College of Agriculture & Natural Resources
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item The Importance of Transfer Receptor 1 in Adipose Tissue(2021) Mejia-Guevara, Yasmin; Kim, Byung-Eun; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Iron homeostasis is essential for maintaining cellular function in a variety of cell types. Transferrin receptor 1 (TfR1), which is expressed ubiquitously, facilitates cellular iron (Fe) uptake through receptor-mediated endocytosis of Fe-loaded transferrin. This study was undertaken to evaluate the importance of TfR1-mediated Fe import into adipose tissues for thermogenesis and systemic metabolism. We found that adipose-specific TfR1 knockout mice exhibited severe cold susceptibility upon acute cold exposure, leading to death of the mutant mice within hours. This phenotype was exacerbated by dietary Fe limitation and partially rescued by Fe administration. Knockout mice showed marked defects in oxidative phosphorylation components and lipid droplet homeostasis in adipose tissues. Furthermore, elevated levels of plasma glucose and insulin in the mutant’s hint at an unexpected connection between adipocyte Fe deficiency and diabetes. Altogether, our results suggest that TfR1-mediated Fe uptake is critical for multiple aspects of adipose function and systemic energy metabolism.Item MRP5 AND MRP9 PLAY A CONCERTED ROLE IN MALE REPRODUCTION AND MITOCHONDRIAL FUNCTION(2021) Chambers, Ian George; Hamza, Iqbal; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Heme is an essential iron-containing cofactor in proteins that perform diverse functions in biology. Free heme is not only hydrophobic but also generates cytotoxic peroxide radicals. In eukaryotes, heme synthesis occurs in the mitochondria but must be transported to different intracellular organelles to be utilized by hemoproteins, a process that remains poorly understood. In Caenorhabditis elegans, MRP5/ABCC5 is an essential heme exporter as mrp-5 knockout worms are unviable due to their inability to export nutritional heme from the intestine to extra-intestinal tissues. Heme supplementation restores viability of these mutants but fails to restore male reproductive deficits. By contrast, MRP5 in mammals regulates heme levels in the secretory pathway but shows no reproductive phenotypes. Phylogenetically, the closest homolog of MRP5 in vertebrates is MRP9/ABCC12, which is absent in C. elegans raising the possibility that MRP9 may genetically compensate for MRP5 lossin vertebrates. Here, we show that MRP5 and MRP9 double knockout (DKO) mice are viable but reveal significant male reproductive deficits, reminiscent of mrp-5 worms. Although MRP9 is highly expressed in sperm, MRP9 knockout mice show reproductive phenotypes only when MRP5 is absent. Unlike other ABCC transporters, these proteins localize to mitochondrial-associated membranes (MAMs), dynamic scaffolds that associate the mitochondria and endoplasmic reticulum. Consequently, combined loss of both transporters results in abnormal sperm mitochondria and reduced fertilization rates in DKO mice. Untargeted metabolomics show striking differences in metabolite profiles in the DKO testes, consistent with the localization of these transporters to MAMs where inter-organellar metabolite exchange occurs. RNA-seq results show significant alterations in genes related to mitochondria function and energy production, EIF2 signaling, and retinoic acid metabolism. Targeted functional metabolomics reveal retinoic acid levels are significantly lower in the DKO testes. These findings establish a model in which MRP5 and MRP9 play a concerted role in regulating normal male reproductive functions and mitochondrial sufficiency.Item Redox and Soil Manipulation Effects on Ditch Soil Phosphorus Processing(2012) Ruppert, David Emmanuel; Needelman, Brian A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ditches increase the connectivity of landscapes to open water systems, potentially facilitating the degradation of downstream waterways. A treatment and an observational experiment were conducted to identify processes behind phosphorus (P) cycling in ditch soils. If the ditch had not undergone recent dredging soils were observed in the treatment experiment to release P to surface water whether the soil system was iron (Fe)-oxidizing or Fe-reducing. Also in the treatment experiment, Fe was released to surface water in appreciable amounts only if the soil system was Fe-reducing. From the observational experiment P release due to mineralization was inferred due to a positive trend with temperature. Also in the observational experiment Fe-reducing conditions were weakly correlated with diminished P concentrations in the ditch water. It was inferred that emergent Fe(II) released from within the soil through reductive dissolution captures P from ditch surface water upon oxidation. In the treatment experiment dredging and saturated conditions resulted in similar effluent P concentrations as drained soils that were undredged. This may explain a lack of dredging effect that was observed in the field.Item Supplementation strategy and its impact on hematological status in the control of anemia of pregnancy in Senegal(2007-07-31) Seck, Binetou Cheikh; Jackson, Robert T; Nutrition; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Anemia of pregnancy remains highly prevalent in Senegal despite the national iron/folic acid (IFA) supplementation program, which consists of providing prescriptions to purchase IFA to women during prenatal visits. The purpose of this study was to provide a framework for recommendations to improve the effectiveness of the program. We determined the prevalence and risk factors of anemia in a cohort of 480 pregnant women at 6 prenatal health centers in Dakar; we compared compliance after 20 weeks of supplementation between women who received prescriptions at 3 control centers and those who received free IFA at 3 intervention centers; and we assessed the factors that influenced high and low compliance in both groups. Overall, 39% of women were anemic and 71% were iron deficient (ID). Twelve percent were infected with P. falciparum; 21% had intestinal helminthes, and 6.5% had Hb AS. Women consumed foods containing iron absorption inhibitors at high frequency. ID > quadrupled the risk of anemia; malaria and Hb AS also significantly increased the risk for anemia. Compliance was 48% and 86% in the control and intervention groups, respectively (P<.001). Anemia prevalence was 62% among controls versus 31% among interventions (P<.01); ID prevalence was 84% and 57% in the control and intervention groups, respectively (P<.01). Women with high compliance were motivated by 1) the perception of improved health upon taking the tablets, 2) the insistence by midwives that they take them, and 3) the mention that the tablets would improve health. Women with low compliance indicated 1) experiencing side effects that they associated with the tablets, 2) misunderstanding that they needed to continue taking the tablets throughout pregnancy, and 3) forgetfulness. Our findings indicate that for effective control of anemia in Senegal, iron supplementation is needed in addition to educating women about better food choices. Antimalarial chemoprophylaxis and helminthes screening should be made available to all women. In addition, increasing access to IFA and educating women about the health benefits of the tablets can dramatically increase compliance and therefore improve iron status and decrease the incidence of anemia.