Short-term physiological hypoxia potentiates the therapeutic function of mesenchymal stem cells

Conditioned media from dental pulp stem cells to counteract age-related macular degeneration

PURPOSE

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly. To date, there are no effective therapies to counteract AMD towards the most severe stages characterised by a progressive loss of photoreceptors triggered by retinal pigmented epithelium dysfunction. Given their easy source and their high proliferative potential, Dental Pulp Stem Cells (DPSCs) are considered promising for regenerative medicine. The main advantage of DPSCs is related to their paracrine immunosuppressive and immunoregulatory abilities, including the capability to promote regeneration of damaged tissues. Recent studies demonstrated the therapeutic potential of DPSCs-conditioned media (CM) in neurodegenerative diseases. In addition, we have already shown a differential expression of some growth factors and cytokines in CM derived from DPSCs cultured in hypoxia and normoxia conditions.

AIM

In this study we evaluated the capability of DPSCs-CM to counteract retinal degeneration in an animal model of AMD. DPSCs-CM were intravitreally injected the day before the exposure of albino rats to high intensity light (LD).

RESULTS

We evaluated the retinal function, and we performed morphological and molecular analysis a week after the LD, in accordance with the well-established protocol of our light damage model. DPSCs-CM obtained from hypoxia (HYPO-CM) or normoxia (NORM-CM), were able to preserve the retinal function, to reduce the damaged area and to counteract the upregulation of key factors involved in retinal degeneration, like FGF-2. Furthermore, we demonstrated that neither conditioned media modified inflammatory activation, as shown by both microglia activation and GFAP upregulation, but in vitro studies demonstrated a significant effect of both CM to counteract oxidative stress, one of the main causes of AMD.

CONCLUSION

Taken together, our study demonstrated that NORM-CM and HYPO-CM, albeit with a different chemical composition, could represent eligible candidates to counteract retinal degeneration in an animal model of AMD. Further studies are needed to obtain conditioned media with the best performance in term of retinal protection.

Concurrent hypoxia and apoptosis imparts immune programming potential in mesenchymal stem cells: Lesson from acute graft-versus-host-disease model

BACKGROUND

Mesenchymal stem cells (MSCs) have emerged as promising candidates for immune modulation in various diseases that are associated with dysregulated immune responses like Graft-versus-Host-Disease (GVHD). MSCs are pleiotropic and the fate of MSCs following administration is a major determinant of their therapeutic efficacy.

METHODS

Human MSCs were derived from bone marrow (BM) and Wharton's Jelly (WJ) and preconditioned through exposure to hypoxia and induction of apoptosis, either sequentially or simultaneously. The immune programming potential of preconditioned MSCs was evaluated by assessing their effects on T cell proliferation, induction of Tregs, programming of effector T-cell towards Th2 phenotype, macrophage polarization in the direct co-culture of MSCs and aGVHD patients-derived PBMNCs. Additionally, efferocytosis of MSCs and relative change in the expression of immunomodulatory soluble factors were examined.

RESULTS

Our study demonstrated that hypoxia preconditioned apoptotic MSCs (BM-MSCs, WJ-MSCs) bear more immune programming ability in a cellular model of acute Graft-versus-Host-Disease (aGVHD). Our findings revealed that WJ-MSCsHYP+APO were superior to BM-MSCsHYP+APO for immune regulation. These induced the differentiation of CD4+T-cell into Tregs, enhanced Th2 effector responses, and simultaneously mitigated Th1- and Th17 responses. Additionally, this approach led to the polarization of M1 macrophages toward an M2 phenotype.

CONCLUSION

Our study highlights the potential of WJ-MSCs conditioned with hypoxia and apoptosis concurrently, as a promising therapeutic strategy for aGVHD. It underscores the importance of considering MSC apoptosis in optimizing MSCs-based cellular therapy protocols for enhanced therapeutic efficacy in aGvHD.

Characterization of MSC Growth, Differentiation, and EV Production in CNF Hydrogels Under Static and Dynamic Cultures in Hypoxic and Normoxic Conditions

Mesenchymal stem cells (MSCs) hold immense therapeutic potential due to their regenerative and immunomodulatory properties. However, to utilize this potential, it is crucial to optimize their in vitro cultivation conditions. Three-dimensional (3D) culture methods using cell-laden hydrogels aim to mimic the physiological microenvironment in vitro, thus preserving MSC biological functionalities. Cellulosic hydrogels are particularly promising due to their biocompatibility, sustainability, and tunability in terms of chemical, morphological, and mechanical properties. This study investigated the impact of (1) two physical crosslinking scenarios for hydrogels derived from anionic cellulose nanofibers (to-CNF) used to encapsulate adipose-derived MSCs (adMSCs) and (2) physiological culture conditions on the in vitro proliferation, differentiation, and extracellular vesicle (EV) production of these adMSCs. The results revealed that additional Ca2+-mediated crosslinking, intended to complement the self-assembly and gelation of aqueous to-CNF in the adMSC cultivation medium, adversely affected both the mechanical properties of the hydrogel spheres and the growth of the encapsulated cells. However, cultivation under dynamic and hypoxic conditions significantly improved the proliferation and differentiation of the encapsulated adMSCs. Furthermore, it was demonstrated that the adMSCs in the CNF hydrogel spheres exhibited potential for scalable EV production with potent immunosuppressive capacities in a bioreactor system. These findings underscore the importance of physiological culture conditions and the suitability of cellulosic materials for enhancing the therapeutic potential of MSCs. Overall, this study provides valuable insights for optimizing the in vitro cultivation of MSCs for various applications, including tissue engineering, drug testing, and EV-based therapies.

Role of Hypoxic Secretome from Mesenchymal Stem Cells in Enhancing Tissue Repair: Regulatory Effects on HIF-1α, VEGF, and Fibroblast in a Sphincterotomy Rat Model

Background

Fecal incontinence (FI) is the inability to control bowel movements, resulting in fecal leakage. If left untreated, FI can seriously impact the long-term well-being of individuals affected. Recently, using secretome has become a promising new treatment method. The secretome combines growth factors released outside cells during stem cell development, such as mesenchymal stem cells. It consists of soluble proteins, nucleic acids, fats, and extracellular vesicles, which contribute to different cell processes. The primary aim is to assess the impact of hypoxic secretome administration on accelerating wound healing through the HIF-1α pathway in a post-sphincterotomy rat model.

Methods

The study was conducted with two distinct groups of 10 rats each, the control and treatment groups, which were injected with hypoxic secretome at 0.3 mL. The inclusion criteria for the rats were as follows: male gender, belonging to the Sprague-Dawley strain, aged between 12 to 16 weeks, with an average body weight ranging from 240 to 250 grams.

Results

There was an increase in HIF-1α gene expression in both groups. The treatment group 37 was significantly higher on day 42 (p = 0.001). VEGF increased significantly in the treatment 38 group on day 42 (p = 0.015). The neovascularization score increased significantly in the treatment 39 group during the first 24 hours (p = 0.004). The fibroblast score increased significantly in the 40 treatment group in the first 24 hours (p = 0.000) and 42 days (p = 0.035). After being given secretome, there was a higher increase in % collagen area and collagen area (µm2) in the treatment group compared to the control group (27,77 vs 11.01) and (419.027,66 vs 186.694,16).

Conclusion

The use of hypoxic secretome has a significant effect as a choice for the treatment of anal sphincter injury after sphincterotomy through the HIF-1α-VEGF-Fibroblast pathway.

Effect of hypoxia on proliferation and differentiation of induced pluripotent stem cell-derived mesenchymal stem cells

Although mesenchymal stem cells (MSCs) are extensively applied in the regenerative field, the majority of MSCs die after a few weeks of transplantation. Therefore, hypoxia pre-conditioning is a crucial step in increasing the MSCs' tolerance to physiological conditions. Meanwhile, induced pluripotent stem cell-derived MSCs (iMSCs) were proposed as a possible alternative to MSCs, and recently, the interest is growing in applying iMSCs in the regenerative field. This study examined the effect of hypoxia pre-conditioning on the proliferation, viability, and differentiation of iMSCs. Both iMSCs and MSCs were subjected to two rounds of severe short-term hypoxia (1 % O2 for 24h). After that, iMSCs and MSCs were characterized by testing their surface markers' expression, proliferation, viability, oxidative stress, and differentiation potential. Our findings revealed that hypoxia did not have a consistent effect among all the analyzed lines: the severe short-term hypoxia (1 % O2) reduced iMSCs proliferation, cell viability, and MMP while showing a benign effect on surface markers expression, colony formation, ROS accumulation, and osteogenic and adipogenic differentiation. Though hypoxia adversely affected iMSCs' proliferation, this does not necessarily mean that hypoxia is harmful to iMSCs; on the contrary, our results suggest that short-term hypoxia might have a beneficial long-term effect on the proliferation of iMSCs. Thus, the effect of hypoxia on proliferation, viability, and differentiation should also be tested after a long recovery period from iMSCs. Our next step will be to test the effect of hypoxia for a longer period besides uncovering the changes in the expression profile of hypoxic iMSCs.

Multipotent mesenchymal stromal/stem cell-based therapies for acute respiratory distress syndrome: current progress, challenges, and future frontiers

Acute respiratory distress syndrome (ARDS) is a critical, life-threatening condition marked by severe inflammation and impaired lung function. Mesenchymal stromal/stem cells (MSCs) present a promising therapeutic avenue due to their immunomodulatory, anti-inflammatory, and regenerative capabilities. This review comprehensively evaluates MSC-based strategies for ARDS treatment, including direct administration, tissue engineering, extracellular vesicles (EVs), nanoparticles, natural products, artificial intelligence (AI), gene modification, and MSC preconditioning. Direct MSC administration has demonstrated therapeutic potential but necessitates optimization to overcome challenges related to effective cell delivery, homing, and integration into damaged lung tissue. Tissue engineering methods, such as 3D-printed scaffolds and MSC sheets, enhance MSC survival and functionality within lung tissue. EVs and MSC-derived nanoparticles offer scalable and safer alternatives to cell-based therapies. Likewise, natural products and bioactive compounds derived from plants can augment MSC function and resilience, offering complementary strategies to enhance therapeutic outcomes. In addition, AI technologies could aid in optimizing MSC delivery and dosing, and gene editing tools like CRISPR/Cas9 allow precise modification of MSCs to enhance their therapeutic properties and target specific ARDS mechanisms. Preconditioning MSCs with hypoxia, growth factors, or pharmacological agents further enhances their therapeutic potential. While MSC therapies hold significant promise for ARDS, extensive research and clinical trials are essential to determine optimal protocols and ensure long-term safety and effectiveness.

Engineering next-generation oxygen-generating scaffolds to enhance bone regeneration

In bone, an adequate oxygen (O2) supply is crucial during development, homeostasis, and healing. Oxygen-generating scaffolds (OGS) have demonstrated significant potential to enhance bone regeneration. However, the complexity of O2 delivery and signaling in vivo makes it challenging to tailor the design of OGS to precisely meet this biological requirement. We review recent advances in OGS and analyze persisting engineering and translational hurdles. We also discuss the potential of computational and machine learning (ML) models to facilitate the integration of novel imaging data with biological readouts and advanced biomanufacturing technologies. By elucidating how to tackle current challenges using cutting-edge technologies, we provide insights for transitioning from traditional to next-generation OGS to improve bone regeneration in patients.

Stem Cell Secretome Modulated by Arsenicum album 30C Ameliorates Lipopolysaccharide-induced Cytokine Storm in Blood Mononuclear Cells in vitro

BACKGROUND

The therapeutic effectiveness of mesenchymal stem cells (MSCs) and their secretome can be enhanced by means of physical, chemical and biological preconditioning. Arsenicum album 30C (AA30) has been one of the leading homeopathic medicines used in prophylaxis against SARS-CoV-2 infection.

AIMS

This study aimed to investigate whether AA30 preconditioning could influence the growth factors and cytokine profile of the human dental pulp-derived MSC (DPD-MSC) secretome. Also, to test the efficacy of the AA30-preconditioned DPD-MSC secretome in ameliorating the lipopolysaccharide (LPS)-induced cytokine storm in human peripheral blood mononuclear cells (PBMCs) as an in-vitro cellular model.

METHODS

The cytotoxicity of AA30 was assessed in DPD-MSCs by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Growth factors and cytokine levels in the AA30-preconditioned DPD-MSC secretome were analysed by fluorescence-activated cell sorting (FACS) analysis. The angiogenic potential of the AA30-preconditioned DPD-MSC secretome was assessed by chick yolk-sac membrane (YSM) assay. Culture medium with 0.001% ethanol was used as vehicle control. The efficacy of the AA30-preconditioned DPD-MSC secretome in ameliorating the cytokine storm was assessed in LPS pre-treated PBMCs. The mRNA and protein expression of inflammatory markers such as IL-1β, IL-6 and IL-10 were analysed by using RT-PCR and FACS analysis respectively.

RESULTS

AA30 did not exhibit cytotoxicity in the concentration range of 1% to 50%. Furthermore, the AA30-preconditioned DPD-MSC secretome exhibited a significant increase in the levels of angiogenic factors, such as human angiopoietin-2, EPO and PDGF-AA, and decreased levels of cytokines, such as TNF-α, CXCL-8 and IL-6. The AA30-preconditioned DPD-MSC secretome showed augmented angiogenesis compared to vehicle controls. The DPD-MSC secretome ameliorated LPS-induced mRNA and protein expression of IL-1β, IL-6 and IL-10 in PBMCs.

CONCLUSION

The AA30-preconditioned DPD-MSC secretome augmented angiogenesis and ameliorated the LPS-induced cytokine storm in human PBMCs in vitro. Our data demonstrate that AA30 preconditioning enhances the therapeutic potency of MSCs and their secretome.

Functional variation among mesenchymal stem cells derived from different tissue sources

Background

Mesenchymal stem cells (MSCs) are increasingly recognized for their regenerative potential. However, their clinical application is hindered by their inherent variability, which is influenced by various factors, such as the tissue source, culture conditions, and passage number.

Methods

MSCs were sourced from clinically relevant tissues, including adipose tissue-derived MSCs (ADMSCs, n = 2), chorionic villi-derived MSCs (CMMSCs, n = 2), amniotic membrane-derived MSCs (AMMSCs, n = 3), and umbilical cord-derived MSCs (UCMSCs, n = 3). Passages included the umbilical cord at P0 (UCMSCP0, n = 2), P3 (UCMSCP3, n = 2), and P5 (UCMSCP5, n = 2) as well as the umbilical cord at P5 cultured under low-oxygen conditions (UCMSCP5L, n = 2).

Results

We observed that MSCs from different tissue origins clustered into six distinct functional subpopulations, each with varying proportions. Notably, ADMSCs exhibited a higher proportion of subpopulations associated with vascular regeneration, suggesting that they are beneficial for applications in vascular regeneration. Additionally, CMMSCs had a high proportion of subpopulations associated with reproductive processes. UCMSCP5 and UCMSCP5L had higher proportions of subpopulations related to female reproductive function than those for earlier passages. Furthermore, UCMSCP5L, cultured under low-oxygen (hypoxic) conditions, had a high proportion of subpopulations associated with pro-angiogenic characteristics, with implications for optimizing vascular regeneration.

Conclusions

This study revealed variation in the distribution of MSC subpopulations among different tissue sources, passages, and culture conditions, including differences in functions related to vascular and reproductive system regeneration. These findings hold promise for personalized regenerative medicine and may lead to more effective clinical treatments across a spectrum of medical conditions.

Mesenchymal stem cell secretome for regenerative medicine: Where do we stand?

BACKGROUND

Mesenchymal stem cell (MSC)-based therapies have yielded beneficial effects in a broad range of preclinical models and clinical trials for human diseases. In the context of MSC transplantation, it is widely recognized that the main mechanism for the regenerative potential of MSCs is not their differentiation, with in vivo data revealing transient and low engraftment rates. Instead, MSCs therapeutic effects are mainly attributed to its secretome, i.e., paracrine factors secreted by these cells, further offering a more attractive and innovative approach due to the effectiveness and safety of a cell-free product.

AIM OF REVIEW

In this review, we will discuss the potential benefits of MSC-derived secretome in regenerative medicine with particular focus on respiratory, hepatic, and neurological diseases. Both free and vesicular factors of MSC secretome will be detailed. We will also address novel potential strategies capable of improving their healing potential, namely by delivering important regenerative molecules according to specific diseases and tissue needs, as well as non-clinical and clinical studies that allow us to dissect their mechanisms of action.

KEY SCIENTIFIC CONCEPTS OF REVIEW

MSC-derived secretome includes both soluble and non-soluble factors, organized in extracellular vesicles (EVs). Importantly, besides depending on the cell origin, the characteristics and therapeutic potential of MSC secretome is deeply influenced by external stimuli, highlighting the possibility of optimizing their characteristics through preconditioning approaches. Nevertheless, the clarity around their mechanisms of action remains ambiguous, whereas the need for standardized procedures for the successful translation of those products to the clinics urges.

Interplay between mesenchymal stem cells and macrophages: Promoting bone tissue repair

The repair of bone tissue damage is a complex process that is well-orchestrated in time and space, a focus and difficulty in orthopedic treatment. In recent years, the success of mesenchymal stem cells (MSCs)-mediated bone repair in clinical trials of large-area bone defects and bone necrosis has made it a candidate in bone tissue repair engineering and regenerative medicine. MSCs are closely related to macrophages. On one hand, MSCs regulate the immune regulatory function by influencing macrophages proliferation, infiltration, and phenotype polarization, while also affecting the osteoclasts differentiation of macrophages. On the other hand, macrophages activate MSCs and mediate the multilineage differentiation of MSCs by regulating the immune microenvironment. The cross-talk between MSCs and macrophages plays a crucial role in regulating the immune system and in promoting tissue regeneration. Making full use of the relationship between MSCs and macrophages will enhance the efficacy of MSCs therapy in bone tissue repair, and will also provide a reference for further application of MSCs in other diseases.

Stem cell therapy for cardiac regeneration: past, present, and future

Cardiac disorders remain the leading cause of mortality worldwide. Current clinical strategies, including drug therapy, surgical interventions, and organ transplantation offer limited benefits to patients without regenerating the damaged myocardium. Over the past decade, stem cell therapy has generated a keen interest owing to its unique self-renewal and immune privileged characteristics. Furthermore, the ability of stem cells to differentiate into specialized cell types, has made them a popular therapeutic tool against various diseases. This comprehensive review provides an overview of therapeutic potential of different types of stem cells in reference to cardiovascular diseases. Furthermore, it sheds light on the advantages and limitations associated with each cell type. An in-depth analysis of the challenges associated with stem cell research and the hurdles for its clinical translation and their possible solutions have also been elaborated upon. It examines the controversies surrounding embryonic stem cells and the emergence of alternative approaches, such as the use of induced pluripotent stem cells for cardiac therapeutic applications. Overall, this review serves as a valuable resource for researchers, clinicians, and policymakers involved in the field of regenerative medicine, guiding the development of safe and effective stem cell-based therapies to revolutionize patient care.

Metabolic and proteostatic differences in quiescent and active neural stem cells

Adult neural stem cells are neurogenesis progenitor cells that play an important role in neurogenesis. Therefore, neural regeneration may be a promising target for treatment of many neurological illnesses. The regenerative capacity of adult neural stem cells can be characterized by two states: quiescent and active. Quiescent adult neural stem cells are more stable and guarantee the quantity and quality of the adult neural stem cell pool. Active adult neural stem cells are characterized by rapid proliferation and differentiation into neurons which allow for integration into neural circuits. This review focuses on differences between quiescent and active adult neural stem cells in nutrition metabolism and protein homeostasis. Furthermore, we discuss the physiological significance and underlying advantages of these differences. Due to the limited number of adult neural stem cells studies, we referred to studies of embryonic adult neural stem cells or non-mammalian adult neural stem cells to evaluate specific mechanisms.

Hypoxia and Hypoxia Mimetic Agents As Potential Priming Approaches to Empower Mesenchymal Stem Cells

Mesenchymal stem cells (MSC) exhibit self-renewal capacity and multilineage differentiation potential, making them attractive for research and clinical application. The properties of MSC can vary depending on specific micro-environmental factors. MSC resides in specific niches with low oxygen concentrations, where oxygen functions as a metabolic substrate and a signaling molecule. Conventional physical incubators or chemically hypoxia mimetic agents are applied in cultures to mimic the original low oxygen tension settings where MSC originated. This review aims to focus on the current knowledge of the effects of various physical hypoxic conditions and widely used hypoxia-mimetic agents-PHD inhibitors on mesenchymal stem cells at a cellular and molecular level, including proliferation, stemness, differentiation, viability, apoptosis, senescence, migration, immunomodulation behaviors, as well as epigenetic changes.

Hypoxia and inflammatory factor preconditioning enhances the immunosuppressive properties of human umbilical cord mesenchymal stem cells

BACKGROUND

Mesenchymal stem cells (MSCs) have great potential for the treatment of various immune diseases due to their unique immunomodulatory properties. However, MSCs exposed to the harsh inflammatory environment of damaged tissue after intravenous transplantation cannot exert their biological effects, and therefore, their therapeutic efficacy is reduced. In this challenging context, an in vitro preconditioning method is necessary for the development of MSC-based therapies with increased immunomodulatory capacity and transplantation efficacy.

AIM

To determine whether hypoxia and inflammatory factor preconditioning increases the immunosuppressive properties of MSCs without affecting their biological characteristics.

METHODS

Umbilical cord MSCs (UC-MSCs) were pretreated with hypoxia (2% O2) exposure and inflammatory factors (interleukin-1β, tumor necrosis factor-α, interferon-γ) for 24 h. Flow cytometry, polymerase chain reaction, enzyme-linked immunosorbent assay and other experimental methods were used to evaluate the biological characteristics of pretreated UC-MSCs and to determine whether pretreatment affected the immunosuppressive ability of UC-MSCs in coculture with immune cells.

RESULTS

Pretreatment with hypoxia and inflammatory factors caused UC-MSCs to be elongated but did not affect their viability, proliferation or size. In addition, pretreatment significantly decreased the expression of coagulation-related tissue factors but did not affect the expression of other surface markers. Similarly, mitochondrial function and integrity were retained. Although pretreatment promoted UC-MSC apoptosis and senescence, it increased the expression of genes and proteins related to immune regulation. Pretreatment increased peripheral blood mononuclear cell and natural killer (NK) cell proliferation rates and inhibited NK cell-induced toxicity to varying degrees.

CONCLUSION

In summary, hypoxia and inflammatory factor preconditioning led to higher immunosuppressive effects of MSCs without damaging their biological characteristics.

Transglutaminase 2 Prevents Premature Senescence and Promotes Osteoblastic Differentiation of Mesenchymal Stem Cells through NRF2 Activation

Transglutaminase 2 (TG2) is a multifunctional enzyme that exhibits transamidase, GTPase, kinase, and protein disulfide isomerase (PDI) activities. Of these, transamidase-mediated modification of proteins regulates apoptosis, differentiation, inflammation, and fibrosis. TG2 is highly expressed in mesenchymal stem cells (MSCs) compared with differentiated cells, suggesting a role of TG2 specific for MSC characteristics. In this study, we report a new function of TG2 in the regulation of MSC redox homeostasis. During in vitro MSC expansion, TG2 is required for cell proliferation and self-renewal by preventing premature senescence but has no effect on the expression of surface antigens and oxidative stress-induced cell death. Moreover, induction of differentiation upregulates TG2 that promotes osteoblastic differentiation. Molecular analyses revealed that TG2 mediates tert-butylhydroquinone, but not sulforaphane, -induced nuclear factor erythroid 2-related factor 2 (NRF2) activation in a transamidase activity-independent manner. Differences in the mechanism of action between two NRF2 activators suggest that PDI activity of TG2 may be implicated in the stabilization of NRF2. The role of TG2 in the regulation of antioxidant response was further supported by transcriptomic analysis of MSC. These results indicate that TG2 is a critical enzyme in eliciting antioxidant response in MSC through NRF2 activation, providing a target for optimizing MSC manufacturing processes to prevent premature senescence.

Application of hypoxia-mesenchymal stem cells in treatment of anaerobic bacterial wound infection: wound healing and infection recovery

Mesenchymal stromal cells, commonly referred to as MSCs, are a type of multipotent stem cells that are typically extracted from adipose tissue and bone marrow. In the field of tissue engineering and regenerative medicine, MSCs and their exosomes have emerged as revolutionary tools. Researchers are now devoting greater attention to MSCs because of their ability to generate skin cells like fibroblasts and keratinocytes, as well as their distinctive potential to decrease inflammation and emit pro-angiogenic molecules at the site of wounds. More recent investigations revealed that MSCs can exert numerous direct and indirect antimicrobial effects that are immunologically mediated. Collectively, these antimicrobial properties can remove bacterial infections when the MSCs are delivered in a therapeutic setting. Regardless of the positive therapeutic potential of MSCs for a multitude of conditions, transplanted MSC cell retention continues to be a major challenge. Since MSCs are typically administered into naturally hypoxic tissues, understanding the impact of hypoxia on the functioning of MSCs is crucial. Hypoxia has been postulated to be among the factors determining the differentiation of MSCs, resulting in the production of inflammatory cytokines throughout the process of tissue regeneration and wound repair. This has opened new horizons in developing MSC-based systems as a potent therapeutic tool in oxygen-deprived regions, including anaerobic wound infection sites. This review sheds light on the role of hypoxia-MSCs in the treatment of anaerobic bacterial wound infection in terms of both their regenerative and antimicrobial activities.

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.

Isolation, culture, and delivery considerations for the use of mesenchymal stem cells in potential therapies for acute liver failure

Acute liver failure (ALF) is a high-mortality syndrome for which liver transplantation is considered the only effective treatment option. A shortage of donor organs, high costs and surgical complications associated with immune rejection constrain the therapeutic effects of liver transplantation. Recently, mesenchymal stem cell (MSC) therapy was recognized as an alternative strategy for liver transplantation. Bone marrow mesenchymal stem cells (BMSCs) have been used in clinical trials of several liver diseases due to their ease of acquisition, strong proliferation ability, multipotent differentiation, homing to the lesion site, low immunogenicity and anti-inflammatory and antifibrotic effects. In this review, we comprehensively summarized the harvest and culture expansion strategies for BMSCs, the development of animal models of ALF of different aetiologies, the critical mechanisms of BMSC therapy for ALF and the challenge of clinical application.

MSCs Deliver Hypoxia-Treated Mitochondria Reprogramming Acinar Metabolism to Alleviate Severe Acute Pancreatitis Injury

Mitochondrial function impairment due to abnormal opening of the mitochondrial permeability transition pore (MPTP) is considered the central event in acute pancreatitis; however, therapeutic choices for this condition remain controversial. Mesenchymal stem cells (MSCs) are a family member of stem cells with immunomodulatory and anti-inflammatory capabilities that can mitigate damage in experimental pancreatitis. Here, it is shown that MSCs deliver hypoxia-treated functional mitochondria to damaged pancreatic acinar cells (PACs) via extracellular vesicles (EVs), which reverse the metabolic function of PACs, maintain ATP supply, and exhibit an excellent injury-inhibiting effect. Mechanistically, hypoxia inhibits superoxide accumulation in the mitochondria of MSCs and upregulates the membrane potential, which is internalized into PACs via EVs, thus, remodeling the metabolic state. In addition, cargocytes constructed via stem cell denucleation as mitochondrial vectors are shown to exert similar therapeutic effects to MSCs. These findings reveal an important mechanism underlying the role of mitochondria in MSC therapy and offer the possibility of applying mitochondrial therapy to patients with severe acute pancreatitis.

Recent advances in pre-conditioned mesenchymal stem/stromal cell (MSCs) therapy in organ failure; a comprehensive review of preclinical studies

Mesenchymal stem/stromal cells (MSCs)-based therapy brings the reassuring capability to regenerative medicine through their self-renewal and multilineage potency. Also, they secret a diversity of mediators, which are complicated in moderation of deregulated immune responses, and yielding angiogenesis in vivo. Nonetheless, MSCs may lose biological performance after procurement and prolonged expansion in vitro. Also, following transplantation and migration to target tissue, they encounter a harsh milieu accompanied by death signals because of the lack of proper tensegrity structure between the cells and matrix. Accordingly, pre-conditioning of MSCs is strongly suggested to upgrade their performances in vivo, leading to more favored transplantation efficacy in regenerative medicine. Indeed, MSCs ex vivo pre-conditioning by hypoxia, inflammatory stimulus, or other factors/conditions may stimulate their survival, proliferation, migration, exosome secretion, and pro-angiogenic and anti-inflammatory characteristics in vivo. In this review, we deliver an overview of the pre-conditioning methods that are considered a strategy for improving the therapeutic efficacy of MSCs in organ failures, in particular, renal, heart, lung, and liver.

Mesenchymal and induced pluripotent stem cell-based therapeutics: a comparison

Stem cell-based cell therapeutics and especially those based on human mesenchymal stem cells (hMSCs) and induced pluripotent stem cells (hiPSCs) are said to have enormous developmental potential in the coming years. Their applications range from the treatment of orthopedic disorders and cardiovascular diseases to autoimmune diseases and even cancer. However, while more than 27 hMSC-derived therapeutics are currently commercially available, hiPSC-based therapeutics have yet to complete the regulatory approval process. Based on a review of the current commercially available hMSC-derived therapeutic products and upcoming hiPSC-derived products in phase 2 and 3, this paper compares the cell therapy manufacturing process between these two cell types. Moreover, the similarities as well as differences are highlighted and the resulting impact on the production process discussed. Here, emphasis is placed on (i) hMSC and hiPSC characteristics, safety, and ethical aspects, (ii) their morphology and process requirements, as well as (iii) their 2- and 3-dimensional cultivations in dependence of the applied culture medium and process mode. In doing so, also downstream processing aspects are covered and the role of single-use technology is discussed. KEY POINTS: • Mesenchymal and induced pluripotent stem cells exhibit distinct behaviors during cultivation • Single-use stirred bioreactor systems are preferred for the cultivation of both cell types • Future research should adapt and modify downstream processes to available single-use devices.

Hypoxia activates the PI3K/AKT/HIF-1α pathway to promote the anti-inflammatory effect of adipose mesenchymal stem cells

This study aimed to investigate the effect of hypoxia on the anti-inflammatory effect of adipose-derived mesenchymal stem cells (AMSCs) in vitro and its possible mechanism. AMSCs were cultured in vitro in a hypoxic environment with 3% O₂, and a normoxic (21% O₂) environment was used as the control. The cells were identified by in vitro adipogenic and osteogenic differentiation and cell surface antigen detection, and the cell viability were detected. The effect of hypoxic AMSCs on macrophage inflammation was analyzed by co-culture. The results showed that under hypoxia, AMSCs had better viability, significantly downregulated the expression of inflammatory factors, alleviated macrophage inflammation, and activated the PI3K/AKT/HIF-1α pathway.

The Role of HIF-1α in Bone Regeneration: A New Direction and Challenge in Bone Tissue Engineering

The process of repairing significant bone defects requires the recruitment of a considerable number of cells for osteogenesis-related activities, which implies the consumption of a substantial amount of oxygen and nutrients. Therefore, the limited supply of nutrients and oxygen at the defect site is a vital constraint that affects the regenerative effect, which is closely related to the degree of a well-established vascular network. Hypoxia-inducible factor (HIF-1α), which is an essential transcription factor activated in hypoxic environments, plays a vital role in vascular network construction. HIF-1α, which plays a central role in regulating cartilage and bone formation, induces vascular invasion and differentiation of osteoprogenitor cells to promote and maintain extracellular matrix production by mediating the adaptive response of cells to changes in oxygen levels. However, the application of HIF-1α in bone tissue engineering is still controversial. As such, clarifying the function of HIF-1α in regulating the bone regeneration process is one of the urgent issues that need to be addressed. This review provides insight into the mechanisms of HIF-1α action in bone regeneration and related recent advances. It also describes current strategies for applying hypoxia induction and hypoxia mimicry in bone tissue engineering, providing theoretical support for the use of HIF-1α in establishing a novel and feasible bone repair strategy in clinical settings.

Menstrual blood-derived stromal cells: insights into their secretome in acute hypoxia conditions

BACKGROUND

Despite constant advances in regenerative medicine, the closure of chronic wounds is still challenging. Therapeutic approaches using locally administered MSCs have been considered a promising option. However, the viability of these cells is seriously threatened by acute hypoxic stress linked to wound healing. In this work, we aimed to study the tolerance of Menstrual blood-derived stromal cells (MenSCs) to acute hypoxia and their therapeutic paracrine effect.

METHODS

Isolated MenSCs were phenotypically characterized and evaluated in terms of proliferation, viability, and gene expression, under acute hypoxia (AH) compared with conventional cultured condition or normoxia (N). A step further, the secretome of MenSCs under acute hypoxia was analyzed with respect to their miRNAs content and by in vitro functional assays. For the analysis of differences between the two groups, Student's t-test was performed and one-way ANOVA and Tukey's multiple comparisons test for multiple groups were used.

RESULTS

Our results revealed that the viability of MenSCs was not affected under acute hypoxia, although proliferation rate slowed down. Gene analysis revealed 5 up-regulated (BNIP3, ANGPTL4, IL6, IL1B, and PDK1) and 4 down-regulated genes (IDO1, HMOX1, ANGPTL2, and HGF) in AH compared to N. Global gene expression analysis revealed a decrease in the gene ontology functions of migration and wound response with respect to the normoxic condition. In contrast, functions such as angiogenesis were enriched under the AH condition. Regarding the secretome analysis, two miRNAs involved in angiogenic processes (hsa-miR-148a-3p and hsa-miR-378a-3p), were significantly up-expressed when compared to the normoxic condition, being MYC gene, the unique target of both. Functional assays on HUVECs revealed a potential pro-angiogenic capacity of MenSCs cultured in both oxygen conditions (N and AH) based on the wound closure and tube formation results of their released paracrine factors. However, when compared to normoxia, the paracrine factors of MenSCs under acute hypoxia slightly reduced the proliferation, migration, and in vitro wound closure of HUVECs.

CONCLUSIONS

MenSC exhibited a good survival capacity under acute hypoxic conditions as well as beneficial properties applicable in the field of tissue regeneration through their secretome, which makes them a potential cell source for wound healing interventions.

Basic Properties of Adipose-Derived Mesenchymal Stem Cells of Rheumatoid Arthritis and Osteoarthritis Patients

Rheumatoid arthritis (RA) and osteoarthritis (OA) are destructive joint diseases, the development of which are associated with the expansion of pathogenic T lymphocytes. Mesenchymal stem cells may be an attractive therapeutic option for patients with RA or OA due to the regenerative and immunomodulatory abilities of these cells. The infrapatellar fat pad (IFP) is a rich and easily available source of mesenchymal stem cells (adipose-derived stem cells, ASCs). However, the phenotypic, potential and immunomodulatory properties of ASCs have not been fully characterised. We aimed to evaluate the phenotype, regenerative potential and effects of IFP-derived ASCs from RA and OA patients on CD4+ T cell proliferation. The MSC phenotype was assessed using flow cytometry. The multipotency of MSCs was evaluated on the basis of their ability to differentiate into adipocytes, chondrocytes and osteoblasts. The immunomodulatory activities of MSCs were examined in co-cultures with sorted CD4+ T cells or peripheral blood mononuclear cells. The concentrations of soluble factors involved in ASC-dependent immunomodulatory activities were assessed in co-culture supernatants using ELISA. We found that ASCs with PPIs from RA and OA patients maintain the ability to differentiate into adipocytes, chondrocytes and osteoblasts. ASCs from RA and OA patients also showed a similar phenotype and comparable abilities to inhibit CD4+ T cell proliferation, which was dependent on the induction of soluble factors The results of our study constitute the basis for further research on the therapeutic potential of ASCs in the treatment of patients with RA and OA.

Role of Mesenchymal Stem/Stromal Cells in Modulating Ischemia/Reperfusion Injury: Current State of the Art and Future Perspectives

Ischemia/reperfusion injury (IRI) is a multistep damage that occurs in several tissues when a blood flow interruption is inevitable, such as during organ surgery or transplantation. It is responsible for cell death and tissue dysfunction, thus leading, in the case of transplantation, to organ rejection. IRI takes place during reperfusion, i.e., when blood flow is restored, by activating inflammation and reactive oxygen species (ROS) production, causing mitochondrial damage and apoptosis of parenchymal cells. Unfortunately, none of the therapies currently in use are definitive, prompting the need for new therapeutic approaches. Scientific evidence has proven that mesenchymal stem/stromal cells (MSCs) can reduce inflammation and ROS, prompting this cellular therapy to also be investigated for treatment of IRI. Moreover, it has been shown that MSC therapeutic effects were mediated in part by their secretome, which appears to be involved in immune regulation and tissue repair. For these reasons, mediated MSC paracrine function might be key for injury amelioration upon IRI damage. In this review, we highlight the scientific literature on the potential beneficial use of MSCs and their products for improving IRI outcomes in different tissues/organs, focusing in particular on the paracrine effects mediated by MSCs, and on the molecular mechanisms behind these effects.

Vitronectin acts as a key regulator of adhesion and migration in human umbilical cord-derived MSCs under different stress conditions

To improve mesenchymal stem cell (MSC)-based therapy efficacy, it is critical to identify factors involved in regulating migration and adhesion of MSCs under microenvironmental stress conditions. We observed that human Wharton's jelly-derived MSCs (WJ-MSCs) exhibited increase in cell spread area and adhesion, with reduction in cellular migration under serum starvation stress. The changes in adhesion and migration characteristics were accompanied by formation of large number of super mature focal adhesions along with extensive stress fibres and altered ECM gene expression with notable induction in vitronectin (VTN) expression. NF-κβ was found to be a positive regulator of VTN expression while ERK pathway regulated it negatively. Inhibition of these signalling pathways or knocking down of VTN under serum starvation established the correlation between increase in VTN expression and increased cellular adhesion with corresponding reduction in cell migration. VTN knockdown also resulted in reduction of super mature focal adhesions and extensive stress fibres, formed under serum starvation stress. Additionally, VTN induction was not detected in hypoxia-treated WJ-MSCs, and the MSCs showed no significant change in the adhesion or migration properties under hypoxia. VTN is established as a key player which possibly regulates the adhesion and migration properties of WJ-MSCs via focal adhesion signalling.

Iron Oxide Nanoparticle-Incorporated Mesenchymal Stem Cells for Alzheimer's Disease Treatment

Alzheimer's disease (AD) is a neurodegenerative disease with multifactorial pathogenesis. However, most current therapeutic approaches for AD target a single pathophysiological mechanism, generally resulting in unsatisfactory therapeutic outcomes. Recently, mesenchymal stem cell (MSC) therapy, which targets multiple pathological mechanisms of AD, has been explored as a novel treatment. However, the low brain retention efficiency of administered MSCs limits their therapeutic efficacy. In addition, autologous MSCs from AD patients may have poor therapeutic abilities. Here, we overcome these limitations by developing iron oxide nanoparticle (IONP)-incorporated human Wharton's jelly-derived MSCs (MSC-IONPs). IONPs promote therapeutic molecule expression in MSCs. Following intracerebroventricular injection, MSC-IONPs showed a higher brain retention efficiency under magnetic guidance. This potentiates the therapeutic efficacy of MSCs in murine models of AD. Furthermore, human Wharton's jelly-derived allogeneic MSCs may exhibit higher therapeutic abilities than those of autologous MSCs in aged AD patients. This strategy may pave the way for developing MSC therapies for AD.

Osteocyte Egln1/Phd2 links oxygen sensing and biomineralization via FGF23

Osteocytes act within a hypoxic environment to control key steps in bone formation. FGF23, a critical phosphate-regulating hormone, is stimulated by low oxygen/iron in acute and chronic diseases, however the molecular mechanisms directing this process remain unclear. Our goal was to identify the osteocyte factors responsible for FGF23 production driven by changes in oxygen/iron utilization. Hypoxia-inducible factor-prolyl hydroxylase inhibitors (HIF-PHI) which stabilize HIF transcription factors, increased Fgf23 in normal mice, as well as in osteocyte-like cells; in mice with conditional osteocyte Fgf23 deletion, circulating iFGF23 was suppressed. An inducible MSC cell line ('MPC2') underwent FG-4592 treatment and ATACseq/RNAseq, and demonstrated that differentiated osteocytes significantly increased HIF genomic accessibility versus progenitor cells. Integrative genomics also revealed increased prolyl hydroxylase Egln1 (Phd2) chromatin accessibility and expression, which was positively associated with osteocyte differentiation. In mice with chronic kidney disease (CKD), Phd1-3 enzymes were suppressed, consistent with FGF23 upregulation in this model. Conditional loss of Phd2 from osteocytes in vivo resulted in upregulated Fgf23, in line with our findings that the MPC2 cell line lacking Phd2 (CRISPR Phd2-KO cells) constitutively activated Fgf23 that was abolished by HIF1α blockade. In vitro, Phd2-KO cells lost iron-mediated suppression of Fgf23 and this activity was not compensated for by Phd1 or -3. In sum, osteocytes become adapted to oxygen/iron sensing during differentiation and are directly sensitive to bioavailable iron. Further, Phd2 is a critical mediator of osteocyte FGF23 production, thus our collective studies may provide new therapeutic targets for skeletal diseases involving disturbed oxygen/iron sensing.

Boosting therapeutic efficacy of mesenchymal stem cells in pulmonary fibrosis: The role of genetic modification and preconditioning strategies

Pulmonary fibrosis (PF) is the end stage of severe lung diseases, in which the lung parenchyma is replaced by fibrous scar tissue. The result is a remarkable reduction in pulmonary compliance, which may lead to respiratory failure and even death. Idiopathic pulmonary fibrosis (IPF) is the most prevalent form of PF, with no reasonable etiology. However, some factors are believed to be behind the etiology of PF, including prolonged administration of several medications (e.g., bleomycin and amiodarone), environmental contaminant exposure (e.g., gases, asbestos, and silica), and certain systemic diseases (e.g., systemic lupus erythematosus). Despite significant developments in the diagnostic approach to PF in the last few years, efforts to find more effective treatments remain challenging. With their immunomodulatory, anti-inflammatory, and anti-fibrotic properties, stem cells may provide a promising approach for treating a broad spectrum of fibrotic conditions. However, they may lose their biological functions after long-term in vitro culture or exposure to harsh in vivo situations. To overcome these limitations, numerous modification techniques, such as genetic modification, preconditioning, and optimization of cultivation methods for stem cell therapy, have been adopted. Herein, we summarize the previous investigations that have been designed to assess the effects of stem cell preconditioning or genetic modification on the regenerative capacity of stem cells in PF.

Evaluating the Effect of Hypoxia on Human Adult Mesenchymal Stromal Cell Chondrogenesis In Vitro: A Systematic Review

Human adult mesenchymal stromal cells (MSCs) from a variety of sources may be used to repair defects in articular cartilage by inducing them into chondrogenic differentiation. The conditions in which optimal chondrogenic differentiation takes place are an area of interest in the field of tissue engineering. Chondrocytes exist in vivo in a normally hypoxic environment and thus it has been suggested that exposing MSCs to hypoxia may also contribute to a beneficial effect on their differentiation. There are two main stages in which MSCs can be exposed to hypoxia, the expansion phase when cells are cultured, and the differentiation phase when cells are induced with a chondrogenic medium. This systematic review sought to explore the effect of hypoxia at these two stages on human adult MSC chondrogenesis in vitro. A literature search was performed on PubMed, EMBASE, Medline via Ovid, and Cochrane, and 24 studies were ultimately included. The majority of these studies showed that hypoxia during the expansion phase or the differentiation phase enhances at least some markers of chondrogenic differentiation in adult MSCs. These results were not always demonstrated at the protein level and there were also conflicting reports. Studies evaluating continuous exposure to hypoxia during the expansion and differentiation phases also had mixed results. These inconsistent results can be explained by the heterogeneity of studies, including factors such as different sources of MSCs used, donor variability, level of hypoxia used in each study, time exposed to hypoxia, and differences in culture methodology.

Nestin prevents mesenchymal stromal cells from apoptosis in LPS-induced lung injury via inhibition of unfolded protein response sensor IRE1α

The clinical applications of MSC therapy have been intensely investigated in acute respiratory distress syndrome. However, clinical studies have fallen short of expectations despite encouraging preclinical results. One of the key problems is that transplanted stem cells can hardly survive in the harsh inflammatory environment. Prolonging the survival of transplanted MSCs might be a promising strategy to enhance the therapeutic efficacy of MSC therapy. Here, we identified Nestin, a class VI intermediate filament, as a positive regulator of MSC survival in the inflammatory microenvironment. We showed that Nestin knockout led to a significant increase of MSC apoptosis, which hampered the therapeutic effects in an LPS-induced lung injury model. Mechanistically, Nestin knockout induced a significant elevation of endoplasmic reticulum (ER) stress level. Further investigations showed that Nestin could bind to IRE1α and inhibit ER stress-induced apoptosis under stress. Furthermore, pretreatment with IRE1α inhibitor 4μ8C improved MSC survival and improved therapeutic effect. Our data suggests that Nestin enhances stem cell survival after transplantation by inhibiting ER stress-induced apoptosis, improving protection, and repair of the lung inflammatory injury.

Proteomics profile of mesenchymal stromal cells and extracellular vesicles in normoxic and hypoxic conditions

BACKGROUND AIMS

Although bone marrow-derived mesenchymal stromal cells (MSCs) have demonstrated success in pre-clinical studies, they have shown only mild therapeutic effects in clinical trials. Hypoxia pre-conditioning may optimize the performance of bone marrow-derived MSCs because it better reflects the physiological conditions of their origin. It is not known whether changes in the protein profile caused by hypoxia in MSCs can be extended to the extracellular vesicles (EVs) released from them. The aim of this study was to evaluate the proteomics profile of MSCs and their EVs under normoxic and hypoxic conditions.

METHODS

Bone marrow-derived MSCs were isolated from six healthy male Wistar rats. After achieving 80% confluence, MSCs were subjected to normoxia (MSC-Norm) (21% oxygen, 5% carbon dioxide, 74% nitrogen) or hypoxia (MSC-Hyp) (1% oxygen, 5% carbon dioxide, 94% nitrogen) for 48 h. Cell viability and oxygen consumption rate were assessed. EVs were extracted from MSCs for each condition (EV-Norm and EV-Hyp) by ultracentrifugation. Total proteins were isolated from MSCs and EVs and prepared for mass spectrometry. EVs were characterized by nanoparticle tracking analysis. Proteomics data were analyzed by PatternLab 4.0, Search Tool for the Retrieval of Interacting Genes/Proteins, Gene Ontology, MetaboAnalyst and Reactome software.

RESULTS

Cell viability was higher in MSC-Hyp than MSC-Norm (P = 0.007). Basal respiration (P = 0.001), proton leak (P = 0.004) and maximal respiration (P = 0.014) were lower in MSC-Hyp than MSC-Norm, and no changes in adenosine triphosphate-linked and residual respiration were observed. The authors detected 2177 proteins in MSC-Hyp and MSC-Norm, of which 147 were identified in only MSC-Hyp and 512 were identified in only MSC-Norm. Furthermore, 718 proteins were identified in EV-Hyp and EV-Norm, of which 293 were detected in only EV-Hyp and 30 were detected in only EV-Norm. Both MSC-Hyp and EV-Hyp showed enrichment of pathways and biological processes related to glycolysis, the immune system and extracellular matrix organization.

CONCLUSIONS

MSCs subjected to hypoxia showed changes in their survival and metabolic activity. In addition, MSCs under hypoxia released more EVs, and their content was related to expression of regulatory proteins of the immune system and extracellular matrix organization. Because of the upregulation of proteins involved in glycolysis, gluconeogenesis and glucose uptake during hypoxia, production of reactive oxygen species and expression of immunosuppressive properties may be affected.

Zinc and hypoxic preconditioning: a strategy to enhance the functionality and therapeutic potential of bone marrow-derived mesenchymal stem cells

The therapeutic use of bone marrow mesenchymal stem cells (BM-MSCs) requires a large number of cells (1-100 × 10⁶ cells/kg of body weight). Extensive in vitro growth is limited due to the aging of cultured BM-MSCs which leads to abnormal morphology and senescence. Hypoxia increases BM-MSC proliferation, but the question of whether hypoxia preconditioning is safe for clinical application of BM-MSCs remains to be answered. Zinc is essential for cell proliferation and differentiation, especially for the regulation of DNA synthesis and mitosis. It is a structural constituent of numerous proteins on a molecular level, including transcription factors and enzymes of cellular signaling machinery. All the tissues, fluids, and organs of the human body contain zinc. More than 95% of zinc is intracellular, of which 44% is involved in the transcription of DNA. We investigated the effects of ZnCl₂ on proliferation, morphology, migration, population doubling time (PDT), and gene expression of BM-MSCs under hypoxic (1% O₂) and normoxic (21% O₂) environments. BM-MSCs were preconditioned with optimized concentrations of ZnCl₂ under normoxic and hypoxic environments and further examined for morphology by the phase-contrast inverted microscope, cell proliferation by MTT assay, PDT, cell migration ability, and gene expression analysis. Zinc significantly enhanced the proliferation of BM-MSCs, and it decreases PDT under hypoxic and normoxic environments as compared to control cells. Migration of BM-MSCs toward the site of injury increased and expression of HIF1-α significantly decreased under hypoxic conditions as compared to non-treated hypoxic cells and control. At late passages (P₉), the morphology of normoxic BM-MSCs was transformed into large, wide, and flat cells, and they became polygonal and lost their communication with other cells. Conversely, zinc-preconditioned BM-MSCs retained their spindle-shaped, fibroblast-like morphology at P₉. The expression of proliferative genes was found significantly upregulated, while downregulation of genes OCT4 and CCNA2 was observed in zinc-treated BM-MSCs under both normoxic and hypoxic conditions. ZnCl₂ treatment can be used for extensive expansion of BM-MSCs in aged populations to obtain a large number of cells required for systemic administration to produce therapeutic efficacy.

HIF-1α Regulates Bone Homeostasis and Angiogenesis, Participating in the Occurrence of Bone Metabolic Diseases

In the physiological condition, the skeletal system's bone resorption and formation are in dynamic balance, called bone homeostasis. However, bone homeostasis is destroyed under pathological conditions, leading to the occurrence of bone metabolism diseases. The expression of hypoxia-inducible factor-1α (HIF-1α) is regulated by oxygen concentration. It affects energy metabolism, which plays a vital role in preventing bone metabolic diseases. This review focuses on the HIF-1α pathway and describes in detail the possible mechanism of its involvement in the regulation of bone homeostasis and angiogenesis, as well as the current experimental studies on the use of HIF-1α in the prevention of bone metabolic diseases. HIF-1α/RANKL/Notch1 pathway bidirectionally regulates the differentiation of macrophages into osteoclasts under different conditions. In addition, HIF-1α is also regulated by many factors, including hypoxia, cofactor activity, non-coding RNA, trace elements, etc. As a pivotal pathway for coupling angiogenesis and osteogenesis, HIF-1α has been widely studied in bone metabolic diseases such as bone defect, osteoporosis, osteonecrosis of the femoral head, fracture, and nonunion. The wide application of biomaterials in bone metabolism also provides a reasonable basis for the experimental study of HIF-1α in preventing bone metabolic diseases.

Hypoxia-related tumor environment correlated with immune infiltration and therapeutic sensitivity in diffuse large B-cell lymphoma

Background: Due to the high heterogeneity of diffuse large B-cell lymphoma (DLBCL), traditional chemotherapy treatment ultimately failed in one-third of the patients. Big challenges existed in finding how to accurately predict prognosis and provide individualized treatment. Hypoxia, although being a key factor in the development and progression of DLBCL, plays its role in DLBCL prognosis, which has yet to be fully explored.

Methods: Data used in the current study were sourced from the Gene Expression Omnibus (GEO) database. DLBCL patients were divided according to different hypoxia-related subtypes based on the expressions of hypoxia-related genes (HRGs) relevant to survival. Differentially expressed genes (DEGs) between subtypes were identified using the limma package. Using univariate Cox regression and least absolute shrinkage and selection operator (LASSO) analyses, the prognostic signature was established to calculate risk scores. The tumor microenvironment (TME) in low- and high-risk groups was evaluated by single-sample gene set enrichment analysis (ssGSEA) and ESTIMATE. The chemotherapeutic sensitivity in two groups was assessed by IC50 values.

Results: DLBCL patients were clustered into two hypoxia-related subtype groups according to different gene survival and expressions associated with increasing oxygen delivery and reducing oxygen consumption, and these two subtype groups were compared. Based on the differential expression, a risk model was established using univariate cox and LASSO regression analyses, FNDC1, ANTXR1, RARRES2, S100A9, and MT1M. The performance of the risk signature in predicting the prognosis of DLBCL patients was validated in the internal and external datasets, as evidenced by receiver operating characteristic (ROC) curves. In addition, we observed significant differences in the tumor microenvironment and chemotherapeutic response between low- and high-risk groups.

Conclusion: Our study developed novel hypoxia-related subtypes in DLBCL and identified five prognostic signatures for DLBCL patients. These findings may enrich our understanding of the role of hypoxia in DLBCL and help improve the treatment of DLBCL patients.

Supraphysiological Oxygen Levels in Mammalian Cell Culture: Current State and Future Perspectives

Most conventional incubators used in cell culture do not regulate O2 levels, making the headspace O2 concentration ~18%. In contrast, most human tissues are exposed to 2-6% O2 (physioxia) in vivo. Accumulating evidence has shown that such hyperoxic conditions in standard cell culture practices affect a variety of biological processes. In this review, we discuss how supraphysiological O2 levels affect reactive oxygen species (ROS) metabolism and redox homeostasis, gene expression, replicative lifespan, cellular respiration, and mitochondrial dynamics. Furthermore, we present evidence demonstrating how hyperoxic cell culture conditions fail to recapitulate the physiological and pathological behavior of tissues in vivo, including cases of how O2 alters the cellular response to drugs, hormones, and toxicants. We conclude that maintaining physioxia in cell culture is imperative in order to better replicate in vivo-like tissue physiology and pathology, and to avoid artifacts in research involving cell culture.

The Characteristics and Survival Potential Under Sub-lethal Stress of Mesenchymal Stromal/Stem Cells Isolated from the Human Vascular Wall

Mesenchymal stromal/stem cells (MSCs) have been identified in multiple human tissues, including the vascular wall. High proliferative potential, multilineage, and immunomodulatory properties make vascular MSCs promising candidates for regenerative medicine. Indeed, their location is strategic for controlling vascular and extra-vascular tissue homeostasis. However, the clinical application of MSCs, and in particular vascular MSCs, is still challenging. Current studies are focused on developing strategies to improve MSC therapeutic applications, like priming MSCs with stress conditions (hypoxia, nutrient deprivation) to achieve a higher therapeutic potential. The goal of the present study is to review the main findings regarding the MSCs isolated from the human vascular wall. Further, the main priming strategies tested on MSCs from different sources are reported, together with the experience on vascular MSCs isolated from healthy cryopreserved and pathological arteries. Stress induction can be a priming approach able to improve MSC effectiveness through several mechanisms that are discussed in this review. Nevertheless, these issues have not been completely explored in vascular MSCs and potential side effects need to be investigated.

Role of hypoxia preconditioning in therapeutic potential of mesenchymal stem-cell-derived extracellular vesicles

The use of mesenchymal stem-cells (MSC) in cell therapy has received considerable attention because of their properties. These properties include high expansion and differentiation in vitro, low immunogenicity, and modulation of biological processes, such as inflammation, angiogenesis and hematopoiesis. Curiously, the regenerative effect of MSC is partly due to their paracrine activity. This has prompted numerous studies, to investigate the therapeutic potential of their secretome in general, and specifically their extracellular vesicles (EV). The latter contain proteins, lipids, nucleic acids, and other metabolites, which can cause physiological changes when released into recipient cells. Interestingly, contents of EV can be modulated by preconditioning MSC under different culture conditions. Among them, exposure to hypoxia stands out; these cells respond by activating hypoxia-inducible factor (HIF) at low O₂ concentrations. HIF has direct and indirect pleiotropic effects, modulating expression of hundreds of genes involved in processes such as inflammation, migration, proliferation, differentiation, angiogenesis, metabolism, and cell apoptosis. Expression of these genes is reflected in the contents of secreted EV. Interestingly, numerous studies show that MSC-derived EV conditioned under hypoxia have a higher regenerative capacity than those obtained under normoxia. In this review, we show the implications of hypoxia responses in relation to tissue regeneration. In addition, hypoxia preconditioning of MSC is being evaluated as a very attractive strategy for isolation of EV, with a high potential for clinical use in regenerative medicine that can be applied to different pathologies.

Impact of Microenvironmental Changes during Degeneration on Intervertebral Disc Progenitor Cells: A Comparison with Mesenchymal Stem Cells

Intervertebral disc (IVD) degeneration occurs with natural ageing and is linked to low back pain, a common disease. As an avascular tissue, the microenvironment inside the IVD is harsh. During degeneration, the condition becomes even more compromised, presenting a significant challenge to the survival and function of the resident cells, as well as to any regeneration attempts using cell implantation. Mesenchymal stem cells (MSCs) have been proposed as a candidate stem cell tool for IVD regeneration. Recently, endogenous IVD progenitor cells have been identified inside the IVD, highlighting their potential for self-repair. IVD progenitor cells have properties similar to MSCs, with minor differences in potency and surface marker expression. Currently, it is unclear how IVD progenitor cells react to microenvironmental factors and in what ways they possibly behave differently to MSCs. Here, we first summarized the microenvironmental factors presented in the IVD and their changes during degeneration. Then, we analyzed the available studies on the responses of IVD progenitor cells and MSCs to these factors, and made comparisons between these two types of cells, when possible, in an attempt to achieve a clear understanding of the characteristics of IVD progenitor cells when compared to MSCs; as well as, to provide possible clues to cell fate after implantation, which may facilitate future manipulation and design of IVD regeneration studies.

The Intercellular Communication Between Mesenchymal Stromal Cells and Hematopoietic Stem Cells Critically Depends on NF-κB Signalling in the Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) regulate the fate of the hematopoietic stem cells (HSCs) through both cell-cell interactions and paracrine mechanisms involving multiple signalling pathways. We have previously shown that co-culturing of HSCs with CoCl₂-treated MSCs expands functional HSCs. While performing these experiments, we had observed that the growth of CoCl₂-treated MSCs was significantly stunted. Here, we show that CoCl₂-treated MSCs possess activated NF-κB signalling pathway, and its pharmacological inhibition significantly relieves their growth arrest. Most interestingly, we found that pharmacological inhibition of NF-κB pathway in both control and CoCl₂-treated MSCs completely blocks their intercellular communication with the co-cultured hematopoietic stem and progenitor cells (HSPCs), resulting in an extremely poor output of hematopoietic cells. Mechanistically, we show that this is due to the down-regulation of adhesion molecules and various HSC-supportive factors in the MSCs. This loss of physical interaction with HSPCs could be partially restored by treating the MSCs with calcium ionophore or calmodulin, suggesting that NF-κB regulates intracellular calcium flux in the MSCs. Importantly, the HSPCs co-cultured with NF-κB-inhibited-MSCs were in a quiescent state, which could be rescued by re-culturing them with untreated MSCs. Our data underscore a critical requirement of NF-κB signalling in the MSCs in intercellular communication between HSCs and MSCs for effective hematopoiesis to occur ex vivo. Our data raises a cautionary note against excessive use of anti-inflammatory drugs targeting NF-κB.

Insight in Hypoxia-Mimetic Agents as Potential Tools for Mesenchymal Stem Cell Priming in Regenerative Medicine

Hypoxia-mimetic agents are new potential tools in MSC priming instead of hypoxia incubators or chambers. Several pharmaceutical/chemical hypoxia-mimetic agents can be used to induce hypoxia in the tissues: deferoxamine (DFO), dimethyloxaloylglycine (DMOG), 2,4-dinitrophenol (DNP), cobalt chloride (CoCl2), and isoflurane (ISO). Hypoxia-mimetic agents can increase cell proliferation, preserve or enhance differentiation potential, increase migration potential, and induce neovascularization in a concentration- and stem cell source-dependent manner. Moreover, hypoxia-mimetic agents may increase HIF-1α, changing the metabolism and enhancing glycolysis like hypoxia. So, there is clear evidence that treatment with hypoxia-mimetic agents is beneficial in regenerative medicine, preserving stem cell capacities. These agents are not studied so wildly as hypoxia but, considering the low cost and ease of use, are believed to find application as pretreatment of many diseases such as ischemic heart disease and myocardial fibrosis and promote cardiac and cartilage regeneration. The knowledge of MSC priming is critical in evaluating safety procedures and use in clinics. In this review, similarities and differences between hypoxia and hypoxia-mimetic agents in terms of their therapeutic efficiency are considered in detail. The advantages, challenges, and future perspectives in MSC priming with hypoxia mimetic agents are also discussed.

Secretomes as an emerging class of bioactive ingredients for enhanced cosmeceutical applications

Skin aging is predominantly caused by either intrinsic or extrinsic factors, leading to undesirable skin features. Advancements in both molecular and cellular fields have created possibilities in developing novel stem cell-derived active ingredients for cosmeceutical applications and the beauty industry. Mesenchymal stromal cell (MSC)-derived secretomes or conditioned media hold great promise for advancing skin repair and regeneration due to the presence of varying cytokines. These cytokines signal our cells and trigger biological mechanisms associated with anti-inflammatory, antioxidant, anti-aging, proliferative, and immunomodulatory effects. In this review, we discuss the potential of MSC secretomes as novel biomaterials for skincare and rejuvenation by illustrating their mechanism of action related to wound healing, anti-aging, and whitening properties. The advantages and disadvantages of secretomes are compared to both plant-based and animal-derived extracts. In addition, this paper reviews the current safety standards, regulations, market products and research work related to the cosmeceutical applications of secretomes along with strategies to maintain and improve the therapeutic efficacy and production of secretomes. The future outlook of beauty industry is also presented. Lastly, we highlight significant challenges to be addressed for the clinical realization of MSC secretomes-based skin therapies as well as providing perspectives for the future direction of secretomes.

Pre-conditioning Strategies for Mesenchymal Stromal/Stem Cells in Inflammatory Conditions of Livestock Species

Mesenchymal stem/stromal cells (MSCs) therapy has been a cornerstone of regenerative medicine in humans and animals since their identification in 1968. MSCs can interact and modulate the activity of practically all cellular components of the immune response, either through cell-cell contact or paracrine secretion of soluble mediators, which makes them an attractive alternative to conventional therapies for the treatment of chronic inflammatory and immune-mediated diseases. Many of the mechanisms described as necessary for MSCs to modulate the immune/inflammatory response appear to be dependent on the animal species and source. Although there is evidence demonstrating an in vitro immunomodulatory effect of MSCs, there are disparate results between the beneficial effect of MSCs in preclinical models and their actual use in clinical diseases. This discordance might be due to cells' limited survival or impaired function in the inflammatory environment after transplantation. This limited efficacy may be due to several factors, including the small amount of MSCs inoculated, MSC administration late in the course of the disease, low MSC survival rates in vivo, cryopreservation and thawing effects, and impaired MSC potency/biological activity. Multiple physical and chemical pre-conditioning strategies can enhance the survival rate and potency of MSCs; this paper focuses on hypoxic conditions, with inflammatory cytokines, or with different pattern recognition receptor ligands. These different pre-conditioning strategies can modify MSCs metabolism, gene expression, proliferation, and survivability after transplantation.

Hypoxia, a dynamic tool to amplify the gingival mesenchymal stem cells potential for neurotrophic factor secretion

Gingival mesenchymal stem cells (GMSCs) have significant regenerative potential. Their potential applications range from the treatment of inflammatory diseases, wound healing, and oral disorders. Preconditioning these stem cells can optimize their biological properties. Hypoxia preconditioning of MSCs improves stem cell properties like proliferation, survival, and differentiation potential. This research explored the possible impact of hypoxia on the pluripotent stem cell properties that GMSCs possess. We evaluated the morphology, stemness, neurotrophic factors, and stemness-related genes. We compared the protein levels of secreted neurotrophic factors between normoxic and hypoxic GMSC-conditioned media (GMSC-CM). Results revealed that hypoxic cultured GMSC’s had augmented expression of neurotrophic factors BDNF, GDNF, VEGF, and IGF1 and stemness-related gene NANOG. Hypoxic GMSCs showed decreased expression of the OCT4 gene. In hypoxic GMSC-CM, the neurotrophic factors secretions were significantly higher than normoxic GMSC-CM. Our data demonstrate that culturing of GMSCs in hypoxia enhances the secretion of neurotrophic factors that can lead to neuronal lineage differentiation.

Hypoxia-Mimetic CoCl2 Agent Enhances Pro-Angiogenic Activities in Ovine Amniotic Epithelial Cells-Derived Conditioned Medium

Amniotic epithelial stem cells (AECs) are largely studied for their pro-regenerative properties. However, it remains undetermined if low oxygen (O₂) levels that AECs experience in vivo can be of value in maintaining their biological properties after isolation. To this aim, the present study has been designed to evaluate the effects of a hypoxia-mimetic agent, cobalt chloride (CoCl₂), on AECs’ stemness and angiogenic activities. First, a CoCl₂ dose-effect was performed to select the concentration able to induce hypoxia, through HIF-1α stabilization, without promoting any cytotoxicity effect assessed through the analysis of cell vitality, proliferation, and apoptotic-related events. Then, the identified CoCl₂ dose was evaluated on the expression and angiogenic properties of AECs’ stemness markers (OCT-4, NANOG, SOX-2) by analysing VEGF expression, angiogenic chemokines’ profiles, and AEC-derived conditioned media activity through an in vitro angiogenic xeno-assay. Results demonstrated that AECs are sensitive to the cytotoxicity effects of CoCl₂. The unique concentration leading to HIF-1α stabilization and nuclear translocation was 10 µM, preserving cell viability and proliferation up to 48 h. CoCl₂ exposure did not modulate stemness markers in AECs while progressively decreasing VEGF expression. On the contrary, CoCl₂ treatment promoted a significant short-term release of angiogenic chemokines in culture media (CM). The enrichment in bio-active factors was confirmed by the ability of CoCl₂-derived CM to induce HUVEC growth and the cells’ organization in tubule-like structures. These findings demonstrate that an appropriate dose of CoCl₂ can be adopted as a hypoxia-mimetic agent in AECs. The short-term, chemical-induced hypoxic condition can be targeted to enhance AECs’ pro-angiogenic properties by providing a novel approach for stem cell-free therapy protocols.

Directing hypoxic tumor microenvironment and HIF to illuminate cancer immunotherapy's existing prospects and challenges in drug targets

Cancer is now also reflected as a disease of the tumor microenvironment, primarily supposed to be a decontrolled genetic and cellular expression disease. Over the past two decades, significant and rapid progress has been made in recognizing the dynamics of the tumor's microenvironment and its contribution to influencing the response to various anti-cancer therapies and drugs. Modulations in the tumor microenvironment and immune checkpoint blockade are interesting in cancer immunotherapy and drug targets. Simultaneously, the immunotherapeutic strategy can be done by modulating the immune regulatory pathway; however, the tumor microenvironment plays an essential role in suppressing the antitumor's immunity by its substantial heterogeneity. Hypoxia inducible factor (HIF) is a significant contributor to solid tumor heterogeneity and a key stressor in the tumor microenvironment to drive adaptations to prevent immune surveillance. Checkpoint inhibitors here halt the ability of cancer cells to stop the immune system from activating, and in turn, amplify your body's immune system to help destroy cancer cells. Common checkpoints that these inhibitors affect are the PD-1/PD-L1 and CTLA-4 pathways and important drugs involved are Ipilimumab and Nivolumab, mainly along with other drugs in this group. Targeting the hypoxic tumor microenvironment may provide a novel immunotherapy strategy, break down traditional cancer therapy resistance, and build the framework for personalized precision medicine and cancer drug targets. We hope that this knowledge can provide insight into the therapeutic potential of targeting Hypoxia and help to develop novel combination approaches of cancer drugs to increase the effectiveness of existing cancer therapies, including immunotherapy.

Designing Olfactory Ensheathing Cell Transplantation Therapies: Influence of Cell Microenvironment

Olfactory ensheathing cell (OEC) transplantation is emerging as a promising treatment option for injuries of the nervous system. OECs can be obtained relatively easily from nasal biopsies, and exhibit several properties such as secretion of trophic factors, and phagocytosis of debris that facilitate neural regeneration and repair. But a major limitation of OEC-based cell therapies is the poor survival of transplanted cells which subsequently limit their therapeutic efficacy. There is an unmet need for approaches that enable the in vitro production of OECs in a state that will optimize their survival and integration after transplantation into the hostile injury site. Here, we present an overview of the strategies to modulate OECs focusing on oxygen levels, stimulating migratory, phagocytic, and secretory properties, and on bioengineering a suitable environment in vitro.