A dominant dendrite phenotype caused by the disease-associated G253D mutation in doublecortin (DCX) is not due to its endocytosis defect

Bexarotene enhances astrocyte phagocytosis via ABCA1-mediated pathways in a mouse model of subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Enhancing phagocytosis can facilitate the removal of inflammatory molecules, limit the toxicity of dead cells and debris, and promote recovery after brain injury. In this study, we aimed to explore the role of bexarotene (Bex), a retinoid X receptor (RXR) agonist, in promoting astrocyte phagocytosis and neurobehavioral recovery after subarachnoid hemorrhage (SAH).

METHODS

Mice SAH model was induced by pre-chiasmatic injection of blood. Modified Garcia score, novel object recognition, rotarod test, and Morris water maze were performed to assess neurological function. Immunofluorescence and electron microscopy were used to evaluate astrocyte phagocytosis in vivo. In addition， ABCA1/MEGF10&GULP1, the primary astrocyte phagocytosis pathway, were stimulated by Bex or suppressed by HX531 (a RXR antagonist) to evaluate their impacts on astrocyte phagocytosis and neurological recovery.

RESULTS

Astrocytes phagocytosis of blood components were observed in mice after SAH induction, which is further increased by Bex treatment. Bex dramatically attenuated neuroinflammation, reduced brain edema, improved early neurological performance and promoted neurocognitive recovery. Meanwhile, Bex decreased neurotoxic reactive astrocytes and preserved neurogenesis after SAH. Bex increased the expression of astrocyte phagocytosis-related proteins ABCA1, MEGF10, and GULP1. Bex also increased the lysosomal processing of engulfed blood components in astrocytes. Moreover, Bex significantly promoted astrocytes to phagocytize debris in vitro by increasing the expression of ABCA1, MEGF10 and GULP1, while HX531 inhibited astrocyte phagocytosis and decreased these protein levels.

CONCLUSIONS

Bex enhanced astrocyte phagocytosis through the ABCA1-mediated pathways, and promoted neurobehavior recovery in mice after SAH induction.

Effect of a neurostimulator on postnatal neurogenesis in rodent olfactory bulbs

The aim of the study was to reveal the effect of neurostimulation with the TKPRPGP neuropeptide on the expression intensity of Doublecortin and Nestin in the olfactory bulb of white Wistar rats using immunohistochemical and computer analysis methods. An isolated assessment of early progenitor differentiation by the density of nestin-positive structures showed that stimulation from birth to 14 days preserves the level of nestin expression, preventing its decrease. When the administration of the neuropeptide is stopped, the expression of nestin decreases sharply, starting from the central zones of the bulb, and after three weeks it is no longer present. The dynamics of doublecortin positive structure density reflects an increase upon neuropeptide administration. Each course of neuropeptide administration caused an increase in the density of the marker, but the degree of effectiveness decreased with age, and the duration of the effect decreased. In conclusion, administration of the neuropeptide TKPRPGP to rats at an early age prolongs the expression of nestin and doublecortin in the olfactory bulbs of rats up to 35 days and up to 74 days of observation, respectively. The administration of the neuropeptide in adulthood does not lead to re-expression of these markers.

Sensorineural hearing loss may lead to dementia-related pathological changes in hippocampal neurons

Presbycusis contributes to cognitive decline and Alzheimer's disease. However, most research in this area involves clinical observations and statistical modeling, and few studies have examined the relationship between hearing loss and the molecular changes that lead to cognitive dysfunction. The present study investigated whether hearing loss contributes to dementia in the absence of aging and noise using a mouse model of severe bilateral hearing loss induced by kanamycin (1000 mg/kg) and furosemide (400 mg/kg). Immunohistochemistry, silver staining, immunofluorescence analysis, and Western blotting were used to observe pathological changes in different regions of the hippocampus in animals with hearing loss. Changes in the cognitive function of animals with hearing loss were assessed using the Morris water maze test. The results showed that neurons began to degenerate 60 days after hearing loss, and this degeneration was accompanied by structural disorganization and decreased neurogenesis. The level of phosphorylated tau increased over time. Increases in escape latency and distance traveled during the training phase of the Morris water maze test were observed 90 days after hearing loss. Activated microglia and astrocytes with increased levels of inflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were detected in the hippocampus. These results suggest that hearing loss alone causes neuronal degeneration, inhibition of neurogenesis, increased tau protein phosphorylation, and increased neuroinflammation in the hippocampus. Early intervention in individuals with hearing loss may reduce the risk of cognitive decline.

Brain-specific functions of the endocytic machinery

Endocytosis is an essential cellular process required for multiple physiological functions, including communication with the extracellular environment, nutrient uptake, and signaling by the cell surface receptors. In a broad sense, endocytosis is accomplished through either constitutive or ligand-induced invagination of the plasma membrane, which results in the formation of the plasma membrane-retrieved endocytic vesicles, which can either be sent for degradation to the lysosomes or recycled back to the PM. This additional function of endocytosis in membrane retrieval has been adopted by excitable cells, such as neurons, for membrane equilibrium maintenance at synapses. The last two decades were especially productive with respect to the identification of brain-specific functions of the endocytic machinery, which additionally include but not limited to regulation of neuronal differentiation and migration, maintenance of neuron morphology and synaptic plasticity, and prevention of neurotoxic aggregates spreading. In this review, we highlight the current knowledge of brain-specific functions of endocytic machinery with a specific focus on three brain cell types, neuronal progenitor cells, neurons, and glial cells.

Epstein-Barr Virus Early Protein BFRF1 Suppresses IFN-β Activity by Inhibiting the Activation of IRF3

Epstein-Barr virus (EBV) is the causative agent of infectious mononucleosis that is closely associated with several human malignant diseases, while type I interferon (IFN-I) plays an important role against EBV infection. As we all know, EBV can encode some proteins to inhibit the production of IFN-I, but it’s not clear whether other proteins also take part in this progress. EBV early lytic protein BFRF1 is shown to be involved in viral maturation, however, whether BFRF1 participates in the host innate immune response is still not well known. In this study, we found BFRF1 could down-regulate sendai virus-induced IFN-β promoter activity and mRNA expression of IFN-β and ISG54 during BFRF1 plasmid transfection and EBV lytic infection, but BFRF1 could not affect the promoter activity of NF-κB or IRF7. Specifically, BFRF1 could co-localize and interact with IKKi. Although BFRF1 did not interfere the interaction between IKKi and IRF3, it could block the kinase activity of IKKi, which finally inhibited the phosphorylation, dimerization, and nuclear translocation of IRF3. Taken together, BFRF1 may play a critical role in disrupting the host innate immunity by suppressing IFN-β activity during EBV lytic cycle.

Independent anterograde transport and retrograde cotransport of domain components of myelinated axons

Neurons are highly polarized cells organized into functionally and molecularly distinct domains. A key question is whether the multiprotein complexes that comprise these domains are preassembled, transported, and inserted as a complex or whether their components are transported independently and assemble locally. Here, we have dynamically imaged, in pairwise combinations, the vesicular transport of fluorescently tagged components of the nodes of Ranvier and other myelinated axonal domains in sensory neurons cultured alone or together with Schwann cells at the onset of myelination. In general, most proteins are transported independently in the anterograde direction. In contrast, there is substantial cotransport of proteins from distinct domains in the retrograde direction likely due to coendocytosis along the axon. Early myelination did not substantially change these patterns of transport, although it increased the overall numbers of axonal transport vesicles. Our results indicate domain components are transported in separate vesicles for local assembly, not as preformed complexes, and implicate endocytosis along axons as a mechanism of clearance.

Nestin Selectively Facilitates the Phosphorylation of the Lissencephaly-Linked Protein Doublecortin (DCX) by cdk5/p35 to Regulate Growth Cone Morphology and Sema3a Sensitivity in Developing Neurons

Nestin, an intermediate filament protein widely used as a marker of neural progenitors, was recently found to be expressed transiently in developing cortical neurons in culture and in developing mouse cortex. In young cortical cultures, nestin regulates axonal growth cone morphology. In addition, nestin, which is known to bind the neuronal cdk5/p35 kinase, affects responses to axon guidance cues upstream of cdk5, specifically, to Sema3a. Changes in growth cone morphology require rearrangements of cytoskeletal networks, and changes in microtubules and actin filaments are well studied. In contrast, the roles of intermediate filament proteins in this process are poorly understood, even in cultured neurons. Here, we investigate the molecular mechanism by which nestin affects growth cone morphology and Sema3a sensitivity. We find that nestin selectively facilitates the phosphorylation of the lissencephaly-linked protein doublecortin (DCX) by cdk5/p35, but the phosphorylation of other cdk5 substrates is not affected by nestin. We uncover that this substrate selectivity is based on the ability of nestin to interact with DCX, but not with other cdk5 substrates. Nestin thus creates a selective scaffold for DCX with activated cdk5/p35. Last, we use cortical cultures derived from Dcx KO mice to show that the effects of nestin on growth cone morphology and on Sema3a sensitivity are DCX-dependent, thus suggesting a functional role for the DCX-nestin complex in neurons. We propose that nestin changes growth cone behavior by regulating the intracellular kinase signaling environment in developing neurons. The sex of animal subjects is unknown.SIGNIFICANCE STATEMENT Nestin, an intermediate filament protein highly expressed in neural progenitors, was recently identified in developing neurons where it regulates growth cone morphology and responsiveness to the guidance cue Sema3a. Changes in growth cone morphology require rearrangements of cytoskeletal networks, but the roles of intermediate filaments in this process are poorly understood. We now report that nestin selectively facilitates phosphorylation of the lissencephaly-linked doublecortin (DCX) by cdk5/p35, but the phosphorylation of other cdk5 substrates is not affected. This substrate selectivity is based on preferential scaffolding of DCX, cdk5, and p35 by nestin. Additionally, we demonstrate a functional role for the DCX-nestin complex in neurons. We propose that nestin changes growth cone behavior by regulating intracellular kinase signaling in developing neurons.