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

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 ß-secretase, but not α- secretase, the processing of the protein was reduced. Experimental APP depletion or γ-secretase (but not α- or ß-secretase) inhibition ablated the detrimental effect of UVA on cell viability. In contrast, α-secretase, and possibly γ-secretase but not ß-secretase activity, appeared to promote the longerterm proliferation of ARPE-19 cells in the absence of UVA irradiation. CONCLUSION: 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.

A rare presentation of a rare disease: pulmonary lymphomatoid granulomatosis.

A 70-year-old female presented with a 4-week history of dry cough and wheezing. Chest radiograph showed a 10.5 cm mass-like density in the anterior mediastinum which had not been previously visualized. Computed tomography scan (CT) of the chest showed a right hilar mass encasing and narrowing right upper lobe bronchus and right mainstem bronchus and secondary atelectatic changes. Biopsy was consistent with a diagnosis of lymphomatoid granulomatosis Grade 3. She responded well clinically and radiologically to therapy. Lymphomatoid granulomatosis is a rare EBV-associated disorder which is considered a lymphoproliferative disease. The most common radiographic feature is multiple lung nodules. An isolated hilar mass is an exceptionally rare presentation of this rare disease.