Am J Physiol Heart Circ Physiol-2009-Gao-H559-60

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    doi:10.1152/ajpheart.00045.2009296:H559-H560, 2009. First published 23 January 2009;Am J Physiol Heart Circ Physiol

    Erhe Gao and Walter J. Kochfailure?Is erythropoietin behind maladaptive anemic heart

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    intact animal to the cellular, subcellular, and molecular levels. It is published 12 times a year (monthly) by the Americanlymphatics, including experimental and theoretical studies of cardiovascular function at all levels of organization ranging from the

    publishes original investigations on the physiology of the heart, blood vessels, andAJP - Heart and Circulatory Physiology

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    Editorial Focus

    Is erythropoietin behind maladaptive anemic heart failure?

    Erhe Gao and Walter J. Koch

    George Zallie and Family Laboratory for Cardiovascular Gene Therapy, Center for Translational Medicine, and Department

    of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania

    HEART FAILURE (HF) is a major public health problem world-wide. HF is a syndrome arising from multiple causes that willaffect one in five adults in their lifetime. Despite the progressthat has been made in the treatment of chronic HF, the overallmorbidity and mortality remain high (8). Therefore, it isimperative that there is a continued push to more fully under-stand the molecular mechanisms responsible for this disease todiscover and develop novel therapies. Among the multiplecharacteristics of chronic HF, anemia, defined by the WorldHealth Organization criteria as a hemoglobin (Hb) concentra-tion of13 g/dl in adult men and 12 g/dl in adult women, isfound in 30% to 40% of cases and is an independent risk factorfor more severe HF (1, 2, 12, 17).

    When compared with HF patients with normal Hb levels, thepresence of anemia is associated with worsened clinical symp-toms, more severe systolic and diastolic dysfunction, and asignificant increase in mortality in patients with advanced HF(4, 6, 7, 17). Moreover, these patients have higher brainnatriuretic peptide levels, increased extracellular and plasmavolume, and more rapid deterioration of renal function. It hasbeen shown that chronic untreated anemia can result in in-creased cardiac output that eventually can lead to ventriculardilation, increased left ventricular (LV) mass, and the devel-opment of LV hypertrophy, which represent cardiac remodel-ing parameters that are strong predictors of morbidity andmortality (12). Understanding how chronic anemia leads to LVremodeling and poorer outcomes in HF is essential to improve

    how we may treat these large number of patients with HF.Naito and colleagues (12a) report an animal model of

    chronic anemia that leads initially to an adaptive phase ofpreserved cardiac function despite LV remodeling followedover time by maladaptation and severe LV dysfunction. Thecompensatory phase followed by decompensation appears tocorrelate with the dynamic regulation of serum erythropoietin(EPO) levels and cardiac EPO signaling. This study under-scores the significance of cardiac EPO-EPO receptor (EPO-R)signaling as a cardioprotective axis.

    EPO, a hematopoietic cytokine that is primarily synthesizedin kidney peritubular cells in response to hypoxia, has longbeen used as a clinical treatment for conditions of low Hb. The

    physiological effects of EPO in hematopoietic cells are medi-ated through its interaction with its specific cellular receptor,EPO-R, a member of the type I superfamily of single-trans-membrane cytokine receptors (3, 9). Recently, data have ac-cumulated demonstrating that the EPO-R is present in a varietyof other tissues outside the blood, including cardiomyocytes,suggesting the potential roles of EPO signaling beyond hema-topoiesis and the treatment of anemia (20). Recombinant-

    human EPO administration has been shown to exert a broadtissue-protective effect in a variety of experimental models. Inthe cardiovascular system, EPO has been shown to exertmarked myocardial protective effects against ischemia-reper-fusion injury via a reduction of LV infarct size and a signifi-cantly decreased apoptotic cell death of cardiomyocytes, whichleads to an enhanced recovery of LV function (5, 16). Mech-anistically, studies have shown that EPO-EPO-R signaling canstimulate the JAK/STAT, MAPK, and phosphatidylinositol3-kinase/Akt signaling pathways in cardiac cells, much like thesignaling in hematopoietic cells (13, 14). Cardioprotectionafter ischemic injury characterized by increased angiogenesisin the heart has also been found using darbepoetin-, a longer-

    acting synthetic EPO analog (11, 18). In apparent support ofthe cardioprotective actions of EPO and analogs, recent clinicaltrials have shown that in anemic patients with HF, EPOtreatment increases and maintains Hb and LV ejection fractionwith improved quality-of-life scores and exercise duration (10,15, 19). However, the mechanism of these beneficial effects ofEPO in patients with anemic HF has not been fully understoodor clarified.

    In the study by Naito et al. (12a), important mechanismsbehind the adaptive and maladaptive responses of the heart toa long-term anemia induced by iron deficiency have beenuncovered. First, they demonstrate in rats that iron deficiencyanemia (IDA) leads to cardiac hypertrophy at 12 wk with amaintained cardiac output. However, after 20 wk of IDA, serial

    echocardiographic measurements revealed significant cardiacdysfunction characterized at the end of the study by an increasein the LV weight-to-tibia length ratio and the lung wet weight-to-lung dry weight ratio. Moreover, at a molecular level, atrialnatriuretic peptide, brain natriuretic peptide, and collagen type3 gene expressions were increased, consistent with the myo-cardial interstitial fibrosis that was evident in IDA rats. Inter-estingly, circulating levels of EPO were inversely correlatedwith these phenotypic findings, with upregulation at 12 wk anda significant decrease at 20 wk, suggesting a change in EPO-EPO-R signaling in the late-stage HF induced by IDA.

    This study revealed some potentially important mechanisticfindings implicating STAT3 activation as a culprit in IDA-

    induced maladaptation. Of note, serum EPO levels and thephosphorylation of STAT3 peaked at 12 wk and subsequentlydecreased at 20 wk, raising the possibility that a compensatoryand decompensatory EPO-EPO-R signaling mechanism mayexist in the hearts of rats with chronic IDA (12a). Consistentwith this, a previous study has showed that activated (i.e.,phosphorylated) STAT3 can occur in cardiac cells stimulatedwith EPO (14). Importantly, to further explore whether thepreservation of increased EPO levels is associated with adap-tive cardiac remodeling, Naito et al. (12a) evaluated the cardiaceffects of EPO therapy on rats after they had been on aniron-deficient diet for 12 wk. EPO administration attenuatedthe downregulation of cardiac STAT3 phosphorylation and

    Address for reprint requests and other correspondence: W. J. Koch, Centerfor Translational Medicine, George Zallie and Family Laboratory for Cardio-vascular Gene Therapy, Thomas Jefferson Univ., 1025 Walnut St., Rm. 317,Philadelphia, PA 19107 (e-mail: [email protected]).

    Am J Physiol Heart Circ Physiol 296: H559H560, 2009;doi:10.1152/ajpheart.00045.2009.

    0363-6135/09 $8.00 Copyright 2009 the American Physiological Societyhttp://www.ajpheart.org H559

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    prevented cardiac dysfunction in the IDA group. Meanwhile,blood Hb and systolic blood pressure were not altered in theIDA group receiving EPO. Increasing EPO levels in these ratsclearly prevented the transition from adaptive cardiac hyper-trophy to maladaptive LV remodeling and HF even withsustained IDA. Accordingly, the study implicates STAT3 ac-tivation to be critical for the EPO-dependent maintenance of

    LV function despite IDA.Overall, this study underscores the importance of maintain-

    ing EPO levels in HF patients and may open up a newtherapeutic window to use this cardioprotective cytokine morefrequently, even in patients without anemia. Of course, furtherstudies, especially in larger animals and different models ofHF, are warranted since EPO can increase the risk of throm-botic events. Nevertheless, Naito et al. (12a) have shed newlight on this interesting field.

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    Editorial Focus

    H560

    AJP-Heart Circ Physiol VOL 296 MARCH 2009 www.ajpheart.org

    http://dx.doi.org/10.1152/ajpheart.00463.2008http://dx.doi.org/10.1152/ajpheart.00463.2008http://dx.doi.org/10.1152/ajpheart.00463.2008http://dx.doi.org/10.1152/ajpheart.00463.2008http://dx.doi.org/10.1152/ajpheart.00463.2008http://dx.doi.org/10.1152/ajpheart.00463.2008