AGEs in human lens capsule promote the TGFβ2-mediated EMT of lens epithelial cells: implications for age-associated fibrosis.

Cibin T Raghavan,Dawn G Smith,Andrew J O Smith,Scott Howell,Pankaj Gupta,Mareen Smuda,Ian Michael Wormstone,Marcus A Glomb,Annapurna Singh,Ram H Nagaraj

doi:10.1111/acel.12450

Abstract

SummaryProteins in basement membrane (BM) are long‐lived and accumulate chemical modifications during aging; advanced glycation endproduct (AGE) formation is one such modification. The human lens capsule is a BM secreted by lens epithelial cells. In this study, we have investigated the effect of aging and cataracts on the AGE levels in the human lens capsule and determined their role in the epithelial‐to‐mesenchymal transition (EMT) of lens epithelial cells. EMT occurs during posterior capsule opacification (PCO), also known as secondary cataract formation. We found age‐dependent increases in several AGEs and significantly higher levels in cataractous lens capsules than in normal lens capsules measured by LC‐MS/MS. The TGFβ2‐mediated upregulation of the mRNA levels (by qPCR) of EMT‐associated proteins was significantly enhanced in cells cultured on AGE‐modified BM and human lens capsule compared with those on unmodified proteins. Such responses were also observed for TGFβ1. In the human capsular bag model of PCO, the AGE content of the capsule proteins was correlated with the synthesis of TGFβ2‐mediated α‐smooth muscle actin (αSMA). Taken together, our data imply that AGEs in the lens capsule promote the TGFβ2‐mediated fibrosis of lens epithelial cells during PCO and suggest that AGEs in BMs could have a broader role in aging and diabetes‐associated fibrosis.

Highlights

The human lens capsule is a basement membrane (BM) secreted by lens epithelial cells and is composed of interacting networks of laminin and type IV collagen in Accepted for publication 10 January 2016 addition to several heparin sulfate proteoglycans (Danysh & Duncan, 2009)
The human lens capsule is a BM secreted by lens epithelial cells and is composed of interacting networks of laminin and type IV collagen in Correspondence Ram H
Glycation is the reaction of carbonyl compounds, including glucose, ascorbate oxidation products, and methylglyoxal, that forms a variety of structurally diverse stable adducts in proteins; these adducts are collectively known as advanced glycation endproducts or AGEs (Singh et al, 2001)

Summary

Introduction

The human lens capsule is a BM secreted by lens epithelial cells and is composed of interacting networks of laminin and type IV collagen in Accepted for publication 10 January 2016 addition to several heparin sulfate proteoglycans (Danysh & Duncan, 2009). The capsule encloses the lens, sequestering it from other ocular tissue and protecting it from infections. It provides vital epitopes for the surface receptors of lens cells, which promote lens cell survival, cell migration, and differentiation (Blakely et al, 2000; Tholozan et al, 2007). Because BM proteins, including proteins in the lens capsule, are longlived, these proteins accumulate post-synthetic modifications from enzymatic amino acid cross-linking, lipid peroxidation, and glycation during aging (Sell & Monnier, 1995). Several studies have shown the accumulation of AGEs in the aged BM of the kidneys, lungs, and lens capsule (Bailey et al, 1993; Oldfield et al, 2001; Song et al, 2011)

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