Neurodegenerative diseases (ND), such as ALS, are highly debilitating diseases affecting the nervous system, more specifically the neurons responsible for movement, called motor neurons (MN). Although ND have different causes, onset, and prognosis, a common denominator includes selective vulnerability and consequential loss or dysfunction of neurons. Not all neurons are equally susceptible to disease as some neurons are more vulnerable and degenerate first, while others continue to function even at the last stages of the disease. The molecular reason beyond this selective vulnerability of specific MN subtype is not known. While many studies have greatly advanced our understanding on the molecular identities of neuronal subtypes, transcriptional signatures of the different subtypes are still critically missing. MOVEMeNt offers the first comprehensive analysis of the transcriptional profile of distinct MN classes on a genome-wide base. This is essential to uncover the molecular cues governing motor neuron vulnerability to ND. Unfortunately, there are limited techniques available to isolate distinct motor neuron types from the adult mouse, hampering the development of therapeutic treatment that specifically target vulnerable neurons.
The overall objective of the MOVEMeNt project is therefore to dissect the molecular fingerprints of vulnerable and resistant motor neuron subtypes to ultimately pinpoint at the determinants of vulnerability, instrumental for therapy development.
To this aim, MOVEMeNt project aimed to identify the molecular fingerprints of distinct MN subtypes in mouse adult spinal cords, otherwise impossible to be told apart without genetic labelling. I therefore developed a new methodology that leverage on the cell type-specific expression of markers to enrich the population of investigation for MN, while depleting it from other cell types, including astrocytes, microglia and oligodendrocytes. This enabled me to sample for rare cell types more frequently than we would be able to in an unbiased fashion.
I then characterized the isolated MN at the molecular level with a cellular resolution. Single nuclei sequencing analysis revealed the degree of diversity of MN in the spinal cord. I found several classes of neurons, of which molecular profile was subject of a deeper bioinformatic analysis. I have identified subtype-specific markers and gene assemblies that are likely important for the function of a specific subtype, ultimately revealing the subtype-specific molecular landscapes of distinct MN subtypes, including vulnerable and resistant MN. This will serve as a reference to determine the molecular substrate of selective disease vulnerability and instruct on novel candidates for the development of new successful therapeutic strategies.
Also, it is known that sprouting capacity is crucial for remodeling at the neuromuscular junctions, and to compensate for neuronal loss upon insult. Upon insult, vulnerable MN degenerate and do not retain sprouting capacity. In the MOVEMeNt project, I also aimed at deciphering the genome-wide transcriptomic profiles of “sproutogenic” and “non-sproutogenic” MN to extrapolate the molecular logics underpinning remodeling capacity. To this aim, vulnerable and resistant MN have been retrogradelly labelled by muscle-specific dye injection. This enabled us to visualize and isolate by laser capture microdissection distinct MN types having different sproutogenic capacity. Molecular analysis of the isolated MNs, will inform beyond the lack of remodeling capacity of vulnerable MN.
Taken together, MOVEMeNt provides the molecular substrate of vulnerability, which will serve as a pool of draggable candidates for new therapeutic strategies.
