Cholinergic pathway modulation by age‐dependent amyloid‐beta pathology in an APP‐knock‐in AD mice model
Sumonto Mitra, Ruchi Gera, Simone Tambaro, Per Nilsson, Bengt Linderoth, Homira Behbahani, Taher Darreh‐Shori, Maria Eriksdotter- Psychiatry and Mental health
- Cellular and Molecular Neuroscience
- Geriatrics and Gerontology
- Neurology (clinical)
- Developmental Neuroscience
- Health Policy
- Epidemiology
Abstract
Background
Altered cholinergic pathways and memory dysfunction are well‐known changes during Alzheimer’s disease (AD), linked to the early loss of basal forebrain cholinergic neurons (BFCNs). BFCN’s innervates wide regions of the brain, including hippocampus which is a crucial site of neurotrophic factor production like nerve growth factor (NGF) – the master regulator of cholinergic pathways and brain derived neurotrophic factor (BDNF). Hippocampus coordinates memory and cognition and is found affected with amyloid‐beta (Aβ) pathology in AD. Till date, a clear connection between Aβ pathology in modulating cholinergic alteration has not been proven. Recently, the anti‐amyloid antibody Aducanumab and Lecanemab was approved for AD therapy by the United States of America Food and Drug Administration but whether Aβ deposition or clearance modulates cholinergic activity is not established. We evaluated cholinergic status in hippocampus of AD mice model in‐comparison with matched wildtype control.
Method
Hippocampus tissue was isolated from a humanized APP‐knock‐in mouse model of AD (AppNL‐G‐F) at different stages of amyloid pathology – 2‐month age (pre‐plaque stage), 7‐month age (plaques present + initiation of cognitive deficits), and 12‐month age (advanced amyloid pathology), and age‐matched wildtype control (C57BL/6JRj) respectively. Tissues were then processed to isolate total protein which was achieved by extracting them in various buffers (soluble, ionic, and detergent soluble fractions) and pooled together. Enzyme assays for cholinergic markers including acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), choline acetyltransferase (ChAT) was performed, along with ELISA for the estimation of total NGF and BDNF levels, respectively.
Result
Age‐dependent changes were observed in AppNL‐G‐F mice compared to wild‐type controls. Cholinesterase activity was increased for AChE at 7 months, while BuChE activity was less in the AppNL‐G‐F mice from 7 month onwards, with respect to wildtype control mice respectively. ChAT levels were nominally affected but the cholinergic index (ChAT/AChE) was considerably altered in AppNL‐G‐F mice. NGF levels remained unchanged, but BDNF levels increased in an age‐dependent manner in AppNL‐G‐F mice as compared to control mice.
Conclusion
Significant age‐dependent alteration in cholinergic activity and neurotrophic factors were evident in hippocampus tissue of AppNL‐G‐F mice, when compared to wild‐type counterparts underlining the importance of the cholinergic activity in relation to amyloid pathology.