Characterization of a mutant samhd1 zebrafish model implicates dysregulation of cholesterol biosynthesis in Aicardi-Goutières syndrome

Aicardi-Goutières syndrome (AGS1-9) is a genetically determined encephalopathy that falls under the type I interferonopathy disease class, characterized by excessive type I interferon (IFN-I) activity, coupled with upregulation of IFN-stimulated genes (ISGs), which can be explained by the vital role these proteins play in self-non-self-discrimination. To date, few mouse models fully replicate the vast clinical phenotypes observed in AGS patients. Therefore, we investigated the use of zebrafish as an alternative species for generating a clinically relevant model of AGS. Using CRISPR-cas9 technology, we generated a stable mutant zebrafish line recapitulating AGS5, which arises from recessive mutations in SAMHD1. The resulting homozygous mutant zebrafish larvae possess a number of neurological phenotypes, exemplified by variable, but increased expression of several ISGs in the head region, a significant increase in brain cell death, microcephaly and locomotion deficits. A link between IFN-I signaling and cholesterol biosynthesis has been highlighted by others, but not previously implicated in the type I interferonopathies. Through assessment of neurovascular integrity and qPCR analysis we identified a significant dysregulation of cholesterol biosynthesis in the zebrafish model. Furthermore, dysregulation of cholesterol biosynthesis gene expression was also observed through RNA sequencing analysis of AGS patient whole blood. From this novel finding, we hypothesize that cholesterol dysregulation may play a role in AGS disease pathophysiology. Further experimentation will lend critical insight into the molecular pathophysiology of AGS and the potential links involving aberrant type I IFN signaling and cholesterol dysregulation.

SARS-CoV-2 mRNA-based vaccines in the Aicardi Goutières Syndrome

Aicardi Goutières Syndrome (AGS) is an autoinflammatory disorder resulting in sustained interferon activation through defects in nucleic acid modification and sensing pathways. Thus, mRNA-based vaccination used against SARS-CoV-2, raise disease-specific safety concerns. To assess interferon signaling, we tested mRNA SARS-CoV-2 vaccines in AGS whole blood samples. Interferon activation is measured through quantitation of interferon signaling gene (ISG) expression and is increased in AGS patients. There was no increase in ISG scores from baseline following treatment with the nucleoside modified mRNA formulation compared to an increase with unmodified. A patient-family survey reported that the vaccines were well tolerated. These findings suggest that COVID vaccination using nucleoside-modified forms of mRNA vaccines are unlikely to directly stimulate ISG expression in response to mRNA internalization in AGS tissues. With continued community spread, we recommend vaccination using nucleoside-modified mRNA vaccines in this rare disease group in individuals for whom vaccines were previously well tolerated.

Restricting retrotransposons: ADAR1 is another guardian of the human genome

ADAR1 is an enzyme that belongs to the Adenosine Deaminases Acting on RNA (ADARs) family. These enzymes deaminate adenosines to inosines (RNA editing A-to-I) within double-stranded RNA regions in transcripts. Since inosines are recognized as guanosines by the cellular machinery, RNA editing mediated by ADARs can either lead to the formation of an altered protein (recoding) or affect different aspects of RNA metabolism. Recently, a proteomic analysis led to the identification of novel ADAR1-associated factors and found that a good fraction of them is shared with the Long Interspersed Element 1 (LINE-1 or L1) ribonucleoparticles (RNPs). This evidence suggested a possible role of ADAR1 in regulating the L1 life cycle. By taking advantage of the use of cell culture retrotransposition assays, a novel function of this deaminase as an inhibitor of L1 retrotransposition was demonstrated. These results pave the way toward a better comprehension of the mechanisms of restriction of retrotransposons.