Browsing by Subject "Hypoxia"
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Item Carbonic anhydrase function and evolution in the respiratory gas exchange system of marine fishes(2021-08-15) Dichiera, Angelina Maria; Esbaugh, Andrew; Thomas, Peter; Brandl, Simon J; Brauner, Colin JMany marine fishes have adaptive respiratory strategies to enable sufficient oxygen (O₂) uptake, as well as the excretion of metabolically-produced carbon dioxide (CO₂). A central figure in the intertwined systems of CO₂ excretion and tissue O₂ delivery is the metalloenzyme carbonic anhydrase (CA). In my dissertation I expand, and in some cases challenge, the classical role of CA in CO₂ excretion and its emerging role in tissue O₂ extraction in both the red blood cell (RBC) and tissue membranes. I investigated the role of RBC CA in a diverse group of fishes, and demonstrated basal fishes with a membrane-bound CA isoform in their gills (branchial CA-IV) possess a low-activity RBC CA. Using site-directed mutagenesis, I restored increased function to a basal fish RBC CA to demonstrate that a single amino acid is critical for CA function. Furthermore, phylogenetic analysis suggested high-activity RBC CA may have coevolved with enhanced hemoglobin (Hb) pH sensitivity in teleosts. I explored this relationship and demonstrated RBC CA activity dictated Hb-O₂ offloading rate in almost a 1:1 manner in red drum (Sciaenops ocellatus). RBC CA is best known for its role in CO₂ excretion so this study is the first to demonstrate RBC CA may be rate-limiting for O₂ offloading as well. An additional CA isoform has recently been implicated in tissue O₂ extraction: membrane-bound CA-IV found in the red muscle, heart, and eye. With the plethora of CA-IV isoforms that function in other physiological systems (e.g. acid-base and ion regulation), I sought to define which isoforms should be studied for respiration, using publicly available membrane-bound CA sequences for a comprehensive phylogeny, and paired with tissue distribution analyses. I demonstrated functional divergence in CA-IV isoforms in which some species possess multiple CA-IV isoforms for disparate physiological functions. This highlighted CA-IVa as the primary isoform to target for future respiratory gas exchange studies. Finally, I challenged fish with low O₂ exposure (hypoxia) to understand the role CA-IV may play under environmental stress, and in contribution to whole-animal performance. While fish did not recruit CA-IV under hypoxia acclimation as predicted, they maintained CA-IV protein synthesis to theoretically sustain tissue O₂ extraction. Furthermore, hypoxia acclimation improved swim performance under control conditions; however, anaerobic rather than aerobic processes seem to be driving this performance. Overall, my work presents critical information regarding the emerging roles of CA in tissue O₂ extraction in marine fishes, providing mechanistic and evolutionary insight on the enzyme’s function in respiratory gas exchange.Item Computational modeling of tumor cell growth as a function of nutrient dynamics guided by time-resolved microscopy(2021-12-03) Yang, Jianchen (Ph. D. in biomedical engineering); Yankeelov, Thomas E.; Brock, Amy; Dunn, Andrew K; Virostko, JackThe varying and extreme nutrient conditions found in the tumor microenvironment force reprogramming of metabolism in tumor cells. This metabolic reprogramming has been identified as a hallmark of cancer. This dissertation focuses on the development and validation of an experimental-mathematical approach that predicts how the dynamics of glucose and lactate influence tumor metabolism and development. Firstly, we developed a baseline model that predicts tumor cell growth as a function of glucose availability. We employed time-resolved microscopy to track the temporal change in the number of live and dead tumor cells under different initial conditions and seeding densities. A family of mathematical models that describes the overall tumor cell growth in response to the initial glucose and confluence was constructed. The most parsimonious model selected from the family using the Akaike Information Criteria was calibrated and validated in two breast cancer cell lines (BT-474 and MDA-MB-231) and demonstrated accuracy in predicting tumor growth. Secondly, we developed noninvasive imaging of nutrient dynamics with a stable transfection of two FRET reporters, one assaying glucose concentration and one assaying lactate concentration, in the MDA-MB-231 breast cancer cell line. The FRET ratio from both reporters was found to increase with increasing concentration of the corresponding ligand and decrease over time for high initial concentration of the ligand. Significant differences in the FRET ratio corresponding to metabolic inhibition were found when cells were treated with glucose/lactate transporter inhibitors. The FRET reporters enabled us to track intracellular glucose and lactate dynamics, providing insight into tumor metabolism and response to therapy over time. Finally, we compared mechanism-based and machine learning models for predicting tumor cells growth when we introduced an inhibitor of glucose uptake as a potential treatment. We extended the baseline model to account for glucose uptake inhibition, considering both the real glucose level in the system and the glucose level accessible to tumor cells. The random forest model provided the best prediction while the mechanism-based model presented a comparable predictive capability.Item Effect of intermittent hypoxia on plasma glucose levels during an oral glucose tolerance test(2022-05-05) Massoudian, Sahar Dawn; Lalande, SophieHypoxia triggers glucose uptake independently from the action of insulin. The purpose of this study was to determine the acute effect of intermittent hypoxia, defined as alternating short bouts of breathing hypoxic and room air, on plasma glucose levels during an oral glucose tolerance test in healthy individuals. We hypothesized that exposure to intermittent hypoxia would attenuate the increase in glucose levels in response to an oral glucose tolerance test. Nine individuals (5 men, age: 24±4 years, height: 175±9 cm, weight: 71.0±13.5 kg, HbA1c: 5.4±0.1%) participated in the study. Participants visited the laboratory on two occasions. On both visits, a 2-hour oral glucose tolerance test was performed, with venous blood samples collected 0, 30, 60, 90 and 120 minutes following the ingestion of a 75 g glucose drink. On visit 1, an intermittent hypoxia (IH) protocol, consisting of eight 4-minute hypoxic cycles at a targeted arterial oxygen saturation of 80% interspersed with breathing room air to resaturation, was performed following ingestion of the glucose drink. On visit 2, an intermittent normoxia protocol consisting of eight 4-minute normoxic cycles interspersed with breathing room air was performed following ingestion of the glucose drink. Visit order was randomized and participants were blinded to the condition. As expected, intermittent hypoxia resulted in a lower arterial oxygen saturation than intermittent normoxia (IH: 83±3, IN: 98±1%, p<0.01) which corresponded to lower levels of inspired oxygen (IH: 10.9±0.7, IN: 20.9±0.3%, p<0.01). Plasma glucose responses to the oral glucose tolerance test were not different between conditions (IH vs. IN: 0: 90±7 vs. 89±6; 30: 135±21 vs. 137±24; 60: 110±28 vs. 108±25; 90: 96±18 vs. 88±14; and 120: 101±19 vs. 83±14 mg/dl, p=0.29). Intermittent hypoxia triggered an increase in cardiac output (6.1±0.9 to 6.8±1.3 L/min, p<0.01) caused by an increase in heart rate (67±10 to 79±12 bpm, p<0.01). Contrary to our hypothesis, intermittent exposure to hypoxia did not attenuate the increase in plasma glucose levels during an oral glucose tolerance test in individuals with normal glycemic control. It remains to be determined whether intermittent hypoxia can attenuate the increase in plasma glucose levels in response to an oral glucose tolerance test in individuals with impaired glucose tolerance.Item Elucidating the signal cascades induced by progestins that mediate sperm hypermotility in Atlantic croaker (Micropogonias undulatus) and southern flounder (Paralichthys lethostigma)(2013-12) Tan, Wenxian; Thomas, P. (Peter)The overall goal of this research was to verify the involvement of membrane progestin receptor alpha (mPRα) in mediating progestin-stimulated sperm hypermotility in the Atlantic croaker and southern flounder. Sperm motility in Atlantic croaker and southern flounder were tested with both the endogenous progestin, 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) or the selective mPRα agonist, 10-ethenyl-19-norprogesterone (Org OD 02-0). In croaker, the Pi3k/Akt/Pde and ErbB2/Mapk intracellular signaling pathways were examined. The role of mPRα in mediating sperm hypermotility and fertility in southern flounder was also studied. The effects of seasonal hypoxia on sperm motility in croaker were investigated in a field study in the northern Gulf of Mexico in the fall of 2010. Finally, the effects of acidified activator solution (simulating ocean acidification) were studied in the laboratory. In vitro, Org OD 02-0 mimicked the stimulatory actions of 20β-S in inducing sperm hypermotility and intracellular signaling cascades in croaker and flounder sperm, indicating that mPRα is the mediator of progestin signaling in the sperm of these species. In croaker sperm, both the Pi3k/Akt/Pde and ErbB2/Mapk intracellular signaling pathways were shown to be important mediators of progestin-induced sperm hypermotility, suggesting novel functions of G [subscript olf] βγ-subunits in teleost sperm. In flounder sperm, mPRα was shown to be important in mediating sperm hypermotility as only high motility sperm with high expression of mPRα were responsive to progestin stimulation, resulting in higher fertilization success compared to low motility sperm. A single LHRHa injection resulted in increased sperm motility and fertility, associated with an increase in mPRα expression in the sperm plasma membrane. The results also suggest that the mPRα/Acy/cAMP pathway first described in croaker sperm is present in flounder sperm. Field studies of male Atlantic croaker exposed to chronic seasonal hypoxia showed that hypoxia exposure resulted in smaller gonads, lower spermatogenesis, reduced testicular mPRα expression, and in some sites, reduced sperm motility. Studies with croaker sperm using acidified activator solution to simulate ocean acidification indicated that croaker sperm were sensitive to environmental insult. Furthermore, the results suggested that the progestin signaling mechanism is more sensitive to changes in ocean pH levels than the mechanism that controls sperm motility.Item Erythropoietin response to intermittent hypoxia in health and type 2 diabetes(2023-04-24) Wojan, Frank; Lalande, Sophie; Tanaka, Hirofumi; Coyle, Edward; Burtscher, MartinPatients with type 2 diabetes and aging individuals experience declines in maximal oxygen consumption. Hemoglobin mass, a component of oxygen transport, strongly correlates to maximal oxygen consumption. Interventions that increase hemoglobin mass may therefore increase maximal oxygen consumption in older adults and patients with type 2 diabetes. Intermittent hypoxia, characterized by alternating periods of breathing low levels of oxygen interspersed with periods breathing normoxic air, has the potential to elicit an acute increase in erythropoietin levels and hemoglobin mass. Despite several instances of repeated exposures to intermittent hypoxia increasing red blood cell count over the course of five days to three weeks, there exists a lack of consistent stimuli across the literature, with deviations in hypoxic duration, number of cycles, and hypoxic severity. Furthermore, studies that successfully increased oxygen transport following intermittent hypoxia did not measure erythropoietin levels, the hormone regulating red cell production, thereby eliminating the possibility for protocol comparison. Therefore, the following three studies aimed to identify the shortest intermittent hypoxia protocol to increase erythropoietin levels in healthy young individuals, and to apply this intermittent hypoxia protocol to older individuals and patients with type 2 diabetes, with the goal of potentially increasing hemoglobin mass. In the first study, we identified the shortest hypoxic protocol within the literature to increase EPO concentrations among young healthy adults. The EPO response to the 32 total hypoxic minutes was no different than a 2-hour continuous hypoxia protocol. In the second study, we demonstrated that EPO concentrations increased following the same intermittent hypoxia in middle-aged adults but found no increase to hemoglobin mass. In the third study, we demonstrated a lack of EPO response to intermittent hypoxia in patients with type 2 diabetes. Furthermore, this study was the first to report hemoglobin mass levels in patients with type 2 diabetes. Collectively, the overall findings highlight the acute effects of intermittent hypoxia on erythropoietin in health and type 2 diabetes.Item Hypoxia modeling in Corpus Christi Bay using a hydrologic information system(Center for Research in Water Resources, University of Texas at Austin, 2009-05) To, Ernest Sin Chit; Maidment, David R.Item Hypoxia modeling in Corpus Christi Bay using a hydrologic information system(2009-05) To, Sin Chit; Maidment, David R.Hypoxia is frequently detected during summer in Corpus Christi Bay, Texas, and causes significant harm to benthic organism population and diversity. Hypoxia is associated with the density stratification in the Bay but the cause of stratification is uncertain. To support the study of hypoxia and stratification, a cyberinfrastructure based on the CUAHSI (Consortium of Universities for the Advancement of Hydrologic Science, Inc) Hydrologic Information System (HIS) is implemented. HIS unites the sensor networks in the Bay by providing a standard data language and protocol for transferring data. Thus hypoxia-related data from multiple sources can be compiled into a structured database. In Corpus Christi Bay, salinity data collected from many locations and times are synthesized into a three-dimensional space-time continuum using geostatistical methods. The three dimensions are the depth, the distance along a transect line, and time. The kriged salinity concentration in space and time illuminates the pattern of movement of a saline gravity current along the bottom of the Bay. The travel time of a gravity current in the Bay is estimated to be on the order of one week and the speed is on the order of 1 km per day. Statistical study of high-resolution wind data shows that the stratification pattern in the Bay is related to the occurrence of strong, southeasterly winds in the 5 days prior to the observation. This relationship supports the hypothesis that stratification is caused by the wind initiating hypersaline gravity currents which flow from Laguna Madre into Corpus Christi Bay. An empirical physical hypoxia model is created that tracks the fate and transport of the gravity currents. The model uses wind and water quality data from real-time sensors published by HIS to predict the extent and duration of hypoxic regions in the Bay. Comparison of model results with historical data from 2005 to 2008 shows that wind-driven gravity currents can explain the spatially heterogeneous patterns of hypoxic zones in Corpus Christi Bay.Item The Influence of Body Size and Hemoglobin Multiplicity on Critical Oxygen Threshold in Red Drum (Sciaenops ocellatus)(2016-05) Pan, Yihang; Esbaugh, AndrewHypoxia is common in marine environments and fishes use a suite of cardiorespiratory adjustments to defend aerobic metabolism, including reducing standard metabolic rate (SMR), the minimum metabolic rate needed to sustain life at a specified temperature, or increasing hemoglobin (Hb)-O2 affinity. Nonetheless, hypoxia can constrain oxygen transport whereby fish cannot accommodate standard metabolic rate; a point known as critical oxygen tension (Pcrit). Currently, it is unclear how life history traits may impact Pcrit, but available data on red drum (Sciaenops ocellatus) suggest that its SMR decreases with size, and its transcriptome contains multiple Hb-α and Hb-β subunits. Therefore we sought to explore the influence of body size and acclimation to hypoxia. Critical oxygen tension (Pcrit) was measured for fish over a 2500-fold range in mass (0.26 - 686 g) and surprisingly showed an increase (Pcrit = 3.15 logM + 16.19; R2 = 0.44) despite decreasing SMR. Two groups of S. ocellatus (90.96 ± 5.00 g ranging from 69.7 g to 141.9 g) were also subjected to either normoxia ( > 95% P_(O_2 )) or hypoxia (30%±5% P_(O_2 )) treatment for two weeks. Only fish subjected to hypoxia treatment showed a statistically significant decrease in Pcrit after the treatment. Acclimation had no impact on gill surface area, diffusion distance or relative ventricular mass, but mRNA expression levels of the major Hb-α subunit switched from Hbα-3.1 in the normoxia group to Hbα-3.2 in the hypoxia treatment group and expression levels of Hbα-2, Hbα-3.2 and Hbβ-3.1 showed a statistically significant increase in the hypoxia treatment group. Decrease in P50 and thus an increase in Hb-O2 binding affinity was observed for fish subjected to hypoxia treatment. Taken together these data indicate that hypoxia tolerance is affected by both developmental stage and hypoxia acclimation.Item Modeling a gravity current in a shallow fluid system(2011-12) Kulis, Paula Sharon; Hodges, Ben R.; Maidment, David R.; Katz, Lynn E.; Reible, Danny D.; Raman, VenkatramanCorpus Christi Bay in Texas is a wind driven system, and under most conditions winds over the bay mix the water column vertically. However, seasonal, episodic, bottom-water hypoxia has been observed in the bay in conjunction with vertical salinity stratification. This stratification may be caused by dense gravity currents entering the bay. Understanding and modeling the mechanisms that result in stratification in Corpus Christi Bay may help predict hypoxia, and for this reason that is the focus of this dissertation. An evaluation of existing gravity current modeling techniques shows that most currently available models are designed to capture either phenomena local to a gravity current, such as gravity current entrainment and spreading, or larger scale phenomena such as wind mixing and large-scale circulation, but not both. Because gravity current mixing in Corpus Christi Bay is enhanced by wind-induced turbulence, both local gravity current physics and wind mixing effects are critical elements governing gravity current propagation in Corpus Christi Bay. As existing models do not represent gravity current entrainment and wind mixing together, this dissertation develops a coupled model system that accounts explicitly for turbulent wind mixing of a bottom-boundary layer, in addition to representing other local features of dense gravity current propagation such as entrainment and spreading. The coupled model system consists of a 2D depth-averaged hydrodynamic model that calculates gravity current mixing and spreading, coupled with a 3D hydrodynamic model whose domain includes a lighter ambient fluid surrounding the gravity current. The coupled models have flexible boundary conditions that allow fluid exchange to represent mixing from both gravity current entrainment and wind mixing. The coupled model system’s development, verification and application in Corpus Christi Bay advances understanding of gravity current mechanisms, and contributes to our scientific understanding of hypoxia in Corpus Christi Bay. This modeling technique has the flexibility to be applied to other density-stratified systems that are shallow and potentially wind-driven, such as shallow desalination brine disposal sites.Item Modulation by hypoxia of membrane steroid receptor expression and functions in ovaries of Atlantic croaker (Micropogonias undulatus)(2015-12) Ondricek, Kathryn Elise; Thomas, P.(Peter),; Black, Bryan; Walther, Ben; Rahman, Md SaydurHypoxia is an endocrine disruptor, altering estrogen, testosterone, and progestin hormone levels and stunting gonadal growth in Atlantic croaker. Steroids act through specific hormone receptors to alter reproductive functions, and the hormonal response is dependent on the concentrations of these receptors. However, information is currently lacking on the effects of hypoxia on expression and functions of membrane receptors mediating rapid, non-genomic steroid actions such as final oocyte maturation and apoptosis. Atlantic croakers were exposed to normoxia (7.0 mg DO/L) or hypoxia (1.7 mg DO/L) for 6 weeks during their period of gonadal recrudescence (October-December). Relative gene expression was quantified using quantitative real-time PCR (qRT-PCR). mRNA expression of the membrane androgen receptor, ZIP9, was increased in hypoxia-exposed fish compared to normoxia-exposed controls, whereas mRNA expression of the membrane estrogen receptor, GPER, and membrane progestin receptor, mPRα, was decreased in hypoxia-exposed fish compared to controls. mRNA expression of pro-apoptotic factors Bax and p53 was also measured and expression of both genes was increased in hypoxia-exposed fish compared to controls. Relative protein expression of these receptors was quantified using Western blotting and the results were consistent with the qRT-PCR findings. Oocytes from both hypoxia-exposed and control fish were tested in an in vitro final oocyte maturation (FOM) assay to examine possible alterations in receptor functions. When oocyte maturation was stimulated with progestin, which acts through mPRα, significantly fewer oocytes of hypoxia-exposed fish underwent FOM compared to oocytes of normoxia-exposed controls. These results are consistent with the decrease in mPRα expression following hypoxia exposure. Ovaries were sectioned and stained with hematoxylin and eosin, and the proportions of perinucleolar stage, tertiary yolk stage, and atretic oocytes were determined. Ovaries from fish exposed to hypoxia showed an increase in the proportion of perinucleolar stage and atretic oocytes and a decrease in the proportion of tertiary yolk stage oocytes compared to controls. Finally, apoptotic cells in ovarian tissue sections were labeled using in situ TUNEL staining. Ovaries from fish exposed to hypoxia showed an increased proportion of TUNEL-positive ovarian follicle cells compared to controls. Collectively, these results show the concurrence of increased ZIP9 expression and apoptotic follicle cells in ovaries of Atlantic croaker exposed to hypoxia in vivo.Item Pulmonary gas exchange in response to rebreathing-induced hypoxia(2023-04-18) Guei, Jamie Gaytan; Lalande, SophieRebreathing-induced hypoxia elicits changes in pulmonary gas exchange variables. PURPOSE: This report aims to determine the changes in pulmonary gas exchange variables in response to a rebreathing-induced hypoxia protocol in individuals who are healthy, have prediabetes, or have type 2 diabetes. METHODS: Fifteen participants (M: 9, age 45 ± 17 years, body mass index: 34.2 ± 8.0 kg/m²) visited the laboratory. A 2-hour, 75 g oral glucose tolerance test was conducted during the study visit while simultaneously performing a rebreathing-induced hypoxia protocol. Venous blood samples were collected 0, 30-, 60-, 90-, and 120-min following ingestion of the glucose drink to measure plasma glucose and insulin levels. The rebreathing-induced hypoxia protocol consisted of two series of five 2-min rebreathing bouts in a low-volume, closed circuit system interspersed with two minutes of breathing room air. The first and second series of rebreathing bouts were performed within the first 30 min and 30-60 min after ingesting the glucose drink, respectively. Pulmonary gas exchange was measured using a metabolic cart. RESULTS: End-tidal oxygen, fraction of inspired oxygen, and respiratory rate decreased during rebreathing-induced hypoxia. Tidal volume, minute ventilation, oxygen uptake, and end-tidal carbon dioxide increased during rebreathing-induced hypoxia. CONCLUSION: Rebreathing-induced hypoxia elicits changes in pulmonary gas exchange in individuals who are healthy, have prediabetes, or have type 2 diabetes.Item Respiratory plasticity of red drum to chronic hypoxia(2022-12-01) Negrete, Benjamin Jr.; Esbaugh, Andrew; Thomas, Peter; Brandl, Simon J; Richards, Jeffrey GOcean deoxygenation (hypoxia) is a pressing concern in the face of climate change as hypoxic areas increase in size, duration, and magnitude with each year. When a fish cannot escape hypoxia, it must be able to make the appropriate physiological adjustments to maintain fitness. Juveniles and adults can display reversible phenotypic changes in low oxygen (O₂), while embryos and larvae may producing fixed traits that are carried to adulthood through developmental plasticity. Across all life stages aerobic metabolism is the most efficient way that fish generate energy, and the most impacted pathway under hypoxia. In my dissertation, I explore the flexible responses that compensate for changes to aerobic metabolism across different life stages of the marine teleost red drum (Sciaenops ocellatus) exposed to chronic, sub-lethal hypoxia. Hypoxia-acclimated juvenile drum demonstrated significant changes in hemoglobin (Hb) isoform expression relative to control. Changes in Hb expression co-occurred with reduced pH sensitivity, and increased O₂ binding affinity. Additionally, this correlated with increased maximum metabolic rate and aerobic scope relative to controls in hypoxia. These results demonstrate an important role for Hb isoforms in maximizing respiratory performance in hypoxia with implications at the whole-animal level. Furthermore, I investigated how acclimated fish respond to exhaustive exercise, and their anaerobic swim performance. I found that hypoxia-acclimated juveniles decreased ATP in the red muscle and increased ATP and glycolytic potential in their white muscle. This phenotype recruited white muscle at lower swim speeds than control fish, indicating a prioritization of glycolytic white muscle swimming over aerobic red muscle. Finally, I assess whole animal respiratory and swim performance in fish exposed to hypoxia during a critical window in early development. These fish show increases in aerobic performance in normoxia, while becoming more vulnerable to hypoxia in later life. I sought to understand the mechanisms and implications of hypoxia-induced respiratory adaptations, and demonstrated the ability of a marine fish to adapt to environmental stress, and how these adaptations changed in different life stages. This work demonstrates the species-specific resiliency and limitations in environmental stress, and illustrates the need for more species-specific work in a changing ocean.Item Sub-lethal effects of hypoxia on harpacticoid copepod reproduction(2010-05) Ryckman, Laura Yukiko Chu; Buskey, Edward Joseph, 1952-; Montagna, Paul A.; Gardner, Wayne S.; Thomas, Peter; Fleeger, John W.Areas of hypoxia are found in coastal areas worldwide, and have become increasingly widespread. These areas vary in their duration and dissolved oxygen concentration from occasional diurnal hypoxia, as found in Corpus Christi Bay, Texas, seasonal hypoxia as in the northern Gulf of Mexico, to continuous hypoxia as found in oceanic oxygen minimum zones. The effects of exposure to low dissolved oxygen (DO) depend on the duration of exposure, the DO concentration and an organism’s tolerance to hypoxic conditions. Most studies have focused on lethal effects of hypoxia by comparing the abundance of benthic organisms and the species composition of benthic communities between hypoxic and normoxic areas. Sub-lethal effects of such as changes in reproduction may occur at less severe hypoxic conditions (by definition), but may still have effects at the population level. The goal of this study is to examine the sub-lethal reproductive effects of low DO on harpacticoid copepods. The life-history traits and reproductive biology of meiobenthic harpacticoid copepods make this group of organisms useful as test organisms to measure the sub-lethal effects of hypoxia on reproduction. It is hypothesized that changes in reproductive traits may be observed at DO concentrations higher than those that cause lethal effects because of the high energetic cost of female harpacticoid reproduction which may result in reduced fitness. Laboratory studies were conducted to examine the effects of low DO concentrations on survival, egg production, and the number and size of eggs. Harpacticoid population abundance, biomass and the abundance of ovigerous females were measured from field samples collected across sites that varied in their degree and duration of exposure to low DO. To contrast the effects of hypoxia in environments with different hypoxic exposures, field studies were carried out in the northwestern Gulf of Mexico in an area with near constant summer hypoxia, and in southeast corner of Corpus Christi Bay, Texas which experiences intermittent hypoxia often for less than one hour in the early morning hours during summer. At both field sites total copepod abundance, biomass and the abundance of ovigerous females were reduced at the most hypoxic site type compared the reference sites. In Corpus Christi Bay, total and ovigerous female abundance varied with exposure to hypoxia, but the relative declines in abundance and biomass were less dramatic than in the northern Gulf of Mexico. In the northern Gulf of Mexico, the percentage of ovigerous females within the total harpacticoids collected was reduced (p<0.001) to 3% at the Intermediate and 1% at the Hypoxic sites during the summers, but in the fall of 2007 at all transects had similar percentages (p = 0.81) of ovigerous females which ranged from 13 to 16%. Reference sites had a higher number of families with ovigerous females, and the relative abundances of those families were more evenly distributed at Reference sites compared to Hypoxic and Intermediate transects. Patterns of ovigerous female abundance with respect to DO concentration were similar across numerous harpacticoid families found at the study sites. Harpacticoid copepods in laboratory studies tolerated near anoxic DO conditions for longer than 120 hours. Average survival rates of the harpacticoids Schizopera knabeni and Nitokra affinis during periods of low DO with elevated ammonium concentrations were less than 50%, while survival rates for the other treatments were near 100%. The formation of an egg mass was reduced in the near anoxia treatment, but egg clutches did not form at all in the treatment that combined near anoxia and 10 micromolar ammonium. The DO concentration and presence of ammonium were important factors to the severity of population decline that were illustrated by population estimate calculations. Population estimates based on laboratory measurements of Nitokra affinis resulted in calculations of reduced survival and reproductive rates related to hypoxic exposure greatly decrease the potential population of the group, which may affect the copepod population’s ability to recover from hypoxic events. The effects of hypoxia on harpacticoid copepods are the result of the length of exposure, the concentration of low dissolved oxygen and exposure to other chemical fluxes that increase during periods of hypoxia. The measurement of reproductive indicators, such as the presence of an egg mass and the proportion of ovigerous females in a population, could be used to indicate the adverse environmental effects of low dissolved oxygen exposure. The studies from this dissertation are the first to document reproductive effects of low dissolved oxygen on harpacticoid populations in the field. Laboratory studies within this dissertation indicate the interaction between ammonium and hypoxia on survival and reproduction in harpacticoids. Future studies are needed to further determine the effects of hypoxia on the whole-life cycle of harpacticoid copepods.Item Targeting multifunctional human ALDOA in cancer signaling(2018-08-16) Stancu, Bogdan Gabriel; Dalby, Kevin N.; Fast, Walter; Mills, Edward; Ren, Pengyu; Tiziani, StefanoHuman fructose-bisphosphate aldolase A (ALDOA) is a key enzyme in glycolysis that catalyzes the conversion of fructose 1,6-bisphosphate to glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. ALDOA has also been shown to play key moonlighting roles associated with cellular structure, motility and proliferation. This aldolase isoenzyme is significantly overexpressed in a number of human tumors and has been shown to have oncogenic potential. We have demonstrated that ALDOA overexpression has further inference through cycling of hypoxia inducible transcription factor-1 (HIF-1) regulation. This feed-forward loop mediated through AMPK is a new target to consider in the irregular hypoxic environment of solid tumors. The body of work that follows presents five different methods of targeting and inhibiting ALDOA function. Using small molecule probes, the function and regulation of these iterations is characterized, towards better understanding of the role of ALDOA in cells and in cancer