Kireet Koganti

Introduction. Amyotrophic lateral sclerosis (ALS) is a rare neurodegenerative disease with a 2-5 year prognosis that starts with limb and/or speech paralysis that progresses to the respiratory muscles, eventually leading to death¹. Treatment is supportive and diagnosis is made by exclusion, therefore there is a need for biomarkers that can screen for ALS and track disease progression^1,2,3. ALS can be familial or sporadic, with majority of cases being sporadic². Superoxide dismutase 1 (SOD1) is an antioxidant protein present on the ALS1 gene locus that’s classically been studied in familial ALS, with loss-of-function mutations increasing intracellular reactive oxygen species (ROS) and gain-of-function mutations causing SOD1 aggregation, causing neurotoxicity⁴. TDP-43, a nuclear RNA-binding protein, and VAPB, an integral membrane protein at the ALS8 locus, aggregate in both familial and sporadic ALS^4,5. Methods. CRISPR/Cas9-mediated genome editing of SOD1 was performed in C. elegans to produce single-copy/knock-in models to determine differences in neuronal specificity for loss-of-function versus gain-of-function SoD1 mutations⁶. To induce VAPB aggregation, a P56S missense mutation was introduced into Drosophila models⁵. Drosophila lacking SOD1 were used to see if increased ROS affected VAPB aggregates⁵. Urate, a potential antioxidant, was explored in mutant hSOD1 cell and Drosophila models of ALS³. SOD1’s use as a biomarker was studied by using a 7-amino acid endogenous peptide in CSF of human SOD1 mutation carriers². Antisense oligonucleotide-mediated SOD1 silencing was explored as a therapy for gain-of-function SOD1 mutations². Results. Percent intact glutamatergic neurons in ALS model animals decreased significantly after oxidative stress exposure⁶. In gain-of-function SOD1 models, oxidative stress caused degeneration of cholinergic motor neurons⁶. VAPB aggregates decreased when SOD1 levels were reduced in Drosophila brains, suggesting that ROS may clear VAPB aggregates⁵. Urate upregulated the Akt pathway, increasing synthesis of Glutathione (GSH), an antioxidant, which attenuated mutant hSOD1 elevations in ROS³. SOD1 peptide levels were elevated in rats and human subjects with gain-of-function mutations². ASO SOD1 silencing decreased SOD1 translation and decreased SOD1 levels in neurons of rat models of ALS². Conclusions. The mutation type at the ALS1 locus indicates specificity for neuronal degeneration⁶. Intracellular levels of SOD1 can influence aggregation of VAPB, with decreased SOD1 levels leading to ROS-mediated clearance of VAPB aggregates⁵. Urate should be further explored as a therapy to reduce ROS-mediated damage of motor neurons in ALS³. Additionally, screening methods such as SOD1 peptide levels in CSF should be further assessed for validity since there is no current screening method².

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3. Zhang C, Yang Y, Liang W, et al. Neuroprotection by urate on the mutant hSOD1-related cellular and Drosophila models of amyotrophic lateral sclerosis: Implication for GSH synthesis via activating Akt/GSK3β/Nrf2/GCLC pathways. Brain Research Bulletin. 2019;146:287-301. doi:10.1016/j.brainresbull.2019.01.019
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5. Chaplot K, Pimpale L, Ramalingam B, Deivasigamani S, Kamat SS, Ratnaparkhi GS. SOD1 activity threshold and TOR signaling modulate VAP(P58S) aggregation via reactive oxygen species-induced proteasomal degradation in a <em>Drosophila</em> model of amyotrophic lateral sclerosis. Dis Models Mech. 2019;12(2):dmm033803. doi:10.1242/dmm.033803
6. Baskoylu SN, Yersak J, O’Hern P, et al. Single copy/knock-in models of ALS SOD1 in C. elegans suggest loss and gain of function have different contributions to cholinergic and glutamatergic neurodegeneration. PLoS Genet. 2018;14(10):e1007682. Published 2018 Oct 8. doi:10.1371/journal.pgen.1007682