-cadherin) was observed under the environment of VEGF sustained release. Moreover, an in vivo study revealed that the BVP@PLLA membrane could enhance vascular formation and new bone formation, which accelerates bone regeneration in rat femoral defects along with a massive periosteum defect. Therefore, our study suggests that the novel artificial periosteum with dual growth factor controlled release is a promising system to improve bone regeneration in bone defects along with a massive periosteum defect.

The Vital Roles of Mesenchymal Stem Cells and the Derived Extracellular Vesicles in Promoting Angiogenesis After Acute Myocardial Infarction

Acute myocardial infarction (AMI) is an event of ischemic myocardial necrosis caused by acute coronary artery occlusion, which ultimately leads to a large loss of cardiomyocytes. The prerequisite of salvaging ischemic myocardium and improving cardiac function of patients is to provide adequate blood perfusion in the infarcted area. Apart from reperfusion therapy, it is also urgent and imperative to promote angiogenesis. Recently, growing evidence based on promising preclinical data indicates that mesenchymal stem cells (MSCs) can provide therapeutic effects on AMI by promoting angiogenesis. Extracellular vesicles (EVs), membrane-encapsulated vesicles with complex cargoes, including proteins, nucleic acids, and lipids, can be derived from MSCs and represent part of their functions, so EVs also possess the ability to promote angiogenesis. However, poor control of the survival and localization of MSCs hindered clinical transformation and made scientists start looking for new approaches based on MSCs. Identifying the role of MSCs and their derived EVs in promoting angiogenesis can provide a theoretical basis for improved MSC-based methods, and ultimately promote the clinical treatment of AMI. This review highlights potential proangiogenic mechanisms of transplanted MSCs and the derived EVs after AMI and summarizes the latest literature concerning the novel methods based on MSCs to maximize the angiogenesis capability.

The Effect of Normobaric Intermittent Hypoxia Therapy on Bone in Normal and Disuse Osteopenic Mice

Bromer, Frederik Duch, Mikkel Bo Brent, Michael Pedersen, Jesper Skovhus Thomsen, Annemarie Brüel, and Casper Bindzus Foldager. The effect of normobaric intermittent hypoxia therapy on bone in normal and disuse osteopenic mice. High Alt Med Biol. 22: 225-234, 2021. Background: Systemic intermittent hypoxia therapy (IHT) has been shown to elicit beneficial effects on multiple physiological systems. However, only few studies have investigated the effect of long-term normobaric IHT on bone mass and mechanical and microstructural properties. The aim of the present study was to examine the effect of IHT on bone in both healthy and osteopenic mice. Materials and Methods: Thirty mice were stratified into four groups: Ctrl, Ctrl+IHT, Botox, and Botox+IHT. Osteopenia was induced by injecting Botox into the right hindlimb of the mice causing paralysis and disuse. IHT animals were placed in a normobaric hypoxia-chamber (10% oxygen) for 1 hour twice daily 5 days/week. Animals were sacrificed after 21 days, and DEXA, micro-computed tomography, and mechanical testing were performed on the femora. Results: As expected, Botox resulted in a significant reduction of bone mineral content (-23.4%), area bone mineral density (-19.1%), femoral neck strength (F_max: -54.7%), bone volume fraction (bone volume/tissue volume: -41.8%), and trabecular thickness (-32.4%). IHT had no measurable effect on the bone properties in either healthy or osteopenic mice. Conclusion: The study confirmed that Botox led to loss of bone mass, deterioration of trabecular microstructure, and loss of bone strength. These changes were not influenced by IHT. Notably, IHT had no detrimental effect on bone in either healthy or osteopenic mice. This indicates that IHT of ailments outside of the skeletal system may be administered without causing harm to the bone.

Discrepancies on the Role of Oxygen Gradient and Culture Condition on Mesenchymal Stem Cell Fate

Over the past few years, mesenchymal stem (or stromal) cells (MSCs) have garnered enormous interest due to their therapeutic value especially for their multilineage differentiation potential leading to regenerative medicine applications. MSCs undergo physiological changes upon in vitro expansion resulting in expression of different receptors, thereby inducing high variabilities in therapeutic efficacy. Therefore, understanding the biochemical cues that influence the native local signals on differentiation or proliferation of these cells is very important. There have been several reports that in vitro culture of MSCs in low oxygen gradient (or hypoxic conditions) upregulates the stemness markers and promotes cell proliferation in an undifferentiated state, as hypoxia mimics the conditions the progenitor cells experience within the tissue. However, different studies report different oxygen gradients and culture conditions causing ambiguity in their interpretation of the results. In this progress report, it is aimed to summarize recent studies in the field with specific focus on conflicting results reported during the application of hypoxic conditions for improving the proliferation or differentiation of MSCs. Further, it is tried to decipher the factors that can affect characteristics of MSC under hypoxia and suggest a few techniques that could be combined with hypoxic cell culture to better recapitulate the MSC tissue niche.

Hypoxic Preconditioning Enhances Cellular Viability and Pro-angiogenic Paracrine Activity: The Roles of VEGF-A and SDF-1a in Rat Adipose Stem Cells

To achieve the full therapeutic potential of implanted adipose stem cells (ASCs) in vivo, it is crucial to improve the viability and pro-angiogenic properties of the stem cells. Here, we first simulated the conditions of ischemia and hypoxia using the in vitro oxygen-glucose deprivation (OGD) model and confirmed that hypoxic preconditioning of ASCs could provide improved protection against OGD and enhance ASC viability. Second, we assessed the effect of hypoxic preconditioning on pro-angiogenic potential of ASCs, with a particular focus on the role of vascular endothelial growth factor-A (VEGF-A) and stromal derived factor-1a (SDF-1a) paracrine activity in mediating angiogenesis. We found that the conditioned medium of ASCs (ASC^CM) with hypoxic preconditioning enhanced angiogenesis by a series of angiogenesis assay models in vivo and in vitro through the upregulation of and a synergistic effect between VEGF-A and SDF-1a. Finally, to investigate the possible downstream mechanisms of VEGF/VEGFR2 and SDF-1a/CXCR4 axes-driven angiogenesis, we evaluated relevant protein kinases involved the signal transduction pathway of angiogenesis and showed that VEGF/VEGFR2 and SDF-1a/CXCR4 axes may synergistically promote angiogenesis by activating Akt. Collectively, our findings demonstrate that hypoxic preconditioning may constitute a promising strategy to enhance cellular viability and angiogenesis of transplanted ASCs, therein improving the success rate of stem cell-based therapies in tissue engineering.

Endosome-triggered ion-releasing nanoparticles as therapeutics to enhance the angiogenic efficacy of human mesenchymal stem cells

Here, we report that Fe ions delivered into human mesenchymal stem cells (hMSCs) by bioreducible metal nanoparticles (NPs) enhance their angiogenic and cell-homing efficacy by controlling ion-triggered intracellular reactive oxygen species (ROS) and improve cell migration, while reducing cytotoxicity. Endosome-triggered iron-ion-releasing nanoparticles (ETIN) were designed to be low-pH responsive to take advantage of the low-pH conditions (4-5) of endosomes for in situ iron-ion release. Due to the different redox potentials of Fe and Au, only Fe could be ionized and released from our novel ETIN, while Au remained intact after ETIN endocytosis. Treatment with an optimal amount of ETIN led to a mild increase in intracellular ROS levels in hMSCs, which enhanced the expression of HIF-1α, a key trigger for angiogenic growth factor secretion from hMSCs. Treatmetn of hMSCs with ETIN significantly enhanced the expression of angiogenesis- and lesion-targeting-related genes and proteins. Transplantation of ETIN-treated hMSCs significantly enhanced angiogenesis and tissue regeneration in a wound-closing mouse model compared with those in untreated mice and mice that underwent conventional hMSC transplantation.

IL-11 and soluble VCAM-1 are important components of Hypoxia Conditioned Media and crucial for Mesenchymal Stromal Cells attraction

INTRODUCTION

Bone marrow stromal cells (BMSC) are highly attractive for tissue engineering due to their ability to differentiate into different cell types, to expand extensively in vitro and to release paracrine soluble factors with a high regenerative potential. They were observed to migrate towards the sites of injury in response to chemotactic signals in vivo. During the last years hypoxia has become a proven method to control proliferation, differentiation and multipotency of BMSC. Conditioned medium from hypoxia-treated BMSC (Hypoxia-conditioned Medium; HCM) has been shown to have various favorable properties on tissue regeneration - such as on cell recruitment, wound healing, angiogenesis and revascularization. Due to this regenerative potential many studies attempt to further characterize HCM and its main functional components. In this study we used HCM generated from umbilical cord mesenchymal stem cells (UC-MSC) instead of BMSC, because GMP-verified methods were used to isolate and cultivate the cells and ensure their constant quality. UC-MSC have a high regenerative potential and are still immunologically naive and therefore highly unlikely to cause an immune reaction. In our article we took the first steps to closer investigate the role of umbilical cord MSC-derived HCM components, namely stromal cell-derived factor 1 (SDF-1α), interleukin 11 (IL-11) and soluble vascular cell adhesion molecule 1 (sVCAM-1).

RESULTS

Our results show previously unknown roles of IL-11 and sVCAM-1 in the attraction of BMSC. The synergistic effect of the investigated protein mixture consisting of IL-11, sVCAM-1 and SDF-1α as well as those recombinant proteins alone revealed a significantly higher chemoattractive capacity towards human BMSC compared to normoxic control medium. Both, the protein mixtures and proteins alone as well as UC-HCM showed an angiogenic effect by promoting the formation of significantly longer tubule structures and higher amounts of junctions and tubules compared to normoxic control medium.

CONCLUSIONS

By showing the prominent upregulation of IL-11, sVCAM-1 and SDF-1α under hypoxic conditions compared to normoxic control and revealing their crucial role in migration of human BMSC we took a further step forward in characterization of the chemoattractive components of HCM.

Single cell migration profiling on a microenvironmentally tunable hydrogel microstructure device that enables stem cell potency evaluation

Cell migration is a key function in a myriad of physiological events and disease conditions. Efficient, quick and descriptive profiling of migration behaviour in response to different treatments or conditions is highly desirable in a series of applications, ranging from fundamental studies of the migration mechanism to drug discovery and cell therapy. This investigation applied the use of methacrylamide gelatin (GelMA) to microfabricate migration lanes based on GelMA hydrogel with encapsulated migration stimuli and structural stability under culture medium conditions, providing the possibility of tailoring the microenvironment during cell-based assays. The actual device provides 3D topography, cell localization and a few step protocol, allowing the quick evaluation and quantification of individual migrated distances of a cell sample by an ImageJ plugin for automated microscopy processing. The detailed profiling of migration behaviour given by the new device has demonstrated a broader assay sensitivity compared to other migration assays and higher versatility to study cell migration in different settings of applications. In this study, parametric information extracted from the migration profiling was successfully used to develop predictive models of immunosuppressive cell function that could be applied as a potency test for mesenchymal stem cells.

Anti-angiogenesis by dual action of R5K peptide conjugated itraconazole nanoparticles

Neovascular age-related macular degeneration (AMD) is a leading cause of central vision loss and irreversible blindness. Vascular endothelial growth factor (VEGF) plays an important role in neovascularization under the retina and macula by promoting endothelial cell proliferation, migration, and angiogenesis. Although anti-VEGF drugs have shown their efficacy in visual improvement, long-term use of these drugs leads to ocular and systemic complications due to the non-selectivity of the drug. In this study, the dual-mode anti-angiogenic drug delivery system, which potentially inhibited VEGF in two different ways, was developed. The itraconazole encapsulated nanoparticles, conjugated with R5K peptide, were fabricated to allow multivalent binding interactions with VEGF. The R5K peptide blocked VEGF binding to its receptor, while itraconazole altered the signaling pathway of VEGF stimulation. The dual action of this novel drug delivery system aimed to enhance the anti-angiogenic effects of individual drugs. R5K-ITZ-NPs demonstrated potent, cell-type specific, and dose-dependent inhibition of vascular endothelial cell proliferation, migration, and tube formation in response to VEGF stimulation. The physical stability study showed that R5K-ITZ-NPs were stable when stored at 4 °C. However, the drug remaining in R5K-ITZ-NPs when stored at 4 °C for 28 days were only 17.2%. The chemical stability test revealed that the degradation of R5K-ITZ-NPs followed second-order kinetics. The release profile showed the burst release of ITZ followed by sustained release of the drug This novel drug delivery system may be an option for neovascular AMD patients who are resistant to ITZ and may represent a novel therapy for AMD.

Therapeutic Potential of “Exosomes Derived Multiple Allogeneic Proteins Paracrine Signaling: Exosomes d-MAPPS” is Based on the Effects of Exosomes, Immunosuppressive and Trophic Factors

Due to their differentiation capacity and potent immunosuppressive and pro-angiogenic properties, mesenchymal stem cells (MSCs) have been considered as new therapeutic agents in regenerative medicine. Since most of MSC-mediated beneficent effects are a consequence of their paracrine action, we designed MSC-based product “Exosomes Derived Multiple Allogeneic Proteins Paracrine Signaling (Exosomes d-MAPPS), which activity is based on MSCs-derived growth factors and immunomodulatory cytokines capable to attenuate inflammation and to promote regeneration of injured tissues. Interleukin 1 receptor antagonist (IL-1Ra) and IL-27 were found in high concentrations in Exosomes d-MAPPS samples indicating strong anti-inflammatory and immunosuppressive potential of Exosomes d-MAPPS. Additionally, high concentrations of vascular endothelial growth factor receptor (VEGFR1) and chemokines (CXCL16, CCL21, CXCL14) were noticed at Exosomes d-MAPPS samples suggesting their potential to promote generation of new blood vessels and migration of CXCR6, CCR7 and CXCR4 expressing cells. Since all proteins which were found in high concentration in Exosomes d-MAPPS samples (IL-1Ra, CXCL16, CXCL14, CCL21, IL-27 and VEGFR1) are involved in modulation of lung, eye, and synovial inflammation, Exosomes d-MAPPS samples were prepared as inhalation and ophthalmic solutions in addition to injection formulations; their application in several patients suffering from chronic obstructive pulmonary disease, osteoarthritis, and dry eye syndrome resulted with significant improvement of biochemical and functional parameters. In conclusion, Exosomes d-MAPPS, due to the presence of important anti-inflammatory, immunomodulatory, and pro-angiogenic factors, represents potentially new therapeutic agent in regenerative medicine that should be further tested in large clinical studies.

Bidirectional and Opposite Effects of Naïve Mesenchymal Stem Cells on Tumor Growth and Progression

Cancer has long been considered as a heterogeneous population of uncontrolled proliferation of different transformed cell types. The recent findings concerning tumorigeneses have highlighted the fact that tumors can progress through tight relationships among tumor cells, cellular, and non-cellular components which are present within tumor tissues. In recent years, studies have shown that mesenchymal stem cells (MSCs) are essential components of non-tumor cells within the tumor tissues that can strongly affect tumor development. Several forms of MSCs have been identified within tumor stroma. Naïve (innate) mesenchymal stem cells (N-MSCs) derived from different sources are mostly recruited into the tumor stroma. N-MSCs exert dual and divergent effects on tumor growth through different conditions and factors such as toll-like receptor priming (TLR-priming), which is the primary underlying causes of opposite effects. Moreover, MSCs also have the contrary effects by various molecular mechanisms relying on direct cellto- cell connections and indirect communications through the autocrine, paracrine routes, and tumor microenvironment (TME).

Overall, cell-based therapies will hold great promise to provide novel anticancer treatments. However, the application of intact MSCs in cancer treatment can theoretically cause adverse clinical outcomes. It is essential that to extensively analysis the effective factors and conditions in which underlying mechanisms are adopted by MSCs when encounter with cancer.

The aim is to review the cellular and molecular mechanisms underlying the dual effects of MSCs followed by the importance of polarization of MSCs through priming of TLRs.

Hypoxia-Mimicking Cobalt-Doped Borosilicate Bioactive Glass Scaffolds with Enhanced Angiogenic and Osteogenic Capacity for Bone Regeneration

The osteogenic capacity of synthetic bone substitutes is will be highly stimulated by a well-established functional vascularized network. Cobalt (Co) ions are known that can generate a hypoxia-like response and stimulates the production of kinds of angiogenic factors. Herein, we investigated the mechanism of cobalt-doped bioactive borosilicate (36B2O3, 22CaO, 18SiO2, 8MgO, 8K2O, 6Na2O, 2P2O5; mol%) glass scaffolds for bone tissues repairing and blood vessel formation in the critical-sized cranial defect site of rats and their effects on the hBMSCs in vitro were researched. The scaffolds can control release Co2+ ions and convert into hydroxyapatite soaking in simulative body fluids (SBF). The fabircated scaffolds without cytotoxic strongly improves HIF-1α generation, VEGF protein secretion, ALP activity and upregulates the expression of osteoblast and angiogenic relative genes in hBMSCs. Eight weeks after implantation, the bioactive glass scaffolds with 3wt % CoO remarkablely enhance bone regeneration and blood vascularized network at the defective site. In conclusion, as a graft material for bone defects, low-oxygen simulated cobalt-doped bioactive glass scaffold is promising.

Tumor-Associated Macrophages Enhance Tumor Hypoxia and Aerobic Glycolysis

Tumor hypoxia and aerobic glycolysis are well-known resistance factors for anticancer therapies. Here, we demonstrate that tumor-associated macrophages (TAM) enhance tumor hypoxia and aerobic glycolysis in mice subcutaneous tumors and in patients with non-small cell lung cancer (NSCLC). We found a strong correlation between CD68 TAM immunostaining and PET ¹⁸fluoro-deoxyglucose (FDG) uptake in 98 matched tumors of patients with NSCLC. We also observed a significant correlation between CD68 and glycolytic gene signatures in 513 patients with NSCLC from The Cancer Genome Atlas database. TAM secreted TNFα to promote tumor cell glycolysis, whereas increased AMP-activated protein kinase and peroxisome proliferator-activated receptor gamma coactivator 1-alpha in TAM facilitated tumor hypoxia. Depletion of TAM by clodronate was sufficient to abrogate aerobic glycolysis and tumor hypoxia, thereby improving tumor response to anticancer therapies. TAM depletion led to a significant increase in programmed death-ligand 1 (PD-L1) expression in aerobic cancer cells as well as T-cell infiltration in tumors, resulting in antitumor efficacy by PD-L1 antibodies, which were otherwise completely ineffective. These data suggest that TAM can significantly alter tumor metabolism, further complicating tumor response to anticancer therapies, including immunotherapy. SIGNIFICANCE: These findings show that tumor-associated macrophages can significantly modulate tumor metabolism, hindering the efficacy of anticancer therapies, including anti-PD-L1 immunotherapy.

HIF-2α, but not HIF-1α, mediates hypoxia-induced up-regulation of Flt-1 gene expression in placental trophoblasts

Placental hypoxia and elevated levels of circulating soluble Fms-like tyrosine kinase-1 (sFlt-1), an anti-angiogenic factor, are closely related to the pathogenesis of preeclampsia. Although sFlt-1 secretion from the placental trophoblasts is increased under hypoxic conditions, the underlying molecular mechanism remains unclear. Previously, an authentic hypoxia response element in the Flt-1 gene promoter was shown to be a potential binding site for hypoxia-inducible factors (HIFs). Here, we investigated the roles of HIF-1α and HIF-2α in Flt-1 gene expression in trophoblast-derived choriocarcinoma cell lines and cytotrophoblasts exposed to hypoxic conditions. In the cell lines, increased expression of sFlt-1 splice variants and nuclear accumulation of HIF-1α and HIF-2α were observed after hypoxic stimulation. A specific small interfering RNA or an inhibitor molecule targeting HIF-2α decreased hypoxia-induced up-regulation of Flt-1 gene expression. Moreover, in cytotrophoblasts, increased sFlt-1 mRNA expression and elevated sFlt-1 production were induced by hypoxic stimulation. Notably, hypoxia-induced elevation of sFlt-1 secretion from the cytotrophoblasts was inhibited by silencing the HIF-2α, but not HIF-1α mRNA. These findings suggest that hypoxia-induced activation of HIF-2α is essential for the increased production of sFlt-1 proteins in trophoblasts. Targeting the HIF-2α may be a novel strategy for the treatment of preeclampsia.

Hypoxic Preconditioning of Mesenchymal Stem Cells with Subsequent Spheroid Formation Accelerates Repair of Segmental Bone Defects

Cell-based approaches for musculoskeletal tissue repair are limited by poor cell survival and engraftment. Short-term hypoxic preconditioning of mesenchymal stem cells (MSCs) can prolong cell viability in vivo, while the aggregation of MSCs into spheroids increases cell survival, trophic factor secretion, and tissue formation in vivo. We hypothesized that preconditioning MSCs in hypoxic culture before spheroid formation would increase cell viability, proangiogenic potential, and resultant bone repair compared with that of individual MSCs. Human MSCs were preconditioned in 1% O2 in monolayer culture for 3 days (PC3) or kept in ambient air (PC0), formed into spheroids of increasing cell density, and then entrapped in alginate hydrogels. Hypoxia-preconditioned MSC spheroids were more resistant to apoptosis than ambient air controls and this response correlated with duration of hypoxia exposure. Spheroids of the highest cell density exhibited the greatest osteogenic potential in vitro and vascular endothelial growth factor (VEGF) secretion was greatest in PC3 spheroids. PC3 spheroids were then transplanted into rat critical-sized femoral segmental defects to evaluate their potential for bone healing. Spheroid-containing gels induced significantly more bone healing compared with gels containing preconditioned individual MSCs or acellular gels. These data demonstrate that hypoxic preconditioning represents a simple approach for enhancing the therapeutic potential of MSC spheroids when used for bone healing. Stem Cells 2018;36:1393-1403.

Diverse roles of fatty acid binding proteins (FABPs) in development and pathogenesis of cancers

One of the most importantly involved pathways in cancer development is fatty-acid signaling pathway. Synthesized lipids as energetic sources are consumed by cancer cells for proliferation, growth, survival, invasion and angiogenesis. Fatty acids as signaling compounds regulate metabolic and transcriptional networks, survival pathways and inflammatory responses. Aggregation of fatty acids with fatty acid binding proteins (FABPs) facilitates their transportation to different cell organelles. FABPs, a group of lipid binding proteins modulate fatty acid metabolism, cell growth and proliferation and cancer development. They may be used as tumor marker in some cancers. FABPs are expressed in most malignancies such as prostate, breast, liver, bladder and lung cancer which are associated with the incidence, proliferation, metastasis, invasion of tumors. This review introduces several isoforms of FABPs (FABP1-12) and summarizes their function and their possible roles in cancer development through some proposed mechanisms.

Loss of Caveolin-1 in Metastasis-Associated Macrophages Drives Lung Metastatic Growth through Increased Angiogenesis

Although it is well established that tumor-associated macrophages take part in each step of cancer progression, less is known about the distinct role of the so-called metastasis-associated macrophages (MAMs) at the metastatic site. Previous studies reported that Caveolin-1 (Cav1) has both tumor-promoting and tumor-suppressive functions. However, the role of Cav1 in bone-marrow-derived cells is unknown. Here, we describe Cav1 as an anti-metastatic regulator in mouse models of lung and breast cancer pulmonary metastasis. Among all the recruited inflammatory cell populations, we show that MAMs uniquely express abundant levels of Cav1. Using clodronate depletion of macrophages, we demonstrate that macrophage Cav1 signaling is critical for metastasis and not for primary tumor growth. In particular, Cav1 inhibition does not affect MAM recruitment to the metastatic site but, in turn, favors angiogenesis. We describe a mechanism by which Cav1 in MAMs specifically restrains vascular endothelial growth factor A/vascular endothelial growth factor receptor 1 (VEGF-A/VEGFR1) signaling and its downstream effectors, matrix metallopeptidase 9 (MMP9) and colony-stimulating factor 1 (CSF1).

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Macrophage Cav1 signaling is critical for restraining lung metastatic growth

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Cav1 deletion in macrophages favors angiogenesis at the lung metastatic site

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Cav1 suppresses VEGF-A/VEGFR1 activity and its downstream effectors, MMP9 and CSF1

Design and Applications of Cell-Selective Surfaces and Interfaces

Tissue regeneration involves versatile types of cells. The accumulation and disorganized behaviors of undesired cells impair the natural healing process, leading to uncontrolled immune response, restenosis, and/or fibrosis. Cell-selective surfaces and interfaces can have specific and positive effects on desired types of cells, allowing tissue regeneration with restored structures and functions. This review outlines the importance of surfaces and interfaces of biomaterials with cell-selective properties. The chemical and biological cues including peptides, antibodies, and other molecules, physical cues such as topography and elasticity, and physiological cues referring mainly to interactions between cells-cells and cell-chemokines or cytokines are effective modulators for achieving cell selectivity upon being applied into the design of biomaterials. Cell-selective biomaterials have also shown practical significance in tissue regeneration, in particular for endothelialization, nerve regeneration, capture of stem cells, and regeneration of tissues of multiple structures and functions.

Selective capture of mesenchymal stem cells over fibroblasts and immune cells on E7-modified collagen substrates under flow circumstances

A substrate with selective capture of MSCs (BMSCs) over fibroblasts (NIH3T3 cells) and immune cells (RAW264.7 cells) was developed by conjugating E7 peptides on collagen substrates.

The balance between proliferation and transcription of angiogenic factors of mesenchymal stem cells in hypoxia

Bridging large bone defects with mesenchymal stromal cells-seeded scaffolds remains a big challenge in orthopedic surgery, due to the lack of vascularization. Within such a cell-scaffold construct, cells are exposed to ischemic conditions. When human mesenchymal stem cells (hMSCs) encounter hypoxic conditions, they show higher cell proliferation than at ambient oxygen levels. However, when hMSCs are exposed to prolonged ischemia, cell proliferation ceases completely. Exposure of hMSCs to hypoxic conditions is known to result in the transcription of angiogenic factors (AGF), which can promote the development of new blood vessels. In this study, we investigated at which oxygen level hMSC proliferation and the transcription of AGF were optimal. Human bone marrow-derived hMSCs were cultured at 0.1, 1, 2, 3, 4, 5, and 21% oxygen. Cell proliferation over 14 days was assayed using a DNA quantification method. hMSC metabolic activity over 14 days was measured using a MTT test. Quantitative RT-PCR was used to assess mRNA levels of angiogenic factors at the tested oxygen percentages. hMSCs showed the highest cell proliferation rate at 1% oxygen. The highest corrected cell metabolic rate was found at 21% oxygen, followed by 2% oxygen. HIF1α transcription did not increase under hypoxic conditions compared to 21% oxygen conditions. However, transcription of VEGF and ANG-1 was significantly higher at 2% oxygen than at 21% O₂. The optimum oxygen range at which hMSCs proliferated rapidly and angiogenic factors ANG-1 and VEGF simultaneously came to expression was from 1 to 2% oxygen.

Metabolically conditioned media derived from bone marrow stromal cells or human skin fibroblasts act as effective chemoattractants for mesenchymal stem cells

Background

The main goal of bone tissue engineering has been the generation of healthy bone in order to replace affected tissue. Therefore, optimized biomaterials are needed which allow the survival and growth of mesenchymal stem cells. Until now the key challenge in the clinical application of cell-based tissue engineering bone implants was poor diffusion of oxygen into the tissue, making functional blood vessel networks a necessity. With their ability to evolve into different cell types, to expand extensively in vitro, and to release paracrine soluble factors, bone marrow stromal cells (BMSC) are highly attractive for tissue engineering. During the last years hypoxia became a proven method to control proliferation, differentiation, and pluripotency of BMSC. Here we applied different methods to characterize metabolically conditioned media (MCM) in comparison to hypoxia conditioned media (HCM) and evaluated their ability to attract BMSC in 2-D migration assays.

Methods

BMSC and fibroblasts of human origin were isolated and cultivated to obtain HCM and MCM. Both media were characterized by angiogenesis arrays, cytokine arrays, and ELISA for selected factors. 2-D migration tests were performed with Corning Transwell®-96 permeable support chambers with porous polyester membranes with a pore size of 8.0 μm.

Results

Characterization of HCM and MCM revealed that the concentration of angiogenic factors was higher in MCM than in HCM. However, the chemoattractive capacity of MCM for BMSC was equivalent to that of HCM. HCM and MCM produced by human skin fibroblasts attracted human BMSC as efficiently as HCM and MCM produced by human BMSC.

Conclusions

HCM and MCM have a high chemoattractive capacity for BMSC. Both conditioned media harbor high concentrations of angiogenic factors which are important for angiogenesis and cell migration. Both chemoattracting conditioned media can also be derived from skin fibroblasts which can easily be obtained from patients in individualized therapy approaches.

Vascular Endothelial Growth Factor Isoform-B Stimulates Neurovascular Repair After Ischemic Stroke by Promoting the Function of Pericytes via Vascular Endothelial Growth Factor Receptor-1

Ischemic stroke triggers endogenous angiogenic mechanisms, which correlates with longer survival in patients. As such, promoting angiogenesis appears to be a promising approach. Experimental studies investigated mostly the potent angiogenic factor vascular endothelial growth factor isoform-A (VEGF-A). However, VEGF-A increases the risk of destabilizing the brain microvasculature, thus hindering the translation of its usage in clinics. An attractive alternative VEGF isoform-B (VEGF-B) was recently reported to act as a survival factor rather than a potent angiogenic factor. In this study, we investigated the therapeutic potential of VEGF-B in ischemic stroke using different in vivo and in vitro approaches. We showed that the delayed intranasal administration of VEGF-B reduced neuronal damage and inflammation. Unexpectedly, VEGF-B stimulated the formation of stable brain microvasculature within the injured region by promoting the interaction between endothelial cells and pericytes. Our data indicate that the effects of VEGF-B were mediated via its specific receptor VEGF receptor-1 (VEGFR-1) that is predominately expressed in brain pericytes. Importantly, VEGF-B promoted the survival of pericytes, and not brain endothelial cells, by inducing expression of the anti-apoptotic protein B-cell lymphoma 2 (Bcl-2) and the main protein involved in energy homeostasis AMP-activated protein kinase α (AMPKα). Moreover, we showed that VEGF-B stimulated the pericytic release of factors stimulating a "reparative angiogenesis" that does not compromise microvasculature stability. Our study unraveled hitherto unknown role of VEGF-B/VEGFR-1 signaling in regulating the function of pericytes. Furthermore, our findings suggest that brain microvasculature stabilization via VEGF-B constitutes a safe therapeutic approach for ischemic stroke.

iTRAQ-Based Quantitative Proteomic Analysis of the Potentiated and Dormant Antler Stem Cells

As the only known organ that can completely regenerate in mammals, deer antler is of real significance in the field of regenerative medicine. Recent studies have shown that the regenerative capacity of the antlers comes from the pedicle periosteum and the cells resident in the periosteum possess the attributes of stem cells. Currently, the molecular mechanism of antler regeneration remains unclear. In the present study, we compared the potentiated and dormant antler stem cells using isobaric tags for the relative and absolute quantification (iTRAQ) labeling of the peptides, coupled with two-dimensional liquid chromatography-tandem mass spectrometry (LC-MS/MS) to compare the proteome profiles. Proteins were identified by searching against the NCBI nr database and our own Cervine transcriptome database, and bioinformatics analysis was conducted to identify the differentially expressed proteins. Based on this searching strategy, we identified 169 differentially expressed proteins in total, consisting of 70 up- and 99 down-regulated in the potentiated vs. dormant antler stem cells. Reliability of the iTRAQ was confirmed via quantitative real-time polymerase chain reaction (qRT-PCR) to measure the expression of selected genes. We identified transduction pathways through the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, such as HIF-1 and PI3K-AKT signaling pathways that play important roles in regulating the regeneration of antlers. In summary, the initiation stage of antler regeneration, a process from dormant to potentiated states in antler stem cells, is regulated by multiple proteins and complicated signal networks.

Multidimensional Screening Platform for Simultaneously Targeting Oncogenic KRAS and Hypoxia-Inducible Factors Pathways in Colorectal Cancer

Colorectal cancer (CRC) is a genetic disease, due to progressive accumulation of mutations in oncogenes and tumor suppressor genes. Large scale genomic sequencing projects revealed >100 mutations in any individual CRC. Many of these mutations are likely passenger mutations, and fewer are driver mutations. Of these, activating mutations in RAS proteins are essential for cancer initiation, progression, and/or resistance to therapy. There has been significant interest in developing drugs targeting mutated cancer gene products or downstream signaling pathways. Due to the number of mutations involved and inherent redundancy in intracellular signaling, drugs targeting one mutation or pathway have been either ineffective or led to rapid resistance. We have devised a strategy whereby multiple cancer pathways may be simultaneously targeted for drug discovery. For proof-of-concept, we targeted the oncogenic KRAS and HIF pathways, since oncogenic KRAS has been shown to be required for cancer initiation and progression, and HIF-1α and HIF-2α are induced by the majority of mutated oncogenes and tumor suppressor genes in CRC. We have generated isogenic cell lines defective in either oncogenic KRAS or both HIF-1α and HIF-2α and subjected them to multiplex genomic, siRNA, and high-throughput small molecule screening. We have identified potential drug targets and compounds for preclinical and clinical development. Screening of our marine natural product library led to the rediscovery of the microtubule agent dolastatin 10 and the class I histone deacetylase (HDAC) inhibitor largazole to inhibit oncogenic KRAS and HIF pathways. Largazole was further validated as an antiangiogenic agent in a HIF-dependent manner in human cells and in vivo in zebrafish using a genetic model with activated HIF. Our general strategy, coupling functional genomics with drug susceptibility or chemical-genetic interaction screens, enables the identification of potential drug targets and candidates with requisite selectivity. Molecules prioritized in this manner can easily be validated in suitable zebrafish models due to the genetic tractability of the system. Our multidimensional platform with cellular and organismal components can be extended to larger scale multiplex screens that include other mutations and pathways.

Melanoma educates mesenchymal stromal cells towards vasculogenic mimicry

Accumulating evidence suggests that mesenchymal stromal cells (MSCs) are recruited to the tumor, and promote tumor development and growth. The present study was performed to investigate the communication between aggressive melanoma and MSCs in vasculogenic mimicry (VM). Normal human MSCs plated on Matrigel were unable to form capillary-like structures (CLSs). By contrast, MSCs co-cultured with aggressive melanoma cell lines, namely, Mel Cher, Mel Kor and Mel P, generated CLSs. Significantly, MSCs co-cultured with poorly aggressive melanoma cells, namely, Mel Me, failed to form CLSs. To identify factors responsible for VM, the effects of vascular endothelial growth factor A (VEGFA), pro-epidermal growth factor, basic fibroblast growth factor and stromal cell-derived factor 1α on the formation of CLSs by MSCs were tested. VM was induced by the addition of VEGFA, whereas other cytokines were inefficient. To confirm the hypothesis that aggressive tumor cells can increase the vasculogenic ability of MSCs, a standard B16/F10 mouse melanoma test system was used. MSCs isolated from the adipose tissues of C57BL/6 mice with melanoma formed a vascular-like network on Matrigel, whereas MSCs from healthy mice failed to form such structures. This study provides the first direct evidence that melanoma tumors educate MSCs to engage in VM. The education may occur distantly. These findings offer promise for novel therapeutic directions in the treatment of metastatic melanoma.

Hypoxyprobe™ reveals dynamic spatial and temporal changes in hypoxia in a mouse model of endometrial breakdown and repair

BACKGROUND

Menstruation is the culmination of a cascade of events, triggered by the withdrawal of progesterone at the end of the menstrual cycle. Initiation of tissue destruction and endometrial shedding causes spiral arteriole constriction in the functional layer of the endometrium. Upregulation of genes involved in angiogenesis and immune cell recruitment, two processes that are essential to successful repair and remodelling of the endometrium, both thought to be induced by reduced oxygen has been reported. Evidence for stabilisation/increased expression of the transcriptional regulator hypoxia inducible factor in the human endometrium at menses has been published. The current literature debates whether hypoxia plays an essential role during menstrual repair, therefore this study aims to delineate a role for hypoxia using a sensitive detection method (the Hypoxyprobe™) in combination with an established mouse model of endometrial breakdown and repair.

RESULTS

Using our mouse model of menses, during which documented breakdown and synchronous repair occurs in a 24 h timeframe, in combination with the Hypoxyprobe™ detection system, oxygen tensions within the uterus were measured. Immunostaining revealed striking spatial and temporal fluctuations in hypoxia during breakdown and showed that the epithelium is also exposed to hypoxic conditions during the repair phase. Furthermore, time-dependent changes in tissue hypoxia correlated with the regulation of mRNAs encoding for the angiogenic genes vascular endothelial growth factor and stromal derived factor (Cxcl12).

CONCLUSIONS

Our findings are consistent with a role for focal hypoxia during endometrial breakdown in regulating gene expression during menses. These data have implications for treatment of endometrial pathologies such as heavy menstrual bleeding.

Uremic toxin p-cresol induces Akt-pathway-selective insulin resistance in bone marrow-derived mesenchymal stem cells

We reported a functional incompetence in mesenchymal stem cells (MSCs) under uremia, but the mechanisms have not been explored. To study the mechanisms of dysfunctional MSCs induced by uremia, we characterized insulin signaling in MSCs and investigated the effect of uremic toxin, p-cresol, on the proangiogenic actions of insulin. In MSCs, insulin induced hypoxia-inducible factor (HIF)-1α, vascular endothelial growth factor, and stromal cell-derived factor 1α expressions via PI3K/Akt-dependent pathway. MSCs treated with p-cresol exhibited altered insulin signaling in a selective manner for insulin receptor substrate-1/PI3K/Akt pathway, whereas ERK pathway remained active. The insulin-induced increase of HIF-1α was blunted by p-cresol treatment. This Akt-selective insulin resistance was also observed in MSCs isolated from chronic kidney disease (CKD) mice. In mice model of hindlimb ischemia, blood flow recovery, capillary density, and local production of angiogenic factors in the ischemic limb treated with CKD MSCs were significantly inferior to those promoted by control MSCs. However, modifying CKD MSCs by overexpression of HIF-1α restored all of these changes. Taken together, these data suggest that p-cresol contributes to insulin resistance in a selective manner for Akt pathway. This might be a biological explanation for the functional incompetence of MSCs under uremia through defects in the insulin-induced elevation of HIF-1α protein expression.

Overexpression of Hif-1α in Mesenchymal Stem Cells Affects Cell-Autonomous Angiogenic and Osteogenic Parameters

Reconstruction of large bone defects still represents a major medical challenge. In recent years tissue engineering has developed techniques based on adult mesenchymal stem cells (MSCs) that could represent an attractive therapeutical option to treat large bone defects in the future. It has been demonstrated in various animal models that ex vivo expanded MSCs are capable of promoting the regeneration of skeletal defects after implantation. However, for the efficient regeneration of bone in tissue engineering applications, a rapid vascularization of implanted grafts is essential to ensure the survival of cells in the early post-implantational phase. A promising strategy to enhance vascularization of MSC-containing implants could consist of overexpression of the angiogenic master transcription factor Hypoxia-inducible factor 1 (Hif-1) in the MSCs in order to induce angiogenesis and support osteogenesis. In the present study, we overexpressed Hif-1α in MSCs by using recombinant adenoviruses and investigated cell-autonomous effects. Overexpression of Hif-1α enhanced proliferation, migration, cell survival and expression of pro-angiogenic genes. Other parameters such as expression of the osteogenic markers BMP-2 and RunX2 were decreased. Hif-1α overexpression had no effect on invasion, senescence and osteogenic differentiation of MSCs. Our experiments revealed multifarious effects of Hif-1α overexpression on cell-autonomous parameters. Therefore, Hif-1α overexpression may represent a therapeutic option to improve cellular functions of MSCs to treat critical sized bone defects.

Integrating new discoveries into the "vicious cycle" paradigm of prostate to bone metastases

In prostate to bone metastases, the "vicious cycle" paradigm has been traditionally used to illustrate how metastases manipulate the bone forming osteoblasts and resorbing osteoclasts in order to yield factors that facilitate growth and establishment. However, recent advances have illustrated that the cycle is far more complex than this simple interpretation. In this review, we will discuss the role of exosomes and hematopoietic/mesenchymal stem/stromal cells (MSC) that facilitate the establishment and activation of prostate metastases and how cells including myeloid-derived suppressor cells, macrophages, T cells, and nerve cells contribute to the momentum of the vicious cycle. The increased complexity of the tumor-bone microenvironment requires a system level approach. The evolution of computational models to interrogate the tumor-bone microenvironment is also discussed, and the application of this integrated approach should allow for the development of effective therapies to treat and cure prostate to bone metastases.

HIF1α is necessary for exercise-induced neuroprotection while HIF2α is needed for dopaminergic neuron survival in the substantia nigra pars compacta

Exercise reduces the risk of developing a number of neurological disorders and increases the efficiency of cellular energy production. However, overly strenuous exercise produces oxidative stress. Proper oxygenation is crucial for the health of all tissues, and tight regulation of cellular oxygen is critical to balance O2 levels and redox homeostasis in the brain. Hypoxia Inducible Factor (HIF)1α and HIF2α are transcription factors regulated by cellular oxygen concentration that initiate gene regulation of vascular development, redox homeostasis, and cell cycle control. HIF1α and HIF2α contribute to important adaptive mechanisms that occur when oxygen and ROS homeostasis become unbalanced. It has been shown that preconditioning by exposure to a stressor prior to a hypoxic event reduces damage that would otherwise occur. Previously we reported that 3 months of exercise protects SNpc dopaminergic (DA) neurons from toxicity caused by Complex I inhibition. Here, we identify the cells in the SNpc that express HIF1α and HIF2α and show that running exercise produces hypoxia in SNpc DA neurons, and alters the expression of HIF1α and HIF2α. In mice carrying a conditional knockout of Hif1α in postnatal neurons we observe that exercise alone produces SNpc TH+ DA neuron loss. Loss of HIF1α also abolishes exercise-induced neuroprotection. In mice lacking Hif2α in postnatal neurons, the number of TH+ DA neurons in the adult SNpc is diminished, but 3months of exercise rescues this loss. We conclude that HIF1α is necessary for exercise-induced neuroprotection and both HIF1α and HIF2α are necessary for the survival and function of adult SNpc DA neurons.

Stromal cells and stem cells in clinical bone regeneration

Stem-cell-mediated bone repair has been used in clinical trials for the regeneration of large craniomaxillofacial defects, to slow the process of bone degeneration in patients with osteonecrosis of the femoral head and for prophylactic treatment of distal tibial fractures. Successful regenerative outcomes in these investigations have provided a solid foundation for wider use of stromal cells in skeletal repair therapy. However, employing stromal cells to facilitate or enhance bone repair is far from being adopted into clinical practice. Scientific, technical, practical and regulatory obstacles prevent the widespread therapeutic use of stromal cells. Ironically, one of the major challenges lies in the limited understanding of the mechanisms via which transplanted cells mediate regeneration. Animal models have been used to provide insight, but these models largely fail to reproduce the nuances of human diseases and bone defects. Consequently, the development of targeted approaches to optimize cell-mediated outcomes is difficult. In this Review, we highlight the successes and challenges reported in several clinical trials that involved the use of bone-marrow-derived mesenchymal or adipose-tissue-derived stromal cells. We identify several obstacles blocking the mainstream use of stromal cells to enhance skeletal repair and highlight technological innovations or areas in which novel techniques might be particularly fruitful in continuing to advance the field of skeletal regenerative medicine.

Paracrine factors secreted by umbilical cord-derived mesenchymal stem cells induce angiogenesis in vitro by a VEGF-independent pathway

Improvement in angiogenesis using mesenchymal stem cells (MSCs) is evolving as an option in patients with vascular insufficiencies. The paracrine factors secreted by MSCs have been attributed to the angiogenic response. This study was conducted to identify the factors secreted by umbilical cord-derived MSCs (UCMSCs) that might play a role in angiogenesis. To this aim, we evaluated the presence of well known proangiogenic factors in the conditioned media (CM) derived from UCMSCs by ELISA. While vascular endothelial growth factor (VEGF), a well known angiogenic factor, was not detected in the CM, gene expression was nevertheless detected in these cells. Further investigations revealed the presence of soluble VEGF receptors (sVEGF-R1 and R2) that were capable of neutralizing exogenous VEGF. Human umbilical cord vein-derived endothelial cells exposed in vitro to CM, in comparison to control media, showed improved migration (P<0.007) and capillary-like network formation (P<0.001) with no significant change in endothelial cell proliferation. The angiogenic response observed with the paracrine factors secreted by UCMSC could be due to the presence of significant levels of a metalloprotease and matrix metalloproteases-2 (237.4±47.1 ng/10(6) cells). Data suggest that a VEGF-independent pathway is involved in the angiogenic response observed with endothelial cells in the presence of UCMSC-CM.

Bioactive copper-doped glass scaffolds can stimulate endothelial cells in co-culture in combination with mesenchymal stem cells

Bioactive glass (BG) scaffolds are being investigated for bone tissue engineering applications because of their osteoconductive and angiogenic nature. However, to increase the in vivo performance of the scaffold, including enhancing the angiogenetic growth into the scaffolds, some researchers use different modifications of the scaffold including addition of inorganic ionic components to the basic BG composition. In this study, we investigated the in vitro biocompatibility and bioactivity of Cu2+-doped BG derived scaffolds in either BMSC (bone-marrow derived mesenchymal stem cells)-only culture or co-culture of BMSC and human dermal microvascular endothelial cells (HDMEC). In BMSC-only culture, cells were seeded either directly on the scaffolds (3D or direct culture) or were exposed to ionic dissolution products of the BG scaffolds, kept in permeable cell culture inserts (2D or indirect culture). Though we did not observe any direct osteoinduction of BMSCs by alkaline phosphatase (ALP) assay or by PCR, there was increased vascular endothelial growth factor (VEGF) expression, observed by PCR and ELISA assays. Additionally, the scaffolds showed no toxicity to BMSCs and there were healthy live cells found throughout the scaffold. To analyze further the reasons behind the increased VEGF expression and to exploit the benefits of the finding, we used the indirect method with HDMECs in culture plastic and Cu2+-doped BG scaffolds with or without BMSCs in cell culture inserts. There was clear observation of increased endothelial markers by both FACS analysis and acetylated LDL (acLDL) uptake assay. Only in presence of Cu2+-doped BG scaffolds with BMSCs, a high VEGF secretion was demonstrated by ELISA; and typical tubular structures were observed in culture plastics. We conclude that Cu2+-doped BG scaffolds release Cu2+, which in turn act on BMSCs to secrete VEGF. This result is of significance for the application of BG scaffolds in bone tissue engineering approaches.

Role of copper in regression of cardiac hypertrophy

Pressure overload causes an accumulation of homocysteine in the heart, which is accompanied by copper depletion through the formation of copper-homocysteine complexes and the excretion of the complexes. Copper supplementation recovers cytochrome c oxidase (CCO) activity and promotes myocardial angiogenesis, along with the regression of cardiac hypertrophy and the recovery of cardiac contractile function. Increased copper availability is responsible for the recovery of CCO activity. Copper promoted expression of angiogenesis factors including vascular endothelial growth factor (VEGF) in endothelial cells is responsible for angiogenesis. VEGF receptor-2 (VEGFR-2) is critical for hypertrophic growth of cardiomyocytes and VEGFR-1 is essential for the regression of cardiomyocyte hypertrophy. Copper, through promoting VEGF production and suppressing VEGFR-2, switches the VEGF signaling pathway from VEGFR-2-dependent to VEGFR-1-dependent, leading to the regression of cardiomyocyte hypertrophy. Copper is also required for hypoxia-inducible factor-1 (HIF-1) transcriptional activity, acting on the interaction between HIF-1 and the hypoxia responsible element and the formation of HIF-1 transcriptional complex by inhibiting the factor inhibiting HIF-1. Therefore, therapeutic targets for copper supplementation-induced regression of cardiac hypertrophy include: (1) the recovery of copper availability for CCO and other critical cellular events; (2) the activation of HIF-1 transcriptional complex leading to the promotion of angiogenesis in the endothelial cells by VEGF and other factors; (3) the activation of VEGFR-1-dependent regression signaling pathway in the cardiomyocytes; and (4) the inhibition of VEGFR-2 through post-translational regulation in the hypertrophic cardiomyocytes. Future studies should focus on target-specific delivery of copper for the development of clinical application.

Hypoxia inducible factor-stabilizing bioactive glasses for directing mesenchymal stem cell behavior

Oxygen tension is a known regulator of mesenchymal stem cell (MSC) plasticity, differentiation, proliferation, and recruitment to sites of injury. Materials capable of affecting the MSC oxygen-sensing pathway, independently of the environmental oxygen pressure, are therefore of immense interest to the tissue engineering (TE) and regenerative medicine community. In this study, we describe the evaluation of the effect of hypoxia inducible factor (HIF)-stabilizing bioactive glasses (BGs) on human MSCs. The dissolution products from these hypoxia-mimicking BGs stabilized HIF-1α in a concentration-dependent manner, altered cell proliferation and metabolism, and upregulated a number of genes involved in the hypoxic response (HIF1A, HIF2A, and VHL), MSC survival (SAG and BCL2), extracellular matrix remodeling (MMP1), and angiogenesis (VEGF and PDGF). These HIF-stabilizing materials can therefore be used to improve MSC survival and enhance regeneration in a number of TE strategies.

Adipose tissue-derived mesenchymal stem cells in long-term dialysis patients display downregulation of PCAF expression and poor angiogenesis activation

We previously demonstrated that mesenchymal stem cells (MSCs) differentiate into functional kidney cells capable of urine and erythropoietin production, indicating that they may be used for kidney regeneration. However, the viability of MSCs from dialysis patients may be affected under uremic conditions. In this study, we isolated MSCs from the adipose tissues of end-stage kidney disease (ESKD) patients undergoing long-term dialysis (KD-MSCs; mean: 72.3 months) and from healthy controls (HC-MSCs) to compare their viability. KD-MSCs and HC-MSCs were assessed for their proliferation potential, senescence, and differentiation capacities into adipocytes, osteoblasts, and chondrocytes. Gene expression of stem cell-specific transcription factors was analyzed by PCR array and confirmed by western blot analysis at the protein level. No significant differences of proliferation potential, senescence, or differentiation capacity were observed between KD-MSCs and HC-MSCs. However, gene and protein expression of p300/CBP-associated factor (PCAF) was significantly suppressed in KD-MSCs. Because PCAF is a histone acetyltransferase that mediates regulation of hypoxia-inducible factor-1α (HIF-1α), we examined the hypoxic response in MSCs. HC-MSCs but not KD-MSCs showed upregulation of PCAF protein expression under hypoxia. Similarly, HIF-1α and vascular endothelial growth factor (VEGF) expression did not increase under hypoxia in KD-MSCs but did so in HC-MSCs. Additionally, a directed in vivo angiogenesis assay revealed a decrease in angiogenesis activation of KD-MSCs. In conclusion, long-term uremia leads to persistent and systematic downregulation of PCAF gene and protein expression and poor angiogenesis activation of MSCs from patients with ESKD. Furthermore, PCAF, HIF-1α, and VEGF expression were not upregulated by hypoxic stimulation of KD-MSCs. These results suggest that the hypoxic response may be blunted in MSCs from ESKD patients.

A comparative analysis of human mesenchymal stem cell response to hypoxia in vitro: Implications to translational strategies

PURPOSE

Mesenchymal stem cells (MSCs) are particularly valuable for structural tissue replacement. We compared the response to hypoxia among human MSCs derived from four different clinically relevant sources as an adjunct to translational developments.

METHODS

Immunophenotypically indistinguishable human MSC lineages derived from bone marrow (bmMSCs), adipose tissue (adMSCs), amniotic fluid (afMSCs), and umbilical cord blood (cbMSCs) were submitted to either room air or 1% O2, under otherwise standard culture conditions. Cell expansion and quantitative RT-PCR data were obtained at different time points. Statistical analysis was by two-way mixed model and the F-test (P<0.05).

RESULTS

The effect of hypoxia on expansion kinetics was dependent on cell source. Only prenatal sources of MSCs - afMSCs (P=0.002) and cbMSCs (P<0.001) - proliferated significantly faster under hypoxia than normoxia. Increased HIF1-alpha expression correlated consistently with increased cell expansion only among afMSCs. There were no significant variabilities in Survivin, Oct-4, and VEGF expressions.

CONCLUSIONS

Mesenchymal stem cell tolerance to hypoxia in vitro varies with cell source. Prenatal cells, particularly those derived from amniotic fluid, are more robust than their postnatal counterparts. HIF1-alpha may play a role in the amniotic fluid-derived cells' enhanced response. These findings should inform the choice of mesenchymal stem cells for prospective regenerative strategies.

The hypoxia-inducible factor pathway, prolyl hydroxylase domain protein inhibitors, and their roles in bone repair and regeneration

Hypoxia-inducible factors (HIFs) are oxygen-dependent transcriptional activators that play crucial roles in angiogenesis, erythropoiesis, energy metabolism, and cell fate decisions. The group of enzymes that can catalyse the hydroxylation reaction of HIF-1 is prolyl hydroxylase domain proteins (PHDs). PHD inhibitors (PHIs) activate the HIF pathway by preventing degradation of HIF-α via inhibiting PHDs. Osteogenesis and angiogenesis are tightly coupled during bone repair and regeneration. Numerous studies suggest that HIFs and their target gene, vascular endothelial growth factor (VEGF), are critical regulators of angiogenic-osteogenic coupling. In this brief perspective, we review current studies about the HIF pathway and its role in bone repair and regeneration, as well as the cellular and molecular mechanisms involved. Additionally, we briefly discuss the therapeutic manipulation of HIFs and VEGF in bone repair and bone tumours. This review will expand our knowledge of biology of HIFs, PHDs, PHD inhibitors, and bone regeneration, and it may also aid the design of novel therapies for accelerating bone repair and regeneration or inhibiting bone tumours.

Hypoxia-conditioned media allows species-specific attraction of bone marrow stromal cells without need for recombinant proteins

Background

In vivo tissue regeneration depends on migration of stem cells into injured areas, their differentiation into specific cell types, and their interaction with other cells that are necessary to generate new tissue. Human mesenchymal stem cells, a subset of bone marrow stromal cells (BMSCs), can migrate and differentiate into osteoblasts in bone tissue. This can be facilitated by recombinant growth factors and cytokines. In many animal species, the availability of genomic sequences, recombinant proteins, and/or antibodies is limited so that new approaches are needed to generate resources that facilitate migration of stem cells into tissue defect areas. Here we used bone marrow stromal cells of human, ovine, equine, and canine origin to generate hypoxia-conditioned media (HCM) in order to attract BMSCs of the respective species in migration assays.

Results

We show that HCM contain attractors even more potent than vascular endothelial growth factor and can therefore be used in many animal species without the need for purified proteins.

Conclusion

Generation of HCM is easy and cheap compared to preparation and purification of protein fractions and/or recombinant proteins. Hence, HCM could be applied in large animals (e.g. sheep, horse, dogs) for attraction of BMSCs into tissue defects caused by tumor resection or trauma.

Overexpression of FABP3 inhibits human bone marrow derived mesenchymal stem cell proliferation but enhances their survival in hypoxia

Studying the proliferative ability of human bone marrow derived mesenchymal stem cells in hypoxic conditions can help us achieve the effective regeneration of ischemic injured myocardium. Cardiac-type fatty acid binding protein (FABP3) is a specific biomarker of muscle and heart tissue injury. This protein is purported to be involved in early myocardial development, adult myocardial tissue repair and responsible for the modulation of cell growth and proliferation. We have investigated the role of FABP3 in human bone marrow derived mesenchymal stem cells under ischemic conditions. MSCs from 12 donors were cultured either in standard normoxic or modified hypoxic conditions, and the differential expression of FABP3 was tested by quantitative (RT)PCR and western blot. We also established stable FABP3 expression in MSCs and searched for variation in cellular proliferation and differentiation bioprocesses affected by hypoxic conditions. We identified: (1) the FABP3 differential expression pattern in the MSCs under hypoxic conditions; (2) over-expression of FABP3 inhibited the growth and proliferation of the MSCs; however, improved their survival in low oxygen environments; (3) the cell growth factors and positive cell cycle regulation genes, such as PCNA, APC, CCNB1, CCNB2 and CDC6 were all down-regulated; while the key negative cell cycle regulation genes TP53, BRCA1, CASP3 and CDKN1A were significantly up-regulated in the cells with FABP3 overexpression. Our data suggested that FABP3 was up-regulated under hypoxia; also negatively regulated the cell metabolic process and the mitotic cell cycle. Overexpression of FABP3 inhibited cell growth and proliferation via negative regulation of the cell cycle and down-regulation of cell growth factors, but enhances cell survival in hypoxic or ischemic conditions.

The role of bone marrow mesenchymal stem cells in the treatment of acute liver failure

Objective. This study is to investigate the effects of bone marrow mesenchymal stem cell (BMSC) transplantation on acute liver failure (ALF). Methods. BMSCs were separated from rat bone marrow, cultured, and identified by flow cytometry. Rat model with ALF was established by injecting D-galactosamine and lipopolysaccharide. Rats were randomly divided into the control group and BMSC transplantation group. The serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured at 24 h, 120 h, and 168 h after BMSC transplantation. Apoptosis was detected by TUNEL assay. The expression of VEGF and AFP proteins was detected by immunofluorescence. Caspase-1 and IL-18 proteins and mRNA were detected by immunohistochemistry and RT-PCR. Results. Compared with the control group, levels of ALT, AST, caspase-1 and IL-18 proteins, and mRNA in the transplantation group were significantly lower at 120 h and 168 h after BMSCs transplantation. Apoptosis was inhibited by BMSCs transplantation. The VEGF protein levels were increased with the improvement of liver function, and the AFP protein levels were increased with the deterioration of the liver function after BMSCs transplantation. Conclusions. BMSCs transplantation can improve liver function and inhibit hepatocyte apoptosis as well as promote hepatocyte proliferation in rat model with ALF.