Childhood oral health and disease – a multifactorial model
Associate Professor Toby Hughes
The University of Adelaide
Tooth decay is the most common chronic disease of Australian children, affecting 50% of 6 year olds. It causes pain, systemic infection, speech/learning problems, and is a predictor for poor general health. Treatment accounts for $5.3 billion in spending in Australia annually.
The role of dietary sugar in tooth decay is well established, however population lifestyle changes are difficult and costly to implement. This project will identify factors in dental plaque for use in early screening to identify high risk children, promoting targeted, less invasive, and more cost-effective interventions.
Toby Hughes, Grant Townsend, Christina Adler, Michelle Bockmann
The overall aim of this proposal was to identify the role of the non-channel gene PRRT2 (Proline-rich transmembrane protein 2) in neuronal function and neurological diseases. We and others had previously shown that mutations in this gene cause a range of neurological disorders including infantile epilepsy, movement disorders and intellectual disability. Widespread expression of PRRT2 in the central nervous system and the association of the PRRT2 protein with Synaptosomal Associated Protein 25 (SNAP25) indicate an important role in the regulation of neuronal activity. Based on our published and preliminary data, we hypothesised that reduction of functional PRRT2 protein in the presynaptic membrane leads to dysregulation of neurotransmitter release and altered neuronal activity. To investigate this hypothesis, we generated and validated a Prrt2 KO mouse model. Interestingly, routine handing of Prrt2 mutant mice revealed evidence of spontaneous seizures and abnormal gait. Our specific aims were:
Aim 1: To determine the sub-cellular localisation of endogenous PRRT2 in neurons
Aim 2: To determine the electrophysiological impact of PRRT2 loss of function in neurons
Aim 3: To determine whether Prrt2 KO mice have increased seizure susceptibility and dyskinesia
Two key publications appeared in this very competitive area over the course of 2016 that forced us to re-evaluate our initial aims. In the first publication shRNA knockdown in cultured neurons was used to demonstrate a role for Prrt2 in calcium release at the synapse 1. Prrt2 knockdown was also shown to cause a build-up of presynaptic vesicles, in line with our hypothesis that Prrt2 functions in the presynaptic terminal to control vesicle release. A second paper towards the end of the year published findings from knockout mice and showed that Prrt2 deletion caused audiogenic seizures and movement disorders. EEG recording of these mice was however relatively normal and in neither paper were the authors able to show endogenous protein localisation owing to a lack of a suitable commercial antibody 2.
We were also unable to identify a suitable antibody for immunolocalisation of endogenous protein. We are close to finalising an electron microscope analysis of synapses in normal and Prrt2 null mouse brain that will provide a useful confirmation of recently published results. We have performed seizure testing with the proconvulsant PTZ and find no difference between normal and knockout mice. This is in agreement with recently published findings and suggests that the mice may not recapitulate this aspect of the human disease. To complete this aim we have initiated collaboration with David Reutens at Queensland Brain Institute to perform EEG, which is a more sensitive measure of brain activity than PTZ assays.
In addition we have conducted extensive behavioural testing to assess motor and cognitive performance of knockout mice. Motor assays used were rotarod, digigait and locomotor analysis, while cognition was assessed using a Y-maze and Morris Water Maze. We are now undertaking statistical analysis of the raw data but preliminary analysis is pointing towards possible movement defects in the absence of cognitive deficits. This analysis is ongoing and together with our characterisation of the knockout mouse is being prepared for publication and will provide a valuable addition to the current state of knowledge relating to Prrt2 function.
All our findings are being written up for publication in the near future.