Modifications of the endosomal compartment in fibroblasts from sporadic Alzheimer’s disease patients are associated with cognitive impairment

Abstract

Morphological alterations of the endosomal compartment have been widely described in post-mortem brains from Alzheimer’s disease (AD) patients and subjects with Down syndrome (DS) who are at high risk for AD. Immunostaining with antibodies against endosomal markers such as Early Endosome Antigen 1 (EEA1) revealed increased size of EEA1-positive puncta. In DS, peripheral cells such as peripheral blood mononuclear cells (PBMCs) and fibroblasts, share similar phenotype even in the absence of AD. We previously found that PBMCs from AD patients have larger EEA1-positive puncta, correlating with brain amyloid load. Here we analysed the endosomal compartment of fibroblasts from a very well characterised cohort of AD patients (IMABio3) who underwent thorough clinical, imaging and biomarkers assessments. Twenty-one subjects were included (7 AD with mild cognitive impairment (AD-MCI), 7 AD with dementia (AD-D) and 7 controls) who had amyloid-PET at baseline (PiB) and neuropsychological tests at baseline and close to skin biopsy. Fibroblasts isolated from skin biopsies were immunostained with anti-EEA1 antibody and imaged using a spinning disk microscope. Endosomal compartment ultrastructure was also analysed by electron microscopy. All fibroblast lines were genotyped and their AD risk factors identified. Our results show a trend to an increased EEA1-positive puncta volume in fibroblasts from AD-D as compared to controls (p.adj = 0.12) and reveal enhanced endosome area in fibroblasts from AD-MCI and AD-AD versus controls. Larger puncta size correlated with PiB retention in different brain areas and with worse cognitive scores at the time of biopsy as well as faster decline from baseline to the time of biopsy. Finally, we identified three genetic risk factors for AD (ABCA1, COX7C and MYO15A) that were associated with larger EEA1 puncta volume. In conclusion, the endosomal compartment in fibroblasts could be used as cellular peripheral biomarker for both amyloid deposition and cognitive decline in AD patients.

Mitochondria alterations in fibroblasts from sporadic Alzheimer’s disease (AD) patients correlate with AD-related clinical hallmarks

“…However, we observed an enlargement of autophagosome and lysosomes indicative for defective degradation processes (Figure 5A-F). Previous studies have reported an enlargement of endosomes in both PBMCs and fibroblasts of IMABio3 cohort 17,20 . As a whole, these results demonstrate a global alteration of the endolysosomal compartments in SAD and FAD fibroblasts as it was already described [53][54][55] .…”

“…Importantly, TFAM expression is reduced in both MCI and AD PBMCs and correlates with AD severity and mtDNA content 67 . Polymorphisms in COX7C gene, encoding for COX7C protein a component of OXPHOS complex IV, was recently described in the IMABio3 cohort 20 . Moreover, COX7C has lower expression in the blood of MCI/AD relative to age-matched controls 68 .…”

“…Several clinical studies suggest that fibroblasts obtained from AD patients harbor cellular dysfunctions observed in post-mortem AD brains 20 . In this study, we investigated mitochondria structure and function and examined autophagy and mitophagy processes in fibroblasts obtained from AD patients with a final objective to identify potential correlations between changes in mitochondria homeostasis and AD clinical onset.…”

“…Fibroblasts were cultured as described previously 20 and kept under liquid nitrogen at the DNA & Cell Bank core facilities of the Brain and Spinal Cord Institute (ICM). Briefly, cells were cultured at 37°C in a humidified atmosphere containing 5% CO2 in DMEM (Dulbecco modified Eagle’s minimal essential medium) supplemented with 10% heat-inactivated fetal bovine serum (FBS), 1% pyruvate sodium, Penicillin (100 U/mL) and streptomycin (50 μg/mL).…”

Advancements in high-resolution 3D microscopy analysis of endosomal morphology in postmortem Alzheimer’s disease brains

“…Abnormal endo-lysosomal morphology, for example vesicle enlargement, is a characteristic early cytopathological change in AD associated with endosomal "traffic jams" that cause neuronal dysfunction (Cataldo et al, 1997(Cataldo et al, , 2000Botte et al, 2020;Knupp et al, 2020;Mishra et al, 2022). ELN abnormalities have also been described in peripheral blood mononuclear cells, dermal fibroblasts and human induced pluripotent stem cell (hiPSC)-derived neurons sampled from LOAD patients (Israel et al, 2012;Corlier et al, 2015;Xicota et al, 2023).…”