Advanced glycation end products‐related modulation of cathepsin L and NF‐κB signalling effectors in retinal pigment epithelium lead to augmented response to TNFα

Abstract

The retinal pigment epithelium (RPE) plays a central role in neuroretinal homoeostasis throughout life. Altered proteolysis and inflammatory processes involving RPE contribute to the pathophysiology of age‐related macular degeneration (AMD), but the link between these remains elusive. We report for the first time the effect of advanced glycation end products (AGE)—known to accumulate on the ageing RPE's underlying Bruch's membrane in situ—on both key lysosomal cathepsins and NF‐κB signalling in RPE. Cathepsin L activity and NF‐κB effector levels decreased significantly following 2‐week AGE exposure. Chemical cathepsin L inhibition also decreased total p65 protein levels, indicating that AGE‐related change of NF‐κB effectors in RPE cells may be modulated by cathepsin L. However, upon TNFα stimulation, AGE‐exposed cells had significantly higher ratio of phospho‐p65(Ser536)/total p65 compared to non‐AGEd controls, with an even higher fold increase than in the presence of cathepsin L inhibition alone. Increased proportion of active p65 indicates an AGE‐related activation of NF‐κB signalling in a higher proportion of cells and/or an enhanced response to TNFα. Thus, NF‐κB signalling modulation in the AGEd environment, partially regulated via cathepsin L, is employed by RPE cells as a protective (para‐inflammatory) mechanism but renders them more responsive to pro‐inflammatory stimuli.

Mechanisms of mitochondrial dysfunction and their impact on age-related macular degeneration

“…NF-κB p65 activity may be a critical upstream initiator of p62/SQSTM1 expression in RPE cells under oxidative stress that links inflammatory signaling to autophagy and NFE2L2 cascades ( Song et al, 2017 ). Furthermore, Advanced Glycation End (AGE) product activates NF-κB and renders it more responsive to pro-inflammatory stimuli and extracellular matrix modifications in RPE cells ( Kay et al, 2014 ; Sharif et al, 2019 ).…”

A Review on Molecular Functional and Structural Characterization of Human Cysteine Cathepsins in Bacterial Expression Systems

“…The study suggests that this ability to produce large amounts of enzymatically active Cathepsin L in E. coli will make it possible to produce large amounts of enzyme for structural studies and other studies with pathophysiological implications 44 , while making it possible to perform detailed analysis on additional mutant forms and gross studies that could relate to the metabolism and other properties of this enzyme which is known to be an acid protease 45 . A recent study was also able to reveal that Cathepsin L has a regulatory effect on neuroretinal homeostasis by regulating a variety of inflammatory effects that are related with age related macular degradation in human 46 . Such homeostatic processes that function in the body could be better understood with the availability of recombinant Cathepsin L and accordingly, efficient inducers or inhibitors that are capable of determining the rate of such enzyme catalysed biochemical processes in the body could be controlled.…”

Thymoquinone in Ocular Neurodegeneration: Modulation of Pathological Mechanisms via Multiple Pathways

“…Accumulation and prolong exposure to oxidative stress triggers exaggerated inflammatory response of cells termed as chronic inflammation. Studies showed that chronic inflammation does play an important role in age-related disease ( Sharif et al, 2019 ). Inflammation is considered as the primary immune system reaction to eliminate pathogens or other stimuli in order to restore the cells to normal state ( Chen et al, 2017 ).…”