Roles of NR2F1 in Hippocampal Circuit Function and Mitochondrial Regulation: Insights into NR2F1-Related Neurodevelopmental Disorder

Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS) is a rare neurodevelopmental disorder caused by pathogenic variants in the gene NR2F1, a nuclear transcriptional regulator with essential roles in brain development and neuronal function. While the clinical phenotype includes cognitive impairments, visual deficits, and autistic traits, the cellular and circuit-level mechanisms linking NR2F1 haploinsufficiency to altered brain function remain poorly understood. This thesis investigates how NR2F1 deficiency affects hippocampal circuitry and mitochondrial biology, two interconnected aspects increasingly implicated in the pathophysiology of neurodevelopmental disorders. In the first part of this PhD work, I examined the impact of constitutive Nr2f1 haploinsufficiency on the adult dentate gyrus (DG) function using a validated mouse model of BBSOAS (Nr2f1+/-). Behavioral analyses revealed deficits in short-term spatial memory, consistent with DG-dependent processes. Electrophysiological and morphological investigations uncovered a disruption of inhibitory control onto DG mature granule cells, characterized by reduced GABAergic input, increased activation of excitatory neurons, and altered properties of inhibitory circuit function. These findings demonstrate that Nr2f1 haploinsufficiency may perturb the inhibitory-excitatory balance required for DG computations, identifying inhibitory circuitry as a potential therapeutic target. The second part of the thesis explores the role of Nr2f1 in mitochondrial regulation. Genome-wide and in silico analyses identified numerous nuclear-encoded mitochondrial genes as putative Nr2f1 targets. Using conditional mouse genetics, we showed that Nr2f1 loss-of-function within the adult hippocampal neurogenic niche leads to reduced mitochondrial mass, fragmented mitochondrial morphology, and downregulation of key mitochondrial proteins in newborn neurons, impairing their maturation and integration. Similar alterations were detected in the brains of Nr2f1+/- mice, supporting a broader role for Nr2f1 in maintaining mitochondrial homeostasis in neurons. Finally, to translate these findings to a human context, I established an isogenic iPSC-derived neuronal model. Human NR2F1-deficient neurons exhibited mitochondrial fragmentation, reduced dendritic mitochondrial content, and decreased levels of essential ETC/OxPhos proteins, mirroring the defects observed in mouse models. This human system provides the first evidence that NR2F1 may regulate mitochondrial organization and function in human neurons and offers a tractable platform for future mechanistic and therapeutic studies. ii Collectively, this thesis uncovers circuit- and subcellular-level mechanisms through which NR2F1 haploinsufficiency may lead to functional and cognitive dysfunctions in BBSOAS. By integrating mouse in vivo and ex vivo models with human in vitro approaches, this work highlights Nr2f1 as a key regulator of both inhibitory circuitry and mitochondrial homeostasis and reveals these pathways as promising targets for future interventions in BBSOAS and related neurodevelopmental conditions.