Jeffrey Johnson

Cerebroside sulfate activator protein (Saposin B): chromatographic and electrospray mass spectrometric properties.

Cerebroside sulfate activator protein is a small, heat-stable protein that is exceptionally resistant to proteolytic attack. This protein is essential for the catabolism of cerebroside sulfate and several other glycosphingolipids. Protein purified from pig kidney and human urine was extensively characterized by reversed-phase liquid chromatography and electrospray mass spectrometry. These two sources revealed 20 and 18 different molecular isoforms of the protein, respectively. Plausible explanations of the structures of the majority of these isoforms can be made on the basis of accurate molecular mass assignments. The reversed-phase chromatographic and electrospray mass spectrometric properties of enzymatically deglycosylated and disulfide-reduced protein were also compared. In addition to a demonstration of the power of electrospray ionization mass spectrometry for revealing a wealth of information on protein microheterogeneity and structural detail, the results also demonstrate the utility of this technique for monitoring spontaneous chemical and enzymatically mediated changes that occur as a result of metabolic processing and protein purification.

Tectono-stratigraphic model for the Massif D'Igountze–Mendibelza, western Pyrenees

The Massif dIgountze–Mendibelza, western Pyrenees, is a fault-bounded block of Palaeozoic basement overlain by an exceptionally thick Cretaceous siliciclastic sequence. North of the Massif, the Cretaceous sequence conformably overlies Lower Cretaceous carbonates, yet, immediately south of the Massif, it is entirely absent. The sequence fines northward and has NNE palaeotransport. The basement is commonly brecciated near the contact with the sedimentary cover, and the uppermost beds dip less steeply than the lowermost. These tectono-stratigraphic relationships are best explained by Cretaceous deposition above a relatively low-angle normal fault. The Cretaceous deposits of the Massif dIgountze–Mendibelza are part of the western extension of the North Pyrenean basin, a basin or series of sub-basins that began to form in the latest Aptian to Albian north of and along most of the length of the North Pyrenean fault. The precise relationship between deposition on the Massif and in the rest of the North Pyrenean basin is not known. There may have been many local variations in stress regime and structural style along the basin or sub-basins, but the regional episode of basin formation was a result of the same plate-reorganizational event. Later basin inversion was due to the latest Cretaceous to Eocene Pyrenean orogeny.

The structural and sedimentary evolution of the Cretaceous North Pyrenean Basin, southern France

During the Cretaceous, the North Pyrenees of southern France suffered complex deformation. The relatively deep marine North Pyrenean Basin formed, a narrow band of rock adjacent to the North Pyrenean fault was metamorphosed, Iherzolite was emplaced, and the Bay of Biscay opened. Compression during the Late Cretaceous and Tertiary Pyrenean orogeny overprinted and partially masked this earlier history. In order to better understand the regional tectonics off the Cretaceous northern Pyrenees and, specifically, the early history of the North Pyrenean Basin, we compiled and then palinspastically restored a geologic map of the western North Pyrenees. Lithofacies, paleotransport, and isopach maps for the early deposits of the basin, and a pre-Albian palinspastic subcrop map show that the basin was an east-west-elongate, fault-bounded trough at least 300 km long and from 40 to 60 km wide, containing a siliciclastic composite sedimentary package as much as 4,700 m thick. Detailed structural and stratigraphic studies of the Massif d9Igountze-Mendibelza, which is located along the southern limit of the North Pyrenean Basin in the western Pyrenees, suggest that its Cretaceous cover was deposited against an active, relatively low-angle listric normal fault. This fault is on strike with the North Pyrenean fault zone, a major long-lived zone of deformation in the central and eastern North Pyrenees.

Tensor-Based Morphometry Reveals Volumetric Deficits in Moderate/Severe Pediatric Traumatic Brain Injury

Abstract Traumatic brain injury (TBI) can cause widespread and prolonged brain degeneration. TBI can affect cognitive function and brain integrity for many years after injury, often with lasting effects in children, whose brains are still immature. Although TBI varies in how it affects different individuals, image analysis methods such as tensor-based morphometry (TBM) can reveal common areas of brain atrophy on magnetic resonance imaging (MRI), secondary effects of the initial injury, which will differ between subjects. Here we studied 36 pediatric moderate to severe TBI (msTBI) participants in the post-acute phase (1–6 months post-injury) and 18 msTBI participants who returned for their chronic assessment, along with well-matched controls at both time-points. Participants completed a battery of cognitive tests that we used to create a global cognitive performance score. Using TBM, we created three-dimensional (3D) maps of individual and group differences in regional brain volumes. At both the post-acute and chronic time-points, the greatest group differences were expansion of the lateral ventricles and reduction of the lingual gyrus in the TBI group. We found a number of smaller clusters of volume reduction in the cingulate gyrus, thalamus, and fusiform gyrus, and throughout the frontal, temporal, and parietal cortices. Additionally, we found extensive associations between our cognitive performance measure and regional brain volume. Our results indicate a pattern of atrophy still detectable 1-year post-injury, which may partially underlie the cognitive deficits frequently found in TBI.

Diverging white matter trajectories in children after traumatic brain injury: The RAPBI study

Objective: To examine longitudinal trajectories of white matter organization in pediatric moderate/severe traumatic brain injury (msTBI) over a 12-month period. Methods: We studied 21 children (16 M/5 F) with msTBI, assessed 2–5 months postinjury and again 13–19 months postinjury, as well as 20 well-matched healthy control children. We assessed corpus callosum function through interhemispheric transfer time (IHTT), measured using event-related potentials, and related this to diffusion-weighted MRI measures of white matter (WM) microstructure. At the first time point, half of the patients with TBI had significantly slower IHTT (TBI-slow-IHTT, n = 11) and half were in the normal range (TBI-normal-IHTT, n = 10). Results: The TBI-normal-IHTT group did not differ significantly from healthy controls, either in WM organization in the chronic phase or in the longitudinal trajectory of WM organization between the 2 evaluations. In contrast, the WM organization of the TBI-slow-IHTT group was significantly lower than in healthy controls across a large portion of the WM. Longitudinal analyses showed that the TBI-slow-IHTT group experienced a progressive decline between the 2 evaluations in WM organization throughout the brain. Conclusions: We present preliminary evidence suggesting a potential biomarker that identifies a subset of patients with impaired callosal organization in the first months postinjury who subsequently experience widespread continuing and progressive degeneration in the first year postinjury.

Structure of the asparagine-linked sugar chains of porcine kidney and human urine cerebroside sulfate activator protein

The specific sugar residues and their linkages in the oligosaccharides from pig kidney and human urine cerebroside sulfate activator proteins (saposin B), although previously hypothesized, have been unambiguously characterized. Exhaustive sequential exoglycosidase digestion of the trimethyl-p-aminophenyl derivatives, followed by either matrix-assisted laser desorption/ionization and/or mass spectrometry, was used to define the residues and their linkages. The oligosaccharides were enzymatically released from the proteins by treatment with peptidyl-N-glycosidase F and separated from the proteins by reversed-phase high-performance liquid chromatography (HPLC). Reducing termini were converted to the trimethyl-p-aminophenyl derivative and the samples were further purified by normal-phase HPLC. The derivatized carbohydrates were then treated sequentially with a series of exoglycosidases of defined specificity, and the products of each digestion were examined by mass spectrometry. The pentasaccharides from pig kidney and human urine protein were shown to be of the asparagine-linked complex type composed of mannose-alpha 1-6-mannose-beta 1-4-N-acetylglucosamine-N-acetylglucosamine(alpha 1-6-fucose). This highly degraded structure probably represents the final product of intra-lysosomal exoglycosidase digestion. Oligosaccharide sequencing by specific exoglycosidase degradation coupled with mass spectrometry is more rapid than conventional oligosaccharide sequencing. The procedures developed will be useful for sequencing other oligosaccharides including those from other members of the lipid-binding protein class to which cerebroside sulfate activator belongs. (c) 2000 John Wiley & Sons, Ltd.

Variable clustering reveals associations between subcortical brain volume and cognitive changes in pediatric traumatic brain injury

Outcomes after traumatic brain injury (TBI) are variable and only partially predicted by acute injury factors. With rich datasets, we can examine how numerous factors – cognitive scores, acute injury variables, demographic variables, and brain imaging variables – are interrelated and aid in outcome prediction. To help study this rich data, we applied CorEx, a novel method for unsupervised machine learning. CorEx decodes the hierarchical structure, identifying latent causes of dependence in the data. It groups predictor variables based on their joint information and inter-dependence. We examined 21 TBI patients 2-5 months post-injury along with healthy controls; both groups were assessed again 12 months later. Although we were limited in the number of participants, this tool for exploratory analysis found potential relationships between change in cognitive scores over the 12-month period and baseline brain volumes. Certain regional brain volumes measured post-injury could serve as predictors of patient recovery. As future planned analyses will examine greater sample sizes, we hope to perform follow-up statistical analysis of variables identified by CorEx in independent data.

Adaptive algorithms to map how brain trauma affects anatomical connectivity in children

Deficits in white matter (WM) integrity occur following traumatic brain injury (TBI), and often persist long after the visible scars have healed. Heterogeneity in injury types and locations can complicate analyses, making it harder to discover common biomarkers for tracking recovery. Here we apply a newly developed adaptive connectivity method, EPIC (evolving partitions to improve connectomics) to identify differences in structural connectivity that persist longitudinally. This data comes from a longitudinal study, in which we scanned participants (aged 8-19 years) with anatomical and diffusion MRI in both the post-acute and chronic phases (1-6 months and 13-19 months post-injury). To identify patterns of abnormal connectivity, we trained a model on data from 32 TBI patients in the post-acute phase and 45 well-matched healthy controls, reducing an initial 68x68 connectivity matrix to a 14x14 matrix. We then applied this reduced parcellation to the chronic data in participants who had returned for their chronic assessment (21 TBI and 26 healthy controls) and tested for group differences. We found significant differences in two connections, comprising callosal fibers and long anterior-posterior fibers, with the TBI group showing increased fiber density relative to controls. Longitudinal analysis revealed that these were connections that were decreasing over time in the healthy controls, as is a common developmental phenomenon, but they were increasing in the TBI group. While we cannot definitively tell why this may occur with our current data, this study provides targets for longitudinal tracking, and poses questions for future investigation.

Altered network topology in pediatric traumatic brain injury

Outcome after a traumatic brain injury (TBI) is quite variable, and this variability is not solely accounted for by severity or demographics. Identifying sub-groups of patients who recover faster or more fully will help researchers and clinicians understand sources of this variability, and hopefully lead to new therapies for patients with a more prolonged recovery profile. We have previously identified two subgroups within the pediatric TBI patient population with different recovery profiles based on an ERP-derived (event-related potential) measure of interhemispheric transfer time (IHTT). Here we examine structural network topology across both patient groups and healthy controls, focusing on the ‘rich-club’ - the core of the network, marked by high degree nodes. These analyses were done at two points post-injury - 2-5 months (post-acute), and 13-19 months (chronic). In the post-acute time-point, we found that the TBI-slow group, those showing longitudinal degeneration, showed hyperconnectivity within the rich-club nodes relative to the healthy controls, at the expense of local connectivity. There were minimal differences between the healthy controls and the TBI-normal group (those patients who show signs of recovery). At the chronic phase, these disruptions were no longer significant, but closer analysis showed that this was likely due to the loss of power from a smaller sample size at the chronic time-point, rather than a sign of recovery. We have previously shown disruptions to white matter (WM) integrity that persist and progress over time in the TBI-slow group, and here we again find differences in the TBI-slow group that fail to resolve over the first year post-injury.