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JCI Insight ; 4(7)2019 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-30779710


Iron deficiency is present in ~50% of heart failure (HF) patients. Large multicenter trials have shown that treatment of iron deficiency with i.v. iron benefits HF patients, but the underlying mechanisms are not known. To investigate the actions of iron deficiency on the heart, mice were fed an iron-depleted diet, and some received i.v. ferric carboxymaltose (FCM), an iron supplementation used clinically. Iron-deficient animals became anemic and had reduced ventricular ejection fraction measured by magnetic resonance imaging. Ca2+ signaling, a pathway linked to the contractile deficit in failing hearts, was also significantly affected. Ventricular myocytes isolated from iron-deficient animals produced smaller Ca2+ transients from an elevated diastolic baseline but had unchanged sarcoplasmic reticulum (SR) Ca2+ load, trigger L-type Ca2+ current, or cytoplasmic Ca2+ buffering. Reduced fractional release from the SR was due to downregulated RyR2 channels, detected at protein and message levels. The constancy of diastolic SR Ca2+ load is explained by reduced RyR2 permeability in combination with right-shifted SERCA activity due to dephosphorylation of its regulator phospholamban. Supplementing iron levels with FCM restored normal Ca2+ signaling and ejection fraction. Thus, 2 Ca2+-handling proteins previously implicated in HF become functionally impaired in iron-deficiency anemia, but their activity is rescued by i.v. iron supplementation.

Elife ; 52016 11 29.
Artigo em Inglês | MEDLINE | ID: mdl-27897970


Hepcidin is the master regulator of systemic iron homeostasis. Derived primarily from the liver, it inhibits the iron exporter ferroportin in the gut and spleen, the sites of iron absorption and recycling respectively. Recently, we demonstrated that ferroportin is also found in cardiomyocytes, and that its cardiac-specific deletion leads to fatal cardiac iron overload. Hepcidin is also expressed in cardiomyocytes, where its function remains unknown. To define the function of cardiomyocyte hepcidin, we generated mice with cardiomyocyte-specific deletion of hepcidin, or knock-in of hepcidin-resistant ferroportin. We find that while both models maintain normal systemic iron homeostasis, they nonetheless develop fatal contractile and metabolic dysfunction as a consequence of cardiomyocyte iron deficiency. These findings are the first demonstration of a cell-autonomous role for hepcidin in iron homeostasis. They raise the possibility that such function may also be important in other tissues that express both hepcidin and ferroportin, such as the kidney and the brain.

Hepcidinas/metabolismo , Homeostase , Ferro/metabolismo , Miócitos Cardíacos/metabolismo , Animais , Proteínas de Transporte de Cátions/genética , Proteínas de Transporte de Cátions/metabolismo , Técnicas de Introdução de Genes , Técnicas de Inativação de Genes , Hepcidinas/genética , Camundongos
Mol Cell Biol ; 36(18): 2328-43, 2016 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-27325674


Prolyl hydroxylase domain protein 2 (PHD2) (also known as EGLN1) is a key oxygen sensor in mammals that posttranslationally modifies hypoxia-inducible factor α (HIF-α) and targets it for degradation. In addition to its catalytic domain, PHD2 contains an evolutionarily conserved zinc finger domain, which we have previously proposed recruits PHD2 to the HSP90 pathway to promote HIF-α hydroxylation. Here, we provide evidence that this recruitment is critical both in vitro and in vivo We show that in vitro, the zinc finger can function as an autonomous recruitment domain to facilitate interaction with HIF-α. In vivo, ablation of zinc finger function by a C36S/C42S Egln1 knock-in mutation results in upregulation of the erythropoietin gene, erythrocytosis, and augmented hypoxic ventilatory response, all hallmarks of Egln1 loss of function and HIF stabilization. Hence, the zinc finger ordinarily performs a critical positive regulatory function. Intriguingly, the function of this zinc finger is impaired in high-altitude-adapted Tibetans, suggesting that their adaptation to high altitude may, in part, be due to a loss-of-function EGLN1 allele. Thus, these findings have important implications for understanding both the molecular mechanism of the hypoxic response and human adaptation to high altitude.

Proteínas de Choque Térmico HSP90/metabolismo , Prolina Dioxigenases do Fator Induzível por Hipóxia/química , Prolina Dioxigenases do Fator Induzível por Hipóxia/metabolismo , Hipóxia/metabolismo , Policitemia/genética , Fatores de Transcrição/metabolismo , Adaptação Fisiológica , Animais , Domínio Catalítico , Células Cultivadas , Técnicas de Inativação de Genes , Humanos , Hidroxilação , Prolina Dioxigenases do Fator Induzível por Hipóxia/genética , Camundongos , Transdução de Sinais , Tibet , Dedos de Zinco