'Organotypic hippocampal slice cultures as tools to investigate mechanisms of presynaptic disruption in sporadic and familial Alzheimer's disease models'
Claire Durrant (John van Geest Centre for Brain Repair)
Loss of presynaptic proteins in the hippocampus is an early and clinically-relevant alteration in the brains of patients with Alzheimer’s disease (AD). Long term organotypic hippocampal slice cultures (OHSCs) from neonatal amyloid mice provide an excellent platform to examine mechanisms of synaptic disruption, largely retaining the cellular composition and neuronal architecture of the in vivo hippocampus, but with in vitro advantages of accessibility to live imaging, sampling and intervention.
OHSCs were made from P6-P9 wild-type, TgCRND8 or APP NL-G-F knockin mice and maintained in culture for up to 2 months. Transgenic cultures were monitored for spontaneous pathology development and the mechanisms behind presynaptic disruption were probed via pharmacological manipulation of Aβ production and genetic knockdown of tau. Wild-type cultures were treated with a battery of environmental factors associated with risk of sporadic AD, such as pro-inflammatory compounds, and assessed for AD-related pathological changes.
In both TgCRND8 and APP-knockin OHSCs there is a progressive accumulation of intra-axonal Aβ. In TgCRND8 cultures, this correlates with a decline in presynaptic proteins and alterations in mRNA levels for synaptic proteins. Beta-secretase inhibitor abolished accumulation of Aβ1-42 but surprisingly did not rescue synaptophysin levels. This raises the question of whether BACE1-independent APP products, or APP overexpression as in Down syndrome and APP duplication patients, underlie some synaptic defects. Elucidation of any synaptic changes in the APP-knockin model is ongoing, providing an effective experimental system to test this hypothesis. LPS or IL1β treatment of wild-type slices resulted in a significant loss of synaptophysin protein, similar to that seen in the TgCRND8 model.
OHSCs represent an important new system for understanding mechanisms of presynaptic disruption in AD. Comparison between genetic and sporadic models of AD may help identify common pathways to target for therapeutic intervention. Future work will examine mechanisms resulting in synaptophysin depletion, particularly in relation to the involvement of tau, relative contribution of APP overexpression and mutations, as well as alternative APP processing products.