Submicromolar Aβ42 reduces hippocampal glutamate receptors and presynaptic markers in an aggregation-dependent manner

Abstract

Synaptic pathology in Alzheimer's disease brains is thought to involve soluble Aβ42 peptide. Here, sterile incubation in PBS caused small Aβ42 oligomer formation as well as heterogeneous, 6E10-immunopositive aggregates of 80-100 kDa. High molecular weight aggregates (H-agg) formed in a time-dependent manner over an extended 30-day period. Interestingly, an inverse relationship between dimeric and H-agg formation was more evident when incubations were performed at 37°C as compared to 23°C, thus providing an experimental strategy with which to address synaptic compromise produced by the different Aβ aggregates. H-agg species formed faster and to higher levels at 37°C compared to 23°C, and the two aggregate preparations were evaluated in hippocampal slice cultures, a sensitive system for monitoring synaptic integrity. Applied daily at 80-600 nM for 7 days, the Aβ42 preparations caused dose-dependent and aggregation-dependent declines in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-D-aspartate (NMDA) receptor subunits as well as in presynaptic components. Unlike the synaptic effects, Aβ42 induced only trace cellular degeneration that was CA1 specific. The 37°C preparation was less effective at decreasing synaptic markers, corresponding with its reduced levels of Aβ42 monomers and dimers. Aβ42 dimers decayed significantly faster at 37°C than 23°C, and more rapidly than monomers at either temperature. These findings indicate that Aβ42 can self-aggregate into potent synaptotoxic oligomers as well as into larger aggregates that may serve to neutralize the toxic formations. These results will add to the growing debate concerning whether high molecular weight Aβ complexes that form amyloid plaques are protective through the sequestration of oligomeric species.

Blast waves from detonated military explosive reduce GluR1 and synaptophysin levels in hippocampal slice cultures

“…It should be noted that protein accumulation events involving Aβ and tau have been linked to brain trauma including a TBI model with a compressed-gas blast tube (see Goldstein et al, 2012; Du et al, 2016; Scott et al, 2016). On the other hand, the RDX synaptotoxic effect appears to occur earlier than the synaptic decline reported in hippocampal slice studies of protein accumulation stress related to Aβ and tau (Bendiske and Bahr, 2003; Butler et al, 2007; Wisniewski et al, 2011). Thus, from the above discussion, the level of detonated RDX used in the present study appears to produce a unique type of pathology comprised of altered synaptic integrity in the absence of cellular deterioration.…”

“…6, the synaptic decline profile induced by RDX detonations was compared to 1) synaptic declines reported in excitotoxicity studies using hippocampal slice cultures (Bahr et al, 2002; Karanian et al, 2005; Naidoo et al, 2012) vs . 2) hippocampal slice synaptic declines from protein accumulation stress studies (Bendiske and Bahr, 2003; Butler et al, 2007; Wisniewski et al, 2011). As shown, the synaptic marker loss profile for multiple RDX blasts (solid black line) aligns much closer to the excitotoxic profile than the protein accumulation stress profile.…”

“…Hippocampal slice cultures were prepared from 12-day-old rats as previously described (Bendiske et al, 2002; Wisniewski et al, 2011). Slices were cut from pre-cooled hippocampi and briefly placed in ice-cold buffer containing 124 mM NaCl, 3 mM KCl, 2 mM CaCl 2 , 4 mM MgSO 4 , 1.25 mM KH 2 PO 4 , 26 mM NaHCO 3 , 10 mM d -glucose, and 2 mM ascorbic acid.…”

“…The organotypic cultures allow studies to address specific issues in the absence of systemic variables, thus avoiding interpretation issues in the present study regarding whether subtle vs. severe neuronal changes are produced by single or multiple RDX blasts. Such slice cultures have proved valuable for determining pathways of neuropathology because of their similar cellular and genetic responses to various insults as compared to in vivo studies describing the unique pathogenic responsiveness of the hippocampus (Vornov et al, 1994; Bahr et al, 2002; Bendiske et al, 2002; Caba and Bahr, 2004; Bonde et al, 2005; Karanian et al, 2005; Noraberg et al, 2005; Wisniewski et al, 2011). In the current report, cultured hippocampal slices were placed in a specialized chamber in which defined assemblies of RDX were detonated outside the chamber to generate blast shockwaves from the military charge.…”

Positive Lysosomal Modulation As a Unique Strategy to Treat Age-Related Protein Accumulation Diseases

“…Another potential therapeutic strategy that may involve the endosomal-lysosomal system is the disaggregation of extracellular Ab peptide, with the idea that the disaggregation would promote uptake of monomers and small oligomers into neurons and microglia where they are trafficked to lysosomes for degradation by cysteine proteases, including cathepsin B. 15,29,47 Note that besides the disaggregation of intra-and extracellular Ab to facilitate clearance in this manner, extracellular proaggregation of soluble Ab oligomers has been proposed as protective, 48 whereby the formation of large nontoxic complexes reduces the smaller oligomeric species that are responsible for synaptic pathology and cognitive deterioration.…”