The role of miRNAs in the regulation of neuronal polarisation and connectivity

Amyotrophic lateral sclerosis and associated frontotemporal lobe dementia (ALS-FTLD) is a complex, fatal degenerative disease encompassing selective degeneration of both cortical and spinal motor neurons, leading to neuromuscular failure accompanied by dementia-like cognitive defects. Approximately 90% of ALS cases are sporadic, with familial ALS contributing 5-10% of cases. Both sporadic and familial forms of the disease are genetically heterogeneous, with several genetic factors being identified in recent years that are implicated in both forms. Recently, an autophagy the autophagy protein P62/SQSTM1 was identified as a components of intracellular protein aggregates typically present in affected ALS-FTLD affected motor neurons.

Autophagy is a vital homeostatic mechanism governing the turnover of long-lived proteins and organelles. Primarily induced during stress or starvation, it is often seen as a cells survival response that can, in the short-term, link non-essential cellular proteins to a cell's lysosomal pathways to provide more resource materials. However, work over recent years has begun to show the importance of autophagy in the long term maintenance of cellular proteostasis, particularly in long-lived, post-mitotic cells, such as neurons where the presence of protein aggregates and damaged organelles are known pathologies of several neurodegenerative disorders.
P62 is a stress-inducible ubiquitin binding protein involved in the degradation by autophagy of ubiquitin 'tagged' cargoes. Its primary role is to sequester cargoes tagged for degradation within autophagosomal membranes and link them to acidic autolysosomes for further processing.

The development of axons by the process of neuronal polarisation and the maintenance of their connectivity throughout a cell's life is vital to correct neuronal function. Emerging evidence has shown that a likely key conductor of these processes are miRNAs; non-coding RNAs which mediate the translation of mRNA of many important, functional genes.

In neurodegenerative states such as ALS-FTLD, mounting evidence links numerous defects in the autophagy pathway, such as the L341V mutation to the P62 protein. Considering the high levels of finely tuned protein turnover present in the axon, it is becoming increasingly important to understand the regulatory mechanisms in place that control neuronal autophagy and how they can go wrong.

Throughout this project, we will be using primary neuronal & neuron-like cell line cultures to assess the mechanistic role of P62, and potentially its mediation by miRNAS, in-vitro on axon development and function. We also intend to use the Drosophila melanogaster fruit fly as an in-vivo model through which to gain a better understanding of how the molecular role of P62 in the nervous system impacts a whole organism system.