Abstract
The present study aims to understand the mechanism of the lens epithelial cell’s strong anti-apoptotic capacity and survival in the mature human lens that, on the one hand, maintains lens transparency over several decades, while on the other hand, increases the risk of posterior capsule opacification (PCO). Here we compared FHL124 cells and HeLa cells, spontaneously immortalized epithelial cell lines derived from the human lens and cervical cancer cells, respectively, of their resistance to TNFα-mediated cell death. TNFα plus cycloheximide (CHX) triggered almost all of HeLa cell death. FHL124 cells, however, were unaffected and able to block caspase-8 activation as well as prevent caspase-3 and PARP-1 cleavage. Interestingly, despite spontaneous NFκB and AP-1 activation and upregulation of multiple cell survival/anti-apoptotic genes in both cell types, only FHL124 cells were able to survive the TNFα challenge. After screening and comparing the cell survival genes, cFLIP was found to be highly expressed in FHL124 cells and substantially upregulated by TNFα stimulation. FHL124 cells with a mild cFLIP knockdown manifested a profound apoptotic response to TNFα stimulus similar to HeLa cells. Most importantly, we confirmed these findings in an ex vivo lens capsular bag culture system. In conclusion, our results show that cFLIP is a critical gene that is regulating lens epithelial cell survival.
Highlights
For most people, the mature human lens maintains its transparency for several decades before beginning to increase the risk of developing cataracts[1,2]
We demonstrate a distinct insensitivity of human lens epithelial cells (FHL24) to tumor necrosis factor α (TNFα, a known promoter of apoptosis) apoptosis relative to HeLa cells and report that cellular FLICE-like inhibitory protein is a pivotal antiapoptotic gene that is critical for lens epithelial cell survival
The FHL124 cell line is a spontaneously immortalized cell line derived from the human lens epithelium[18]
Summary
Whether LECs undergo programmed cell death (apoptosis) in the mature human lens with or without cataract has gained much attention in the field. In 1998, Harocopos et al.[9] showed that minimal evidence of apoptotic LECs in both healthy and cataract lenses were detected and the study suggested that the high level of TUNEL positive stain from the Li et al.[13] study was likely resulted from necrotic cell death generated during tissue processing. A relatively high threshold to apoptosis is beneficial for lens maintenance and protection against cataracts. This intrinsic ability to survive becomes problematic following cataract surgery. The cellular events subsequently give rise to physical changes, such as matrix wrinkling which scatters light and significantly reduces vision quality[17] This post-surgical complication of cataract surgery is called posterior capsule opacification (PCO). We demonstrate a distinct insensitivity of human lens epithelial cells (FHL24) to tumor necrosis factor α (TNFα, a known promoter of apoptosis) apoptosis relative to HeLa cells and report that cellular FLICE-like inhibitory protein (cFLIP) is a pivotal antiapoptotic gene that is critical for lens epithelial cell survival
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