Selective neurovascular regulation by a vascular dementia-related noncoding RNA Snord118

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PROJECT SUMMARY/ABSTRACT Dysfunction of neurovascular unit (NVU) is a key pathological event of neurodegenerative diseases, including Alzheimer's disease and Alzheimer's disease-related dementias (AD/ADRD). The mechanism underlying cell- type selective vulnerability in NVU is poorly understood. The goal of this proposal is to establish a novel mechanism by which NVU cell(s) are selectively impaired by the disruption of a global ribosome biogenesis. We will focus on a newly identified ribosomopathy disease gene Snord118, which encodes a noncoding RNA acting as a ribosome biogenesis factor. This is interesting because Snord118 mutations cause the first purely neurological disorder in ribosomopathies, named leukoencephalopathy with calcifications and cysts (LCC), with NVU lesions. There is very little understanding of Snord118 and LCC pathogenesis. This study has an opportunity to determine functions and mechanisms of Snord118 and LCC disease. We have assembled the following preliminary data: 1) generated two disease point mutation knock-in (KI) mice, which display early pericyte and BBB defects. These results suggest that brain endothelial cells (ECs) and pericytes are selectively affected in LCC, which justifies our iPSC research focus on brain ECs and pericytes; 2) generated five Snord118 mutant iPSC lines with isogenic controls, established protocols of directing iPSCs into brain microvascular endothelial cells (BMECs) and pericytes with the CNS identities, and prepared functional assays for BMEC, pericyte, and blood-brain barrier (BBB) properties; 3) developed the PARIS method to high throughput map RNA structures and identify RNA targets at single molecule and genome-wide levels with base-pair resolution. Our PARIS revealed a dynamic RNA structure and interaction network in Snord118 ribosome biogenesis and LCC. Leveraging on these preliminary data and tools, we propose to test the hypothesis that Snord118 mutation-mediated disruption of ribosome biogenesis selectively affects BMECs and pericytes via targeting rRNAs and non-rRNAs. Aim 1 will determine cellular functions of Snord118 in neurovascular cells focusing on BMECs and pericytes. Aim 2 will identify Snord118 targets and its RNA structure-function relationships. Overall, using our new iPSC-derived NVU cells and latest PARIS2, this study will generate the first human cellular models that do not currently exist for SNORD118 LCC, identify mechanisms of SNORD118 action and LCC disease, uncover a previously unknown vulnerability of specific NVU cells to the disruption of a ubiquitous ribosome biogenesis process, and therefore help to reconcile the neurological phenotype specificity of ribosomopathies with the global requirement for ribosome biogenesis.