Amyloid beta and its naturally occurring N-terminal variants are potent activators of human and mouse formyl peptide receptor 1.

Formyl peptide receptors (FPRs) may contribute to inflammation in Alzheimer's disease through interactions with neuropathological Amyloid beta (Aß) peptides. Previous studies reported activation of FPR2 by Aß1-42, but further investigation of other FPRs and Aß variants is needed. This study provides a comprehensive overview of the interactions of mouse and human FPRs with different physiologically relevant Aß-peptides using transiently transfected cells in combination with calcium imaging. We observed that, in addition to hFPR2, all other hFPRs also responded to Aß1-42, Aß1-40, and the naturally occurring variants Aß11-40 and Aß17-40. Notably, Aß11-40 and Aß17-40 are very potent activators of mouse and human FPR1, acting at nanomolar concentrations. Buffer composition and aggregation state are extremely crucial factors that critically affect the interaction of Aß with different FPR subtypes. To investigate the physiological relevance of these findings, we examined the effects of Aß11-40 and Aß17-40 on the human glial cell line U87. Both peptides induced a strong calcium flux at concentrations that are very similar to those obtained in experiments for hFPR1 in HEK cells. Further immunocytochemistry, qPCR, and pharmacological experiments verified that these responses were primarily mediated through hFPR1. Chemotaxis experiments revealed that Aß11-40 but not Aß17-40 evoked cell migration, which argues for a functional selectivity of different Aß peptides. Together, these findings provide the first evidence that not only hFPR2 but also hFPR1 and hFPR3 may contribute to neuroinflammation in Alzheimer's disease through an interaction with different Aß variants.

Differential transcriptional regulation of hypoxia-inducible factor-1α by arsenite under normoxia and hypoxia: involvement of Nrf2.

Arsenite (As(III)) is widely distributed in nature and can be found in water, food, and air. There is significant evidence that exposure to As(III) is associated with human cancers originated from liver, lung, skin, bladder, kidney, and prostate. Hypoxia plays a role in tumor growth and aggressiveness; adaptation to it is, at least to a large extent, mediated by hypoxia-inducible factor-1α (HIF-1α). In the current study, we investigated As(III) effects on HIF-1α under normoxia and hypoxia in the hepatoma cell line HepG2. We found that As(III) increased HIF-1α protein levels under normoxia while the hypoxia-mediated induction of HIF1α was reduced. Thereby, the As(III) effects on HIF-1α were dependent on both, transcriptional regulation via the transcription factor Nrf2 mediated by NOX4, PI3K/Akt, and ERK1/2 as well as by modulation of HIF-1α protein stability. In line, the different effects of As(III) via participation of HIF-1α and Nrf2 were also seen in tube formation assays with endothelial cells where knockdown of Nrf2 and HIF-1α abolished As(III) effects. Overall, the present study shows that As(III) is a potent inducer of HIF-1α under normoxia but not under hypoxia which may explain, in part, its carcinogenic as well as anti-carcinogenic actions. KEY MESSAGE: As(III) increased HIF-1α under normoxia but reduced its hypoxia-dependent induction. The As(III) effects on HIF-1α were dependent on ROS, NOX4, PI3K/Akt, and ERK1/2. The As(III) effects under normoxia involved transcriptional regulation via Nrf2. Knockdown of Nrf2 and HIF-1α abolished As(III) effects in tube formation assays. The data may partially explain As(III)'s carcinogenic and anti-carcinogenic actions.