Memory and synaptic plasticity are impaired by dysregulated hippocampal O-GlcNAcylation

O-GlcNAcylated proteins are abundant in the brain and are associated with neuronal functions and neurodegenerative diseases. Although several studies have reported the effects of aberrant regulation of O-GlcNAcylation on brain function, the roles of O-GlcNAcylation in synaptic function remain unclear. To understand the effect of aberrant O-GlcNAcylation on the brain, we used Oga+/- mice which have an increased level of O-GlcNAcylation, and found that Oga+/- mice exhibited impaired spatial learning and memory. Consistent with this result, Oga+/- mice showed a defect in hippocampal synaptic plasticity. Oga heterozygosity causes impairment of both long-term potentiation and long-term depression due to dysregulation of AMPA receptor phosphorylation. These results demonstrate a role for hyper-O-GlcNAcylation in learning and memory.ope

Bi-allelic variants in <em>RALGAPA1</em> cause profound neurodevelopmental disability, muscular hypotonia, infantile spasms, and feeding abnormalities.

Ral (Ras-like) GTPases play an important role in the control of cell migration and have been implicated in Ras-mediated tumorigenicity. Recently, variants in RALA were also described as a cause of intellectual disability and developmental delay, indicating the relevance of this pathway to neuropediatric diseases. Here, we report the identification of bi-allelic variants in RALGAPA1 (encoding Ral GTPase activating protein catalytic alpha subunit 1) in four unrelated individuals with profound neurodevelopmental disability, muscular hypotonia, feeding abnormalities, recurrent fever episodes, and infantile spasms . Dysplasia of corpus callosum with focal thinning of the posterior part and characteristic facial features appeared to be unifying findings. RalGAPA1 was absent in the fibroblasts derived from two affected individuals suggesting a loss-of-function effect of the RALGAPA1 variants. Consequently, RalA activity was increased in these cell lines, which is in keeping with the idea that RalGAPA1 deficiency causes a constitutive activation of RalA. Additionally, levels of RalGAPB, a scaffolding subunit of the RalGAP complex, were dramatically reduced, indicating a dysfunctional RalGAP complex. Moreover, RalGAPA1 deficiency clearly increased cell-surface levels of lipid raft components in detached fibroblasts, which might indicate that anchorage-dependence of cell growth signaling is disturbed. Our findings indicate that the dysregulation of the RalA pathway has an important impact on neuronal function and brain development. In light of the partially overlapping phenotype between RALA- and RALGAPA1-associated diseases, it appears likely that dysregulation of the RalA signaling pathway leads to a distinct group of genetic syndromes that we suggest could be named RALopathies

Chemical reporters for fluorescent detection and identification of O-GlcNAc-modified proteins reveal glycosylation of the ubiquitin ligase NEDD4-1

The dynamic modification of nuclear and cytoplasmic proteins by the monosaccharide N-acetyl-glucosamine (GlcNAc) continues to emerge as an important regulator of many biological processes. Herein we describe the development of an alkynyl-modified GlcNAc analog (GlcNAlk) as a new chemical reporter of O-GlcNAc modification in living cells. This strategy is based on metabolic incorporation of reactive functionality into the GlcNAc biosynthetic pathway. When combined with the Cu(I)-catalyzed [3 + 2] azide-alkyne cycloaddition, this chemical reporter allowed for the robust in-gel fluorescent visualization of O-GlcNAc and affinity enrichment and identification of O-GlcNAc-modified proteins. Using in-gel fluorescence detection, we characterized the metabolic fates of GlcNAlk and the previously reported azido analog, GlcNAz. We confirmed previous results that GlcNAz can be metabolically interconverted to GalNAz, whereas GlcNAlk does not, thereby yielding a more specific metabolic reporter of O-GlcNAc modification. We also used GlcNAlk, in combination with a biotin affinity tag, to identify 374 proteins, 279 of which were not previously reported, and we subsequently confirmed the enrichment of three previously uncharacterized proteins. Finally we confirmed the O-GlcNAc modification of the ubiquitin ligase NEDD4-1, the first reported glycosylation of this protein