Prof Nick Allen, Prof Derek Blake & Dr Adrian Waite - Cardiff University

Pilot Project: 2017 - 2018

Using stem cells to model protein quality control dysfunction in dementia (Pilot Project)

See glossary at bottom of page for definition of underlined words.

Summary

The proteostasis network (PN) is responsible for the ‘quality control’ of proteins produced by the cell. The breakdown of the PN may lead to the build up of toxic proteins which is characteristic of most forms of dementia. Ubiquilin-2 is a protein which has been shown to be mutated in sufferers of X-linked fronto-temporal dementia and is thought to be required for the normal functioning of the PN. Using induced pluripotent stem cells (iPSCs), this group seeks to characterise the role of Ubiquilin-2 in the PN of human brain cells. This research will provide the basis for understanding why certain genes (such as the one that codes for Ubiquilin-2) increase the risk of dementia and how they can be targeted to produce new therapeutic treatments.

What do we already know?

Maintenance of functional proteins is vital for cell survival, and the mechanisms responsible for this are collectively known as the proteostasis network (PN). This network is a collection of over 1000 proteins that co-ordinate processes such as protein synthesis, folding and degradation. The PN is able to adapt to environmental stresses, however disease, genetic variation and ageing can reduce the efficiency of this quality control network, leading to build up of toxic proteins (i.e. amyloid-β) and dementia.

Ubiquilin-2 is one protein involved, and the gene encoding this protein is mutated in X-linked fronto-temporal dementia (FTD). Prof. Blake and Dr Waite have previously shown that ubiquilin-2 associates with proteins involved in synaptic regulation and protein trafficking, which may explain why synaptic dysfunction has been reported in mouse models with ubiquitin-2 mutations. With Prof. Allen’s expertise in stem cell models of disease this research team will translate these previous findings into a novel disease-relevant cell model.

What is this project trying to find out?

Current cell models investigating the role of ubiqilin-2 have yielded variable results due to their non-physiological design, therefore a more physiologically-relevant cell model is needed. Enter induced pluripotent stem cells (iPSCs). Stem cells are the most versatile cell type in the body, since they possess the capability to turn into any type of cell by switching the relevant genes on or off. Our understanding of stem cells is quite substantial, and we can now control the types of cells they differentiate into (e.g. neurons). In the early days of stem cell technology, these cells would have to be isolated from embryos or adult bone marrow (however the latter are limited in the number of cell types they can become). However, recent major advances in genetics mean that we can now “reset” skin cells isolated from individuals and transform them into stem cells that are able to differentiate into neurons. These types of stem cells are known as “induced pluripotent stem cells” (iPS cells for short) and can be used to create immortal cell lines from healthy and diseased individuals to study the differences between various cell types.

The overall aim of the study is to successfully generate of a human iPSC model of X-linked FTD (and a healthy control) to further characterise the role of ubiqulin-2 in the PN, and how it may be non-functional in FTD. These studies will help increase our understanding of the neuronal PN that is relevant to other forms of dementia such as Alzheimer’s disease and motor neuron disease.

How do they do this?

The cutting-edge gene editing technology (the CRISPR-cas9 system) will be used to introduce the ubiquilin-2 mutation to a human iPSC line. The cells will then be assessed for stem cell properties using imaging and genotyping methods.

Why is it important?

This validated iPSC editing protocol and the cell lines will be used for future projects modelling risk gene variants for other forms of dementia, ultimately untangling the effects of these gene variations and revealing new drug targets.

Glossary

Proteostasis network – The network of processes in cells responsible for the synthesis of correctly functioning proteins.
Protein synthesis – The process responsible for the production (synthesis) of new proteins in cells.
Folding (of a protein) – Proteins consist of amino acids which are linked together in a specific sequence. Once the chain of amino acids has been formed the protein will ‘fold’ into its correct three dimensional structure.
Physiological – The study of the various mechanisms and processes that occur within living systems.
CRISPR-cas9 – A cutting edge genome editing technique adapted from bacteria. This method allows cutting and splicing of DNA at specific positions on the gene.
Genotyping methods – Methods used to determine the differences in genetic make-up of an individual’s DNA sequence using biological assays.