Sandhoff disease, one of the GM2 gangliosidoses, is a lysosomal storage disorder characterized by the absence of β-hexosaminidase A and B activity and the concomitant lysosomal accumulation of its substrate, GM2 ganglioside. It features catastrophic neurodegeneration and death in early childhood. How the lysosomal accumulation of ganglioside might affect the early development of the nervous system is not understood. Recently, cerebral organoids derived from induced pluripotent stem (iPS) cells have illuminated early developmental events altered by disease processes. To develop an early neurodevelopmental model of Sandhoff disease, we first generated iPS cells from the fibroblasts of an infantile Sandhoff disease patient, then corrected one of the mutant HEXB alleles in those iPS cells using CRISPR/Cas9 genome-editing technology, thereby creating isogenic controls. Next, we used the parental Sandhoff disease iPS cells and isogenic HEXB-corrected iPS cell clones to generate cerebral organoids that modeled the first trimester of neurodevelopment. The Sandhoff disease organoids, but not the HEXB-corrected organoids, accumulated GM2 ganglioside and exhibited increased size and cellular proliferation compared with the HEXB-corrected organoids. Whole-transcriptome analysis demonstrated that development was impaired in the Sandhoff disease organoids, suggesting that alterations in neuronal differentiation may occur during early development in the GM2 gangliosidoses.

HighlightsCortical GABA levels correlate with visuo-spatial IQ and surround suppression.Higher levels predict higher intelligence and stronger surround suppression.Results provide mechanism linking surround suppression and intelligence.Results suggest role of cortical GABA levels in determining cognitive performance.

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Sphingosine-1-phosphate (S1P) is a sphingolipid metabolite that regulates basic cell functions through metabolic and signaling pathways. Intracellular metabolism of S1P is controlled, in part, by two homologous S1P phosphatases (SPPases), 1 and 2, which are encoded by the Sgpp1 and Sgpp2 genes, respectively. SPPase activity is needed for efficient recycling of sphingosine into the sphingolipid synthesis pathway. SPPase 1 is important for skin homeostasis, but little is known about the functional role of SPPase 2. To identify the functions of SPPase 2 in vivo, we studied mice with the Sgpp2 gene deleted. In contrast to Sgpp1 ؊/؊ mice, Sgpp2 ؊/؊ mice had normal skin and were viable into adulthood. Unexpectedly, WT mice expressed Sgpp2 mRNA at high levels in pancreatic islets when compared with other tissues. Sgpp2 ؊/؊ mice had normal pancreatic islet size; however, they exhibited defective adaptive ␤-cell proliferation that was demonstrated after treatment with either a high-fat diet or the ␤-cell-specific toxin, streptozotocin. Importantly, ␤-cells from untreated Sgpp2 ؊/؊ mice showed significantly increased expression of proteins characteristic of the endoplasmic reticulum stress response compared with ␤-cells from WT mice, indicating a basal islet defect. Our results show that Sgpp2 deletion causes ␤-cell endoplasmic reticulum stress, which is a known cause of ␤-cell dysfunction, and reveal a juncture in the sphingolipid recycling pathway that could impact the development of diabetes.Sphingosine 1-phosphate (S1P) 3 is a potent bioactive lipid produced from the degradation of plasma membrane sphingolipids (1-3). As a signaling molecule, S1P exerts effects in a variety of biological processes through interactions with both extracellular receptors and intracellular targets. As an intracellular metabolic intermediate, S1P is readily metabolized to other bioactive sphingolipids, such as ceramide and sphingosine, as well as to other lipids (Fig. 1A). S1P and its metabolites control basic cell functions, such as proliferation, apoptosis, and migration, and are involved in several pathologic conditions, including inflammation, metabolic disease, and cancer (1, 2). Thus, insight into S1P metabolism and how this regulates its functional activity is of key importance in understanding the role of S1P in biology and disease. S1P is produced by the sphingosine kinase-dependent phosphorylation of sphingosine, which is created as a degradation product of ceramide (4). Within cells, S1P is degraded through two pathways, either by irreversible cleavage by S1P lyase (5) or by dephosphorylation by specific S1P phosphatases (SPPases) (also known as S1P phosphohydrolases) (6). When cleaved by S1P lyase (Sgpl1), phosphoethanolamine and hexadecenal are produced, which are then transferred as substrates from the sphingolipid pathway to the glycerophospholipid pathway.In an alternative catabolic route catalyzed by S1P phosphatases, the resulting sphingosine product can be derivatized with a fatty acid by ceramide synthase to produce cer...

In the kidney, the epithelial sodium channel (ENaC) regulates blood pressure through control of sodium and volume homeostasis, and in the lung, ENaC regulates the volume of airway and alveolar fluids. ENaC is a heterotrimer of homologous α-, β- and γ-subunits, and assembles in the endoplasmic reticulum (ER) before it traffics to and functions at the plasma membrane. Improperly folded or orphaned ENaC subunits are subject to ER quality control and targeted for ER-associated degradation (ERAD). We previously established that a conserved, ER lumenal, molecular chaperone, Lhs1/GRP170, selects αENaC, but not β- or γ-ENaC, for degradation when the ENaC subunits were individually expressed. We now find that when all three subunits are co-expressed, Lhs1-facilitated ERAD was blocked. To determine which domain–domain interactions between the ENaC subunits are critical for chaperone-dependent quality control, we employed a yeast model and expressed chimeric α/βENaC constructs in the context of the ENaC heterotrimer. We discovered that the βENaC transmembrane domain was sufficient to prevent the Lhs1-dependent degradation of the α-subunit in the context of the ENaC heterotrimer. Our work also found that Lhs1 delivers αENaC for proteasome-mediated degradation after the protein has become polyubiquitinated. These data indicate that the Lhs1 chaperone selectively recognizes an immature form of αENaC, one which has failed to correctly assemble with the other channel subunits via its transmembrane domain.

SUMMARY Protein kinase C (PKC)-dependent mechanisms promote synaptic function in the mature brain. However, the roles of PKC signaling during synapse development remain largely unknown. Investigating each brain-enriched PKC isoform in early neuronal development, we show that PKCε acutely and specifically reduces the number of dendritic spines, sites of eventual synapse formation on developing dendrites. This PKCε-mediated spine suppression is temporally restricted to immature neurons and mediated through the phosphorylation and activation of Ephexin5, a RhoA guanine nucleotide exchange factor (GEF) and inhibitor of hippocampal synapse formation. Our data suggest that PKCε acts as an early developmental inhibitor of dendritic spine formation, in contrast to its emerging pro-synaptic roles in mature brain function. Moreover, we identify a substrate of PKCε, Ephexin5, whose early-elevated expression in developing neurons may in part explain the mechanism by which PKCε plays seemingly opposing roles that depend on neuronal maturity.

Highlights Cortical GABA levels correlate with contrast detection thresholds. GABA appears to reduce contrast response gain and intrinsic noise. Changes in contrast discrimination can be characterised by the Wilson-Cowan model.

In humans, loss-of-function mutations in the UBE3A gene lead to the neurodevelopmental disorder Angelman syndrome (AS). AS patients have severe impairments in speech, learning and memory, and motor coordination, for which there is currently no treatment. In addition, UBE3A is duplicated in >1-2% of patients with autism spectrum disorders – a further indication of the significant role it plays in brain development. Altered expression of UBE3A, an E3 ubiquitin ligase, is hypothesized to lead to impaired levels of its target proteins, but identifying the contribution of individual UBE3A targets to UBE3A-dependent deficits remains of critical importance. Ephexin5 is a putative UBE3A substrate that has restricted expression early in development, regulates synapse formation during hippocampal development, and is abnormally elevated in AS mice, modeled by maternally-derived Ube3a gene deletion. Here, we report that Ephexin5 is a direct substrate of UBE3A ubiquitin ligase activity. Furthermore, removing Ephexin5 from AS mice specifically rescued hippocampus-dependent behaviors, CA1 physiology, and deficits in dendritic spine number. Our findings identify Ephexin5 as a key driver of hippocampal dysfunction and related behavioral deficits in AS mouse models. These results demonstrate the exciting potential of targeting Ephexin5, and possibly other UBE3A substrates, to improve symptoms of AS and other UBE3A-related developmental disorders.