Understanding and treating neurogenetic conditions related to the Kennedy pathway

The hereditary spastic paraplegias (HSP)s are a large group of debilitating genetic disorders that lead to lower limb weakness and stiffness (spasticity). Unfortunately, the condition progresses, leading to patients experiencing increasing difficulties. In some forms of HSP, symptoms are confined to the lower limbs, while other patients may suffer a wider range of medical problems (referred to as complex HSP).

In this proposal we will investigate two complex forms of HSP, known as SPG81 and SPG82. These complex HSPs are caused by mutations in genes that encode enzymes of the so-called Kennedy pathway of lipid metabolism. This pathway makes two types of phospholipids, which are essential fat-like molecules that help generate cell membranes (barriers that enclose the cell from the surrounding environment and also make internal compartments inside the cell).

We will also study a third disease that affects the nervous system, with similar clinical features to SPG81 and SPG82, called NEDMIMS, which is caused by mutations in another gene encoding an enzyme in the Kennedy pathway.

Currently, we lack understanding of the pathological mechanisms of NEDMIMS and SPG81 and 82, and there are no effective treatments. In this proposal, we will use zebrafish to model the three genetic conditions (SPG81, SPG82 and NEDMIMS) to reveal disease mechanisms and test new potential therapeutic strategies. Our preliminary work indicates that SPG82 can be modelled faithfully in zebrafish, with reduced head size and defective movement, and changes in lipids similar to those seen in patients.

Our initial experiments will perform the analysis of the physical features of the SPG81 and NEDMIMS zebrafish models, which will be combined with measurements of lipid types and abundance. In subsequent experiments we will carry out a detailed analysis of the nervous system in all 3 models using a variety of advanced approaches, which includes microscopy and an extensive analysis of the cell types, cellular components, and molecular pathways that are affected.

This will allow us to obtain a detailed molecular description of the processes that occur in the disease state, and hence identify the pathological mechanisms involved. In the final part of the project we will try various approaches to rescue the disease pathology. This will include genetic approaches where we re-express a 'normal' copy of the affected gene, and chemical ones, where we will treat the zebrafish with selected drugs or a larger library of drugs.

Those treatments that rescue the pathology may then be exploited in further testing that would follow on from this award. Importantly, the HSPs are progressive in nature and hence there is a therapeutic window, making treatment of patients possible.

This work is important because it will identify the mechanisms of three highly debilitating genetic conditions, and allow the identification of new potential treatments for them. It will also have relevance for other similar types of neurological conditions, including the HSPs more generally, as well other types of motor neurone disease.