The Amyloid Precursor Protein Plays Differential Roles in the UVA Resistance and Proliferation of Human Retinal Pigment Epithelial Cells

Abstract

Background: Age-related macular degeneration (AMD) can be characterised by degeneration of retinal pigment epithelial (RPE) cells and the accumulation, in retinal drusen deposits, of amyloid beta-peptides proteolytically derived, by secretases, from the amyloid precursor protein (APP). Ultraviolet (UV) light exposure is a risk factor for the development of AMD. Objectives: In the current study, we investigated whether APP and/or its proteolysis are linked to the UVA resistance or proliferation of ARPE-19 human RPE cells. Methods: Cell viability was determined, following UVA exposure, with prior small interfering RNA-mediated APP depletion or secretase inhibitor treatments. APP levels/proteolysis were analysed by immunoblotting. Cells were also grown in the presence/absence of secretase inhibitors to assess their effects on longer-term culture growth. Finally, the effects of APP proteolytic fragments on ARPE-19 cell proliferation were monitored following co-culture with human embryonic kidney cells stably over-expressing these fragments. Results: Endogenous APP was depleted following UVA irradiation and β-secretase, but not -secretase, processing of the protein was reduced. Experimental APP depletion or -secretase (but not - or β-secretase) inhibition ablated the detrimental effect of UVA on cell viability. In contrast, -secretase, and possibly -secretase but not β-secretase activity, appeared to promote the longer-term proliferation of ARPE-19 cells in the absence of UVA irradiation Conclusions: There are clear but differential links between APP expression/proteolysis and the proliferation and UVA resistance of ARPE-19 cells indicating that the protein should be investigated further in relation to the identification of possible drug targets for the treatment of AMD.

Non-Neovascular Age-Related Macular Degeneration Assessment: Focus on Optical Coherence Tomography Biomarkers

“…Oxidative stress within the retina is exacerbated by chronic UVA exposure affecting all retinal structures. Moreover, blue light exposure is known to induce oxidative stress within the retinal pigment epithelium (RPE) layer [7,8]. The cumulative oxidative stress from UV and blue light, which is further potentiated by cigarette smoke and the aging process, elevates the reactive oxygen species (ROS) levels produced by the RPE.…”

Realization of Amyloid-like Aggregation as a Common Cause for Pathogenesis in Diseases

“…It is well-documented that the astrocytes affected by AD express high levels of APP, βsecretase, and γ-secretase, the three main components required for amyloid production [29]. Proteolysis of APP by α-secretase and β-secretase leads to the secretion of sAPPα and sAPPβ, respectively [36]. The secreted sAPPα or sAPPβ have C-terminal fragments which can be cleaved by γ-secretase extracellularly to release the peptides Aβ42 and Aβ40 [36].…”

“…Proteolysis of APP by α-secretase and β-secretase leads to the secretion of sAPPα and sAPPβ, respectively [36]. The secreted sAPPα or sAPPβ have C-terminal fragments which can be cleaved by γ-secretase extracellularly to release the peptides Aβ42 and Aβ40 [36]. Zhao et al studied the effect of cytokines on the production of amyloids in the astrocytes of the brain in AD-affected patients.…”

Pathophysiology of Age-Related Macular Degeneration: Implications for Treatment

“…Then amyloid beta can activate the alternative complement pathway. It has been claimed that these effects can be mitigated by using blue light-filtering devices [19]. Nevertheless, there are conflicting results in the scientific literature regarding its use to prevent the onset of AMD in humans, and more studies are needed to demonstrate with certainty the benefit beyond what was observed in vitro [20].…”