Aβ and NMDAR activation cause mitochondrial dysfunction involving ER calcium release

Early cognitive deficits in Alzheimer's disease (AD) seem to be correlated to dysregulation of glutamate receptors evoked by amyloid-beta (Aβ) peptide. Aβ interference with the activity of N-methyl-d-aspartate receptors (NMDARs) may be a relevant factor for Aβ-induced mitochondrial toxicity and neuronal dysfunction. To evaluate the role of mitochondria in NMDARs activation mediated by Aβ, we followed in situ single-cell simultaneous measurement of cytosolic free Ca2+(Cai2+) and mitochondrial membrane potential in primary cortical neurons. Our results show that direct exposure to Aβ + NMDA largely increased Cai2+ and induced immediate mitochondrial depolarization, compared with Aβ or NMDA alone. Mitochondrial depolarization induced by rotenone strongly inhibited the rise in Cai2+ evoked by Aβ or NMDA, suggesting that mitochondria control Ca2+ entry through NMDARs. However, incubation with rotenone did not preclude mitochondrial Ca2+ (mitCa2+) retention in cells treated with Aβ. Aβ-induced Cai2+ and mitCa2+ rise were inhibited by ifenprodil, an antagonist of GluN2B-containing NMDARs. Exposure to Aβ + NMDA further evoked a higher mitCa2+ retention, which was ameliorated in GluN2B−/− cortical neurons, largely implicating the involvement of this NMDAR subunit. Moreover, pharmacologic inhibition of endoplasmic reticulum (ER) inositol-1,4,5-triphosphate receptor (IP3R) and mitCa2+ uniporter (MCU) evidenced that Aβ + NMDA-induced mitCa2+ rise involves ER Ca2+ release through IP3R and mitochondrial entry by the MCU. Altogether, data highlight mitCa2+ dyshomeostasis and subsequent dysfunction as mechanisms relevant for early neuronal dysfunction in AD linked to Aβ-mediated GluN2B-composed NMDARs activation.