Amyloid-? (A?) is a peptide that is produced and secreted by neurons throughout life via mechanisms that are regulated by synaptic activity. A? peptides have been extensively studied as the pathological plaque-forming protein species in Alzheimer's Disease. However, the normal physiological role(s) and target(s) of A? peptides are currently unknown. When physiologically relevant (picomolar) amounts of A? peptides are applied to acute hippocampal slices or directly in-vivo, synaptic plasticity and memory are enhanced in mice via a process that is dependent on the a7 nicotinic acetylcholine receptor (a7-nAChR). Astrocytes, as crucial glial support cells and participants in synaptic transmission, are likely candidates for mediating A? signaling. I hypothesize that similar to what has been found for other signaling molecules, astrocytes may sense neuronal A? release at the synapse and respond with """"""""gliotransmitter"""""""" exocytosis which can produce neuromodulation. A possible molecular candidate in this pathway is the a7-nAChR, which is expressed by neurons and glia and can be directly bound or affected by AP42 peptides with high picomolar affinity. Furthermore, in astrocytes, a7-nAChR activation elevates intracellular calcium levels and can result in glutamate release. Thus, a7-nAChRs are well-poised to be a molecular link between A? signaling and astrocyte-mediated neuromodulation. To investigate this hypothesis using hippocampal cell culture systems (which enable direct manipulation of constituent cellular populations), the following aims will be addressed.
Aim 1 : The effects of picomolar amounts of A? peptides on the intracellular calcium signaling dynamics of astrocytes will examined with calcium dye imaging on astrocyte cultures. The involvement of a7-nAChRs will be tested using pharmacological compounds and an a7 subunit knockout mouse model.
Aim 2 : The astrocytic output in response to A? peptides will be examined with a glutamate gliotransmitter assay involving """"""""biosensor"""""""" sniffer cells for fine temporal and spatial resolution.
Aim 3 : The effects of picomolar A? peptides on neurotransmission and synaptic plasticity in neuron-glia mixed cultures will be analyzed using patch-clamp technique. To determine the role of astrocytic a7-nAChRs, these experiments will be concurrently done on mixed cultures of wild-type neurons plated on a7 subunit knockout astrocytes. Considering the huge clinical significance and large amount of Alzheimer's Disease research that is being done on A? peptides, it is highly important to discover their normal physiological roles in addition to their involvement in disease pathogenesis. An understanding of their basic functions and targets would enlighten Alzheimer's Disease research and could provide new therapeutic insights and possibilities.
|Lee, Linda; Kosuri, Pallav; Arancio, Ottavio (2014) Picomolar amyloid-? peptides enhance spontaneous astrocyte calcium transients. J Alzheimers Dis 38:49-62|