Intracellular amyloid and the neuronal origin of Alzheimer neuritic plaques

Abstract

Genetic analysis of familial forms of Alzheimer's disease (AD) causally links the proteolytic processing of the amyloid precursor protein (APP) and AD. However, the specific type of amyloid and mechanisms of amyloid pathogenesis remain unclear. We conducted a detailed analysis of intracellular amyloid with an aggregation specific conformation dependent monoclonal antibody, M78, raised against fibrillar Aß42. M78 immunoreactivity colocalizes with Aß and the carboxyl terminus of APP (APP-CTF) immunoreactivities in perinuclear compartments at intermediate times in 10 mo 3XTg-AD mice, indicating that this represents misfolded and aggregated protein rather than normally folded APP. At 12 mo, M78 immunoreactivity also accumulates in the nucleus. Neuritic plaques at 12 mo display the same spatial organization of centrally colocalized M78, diffuse chromatin and neuronal nuclear NeuN staining surrounded by peripheral M78 and APP-CTF immunoreactivity as observed in neurons, indicating that neuritic plaques arise from degenerating neurons with intracellular amyloid immunoreactivity. The same staining pattern was observed in neuritic plaques in human AD brains, showing elevated intracellular M78 immunoreactivity at intermediate stages of amyloid pathology (Braak A and B) compared to no amyloid pathology and late stage amyloid pathology (Braak 0 and C, respectively). These results indicate that intraneuronal protein aggregation and amyloid accumulation is an early event in AD and that neuritic plaques are initiated by the degeneration and death of neurons by a mechanism that may be related to the formation of extracellular traps by neutrophils.

Amyloid-β precursor protein: Multiple fragments, numerous transport routes and mechanisms

“…In addition, phosphorylation of APP – which occurs to a large extent at the ER [20], and is increased in AD [39] and stress [40] – could favor APP cleavage at the slightly higher pH in the ER lumen. Recent studies reported that, in the aging brain, APP fragments accumulate in perinuclear compartments in the soma [41, 42]. In cultured neuronal cells, bona fide APP fragments are occasionally detected in a perinuclear compartment of the ER that associates with neurofilaments [43] (Fig.…”

Molecular Structure of Aggregated Amyloid-β: Insights from Solid-State Nuclear Magnetic Resonance

“…Most Aβ peptides in human brain tissue are either 40 or 42 residues in length (Aβ40 and Aβ42), typically produced in an approximate 5:1 abundance ratio, but with more pronounced aggregation of Aβ42 (Gravina et al 1995). Aβ aggregation is traditionally considered to be an extracellular process, although there is also evidence that Aβ aggregation can occur intracellularly (Pensalfini et al 2014). …”

Data-driven modeling of mitochondrial dysfunction in Alzheimer's disease

“…Understanding the downstream effects of intracellular A β oligomers accumulation in AD-affected neurons is crucial as they are shown to lead to profound deficits in memory and cognitive function [29, 30], and are likely to play a major role in the earliest phase of AD pathogenesis [23, 27]. As reported by different groups including us, the liberation of Ca 2+ from intracellular stores is seen as a possible mechanism for the cytotoxicity of intracellular A β oligomers [8, 31–33].…”

“…Thus the oligomer concentrations used in our experiments are in reality much smaller than the numbers give in Table 4. Furthermore, the intracellular accumulation of A β 42 can be two to three folds higher than the extracellular concentration [27, 56–61]. …”

“…While most studies on A β toxicity to date have focused on the effect of extracellular A β oligomers, understanding the effect of intracellular A β on cell’s function is becoming increasingly relevant, substantiated by the following observations: (i) intracellular A β accumulation precedes extracellular deposition [23–25]; (ii) intracellular A β are likely to contribute in the earliest phase of the pathogenesis of AD [23, 26, 27]; (iii) the endoplasmic reticulum (ER) of neurons has been identified as the specific site of A β production [28]; (iv) accumulation of intracellular A β have been linked to profound deficits of long-term potentiation and cognitive dysfunction in AD mice models [29, 30]; and (v) the ER membrane is the site of action for fundamental Ca 2+ release due to opening of inositol 1,4,5-trisphosphate (IP 3 ) receptors (IP 3 Rs) and ryanodine receptors (RyRs), regulating numerous cell’s functions. Furthermore, there is compelling evidence that intracellular A β evokes the liberation of Ca 2+ from intracellular stores [8, 31–33].…”