Cytoplasmic TDP-43 accumulation drives changes in C-bouton number and size in a mouse model of sporadic Amyotrophic Lateral Sclerosis

• Published in: Molecular and cellular neuroscience 2023-06, Vol.125, p.103840-103840, Article 103840
• Main Authors: Bak, Anna Normann, Djukic, Svetlana, Kadlecova, Marion, Braunstein, Thomas Hartig, Jensen, Dennis Bo, Meehan, Claire Francesca
• Format: Article
• Language: English
• Subjects: Amyotrophic Lateral Sclerosis; Amyotrophic Lateral Sclerosis - metabolism; Animals; C-boutons; Disease Models, Animal; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Female; Male; Mice; Mice, Transgenic; Motoneurones; Motor Neurons - metabolism; Spinal Cord - metabolism; Superoxide Dismutase - genetics; Superoxide Dismutase - metabolism
• ISSN: 1044-7431; 1095-9327
• DOI: 10.1016/j.mcn.2023.103840

An altered neuronal excitability of spinal motoneurones has consistently been implicated in Amyotrophic Lateral Sclerosis (ALS) leading to several investigations of synaptic input to these motoneurones. One such input that has repeatedly been shown to be affected is a population of large cholinergic synapses terminating mainly on the soma of the motoneurones referred to as C-boutons. Most research on these synapses during disease progression has used transgenic Superoxide Dismutase 1 (SOD1) mouse models of the disease which have not only produced conflicting findings, but also fail to recapitulate the key pathological feature seen in ALS; cytoplasmic accumulations of TAR DNA-binding protein 43 (TDP-43). Additionally, they fail to distinguish between slow and fast motoneurones, the latter of which have more C-boutons, but are lost earlier in the disease. To circumvent these issues, we quantified the frequency and volume of C-boutons on traced soleus and gastrocnemius motoneurones, representing predominantly slow and fast motor pools respectively. Experiments were performed using the TDP-43ΔNLS mouse model that carries a transgenic construct of TDP-43 devoid of its nuclear localization signal, preventing its nuclear import. This results in the emergence of pathological TDP-43 inclusions in the cytoplasm, modelling the main pathology seen in this disorder, accompanied by a severe and lethal ALS phenotype. Our results confirmed changes in both the number and volume of C-boutons with a decrease in number on the more vulnerable, predominantly fast gastrocnemius motoneurones and an increase in number on the less vulnerable, predominantly slow soleus motoneurones. Importantly, these changes were only found in male mice. However, both sexes and motor pools showed a decrease in C-bouton volume. Our experiments confirm that cytoplasmic TDP-43 accumulation is sufficient to drive C-bouton changes. •Cytoplasmic relocation/aggregation of TDP-43 is sufficient to drive C-bouton changes.•We show changes in both the number and volume of C-boutons on spinal motoneurones.•A decrease in number is seen on the predominantly fast gastrocnemius motoneurones.•An increase in number is seen on the predominantly slow soleus motoneurones.•Both motor pools showed a decrease in C-bouton volume.