Systemic Administration of Epothilone B Promotes Axon Regeneration and Functional Recovery after Spinal Cord Injury

After central nervous system (CNS) injury, such as a traumatic spinal cord injury (SCI), damaged axons fail to regenerate resulting in a permanent loss of sensorimotor functions. Regeneration is prevented by growth inhibitory factors in the lesion scar and in CNS myelin as well as by a poor axon intrinsic growth potential. Microtubule dynamics regulate key processes that are instrumental in regeneration including axon growth and scar formation. Moderate microtubule stabilization by the anti-cancer drug Taxol promotes axon integrity and axons growth and prevents the formation of the lesion scar leading to enhanced axon regeneration after SCI. However, Taxol is impractical for clinical situations. Due its poor blood-brain-barrier permeability Taxol requires CNS invasive delivery bearing the risk of additional neuronal tissue damage. Here, I report that systemic and post-injury administration of epothilone B, a microtubule stabilizing drug that crosses the blood-brain barrier, has beneficial effects after SCI. Systemic administration of epothilone B decreases fibrotic scarring in spinal cord injured rodents by disrupting cell polarity of meningeal fibroblasts, which abrogates directed cell migration. Time lapse microscopy and in vivo live imaging of individual axons reveal that epothilone B allows the microtubular network to protrude into the distal tip of the axon to propel axon growth through an otherwise inhibitory environment. Finally, epothilone B improves gait and coordinated walking after thoracic spinal cord contusion injury. As the epothilone B derivative ixabepilone received clinical approval, these data suggest that epothilones hold promise for clinical translation in enabling axon regeneration and functional recovery after central nervous system injury

Systemic epothilone D improves hindlimb function after spinal cord contusion injury in rats

Following a spinal cord injury (SCI) a growth aversive environment forms, consisting of a fibroglial scar and inhibitory factors, further restricting the already low intrinsic growth potential of injured adult central nervous system (CNS) neurons. Previous studies have shown that local administration of the microtubule-stabilizing drug paclitaxel or epothilone B (Epo B) reduce fibrotic scar formation and axonal dieback as well as induce axonal growth/sprouting after SCI. Likewise, systemic administration of Epo B promoted functional recovery. In this study, we investigated the effects of epothilone D (Epo D), an analog of Epo B with a possible greater therapeutic index, on fibrotic scarring, axonal sprouting and functional recovery after SCI. Delayed systemic administration of Epo D after a moderate contusion injury (150 kDyn) in female Fischer 344 rats resulted in a reduced number of footfalls when crossing a horizontal ladder at 4 and 8 weeks post-injury. Hindlimb motor function assessed with the BBB open field locomotor rating scale and Catwalk gait analysis were not significantly altered. Moreover, formation of laminin positive fibrotic scar tissue and 5-HT positive serotonergic fiber length caudal to the lesion site were not altered after treatment with Epo D. These findings recapitulate a functional benefit after systemic administration of a microtubule-stabilizing drug in rat contusion SCI

Rhythmicity in Mice Selected for Extremes in Stress Reactivity: Behavioural, Endocrine and Sleep Changes Resembling Endophenotypes of Major Depression

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, including hyper- or hypo-activity of the stress hormone system, plays a critical role in the pathophysiology of mood disorders such as major depression (MD). Further biological hallmarks of MD are disturbances in circadian rhythms and sleep architecture. Applying a translational approach, an animal model has recently been developed, focusing on the deviation in sensitivity to stressful encounters. This so-called 'stress reactivity' (SR) mouse model consists of three separate breeding lines selected for either high (HR), intermediate (IR), or low (LR) corticosterone increase in response to stressors.In order to contribute to the validation of the SR mouse model, our study combined the analysis of behavioural and HPA axis rhythmicity with sleep-EEG recordings in the HR/IR/LR mouse lines. We found that hyper-responsiveness to stressors was associated with psychomotor alterations (increased locomotor activity and exploration towards the end of the resting period), resembling symptoms like restlessness, sleep continuity disturbances and early awakenings that are commonly observed in melancholic depression. Additionally, HR mice also showed neuroendocrine abnormalities similar to symptoms of MD patients such as reduced amplitude of the circadian glucocorticoid rhythm and elevated trough levels. The sleep-EEG analyses, furthermore, revealed changes in rapid eye movement (REM) and non-REM sleep as well as slow wave activity, indicative of reduced sleep efficacy and REM sleep disinhibition in HR mice.Thus, we could show that by selectively breeding mice for extremes in stress reactivity, clinically relevant endophenotypes of MD can be modelled. Given the importance of rhythmicity and sleep disturbances as biomarkers of MD, both animal and clinical studies on the interaction of behavioural, neuroendocrine and sleep parameters may reveal molecular pathways that ultimately lead to the discovery of new targets for antidepressant drugs tailored to match specific pathologies within MD

Sleep disturbances in highly stress reactive mice: Modeling endophenotypes of major depression

<p>Abstract</p> <p>Background</p> <p>Neuronal mechanisms underlying affective disorders such as major depression (MD) are still poorly understood. By selectively breeding mice for high (HR), intermediate (IR), or low (LR) reactivity of the hypothalamic-pituitary-adrenocortical (HPA) axis, we recently established a new genetic animal model of extremes in stress reactivity (SR). Studies characterizing this SR mouse model on the behavioral, endocrine, and neurobiological levels revealed several similarities with key endophenotypes observed in MD patients. HR mice were shown to have changes in rhythmicity and sleep measures such as rapid eye movement sleep (REMS) and non-REM sleep (NREMS) as well as in slow wave activity, indicative of reduced sleep efficacy and increased REMS. In the present study we were interested in how far a detailed spectral analysis of several electroencephalogram (EEG) parameters, including relevant frequency bands, could reveal further alterations of sleep architecture in this animal model. Eight adult males of each of the three breeding lines were equipped with epidural EEG and intramuscular electromyogram (EMG) electrodes. After recovery, EEG and EMG recordings were performed for two days.</p> <p>Results</p> <p>Differences in the amount of REMS and wakefulness and in the number of transitions between vigilance states were found in HR mice, when compared with IR and LR animals. Increased frequencies of transitions from NREMS to REMS and from REMS to wakefulness in HR animals were robust across the light-dark cycle. Detailed statistical analyses of spectral EEG parameters showed that especially during NREMS the power of the theta (6-9 Hz), alpha (10-15 Hz) and eta (16-22.75 Hz) bands was significantly different between the three breeding lines. Well defined distributions of significant power differences could be assigned to different times during the light and the dark phase. Especially during NREMS, group differences were robust and could be continuously monitored across the light-dark cycle.</p> <p>Conclusions</p> <p>The HR mice, i.e. those animals that have a genetic predisposition to hyper-activating their HPA axis in response to stressors, showed disturbed patterns in sleep architecture, similar to what is known from depressed patients. Significant alterations in several frequency bands of the EEG, which also seem to at least partly mimic clinical observations, suggest the SR mouse lines as a promising animal model for basic research of mechanisms underlying sleep impairments in MD.</p

Distribution of motor activity over the 24-h light-dark cycle in high (HR), intermediate (IR), and low (LR) reactivity males from generation VII.

<p>Data are given as means±SEM for each line. Statistical differences between the three lines are indicated by asterisks (KWH-tests, for details see text, p<0.05 *). The dark phase of the light-dark cycle is indicated by the shaded area.</p

Distribution of vigilance states over the 24-h light-dark cycle in high (HR), intermediate (IR), and low (LR) reactivity males from generation VII.

<p>The relative amount of wakefulness, non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep are plotted in panel A, B and C, respectively. Data are given as means±SEM for HR and LR mice and as SEM-area for the IR mouse line. Statistical differences between the three lines are indicated by asterisks (KWH-tests, for details see text, p<0.05 *). The dark phase of the light-dark cycle is indicated by the shaded area.</p

Diurnal variation of immunoreactive corticosterone metabolites (CM) in faecal samples of high (HR), intermediate (IR), and low (LR) reactivity males from generation VII over the 24-h light-dark cycle.

<p>Data are given as means±SEM for each line. Statistical differences between the three lines are indicated by asterisks (KWH-tests, for details see text, p<0.05 *, p<0.01 **, p<0.001 ***). The dark phase of the light-dark cycle is indicated by the shaded area.</p

Corticosterone increase in the stress reactivity test (SRT) of the experimental animals selected from the seventh generation of the high (HR), intermediate (IR) and low (LR) reactivity mouse lines.

<p>Data are given as box plots showing medians (lines in the boxes), 25% and 75% percentiles (boxes) as well as 10% and 90% percentiles (whiskers). Statistical differences between the three lines (KWH-test, for details see text) are given at the top of the panel and results of the pairwise group comparisons (post-hoc MWU-tests) are indicated below (Bonferroni corrected p<0.001 ***).</p