腸道微量元素代謝機(jī)制研究課件

1、腸道銅鐵微量元素代謝與調(diào)控OutlineBackgroundQuestions 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 AbsorptionFerric iron reduced by DcytBImported by iron transporter Dmt1 on apical surface and exported by Ferroportin on basolateral sideFerrous iron oxidized by hephaestin or ceruloplasminDuring iron-deficiency, Dmt1 could transport some other metals such as copperMackenzie, M., et

3、 al. 2005CeruloplasminCopper absorptionCopper also absorbed via enterocytes of small intestine, localized to trans-Golgi and exported by Atp7aStored in liverSecreted through bileKim, B. et al. 2008Iron-deficiency and systemic copper homeostasisLiver copper level in iron-deficient ratMicroarray of ge

4、ne 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 intestineAimWhat are the regulatory mechanisms that induce Atp7a expression levels during iron-deficiency?What is the physiolog

5、ical importance 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

6、J Physiol Cell Physiol, 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 Atp7

7、a promoter activity224 bp Atp7a 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 no

8、t affected by Sp1 inhibitorOverexpression 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-

9、deprived diet leads to increase 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 migra

10、tes into cell and interact with Atp7aIntracellular copper level associated to Atp7a protein stabilitySummaryThere are two regulatory mechanisms involved:Transcriptional regulation by HIF-2 and Sp1Post-translational regulation via copper binding to increase Atp7a protein stabilityIncreased copper absorption will increase production of Cp and Hp expression and activity, which are important for iron released from enterocytesCollins. J.F. et al. 2010 ProspectiveOnly the iron and copper transporters are related by HIF2. Thus, further transcriptomic studies are necessary to uncover the regulato