Title: Amyotrophic lateral sclerosis associated mislocalisation of TDP-43 to the cytoplasm causes cortical hyperexcitability and reduced excitatory neurotransmission in the motor cortex.

No abstract

There is increasing interest in the role of epigenetic alterations in Alzheimer’s disease (AD). The epigenome of every cell type is distinct, yet data regarding epigenetic change in specific cell types in aging and AD is limited. We investigated histone tail modifications in neuronal subtypes in wild-type and APP/PS1 mice at 3 (pre-pathology), 6 (pathology-onset) and 12 (pathology-rich) months of age. In neurofilament (NF)-positive pyramidal neurons (vulnerable to AD pathology), and in calretinin-labeled interneurons (resistant to AD pathology) there were no global alterations in histone 3 lysine 4 trimethylation (H3K4me3), histone 3 lysine 27 acetylation (H3K27ac) or histone 3 lysine 27 trimethylation (H3K27me3) in APP/PS1 compared to wild-type mice at any age. Interestingly, age-related changes in the presence of H3K27ac and H3K27me3 were detected in NF-labeled pyramidal neurons and calretinin-positive interneurons, respectively. These data suggest that the global levels of histone modifications change with age, whilst amyloid plaque deposition and its sequelae do not result in global alterations of H3K4me3, H3K27ac and H3K27me3 in NF-positive pyramidal neurons or calretinin-labeled interneurons.

Amyotrophic lateral sclerosis (ALS) is defined by the destruction of upper- and lower motor neurons. Post-mortem, nearly all ALS cases are positive for cytoplasmic aggregates containing the DNA/RNA binding protein TDP-43. Recent studies indicate that this pathogenic mislocalization of TDP-43 may participate in generating hyperexcitability of the upper motor neurons, the earliest detectable change in ALS patients, yet the mechanisms driving this remain unclear. We investigated how mislocalisation of TDP-43 could initiate network dysfunction in ALS. We employed a tetracycline inducible system to express either human wildtype TDP-43 (TDP-43WT) or human TDP-43 that cannot enter the nucleus (TDP-43ΔNLS) in excitatory neurons (Camk2α promoter), crossed Thy1-YFPH mice to visualize dendritic spines, the major site of excitatory synapses. In comparison to both TDP-43WT and controls, TDP-43ΔNLS drove a robust loss in spine density in all the dendrite regions of the upper motor neurons, most affecting thin spines. This indicates that TDP-43 is involved in the generation of network dysfunction in ALS likely through impacting the formation or durability of excitatory synapses. These findings are relevant to the vast majority of ALS cases, and provides further evidence that upper motor neurons may need to be protected from TDP-43 mediated synaptic excitatory changes early in disease.

Brain penetrant microtubule stabilising agents (MSAs) are being increasingly validated as potential therapeutic strategies for neurodegenerative diseases and traumatic injuries of the nervous system. MSAs are historically used to treat malignancies to great effect. However, this treatment strategy can also cause adverse off-target impacts, such as the generation of debilitating neuropathy and axonal loss. Understanding of the effects that individual MSAs have on neurons of the central nervous system is still incomplete. previous research has revealed that aberrant microtubule stabilisation can perturb many neuronal functions, such as neuronal polarity, neurite outgrowth, microtubule dependant transport and overall neuronal viability. in the current study, we evaluate the dose dependant impact of epothilone D, a brain penetrant MSA, on both immature and relatively mature mouse cortical neurons in vitro. We show that epothilone D reduces the viability, growth and complexity of immature cortical neurons in a dose dependant manner. furthermore, in relatively mature cortical neurons, we demonstrate that while cellularly lethal doses of epothilone D cause cellular demise, low sub lethal doses can also affect mitochondrial transport over time. Our results reveal an underappreciated mitochondrial disruption over a wide range of epothilone D doses and reiterate the importance of understanding the dosage, timing and intended outcome of MSAs, with particular emphasis on brain penetrant MSAs being considered to target neurons in disease and trauma. Historically, the adult neuronal cytoskeleton was considered relatively stable, being involved only in neuroprogenitor cell division during de novo neurogenesis 1,2. With our increased understanding of the neuronal microtubule environment and function, and the adult brains capacity for neuroplasticity 3 , it is now evident that neuronal microtubules, the largest of the three filament components of the cytoskeleton, form a critical dynamic intracellular network 4. In this regard, microtubules consist of both stable and labile domains 5,6 within tubular protofilaments comprised of αand β-tubulin heterodimers. Microtubules display a phenomenon termed "dynamic instability" 7 , which describes the stochastic variations between bouts of growth, pausing and shrinkage of the microtubule population. Microtubules can transition from a growing to a shrinking state, termed catastrophe, which may or may not be rescued back to a growing state. The microtubule protofilament consists of a slow growing "minus end" and a fast growing, highly dynamic "plus end" 8,9 , which plays a critical role in normal neuronal functions including neuronal growth, intracellular transport, establishment and maintenance of cellular polarity, and process remodelling 10-12. Changes to the growth state of microtubules can have downstream consequences for their normal physiological functions, such as the binding of specific motor transport units 13 , and the association of + TIP proteins that facilitate interactions bet...