Abstract:
Alzheimer’s disease (AD) is a progressive neurodegenerative disease mainly affecting the elderly population. Amyloid-β (Aβ) peptide is a 40-42 residue peptide found in the amyloid plaques, one of the pathological hallmarks of the disease. Aβ is toxic to cells in culture and it is now widely accepted that deposition of Aβ is the primary driving force of AD. Aβ toxicity has predominantly focused on neurons. However, recent understanding about the functions of astrocytes in the central nervous system has challenged this view. Accumulating evidence suggests that Aβ causes disruptions in astrocyte calcium (Ca2+) signalling and oxidative stress which can lead to neuron death as a result of the loss of functional supports provided by astrocytes. Here we hypothesize that the Ca2+-permeable, astrocyte-specific TRPV4 channel, which is specifically expressed in hippocampal astrocytes, contributes to Aβ-mediated Ca2+ overload and oxidative stress leading to subsequent neuronal death. This hypothesis is tested in this study by using two model systems from the hippocampus: organotypic slice cultures and mixed monolayer cultures of astrocytes and neurons. To represent the aging brain, oxidative stress was induced in the slice cultures by applying buthionine sulfoximine (BSO). Aβ40-evoked cell death in the BSO-conditioned slice cultures was determined by propidium iodide (PI) uptake. Consistent with the hypothesis, Aβ40 exposure (10 μM and 20 μM for 24 h) caused extensive cell death in the astrocyte-rich regions of the hippocampal slice cultures, while the CA1-CA3 neurons were less affected. Aβ40-induced death in astrocyte-rich regions was completely prevented by blockers of TRPV4 channels ruthenium red (RR; 2 μM) and gadolinium (Gd3+; 500 μM). Trolox, an antioxidant, prevented Aβ40-induced astrocytic death in a similar fashion to RR and Gd3+. Further time-lapse imaging studies of primary mixed monolayer cultures also indicated astrocytic damage preceding neuronal damage as a result of Aβ40 exposure. The results obtained in this study strongly suggest the involvement of TRPV4 channels in Aβ-induced astrocyte death and possibly subsequent neuronal death. Further investigations are required but TRPV4 blockade, combined with antioxidant-based therapies, may prove effective for the treatment of AD.