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

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.

AGE-RAGE interaction in the TGFβ2-mediated epithelial to mesenchymal transition of human lens epithelial cells

“…We previously showed that AGEs in the lens capsule promote the TGFβ2-mediated EMT of lens epithelial cells [4]. Because cataract surgery is mostly performed in the elderly and their capsule proteins are expected to contain relatively high levels of AGEs, we proposed that PCO formation after cataract surgery could be due, at least partially, to AGEs in the capsule, based on our findings.…”

“…Laminin, collagen IV, entactin and heparin sulfate proteoglycan are the major components of BME. AGE modification of BME was carried out as previously described [4]. Briefly, after coating the plates with BME (50 μg/ml), the plate was incubated at 37 °C with a glycating mixture, which consisted of 2 mM ascorbate (Sigma-Aldrich), 25 mM glucose (Sigma-Aldrich) and 250 μM methylglyoxal (Sigma-Aldrich), for one week at pH 7.4 under aseptic conditions.…”

“…We have previously reported that this glycation procedure produced AGEs in BME, such as CML, MG-H1, MODIC etc. [4]. …”

“…Furthermore, AGE levels in proteins are inversely related to the turnover rate of proteins, and thus the BM proteins with a low turnover rate are expected to accumulate AGEs. We reported recently that AGEs accumulate in the human lens capsule with aging and at a higher rate in the capsules of cataractous lenses [4]. …”

Influence of aldose reductase on epithelial-to-mesenchymal transition signaling in lens epithelial cells

“…In an potentially related area, it is interesting to note that fructose, the end product of AR polyol pathway, has been demonstrated to form advanced glycated end-products (AGEs) much faster than glucose [35]. Raghavan and colleagues recently reported that AGEs in lens capsule enhance EMT of LECs under TGF-β2 treatment [36, 37]. Accordingly, AR-induced AGEs production might be another stimulus for PCO development following cataract surgery.…”