Perforant path synaptic loss correlates with cognitive impairment and Alzheimer's disease in the oldest-old

Abstract

Alzheimer's disease, which is defined pathologically by abundant amyloid plaques and neurofibrillary tangles concurrent with synaptic and neuronal loss, is the most common underlying cause of dementia in the elderly. Among the oldest-old, those aged 90 and older, other ageing-related brain pathologies are prevalent in addition to Alzheimer's disease, including cerebrovascular disease and hippocampal sclerosis. Although definite Alzheimer's disease pathology can distinguish dementia from normal individuals, the pathologies underlying cognitive impairment, especially in the oldest-old, remain poorly understood. We therefore conducted studies to determine the relative contributions of Alzheimer's disease pathology, cerebrovascular disease, hippocampal sclerosis and the altered expression of three synaptic proteins to cognitive status and global cognitive function. Relative immunohistochemistry intensity measures were obtained for synaptophysin, Synaptic vesicle transporter Sv2 (now known as SV2A) and Vesicular glutamate transporter 1 in the outer molecular layer of the hippocampal dentate gyrus on the first 157 participants of 'The 90+ Study' who came to autopsy, including participants with dementia (n = 84), those with cognitive impairment but no dementia (n = 37) and those with normal cognition (n = 36). Thal phase, Braak stage, cerebrovascular disease, hippocampal sclerosis and Pathological 43-kDa transactive response sequence DNA-binding protein (TDP-43) were also analysed. All measures were obtained blind to cognitive diagnosis. Global cognition was tested by the Mini-Mental State Examinaton. Logistic regression analysis explored the association between the pathological measures and the odds of being in the different cognitive groups whereas multiple regression analyses explored the association between pathological measures and global cognition scores. No measure clearly distinguished the control and cognitive impairment groups. Comparing the cognitive impairment and dementia groups, synaptophysin and SV2 were reduced, whereas Braak stage, TDP-43 and hippocampal sclerosis frequency increased. Thal phase and VGLUT1 did not distinguish the cognitive impairment and dementia groups. All measures distinguished the dementia and control groups and all markers associated with the cognitive test scores. When all markers were analysed simultaneously, a reduction in synaptophysin, a high Braak stage and the presence of TDP-43 and hippocampal sclerosis associated with global cognitive function. These findings suggest that tangle pathology, hippocampal sclerosis, TDP-43 and perforant pathway synaptic loss are the major contributors to dementia in the oldest-old. Although an increase in plaque pathology and glutamatergic synaptic loss may be early events associated with cognitive impairment, we conclude that those with cognitive impairment, but no dementia, are indistinguishable from cognitively normal subjects based on the measures reported here.

Prophylactic liraglutide treatment prevents amyloid plaque deposition, chronic inflammation and memory impairment in APP/PS1 mice

“…This loss was prevented to some degree by liraglutide treatment. Synapse loss is commonly observed in human AD brains [38]. This loss of connections between neurons is most likely the reason for the loss of cognitive function in AD patients.…”

Altered Machinery of Protein Synthesis in Alzheimer's: From the Nucleolus to the Ribosome

“…This change has been mainly interpreted as being the result of loss of afferents to the DG and to the loss of neurons in the CA1 region of the hippocampus (107). However, morphological and immunohistochemical studies have shown reduced dendritic arbors, reduced numbers of synapses, and reduced synaptic protein markers both in the CA1 region of the hippocampus and in the DG (32,36,56,82,(86)(87)(88)(89).…”

Synthesis and Preclinical Evaluation of11C-UCB-J as a PET Tracer for Imaging the Synaptic Vesicle Glycoprotein 2A in the Brain

“…Mice deficient in SV2A develop seizures and die within 3 wk of birth (4). In addition to its well-established role as the target for the antiepileptic drug levetiracetam (5,6), dysfunction of SV2A has been implicated in other neurologic disorders such as Alzheimer's disease (7)(8)(9).…”