Role of transient receptor potential ankyrin 1 channels in Alzheimer's disease

Background: Transient receptor potential ankyrin 1 (TRPA1) channel plays an important role in pain and inflammation. However, little is known about the significance of the TRPA1 channel in the pathophysiology of Alzheimer's disease (AD). Methods: Wild-type (WT), TRPA1^-/-, amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic (APP/PS1 Tg) mice, the mouse model of AD, and APP/PS1 Tg/TRPA1^-/- mice were used to examine the role of TRPA1 in pathogenesis of AD. Western blot was used for protein expression; immunohistochemistry was used for histological examination. The mouse behaviors were evaluated by locomotion, nesting building, Y-maze and Morris water maze tests; levels of interleukin (IL)-1β, IL-4, IL-6 and IL-10 and the activities of protein phosphatase 2B (PP2B), NF-ΚB and nuclear factor of activated T cells (NFAT) were measured by conventional assay kits; Fluo-8 NW calcium (Ca²⁺) assay kit was used for the measurement of intracellular Ca²⁺ level in primary astrocytes and HEK293 cells. Results: The protein expression of TRPA1 channels was higher in brains, mainly astrocytes of the hippocampus, from APP/PS1 Tg mice than WT mice. Ablation of TRPA1-channel function in APP/PS1 Tg mice alleviated behavioral dysfunction, Aβ plaque deposition and pro-inflammatory cytokine production but increased astrogliosis in brain lesions. TRPA1 channels were activated and Ca²⁺ influx was elicited in both astrocytes and TRPA1-transfected HEK293 cells treated with fibrilized Aβ_1-42; these were abrogated by pharmacological inhibition of TRPA1 channel activity, disruption of TRPA1 channel function or removal of extracellular Ca²⁺. Inhibition of TRPA1 channel activity exacerbated Aβ_1-42-induced astrogliosis but inhibited Aβ_1-42-increased PP2B activation, the production of pro-inflammatory cytokines and activities of transcriptional factors NF-ΚB and NFAT in astrocytes and in APP/PS1 Tg mice. Pharmacological inhibition of PP2B activity diminished the fibrilized Aβ_1-42-induced production of pro-inflammatory cytokines, activation of NF-ΚB and NFAT and astrogliosis in astrocytes. Conclusions: TRPA1 - Ca²⁺ - PP2B signaling may play a crucial role in regulating astrocyte-derived inflammation and pathogenesis of AD.