Oxygen Regulation in Development: Lessons from Embryogenesis towards Tissue Engineering

Oxygen control in bioreactor drives high yield production of functional hiPSC-like hepatocytes for advanced liver disease modelling

Hepatocytes-like cells (HLC) derived from human induced pluripotent stem cells show great promise for cell-based liver therapies and disease modelling. However, their application is currently hindered by the low production yields of existing protocols. We aim to develop a bioprocess able to generate high numbers of HLC. We used stirred-tank bioreactors with a rational control of dissolved oxygen concentration (DO) for the optimization of HLC production as 3D aggregates. We evaluated the impact of controlling DO at physiological levels (4%O2) during hepatic progenitors' stage on cell proliferation and differentiation efficiency. Whole transcriptome analysis and biochemical assays were performed to provide a detailed characterization of HLC quality attributes. When DO was controlled at 4%O2 during the hepatic progenitors' stage, cells presented an upregulation of genes associated with hypoxia-inducible factor pathway and a downregulation of oxidative stress genes. This condition promoted higher HLC production (maximum cell concentration: 2 × 106 cell/mL) and improved differentiation efficiencies (80% Albumin-positive cells) when compared to the bioreactor operated under atmospheric oxygen levels (21%O2, 0.6 × 106 cell/mL, 43% Albumin positive cells). These HLC exhibited functional characteristics of hepatocytes: capacity to metabolize drugs, ability to synthesize hepatic metabolites, and inducible cytochrome P450 activity. Bioprocess robustness was confirmed with HLC derived from different donors, including a primary hyperoxaluria type 1 (PH1) patient. The generated PH1.HLC showed metabolic features of PH1 disease with higher secretion of oxalate compared with HLC generated from healthy individuals. This work reports a reproducible bioprocess, that shows the importance of controlling DO at physiological levels to increase HLC production, and the HLC capability to display PH1 disease features.

Transient Changes in Cerebral Tissue Oxygen, Glucose, and Temperature by Microstrokes: A Computational Study

OBJECTIVE

This study focuses on evaluating the disruptions in key physiological parameters during microstroke events to assess their severity.

METHODS

A mathematical model was developed to simulate the changes in cerebral tissue pO2, glucose concentration, and temperature due to blood flow interruptions. The model considers variations in baseline cerebral blood flow (CBF), capillary density, and blood oxygen/glucose levels, as well as ambient temperature changes.

RESULTS

Simulations indicate that complete blood flow obstruction still allows for limited glucose availability, supporting nonoxidative metabolism and potentially exacerbating lactate buildup and acidosis. Partial obstructions decrease tissue pO2, with minimal impact on glucose level, which can remain almost unchanged or even slightly increase. Reduced CBF, capillary density, or blood oxygen due to aging or disease enhances hypoxia risk at lower obstruction levels, with capillary density having a significant effect on stroke severity by influencing both pO2 and glucose levels. Conditions could lead to co-occurrence of hypoxia/hypoglycemia or hypoxia/hyperglycemia, each worsening outcomes. Temperature effects were minimal in deep brain regions but varied near the skull by 0.2-0.8°C depending on ambient temperature.

CONCLUSIONS

The model provides insights into the conditions driving severe stroke outcomes based on estimated levels of hypoxia, hypoglycemia, hyperglycemia, and temperature changes.

Vhl safeguards thymic epithelial cell identity and thymopoietic capacity by constraining Hif1a activity during development

The thymus is a physiologically hypoxic organ and fulfills its role of generating T cells under low-oxygen conditions. We have therefore investigated how thymic epithelial cells (TECs) cope with physiological hypoxia by focusing on the role of the Hif1a-Vhl axis. In most cell types, the oxygen-labile transcriptional regulator Hif1a is a central player in co-ordinating responses to low oxygen: under normoxic conditions Hif1a is rapidly degraded in a Vhl-guided manner; however, under hypoxic conditions Hif1a is stabilized and can execute its transcriptional functions. Unexpectedly, we find that, although TECs reside in a hypoxic microenvironment, they express little Hif1a protein and do not require Hif1a for their development or function. Instead, we find that Vhl function in TECs is vital to constrain Hif1a activity, as loss of Vhl results in dramatic defects in TEC differentiation and thymopoiesis, which can be rescued by Hif1a co-depletion.

Chitosan-based multifunctional oxygenating antibiotic hydrogel dressings for managing chronic infection in diabetic wounds

Current treatment strategies for infection of chronic wounds often result in compromised healing and necrosis due to antibiotic toxicity, and underlying biomarkers affected by treatments are not fully known. Here, a multifunctional dressing was developed leveraging the unique wound-healing properties of chitosan, a natural polysaccharide known for its numerous benefits in wound care. The dressing consists of an oxygenating perfluorocarbon functionalized methacrylic chitosan (MACF) hydrogel incorporated with antibacterial polyhexamethylene biguanide (PHMB). A non-healing diabetic infected wound model with emerging metabolomics tools was used to explore the anti-infective and wound healing properties of the resultant multifunctional dressing. Direct bacterial bioburden assessment demonstrated superior antibacterial properties of hydrogels over a commercial dressing. However, wound tissue quality analyses confirmed that sustained PHMB for 21 days resulted in tissue necrosis and disturbed healing. Therefore, a follow-up comparative study investigated the best treatment course for antiseptic application ranging from 7 to 21 days, followed by the oxygenating chitosan-based MACF treatment for the remainder of the 21 days. Bacterial counts, tissue assessments, and lipidomics studies showed that 14 days of application of MACF-PHMB dressings followed by 7 days of MACF dressings provides a promising treatment for managing infected non-healing diabetic skin ulcers.

Hypoxia as a stimulus for tissue formation: The concept of organogenesis in microsurgically vascularized tissue engineering constructs

Axial vascularization of tissue constructs is essential to maintain an adequate blood supply for a stable regeneration of a clinically relevant tissue size. The versatility of the arterio-venous loop (AVL) has been previously shown in various small and large animal models as well as in clinical reports for bone regeneration. We have previously demonstrated the capability of the AVL to induce axial vascularization and to support the nourishment of tissue constructs in small animal models after applying high doses of ionizing radiation comparable to those applied for adjuvant radiotherapy after head and neck cancer. We hypothesize that this robust ability to induce regeneration after irradiation could be related to a state of hypoxia inside the constructs that triggers the HIF1 (hypoxia induced factor 1) - SDF1 (stromal derived factor 1) axis leading to chemotaxis of progenitor cells and induction of tissue regeneration and vascularization. We analyzed the expression of HIF1 and SDF1 via immunofluorescence in axially vascularized bone tissue engineering constructs in Lewis rats 2 and 5 weeks after local irradiation with 9Gy or 15Gy. We also analyzed the expression of various genes for osteogenic differentiation (collagen 1, RUNX, alkaline phosphatase and osteonectin) via real time PCR analysis. The expression of HIF1 and SDF1 was enhanced two weeks after irradiation with 15Gy in comparison to non-irradiated constructs. The expression of osteogenic markers was enhanced at the 5-weeks time point with significant results regarding collagen, alkaline phosphatase and osteonectin. These results indicate that the hypoxia within the AVL constructs together with an enhanced SDF1 expression probably play a role in promoting tissue differentiation. The process of tissue generation triggered by hypoxia in the vicinity of a definite vascular axis with enhanced tissue differentiation over time resembles hereby the well-known concept of organogenesis in fetal life.

Hypoxia modulates P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) drug transporters in brain endothelial cells of the developing human blood-brain barrier

P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP) multidrug resistance (MDR) transporters are localized at the luminal surface of the blood-brain barrier (BBB). They confer fetal brain protection against harmful compounds that may be circulating in the peripheral blood. The fetus develops in low oxygen levels; however, some obstetric pathologies such as pre-eclampsia, placenta accreta/previa may result in even greater fetal hypoxic states. We investigated how hypoxia impacts MDR transporters in human fetal brain endothelial cells (hfBECs) derived from early and mid-stages of pregnancy. Hypoxia decreased BCRP protein and activity in hfBECs derived in early pregnancy. In contrast, in hfBECs derived in mid-pregnancy there was an increase in P-gp and BCRP activity following hypoxia. Results suggest a hypoxia-induced reduction in fetal brain protection in early pregnancy, but a potential increase in transporter-mediated protection at the BBB during mid-gestation. This would modify accumulation of various key physiological and pharmacological substrates of P-gp and BCRP in the developing fetal brain and potentially contribute to the pathogenesis of neurodevelopmental disorders commonly associated with in utero hypoxia.

Parental exposure to antidepressants has lasting effects on offspring? A case study with zebrafish

Fish have common neurotransmitter pathways with humans, exhibiting a significant degree of conservation and homology. Thus, exposure to fluoxetine makes fish potentially susceptible to biochemical and physiological changes, similarly to what is observed in humans. Over the years, several studies demonstrated the potential effects of fluoxetine on different fish species and at different levels of biological organization. However, the effects of parental exposure to unexposed offspring remain largely unknown. The consequences of 15-day parental exposure to relevant concentrations of fluoxetine (100 and 1000 ng/L) were assessed on offspring using zebrafish as a model organism. Parental exposure resulted in offspring early hatching, non-inflation of the swimming bladder, increased malformation frequency, decreased heart rate and blood flow, and reduced growth. Additionally, a significant behavioral impairment was also found (reduced startle response, basal locomotor activity, and altered non-associative learning during early stages and a negative geotaxis and scototaxis, reduced thigmotaxis, and anti-social behavior at later life stages). These behavior alterations are consistent with decreased anxiety, a significant increase in the expression of the monoaminergic genes slc6a4a (sert), slc6a3 (dat), slc18a2 (vmat2), mao, tph1a, and th2, and altered levels of monoaminergic neurotransmitters. Alterations in behavior, expression of monoaminergic genes, and neurotransmitter levels persisted until offspring adulthood. Given the high conservation of neuronal pathways between fish and humans, data show the possibility of potential transgenerational and multigenerational effects of pharmaceuticals' exposure. These results reinforce the need for transgenerational and multigenerational studies in fish, under realistic scenarios, to provide realistic insights into the impact of these pharmaceuticals.

A highly efficient cell culture method using oxygen-permeable PDMS-based honeycomb microwells produces functional liver organoids from human induced pluripotent stem cell-derived carboxypeptidase M liver progenitor cells

Recent advancements in bioengineering have introduced potential alternatives to liver transplantation via the development of self-assembled liver organoids, derived from human-induced pluripotent stem cells (hiPSCs). However, the limited maturity of the tissue makes it challenging to implement this technology on a large scale in clinical settings. In this study, we developed a highly efficient method for generating functional liver organoids from hiPSC-derived carboxypeptidase M liver progenitor cells (CPM+ LPCs), using a microwell structure, and enhanced maturation through direct oxygenation in oxygen-permeable culture plates. We compared the morphology, gene expression profile, and function of the liver organoid with those of cells cultured under conventional conditions using either monolayer or spheroid culture systems. Our results revealed that liver organoids generated using polydimethylsiloxane-based honeycomb microwells significantly exhibited enhanced albumin secretion, hepatic marker expression, and cytochrome P450-mediated metabolism. Additionally, the oxygenated organoids consisted of both hepatocytes and cholangiocytes, which showed increased expression of bile transporter-related genes as well as enhanced bile transport function. Oxygen-permeable polydimethylsiloxane membranes may offer an efficient approach to generating highly mature liver organoids consisting of diverse cell populations.

β-Adrenoceptors in Cancer: Old Players and New Perspectives

Distress, or negative stress, is known to considerably increase the incidence of several diseases, including cancer. There is indeed evidence from pre-clinical models that distress causes a catecholaminergic overdrive that, mainly through the activation of β-adrenoceptors (β-ARs), results in cancer cell growth and cancer progression. In addition, clinical studies have evidenced a role of negative stress in cancer progression. Moreover, plenty of data demonstrates that β-blockers have positive effects in reducing the pro-tumorigenic activity of catecholamines, correlating with better outcomes in some type of cancers as evidenced by several clinical trials. Among β-ARs, β2-AR seems to be the main β-AR subtype involved in tumor development and progression. However, there are data indicating that also β1-AR and β3-AR may be involved in certain tumors. In this chapter, we will review current knowledge on the role of the three β-AR isoforms in carcinogenesis as well as in cancer growth and progression, with particular emphasis on recent studies that are opening new avenues in the use of β-ARs as therapeutic targets in treating tumors.

β3 Adrenoceptor Agonism Prevents Hyperoxia-Induced Colonic Alterations

Oxygen level is a key regulator of organogenesis and its modification in postnatal life alters the maturation process of organs, including the intestine, which do not completely develop in utero. The β3-adrenoreceptor (β3-AR) is expressed in the colon and has an oxygen-dependent regulatory mechanism. This study shows the effects of the β3-AR agonist BRL37344 in a neonatal model of hyperoxia-driven colonic injury. For the first 14 days after birth, Sprague-Dawley rat pups were exposed to ambient oxygen levels (21%) or hyperoxia (85%) and treated daily with BRL37344 at 1, 3, 6 mg/kg or untreated. At the end of day 14, proximal colon samples were collected for analysis. Hyperoxia deeply influences the proximal colon development by reducing β3-AR-expressing cells (27%), colonic length (26%) and mucin production (47%), and altering the neuronal chemical coding in the myenteric plexus without changes in the neuron number. The administration of BRL37344 at 3 mg/kg, but not at 1 mg/kg, significantly prevented these alterations. Conversely, it was ineffective in preventing hyperoxia-induced body weight loss. BRL37344 at 6 mg/kg was toxic. These findings pave the way for β3-AR pharmacological targeting as a therapeutic option for diseases caused by hyperoxia-impaired development, typical prematurity disorders.

Teratogenicity and Reactive Oxygen Species after transient embryonic hypoxia: Experimental and clinical evidence with focus on drugs causing failed abortion in humans

Teratogenicity and Reactive Oxygen Species after transient embryonic hypoxia: Experimental and clinical evidence with focus on drugs with human abortive potential. Reactive Oxygen Species (ROS) can be harmful to embryonic tissues. The adverse embryonic effects are dependent on the severity and duration of the hypoxic event and when during organongenesis hypoxia occurs. The vascular endothelium of recently formed arteries in the embryo is highly susceptible to ROS damage. Endothelial damage results in vascular disruption, hemorrhage and maldevelopment of organs, which normally should have been supplied by the artery. ROS can also induce irregular heart rhythm in the embryo resulting in alterations in blood flow and pressure from when the tubular heart starts beating. Such alterations in blood flow and pressure during cardiogenesis can result in a variety of cardiovascular defects, for example transpositions and ventricular septal defects. One aim of this article is to review and compare the pattern of malformations produced by transient embryonic hypoxia of various origins in animal studies with malformations associated with transient embryonic hypoxia in human pregnancy due to a failed abortion process. The results show that transient hypoxia and compounds with potential to cause failed abortion in humans, such as misoprostol and hormone pregnancy tests (HPTs) like Primodos, have been associated with a similar spectrum of teratogenicity. The spectrum includes limb reduction-, cardiovascular- and central nervous system defects. The hypoxia-ROS related teratogenicity of misoprostol and HPTs, is likely to be secondary to uterine contractions and compression of uterinoplacental/embryonic vessels during organogenesis.

A Review of Foods of Plant Origin as Sources of Vitamins with Proven Activity in Oxidative Stress Prevention according to EFSA Scientific Evidence

Beyond their nutritional benefits, vitamins could decrease the risk of chronic diseases due to their potent antioxidant capacity. The present work is aimed at reviewing the state of the art regarding (1) the vitamins involved in oxidative stress prevention in accordance with the requirements established by the European Food Safety Authority (EFSA) and (2) the foods of plant origin that are sources of those vitamins and have potential benefits against oxidative stress in humans. According to the European regulations based on EFSA scientific evidence, riboflavin, vitamin C, and vitamin E are those vitamins subjected to the approved health claim "contribute to the protection of cells from oxidative stress". Scientific studies conducted in humans with some natural food sources of riboflavin (almonds, wheat germ, mushrooms, oat bran), vitamin C (guava, kale, black currant, Brussels sprouts, broccoli, orange), and vitamin E (hazelnuts, almonds, peanuts, pistachio nuts, extra virgin olive oil, dates, rye) have been performed and published in the literature. However, no food of plant origin has obtained a favorable EFSA opinion to substantiate the approval of health claims related to its potential properties related to oxidative stress prevention. Further studies (concretely, well-controlled human intervention studies) must be carried out in accordance with EFSA requirements to provide the highest level of scientific evidence that could demonstrate the potential relationship between foods of plant origin and antioxidant capacity. This review could be useful for the scientific community to study the application of health claims referring to the antioxidant capacity potentially exerted by foods of plant origin.

Influence of hypoxia on retinal progenitor and ganglion cells in human induced pluripotent stem cell-derived retinal organoids

AIM

To observe the effect of low oxygen concentration on the neural retina in human induced pluripotent stem cell (hiPSC)-derived retinal organoids (ROs).

METHODS

The hiPSC and a three-dimensional culture method were used for the experiments. Generated embryoid bodies (EBs) were randomly and equally divided into hypoxic and normoxic groups. Photographs of the EBs were taken on days 38, 45, and 52, and the corresponding volume of EBs was calculated. Simultaneously, samples were collected at these three timepoints, followed by fixation, sectioning, and immunofluorescence.

RESULTS

The proportion of Ki67-positive proliferating cells increased steadily on day 38; this proliferation-promoting effect tended to increase tissue density rather than tissue volume. On days 45 and 52, the two groups had relatively similar ratios of Ki67-positive cells. Further immunofluorescence analysis showed that the ratio of SOX2-positive cells significantly increased within the neural retina on day 52 (P<0.05). In contrast, the percentage of PAX6- and CHX10-positive cells significantly decreased following hypoxia treatment at all three timepoints (P<0.01), except for CHX10 at day 45 (P>0.05). Moreover, the proportion of PAX6-/TUJ1+ cells within the neural retinas increased considerably (P<0.01, <0.05, <0.05 respectively).

CONCLUSION

Low oxygen promotes stemness and proliferation of neural retinas, suggesting that hypoxic conditions can enlarge the retinal progenitor cell pool in hiPSC-derived ROs.

Fabrication of oxygen-carrying microparticles functionalized with liver ECM-proteins to improve phenotypic three-dimensional in vitro liver assembly, function, and responses

Oxygen and extracellular matrix (ECM)-derived biopolymers play vital roles in regulating many cellular functions in both the healthy and diseased liver. This study highlights the significance of synergistically tuning the internal microenvironment of three-dimensional (3D) cell aggregates composed of hepatocyte-like cells from the HepG2 human hepatocellular carcinoma cell line and hepatic stellate cells (HSCs) from the LX-2 cell line to enhance oxygen availability and phenotypic ECM ligand presentation for promoting the native metabolic functions of the human liver. First, fluorinated (PFC) chitosan microparticles (MPs) were generated with a microfluidic chip, then their oxygen transport properties were studied using a custom ruthenium-based oxygen sensing approach. Next, to allow for integrin engagements the surfaces of these MPs were functionalized using liver ECM proteins including fibronectin, laminin-111, laminin-511, and laminin-521, then they were used to assemble composite spheriods along with HepG2 cells and HSCs. After in vitro culture, liver-specific functions and cell adhesion patterns were compared between groups and cells showed enhanced liver phenotypic responses to laminin-511 and 521 as evidenced via enhanced E-cadherin and vinculin expression, as well as albumin and urea secretion. Furthermore, hepatocytes and HSCs exhibited more pronounced phenotypic arrangements when cocultured with laminin-511 and 521 modified MPs providing clear evidence that specific ECM proteins have distinctive roles in the phenotypic regulation of liver cells in engineering 3D spheroids. This study advances efforts to create more physiologically relevant organ models allowing for well-defined conditions and phenotypic cell signaling which together improve the relevance of 3D spheroid and organoid models.

Factors Influencing the Maturation and Developmental Competence of Yak (Bos grunniens) Oocytes In Vitro

The yak (Bos grunniens) is a unique breed living on the Qinghai-Tibet Plateau and its surrounding areas, providing locals with a variety of vital means of living and production. However, the yak has poor sexual maturity and low fertility. High-quality mature oocytes are the basis of animal breeding technology. Recently, in vitro culturing of oocytes and embryo engineering technology have been applied to yak breeding. However, compared to those observed in vivo, the maturation rate and developmental capacity of in vitro oocytes are still low, which severely limits the application of in vitro fertilization and embryo production in yaks. This review summarizes the endogenous and exogenous factors affecting the in vitro maturation (IVM) and developmental ability of yak oocytes reported in recent years and provides a theoretical basis for obtaining high-quality oocytes for in vitro fertilization and embryo production in yaks.

Fetal Oxygenation from the 23rd to the 36th Week of Gestation Evaluated through the Umbilical Cord Blood Gas Analysis

The embryo and fetus grow in a hypoxic environment. Intrauterine oxygen levels fluctuate throughout the pregnancy, allowing the oxygen to modulate apparently contradictory functions, such as the expansion of stemness but also differentiation. We have recently demonstrated that in the last weeks of pregnancy, oxygenation progressively increases, but the trend of oxygen levels during the previous weeks remains to be clarified. In the present retrospective study, umbilical venous and arterial oxygen levels, fetal oxygen extraction, oxygen content, CO2, and lactate were evaluated in a cohort of healthy newborns with gestational age < 37 weeks. A progressive decrease in pO2 levels associated with a concomitant increase in pCO2 and reduction in pH has been observed starting from the 23rd week until approximately the 33-34th week of gestation. Over this period, despite the increased hypoxemia, oxygen content remains stable thanks to increasing hemoglobin concentration, which allows the fetus to become more hypoxemic but not more hypoxic. Starting from the 33-34th week, fetal oxygenation increases and ideally continues following the trend recently described in term fetuses. The present study confirms that oxygenation during intrauterine life continues to vary even after placenta development, showing a clear biphasic trend. Fetuses, in fact, from mid-gestation to near-term, become progressively more hypoxemic. However, starting from the 33-34th week, oxygenation progressively increases until birth. In this regard, our data suggest that the placenta is the hub that ensures this variable oxygen availability to the fetus, and we speculate that this biphasic trend is functional for the promotion, in specific tissues and at specific times, of stemness and intrauterine differentiation.

Unraveling the Consequences of Oxygen Imbalance on Early Embryo Development: Exploring Mitigation Strategies

Although well-established and adopted by commercial laboratories, the in vitro embryo production system still requires refinements to achieve its highest efficiency. Early embryonic development is a dynamic event, demanding suitable conditions to provide a high number of embryos with quality and competence. The first step to obtaining an optimized in vitro environment is to know the embryonic metabolism and energy request throughout the different stages of development. Oxygen plays a crucial role in several key biological processes necessary to sustain and complete embryonic development. Nonetheless, there is still controversy regarding the optimal in vitro atmospheric concentrations during culture. Herein, we discuss the impact of oxygen tension on the viability of in vitro-produced embryos during early development. The importance of oxygen tension is addressed as its roles regarding essential embryonic traits, including embryo production rates, embryonic cell viability, gene expression profile, epigenetic regulation, and post-cryopreservation survival. Finally, we highlight the damage caused by in vitro unbalanced oxygen tensions and strategies to mitigate the harmful effects.

Asiatic acid in Centella asiatica extract towards morphological development in an intermittent hypoxia intrauterine embryo model and molecular prediction pathway of insulin-like growth factor-1 receptor signalling

Background

Hypoxia during pregnancy generates oxidative stress that alters the growth and development of the human fetus. Insulin-like growth factor-1 (IGF-1) receptors are essential for normal fetal growth. Asiatic acid in Centella asiatica (CA) has antioxidant properties to prevent growth impairment in hypoxia.

Aims

This study aimed to investigate the effect of asiatic acid on the morphological development of an intermittent hypoxia (IH) zebrafish embryo model and analyze molecular docking prediction in IGF-1 receptor (IGF-1R) signaling.

Methods

Embryos of zebrafish at 2 hours postfertilization (hpf) were assigned to control negative (C), IH, and combination IH and CA extract groups consisting of 1.25 (IHCA1), 2.5 (IHCA2), and 5 (IHCA3) µg/ml. Hypoxia treatment (conducted 4 hours/day) and CA extract were administered for 3 days (2-72 hpf). The parameters of body length and head length were evaluated at 3, 6, and 9 days postfertilization (dpf). The data were analyzed by a two-way analysis of variance (p < 0.05). Molecular docking was performed to explore the binding affinity of asiatic acid to IGF-1R by Molegro Virtual Docker ver.5 software.

Results

The body length and head length of embryos in the IH and treatment groups (IHCA) were shorter than those in the control group at 3 dpf (p < 0.05). However, the body length was more prolonged in the IHCA1 group, but the head length was longer in the IHCA2 group than in the IH group at 6 and 9 dpf. Molecular docking showed the reliable interaction of asiatic acid with IGF-1R signaling in an IH animal model.

Conclusion

The administration of CA extract benefits IH through the development and growth of zebrafish embryos at a dose of 2.5-5 µg/ml. Asiatic acid has a binding affinity for IGF-1R signaling.

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.

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.

Microphase separation of living cells

Self-organization of cells is central to a variety of biological systems and physical concepts of condensed matter have proven instrumental in deciphering some of their properties. Here we show that microphase separation, long studied in polymeric materials and other inert systems, has a natural counterpart in living cells. When placed below a millimetric film of liquid nutritive medium, a quasi two-dimensional, high-density population of Dictyostelium discoideum cells spontaneously assembles into compact domains. Their typical size of 100 μm is governed by a balance between competing interactions: an adhesion acting as a short-range attraction and promoting aggregation, and an effective long-range repulsion stemming from aerotaxis in near anoxic condition. Experimental data, a simple model and cell-based simulations all support this scenario. Our findings establish a generic mechanism for self-organization of living cells and highlight oxygen regulation as an emergent organizing principle for biological matter.

Genes Involved in DNA Repair and Mitophagy Protect Embryoid Bodies from the Toxic Effect of Methylmercury Chloride under Physioxia Conditions

The formation of embryoid bodies (EBs) from human pluripotent stem cells resembles the early stages of human embryo development, mimicking the organization of three germ layers. In our study, EBs were tested for their vulnerability to chronic exposure to low doses of MeHgCl (1 nM) under atmospheric (21%O₂) and physioxia (5%O₂) conditions. Significant differences were observed in the relative expression of genes associated with DNA repair and mitophagy between the tested oxygen conditions in nontreated EBs. When compared to physioxia conditions, the significant differences recorded in EBs cultured at 21% O₂ included: (1) lower expression of genes associated with DNA repair (ATM, OGG1, PARP1, POLG1) and mitophagy (PARK2); (2) higher level of mtDNA copy number; and (3) higher expression of the neuroectodermal gene (NES). Chronic exposure to a low dose of MeHgCl (1 nM) disrupted the development of EBs under both oxygen conditions. However, only EBs exposed to MeHgCl at 21% O₂ revealed downregulation of mtDNA copy number, increased oxidative DNA damage and DNA fragmentation, as well as disturbances in SOX17 (endoderm) and TBXT (mesoderm) genes expression. Our data revealed that physioxia conditions protected EBs genome integrity and their further differentiation.

Fetal oxygenation in the last weeks of pregnancy evaluated through the umbilical cord blood gas analysis

Introduction

Embryo and fetus grow and mature over the first trimester of pregnancy in a dynamic hypoxic environment, where placenta development assures an increased oxygen availability. However, it is unclear whether and how oxygenation changes in the later trimesters and, more specifically, in the last weeks of pregnancy.

Methods

Observational study that evaluated the gas analysis of the umbilical cord blood collected from a cohort of healthy newborns with gestational age ≥37 weeks. Umbilical venous and arterial oxygen levels as well as fetal oxygen extraction were calculated to establish whether oxygenation level changes over the last weeks of pregnancy. In addition, fetal lactate, and carbon dioxide production were analyzed to establish whether oxygen oscillations may induce metabolic effects in utero.

Results

This study demonstrates a progressive increase in fetal oxygenation levels from the 37th to the 41st weeks of gestation (mean venous PaO₂ approximately from 20 to 25 mmHg; p < 0.001). This increase is largely attributable to growing umbilical venous PaO₂, regardless of delivery modalities. In neonates born by vaginal delivery, the increased oxygen availability is associated with a modest increase in oxygen extraction, while in neonates born by cesarean section, it is associated with reduced lactate production. Independently from the type of delivery, carbon dioxide production moderately increased. These findings suggest a progressive shift from a prevalent anaerobic metabolism (Warburg effect) towards a growing aerobic metabolism.

Conclusion

This study confirms that fetuses grow in a hypoxic environment that becomes progressively less hypoxic in the last weeks of gestation. The increased oxygen availability seems to favor aerobic metabolic shift during the last weeks of intrauterine life; we hypothesize that this environmental change may have implications for fetal maturation during intrauterine life.

Effect of Hypoxia on Branching Characteristics and Cell Subpopulations during Kidney Organ Culture

During early developmental stages, embryonic kidneys are not fully vascularized and are potentially exposed to hypoxic conditions, which is known to influence cell proliferation and survival, ureteric bud branching, and vascularization of the developing kidney. To optimize the culture conditions of in vitro cultured kidneys and gain further insight into the effect of hypoxia on kidney development, we exposed mouse embryonic kidneys isolated at E11.5, E12.5, and E13.5 to hypoxic and normal culture conditions and compared ureteric bud branching patterns, the growth of the progenitor subpopulation hoxb7+, and the expression patterns of progenitor and differentiation markers. Branching patterns were quantified using whole organ confocal imaging and gradient-vector-based analysis. In our model, hypoxia causes an earlier expression of UB tip cell markers, and a delay in stalk cell marker gene expression. The metanephric mesenchyme (MM) exhibited a later expression of differentiation marker FGF8, marking a delay in nephron formation. Hypoxia further delayed the expression of stroma cell progenitor markers, a delay in cortical differentiation markers, as well as an earlier expression of medullary and ureteral differentiation markers. We conclude that standard conditions do not apply universally and that tissue engineering strategies need to optimize suitable culture conditions for each application. We also conclude that adapting culture conditions to specific aspects of organ development in tissue engineering can help to improve individual stages of tissue generation.

Approaches to investigating metabolism in human neurodevelopment using organoids: insights from intestinal and cancer studies

Interrogating the impact of metabolism during development is important for understanding cellular and tissue formation, organ and systemic homeostasis, and dysregulation in disease states. To evaluate the vital functions metabolism coordinates during human brain development and disease, pluripotent stem cell-derived models, such as organoids, provide tractable access to neurodevelopmental processes. Despite many strengths of neural organoid models, the extent of their replication of endogenous metabolic programs is currently unclear and requires direct investigation. Studies in intestinal and cancer organoids that functionally evaluate dynamic bioenergetic changes provide a framework that can be adapted for the study of neural metabolism. Validation of in vitro models remains a significant challenge; investigation using in vivo models and primary tissue samples is required to improve our in vitro model systems and, concomitantly, improve our understanding of human development.

Differential methylation in EGLN1 associates with blood oxygen saturation and plasma protein levels in high-altitude pulmonary edema

BACKGROUND

High-altitude (HA, 2500 m) hypoxic exposure evokes a multitude of physiological processes. The hypoxia-sensing genes though influence transcriptional output in disease susceptibility; the exact regulatory mechanisms remain undetermined in high-altitude pulmonary edema (HAPE). Here, we investigated the differential DNA methylation distribution in the two genes encoding the oxygen-sensing HIF-prolyl hydroxylases, prolyl hydroxylase domain protein 2 (PHD2) and factor inhibiting HIF-1α and the consequent contributions to the HAPE pathophysiology.

METHODS

Deep sequencing of the sodium bisulfite converted DNA segments of the two genes, Egl nine homolog 1 (EGLN1) and Hypoxia Inducible Factor 1 Subunit Alpha Inhibitor (HIF1AN), was conducted to analyze the differential methylation distribution in three study groups, namely HAPE-patients (HAPE-p), HAPE-free sojourners (HAPE-f) and healthy HA natives (HLs). HAPE-p and HAPE-f were permanent residents of low altitude (< 200 m) of North India who traveled to Leh (3500 m), India, and were recruited through Sonam Norboo Memorial (SNM) hospital, Leh. HLs were permanent residents of altitudes at and above 3500 m. In addition to the high resolution, bisulfite converted DNA sequencing, gene expression of EGLN1 and HIF1AN and their plasma protein levels were estimated.

RESULTS

A significantly lower methylation distribution of CpG sites was observed in EGLN1 and higher in HIF1AN (P < 0.01) in HAPE-p compared to the two control groups, HAPE-f and HLs. Of note, differential methylation distribution of a few CpG sites, 231,556,748, 231,556,804, 231,556,881, 231,557,317 and 231,557,329, in EGLN1 were significantly associated with the risk of HAPE (OR = 4.79-10.29; P = 0.048-004). Overall, the methylation percentage in EGLN1 correlated with upregulated plasma PHD2 levels (R = - 0.36, P = 0.002) and decreased peripheral blood oxygen saturation (SpO₂) levels (R = 0.34, P = 0.004). We also identified a few regulatory SNPs in the DNA methylation region of EGLN1 covering chr1:231,556,683-231,558,443 suggestive of the functional role of differential methylation distribution of these CpG sites in the regulation of the genes and consequently in the HIF-1α signaling.

CONCLUSIONS

Significantly lower methylation distribution in EGLN1 and the consequent physiological influences annotated its functional epigenetic relevance in the HAPE pathophysiology.

Opportunities and Limits of Conventional IVF versus ICSI: It Is Time to Come off the Fence

Conventional IVF (c-IVF) is one of the most practiced assisted reproductive technology (ART) approaches used worldwide. However, in the last years, the number of c-IVF procedures has dropped dramatically in favor of intracytoplasmic sperm injection (ICSI) in cases of non-male-related infertility. In this review, we have outlined advantages and disadvantages associated with c-IVF, highlighting the essential steps governing its success, its limitations, the methodology differences among laboratories and the technical progress. In addition, we have debated recent insights into fundamental questions, including indications regarding maternal age, decreased ovarian reserve, endometriosis, autoimmunity, single oocyte retrieval-cases as well as preimplantation genetic testing cycles. The “overuse” of ICSI procedures in several clinical situations of ART has been critically discussed. These insights will provide a framework for a better understanding of opportunities associated with human c-IVF and for best practice guidelines applicability in the reproductive medicine field.

Modulatory Contribution of Oxygenating Hydrogels and Polyhexamethylene Biguanide on the Antimicrobial Potency of Neutrophil-like Cells

Neutrophils are a first line of host defense against infection and utilize a series of oxygen-dependent processes to eliminate pathogens. Research suggests that oxygen availability can improve anti-infective mechanisms by promoting the formation of reactive oxygen species. Also, oxygen can synergistically upregulate the antibacterial properties of certain antibiotics against bacteria by altering their metabolism and causing an increase in the antibiotic uptake of bacteria. Therefore, understanding the effects of oxygen availability, as provided via a biomaterial treatment alone or along with potent antibacterial agents, on neutrophil functions can lead us to the development of new anti-inflammatory and anti-infective approaches. However, the study of neutrophil functions in vitro is often limited by their short life span and nonreproducibility, which suggests the need for cell line-based models as a substitute for primary neutrophils. Here, we took advantage of the differentiated human leukemia-60 cell line (HL-60), as an in vitro neutrophil model, to test the effects of local oxygen and antibacterial delivery by fluorinated methacrylamide chitosan (MACF) hydrogels incorporated with polyhexamethylene biguanide (PHMB) antibacterial agent. Considering the natural modes of neutrophil actions to combat bacteria, we studied the impact of our dual functioning oxygenating-antibacterial platforms on neutrophil phagocytosis and antibacterial properties as well as the formation of neutrophil extracellular traps (NETs) and reactive oxygen species (ROS). Our results demonstrated that supplemental oxygen and antibacterial delivery from MACF-PHMB hydrogel platforms upregulated neutrophil antibacterial properties and ROS production. NET formation by neutrophils upon treatment with MACF and PHMB varied when chemical and biological stimuli were used. Overall, this study presents a model to study immune responses in vitro and lays the foundation for future studies to investigate if similar responses also occur in vivo.

Diphyodont tooth replacement of Brasilodon-A Late Triassic eucynodont that challenges the time of origin of mammals

Two sets of teeth (diphyodonty) characterise extant mammals but not reptiles, as they generate many replacement sets (polyphyodonty). The transition in long-extinct species from many sets to only two has to date only been reported in Jurassic eucynodonts. Specimens of the Late Triassic brasilodontid eucynodont Brasilodon have provided anatomical and histological data from three lower jaws of different growth stages. These reveal ordered and timed replacement of deciduous by adult teeth. Therefore, this diphyodont dentition, as contemporary of the oldest known dinosaurs, shows that Brasilodon falls within a range of wide variations of typically mammalian, diphyodont dental patterns. Importantly, these three lower jaws represent distinct ontogenetic stages that reveal classic features for timed control of replacement, by the generation of only one replacement set of teeth. This data shows that the primary premolars reveal a temporal replacement pattern, importantly from directly below each tooth, by controlled regulation of tooth resorption and regeneration. The complexity of the adult prismatic enamel structure with a conspicuous intra-structural Schmelzmuster array suggests that, as in the case of extant mammals, this extinct species would have probably sustained higher metabolic rates than reptiles. Furthermore, in modern mammals, diphyodonty and prismatic enamel are inextricably linked, anatomically and physiologically, to a set of other traits including placentation, endothermy, fur, lactation and even parental care. Our analysis of the osteodental anatomy of Brasilodon pushes back the origin of diphyodonty and consequently, its related biological traits to the Norian (225.42 ± 0.37 myr), and around 25 myr after the End-Permian mass extinction event.

Functionalized 3D scaffolds for engineering the hematopoietic niche

Hematopoietic stem cells (HSCs) reside in a subzone of the bone marrow (BM) defined as the hematopoietic niche where, via the interplay of differentiation and self-renewal, they can give rise to immune and blood cells. Artificial hematopoietic niches were firstly developed in 2D in vitro cultures but the limited expansion potential and stemness maintenance induced the optimization of these systems to avoid the total loss of the natural tissue complexity. The next steps were adopted by engineering different materials such as hydrogels, fibrous structures with natural or synthetic polymers, ceramics, etc. to produce a 3D substrate better resembling that of BM. Cytokines, soluble factors, adhesion molecules, extracellular matrix (ECM) components, and the secretome of other niche-resident cells play a fundamental role in controlling and regulating HSC commitment. To provide biochemical cues, co-cultures, and feeder-layers, as well as natural or synthetic molecules were utilized. This review gathers key elements employed for the functionalization of a 3D scaffold that demonstrated to promote HSC growth and differentiation ranging from 1) biophysical cues, i.e., material, topography, stiffness, oxygen tension, and fluid shear stress to 2) biochemical hints favored by the presence of ECM elements, feeder cell layers, and redox scavengers. Particular focus is given to the 3D systems to recreate megakaryocyte products, to be applied for blood cell production, whereas HSC clinical application in such 3D constructs was limited so far to BM diseases testing.

Systemically injected bone marrow mononuclear cells specifically home to axially vascularized tissue engineering constructs

Inducing axial vascularisation of tissue engineering constructs is a well-established method to support tissue growth in large 3-dimensional tissues. Progenitor cell chemotaxis towards axially vascularized tissues has not been well characterized. In a prospective randomized controlled study including 32 male syngeneic Lewis rats we investigated the capability of the axially vascularized constructs to attract systemically injected bone marrow mononuclear cells (BMMNCs). The underlying mechanism for cell homing was investigated focusing on the role of hypoxia and the SDF1-CXCR4-7 axis. Sixteen animals were used as donors for BMMNCs. The other animals were subjected to implantation of a tissue engineering construct in the subcutaneous groin region. These constructs were axially vascularized either via an arteriovenous loop (AVL, n = 6) or via uninterrupted flow-through vessels (non-AVL, n = 10). BMMNCs were labelled with quantum dots (Qdot® 655) and injected 12 days after surgery either via intra-arterial or intravenous routes. 2 days after cell injection, the animals were sacrificed and examined using fluorescence microscopy. The Qdot® 655 signals were detected exclusively in the liver, spleen, AVL constructs and to a minimal extent in the non-AVL constructs. A significant difference could be detected between the number of labelled cells in the AVL and non-AVL constructs with more cells detected in the AVL constructs specially in central zones (p <0.0001). The immunohistological analysis showed a significant increase in the absolute expression of HIF-1 in the AVL group in comparison to the non-AVL group. The PCR analysis confirmed a 1.4-fold increase in HIF-1 expression in AVL constructs. Although PCR analysis showed an enhanced expression of CXCR4 and CXCR7 in AVL constructs, no significant differences in SDF1 expression were detected via immunohistological or PCR analysis. At the examined time point, the AVL constructs can attract BMMNCs in a mechanism probably related to the hypoxia associated with a robust tissue formation.

Neonatal Oxidative Stress Impairs Cortical Synapse Formation and GABA Homeostasis in Parvalbumin-Expressing Interneurons

Neonatal brain injury is often caused by preterm birth. Brain development is vulnerable to increased environmental stress, including oxidative stress challenges. Due to a premature change of the fetal living environment from low oxygen in utero into postnatal high-oxygen room air conditions ex utero, the immature preterm brain is exposed to a relative hyperoxia, which can induce oxidative stress and impair neuronal cell development. To simulate the drastic increase of oxygen exposure in the immature brain, 5-day-old C57BL/6 mice were exposed to hyperoxia (80% oxygen) for 48 hours or kept in room air (normoxia, 21% oxygen) and mice were analyzed for maturational alterations of cortical GABAergic interneurons. As a result, oxidative stress was indicated by elevated tyrosine nitration of proteins. We found perturbation of perineuronal net formation in line with decreased density of parvalbumin-expressing (PVALB) cortical interneurons in hyperoxic mice. Moreover, maturational deficits of cortical PVALB+ interneurons were obtained by decreased glutamate decarboxylase 67 (GAD67) protein expression in Western blot analysis and lower gamma-aminobutyric acid (GABA) fluorescence intensity in immunostaining. Hyperoxia-induced oxidative stress affected cortical synaptogenesis by decreasing synapsin 1, synapsin 2, and synaptophysin expression. Developmental delay of synaptic marker expression was demonstrated together with decreased PI3K-signaling as a pathway being involved in synaptogenesis. These results elucidate that neonatal oxidative stress caused by increased oxygen exposure can lead to GABAergic interneuron damage which may serve as an explanation for the high incidence of psychiatric and behavioral alterations found in preterm infants.

Calcium peroxide aids tyramine-alginate gel to crosslink with tyrosinase for efficient cartilage repair

The innate cartilage extracellular matrix is avascular and plays a vital role in innate chondrocytes. Recapping the crucial components of the extracellular matrix in engineered organs via polymeric gels and bioinspired approaches is promising for improving the regenerative aptitude of encapsulated cartilage/chondrocytes. Conventional gel formation techniques for polymeric materials rely on employing oxidative crosslinking, which is constrained in this avascular environment. Further, poor mechanical properties limit the practical applications of polymeric gels and reduce their therapeutic efficacy. Herein, the purpose of this study was to develop a bioadhesive gel possessing dual crosslinking for engineering cartilage. Tyramine (TYR) was first chemically conjugated to the alginate (ALG) backbone to form an ALG-TYR precursor, followed by the addition of calcium peroxide (CaO₂); calcium ions of CaO₂ physically crosslink with ALG, and oxygen atoms of CaO₂ chemically crosslink TYR with tyrosinase, thus enabling dual/enhanced crosslinking and possessing injectability. The ALG-TYR/tyrosinase/CaO₂ gel system was chemically, mechanically, cellularly, and microscopically characterized. The gel system developed herein was biocompatible and showed augmented mechanical strength. The results showed, for the first time, that CaO₂ supplementation preserved cell viability and enhanced the crosslinking ability, bioadhesion, mechanical strength, chondrogenesis, and stability for cartilage regeneration.

Physiologic isolation and expansion of human mesenchymal stem/stromal cells for manufacturing of cell-based therapy products

The utilization of mesenchymal stem/stromal cells raises new hopes in treatment of diseases and pathological conditions, while at the same time bringing immense challenges for researchers, manufacturers and physicians. It is essential to consider all steps along the in vitro fabrication of cell-based products in order to reach efficient and reproducible treatment outcomes. Here, the optimal protocols for isolation, cultivation and differentiation of mesenchymal stem cells are required. In this review we discuss these aspects and their influence on the final cell-based product quality. We demonstrate that physiological in vitro cell cultivation conditions play a crucial role in therapeutic functionalities of cultivated cells. We show that three-dimensional cell culture, dynamic culture conditions and physiologically relevant in vitro oxygen concentrations during isolation and expansion make a decisive contribution towards the improvement of cell-based products in regenerative medicine.

Permeability, anti-inflammatory and anti-VEGF profiles of steroidal-loaded cationic nanoemulsions in retinal pigment epithelial cells under oxidative stress

Age-related macular degeneration (AMD) is defined as a degenerative, progressive and multifactorial disorder that affects the macula with a complex etiology. The retinal pigment epithelium is a monolayer of cells that has the function to separate the surface of the choroid from the neural retina that is involved in the signal transduction leading to vision. The blood-aqueous barrier and the blood retinal barrier limit the permeation of drugs into the retina and thereby reducing their efficacy. Triamcinolone acetonide (TA) is widely used as anti-inflammatory and immunomodulatory drug that promotes the inhibition of the inflammatory processes. The factors that stimulate or inhibit angiogenesis in AMD create a local balance that is responsible for the growth of sub-retinal neovascularization. In AMD, the main angiogenic stimulus is the vascular endothelial growth factor (VEGF). In this work, nanoemulsions with cationic surfactants (mono- and dicationic DABCO and quinuclidine) were produced to deliver TA, and were found to reduce the production of tumor necrosis factor alpha (TNF-α), which stimulates the choroidal neovascularization development by upregulating the VEGF production, and consequently decreased the VEGF levels. Our results support the potential use of mono- and dicationic DABCO and quinuclidine-based cationic nanoemulsions for the delivery of TA in the treatment of AMD.

Reduction of Deuterium Level Supports Resistance of Neurons to Glucose Deprivation and Hypoxia: Study in Cultures of Neurons and on Animals

The effect of a reduced deuterium (D) content in the incubation medium on the survival of cultured neurons in vitro and under glucose deprivation was studied. In addition, we studied the effect of a decrease in the deuterium content in the rat brain on oxidative processes in the nervous tissue, its antioxidant protection, and training of rats in the T-shaped maze test under hypoxic conditions. For experiments with cultures of neurons, 7-8-day cultures of cerebellar neurons were used. Determination of the rate of neuronal death in cultures was carried out using propidium iodide. Acute hypoxia with hypercapnia was simulated in rats by placing them in sealed vessels with a capacity of 1 L. The effect on oxidative processes in brain tissues was assessed by changes in the level of free radical oxidation and malondialdehyde. The effect on the antioxidant system of the brain was assessed by the activity of catalase. The study in the T-maze was carried out in accordance with the generally accepted methodology, the skill of alternating right-sided and left-sided loops on positive reinforcement was developed. This work has shown that a decrease in the deuterium content in the incubation medium to a level of -357‱ has a neuroprotective effect, increasing the survival rate of cultured neurons under glucose deprivation. When exposed to hypoxia, a preliminary decrease in the deuterium content in the rat brain to -261‱ prevents the development of oxidative stress in their nervous tissue and preserves the learning ability of animals in the T-shaped maze test at the level of the control group. A similar protective effect during the modification of the 2H/1H internal environment of the body by the consumption of DDW can potentially be used for the prevention of pathological conditions associated with the development of oxidative stress with damage to the central nervous system.

Oxygen-sensing mechanisms in development and tissue repair

Under normoxia, hypoxia inducible factor (HIF) α subunits are hydroxylated by PHDs (prolyl hydroxylase domain proteins) and subsequently undergo polyubiquitylation and degradation. Normal embryogenesis occurs under hypoxia, which suppresses PHD activities and allows HIFα to stabilize and regulate development. In this Primer, we explain molecular mechanisms of the oxygen-sensing pathway, summarize HIF-regulated downstream events, discuss loss-of-function phenotypes primarily in mouse development, and highlight clinical relevance to angiogenesis and tissue repair.

Green oxygen power plants in the brain rescue neuronal activity

Neuronal activity in the brain depends on mostly aerobic generation of energy equivalents and thus on a constant O₂ supply. Oxygenation of the vertebrate brain has been optimized during evolution by species-specific uptake and transport of O₂ that originally derives from the phototrophic activity of prokaryotic and eukaryotic organisms in the environment. Here, we employed a concept that exploits transcardial injection and vascular distribution of unicellular green algae or cyanobacteria in the brain of Xenopus laevis tadpoles. Using oxygen measurements in the brain ventricle, we found that these microorganisms robustly produce sizable amounts of O₂ upon illumination. In a severe hypoxic environment, when neuronal activity has completely ceased, the photosynthetic O₂ reliably provoked a restart and rescue of neuronal activity. In the future, phototrophic microorganisms might provide a novel means to directly increase oxygen levels in the brain in a controlled manner under particular eco-physiological conditions or following pathological impairments.

The Impact of Hypoxia in Early Pregnancy on Placental Cells

Oxygen levels in the placental microenvironment throughout gestation are not constant, with severe hypoxic conditions present during the first trimester. This hypoxic phase overlaps with the most critical stages of placental development, i.e., blastocyst implantation, cytotrophoblast invasion, and spiral artery remodeling initiation. Dysregulation of any of these steps in early gestation can result in pregnancy loss and/or adverse pregnancy outcomes. Hypoxia has been shown to regulate not only the self-renewal, proliferation, and differentiation of trophoblast stem cells and progenitor cells, but also the recruitment, phenotype, and function of maternal immune cells. In this review, we will summarize how oxygen levels in early placental development determine the survival, fate, and function of several important cell types, e.g., trophoblast stem cells, extravillous trophoblasts, syncytiotrophoblasts, uterine natural killer cells, Hofbauer cells, and decidual macrophages. We will also discuss the cellular mechanisms used to cope with low oxygen tensions, such as the induction of hypoxia-inducible factor (HIF) or mammalian target of rapamycin (mTOR) signals, regulation of the metabolic pathway, and adaptation to autophagy. Understanding the beneficial roles of hypoxia in early placental development will provide insights into the root cause(s) of some pregnancy disorders, such as spontaneous abortion, preeclampsia, and intrauterine growth restriction.

Oxygen in Metabolic Dysfunction and Its Therapeutic Relevance

Significance: In recent years, a number of studies have shown altered oxygen partial pressure at a tissue level in metabolic disorders, and some researchers have considered oxygen to be a (macro) nutrient. Oxygen availability may be compromised in obesity and several other metabolism-related pathological conditions, including sleep apnea-hypopnea syndrome, the metabolic syndrome (which is a set of conditions), type 2 diabetes, cardiovascular disease, and cancer. Recent Advances: Strategies designed to reduce adiposity and its accompanying disorders have been mainly centered on nutritional interventions and physical activity programs. However, novel therapies are needed since these approaches have not been sufficient to counteract the worldwide increasing rates of metabolic disorders. In this regard, intermittent hypoxia training and hyperoxia could be potential treatments through oxygen-related adaptations. Moreover, living at a high altitude may have a protective effect against the development of abnormal metabolic conditions. In addition, oxygen delivery systems may be of therapeutic value for supplying the tissue-specific oxygen requirements. Critical Issues: Precise in vivo methods to measure oxygenation are vital to disentangle some of the controversies related to this research area. Further, it is evident that there is a growing need for novel in vitro models to study the potential pathways involved in metabolic dysfunction to find appropriate therapeutic targets. Future Directions: Based on the existing evidence, it is suggested that oxygen availability has a key role in obesity and its related comorbidities. Oxygen should be considered in relation to potential therapeutic strategies in the treatment and prevention of metabolic disorders. Antioxid. Redox Signal. 35, 642-687.

The Role of Metabolism in Heart Failure and Regeneration

Heart failure is the leading cause of death worldwide. The inability of the adult mammalian heart to regenerate following injury results in the development of systolic heart failure. Thus, identifying novel approaches toward regenerating the adult heart has enormous therapeutic potential for adult heart failure. Mitochondrial metabolism is an essential homeostatic process for maintaining growth and survival. The emerging role of mitochondrial metabolism in controlling cell fate and function is beginning to be appreciated. Recent evidence suggests that metabolism controls biological processes including cell proliferation and differentiation, which has profound implications during development and regeneration. The regenerative potential of the mammalian heart is lost by the first week of postnatal development when cardiomyocytes exit the cell cycle and become terminally differentiated. This inability to regenerate following injury is correlated with the metabolic shift from glycolysis to fatty acid oxidation that occurs during heart maturation in the postnatal heart. Thus, understanding the mechanisms that regulate cardiac metabolism is key to unlocking metabolic interventions during development, disease, and regeneration. In this review, we will focus on the emerging role of metabolism in cardiac development and regeneration and discuss the potential of targeting metabolism for treatment of heart failure.

Hypoxia-Inducible Factor Regulates Endothelial Metabolism in Cardiovascular Disease

Endothelial cells (ECs) form a physical barrier between the lumens and vascular walls of arteries, veins, capillaries, and lymph vessels; thus, they regulate the extravasation of nutrients and oxygen from the circulation into the perivascular space and participate in mechanisms that maintain cardiovascular homeostasis and promote tissue growth and repair. Notably, their role in tissue repair is facilitated, at least in part, by their dependence on glycolysis for energy production, which enables them to resist hypoxic damage and promote angiogenesis in ischemic regions. ECs are also equipped with a network of oxygen-sensitive molecules that collectively activate the response to hypoxic injury, and the master regulators of the hypoxia response pathway are hypoxia-inducible factors (HIFs). HIFs reinforce the glycolytic dependence of ECs under hypoxic conditions, but whether HIF activity attenuates or exacerbates the progression and severity of cardiovascular dysfunction varies depending on the disease setting. This review summarizes how HIF regulates the metabolic and angiogenic activity of ECs under both normal and hypoxic conditions and in a variety of diseases that are associated with cardiovascular complications.

Advances in removing mass transport limitations for more physiologically relevant in vitro 3D cell constructs

Spheroids and organoids are promising models for biomedical applications ranging from human disease modeling to drug discovery. A main goal of these 3D cell-based platforms is to recapitulate important physiological parameters of their in vivo organ counterparts. One way to achieve improved biomimetic architectures and functions is to culture cells at higher density and larger total numbers. However, poor nutrient and waste transport lead to low stability, survival, and functionality over extended periods of time, presenting outstanding challenges in this field. Fortunately, important improvements in culture strategies have enhanced the survival and function of cells within engineered microtissues/organs. Here, we first discuss the challenges of growing large spheroids/organoids with a focus on mass transport limitations, then highlight recent tools and methodologies that are available for producing and sustaining functional 3D in vitro models. This information points toward the fact that there is a critical need for the continued development of novel cell culture strategies that address mass transport in a physiologically relevant human setting to generate long-lasting and large-sized spheroids/organoids.

Oxygen-generating microparticles in chondrocytes-laden hydrogels by facile and versatile click chemistry strategy

Currently, oxygen supply for in vitro cell culture is one of the major challenges in tissue engineering, especially in three-dimensional (3D) structures, such as polymeric hydrogels, because oxygen is an essential element for cells survival. In this context, oxygen levels must be maintained in articular cartilage to promote the differentiation, viability, and proliferation of chondrocytes due to the low level of oxygen presence in this region. Although some technologies employ oxygen-generating materials to add sufficient oxygen levels, the limitations and challenges of current technologies include the lack of controlled, sustained, and prolonged release of the oxygen. Moreover, the fabrication methods may leave some impurities or residues resulting in toxicity to the cells. "Click" chemistry is a facile, versatile, and compatible chemical strategy to engineer hydrogels for tissue engineering applications. Herein, we disclose the engineering of oxygen-generating microparticles in chondrocytes-laden hydrogels through a versatile catalyst-free tetrazine and norbornene inverse electron demand Diels‒Alder (iEDDA) click reaction. The hydrogels combine chondroitin sulfate (CS) and poly(ethylene glycol) (PEG) crosslinked in situ, displaying tunable rheological and mechanical properties, for sustained and prolonged oxygen-release. Gene expression analysis of the chondrocytes by real-time reverse transcription polymerase chain reaction (RT-PCR) demonstrated promising cell response within the engineered hydrogel.

Integrative developmental biology in the age of anthropogenic change

Humans are changing and challenging nature in many ways. Conservation Biology seeks to limit human impacts on nature and preserve biological diversity. Traditionally, Developmental Biology and Conservation Biology have had nonoverlapping objectives, operating in distinct spheres of biological science. However, this chasm can and should be filled to help combat the emerging challenges of the 21st century. The means by which to accomplish this goal were already established within the conceptual framework of evo- and eco-devo and can be further expanded to address the ways that anthropogenic disturbance affect embryonic development. Herein, I describe ways that these approaches can be used to advance the study of reptilian embryos. More specifically, I explore the ways that a developmental perspective can advance ongoing studies of embryonic physiology in the context of global warming and chemical pollution, both of which are known stressors of reptilian embryos. I emphasize ways that these developmental perspectives can inform conservation biologists trying to develop management practices that will address the complexity of challenges facing reptilian embryos.

Advances in bioreactors for lung bioengineering: From scalable cell culture to tissue growth monitoring

Lung bioengineering has emerged to resolve the current lung transplantation limitations and risks, including the shortage of donor organs and the high rejection rate of transplanted lungs. One of the most critical elements of lung bioengineering is bioreactors. Bioreactors with different applications have been developed in the last decade for lung bioengineering approaches, aiming to produce functional reproducible tissue constructs. Here, the current status and advances made in the development and application of bioreactors for bioengineering lungs are comprehensively reviewed. First, bioreactor design criteria are explained, followed by a discussion on using bioreactors as a culture system for scalable expansion and proliferation of lung cells, such as producing epithelial cells from induced pluripotent stem cells (iPSCs). Next, bioreactor systems facilitating and improving decellularization and recellularization of lung tissues are discussed, highlighting the studies that developed bioreactors for producing engineered human-sized lungs. Then, monitoring bioreactors are reviewed, showing their ability to evaluate and optimize the culture conditions for maturing engineered lung tissues, followed by an explanation on the ability of ex vivo lung perfusion systems for reconditioning the lungs before transplantation. After that, lung cancer studies simplified by bioreactors are discussed, showing the potentials of bioreactors in lung disease modeling. Finally, other platforms with the potential of facilitating lung bioengineering are described, including the in vivo bioreactors and lung-on-a-chip models. In the end, concluding remarks and future directions are put forward to accelerate lung bioengineering using bioreactors.

Molecular mechanisms of transcription factor mediated cell reprogramming: conversion of liver to pancreas

Transdifferentiation is a type of cellular reprogramming involving the conversion of one differentiated cell type to another. This remarkable phenomenon holds enormous promise for the field of regenerative medicine. Over the last 20 years techniques used to reprogram cells to alternative identities have advanced dramatically. Cellular identity is determined by the transcriptional profile which comprises the subset of mRNAs, and therefore proteins, being expressed by a cell at a given point in time. A better understanding of the levers governing transcription factor activity benefits our ability to generate therapeutic cell types at will. One well-established example of transdifferentiation is the conversion of hepatocytes to pancreatic β-cells. This cell type conversion potentially represents a novel therapy in T1D treatment. The identification of key master regulator transcription factors (which distinguish one body part from another) during embryonic development has been central in developing transdifferentiation protocols. Pdx1 is one such example of a master regulator. Ectopic expression of vector-delivered transcription factors (particularly the triumvirate of Pdx1, Ngn3 and MafA) induces reprogramming through broad transcriptional remodelling. Increasingly, complimentary cell culture techniques, which recapitulate the developmental microenvironment, are employed to coax cells to adopt new identities by indirectly regulating transcription factor activity via intracellular signalling pathways. Both transcription factor-based reprogramming and directed differentiation approaches ultimately exploit transcription factors to influence cellular identity. Here, we explore the evolution of reprogramming and directed differentiation approaches within the context of hepatocyte to β-cell transdifferentiation focussing on how the introduction of new techniques has improved our ability to generate β-cells.

Hypoxic Preconditioning Induces Neuronal Differentiation of Infrapatellar Fat Pad Stem Cells through Epigenetic Alteration

Hypoxia is considered a key factor in cellular differentiation and proliferation, particularly during embryonic development; the process of early neurogenesis also occurs under hypoxic conditions. Apart from these developmental processes, hypoxia preconditioning or mild hypoxic sensitization develops resistance against ischemic stroke in deteriorating tissues. We therefore hypothesized that neurons resulting from hypoxia-regulated neuronal differentiation could be the best choice for treating brain ischemia, which contributes to neurodegeneration. In this study, infrapatellar fat pad (IFP), an adipose tissue present beneath the knee joint, was used as the stem cell source. IFP-derived stem cells (IFPSCs) are totally adherent and are mesenchymal stem cells. The transdifferentiation protocol involved hypoxia preconditioning, the use of hypoxic-conditioned medium, and maintenance in maturation medium with α-lipoic acid. The differentiated cells were characterized using microscopy, reverse transcription PCR, real time PCR, and immunocytochemistry. To evaluate the epigenetic reprogramming of IFPSCs to become neuron-like cells, methylation microarrays were performed. Hypoxia preconditioning stabilized and allowed for the translocation of hypoxia inducible factor 1α into the nucleus and induced achaete-scute homologue 1 and doublecortin expression. Following induction, the resultant cells expressed neuronal markers neuron-specific enolase, neurofilament-light chain, growth associated protein 43, synaptosome associated protein 25, and β-III tubulin. The differentiated neural-lineage cells had functional gene expression pertaining to neurotransmitters, their release, and their receptors. The molecular signaling mechanisms regulated developmental neurogenesis. Furthermore, the in vitro physiological condition regulated neurotransmitter respecification or switching during IFPSC differentiation to neurons. Thus, differentiated neurons were fabricated against the ischemic region to treat neurodegenerative diseases.

Niche Modulation of IGF-1R Signaling: Its Role in Stem Cell Pluripotency, Cancer Reprogramming, and Therapeutic Applications

Stem cells work with their niches harmoniously during development. This concept has been extended to cancer pathology for cancer stem cells (CSCs) or cancer reprogramming. IGF-1R, a classical survival signaling, has been shown to regulate stem cell pluripotency, CSCs, or cancer reprogramming. The mechanism underlying such cell fate determination is unclear. We propose the determination is due to different niches in embryo development and tumor malignancy which modulate the consequences of IGF-1R signaling. Here we highlight the modulations of these niche parameters (hypoxia, inflammation, extracellular matrix), and the targeted stem cells (embryonic stem cells, germline stem cells, and mesenchymal stem cells) and CSCs, with relevance to cancer reprogramming. We organize known interaction between IGF-1R signaling and distinct niches in the double-sided cell fate with emerging trends highlighted. Based on these new insights, we propose that, through targeting IGF-1R signaling modulation, stem cell therapy and cancer stemness treatment can be further explored.

Symbiotic Photosynthetic Oxygenation within 3D-Bioprinted Vascularized Tissues

In this study, we present the photosynthetic oxygen (O2) supply to mammalian cells within a volumetric extracellular matrix-like construct, whereby a three-dimensional (3D)-bioprinted fugitive pattern encapsulating unicellular green algae, Chlamydomonas reinhardtii (C. reinhardtii), served as a natural photosynthetic O2-generator. The presence of bioprinted C. reinhardtii enhanced the viability and functionality of mammalian cells while reducing the hypoxic conditions within the tissues. We were able to subsequently endothelialize the hollow perfusable microchannels formed after enzymatic removal of the bioprinted C. reinhardtii-laden patterns from the matrices following the initial oxygenation period, to obtain biologically relevant vascularized mammalian tissue constructs. The feasibility of co-culture of C. reinhardtii with human cells, the printability and the enzymatic degradability of the fugitive bioink, as well as the exploration of C. reinhardtii as a natural, eco-friendly, cost-effective, and sustainable source of O2 would likely promote the development of engineered tissues, tissue models, and food for various applications.