Transcription Factor PU.1 Promotes Conventional Dendritic Cell Identity and Function via Induction of Transcriptional Regulator DC-SCRIPT

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The role of the protein glycosylation state in the control of cellular transport of the amyloid beta precursor protein

The amyloid beta precursor protein can exist as both a membrane-bound and a secreted protein, with the former having the potential to generate the amyloid beta peptide present in the neuritic plaques which are characteristic of Alzheimer's disease. In this study, we have used a clone of the AtT20 mouse pituitary cell line which expresses high levels of the amyloid beta precursor protein to characterize the glycosylation state of the secreted and membrane-bound forms of the protein and to examine the role of post-translational modifications in protein processing. Lectin blot analysis of immunoprecipitated amyloid beta precursor protein demonstrated that the soluble form of the protein contains significant amounts of sialic acid, with the lectin staining being reduced in the particulate cellular fractions. Treatment of the cells with mannosidase inhibitors to interfere with the formation of complex-type N-linked glycans resulted in a decrease in secreted amyloid beta precursor protein and an increase in the level of the cellular form of the protein. The increase in amyloid beta precursor protein levels in the cellular fraction was accompanied by an increase in perinuclear staining. Furthermore, cells overexpressing the alpha2,6(N)-sialyltransferase enzyme also demonstrated an increase in amyloid beta precursor protein secretion. These results suggest that the presence of terminal sialic acid residues on complex-type N-glycans may be required for the optimal transport of the amyloid beta precursor protein from the Golgi to the cell membrane with the subsequent cleavage to generate the secreted form of the protein.     

Longitudinal assessment of thrombin generation potential in response to alteration of antiplatelet therapy after TIA or ischaemic stroke

The impact of changing antiplatelet therapy on thrombin generation potential in patients with ischaemic cerebrovascular disease (CVD) is unclear. We assessed patients within 4 weeks of TIA or ischaemic stroke (baseline), and then 14 days (14d) and >90 days (90d) after altering antiplatelet therapy. Thrombin generation was assessed in platelet poor plasma. Ninety-one patients were recruited. Twenty-four were initially assessed on no antiplatelet therapy, and then after 14d (N = 23) and 90d (N = 8) on aspirin monotherapy; 52 were assessed on aspirin monotherapy, and after 14 and 90 days on aspirin and dipyridamole combination therapy; 21 patients were assessed on aspirin and after 14 days (N = 21) and 90 days (N = 19) on clopidogrel. Peak thrombin generation and endogenous thrombin potential were reduced at 14 and 90 days (p ≤ 0.04) in the overall cohort. We assessed the impact of individual antiplatelet regimens on thrombin generation parameters to investigate the cause of this effect. Lag time and time-to-peak thrombin generation were unchanged at 14 days, but reduced 90 days after commencing aspirin (p ≤ 0.009). Lag time, peak thrombin generation and endogenous thrombin potential were reduced at both 14 and 90 days after adding dipyridamole to aspirin (p ≤ 0.01). Lag time was reduced 14 days after changing from aspirin to clopidogrel (p = 0.045), but this effect was not maintained at 90 days (p = 0.2). This pilot study did not show any consistent effects of commencing aspirin, or of changing from aspirin to clopidogrel on thrombin generation potential during follow-up. The addition of dipyridamole to aspirin led to a persistent reduction in peak and total thrombin generation ex vivo, and illustrates the diverse, potentially beneficial, newly recognised ‘anti-coagulant’ effects of dipyridamole in ischaemic CVD.     

Identifying Stage B colorectal cancer patients at high risk of tumor recurrence and death

PURPOSE: This study was designed to determine clinical and pathologic variables associated with poor outcome following resection of Stage B colorectal cancer. METHODS: This was a retrospective study of 117 patients with Stage B cancer who underwent curative surgery and survived the postoperative period. Fourteen clinical and pathologic features were studied. Clinical data were extracted from a prospective colorectal cancer database, and histologic slides were retreived and examined by a pathologist blinded as to clinical details and outcome. RESULTS: After a median follow-up period of 8.2 years, bowel obstruction was significantly related to a poor prognosis (log-rank test; P=0.03). Extensive necrosis (P =0.01) and perineural invasion (P = 0.03) were also associated with decreased survival. Vascular invasion was associated with poor long-term outcome in the subgroup of patients with rectal (P =0.07) but not colonic (P =0.57) cancer. Multivariate regression analysis identified both tumor necrosis (P =0.01) and perineural invasion (P =0.03) as independently related to outcome. CONCLUSION: Further study of prognostic indicators might result in an algorithm to distinguish Stage B cases at high risk of tumor recurrence and death. Such patients could be included in future trials of adjuvant therapies.Presented in part at the meeting of the American Gastroenterological Association, Boston, Massachusetts, May 16 to 19, 1993. Published in abstract form in Gastroenterology 1993;104:A432.     

Dynamic Postural-Stability Deficits After Cryotherapy to the Ankle Joint

Context

 Decreased postural stability is a primary risk factor for lower limb musculoskeletal injuries. During athletic competitions, cryotherapy may be applied during short breaks in play or during half-time; however, its effects on postural stability remain unclear.

Objective

 To investigate the acute effects of a 15-minute ankle-joint cryotherapy application on dynamic postural stability.

Design

 Controlled laboratory study.

Setting

 University biomechanics laboratory.

Patients or Other Participants

 A total of 29 elite-level collegiate male field-sport athletes (age = 20.8 ± 1.12 years, height = 1.80 ± 0.06 m, mass = 81.89 ± 8.59 kg) participated.

Intervention(s)

 Participants were tested on the anterior (ANT), posterolateral (PL), and posteromedial (PM) reach directions of the Star Excursion Balance Test before and after a 15-minute ankle-joint cryotherapy application.

Main Outcome Measure(s)

 Normalized reach distances; sagittal-plane kinematics of the hip, knee, and ankle joints; and associated mean velocity of the center-of-pressure path during performance of the ANT, PL, and PM reach directions of the Star Excursion Balance Test.

Results

 We observed a decrease in reach-distance scores for the ANT, PL, and PM reach directions from precryotherapy to postcryotherapy (P < .05). No differences were observed in hip-, knee-, or ankle-joint sagittal-plane kinematics (P > .05). We noted a decrease in mean velocity of the center-of-pressure path from precryotherapy to postcryotherapy (P < .05) in all reach directions.

Conclusions

 Dynamic postural stability was adversely affected immediately after cryotherapy to the ankle joint.Key Words: postural balance, lower limb, kinetics

Key Points

• A 15-minute cryotherapy application to the ankle joint decreased cutaneous temperature recorded over the anterior talofibular ligament and deltoid ligament.
• Reach distances in the anterior, posterolateral, and posteromedial directions of the Star Excursion Balance Test and center-of-pressure mean velocity decreased after cryotherapy.
• A 15-minute cryotherapy application negatively influenced dynamic postural-stability performance.
• Elite-level field-based athletes should undergo a rewarming period before returning to participation after cryotherapy to the ankle joint to ensure they are not predisposed to injury due to decreased dynamic postural stability.

Cryotherapy is a treatment modality that clinicians commonly use to promote quicker recovery from soft tissue injury in athletes to expedite return to participation. It has been described as the application of cold therapy to living tissues that results in a lower tissue temperature^1,2 and often is used as an immediate treatment method to relieve the acute pain of soft tissue injuries.¹The proposed physiologic benefits of cryotherapy for injury have been widely reported. Cryotherapy facilitates edema reduction, produces analgesia,^2,3–6 reduces muscle temperature,⁷ and reduces injury-induced inflammation.^8,9 If an athlete incurs a mild sprain or contusion to the ankle joint in a game, the accepted practice during a break in participation (eg, during a half-time period) is to apply cryotherapy to the affected area.In contrast to the aforementioned positive physiologic effects, Bleakley et al¹⁰ reported in a recent literature review that cryotherapy application negatively affected at least 1 of the following outcomes: vertical-jump height, sprint time, or agility performance. These tasks are integral components of field-based sports, and any decrement in performance could predispose individuals to injury during participation. Pritchard and Saliba¹¹ suggested that athletic performance may be adversely affected when athletes return to participation immediately after cryotherapy. Furthermore, Costello and Donnelly¹² reported that cryotherapy negatively affects knee-joint positional sense. Uchio et al¹³ observed that a 15-minute cryotherapy application increased knee-joint stiffness and decreased knee-joint position sense acuity. Stal et al¹⁴ reported that ankle-joint sensorimotor control as quantified by static postural stability was negatively affected by a 20-minute cooling procedure known as hypothermic anesthesia, which is similar to a cryotherapy application.Postural stability refers to the ability to control the center of mass in relation to the base of support to prevent falls¹⁵ and is considered a fundamental component required for performing movement skills.¹⁶ Dynamic postural stability can be defined and measured as an assessment of an individual''s ability to maintain balance while transitioning from a dynamic to a static state.¹⁷ It is an essential part of an athlete''s physical attributes, especially for field sports, given their dynamic nature.¹⁸ Both static and dynamic postural stability result from the complex coordination of central processing from visual, vestibular, and somatosensory pathways, as well as the resultant efferent response.¹⁹Static-standing balance ability decreases after cryotherapy application. Cross et al²⁰ reported that after cryotherapy to the lower extremity, study participants had difficulty maintaining their balance on the treated extremity. More recently, Kernozek et al²¹ reported a deficit in mediolateral (ML) ground reaction force variability on the test leg immediately after a 20-minute cryotherapy application to the ankle joint, with a mean difference of 0.48 N relative to precryotherapy measures (P < .001; d = 1.20). At the 10-minute and 20-minute measurements postcryotherapy, participants continued to exhibit deficits in static-standing balance. However, traditional laboratory measures of postural stability, including static single-legged stance on instrumented force plates, may not be sensitive enough to detect postural-stability deficits associated with lower limb injury.²² Furthermore, Hrysomallis et al²³ indicated that postural-stability performance in static positions cannot be extrapolated to dynamic postural-stability performance, concluding that it is not advisable to infer the latter based on the former. Douglas et al²⁴ reaffirmed this conclusion, postulating that measures of dynamic standing balance may better represent the demands of the lower extremity during functional tasks and, therefore, may be a more appropriate assessment than static standing balance. In addition, Hrysomallis²⁵ showed that Australian Rules football players with an increased ML center-of-pressure (COP) excursion incurred at least twice as many ankle-ligament injuries as players with average or good postural stability. Kernozek et al²¹ and Douglas et al²⁴ observed that cryotherapy debilitated dynamic postural stability, potentially increasing the risk of lower limb injury.Considering the potential shortcomings of static postural-stability testing, our contention was that further investigations of the effects of cryotherapy application to the ankle joint on dynamic postural-stability performance are warranted. One potential method to investigate the influence of ankle-joint cryotherapy application on dynamic postural-stability performance is to use the Star Excursion Balance Test (SEBT) as a primary assessment, supplemented by lower limb sagittal-plane motion analysis and force-plate–derived kinetic assessment. Therefore, the purpose of our study was to evaluate the acute influence of a 15-minute cryotherapy application to the ankle joint on dynamic postural stability as quantified by performance on selected reach directions of the SEBT, associated lower limb sagittal-plane kinematic profiles, and kinetic measures of postural stability. We hypothesized that a 15-minute cryotherapy application to the ankle joint would result in decreased reach distances on the selected directions of the SEBT and altered sagittal-plane ankle-joint kinematics and kinetic measures of postural stability.     

Modeling local and cross-species neuron number variations in the cerebral cortex as arising from a common mechanism

A massive increase in the number of neurons in the cerebral cortex, driving its size to increase by five orders of magnitude, is a key feature of mammalian evolution. Not only are there systematic variations in cerebral cortical architecture across species, but also across spatial axes within a given cortex. In this article we present a computational model that accounts for both types of variation as arising from the same developmental mechanism. The model employs empirically measured parameters from over a dozen species to demonstrate that changes to the kinetics of neurogenesis (the cell-cycle rate, the progenitor death rate, and the “quit rate,” i.e., the ratio of terminal cell divisions) are sufficient to explain the great diversity in the number of cortical neurons across mammals. Moreover, spatiotemporal gradients in those same parameters in the embryonic cortex can account for cortex-wide, graded variations in the mature neural architecture. Consistent with emerging anatomical data in several species, the model predicts (i) a greater complement of neurons per cortical column in the later-developing, posterior regions of intermediate and large cortices, (ii) that the extent of variation across a cortex increases with cortex size, reaching fivefold or greater in primates, and (iii) that when the number of neurons per cortical column increases, whether across species or within a given cortex, it is the later-developing superficial layers of the cortex which accommodate those additional neurons. We posit that these graded features of the cortex have computational and functional significance, and so must be subject to evolutionary selection.Changes in brain structure follow a remarkably stable pattern over ∼450 My in the vertebrate lineage: it is always the same brain parts that become enlarged when overall brain size increases (1). Moreover, in studies of individual variation in humans and other mammals, when overall brain size is larger, those same divisions as would be predicted by looking at brain enlargement across taxa are also found to be preferentially enlarged (2, 3). Such regularities in brain scaling from the individual to the taxon level suggest that the developmental mechanisms which generate central nervous systems are strongly conserved across species (4).To tease apart the features of the isocortex contributed by the scaling of conserved developmental mechanisms from those features which might be specially selected for in a given niche or species, we have created an empirically informed, mathematical model of cortical neurogenesis. The model elucidates how the dials and levers made available by conserved developmental mechanisms allow selection to shape the basic landscape of the embryonic cortex. The extent to which any particular cortical area (e.g., a visual or language area) has been a special subject of selection can be better evaluated given the baselines provided by this evolutionary developmental or “evo-devo” model.The modeling approach presented here provides an explicit structure to assimilate known data and predict unknowns, both for developmental kinetic parameters and for the resultant time courses of neuronal and progenitor cell populations, for the entire range of mammalian brain sizes and across a spatial axis within the respective cortices. Our model incorporates important insights from several previously published mathematical models of cortical neurogenesis which focus on more limited sets of species or which consider spatial variations in a single species (5–10).