Regulation of Iron Homeostasis by BMP Signaling

铁调素是一种关键的铁调节激素，其控制铁输出体膜铁转运蛋白的表达，以在需要时增加铁供应以支持红细胞生成和其他基本功能，但防止铁过量的毒性。铁调素的异常低表达导致铁超负荷紊乱遗传性血色病，并导致铁负荷性贫血，如b-地中海贫血。过量的铁调素导致许多慢性疾病中的铁限制性红细胞生成和贫血。一个关键的未回答的问题是肝脏如何感知体内的铁水平，以适当地协调铁调素的表达。我们以前发现，骨形态发生蛋白（BMP）6-SMAD信号通路是铁调素转录响应铁的一个中心调节因子。此外，BMP 6-SMAD通路的调节剂调节铁调素表达以治疗动物模型中慢性疾病的血色素沉着症和贫血。这些研究已经对血色素沉着症的病理生理学产生了重要的见解，并将BMP 6-SMAD途径确定为铁紊乱的可行治疗靶点。然而，铁如何被肝脏感知以调节BMP 6-SMAD信号传导，从而调节铁调素的产生，这在很大程度上仍然是未知的。在上一个资助期，我们发现肝内皮细胞是BMP 6调节hepcidin产生的关键来源。我们还建立了原代肝内皮细胞培养模型，并证明了肝内皮细胞中BMP 6的转录受细胞内铁含量的控制。最后，我们使用这种细胞培养模型结合定量蛋白质组学和RNA-seq筛选来鉴定铁转运蛋白和转录因子途径，我们假设它们在介导响应于铁的BMP 6产生以控制铁调素表达和全身铁稳态中起关键作用。在特定目标I中，我们将使用原代肝内皮细胞培养物和遗传小鼠模型来确定特定铁转运蛋白在控制肝内皮细胞铁含量和铁调节途径中的作用，从而控制BMP 6的表达。在特定目标II中，我们将使用原代肝内皮细胞培养、染色质免疫沉淀、报告基因测定、药理学方法和内皮条件性基因敲除小鼠模型来确定候选转录因子通路的作用及其在控制BMP 6响应于铁的产生中的激活机制。该项目的长期目标是了解BMP信号通路如何通过不同信号调节铁调素表达和全身铁平衡，以深入了解健康和疾病中铁稳态的生理学和病理生理学，并最终开发治疗铁代谢紊乱的新治疗策略。

Hepcidin is a key iron regulatory hormone that controls expression of the iron exporter ferroportin to increase the iron supply when needed to support erythropoiesis and other essential functions, but to prevent the toxicity of iron excess. Abnormally low hepcidin expression leads to the iron overload disorder hereditary hemochromatosis and contributes to iron loading anemias such as b-thalassemia. Excess hepcidin contributes to iron restricted erythropoiesis and anemia in a number of chronic diseases. A key unanswered question is how the liver senses iron levels in the body to appropriately coordinate hepcidin expression. We previously discovered that the bone morphogenetic protein (BMP)6-SMAD signaling pathway is a central regulator of hepcidin transcription in response to iron. Moreover, modulators of the BMP6-SMAD pathway regulate hepcidin expression to treat hemochromatosis and anemia of chronic disease in animal models. These studies have already yielded important insights into the pathophysiology of hemochromatosis and have identified the BMP6-SMAD pathway as a viable therapeutic target for iron disorders. However, it remains largely unknown how iron is sensed by the liver to regulate BMP6-SMAD signaling and thereby hepcidin production. In the last funding period, we discovered that liver endothelial cells are a key source for BMP6 in the regulation of hepcidin production. We also established a primary liver endothelial cell culture model and demonstrated that BMP6 transcription in liver endothelial cells is governed by intracellular iron content. Finally, we used this cell culture model in conjunction with quantitative proteomics and RNA-seq screens to identify iron transporters and transcription factor pathways that we hypothesize play a key role in mediating BMP6 production in response to iron to control hepcidin expression and systemic iron homeostasis. In Specific Aim I, we will use primary liver endothelial cultures and genetic mouse models to establish the role of specific iron transporters in controlling liver endothelial cell iron content and iron-regulated pathways to govern BMP6 expression. In Specific Aim II, we will use primary liver endothelial cell cultures, chromatin immunoprecipitation, reporter assays, pharmacologic approaches, and endothelial conditional knockout mouse models to determine the role of candidate transcription factor pathways and their mechanism of activation in controlling BMP6 production in response to iron. The long-term goals of this project are to understand how the BMP signaling pathway is modulated by different signals to regulate hepcidin expression and systemic iron balance, to gain insights into the physiology and pathophysiology of iron homeostasis in health and disease, and ultimately to develop new therapeutic strategies for treating disorders of iron metabolism.