Mitochondrial Localized Amyloid Precursor Protein Alters Mitochondrial Function and Mitophagy

Abstract

AbstractBackgroundMitochondrial dysfunction and Aβ accumulation are hallmarks of Alzheimer’s disease (AD). Decades of research describe a relationship between mitochondrial function and Aβ production. Amyloid precursor protein (APP), from which Aβ is generated, is found in mitochondria. APP and Aβ alter mitochondrial function, while mitochondrial function alters Aβ production from APP. How these interactions contribute to AD pathology and progression are unknown. Here we interrogated the association of full‐length APP with mitochondria, mitochondrial function, and AD pathological hallmarks.MethodND (n = 5, without DS) and DS with dementia (DSD, n = 5) postmortem brain tissue was obtained from the University of California Irvine. A human iPSC line underwent Crispr/Cas9 genome editing to mutate three amino acids in APP and generate a 3M APP model, with reduced mitochondrial APP localization. We also leveraged a human iPSC line with triplication of the APP gene. iPSC models were differentiated into neurons using StemCell Technologies reagents and protocols. We examined mitochondrial function using a Seahorse XF analyzer. We measured full‐length APP protein levels in whole cell extracts and mitochondrial fractions via Western Blotting. We measured Aβ levels with ELISA kits from ThermoFisher. Mitophagy and mitochondrial mass/biogenesis was measured using MitoTimer and EGFP‐Cox8 adenoviral constructs.ResultiPSC derived neurons showed alterations to Aβ production. 3M APP models had reduced Aβ production while APP triplication models had increased production. 3M APP models had reduced mitochondrial APP levels and APP triplication models had increased mitochondrial APP levels. 3M APP models had reduced mitophagy, increased mitochondrial biogenesis, and increased mitochondrial mass. APP triplication models had increased mitophagy and reduced mitochondrial mass. Mitochondrial respiratory function was reduced in both 3M APP and APP triplication models. DSD postmortem brain tissue had reduced mitochondrial function in females. Full‐length APP levels were significantly higher in mitochondrial fractions in DSD brain tissue. Full‐length APP levels in mitochondrial fractions correlated with mitochondrial function. Higher mitochondrial APP (full‐length) levels associated with lower mitochondrial function.ConclusionWe describe a relationship between mitochondrial APP accumulation, mitochondrial function, and Aβ. These data support a centralized role for mitochondrial function in APP physiology and APP may play a role in modulating mitophagy.