Investigation of the role of the snoRNA U8 in human health and disease

We want to understand the cause of a rare disease of the brain called leukoencephalopathy with calcifications and cysts (LCC). Although LCC most often affects children, it can actually present at any age, causing problems with seizures, movement and thinking over a period of several years. Patients eventually die of their illness because there is currently no known treatment for LCC.

The name LCC comes from the changes that doctors see when they look at the brain scans of affected patients - white matter damage ('leukoencephalopathy'), calcium accumulation (in a particular pattern), and cysts ('holes' in the brain white matter). Because LCC is rare and poorly recognised, and because no diagnostic blood test has been available until recently, affected patients sometimes have a piece of the brain taken out to be looked at under a microscope. Studies of these samples suggest that the problem causing LCC involves the brain blood vessels.

We recently discovered changes ('mutations') in a piece of our genetic material (our DNA) called SNORD118 as the cause of LCC. SNORD118 helps our cells to make a different type of genetic material referred to as RNA. The specific piece of RNA mutated in LCC is called U8. We know that U8 is important for producing proteins i.e. chemicals that are crucial for how our cells work. However, how these genetic and chemical changes lead to a problem in the cells of the brain blood vessels is still not known.

To improve our understanding of the cause of LCC, we have developed a special zebrafish with a similar genetic problem as is seen in patients affected with LCC. Our recent work shows that this 'animal model' represents a very useful tool for studying how LCC happens in humans, already providing new clues about the function of U8.

In this project we want to do more experiments, including using our zebrafish, to try to find out why U8 is so important for keeping the blood vessels in our brain healthy, and how problems with the working of U8 cause the disease LCC. We think that this could be relevant not only for the development of future treatments in LCC, but also for our understanding of more common diseases involving the brain blood vessels, such as stroke.

Ribosome biogenesis is an evolutionarily conserved process required for protein production in all living cells. Ribosomal RNA (rRNA) is transcribed as a precursor, and then subjected to extensive processing and post-transcriptional modification with the help of small nucleolar RNAs (snoRNAs). snoRNAs are divided into two major classes, box C/D and H/ACA, based on the presence of conserved sequence elements and differential protein interactions. Whilst some box snoRNAs modify rRNA, either by 2'-O-methylation (2'-O-Me) (C/D) or pseudouridylation (H/ACA), the box C/D snoRNA U8 is involved in precursor (pre)-rRNA processing. Of note, non-canonical actions of snoRNAs are also being increasingly recognised, but are much less studied.

Understanding the function of snoRNAs addresses a biological question fundamental to human health. Our project explores snoRNA biology in health and disease through a focus on the snoRNA U8, informed by our identification (Jenkinson et al. Nat Genet 2016;48:1185-92) and characterisation (Badrock et al. Am J Hum Genet 2020 AOP) of mutations in SNORD118, encoding U8, as the cause of a Mendelian disease of the cerebral vasculature called leukoencephalopathy with calcifications and cysts (LCC). Interestingly, in addition to its role in ribosomal biogenesis, clinical observation, in vitro analyses and in silico modelling suggest to us that U8 might play a previously unsuspected role in telomere maintenance.

To investigate the role of U8 in human health and disease, we will use a combination of clinical phenotyping, Mendelian and population genetics, specialised in vitro assays, and our zebrafish animal model. The derived data will inform our general understanding of snoRNA biology, and the pathogenesis of LCC.