Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder affecting motor neurons. Cu, Zn superoxide dismutase (SOD1), a cytoplasmic free radical scavenging enzyme, is mutated in familial ALS (fALS) and post-translational modification of the wild-type protein has been associated with sporadic ALS (sALS). Proteomic studies indicate that SOD1 is acetylated at Lys123; however, the role of this modification remains unknown. To investigate its function, we generated antibodies for Lys123-acetylated SOD1 (Ac-K123 SOD1). Sod1 deletion in Sod1-/- mice, K123 mutation, or preabsorption with Ac-K123 peptide suppressed immunoreactivity, confirming antibody specificity. In the normal central nervous system, Ac-K123 SOD1 maps to glutamatergic neurons of the cerebellar cortex, dentate gyrus, hippocampus, olfactory bulb, and retina. In cultured neurons, Ac-K123 SOD1 localized to defined regions of axons and dendrites. Previous studies have suggested a role for SOD1 in cell cycle regulation. Therefore, we tested the distribution of Ac-K123 SOD1 during the cell cycle of astrocytes. In G1 Ac-K123 SOD1 localized to the nucleus, in G0 to the primary cilium, in metaphase and anaphase to chromosomes, and in telophase to the midbody. The deacetylase HDAC6 and acetyl-transferase ?-TAT1 are associated with the primary cilium. Therefore, we tested whether they regulate reversible acetylation of SOD1. HDAC6 knockdown or pharmacological inhibition markedly increased, while HDAC6 overexpression decreased, SOD1 Lys123 acetylation. By contrast, SOD1 Lys123 acetylation was decreased by ?-TAT1 knockdown and increased by ?-TAT1 overexpression. These results suggest that HDAC6 and ?-TAT1 regulate SOD1 Lys123 acetylation. Next, we examined Lys123 acetylation in fALS SOD1 mutants. Remarkably, Lys123 acetylation was dramatically increased in fALS mutants including SOD1 A4V. The acetyl-Lys123 mimetic of wild-type SOD1 caused axonal transport deficits similar to those observed in SOD1 pathogenic mutants such as A4V. Interestingly, HDAC6 deacetylation or acetylation resistance by Lys123 mutation, abolished A4V protein misfolding, axonal transport defects, and neuronal cell death. These results suggest that Lys123 acetylation plays a key role in the neurotoxicity of fALS mutants and may have implications in sALS. Because Ac-K123 SOD1 maps to the primary cilium, we examined whether ciliogenesis is altered in fALS mutant SOD1 astrocytes. Strikingly, fALS mutants caused centriole and primary cilia proliferation with ciliary ectosome secretion. Notably, multiciliated ependymal cells in the brain ventricles and spinal cord central canal, which are critical for cerebral spinal fluid circulation, stained strongly for Ac-K123 SOD1. Thus, we speculate that ciliary ectosome shedding from ependymal cells accounts for the presence of misfolded SOD1 in the CSF in fALS and perhaps sALS. In summary, we identified SOD1 Lys123 acetylation as a novel mechanism underlying protein misfolding and neurodegeneration in ALS. Ac-K123 SOD1 may emerge as novel target for the diagnosis and treatment of ALS.
Doctor of Philosophy (Ph.D.)
College of Medicine
Burnett School of Biomedical Sciences
Length of Campus-only Access
Doctoral Dissertation (Campus-only Access)
Kaliszewski, Michael, "The Role of SOD1 Acetylation in Neurodegeneration" (2016). Electronic Theses and Dissertations. 5311.