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Protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is a major signal transducer of the endoplasmic reticulum stress response (ERSR) pathway. Outcomes of PERK activation range from abrogating ER stress to induction of cell death, dependent on its level, duration and cellular context. After thoracic contusive spinal cord injury (SCI), acute inhibition of PERK (0-72 hours) with the small molecule inhibitor GSK2656157 reduced ERSR while improving white matter sparing and hindlimb locomotion recovery. GSK2656157-treated mice showed increased numbers of oligodendrocytes at the injury epicenter. Moreover, GSK2656157 protected cultured primary mouse oligodendrocyte precursor cells from ER stress-induced cytotoxicity.

The endoplasmic reticulum stress response (ERSR) is activated in various neurodegenerative diseases and/or after CNS traumatic injuries. The ERSR is comprised of three major arms, PERK, IRE-1, and activating transcription factor-6, with the latter two contributing to the unfolded protein response (UPR). PERK activity overlaps with the integrated stress response (ISR) kinases, PKR, HRI, and GCN2 which all signal through, eukaryotic initiation factor 2α, ATF4, and CHOP. All initially attempt to restore endoplasmic reticulum (ER) homeostasis, but if ER stress is unresolved, ATF4/CHOP-mediated cell death is initiated. Here, we investigate the contribution of the inositol-requiring protein-1α-X-box binding protein-1 (XBP1)-mediated UPR signaling pathway to the pathogenesis of spinal cord injury (SCI). We demonstrate that deletion of Xbp1 caused an exacerbated ATF4/CHOP signaling in cultured mouse oligodendrocyte (OL) progenitor cells and enhanced their sensitivity to ER stress. Similar effects were also observed with the Xbp1 pathway inhibitor toyocamycin. Furthermore, OL lineage-specific loss of Xbp1 resulted in enhanced ISR in mice that underwent moderate contusive SCI at the T9 level. Consistently, post-injury recovery of hindlimb locomotion and white matter sparing were reduced in OL Xbp1-deficient mice, which correlated with chronically decreased relative density of OPCs and OLs at the injury epicenter at 6 weeks post-SCI. We conclude that the IRE1-XBP1-mediated UPR signaling pathway contributes to restoration of ER homeostasis in OLs and is necessary for enhanced white matter sparing and functional recovery post-SCI.

We present images of Venus from the Wide-Field Imager for Parker Solar Probe (WISPR) telescope on board the Parker Solar Probe (PSP) spacecraft, obtained during PSP's third and fourth flybys of Venus on 2020 July 11 and 2021 February 20, respectively. Thermal emission from the surface is observed on the night side, representing the shortest wavelength observations of this emission ever, the first detection of the Venusian surface by an optical telescope observing below 0.8 μm. Consistent with previous observations at 1 μm, the cooler highland areas are fainter than the surrounding lowlands. The irradiances measured by WISPR are consistent with model predictions assuming a surface temperature of

The closest perihelion pass of Parker Solar Probe (PSP), so far, occurred between 16 and 26 of November 2021 and reached ~13.29 Rsun from Sun center. This pass resulted in very unique observations of the solar corona by the Wide-field Instrument for Solar PRobe (WISPR). WISPR observed at least ten CMEs, some of which were so close that the structures appear distorted. All of the CMEs appeared to have a magnetic flux rope (MFR) structure and most were oriented such that the view was along the axis orientation, revealing very complex interiors. Two CMEs had a small MFR develop in the interior, with a bright circular boundary surrounding a very dark interior. Trailing the larger CMEs were substantial outflows of small blobs and flux-rope like structures within striated ribbons, lasting for many hours. When the heliophysics plasma sheet (HPS) was inclined, as it was during the days around perihelion on November 21, 2021, the outflow was over a very wide latitude range. One CME was overtaken by a faster one, with a resultant compression of the rear of the leading CME and an unusual expansion in the trailing CME. The small Thomson Surface creates brightness variations of structures as they pass through the field of view. In addition to this dynamic activity, a brightness band from excess dust along the orbit of asteroid/comet 3200 Phaethon is also seen for several days., Comment: 28 pages, 15 figures, accepted to ApJ

We present the calibration status and data reduction methodology for the Wide Field Imager for Solar Probe (WISPR) on board the Parker Solar Probe (PSP) mission. In particular, we describe the process for converting a raw image, measured in digital numbers (DN), to a calibrated image, measured in mean solar brightness (MSB). We also discuss details of the on board image processing including bias removal, the linearity of the electronics, pointing, geometric distortion, and photometric calibration using stellar measurements, and the characterization of vignetting and other instrumental artifacts. The analysis presented here is based on data from the first four WISPR orbits. As the PSP perihelia get progressively closer to the Sun and the WISPR concept of operation evolves to deal with the brighter scene, the calibration will likely need to be updated. Aging of the optics and the possibility of detector degradation may also occur. Hence, we consider the WISPR calibration as work in progress with updates reported as necessary.

The Wide-Field Imager for Parker Solar Probe (WISPR/PSP) has recorded intermittent bright streaks radiating across its field of view during close encounters with the Sun. As part of a broader effort to ensure PSP safety in the near Sun dust environment, we explore the hypothesis that some observed “streaks” are images of solar-illuminated particulate ejecta following dust hypervelocity impacts on the spacecraft thermal protection system (TPS) or radiative cooling system. We present a geometrical model for illuminated grains moving across the WISPR field of view, enabling the inference of source size, distance, and spatial origin. A software framework is developed and used for tracing streaks in calibrated L3 images and analyzing the streaks' individual and statistical properties. Evidence is consistent with some “conical” populations of streaks originating from well-defined point-like regions on the PSP radiator or TPS, implying that a hypervelocity impact may have generated the observed particles from those locations.

Visible light observations from the Wide-field Imager for Solar PRobe (WISPR) aboard the Parker Solar Probe (PSP) mission offer a unique opportunity to study the dust environment near the Sun. The existence of a dust-free zone (DFZ) around stars was postulated almost a century ago. Despite numerous attempts to detect it from as close as 0.3 au, observational evidence of a circumsolar DFZ has remained elusive. Analysis of WISPR images obtained from heliocentric distances between 13.3–53.7 R ⊙ over multiple PSP orbits shows a gradually decreasing brightness gradient along the symmetry axis of the F-corona for coronal heights between 19 and 9 R ⊙. Below 9 R ⊙, the gradient reverses its trend, approaching the radial dependence exhibited at heights above 19 R ⊙. After taking into account the effects of both the electron corona background and the nonresolved starlight, the WISPR observations down to 4 R ⊙ are consistent with forward-modeling simulations of the F-corona brightness within [−6, 5]% if a circumsolar region of depleted dust density between 19 and 5 R ⊙ enclosing a DFZ is considered. In addition, we show, for the first time, that the F-corona brightness inward of about 15 R ⊙ depends on the observer’s location for observing distances below 35 R ⊙.

The {\it Wide-field Imager for Solar Probe} (WISPR) on {\it Parker Solar Probe} (PSP), observing in white light, has a fixed angular field of view, extending from 13.5$^{\circ}$ to 108$^{\circ}$ from the Sun and approximately 50$^{\circ}$ in the transverse directions. Because of the highly elliptical orbit of PSP, the physical extent of the imaged coronal region varies directly as the distance from the Sun, requiring new techniques for analysis of the motions of observed density features. Here, we present a technique for determining the 3D trajectory of CMEs and other coronal ejecta moving radially at a constant velocity by first tracking the motion in a sequence of images and then applying a curve-fitting procedure to determine the trajectory parameters (distance vs. time, velocity, longitude and latitude). To validate the technique, we have determined the trajectory of two CMEs observed by WISPR that were also observed by another white-light imager, either LASCO/C3 or STEREO-A/HI1. The second viewpoint was used to verify the trajectory results from this new technique and help determine its uncertainty., 28 pages, 11 figures, accepted by Solar Physics

We present details on the first white-light detection of a dust trail following the orbit of asteroid 3200 Phaethon, seen in images recorded by the Wide-field Imager for Parker Solar Probe (WISPR) instrument on the NASA Parker Solar Probe (PSP) mission. In this talk we will present a brief introduction to the PSP mission and the WISPR instrument. We will then show observations returned by WISPR in multiple perihelion 'encounters' that clearly show a diffuse dust trail perfectly aligned with the perihelion portion of the orbit of 3200 Phaethon, recorded while the asteroid itself was near aphelion. We will discuss the physical parameters that we have derived for the dust trail, including its visual magnitude, surface brightness and mass. We also speculate on the relationship of this trail to the Geminid meteor shower, of which Phaethon is assumed to be the parent, and demonstrate why the trail has not been detected visually until now, despite a number of dedicated observing campaigns. We also hope to present initial analyses of the most recent set of WISPR observations (January 2020), where we anticipate the trail should again be visible in the WISPR observations.

The Parker Solar Probe (PSP) mission has completed 4 encounters through the solar corona significantly closer to the Sun than previous measurements. While PSP does not have a dedicated dust detector, measurements by the various instruments can provide insights into the dust environment in the inner heliosphere. Throughout the PSP orbit, interplanetary dust is impacting the spacecraft. Three-dimensional reconstructions of FIELDS observations show that the rate and direction of the dust impacts varies throughout the PSP orbit. During the encounter WISPR also finds the rate of impacts changes through the encounter period, but also a decrease in the intensity of the light scattered by the dust particles. The smooth decrease in the WISPR intensity beginning at about 0.1 AU is consistent with the production of Beta-meteroids seen by FIELDS. In this presentation, we will discuss the observations from the FIELDS and WISPR instruments and discuss initial models of the dust environment. The authors acknowledge support from the NASA Parker Solar Probe program.

The Wide-field Imager for Solar PRobe (WISPR) obtained the first high-resolution images of coronal rays at heights below 15 Rsun when Parker Solar Probe (PSP) was located inside 0.25 AU during the first encounter. We exploit these remarkable images to reveal the structure of coronal rays at scales that are not easily discernible in images taken from near 1 AU. To analyze and interpret WISPR observations which evolve rapidly both radially and longitudinally, we construct a latitude versus time map using full WISPR dataset from the first encounter. From the exploitation of this map and also from sequential WISPR images we show the presence of multiple sub-structures inside streamers and pseudo-streamers. WISPR unveils the fine-scale structure of the densest part of streamer rays that we identify as the solar origin of the heliospheric plasma sheet typically measured in situ in the solar wind. We exploit 3-D magneto-hydrodynamic (MHD) models and we construct synthetic white-light images to study the origin of the coronal structures observed by WISPR. Overall, including the effect of the spacecraft relative motion towards the individual coronal structures we can interpret several observed features by WISPR. Moreover, we relate some coronal rays to folds in the heliospheric current sheet that are unresolved from 1 AU. Other rays appear to form as a result of the inherently inhomogeneous distribution of open magnetic flux tubes. This work was funded by the European Research Council through the project SLOW_SOURCE - DLV-819189.

During its first solar encounter, the Parker Solar Probe (PSP) acquired unprecedented up-close imaging of a small Coronal Mass Ejection (CME) propagating in the forming slow solar wind. The CME originated as a cavity imaged in extreme ultraviolet that moved very slowly ($, 19 pages, 10 figures, to appear in ApJS, 2 animations of Figure 2 available at https://nuage.irap.omp.eu/index.php/s/8ynNotNVWU6PrtN and https://nuage.irap.omp.eu/index.php/s/dflQ94DKuMbiaTv

We present the construction of a new white-light coronal brightness index (CBI) from the entire archive of observations recorded by the Large Angle Spectrometric Coronagraph (LASCO) C2 camera between 1996 and 2017, comprising two full solar cycles. We reduce all fully calibrated daily C2 observations of the white light corona into a single daily coronal brightness observation for every day of observation recorded by the instrument, with mean daily brightness values binned into 0.1 Rsun radial x 1 degree angular regions from 2.4 -- 6.2 Rsun for a full 360-degrees. As a demonstration of the utility of the CBI, we construct a new solar irradiance proxy that correlates well with a variety of direct solar irradiance observations, with correlations shown to be in the range of 0.77-0.89. We also present a correlation mapping technique to show how irradiance correlations depend on, and relate to, coronal structure/locations, and to demonstrate how the LASCO CBI can be used to perform long-term "spatial correlation" studies to investigate relationships between the solar corona and any arbitrary concurrent geophysical index. Using this technique we find possible relationships between coronal brightness and plasma temperature, interplanetary magnetic field magnitude and (very weakly) proton density., Comment: 35 pages, 9 Figures. Accepted to Solar Physics

Aims. Solar Orbiter, the first mission of ESA's Cosmic Vision 2015-2025 programme and a mission of international collaboration between ESA and NASA, will explore the Sun and heliosphere from close up and out of the ecliptic plane. It was launched on 10 February 2020 04:03 UTC from Cape Canaveral and aims to address key questions of solar and heliospheric physics pertaining to how the Sun creates and controls the Heliosphere, and why solar activity changes with time. To answer these, the mission carries six remote-sensing instruments to observe the Sun and the solar corona, and four in-situ instruments to measure the solar wind, energetic particles, and electromagnetic fields. In this paper, we describe the science objectives of the mission, and how these will be addressed by the joint observations of the instruments onboard. Methods. The paper first summarises the mission-level science objectives, followed by an overview of the spacecraft and payload. We report the observables and performance figures of each instrument, as well as the trajectory design. This is followed by a summary of the science operations concept. The paper concludes with a more detailed description of the science objectives. Results. Solar Orbiter will combine in-situ measurements in the heliosphere with high-resolution remote-sensing observations of the Sun to address fundamental questions of solar and heliospheric physics. The performance of the Solar Orbiter payload meets the requirements derived from the mission's science objectives. Its science return will be augmented further by coordinated observations with other space missions and ground-based observatories. © 2020 ESO., Solar Orbiter is a space mission of international collaboration between ESA and NASA. The spacecraft has been developed by Airbus and is being operated by ESA from the European Space Operations Centre (ESOC) in Darmstadt, Germany. Science operations are carried out at ESA's European Space Astronomy Centre (ESAC) in Villafranca del Castillo, Spain. Conceiving, designing and building Solar Orbiter has been an international team e ffort of many people. In particular, the authors would like to thank ESA's Mission Operations Centre (MOC) and Science Operations Centre (SOC) teams, Yves Langevin and Jose-Manuel Sanchez Perez for their skillful optimisation of mission trajectories, the ESA and NASA Project o ffices, Airbus, IABG, NASA-LSP, ULA, and all national funding agencies that have enabled Solar Orbiter. The German contribution to SO/PHI is funded by the Bundesministerium fur Wirtschaft und Technologie through Deutsches Zentrum fur Luftund Raumfahrt e.V. (DLR), Grants No. 50 OT 1001/1201/1901 as well as 50 OT 0801/1003/1203/1703, and by the President of the Max Planck Society (MPG). The Spanish contribution has been partially funded by Ministerio de Ciencia, Innovacion y Universidades through projects ESP2014-56169-C6 and ESP2016-77548-C5. IAA-CSIC acknowledges financial support from the Spanish Research Agency (AEI/MCIU) through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). The French contribution is funded by the Centre National d'Etudes Spatiales. Further detailed acknowledgements regarding each instrument can be found in the individual instrument papers of this special issue. R.A.H. is supported by the NASA Solar Orbiter Collaboration Office, under contract NNG09EK11I. The Spanish contribution to SO/PHI has been funded by the Spanish Ministry of Science and Innovation through several projects, the last one of which being RTI2018-096886-B-C5, and by "Centro de Excelencia Severo Ochoa" Programme under grant SEV-2017-0709. The authors would like to highlight Rainer Schwenn's (1941-2017) important and enthusiastic contribution to the Solar Orbiter mission in its early phase. Portions of the text have been reproduced with permission from Muller & Marsden (2013) copyright by Springer. The authors would like to thank John Leibacher and Bernhard Fleck for their support, and the referee for providing helpful suggestions.

On 2018 November 5, about 24 hours before the first close perihelion passage of Parker Solar Probe (PSP), a coronal mass ejection (CME) entered the field of view of the inner detector of the Wide-field Imager for Solar PRobe (WISPR) instrument onboard PSP, with the northward component of its trajectory carrying the leading edge of the CME off the top edge of the detector about four hours after its first appearance. We connect this event to a very small jet-like transient observed from 1 au by coronagraphs on both the SOlar and Heliospheric Observatory (SOHO) and the A component of the Solar TErrestrial RElations Observatory mission (STEREO-A). This allows us to make the first three-dimensional reconstruction of a CME structure considering both observations made very close to the Sun and images from two observatories at 1 au. The CME may be small and jet-like as viewed from 1 au, but the close-in vantage point of PSP/WISPR demonstrates that it is not intrinsically jet-like, but instead has a structure consistent with a flux rope morphology. Based on its appearance in the SOHO and STEREO-A images, the event belongs in the "streamer blob" class of transients, but its kinematic behavior is very unusual, with a more impulsive acceleration than previously studied blobs., Comment: 9 pages, 8 figures, to appear in The Astrophysical Journal Supplement

Autophagy mechanisms are well documented in neurons after spinal cord injury (SCI), but the direct functional role of autophagy in oligodendrocyte (OL) survival in SCI pathogenesis remains unknown. Autophagy is an evolutionary conserved lysosomal-mediated catabolic pathway that ensures degradation of dysfunctional cellular components to maintain homeostasis in response to various forms of stress, including nutrient deprivation, hypoxia, reactive oxygen species, DNA damage, and endoplasmic reticulum (ER) stress. Using pharmacological gain and loss of function and genetic approaches, we investigated the contribution of autophagy in OL survival and its role in the pathogenesis of thoracic contusive SCI in female mice. Although upregulation of Atg5 (an essential autophagy gene) occurs after SCI, autophagy flux is impaired. Purified myelin fractions of contused 8 d post-SCI samples show enriched protein levels of LC3B, ATG5, and BECLIN 1. Data show that, while the nonspecific drugs rapamycin (activates autophagy) and spautin 1 (blocks autophagy) were pharmacologically active on autophagy in vivo, their administration did not alter locomotor recovery after SCI. To directly analyze the role of autophagy, transgenic mice with conditional deletion of Atg5 in OLs were generated. Analysis of hindlimb locomotion demonstrated a significant reduction in locomotor recovery after SCI that correlated with a greater loss in spared white matter. Immunohistochemical analysis demonstrated that deletion of Atg5 from OLs resulted in decreased autophagic flux and was detrimental to OL function after SCI. Thus, our study provides evidence that autophagy is an essential cytoprotective pathway operating in OLs and is required for hindlimb locomotor recovery after thoracic SCI.SIGNIFICANCE STATEMENT This study describes the role of autophagy in oligodendrocyte (OL) survival and pathogenesis after thoracic spinal cord injury (SCI). Modulation of autophagy with available nonselective drugs after thoracic SCI does not affect locomotor recovery despite being pharmacologically active in vivo, indicating significant off-target effects. Using transgenic mice with conditional deletion of Atg5 in OLs, this study definitively identifies autophagy as an essential homeostatic pathway that operates in OLs and exhibits a direct functional role in SCI pathogenesis and recovery. Therefore, this study emphasizes the need to discover novel autophagy-specific drugs that specifically modulate autophagy for further investigation for clinical translation to treat SCI and other CNS pathologies related to OL survival.

We present the identification and preliminary analysis of a dust trail following the orbit of (3200) Phaethon as seen in white light images recorded by the Wide-field Imager for Parker Solar Probe (WISPR) instrument on the NASA Parker Solar Probe (PSP) mission. During PSP's first solar encounter in November 2018, a dust trail following Phaethon's orbit was visible for several days and crossing two fields of view. Preliminary analyses indicate this trail to have a visual magnitude of 15.8 $\pm$0.3 per pixel and a surface brightness of 25.0 mag arcsec$^{-2}$ as seen by PSP/WISPR from a distance of $\sim$0.2 au from the trail. We estimate the total mass of the stream to be $\sim(0.4-1.3){\times}10^{12}$ kg, which is consistent with, though slightly underestimates, the assumed mass of the Geminid stream but is far larger than the current dust production of Phaethon could support. Our results imply that we are observing a natural clustering of at least some portion of the Geminid meteor stream through its perihelion, as opposed to dust produced more recently from perihelion activity of Phaethon., 14 Pages, 7 Figures; Accepted to ApJS (Parker Solar Probe Special Edition)

The Wide-field Imager for the Parker Solar Probe (PSP/WISPR) comprises two telescopes that record white-light total brightness $[B]$ images of the solar corona. Their fields of view cover a widely changing range of heliocentric heights over the 24 highly eccentric orbits planned for the mission. In this work, the capability of PSP/WISPR data to carry out tomographic reconstructions of the three-dimensional (3D) distribution of the coronal electron density is investigated. Based on the precise orbital information of the mission, $B$-images for Orbits 1, 12, and 24 are synthesized from a 3D magnetohydrodynamic model of the corona. For each orbit, the time series of synthetic images is used to carry out a tomographic reconstruction of the coronal electron density and results are compared with the model. As the PSP perihelion decreases, the range of heights that can be tomographically reconstructed progressively shifts to lower values, and the period required to gather the data decreases. For Orbit 1 tomographic reconstruction is not possible. For Orbit 12, tomographic reconstruction is possible in the heliocentric height range ${\approx}\, 5\,\mbox{--}\,15~\mathrm{{R}_{\odot}}$, over a region spanning up to ${\approx}\,160^{\circ}$ in Carrington longitude, with data gathered over a ${\approx}\, 3.4$ day-long period. For Orbit 24, tomographic reconstruction is possible in the heliocentric height range ${\approx}\,3\,\mbox{--}\,10~\mathrm {R}_{\odot}$, over a region spanning up to ${\approx} \,170^{\circ}$ in Carrington longitude, with data gathered over a ${\approx}\, 2.8$ day-long period.