title: Wnt signaling in age-related macular degeneration: human macular tissue and mouse model.
abstract: BACKGROUND
  The wingless-type MMTV integration site (Wnt) signaling is a group of signal transduction pathways. In canonical Wnt pathway, Wnt ligands bind to low-density lipoprotein receptor-related protein 5 or 6 (LRP5 or LRP6), resulting in phosphorylation and activation of the receptor. We hypothesize that canonical Wnt pathway plays a role in the retinal lesion of age-related macular degeneration (AMD), a leading cause of irreversible central visual loss in elderly.
  
  
  METHODS
  We examined LRP6 phosphorylation and Wnt signaling cascade in human retinal sections and plasma kallistatin, an endogenous inhibitor of the Wnt pathway in AMD patients and non-AMD subjects. We also used the Ccl2 (-/-) /Cx3cr1 (-/-) /rd8 and Ccl2 (-/-) /Cx3cr1 (gfp/gfp) mouse models with AMD-like retinal degeneration to further explore the involvement of Wnt signaling activation in the retinal lesions in those models and to preclinically evaluate the role of Wnt signaling suppression as a potential therapeutic option for AMD.
  
  
  RESULTS
  We found higher levels of LRP6 (a key Wnt signaling receptor) protein phosphorylation and transcripts of the Wnt pathway-targeted genes, as well as higher beta-catenin protein in AMD macula compared to controls. Kallistatin was decreased in the plasma of AMD patients. Retinal non-phosphorylated-β-catenin and phosphorylated-LRP6 were higher in Ccl2 (-/-) /Cx3cr1 (-/-) /rd8 mice than that in wild type. Intravitreal administration of an anti-LRP6 antibody slowed the progression of retinal lesions in Ccl2 (-/-) /Cx3cr1 (-/-) /rd8 and Ccl2 (-/-) /Cx3cr1 (gfp/gfp) mice. Electroretinography of treated eyes exhibited larger amplitudes compared to controls in both mouse models. A2E, a retinoid byproduct associated with AMD was lower in the treated eyes of Ccl2 (-/-) /Cx3cr1 (-/-) /rd8 mice. Anti-LRP6 also suppressed the expression of Tnf-α and Icam-1 in Ccl2 (-/-) /Cx3cr1 (-/-) /rd8 retinas.
  
  
  CONCLUSIONS
  Wnt signaling may be disturbed in AMD patients, which could contribute to the retinal inflammation and increased A2E levels found in AMD. Aberrant activation of canonical Wnt signaling might also contribute to the focal retinal degenerative lesions of mouse models with Ccl2 and Cx3cr1 deficiency, and intravitreal administration of anti-LRP6 antibody could be beneficial by deactivating the canonical Wnt pathway.
authors.affiliation: Laboratory of Immunology, National Eye Institute, National Institutes of Health, 10 Center Drive, Bldg. 10, Rm. 10N103, NIH/NEI, Bethesda, MD, 20892-1857, USA. tuoj@csr.nih.gov.
authors.forename: Jingsheng
authors.initials: J
authors.lastname: Tuo
authors.affiliation: Laboratory of Immunology, National Eye Institute, National Institutes of Health, 10 Center Drive, Bldg. 10, Rm. 10N103, NIH/NEI, Bethesda, MD, 20892-1857, USA. yujuanwang2013@gmail.com.
authors.forename: Yujuan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA. rui-cheng@ouhsc.edu.
authors.forename: Rui
authors.initials: R
authors.lastname: Cheng
authors.affiliation: Visual Function Core, National Eye Institute, National Institutes of Health, Bethesda, MD, USA. yichao.li@nih.gov.
authors.forename: Yichao
authors.initials: Y
authors.lastname: Li
authors.affiliation: Centre for Experimental Medicine, Queen's University Belfast, Belfast, UK. m.chen@qub.ac.uk.
authors.forename: Mei
authors.initials: M
authors.lastname: Chen
authors.affiliation: Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA. Jian-Xing-Ma@ouhsc.edu.
authors.forename: Fangfang
authors.initials: F
authors.lastname: Qiu
authors.affiliation: Visual Function Core, National Eye Institute, National Institutes of Health, Bethesda, MD, USA. haohua.qian@nih.gov.
authors.forename: Haohua
authors.initials: H
authors.lastname: Qian
authors.affiliation: Laboratory of Immunology, National Eye Institute, National Institutes of Health, 10 Center Drive, Bldg. 10, Rm. 10N103, NIH/NEI, Bethesda, MD, 20892-1857, USA. defen.shen@gmail.com.
authors.forename: Defen
authors.initials: D
authors.lastname: Shen
authors.affiliation: Centre for Experimental Medicine, Queen's University Belfast, Belfast, UK. heping.xu@qub.ac.uk.
authors.forename: Rosana
authors.initials: R
authors.lastname: Penalva
authors.affiliation: Centre for Experimental Medicine, Queen's University Belfast, Belfast, UK. heping.xu@qub.ac.uk.
authors.forename: Heping
authors.initials: H
authors.lastname: Xu
authors.affiliation: Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA. Jian-Xing-Ma@ouhsc.edu.
authors.forename: Jian-Xing
authors.initials: JX
authors.lastname: Ma
authors.affiliation: Laboratory of Immunology, National Eye Institute, National Institutes of Health, 10 Center Drive, Bldg. 10, Rm. 10N103, NIH/NEI, Bethesda, MD, 20892-1857, USA. chanc@nei.nih.gov.
authors.forename: Chi-Chao
authors.initials: CC
authors.lastname: Chan
mesh_terms: D000368:Aged; D000375:Aging; D000818:Animals; D000073883:CX3C Chemokine Receptor 1; D018932:Chemokine CCL2 / Q000235:genetics; D004195:Disease Models, Animal; D004596:Electroretinography; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D058449:Intravitreal Injections; D060488:Low Density Lipoprotein Receptor-Related Protein-6 / Q000378:metabolism; D008268:Macular Degeneration / Q000097:blood* / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008875:Middle Aged; D010766:Phosphorylation; D019707:Receptors, Chemokine / Q000235:genetics; D012160:Retina / Q000378:metabolism; D012162:Retinal Degeneration; D015843:Serpins / Q000097:blood; D015398:Signal Transduction; D051153:Wnt Proteins / Q000378:metabolism*
chemical_list: C111835:CCL2 protein, human; D000073883:CX3C Chemokine Receptor 1; C095235:CX3CR1 protein, human; C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; C471885:Cx3cr1 protein, mouse; C555475:LRP6 protein, human; D060488:Low Density Lipoprotein Receptor-Related Protein-6; C555476:Lrp6 protein, mouse; D019707:Receptors, Chemokine; D015843:Serpins; D051153:Wnt Proteins; C051324:kallistatin