Identification of B6SJL mSOD1(G93A) mouse subgroups with different disease progression rates

Assessing neuraxial microstructural changes in a transgenic mouse model of early stage Amyotrophic Lateral Sclerosis by ultra-high field MRI and diffusion tensor metrics

OBJECTIVE

Cell structural changes are one of the main features observed during the development of amyotrophic lateral sclerosis (ALS). In this work, we propose the use of diffusion tensor imaging (DTI) metrics to assess specific ultrastructural changes in the central nervous system during the early neurodegenerative stages of ALS.

METHODS

Ultra-high field MRI and DTI data at 17.6T were obtained from fixed, excised mouse brains, and spinal cords from ALS (G93A-SOD1) mice.

RESULTS

Changes in fractional anisotropy (FA) and linear, planar, and spherical anisotropy ratios (CL, CP, and CS, respectively) of the diffusion eigenvalues were measured in white matter (WM) and gray matter (GM) areas associated with early axonal degenerative processes (in both the brain and the spinal cord). Specifically, in WM structures (corpus callosum, corticospinal tract, and spinal cord funiculi) as the disease progressed, FA, CL, and CP values decreased, whereas CS values increased. In GM structures (prefrontal cortex, hippocampus, and central spinal cord) FA and CP decreased, whereas the CL and CS values were unchanged or slightly smaller. Histological studies of a fluorescent mice model (YFP, G93A-SOD1 mouse) corroborated the early alterations in neuronal morphology and axonal connectivity measured by DTI.

CONCLUSIONS

Changes in diffusion tensor shape were observed in this animal model at the early, nonsymptomatic stages of ALS. Further studies of CL, CP, and CS as imaging biomarkers should be undertaken to refine this neuroimaging tool for future clinical use in the detection of the early stages of ALS.

Carboxyl-terminal modulator protein regulates Akt signaling during skeletal muscle atrophy in vitro and a mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neuromuscular disease involving motor neuron death, paralysis and, ultimately, respiratory failure. Motor neuron dysfunction leads to target skeletal muscle atrophy involving dysregulation of downstream cell survival, growth and metabolic signaling. Decreased Akt activity is linked to muscle atrophy in ALS and is associated with increased atrophy gene expression. Unfortunately, the regulating mechanism of Akt activity in atrophic muscle remains unclear. Recent research indicates a role of carboxyl-terminal modulator protein (CTMP) in Akt-signaling related neurologic dysfunction and skeletal muscle metabolism. CTMP is known to bind and reduce Akt phosphorylation and activation. We hypothesized that CTMP expression might progressively increase in ALS skeletal muscle as the disease progresses, downregulating Akt activity. We found that CTMP protein expression significantly increased in hindlimb skeletal muscle in the mSOD1^G93A mouse model of ALS in late stages of the disease (P < 0.05), which negatively correlated with Akt phosphorylation over this period (R² = -0.77). Co-immunoprecipitation of Akt revealed CTMP binding in pre-symptomatic and end-stage skeletal muscle, suggesting a possible direct role in reduced Akt signaling during disease progression. Inflammatory TNFα and downstream cellular degradation process markers for autophagy, lysosome production, and atrophy significantly increased in a pattern corresponding to increased CTMP expression and reduced Akt phosphorylation. In an in vitro model of skeletal muscle atrophy, differentiated C2C12 cells exhibited reduced Akt activity and decreased FOXO1 phosphorylation, a process known to promote transcription of atrophy genes in skeletal muscle. These results corresponded with  increased  Atrogin-1 expression  compared to healthy control cells  (P < 0.05). Transfection with CTMP siRNA significantly increased Akt phosphorylation in atrophic C2C12 cells, corresponding to significantly decreased CTMP expression. In conclusion, this is the first study to provide evidence for a link between elevated CTMP expression, downregulated Akt phosphorylation and muscle atrophy in ALS and clearly demonstrates a direct influence of CTMP on Akt phosphorylation in an in vitro muscle cell atrophy model.

Outdoor Ambient Air Pollution and Neurodegenerative Diseases: the Neuroinflammation Hypothesis

PURPOSE OF REVIEW

Accumulating research indicates that ambient outdoor air pollution impacts the brain and may affect neurodegenerative diseases, yet the potential underlying mechanisms are poorly understood.

RECENT FINDINGS

The neuroinflammation hypothesis holds that elevation of cytokines and reactive oxygen species in the brain mediates the deleterious effects of urban air pollution on the central nervous system (CNS). Studies in human and animal research document that neuroinflammation occurs in response to several inhaled pollutants. Microglia are a prominent source of cytokines and reactive oxygen species in the brain, implicated in the progressive neuron damage in diverse neurodegenerative diseases, and activated by inhaled components of urban air pollution through both direct and indirect pathways. The MAC1-NOX2 pathway has been identified as a mechanism through which microglia respond to different forms of air pollution, suggesting a potential common deleterious pathway. Multiple direct and indirect pathways in response to air pollution exposure likely interact in concert to exert CNS effects.

Locomotor analysis identifies early compensatory changes during disease progression and subgroup classification in a mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a motoneuron degenerative disease that is challenging to diagnose and presents with considerable variability in survival. Early identification and enhanced understanding of symptomatic patterns could aid in diagnosis and provide an avenue for monitoring disease progression. Use of the mSOD1G93A mouse model provides control of the confounding environmental factors and genetic heterogeneity seen in amyotrophic lateral sclerosis patients, while investigating underlying disease-induced changes. In the present study, we performed a longitudinal behavioral assessment paradigm and identified an early hindlimb symptom, resembling the common gait abnormality foot drop, along with an accompanying forelimb compensatory mechanism in the mSOD1G93A mouse. Following these initial changes, mSOD1 mice displayed a temporary hindlimb compensatory mechanism resembling an exaggerated steppage gait. As the disease progressed, these compensatory mechanisms were not sufficient to sustain fundamental locomotor parameters and more severe deficits appeared. We next applied these initial findings to investigate the inherent variability in B6SJL mSOD1G93A survival. We identified four behavioral variables that, when combined in a cluster analysis, identified two subpopulations with different disease progression rates: a fast progression group and a slow progression group. This behavioral assessment paradigm, with its analytical approaches, provides a method for monitoring disease progression and detecting mSOD1 subgroups with different disease severities. This affords researchers an opportunity to search for genetic modifiers or other factors that likely enhance or slow disease progression. Such factors are possible therapeutic targets with the potential to slow disease progression and provide insight into the underlying pathology and disease mechanisms.