Effects of the NR2E1 mutation on cellular and molecular determinants of neurogenesis - Abstract The ability of neural stem cells to give rise to mature neurons, a process known as neurogenesis, is crucial for the developing and adult mammalian brain. Dysregulation of this process has been associated with several pathologies including cognitive impairment and depression. Thus, there has been an increased interest to study neurogenesis as a potential therapeutic target to counteract these pathologies. Nuclear receptor subfamily 2, group E, member 1 (NR2E1) has been considered a master regulator of neurogenesis. Loss of Nr2e1 in the mouse model significantly impairs neural stem and progenitor cell proliferation and neurogenesis, ultimately leading to hippocampal hypoplasia and a decline in learning and memory. In contrast, overexpression of Nr2e1 improves learning and memory and diminishes anxiety behaviors. Despite the importance of Nr2e1 for neural stem cell biology and neurogenesis, we still do not know whether NR2E1 is important in humans, whether NR2E1 genetic variants exist, and if so, whether they cause any pathology. To answer these questions, we performed a thorough screening of multiple undiagnosed patient databases and identified several patients with different NR2E1 de novo single nucleotide variants leading to missense mutations in its coding sequence. All patients present with mild-to-moderate intellectual disability and various behavioral issues, from impulsive to aggressive behaviors. To establish causality, in this proposal we focus on one identified mutation, I385T, located at the C-terminal of the NR2E1 ligand-binding domain. We hypothesize that NR2E1 I385T mutation dysregulates neurogenesis by impairing NR2E1 function, leading to poor learning and memory. To understand the molecular consequences of this mutation, we will first assess how I385T affects NR2E1's ability to interact with its ligand and co-regulators using biophysical and in vitro assays (Aim 1). Second, we will determine the cellular and behavioral effects of I385T mutation by studying it in two complementary models: a CRISPR-Cas9 engineered mouse model (Aim 2) and a patient-derived human brain organoid model (Aim 3). Mouse model studies will inform whether neurogenesis is impaired throughout life from the embryonic stage to adulthood, resulting in behavioral anomalies. Patient-derived brain organoid studies will inform how I385T mutation specifically affects early human neurogenesis. This is very important for future attempts to develop small molecules to rescue NR2E1 activity in patients with this mutation. Overall, the findings of this proposal will further our understanding of the causative relationship between NR2E1 mutation and human pathology and pave the way for a personalized therapeutic approach for the affected individuals.
