Hemichannels Are Required for Amyloid β-Peptide-Induced Degranulation and Are Activated in Brain Mast Cells of APPswe/PS1dE9 Mice

Mast cells (MCs) store an array of proinflammatory mediators in secretory granules that are rapidly released upon activation by diverse conditions including amyloid beta (A beta) peptides. In the present work, we found a rapid degranulation of cultured MCs through a pannexin1 hemichannel (Panx1 HC)-dependent mechanism induced by A beta(25-35) peptide. Accordingly, A beta(25-35) peptide also increased membrane current and permeability, as well as intracellular Ca2+ signal, mainly via Panx1 HCs because all of these responses were drastically inhibited by Panx1 HC blockers and absent in the MCs of Panx1(-/-) mice. Moreover, in acute coronal brain slices of control mice, A beta(25-35) peptide promoted both connexin 43 (Cx43)- and Panx1 HC-dependent MC dye uptake and histamine release, responses that were only Cx43 HC dependent in Panx1(-/-) mice. Because MCs have been found close to amyloid plaques of patients with Alzheimer's disease (AD), their distribution in brain slices of APPswe/PS1dE9 mice, a murine model of AD, was also investigated. The number of MCs in hippocampal and cortical areas increased drastically even before amyloid plaque deposits became evident. Therefore, MCs might act as early sensors of amyloid peptide and recruit other cells to the neuroinflammatory response, thus playing a critical role in the onset and progression of AD.