Neuromuscular proteins as potential biomarkers in ALS
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the loss of upper and lower motor neurons (MNs). Symptoms include muscle paralysis which rapidly progresses and ultimately results in respiratory failure within 2-5 years after diagnosis. Even if several genes causing ALS have been identified, still up to ~90% of the sporadic cases remains genetically unexplained. Interestingly, one of the hallmarks of all ALS cases is the destruction of the neuromuscular junction (NMJ). As no cure yet exists, this disease is in desperate need of effective therapeutics. Our group and others have exploited successful preclinical NMJ-targeted therapies in animal models of ALS. However, despite their importance and the emergency to enter into a clinical trial, a number of issues remain unaddressed. Perhaps one of the most important ones remain the lack of biomarkers for early diagnostic, to monitor disease progression and treatment response. The absence of biomarkers has hampered the development of therapies in ALS. To overcome these issues, we identified NMJ-related candidate biomarkers from a comparative proteomic study between vulnerable and resistant NMJ-enriched samples from ALS murine models. Importantly, these NMJ-proteins are consistent with the complex and dynamic NMJ denervation process in ALS, whereby cycles of NMJ denervation and reinnervation take place months prior to the complete retraction of the axons within muscles. During these cycles, NMJ components are dynamically modulated, where NMJ- and axonal-related proteins are removed and eliminated into the bloodstream. Interestingly, semi-quantitative (immunofluorescence) and quantitative analyses (Western blots and ELISA) revealed that levels of NMJ-related proteins change according to the genotype and disease progression. From a therapeutic standpoint, we posit that the NMJ dynamism is a promising avenue to identify new ALS biomarkers warranting the need to investigate candidates implicated in biological processes such as morphological stability/instability, axonal degeneration and regeneration and synaptic/glial plasticity.
Hence, we hypothesise that: NMJ and axonal-related proteins are good ALS biomarkers as they tightly reflect the state of the disease and its progression.
NMJ and axonal proteins have the potential of being reliable biomarkers of ALS owing to their close representation of the status of NMJ denervation. Our goal is to conduct a study to explore NMJ-related biomarkers in ALS patients. This will be achieved by targeting three (3) aims:
Aim 1: NMJ-related proteins as potential Diagnostic biomarkers.
Aim 2: NMJ-related proteins as potential Monitoring biomarkers.
Aim 3: NMJ-related proteins as potential Pharmacodynamic/response biomarkers.
We will obtain human fluid samples from two distinct biobanks and we will use an established detection technique (ELISA) to validate our potential biomarkers. Importantly, our candidate proteins have been already reported and measured in human CSF and blood, supporting the feasibility and the likely relevance of our candidate proteins. This approach will serve as a framework for the development of essential ALS biomarkers. As a long-term goal, the correlation of fluid- and tissues-based biomarkers can be explored. In addition, these ALS candidate biomarkers may prove useful for other NMJ-related diseases or aging. This would be a significant step towards the development of a major research effort to reconcile mouse and human tissues to study, and eventually, treat ALS.
Richard Robitaille , Université de Montréal
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