PDF(Pubmed)
Abstract：
UNASSIGNED: Hemojuvelin (HJV) is a glycosylphosphatidylinositol-anchored protein of the repulsive guidance molecule family acting as a bone morphogenetic protein (BMP) coreceptor to induce the hepatic iron regulatory protein hepcidin. Hepcidin causes ubiquitination and degradation of the sole known iron exporter ferroportin, thereby limiting iron availability. The detailed signaling mechanism of HJV in vivo has yet to be investigated. In the current manuscript, we used an established model of adeno-associated virus (AAV)-mediated liver-specific overexpression of HJV in murine models of hepatocyte-specific deficiency of the BMP type I receptors Alk2 or Alk3. In control mice, HJV overexpression increased hepatic Hamp messenger RNA (mRNA) levels, soluble HJV (sHJV), splenic iron content (SIC), as well as phosphorylated small mothers against decapentaplegic protein (pSMAD1/5/8) levels. In contrast, in Alk2fl/fl;Alb-Cre and Alk3fl/fl;Alb-Cre mice, which present with moderate and severe iron overload, respectively, the administration of AAV-HJV induced HJV and sHJV. However, it did not rescue the iron overload phenotypes of those mice. Serum iron levels were induced in Alk2fl/fl;Alb-Cre mice after HJV overexpression. In phosphate-buffered saline-injected Alk3fl/fl;Alb-Cre mice, serum iron levels and the expression of duodenal ferroportin remained high, whereas Hamp mRNA levels were decreased to 1% to 5% of the levels detected in controls. This was reduced even further by AAV-HJV overexpression. SIC remained low in mice with hepatocyte-specific Alk2 or Alk3 deficiency, reflecting disturbed iron homeostasis with high serum iron levels and transferrin saturation and an inability to induce hepcidin by HJV overexpression. The data indicate that ALK2 and ALK3 are both required in vivo for the HJV-mediated induction of hepcidin.
摘要：
Hemojuvelin（HJV）是排斥指导分子（RGM）家族的GPI锚定蛋白，充当骨形态发生蛋白（BMP）共受体，以诱导肝铁调节蛋白hepcidin。铁调素导致唯一已知的铁出口国铁转运蛋白的泛素化和降解，从而限制了铁的可用性。HJV在体内的详细信号传导机制尚待研究。在目前的手稿中，我们在肝细胞特异性缺乏BMPI型受体Alk2或Alk3的小鼠模型中使用了腺相关病毒（AAV）介导的HJV肝脏特异性过表达的模型。在对照小鼠中，HJV过表达增加肝脏HampmRNA水平，可溶性HJV（sHJV），脾脏铁含量（SIC），以及pSMAD1/5/8级别。相比之下,Alk2fl/fl；Alb-Cre和Alk3fl/fl；Alb-Cre小鼠，表现为中度和重度铁过载，分别,AAV-HJV诱导HJV和sHJV。然而,它并不能挽救那些小鼠的铁过载表型。在HJV过表达后,在Alk2fl/fl;Alb-Cre小鼠中诱导血清铁水平。在PBS注射的Alk3fl/fl中；Alb-Cre小鼠血清铁水平和十二指肠铁转运蛋白的表达仍然很高，而HampmRNA水平降低至对照组检测水平的1-5％。这通过AAV-HJV过表达甚至进一步减少。SIC在肝细胞特异性Alk2或Alk3缺乏的小鼠中仍然很低，反映了高血清铁水平和转铁蛋白饱和度以及HJV过表达无法诱导铁调素的铁稳态。数据表明ALK2和ALK3都是体内HJV介导的铁调素诱导所需的。
