Poly-dipeptides produced from C9orf72 hexanucleotide repeats cause selective motor neuron hyperexcitability in ALS

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• The GGGGCC hexanucleotide repeat expansion in the C9orf72 gene is the leading genetic cause of amyotrophic lateral sclerosis (ALS).
• Early stages of C9orf72-linked ALS are characterized by motor cortex hyperexcitability, but the underlying mechanisms are not fully understood.
• Previous research focused on toxic poly-dipeptides, yet their precise role in motor neuron dysfunction remains unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms responsible for motor cortex hyperexcitability in C9orf72-related ALS.
• To investigate the role of proline-arginine poly-dipeptides in altering neuronal excitability.
• To identify the specific ion channels involved in the observed motor neuron hyperactivation.

Main Methods:

• Investigated the effects of proline-arginine poly-dipeptides on cortical motor neurons.
• Assessed changes in neuronal excitability using electrophysiological recordings.
• Examined the involvement of the Nav1.2/β4 sodium channel complex in motor cortex neurons.

Main Results:

• Proline-arginine poly-dipeptides were found to induce hyperexcitability in cortical motor neurons.
• This hyperexcitability is mediated by an increase in persistent sodium currents.
• The Nav1.2/β4 sodium channel complex, highly expressed in the motor cortex, was identified as the key conductor of these currents.

Conclusions:

• The C9orf72 mutation leads to motor neuron hyperexcitability via proline-arginine poly-dipeptides.
• These peptides enhance persistent sodium currents through the Nav1.2/β4 sodium channel complex.
• This mechanism provides a basis for understanding motor neuron hyperactivation and subsequent degeneration in C9orf72-linked ALS.