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Biochem Biophys Rep. 2018 Jan 28;13:83-92. doi: 10.1016/j.bbrep.2018.01.005. eCollection 2018 Mar.

Involvement of the ubiquitin-proteasome system in the expression of extracellular matrix genes in retinal pigment epithelial cells.

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Ocular Angiogenesis Group, Departments of Ophthalmology and Medical Biology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Department of Medical Biology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.


Emerging evidence suggests that dysfunction of the ubiquitin-proteasome system is involved in the pathogenesis of numerous senile degenerative diseases including retinal disorders. The aim of this study was to assess whether there is a link between proteasome regulation and retinal pigment epithelium (RPE)-mediated expression of extracellular matrix genes. For this purpose, human retinal pigment epithelial cells (ARPE-19) were treated with different concentrations of transforming growth factor-β (TGFβ), connective tissue growth factor (CTGF), interferon-γ (IFNγ) and the irreversible proteasome inhibitor epoxomicin. First, cytotoxicity and proliferation assays were carried out. The expression of proteasome-related genes and proteins was assessed and proteasome activity was determined. Then, expression of fibrosis-associated factors fibronectin (FN), fibronectin EDA domain (FN EDA), metalloproteinase-2 (MMP-2), tissue inhibitor of metalloproteinases-1 (TIMP-1) and peroxisome proliferator-associated receptor-γ (PPARγ) was assessed. The proteasome inhibitor epoxomicin strongly arrested cell cycle progression and down-regulated TGFβ gene expression, which in turn was shown to induce expression of pro-fibrogenic genes in ARPE-19 cells. Furthermore, epoxomicin induced a directional shift in the balance between MMP-2 and TIMP-1 and was associated with down-regulation of transcription of extracellular matrix genes FN and FN-EDA and up-regulation of the anti-fibrogenic factor PPARγ. In addition, both CTGF and TGFβ were shown to affect expression of proteasome-associated mRNA and protein levels. Our results suggest a link between proteasome activity and pro-fibrogenic mechanisms in the RPE, which could imply a role for proteasome-modulating agents in the treatment of retinal disorders characterized by RPE-mediated fibrogenic responses.


AMD, age-related macular degeneration; ARPE-19, human retinal pigment epithelial cells; CNV, choroidal neovascularization; CTGF; CTGF, connective tissue growth factor; ECM, extracellular matrix; EMT, epithelial-mesenchymal transition; Epoxomicin; FN EDA, fibronectin EDA domain; FN, fibronectin; Fibrosis; IFNγ, interferon-γ; MMP-2, matrix metalloproteinase-2; PPARγ; PPARγ, peroxisome proliferator-associated receptor-γ; Proteasome; RPE; RPE, retinal pigment epithelium; Retina; TGFβ; TGFβ, transforming growth factor-β; TIMP-1, tissue inhibitor of metalloproteinases-1; UPS, ubiquitin-proteasome system; nAMD, neovascular age-related macular degeneration

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