HIF-1α Overexpression Induces Angiogenesis in Mesenchymal Stem Cells

Optimizing mesenchymal stem cell extracellular vesicles for chronic wound healing: Bioengineering, standardization, and safety

Chronic wounds represent a significant global burden, afflicting millions with debilitating complications. Despite standard care, impaired healing persists due to factors like persistent inflammation and impaired tissue regeneration. Mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs) offer an innovative regenerative medicine approach, delivering stem cell-derived therapeutic cargo in engineered nanoscale delivery systems. This review examines pioneering bioengineering strategies to engineer MSC-EVs into precision nanotherapeutics for chronic wounds. Emerging technologies like CRISPR gene editing, microfluidic manufacturing, and biomimetic delivery systems are highlighted for their potential to enhance MSC-EV targeting, optimize therapeutic cargo enrichment, and ensure consistent clinical-grade production. However, key hurdles remain, including batch variability, rigorous safety assessment for potential tumorigenicity, immunogenicity, and biodistribution profiling. Crucially, collaborative frameworks harmonizing regulatory science with bioengineering and patient advocacy hold the key to expediting global clinical translation. By overcoming these challenges, engineered MSC-EVs could catalyze a new era of off-the-shelf regenerative therapies, restoring hope and healing for millions afflicted by non-healing wounds.

HIF-1α and periodontitis: Novel insights linking host-environment interplay to periodontal phenotypes

Periodontitis, the sixth most prevalent epidemic disease globally, profoundly impacts oral aesthetics and masticatory functionality. Hypoxia-inducible factor-1α (HIF-1α), an oxygen-dependent transcriptional activator, has emerged as a pivotal regulator in periodontal tissue and alveolar bone metabolism, exerts critical functions in angiogenesis, erythropoiesis, energy metabolism, and cell fate determination. Numerous essential phenotypes regulated by HIF are intricately associated with bone metabolism in periodontal tissues. Extensive investigations have highlighted the central role of HIF and its downstream target genes and pathways in the coupling of angiogenesis and osteogenesis. Within this concise perspective, we comprehensively review the cellular phenotypic alterations and microenvironmental dynamics linking HIF to periodontitis. We analyze current research on the HIF pathway, elucidating its impact on bone repair and regeneration, while unraveling the involved cellular and molecular mechanisms. Furthermore, we briefly discuss the potential application of targeted interventions aimed at HIF in the field of bone tissue regeneration engineering. This review expands our biological understanding of the intricate relationship between the HIF gene and bone angiogenesis in periodontitis and offers valuable insights for the development of innovative therapies to expedite bone repair and regeneration.

Therapeutic effects of hypoxia-preconditioned bone marrow-derived mesenchymal stromal cells and their extracellular vesicles in experimental pulmonary arterial hypertension

AIMS

To evaluate BM-MSCs and their extracellular vesicles (EVs) preconditioned with hypoxia or normoxia in experimental pulmonary arterial hypertension (PAH).

MAIN METHODS

BM-MSCs were isolated and cultured under normoxia (MSC-N, 21%O2) or hypoxia (MSC-H, 1%O2) for 48 h. EVs were then isolated from MSCs under normoxia (EV-N) or hypoxia (EV-H). PAH was induced in male Wistar rats (n = 35) with monocrotaline (60 mg/kg); control animals (CTRL, n = 7) were treated with saline. On day 14, PAH animals received MSCs or EVs under normoxia or hypoxia, intravenously (n = 7/group). On day 28, right ventricular systolic pressure (RVSP), pulmonary acceleration time (PAT)/pulmonary ejection time (PET), and right ventricular hypertrophy (RVH) index were evaluated. Perivascular collagen content, vascular wall thickness, and endothelium-mesenchymal transition were analyzed.

KEY FINDINGS

PAT/PET was lower in the PAH group (0.26 ± 0.02, P < 0.001) than in CTRLs (0.43 ± 0.02) and only increased in the EV-H group (0.33 ± 0.03, P = 0.014). MSC-N (32 ± 6 mmHg, P = 0.036), MSC-H (31 ± 3 mmHg, P = 0.019), EV-N (27 ± 4 mmHg, P < 0.001), and EV-H (26 ± 5 mmHg, P < 0.001) reduced RVSP compared with the PAH group (39 ± 4 mmHg). RVH was higher in the PAH group than in CTRL and reduced after all therapies. All therapies decreased perivascular collagen fiber content, vascular wall thickness, and the expression of endothelial markers remained unaltered; only MSC-H and EV-H decreased expression of mesenchymal markers in pulmonary arterioles.

SIGNIFICANCE

MSCs and EVs, under normoxia or hypoxia, reduced right ventricular hypertrophy, perivascular collagen, and vessel wall thickness. Under hypoxia, MSCs and EVs were more effective at improving endothelial to mesenchymal transition in experimental PAH.

Physiological oxygen conditions enhance the angiogenic properties of extracellular vesicles from human mesenchymal stem cells

BACKGROUND

Following an ischemic injury to the brain, the induction of angiogenesis is critical to neurological recovery. The angiogenic benefits of mesenchymal stem cells (MSCs) have been attributed at least in part to the actions of extracellular vesicles (EVs) that they secrete. EVs are membrane-bound vesicles that contain various angiogenic biomolecules capable of eliciting therapeutic responses and are of relevance in cerebral applications due to their ability to cross the blood-brain barrier (BBB). Though MSCs are commonly cultured under oxygen levels present in injected air, when MSCs are cultured under physiologically relevant oxygen conditions (2-9% O2), they have been found to secrete higher amounts of survival and angiogenic factors. There is a need to determine the effects of MSC-EVs in models of cerebral angiogenesis and whether those from MSCs cultured under physiological oxygen provide greater functional effects.

METHODS

Human adipose-derived MSCs were grown in clinically relevant serum-free medium and exposed to either headspace oxygen concentrations of 18.4% O2 (normoxic) or 3% O2 (physioxic). EVs were isolated from MSC cultures by differential ultracentrifugation and characterized by their size, concentration of EV specific markers, and their angiogenic protein content. Their functional angiogenic effects were evaluated in vitro by their induction of cerebral microvascular endothelial cell (CMEC) proliferation, tube formation, and angiogenic and tight junction gene expressions.

RESULTS

Compared to normoxic conditions, culturing MSCs under physioxic conditions increased their expression of angiogenic genes SDF1 and VEGF, and subsequently elevated VEGF-A content in the EV fraction. MSC-EVs demonstrated an ability to induce CMEC angiogenesis by promoting tube formation, with the EV fraction from physioxic cultures having the greatest effect. The physioxic EV fraction further upregulated the expression of CMEC angiogenic genes FGF2, HIF1, VEGF and TGFB1, as well as genes (OCLN and TJP1) involved in BBB maintenance.

CONCLUSIONS

EVs from physioxic MSC cultures hold promise in the generation of a cell-free therapy to induce angiogenesis. Their positive angiogenic effect on cerebral microvascular endothelial cells demonstrates that they may have utility in treating ischemic cerebral conditions, where the induction of angiogenesis is critical to improving recovery and neurological function.

Revascularization and angiogenesis for bone bioengineering in the craniofacial region: a review

The revascularization of grafted tissues is a complicated and non-straightforward process, which makes it challenging to perform reconstructive surgery for critical-sized bone defects. This challenge is combined with the low vascularity that results from radiotherapy. This low vascularity could result from ischemia-reperfusion injuries, also known as ischemia which may happen upon grafting. Ischemia may affect the hard tissue during reconstruction, and this can often cause resorption, infections, disfigurement, and malunion. This paper therefore reviews the clinical and experimental application of procedures that were employed to improve the reconstructive surgery process, which would ensure that the vascularity of the tissue is maintained or enhanced. It also presents the key strategies that are implemented to perform tissue engineering within the grafted sites aiming to optimize the microenvironment and to enhance the overall process of neovascularization and angiogenesis. This review reveals that the current strategies, according to the literature, are the seeding of the mature and progenitor cells, use of extracellular matrix (ECM), co-culturing of osteoblasts with the ECM, growth factors and the use of microcapillaries incorporated into the scaffold design. However, due to the unstable and regression-prone capillary structures in bone constructs, further research focusing on creating long-lasting and stable blood vessels is required.

Exploring the Expression of Pro-Inflammatory and Hypoxia-Related MicroRNA-20a, MicroRNA-30e, and MicroRNA-93 in Periodontitis and Gingival Mesenchymal Stem Cells under Hypoxia

Hypoxia associated with inflammation are common hallmarks observed in several diseases, and it plays a major role in the expression of non-coding RNAs, including microRNAs (miRNAs). In addition, the miRNA target genes for hypoxia-inducible factor-1α (HIF-1α) and nuclear factor of activated T cells-5 (NFAT5) modulate the adaptation to hypoxia. The objective of the present study was to explore hypoxia-related miRNA target genes for HIF-1α and NFAT5, as well as miRNA-20a, miRNA-30e, and miRNA-93 expression in periodontitis versus healthy gingival tissues and gingival mesenchymal stem cells (GMSCs) cultured under hypoxic conditions. Thus, a case-control study was conducted, including healthy and periodontitis subjects. Clinical data and gingival tissue biopsies were collected to analyze the expression of miRNA-20a, miRNA-30e, miRNA-93, HIF-1α, and NFAT5 by qRT-PCR. Subsequently, GMSCs were isolated and cultured under hypoxic conditions (1% O₂) to explore the expression of the HIF-1α, NFAT5, and miRNAs. The results showed a significant upregulation of miRNA-20a (p = 0.028), miRNA-30e (p = 0.035), and miRNA-93 (p = 0.026) in periodontitis tissues compared to healthy gingival biopsies. NFAT5 mRNA was downregulated in periodontitis tissues (p = 0.037), but HIF-1α was not affected (p = 0.60). Interestingly, hypoxic GMSCs upregulated the expression of miRNA-20a and HIF-1α, but they downregulated miRNA-93e. In addition, NFAT5 mRNA expression was not affected in hypoxic GMSCs. In conclusion, in periodontitis patients, the expression of miRNA-20a, miRNA-30e, and miRNA-93 increased, but a decreased expression of NFAT5 mRNA was detected. In addition, GMSCs under hypoxic conditions upregulate the HIF-1α and increase miRNA-20a (p = 0.049) expression. This study explores the role of inflammatory and hypoxia-related miRNAs and their target genes in periodontitis and GMSCs. It is crucial to determine the potential therapeutic target of these miRNAs and hypoxia during the periodontal immune–inflammatory response, which should be analyzed in greater depth in future studies.

Endometriosis-Associated Angiogenesis and Anti-angiogenic Therapy for Endometriosis

Endometriosis is a known estrogen-dependent inflammatory disease affecting reproductive-aged women. Common symptoms include pelvic pain, dysmenorrhea, dyspareunia, heavy menstrual bleeding, and infertility. The exact etiology of endometriosis is largely unknown, and, thus, the diagnosis and treatment of endometriosis are challenging. A complex interplay of many molecular mechanisms is thought to aid in the progression of endometriosis, most notably angiogenesis. This mini-review examines our current knowledge of the molecular etiology of endometriosis-associated angiogenesis and discusses anti-angiogenic therapy, in the blockade of endometriosis-associated angiogenesis, as potential non-hormonal therapy for the treatment of endometriosis.

Considerations for the clinical use of stem cells in genitourinary regenerative medicine

The genitourinary tract can be affected by several pathologies which require repair or replacement to recover biological functions. Current therapeutic strategies are challenged by a growing shortage of adequate tissues. Therefore, new options must be considered for the treatment of patients, with the use of stem cells (SCs) being attractive. Two different strategies can be derived from stem cell use: Cell therapy and tissue therapy, mainly through tissue engineering. The recent advances using these approaches are described in this review, with a focus on stromal/mesenchymal cells found in adipose tissue. Indeed, the accessibility, high yield at harvest as well as anti-fibrotic, immunomodulatory and proangiogenic properties make adipose-derived stromal/SCs promising alternatives to the therapies currently offered to patients. Finally, an innovative technique allowing tissue reconstruction without exogenous material, the self-assembly approach, will be presented. Despite advances, more studies are needed to translate such approaches from the bench to clinics in urology. For the 21^st century, cell and tissue therapies based on SCs are certainly the future of genitourinary regenerative medicine.

Bioactive Scaffolds Integrated with Liposomal or Extracellular Vesicles for Bone Regeneration

With population aging and increased life expectancy, an increasing number of people are facing musculoskeletal health problems that necessitate therapeutic intervention at defect sites. Bone tissue engineering (BTE) has become a promising approach for bone graft substitutes as traditional treatments using autografts or allografts involve clinical complications. Significant advancements have been made in developing ideal BTE scaffolds that can integrate bioactive molecules promoting robust bone repair. Herein, we review bioactive scaffolds tuned for local bone regenerative therapy, particularly through integrating synthetic liposomal vesicles or extracellular vesicles to the scaffolds. Liposomes offer an excellent drug delivery system providing sustained release of the loaded bioactive molecules. Extracellular vesicles, with their inherent capacity to carry bioactive molecules, are emerging as an advanced substitute of synthetic nanoparticles and a novel cell-free therapy for bone regeneration. We discuss the recent advance in the use of synthetic liposomes and extracellular vesicles as bioactive materials combined with scaffolds, highlighting major challenges and opportunities for their applications in bone regeneration. We put a particular focus on strategies to integrate vesicles to various biomaterial scaffolds and introduce the latest advances in achieving sustained release of bioactive molecules from the vesicle-loaded scaffolds at the bone defect site.

Translational insights into stem cell preconditioning: From molecular mechanisms to preclinical applications

Cell-based therapy (CBT) is a revolutionary approach for curing a variety of degenerative diseases. Stem cell-based regenerative medicine is a novel strategy for treating tissue damages regarding stem cells unique properties such as differentiation potential, paracrine impacts, and self-renewal ability. However, the current cell-based treatments encounter considerable challenges to be translated into clinical practice, including low cell survival, migration, and differentiation rate of transplanted stem cells. The poor stem cell therapy outcomes mainly originate from the unfavorable condition of damaged tissues for transplanted stem cells. The promising method of preconditioning improves cell resistance against the host environment's stress by imposing certain conditions similar to the harsh microenvironment of the damaged tissues on the transplanted stem cells. Various pharmacological, biological, and physical inducers are able to establish preconditioning. In addition to their known pharmacological effects on tissues and cells, these preconditioning agents improve cell biological aspects such as cell survival, proliferation, differentiation, migration, immunomodulation, paracrine impacts, and angiogenesis. This review focuses on different protocols and inducers of preconditioning along with underlying molecular mechanisms of their effects on stem cell behavior. Moreover, preclinical applications of preconditioned stem cells in various damaged organs such as heart, lung, brain, bone, cartilage, liver, and kidney are discussed with prospects of their translation into the clinic.

Comparing the Therapeutic Potential of Stem Cells and their Secretory Products in Regenerative Medicine

Cell therapy involves the transplantation of human cells to replace or repair the damaged tissues and modulate the mechanisms underlying disease initiation and progression in the body. Nowadays, many different types of cell-based therapy are developed and used to treat a variety of diseases. In the past decade, cell-free therapy has emerged as a novel approach in regenerative medicine after the discovery that the transplanted cells exerted their therapeutic effect mainly through the secretion of paracrine factors. More and more evidence showed that stem cell-derived secretome, i.e., growth factors, cytokines, and extracellular vesicles, can repair the injured tissues as effectively as the cells. This finding has spurred a new idea to employ secretome in regenerative medicine. Despite that, will cell-free therapy slowly replace cell therapy in the future? Or are these two modes of treatment still needed to address different diseases and conditions? This review provides an indepth discussion about the values of stem cells and secretome in regenerative medicine. In addition, the safety, efficacy, advantages, and disadvantages of using these two modes of treatment in regenerative medicine are also critically reviewed.

Therapeutic efficiency of adipose-derived mesenchymal stem cells in healing of experimentally induced gastric ulcers in rats

Gastric (peptic) ulcer is a major gastrointestinal disorder with high morbidity and mortality. While several drugs have been used to treat gastric ulcers, such as proton pump inhibitor-based triple therapy for Helicobacter pylori eradication, but hey result in adverse side effects. Therefore, development of new alternative therapies is desirable. Many recent studies have shown that mesenchymal stem cells (MSCs) might have an enhancing effect on the ulcerated gastric mucosa. The aim of this study is to evaluate the efficacy of MSCs in the treatment of indomethacin-induced gastric ulcer, and to compare it with the normal ulcer autohealing. This work was performed on 36 adult male albino rats, divided into four groups: Group I (control group), Group II (ulcer group), Group III (autohealing group), and Group IV (stem cells-treated group). The histological changes of gastric mucosa were examined in sections stained with H&E using light microscope for expression of vascular endothelial growth factors (VEGF) and proliferating cell nuclear antigen (PCNA) in immunohistochemical stained sections using image analyzer. The results from MSCs-treated group revealed restoration of the normal architecture of the gastric mucosa with comparison to the autohealing group which showed excessive granulation tissue and heavy cellular infiltration with disorganized architecture of the fundic mucosa. Immunohistochemical examination showed strong expression of both VEGF and PCNA in the MSCs-treated group. So it was concluded that MSCs accelerate gastric ulcer healing when injected intraperitoneally, compared to autohealing process which showed delayed healing.

Mesenchymal stem cells in the treatment of osteonecrosis of the jaw

Medication-related osteonecrosis of the jaw (MRONJ) has recently associated to the increase in antiresorptive and anti-angiogenic drugs prescriptions in the treatment of oncologic and osteoporotic patients. The physiopathogenesis of MRONJ remains unclear and available treatments are unsatisfactory. Newer pharmacological treatments have shown good results, but are not curative and could have major side effects. At the same time as pharmacological treatments, mesenchymal stem cells (MSCs) have emerged as a promising therapeutic modality for tissue regeneration and repair. MSCs are multipotential non-hematopoietic progenitor cells capable to differentiating into multiple lineages of the mesenchyme. Bone marrow MSCs can differentiate into osteogenic cells and display immunological properties and secrete paracrine anti-inflammatory factors in damaged tissues. The immunomodulatory, reparative, and anti-inflammatory properties of bone marrow MSCs have been tested in a variety of animal models of MRONJ and applied in specific clinical settings. The aim of this review is to discuss critically the immunogenicity and immunomodulatory properties of MSCs, both in vitro and in vivo, the possible underlying mechanisms of their effects, and their potential clinical use as modulators of immune responses in MRONJ, and to identify clinical safety and recommendations for future research.

Dual effects of hypoxia on proliferation and osteogenic differentiation of mouse clonal mesenchymal stem cells

Mouse clonal mesenchymal stem cells (mc-MSCs) were cultured on a Cytodex 3 microcarrier in a spinner flask for a suspension culture under hypoxia condition to increase mass productivity. The hypoxia environment was established using 4.0 mM Na₂SO₃ with 10 μM or 100 µM CoCl₂ for 24 h in a low glucose DMEM medium. As a result, the proliferation of mc-MSCs under hypoxic conditions was 1.56 times faster than the control group over 7 days. The gene expression of HIF-1a and VEGFA increased 4.62 fold and 2.07 fold, respectively. Furthermore, the gene expression of ALP, RUNX2, COL1A, and osteocalcin increased significantly by 9.55, 1.55, 2.29, and 2.53 times, respectively. In contrast, the expression of adipogenic differentiation markers, such as PPAR-γ and FABP4, decreased. These results show that the hypoxia environment produced by these chemicals in a suspension culture increases the proliferation of mc-MSCs and promotes the osteogenic differentiation of mc-MSCs.

Optimal Hypoxic Preconditioning of Human Embryonic Stem Cell-Derived Mesenchymal Stem Cells (hES-MSCs) and Their Characteristics

Background and Objectives

Hypoxia is frequently used to enhance stem cell function. However, the optimal level of hypoxia for growth and function of human embryonic stem cell-derived mesenchymal stem cells (hES-MSCs) is yet to be determined. The purpose of this study was to find the optimal level of hypoxia for hES-MSCs and characteristics of hES-MSCs cultured under these optimal hypoxic conditions.

Methods and Results

Cell viability and changes in the morphology of hES-MSCs were determined through cell proliferation and CCK-8 assay. The hES-MSCs were preconditioned under various hypoxic conditions (0.5∼5% O₂ and 24∼72 h). The expression of cytokines in each culture condition was compared using cytokine array analysis. The morphology of hES-MSCs did not change under various hypoxic culture conditions. hES-MSCs viability after 48 h incubation in 2% O₂ condition was higher than that in normoxic condition. HIF1α expression was increased up to six folds after 48 h of hypoxic preconditioning. HIF1α expression in hES-MSCs peaked after 48 h of incubation in 1% O₂ condition. The expressions of PDGF-BB, IGFBP-6, VEGF-A, and angiogenin were increased after hES-MSCs were incubated for 48 h in 2% O₂ condition.

Conclusions

The hES-MSCs viability and expressions of PDGF-BB, IGFBP-6, VEGF-A, and angiogenin increased after 48 h incubation in 2% O₂ condition.

Mesenchymal stem cells as a double-edged sword in tumor growth: focusing on MSC-derived cytokines

Mesenchymal stem cells (MSCs) show homing capacity towards tumor sites. Numerous reports indicate that they are involved in multiple tumor-promoting processes through several mechanisms, including immunosuppression; stimulation of angiogenesis; transition to cancer-associated fibroblasts; inhibition of cancer cell apoptosis; induction of epithelial-mesenchymal transition (EMT); and increase metastasis and chemoresistance. However, other studies have shown that MSCs suppress tumor growth by suppressing angiogenesis, incrementing inflammatory infiltration, apoptosis and cell cycle arrest, and inhibiting the AKT and Wnt signaling pathways. In this review, we discuss the supportive and suppressive impacts of MSCs on tumor progression and metastasis. We also discuss MSC-based therapeutic strategies for cancer based on their potential for homing to tumor sites.

Key Metabolic Pathways in MSC-Mediated Immunomodulation: Implications for the Prophylaxis and Treatment of Graft Versus Host Disease

Mesenchymal stromal cells (MSCs) are spindle-shaped, plastic-adherent cells in vitro with potent immunosuppressive activity both in vitro and in vivo. MSCs have been employed as a cellular immunotherapy in diverse preclinical models and clinical trials, but most commonly as agents for the prophylaxis or therapy of graft versus host disease after hematopoietic cell transplantation. In addition to the oft studied secreted cytokines, several metabolic pathways intrinsic to MSCs, notably indoleamine 2,3-dioxygenase, prostaglandin E2, hypoxia-inducible factor 1 α, heme oxygenase-1, as well as energy-generating metabolism, have been shown to play roles in the immunomodulatory activity of MSCs. In this review, we discuss these key metabolic pathways in MSCs which have been reported to contribute to MSC therapeutic effects in the setting of hematopoietic cell transplantation and graft versus host disease. Understanding the contribution of MSC metabolism to immunomodulatory activity may substantially inform the development of future clinical applications of MSCs.

Conditioned medium harvested from Hif1α engineered mesenchymal stem cells ameliorates LAD-occlusion -induced injury in rat acute myocardial ischemia model

Acute myocardial infarction (AMI) is the most common type of ischemic heart diseases with a high mortality rate. Although recent advances in medical cares and therapies have increased the patient's outcomes, but, still there is no real and effective therapeutic modality for AMI. Hence, development of novel therapeutic strategies is under focus of investigations. MSCs-based therapy has been proposed for AMI, though its efficacy is controversial yet. It is believed that MSCs exert their healing effects via secretion of growth factors/cytokines. However, these cells produce a very minute amount of the factors under normal cultivation. Here, in an attempt to improve the potential therapeutic effect of MSCs-derived conditioned medium (CM) on AMI, we transfected the cells with a recombinant plasmid encoding Hif1α-3A (a mutant form of Hif1α stable under normoxic condition), so Hif1α expression and secretion into CM (MSCs-Hif1α-CM) could be up-regulated under normoxic condition. The therapeutic potential of the MSCs-Hif1α-3A-CM was investigated in a rat model of AMI and compared to the CM harvested from non-manipulated MSCs. Our results showed that the MSCs-Hif1α-3A-CM mitigated MI-induced tissues injury, decreased fibrosis, reduced apoptosis, and limited infarct area size. These findings propose a potential therapeutic strategy for treatment of AMI. However, further preclinical and clinical investigations in this regard are still needed.

HIF-1α Directly Controls WNT7A Expression During Myogenesis

Herein we unveil that Hypoxia-inducible factor-1α (HIF-1α) directly regulates WNT7A expression during myogenesis. In fact, chromatin immunoprecipitation (ChiP) and site-directed mutagenesis experiments revealed two distinct hypoxia response elements (HREs) that are specific HIF-1α binding sites on the WNT7A promoter. Remarkably, a pharmacological activation of HIF-1α induced WNT7A expression and enhanced muscle differentiation. On the other hand, silencing of WNT7A using CRISPR/Cas9 genome editing blocked the effects of HIF-1α activation on myogenesis. Finally, treatment with prolyl hydroxylases (PHDs) inhibitors improved muscle regeneration in vitro and in vivo in a cardiotoxin (CTX)-induced muscle injury mouse model, paving the way for further studies to test its efficacy on acute and chronic muscular pathologies.

Biomaterials functionalized with MSC secreted extracellular vesicles and soluble factors for tissue regeneration

The therapeutic benefits of mesenchymal stromal cell (MSC) transplantation have been attributed to their secreted factors, including extracellular vesicles (EVs) and soluble factors. The potential of employing the MSC secretome as an alternative acellular approach to cell therapy is being investigated in various tissue injury indications, but EVs administered via bolus injections are rapidly sequestered and cleared. However, biomaterials offer delivery platforms to enhance EV retention rates and healing efficacy. In this review, we highlight the mechanisms underpinning the therapeutic effects of MSC-EVs and soluble factors as effectors of immunomodulation and tissue regeneration, conferred primarily via their nucleic acid and protein contents. We discuss how manipulating the cell culture microenvironment or genetic modification of MSCs can further augment the potency of their secretions. The most recent advances in the development of EV-functionalized biomaterials that mediate enhanced angiogenesis and cell survival, while attenuating inflammation and fibrosis, are presented. Finally, some technical challenges to be considered for the clinical translation of biomaterials carrying MSC-secreted bioactive cargo are discussed.

Genetic Engineering as a Strategy to Improve the Therapeutic Efficacy of Mesenchymal Stem/Stromal Cells in Regenerative Medicine

Mesenchymal stem/stromal cells (MSCs) have been widely studied in the field of regenerative medicine for applications in the treatment of several disease settings. The therapeutic potential of MSCs has been evaluated in studies in vitro and in vivo, especially based on their anti-inflammatory and pro-regenerative action, through the secretion of soluble mediators. In many cases, however, insufficient engraftment and limited beneficial effects of MSCs indicate the need of approaches to enhance their survival, migration and therapeutic potential. Genetic engineering emerges as a means to induce the expression of different proteins and soluble factors with a wide range of applications, such as growth factors, cytokines, chemokines, transcription factors, enzymes and microRNAs. Distinct strategies have been applied to induce genetic modifications with the goal to enhance the potential of MCSs. This review aims to contribute to the update of the different genetically engineered tools employed for MSCs modification, as well as the factors investigated in different fields in which genetically engineered MSCs have been tested.

Mechanisms behind the Immunoregulatory Dialogue between Mesenchymal Stem Cells and Th17 Cells

Mesenchymal stem cells (MSCs) exhibit potent immunoregulatory abilities by interacting with cells of the adaptive and innate immune system. In vitro, MSCs inhibit the differentiation of T cells into T helper 17 (Th17) cells and repress their proliferation. In vivo, the administration of MSCs to treat various experimental inflammatory and autoimmune diseases, such as rheumatoid arthritis, type 1 diabetes, multiple sclerosis, systemic lupus erythematosus, and bowel disease showed promising therapeutic results. These therapeutic properties mediated by MSCs are associated with an attenuated immune response characterized by a reduced frequency of Th17 cells and the generation of regulatory T cells. In this manuscript, we review how MSC and Th17 cells interact, communicate, and exchange information through different ways such as cell-to-cell contact, secretion of soluble factors, and organelle transfer. Moreover, we discuss the consequences of this dynamic dialogue between MSC and Th17 well described by their phenotypic and functional plasticity.

Advanced Strategies for the Regeneration of Lumbar Disc Annulus Fibrosus

Damage to the annulus fibrosus (AF), the outer region of the intervertebral disc (IVD), results in an undesirable condition that may accelerate IVD degeneration causing low back pain. Despite intense research interest, attempts to regenerate the IVD have failed so far and no effective strategy has translated into a successful clinical outcome. Of particular significance, the failure of strategies to repair the AF has been a major drawback in the regeneration of IVD and nucleus replacement. It is unlikely to secure regenerative mediators (cells, genes, and biomolecules) and artificial nucleus materials after injection with an unsealed AF, as IVD is exposed to significant load and large deformation during daily activities. The AF defects strongly change the mechanical properties of the IVD and activate catabolic routes that are responsible for accelerating IVD degeneration. Therefore, there is a strong need to develop effective therapeutic strategies to prevent or reconstruct AF damage to support operational IVD regenerative strategies and nucleus replacement. By the way of this review, repair and regenerative strategies for AF reconstruction, their current status, challenges ahead, and future outlooks were discussed.

Modulation of the in vitro angiogenic potential of human mesenchymal stromal cells from different tissue sources

Mesenchymal stromal cells (MSCs) have been widely exploited for the treatment of several conditions due to their intrinsic regenerative and immunomodulatory properties. MSC have demonstrated to be particularly relevant for the treatment of ischemic diseases, where MSC-based therapies can stimulate angiogenesis and induce tissue regeneration. Regardless of the condition targeted, recent analyses of MSC-based clinical trials have demonstrated limited benefits indicating a need to improve the efficacy of this cell product. Preconditioning MSC ex vivo through microenvironment modulation was found to improve MSC survival rate and thus prolong their therapeutic effect. This workstudy aims at enhancing the in vitro angiogenic capacity of a potential MSC-based medicinal product by comparing different sources of MSC and culture conditions. MSC from three different sources (bone marrow [BM], adipose tissue [AT], and umbilical cord matrix [UCM]) were cultured with xenogeneic-/serum-free culture medium under static conditions and their angiogenic potential was studied. Results indicated a higher in vitro angiogenic capacity of UCM MSC, compared with cells derived from BM and AT. Physicochemical preconditioning of UCM MSC through a microcarrier-based culture platform and low oxygen concentration (2% O₂ , compared with atmospheric air) increased the in vitro angiogenic potential of the cultured cells. Envisaging the clinical manufacturing of an allogeneic, off-the-shelf MSC-based product, preconditioned UCM MSC maintain the angiogenic gene expression profile upon cryopreservation and delivery processes in the conditions of our study. These results are expected to contribute to the development of MSC-based therapies in the context of angiogenesis.

Engineered Human Adipose-Derived Stem Cells Inducing Endothelial Lineage and Angiogenic Response

IMPACT STATEMENT

With respect to the persistent hunt for a cytocompatible, translational, reproducible, and effective approach in engineering primary human adipose-derived mesenchymal stromal cells (hADMSCs), we demonstrate the application of Neon^® Transfection System in adequate transient delivery of angiogenic factors. The study presents functional assessment of this approach in vitro, with two notable outcomes at translational perspective; (1) Bioengineered hADMSCs secretome does induce endothelial lineage commitment of stem cells at both transcriptional and translational levels and (2) Combinatorial delivery of vascular endothelial growth factor A and hypoxia-inducible factor-1α by bioengineered hADMSCs enhance upregulation of endothelial cell proliferation, migration-associated wound closure, and endothelial tube formation with augmented Flk-1 expression, as compared with their independent actions. The methods described in this study paves way for in vivo evaluation on identification of appropriate chronic wound models and subsequently for clinical translation. The technology developed also has application in vascularization of tissue-engineered constructs.

Materials Stiffness-Dependent Redox Metabolic Reprogramming of Mesenchymal Stem Cells for Secretome-Based Therapeutic Angiogenesis

Cellular redox metabolism has emerged as a key tenet in stem cell biology that can profoundly influence the paracrine activity and therapeutic efficacy of mesenchymal stem cells (MSCs). Although the use of materials cues to direct the differentiation of MSCs has been widely investigated, little is known regarding the role of materials in the control of redox paracrine signaling in MSCs. Herein, using a series of mechanically tunable fibronectin-conjugated polyacrylamide (FN-PAAm) hydrogel substrates, it is shown that a mechanically compliant microenvironment with native-tissue mimicking stiffness (E = 0.15 kPa) can mechano-regulate the intracellular reactive oxygen species (ROS) level in human adipose-derived MSCs (ADMSCs). The cells reciprocate to the ROS imbalance by co-activating the nuclear factor erythroid 2-related factor 2 and hypoxia-inducible factor 1 alpha stress response signaling pathways to increase the production of vascular endothelial growth factor and basic fibroblast growth factor. Conditioned medium collected from ADMSCs grown on the 0.15 kPa FN-PAAm is found to significantly promote in vitro and ex ovo vascularization events. Collectively, these findings highlight the importance of delineating critical materials properties that can enable the reprogramming of cellular redox signaling for advanced MSCs-based secretome regenerative medicine.

The multifaceted role of mesenchymal stem cells in cancer

Mesenchymal stem cells (MSCs) are multipotent stem cells derived from the mesoderm that give rise to several mesenchymal lineages, including osteoblasts, adipocytes, chondrocytes and myocytes. Their potent ability to home to tumors coupled with their differentiation potential and immunosuppressive function positions MSCs as key regulators of tumor fate. Here we review the existing knowledge on the involvement of MSCs in multiple tumor-promoting processes, including angiogenesis, epithelial-mesenchymal transition, metastasis, immunosuppression and therapy resistance. We also discuss the clinical potential of MSC-based therapy for cancer.

The Winding Road of Cardiac Regeneration-Stem Cell Omics in the Spotlight

Despite significant progress in treating ischemic cardiac disease and succeeding heart failure, there is still an unmet need to develop effective therapeutic strategies given the persistent high-mortality rate. Advances in stem cell biology hold great promise for regenerative medicine, particularly for cardiac regeneration. Various cell types have been used both in preclinical and clinical studies to repair the injured heart, either directly or indirectly. Transplanted cells may act in an autocrine and/or paracrine manner to improve the myocyte survival and migration of remote and/or resident stem cells to the site of injury. Still, the molecular mechanisms regulating cardiac protection and repair are poorly understood. Stem cell fate is directed by multifaceted interactions between genetic, epigenetic, transcriptional, and post-transcriptional mechanisms. Decoding stem cells’ “panomic” data would provide a comprehensive picture of the underlying mechanisms, resulting in patient-tailored therapy. This review offers a critical analysis of omics data in relation to stem cell survival and differentiation. Additionally, the emerging role of stem cell-derived exosomes as “cell-free” therapy is debated. Last but not least, we discuss the challenges to retrieve and analyze the huge amount of publicly available omics data.

Bone marrow-derived mesenchymal stromal cell: what next?

Bone marrow mesenchymal stromal cell (MSC) is a potential alternative in regenerative medicine and has great potential in many pathologic conditions including kidney disease. Although most of the studies demonstrate MSC efficiency, the regenerative potential may not be efficient in all diseases and patients. Stem cell feasibility is modified by donor characteristics as gender, age, diet, and health status, producing both positive and negative results. The conditioning of MSC can potentiate its effects and modify its culture medium (CM). In current practices, the cell-free treatment is gaining notable attention, while MSC-conditioned CM is being applied and studied in many experimental diseases, including, but not limited to, certain kidney diseases. This may be the next step for clinical trials. Studies in stem cell CM have focused mainly on extracellular vesicles, nucleic acids (mRNA and microRNA), lipids, and proteins presented in this CM. They mediate regenerative effects of MSC in a harmonic manner. In this review, we will analyze the regenerative potential of MSC and its CM as well as discuss some effective techniques for modifying its fractions and improving its therapeutic potential. CM fractions may be modified by hypoxic conditions, inflammation, lipid exposition, and protein growth factors. Other possible mechanisms of action of stem cells are also suggested. In the future, the MSC paracrine effect may be modified to more closely meet each patient’s needs.

Regenerative medicine in kidney disease: where we stand and where to go

The kidney is a complex organ with more than 20 types of specialized cells that play an important role in maintaining the body's homeostasis. The epithelial tubular cell is formed during embryonic development and has little proliferative capacity under physiological conditions, but after acute injury the kidney does have regenerative capacity. However, after repetitive or severe lesions, it may undergo a maladaptation process that predisposes it to chronic kidney injury. Regenerative medicine includes various repair and regeneration techniques, and these have gained increasing attention in the scientific literature. In the future, not only will these techniques contribute to the repair and regeneration of the human kidney, but probably also to the construction of an entire organ. New mechanisms studied for kidney regeneration and repair include circulating stem cells as mesenchymal stromal/stem cells and their paracrine mechanisms of action; renal progenitor stem cells; the leading role of tubular epithelial cells in the tubular repair process; the study of zebrafish larvae to understand the process of nephron development, kidney scaffold and its repopulation; and, finally, the development of organoids. This review elucidates where we are in terms of current scientific knowledge regarding these mechanisms and the promises of future scientific perspectives.

3D Printed porous polyamide macrocapsule combined with alginate microcapsules for safer cell-based therapies

Cell microencapsulation is an attractive strategy for cell-based therapies that allows the implantation of genetically engineered cells and the continuous delivery of de novo produced therapeutic products. However, the establishment of a way to retrieve the implanted encapsulated cells in case the treatment needs to be halted or when cells need to be renewed is still a big challenge. The combination of micro and macroencapsulation approaches could provide the requirements to achieve a proper immunoisolation, while maintaining the cells localized into the body. We present the development and characterization of a porous implantable macrocapsule device for the loading of microencapsulated cells. The device was fabricated in polyamide by selective laser sintering (SLS), with controlled porosity defined by the design and the sintering conditions. Two types of microencapsulated cells were tested in order to evaluate the suitability of this device; erythropoietin (EPO) producing C2C12 myoblasts and Vascular Endothelial Growth Factor (VEGF) producing BHK fibroblasts. Results showed that, even if the metabolic activity of these cells decreased over time, the levels of therapeutic protein that were produced and, importantly, released to the media were stable.

Relevant biological processes for tissue development with stem cells and their mechanistic modeling: A review

A potential alternative for tissue transplants is tissue engineering, in which the interaction of cells and biomaterials can be optimized. Tissue development in vitro depends on the complex interaction of several biological processes such as extracellular matrix synthesis, vascularization and cell proliferation, adhesion, migration, death, and differentiation. The complexity of an individual phenomenon or of the combination of these processes can be studied with phenomenological modeling techniques. This work reviews the main biological phenomena in tissue development and their mathematical modeling, focusing on mesenchymal stem cell growth in three-dimensional scaffolds.

Low oxygen tension modulates the osteogenic differentiation of mouse embryonic stem cells

This study examined the effects of low oxygen tension on the osteogenic differentiation of embryonic stem cells (ESCs) in a three-dimensional culture system. The high expression levels of hypoxia-related proteins hypoxia-inducible factor-1α and vascular endothelial growth factor were first validated in ESCs subjected to hypoxic conditions compared with normoxic controls. The osteogenic differentiation of hypoxic ESCs with either osteogenic or osteogenic factor-free media was subsequently evaluated by measuring alkaline phosphatase activity, intracellular calcium levels, matrix mineralization, and the protein levels of osteogenic markers Runt-related transcription factor 2 and osterix. We confirmed that hypoxia significantly stimulated ESC osteogenic activity; the strongest stimulation of ESC osteogenesis was exerted when cells were grown in osteogenic media. To identify differentially expressed genes associated with hypoxia-induced ESC differentiation, we performed microarray analysis of ESCs cultured in osteogenic media under normoxic and hypoxic conditions. This study demonstrated that differences in oxygen tension induced the differential expression of genes known to play roles in such processes as skeletal system development and signaling pathways for bone morphogenetic protein, Wnt, Notch, mitogen-activated protein kinase, and integrin. These findings reveal the effects of low oxygen tension on osteogenic progression in ESCs and provide insight into the molecular pathways that regulate ESC differentiation following exposure to hypoxia.

Transplantation of Rat Mesenchymal Stem Cells Overexpressing Hypoxia-Inducible Factor 2α Improves Blood Perfusion and Arteriogenesis in a Rat Hindlimb Ischemia Model

Mesenchymal stem cells (MSCs) have been increasingly tested in cell-based therapy to treat numerous diseases. Genetic modification to improve MSC behavior may enhance posttransplantation outcome. This study aims to test the potential therapeutic benefits of rat bone marrow MSCs overexpressing hypoxia-inducible factor 2α (rMSCs^HIF-2α) in a rat hindlimb ischemia model. PBS, rMSCs, or rMSCs^HIF-2α were injected into rat ischemic hindlimb. Compared with the injection of PBS or rMSCs, transplantation of rMSCs^HIF-2α significantly improved blood perfusion, increased the number of vessel branches in the muscle of the ischemic hindlimb, and improved the foot mobility of the ischemic hindlimb (all P < 0.05). rMSC^HIF-2α transplantation also markedly increased the expression of proangiogenic factors VEGF, bFGF, and SDF1 and Notch signaling proteins including DII4, NICD, Hey1, and Hes1, whereas it reduced the expression of proapoptotic factor Bax in the muscle of the ischemic hindlimb. Overexpression of HIF-2α did not affect rMSC stemness and proliferation under normoxia but significantly increased rMSC migration and tube formation in matrigel under hypoxia (all P < 0.05). RMSCs^HIF-2α stimulated endothelial cell invasion under hypoxia significantly (P < 0.05). Genetic modification of rMSCs via overexpression of HIF-2α improves posttransplantation outcomes in a rat hindlimb ischemia model possibly by stimulating proangiogenic growth factors and cytokines.

HIF1A overexpression using cell-penetrating DNA-binding protein induces angiogenesis in vitro and in vivo

Hypoxia-inducible factor-1 alpha (HIF1A) is an important transcription factor for angiogenesis. Recent studies have used the protein transduction domain (PTD) to deliver genes, but the PTD has not been used to induce the expression of HIF1A. This study aimed at using a novel PTD (Hph-1-GAL4; ARVRRRGPRR) to overexpress the HIF1A and identify the effects on angiogenesis in vitro and in vivo. Overexpression of HIF1A was induced using Hph-1-GAL4 in human umbilical vein/vascular endothelium cells (HUVEC). The expression levels of genes were analyzed by the quantitative real-time polymerase chain reaction (qPCR) after 2 and 4 days, respectively. An in vitro tube formation was performed using Diff-Quik staining. HIF1A and Hph-1-GAL4 were injected subcutaneously into the ventral area of each 5-week-old mouse. All of the plugs were retrieved after 1 week, and the gene expression levels were evaluated by qPCR. Each Matrigel plug was evaluated using the hemoglobin assay and hematoxylin and eosin (HE) staining. The expression levels of HIF1A and HIF1A target genes were significantly higher in HIF1A-transfected HUVEC than in control HUVEC in vitro. In the in vivo Matrigel plug assay, the amount of hemoglobin was significantly higher in the HIF1A-treatment group than in the PBS-treatment group. Blood vessels were identified in the HIF1A-treatment group. The expression levels of HIF1A, vascular endothelial growth factor (Vegf), and Cd31 were significantly higher in the HIF1A-treatment group than in the PBS-treatment group. These findings suggest that using Hph-1-G4D to overexpress HIF1A might be useful for transferring genes and regenerating tissues.

Optimizing stem cells for cardiac repair: Current status and new frontiers in regenerative cardiology

Cell therapy has the potential to improve healing of ischemic heart, repopulate injured myocardium and restore cardiac function. The tremendous hope and potential of stem cell therapy is well understood, yet recent trials involving cell therapy for cardiovascular diseases have yielded mixed results with inconsistent data thereby readdressing controversies and unresolved questions regarding stem cell efficacy for ischemic cardiac disease treatment. These controversies are believed to arise by the lack of uniformity of the clinical trial methodologies, uncertainty regarding the underlying reparative mechanisms of stem cells, questions concerning the most appropriate cell population to use, the proper delivery method and timing in relation to the moment of infarction, as well as the poor stem cell survival and engraftment especially in a diseased microenvironment which is collectively acknowledged as a major hindrance to any form of cell therapy. Indeed, the microenvironment of the failing heart exhibits pathological hypoxic, oxidative and inflammatory stressors impairing the survival of transplanted cells. Therefore, in order to observe any significant therapeutic benefit there is a need to increase resilience of stem cells to death in the transplant microenvironment while preserving or better yet improving their reparative functionality. Although stem cell differentiation into cardiomyocytes has been observed in some instance, the prevailing reparative benefits are afforded through paracrine mechanisms that promote angiogenesis, cell survival, transdifferentiate host cells and modulate immune responses. Therefore, to maximize their reparative functionality, ex vivo manipulation of stem cells through physical, genetic and pharmacological means have shown promise to enable cells to thrive in the post-ischemic transplant microenvironment. In the present work, we will overview the current status of stem cell therapy for ischemic heart disease, discuss the most recurring cell populations employed, the mechanisms by which stem cells deliver a therapeutic benefit and strategies that have been used to optimize and increase survival and functionality of stem cells including ex vivo preconditioning with drugs and a novel “pharmaco-optimizer” as well as genetic modifications.

Oxygen cycling to improve survival of stem cells for myocardial repair: A review

Heart disease represents the leading cause of death among Americans. There is currently no clinical treatment to regenerate viable myocardium following myocardial infarction, and patients may suffer progressive deterioration and decreased myocardial function from the effects of remodeling of the necrotic myocardium. New therapeutic strategies hold promise for patients who suffer from ischemic heart disease by directly addressing the restoration of functional myocardium following death of cardiomyocytes. Therapeutic stem cell transplantation has shown modest benefit in clinical human trials with decreased fibrosis and increased functional myocardium. Moreover, autologous transplantation holds the potential to implement these therapies while avoiding the immunomodulation concerns of heart transplantation. Despite these benefits, stem cell therapy has been characterized by poor survival and low engraftment of injected stem cells. The hypoxic tissue environment of the ischemic/infracting myocardium impedes stem cell survival and engraftment in myocardial tissue. Hypoxic preconditioning has been suggested as a viable strategy to increase hypoxic tolerance of stem cells. A number of in vivo and in vitro studies have demonstrated improved stem cell viability by altering stem cell secretion of protein signals and up-regulation of numerous paracrine signaling pathways that affect inflammatory, survival, and angiogenic signaling pathways. This review will discuss both the mechanisms of hypoxic preconditioning as well as the effects of hypoxic preconditioning in different cell and animal models, examining the pitfalls in current research and the next steps into potentially implementing this methodology in clinical research trials.

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.

Novel therapeutic core-shell hydrogel scaffolds with sequential delivery of cobalt and bone morphogenetic protein-2 for synergistic bone regeneration

Enabling early angiogenesis is a crucial issue in the success of bone tissue engineering. Designing scaffolds with therapeutic potential to stimulate angiogenesis as well as osteogenesis is thus considered a promising strategy. Here, we propose a novel scaffold designed to deliver angiogenic and osteogenic factors in a sequential manner to synergize the bone regeneration event. Hydrogel fibrous scaffolds comprised of a collagen-based core and an alginate-based shell were constructed. Bone morphogenetic protein 2 (BMP2) was loaded in the core, while the shell incorporated Co ions, enabled by the alginate crosslinking in CoCl2/CaCl2 solution. The incorporation of Co ions was tunable by altering the concentration of Co ions in the crosslinking solution. The incorporated Co ions, that are known to play a role in angiogenesis, were released rapidly within a week, while the BMP2, acting as an osteogenic factor, was released in a highly sustainable manner over several weeks to months. The release of Co ions significantly up-regulated the in vitro angiogenic properties of cells, including the expression of angiogenic genes (CD31, VEGF, and HIF-1α), secretion of VEGF, and the formation of tubule-like networks. However, BMP2 did not activate the angiogenic processes. Osteogenesis was also significantly enhanced by the release of Co ions as well as BMP2, characterized by higher expression of osteogenic genes (OPN, ALP, BSP, and OCN), and OCN protein secretion. An in vivo study on the designed scaffolds implanted in rat calvarium defect demonstrated significantly enhanced bone formation, evidenced by new bone volume and bone density, due to the release of BMP2 and Co ions. This is the first study using Co ions as an angiogenic element together with the osteogenic factor BMP2 within scaffolds, and the results demonstrated the possible synergistic role of Co ions with BMP2 in the bone regeneration process, suggesting a novel potential therapeutic scaffold system.

STATEMENT OF SIGNIFICANCE

This is the first report that utilizes Co ion as a pro-angiogenic factor in concert with osteogenic factor BMP-2 in the fine-tuned core-shell hydrogel fiber scaffolds, and ultimately achieves osteo/angiogenesis of MSCs and bone regeneration through the sequential delivery of both biofactors. This novel approach facilitates a new class of therapeutic scaffolds, aiming at successful bone regeneration with the help of angiogenesis.

Genetic Engineering of Mesenchymal Stem Cells for Regenerative Medicine

Mesenchymal stem cells (MSCs), which can be obtained from various organs and easily propagated in vitro, are one of the most extensively used types of stem cells and have been shown to be efficacious in a broad set of diseases. The unique and highly desirable properties of MSCs include high migratory capacities toward injured areas, immunomodulatory features, and the natural ability to differentiate into connective tissue phenotypes. These phenotypes include bone and cartilage, and these properties predispose MSCs to be therapeutically useful. In addition, MSCs elicit their therapeutic effects by paracrine actions, in which the metabolism of target tissues is modulated. Genetic engineering methods can greatly amplify these properties and broaden the therapeutic capabilities of MSCs, including transdifferentiation toward diverse cell lineages. However, cell engineering can also affect safety and increase the cost of therapy based on MSCs; thus, the advantages and disadvantages of these procedures should be discussed. In this review, the latest applications of genetic engineering methods for MSCs with regenerative medicine purposes are presented.

Effects of hypoxia and its relationship with apoptosis, stem cells, and angiogenesis on the thymus of children with congenital heart defects: a morphological and immunohistochemical study

INTRODUCTION

The thymus slowly involutes with age after puberty. Various stress conditions accelerate the involution of the thymus and cause changes in the histologic structure of the gland.

OBJECTIVE

The present study performed histomorphological and immunohistochemical (IHC) evaluations of the thymus glands removed during surgical repair in patients with cyanotic or acyanotic congenital heart disease (CHD). The thymus glands in the hypoxic group were compared to those in the non-hypoxic group. This study suggested that the activation of HIF-1 alpha promotes tumor progression and impair prognosis due to the inhibition of apoptosis, increased population of stem cells, and induction of angiogenesis also suggested that inactivation of HIF-1 alpha in tumor-infiltrated tissues could halt tumor progression and improve prognosis.

MATERIALS AND METHODS

The study included 76 thymus glands removed from patients who underwent an operation due to CHD. Of these cases, 38 had cyanotic CHD, and constituted the hypoxic group. The remaining 38 patients had acyanotic CHD, and constituted the non-hypoxic group. IHC procedures were performed for HIF-1 alpha, FoxP3, CD44, Bcl-2, and CD34.

RESULTS

There were statistically significant differences between the hypoxic and non-hypoxic groups only in terms of medullary enlargement toward the cortex and effacement of the corticomedullary junction. In the immunohistochemical examination for five markers, staining intensity and staining rates increased with decreasing oxygen saturation.

CONCLUSION

It can be concluded that the activation of HIF-1 alpha promotes tumor progression and impair prognosis due to the inhibition of apoptosis, increased population of stem cells, and induction of angiogenesis.

Mechanisms of tubulogenesis and endothelial phenotype expression by MSCs

Stem cell-based therapies are a promising new avenue for treating ischemic disease and chronic wounds. Mesenchymal stem cells (MSCs) have a proven ability to augment the neovascularization processes necessary for wound healing and are widely popular as an autologous source of progenitor cells. Our lab has previously reported on PEGylated fibrin as a unique hydrogel that promotes spontaneous tubulogenesis of encapsulated MSCs without exogenous factors. However, the mechanisms underlying this process have remained unknown. To better understand the therapeutic value of PEGylated fibrin delivery of MSCs, we sought to clarify the relationship between biomaterial properties and cell behavior. Here we find that fibrin PEGylation does not dramatically alter the macroscopic mechanical properties of the fibrin-based matrix (less than 10% difference). It does, however, dramatically reduce the rate of diffusion through the gel matrix. PEGylated fibrin enhances the tubulogenic growth of encapsulated MSCs demonstrating fluid-filled lumens by interconnected MSCs. Image analysis gave a value of 4320 ± 1770 μm total network length versus 618 ± 443 μm for unmodified fibrin. PEGylation promotes the endothelial phenotype of encapsulated MSCs--compared to unmodified fibrin--as evidenced by higher levels of endothelial markers (von Willebrand factor, 2.2-fold; vascular endothelial cadherin, 1.8-fold) and vascular endothelial growth factor (VEGF, up to 1.8-fold). Prospective analysis of underlying molecular pathways demonstrated that this endothelial-like MSC behavior is sensitively modulated by hypoxic stress, but not VEGF supplementation as evidenced by a significant increase in VEGF and MMP-2 secretion per cell under hypoxia. Further gain-of-function studies under hypoxic stress demonstrated that hypoxia culture of MSCs in unmodified fibrin could increase both vWF and VE-cadherin levels to values that were not significantly different than cells cultured in PEGylated fibrin. This result corroborated our hypothesis that the diffusion-limited environment of PEGylated fibrin is augmenting endothelial differentiation cues provided by unmodified fibrin. However, MSC networks lack platelet endothelial cell adhesion molecule-1 (PECAM-1) expression, which indicates incomplete differentiation towards an endothelial cell type. Collectively, the data here supports a revised understanding of MSC-derived neovascularization that contextualizes their behavior and utility as a hybrid endothelial-stromal cell type, with mixed characteristics of both populations.