Serotonergic dysfunction impairs locomotor coordination in spinal muscular atrophy

Area of Science:

• Neuroscience
• Genetics
• Motor Neuron Disease

Background:

• Serotonin (5-HT) is crucial for regulating neuronal networks and motor behaviors.
• Dysregulation of serotonergic neurotransmission is linked to mood disorders and spinal cord injury, but its role in movement disorders is unclear.
• Spinal muscular atrophy (SMA) is a neurodegenerative disease characterized by motor neuron loss and muscle atrophy due to SMN protein deficiency.

Purpose of the Study:

• To investigate serotonergic neuromodulation in a mouse model of spinal muscular atrophy (SMA).
• To determine if SMN deficiency impacts serotonin signaling in the spinal cord and brainstem.
• To explore the therapeutic potential of targeting serotonergic pathways in SMA.

Main Methods:

• Utilized a severe SMA mouse model recapitulating type I SMA symptoms.
• Employed mouse genetics, optogenetics, physiology, morphology, and behavioral analysis.
• Assessed serotonergic neurotransmission, 5-HT synapse density, and motor neuron function.

Main Results:

• Identified severe dysfunction of serotonergic neurotransmission in SMA mice at both early and late disease stages.
• Observed a reduction in 5-HT synapses on motor neurons, particularly those innervating axial and trunk muscles.
• Demonstrated that SMN deficiency in brainstem serotonergic neurons causes this dysfunction, leading to inter-limb discoordination.

Conclusions:

• SMA involves significant serotonergic neuromodulation deficits, potentially contributing to disease progression and scoliosis.
• Selective restoration of SMN in serotonergic neurons ameliorates motor discoordination in SMA mice.
• Targeting 5-HT neuromodulation presents a promising therapeutic strategy for SMA.