Exacerbated deep-water hypoxia, brought about by anthropogenic-derived dissolved organic carbon (DOC) input, has potentially detrimental impacts on organisms residing in freshwater ecosystems. Oxygenation of the water column is a potential management strategy to mitigate this impact, and used to alleviate DOC induced oxygen depletion. In this thesis, I investigated the effects of hypolimnic oxygenation on benthic macroinvertebrate and zooplankton biomass and size assemblages in an experimental dystrophic lake. The experiment, which took place between 2017-2020 in a dystrophic brown-water lake consisting of two interconnected basins, was performed according to a Before-After-Control-Impact design. One basin was continuously monitored under reference conditions while the oxygen concentrations of the other basin was experimentally increased halfway through the experimental period. Macroinvertebrates were sampled from the epi-, meta- and hypolimnion while zooplankton were sampled from throughout the water column (0-6 m) and, during 2020, also the hypolimnion (3-6 m) separately. Collected macroinvertebrate and zooplankton samples were analyzed for biomass, chironomid body lengths and zooplankton community compositions per basin and treatment. Mean benthic biomass, chironomid biomass and chironomid body length increased in response to oxygenation in the hypolimnion but no effect was found in the epi- or metalimnion habitats. Observed biomass responses were mainly driven by the increase in chironomid biomass. No differences were found in neither zooplankton community assemblages nor biomass following oxygenation. These results suggest that the lack of oxygen-rich habitats act as a major limiting factor for hypolimnic macroinvertebrates and especially for chironomids. Zooplankton, on the other hand, appear to be limited by resource availability as opposed to the abundance of suitable, oxygen-rich habitats only. The results suggest that oxygenation may have clear benefits for deep-water macroinvertebrates. However, as a management tool, it is ineffective as a means to increase zooplankton abundances.

Adaptation to variations in oxygen concentration is a conserved mechanism in all metazoans as this process is central for the maintenance of cell and tissue homeostasis. Two major and highly conserved processes contribute to hypoxia-induced gene reprogramming. The first one relies on the transcriptional activation of gene expression by the Hypoxia Inducible Factors (HIFs) leading to the upregulation of a large panel of genes. The second one corresponds to a strong modification of the translation program. While the mechanisms underlying HIF-dependent transcriptional activation have been well characterized, the ones governing translation reprogramming are only partially understood. 
To uncover how mRNA translation takes place at low oxygen tension, we used Drosophila as our research model since both Drosophila flies and S2 cells are highly resistant to low O2. We first demonstrate that several genes are efficiently translated under hypoxia in Drosophila S2 cells. By a gene reporter-based approach, we demonstrate that Ldh mRNA 3’UTR is sufficient to promote reporter mRNA association to polysomes in hypoxia. A deletion analysis of Ldh 3’UTR leads to the identification of a ACAAA-rich sequence important for polysomal association and translation in hypoxia.Cap-binding factors play a key role in controlling translational initiation. We have shown that the cap-binding translation initiation factor eIF4EHP (4EHP) plays a dual role on translation under hypoxic conditions. Despite having a general repressive function on global translation under normoxic and hypoxic conditions, we demonstrated that 4EHP also positively controls the translation of specific mRNAs under hypoxia. Inactivation of 4ehp reduces LDH protein synthesis and impairs reporter mRNA translation in hypoxia. Deletion of 4ehp inhibites the translation of several candidate genes harboring a ACAAA motif in 3’UTR under hypoxia, suggesting that 4EHP is required for hypoxic translation of mRNAs carrying ACAAA-rich motifs. Most interestingly, we observed that 4EHP is strongly enriched in polysomal fractions in hypoxia, further supporting a role of this initiation factor in hypoxic translation. The reduction of 4ehp expression also impairs Drosophila development under hypoxic conditions. Taken together, our results indicate that specific mRNAs can bypass the translational blockade imposed by hypoxic conditions. This process is controlled by mRNA 3’UTR “CA” rich element and is positively regulated by the translation initiation factor 4EHP. / L'adaptation aux variations de la concentration en oxygène est un mécanisme conservé chez tous les métazoaires car ce processus est central pour le maintien de l'homéostasie cellulaire et tissulaire. Deux processus hautement conservés contribuent à la reprogrammation génétique induite par l'hypoxie. Le premier repose sur l'activation transcriptionnelle de l'expression génique par les facteurs inductibles de l'hypoxie (HIF) conduisant à l’induction d'un large panel de gènes. Le second correspond à une forte modification du programme traductionnel. Alors que les mécanismes sous-jacents à l'activation transcriptionnelle dépendante de HIF ont été bien caractérisés, ceux qui régissent la reprogrammation de la traduction ne sont que partiellement compris.Pour découvrir comment la traduction de l'ARNm se déroule à faible tension d'oxygène, nous avons utilisé la drosophile comme modèle d’étude, car les mouches Drosophila melanogaster et les cellules S2 issue de cet organisme sont très résistantes à de faibles teneurs en O2. Nous avons tout d’abord démontré que plusieurs gènes sont efficacement traduits en hypoxie dans les cellules S2 de drosophile. Par une approche basée sur l’utilisation de gènes rapporteurs, nous avons démontré que la région 3’ Non traduite (3’UTR) de l’ARNm Ldh est suffisante pour promouvoir l’association de l’ARNm du rapporteur aux polysomes en conditions hypoxiques. Une analyse par délétion de la région 3’UTR de l’ARNm Ldh a conduit à l’identification d’une séquence riche en ACAAA importante pour l’association polysomale et la traduction en hypoxie. La reconnaissance de la coiffe joue un rôle clé dans le contrôle de l'initiation de la traduction Nous avons montré que le facteur d'initiation de la traduction eIF4EHP (4EHP), qui se lie à la coiffe, joue un double rôle sur la traduction dans des conditions hypoxiques. Bien qu'il ait une fonction répressive sur la traduction générale dans des conditions normoxiques et hypoxiques, nous avons démontré que 4EHP contrôle aussi positivement la traduction d'ARNm spécifiques dans des conditions hypoxiques. L'inactivation de 4ehp réduit la synthèse de la protéine LDH et altère la traduction de l'ARNm rapporteur contenant la partir 3’UTR du messager Ldh en hypoxie. La délétion de 4ehp peut atténuer la traduction de plusieurs gènes candidats contenant un motif ACAAA dans leur région 3’UTR 3' en hypoxie, ce qui suggère que 4EHP est nécessaire pour la traduction hypoxique des ARNm portant des motifs riches en ACAAA. De façon intéressante, nous avons observé que 4EHP est fortement enrichi dans les fractions polysomales en hypoxie, ce qui confirme le rôle de ce facteur d'initiation dans la traduction en hypoxie. La réduction de l'expression de 4ehp altère également le développement de la Drosophile dans des conditions hypoxiques. Ensemble, nos résultats indiquent que des ARNm spécifiques peuvent contourner le blocage traductionnel imposé par les conditions hypoxiques. Ce processus est contrôlé par l'élément riche en "CA" situé dans la partie 3'UTR de l’ARNm et est régulé positivement par le facteur d'initiation de la traduction 4EHP. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

The naked mole-rat possesses several unique physiological and molecular features that underlie their remarkably and exceptional resistance to tissue hypoxia. Elevated pattern of Epo, an erythropoietin (Epo) factor; c-fos; vascular endothelial growth factor (VEGF); and hypoxia-inducible factors (HIF-1α) contribute to the adaptive strategy to cope with hypoxic stress. Moreover, the naked mole-rat has a lower metabolic rate than any other eutherian mammal of comparable size that has been studied. The ability to actively reduce metabolic rate represents a strategy widely used in the face of decreased tissue oxygen availability. Understanding the different molecular and physiological factors that induce metabolic suppression could guide the development of pharmacological agents for the clinical management of stroke patient.

The search for the optimal choice of treatment time, dose and fractionation regimen is one of the major challenges in radiation therapy. Several aspects of the radiation response of tumours and normal tissues give different indications of how the parameters defining a fractionation schedule should be altered relative to each other which often results in contradictory conclusions. For example, the increased sensitivity to fractionation in late-reacting as opposed to early-reacting tissues indicates that a large number of fractions is beneficial, while the issue of accelerated repopulation of tumour cells starting at about three weeks into a radiotherapy treatment would suggest as short overall treatment time as possible. Another tumour-to-normal tissue differential relevant to the sensitivity as well as the fractionation and overall treatment time is the issue of tumour hypoxia and reoxygenation. The tumour oxygenation is one of the most influential factors impacting on the outcome of many types of treatment modalities. Hypoxic cells are up to three times as resistant to radiation as well oxygenated cells, presenting a significant obstacle to overcome in radiotherapy as solid tumours often contain hypoxic areas as a result of their poorly functioning vasculature. Furthermore, the oxygenation is highly dynamic, with changes being observed both from fraction to fraction and over a time period of weeks as a result of fast and slow reoxygenation of acute and chronic hypoxia. With an increasing number of patients treated with hypofractionated stereotactic body radiotherapy (SBRT), the clinical implications of a substantially reduced number of fractions and hence also treatment time thus have to be evaluated with respect to the oxygenation status of the tumour. The perhaps most promising tool available for the type of study aiming at determining the optimal SBRT approach with respect to fractionation is radiobiological modelling. With clinically-derived tissue-specific radiobiological parameters and well-established survival models, in silico modelling offers a wide range of opportunities to test various hypotheses with respect to time, dose, fractionation and details of the tumour microenvironment. Any type of radiobiological modelling study intended to provide a realistic representation of a clinical tumour should therefore take into account details of both the spatial and temporal tumour oxygenation. This thesis, consisting of papers I-III and a summary, presents the results of three-dimensional radiobiological modelling of the response of tumours with heterogeneous oxygenation to various radiation qualities, fractionation schemes, oxygenation levels and dynamics using different survival models. The results of this work indicate that hypoxia and its dynamics play a major role in the outcome of both photon and carbon ion radiotherapy, and that neglecting the oxygenation status of tumours treated with SBRT may compromise the treatment outcome substantially. Continued to include clinical studies on the impact of hypoxia on the treatment outcome in lung cancer patients treated with SBRT, this project will hopefully advance the evolution towards routinely incorporating functional imaging of hypoxia into treatment planning. This is ultimately expected to result in increased levels of local control with more patients being cured from their cancer.

The northwestern (NW) continental shelf of the Black Sea undergoes seasonal hypoxia. The benthic environment, the exchanges at the water-sediment interface and the diagenetic reactions are influenced by this phenomenon. In the framework of the BENTHOX project, two field cruises were conducted on the shelf in spring 2016 and in summer 2017.The first part of this investigation concerned the study of the impact of low oxygen levels in bottom waters on the diagenetic reactions. The microprofilings of geochemical parameters and the flux measurements showed both spatial and temporal variabilities in the benthic compartment of the NW continental shelf for the two seasons studied. The areas closest to the coasts exhibited the most important fluxes of oxygen consumption and of sulfate. These regions were strongly influenced by riverine inputs inducing a higher productivity and in turn resulting in an increase in the fluxes of organic matter deposited on the seabed.The diagenetic reactions were impacted by seasonal deoxygenation in bottom waters. The oxic respiration was less important in the summer as reflected by the shallower penetration depth of dissolved oxygen. Since 1995, the diffusive oxygen uptake (DOU) reported during hypoxic period indicated that the concentration of dissolved oxygen played an important role in the benthic exchange fluxes. Furthermore, a shallower reduction of sulphate and of Mn- and Fe-oxides observed in the sediments evidenced the impact of low oxygen levels on the diagenetic cascade. As a consequence, the benthic mineralization of organic matter was affected. During summer 2017, the oxic mineralization of organic carbon was less important and the contribution of the reducing species to oxygen consumption increased. The anaerobic mineralization of organic matter became thus the dominant process during the period of deoxygenation.The second part concerned the study of the sulfur and iron cycling in the shelf sediments during the low oxygen event of summer 2017. The sediments from the station close to the mouth of the Danube and that near the Dnieper exhibited a signature of detrital material different from that of the upper crust. The inputs of organic matter, in particular transported by the rivers, could influence the signal. The sediments of the NW shelf investigated were however of marine origin.Following the sulfate reduction already observed and mentioned above, the hydrogen sulfides produced were rapidly consumed as suggested by the low concentrations of acid volatile sulfide (AVS) and of the dissolved sulfide. The presence of pyrite in the upper layers of the sediments close to the water-sediment interface was plausible because the formation of pyrite in the water column had been reported due to the higher resistance of pyrite to oxidation compared to AVS (Wijsman et al. 2001). A non steady-state deposition was observed as suggested by Wijsman et al. (1999). It was characterized by an abrupt drop in the pyrite content caused possibly by fluctuations in salinity, dissolved O2 concentrations and organic matter fluxes.The non-reactive iron constituted the principal fraction of the total iron present in the sediments. Its contribution fell in the range reported for the marine sediments of the continental margins. A spatial variation of the concentration of highly reactive iron was nevertheless observed. Near the Dnieper mouth, the contents of reactive iron were lower and could be attributed to the less important fluvial inputs, to the sorption and/or precipitation processes or yet to the reallocation of the reactive iron of the shelf deposits towards the sediments in deep and euxinic waters.The last part of this thesis concerned the biogeochemistry of metals (Fe, Mn, Zn, Cu, Ni, Hg, Co and Cd) during the early diagenesis and the assessment of enrichment and pollution of these metals in the sediments of the shelf. The results showed that trace metals are probably linked to iron and manganese oxides as well as to sulphides. Ni and Zn could be involved in adsorption onto and co-precipitation with Fe- and Mn-oxides. Cu seemed to be associated preferentially to sulphides but no clear correlation was found. The enrichment and pollution of these metals in the shelf sediments showed spatial variability. The Danube delta area was enriched in Ni, Cu and Zn while the Odessa region was enriched in Co and Cd. The pollution of shelf sediments ranged from “unpolluted” to “very highly polluted”. Since the late 20th century, the heavy metal contents in shelf sediments remained stable in the Odessa region but increased in the Danube delta area. / Le plateau continental du Nord-Ouest de la Mer Noire subit une hypoxie saisonnière. L'environnement benthique, l'échange à l'interface eau-sédiment et les réactions diagénétiques sont influencés par ce phénomène. Dans le cadre du projet BENTHOX, deux campagnes de prélèvement ont été menées sur le plateau au printemps 2016 et à l'été 2017 dans le but de comprendre ces changements.La première partie de cette recherche concerne l’impact des faibles concentrations en oxygène dans les eaux de fond sur les réactions diagénétiques. Les micro-profils de paramètres géochimiques et les mesures de flux ont montré des variabilités spatiales et temporelles dans le compartiment benthique pour les deux saisons étudiées. Les zones les plus proches des côtes ont présenté les flux les plus importants de consommation d'oxygène et de sulfate. Ces régions ont été fortement influencées par les apports fluviaux induisant une productivité plus élevée et entraînant à son tour une augmentation des flux de matière organique déposée sur le fond marin. Les réactions diagénétiques sont affectées par la désoxygénation saisonnière des eaux de fond. La respiration oxique etait moins importante en été comme en témoigne la profondeur de pénétration moins profonde de l’oxygène. Depuis 1995, l’absorption d’oxygène dissous (DOU) rapportée pendant la période limitée en oxygène a indiqué que la concentration d'oxygène dissous jouait un rôle important dans les flux d'échanges benthiques. De plus, une diminution de la profondeur à laquelle la réduction des sulfates et la réduction des oxydes métalliques témoigne de l'impact d'une faible concentration en oxygène sur la cascade diagénétique. En conséquence, la minéralisation benthique de la matière organique a été affectée. Au cours de l'été 2017, la minéralisation oxique du carbone a été moins importante et la contribution des espèces réductrices à la consommation d’oxygène a augmenté. La respiration anaérobie de la matière organique est ainsi devenue le processus dominant pendant la période d'hypoxie.La deuxième partie portait sur l'étude du cycle du soufre et du fer dans les sédiments du plateau lors de l'événement de faible teneur en oxygène de l'été 2017. Les sédiments de la station proche de l'embouchure du Danube et de celle du Dniepr présentaient une signature de matière détritique différente de celle de la croûte supérieure. Les apports de matière organique, notamment transportés par les rivières, pourraient influencer le signal. Les sédiments du plateau nord-ouest étudiés étaient cependant d'origine marine. Suite à la réduction du sulfate déjà observée et mentionnée ci-dessus, les sulfures d'hydrogène produits ont été rapidement consommés comme le suggèrent les faibles concentrations en sulfure acide volatil (AVS) et en sulfure dissous. La présence de pyrite dans les couches supérieures des sédiments près de l'interface eau-sédiment était plausible car la formation de pyrite dans la colonne d'eau avait été signalée en raison de la résistance plus élevée de la pyrite à l'oxydation par rapport à l'AVS (Wijsman et al. 2001). Un dépôt à l'état non stationnaire a été observé comme le suggèrent Wijsman et al. (1999). Elle a été caractérisée par une chute brutale de la teneur en pyrite causée peut-être par des fluctuations de salinité, des concentrations d'O2 dissous et des flux de matière organiqueLe fer non réactif constituait la fraction principale du fer total présent dans les sédiments. Sa contribution est tombée dans la gamme signalée pour les sédiments marins des marges continentales. Une variation spatiale de la concentration en fer hautement réactif a néanmoins été observée. Près de l'embouchure du Dniepr, les teneurs en fer réactif étaient plus faibles et pouvaient être attribuées aux apports fluviaux moins importants, aux processus de sorption et / ou de précipitation ou encore à la réallocation du fer réactif des dépôts du plateau vers les sédiments en profondeur et eaux euxiniques.La dernière partie de cette thèse concerne la biogéochimie des métaux (Fe, Mn, Zn, Cu, Ni, Hg, Co et Cd) lors de la diagenèse précoce et l'évaluation de l'enrichissement et de la pollution de ces métaux dans les sédiments du plateau. Les résultats ont montré que les métaux traces sont probablement liés aux oxydes de fer et de manganèse ainsi qu'aux sulfures. Ni et Zn pourraient être impliqués dans l'adsorption et la coprécipitation avec les oxydes de Fe et de Mn. Le Cu semble être associé préférentiellement aux sulfures mais aucune corrélation claire n'a été trouvée. L'enrichissement et la pollution de ces métaux dans les sédiments du plateau ont montré une variabilité spatiale. La zone du delta du Danube a été enrichie en Ni, Cu et Zn tandis que la région d'Odessa s'est enrichie en Co et Cd. La pollution des sédiments du plateau allait de « non polluée » à « très fortement polluée ». Depuis la fin du 20e siècle, la teneur en métaux lourds des sédiments du plateau est restée stable dans la région d'Odessa mais a augmenté dans la région du delta du Danube. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Brisket disease, an affliction of cattle, is important because of : (1) economic losses, (2) similarities to chronic mountain sickness in humans, and (3) the provision of experimental animals for cardiac research. In afflicted cattle, right cardiac ventricular hypertrophy and dilatation occur and are manifestations of attempted compensation for reduced alveolar oxygen by increasing pulmonary circulation. Geographic variations in occurrence of brisket disease in Utah indicate that hypoxia is not the sole causative factor. From the findings that afflicted cattle exhibit hypocalcemia and hyperkalemia, and the disease occurs most commonly in wet meadowland environments where potassium is high and calcium low in browse, a dual stress theory of cause was hypothesized; i.e., altitude-induced hypoxia plus ionic calcium-potassium imbalance. To test the hypothesis, 40 Hereford calves were randomized into four equal groups, two at 1,372 meters (normal) and two at 2,745 meters (hypoxic) elevation. At each elevation there were control (balanced) and treated (calcium-potassium) groups. For 16 weeks, treated calves received, by diet, one-fourth the calcium and 10 times the potassium requirements; also, repeated injections of dipotassium ethylenediaminetetraacetate, potassium chloride, and an aldosterone inhibitor to further induce hypocalcemia and hyperkalemia. Control groups at each elevation received a balanced diet and no injections. Since optimal myocardial function is dependent upon proper ion balance, and concentrations of calcium, potassium, sodium, phosphorus, magnesium, chloride, iron, zinc, and copper in blood, heart, liver, kidney, and bone are indices, these elements were quantitated. Calcium concentration in serum was reduced by 1.6 milligrams per 100 milliliters from an initial value of 9.4 milligrams per 100 milliliters, and an average increase of 1.8 milliequivalents per liter in potassium concentration in whole blood, from the initial concentration of 12. 4 milliequivalents per liter, occurred in treated calves . Elevation caused an increase of 1.7 milliequivalents per liter in potassium concentration in serum from the initial concentration of 6.2 milliequivalents per liter. Iron concentration in whole blood increased in response to hypoxia and decreased due to treatment. In the serum, sodium and copper decreased and chloride increased due to treatment. Compared to low elevation, significant tissue compositional changes in calves at high elevation were as follows: (l) calcium: kidney 12 percent higher, heart 9 percent lower: (2) sodium: liver 5 percent lower, kidney 3 percent higher: (2) phosphorus: kidney 2 percent higher. More profound changes occurred in cattle subjected to treatment: compared to controls, the tissue compositions in imbalanced cattle were as follows: (1) calcium: heart 10 percent and liver 13 percent lower, kidney 92 percent higher; (2) potassium: heart 13 percent higher, liver and kidney 6 percent lower; (3) sodium: heart 18 percent, liver 8 percent, and kidney 14 percent lower; (4) magnesium: heart 20 percent and liver 5 percent higher, kidney 11 percent lower; (5) phosphorus: heart 6 percent and kidney 21 percent higher, liver xvi 2 percent lower; (6) absolute dry matter: liver 5 percent and kidney 13 percent lower; (7) total ash: kidney 4 percent lower. In addition, iron, zinc, and copper were decreased in both cardiac and hepatic tissues of treated calves. Treatment influenced bone ash composition as follows: compared to controls, calcium decreased to 25.3 from 32.5 percent; phosphorus decreased to 16.5 from 19.0 percent; potassium increased to 0.16 from 0.08 percent; and zinc increased to 319 parts per million from 227 parts per million. High altitude was also influential. Compared to controls, phosphorus increased to 18.1 percent from 17.5 percent, potassium decreased to 0.112 from 0.129 percent, sodium to 1.09 from 1.17 percent, and magnesium to 0. 64 from 0.70 percent.

Glaucoma is a group of ocular disorders characterized by optic nerve damage that leads to vision loss and blindness. Damage to retinal ganglion cells (RGCs), particularly through axonal damage due to an increase in intraocular pressure (IOP), is a proposed mechanism behind glaucomatous injury. Other than increased IOP, vascular changes leading to ischemia are another explanation for glaucoma. A state of ischemia leads to a decrease in nutrients supplied to neurons of the retina and creates a hypoxic environment which is linked to cell death in both IOP- and non-IOP-related injury. Injury during glaucoma not only affects RGCs but also has secondary effects that impact the function of other cells in the retina like amacrine cells (ACs). To better understand how RGCs and ACs respond during glaucomatous injury, this study characterized the changes in viability of these cells under hypoxic conditions over time. With the use of a unique immunopanning technique, RGCs and two subpopulations of ACs (CD15+ and CD57+) were isolated from 12-week-old C57BL/6J mice and cultured for 6 to 9 days. After about a week of culturing, the three cell types were placed under either normoxic (n = 5) or hypoxic (n = 6) conditions, and cell viabilities were measured at 1-hour time intervals over 24 hours. RGC and AC isolations based on the immunopanning technique resulted in high yield and viability, confirming the findings of previous optimization studies. In response to hypoxic conditions, RGCs and the two subpopulations of ACs all experienced a decrease in cell viability over the course of 24 hours. Surprisingly, CD57+ cells showed increased susceptibility to injury and death during isolation. However, the remaining CD57+ cells that stayed alive in culture by the start of the time-course experiment were the most resilient to cell death during hypoxia, showing significantly higher cell viability compared with CD15+ and Thy1.2+ cells. The characterization of CD15+, CD57+, and Thy1.2+ cells in response to hypoxia highlights a difference in resilience across neuronal cell types in the retina. Although CD57+ exhibited greater resilience than its counterparts, the mechanism behind neuroprotection among these cells is still unknown and requires further study. / 2024-01-28T00:00:00Z

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20970号 / 医博第4316号 / 新制||医||1026(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 小川 修, 教授 戸井 雅和, 教授 万代 昌紀 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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Indiana University-Purdue University Indianapolis (IUPUI) / Hematopoietic stem (HSC) and progenitor (HSPC) cells reside in low oxygen (~1- 4%, low O2) bone marrow niches which provide critical signals for maintenance, selfrenewal, and differentiation. Exposure of HSC/HSPCs to air (~21%) for less than 10 minutes irreversibly diminishes numbers of phenotypic and functional stem cells, a phenomenon termed extra physiologic oxygen stress/shock. Yet, most studies harvest and analyze HSC/HSPCs in air and often in fixed cells, leaving endogenous signaling mechanisms unidentified. To better understand the endogenous mechanisms regulating HSCs and HSPCs, we generated the first low O2 landscape of phenotypic/functional/signaling alterations in live, low O2 harvested/sorted HSC/HSPCs utilizing novel technology. HSC (LSKCD150+) and HSC/HSPC (LSK) expression, frequency, and stem cell maintenance retention were enhanced in low O2 relative to historic data and our air data. Transcriptomics uncovered low O2 differential pathway regulation of HSC/HSPCs and HSCs with analysis identifying low O2 enrichment of genes/pathways including Ca2+ ion binding, altered sodium hydrogen (Na+/H+) activity, viral entry, and transmembrane receptor activity in both HSCs and HSPCs. In exploring the low O2 landscape, we investigated differential low O2 regulation of Ca2+ and SARS-CoV-2 related pathways/mechanisms in HSCs and HSPCs. Differential Ca2+ regulation was observed in our transcriptional/proteomic analysis corroborated by phenotypic/functional data demonstrating increases in low O2 of cytosolic and mitochondrial Ca2+ flux, ABC Transporter (ABCG2) and Na+/H+ (NHE1) expression, discovery of a novel low O2 Ca2+ high HSPC population that enhances HSC maintenance compared to Ca2+ low populations and blunting of this population and subsequent enhanced stem cell maintenance upon NHE1 inhibition (Cariporide). Multi-omics analyses also identified enhancements in COVID19-related pathways in low O2 that corresponded with enhanced expression of SARS-CoV-2 receptors/co-receptors, SARS-CoV-2 spike protein (SP) binding, and expansion of SP-bound HSC/HSPCs in low O2 compared to air, as well as enhanced stem cell maintenance of SP-bound, versus unbound, cells in low O2. Together, these data presented show low O2 harvest/retention of HSC/HSPCs enhances stem cell maintenance, which could be utilized to improve HSC expansion, and leads to differential pathway/signaling regulation of various biological pathways in HSC/HSPCs including Ca2+ and SARS-CoV-2/viral infection that results in phenotypic and functional consequences. / 2024-11-01