1、肠道铜铁微量元素代谢与调控Outline Background Questions from previous studies Three studies related to iron and copper absorption and homeostasis mechanisms Questions left and future studiesIronFe2+Fe3+Iron absorption,utilization and recycling Andrew,N.C.,2008 1-2 mg/daySystemic iron homeostasis iron deficiency i
2、ron overloadIron Absorption Ferric iron reduced by DcytB Imported by iron transporter Dmt1 on apical surface and exported by Ferroportin on basolateral side Ferrous iron oxidized by hephaestin or ceruloplasmin During iron-deficiency,Dmt1 could transport some other metals such as copperMackenzie,M.,e
3、t al.2005CeruloplasminCopper absorption Copper also absorbed via enterocytes of small intestine,localized to trans-Golgi and exported by Atp7a Stored in liver Secreted through bileKim,B.et al.2008Iron-deficiency and systemic copper homeostasisLiver copper level in iron-deficient ratMicroarray of gen
4、e expression in iron-deficient rat duodenum Dmt1Atp7aCollins,J.F.et al.2005 and Ravia,J.J.,et al.2005 Atp7a is a copper exporter located on basolateral side of small intestineAim What are the regulatory mechanisms that induce Atp7a expression levels during iron-deficiency?What is the physiological i
5、mportance of Atp7a during iron-deficiency?Collins.J.F.et al.2010 Potential mechanism mediated by iron-deprivationHIFHypoxiaHypoxia Inducible Factors(HIFs)Shah,Y.and Xie,L.,2013Xie,L.and Collins J.F.Am J Physiol Cell Physiol 300:C1298-1305,2011.(IF:3.817)Xie,L.and J.F.CollinsAm J Physiol Cell Physiol
6、,2013 Feb 1;304(3):C257-62.(IF:3.817)Xie,L.and Collins,J.F.J Bio Chem,2013 Aug 16;288(33):23943-52.(IF:4.573)PublicationsEndogenous Atp7a up-regulated by hypoxia in IEC-6 cellsThree putitive HREs identified on Atp7a promoterOverexpression of HIF2 robustly increases Atp7a promoter activity224 bp Atp7
7、a promoterHRE mutation reduced HIF2-mediated inductionHIF binding site accompanied with GC-rich sequence-binding transcription factorAtp7a promoter has multiple GC-rich sequence Inhibition of Sp1-binding abrogates HIF2-target gene expressionOther HIF-target genes are not affected by Sp1 inhibitorOve
8、rexpression of Sp1 induces endogenous Atp7a levelsSp1 overexpression robustly increases promoter activityFunctional analysis of putative Sp1-binding sites on Atp7a promoterSp1-binding required of HIF2-mediated inductionChIP-analysis of Sp1 binding to Atp7a promoterIron-deprived diet leads to increas
9、e of Atp7a protein levelsCtrl-dietFeD-dietLiver Copper LevelFeD-diet3 ppm iron8 ppm copperCtrl-diet30 ppm iron8 ppm copperCopper transport and deliveryWhite,C.et al.2009 and Tumer,Z.et al.2010 Copper increases Atp7a protein without affect on mRNA levelCopper migrates into cell and interact with Atp7
10、aIntracellular copper level associated to Atp7a protein stabilitySummary There are two regulatory mechanisms involved:u Transcriptional regulation by HIF-2 and Sp1u Post-translational regulation via copper binding to increase Atp7a protein stability Increased copper absorption will increase producti
11、on of Cp and Hp expression and activity,which are important for iron released from enterocytesCollins.J.F.et al.2010 Prospective Only the iron and copper transporters are related by HIF2.Thus,further transcriptomic studies are necessary to uncover the regulatory mechanism of HIF2 in small intestine Dysregulation of intestinal iron and copper absorption and homeostasis affect intestinal microbiota and systemic mineral dysregulation
