Membrane trafficking in neurons regulated by new syntaxin 13-interacting proteins

Recently, it has been shown that correct trafficking of neuronal plasma membrane receptors along the endosomal pathway is directly implicated in molecular mechanisms underlying synaptic plasticity and is fundamental for proper neuronal communication. To understand the molecular mechanisms that regulate neuronal trafficking through endosomes, we used syntaxin 13, an endosomal protein that we had previously characterized, as a bait to immunopurify protein complexes. Among the 5 new syntaxin 13-interacting proteins that we identified, my thesis work has focused on the characterization of 2 of them, Neuron-Enriched Endosomal Protein of 21 kDa (NEEP21) and Reticulon1-C (RTN1-C). NEEP21. Our work revealed that NEEP21 is expressed by neurons in their somatodendritic compartments, where it is mainly found in Rab4-positive subdomains of early endosomes. This domain has been implicated in the sorting of internalized surface receptors. We demonstrated that NEEP21 suppression strongly retards recycling of receptors including AMPA-type glutamate receptors. We recently identified a molecular link between NEEP21 and AMPA-receptor trafficking. NEEP21 is present in a complex with GRIP, a scaffold protein for GluR2, and GluR2, a subunit of AMPA receptors. Overexpression of the NEEP21 binding site for GRIP causes a retraction of dendrites, an effect partially compensated by GluR2 overexpression. In addition, expression of this fragment inhibits AMPA receptor recycling. Based on the recent findings of the importance of AMPA receptor trafficking between endosomes and the cell membrane during synaptic structural and functional plasticity, we postulate that NEEP21 modulates synaptic strength. RTN1-C. The second identified syntaxin 13-associated protein is RTN1-C. Reticulons constitute a family of membrane proteins localized primarily to the endoplasmic reticulum (ER). So far the cellular function of reticulons is little undertsood. We found that RTN1-C interacts with several SNARE proteins. In addition, we showed that overexpression of the RTN1-C binding site for syntaxin 1 significantly enhanced regulated secretion. Based on these findings, we hypothesized that RTN1-C could be a key actor in the regulation of SNARE-dependent membrane fusion processes. Together, our studies contribute to the elucidation of the roles of NEEP21 and RTN1-C in neurons and the molecular mechanisms of membrane protein trafficking that are at fundamental for synaptic plasticity

Genital Dysplasia and Immunosuppression: Why Organ-Specific Therapy Is Important

Background Young patients with Crohn's disease (CD) show a high prevalence of human papillomavirus (HPV) which is the main cause of high-grade squamous intraepithelial lesions (HSIL). A major complication for patients undergoing immunocompromising therapy is the development of genital dysplasia. Methods We report the case of a 32-year-old patient with recurrent genital dysplasia under long-term therapy for CD with a focus on different drug-related, immunosuppressive mechanisms. Results Gynecological examination and biopsy revealed high-grade vulvar intraepithelial neoplasia (VIN) positive for HPV 16 treated with laser vaporization. Due to the combination of HPV positivity, intraoperative multilocularity, and CD, follow-up examinations were performed every 6 months. One year later, the patient showed a VIN at a new location and additionally, a cervical intraepithelial neoplasia (CIN), which were surgically treated. Catch-up HPV vaccination was applied accessorily. After the switch from a TNF-α blocker to vedolizumab, which acts as a gut-selective anti-integrin, the subsequent PAP smear, vulvoscopy, and colposcopy showed no more evidence of dysplasia. Conclusions This case report highlights that gut-selective immunosuppression with vedolizumab might be favorable in young HPV-positive patients due to a good side effect profile. Regular screening and HPV vaccination are a mainstay of dysplasia prevention and control. The risk for HPV-associated dysplasia in immunosuppressed patients is highly dependent on the choice of immunosuppressive therapy

Multiple Slips in Atomic-Scale Friction: An Indicator for the Lateral Contact Damping

The occurrence of multiple jumps in 2D atomic-scale friction measurements is used to quantify the viscous damping accompanying the stick-slip motion of a sharp tip in contact with a NaCl(001) surface. Multiple slips are observed without apparent wear for normal forces between 13 and 91nN. For scans parallel to [100] directions, the tip jumps between minima of the substrate corrugation potential in a zigzag fashion. An algorithm is applied to determine histograms of lateral force jumps which characterize multiple slips. The same algorithm is used to classify multiple slips occurring in calculated lateral force maps. Comparisons between simulations and experiments indicate that the nanometer-sized contact is underdamped at intermediate loads (13-26nN) and becomes slightly overdamped at higher loads. The proposed procedure is a novel way to estimate the lateral contact damping which plays an important role in the interpretation of measurements of the velocity and temperature dependence of friction, of slip duration, and of the reduction of friction by applied perpendicular or parallel oscillation

Refined energy-balance modelling of a supraglacial pond, Langtang Khola, Nepal

Supraglacial ponds on debris-covered glaciers present a mechanism of atmosphere/glacier energy transfer that is poorly studied, and only conceptually included in mass-balance studies of Debris-covered glaciers. This research advances previous efforts to develop a model of mass and energy balance for supraglacial ponds by applying a free-convection approach to account for energy exchanges at the subaqueous bare-ice surfaces. We develop the model using field data from a pond on Lirung Glacier, Nepal, that was monitored during the 2013 and 2014 monsoon periods. Sensitivity testing is performed for several key parameters, and alternative melt algorithms are compared with the model. The pond acts as a significant recipient of energy for the glacier system, and actively participates in the glacier’s hydrologic system during the monsoon. Melt rates are 2–4 cm d–1 (total of 98.5 m3 over the study period) for bare ice in contact with the pond, and <1 mm d–1 (total of 10.6 m3) for the saturated debris zone. The majority of absorbed atmospheric energy leaves the pond system through englacial conduits, delivering sufficient energy to melt 2612m3 additional ice over the study period (38.4 m3 d–1). Such melting might be expected to lead to subsidence of the glacier surface. Supraglacial ponds efficiently convey atmospheric energy to the glacier’s interior and rapidly promote the downwasting process.This research was enabled by PhD studentship funding from the Gates Cambridge Trust. Fieldwork was supported by the USAID (United States Agency for International Development) High Mountain Glacier Watershed Programs Climber-Scientist Grant (CCRDCS0010), Swiss National Science Foundation project UNCOMUN (SNF 200021L146761), Trinity College, Cambridge, the B.B. Roberts Fund and the Philip Lake and William Vaughn Lewis Fund.This is the final version of the article. It first appeared from the International Glaciological Society via http://dx.doi.org/10.3189/2016AoG71A42

Atomic Friction Investigations on Ordered Superstructures

We review recent friction measurements on ordered superstructures performed by atomic force microscopy. In particular, we consider ultrathin KBr films on NaCl(001) and Cu(001) surfaces, single and bilayer graphene on SiC(0001), and the herringbone reconstruction of Au(111). Atomically resolved friction images of these systems show periodic features spanning across several unit cells. Although the physical mechanisms responsible for the formation of these superstructures are quite different, the experimental results can be interpreted within the same phenomenological framework. A comparison between experiments and modeling shows that, in the cases of KBr films on NaCl(001) and of graphene films, the tip-surface interaction is well described by a potential with the periodicity of the substrate which is modulated or, respectively, superimposed with a potential with the symmetry of the superstructur

Modulation of receptor cycling by neuron-enriched endosomal protein of 21 kD

Although correct cycling of neuronal membrane proteins is essential for neurite outgrowth and synaptic plasticity, neuron-specific proteins of the implicated endosomes have not been characterized. Here we show that a previously cloned, developmentally regulated, neuronal protein of unknown function binds to syntaxin 13. We propose to name this protein neuron-enriched endosomal protein of 21 kD (NEEP21), because it is colocalized with transferrin receptors, internalized transferrin (Tf), and Rab4. In PC12 cells, NEEP21 overexpression accelerates Tf internalization and recycling, whereas its down-regulation strongly delays Tf recycling. In primary neurons, NEEP21 is localized to the somatodendritic compartment, and, upon N-methyl-d-aspartate (NMDA) stimulation, the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor subunit GluR2 is internalized into NEEP21-positive endosomes. NEEP21 down-regulation retards recycling of GluR1 to the cell surface after NMDA stimulation of hippocampal neurons. In summary, NEEP21 is a neuronal protein that is localized to the early endosomal pathway and is necessary for correct receptor recycling in neurons

Systemic Lipopolysaccharide Exposure Exacerbates Choroidal Neovascularization in Mice.

This study aims to investigate the effect of a systemic lipopolysaccharide (LPS) stimulus in the course of laser-induced choroidal neovascularization (CNV) in C57BL/6 J mice. A group of CNV-subjected mice received 1 mg/kg LPS via the tail vein immediately after CNV induction. Mouse eyes were monitored in vivo with fluorescein angiography for 2 weeks. In situ hybridization and flow cytometry were performed in the retina at different time points. LPS led to increased fluorescein leakage 3 days after CNV, correlated with a large influx of monocyte-derived macrophages and increase of pro-inflammatory microglia/macrophages in the retina. Additionally, LPS enhanced Vegfα mRNA expression by Glul-expressing cells but not Aif1 positive microglia/macrophages in the laser lesion. These findings suggest that systemic LPS exposure has transient detrimental effects in the course of CNV through activation of microglia/macrophages to a pro-inflammatory phenotype and supports the important role of these cells in the CNV course

Endothelial Toll-like receptor 4 is required for microglia activation in the murine retina after systemic lipopolysaccharide exposure.

BACKGROUND Clustering of microglia around the vasculature has been reported in the retina and the brain after systemic administration of lipopolysaccharides (LPS) in mice. LPS acts via activation of Toll-like receptor 4 (TRL4), which is expressed in several cell types including microglia, monocytes and vascular endothelial cells. The purpose of this study was to investigate the effect of systemic LPS in the pigmented mouse retina and the involvement of endothelial TLR4 in LPS-induced retinal microglia activation. METHODS C57BL/6J, conditional knockout mice that lack Tlr4 expression selectively on endothelial cells (TekCre-posTlr4loxP/loxP) and TekCre-negTlr4loxP/loxP mice were used. The mice were injected with 1 mg/kg LPS via the tail vein once per day for a total of 4 days. Prior to initiation of LPS injections and approximately 5 h after the last injection, in vivo imaging using fluorescein angiography and spectral-domain optical coherence tomography was performed. Immunohistochemistry, flow cytometry, electroretinography and transmission electron microscopy were utilized to investigate the role of endothelial TLR4 in LPS-induced microglia activation and retinal function. RESULTS Activation of microglia, infiltration of monocyte-derived macrophages, impaired ribbon synapse organization and retinal dysfunction were observed after the LPS exposure in C57BL/6J and TekCre-negTlr4loxP/loxP mice. None of these effects were observed in the retinas of conditional Tlr4 knockout mice after the LPS challenge. CONCLUSIONS The findings of the present study suggest that systemic LPS exposure can have detrimental effects in the healthy retina and that TLR4 expressed on endothelial cells is essential for retinal microglia activation and retinal dysfunction upon systemic LPS challenge. This important finding provides new insights into the role of microglia-endothelial cell interaction in inflammatory retinal disease

Supraglacial ice cliffs and ponds on debris-covered glaciers: spatio-temporal distribution and characteristics

Ice cliffs and ponds on debris-covered glaciers have received increased attention due to their role in amplifying local melt. However, very few studies have looked at these features on the catchment scale to determine their patterns and changes in space and time. We have compiled a detailed inventory of cliffs and ponds in the Langtang catchment, central Himalaya, from six high-resolution satellite orthoimages and DEMs between 2006 and 2015, and a historic orthophoto from 1974. Cliffs cover between 1.4% (± 0.4%) in the dry and 3.4% (± 0.9%) in the wet seasons and ponds between 0.6% (± 0.1%) and 1.6% (± 0.3%) of the total debris-covered tongues. We find large variations between seasons, as cliffs and ponds tend to grow in the wetter monsoon period, but there is no obvious trend in total area over the study period. The inventory further shows that cliffs are predominately north-facing irrespective of the glacier flow direction. Both cliffs and ponds appear in higher densities several hundred metres from the terminus in areas where tributaries reach the main glacier tongue. On the largest glacier in the catchment ~10% of all cliffs and ponds persisted over nearly a decade

Refined energy-balance modelling of a supraglacial pond, Langtang Khola, Nepal

AbstractSupraglacial ponds on debris-covered glaciers present a mechanism of atmosphere/glacier energy transfer that is poorly studied, and only conceptually included in mass-balance studies of debris-covered glaciers. This research advances previous efforts to develop a model of mass and energy balance for supraglacial ponds by applying a free-convection approach to account for energy exchanges at the subaqueous bare-ice surfaces. We develop the model using field data from a pond on Lirung Glacier, Nepal, that was monitored during the 2013 and 2014 monsoon periods. Sensitivity testing is performed for several key parameters, and alternative melt algorithms are compared with the model. The pond acts as a significant recipient of energy for the glacier system, and actively participates in the glacier’s hydrologic system during the monsoon. Melt rates are 2-4 cm d-1 (total of 98.5 m3 over the study period) for bare ice in contact with the pond, and &lt;1 mmd-1 (total of 10.6m3) for the saturated debris zone. The majority of absorbed atmospheric energy leaves the pond system through englacial conduits, delivering sufficient energy to melt 2612 m3 additional ice over the study period (38.4 m3 d-1). Such melting might be expected to lead to subsidence of the glacier surface. Supraglacial ponds efficiently convey atmospheric energy to the glacier’s interior and rapidly promote the downwasting process.This research was enabled by PhD studentship funding from the Gates Cambridge Trust. Fieldwork was supported by the USAID (United States Agency for International Development) High Mountain Glacier Watershed Programs Climber-Scientist Grant (CCRDCS0010), Swiss National Science Foundation project UNCOMUN (SNF 200021L146761), Trinity College, Cambridge, the B.B. Roberts Fund and the Philip Lake and William Vaughn Lewis Fund.This is the final version of the article. It first appeared from the International Glaciological Society via http://dx.doi.org/10.3189/2016AoG71A42