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Norrin attenuates protease-mediated death of transformed retinal ganglion cells.

Authors: Lin, S  Cheng, M  Dailey, W  Drenser, K  Chintala, S 
Citation: Lin S, etal., Mol Vis. 2009;15:26-37. Epub 2009 Jan 12.
Pubmed: (View Article at PubMed) PMID:19137075

PURPOSE: To investigate the effects of norrin, a nonconventional ligand for Wingless-Int (Wnt)-beta-catenin signaling pathway, on protease-mediated death of transformed rat retinal ganglion cells (RGC-5). METHODS: Transformed RGC-5 cells were treated with 2.0 microM staurosporine (SS), a broad-spectrum protein kinase-C inhibitor, to induce growth arrest, differentiation, and elevated levels of tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA). RGC-5 cells were also treated with 2.0 microM SS and varying doses of recombinant norrin (3.125 to 100 ng/ml). Activation of Wnt pathway was assessed by nuclear translocation of beta-catenin. Proteolytic activity of tPA and uPA was determined by zymography assays and cell viability was determined by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays. Expression and phosphorylation of the low-density lipoprotein-related receptor-1 (LRP-1), a cell surface receptor for tPA and uPA, was determined by immunoprecipitation and western blot analysis. RESULTS: Compared to RGC-5 cells left untreated, cells treated with either SS alone or SS and norrin secreted elevated levels of tPA and uPA. A significant number of RGC-5 cells treated with only SS underwent cell death, whereas cells treated with SS and norrin did not, even though RGC-5 cells secreted elevated levels of tPA and uPA under both treatment conditions. Although norrin activated the Wnt pathway, Dickkopf related protein 1 (Dkk1), an inhibitor of Wnt/beta-catenin pathway, failed to completely block norrin's neuroprotective effects. Assays for expression and phosphorylation of LRP-1 indicated that tPA and uPA cause RGC-5 cell death, in part, by reducing phosphorylation of LRP-1, whereas norrin attenuated tPA and uPA-mediated RGC cell death, in part, by restoring phosphorylation of LRP-1. CONCLUSIONS: Our results suggest that norrin attenuates tPA- and uPA-mediated death of RGC-5 cells by activating Wnt/beta-catenin pathway and by regulating phosphorylation of LRP-1.


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CRRD Object Information
CRRD ID: 7241807
Created: 2013-03-14
Species: All species
Last Modified: 2013-03-14
Status: ACTIVE


RGD is funded by grant HL64541 from the National Heart, Lung, and Blood Institute on behalf of the NIH.