Research Grant - 2019

Project Summary:

It takes time for proteins made in the cell body of neurons to reach its far compartments, such as “nerve endings” where they communicate with other neurons. Loss of these communication centres is a common feature in brain degeneration in Alzheimer’s disease (AD). If they lack key proteins, neurons cannot communicate effectively. This leads to memory impairment, another common feature of AD. One way around this problem, rather than moving proteins from the neuron’s cell body to nerve terminal endings, is for the neuron to transport the protein blueprint (RNA) instead. The nerve ending then needs the machinery to make proteins locally. We argue that the transport of RNA to faraway nerve terminals is disrupted in AD, resulting in a loss of the proteins needed for neural communication. To test these ideas, our project will prepare isolated nerve endings from re-thawed frozen human brains from AD and non-AD donors. We have tissue from over 600 AD donors and controls in the Queensland Brain Bank. We will measure RNA, and the machinery needed to make proteins from it. We will also examine the function of these nerve endings to test if nerve endings from AD brains may have poor use of oxygen, which could lead to less release of neurochemicals. Lower neurochemical release will impair the nerve endings’ ability to communicate with other neurons. We will also compare and contrast the protein and RNA profiles of human nerve endings isolated from AD regions where nerve communication is poor with regions where it is not, to provide insights into mechanisms for poor neural communication. Our planned research will provide new knowledge of the AD disease process, which is needed to identify new treatment targets.

Outcomes:

Utilizing human disease-affected autopsy brain tissue cryo-stored in the Queensland Brain Bank (QBB), we expected to see different profiles for synaptic protein content, respiration, and Ca2+ influx in synaptosomes isolated from disease-vulnerable regions compared with control regions. However, in our experiments we did not see any significant differences in these parameters – which challenged our original hypothesis that the remaining synapses at end-stage disease would show decreases in these pre-synaptic parameters. This may be because following the loss of vulnerable synapses in the early and mid-disease periods, the remaining synapses at end-stage disease remain functional. This opens a research opportunity to understand what allows the end-stage synaptic population to remain functional, and/or the possibility to look for disease-related fingerprints that may lead to subsequent synapse death.

We have demonstrated that frozen-thawed human and mouse brain tissue can be used to study the metabolic function of nerve terminals; that is, synaptosomes prepared from cryopreserved brain tissue satisfy the metabolic requirements for a pre-synaptic model. With mouse synaptosomes we can interrogate metabolic function prior to and during the loss of synaptic connections; findings can then be translated to human synaptosomes. Perhaps what is most exciting is our observations that remaining synapses at disease end-stage remain metabolically functional. Understanding the basis of this may have implications for how we may prevent or slow the rates synaptic loss in disease and old age.

Outcomes submitted April 2021.