Synaptic Mitochondria: An Early Target of Amyloid-β and Tau in Alzheimer’s Disease

Article type: Review Article

Authors: Torres, Angie K.^{a; b} | Jara, Claudia^a | Park-Kang, Han S.^a | Polanco, Catalina M.^a | Tapia, Diego^a | Alarcón, Fabián^a | de la Peña, Adely^a | Llanquinao, Jesus^a | Vargas-Mardones, Gabriela^a | Indo, Javiera A.^a | Inestrosa, Nibaldo C.^{b; c} | Tapia-Rojas, Cheril^{a; *}

Affiliations: [a] Laboratory of Neurobiology of Aging, Centro de Biología Celular y Biomedicina (CEBICEM), Facultad de Medicina y Ciencia, Universidad San Sebasti´n Sede Los Leones, Santiago, Chile | [b] Centro de Envejecimiento y Regeneración (CARE), Departamento de Biología Celular y Molecular, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile | [c] Centro de Excelencia en Biomedicina de Magallanes (CEBIMA), Universidad de Magallanes, Punta Arenas, Chile

Correspondence: [*] Correspondence to: Dr. Cheril Tapia-Rojas, Laboratory of Neurobiology of Aging, CEBICEM, Universidad San Sebastián, Carmen Sylva 2444, Providencia, Santiago, Chile. Tel.: +56222606309; E-mail: cheril.tapia@uss.cl.

Abstract: Alzheimer’s disease (AD) is characterized by cognitive impairment and the presence of neurofibrillary tangles and senile plaques in the brain. Neurofibrillary tangles are composed of hyperphosphorylated tau, while senile plaques are formed by amyloid-β (Aβ) peptide. The amyloid hypothesis proposes that Aβ accumulation is primarily responsible for the neurotoxicity in AD. Multiple Aβ-mediated toxicity mechanisms have been proposed including mitochondrial dysfunction. However, it is unclear if it precedes Aβ accumulation or if is a consequence of it. Aβ promotes mitochondrial failure. However, amyloid β precursor protein (AβPP) could be cleaved in the mitochondria producing Aβ peptide. Mitochondrial-produced Aβ could interact with newly formed ones or with Aβ that enter the mitochondria, which may induce its oligomerization and contribute to further mitochondrial alterations, resulting in a vicious cycle. Another explanation for AD is the tau hypothesis, in which modified tau trigger toxic effects in neurons. Tau induces mitochondrial dysfunction by indirect and apparently by direct mechanisms. In neurons mitochondria are classified as non-synaptic or synaptic according to their localization, where synaptic mitochondrial function is fundamental supporting neurotransmission and hippocampal memory formation. Here, we focus on synaptic mitochondria as a primary target for Aβ toxicity and/or formation, generating toxicity at the synapse and contributing to synaptic and memory impairment in AD. We also hypothesize that phospho-tau accumulates in mitochondria and triggers dysfunction. Finally, we discuss that synaptic mitochondrial dysfunction occur in aging and correlates with age-related memory loss. Therefore, synaptic mitochondrial dysfunction could be a predisposing factor for AD or an early marker of its onset.

Keywords: Alzheimer’s disease, amyloid-β, amyloid-β protein precursor, cognitive impairment, mitochondria, neurofibrillary tangles, synapses, synaptic mitochondria

DOI: 10.3233/JAD-215139

Journal: Journal of Alzheimer's Disease, vol. 84, no. 4, pp. 1391-1414, 2021