Research article 2022 Reviewed

Neurofilament Light Regulates Axon Caliber, Synaptic Activity, and Organelle Trafficking in Cultured Human Motor Neurons

Markus T. Sainio, Tiina Rasila, Svetlana M. Molchanova, Julius Järvilehto, Rubén Torregrosa-Muñumer, Sandra Harjuhaahto, Jana Pennonen, Nadine Huber, Sanna-Kaisa Herukka, Annakaisa Haapasalo, Henrik Zetterberg, Tomi Taira, Johanna Palmio, Emil Ylikallio, Henna Tyynismaa

Frontiers in Cell and Developmental Biology2022-02-14Frontiers Media SA

Open original source PubMed Europe PMC Explore connections

Abstract via Crossref

Neurofilament light (NFL) is one of the proteins forming multimeric neuron-specific intermediate filaments, neurofilaments, which fill the axonal cytoplasm, establish caliber growth, and provide structural support. Dominant missense mutations and recessive nonsense mutations in the neurofilament light gene ( NEFL ) are among the causes of Charcot–Marie–Tooth (CMT) neuropathy, which affects the peripheral nerves with the longest axons. We previously demonstrated that a neuropathy-causing homozygous nonsense mutation in NEFL led to the absence of NFL in patient-specific neurons. To understand the disease-causing mechanisms, we investigate here the functional effects of NFL loss in human motor neurons differentiated from induced pluripotent stem cells (iPSC). We used genome editing to generate NEFL knockouts and compared them to patient-specific nonsense mutants and isogenic controls. iPSC lacking NFL differentiated efficiently into motor neurons with normal axon growth and regrowth after mechanical axotomy and contained neurofilaments. Electrophysiological analysis revealed that motor neurons without NFL fired spontaneous and evoked action potentials with similar characteristics as controls. However, we found that, in the absence of NFL, human motor neurons 1) had reduced axonal caliber, 2) the amplitude of miniature excitatory postsynaptic currents (mEPSC) was decreased, 3) neurofilament heavy (NFH) levels were reduced and no compensatory increases in other filament subunits were observed, and 4) the movement of mitochondria and to a lesser extent lysosomes was increased. Our findings elaborate the functional roles of NFL in human motor neurons. NFL is not only a structural protein forming neurofilaments and filling the axonal cytoplasm, but our study supports the role of NFL in the regulation of synaptic transmission and organelle trafficking. To rescue the NFL deficiency in the patient-specific nonsense mutant motor neurons, we used three drugs, amlexanox, ataluren (PTC-124), and gentamicin to induce translational read-through or inhibit nonsense-mediated decay. However, the drugs failed to increase the amount of NFL protein to detectable levels and were toxic to iPSC-derived motor neurons.

Evidence snapshot note

This reference is cited by the validated MVA · BUB1B evidence snapshot (data as of 2026-10-17) as NEFL motor-neuron negative rescue.

Model in the source: Human iPSC-derived NEFL nonsense motor neurons
Where in the publication: Figure 6; Treatments
Cited by evidence records: MVA-AMLEXANOX-010

The note describes how the snapshot used the source; it is not a summary of the publication's conclusions.

Identifiers and provenance

DOI: 10.3389/fcell.2021.820105
PMID: 35237613
PMCID: PMC8883324
URL: https://doi.org/10.3389/fcell.2021.820105
Metadata from: Crossref, Europe PMC, OpenAlex, fetched 2026-10-24
License (as declared by the source): https://creativecommons.org/licenses/by/4.0/
Open access: Yes
Added: 2026-10-24 from the MVA evidence snapshot

In the library

Collections: MVA Hackathon 2026 — BUB1B
Tags: None yet
Keywords from the source: Axon, Induced Pluripotent Stem Cells, Charcot-marie-tooth (Cmt) Disease, Neurofilament Light (Nfl), Motor Neurodegeneration, Motor Neuron (Mn)