Basal ganglia signalling mechanisms and aging

Without a doubt aging process involves many changes in the different tissues and organs. It is recognized by now that the basal ganglia circuits, which are primarily involved with movement control, are one of the most vulnerable to age-related effects causing gross and fine motor declines, such as balance and gait deficits, coordination deficits, and slowing of movement. It is unclear, however, how these changes are regulated during aging.
A much better understanding of the specific roles played by the basal ganglia circuits, namely the direct and indirect pathways, both in normal and pathological behaviors (such us Parkinson's or Huntington's disease, considered mainly movement disorders) is needed in order to facilitate development of specific therapies that could precisely target or modulate the activity of the pathway disrupted and eventually reestablish balance to the affected system.

We have recently shown that loss of TrkB signalling in striatopallidal ENK+ neurons lead to age-dependent spontaneous hyperlocomotion, associated with reduced striatopallidal activation, demonstrating that BDNF-TrkB signaling in striatal ENK+ MSNs contributes to the inhibitory control of locomotor behavior exerted by the indirect pathway.
Hence, we have established a unique mouse model that provides a rare example of age-dependent locomotor defect. Here we propose to identify the genes and associated molecular pathways relevant to locomotor activity control. In order to do so we have been able to bring together a unique team of expertise covering behaviour, neurobiology, gene expression, intracellular signalling and protein chemistry. This will allow the use of combinatorial state of the art approaches to first of all understand basic mechanisms regulating age-dependent locomotor activity and at the same time to investigate novel avenues to explore therapeutic interventions against loss of quality of life during aging.

We have recently shown that loss of TrkB signalling in striatopallidal ENK+ neurons lead to age-dependent spontaneous hyperlocomotion, associated with reduced striatopallidal activation, demonstrating that BDNF-TrkB signaling in striatal ENK+ MSNs contributes to the inhibitory control of locomotor behavior exerted by the indirect pathway. Hence, we have established a unique mouse model that provides a rare example of age-dependent locomotor defect.
To address the mechanisms underlying TrkB signalling contribution to normal and altered locomotor activity control during aging we will perform time course transcriptome analysis (by RNAseq) of young and aged striatopallidal neurons, in the presence or absence of TrkB signalling. This analysis will be performed on a mouse line carrying both the fluorescent reporter allele (tdTomato) and specific Trkb deletion in striatopallidal neurons (TrkbPenK-KO;Ai9/+), and a respective control line (BAC-Penk-Cretg/+; Ai9/+ and), to allow isolation of a pure population of striatopallidal neurons, and subsequent data validation analysis by the Biomark Fludigm Dynamic Array system for quantitative real-time PCR analysis. These experiments will then be followed by the in vivo functional validation of identified GOIs. For this analysis we will use a lentiviral shRNA transduction approach. For genes/pathways that are down-regulated in aged/mutant mice we will test if knockdown wholly or partially generates a phenocopy of the hyperlocomotor phenotype. Conversely, for genes/pathways where up-regulation correlates with hyperlocomotion knockdown will be performed on aged mutant mice displaying the phenotype, and these will then be analysed for (wholly or partial) correction of the phenotype. In vivo knockdown efficiency will be validated by FACS of EGFP+/tdTomato+ cells followed by real-time PCR analysis.

The proposed research project will elucidate basic mechanisms and events underlying age-dependent changes in mice carrying altered neurotrophin signaling in a specific population of neurons (namely the striatopallidal neurons), and characterize the cell biological changes that occur in an age-dependent manner. As with any basic research project, its impact on the economy and quality of life is difficult to foresee. However, effective clinical research and trials rely completely on high quality basic science for design and interpretation, and our work will enhance clinical neurologist concepts in basal ganglia age-related normal and pathological behaviors; as well as general practitioners dealing with the aging population, local authority and health trusts.. Importantly it will also allow us to initiate molecular dissection of signalling pathway/s and molecules involved in the regulation of age-dependent neuronal changes, and ultimately this will facilitate the development of therapies that could specifically target or modulate the activity of the pathway disrupted and eventually reestablish balance to the affected system. Therefore, this would be of interest to the pharmaceutical industry.

Although the potential impact of these studies is obvious, there are still difficulties to overcome. By identifying how neurotrophin signalling interacts with the cellular machinery-regulating aging, and the specific changes associated with normal aging or specific to our model, we will have identified potential novel risk factors therapeutic targets and diagnostic markers for basal ganglia age-related normal and pathological behaviors. However, it first needs to be established whether the principle mechanisms observed in the mouse model also apply to humans. These studies in humans are much more challenging. Nonetheless, we will initiate collaborations with local clinical neurologists, communicate our findings to them through the Medical School at the University of Oxford, both to make them aware of the basic molecular mechanisms regulating striatal circuits function in ageing and/or age-dependent basal ganglia pathological behaviors that we have discovered, and to seek their feedback on humans correlation for the specific disorders. We will also discuss the possibility to validate our observations and eventually mechanistic findings on human diseased samples. Depending on the results further steps will be considered.

Moreover, we will effectively communicate the findings of this project and its wider significance to other scientists, policy-makers and the public, all areas where the PI has significant experience acquired in the past from other projects. First of all, the findings of this project will be communicated to other scientists through our original research papers and reviews, which will all be available via PubMed, but also through oral and poster presentations by the applicants and the post-doctoral researcher employed on the project at scientific conferences. The project proposed here is of a basic science nature and as such the dissemination of findings for public engagement will typically be through the scientific literature, press releases and public statements under the guidance of the University of Oxford and the BBSRC as appropriate.

The PI has in the past also worked effectively with press offices of other Institutions such as the European Molecular Biology Laboratory (EMBL) leading to articles in the media about our discoveries in the fields of learning and memory, cell signaling and neurobiology in general; and recently she has worked with the press office at the University of Oxford to disseminate our recent discoveries. We will also work closely with press officers at the BBSRC. Together, this will allow to communicate aspects of this research to the general public and to policy-makers and to explain its potential importance for medicine.