Human microglial cells as a therapeutic target in a neurodevelopmental disease model.

Although microglia are macrophages of the central nervous system, their involvement is not limited to immune functions. The roles of microglia during development in humans remain poorly understood due to limited access to fetal tissue. To understand how microglia can impact human neurodevelopment, the methyl-CpG binding protein 2 (MECP2) gene was knocked out in human microglia-like cells (MGLs). Disruption of the MECP2 in MGLs led to transcriptional and functional perturbations, including impaired phagocytosis. The co-culture of healthy MGLs with MECP2-knockout (KO) neurons rescued synaptogenesis defects, suggesting a microglial role in synapse formation. A targeted drug screening identified ADH-503, a CD11b agonist, restored phagocytosis and synapse formation in spheroid-MGL co-cultures, significantly improved disease progression, and increased survival in MeCP2-null mice. These results unveil a MECP2-specific regulation of human microglial phagocytosis and identify a novel therapeutic treatment for MECP2-related conditions.

CADM2 is implicated in impulsive personality and numerous other traits by genome- and phenome-wide association studies in humans and mice.

Impulsivity is a multidimensional heritable phenotype that broadly refers to the tendency to act prematurely and is associated with multiple forms of psychopathology, including substance use disorders. We performed genome-wide association studies (GWAS) of eight impulsive personality traits from the Barratt Impulsiveness Scale and the short UPPS-P Impulsive Personality Scale (N = 123,509-133,517 23andMe research participants of European ancestry), and a measure of Drug Experimentation (N = 130,684). Because these GWAS implicated the gene CADM2, we next performed single-SNP phenome-wide studies (PheWAS) of several of the implicated variants in CADM2 in a multi-ancestral 23andMe cohort (N = 3,229,317, European; N = 579,623, Latin American; N = 199,663, African American). Finally, we produced Cadm2 mutant mice and used them to perform a Mouse-PheWAS ("MouseWAS") by testing them with a battery of relevant behavioral tasks. In humans, impulsive personality traits showed modest chip-heritability (~6-11%), and moderate genetic correlations (rg = 0.20-0.50) with other personality traits, and various psychiatric and medical traits. We identified significant associations proximal to genes such as TCF4 and PTPRF, and also identified nominal associations proximal to DRD2 and CRHR1. PheWAS for CADM2 variants identified associations with 378 traits in European participants, and 47 traits in Latin American participants, replicating associations with risky behaviors, cognition and BMI, and revealing novel associations including allergies, anxiety, irritable bowel syndrome, and migraine. Our MouseWAS recapitulated some of the associations found in humans, including impulsivity, cognition, and BMI. Our results further delineate the role of CADM2 in impulsivity and numerous other psychiatric and somatic traits across ancestries and species.

Therapeutically viable generation of neurons with antisense oligonucleotide suppression of PTB.

Methods to enhance adult neurogenesis by reprogramming glial cells into neurons enable production of new neurons in the adult nervous system. Development of therapeutically viable approaches to induce new neurons is now required to bring this concept to clinical application. Here, we successfully generate new neurons in the cortex and dentate gyrus of the aged adult mouse brain by transiently suppressing polypyrimidine tract binding protein 1 using an antisense oligonucleotide delivered by a single injection into cerebral spinal fluid. Radial glial-like cells and other GFAP-expressing cells convert into new neurons that, over a 2-month period, acquire mature neuronal character in a process mimicking normal neuronal maturation. The new neurons functionally integrate into endogenous circuits and modify mouse behavior. Thus, generation of new neurons in the dentate gyrus of the aging brain can be achieved with a therapeutically feasible approach, thereby opening prospects for production of neurons to replace those lost to neurodegenerative disease.

MHC class I H2-Kb negatively regulates neural progenitor cell proliferation by inhibiting FGFR signaling.

Proteins of the major histocompatibility complex class I (MHC I), predominantly known for antigen presentation in the immune system, have recently been shown to be necessary for developmental neural refinement and adult synaptic plasticity. However, their roles in nonneuronal cell populations in the brain remain largely unexplored. Here, we identify classical MHC I molecule H2-Kb as a negative regulator of proliferation in neural stem and progenitor cells (NSPCs). Using genetic knockout mouse models and in vivo viral-mediated RNA interference (RNAi) and overexpression, we delineate a role for H2-Kb in negatively regulating NSPC proliferation and adult hippocampal neurogenesis. Transcriptomic analysis of H2-Kb knockout NSPCs, in combination with in vitro RNAi, overexpression, and pharmacological approaches, further revealed that H2-Kb inhibits cell proliferation by dampening signaling pathways downstream of fibroblast growth factor receptor 1 (Fgfr1). These findings identify H2-Kb as a critical regulator of cell proliferation through the modulation of growth factor signaling.

Neuronal O-GlcNAcylation Improves Cognitive Function in the Aged Mouse Brain.

Mounting evidence in animal models indicates potential for rejuvenation of cellular and cognitive functions in the aging brain. However, the ability to utilize this potential is predicated on identifying molecular targets that reverse the effects of aging in vulnerable regions of the brain, such as the hippocampus. The dynamic post-translational modification O-linked N-Acetylglucosamine (O-GlcNAc) has emerged as an attractive target for regulating aging-specific synaptic alterations as well as neurodegeneration. While speculation exists about the role of O-GlcNAc in neurodegenerative conditions, such as Alzheimer's disease, its role in physiological brain aging remains largely unexplored. Here, we report that countering age-related decreased O-GlcNAc transferase (OGT) expression and O-GlcNAcylation ameliorates cognitive impairments in aged mice. Mimicking an aged condition in young adults by abrogating OGT, using a temporally controlled neuron-specific conditional knockout mouse model, recapitulated cellular and cognitive features of brain aging. Conversely, overexpressing OGT in mature hippocampal neurons using a viral-mediated approach enhanced associative fear memory in young adult mice. Excitingly, in aged mice overexpressing neuronal OGT in the aged hippocampus rescued in part age-related impairments in spatial learning and memory as well as associative fear memory. Our data identify O-GlcNAcylaton as a key molecular mediator promoting cognitive rejuvenation.

ß2-microglobulin is a systemic pro-aging factor that impairs cognitive function and neurogenesis.

Aging drives cognitive and regenerative impairments in the adult brain, increasing susceptibility to neurodegenerative disorders in healthy individuals. Experiments using heterochronic parabiosis, in which the circulatory systems of young and old animals are joined, indicate that circulating pro-aging factors in old blood drive aging phenotypes in the brain. Here we identify ß2-microglobulin (B2M), a component of major histocompatibility complex class 1 (MHC I) molecules, as a circulating factor that negatively regulates cognitive and regenerative function in the adult hippocampus in an age-dependent manner. B2M is elevated in the blood of aging humans and mice, and it is increased within the hippocampus of aged mice and young heterochronic parabionts. Exogenous B2M injected systemically, or locally in the hippocampus, impairs hippocampal-dependent cognitive function and neurogenesis in young mice. The negative effects of B2M and heterochronic parabiosis are, in part, mitigated in the hippocampus of young transporter associated with antigen processing 1 (Tap1)-deficient mice with reduced cell surface expression of MHC I. The absence of endogenous B2M expression abrogates age-related cognitive decline and enhances neurogenesis in aged mice. Our data indicate that systemic B2M accumulation in aging blood promotes age-related cognitive dysfunction and impairs neurogenesis, in part via MHC I, suggesting that B2M may be targeted therapeutically in old age.