Comparative Efficacy of High-Intensity Training Versus Conventional Training in Individuals With Chronic Traumatic Brain Injury: A Pilot Randomized Controlled Study

Numerous studies have evaluated the efficacy of interventions to improve locomotion after acute-onset brain injury, although most focus on patients with stroke, with less attention toward traumatic brain injury (TBI). For example, a number of studies in patients post-stroke have evaluated the effects of high-intensity training (HIT) attempting to maximize stepping practice, while no studies have attempted this intervention in patients with TBI. The purpose of this blinded-assessor randomized trial was to evaluate the effects of HIT focused on stepping practice versus conventional training on walking and secondary outcomes in individuals with TBI. Using a crossover design, ambulatory participants with TBI >6-months duration performed HIT focused on stepping in variable contexts (overground, treadmill, stairs) or conventional training for up to 15 sessions over five weeks, with interventions alternated >4 weeks later. HIT focused on maximizing stepping practice while trying to achieve higher cardiovascular intensities (>70% heart rate reserve), while conventional training focused on impairment-based and functional exercises with no restrictions on intensities achieved. Greater increases in 6-min walk test and peak treadmill speed during graded exercise testing were observed after HIT versus conventional training, with moderate associations between differences in stepping practice and outcomes. Greater gains were also observed in estimates of aerobic capacity and efficiency after HIT, with additional improvements in selected cognitive assessments. The present study suggests that the amount and intensity of stepping practice may be important determinants of improved locomotor outcomes in patients with chronic TBI, with possible secondary benefits on aerobic capacity/efficiency and cognition. Clinical Trial Registration-URL: https://clinicaltrials.gov/; Unique Identifier: NCT04503473.

Identification of a know-do gap: An observational study of the assessment and treatment of dysphagia during inpatient stroke rehabilitation in primary healthcare in Norway

PURPOSE

Oropharyngeal dysphagia is a common swallowing impairment post-stroke managed by speech language pathologists (SLP). This article aims to demonstrate a local know-do gap assessment for usual dysphagia care for patients undergoing inpatient stroke rehabilitation in primary healthcare in Norway, which included an assessment of the functional level of the patients and characteristics and outcomes of treatment.

MATERIALS AND METHODS

In this observational study, we assessed the outcomes and interventions of patients admitted to inpatient rehabilitation following stroke. The patients received usual care from SLPs while the research team administered a dysphagia assessment protocol that included assessment of several swallowing domains including oral intake, swallowing, patient self-reported functional health status and health-related quality of life, and oral health. The treating SLPs documented the treatments provided in a treatment diary.

RESULTS

Of 91 patients who consented, 27 were referred for SLP and 14 received treatment. During the median treatment period of 31.5 days (IQR = 8.8-57.0), patients received 7.0 treatment sessions (IQR = 3.8-13.5) of 60 minutes (IQR = 55-60). The patients who received SLP treatment demonstrated no/minor disorders (n = 7) and moderate/severe disorders (n = 7). Dysphagia treatments primarily included oromotor training and advice on bolus modification and were provided without association to dysphagia severity. Patients with moderate/severe swallowing impairments received slightly more SLP sessions over a longer time.

CONCLUSIONS

This study identified gaps between current and best practices and opportunities to improve assessment, decision-making, and implement evidence-based practices.

Increasing Activity After Stroke: A Randomized Controlled Trial of High-Intensity Walking and Step Activity Intervention

BACKGROUND

Physical inactivity in people with chronic stroke profoundly affects daily function and increases recurrent stroke risk and mortality, making physical activity improvements an important target of intervention. We compared the effects of a high-intensity walking intervention (FAST), a step activity monitoring behavioral intervention (SAM), or a combined intervention (FAST+SAM) on physical activity (ie, steps/day). We hypothesized the combined intervention would yield the greatest increase in steps/day.

METHODS

This assessor-blinded multisite randomized controlled trial was conducted at 4 university/hospital-based laboratories. Participants were 21 to 85 years old, walking without physical assistance following a single, unilateral noncerebellar stroke of ≥6 months duration, and randomly assigned to FAST, SAM, or FAST+SAM for 12 weeks (2-3 sessions/week). FAST training consisted of walking-related activities at 70% to 80% heart rate reserve, while SAM received daily feedback and goal setting of walking activity (steps/day). Assessors and study statistician were masked to group assignment. The a priori-determined primary outcome and end point was a comparison of the change in steps/day between the 3 intervention groups from pre- to post-intervention. Adverse events were tracked after randomization. All randomized participants were included in the intent-to-treat analysis.

RESULTS

Participants were enrolled from July 18, 2016, to November 16, 2021. Of 2385 participants initially screened, 250 participants were randomized (mean [SE] age, 63 [0.80] years; 116 females/134 males), with 89 assigned to FAST, 81 to SAM, and 80 to FAST+SAM. Steps/day significantly increased in both the SAM (mean [SE], 1542 [267; 95% CI, 1014-2069] P<0.001) and FAST+SAM group (1307 [280; 95% CI, 752-1861] P<0.001) but not in the FAST group (406 [238; 95% CI, -63 to 876] P=0.09). There were no deaths or serious study-related adverse events.

CONCLUSIONS

Only individuals with chronic stroke who completed a step activity monitoring behavioral intervention with skilled coaching and goal progression demonstrated improvements in physical activity (steps/day).

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT02835313.

Increasing activity after stroke: a randomized controlled trial of highintensity walking and step activity intervention

Background

Physical inactivity in people with chronic stroke profoundly affects daily function and increases recurrent stroke risk and mortality, making physical activity improvements an important target of intervention. We compared the effects of a highintensity walking intervention (FAST), a step activity monitoring behavioral intervention (SAM), or a combined intervention (FAST+SAM) on physical activity (i.e., steps per day). We hypothesized the combined intervention would yield the greatest increase in steps per day.

Methods

This assessor-blinded multi-site randomized controlled trial was conducted at four university/hospital-based laboratories. Participants were 21-85 years old, walking without physical assistance following a single, unilateral non-cerebellar stroke of ≥6 months duration, and randomly assigned to FAST, SAM, or FAST+SAM for 12 weeks (2-3 sessions/week). FAST training consisted of walking-related activities for 40 minutes/session at 70-80% heart rate reserve, while SAM received daily feedback and goal-setting of walking activity (steps per day). Assessors and study statistician were masked to group assignment.The a priori-determined primary outcome and primary endpoint was change in steps per day from pre- to post-intervention. Adverse events (AEs) were tracked after randomization. All randomized participants were included in the intent-to-treat analysis.This study is registered at ClinicalTrials.gov, NCT02835313.

Findings

Participants were enrolled from July 18, 2016-November 16, 2021. Of 250 randomized participants (mean[SE] age 63[0.80], 116F/134M), 89 were assigned to FAST, 81 to SAM, and 80 to FAST+SAM. Steps per day significantly increased in both the SAM (mean[SE] 1542[267], 95%CI:1014-2069, p<0.001) and FAST+SAM groups (1307[280], 752-1861, p<0.001), but not in the FAST group (406[238], 63-876, p=0.09). There were no deaths or serious study-related AEs and all other minor AEs were similar between groups.

Interpretation

Only individuals with chronic stroke who completed a step activity monitoring behavioral intervention with skilled coaching and goal progression demonstrated improvements in physical activity (steps per day).

Increasing the Amount and Intensity of Stepping Training During Inpatient Stroke Rehabilitation Improves Locomotor and Non-Locomotor Outcomes

BACKGROUND

The efficacy of traditional rehabilitation interventions to improve locomotion post-stroke, including providing multiple exercises targeting impairments and activity limitations, is uncertain. Emerging evidence rather suggests attempts to prioritize stepping practice at higher cardiovascular intensities may facilitate greater locomotor outcomes.

OBJECTIVE

The present study was designed to evaluate the comparative effectiveness of high-intensity training (HIT) to usual care during inpatient rehabilitation post-stroke.

METHODS

Changes in stepping activity and functional outcomes were compared over 9 months during usual-care (n = 131 patients < 2 months post-stroke), during an 18-month transition phase with attempts to implement HIT (n = 317), and over 12 months following HIT implementation (n = 208). The transition phase began with didactic and hands-on education, and continued with meetings, mentoring, and audit and feedback. Fidelity metrics included percentage of sessions prioritizing gait interventions and documenting intensity. Demographics, training measures, and outcomes were compared across phases using linear or logistic regression analysis, Kruskal-Wallis tests, or χ² analysis.

RESULTS

Across all phases, admission scores were similar except for balance (usual-care>HIT; P < .02). Efforts to prioritize stepping and achieve targeted intensities during HIT vs transition or usual-care phases led to increased steps/day (P < .01). During HIT, gains in 10-m walk [HIT median = 0.13 m/s (interquartile range: 0-0.35) vs usual-care = 0.07 m/s (0-0.24), P = .01] and 6-min walk [50 (9.3-116) vs 2.1 (0-56) m, P < .01] were observed, with additional improvements in transfers and stair-climbing.

CONCLUSIONS

Greater efforts to prioritize walking and reach higher intensities during HIT led to increased steps/day, resulting in greater gains in locomotor and non-locomotor outcomes.

Gains in Daily Stepping Activity in People With Chronic Stroke After High-Intensity Gait Training in Variable Contexts

OBJECTIVE

Many physical therapist interventions provided to individuals with chronic stroke can lead to gains in gait speed or endurance (eg, 6-Minute Walk Test [6MWT]), although changes in objective measures of participation are not often observed. The goal of this study was to determine the influence of different walking interventions on daily stepping (steps per day) and the contributions of demographic, training, and clinical measures to these changes.

METHODS

In this secondary analysis of a randomized clinical trial, steps per day at baseline and changes in steps per day following 1 of 3 locomotor interventions were evaluated in individuals who were ambulatory and >6 months after stroke. Data were collected on 58 individuals who received ≤30 sessions of high-intensity training (HIT) in variable contexts (eg, tasks and environments; n = 19), HIT focused on forward walking (n = 19), or low-intensity variable training (n = 20). Primary outcomes were steps per day at baseline, at post-training, and at a 3-month follow-up, and secondary outcomes were gait speed, 6MWT, balance, and balance confidence. Correlation and regression analyses identified demographic and clinical variables associated with steps per day.

RESULTS

Gains in steps per day were observed across all groups combined, with no between-group differences; post hoc within-group analyses revealed significant gains only following HIT in variable contexts. Both HIT groups showed gains in endurance (6MWT), with increases in balance confidence only following HIT in variable contexts. Changes in steps per day were associated primarily with gains in 6MWT, with additional associations with baseline 6MWT, lower-extremity Fugl-Meyer scores, and changes in balance confidence.

CONCLUSION

HIT in variable contexts elicited gains in daily stepping, with changes primarily associated with gains in gait endurance.

IMPACT

Providing HIT in variable contexts appears to improve measures of participation (eg, daily stepping) that may be associated with clinical measures of function. Gains in multiple measures of mobility and participation with HIT in variable contexts may improve the efficiency and value of physical therapy services.

Predicting Discharge Walking Function With High-Intensity Stepping Training During Inpatient Rehabilitation in Nonambulatory Patients Poststroke

OBJECTIVE

This cohort investigation identified primary predictors of discharge walking function of nonambulatory individuals poststroke with high-intensity training (HIT) during inpatient rehabilitation.

DESIGN

Observational cohort investigation.

SETTING

Inpatient rehabilitation.

PARTICIPANTS

Data were collected from individuals (N=257) <6 months poststroke who required assistance to walk at admission.

INTERVENTION

Clinical physical therapy interventions attempted to maximize stepping practice at higher intensities.

MAIN OUTCOME MEASURES

Primary outcomes included the discharge level of assistance required during walking (minimal or no assistance) and attainment of specific gait speed thresholds (0.4 and 0.8 m/s) during the 10-m walk test. Independent predictors were demographics, training interventions (including steps/day), baseline Berg Balance Scale (BBS), and paretic leg strength.

RESULTS

Participants performed a median (interquartile range) of 1270 (533-2297) steps per day throughout inpatient rehabilitation, with significant differences between those who walked with versus without assistance at discharge. Logistic regressions indicate steps per day was a primary predictor of unassisted walking recovery; removal of steps per day resulted in primary predictors of baseline BBS and strength. Receiver operating characteristic (ROC) analyses indicate significant areas under the curve for BBS and relatively low cutoff scores of 5.5 points at admission to walk without assistance at any speed. ROC analyses performed using 1-week outcomes indicate BBS scores of 5-17 points were needed to achieve locomotor thresholds.

CONCLUSION

Stepping activity, BBS, and paretic leg strength were primary predictors of walking outcomes in patients performing HIT, and ROC analyses indicated recovery of independent walking could be achieved in low functioning patients early poststroke.

Step Monitor Accuracy During PostStroke Physical Therapy and Simulated Activities

Introduction/Purpose

The amount of stepping activity during rehabilitation post-stroke can predict walking outcomes, although the most accurate methods to evaluate stepping activity are uncertain with conflicting findings on available stepping monitors during walking assessments. Rehabilitation sessions also include non-stepping activities and the ability of activity monitors to differentiate these activities from stepping is unclear. The objective of this study was to examine the accuracy of different activity monitors worn by individuals post-stroke with variable walking speeds during clinical physical therapy (PT) and research interventions focused on walking.

Methods

In Part I, 28 participants post-stroke wore a StepWatch, ActiGraph with and without a Low Frequency Extension (LFE) filter, and Fitbit on paretic and non-paretic distal shanks at or above the ankle during clinical PT or research interventions with steps simultaneously hand counted. Mean absolute percent errors were compared between limbs and tasks performed. In Part II, 12 healthy adults completed 8 walking and 9 non-walking tasks observed during clinical PT or research. Data were descriptively analyzed and used to assist interpretation of Part I results.

Results

Part I results indicate most devices did not demonstrate an optimal limb configuration during research sessions focused on walking, with larger errors during clinical PT on the non-paretic limb. Using the limb that minimized errors for each device, the StepWatch had smaller errors than the ActiGraph and Fitbit (p<0.01), particularly in those who walked < 0.8 m/s. Conversely, errors from the ActiGraph-LFE demonstrated inconsistent differences in step counts between Fitbit and ActiGraph. Part II results indicate that errors observed during different stepping and non-stepping activities were often device-specific, with non-stepping tasks frequently detected as stepping.

Conclusions

The StepWatch and ActiGraph-LFE had smaller errors than the Fitbit or ActiGraph, with greater errors in those walking at slower speeds. Inclusion of non-stepping activities affected step counts and should be considered when measuring stepping activity in individuals post-stroke to predict locomotor outcomes following rehabilitation.

Use of CRISPR/Cas9-mediated disruption of CNS cell type genes to profile transduction of AAV by neonatal intracerebroventricular delivery in mice

Adeno-associated virus (AAV) transduction efficiency and tropism are conventionally determined by high expression of a fluorescent reporter gene. Emerging data has suggested that such conventional methods may underestimate AAV transduction for cells in which reporter expression from AAV vectors is undetectable. To explore an alternative method that captures AAV transduction in cells in which low expression of a cargo is sufficient for the intended activity, we sought after CRISPR/Cas9-mediated gene disruption. In this study, we use AAV to deliver CRISPR/guide RNA designed to abolish the genes NeuN, GFAP, or MOG expressed specifically in neurons, astrocytes, or oligodendrocytes respectively in the central nervous system (CNS) of mice. Abrogated expression of these cell-type-specific genes can be measured biochemically in CNS subregions and provides quantitative assessment of AAV transduction in these CNS cell types. By using this method, we compared CNS transduction of AAV9, AAV-PHP.B, and AAV-PHP.eB delivered via intracerebroventricular injection (ICV) in neonatal mice. We found both AAV-PHP.B and AAV-PHP.eB resulted in marked disruption of the NeuN gene by CRISPR/Cas9, significantly greater than AAV9 in several brain regions and spinal cord. In contrast, only modest disruption of the GFAP gene and the MOG gene was observed by all three AAV variants. Since the procedure of ICV circumvents the blood-brain barrier, our data suggests that, independent of their ability to cross the blood-brain barrier, AAV-PHP.B variants also exhibit remarkably improved neuronal transduction in the CNS. We anticipate this approach will facilitate profiling of AAV cellular tropism in murine CNS.

The Value of High Intensity Locomotor Training Applied to Patients With Acute-Onset Neurologic Injury

Long-standing research in animal models and humans with stroke or incomplete spinal cord injury (iSCI) indicate that specific physical training variables, such as the specificity and amount of practice, may influence neurologic recovery and locomotor function. More recent data highlight the contributions of exercise intensity, as estimated indirectly by cardiovascular exertion, as potentially more important than previously considered. The effects of exercise intensity are well described in neurologically intact individuals, although confusion regarding the definitions of intensity and safety concerns have limited its implementation during physical rehabilitation of patients with neurologic injury. The purpose of this review is to delineate some of the evidence regarding the effects of exercise intensity during locomotor training in patients with stroke and iSCI. We provide specific definitions of exercise intensity used within the literature, describe methods used to ensure appropriate levels of exertion, and discuss potential adverse events and safety concerns during its application. Further details on the effects of locomotor training intensity on clinical outcomes, and on neuromuscular and cardiovascular function will be addressed as available. Existing literature across multiple studies and meta-analyses reveals that exercise training intensity is likely a major factor that can influence locomotor function after neurologic injury. To extend these findings, we describe previous attempts to implement moderate to high intensity interventions during physical rehabilitation of patients with neurologic injury, including the utility of specific strategies to facilitate implementation, and to navigate potential barriers that may arise during implementation efforts.

Stepwise Regression and Latent Profile Analyses of Locomotor Outcomes Poststroke

BACKGROUND AND PURPOSE

Previous data suggest patient demographics and clinical presentation are primary predictors of motor recovery poststroke, with minimal contributions of physical interventions. Other studies indicate consistent associations between the amount and intensity of stepping practice with locomotor outcomes. The goal of this study was to determine the relative contributions of these combined variables to locomotor outcomes poststroke across a range of patient demographics and baseline function.

METHODS

Data were pooled from 3 separate trials evaluating the efficacy of high-intensity training, low-intensity training, and conventional interventions. Demographics, clinical characteristics, and training activities from 144 participants >1-month poststroke were included in stepwise regression analyses to determine their relative contributions to locomotor outcomes. Subsequent latent profile analyses evaluated differences in classes of participants based on their responses to interventions.

RESULTS

Stepwise regressions indicate primary contributions of stepping activity on locomotor outcomes, with additional influences of age, duration poststroke, and baseline function. Latent profile analyses revealed 2 main classes of outcomes, with the largest gains in those who received high-intensity training and achieved the greatest amounts of stepping practice. Regression and latent profile analyses of only high-intensity training participants indicated age, baseline function, and training activities were primary determinants of locomotor gains. Participants with the smallest gains were older (≈60 years), presented with slower gait speeds (<0.40 m/s), and performed 600 to 1000 less steps/session.

CONCLUSIONS

Regression and cluster analyses reveal primary contributions of training interventions on mobility outcomes in patients >1-month poststroke. Age, duration poststroke, and baseline impairments were secondary predictors. Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT02507466 and NCT01789853.

Etv1 Controls the Establishment of Non-overlapping Motor Innervation of Neighboring Facial Muscles during Development

The somatotopic motor-neuron projections onto their cognate target muscles are essential for coordinated movement, but how that occurs for facial motor circuits, which have critical roles in respiratory and interactive behaviors, is poorly understood. We report extensive molecular heterogeneity in developing facial motor neurons in the mouse and identify markers of subnuclei and the motor pools innervating specific facial muscles. Facial subnuclei differentiate during migration to the ventral hindbrain, where neurons with progressively later birth dates—and evolutionarily more recent functions—settle in more-lateral positions. One subpopulation marker, ETV1, determines both positional and target muscle identity for neurons of the dorsolateral (DL) subnucleus. In Etv1 mutants, many markers of DL differentiation are lost, and individual motor pools project indifferently to their own and neighboring muscle targets. The resulting aberrant activation patterns are reminiscent of the facial synkinesis observed in humans after facial nerve injury.

Tenney et al. demonstrate that embryonic facial motor neurons are transcriptionally diverse as they establish somatotopic innervation of the facial muscles, a process that requires the transcription factor ETV1. Facial-motor axon-targeting errors in Etv1 mutants cause coordination of whisking and eyeblink evocative of human blepharospasm.

Locomotor Kinematics and Kinetics Following High-Intensity Stepping Training in Variable Contexts Poststroke

Background and Purpose. Previous studies suggest that individuals poststroke can achieve substantial gains in walking function following high-intensity locomotor training (LT). Recent findings also indicate practice of variable stepping tasks targeting locomotor deficits can mitigate selected impairments underlying reduced walking speeds. The goal of this study was to investigate alterations in locomotor biomechanics following 3 different LT paradigms. Methods. This secondary analysis of a randomized trial recruited individuals 18 to 85 years old and >6 months poststroke. We compared changes in spatiotemporal, joint kinematics, and kinetics following up to 30 sessions of high-intensity (>70% heart rate reserve [HRR]) LT of variable tasks targeting paretic limb and balance impairments (high-variable, HV), high-intensity LT focused only on forward walking (high-forward, HF), or low-intensity LT (<40% HRR) of variable tasks (low-variable, LV). Sagittal spatiotemporal and joint kinematics, and concentric joint powers were compared between groups. Regressions and principal component analyses were conducted to evaluate relative contributions or importance of biomechanical changes to between and within groups. Results. Biomechanical data were available on 50 participants who could walk ≥0.1 m/s on a motorized treadmill. Significant differences in spatiotemporal parameters, kinematic consistency, and kinetics were observed between HV and HF versus LV. Resultant principal component analyses were characterized by paretic powers and kinematic consistency following HV, while HF and LV were characterized by nonparetic powers. Conclusion. High-intensity LT results in greater changes in kinematics and kinetics as compared with lower-intensity interventions. The results may suggest greater paretic-limb contributions with high-intensity variable stepping training that targets specific biomechanical deficits. Clinical Trial Registration. https://clinicaltrials.gov/ Unique Identifier: NCT02507466.

Task-Specific Versus Impairment-Based Training on Locomotor Performance in Individuals With Chronic Spinal Cord Injury: A Randomized Crossover Study

Background. Many research studies attempting to improve locomotor function following motor incomplete spinal cord injury (iSCI) focus on providing stepping practice. However, observational studies of physical therapy strategies suggest the amount of stepping practice during clinical rehabilitation is limited; rather, many interventions focus on mitigating impairments underlying walking dysfunction. Objective. The purpose of this blinded-assessor randomized trial was to evaluate the effects of task-specific versus impairment-based interventions on walking outcomes in individuals with iSCI. Methods. Using a crossover design, ambulatory participants with iSCI >1-year duration performed either task-specific (upright stepping) or impairment-based training for up to 20 sessions over ≤6 weeks, with interventions alternated after >4 weeks delay. Both strategies focused on achieving higher cardiovascular intensities, with training specificity manipulated by practicing only stepping practice in variable contexts or practicing tasks targeting impairments underlying locomotor dysfunction (strengthening, balance tasks, and recumbent stepping). Results. Significantly greater increases in fastest overground and treadmill walking speeds were observed following task-specific versus impairment-based training, with moderate associations between differences in amount of practice and outcomes. Gains in balance confidence were also observed following task-specific vs impairment-based training, although incidence of falls was also increased with the former protocol. Limited gains were observed with impairment-based training except for peak power during recumbent stepping tests. Conclusion. The present study reinforces work from other patient populations that the specificity of task practice is a critical determinant of locomotor outcomes and suggest impairment-based exercises may not translate to improvements in functional tasks. Clinical Trial Registration URL. https://clinicaltrials.gov/ ; Unique Identifier: NCT02115685.

Task-Specific Versus Impairment-Based Training on Locomotor Performance in Individuals With Chronic Spinal Cord Injury: A Randomized Crossover Study

Background. Many research studies attempting to improve locomotor function following motor incomplete spinal cord injury (iSCI) focus on providing stepping practice. However, observational studies of physical therapy strategies suggest the amount of stepping practice during clinical rehabilitation is limited; rather, many interventions focus on mitigating impairments underlying walking dysfunction. Objective. The purpose of this blinded-assessor randomized trial was to evaluate the effects of task-specific versus impairment-based interventions on walking outcomes in individuals with iSCI. Methods. Using a crossover design, ambulatory participants with iSCI >1-year duration performed either task-specific (upright stepping) or impairment-based training for up to 20 sessions over ≤6 weeks, with interventions alternated after >4 weeks delay. Both strategies focused on achieving higher cardiovascular intensities, with training specificity manipulated by practicing only stepping practice in variable contexts or practicing tasks targeting impairments underlying locomotor dysfunction (strengthening, balance tasks, and recumbent stepping). Results. Significantly greater increases in fastest overground and treadmill walking speeds were observed following task-specific versus impairment-based training, with moderate associations between differences in amount of practice and outcomes. Gains in balance confidence were also observed following task-specific vs impairment-based training, although incidence of falls was also increased with the former protocol. Limited gains were observed with impairment-based training except for peak power during recumbent stepping tests. Conclusion. The present study reinforces work from other patient populations that the specificity of task practice is a critical determinant of locomotor outcomes and suggest impairment-based exercises may not translate to improvements in functional tasks. Clinical Trial Registration URL. https://clinicaltrials.gov/ ; Unique Identifier: NCT02115685.

Contributions of Stepping Intensity and Variability to Mobility in Individuals Poststroke

Background and Purpose- The amount of task-specific stepping practice provided during rehabilitation poststroke can influence locomotor recovery and reflects one aspect of exercise dose that can affect the efficacy of specific interventions. Emerging data suggest that markedly increasing the intensity and variability of stepping practice may also be critical, although such strategies are discouraged during traditional rehabilitation. The goal of this study was to determine the individual and combined contributions of intensity and variability of stepping practice to improving walking speed and distance in individuals poststroke. Methods- This phase 2, randomized, blinded assessor clinical trial was performed between May 2015 and November 2018. Individuals between 18 and 85 years old with hemiparesis poststroke of >6 months duration were recruited. Of the 152 individuals screened, 97 were randomly assigned to 1 of 3 training groups, with 90 completing >10 sessions. Interventions consisted of either high-intensity stepping (70%-80% heart rate reserve) of variable, difficult stepping tasks (high variable), high-intensity stepping performing only forward walking (high forward), and low-intensity stepping in variable contexts at 30% to 40% heart rate reserve (low variable). Participants received up to 30 sessions over 2 months, with testing at baseline, post-training, and a 3-month follow-up. Primary outcomes included walking speeds and timed distance, with secondary measures of dynamic balance, transfers, spatiotemporal kinematics, and metabolic measures. Results- All walking gains were significantly greater following either high-intensity group versus low-variable training (all P<0.001) with significant correlations with stepping amount and rate (r=0.48-60; P<0.01). Additional gains in spatiotemporal symmetry were observed with high-intensity training, and balance confidence increased only following high-variable training in individuals with severe impairments. Conclusions- High-intensity stepping training resulted in greater improvements in walking ability and gait symmetry than low-intensity training in individuals with chronic stroke, with potential greater improvements in balance confidence. Clinical Trial Registration- URL: https://www.clinicaltrials.gov. Unique identifier: NCT02507466.

FGF family members differentially regulate maturation and proliferation of stem cell-derived astrocytes

The glutamate transporter 1 (GLT1) is upregulated during astrocyte development and maturation in vivo and is vital for astrocyte function. Yet it is expressed at low levels by most cultured astrocytes. We previously showed that maturation of human and mouse stem cell-derived astrocytes – including functional glutamate uptake – could be enhanced by fibroblast growth factor (FGF)1 or FGF2. Here, we examined the specificity and mechanism of action of FGF2 and other FGF family members, as well as neurotrophic and differentiation factors, on mouse embryonic stem cell-derived astrocytes. We found that some FGFs – including FGF2, strongly increased GLT1 expression and enhanced astrocyte proliferation, while others (FGF16 and FGF18) mainly affected maturation. Interestingly, BMP4 increased astrocytic GFAP expression, and BMP4-treated astrocytes failed to promote the survival of motor neurons in vitro. Whole transcriptome analysis showed that FGF2 treatment regulated multiple genes linked to cell division, and that the mRNA encoding GLT1 was one of the most strongly upregulated of all astrocyte canonical markers. Since GLT1 is expressed at reduced levels in many neurodegenerative diseases, activation of this pathway is of potential therapeutic interest. Furthermore, treatment with FGFs provides a robust means for expansion of functionally mature stem cell-derived astrocytes for preclinical investigation.

Improved walking function in laboratory does not guarantee increased community walking in stroke survivors: Potential role of gait biomechanics

Reduced daily stepping in stroke survivors may contribute to decreased functional capacity and increased mortality. We investigated the relationships between clinical and biomechanical walking measures that may contribute to changes in daily stepping activity following physical interventions provided to participants with subacute stroke. Following ≤40 rehabilitation sessions, 39 participants were categorized into three groups: responders/retainers increased daily stepping >500 steps/day post-training (POST) without decreases in stepping at 2-6 month follow-up (F/U); responders/non-retainers increased stepping at POST but declined >500 steps/day at F/U; and, non-responders did not change daily stepping from baseline testing (BSL). Gait kinematics and kinetics were evaluated during graded treadmill assessments at BSL and POST. Clinical measures of gait speed, timed walking distance, balance and balance confidence were measured at BSL, POST and F/U. Between-group comparisons and regression analyses were conducted to predict stepping activity from BSL and POST measurements. Baseline and changes in clinical measures of walking demonstrated selective associations with stepping, although kinematic measures appeared to better discriminate responders. Specific measures suggest greater paretic vs non-paretic kinematic changes in responders with training, although greater non-paretic changes predicted greater gains (i.e., smaller declines) in stepping in retainers at F/U. No kinetic variables were primary predictors of changes in stepping activity at POST or F/U. The combined findings indicate specific biomechanical assessments may help differentiate changes in daily stepping activity post-stroke.

Kinematic and Neuromuscular Adaptations in Incomplete Spinal Cord Injury after High- versus Low-Intensity Locomotor Training

Recent data demonstrate improved locomotion with high-intensity locomotor training (LT) in individuals with incomplete spinal cord injury (iSCI), although concerns remain regarding reinforcement of abnormal motor strategies. The present study evaluated the effects of LT intensity on kinematic and neuromuscular coordination in individuals with iSCI. Using a randomized, crossover design, participants with iSCI received up to 20 sessions of high-intensity LT, with attempts to achieve 70-85% of age-predicted maximum heart rate (HRmax), or low-intensity LT (50-65% HRmax), following which the other intervention was performed. Specific measures included spatiotemporal variables, sagittal-plane gait kinematics, and neuromuscular synergies from electromyographic (EMG) recordings. Correlation analyses were conducted to evaluate associations between variables. Significant improvements in sagittal-plane joint excursions and intralimb hip-knee coordination were observed following high- but not low-intensity LT when comparing peak treadmill (TM) speed before and after LT. Neuromuscular complexity (i.e., number of synergies to explain >90% of EMG variance) was also increased following high- but not low-intensity LT. Comparison of speed-matched trials confirmed significant improvements in the knee excursion of the less impaired limb and intralimb hip-knee coordination, as well as improvements in neuromuscular complexity following high-intensity LT. These findings suggest greater neuromuscular complexity may be due to LT and not necessarily differences in speeds. Only selected kinematic changes (i.e., weak hip excursion) was correlated to improvements in treadmill speed. In conclusion, LT intensity can facilitate gains in kinematic variables and neuromuscular synergies in individuals with iSCI.

A Stem Cell-Based Screening Platform Identifies Compounds that Desensitize Motor Neurons to Endoplasmic Reticulum Stress

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease selectively targeting motor neurons in the brain and spinal cord. The reasons for differential motor neuron susceptibility remain elusive. We developed a stem cell-based motor neuron assay to study cell-autonomous mechanisms causing motor neuron degeneration, with implications for ALS. A small-molecule screen identified cyclopiazonic acid (CPA) as a stressor to which stem cell-derived motor neurons were more sensitive than interneurons. CPA induced endoplasmic reticulum stress and the unfolded protein response. Furthermore, CPA resulted in an accelerated degeneration of motor neurons expressing human superoxide dismutase 1 (hSOD1) carrying the ALS-causing G93A mutation, compared to motor neurons expressing wild-type hSOD1. A secondary screen identified compounds that alleviated CPA-mediated motor neuron degeneration: three kinase inhibitors and tauroursodeoxycholic acid (TUDCA), a bile acid derivative. The neuroprotective effects of these compounds were validated in human stem cell-derived motor neurons carrying a mutated SOD1 allele (hSOD1A4V). Moreover, we found that the administration of TUDCA in an hSOD1G93A mouse model of ALS reduced muscle denervation. Jointly, these results provide insights into the mechanisms contributing to the preferential susceptibility of ALS motor neurons, and they demonstrate the utility of stem cell-derived motor neurons for the discovery of new neuroprotective compounds.

Compensation or Recovery? Altered Kinetics and Neuromuscular Synergies Following High-Intensity Stepping Training Poststroke

Background. High-intensity, variable stepping training can improve walking speed in individuals poststroke, although neuromuscular strategies used to achieve faster speeds are unclear. We evaluated changes in joint kinetics and neuromuscular coordination following such training; movement strategies consistent with intact individuals were considered evidence of recovery and abnormal strategies indicative of compensation. Methods. A total of 15 individuals with stroke (duration: 23 ± 30 months) received ≤40 sessions of high-intensity stepping in variable contexts (tasks and environments). Lower-extremity kinetics and electromyographic (EMG) activity were collected prior to (BSL) and following (POST) training at peak treadmill speeds and speeds matched to peak BSL (MATCH). Primary measures included positive (concentric) joint and total limb powers, measures of interlimb (paretic/nonparetic powers) and intralimb compensation (hip/ankle or knee/ankle powers), and muscle synergies calculated using nonnegative matrix factorization. Results. Gains in most positive paretic and nonparetic joint powers were observed at higher speeds at POST, with decreased interlimb compensation and limited changes in intralimb compensation. There were very few differences in kinetic measures between BSL to MATCH conditions. However, the number of neuromuscular synergies increased significantly following training at both POST and MATCH conditions, indicating gains from training rather than altered speeds. Despite these results, speed improvements were associated primarily with changes in nonparetic versus paretic powers. Conclusion. Gains in locomotor function were accomplished by movement strategies consistent with both recovery and compensation. These and other data indicate that both strategies may be necessary to maximize walking function in patients poststroke.

Protein Prenylation Constitutes an Endogenous Brake on Axonal Growth

Suboptimal axonal regeneration contributes to the consequences of nervous system trauma and neurodegenerative disease, but the intrinsic mechanisms that regulate axon growth remain unclear. We screened 50,400 small molecules for their ability to promote axon outgrowth on inhibitory substrata. The most potent hits were the statins, which stimulated growth of all mouse- and human-patient-derived neurons tested, both in vitro and in vivo, as did combined inhibition of the protein prenylation enzymes farnesyltransferase (PFT) and geranylgeranyl transferase I (PGGT-1). Compensatory sprouting of motor axons may delay clinical onset of amyotrophic lateral sclerosis (ALS). Accordingly, elevated levels of PGGT1B, which would be predicted to reduce sprouting, were found in motor neurons of early- versus late-onset ALS patients postmortem. The mevalonate-prenylation pathway therefore constitutes an endogenous brake on axonal growth, and its inhibition provides a potential therapeutic approach to accelerate neuronal regeneration in humans.

The Regulatory Machinery of Neurodegeneration in In Vitro Models of Amyotrophic Lateral Sclerosis

Neurodegenerative phenotypes reflect complex, time-dependent molecular processes whose elucidation may reveal neuronal class-specific therapeutic targets. The current focus in neurodegeneration has been on individual genes and pathways. In contrast, we assembled a genome-wide regulatory model (henceforth, "interactome"), whose unbiased interrogation revealed 23 candidate causal master regulators of neurodegeneration in an in vitro model of amyotrophic lateral sclerosis (ALS), characterized by a loss of spinal motor neurons (MNs). Of these, eight were confirmed as specific MN death drivers in our model of familial ALS, including NF-κB, which has long been considered a pro-survival factor. Through an extensive array of molecular, pharmacological, and biochemical approaches, we have confirmed that neuronal NF-κB drives the degeneration of MNs in both familial and sporadic models of ALS, thus providing proof of principle that regulatory network analysis is a valuable tool for studying cell-specific mechanisms of neurodegeneration.

Spinal muscular atrophy: from tissue specificity to therapeutic strategies

Spinal muscular atrophy (SMA) is the most frequent genetic cause of death in infants and toddlers. All cases of spinal muscular atrophy result from reductions in levels of the survival motor neuron (SMN) protein, and so SMN upregulation is a focus of many preclinical and clinical studies. We examine four issues that may be important in planning for therapeutic success. First, neuromuscular phenotypes in the SMNΔ7 mouse model closely match those in human patients but peripheral disease manifestations differ, suggesting that endpoints other than mouse lifespan may be more useful in predicting clinical outcome. Second, SMN plays important roles in multiple central and peripheral cell types, not just motor neurons, and it remains unclear which of these cell types need to be targeted therapeutically. Third, should SMN-restoration therapy not be effective in all patients, blocking molecular changes downstream of SMN reduction may confer significant benefit, making it important to evaluate therapeutic targets other than SMN. Lastly, for patients whose disease progression is slowed, but who retain significant motor dysfunction, additional approaches used to enhance regeneration of the neuromuscular system may be of value.

Intermediate filament protein accumulation in motor neurons derived from giant axonal neuropathy iPSCs rescued by restoration of gigaxonin

Giant axonal neuropathy (GAN) is a progressive neurodegenerative disease caused by autosomal recessive mutations in the GAN gene resulting in a loss of a ubiquitously expressed protein, gigaxonin. Gene replacement therapy is a promising strategy for treatment of the disease; however, the effectiveness and safety of gigaxonin reintroduction have not been tested in human GAN nerve cells. Here we report the derivation of induced pluripotent stem cells (iPSCs) from three GAN patients with different GAN mutations. Motor neurons differentiated from GAN iPSCs exhibit accumulation of neurofilament (NF-L) and peripherin (PRPH) protein and formation of PRPH aggregates, the key pathological phenotypes observed in patients. Introduction of gigaxonin either using a lentiviral vector or as a stable transgene resulted in normalization of NEFL and PRPH levels in GAN neurons and disappearance of PRPH aggregates. Importantly, overexpression of gigaxonin had no adverse effect on survival of GAN neurons, supporting the feasibility of gene replacement therapy. Our findings demonstrate that GAN iPSCs provide a novel model for studying human GAN neuropathologies and for the development and testing of new therapies in relevant cell types.

Gene profiling of human induced pluripotent stem cell-derived astrocyte progenitors following spinal cord engraftment

The generation of human induced pluripotent stem cells (hiPSCs) represents an exciting advancement with promise for stem cell transplantation therapies as well as for neurological disease modeling. Based on the emerging roles for astrocytes in neurological disorders, we investigated whether hiPSC-derived astrocyte progenitors could be engrafted to the rodent spinal cord and how the characteristics of these cells changed between in vitro culture and after transplantation to the in vivo spinal cord environment. Our results show that human embryonic stem cell- and hiPSC-derived astrocyte progenitors survive long-term after spinal cord engraftment and differentiate to astrocytes in vivo with few cells from other lineages present. Gene profiling of the transplanted cells demonstrates the astrocyte progenitors continue to mature in vivo and upregulate a variety of astrocyte-specific genes. Given this mature astrocyte gene profile, this work highlights hiPSCs as a tool to investigate disease-related astrocyte biology using in vivo disease modeling with significant implications for human neurological diseases currently lacking animal models.

Necroptosis drives motor neuron death in models of both sporadic and familial ALS

Most cases of neurodegenerative diseases are sporadic, hindering the use of genetic mouse models to analyze disease mechanisms. Focusing on the motor neuron (MN) disease amyotrophic lateral sclerosis (ALS), we therefore devised a fully humanized coculture model composed of human adult primary sporadic ALS (sALS) astrocytes and human embryonic stem-cell-derived MNs. The model reproduces the cardinal features of human ALS: sALS astrocytes, but not those from control patients, trigger selective death of MNs. The mechanisms underlying this non-cell-autonomous toxicity were investigated in both astrocytes and MNs. Although causal in familial ALS (fALS), SOD1 does not contribute to the toxicity of sALS astrocytes. Death of MNs triggered by either sALS or fALS astrocytes occurs through necroptosis, a form of programmed necrosis involving receptor-interacting protein 1 and the mixed lineage kinase domain-like protein. The necroptotic pathway therefore constitutes a potential therapeutic target for this incurable disease.

Neurotrophic factors in development and plasticity of spinal neurons

Factors affecting neuronal growth may be considered to fall into two major categories: those required for neuronal survival during development or following a lesion, and those which enhance growth or regeneration of axonal or dendritic processes. We briefly review here some recent studies on the former in spinal cord development and plasticity as an introduction to other papers in the session on Factors controlling Neural Growth, and then present in more detail work on factors affecting motoneuron development in vitro. The neurotrophins are a closely-related family of basic neurotrophic factors including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) and neurotrophins -3, -4 and -5 that enhance neuronal survival by binding to surface receptors whose major components are the trk tyrosine kinases and p75NGF-R. Only the latter has been studied in the context of spinal cord neuroplasticity: its levels on motoneurons are up-regulated following central or peripheral trauma, although its function there remains unknown. Much evidence exists for the existence of 'motoneuron growth factors' involved in regulation of survival and development of spinal motoneurons. Following a critical comparison of techniques for their purification, we review results obtained in vitro and in vivo using known growth factors such as ciliary neurotrophic factor (CNTF), basic fibroblast growth factor (bFGF) and transforming growth factor (TGF/β1). Although none of them satisfies all the criteria for the embryonic 'motoneuron growth factor', CNTF is of potential interest for reducing motoneuron loss in pathological situations.

X-ROS signaling: rapid mechano-chemo transduction in heart

We report that in heart cells, physiologic stretch rapidly activates reduced-form nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) to produce reactive oxygen species (ROS) in a process dependent on microtubules (X-ROS signaling). ROS production occurs in the sarcolemmal and t-tubule membranes where NOX2 is located and sensitizes nearby ryanodine receptors (RyRs) in the sarcoplasmic reticulum (SR). This triggers a burst of Ca(2+) sparks, the elementary Ca(2+) release events in heart. Although this stretch-dependent "tuning" of RyRs increases Ca(2+) signaling sensitivity in healthy cardiomyocytes, in disease it enables Ca(2+) sparks to trigger arrhythmogenic Ca(2+) waves. In the mouse model of Duchenne muscular dystrophy, hyperactive X-ROS signaling contributes to cardiomyopathy through aberrant Ca(2+) release from the SR. X-ROS signaling thus provides a mechanistic explanation for the mechanotransduction of Ca(2+) release in the heart and offers fresh therapeutic possibilities.

Postsymptomatic restoration of SMN rescues the disease phenotype in a mouse model of severe spinal muscular atrophy

Spinal muscular atrophy (SMA) is a common neuromuscular disorder in humans. In fact, it is the most frequently inherited cause of infant mortality, being the result of mutations in the survival of motor neuron 1 (SMN1) gene that reduce levels of SMN protein. Restoring levels of SMN protein in individuals with SMA is perceived to be a viable therapeutic option, but the efficacy of such a strategy once symptoms are apparent has not been determined. We have generated mice harboring an inducible Smn rescue allele and used them in a model of SMA to investigate the effects of turning on SMN expression at different time points during the course of the disease. Restoring SMN protein even after disease onset was sufficient to reverse neuromuscular pathology and effect robust rescue of the SMA phenotype. Importantly, our findings also indicated that there was a therapeutic window of opportunity from P4 through P8 defined by the extent of neuromuscular synapse pathology and the ability of motor neurons to respond to SMN induction, following which restoration of the protein to the organism failed to produce therapeutic benefit. Nevertheless, our results suggest that even in severe SMA, timely reinstatement of the SMN protein may halt the progression of the disease and serve as an effective postsymptomatic treatment.

2010 mid-America Orthopaedic Association Physician in Training Award: healing complications are common after locked plating for distal femur fractures

BACKGROUND

Several mechanical studies suggest locking plate constructs may inhibit callus necessary for healing of distal femur fractures. However, the rate of nonunion and factors associated with nonunion are not well established.

QUESTIONS/PURPOSES

We (1) determined the healing rate of distal femur fractures treated with locking plates, (2) assessed the effect of patient injury and treatment variables on fracture healing, and (3) compared callus formation in fractures that healed with those that did not heal.

PATIENTS AND METHODS

We retrospectively reviewed 82 patients treated with 86 distal femur fractures using lateral locking plates. We reviewed all charts and radiographs to determine patient and treatment variables and then determined the effects of these variables on healing. We quantitatively measured callus at 6, 12, and 24 weeks. The minimum time for telephone interviews and SF-36v2(TM) scores was 1 year (mean, 4.2 years; range, 1-7.2 years).

RESULTS

Fourteen fractures (20%) failed to unite. Demographics and comorbidities were similar in patients who achieved healing compared with those who had nonunions. There were more empty holes in the plate adjacent to fractures that healed; comminuted fractures failed to heal more frequently than less comminuted fractures. Less callus formed in fractures with nonunions and in patients treated with stainless steel plates compared with titanium plates. Complications occurred in 28 of 70 fractures (40%), 19 of which had additional surgery.

CONCLUSIONS

We found a high rate of nonunion in distal femur fractures treated with locking plates. Nonunion presented late without hardware failure and with limited callus formation suggesting callus inhibition rather than hardware failure is the primary problem. Mechanical factors may play a role in the high rate of nonunion.

Comparison of MRI-based estimates of articular cartilage contact area in the tibiofemoral joint

Knee osteoarthritis (OA) detrimentally impacts the lives of millions of older Americans through pain and decreased functional ability. Unfortunately, the pathomechanics and associated deviations from joint homeostasis that OA patients experience are not well understood. Alterations in mechanical stress in the knee joint may play an essential role in OA; however, existing literature in this area is limited. The purpose of this study was to evaluate the ability of an existing magnetic resonance imaging (MRI)-based modeling method to estimate articular cartilage contact area in vivo. Imaging data of both knees were collected on a single subject with no history of knee pathology at three knee flexion angles. Intra-observer reliability and sensitivity studies were also performed to determine the role of operator-influenced elements of the data processing on the results. The method's articular cartilage contact area estimates were compared with existing contact area estimates in the literature. The method demonstrated an intra-observer reliability of 0.95 when assessed using Pearson's correlation coefficient and was found to be most sensitive to changes in the cartilage tracings on the peripheries of the compartment. The articular cartilage contact area estimates at full extension were similar to those reported in the literature. The relationships between tibiofemoral articular cartilage contact area and knee flexion were also qualitatively and quantitatively similar to those previously reported. The MRI-based knee modeling method was found to have high intra-observer reliability, sensitivity to peripheral articular cartilage tracings, and agreeability with previous investigations when using data from a single healthy adult. Future studies will implement this modeling method to investigate the role that mechanical stress may play in progression of knee OA through estimation of articular cartilage contact area.

Motor neuron diversity in development and disease

Although often considered as a group, spinal motor neurons are highly diverse in terms of their morphology, connectivity, and functional properties and differ significantly in their response to disease. Recent studies of motor neuron diversity have clarified developmental mechanisms and provided novel insights into neurodegeneration in amyotrophic lateral sclerosis (ALS). Motor neurons of different classes and subtypes--fast/slow, alpha/gamma--are grouped together into motor pools, each of which innervates a single skeletal muscle. Distinct mechanisms regulate their development. For example, glial cell line-derived neurotrophic factor (GDNF) has effects that are pool-specific on motor neuron connectivity, column-specific on axonal growth, and subtype-specific on survival. In multiple degenerative contexts including ALS, spinal muscular atrophy (SMA), and aging, fast-fatigable (FF) motor units degenerate early, whereas motor neurons innervating slow muscles and those involved in eye movement and pelvic sphincter control are strikingly preserved. Extrinsic and intrinsic mechanisms that confer resistance represent promising therapeutic targets in these currently incurable diseases.

Collapsin response mediator protein 4a (CRMP4a) is upregulated in motoneurons of mutant SOD1 mice and can trigger motoneuron axonal degeneration and cell death

Embryonic motoneurons from mutant SOD1 (mSOD1) mouse models of amyotrophic lateral sclerosis (ALS), but not wild-type motoneurons, can be triggered to die by exposure to nitric oxide (NO), leading to activation of a motoneuron-specific signaling pathway downstream of the death receptor Fas/CD95. To identify effectors of mSOD1-dependent cell death, we performed a proteomic analysis. Treatment of cultured mSOD1 motoneurons with NO led to a 2.5-fold increase in levels of collapsin response mediator protein 4a (CRMP4a). In vivo, the percentage of mSOD1 lumbar motoneurons expressing CRMP4 in mSOD1 mice increased progressively from presymptomatic to early-onset stages, reaching a maximum of 25%. Forced adeno-associated virus (AAV)-mediated expression of CRMP4a in wild-type motoneurons in vitro triggered a process of axonal degeneration and cell death affecting 60% of motoneurons, whereas silencing of CRMP4a in mSOD1 motoneurons protected them from NO-induced death. In vivo, AAV-mediated overexpression of CRMP4a but not CRMP2 led to the death of 30% of the lumbar motoneurons and an 18% increase in denervation of neuromuscular junctions in the gastrocnemius muscle. Our data identify CRMP4a as a potential early effector in the neurodegenerative process in ALS.

Stabilization of distal femur fractures with intramedullary nails and locking plates: differences in callus formation

OBJECTIVES

This study compared callus formation in distal femur fractures stabilized with locking plates and intramedullary nails to test the hypothesis that locking plates induce less fracture callus than IM nails.

DESIGN

Retrospective case matched study.

SETTING

Two orthopaedic trauma centers.

PATIENTS

174 distal femur fracture were reviewed to extract cases treated with retrograde IM nails (NAIL group, n = 12). These were then individually matched to cases treated with locking plates (Plate group, n = 12).

INTERVENTION

Retrograde IM nailing or locking plate fracture fixation.

OUTCOME MEASURES

Periosteal callus was measured on lateral and antero-posterior radiographs taken at 12 weeks after injury using validated software to objectively extract the size of peripheral callus from digital radiographs.

RESULTS

The NAIL group had 2.4 times more callus area per location (231 ± 304 mm(2)) than the PLATE group (95 ± 109 mm(2), p=0.028). Compared to the PLATE group, the NAIL group had 3.4 times more callus anteriorly (p=0.31), 2.6 times more callus posteriorly (p=0.25), and 2.3 times more callus medially (p=0.16). At 12 weeks after injury, no or minimal callus for secondary bone healing (<20 mm(2)) was present in 20% of callus locations in the NAIL group and in 54% of callus locations in the PLATE group.

CONCLUSION

Significantly less periosteal callus formed in fractures stabilized with locking plates than with IM nails. This result is likely multifactorial and further study of the interaction between construct stiffness and fracture healing in the distal femur is warranted.

Signaling by death receptors in the nervous system

Cell death plays an important role both in shaping the developing nervous system and in neurological disease and traumatic injury. In spite of their name, death receptors can trigger either cell death or survival and growth. Recent studies implicate five death receptors--Fas/CD95, TNFR1 (tumor necrosis factor receptor-1), p75NTR (p75 neurotrophin receptor), DR4, and DR5 (death receptors-4 and -5)--in different aspects of neural development or degeneration. Their roles may be neuroprotective in models of Parkinson's disease, or pro-apoptotic in ALS and stroke. Such different outcomes probably reflect the diversity of transcriptional and posttranslational signaling pathways downstream of death receptors in neurons and glia.

Induced pluripotent stem cells generated from patients with ALS can be differentiated into motor neurons

The generation of pluripotent stem cells from an individual patient would enable the large-scale production of the cell types affected by that patient's disease. These cells could in turn be used for disease modeling, drug discovery, and eventually autologous cell replacement therapies. Although recent studies have demonstrated the reprogramming of human fibroblasts to a pluripotent state, it remains unclear whether these induced pluripotent stem (iPS) cells can be produced directly from elderly patients with chronic disease. We have generated iPS cells from an 82-year-old woman diagnosed with a familial form of amyotrophic lateral sclerosis (ALS). These patient-specific iPS cells possess properties of embryonic stem cells and were successfully directed to differentiate into motor neurons, the cell type destroyed in ALS.

Gating of Sema3E/PlexinD1 signaling by neuropilin-1 switches axonal repulsion to attraction during brain development

The establishment of functional neural circuits requires the guidance of axons in response to the actions of secreted and cell-surface molecules such as the semaphorins. Semaphorin 3E and its receptor PlexinD1 are expressed in the brain, but their functions are unknown. Here, we show that Sema3E/PlexinD1 signaling plays an important role in initial development of descending axon tracts in the forebrain. Early errors in axonal projections are reflected in behavioral deficits in Sema3E null mutant mice. Two distinct signaling mechanisms can be distinguished downstream of Sema3E. On corticofugal and striatonigral neurons expressing PlexinD1 but not Neuropilin-1, Sema3E acts as a repellent. In contrast, on subiculo-mammillary neurons coexpressing PlexinD1 and Neuropilin-1, Sema3E acts as an attractant. The extracellular domain of Neuropilin-1 is sufficient to convert repulsive signaling by PlexinD1 to attraction. Our data therefore reveal a "gating" function of neuropilins in semaphorin-plexin signaling during the assembly of forebrain neuronal circuits.

Does locked plating of periprosthetic supracondylar femur fractures promote bone healing by callus formation? Two cases with opposite outcomes

Contemporary locking plates promote biological fixation through indirect reduction techniques and by elevating the plate from the bone. They have improved fixation strength in osteoporotic bone. Periarticular locking plates are rapidly being adopted for bridge plating of periprosthetic femur fractures. When these plates are used for indirect reduction and bridge plating osteosynthesis, fracture union occurs by secondary bone healing with callus formation which is stimulated by interfragmentary motion. In two patients with similar periprosthetic femur fractures treated with periarticular locking plates one fracture healed by ample callus formation while the other resulted in a non-union and had no callus formation six months post-operatively. The case, which progressed to secondary bone healing with callus formation, exhibited varus migration as a result of loss of fixation. The non-union case retained stable fixation. The difference in outcome may indicate that callus formation was promoted by interfragmentary motion secondary to loss of fixation. Conversely, in absence of fixation failure, callus formation was suppressed by stable fixation with a stiff locking plate construct which reduced interfragmentary motion. These observations suggest that locked plating constructs should be sufficiently flexible when applied for bridge plating of comminuted fractures to promote callus formation.

The role of muscle in the development and differentiation of spinal motoneurons: in vitro studies

Results of in vivo experiments suggest that muscle cells, and probably other cell types, produce factors upon which motoneurons depend for survival and normal development. Most attempts to characterize such factors have used cultures of enriched or identified motoneurons, and have studied effects of muscle-derived substances on survival, neurite outgrowth and acetylcholine synthesis. Results from different laboratories vary widely, both in terms of the estimated abundance of motoneurons as a fraction of total dissociated spinal cord and in terms of the molecular weight estimates for factors tentatively proposed as candidate motoneuron growth factors. Nevertheless, there are several independent reports of 40-55 kDa species affecting each of the three parameters of spinal neuron development. We have begun to characterize one of these, partially purified from extracts of denervated muscle on the basis of its neurite-promoting activity for a subpopulation of 4.5-day embryonic chicken spinal neurons. Comparison between the factors under study in different systems, and confirmation of their importance in vivo, await the preparation of specific blocking antibodies.

Identification and characterization of cholest-4-en-3-one, oxime (TRO19622), a novel drug candidate for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by progressive death of cortical and spinal motor neurons, for which there is no effective treatment. Using a cell-based assay for compounds capable of preventing motor neuron cell death in vitro, a collection of approximately 40,000 low-molecular-weight compounds was screened to identify potential small-molecule therapeutics. We report the identification of cholest-4-en-3-one, oxime (TRO19622) as a potential drug candidate for the treatment of ALS. In vitro, TRO19622 promoted motor neuron survival in the absence of trophic support in a dose-dependent manner. In vivo, TRO19622 rescued motor neurons from axotomy-induced cell death in neonatal rats and promoted nerve regeneration following sciatic nerve crush in mice. In SOD1(G93A) transgenic mice, a model of familial ALS, TRO19622 treatment improved motor performance, delayed the onset of the clinical disease, and extended survival. TRO19622 bound directly to two components of the mitochondrial permeability transition pore: the voltage-dependent anion channel and the translocator protein 18 kDa (or peripheral benzodiazepine receptor), suggesting a potential mechanism for its neuroprotective activity. TRO19622 may have therapeutic potential for ALS and other motor neuron and neurodegenerative diseases.

Neural adhesion molecules L1 and CHL1 are survival factors for motoneurons

Many neurotrophic factors with survival activity for motoneurons in vivo were first identified using cultures of purified embryonic motoneurons. The L1 neural cell adhesion molecule has multiple roles in brain development. We showed by in situ hybridization and RT-PCR that L1 mRNA was expressed at significant levels in motoneurons of embryonic and postnatal spinal cord. We therefore cultured purified motoneurons from E14 rat embryos in the absence of trophic factors but with L1-Fc and CHL1-Fc fusion proteins. L1-Fc prevented the death of approximately half of the motoneurons that were saved by BDNF in a dose-dependent manner (EC50 = 10 pM). CHL1-Fc saved the same number of motoneurons as did L1-Fc, whereas P0-Fc had little neurotrophic activity at the same concentrations. Survival induced by L1 and CHL1 was completely inhibited by 20 microM LY294002 and PD98059, indicating that both MEK and PI3K pathways are required for signaling by these molecules. L1 can signal in other cell types through the FGF receptor FGFR1. In cultures of motoneurons, effects of suboptimal concentrations of L1 and suboptimal concentrations of FGF-2 were additive, but the effects of optimal concentrations of FGF-2 (50 ng/ml) were not further increased in the presence of L1-Fc. Thus, in this system, too, FGF and L1 may use similar signaling pathways.

A semaphorin code defines subpopulations of spinal motor neurons during mouse development

Abstract In the spinal cord, motor neurons (MNs) with similar muscle targets and sensory inputs are grouped together into motor pools. To date, relatively little is known about the molecular mechanisms that control the establishment of pool-specific circuitry. Semaphorins, a large family of secreted and cell surface proteins, are important mediators of developmental processes such as axon guidance and cell migration. Here, we used mRNA in situ hybridization to study the expression patterns of semaphorins and their receptors, neuropilins and plexins, in the embryonic mouse spinal cord. Our data show that semaphorins and their receptors are differentially expressed in MNs that lie in distinct locations within the spinal cord. Furthermore, we report a combinatorial expression of class 3 (secreted) semaphorins and their receptors that characterizes distinct motor pools within the brachial and lumbar spinal cord. Finally, we found that a secreted semaphorin, Sema3A, elicits differential collapse responses in topologically distinct subpopulations of spinal MNs. These findings lead us to propose that semaphorins and their receptors might play important roles in the sorting of motor pools and the patterning of their afferent and efferent projections.

Lentiviral-mediated silencing of SOD1 through RNA interference retards disease onset and progression in a mouse model of ALS

Mutations in Cu/Zn superoxide dismutase (encoded by SOD1), one of the causes of familial amyotrophic lateral sclerosis (ALS), lead to progressive death of motoneurons through a gain-of-function mechanism. RNA interference (RNAi) mediated by viral vectors allows for long-term reduction in gene expression and represents an attractive therapeutic approach for genetic diseases characterized by acquired toxic properties. We report that in SOD1(G93A) transgenic mice, a model for familial ALS, intraspinal injection of a lentiviral vector that produces RNAi-mediated silencing of SOD1 substantially retards both the onset and the progression rate of the disease.

Expression of vesicular glutamate transporters, VGLUT1 and VGLUT2, in cholinergic spinal motoneurons

Mammalian spinal motoneurons are cholinergic neurons that have long been suspected to use also glutamate as a neurotransmitter. We report that VGLUT1 and VGLUT2, two subtypes of vesicular glutamate transporters, are expressed in rat spinal motoneurons. Both proteins are present in somato-dendritic compartments as well as in axon terminals in primary cultures of immunopurified motoneurons and sections of spinal cord from adult rat. However, VGLUT1 and VGLUT2 are not found at neuromuscular junctions of skeletal muscles. After intracellular injection of biocytin in motoneurons, VGLUT2 is observed in anterogradely labelled terminals contacting Renshaw inhibitory interneurons. These VGLUT2- and VGLUT1-positive terminals do not express VAChT, the vesicular acetylcholine transporter. Overall, our study establishes for the first time that (i) mammalian spinal motoneurons express vesicular glutamate transporters, (ii) these motoneurons have the potential to release glutamate (in addition to acetylcholine) at terminals contacting Renshaw cells, and finally (iii) the VGLUTs are not present at neuromuscular synapses of skeletal muscles.

Foxo3a induces motoneuron death through the Fas pathway in cooperation with JNK

Background

Programmed cell death of motoneurons in the developing spinal cord is thought to be regulated through the availability of target-derived neurotrophic factors. When deprived of trophic support, embryonic spinal motoneurons in vitro over-express FasL, a ligand activating a Fas-mediated death pathway. How trophic factors regulate the expression of FasL is presently unclear, but two regulators of FasL, FOXO3a (FKHRL1) and JNK have been described to play a role in other cell types. Thus, their potential function in motoneurons was investigated in this study.

Results

We show here that as a result of removal of neurotrophic factors and the consequent reduction in signalling through the PI3K/Akt pathway, Foxo3a translocates from the cytoplasm to the nucleus where it triggers cell death. Death is reduced in Fas and FasL mutant motoneurons and in the presence of JNK inhibitors indicating that a significant part of it requires activation of the Fas/FasL pathway through JNK.

Conclusions

Therefore, in motoneurons as in other cell types, FOXO transcriptional regulators provide an important link between other signalling pathways and the cell death machinery.

Semaphorin 3E and plexin-D1 control vascular pattern independently of neuropilins

The development of a patterned vasculature is essential for normal organogenesis. We found that signaling by semaphorin 3E (Sema3E) and its receptor plexin-D1 controls endothelial cell positioning and the patterning of the developing vasculature in the mouse. Sema3E is highly expressed in developing somites, where it acts as a repulsive cue for plexin-D1-expressing endothelial cells of adjacent intersomitic vessels. Sema3E-plexin-D1 signaling did not require neuropilins, which were previously presumed to be obligate Sema3 coreceptors. Moreover, genetic ablation of Sema3E or plexin-D1 but not neuropilin-mediated Sema3 signaling disrupted vascular patterning. These findings reveal an unexpected semaphorin signaling pathway and define a mechanism for controlling vascular patterning.

The b1 isoform of protocadherin-gamma (Pcdhγ) interacts with the microtubule-destabilizing protein SCG10

Due to their structural characteristics and their diversity, the 22 members of the protocadherin-gamma (Pcdhgamma) family have been suggested to contribute to the establishment of specific connections in the nervous system. Here, we focus on a single isoform, Pcdhgamma-b1. Its expression is found in different brain regions and in developing spinal cord it is restricted to scattered cells, whereas all cells are labeled using an antibody that recognizes all Pcdhgamma isoforms. As a first step to understanding the signaling mechanisms downstream of Pcdhgamma, we identify the microtubule-destabilizing protein SCG10 as a cytoplasmic interactor for Pcdhgamma-b1 and other isoforms of the Pcdhgamma-b subfamily, and show that SCG10 and Pcdhgamma-b1 are found together in certain neuronal growth cones.

The CES-2-related transcription factor E4BP4 is an intrinsic regulator of motoneuron growth and survival

The regulation of neuronal growth and survival during development requires interplay between extrinsic and intrinsic factors. Among the latter,transcription factors play a key role. In the nematode, the transcription factor CES-2 predisposes neurosecretory motoneurons to death, whereas E4BP4(NFIL3), one of its vertebrate homologs, regulates survival of pro-B lymphocytes. We show that E4BP4 is expressed by embryonic rat and chicken motoneurons in vivo, with levels being highest in neurons that survive the period of naturally occurring cell death. Overexpression of E4BP4 by electroporation of purified motoneurons in culture protected them almost completely against cell death triggered by removal of neurotrophic factors or activation of death receptors. Moreover, E4BP4 strongly enhanced neuronal cell size and axonal growth. Axons of motoneurons transfected with E4BP4 were 3.5-fold longer than control neurons grown on laminin; this effect required the activity of PI3 kinase. In vivo, overexpression of E4BP4 in chicken embryos reduced the number of dying motoneurons by 45%. Our results define E4BP4 as a novel intrinsic regulator of motoneuron growth and survival. Pathways regulated by E4BP4 are of potential interest both for understanding neuromuscular development and for promoting neuronal survival and regeneration in pathological situations.