ALS is thought to be a multistep disease process that involves a complex interplay between inherited genes indicating the level of risk an individual is born with and subsequent modifiers they confront as they age that determine whether an individual develops the disease or not. Five to ten percent of ALS cases are familial and the remaining cases are sporadic. Familial ALS is defined by a positive family history of the disease, but family history may not always be apparent and many of the mutations identified in cases of familial ALS are also found in those with the sporadic form. Two studies estimate a heritability of 60% in sporadic ALS, and first-degree relatives of patients with sporadic ALS have an eightfold increased risk of developing the disease, demonstrating further the importance of genetics in the sporadic disease (Savage AL, 2019).
Proteins and small non-coding regulatory RNA (miRNA) molecules that control signaling pathways have the potential to be involved with the progression of ALS in an individual, from the missing heritability of the disease to neuronal dysfunction and degenerative processes. Proteins and miRNAs are biomarkers and drug targets for ALS. These molecules influence glia-neuron interactions, axon homeostasis, plasticity, and synaptic transmission that are important in progression of neurodegenerative disease and in ALS.
An inability to find biomarkers in ALS, despite exhaustive studies, suggest dynamic molecules should be examined. Under different physiological or pathological conditions, miRNAs can switch from translational inhibition to activation. Dynamic interplays between miRNAs and mRNAs take place in different tissues and different cellular locations (Ni, 2015). Certainly a place to investigate changes in disease, and perhaps changes induced by treatment are protein kinases.
Serine/threonine protein kinase (MAPK) has a key role in the intracellular signaling networks that transduce and amplify stress signals into physiological changes. The stress related kinase p38α MAPK is a potential neurotherapeutic target in both neurons and glia. MW 150 is a specific p38αMAPK antagonist that is ideal to investigate the role of p38αMAPK in neurological disease (Roy 2015).
Studies show that transposons contribute to the evolution of miRNA genes. miRNA can mediate sequence-specific regulation of endogenous gene expressions by binding to complementary sites on target mRNAs. These sequences may be a source for the missing heritability of sALS (Yang Li, 2011). The general effect of miRNAs is inhibition of the expression of target genes, therefore it is expected that decreasing miRNA will upregulate the involved pathway.
Saucier (Saucier D, 2019) identified a circulating miRNA signature in extracellular vesicles collected from ALS patients. Five miRNA were upregulated in ALS patients (miR-532-3p, miR-144-3p, miR-15a-5p, miR-363-3p, and miR-183-5p) and 22 miRNAs were downregulated in ALS. An interesting observation in one ALS patient was a change in the five miRNA’s Saucier identified as up- regulated in his study. The patient showed the Saucier-miRNA's as elevated and a decrease in all five miRNA’s was apparent in plasma after administration of a MAPK inhibitor in a cocktail of ALS therapies.
Others reported the differential expression of miRNA in spinal cord samples collected from the G93A-SOD1 mouse model of ALS (Zhou F, 2013). If SOD1 mice show similar miRNA changes as patients with ALS, it would be possible to test compounds using the miRNA's as targets of engagement.
An interesting miRNA on Saucier’s list is miR144-3p, it appears to target NRF2 (NFE2L2), which is a major regulator of the oxidative stress response. Lowering miR144-3p should increase levels of NRF2, which could then increase expression of various antioxidant genes. It would be hard to predict in which tissues this might occur. Elevated levels of miR-144-3p induce cholinergic degeneration by impairing the maturation of NFG in Alzheimer’s Disease (Zhou, 2021).
It would be useful to relate a circulating ALS-related miRNA in people and SOD1 mice with a therapeutic target to investigate RNA networks. Based on the anecdotal patient report above, RNA was isolated from spinal/brain tissue from non-treated and MW150 treated SOD1G93A mice to investigate the effect of p38MAPK inhibition in ALS-associated miRNA expression. This is an ongoing collaborative project between Northwestern University (Dr. Siddique provided mouse tissues, RNA isolation and QA), Harvard (Dr. Sadri-Vakili, miRNA data analysis), University of Florida (Dr. Borchelt, is overseeing project).
Works Cited
Ni, W. a. (2015). Dynamic miRNA-mRNA paradigms: new faces of miRNAs. Biochem Biophys Rep, 337-341.
Saucier D, W. G. (2019). Identification of a circulating miRNA signature in extracellular vesicles collected from amyotrophic lateral sclerosis patients. Brain Res, 100-108.
Savage AL, S. G. (2019). Retrotransposons in the development and progression of amyotrophic lateral sclerosis. Journal of Neurology, Neurosurgery & Psychiatry , 284-293.
Yang Li, C. L. (2011, May 11). Domestication of Transposable Elements into MicroRNA Genes in Plants. Retrieved from journals.plos.org: https://journals.plos.org/plosone/articlehttps://doi.org/10.1371/journal.pone.0019212
Zhou F, G. Y. (2013). miRNA-9 expression is upregulated in the spinal cord of G93A-SOD1 transgenic mice. Int J Clin Exp Pathol, 1826-1838.
Zhou, L. e. (2021). Elevated levels of miR-144-3p induce cholinergic degeneration by impairing the maturation of NFG in Alzheimer's Disease. Front Cell Dev Biol, 1-14.