Aggregation of TAR DNA-binding protein of 43 kDa (TDP-43) is a salient feature of amyotrophic lateral sclerosis (ALS), a debilitating neurodegenerative disorder affecting over 200 000 people worldwide. The protein undergoes both functional and pathogenic aggregation; the latter is irreversible and hypothesized to produce soluble oligomers that are toxic to neurons in addition to inclusions made of stable fibrous deposits. Despite progress made toward identifying disease-related proteins, the underlying pathogenic mechanism associated with these toxic oligomers remains elusive. Utilizing a multimodal approach that combines several measurement techniques (circular dichroism (CD), thioflavin T spectroscopy (ThT), Fourier transform infrared spectroscopy (FTIR)) and high spatial resolution imaging tools (electron microscopy (EM) and atomic force microscopy (AFM)), with soft ion mobility mass spectrometry (IM-MS) and atomistic molecular dynamics (MD) simulations, we explore the oligomerization mechanisms, structures, and assembly pathways of TDP-43307–319. This fragment is both amyloidogenic and toxic and is within the glycine-rich C-terminal domain essential for both toxicity and aggregation of the full-length protein. In addition to the wild-type peptide, two ALS-related mutants (A315T and A315E) and a non-axon-toxic mutant (G314V) were investigated to determine how mutations affect the oligomerization of TDP-43307–319 and structures of toxic oligomers. The results of our study provide new insights into how ALS-related mutants, A315T and A315E, accelerate or alter the pathogenic mechanism and highlight the role of an internal glycine, G314, in maintaining efficient packing known to be critical for functional oligomer assembly. More importantly, our data demonstrate that G314 plays a vital role in TDP-43 assembly and prevents cytotoxicity via its unique aversion to oligomers larger than trimer. Our observation is consistent with previous studies showing that G314V mutation of the full-length TDP-43 induced remediation of both axonotoxicity and neuronal apoptosis. Our findings reveal a distinct aggregation mechanism for each peptide and elucidate oligomeric species and possible structures that may be involved in the pathology of ALS.

Background: Oseltamivir is frequently administered to critically ill patients with presumed influenza. It may modulate Na+, K+, and Ca2+ channels to produce bradycardia. Objective: To evaluate the association between oseltamivir and bradycardia in critically ill patients and assess parameters associated with bradycardia. Methods: This was a retrospective audit of 203 critically ill adults with presumed influenza receiving at least 2 doses of oseltamivir. The primary outcome was the occurrence of bradycardia, defined as a heart rate (HR) ≤59 beats per minute (BPM) while receiving oseltamivir or a decrease of ≥20 BPM compared with the lowest HR before initiating oseltamivir. Results: A total of 88 (43.4%) patients manifested bradycardia, 59 with HR ≤59 BPM, 19 with HR decrease of ≥20 BPM, and 10 with both. The time from first dose to bradycardia was 51.4 ± 43 hours. In all, 48 (54.6%) patients received therapies for bradycardia, including increased inotropic/vasopressor dose, electrolyte replacement, electrocardiogram, discontinuation of other medications, cardiology consult, discontinuation of oseltamivir, and pacer placement. There were no significant differences between groups with bradycardia versus without in terms of demographics, laboratory values, hospital characteristics, or oseltamivir dosing. Multivariate logistic regression showed that bradycardia was associated with baseline HR, age, past medical history of neurological issues, and positive influenza status. Between hours 6 through 126, significant differences existed between groups in actual and lowest HR. Conclusion and Relevance: Oseltamivir was associated with clinically relevant bradycardia in critically ill patients. Clinicians should closely monitor HR in critically ill patients receiving oseltamivir.

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