One feature of Alzheimer’s Disease is the elevation of Aβ1-42 peptide. Here we provide a protocol for preparing synthetic Aβ1-42 oligomers, which impairs hippocampal Long-Term Potentiation, a cellular correlate of memory. This procedure is useful for investigating mechanisms of Aβ-induced pathology and drug screening.
Resuspending β-amyloid peptide
Before getting started have ready:
Oligomerization
Before getting started have ready:
Hippocampal slice treatment
When treating hippocampal slices, it is important to avoid non-specific peptide adhesion onto beakers, perfusion tubing surfaces, and the recording chamber. Use preferentially low-binding polypropylene tubing and containers. Avoid the use of glassware or generic plastic-ware. Perfusion media should be serum- or albumin-free.
Aβ perfusion
Before getting started have ready:
Induction of plasticity and follow-up
Representative Results and possible problems
The Aβ oligomerized according to the classical protocol of Stine et coll.1, generates Aβ monomers and a variety of oligomers of different sizes (dimer, trimer, etc.) The perfusion of oligomerized Aβ1-42 leads to decreased LTP in Aβ-treated slices compared to control slices. Under our experimental conditions, where 3-5 month old C57BL/6J male mice are used, LTP in 200 nM Aβ-treated slices is on average 150% of the baseline values at two hours after tetanic stimulation, while in control slices LTP values are on average 200-250% of baseline2. In some cases, treatment with Aβ may fail to reduce hippocampal LTP. Several critical errors that might occur include excessive film drying during Aβ concentration and incomplete oligomerization. Aβ perfusion in hippocampal slices might be another source of concern because of the physicochemical properties of the Aβ peptide in solution, which is prone to non-specific adhesion to plastics. Troubleshooting of these issues is discussed below.
As described above, several problems in the preparation of oligomeric Aβ may result in unimpaired LTP. One way to evaluate whether Aβ degradation or the lack of Aβ oligomerization may have occurred is to evaluate the Aβ preparation using TRIS-Tricine PAGE/Western Blotting analysis and analytical ultracentrifugation (not described in this protocol). When Western Blotting samples are prepared under non-denaturing/non-reducing conditions, a successful preparation should generate a Western Blotting signature featuring bands corresponding to monomers and different oligomers3. An often occurring issue is the peptide instability during the drying step in the SpeedVac concentrator. In fact, high-temperature drying leads to protein degradation, noticeable by marked peptide coloration to brown. Concentration of the HFIP solution has to be carried out at room temperature and monitored carefully. Given the several procedural steps occurring in the protocol, errors in dilution may accidentally lead to poor oligomerization or misleading Aβ concentration. Interestingly, the perfusion with Aβ concentrations lower than suggested would result in increased LTP values3. Again, perfusion affects the possible outcome of Aβ treatment on slices. Indeed, maintaining a constant temperature of the bath solution in our electrophysiological experiments is critical as temperature is known to affect Aβ conformations when solved in phosphate buffer. Another source of concern is that oligomeric Aβ may non-specifically stick to plastic surfaces of containers and tubing used for preparation and perfusion thereby reducing the effective concentration exposed to hippocampal slices. Thus, it is critical to use low-protein binding plastic-ware to ensure reliable preparations and perfusions throughout different experiments. In this issue, we propose polypropylene plastic-ware which has been shown not to affect the ratio of different Aβ species4. Extensive literature suggests that Alzheimer’s Disease originates as a synaptic disorder5. It is likely that the subtlety and variability of the earliest amnesic symptoms, occurring in the absence of any other clinical signs of brain injury, are due to discrete changes in the function of a single synapse, produced at least in part, by Aβ species (e.g. Aβ42 and Aβ40)2,6,7,8. The discovery that a preparation containing oligomerized synthetic Aβ1-42 can impair LTP9 in vitro has led to numerous investigations into mechanisms of synaptic dysfunction induced by Aβ elevation in brain. Using this protocol, we describe a procedure for preparing oligomeric Aβ which successfully impairs LTP at the Shaffer collateral-stratum radiatum connection in hippocampal slices. This experimental paradigm has tremendous value for investigating mechanisms of Aβ-mediated pathogenesis as well as testing potential drugs, which may mitigate synaptic dysfunction2,10,11.
The authors have nothing to disclose.
This work was supported by NIH National Institute of Neurological Disorders and Stroke (NINDS) (NS049442).>
Material Name | タイプ | Company | Catalogue Number | Comment |
---|---|---|---|---|
Aβ 1-42 (lyophilized) | American Peptide Co. | 62-0-80 | ||
1,1,1,3,3,3-Hexafluoro-2-Propanol (HFIP) | Fluka | 52517 | ||
Dimethylsulfoxide (DMSO) | Biotium | 90082 | ||
50mL Polypropylene Centrifuge Tubes | Corning | 05-538-67 | ||
1.5ml MaxyClear microtubes Maximum recovery | Axygen | MCT-150-L-C | ||
Phosphate-Buffered Saline pH 7.4 | Invitrogen-Gibco | 10010-023 | ||
GASTIGHT Syringes 250 μL | Hamilton | 1725 | ||
Bath sonicator | Branson | 3510 | ||
Savant SpeedVac Concentrator System | Various distributors | SC 110A |