Victoria C. Williams

A longitudinal study of diffusion tensor MRI in ALS

In this study, we investigated whether diffusion tensor MRI (DTI) could detect progressive corticospinal tract degeneration in amyotrophic lateral sclerosis (ALS) and whether changes in diffusion variables reflected clinical deterioration. Twenty‐three ALS patients and 25 healthy volunteers underwent whole brain DTI. Patients and a subset (n = 12) of controls returned for a second scan. Clinical measures of disease severity were assessed in the ALS group. Changes in fractional anisotropy (FA) and mean diffusivity (MD) were measured along the corticospinal tract using a region of interest approach. Adequate DTI data were available in 11 ALS patients and 11 controls at two time points. FA and MD differed significantly between ALS patients and controls at both time points, but neither changed significantly over time, while global measures of disease severity in patients increased with time. Although we confirmed that DTI detects corticospinal tract damage in ALS, there were no significant changes in diffusion measures over time. The sensitivity of DTI may be improved by advanced data analysis techniques, although the high dropout rate suggests that use of MRI as a biomarker in ALS may be restricted to earlier stages of disease.

Altered cortical activation during a motor task in ALS - Evidence for involvement of central pathways

ObjectiveTo test the hypothesis that patients with amyotrophic lateral sclerosis (ALS) show increased cortical activation during a motor task compared to both healthy controls and patients with muscle weakness due to peripheral lesions.MethodsFunctional magnetic resonance imaging (fMRI) was used to measure activation during a block design paradigm contrasting right hand movements against rest in sixteen patients with ALS, seventeen healthy controls and nine patients with peripheral lesions. The groups were matched for age and gender and the two patient groups were matched for their degree of upper limb weakness. Analysis used a non-parametric approach to perform a 3 way hypothesis-driven comparison between the groups.ResultsDuring the motor task, patients with ALS showed increased cortical activation bilaterally, extending from the sensorimotor cortex [Brodmann areas (BA) 1, 2, 4] posteriorly into the inferior parietal lobule (BA 40) and inferiorly to the superior temporal gyrus (BA 22) when compared to peripheral lesion patients and controls. In addition, ALS patients showed reduced activation in the dorsolateral prefrontal cortex (DLPFC) extending to anterior and medial frontal cortex (BA 8, 9, 10, 32).ConclusionsWe conclude that alterations in cortical function in ALS differ in sensorimotor and prefrontal regions. Importantly, we have shown that these changes do not reflect confounding by weakness or task difficulty, but are likely to be related to upper motor neuron pathology in ALS.

Defective cranial skeletal development, larval lethality and haploinsufficiency in Myod mutant zebrafish.

Myogenic regulatory factors of the myod family (MRFs) are transcription factors essential for mammalian skeletal myogenesis. Here we show that a mutation in the zebrafish myod gene delays and reduces early somitic and pectoral fin myogenesis, reduces miR-206 expression, and leads to a persistent reduction in somite size until at least the independent feeding stage. A mutation in myog, encoding a second MRF, has little obvious phenotype at early stages, but exacerbates the loss of somitic muscle caused by lack of Myod. Mutation of both myod and myf5 ablates all skeletal muscle. Haploinsufficiency of myod leads to reduced embryonic somite muscle bulk. Lack of Myod causes a severe reduction in cranial musculature, ablating most muscles including the protractor pectoralis, a putative cucullaris homologue. This phenotype is accompanied by a severe dysmorphology of the cartilaginous skeleton and failure of maturation of several cranial bones, including the opercle. As myod expression is restricted to myogenic cells, the data show that myogenesis is essential for proper skeletogenesis in the head.

Diffusion tensor imaging in sporadic and familial (D90A SOD1) forms of amyotrophic lateral sclerosis.

BACKGROUND The basis of heterogeneity in the clinical presentation and rate of progression of amyotrophic lateral sclerosis (ALS) is poorly understood. OBJECTIVES To use diffusion tensor imaging as a measure of axonal pathologic features in vivo in ALS and to compare a homogeneous form of familial ALS (homozygous D90A SOD1 [superoxide dismutase 1]) with sporadic ALS. DESIGN Cross-sectional diffusion tensor imaging study. SETTING Tertiary referral neurology clinic. PATIENTS Twenty patients with sporadic ALS, 6 patients with homozygous D90A SOD1 ALS, and 21 healthy control subjects. MAIN OUTCOME MEASURE Fractional anisotropy in cerebral white matter. RESULTS Patients with homozygous D90A SOD1 ALS showed less extensive pathologic white matter in motor and extramotor pathways compared with patients with sporadic ALS, despite similar disease severity assessed clinically using a standard functional rating scale. Fractional anisotropy correlated with clinical measures of severity and upper motor neuron involvement. CONCLUSION In vivo diffusion tensor imaging measures demonstrate differences in white matter degeneration between sporadic ALS and a unique familial form of the disease, indicating that genotype influences the distribution of cerebral pathologic features in ALS.

Differential corticospinal tract degeneration in homozygous ‘D90A’ SOD-1 ALS and sporadic ALS

Background The homogeneous genotype and stereotyped phenotype of a unique familial form of amyotrophic lateral sclerosis (ALS) (patients homozygous for aspartate-to-alanine mutations in codon 90 (homD90A) superoxide dismutase 1) provides an ideal model for studying genotype/phenotype interactions and pathological features compared with heterogeneous apparently sporadic ALS. The authors aimed to use diffusion tensor tractography to quantify and compare changes in the intracerebral corticospinal tracts of patients with both forms of ALS, building on previous work using whole-brain voxelwise group analysis. Method 21 sporadic ALS patients, seven homD90A patients and 20 healthy controls underwent 1.5 T diffusion tensor MRI. Patients were assessed using ‘upper motor neuron burden,’ El Escorial and ALSFR-R scales. The intracranial corticospinal tract was assessed using diffusion tensor tractography measures of fractional anisotropy (FA), mean diffusivity, and radial and axial diffusivity obtained from its entire length. Results Corticospinal tract FA was reduced in sporadic ALS patients compared with both homD90A ALS patients and controls. The diffusion measures in sporadic ALS patients were consistent with anterograde (Wallerian) degeneration of the corticospinal tracts. In sporadic ALS, corticospinal tract FA was related to clinical measures. Despite a similar degree of clinical upper motor neuron dysfunction and disability in homD90A ALS patients compared with sporadic ALS, there were no abnormalities in corticospinal tract diffusion measures compared with controls. Conclusions Diffusion tensor tractography has shown axonal degeneration within the intracerebral portion of the corticospinal tract in sporadic ALS patients, but not those with a homogeneous form of familial ALS. This suggests significant genotypic influences on the phenotype of ALS and may provide clues to slower progression of disease in homD90A patients.

Cooperation between Shh and IGF-I in Promoting Myogenic Proliferation and Differentiation via the MAPK/ERK and PI3K/Akt Pathways Requires Smo Activity

Sonic Hedgehog (Shh) has been shown to promote adult myoblast proliferation and differentiation and affect Akt phosphorylation via its effector Smoothened (Smo). Here, the relationship between Shh and insulin‐like growth factor I (IGF‐I) was examined with regard to myogenic differentiation via signaling pathways which regulate this process. Each factor enhanced Akt and MAPK/ERK (p42/44) phosphorylation and myogenic factor expression levels in a dose‐responsive manner, while combinations of Shh and IGF‐I showed additive effects. Blockage of the IGF‐I effects by neutralizing antibody partially reduced Shhs effects on signaling pathways, suggesting that IGF‐I enhances, but is not essential for Shh effects. Addition of cyclopamine, a Smo inhibitor, reduced Shh‐ and IGF‐I‐induced Akt phosphorylation in a similar manner, implying that Shh affects gain of the IGF‐I signaling pathway. This implication was also examined via a genetic approach. In cultures derived from Smomut (MCre;Smoflox/flox) mice lacking Smo expression specifically in hindlimb muscles, IGF‐I‐induced Akt and p42/44 phosphorylation was significantly reduced compared to IGF‐Is effect on Smocont cells. Moreover, remarkable inhibition of the stimulatory effect of IGF‐I on myogenic differentiation was observed in Smomut cultures, implying that intact Smo is required for IGF‐I effects in myoblasts. Immunoprecipitation assays revealed that tyrosine‐phosphorylated proteins, including the regulatory unit of PI3K (p85), are recruited to Smo in response to Shh. Moreover, IGF‐IR was found to associate with Smo in response to Shh and to IGF‐I, suggesting that Shh and IGF‐I are already integrated at the receptor level, a mechanism by which their signaling pathways interact in augmenting their effects on adult myoblasts. J. Cell. Physiol. 227: 1455–1464, 2012.

Sonic hedgehog acts cell-autonomously on muscle precursor cells to generate limb muscle diversity

How muscle diversity is generated in the vertebrate body is poorly understood. In the limb, dorsal and ventral muscle masses constitute the first myogenic diversification, as each gives rise to distinct muscles. Myogenesis initiates after muscle precursor cells (MPCs) have migrated from the somites to the limb bud and populated the prospective muscle masses. Here, we show that Sonic hedgehog (Shh) from the zone of polarizing activity (ZPA) drives myogenesis specifically within the ventral muscle mass. Shh directly induces ventral MPCs to initiate Myf5 transcription and myogenesis through essential Gli-binding sites located in the Myf5 limb enhancer. In the absence of Shh signaling, myogenesis is delayed, MPCs fail to migrate distally, and ventral paw muscles fail to form. Thus, Shh production in the limb ZPA is essential for the spatiotemporal control of myogenesis and coordinates muscle and skeletal development by acting directly to regulate the formation of specific ventral muscles.

Cortical activation during motor imagery is reduced in Amyotrophic Lateral Sclerosis

The neural correlates of motor execution in Amyotrophic Lateral Sclerosis (ALS) are challenging to investigate due to muscle weakness. Alternatives to traditional motor execution paradigms are therefore of great interest. This study tested the hypothesis that patients with Amyotrophic Lateral Sclerosis (ALS) would show increased cortical activation during motor imagery compared to healthy controls, as seen in studies of motor execution. Functional MRI was used to measure activation during a block design paradigm contrasting imagery of right hand movements against rest in 16 patients with ALS and 17 age-matched healthy controls. Patients with ALS showed reduced activation during motor imagery in the left inferior parietal lobule, and in the anterior cingulate gyrus and medial pre-frontal cortex. This reduction in cortical activation during motor imagery contrasts with the pattern seen during motor execution. This may represent the disruption of normal motor imagery networks by ALS pathology outside the primary motor cortex.

eIF4EBP3L acts as a gatekeeper of TORC1 in activity-dependent muscle growth by specifically regulating Mef2ca translational initiation.

Muscle activity promotes muscle growth through the TOR-4EBP pathway by controlling the translation of specific mRNAs, including Mef2ca, a muscle transcription factor required for normal growth.

Oesophageal and sternohyal muscle fibres are novel Pax3-dependent migratory somite derivatives essential for ingestion

Striated muscles that enable mouth opening and swallowing during feeding are essential for efficient energy acquisition, and are likely to have played a fundamental role in the success of early jawed vertebrates. The developmental origins and genetic requirements of these muscles are uncertain. Here, we determine by indelible lineage tracing in mouse that fibres of sternohyoid muscle (SHM), which is essential for mouth opening during feeding, and oesophageal striated muscle (OSM), which is crucial for voluntary swallowing, arise from Pax3-expressing somite cells. In vivo Kaede lineage tracing in zebrafish reveals the migratory route of cells from the anteriormost somites to OSM and SHM destinations. Expression of pax3b, a zebrafish duplicate of Pax3, is restricted to the hypaxial region of anterior somites that generate migratory muscle precursors (MMPs), suggesting that Pax3b plays a role in generating OSM and SHM. Indeed, loss of pax3b function led to defective MMP migration and OSM formation, disorganised SHM differentiation, and inefficient ingestion and swallowing of microspheres. Together, our data demonstrate Pax3-expressing somite cells as a source of OSM and SHM fibres, and highlight a conserved role of Pax3 genes in the genesis of these feeding muscles of vertebrates.