Purpose: To investigate the intracellular mechanisms that induce amyloid beta (Abeta) accumulation and angiogenesis in the human retinal pigment epithelial cell line ARPE19.
Methods: The authors used two endoplasmic reticulum (ER) stress-inducing reagents, thapsigargin (TG), which inhibits the sarcoplasmic/endoplasmic calcium (Ca)2+-ATPase, and tunicamycin (TM), which inhibits N-linked glycosylation. The expression pattern of Abeta-precursor protein (APP) splice variants was investigated by reverse transcription (RT)-PCR. Cellular expressions of both a series of Abeta metabolism-related factors and angiogenic factors were evaluated by real-time RT-PCR and Western blot (VEGF). Expression of caspase-4 was examined by real-time RT-PCR and Western blot to evaluate the effect of the ER stressor. Intracellular Ca elevation by TG was evaluated by Ca2+ imaging experiments. Dimethyl sulfoxide and staurosporine were used as a nonreagent control and as an apoptosis-inducing reagent through mitochondria not ER, respectively.
Results: TG-treated ARPE19 cells increased the mRNA expression of Abeta production-inducing APP splice variants and reduced that of neprilysin, a catabolic enzyme for Abeta. TG-treated ARPE19 cells produced increases in VEGF, TNF-alpha, TACE mRNA, and VEGF protein expressions and a decrease in PEDF mRNA expression. TG-treated ARPE19 cells induced the expression of active more than TM-treated casepase-4. The intracellular Ca concentration was elevated in only TG-treated ARPE19 cells.
Conclusions: TG-treated ARPE19 cells showed both Abeta accumulation-inducible and angiogenic factor mRNA expression patterns. This study suggests the possibility that ER stress through ER calcium disruption may induce the expression not only of Abeta deposit-promoting factors but also angiogenic factors in the retinal pigment epithelium.