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Zebrafish disease modelling identifies a link between type I interferon signalling and cholesterol dysregulation in Aicardi-Goutieres syndrome and brain endothelial cells

SAM domain and HD domain-containing protein 1 (SAMHD1) is a protein that is known to function as a viral restriction factor and plays a key role in self non-self discrimination (1). Mutation of the SAMHD1 gene causes a genetic subtype of Aicardi-Goutieres syndrome (AGS) - an inherited inflammatory-based brain disorder associated with enhanced type I interferon (IFN) signalling. Unlike other genetics forms of AGS, SAMHD1-related AGS is associated with a major risk of cerebral vasculopathy, ischaemic stroke and haemorrhagic stroke (2). We have shown that temporal inhibition of the samhd1 gene in zebrafish causes brain haemorrhage and innate immune phenotypes which are reminiscent of the human condition (3). Taken together, these data indicate that SAMHD1 has a currently uncharacterised role in the control of neurovascular integrity. Using CRISPR-Cas9 technology, we have now generated a stable mutant samhd1 zebrafish line. Preliminary whole transcriptomic and phenotypic data indicate that samhd1 mutant larvae exhibit defects in cholesterol biosynthesis pathways and are predisposed to the development of ICH following incubation with sub-threshold doses of atorvastatin - a drug known to inhibit cholesterol production. Interestingly, experimental dysregulation of cholesterol synthesis has been associated with increased activity of IFN signalling (4) and haemorrhagic stroke (5).

The aim of this project is to understand the mechanistic link between SAMHD1, cholesterol and IFN-related ICH. This project will focus on further characterising the mutant samhd1 zebrafish phenotype in terms of a) the classical features of AGS and b) the neurovascular deficits specifically associated with SAMHD1-related AGS. We will continue to study the role of cholesterol dysregulation in this model. To determine the translational relevance of this observation, and to help determine if cholesterol dysregulation is specific to SAMHD1 patients or is observed in other AGS genetic subtypes, we will assess cholesterol gene expression in patient blood transcriptomic datasets. Furthermore, we will utilise an in vitro approach to interrogate the role of type I IFN-related signalling and cholesterol regulation in a human brain endothelial cell line. This work will provide novel insight into the role of SAMHD1, type I IFN and cholesterol in AGS and more broadly, neurovascular stability.