Caffeine Stimulates Amyloid β‐Peptide Release from β‐Amyloid Precursor Protein‐Transfected HEK293 Cells

Abstract

Extracellular amyloid ß-peptide (Aß) deposition is a pathological feature of Alzheimer's disease and the aging brain. Intracellular Aß accumulation is observed in the human muscle disease, inclusion body myositis. Aß has been reported to be toxic to neurons through disruption of normal calcium homeostasis. The pathogenic role of Aß in inclusion body myositis is not as clear. Elevation of intracellular calcium following application of calcium ionophore increases the generation of Aß from its precursor protein (ßAPP). A receptor-based mechanism for the increase in Aß production has not been reported to our knowledge. Here, we use caffeine to stimulate ryanodine receptor (RYR)-regulated intracellular calcium release channels and show that internal calcium stores also participate in the genesis of Aß. In cultured HEK293 cells transfected with ßAPP cDNA, caffeine (5-10 mM) significantly increased the release of Aß fourfold compared with control. These actions of caffeine were saturable, modulated by ryanodine, and inhibited by the RYR antagonists ruthenium red and procaine. The calcium reuptake inhibitors thapsigargin and cyclopiazonic acid potentiated caffeine-stimulated Aß release. NH 4CI and monensin, agents that alter acidic gradients in intracellular vesicles, abolished both the caffeine and ionophore effects. Immunocytochemical studies showed some correspondence between the distribution patterns of RYR and cellular ßAPP immunoreactivities. The relevance of these findings to Alzheimer's disease and inclusion body myositis is discussed. Key Words: CaffeineAmyloid ß-peptide-ß-Amyloid precursor protein-HEK293 cells-Alzheimer's disease-Inclusion body myositis. J. Neurochem. 69, 1580-1591 (1997).ß-Amyloid-laden plaques and vascular deposits are pathologic hallmarks common to Alzheimer' s disease (AD) and the normal aging process. The 4-kDa amybid ß-peptide (Aß) is a secreted 39-42 amino acid peptide by-product of endocytotic and secretory processes (involving unidentified proteases referred to as ß-and y-secretases) acting on the ß-amyloid precursor protein (ßAPP) . The predominant proteolytic event of ßAPP processing leads to the secretion of a large NH2-terminal ectodomain (ßPP5) (Weidemann et al., 1989;Esch et al., 1990;Sisodia et al., 1990) and retention of a 10-kDa COOHterminal membrane fragment (Selkoe et al., 1988) that is catalyzed by an unknown protease termed a-secretase. The latter scission occurs at Aß position 16, thereby precluding formation of intact Aß (Esch et al., 1990;Oltersdorf et al., 1990), and occurs either at the cell surface or within secretory vesicles targeted for exocytosis (Sisodia et al., 1990;Sambamurti et al., 1992;De Strooper et al., 1993; Haass et al., 1995b). A second trafficking pathway involves the reinternalization of cell surface ßAPP by endosomes that are ultimately targeted to lysosomes (Yamazaki et al., 1995). Constitutive production of Aß from wild-type ßAPP molecules occurs mainly via endocytosis of cell surface-associated ßAPP (Koo and Squazzo, 1994).Aß deposits ...

Ca2+ Influx through Store-operated Ca2+ Channels Reduces Alzheimer Disease β-Amyloid Peptide Secretion

“…Studies to date have demonstrated conflicting results. In non-excitable cells, pharmacological elevation of [Ca ϩ2 ] i has been shown to both increase and decrease A␤ levels (43)(44)(45). In neurons, the data on the relationship between Ca 2ϩ influx and A␤ production is equally unclear.…”

Presenilin 2 Interacts with Sorcin, a Modulator of the Ryanodine Receptor

“…Since the large hydrophilic loop regions are divergent between PS1 and PS2 and no FAD mutation has been identified in the putative sorcin binding region of PS2 (synexin homologous domain), the exact contributions of sorcin and other PS1/PS2 loop-interacting molecules to AD neuropathogenesis have not been fully elucidated (16 -19, 58). Interestingly, increased amyloid ␤-peptide levels can result from RyR-driven elevations in intracellular Ca 2ϩ (59). On the other hand, decreased RyR activity correlates with early pathological changes in AD (60).…”

Endoplasmic Reticulum Ca2+Handling in Excitable Cells in Health and Disease

“…On the other hand, by impairing coupling of muscarinic acetylcholine receptors to Gq11 via a membrane lipid peroxidation-mediated mechanism, A␤ can suppress Ca 2ϩ responses to acetylcholine (Kelly et al, 1996). In a cyclical fashion, it has also been shown that Ca 2ϩ can initiate and accelerate the formation of pathogenic A␤ species (Isaacs et al, 2006), but relevant to this topic is that Ca 2ϩ from RyR-sensitive stores in particular can enhance the production and release of A␤ peptides (Querfurth and Selkoe, 1994;Querfurth et al, 1997) (Fig. 4).…”