Dishevelled proteins are associated with olfactory sensory neuron presynaptic terminals

Transplantation of Wnt3a-modified neural stem cells promotes neural regeneration and functional recovery after spinal cord injury via Wnt-Gli2 pathway

Neural stem cell (NSCs) transplantation has great potential in the treatment of spinal cord injury (SCI). Previous studies have indicated that the Wnt pathway could regulate the expression of basic helix-loop-helix (bHLH) family factor Hes5 and Mash1 in NSCs, but not through the notch intracellular domain. This suggests that there are other signals involved in this process. The aim of this study was to investigate the role of Wnt-Gli2 pathway in the treatment of SCI by transplanting neural stem cells. NSCs were isolated from the striata of embryonic day 14 mice. Activation of the Wnt pathway was achieved using Wnt3a protein, while Gli2 was inhibited using Gli2-siRNA. Expression levels of Gli2 and bHLH factors were assessed using western blotting. NSCs proliferation was evaluated using CCK-8 assay, and neural differentiation was determined by immunofluorescence staining. Finally, the modified NSCs were transplanted into mice with SCI, and their effects were assessed using behavioral and histological tests. Our results demonstrated that Wnt3a promoted the expression of Mash1 through Gli2. Moreover, the expression of Ngn1 and Hes1 was up-regulated, while Hes5 was down-regulated. Wnt3a also promoted NSCs proliferation and neural differentiation through this signaling pathway. In vivo experiments showed that NSCs transplantation mediated by Wnt3a-Gli2 signaling increased the number of neurons and resulted in improved Basso Mouse Scale scores. In conclusion, our findings suggest that Gli2 plays a role in mediating the regulation of Wnt3a signaling on promoting NSCs proliferation and neural differentiation. This pathway is therefore important in NSCs-mediated SCI recovery.

Role of Wnt signaling in synaptic plasticity and memory

Ever since their discoveries, the Wnt pathways have been consistently associated with key features of cellular development, including metabolism, structure and cell fate. The three known pathways (the canonical Wnt/β-catenin and the two non-canonical Wnt/Ca⁺⁺ and Wnt/JNK/PCP pathways) participate in complex networks of interaction with a wide range of regulators of cell function, such as GSK-3β, AKT, PKC and mTOR, among others. These proteins are known to be involved in the formation and maintenance of memory. Currently, studies with Wnt and memory have shown that the canonical and non-canonical pathways play key roles in different processes associated with memory. So, in this review we briefly summarize the different roles that Wnt signaling can play in neurons and in memory, as well as in Alzheimer's disease, focusing towards animal studies. We start with the molecular characterization of the family and its receptors, as well as the most commonly used drugs for pharmacological manipulations. Next, we describe its role in synaptic plasticity and memory, and how the regulations of these pathways affect crucial features of neuronal function. Furthermore, we succinctly present the current knowledge on how the Wnt pathways are implicated in Alzheimer's disease, and how studies are seeing them as a potential candidate for effective treatments. Lastly, we point toward challenges of Wnt research, and how knowledge on these pathways can lead towards a better understanding of neurobiological and pathological processes.

Ubiquitin-related processes and innate immunity in C. elegans

Innate immunity is an evolutionary ancient defence strategy that serves to eliminate infectious agents while maintaining host health. It involves a complex network of sensors, signaling proteins and immune effectors that detect the danger, then relay and execute the immune programme. Post-translational modifications relying on conserved ubiquitin and ubiquitin-like proteins are an integral part of the system. Studies using invertebrate models of infection, such as the nematode Caenorhabditis elegans, have greatly contributed to our understanding of how ubiquitin-related processes act in immune sensing, regulate immune signaling pathways, and participate to host defence responses. This review highlights the interest of working with a genetically tractable model organism and illustrates how C. elegans has been used to identify ubiquitin-dependent immune mechanisms, discover novel ubiquitin-based resistance strategies that mediate pathogen clearance, and unravel the role of ubiquitin-related processes in tolerance, preserving host fitness during pathogen attack. Special emphasis is placed on processes that are conserved in mammals.

Insights into olfactory ensheathing cell development from a laser-microdissection and transcriptome-profiling approach

Olfactory ensheathing cells (OECs) are neural crest-derived glia that ensheath bundles of olfactory axons from their peripheral origins in the olfactory epithelium to their central targets in the olfactory bulb. We took an unbiased laser microdissection and differential RNA-seq approach, validated by in situ hybridization, to identify candidate molecular mechanisms underlying mouse OEC development and differences with the neural crest-derived Schwann cells developing on other peripheral nerves. We identified 25 novel markers for developing OECs in the olfactory mucosa and/or the olfactory nerve layer surrounding the olfactory bulb, of which 15 were OEC-specific (that is, not expressed by Schwann cells). One pan-OEC-specific gene, Ptprz1, encodes a receptor-like tyrosine phosphatase that blocks oligodendrocyte differentiation. Mutant analysis suggests Ptprz1 may also act as a brake on OEC differentiation, and that its loss disrupts olfactory axon targeting. Overall, our results provide new insights into OEC development and the diversification of neural crest-derived glia.

Plasma membrane insertion of KCa2.3 (SK3) is dependent upon the SNARE proteins, syntaxin-4 and SNAP23

We previously demonstrated endocytosis of KCa2.3 is caveolin-1-, dynamin II- and Rab5-dependent. KCa2.3 then enters Rab35/EPI64C- and RME-1-containing recycling endosomes and is returned to the plasma membrane (PM). Herein, we report on the mechanism by which KCa2.3 is inserted into the PM during recycling and following exit from the Golgi. We demonstrate KCa2.3 colocalizes with SNAP-23 and Syntaxin-4 in the PM of HEK and endothelial cells by confocal immunofluorescence microscopy. We further show KCa2.3 can be co-immunoprecipitated with SNAP-23 and Syntaxin-4. Overexpression of either Syntaxin-4 or SNAP-23 increased PM expression of KCa2.3, whereas shRNA-mediated knockdown of these SNARE proteins significantly decreased PM KCa2.3 expression, as assessed by cell surface biotinylation. Whole-cell patch clamp studies confirmed knockdown of SNAP-23 significantly decreased the apamin sensitive, KCa2.3 current. Using standard biotinylation/stripping methods, we demonstrate shRNA mediated knockdown of SNAP-23 inhibits recycling of KCa2.3 following endocytosis, whereas scrambled shRNA had no effect. Finally, using biotin ligase acceptor peptide (BLAP)-tagged KCa2.3, coupled with ER-resident biotin ligase (BirA), channels could be biotinylated in the ER after which we evaluated their rate of insertion into the PM following Golgi exit. We demonstrate knockdown of SNAP-23 significantly slows the rate of Golgi to PM delivery of KCa2.3. The inhibition of both recycling and PM delivery of newly synthesized KCa2.3 channels likely accounts for the decreased PM expression observed following knockdown of these SNARE proteins. In total, our results suggest insertion of KCa2.3 into the PM depends upon the SNARE proteins, Syntaxin-4 and SNAP-23.

Environmental Toxicants-Induced Immune Responses in the Olfactory Mucosa

Olfactory sensory neurons (OSNs) are the receptor cells for the sense of smell. Although cell bodies are located in the olfactory mucosa (OM) of the nasal cavity, OSN axons directly project to the olfactory bulb (OB) that is a component of the central nervous system (CNS). Because of this direct and short connection from this peripheral tissue to the CNS, the olfactory system has attracted attention as a port-of-entry for environmental toxicants that may cause neurological dysfunction. Selected viruses can enter the OB via the OM and directly affect the CNS. On the other hand, environmental toxicants may induce inflammatory responses in the OM, including infiltration of immune cells and production of inflammatory cytokines. In addition, these inflammatory responses cause the loss of OSNs that are then replaced with newly generated OSNs that re-connect to the OB after inflammation has subsided. It is now known that immune cells and cytokines in the OM play important roles in both degeneration and regeneration of OSNs. Thus, the olfactory system is a unique neuroimmune interface where interaction between nervous and immune systems in the periphery significantly affects the structure, neuronal circuitry, and immunological status of the CNS. The mechanisms by which immune cells regulate OSN loss and the generation of new OSNs are, however, largely unknown. To help develop a better understanding of the mechanisms involved, we have provided a review of key research that has investigated how the immune response in the OM affects the pathophysiology of OSNs.

Activity-dependent and graded BACE1 expression in the olfactory epithelium is mediated by the retinoic acid metabolizing enzyme CYP26B1

It is well established that environmental influences play a key role in sculpting neuronal connectivity in the brain. One example is the olfactory sensory map of topographic axonal connectivity. While intrinsic odorant receptor signaling in olfactory sensory neurons (OSN) determines anterior-posterior counter gradients of the axonal guidance receptors Neuropilin-1 and Plexin-A1, little is known about stimulus-dependent gradients of protein expression, which correlates with the functional organization of the olfactory sensory map along its dorsomedial (DM)-ventrolateral (VL) axis. Deficiency of the Alzheimer's β-secretase BACE1, which is expressed in a DM(low)-VL(high) gradient, results in OSN axon targeting errors in a DM > VL and gene dose-dependent manner. We show that expression of BACE1 and the all-trans retinoic acid (RA)-degrading enzyme Cyp26B1 form DM-VL counter gradients in the olfactory epithelium. Analyses of mRNA and protein levels in OSNs after naris occlusion, in mice deficient in the olfactory cyclic nucleotide-gated channel and in relation to onset of respiration, show that BACE1 and Cyp26B1 expression in OSNs inversely depend on neuronal activity. Overexpression of a Cyp26B1 or presence of a dominant negative RA receptor transgene selectively in OSNs, inhibit BACE1 expression while leaving the DM(low)-VL(high) gradient of the axonal guidance protein Neuropilin-2 intact. We conclude that stimulus-dependent neuronal activity can control the expression of the RA catabolic enzyme Cyp26B1 and downstream genes such as BACE1. This result is pertinent to an understanding of the mechanisms by which a topographic pattern of connectivity is achieved and modified as a consequence of graded gene expression and sensory experience.

Dishevelled-1 (Dvl-1) protein: a potential participant of oxidative stress induced by selenium deficiency

Oxidative stress induced by selenium deficiency has been shown to be associated with cardiovascular diseases. Nevertheless, the mechanism associated with oxidative stress induced by selenium deficiency is poorly understood. In the present study, 36 weaning C57BL/6 mice were randomly divided into 4 groups as follows: control (n =9), 4-week selenium deficiency (n =9), 8-week selenium deficiency (n = 9), and 12-week selenium deficiency (n =9). The levels of myocardial glutathione peroxidase (GPx), superoxide dismutase (SOD), and malondialdehyde (MDA) were determined by Western blotting or commercial kits. Real-time PCR was performed to detect the mRNA expression of dishevelled-1 (Dvl-1) protein. Western blotting was conducted to evaluate the protein expression levels of Dvl-1 and β-catenin. Our results demonstrated that the levels of GPx and SOD were significantly reduced, along with an increase in MDA in selenium-deficient mice. Importantly, Dvl-1 and β-catenin were clearly upregulated under oxidative stress. Collectively, our findings indicate that Dvl-1 may be an underlying participant of oxidative stress induced by selenium deficiency.