Erythropoietin and the use of a transgenic model of erythropoietin-deficient mice

Abstract

Despite its well-known role in red blood cell production, it is now accepted that erythropoietin (Epo) has other physiological functions. Epo and its receptors are expressed in many tissues, such as the brain and heart. The presence of Epo/Epo receptors in these organs suggests other roles than those usually assigned to this protein. Thus, the aim of this review is to describe the effects of Epo deficiency on adaptation to normoxic and hypoxic environments and to suggest a key role of Epo on main physiological adaptive functions. Our original model of Epo-deficient (Epo-TAg^h) mice allowed us to improve our knowledge of the possible role of Epo in O₂ homeostasis. The use of anemic transgenic mice revealed Epo as a crucial component of adaptation to hypoxia. Epo-TAg^h mice survive well in hypoxic conditions despite low hematocrit. Furthermore, Epo plays a key role in neural control of ventilatory acclimatization and response to hypoxia, in deformability of red blood cells, in cerebral and cardiac angiogenesis, and in neuro- and cardioprotection.

Keywords: Epo-TAgh mice; hypoxia; mouse model; physiological functions.

Figure 1

Cardiac angiogenesis in Epo-TAg^h mice. Notes: HIF-1α and VEGF mRNA (A, C) and protein (B, D) expression in the heart of WT (white bar) and Epo-TAg^h (black bar) mice in normoxia and after 48 hours (AHx) or 14 days (CHx) of hypoxic exposure. Epo deficiency led to a rise of angiogenesis through the HIF-1α and VEGF pathway activation. Epo-TAg^h mice were not able to maintain cardiac adaptation to hypoxia during the long-term exposure. Values are expressed as mean ± SEM. *P<0.05 vs Nx WT; ^&P<0.05 vs Nx Epo-TAg^h; ^#P<0.05 CHx vs AHx; ^@P<0.05 CHx Epo-TAg^h vs CHx WT. ^μP<0.05 AHx Epo-TAg^h vs AHx WT. Reprinted from Respir Physiol Neurobiol, Volume 186(2), El Hasnaoui-Saadani R, Marchant D, Pichon A, et al, Epo deficiency alters cardiac adaptation to chronic hypoxia, pages 146–154. Copyright 2013 with permission from Elsevier. Abbreviations: AHx, acute hypoxia; CHx, chronic hypoxia; Epo, erythropoietin; Epo-TAg^h mice, Epo-deficient mice; HIF-1α, hypoxia-inducible factor-1α; Nx, normoxia; SEM, standard error of the mean; VEGF, vascular endothelial growth factor; WT, wild type.

Figure 2

Ventilatory response to hypoxia in Epo-TAg^h mice. Notes: Minute ventilation measured in normoxia (F_IO₂ 21%) or acute hypoxia (F_IO₂ 8%) in WT (white bar) and Epo-TAg^h (black bar) mice maintained in normoxic (Nx exposed) or hypoxic (14 days, Hx exposed) conditions. Epo-TAg^h mice had a normal ventilation at rest, did not display ventilatory acclimatization to hypoxia, and did not respond to acute hypoxia even after the exposure to chronic hypoxia. Values are expressed as mean ± SD. *P<0.05 21% O₂ vs 8% O₂; ^#P<0.05 Nx exposed vs Hx exposed, same strain, same F_IO₂. Adapted from Voituron N, Jeton F, Cholley Y, et al. Catalyzing role of erythropoietin on the nitric oxide central pathway during the ventilatory responses to hypoxia. Physiol Rep. 2014;2(2):e00223. © 2014 Voituron N, Jeton F, Cholley Y, et al. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society. Abbreviations: Epo, erythropoietin; Epo-TAg^h mice, Epo-deficient mice; Hx, hypoxia; Nx, normoxia; SD, standard deviation; WT, wild type.

Figure 3

Cerebral angiogenesis in Epo-TAg^h mice. Notes: Immunohistological detection of HIF-1α and VEGF at the sensory cortex level in normoxia (Nx exposed) and after chronic hypoxia exposure (Hx exposed) in WT (1, 3, 5, 7) and Epo-TAgh mice (2, 4, 6, 8). Arrowheads and arrow indicate HIF-1α (1)- and VEGF (5)-positive cells, respectively. In normoxia, Epo-TAgh mice showed an increase in HIF-1α (2)- and VEGF (6)-positive cells suggesting an enhancement of cerebral angiogenesis through the HIF-1α/VEGF pathway. In WT mice, chronic hypoxia led to an increase in HIF-1α (3) and VEGF (7), while they led a decrease in Epo-TAgh mice (4, 8). Adapted from Am J Physiol Regul Integr Comp Physiol. Volume 296(3). El Hasnaoui-Saadani R, Pichon A, Marchant D, et al. Cerebral adaptations to chronic anemia in a model of erythropoietin-deficient mice exposed to hypoxia. Pages: R801–R811. Copyright 2009. Abbreviations: Epo, erythropoietin; Epo-TAg^h mice, Epo-deficient mice; HIF-1α, hypoxia-inducible factor-1α; Hx, hypoxia; Nx, normoxia; VEGF, vascular endothelial growth factor; WT, wild type.

Figure 4

Effect of Epo deficiency on Epo-R expression in cerebral cortex. Notes: Quantitative determination of Epo-R in the cerebral cortex of WT and Epo-TAg^h mice in Nx and following AHx and CHx. Epo-R mRNA (A) and protein level (B) are shown next to their corresponding protein bar graphs. Representative Western blot of Epo-receptor (Epo-R) (C). Values are expressed as mean ± SD. *P<0.05 vs Nx WT; ^&P<0.05 vs Nx Epo-TAgh. Adapted from Am J Physiol Regul Integr Comp Physiol. Volume 296(3). El Hasnaoui-Saadani R, Pichon A, Marchant D, et al. Cerebral adaptations to chronic anemia in a model of erythropoietin-deficient mice exposed to hypoxia. Pages: R801–R811. Copyright 2009. Abbreviations: AHx, acute hypoxia; CHx, chronic hypoxia; Epo, erythropoietin; Epo-R, Epo receptor; Epo-TAg^h mice, Epo-deficient mice; Nx, normoxia; SD, standard deviation; WT, wild type; PC, peptide control.