The role of hypoxia in development of the Mammalian embryo

Physiological role for S-nitrosylation of RyR1 in skeletal muscle function and development

Excitation-contraction coupling in skeletal muscle myofibers depends upon Ca2+ release from the sarcoplasmic reticulum through the ryanodine receptor/Ca2+-release channel RyR1. The RyR1 contains ∼100 Cys thiols of which ∼30 comprise an allosteric network subject to posttranslational modification by S-nitrosylation, S-palmitoylation and S-oxidation. However, the role and function of these modifications is not understood. Although aberrant S-nitrosylation of multiple unidentified sites has been associated with dystrophic diseases, malignant hyperthermia and other myopathic syndromes, S-nitrosylation in physiological situations is reportedly specific to a single (1 of ∼100) Cys in RyR1, Cys3636 in a manner gated by pO2. Using mice expressing a form of RyR1 with a Cys3636→Ala point mutation to prevent S-nitrosylation at this site, we showed that Cys3636 was the principal target of endogenous S-nitrosylation during normal muscle function. The absence of Cys3636 S-nitrosylation suppressed stimulus-evoked Ca2+ release at physiological pO2 (at least in part by altering the regulation of RyR1 by Ca2+/calmodulin), eliminated pO2 coupling, and diminished skeletal myocyte contractility in vitro and measures of muscle strength in vivo. Furthermore, we found that abrogation of Cys3636 S-nitrosylation resulted in a developmental defect reflected in diminished myofiber diameter, altered fiber subtypes, and altered expression of genes implicated in muscle development and atrophy. Thus, our findings establish a physiological role for pO2-coupled S-nitrosylation of RyR1 in skeletal muscle contractility and development and provide foundation for future studies of RyR1 modifications in physiology and disease.

Maternal gut Bifidobacterium breve modifies fetal brain metabolism in germ-free mice

BACKGROUND

Recent advances have significantly expanded our understanding of the gut microbiome's influence on host physiology and metabolism. However, the specific role of certain microorganisms in gestational health and fetal development remains underexplored.

OBJECTIVE

This study investigates the impact of Bifidobacterium breve UCC2003 on fetal brain metabolism when colonized in the maternal gut during pregnancy.

METHODS

Germ-free pregnant mice were colonized with or without B. breve UCC2003 during pregnancy. The metabolic profiles of fetal brains were analyzed, focusing on the presence of key metabolites and the expression of critical metabolic and cellular pathways.

RESULTS

Maternal colonization with B. breve resulted in significant metabolic changes in the fetal brain. Specifically, ten metabolites, including citrate, 3-hydroxyisobutyrate, and carnitine, were reduced in the fetal brain. These alterations were accompanied by increased abundance of transporters involved in glucose and branched-chain amino acid uptake. Furthermore, supplementation with this bacterium was associated with elevated expression of critical metabolic pathways such as PI3K-AKT, AMPK, STAT5, and Wnt-β-catenin signaling, including its receptor Frizzled-7. Additionally, there was stabilization of HIF-2 protein and modifications in genes and proteins related to cellular growth, axogenesis, and mitochondrial function.

CONCLUSIONS

The presence of maternal B. breve during pregnancy plays a crucial role in modulating fetal brain metabolism and growth. These findings suggest that Bifidobacterium could modify fetal brain development, potentially offering new avenues for enhancing gestational health and fetal development through microbiota-targeted interventions.

Hypoxia-inducible factors in postnatal mouse molar dental pulp development: insights into expression patterns, localisation and metabolic pathways

Hypoxia is relevant to several physiological and pathological processes and this also applies for the tooth. The adaptive response to lowering oxygen concentration is mediated by hypoxia-inducible factors (HIFs). Since HIFs were shown to participate in the promotion of angiogenesis, stem cell survival, odontoblast differentiation and dentin formation, they may play a beneficial role in the tooth reparative processes. Although some data were generated in vitro, little is known about the in vivo context of HIFs in tooth development. In order to contribute to this field, the mouse mandibular first molar was used as a model.The expression and in situ localisation of HIFs were examined at postnatal (P) days P0, P7, P14, using RT-PCR and immunostaining. The expression pattern of a broad spectrum of hypoxia-related genes was monitored by customised PCR Arrays. Metabolic aspects were evaluated by determination of the lactate level and mRNA expression of the mitochondrial marker Nd1.The results show constant high mRNA expression of Hif1a, increasing expression of Hif2a, and very low expression of Hif3a during early postnatal molar development. In the examined period the localisation of HIFs in the nuclei of odontoblasts and the subodontoblastic layer identified their presence during odontoblastic differentiation. Additionally, the lower lactate level and higher expression of mitochondrial Nd1 in advanced development points to decreasing glycolysis during differentiation. Postnatal nuclear localisation of HIFs indicates a hypoxic state in specific areas of dental pulp as oxygen demands depend on physiological events such as crown and root dentin mineralization.

Characterizing placental pericytes: Hypoxia and proangiogenic signalling

INTRODUCTION

Pericytes wrap microvessels and interact with endothelial cells to regulate vascular growth. Though pericyte dropout has been reported in pathological human placentae and mouse models of placental pathology, there has been limited investigation of the role and function of placental pericytes in vascular health and pathology. This study aimed to investigate the angiogenic potential of human placental pericytes relative to other villous cell populations.

METHODS

Primary human placental pericytes, human umbilical vein endothelial cells (HUVEC), and BeWo cells ( ± 20 μM forskolin) were cultured in 1 % O2 or ambient air, followed by analysis of secreted angiogenic factors (ELISA). Additionally, the placental pericytes and HUVECs were co-cultured in a 3D sprouting assay to assess the capacity of pericytes to contribute to vascular sprouts.

RESULTS

1 % O2 affected secretion of angiogenic factors in placental pericytes, HUVECs, and syncytialized BeWo cells. Specifically, in placental pericytes, angiopoietin-1 (ANG1) and soluble fms-like tyrosine kinase-1 (sFLT1) were decreased, while vascular endothelial growth factor (VEGF) was increased. In HUVECS, matrix metalloproteinase-2 (MMP2), VEGF, angiopoietin-2 (ANG2), platelet-derived growth factor beta (PDGFB), placental growth factor (PlGF), and sFLT1 were increased. In syncytialized BeWo cells, VEGF, MMP2, PDGFB, PlGF, and sFLT1 secretion were increased. Placental pericytes and HUVECS colocalized to vessel sprouts in the 3-D sprouting assay.

DISCUSSION

Hypoxic conditions altered placental pericyte, endothelial, and syncytialized BeWo secretion of angiogenic factors. We speculate that pericyte dropout and, by extension, the loss of pericyte-derived angiogenic factors in hypoxic conditions may contribute to compromised fetal vascular development observed in placental pathologies.

HIF-1α is required to differentiate the neonatal Macrophage protein secretome from adults

The immune response to stress diverges with age, with neonatal macrophages implicated in tissue regeneration versus tissue scarring and maladaptive inflammation in adults. Integral to the macrophage stress response is the recognition of hypoxia and pathogen-associated molecular patterns (PAMPs), which are often coupled. The age-specific, cell-intrinsic nature of this stress response remains vague. To uncover age-defined divergences in macrophage crosstalk potential after exposure to hypoxia and PAMPs, we interrogated the secreted proteomes of neonatal versus adult macrophages via non-biased mass spectrometry. Through this approach, we newly identified age-specific signatures in the secretomes of neonatal versus adult macrophages in response to hypoxia and the prototypical PAMP, lipopolysaccharide (LPS). Neonatal macrophages secreted proteins most consistent with an anti-inflammatory, regenerative phenotype protective against apoptosis and oxidative stress, dependent on hypoxia inducible transcription factor-1α (HIF-1α). In contrast, adult macrophages secreted proteins consistent with a pro-inflammatory, glycolytic phenotypic signature consistent with pathogen killing. Taken together, these data uncover fundamental age and HIF-1α dependent macrophage responses that may be targeted to calibrate the innate immune response during stress and inflammation.

Identification of Succinate Dehydrogenase Gene Variant Carriers by Blood Biomarkers

Background

Carriers of germline pathogenic variants (PVs) in succinate dehydrogenase genes (SDHx) are at risk of developing tumors, including paragangliomas, gastrointestinal stromal tumors, and renal cell carcinomas. Early tumor detection is paramount for improved clinical outcome. Blood-based biomarkers could aid in identifying individuals with PVs early and provide functional evidence in patients with variants of unknown significance.

Methods

Blood plasma, urine, peripheral blood mononuclear cells, and erythrocytes from patients with and without SDHx PVs were investigated for central carbon metabolites. These were measured by liquid chromatography-tandem mass spectrometry and nuclear magnetic resonance spectroscopy and included among others, succinate, fumarate, α-ketoglutarate, and lactate.

Results

Plasma succinate to fumarate ratios effectively distinguished tumor-bearing and asymptomatic patients with and without SDHx PV with promising diagnostic performance (areas under the receiver operating characteristic curve 0.86-0.95), although higher levels were noted in individuals with SDHB PV. Metabolites in urine and in peripheral blood mononuclear cell extracts were largely similar between groups. Erythrocytes showed strong metabolic alterations in patients with SDHx PV compared to controls, with 8 of 13 low-molecular organic acids being significantly different (P < .05). The lactate-α-ketoglutarate-ratio of erythrocytes identified individuals with SDHx PV equally well as plasma, with a sensitivity and specificity of 92% (AUC 0.97).

Conclusion

Blood biomarkers have been underutilized for identifying carriers of SDHx PV or to validate variants of unknown significance. Our findings advocate for further investigation into a combined approach involving plasma and erythrocytes for future diagnostic strategies.

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.

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.

Transcriptional control of cardiac energy metabolism in health and disease: Lessons from animal models

Cardiac ATP production is tightly regulated in order to satisfy the evolving energetic requirements imposed by different cues during health and pathological conditions. In order to sustain high ATP production rates, cardiac cells are endowed with a vast mitochondrial network that is essentially acquired during the perinatal period. Nevertheless, adult cardiac cells also adapt their mitochondrial mass and oxidative function to changes in energy demand and substrate availability by fine-tuning the pathways and mitochondrial machinery involved in energy production. The reliance of cardiac cells on mitochondrial metabolism makes them particularly sensitive to alterations in proper mitochondrial function, so that deficiency in energy production underlies or precipitates the development of heart diseases. Mitochondrial biogenesis is a complex process fundamentally controlled at the transcriptional level by a network of transcription factors and co-regulators, sometimes with partially redundant functions, that ensure adequate energy supply to the working heart. Novel uncovered regulators, such as RIP140, PERM1, MED1 or BRD4 have been recently shown to modulate or facilitate the transcriptional activity of the PGC-1s/ERRs/PPARs regulatory axis, allowing cardiomyocytes to adapt to a variety of physiological or pathological situations requiring different energy provision. In this review, we summarize the current knowledge on the mechanisms that regulate cardiac mitochondrial biogenesis, highlighting the recent discoveries of new transcriptional regulators and describing the experimental models that have provided solid evidence of the relevant contribution of these factors to cardiac function in health and disease.

Regulation of the HIF switch in human endothelial and cancer cells

Hypoxia-inducible factors (HIFs) are transcription factors that reprogram the transcriptome for cells to survive hypoxic insults and oxidative stress. They are important during embryonic development and reprogram the cells to utilize glycolysis when the oxygen levels are extremely low. This metabolic change facilitates normal cell survival as well as cancer cell survival. The key feature in survival is the transition between acute hypoxia and chronic hypoxia, and this is regulated by the transition between HIF-1 expression and HIF-2/HIF-3 expression. This transition is observed in many human cancers and endothelial cells and referred to as the HIF Switch. Here we discuss the mechanisms involved in the HIF Switch in human endothelial and cancer cells which include mRNA and protein levels of the alpha chains of the HIFs. A major continuing effort in this field is directed towards determining the differences between normal and tumor cell utilization of this important pathway, and how this could lead to potential therapeutic approaches.

Single-embryo transcriptomic atlas of oxygen response reveals the critical role of HIF-1α in prompting embryonic zygotic genome activation

Adaptive response to physiological oxygen levels (physO2; 5% O2) enables embryonic survival in a low-oxygen developmental environment. However, the mechanism underlying the role of physO2 in supporting preimplantation development, remains elusive. Here, we systematically studied oxygen responses of hallmark events in preimplantation development. Focusing on impeded transcriptional upregulation under atmospheric oxygen levels (atmosO2; 20% O2) during the 2-cell stage, we functionally identified a novel role of HIF-1α in promoting major zygotic genome activation by serving as an oxygen-sensitive transcription factor. Moreover, during blastocyst formation, atmosO2 impeded H3K4me3 and H3K27me3 deposition by deregulating histone-lysine methyltransferases, thus impairing X-chromosome inactivation in blastocysts. In addition, we found atmosO2 impedes metabolic shift to glycolysis before blastocyst formation, thus resulting a low-level histone lactylation deposition. Notably, we also reported an increased sex-dimorphic oxygen response of embryos upon preimplantation development. Together, focusing on genetic and epigenetic events that are essential for embryonic survival and development, the present study advances current knowledge of embryonic adaptive responses to physO2, and provides novel insight into mechanism underlying irreversibly impaired developmental potential due to a short-term atmosO2 exposure.

Embryos from Prepubertal Hyperglycemic Female Mice Respond Differentially to Oxygen Tension In Vitro

Reduced oxygen during embryo culture in human ART prevents embryo oxidative stress. Oxidative stress is also the major mechanism by which maternal diabetes impairs embryonic development. This study employed induced hyperglycemia prepubertal mice to mimic childhood diabetes to understand the effects of varying oxygen tension during in vitro embryonic development. The oocytes were fertilized and cultured at low (≈5%) oxygen (LOT) or atmospheric (≈20%) oxygen tension (HOT) for up to 96 h. Embryo development, apoptosis in blastocysts, inner cell mass (ICM) outgrowth proliferation, and Hif1α expression were assessed. Though the oocyte quality and meiotic spindle were not affected, the fertilization rate (94.86 ± 1.18 vs. 85.17 ± 2.81), blastocyst rate (80.92 ± 2.92 vs. 69.32 ± 2.54), and ICM proliferation ability (51.04 ± 9.22 vs. 17.08 ± 3.05) of the hyperglycemic embryos were significantly higher in the LOT compared to the HOT group. On the other hand, blastocysts from the hyperglycemic group, cultured at HOT, had a 1.5-fold increase in apoptotic cells compared to the control and lower Hif1α transcripts in ICM outgrowths compared to the LOT. Increased susceptibility of embryos from hyperglycemic mice to higher oxygen tension warrants the need to individualize the conditions for embryo culture systems in ART clinics, particularly when an endogenous maternal pathology affects the ovarian environment.

HIF-1α is Required to Differentiate the Neonatal Macrophage Secretome from Adults

The immune response to stress diverges with age, with neonatal macrophages implicated in tissue regeneration versus tissue scarring and maladaptive inflammation in adults. Integral to the macrophage stress response is the recognition of hypoxia and pathogen-associated molecular patterns (PAMPs), which are often coupled. The age-specific, cell-intrinsic nature of this stress response remains vague. To uncover age-defined divergences in macrophage crosstalk potential after exposure to hypoxia and PAMPs, we interrogated the secreted proteomes of neonatal versus adult macrophages via non-biased mass spectrometry. Through this approach, we newly identified age-specific signatures in the secretomes of neonatal versus adult macrophages in response to hypoxia and the prototypical PAMP, lipopolysaccharide (LPS). Neonatal macrophages polarized to an anti-inflammatory, regenerative phenotype protective against apoptosis and oxidative stress, dependent on hypoxia inducible transcription factor-1α ( HIF-1α). In contrast, adult macrophages adopted a pro-inflammatory, glycolytic phenotypic signature consistent with pathogen killing. Taken together, these data uncover fundamental age and HIF-1α dependent macrophage programs that may be targeted to calibrate the innate immune response during stress and inflammation.

A Novel ARNT-Dependent HIF-2α Signaling as a Protective Mechanism for Cardiac Microvascular Barrier Integrity and Heart Function Post-Myocardial Infarction

Myocardial infarction (MI) significantly compromises the integrity of the cardiac microvascular endothelial barrier, leading to enhanced leakage and inflammation that contribute to the progression of heart failure. While HIF2α is highly expressed in cardiac endothelial cells (ECs) under hypoxic conditions, its role in regulating microvascular endothelial barrier function during MI is not well understood. In this study, we utilized mice with a cardiac-specific deletion of HIF2α, generated through an inducible Cre (Cdh5Cre-ERT2) recombinase system. These mice exhibited no apparent phenotype under normal conditions. However, following left anterior descending (LAD) artery ligation-induced MI, they showed increased mortality associated with enhanced cardiac vascular leakage, inflammation, worsened cardiac function, and exacerbated heart remodeling. These outcomes suggest a protective role for endothelial HIF2α in response to cardiac ischemia. Parallel investigations in human cardiac microvascular endothelial cells (CMVECs) revealed that loss of ecHif2α led to diminished endothelial barrier function, characterized by reduced tight-junction protein levels and increased cell death, along with elevated expression of IL6 and other inflammatory markers. These effects were substantially reversed by overexpressing ARNT, a critical dimerization partner for HIF2α during hypoxia. Additionally, ARNT deletion also led to increased CMVEC permeability. Interestingly, ARNT, rather than HIF2α itself, directly binds to the IL6 promoter to suppress IL6 expression. Our findings demonstrate the critical role of endothelial HIF2α in response to MI and identify the HIF2α/ARNT axis as a transcriptional repressor, offering novel insights for developing therapeutic strategies against heart failure following MI.

Protein neddylation and its role in health and diseases

NEDD8 (Neural precursor cell expressed developmentally downregulated protein 8) is an ubiquitin-like protein that is covalently attached to a lysine residue of a protein substrate through a process known as neddylation, catalyzed by the enzyme cascade, namely NEDD8 activating enzyme (E1), NEDD8 conjugating enzyme (E2), and NEDD8 ligase (E3). The substrates of neddylation are categorized into cullins and non-cullin proteins. Neddylation of cullins activates CRLs (cullin RING ligases), the largest family of E3 ligases, whereas neddylation of non-cullin substrates alters their stability and activity, as well as subcellular localization. Significantly, the neddylation pathway and/or many neddylation substrates are abnormally activated or over-expressed in various human diseases, such as metabolic disorders, liver dysfunction, neurodegenerative disorders, and cancers, among others. Thus, targeting neddylation becomes an attractive strategy for the treatment of these diseases. In this review, we first provide a general introduction on the neddylation cascade, its biochemical process and regulation, and the crystal structures of neddylation enzymes in complex with cullin substrates; then discuss how neddylation governs various key biological processes via the modification of cullins and non-cullin substrates. We further review the literature data on dysregulated neddylation in several human diseases, particularly cancer, followed by an outline of current efforts in the discovery of small molecule inhibitors of neddylation as a promising therapeutic approach. Finally, few perspectives were proposed for extensive future investigations.

HIF-1α Mediates Immunosuppression and Chemoresistance in Colorectal Cancer by Inhibiting CXCL9, -10 and -11

Uncertainty exists regarding the mechanisms by which hypoxia-inducible factors (HIFs) control CD8+T-cell migration into tumor microenvironments. Here, we found that HIF-1α knockdown or overexpression resulted in increased or decreased CXCL9, -10, and -11 expression in vitro, respectively. Gene Set Variation Analysis revealed that elevated HIF-1α levels correlated with a poor prognosis, severe pathological stage, and an absence of CD8+ T cells in the tumor microenvironment in colorectal cancer (CRC) patients. HIF-1α was inversely associated with pathways beneficial to anti-tumor immunotherapy and cytokine/chemokine function. In vivo, inhibiting HIF-1α or its upstream regulator BIRC2 significantly suppressed tumor growth and promoted CD8+ T-cell infiltration. CXCR3 neutralizing antibodies reversed these effects, implicating the involvement of CXCL9, -10, and -11/CXCR3 axis. The presence of HIF-1α weakened the upregulation of CXCL9, -10, and -11 by bleomycin and doxorubicin. Combining HIF-1α inhibition with bleomycin promoted CD8+ T-cell infiltration and tumor suppression in vivo. Moreover, doxorubicin could upregulate CXCL9, -10 and -11 by suppressing HIF-1α. Our findings highlight the potential of HIF-1α inhibition to improve CRC microenvironments and increase chemotherapy sensitivity.

Spatiotemporal development and the regulatory mechanisms of cardiac resident macrophages: Contribution in cardiac development and steady state

Cardiac resident macrophages (CRMs) are integral components of the heart and play significant roles in cardiac development, steady-state, and injury. Advances in sequencing technology have revealed that CRMs are a highly heterogeneous population, with significant differences in phenotype and function at different developmental stages and locations within the heart. In addition to research focused on diseases, recent years have witnessed a heightened interest in elucidating the involvement of CRMs in heart development and the maintenance of cardiac function. In this review, we primarily concentrated on summarizing the developmental trajectories, both spatial and temporal, of CRMs and their impact on cardiac development and steady-state. Moreover, we discuss the possible factors by which the cardiac microenvironment regulates macrophages from the perspectives of migration, proliferation, and differentiation under physiological conditions. Gaining insight into the spatiotemporal heterogeneity and regulatory mechanisms of CRMs is of paramount importance in comprehending the involvement of macrophages in cardiac development, injury, and repair, and also provides new ideas and therapeutic methods for treating heart diseases.

Sex differences in fetal kidney reprogramming: the case in the renin-angiotensin system

During the early stages of the development of the living multiorgan systems, genome modifications other than sequence variation occur that guide cell differentiation and organogenesis. These modifications are known to operate as a fetal programming code during this period, and recent research indicates that there are some tissue-specific codes in organogenesis whose effects may persist after birth until adulthood. Consequently, the events that disrupt the pre-established epigenetic pattern could induce shifts in organ physiology, with implications on health from birth or later in adult life. Chronic kidney disease (CKD) is one of the main causes of mortality worldwide; its etiology is multifactorial, but diabetes, obesity, and hypertension are the main causes of CKD in adults, although there are other risk factors that are mainly associated with an individual's lifestyle. Recent studies suggest that fetal reprogramming in the developing kidney could be implicated in the susceptibility to kidney disease in both childhood and adulthood. Some epigenetic modifications, such as genome methylation status, dysregulation of miRNA, and histone coding alterations in genes related to the regulation of the renin-angiotensin axis, a common denominator in CKD, may have originated during fetal development. This review focuses on epigenetic changes during nephrogenesis and their repercussions on kidney health and disease. In addition, the focus is on the influence of environmental factors during pregnancy, such as maternal metabolic diseases and dietary and metabolic conditions, as well as some sex differences in fetal kidney reprogramming during which dysregulation of the renin-angiotensin system is involved.

The role of metabolism in cardiac development

Metabolism is the fundamental process that sustains life. The heart, in particular, is an organ of high energy demand, and its energy substrates have been studied for more than a century. In recent years, there has been a growing interest in understanding the role of metabolism in the early differentiation of pluripotent stem cells and in cancer research. Studies have revealed that metabolic intermediates from glycolysis and the tricarboxylic acid cycle act as co-factors for intracellular signal transduction, playing crucial roles in regulating cell behaviors. Mitochondria, as the central hub of metabolism, are also under intensive investigation regarding the regulation of their dynamics. The metabolic environment of the fetus is intricately linked to the maternal metabolic status, and the impact of the mother's nutrition and metabolic health on fetal development is significant. For instance, it is well known that maternal diabetes increases the risk of cardiac and nervous system malformations in the fetus. Another notable example is the decrease in the risk of neural tube defects when pregnant women are supplemented with folic acid. These examples highlight the profound influence of the maternal metabolic environment on the fetal organ development program. Therefore, gaining insights into the metabolic environment within developing fetal organs is critical for deepening our understanding of normal organ development. This review aims to summarize recent findings that build upon the historical recognition of the environmental and metabolic factors involved in the developing embryo.

The Prl3d1-Cre mouse line selectively induces the expression of Cre recombinase in parietal trophoblast giant cells

The placenta plays a pivotal role in the maintenance of normal pregnancy, but how it forms, matures, and performs its function remains poorly understood. Here, we describe a novel mouse line (Prl3d1-iCre) that expresses iCre recombinase under the control of the endogenous prl3d1 promoter. Prl3d1 has been proposed as a marker for distinguishing trophoblast giant cells (TGCs) from other trophoblast cells in the placenta. The in vivo efficiency and specificity of the Cre line were analyzed by interbreeding Prl3d1-iCre mice with B6-G/R reporter mice. Through anatomical studies of the placenta and other tissues of Prl3d1-iCre/+; B6-G/R mouse mice, we found that the tdTomato signal was expressed in parietal trophoblast giant cells (P-TGCs). Thus, we report a mouse line with ectopic Cre expression in P-TGCs, which provides a valuable tool for studying human pathological pregnancies caused by implantation failure or abnormal trophoblast secretion due to aberrant gene regulation.

Bifunctional tissue-engineered composite construct for bone regeneration: The role of copper and fibrin

Bifunctional tissue engineering constructs promoting osteogenesis and angiogenesis are essential for bone regeneration. Metal ion-incorporated scaffolds and fibrin encapsulation attract much attention due to low cost, nontoxicity, and tunable control over ion and growth factor release. Herein, we investigated the effect of Cu.nHA/Cs/Gel scaffold and fibrin encapsulation on osteogenic and angiogenic differentiation of Wharton's jelly mesenchymal stem cells (WJMSCs) in vitro and in vivo. Cu-laden scaffolds were synthesized using salt leaching/freeze drying and were characterized using standard techniques. WJMSCs were isolated from the human umbilical cord and characterized. WJMSCs with or without encapsulating in fibrin were seeded onto scaffolds, followed by differentiating into the osteogenic lineage for 7 and 21 days. Osteogenic and angiogenic differentiation were evaluated using real-time polymerase chain reaction, western blot, and Alizarin red staining. Then, scaffolds were implanted into critical-sized calvarial bone defects in rats and histological assessments were performed using hematoxylin/eosin, Masson's trichrome, and CD31 immunohistochemical staining at 4 and 12 weeks. The scaffolds had good physicochemical and biological characteristics suitable for cell attachment and growth. Cu and fibrin increased the expression of ALP, RUNX2, OCN, COLI, VEGF, and HIF1α in differentiated WJMSCs. Implanted scaffolds were also biocompatible and were integrated well with the host tissue. Increased collagen condensation, mineralization, and blood vessel formation were observed in Cu-laden scaffolds. The fibrin-encapsulated groups showed the highest collagen and cell densities, immune cell infiltration, and bone trabeculae. CD31-positive cell population increased with fibrin encapsulation and seeding onto Cu-laden scaffolds. Adding Cu to scaffolds and encapsulating cells in fibrin are promising methods that guide osteogenesis and angiogenesis cellular signaling, leading to better bone regeneration.

Hypoxia A Typical Target in Human Lung Cancer Therapy

Lung cancer (LC) is the leading cause of cancer-related death globally. Comprehensive knowledge of the cellular and molecular etiology of LC is perilous for the development of active treatment approaches. Hypoxia in cancer is linked with malignancy, and its phenotype is implicated in the hypoxic reaction, which is being studied as a prospective cancer treatment target. The hypervascularization of the tumor is the main feature of human LC, and hypoxia is a major stimulator of neo-angiogenesis. It was seen that low oxygen levels in human LC are a critical aspect of this lethal illness. However, as there is a considerable body of literature espousing the presumed functional relevance of hypoxia in LC, the direct measurement of oxygen concentration in Human LC is yet to be determined. This narrative review aims to show the importance and as a future target for novel research studies that can lead to the perception of LC therapy in hypoxic malignancies.

Divergence time estimates for the hypoxia-inducible factor-1 alpha (HIF1α) reveal an ancient emergence of animals in low-oxygen environments

Unveiling the tempo and mode of animal evolution is necessary to understand the links between environmental changes and biological innovation. Although the earliest unambiguous metazoan fossils date to the late Ediacaran period, molecular clock estimates agree that the last common ancestor (LCA) of all extant animals emerged ~850 Ma, in the Tonian period, before the oldest evidence for widespread ocean oxygenation at ~635-560 Ma in the Ediacaran period. Metazoans are aerobic organisms, that is, they are dependent on oxygen to survive. In low-oxygen conditions, most animals have an evolutionarily conserved pathway for maintaining oxygen homeostasis that triggers physiological changes in gene expression via the hypoxia-inducible factor (HIFa). However, here we confirm the absence of the characteristic HIFa protein domain responsible for the oxygen sensing of HIFa in sponges and ctenophores, indicating the LCA of metazoans lacked the functional protein domain as well, and so could have maintained their transcription levels unaltered under the very low-oxygen concentrations of their environments. Using Bayesian relaxed molecular clock dating, we inferred that the ancestral gene lineage responsible for HIFa arose in the Mesoproterozoic Era, ~1273 Ma (Credibility Interval 957-1621 Ma), consistent with the idea that important genetic machinery associated with animals evolved much earlier than the LCA of animals. Our data suggest at least two duplication events in the evolutionary history of HIFa, which generated three vertebrate paralogs, products of the two successive whole-genome duplications that occurred in the vertebrate LCA. Overall, our results support the hypothesis of a pre-Tonian emergence of metazoans under low-oxygen conditions, and an increase in oxygen response elements during animal evolution.

Epigenetic remodelling under hypoxia

Hypoxia is intrinsic to tumours and contributes to malignancy and metastasis while hindering the efficiency of existing treatments. Epigenetic mechanisms play a crucial role in the regulation of hypoxic cancer cell programs, both in the initial phases of sensing the decrease in oxygen levels and during adaptation to chronic lack of oxygen. During the latter, the epigenetic regulation of tumour biology intersects with hypoxia-sensitive transcription factors in a complex network of gene regulation that also involves metabolic reprogramming. Here, we review the current literature on the epigenetic control of gene programs in hypoxic cancer cells. We highlight common themes and features of such epigenetic remodelling and discuss their relevance for the development of therapeutic strategies.

HILPS, a long noncoding RNA essential for global oxygen sensing in humans

Adaptation to low levels of oxygen (hypoxia) is a universal biological feature across metazoans. However, the unique mechanisms how different species sense oxygen deprivation remain unresolved. Here, we functionally characterize a novel long noncoding RNA (lncRNA), LOC105369301, which we termed hypoxia-induced lncRNA for polo-like kinase 1 (PLK1) stabilization (HILPS). HILPS exhibits appreciable basal expression exclusively in a wide variety of human normal and cancer cells and is robustly induced by hypoxia-inducible factor 1α (HIF1α). HILPS binds to PLK1 and sequesters it from proteasomal degradation. Stabilized PLK1 directly phosphorylates HIF1α and enhances its stability, constituting a positive feed-forward circuit that reinforces oxygen sensing by HIF1α. HILPS depletion triggers catastrophic adaptation defect during hypoxia in both normal and cancer cells. These findings introduce a mechanism that underlies the HIF1α identity deeply interconnected with PLK1 integrity and identify the HILPS-PLK1-HIF1α pathway as a unique oxygen-sensing axis in the regulation of human physiological and pathogenic processes.

Somatic EPAS1 Variants in Pheochromocytoma and Paraganglioma in Patients With Sickle Cell Disease

CONTEXT

Somatic EPAS1 variants account for 5% to 8% of all pheochromocytoma and paragangliomas (PPGL) but are detected in over 90% of PPGL in patients with congenital cyanotic heart disease, where hypoxemia may select for EPAS1 gain-of-function variants. Sickle cell disease (SCD) is an inherited hemoglobinopathy associated with chronic hypoxia and there are isolated reports of PPGL in patients with SCD, but a genetic link between the conditions has yet to be established.

OBJECTIVE

To determine the phenotype and EPAS1 variant status of patients with PPGL and SCD.

METHODS

Records of 128 patients with PPGL under follow-up at our center from January 2017 to December 2022 were screened for SCD diagnosis. For identified patients, clinical data and biological specimens were obtained, including tumor, adjacent non-tumor tissue and peripheral blood. Sanger sequencing of exons 9 and 12 of EPAS1, followed by amplicon next-generation sequencing of identified variants was performed on all samples.

RESULTS

Four patients with both PPGL and SCD were identified. Median age at PPGL diagnosis was 28 years. Three tumors were abdominal paragangliomas and 1 was a pheochromocytoma. No germline pathogenic variants in PPGL-susceptibility genes were identified in the cohort. Genetic testing of tumor tissue detected unique EPAS1 variants in all 4 patients. Variants were not detected in the germline, and 1 variant was detected in lymph node tissue of a patient with metastatic disease.

CONCLUSION

We propose that somatic EPAS1 variants may be acquired through exposure to chronic hypoxia in SCD and drive PPGL development. Future work is needed to further characterize this association.

Phenotypically Discordant Anomalies in Conjoined Twins: Quirks of Nature Governed by Molecular Pathways?

A multitude of additional anomalies can be observed in virtually all types of symmetrical conjoined twins. These concomitant defects can be divided into different dysmorphological patterns. Some of these patterns reveal their etiological origin through their topographical location. The so-called shared anomalies are traceable to embryological adjustments and directly linked to the conjoined-twinning mechanism itself, inherently located within the boundaries of the coalescence area. In contrast, discordant patterns are anomalies present in only one of the twin members, intrinsically distant from the area of union. These dysmorphological entities are much more difficult to place in a developmental perspective, as it is presumed that conjoined twins share identical intra-uterine environments and intra-embryonic molecular and genetic footprints. However, their existence testifies that certain developmental fields and their respective developmental pathways take different routes in members of conjoined twins. This observation remains a poorly understood phenomenon. This article describes 69 cases of external discordant patterns within different types of otherwise symmetrical mono-umbilical conjoined twins and places them in a developmental perspective and a molecular framework. Gaining insights into the phenotypes and underlying (biochemical) mechanisms could potentially pave the way and generate novel etiological visions in the formation of conjoined twins itself.

Biology and therapeutic targeting of vascular endothelial growth factor A

The formation of new blood vessels, called angiogenesis, is an essential pathophysiological process in which several families of regulators have been implicated. Among these, vascular endothelial growth factor A (VEGFA; also known as VEGF) and its two tyrosine kinase receptors, VEGFR1 and VEGFR2, represent a key signalling pathway mediating physiological angiogenesis and are also major therapeutic targets. VEGFA is a member of the gene family that includes VEGFB, VEGFC, VEGFD and placental growth factor (PLGF). Three decades after its initial isolation and cloning, VEGFA is arguably the most extensively investigated signalling system in angiogenesis. Although many mediators of angiogenesis have been identified, including members of the FGF family, angiopoietins, TGFβ and sphingosine 1-phosphate, all current FDA-approved anti-angiogenic drugs target the VEGF pathway. Anti-VEGF agents are widely used in oncology and, in combination with chemotherapy or immunotherapy, are now the standard of care in multiple malignancies. Anti-VEGF drugs have also revolutionized the treatment of neovascular eye disorders such as age-related macular degeneration and ischaemic retinal disorders. In this Review, we emphasize the molecular, structural and cellular basis of VEGFA action as well as recent findings illustrating unexpected interactions with other pathways and provocative reports on the role of VEGFA in regenerative medicine. We also discuss clinical and translational aspects of VEGFA. Given the crucial role that VEGFA plays in regulating angiogenesis in health and disease, this molecule is largely the focus of this Review.

Metabolic switches during development and regeneration

Metabolic switches are a crucial hallmark of cellular development and regeneration. In response to changes in their environment or physiological state, cells undergo coordinated metabolic switching that is necessary to execute biosynthetic demands of growth and repair. In this Review, we discuss how metabolic switches represent an evolutionarily conserved mechanism that orchestrates tissue development and regeneration, allowing cells to adapt rapidly to changing conditions during development and postnatally. We further explore the dynamic interplay between metabolism and how it is not only an output, but also a driver of cellular functions, such as cell proliferation and maturation. Finally, we underscore the epigenetic and cellular mechanisms by which metabolic switches mediate biosynthetic needs during development and regeneration, and how understanding these mechanisms is important for advancing our knowledge of tissue development and devising new strategies to promote tissue regeneration.

Beyond energy and growth: the role of metabolism in developmental signaling, cell behavior and diapause

Metabolism is crucial for development through supporting cell growth, energy production, establishing cell identity, developmental signaling and pattern formation. In many model systems, development occurs alongside metabolic transitions as cells differentiate and specialize in metabolism that supports new functions. Some cells exhibit metabolic flexibility to circumvent mutations or aberrant signaling, whereas other cell types require specific nutrients for developmental progress. Metabolic gradients and protein modifications enable pattern formation and cell communication. On an organism level, inadequate nutrients or stress can limit germ cell maturation, implantation and maturity through diapause, which slows metabolic activities until embryonic activation under improved environmental conditions.

Mild hypoxia-induced structural and functional changes of the hippocampal network

Hypoxia causes structural and functional changes in several brain regions, including the oxygen-concentration-sensitive hippocampus. We investigated the consequences of mild short-term hypoxia on rat hippocampus in vivo. The hypoxic group was treated with 16% O2 for 1 h, and the control group with 21% O2. Using a combination of Gallyas silver impregnation histochemistry revealing damaged neurons and interneuron-specific immunohistochemistry, we found that somatostatin-expressing inhibitory neurons in the hilus were injured. We used 32-channel silicon probe arrays to record network oscillations and unit activity from the hippocampal layers under anaesthesia. There were no changes in the frequency power of slow, theta, beta, or gamma bands, but we found a significant increase in the frequency of slow oscillation (2.1-2.2 Hz) at 16% O2 compared to 21% O2. In the hilus region, the firing frequency of unidentified interneurons decreased. In the CA3 region, the firing frequency of some unidentified interneurons decreased while the activity of other interneurons increased. The activity of pyramidal cells increased both in the CA1 and CA3 regions. In addition, the regularity of CA1, CA3 pyramidal cells' and CA3 type II and hilar interneuron activity has significantly changed in hypoxic conditions. In summary, a low O2 environment caused profound changes in the state of hippocampal excitatory and inhibitory neurons and network activity, indicating potential changes in information processing caused by mild short-term hypoxia.

Metformin in Gestational Diabetes Mellitus: To Use or Not to Use, That Is the Question

In recent years, there has been a dramatic increase in the number of pregnancies complicated by gestational diabetes mellitus (GDM). GDM occurs when maternal insulin resistance develops and/or progresses during gestation, and it is not compensated by a rise in maternal insulin secretion. If not properly managed, this condition can cause serious short-term and long-term problems for both mother and child. Lifestyle changes are the first line of treatment for GDM, but if ineffective, insulin injections are the recommended pharmacological treatment choice. Some guidance authorities and scientific societies have proposed the use of metformin as an alternative pharmacological option for treating GDM, but there is not yet a unanimous consensus on this. Although the use of metformin appears to be safe for the mother, concerns remain about its long-term metabolic effects on the child that is exposed in utero to the drug, given that metformin, contrary to insulin, crosses the placenta. This review article describes the existing lines of evidence about the use of metformin in pregnancies complicated by GDM, in order to clarify its potential benefits and limits, and to help clinicians make decisions about who could benefit most from this drug treatment.

Cesarean scar ectopic pregnancy: nuances in diagnosis and treatment

A cesarean scar ectopic pregnancy (CSEP) occurs when the embryo implants on the scar of a previous cesarean delivery. The number of births delivered by cesarean section has climbed by 50% over the last decade, from a nadir of 20.7% in 1996 to 32.1% in 2021. As a result, the incidence of CSEP has also increased. Because CSEP may cause serious morbidity such as life-threatening hemorrhage, uterine rupture, placental accreta spectrum, hysterectomy, and even mortality, accurate diagnosis and appropriate management of this condition are essential. This review focuses on the etiology, incidence, clinical diagnosis, and management of CSEPs.

Maternal metabolism influences neural tube closure

Changes in maternal nutrient availability due to diet or disease significantly increase the risk of neural tube defects (NTDs). Because the incidence of metabolic disease continues to rise, it is urgent that we better understand how altered maternal nutrient levels can influence embryonic neural tube development. Furthermore, primary neurulation occurs before placental function during a period of histiotrophic nutrient exchange. In this review we detail how maternal metabolites are transported by the yolk sac to the developing embryo. We discuss recent advances in understanding how altered maternal levels of essential nutrients disrupt development of the neuroepithelium, and identify points of intersection between metabolic pathways that are crucial for NTD prevention.

Erythropoietin re-wires cognition-associated transcriptional networks

Recombinant human erythropoietin (rhEPO) has potent procognitive effects, likely hematopoiesis-independent, but underlying mechanisms and physiological role of brain-expressed EPO remained obscure. Here, we provide transcriptional hippocampal profiling of male mice treated with rhEPO. Based on ~108,000 single nuclei, we unmask multiple pyramidal lineages with their comprehensive molecular signatures. By temporal profiling and gene regulatory analysis, we build developmental trajectory of CA1 pyramidal neurons derived from multiple predecessor lineages and elucidate gene regulatory networks underlying their fate determination. With EPO as 'tool', we discover populations of newly differentiating pyramidal neurons, overpopulating to ~200% upon rhEPO with upregulation of genes crucial for neurodifferentiation, dendrite growth, synaptogenesis, memory formation, and cognition. Using a Cre-based approach to visually distinguish pre-existing from newly formed pyramidal neurons for patch-clamp recordings, we learn that rhEPO treatment differentially affects excitatory and inhibitory inputs. Our findings provide mechanistic insight into how EPO modulates neuronal functions and networks.

Charting the Path: Navigating Embryonic Development to Potentially Safeguard against Congenital Heart Defects

Congenital heart diseases (CHDs) are structural or functional defects present at birth due to improper heart development. Current therapeutic approaches to treating severe CHDs are primarily palliative surgical interventions during the peri- or prenatal stages, when the heart has fully developed from faulty embryogenesis. However, earlier interventions during embryonic development have the potential for better outcomes, as demonstrated by fetal cardiac interventions performed in utero, which have shown improved neonatal and prenatal survival rates, as well as reduced lifelong morbidity. Extensive research on heart development has identified key steps, cellular players, and the intricate network of signaling pathways and transcription factors governing cardiogenesis. Additionally, some reports have indicated that certain adverse genetic and environmental conditions leading to heart malformations and embryonic death may be amendable through the activation of alternative mechanisms. This review first highlights key molecular and cellular processes involved in heart development. Subsequently, it explores the potential for future therapeutic strategies, targeting early embryonic stages, to prevent CHDs, through the delivery of biomolecules or exosomes to compensate for faulty cardiogenic mechanisms. Implementing such non-surgical interventions during early gestation may offer a prophylactic approach toward reducing the occurrence and severity of CHDs.

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.

Targeting Endothelial HIF2α/ARNT Expression for Ischemic Heart Disease Therapy

Ischemic heart disease (IHD) is a major cause of mortality and morbidity worldwide, with novel therapeutic strategies urgently needed. Endothelial dysfunction is a hallmark of IHD, contributing to its development and progression. Hypoxia-inducible factors (HIFs) are transcription factors activated in response to low oxygen levels, playing crucial roles in various pathophysiological processes related to cardiovascular diseases. Among the HIF isoforms, HIF2α is predominantly expressed in cardiac vascular endothelial cells and has a key role in cardiovascular diseases. HIFβ, also known as ARNT, is the obligate binding partner of HIFα subunits and is necessary for HIFα's transcriptional activity. ARNT itself plays an essential role in the development of the cardiovascular system, regulating angiogenesis, limiting inflammatory cytokine production, and protecting against cardiomyopathy. This review provides an overview of the current understanding of HIF2α and ARNT signaling in endothelial cell function and dysfunction and their involvement in IHD pathogenesis. We highlight their roles in inflammation and maintaining the integrity of the endothelial barrier, as well as their potential as therapeutic targets for IHD.

Glycolytic activity is required for the onset of neural plate folding during neural tube closure in mouse embryos

Physiological hypoxia is critical for placental mammalian development. However, the underlying mechanisms by which hypoxia regulates embryonic development remain unclear. We discovered that the expression of glycolytic genes partially depends on hypoxia in neuroepithelial cells of E8.25 mouse embryos. Consistent with this finding, inhibiting glycolysis during the early phase of neural tube closure (E8.0-8.5) resulted in a neural tube closure defect. In contrast, inhibiting the electron transport chain did not affect neural tube formation. Furthermore, inhibiting glycolysis affected cell proliferation, but not differentiation and survival. Inhibiting glycolysis repressed the phosphorylation of myosin light chain 2, and consequent neural plate folding. Our findings revealed that anaerobic glycolysis regulates neuroepithelial cell proliferation and apical constriction during the early phase of neural tube closure.

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.

HIF and MYC signaling in adrenal neoplasms of the neural crest: implications for pediatrics

Pediatric neural crest-derived adrenal neoplasms include neuroblastoma and pheochromocytoma. Both entities are associated with a high degree of clinical heterogeneity, varying from spontaneous regression to malignant disease with poor outcome. Increased expression and stabilization of HIF2α appears to contribute to a more aggressive and undifferentiated phenotype in both adrenal neoplasms, whereas MYCN amplification is a valuable prognostic marker in neuroblastoma. The present review focuses on HIF- and MYC signaling in both neoplasms and discusses the interaction of associated pathways during neural crest and adrenal development as well as potential consequences on tumorigenesis. Emerging single-cell methods together with epigenetic and transcriptomic analyses provide further insights into the importance of a tight regulation of HIF and MYC signaling pathways during adrenal development and tumorigenesis. In this context, increased attention to HIF-MYC/MAX interactions may also provide new therapeutic options for these pediatric adrenal neoplasms.

The critical role of cardiolipin in metazoan differentiation, development, and maturation

Cardiolipins are phospholipids that are central to proper mitochondrial functioning. Because mitochondria play crucial roles in differentiation, development, and maturation, we would also expect cardiolipin to play major roles in these processes. Indeed, cardiolipin has been implicated in the mechanism of three human diseases that affect young infants, implying developmental abnormalities. In this review, we will: (1) Review the biology of cardiolipin; (2) Outline the evidence for essential roles of cardiolipin during organismal development, including embryogenesis and cell maturation in vertebrate organisms; (3) Place the role(s) of cardiolipin during embryogenesis within the larger context of the roles of mitochondria in development; and (4) Suggest avenues for future research.

VBP1 negatively regulates CHIP and selectively inhibits the activity of hypoxia-inducible factor (HIF)-1α but not HIF-2α

Hypoxia-inducible factor-1 (HIF-1) is a critical transcription factor that regulates expression of genes involved in cellular adaptation to low oxygen levels. Aberrant regulation of the HIF-1 signaling pathway is linked to various human diseases. Previous studies have established that HIF-1α is rapidly degraded in a von Hippel-Lindau protien (pVHL)-dependent manner under normoxic conditions. In this study, we find that pVHL binding protein 1 (VBP1) is a negative regulator of HIF-1α but not HIF-2α using zebrafish as an in vivo model and in vitro cell culture models. Deletion of vbp1 in zebrafish caused Hif-1α accumulation and upregulation of Hif target genes. Moreover, vbp1 was involved in induction of hematopoietic stem cells (HSCs) under hypoxic conditions. However, VBP1 interacted with and promoted the degradation of HIF-1α in a pVHL-independent manner. Mechanistically, we identify the ubiquitin ligase CHIP and HSP70 as new VBP1 binding partners, and demonstrate that VBP1 negatively regulated CHIP and facilitated CHIP-mediated degradation of HIF-1α. In patients with clear cell renal cell carcinoma (ccRCC), lower VBP1 expression was associated with worse survival outcomes. In conclusion, our results link VBP1 with CHIP stability and provide insights into underlying molecular mechanisms of HIF-1α-driven pathological processes.

Umbilical cord pH, blood gases, and lactate at birth: normal values, interpretation, and clinical utility

Normal birth is a eustress reaction, a beneficial hedonic stress with extremely high catecholamines that protects us from intrauterine hypoxia and assists in the rapid shift to extrauterine life. Occasionally the cellular O2 requirement becomes critical and an O2 deficit in blood (hypoxemia) may evolve to a tissue deficit (hypoxia) and finally a risk of organ damage (asphyxia). An increase in H+ concentration is reflected in a decrease in pH, which together with increased base deficit is a proxy for the level of fetal O2 deficit. Base deficit (or its negative value, base excess) was introduced to reflect the metabolic component of a low pH and to distinguish from the respiratory cause of a low pH, which is a high CO2 concentration. Base deficit is a theoretical estimate and not a measured parameter, calculated by the blood gas analyzer from values of pH, the partial pressure of CO2, and hemoglobin. Different brands of analyzers use different calculation equations, and base deficit values can thus differ by multiples. This could influence the diagnosis of metabolic acidosis, which is commonly defined as a pH <7.00 combined with a base deficit ≥12.0 mmol/L in umbilical cord arterial blood. Base deficit can be calculated as base deficit in blood (or actual base deficit) or base deficit in extracellular fluid (or standard base deficit). The extracellular fluid compartment represents the blood volume diluted with the interstitial fluid. Base deficit in extracellular fluid is advocated for fetal blood because a high partial pressure of CO2 (hypercapnia) is common in newborns without concomitant hypoxia, and hypercapnia has a strong influence on the pH value, then termed respiratory acidosis. An increase in partial pressure of CO2 causes less increase in base deficit in extracellular fluid than in base deficit in blood, thus base deficit in extracellular fluid better represents the metabolic component of acidosis. The different types of base deficit for defining metabolic acidosis in cord blood have unfortunately not been noticed by many obstetrical experts and organizations. In addition to an increase in H+ concentration, the lactate production is accelerated during hypoxia and anaerobic metabolism. There is no global consensus on definitions of normal cord blood gases and lactate, and different cutoff values for abnormality are used. At a pH <7.20, 7% to 9% of newborns are deemed academic; at <7.10, 1% to 3%; and at <7.00, 0.26% to 1.3%. From numerous studies of different eras and sizes, it can firmly be concluded that in the cord artery, the statistically defined lower pH limit (mean -2 standard deviations) is 7.10. Given that the pH for optimal enzyme activity differs between different cell types and organs, it seems difficult to establish a general biologically critical pH limit. The blood gases and lactate in cord blood change with the progression of pregnancy toward a mixed metabolic and respiratory acidemia because of increased metabolism and CO2 production in the growing fetus. Gestational age-adjusted normal reference values have accordingly been published for pH and lactate, and they associate with Apgar score slightly better than stationary cutoffs, but they are not widely used in clinical practice. On the basis of good-quality data, it is reasonable to set a cord artery lactate cutoff (mean +2 standard deviations) at 10 mmol/L at 39 to 40 weeks' gestation. For base deficit, it is not possible to establish statistically defined reference values because base deficit is calculated with different equations, and there is no consensus on which to use. Arterial cord blood represents the fetus better than venous blood, and samples from both vessels are needed to validate the arterial origin. A venoarterial pH gradient of <0.02 is commonly used to differentiate arterial from venous samples. Reference values for pH in cord venous blood have been determined, but venous blood comes from the placenta after clearance of a surplus of arterial CO2, and base deficit in venous blood then overestimates the metabolic component of fetal acidosis. The ambition to increase neonatal hemoglobin and iron depots by delaying cord clamping after birth results in falsely acidic blood gas and lactate values if the blood sampling is also delayed. Within seconds after birth, sour metabolites accumulated in peripheral tissues and organs will flood into the central circulation and further to the cord arteries when the newborn starts to breathe, move, and cry. This influence of "hidden acidosis" can be avoided by needle puncture of unclamped cord vessels and blood collection immediately after birth. Because of a continuing anaerobic glycolysis in the collected blood, it should be analyzed within 5 minutes to not result in a falsely high lactate value. If the syringe is placed in ice slurry, the time limit is 20 minutes. For pH, it is reasonable to wait no longer than 15 minutes if not in ice. Routine analyses of cord blood gases enable perinatal audits to gain the wisdom of hindsight, to maintain quality assurance at a maternity unit over years by following the rate of neonatal acidosis, to compare results between hospitals on regional or national bases, and to obtain an objective outcome measure in clinical research. Given that the intrapartum cardiotocogram is an uncertain proxy for fetal hypoxia, and there is no strong correlation between pathologic cardiotocograms and fetal acidosis, a cord artery pH may help rather than hurt a staff person subjected to a malpractice suit based on undesirable cardiotocogram patterns. Contrary to common beliefs and assumptions, up to 90% of cases of cerebral palsy do not originate from intrapartum events. Future research will elucidate whether cell injury markers with point-of-care analysis will become valuable in improving the dating of perinatal injuries and differentiating hypoxic from nonhypoxic injuries.

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

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

Physiological and molecular responses to hypoxia stress in Manila clam Ruditapes philippinarum

Hypoxia has become one of the major environmental problems in the aquaculture industry. As one of the most commercially important bivalves, Manila clam Ruditapes philippinarum may be suffering substantial mortality attributable to hypoxia. The physiological and molecular responses to hypoxia stress in Manila clam were evaluated at two levels of low dissolved oxygen: 0.5 mg/L (DO 0.5 mg/L) and 2.0 mg/L (DO 2.0 mg/L). With the prolongation of hypoxia stress, the mortality rate was 100% at 156 h under DO 0.5 mg/L. In contrast, 50% of clams survived after 240 h of stress at DO 2.0 mg/L. After the hypoxia stress, some severe structural damages were observed in gill, axe foot, hepatopancreas tissues, such as cell rupture and mitochondrial vacuolization. For the hypoxia-stressed clams, the significant rise and decline of enzyme activity (LDH and T-AOC) was observed in gills, in contrast to the reduction of glycogen content. Furthermore, the expression levels of genes related to energy metabolism (SDH, PK, Na⁺/K⁺-ATPase, NF-κB and HIF-1α) was significantly affected by the hypoxia stress. It is therefore suggested that the short-term survival of clams under hypoxia may be dependent on stress protection by antioxidants, energy allocation, and tissue energy reserves (such as glycogen stores). Despite this, the prolongation of hypoxia stress at DO 2.0 mg/L may cause the irreversible damages of cellular structures in clam tissues, eventually leading to the death of clams. We therefore support the hypothesis that the extent of hypoxia impacts on marine bivalves may be underestimated in the coastal areas.

Hypoxia-Inducible Factor-2α Signaling in the Skeletal System

Hypoxia-inducible factors (HIFs) are oxygen-dependent heterodimeric transcription factors that mediate molecular responses to reductions in cellular oxygen (hypoxia). HIF signaling involves stable HIF-β subunits and labile, oxygen-sensitive HIF-α subunits. Under hypoxic conditions, the HIF-α subunit is stabilized, complexes with nucleus-confined HIF-β subunit, and transcriptionally regulates hypoxia-adaptive genes. Transcriptional responses to hypoxia include altered energy metabolism, angiogenesis, erythropoiesis, and cell fate. Three isoforms of HIF-α-HIF-1α, HIF-2α, and HIF-3α-are found in diverse cell types. HIF-1α and HIF-2α serve as transcriptional activators, whereas HIF-3α restricts HIF-1α and HIF-2α. The structure and isoform-specific functions of HIF-1α in mediating molecular responses to hypoxia are well established across a wide range of cell and tissue types. The contributions of HIF-2α to hypoxic adaptation are often unconsidered if not outrightly attributed to HIF-1α. This review establishes what is currently known about the diverse roles of HIF-2α in mediating the hypoxic response in skeletal tissues, with specific focus on development and maintenance of skeletal fitness. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Functional exploration of SNP mutations in HIF2αb gene correlated with hypoxia tolerance in blunt snout bream (Megalobrama amblycephala)

Blunt snout bream (Megalobrama amblycephala) is sensitive to hypoxia environment. Hypoxia-inducible factor (HIF) is the most critical factor in the HIF pathway, which strictly regulates the hypoxia stress process of fish. In this study, we found six hifα genes in blunt snout bream that demonstrated different expressions under hypoxia conditions. In HEK293T cells, all six hifαs were detected to activate the HRE region by luciferase reporter assay. More importantly, we identified two linkage-disequilibrium SNP sites at exon 203 and 752 of the hif2αb gene in blunt snout bream. Haplotype II (A²⁰³A⁷⁵²) and its homozygous diplotype II (A²⁰³A²⁰³A⁷⁵²A⁷⁵²) appeared frequently in a selected strain of blunt snout bream with hypoxia tolerance. Diplotype II has a lower oxygen tension threshold for loss of equilibrium (LOE_crit) over a similar range of temperatures. Moreover, its erythrocyte number increased significantly (p < 0.05) than those in diplotype I and diplotype III strains at 48 h of hypoxia. The enzymes related with hypoxia tolerant traits, i.e., reduced glutathione, superoxide dismutase, and catalase, were also significantly (p < 0.05) induced in diplotype II than in diplotype I or III. In addition, the expression of epo in the liver of diplotype II was significantly (p < 0.01) higher than that in the diplotype I or III strains at 48 h of hypoxia. Taken together, our results found that the hypoxia-tolerant-related diplotype II of hif2αb has the potential to be used as a molecular marker in future genetic breeding of hypoxia-tolerant strain.

Comparative transcriptomic analysis and genome-wide characterization of the Semaphorin family reveal the potential mechanism of angiogenesis around embryo in ovoviviparous black rockfish (Sebastes schlegelii)

To guarantee the quality and survival rate of their offspring, ovoviviparous teleost evolved special characteristics of in vivo fertilization and embryo development. Maternal black rockfish, having over 50 thousand embryos developing within the ovary simultaneously, provided around 40% nutrition throughout oocyte development, while the capillaries around each embryo contributed the rest 60% during pregnancy. Since fertilization, capillaries started to proliferate and developed into a placenta-like structure that covered over half of each embryo. Aimed to characterize the potential mechanism behind, comparative transcriptome analysis of samples collected according to the process of pregnancy. Three important time point in the process, including mature oocyte stage, fertilization and sarcomere period, were chosen for the transcriptome sequencing. Our study identified key pathways and genes involved in the cell cycle as well as DNA replication and repair, cell migration and adhesion, immune, and metabolic functions. Notably, several of the semaphoring gene family members were differently expressed. To confirm the accuracy of these genes, total of 32 sema genes were identified from the whole genome and distinct expression pattern of sema genes was observed in different pregnant stages. Our results revealed a novel insight for further investigating the functions of sema genes in reproduction physiology and embryo processes in ovoviviparous teleost.

Direct Effects of Mifepristone on Mice Embryogenesis: An In Vitro Evaluation by Single-Embryo RNA Sequencing Analysis

The clinical use of mifepristone for medical abortions has been established in 1987 in France and since 2000 in the United States. Mifepristone has a limited medical period that lasts <9 weeks of gestation, and the incidence of mifepristone treatment failure increases with gestation time. Mifepristone functions as an antagonist for progesterone and glucocorticoid receptors. Studies have confirmed that mifepristone treatments can directly contribute to endometrium disability by interfering with the endometrial receptivity of the embryo, thus causing decidual endometrial degeneration. However, whether mifepristone efficacy directly affects embryo survival and growth is still an open question. Some women choose to continue their pregnancy after mifepristone treatment fails, and some women express regret and seek medically unapproved mifepristone antagonization with high doses of progesterone. These unapproved treatments raise the potential risk of embryonic fatality and developmental anomalies. Accordingly, in the present study, we collected mouse blastocysts ex vivo and treated implanted blastocysts with mifepristone for 24 h. The embryos were further cultured to day 8 in vitro to finish their growth in the early somite stage, and the embryos were then collected for RNA sequencing (control n = 3, mifepristone n = 3). When we performed a gene set enrichment analysis, our data indicated that mifepristone treatment considerably altered the cellular pathways of embryos in terms of viability, proliferation, and development. The data indicated that mifepristone was involved in hallmark gene sets of protein secretion, mTORC1, fatty acid metabolism, IL-2-STAT5 signaling, adipogenesis, peroxisome, glycolysis, E2F targets, and heme metabolism. The data further revealed that mifepristone interfered with normal embryonic development. In sum, our data suggest that continuing a pregnancy after mifepristone treatment fails is inappropriate and infeasible. The results of our study reveal a high risk of fetus fatality and developmental problems when pregnancies are continued after mifepristone treatment fails.