Relevance of Oxygen Concentration in Stem Cell Culture for Regenerative Medicine

Progress on oxygen-releasing bioactive polymeric scaffolds in tissue engineering and biomedical treatment: A review

Tissue engineering presents promising avenues for addressing issues related to tissue defects and regenerative medicine. However, the translational efficacy of tissue engineering in clinical settings remains limited, primarily due to the inadequate survival rates of implanted tissue scaffolds. This is attributed to the grafts' inability to adequately supply oxygen and their dependence on the diffusion of oxygen from surrounding tissues for tissue regeneration. The integration of oxygen-releasing materials in human tissue engineering is anticipated to enhance the hypoxic microenvironment for tissue regeneration. In recent years, a variety of oxygen-producing or oxygen-carrying biomacromolecules, including gelatin, chitosan, and alginate, have been developed, offering innovative strategies for controlled drug release efficacy, regenerative medicine, and biological systems engineering. This review examines applications of these oxygen-releasing biological macromolecules, primarily derived from natural polymeric materials, in diverse facets of human tissue engineering including skin, heart tissue, tumor therapy. We also highlight recent advancements in this field, with an emphasis on current challenges, potential solutions, and future perspectives.

Pericytes require physiological oxygen tension to maintain phenotypic fidelity

Pericytes function to maintain tissue homeostasis by regulating capillary blood flow and maintaining endothelial barrier function. Pericyte dysfunction is associated with various pathologies and has recently been found to aid cancer progression. Despite having critical functions in health and disease, pericytes remain an understudied population due to a lack of model systems which accurately reflect in vivo biology. In this study we developed a protocol to isolate and culture murine lung, brain, bone, and liver pericytes, that maintains their known phenotypes and functions. We demonstrate that pericytes, being inherently plastic, benefit from controlled oxygen tension culture conditions, aiding their expansion ex vivo. Primary pericytes grown in physiologically relevant oxygen tensions (10% O2 for lung; 5% O2 for brain, bone, and liver) also better retain pericyte phenotypes indicated by stable expression of characteristic transcriptional and protein markers. In functional tube formation assays, pericytes were observed to significantly associate with endothelial junctions. Importantly, we identified growth conditions that limit expression of the plasticity factor Klf4 to prevent spontaneous phenotypic switching in vitro. Additionally, we were able to induce pathological pericyte phenotypic switching in response to metastatic stimuli to accurately recapitulate in vivo biology. Here, we present a robust method for studying pericyte biology in both physiology and disease.

Targeted intracellular delivery of molecular cargo to hypoxic human breast cancer stem cells

Cancer stem cells (CSCs) drive tumorigenesis, are responsible for metastasis, and resist conventional therapies thus posing significant treatment challenges. CSCs reside in hypoxic tumor regions and therefore, effective therapies must target CSCs within this specific microenvironment. CSCs are characterized by limited distinguishable features, however, surface displayed phosphatidylserine (PS) appears to be characteristic of stem cells and offers a potential target. GlaS, a truncated coagulation protein that is internalized after binding PS, was investigated for intracellular delivery of molecular payloads to CSCs. Intracellular delivery via GlaS was enhanced in patient-derived CD44+ mammary CSCs under hypoxic conditions relative to physoxia or hyperoxia. In vivo, GlaS successfully targeted hypoxic tumor regions, and functional delivery of molecular cargo was confirmed using luciferin conjugated to GlaS via a disulfide linkage (GlaS-SS-luc), which releases luciferin upon intracellular glutathione reduction. Bioluminescence imaging demonstrated effective GlaS-mediated delivery of luciferin, a model drug, to CSCs in culture and in vivo. These findings offer the promise of directed delivery of therapeutic agents to intracellular targets in CSCs.

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.

Patient-derived colon epithelial organoids reveal lipid-related metabolic dysfunction in pediatric ulcerative colitis

Background & Aims

Ulcerative colitis (UC) is associated with epithelial metabolic derangements which exacerbate gut inflammation. Patient-derived organoids recapitulate complexities of the parent tissue in health and disease; however, whether colon organoids (colonoids) model metabolic impairments in the pediatric UC epithelium is unclear. This study determined the functional metabolic differences in the colon epithelia using epithelial colonoids from pediatric patients.

Methods

We developed biopsy-derived colonoids from pediatric patients with endoscopically active UC, inactive UC, and those without endoscopic or histologic evidence of colon inflammation (non-IBD controls). We extensively interrogated metabolic dysregulation through extracellular flux analyses and tested potential therapies that recapitulate or ameliorate such metabolic dysfunction.

Results

Epithelial colonoids from active UC patients exhibit elevated oxygen consumption and proton leak supported by enhanced glycolytic capacity and dysregulated lipid metabolism. The hypermetabolic features in active UC colonoids were associated with increased cellular stress and chemokine secretion, specifically during differentiation. Transcriptomic and pathway analyses indicated a role for PPAR-α in lipid-induced hypermetabolism in active UC colonoids, which was validated by PPAR-α activation in non-IBD colonoids. Accordingly, limiting neutral lipid accumulation in active UC colonoids through pharmacological inhibition of PPAR-α induced a metabolic shift towards glucose consumption, suppressed hypermetabolism and chemokine secretion, and improved cellular stress markers. Control and inactive UC colonoids had similar metabolic and transcriptomic profiles.

Conclusions

Our pediatric colonoids revealed significant lipid-related metabolic dysregulation in the pediatric UC epithelium that may be alleviated by PPAR-α inhibition. This study supports the advancement of colonoids as a preclinical human model for testing epithelial-directed therapies against such metabolic dysfunction.

What You Need to Know

Background and Context: Colon mucosa healing in pediatric UC requires reinstating normal epithelial function but a lack of human preclinical models of the diseased epithelium hinders the development of epithelial-directed interventions.

New Findings

Using colon biopsy-derived epithelial organoids, samples from pediatric patients with active UC show hyperactive metabolic function largely driven by enhanced lipid metabolism. Pharmacologic inhibition of lipid metabolism alleviates metabolic dysfunction, cellular stress, and chemokine production.

Limitations

Though our epithelial colon organoids from active UC patients show targetable metabolic and molecular features from non-IBD controls, they were cultured under sterile conditions, which may not fully capture any potential real-time contributions of the complex inflammatory milieu typically present in the disease.

Clinical Research Relevance

Current therapies for pediatric UC mainly target the immune system despite the need for epithelial healing to sustain remission. We identified a pharmacologic target that regulates epithelial metabolism and can be developed for epithelial-directed therapy in UC.Basic Research Relevance: Pediatric UC patient tissue adult stem cell-derived colon epithelial organoids retain disease-associated metabolic pathology and can serve as preclinical human models of disease. Excess reliance on lipids as an energy source leads to oxidative and inflammatory dysfunction in pediatric UC colon organoids. Preprint: This manuscript is currently on bioRxiv. doi: https://doi.org/10.1101/2024.08.22.609271 Lay Summary: Using patient tissue-derived colon epithelial organoids, the investigators identified epithelial metabolic dysfunction and inflammation in pediatric ulcerative colitis that can be alleviated by PPAR-a inhibition.

Potential mechanisms and therapeutic strategies for LPS-associated female fertility decline

As a major component of the outer membrane of Gram-negative bacteria, lipopolysaccharide (LPS) can be recognized by toll-like receptors (TLRs) and induce inflammation through MyD88 or the TIR domain-containing adapter-inducing interferon-β (TRIF) pathway. Previous studies have found that LPS-associated inflammatory/immune challenges were associated with ovarian dysfunction and reduced female fertility. However, the etiology and pathogenesis of female fertility decline associated with LPS are currently complex and multifaceted. In this review, PubMed was used to search for references on LPS and fertility decline so as to elucidate the potential mechanisms of LPS-associated female fertility decline and summarize therapeutic strategies that may improve LPS-associated fertility decline.

Protocol for the derivation of primary cancer stem cell lines from human ependymal tumors

Cancer stem cells (CSCs) established from surgical biopsies closely mimic the human context and can be used to investigate disease mechanisms, genetic fitness, and therapeutic evaluation. Here, we present a protocol for the derivation of primary patient-derived CSC lines from ependymal tumors. We describe the necessary steps, from surgical intervention and biopsy to the dissociation of ependymomas to derive cultures. We then detail procedures for cell line propagation and define the characteristics of these primary cancer cell lines. For complete details on the use and execution of this protocol, please refer to Michealraj et al.1.

Quiescent Adult Neural Stem Cells: Developmental Origin and Regulatory Mechanisms

The existence of neural stem cells (NSCs) in the adult mammalian nervous system, although small in number and restricted to the sub-ventricular zone of the lateral ventricles, the dentate gyrus of the hippocampus, and the olfactory epithelium, is a gift of evolution for the adaptive brain function which requires persistent plastic changes of these regions. It is known that most adult NSCs are latent, showing long cell cycles. In the past decade, the concept of quiescent NSCs (qNSCs) has been widely accepted by researchers in the field, and great progress has been made in the biology of qNSCs. Although the spontaneous neuronal regeneration derived from adult NSCs is not significant, understanding how the behaviors of qNSCs are regulated sheds light on stimulating endogenous NSC-based neuronal regeneration. In this review, we mainly focus on the recent progress of the developmental origin and regulatory mechanisms that maintain qNSCs under normal conditions, and that mobilize qNSCs under pathological conditions, hoping to give some insights for future study.

CRISPR-based functional profiling of the Toxoplasma gondii genome during acute murine infection

Examining host-pathogen interactions in animals can capture aspects of infection that are obscured in cell culture. Using CRISPR-based screens, we functionally profile the entire genome of the apicomplexan parasite Toxoplasma gondii during murine infection. Barcoded gRNAs enabled bottleneck detection and mapping of population structures within parasite lineages. Over 300 genes with previously unknown roles in infection were found to modulate parasite fitness in mice. Candidates span multiple axes of host-parasite interaction. Rhoptry Apical Surface Protein 1 was characterized as a mediator of host-cell tropism that facilitates repeated invasion attempts. GTP cyclohydrolase I was also required for fitness in mice and druggable through a repurposed compound, 2,4-diamino-6-hydroxypyrimidine. This compound synergized with pyrimethamine against T. gondii and malaria-causing Plasmodium falciparum parasites. This work represents a complete survey of an apicomplexan genome during infection of an animal host and points to novel interfaces of host-parasite interaction.

Redox heterogeneity in mouse embryonic stem cells individualizes cell fate decisions

Pluripotent embryonic stem cells (ESCs) can develop into any cell type in the body. Yet, the regulatory mechanisms that govern cell fate decisions during embryogenesis remain largely unknown. We now demonstrate that mouse ESCs (mESCs) display large natural variations in mitochondrial reactive oxygen species (mitoROS) levels that individualize their nuclear redox state, H3K4me3 landscape, and cell fate. While mESCs with high mitoROS levels (mitoROSHIGH) differentiate toward mesendoderm and form the primitive streak during gastrulation, mESCs, which generate less ROS, choose the alternative neuroectodermal fate. Temporal studies demonstrated that mesendodermal (ME) specification of mitoROSHIGH mESCs is mediated by a Nrf2-controlled switch in the nuclear redox state, triggered by the accumulation of redox-sensitive H3K4me3 marks, and executed by a hitherto unknown ROS-dependent activation process of the Wnt signaling pathway. In summary, our study explains how ESC heterogeneity is generated and used by individual cells to decide between distinct cellular fates.

Hypoxic Functional Regulation Pathways in the GI Tract: Focus on the HIF-1α and Microbiota's Crosstalk

Hypoxia is an essential gastrointestinal (GI) tract phenomenon that influences both physiologic and pathologic states. Hypoxia-inducible factors (HIFs), the primary drivers of cell adaptation to low-oxygen environments, have been identified as critical regulators of gut homeostasis: directly, through the induction of different proteins linked to intestinal barrier stabilization (ie, adherent proteins, tight junctions, mucins, integrins, intestinal trefoil factor, and adenosine); and indirectly, through the regulation of several immune cell types and the modulation of autophagy and inflammatory processes. Furthermore, hypoxia and HIF-related sensing pathways influence the delicate relationship existing between bacteria and mammalian host cells. In turn, gut commensals establish and maintain the physiologic hypoxia of the GI tract and HIF-α expression. Based on this premise, the goals of this review are to (1) highlight hypoxic molecular pathways in the GI tract, both in physiologic and pathophysiologic settings, such as inflammatory bowel disease; and (2) discuss a potential strategy for ameliorating gut-related disorders, by targeting HIF signaling, which can alleviate inflammatory processes, restore autophagy correct mechanisms, and benefit the host-microbiota equilibrium.

Hypoxia drives HIF2-dependent reversible macrophage cell cycle entry

Low-oxygen conditions (hypoxia) have been associated primarily with cell-cycle arrest in dividing cells. Macrophages are typically quiescent in G0 but can proliferate in response to tissue signals. Here we show that hypoxia (1% oxygen tension) results in reversible entry into the cell cycle in macrophages. Cell cycle progression is largely limited to G0-G1/S phase transition with little progression to G2/M. This cell cycle transitioning is triggered by an HIF2α-directed transcriptional program. The response is accompanied by increased expression of cell-cycle-associated proteins, including CDK1, which is known to phosphorylate SAMHD1 at T592 and thereby regulate antiviral activity. Prolyl hydroxylase (PHD) inhibitors are able to recapitulate HIF2α-dependent cell cycle entry in macrophages. Finally, tumor-associated macrophages (TAMs) in lung cancers exhibit transcriptomic profiles representing responses to low oxygen and cell cycle progression at the single-cell level. These findings have implications for inflammation and tumor progression/metastasis where low-oxygen environments are common.

Hypoxic Preconditioning Promotes Survival of Human Adipose Derived Mesenchymal Stem Cell

Background: Contributing factors for improved survival of human adipocytes mesenchymal stem cells (h-AMSCs) cultured through hypoxia preconditioning, in example apoptosis inhibition involving BCL2 and HSP27 expression, trigger signal expression (VEGF), SCF expression, OCT-4 expression, and CD44+ expression. The objective if this study was to explain the mechanism and role of hypoxic preconditioning and the optimal duration of hypoxic preconditioning exposure to improve survival of h-AMSCs. Methods: An experimental laboratory explorative study ( in vitro) with hypoxic preconditioning in h-AMSCs cultures. This research was conducted through four stages. First, isolation of h-AMSCs culture from adipose tissue of patients. Second, the characterization of h-AMSCs from adipose tissue by phenotype (flowcytometry) through CD44+, CD90+ and CD45-expression before being pre-conditioned for hypoxic treatment. Third, the hypoxic preconditioning in h-AMSCs culture ( in vitro) was performed with an oxygen concentration of 1% for 24, 48 and 72 hours. Fourth, observation of survival from h-AMSCs culture was tested on the role of CD44+, VEGF, SCF, OCT-4, BCL2, HSP27 with Flowcytometry and apoptotic inhibition by Tunnel Assay method. Results: The result of regression test showed that time difference had an effect on VEGF expression ( p<0.001; β=-0.482) and hypoxia condition also influenced VEGF expression ( p<0.001; β=0.774). The result of path analysis showed that SCF had effect on OCT-4 expression ( p<0.001; β=0.985). The regression test results showed that time effects on HSP27 expression ( p<0.001; β=0.398) and hypoxia precondition also affects HSP27 expression ( p<0.001; β=0.847). Pathway analysis showed that BCL2 expression inhibited apoptosis ( p=0.030; β=-0.442) and HSP27 expression also inhibited apoptosis ( p<0,001; β=-0.487). Conclusion: Hypoxic preconditioning of h-AMSC culture has proven to increase the expression of VEGF, SCF, OCT-4, and BCL2 and HSP27. This study demonstrated and explained the existence of a new mechanism of increased h-AMSC survival in cultures with hypoxic preconditioning (O2 1%) via VEGF, SCF, OCT-4, BCL2, and HSP 27.

A gene for all seasons: The evolutionary consequences of HIF-1 in carcinogenesis, tumor growth and metastasis

Oxygen played a pivotal role in the evolution of multicellularity during the Cambrian Explosion. Not surprisingly, responses to fluctuating oxygen concentrations are integral to the evolution of cancer-a disease characterized by the breakdown of multicellularity. Poorly organized tumor vasculature results in chaotic patterns of blood flow characterized by large spatial and temporal variations in intra-tumoral oxygen concentrations. Hypoxia-inducible growth factor (HIF-1) plays a pivotal role in enabling cells to adapt, metabolize, and proliferate in low oxygen conditions. HIF-1 is often constitutively activated in cancers, underscoring its importance in cancer progression. Here, we argue that the phenotypic changes mediated by HIF-1, in addition to adapting the cancer cells to their local environment, also "pre-adapt" them for proliferation at distant, metastatic sites. HIF-1-mediated adaptations include a metabolic shift towards anaerobic respiration or glycolysis, activation of cell survival mechanisms like phenotypic plasticity and epigenetic reprogramming, and formation of tumor vasculature through angiogenesis. Hypoxia induced epigenetic reprogramming can trigger epithelial to mesenchymal transition in cancer cells-the first step in the metastatic cascade. Highly glycolytic cells facilitate local invasion by acidifying the tumor microenvironment. New blood vessels, formed due to angiogenesis, provide cancer cells a conduit to the circulatory system. Moreover, survival mechanisms acquired by cancer cells in the primary site allow them to remodel tissue at the metastatic site generating tumor promoting microenvironment. Thus, hypoxia in the primary tumor promoted adaptations conducive to all stages of the metastatic cascade from the initial escape entry into a blood vessel, intravascular survival, extravasation into distant tissues, and establishment of secondary tumors.

Progress on Electro-Enhancement of Cell Manufacturing

With the long persistence of complex, chronic diseases in society, there is increasing motivation to develop cells as living medicine to treat diseases ranging from cancer to wounds. While cell therapies can significantly impact healthcare, the shortage of starter cells meant that considerable raw materials must be channeled solely for cell expansion, leading to expensive products with long manufacturing time which can prevent accessibility by patients who either cannot afford the treatment or have highly aggressive diseases and cannot wait that long. Over the last three decades, there has been increasing knowledge on the effects of electrical modulation on proliferation, but to the best of the knowledge, none of these studies went beyond how electro-control of cell proliferation may be extended to enhance industrial scale cell manufacturing. Here, this review is started by discussing the importance of maximizing cell yield during manufacturing before comparing strategies spanning biomolecular/chemical/physical to modulate cell proliferation. Next, the authors describe how factors governing invasive and non-invasive electrical stimulation (ES) including capacitive coupling electric field may be modified to boost cell manufacturing. This review concludes by describing what needs to be urgently performed to bridge the gap between academic investigation of ES to industrial applications.

Chip collection of hepatocellular carcinoma based on O2 heterogeneity from patient tissue

Hepatocellular carcinoma frequently recurs after surgery, necessitating personalized clinical approaches based on tumor avatar models. However, location-dependent oxygen concentrations resulting from the dual hepatic vascular supply drive the inherent heterogeneity of the tumor microenvironment, which presents challenges in developing an avatar model. In this study, tissue samples from 12 patients with hepatocellular carcinoma are cultured directly on a chip and separated based on preference of oxygen concentration. Establishing a dual gradient system with drug perfusion perpendicular to the oxygen gradient enables the simultaneous separation of cells and evaluation of drug responsiveness. The results are further cross-validated by implanting the chips into mice at various oxygen levels using a patient-derived xenograft model. Hepatocellular carcinoma cells exposed to hypoxia exhibit invasive and recurrent characteristics that mirror clinical outcomes. This chip provides valuable insights into treatment prognosis by identifying the dominant hepatocellular carcinoma type in each patient, potentially guiding personalized therapeutic interventions.

Harnessing Mitochondrial Stress for Health and Disease: Opportunities and Challenges

Mitochondria, essential organelles orchestrating cellular metabolism, have emerged as central players in various disease pathologies. Recent research has shed light on mitohormesis, a concept proposing an adaptive response of mitochondria to minor disturbances in homeostasis, offering novel therapeutic avenues for mitochondria-related diseases. This comprehensive review explores the concept of mitohormesis, elucidating its induction mechanisms and occurrence. Intracellular molecules like reactive oxygen species (ROS), calcium, mitochondrial unfolded proteins (UPRmt), and integrated stress response (ISR), along with external factors such as hydrogen sulfide (H2S), physical stimuli, and exercise, play pivotal roles in regulating mitohormesis. Based on the available evidence, we elucidate how mitohormesis maintains mitochondrial homeostasis through mechanisms like mitochondrial quality control and mitophagy. Furthermore, the regulatory role of mitohormesis in mitochondria-related diseases is discussed. By envisioning future applications, this review underscores the significance of mitohormesis as a potential therapeutic target, paving the way for innovative interventions in disease management.

Organosilica Nanosensors for Monitoring Spatiotemporal Changes in Oxygen Levels in Bacterial Cultures

Oxygen plays a central role in aerobic metabolism, and while many approaches have been developed to measure oxygen concentration in biological environments over time, monitoring spatiotemporal changes in dissolved oxygen levels remains challenging. To address this, we developed a ratiometric core-shell organosilica nanosensor for continuous, real-time optical monitoring of oxygen levels in biological environments. The nanosensors demonstrate good steady state characteristics (KpSV = 0.40 L/mg, R2 = 0.95) and respond reversibly to changes in oxygen concentration in buffered solutions and report similar oxygen level changes in response to bacterial cell growth (Escherichia coli) in comparison to a commercial bulk optode-based sensing film. We further demonstrated that the oxygen nanosensors could be distributed within a growing culture of E. coli and used to record oxygen levels over time and in different locations within a static culture, opening the possibility of spatiotemporal monitoring in complex biological systems.

A Nanorobotics-Based Approach of Breast Cancer in the Nanotechnology Era

We are living in an era of advanced nanoscience and nanotechnology. Numerous nanomaterials, culminating in nanorobots, have demonstrated ingenious applications in biomedicine, including breast cancer (BC) nano-theranostics. To solve the complicated problem of BC heterogeneity, non-targeted drug distribution, invasive diagnostics or surgery, resistance to classic onco-therapies and real-time monitoring of tumors, nanorobots are designed to perform multiple tasks at a small scale, even at the organelles or molecular level. Over the last few years, most nanorobots have been bioengineered as biomimetic and biocompatible nano(bio)structures, resembling different organisms and cells, such as urchin, spider, octopus, fish, spermatozoon, flagellar bacterium or helicoidal cyanobacterium. In this review, readers will be able to deepen their knowledge of the structure, behavior and role of several types of nanorobots, among other nanomaterials, in BC theranostics. We summarized here the characteristics of many functionalized nanodevices designed to counteract the main neoplastic hallmark features of BC, from sustaining proliferation and evading anti-growth signaling and resisting programmed cell death to inducing angiogenesis, activating invasion and metastasis, preventing genomic instability, avoiding immune destruction and deregulating autophagy. Most of these nanorobots function as targeted and self-propelled smart nano-carriers or nano-drug delivery systems (nano-DDSs), enhancing the efficiency and safety of chemo-, radio- or photodynamic therapy, or the current imagistic techniques used in BC diagnosis. Most of these nanorobots have been tested in vitro, using various BC cell lines, as well as in vivo, mainly based on mice models. We are still waiting for nanorobots that are low-cost, as well as for a wider transition of these favorable effects from laboratory to clinical practice.

The use of microphysiological systems to model metastatic cancer

Cancer is one of the leading causes of death in the 21st century, with metastasis of cancer attributing to 90% of cancer-related deaths. Therefore, to improve patient outcomes there is a need for better preclinical models to increase the success of translating oncological therapies into the clinic. Current traditional staticin vitromodels lack a perfusable network which is critical to overcome the diffusional mass transfer limit to provide a mechanism for the exchange of essential nutrients and waste removal, and increase their physiological relevance. Furthermore, these models typically lack cellular heterogeneity and key components of the immune system and tumour microenvironment. This review explores rapidly developing strategies utilising perfusable microphysiological systems (MPS) for investigating cancer cell metastasis. In this review we initially outline the mechanisms of cancer metastasis, highlighting key steps and identifying the current gaps in our understanding of the metastatic cascade, exploring MPS focused on investigating the individual steps of the metastatic cascade before detailing the latest MPS which can investigate multiple components of the cascade. This review then focuses on the factors which can affect the performance of an MPS designed for cancer applications with a final discussion summarising the challenges and future directions for the use of MPS for cancer models.

Unlocking the Potential of Stem Cell Microenvironments In Vitro

The field of regenerative medicine has recently witnessed groundbreaking advancements that hold immense promise for treating a wide range of diseases and injuries. At the forefront of this revolutionary progress are stem cells. Stem cells typically reside in specialized environments in vivo, known as microenvironments or niches, which play critical roles in regulating stem cell behavior and determining their fate. Therefore, understanding the complex microenvironments that surround stem cells is crucial for advancing treatment options in regenerative medicine and tissue engineering applications. Several research articles have made significant contributions to this field by exploring the interactions between stem cells and their surrounding niches, investigating the influence of biomechanical and biochemical cues, and developing innovative strategies for tissue regeneration. This review highlights the key findings and contributions of these studies, shedding light on the diverse applications that may arise from the understanding of stem cell microenvironments, thus harnessing the power of these microenvironments to transform the landscape of medicine and offer new avenues for regenerative therapies.

Impacts of priming on distinct immunosuppressive mechanisms of mesenchymal stromal cells under translationally relevant conditions

BACKGROUND

The multimodal properties of mesenchymal stromal cells (MSCs), particularly their ability to modulate immune responses is of high interest in translational research. Pro-inflammatory, hypoxic, and 3D culture priming are promising and often used strategies to improve the immunosuppressive potency of MSCs, but the underlying mechanisms are not well understood. Therefore, the aims of this study were (i) to compare the effects of pro-inflammatory, hypoxic, and 3D culture priming on the in vitro immunosuppressive potential of MSCs, (ii) to assess if immunosuppressive priming effects are temporally preserved under standard and translationally relevant culture conditions, and (iii) to investigate if the three priming strategies engage the same immunosuppressive mechanisms.

METHODS

Functional in vitro T cell suppressive potency measurements were conducted to assess the impact of pro-inflammatory, hypoxic, and 3D culture priming on the immunosuppressive potential of human bone marrow-derived MSCs. Primed MSCs were either cultured under standard cell culture conditions or translationally relevant culture conditions, and their transcriptomic adaptations were monitored over time. Next-generation sequencing was performed to assess if different priming strategies activate distinct immunosuppressive mechanisms.

RESULTS

(i) Pro-inflammatory, hypoxic, and 3D culture priming induced profound transcriptomic changes in MSCs resulting in a significantly enhanced T cell suppressive potential of pro-inflammatory and 3D culture primed MSCs. (ii) Priming effects rapidly faded under standard cell culture conditions but were partially preserved under translationally relevant conditions. Interestingly, continuous 3D culture priming of MSCs maintained the immunosuppressive potency of MSCs. (iii) Next-generation sequencing revealed that priming strategy-specific differentially expressed genes are involved in the T cell suppressive capacity of MSCs, indicating that different priming strategies engage distinct immunosuppressive mechanisms.

CONCLUSION

Priming can be a useful approach to improve the immunosuppressive potency of MSCs. However, future studies involving primed MSCs should carefully consider the significant impact of translationally relevant conditions on the preservation of priming effects. Continuous 3D culture could act as a functionalized formulation, supporting the administration of MSC spheroids for a sustainably improved immunosuppressive potency.

Regulation Mechanisms and Maintenance Strategies of Stemness in Mesenchymal Stem Cells

Stemness pertains to the intrinsic ability of mesenchymal stem cells (MSCs) to undergo self-renewal and differentiate into multiple lineages, while simultaneously impeding their differentiation and preserving crucial differentiating genes in a state of quiescence and equilibrium. Owing to their favorable attributes, including uncomplicated isolation protocols, ethical compliance, and ease of procurement, MSCs have become a focal point of inquiry in the domains of regenerative medicine and tissue engineering. As age increases or ex vivo cultivation is prolonged, the functionality of MSCs decreases and their stemness gradually diminishes, thereby limiting their potential therapeutic applications. Despite the existence of several uncertainties surrounding the comprehension of MSC stemness, considerable advancements have been achieved in the clarification of the potential mechanisms that lead to stemness loss, as well as the associated strategies for stemness maintenance. This comprehensive review provides a systematic overview of the factors influencing the preservation of MSC stemness, the molecular mechanisms governing it, the strategies for its maintenance, and the therapeutic potential associated with stemness. Finally, we underscore the obstacles and prospective avenues in present investigations, providing innovative perspectives and opportunities for the preservation and therapeutic utilization of MSC stemness.

Fumarate respiration of Fasciola flukes as a potential drug target

Fascioliasis is a neglected tropical zoonotic disease caused by liver flukes belonging to the genus Fasciola. The emergence of resistance to triclabendazole, the only World Health Organization-recommended drug for this disease, highlights the need for the development of new drugs. Helminths possess an anaerobic mitochondrial respiratory chain (fumarate respiration) which is considered a potential drug target. This study aimed to evaluate the occurrence of fumarate respiration in Fasciola flukes. We analyzed the properties of the respiratory chain of Fasciola flukes in both adults and newly excysted juveniles (NEJs). Fasciola flukes travel and mature through the stomach, bowel, and abdominal cavity to the liver, where oxygen levels gradually decline. High fumarate reductase activity was observed in the mitochondrial fraction of adult Fasciola flukes. Furthermore, rhodoquinone-10 (RQ10 Em'= -63 mV), a low-potential electron mediator used in fumarate respiration was found to be predominant in adults. In contrast, the activity of oxygen respiration was low in adults. Rotenone, atpenin A5, and ascochlorin, typical inhibitors of mitochondrial enzymes in complexes I, II, and III, respectively, inhibit the activity of each enzyme in the adult mitochondrial fraction. These inhibitors were then used for in vitro viability tests of NEJs. Under aerobic conditions, NEJs were killed by rotenone or ascochlorin, which inhibit aerobic respiration (complex I-III), whereas atpenin A5, which inhibits complex II involved in fumarate respiration, did not affect NEJs. Moreover, ubiquinone-10 (UQ10 Em'= +110 mV), which is used in oxidative respiration, was detected in NEJs, in addition to RQ10. In contrast, under anaerobic conditions, rotenone and atpenin A5, which inhibit fumarate respiration (complex I-II), were crucial for NEJs. These findings demonstrate that NEJs have active hybrid respiration, in which they can properly use both oxygen and fumarate respiration, depending on oxygen availability. Thus, fumarate respiration is a promising drug target for Fasciola flukes, because it plays an essential role in both adults and NEJs.

Harnessing the Stem Cell Niche in Regenerative Medicine: Innovative Avenue to Combat Neurodegenerative Diseases

Regenerative medicine harnesses the body's innate capacity for self-repair to restore malfunctioning tissues and organs. Stem cell therapies represent a key regenerative strategy, but to effectively harness their potential necessitates a nuanced understanding of the stem cell niche. This specialized microenvironment regulates critical stem cell behaviors including quiescence, activation, differentiation, and homing. Emerging research reveals that dysfunction within endogenous neural stem cell niches contributes to neurodegenerative pathologies and impedes regeneration. Strategies such as modifying signaling pathways, or epigenetic interventions to restore niche homeostasis and signaling, hold promise for revitalizing neurogenesis and neural repair in diseases like Alzheimer's and Parkinson's. Comparative studies of highly regenerative species provide evolutionary clues into niche-mediated renewal mechanisms. Leveraging endogenous bioelectric cues and crosstalk between gut, brain, and vascular niches further illuminates promising therapeutic opportunities. Emerging techniques like single-cell transcriptomics, organoids, microfluidics, artificial intelligence, in silico modeling, and transdifferentiation will continue to unravel niche complexity. By providing a comprehensive synthesis integrating diverse views on niche components, developmental transitions, and dynamics, this review unveils new layers of complexity integral to niche behavior and function, which unveil novel prospects to modulate niche function and provide revolutionary treatments for neurodegenerative diseases.

Hypoxia-Inducible Factor and Oxidative Stress in Tendon Degeneration: A Molecular Perspective

Tendinopathy is a debilitating condition marked by degenerative changes in the tendons. Its complex pathophysiology involves intrinsic, extrinsic, and physiological factors. While its intrinsic and extrinsic factors have been extensively studied, the role of physiological factors, such as hypoxia and oxidative stress, remains largely unexplored. This review article delves into the contribution of hypoxia-associated genes and oxidative-stress-related factors to tendon degeneration, offering insights into potential therapeutic strategies. The unique aspect of this study lies in its pathway-based evidence, which sheds light on how these factors can be targeted to enhance overall tendon health.

PODO/TERT256 - A promising human immortalized podocyte cell line and its potential use for in vitro research at different oxygen levels

Podocytes are of key interest for the prediction of nephrotoxicity as they are especially sensitive to toxic insults due to their central role in the glomerular filtration apparatus. However, currently, prediction of nephrotoxicity in humans remains insufficiently reliable, thus highlighting the need for advanced in vitro model systems using human cells with improved prediction capacity. Recent approaches for refining in vitro model systems focus on closely replicating physiological conditions as observed under the in vivo situation typical of the respective nephron section of interest. PODO/TERT256, a human immortalized podocyte cell line, were employed in a semi-static transwell system to evaluate its potential use as a human podocyte in vitro system for modelling potential human glomerular toxicity. Furthermore, the impact of routinely employed excessive oxygen tension (21 % - AtmOx), when compared to the physiological oxygen tensions (10 % - PhysOx) observed in vivo, was analyzed. Generally, cultured PODO/TERT256 formed a stable, contact-inhibited monolayer with typical podocyte morphology (large cell body, apical microvilli, finger-like cytoplasmic projections (reminiscent of foot processes), and interdigitating cell-cell junctions) and developed a size-selective filtration barrier. PhysOx, however, induced a more pronounced in vivo like phenotype, comprised of significantly larger cell bodies, significantly enhanced filtration barrier size-selectivity, and a remarkable re-localization of nephrin to the cell membrane, thus suggesting an improved in vitro replication of in vivo characteristics. Preliminary toxicity characterization with the known glomerulotoxin doxorubicin (DOX) suggested an increasing change in filtration permeability, already at the lowest DOX concentrations tested (0.01 μM) under PhysOx, whereas obvious changes under AtmOx were observed as of 0.16 μM and higher with a near all or nothing effect. The latter findings suggested that PODO/TERT256 could serve as an in vitro human podocyte model for studying glomerulotoxicity, whereby culturing at PhyOx tension appeared critical for an improved in vivo-like phenotype and functionality. Moreover, PODO/TERT256 could be incorporated into advanced human glomerulus systems in vitro, recapitulating microfluidic conditions and multiple cell types (endothelial and mesenchymal cells) that can even better predict human glomerular toxicity.

The effects of propolis-loaded chitosan nanoparticles and menstrual blood stem cells on LPS-induced ovarian inflammation in the murine ovary in vivo: An in vitro and in vivo study

Mammary glands infection via Gram-negative bacteria may cause infertility or reduced ovarian function. In the current study, a potential treatment for LPS-induced ovarian inflammation was developed. Propolis was loaded into chitosan nanoparticles and co-administered with menstrual blood stem cells (MenSCs) in mice infused with LPS. Various properties of propolis-loaded chitosan nanoparticles were evaluated using scanning electron microscopy, drug release assay, antibacterial assay, and radical scavenging assay. In vitro studies showed biocompatibility, anti-oxidative, and antibacterial properties of the developed propolis nanoformulation. In vivo study showed that mice treated with co-administration of propolis-loaded chitosan nanoparticles and MenSCs significantly increased the total ovarian follicle reserve in mice infused with LPS. Percentage of mature follicles in co-administration method was around 13.89 ± 1.72 %. Gene expression studies showed that the expression levels of inflammation related cytokines including IL6, IL8, IL-1β, and TNF-α were downregulated in this group compared with other groups. However, the expression levels of PTEN, AKT, FOXO3 did not show a significant difference between groups. The developed treatment may potentially considered as an approach for treating ovarian infection with gram-negative bacteria.

Strategies to improve the therapeutic efficacy of mesenchymal stem cell-derived extracellular vesicle (MSC-EV): a promising cell-free therapy for liver disease

Liver disease has emerged as a significant worldwide health challenge due to its diverse causative factors and therapeutic complexities. The majority of liver diseases ultimately progress to end-stage liver disease and liver transplantation remains the only effective therapy with the limitations of donor organ shortage, lifelong immunosuppressants and expensive treatment costs. Numerous pre-clinical studies have revealed that extracellular vesicles released by mesenchymal stem cells (MSC-EV) exhibited considerable potential in treating liver diseases. Although natural MSC-EV has many potential advantages, some characteristics of MSC-EV, such as heterogeneity, uneven therapeutic effect, and rapid clearance in vivo constrain its clinical translation. In recent years, researchers have explored plenty of ways to improve the therapeutic efficacy and rotation rate of MSC-EV in the treatment of liver disease. In this review, we summarized current strategies to enhance the therapeutic potency of MSC-EV, mainly including optimization culture conditions in MSC or modifications of MSC-EV, aiming to facilitate the development and clinical application of MSC-EV in treating liver disease.

Influence of standard culture conditions and effect of oleoresin from the microalga Haematococcus pluvialis on splenic cells from healthy Balb/c mice - a pilot study

In this work, we used splenocytes from healthy mice to study the effects of the two most commonly used cell culture media (A, B) with different compositions of redox reagents. The incubation of cells for 24 h resulted in a significant decrease in viability and metabolic activity of splenocytes, and the negative effects of incubation in medium B were more pronounced. In standard conditions, oxidative stress in cells was manifested by reduced mitochondrial potential, and this effect correlated with the transition of 58.3% of cells to the early stage of apoptosis under reducing conditions of medium A and up to 66.1% of cells under super-reducing conditions in medium B, suggesting altered cell physiology. High levels of ROS/RNS activated transcription factor Nrf2, superoxide dismutase 1, and catalase. The higher mRNA levels of these genes were under the conditions of medium B, whose super-reducing environment in combination with the environment of conventional incubators proved to be less suitable for the cells compared to medium A. Treatment of the cells with a lower concentration (10 µg/ml) of oleoresin obtained from the microalga H. pluvialis partially eliminated the negative effects of cultivation. Higher concentration of oleoresin (40 µg/ml) was slightly cytotoxic, due to the significant antioxidant effect of astaxanthin, the main bioactive component of the extract, which eliminated most of the ROS/RNS acting as signalling molecules. This study shows that the standard culture conditions do not reflect the physiological in vivo cell conditions; therefore, they are not generally suitable for incubation of all cell types.

Effect of umbilical cord mesenchymal stem cells on hypoxia-inducible factor-1 alpha (HIF-1α) production in arteriovenous fistula (AVF) animal model: A preliminary study

Hypoxia-inducible factor-1 alpha (HIF-1α) is a transcription factor that plays a crucial role in cellular responses to hypoxia, such as in the development of intimal hyperplasia, a common complication in arteriovenous fistula (AVF) creation. While the application of umbilical cord mesenchymal stem cells (UC-MSCs) has shown promise in various regenerative medicine applications, including tissue repair and angiogenesis, the effect of UC-MSCs on HIF-1α level in the AVF has not been tested. Therefore, the aim of this study was to evaluate the effect of UC-MSCs administration on HIF-1α levels in the AVF animal model. An experimental study was conducted on 28 local male rabbits (Lepus domestica) using a post-test-only design. The rabbits were divided randomly into four groups: normal rabbit group (negative control), placebo-treated AVF rabbit group (positive control), AVF rabbits treated with in-situ UC-MSCs injection (one dose, 106 UC-MSCs/kg body weight), and AVF rabbits treated with intravenous UC-MSCs (one dose, 106 UC-MSCs/kg body weight (BW). HIF-1α level was measured using ELISA method after 28 days post-treatment. All data were analyzed using the one-way analysis of variance (ANOVA) and continued with the Duncan's post-hoc test. The data indicated that the levels of HIF-1α were different among all four groups (p<0.001). The post-hoc analysis revealed that the HIF-1α levels in both UC-MSC treated groups were significantly lower compared to untreated AVF rabbits (p<0.05). This study suggests that UC-MSCs could be a promising therapy to prevent and reduce intimal hyperplasia in AVF.

Mitochondria pleiotropism in stem cell senescence: Mechanisms and therapeutic approaches

Aging is a complex biological process characterized by a progressive decline in cellular and tissue function, ultimately leading to organismal aging. Stem cells, with their regenerative potential, play a crucial role in maintaining tissue homeostasis and repair throughout an organism's lifespan. Mitochondria, the powerhouses of the cell, have emerged as key players in the aging process, impacting stem cell function and contributing to age-related tissue dysfunction. Here are discuss the mechanisms through which mitochondria influence stem cell fate decisions, including energy production, metabolic regulation, ROS signalling, and epigenetic modifications. Therefore, this review highlights the role of mitochondria in driving stem cell senescence and the subsequent impact on tissue function, leading to overall organismal aging and age-related diseases. Finally, we explore potential anti-aging therapies targeting mitochondrial health and discuss their implications for promoting healthy aging. This comprehensive review sheds light on the critical interplay between mitochondrial function, stem cell senescence, and organismal aging, offering insights into potential strategies for attenuating age-related decline and promoting healthy longevity.

Mitochondrial complex I ROS production and redox signaling in hypoxia

Mitochondria are a main source of cellular energy. Oxidative phosphorylation (OXPHOS) is the major process of aerobic respiration. Enzyme complexes of the electron transport chain (ETC) pump protons to generate a protonmotive force (Δp) that drives OXPHOS. Complex I is an electron entry point into the ETC. Complex I oxidizes nicotinamide adenine dinucleotide (NADH) and transfers electrons to ubiquinone in a reaction coupled with proton pumping. Complex I also produces reactive oxygen species (ROS) under various conditions. The enzymatic activities of complex I can be regulated by metabolic conditions and serves as a regulatory node of the ETC. Complex I ROS plays diverse roles in cell metabolism ranging from physiologic to pathologic conditions. Progress in our understanding indicates that ROS release from complex I serves important signaling functions. Increasing evidence suggests that complex I ROS is important in signaling a mismatch in energy production and demand. In this article, we review the role of ROS from complex I in sensing acute hypoxia.

Hypoxia enhances anti-fibrotic properties of extracellular vesicles derived from hiPSCs via the miR302b-3p/TGFβ/SMAD2 axis

BACKGROUND

Cardiac fibrosis is one of the top killers among fibrotic diseases and continues to be a global unaddressed health problem. The lack of effective treatment combined with the considerable socioeconomic burden highlights the urgent need for innovative therapeutic options. Here, we evaluated the anti-fibrotic properties of extracellular vesicles (EVs) derived from human induced pluripotent stem cells (hiPSCs) that were cultured under various oxygen concentrations.

METHODS

EVs were isolated from three hiPSC lines cultured under normoxia (21% O2; EV-N) or reduced oxygen concentration (hypoxia): 3% O2 (EV-H3) or 5% O2 (EV-H5). The anti-fibrotic activity of EVs was tested in an in vitro model of cardiac fibrosis, followed by a detailed investigation of the underlying molecular mechanisms. Sequencing of EV miRNAs combined with bioinformatics analysis was conducted and a selected miRNA was validated using a miRNA mimic and inhibitor. Finally, EVs were tested in a mouse model of angiotensin II-induced cardiac fibrosis.

RESULTS

We provide evidence that an oxygen concentration of 5% enhances the anti-fibrotic effects of hiPS-EVs. These EVs were more effective in reducing pro-fibrotic markers in activated human cardiac fibroblasts, when compared to EV-N or EV-H3. We show that EV-H5 act through the canonical TGFβ/SMAD pathway, primarily via miR-302b-3p, which is the most abundant miRNA in EV-H5. Our results show that EV-H5 not only target transcripts of several profibrotic genes, including SMAD2 and TGFBR2, but also reduce the stiffness of activated fibroblasts. In a mouse model of heart fibrosis, EV-H5 outperformed EV-N in suppressing the inflammatory response in the host and by attenuating collagen deposition and reducing pro-fibrotic markers in cardiac tissue.

CONCLUSIONS

In this work, we provide evidence of superior anti-fibrotic properties of EV-H5 over EV-N or EV-H3. Our study uncovers that fine regulation of oxygen concentration in the cellular environment may enhance the anti-fibrotic effects of hiPS-EVs, which has great potential to be applied for heart regeneration.

The Dual Luminescence Lifetime pH/Oxygen Sensor: Evaluation of Applicability for Intravital Analysis of 2D- and 3D-Cultivated Human Endometrial Mesenchymal Stromal Cells

The oxygenation of cells and tissues and acidification of the cellular endolysosomal system are among the major factors that ensure normal functioning of an organism and are violated in various pathologies. Recording of these parameters and their changes under various conditions is an important task for both basic research and clinical applications. In the present work, we utilized internalizable dual pH/O2 lifetime sensor (Ir-HSA-FITC) based on the covalent conjugation of human serum albumin (HSA) with fluorescein isothiocyanate (FITC) as pH sensor and an orthometalated iridium complex as O2 sensor. The probe was tested for simultaneous detection of acidification level and oxygen concentration in endolysosomes of endometrial mesenchymal stem/stromal cells (enMSCs) cultivated as 2D monolayers and 3D spheroids. Using a combined FLIM/PLIM approach, we found that due to high autofluorescence of enMSCs FITC lifetime signal in control cells was insufficient to estimate pH changes. However, using flow cytometry and confocal microscopy, we managed to detect the FITC signal response to inhibition of endolysosomal acidification by Bafilomycin A1. The iridium chromophore phosphorescence was detected reliably by all methods used. It was demonstrated that the sensor, accumulated in endolysosomes for 24 h, disappeared from proliferating 2D enMSCs by 72 h, but can still be recorded in non-proliferating spheroids. PLIM showed high sensitivity and responsiveness of iridium chromophore phosphorescence to experimental hypoxia both in 2D and 3D cultures. In spheroids, the phosphorescence signal was detected at a depth of up to 60 μm using PLIM and showed a gradient in the intracellular O2 level towards their center.

Searching for molecular hypoxia sensors among oxygen-dependent enzymes

The ability to sense and respond to changes in cellular oxygen levels is critical for aerobic organisms and requires a molecular oxygen sensor. The prototypical sensor is the oxygen-dependent enzyme PHD: hypoxia inhibits its ability to hydroxylate the transcription factor HIF, causing HIF to accumulate and trigger the classic HIF-dependent hypoxia response. A small handful of other oxygen sensors are known, all of which are oxygen-dependent enzymes. However, hundreds of oxygen-dependent enzymes exist among aerobic organisms, raising the possibility that additional sensors remain to be discovered. This review summarizes known and potential hypoxia sensors among human O2-dependent enzymes and highlights their possible roles in hypoxia-related adaptation and diseases.

Oxygen Level Modifies the Expression of Genes Involved in the Epigenetic Regulation of Multipotent Stromal Cells In Vitro

Changes in the transcriptional activity of genes involved in the epigenetic regulation of adipose tissue multipotent mesenchymal stromal cells were analyzed in vitro at different O2 levels. DNA microarray study showed that the most pronounced changes in gene expression, including genes responsible for the epigenetic regulation of mesenchymal stromal cells, occurred at 3% O2. A lower number of genes changed the expression at 1% O2, and a minimum response was observed at 5% O2 in comparison with standard culturing conditions (20% O2). The greatest number of differentially expressed genes were genes responsible for the regulation of histones; the genes encoding products that regulate chromatin, DNA, and RNA constituted a lower part. Thus, the degree of hypoxia can modify the response of multipotent mesenchymal stromal cells at the level of epigenetic regulators.

Understanding human aging and the fundamental cell signaling link in age-related diseases: the middle-aging hypovascularity hypoxia hypothesis

Aging-related hypoxia, oxidative stress, and inflammation pathophysiology are closely associated with human age-related carcinogenesis and chronic diseases. However, the connection between hypoxia and hormonal cell signaling pathways is unclear, but such human age-related comorbid diseases do coincide with the middle-aging period of declining sex hormonal signaling. This scoping review evaluates the relevant interdisciplinary evidence to assess the systems biology of function, regulation, and homeostasis in order to discern and decipher the etiology of the connection between hypoxia and hormonal signaling in human age-related comorbid diseases. The hypothesis charts the accumulating evidence to support the development of a hypoxic milieu and oxidative stress-inflammation pathophysiology in middle-aged individuals, as well as the induction of amyloidosis, autophagy, and epithelial-to-mesenchymal transition in aging-related degeneration. Taken together, this new approach and strategy can provide the clarity of concepts and patterns to determine the causes of declining vascularity hemodynamics (blood flow) and physiological oxygenation perfusion (oxygen bioavailability) in relation to oxygen homeostasis and vascularity that cause hypoxia (hypovascularity hypoxia). The middle-aging hypovascularity hypoxia hypothesis could provide the mechanistic interface connecting the endocrine, nitric oxide, and oxygen homeostasis signaling that is closely linked to the progressive conditions of degenerative hypertrophy, atrophy, fibrosis, and neoplasm. An in-depth understanding of these intrinsic biological processes of the developing middle-aged hypoxia could provide potential new strategies for time-dependent therapies in maintaining healthspan for healthy lifestyle aging, medical cost savings, and health system sustainability.

The potential mechanism of hypoxia-induced tenogenic differentiation of mesenchymal stem cell for tendon regeneration

Tendon injuries account up to 50% of all musculoskeletal problems and remains a challenge to treat owing to the poor intrinsic reparative ability of tendon tissues. The natural course of tendon healing is very slow and often leads to fibrosis and disorganized tissues with inferior biomechanical properties. Mesenchymal stem cells (MSC) therapy is a promising alternative strategy to augment tendon repair due to its proliferative and multilineage differentiation potential. Hypoxic conditioning of MSC have been shown to enhance their tenogenic differentiation capacity. However, the mechanistic pathway by which this is achieved is yet to be fully defined. A key factor involved in this pathway is hypoxia-inducible factor-1-alpha (HIF-1α). This review aims to discuss the principal mechanism underlying the enhancement of MSC tenogenic differentiation by hypoxic conditioning, particularly the central role of HIF-1α in mediating activation of tenogenic pathways in the MSC. We focus on the interaction between HIF-1α with fibroblast growth factor-2 (FGF-2) and transforming growth factor-beta 1 (TGF-β1) in regulating MSC tenogenic differentiation pathways in hypoxic conditions. Strategies to promote stabilization of HIF-1α either through direct manipulation of oxygen tension or the use of hypoxia mimicking agents are therefore beneficial in increasing the efficacy of MSC therapy for tendon repair.

Oxygen availability influences the incidence of testicular teratoma in Dnd1Ter/+ mice

Testicular teratomas and teratocarcinomas are the most common testicular germ cell tumors in early childhood and young men, and they are frequently found unilaterally in the left testis. In 129/SvJ mice carrying a heterozygous copy of the potent modifier of tumor incidence Ter, a point mutation in the dead-end homolog one gene (Dnd1 Ter/+), ∼70% of the unilateral teratomas arise in the left testis. We previously showed that in mice, left/right differences in vascular architecture are associated with reduced hemoglobin saturation and increased levels of the hypoxia inducible factor-1 alpha (HIF-1α) in the left compared to the right testis. To test the hypothesis that systemic reduction of oxygen availability in Dnd1 Ter/+ mice would lead to an increased incidence of bilateral tumors, we placed pregnant females from 129/SvJ Dnd1 Ter/+ intercross matings in a hypobaric chamber for 12-h intervals. Our results show that in 129/SvJ Dnd1 Ter/+ male gonads, the incidence of bilateral teratoma increased from 3.3% to 64% when fetuses were exposed to acute low oxygen conditions for 12-h between E13.8 and E14.3. The increase in tumor incidence correlated with the maintenance of high expression of pluripotency genes Oct4, Sox2 and Nanog, elevated activity of the Nodal signaling pathway, and suppression of germ cell mitotic arrest. We propose that the combination of heterozygosity for the Ter mutation and hypoxia causes a delay in male germ cell differentiation that promotes teratoma initiation.

The evolutionary cancer genome theory and its reasoning

Oncogenesis and the origin of cancer are still not fully understood despite the efforts of histologists, pathologists, and molecular geneticists to determine how cancer develops. Previous embryogenic and gene- and genome-based hypotheses have attempted to solve this enigma. Each of them has its kernel of truth, but a unifying, universally accepted theory is still missing. Fortunately, a unicellular cell system has been found in amoebozoans, which exhibits all the basic characteristics of the cancer life cycle and demonstrates that cancer is not a biological aberration but a consequence of molecular and cellular evolution. The impressive systemic similarities between the life cycle of Entamoeba and the life cycle of cancer demonstrate the deep homology of cancer to the amoebozoans, metazoans, and fungi ancestor that branched into the clades of Amoebozoa, Metazoa, and Fungi (AMF) and shows that the roots of oncogenesis and tumorigenesis lie in an ancient gene network, which is conserved in the genome of all metazoans and humans. This evolutionary gene network theory of cancer (evolutionary cancer genome theory) integrates previous findings and hypotheses and is one step further along the road to a universal cancer cell theory. It supports genetic cancer medicine and recommends soma-to-germ transitions-referred to as epithelial-to-mesenchymal transition in cancer-and cancer germline as potential targets. According to the evolutionary cancer genome theory, cancer exploits an ancient gene network module of premetazoan origin.

Pulse Oximetry Imaging System Using Spatially Uniform Dual Wavelength Illumination

Pulse oximetry is a non-invasive method for measuring blood oxygen saturation. However, its detection scheme heavily relies on single-point measurements. If the oxygen saturation is measured at a single location, the measurements are influenced by the profile of illumination, spatial variations in blood flow, and skin pigment. To overcome these issues, imaging systems that measure the distribution of oxygen saturation have been demonstrated. However, previous imaging systems have relied on red and near-infrared illuminations with different profiles, resulting in inconsistent ratios between transmitted red and near-infrared light over space. Such inconsistent ratios can introduce fundamental errors when calculating the spatial distribution of oxygen saturation. In this study, we developed a novel illumination system specifically designed for a pulse oximetry imaging system. For the illumination system, we customized the integrating sphere by coating a mixture of barium sulfate and white paint inside it and by coupling eight red and eight near-infrared LEDs. The illumination system created identical patterns of red and near-infrared illuminations that were spatially uniform. This allowed the ratio between transmitted red and near-infrared light to be consistent over space, enabling the calculation of the spatial distribution of oxygen saturation. We believe our developed pulse oximetry imaging system can be used to obtain spatial information on blood oxygen saturation that provides insight into the oxygenation of the blood contained within the peripheral region of the tissue.

Versatility of mesenchymal stem cell-derived extracellular vesicles in tissue repair and regenerative applications

Mesenchymal stem/stromal cells (MSCs) are multipotent somatic cells that have been widely explored in the field of regenerative medicine. MSCs possess the ability to secrete soluble factors as well as lipid bound extracellular vesicles (EVs). MSCs have gained increased interest and attention as a result of their therapeutic properties, which are thought to be attributed to their secretome. However, while the use of MSCs as whole cells pose heterogeneity concerns and survival issues post-transplantation, such limitations are absent in cell-free EV-based treatments. EVs derived from MSCs are promising therapeutic agents for a range of clinical conditions and disorders owing to their immunomodulatory, pro-regenerative, anti-inflammatory, and antifibrotic activity. Recent successes with preclinical studies using EVs for repair and regeneration of damaged tissues such as cardiac tissue, lung, liver, pancreas, bone, skin, cornea, and blood diseases are discussed in this review. We also discuss delivery strategies of EVs using biomaterials as delivery vehicles through systemic or local administration. Despite its effectiveness in preclinical investigations, the application of MSC-EV in clinical settings will necessitate careful consideration surrounding issues such as: i) scalability and isolation, ii) biodistribution, iii) targeting specific tissues, iv) quantification and characterization, and v) safety and efficacy of dosage. The future of EVs in regenerative medicine is promising yet still needs further investigation on enhancing the efficacy, scalability, and potency for clinical applications.

Oxygen-Generating Biomaterials for Translational Bone Regenerative Engineering

Successful regeneration of critical-size defects remains one of the significant challenges in regenerative engineering. These large-scale bone defects are difficult to regenerate and are often reconstructed with matrices that do not provide adequate oxygen levels to stem cells involved in the regeneration process. Hypoxia-induced necrosis predominantly occurs in the center of large matrices since the host tissue's local vasculature fails to provide sufficient nutrients and oxygen. Indeed, utilizing oxygen-generating materials can overcome the central hypoxic region, induce tissue in-growth, and increase the quality of life for patients with extensive tissue damage. This article reviews recent advances in oxygen-generating biomaterials for translational bone regenerative engineering. We discussed different oxygen-releasing and delivery methods, fabrication methods for oxygen-releasing matrices, biology, oxygen's role in bone regeneration, and emerging new oxygen delivery methods that could potentially be used for bone regenerative engineering.

O2 variant chip to simulate site-specific skeletogenesis from hypoxic bone marrow

The stemness of bone marrow mesenchymal stem cells (BMSCs) is maintained by hypoxia. The oxygen level increases from vessel-free cartilage to hypoxic bone marrow and, furthermore, to vascularized bone, which might direct the chondrogenesis to osteogenesis and regenerate the skeletal system. Hence, oxygen was diffused from relatively low to high levels throughout a three-dimensional chip. When we cultured BMSCs in the chip and implanted them into the rabbit defect models of low-oxygen cartilage and high-oxygen calvaria bone, (i) the low oxygen level (base) promoted stemness and chondrogenesis of BMSCs with robust antioxidative potential; (ii) the middle level (two times ≥ low) pushed BMSCs to quiescence; and (iii) the high level (four times ≥ low) promoted osteogenesis by disturbing the redox balance and stemness. Last, endochondral or intramembranous osteogenesis upon transition from low to high oxygen in vivo suggests a developmental mechanism-driven solution to promote chondrogenesis to osteogenesis in the skeletal system by regulating the oxygen environment.

Small extracellular vesicles from senescent stem cells trigger adaptive mechanisms in young stem cells by increasing antioxidant enzyme expression

Extracellular vesicles' biogenesis, shedding, and uptake are redox-sensitive. Indeed, oxidative stress conditions influence extracellular vesicles' release and content, which can modulate the redox status of the receiving cells. In this study, we aimed to assess the effect of extracellular vesicles from human dental pulp stem cells cultured under 21% O₂ (senescent stem cells) on human dental pulp stem cells cultured under 3% O₂ (young stem cells). Extracellular vesicles were isolated by ultracentrifugation from senescent stem cells and prepared for the treatment of young stem cells at a final concentration of 10 μg/mL. Cells were analyzed for antioxidant gene expression, mitochondrial bioenergetic parameters, ROS production, culture kinetics, and apoptosis. The results show that extracellular vesicles from senescent stem cells induce overexpression of antioxidant genes (MnSOD, CAT, and GPx) in young stem cells, which show an increased non-mitochondrial oxygen consumption, accompanied by reduced maximal respiration and spare respiratory capacity without altering mitochondrial membrane potential. This is accompanied by improved cell proliferation, viability, and migration rates and a reduction of apoptosis. In conclusion, extracellular vesicles from senescent stem cells trigger an adaptive response in young stem cells which improves their antioxidant defenses and their proliferation, migration, and survival rates. This suggests that extracellular vesicles can modulate the cells' microenvironment and the balance between proliferation and senescence.

Functional profiling of the Toxoplasma genome during acute mouse infection

Within a host, pathogens encounter a diverse and changing landscape of cell types, nutrients, and immune responses. Examining host-pathogen interactions in animal models can therefore reveal aspects of infection absent from cell culture. We use CRISPR-based screens to functionally profile the entire genome of the model apicomplexan parasite Toxoplasma gondii during mouse infection. Barcoded gRNAs were used to track mutant parasite lineages, enabling detection of bottlenecks and mapping of population structures. We uncovered over 300 genes that modulate parasite fitness in mice with previously unknown roles in infection. These candidates span multiple axes of host-parasite interaction, including determinants of tropism, host organelle remodeling, and metabolic rewiring. We mechanistically characterized three novel candidates, including GTP cyclohydrolase I, against which a small-molecule inhibitor could be repurposed as an antiparasitic compound. This compound exhibited antiparasitic activity against T. gondii and Plasmodium falciparum, the most lethal agent of malaria. Taken together, we present the first complete survey of an apicomplexan genome during infection of an animal host, and point to novel interfaces of host-parasite interaction that may offer new avenues for treatment.

Randomization to a Liberal Versus Conservative Oxygenation Target: Redox Responses in Critically Ill Children

RATIONALE

Optimal systemic oxygenation targets in pediatric critical illness are unknown. A U-shaped relationship exists between blood oxygen levels and PICU mortality. Redox stress or iatrogenic injury from intensive treatments are potential mechanisms of harm from hyperoxia.

OBJECTIVES

To measure biomarkers of oxidative status in children admitted to PICU and randomized to conservative (oxygen-hemoglobin saturation [Sp o2 ] 88-92%) versus liberal (Sp o2 > 94%) peripheral oxygenation targets.

DESIGN

Mechanistic substudy nested within the Oxygen in PICU (Oxy-PICU) pilot randomized feasibility clinical trial ( ClinicalTrials.gov : NCT03040570).

SETTING

Three U.K. mixed medical and surgical PICUs in university hospitals.

PATIENTS

Seventy-five eligible patients randomized to the Oxy-PICU randomized feasibility clinical trial.

INTERVENTIONS

Randomization to a conservative (Sp o2 88-92%) versus liberal (Sp o2 > 94%) peripheral oxygenation target.

MEASUREMENTS AND MAIN RESULTS

Blood and urine samples were collected at two timepoints: less than 24 hours and up to 72 hours from randomization in trial participants (March 2017 to July 2017). Plasma was analyzed for markers of ischemic/oxidative response, namely thiobarbituric acid-reactive substances (TBARS; lipid peroxidation marker) and ischemia-modified albumin (protein oxidation marker). Total urinary nitrate/nitrite was measured as a marker of reactive oxygen and nitrogen species (RONS). Blood hypoxia-inducible factor (HIF)-1a messenger RNA (mRNA) expression (hypoxia response gene) was measured by reverse transcription- polymerase chain reaction. Total urinary nitrate/nitrite levels were greater in the liberal compared with conservative oxygenation group at 72 hours (median difference 32.6 μmol/mmol of creatinine [95% CI 13.7-93.6]; p < 0.002, Mann-Whitney test). HIF-1a mRNA expression was increased in the conservative group compared with liberal in less than 24-hour samples (6.0-fold [95% CI 1.3-24.0]; p = 0.032). There were no significant differences in TBARS or ischemia-modified albumin.

CONCLUSIONS

On comparing liberal with conservative oxygenation targets, we show, first, significant redox response (increase in urinary markers of RONS), but no changes in markers of lipid or protein oxidation. We also show what appears to be an early hypoxic response (increase in HIF-1a gene expression) in subjects exposed to conservative rather than liberal oxygenation targets.

Harnessing the potential of oxygen-generating materials and their utilization in organ-specific delivery of oxygen

The limited availability of transplantable organs hinders the success of patient treatment through organ transplantation. In addition, there are challenges with immune rejection and the risk of disease transmission when receiving organs from other individuals. Tissue engineering aims to overcome these challenges by generating functional three-dimensional (3D) tissue constructs. When developing tissues or organs of a particular shape, structure, and size as determined by the specific needs of the therapeutic intervention, a tissue specific oxygen supply to all parts of the tissue construct is an utmost requirement. Moreover, the lack of a functional vasculature in engineered tissues decreases cell survival upon implantation in the body. Oxygen-generating materials can alleviate this challenge in engineered tissue constructs by providing oxygen in a sustained and controlled manner. Oxygen-generating materials can be incorporated into 3D scaffolds allowing the cells to receive and utilize oxygen efficiently. In this review, we present an overview of the use of oxygen-generating materials in various tissue engineering applications in an organ specific manner as well as their potential use in the clinic.

Low oxygen tension affects proliferation and senescence of caprine bone marrow mesenchymal stem cells in in vitro culture condition

The culture system of bone marrow mesenchymal stem cells (bmMSCs) in the normoxic environment does not imitate the hypoxic milieu of typical biological conditions, thus hypoxic culture conditions may improve survival, and growth attributes of bmMSCs during in vitro culture. Therefore, the present study was conducted at ICAR-CIRG, Makhdoom during year 2020 with the objective to investigate the changes in biological characteristics of cultured caprine bmMSCs (cbmMSCs) including the cellular senescence, survival, rate of proliferation, immuno-phenotypic characteristics, and gene expression pattern in a normal and hypoxic microenvironment condition. For this, cbmMSCs isolated from bone marrow collected from iliac crest were enriched and grown under either hypoxic (5% O2) or normoxic (20% O2) conditions. Thereafter, the outcome of hypoxic (5% O2) culturing of cbmMSCs on growth characteristics, proliferation, senescence, and expression profile of important stemness-associated (OCT-4) and oxidative stress [glutathione peroxidase (GPx1) and copper-zinc superoxide dismutase (CuZnSOD)] marker genes was evaluated. cbmMSCs cultivated in hypoxic conditions showed higher proliferation and decreased population doubling time and senescence-associated β-GAL expression; however, the immune-phenotypic characteristics of the cells remain unchanged. Furthermore, the culture of cbmMSCs in hypoxia increased the expression of OCT-4, GPx1, and CuZnSOD, compared with the cells grown under normoxia. In conclusion, the culture condition with low O2 level improved the growth characteristics and proliferation of cbmMSCs. These outcomes would provide information to formulate strategies for the collection and efficient in vitro expansion of bmMSCs from goats and other farm animals before their downstream applications.