title: LRP5 is required for vascular development in deeper layers of the retina.
abstract: BACKGROUND
  The low-density lipoprotein receptor-related protein 5 (LRP5) plays an important role in the development of retinal vasculature. LRP5 loss-of-function mutations cause incomplete development of retinal vessel network in humans as well as in mice. To understand the underlying mechanism for how LRP5 mutations lead to retinal vascular abnormalities, we have determined the retinal cell types that express LRP5 and investigated specific molecular and cellular functions that may be regulated by LRP5 signaling in the retina.
  
  
  RESULTS
  We characterized the development of retinal vasculature in LRP5 mutant mice using specific retinal cell makers and a GFP transgene expressed in retinal endothelial cells. Our data revealed that retinal vascular endothelial cells predominantly formed cell clusters in the inner-plexiform layer of LRP5 mutant retina rather than sprouting out or migrating into deeper layers to form normal vascular network in the retina. The IRES-beta-galactosidase (LacZ) report gene under the control of the endogenous LRP5 promoter was highly expressed in Müller cells and was also weakly detected in endothelial cells of the retinal surface vasculature. Moreover, the LRP5 mutant mice had a reduction of a Müller cell-specific glutamine transporter, Slc38a5, and showed a decrease in b-wave amplitude of electroretinogram.
  
  
  CONCLUSIONS
  LRP5 is not only essential for vascular endothelial cells to sprout, migrate and/or anastomose in the deeper plexus during retinal vasculature development but is also important for the functions of Müller cells and retinal interneurons. Müller cells may utilize LRP5-mediated signaling pathway to regulate vascular development in deeper layers and to maintain the function of retinal interneurons.
authors.affiliation: School of Optometry and Vision Science Program, University of California, Berkeley, California, USA. chxia@berkeley.edu
authors.forename: Chun-hong
authors.initials: CH
authors.lastname: Xia
authors.forename: Zipora
authors.initials: Z
authors.lastname: Yablonka-Reuveni
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Gong
mesh_terms: D026921:Amino Acid Transport Systems, Neutral / Q000235:genetics; D000818:Animals; D004596:Electroretinography; D042783:Endothelial Cells / Q000378:metabolism / Q000473:pathology; D005260:Female; D026502:LDL-Receptor Related Proteins / Q000235:genetics / Q000502:physiology*; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008817:Mice, Mutant Strains; D016133:Polymerase Chain Reaction; D012160:Retina / Q000254:growth & development* / Q000378:metabolism*; D012171:Retinal Vessels / Q000254:growth & development* / Q000378:metabolism*
chemical_list: D026921:Amino Acid Transport Systems, Neutral; D026502:LDL-Receptor Related Proteins; C555482:LRP5 protein, human; D060492:Low Density Lipoprotein Receptor-Related Protein-5; C555483:Lrp5 protein, mouse