Axonal translatome profiling to identify molecular pathways underlying axonal degeneration in spinal muscular atrophy

• Applicant: Dr. Saeede Salehi, Ph.D.
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 559287218

Motor neurons are highly polarized cells that extend axons over extensive distances to reach their target muscle and form synapses. Motor axon growth and maintenance is supported by the temporal and spatial localization of mRNAs for local protein production. Impairment of axon growth and maintenance are implicated in the pathogenesis of neurodegenerative disorders such as spinal muscular atrophy (SMA). SMA is an autosomal recessive motor neuron disorder caused by mutations or deletions in the survival motoneuron 1 (SMN1) gene, leading to deficiency of the SMN protein that is crucial for motor neuron function. We previously showed that SMN defciency disturbs the axonal localization of many mRNAs. However, the impact of SMN loss on axonal mRNA translation and its role in local protein synthesis within axons remain unclear. In the cytosol, SMN not only assembles spliceosomal small nuclear ribonucleoproteins (snRNPs) but is also involved in translation by associating with ribosomes. This project aims to characterize ribosome-associated mRNAs that are translated in an SMN-dependent manner in axons of motor neurons and examine whether axonal translatome alterations in SMA motor neurons contribute to their axonal defects. For this purpose, we will first identify the RNA and protein interactome of SMN in axons to obtain insights into the composition of axonal SMN particles and their regulatory potential. Next, we will assess to what extent SMN deficiency alters the association of mRNAs with axonal ribosomes. Finally, we will investigate whether SMN loss alters the protein composition of the axonal translation machinery itself in axons of SMA motor neurons. For the project, we will use human SMA motor neurons from patient-derived iPSCs as well as primary motor neurons from an SMA mouse model. We anticipate that the results of this project will not only advance our knowledge of axonal SMN functions in motor neurons but also reveal novel pathomechanisms contributing to the axonopathy and synaptic dysfunction in SMA motor neurons. Such findings could help to identify additional therapeutic targets, which could complement existing FDA-approved SMA therapeutic strategies, potentially leading to improved outcomes for individuals affected by SMA.

• DFG Programme: Research Grants