Project description:O-GlcNAcylation is an abundant post-translational modification in the nervous system, linked to both neurodevelopmental and neurodegenerative disease. However, the mechanistic links between these phenotypes and site-specific O-GlcNAcylation remain largely unexplored. Here, we show that Ser517 O-GlcNAcylation of the microtubule-binding protein Collapsin Response Mediator Protein-2 (CRMP2) increases with age. By generating and characterizing a Crmp2S517A knock-in mouse model, we demonstrate that loss of O-GlcNAcylation leads to a small decrease in body weight and mild memory impairment, suggesting that Ser517 O-GlcNAcylation has a small but detectable impact on mouse physiology and cognitive function.
Project description:Myotonic dystrophy type I (DM1) patients demonstrate visuospatial dysfunction and impaired performance in tasks requiring recognition or memory of figures and objects. In DM1, CUG expansion RNAs inactivate the Muscleblind-like (MBNL) proteins. We show that constitutive Mbnl2 inactivation in Mbnl2ΔE2/ΔE2 mice, selectively impairs object recognition memory in the novel object recognition test. When exploring the context of a novel arena in which the objects are later encountered, the Mbnl2ΔE2/ΔE2 dorsal hippocampus responds with a lack of enrichment for learning and memory related pathways, mounting instead transcriptome alterations predicted to impair growth and neuron viability. In Mbnl2ΔE2/ΔE2 mice, saturation effects may prevent deployment of a functionally relevant transcriptome response during novel context exploration. Post-novel context exploration alterations in genes implicated in tauopathy and dementia are observed in the Mbnl2ΔE2/ΔE2 dorsal hippocampus. Thus MBNL2 inactivation in DM1 patients may alter novel context processing in the dorsal hippocampus and impair object recognition memory.
Project description:Patients with myotonic dystrophy type I (DM1) demonstrate visuospatial dysfunction and impaired performance in tasks requiring recognition or memory of figures and objects. In DM1, CUG expansion RNAs inactivate the muscleblind-like (MBNL) proteins. We show that constitutive Mbnl2 inactivation in Mbnl2ΔE2/ΔE2 mice selectively impairs object recognition memory in the novel object recognition test. When exploring the context of a novel arena in which the objects are later encountered, the Mbnl2ΔE2/ΔE2 dorsal hippocampus responds with a lack of enrichment for learning and memory-related pathways, mounting instead transcriptome alterations predicted to impair growth and neuron viability. In Mbnl2ΔE2/ΔE2 mice, saturation effects may prevent deployment of a functionally relevant transcriptome response during novel context exploration. Post-novel context exploration alterations in genes implicated in tauopathy and dementia are observed in the Mbnl2ΔE2/ΔE2 dorsal hippocampus. Thus, MBNL2 inactivation in patients with DM1 may alter novel context processing in the dorsal hippocampus and impair object recognition memory.
Project description:Experimental studies of cognitive detriments in mice and rats after proton and heavy ion exposures have been performed by several laboratories to investigate possible risks to astronauts exposed to cosmic rays in space travel and patients treated for brain cancers with proton and carbon beams in Hadron therapy. However, distinct radiation types and doses, cognitive tests and rodent models have been used by different laboratories, while few studies have considered detailed dose-response characterizations, including estimates of relative biological effectiveness (RBE). Here we report on the first quantitative meta-analysis of the dose response for proton and heavy ion rodent studies of the widely used novel object recognition (NOR) test, which estimates detriments in recognition or object memory. Our study reveals that linear or linear-quadratic dose-response models of relative risk (RR) do not provide accurate descriptions. However, good descriptions for doses up to 1 Gy are provided by exponentially increasing fluence or dose-response models observed with an LET dependence similar to a classical radiation quality response, which peaks near 100-120 keV/µm and declines at higher LET values. Exponential models provide accurate predictions of experimental results for NOR in mice after mixed-beam exposures of protons and 56Fe, and protons, 16O and 28Si. RBE estimates are limited by available X-ray or gamma-ray experiments to serve as a reference radiation. RBE estimates based on use of data from combined gamma-ray and high-energy protons of low-LET experiments suggest modest RBEs, with values <8 for most heavy ions, while higher values <20 are based on limited gamma-ray data. In addition, we consider a log-normal model for the variation of subject responses at defined dose levels. The log-normal model predicts a heavy ion dose threshold of approximately 0.01 Gy for NOR-related cognitive detriments.
Project description:The normal aging process is commonly associated with mild cognitive deficits including memory decline. Previous studies indicate a role of dysregulated messenger ribonucleic acid translation capacity in cognitive defects associated with aging and aging-related diseases, including hyperphosphorylation of eukaryotic elongation factor 2 (eEF2). Phosphorylation of eEF2 by the kinase eEF2K inhibits its activity, hindering general protein synthesis. Here, we sought to determine whether cognitive deficits in aged mice can be improved by genetically deleting eEF2K (eEF2K KO) and consequently reduction of eEF2 phosphorylation. We found that suppression of eEF2K prevented aging-related deficits in novel object recognition memory. Interestingly, deletion of eEF2K did not alter overall protein synthesis in the hippocampus. Ultrastructural analysis revealed increase size and larger active zone lengths of postsynaptic densities in the hippocampus of aged eEF2K KO mice. Biochemical assays showed hippocampal eIF2α hyperphosphorylation in aged eEF2K KO mice, indicating inhibition of translation initiation. Our findings may provide insight into mechanistic understanding and thus development of novel therapeutic strategies for aging-related cognitive decline.
Project description:Hyperpolarization-activated Cyclic Nucleotide-gated (HCN) channels are important regulators of excitability in neural, cardiac, and other pacemaking cells, which are often altered in disease. In mice, loss of HCN2 leads to cardiac dysrhythmias, persistent spike-wave discharges similar to those seen in absence epilepsy, ataxia, tremor, reduced neuropathic and inflammatory pain, antidepressant-like behavior, infertility, and severely restricted growth. While many of these phenotypes have tissue-specific mechanisms, the cause of restricted growth in HCN2 knockout animals remains unknown. Here, we characterize a novel, 3kb insertion mutation of Hcn2 in the Tremor and Reduced Lifespan 2 (TRLS/2J) mouse that leads to complete loss of HCN2 protein, and we show that this mutation causes many phenotypes similar to other mice lacking HCN2 expression. We then demonstrate that while TRLS/2J mice have low blood glucose levels and impaired growth, dysfunction in hormonal secretion from the pancreas, pituitary, and thyroid are unlikely to lead to this phenotype. Instead, we find that homozygous TRLS/2J mice have abnormal gastrointestinal function that is characterized by less food consumption and delayed gastrointestinal transit as compared to wildtype mice. In summary, a novel mutation in HCN2 likely leads to impaired GI motility, causing the severe growth restriction seen in mice with mutations that eliminate HCN2 expression.
Project description:Mutations of the X-linked methyl-CpG-binding protein 2 (MECP2) gene in humans are responsible for most cases of Rett syndrome (RTT), an X-linked progressive neurological disorder. While genome-wide screens in clinical trials have revealed several putative RTT-associated mutations in MECP2, their causal relevance regarding the functional regulation of MeCP2 at the etiologic sites at the protein level requires more evidence. In this study, we demonstrated that MeCP2 was dynamically modified by O-linked-β-N-acetylglucosamine (O-GlcNAc) at threonine 203 (T203), an etiologic site in RTT patients. Disruption of the O-GlcNAcylation of MeCP2 specifically at T203 impaired dendrite development and spine maturation in cultured hippocampal neurons, and disrupted neuronal migration, dendritic spine morphogenesis, and caused dysfunction of synaptic transmission in the developing and juvenile mouse cerebral cortex. Mechanistically, genetic disruption of O-GlcNAcylation at T203 on MeCP2 decreased the neuronal activity-induced induction of Bdnf transcription. Our study highlights the critical role of MeCP2 T203 O-GlcNAcylation in neural development and synaptic transmission potentially via brain-derived neurotrophic factor.
Project description:The qk(v) mutation is a one megabase deletion resulting in abnormal expression of the qkI gene. qk(v) mice exhibit hypomyelination of the central nervous system and display rapid tremors and seizures as adults. The qkI locus on 6q26-27 has also been implicated as a candidate tumor suppressor gene as the qkI locus maps to a region of genetic instability in Glioblastoma Multiforme (GBM), an aggressive brain tumor of astrocytic lineage. As GBM frequently harbors mutations affecting p53, we crossbred qk(v) and p53 mutant mice to examine whether qk(v) mice on a p53(-/-) background have an increased incidence of GBM. qk(v) (/v); p53(-/-) mice had a reduced survival rate compared to p53(-/-) littermates, and the cause of death of the majority of the mice remains unknown. In addition, immunohistochemistry revealed Purkinje cell degeneration in the cerebellum. These results suggest that p53 and qkI are genetically linked for neuronal maintenance and survival.
Project description:Disruptions in early life care, including neglect, extreme poverty, and trauma, influence neural development and increase the risk for and severity of pathology. Significant sex disparities have been identified for affective pathology, with females having an increased risk of developing anxiety and depressive disorder. However, the effects of early life stress (ELS) on cognitive development have not been as well characterized, especially in reference to sex specific impacts of ELS on cognitive abilities over development. In mice, fragmented maternal care resulting from maternal bedding restriction, was used to induce ELS. The development of spatial abilities were tracked using a novel object placement (NOP) task at several different ages across early development (P21, P28, P38, P50, and P75). Male mice exposed to ELS showed significant impairments in the NOP task compared with control reared mice at all ages tested. In female mice, ELS led to impaired NOP performance immediately following weaning (P21) and during peri-adolescence (P38), but these effects did not persist into early adulthood. Prior work has implicated impaired hippocampus neurogenesis as a possible mediator of negative outcomes in ELS males. In the hippocampus of behaviorally naïve animals there was a significant decrease in expression of Ki-67 (proliferative marker) and doublecortin (DCX-immature cell marker) as mice aged, and a more rapid developmental decline in these markers in ELS reared mice. However, the effect of ELS dissipated by P28 and no main effect of sex were observed. Together these results indicate that ELS impacts the development of spatial abilities in both male and female mice and that these effects are more profound and lasting in males.