Effects of Thyroid Hormone and Hypoxia on 2,3-Bisphosphoglycerate, Bisphosphoglycerate Synthase and Phosphoglycerate Mutase in Rabbit Erythroblasts and Reticulocytes in vivo

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Abstract

Objectives: The effects of triiodothyronine (T3) and hypoxia on 2,3-bisphosphoglycerate (2,3-BPG) studied in vitro are unclear. To clarify these effects we selected a more physiologic approach: the in vivo study in rabbits. We also present the changes produced by T3 and hypoxia on phosphoglycerate mutase (PGAM), which requires 2,3-BPG as a cofactor, and 2,3-BPG synthase (BPGS), the enzyme responsible for 2,3-BPG synthesis in erythroblasts and reticulocytes. Methods: Hyperthyroidism was induced by daily T3 injection (250 µg/kg), hypoxia by a mixture of 90% nitrogen and 10% oxygen and hypothyroidism by propylthiouracil (PTU) added to drinking water. Results: Both T3 administration and hypoxic conditions increased 2,3-BPG levels and BPGS mRNA levels and activity in erythroblasts but not in reticulocytes. Unlike BPGS, both PGAM mRNA levels and activity were increased in erythroblasts and reticulocytes under hyperthyrodism and hypoxia. The antihormone PTU produced opposite effects to T3. Conclusion: The results presented here suggest that both hyperthyroidism and hypoxia modulate in vivo red cell 2,3-BPG content by changes in the expression of BPGS. Similarly, the changes in PGAM activity are also explained by changes in its expression.

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Cellular mechanism of oxygen sensing.

R Pardal, J Lopez-Libano, P Sáenz (2000)

O2 sensing is a fundamental biological process necessary for adaptation of living organisms to variable habitats and physiological situations. Cellular responses to hypoxia can be acute or chronic. Acute responses rely mainly on O2-regulated ion channels, which mediate adaptive changes in cell excitability, contractility, and secretory activity. Chronic responses depend on the modulation of hypoxia-inducible transcription factors, which determine the expression of numerous genes encoding enzymes, transporters and growth factors. O2-regulated ion channels and transcription factors are part of a widely operating signaling system that helps provide sufficient O2 to the tissues and protect the cells against damage due to O2 deficiency. Despite recent advances in the molecular characterization of O2-regulated ion channels and hypoxia-inducible factors, several unanswered questions remain regarding the nature of the O2 sensor molecules and the mechanisms of interaction between the sensors and the effectors. Current models of O2 sensing are based on either a heme protein capable of reversibly binding O2 or the production of oxygen reactive species by NAD(P)H oxidases and mitochondria. Complete molecular characterization of the hypoxia signaling pathways will help elucidate the differential sensitivity to hypoxia of the various cell types and the gradation of the cellular responses to variable levels of PO2. A deeper understanding of the cellular mechanisms of O2 sensing will facilitate the development of new pharmacological tools effective in the treatment of diseases such as stroke or myocardial ischemia caused by localized deficits of O2.

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The molecular basis of thyroid hormone action.

David A Brent (1994)

Progress has been made in understanding the molecular basis of a number of clinical manifestations of thyroid disease, yet many questions remain. Why are there two thyroid hormone-receptor genes? Is the function of each of the two receptors indeed unique? How T3 receptors interact with other nuclear proteins and DNA-binding sites and how these interactions are influenced by T3 is incompletely understood. The developmental regulatory role of T3 receptor alpha 1 and its non-T3-binding alpha 2 variant needs to be defined. Most T3-regulated processes, especially those related to metabolism, muscle contraction, and brain development, function in concert with a number of other regulatory factors. The therapeutic applications of knowledge gained about the basic mechanisms of thyroid hormone action should ultimately extend beyond thyroid disease to processes regulated or influenced by T3; these include cardiac function, lipid metabolism, pituitary hormone secretion, and neural development.

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Role of hypoxia-inducible factor-1 in transcriptional activation of ceruloplasmin by iron deficiency.

B. Mazumder, Matthew Fox, C Mukhopadhyay (2000)

A role of the copper protein ceruloplasmin (Cp) in iron metabolism is suggested by its ferroxidase activity and by the tissue iron overload in hereditary Cp deficiency patients. In addition, plasma Cp increases markedly in several conditions of anemia, e.g. iron deficiency, hemorrhage, renal failure, sickle cell disease, pregnancy, and inflammation. However, little is known about the cellular and molecular mechanism(s) involved. We have reported that iron chelators increase Cp mRNA expression and protein synthesis in human hepatocarcinoma HepG2 cells. Furthermore, we have shown that the increase in Cp mRNA is due to increased rate of transcription. We here report the results of new studies designed to elucidate the molecular mechanism underlying transcriptional activation of Cp by iron deficiency. The 5'-flanking region of the Cp gene was cloned from a human genomic library. A 4774-base pair segment of the Cp promoter/enhancer driving a luciferase reporter was transfected into HepG2 or Hep3B cells. Iron deficiency or hypoxia increased luciferase activity by 5-10-fold compared with untreated cells. Examination of the sequence showed three pairs of consensus hypoxia-responsive elements (HREs). Deletion and mutation analysis showed that a single HRE was necessary and sufficient for gene activation. The involvement of hypoxia-inducible factor-1 (HIF-1) was shown by gel-shift and supershift experiments that showed HIF-1alpha and HIF-1beta binding to a radiolabeled oligonucleotide containing the Cp promoter HRE. Furthermore, iron deficiency (and hypoxia) did not activate Cp gene expression in Hepa c4 hepatoma cells deficient in HIF-1beta, as shown functionally by the inactivity of a transfected Cp promoter-luciferase construct and by the failure of HIF-1 to bind the Cp HRE in nuclear extracts from these cells. These results are consistent with in vivo findings that iron deficiency increases plasma Cp and provides a molecular mechanism that may help to understand these observations.

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Author and article information

Journal

Journal ID (publisher-id): HRE

Journal ID (nlm-ta): Horm Res Paediatr

Journal ID (doi): 10.1159/issn.1663-2818

Title: Hormone Research in Paediatrics

Publisher: S. Karger AG

ISSN (Print): 1663-2818

ISSN (Electronic): 1663-2826

Publication date Subscription-year: 2004

Publication date (Print): October 2004

Publication date (Electronic): 21 October 2004

Volume: 62

Issue: 4

Pages: 191-196

Affiliations

Unitat de Bioquímica, Departament de Ciéncies Fisiològiques I, Institut d’Investigacions Biomèdiques August Pi i Sunyer, Universitat de Barcelona, Barcelona, Spain

Article

Publisher ID: 80897 Other ID: Horm Res 2004;62:191–196

DOI: 10.1159/000080897

PubMed ID: 15375329

SO-VID: 5950a523-972a-4fc7-8aa0-a308babceec7

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Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

History

Date received : 10 November 2003

Date accepted : 07 July 2004

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Figures: 3, References: 36, Pages: 6

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Effects of Thyroid Hormone and Hypoxia on 2,3-Bisphosphoglycerate, Bisphosphoglycerate Synthase and Phosphoglycerate Mutase in Rabbit Erythroblasts and Reticulocytes in vivo

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Karger: Endocrinology

Most cited references 23

Cellular mechanism of oxygen sensing.

The molecular basis of thyroid hormone action.

Role of hypoxia-inducible factor-1 in transcriptional activation of ceruloplasmin by iron deficiency.

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