Broad Influence of Mutant Ataxin-3 on the Proteome of the Adult Brain, Young Neurons, and Axons Reveals Central Molecular Processes and Biomarkers in SCA3/MJD Using Knock-In Mouse Model

Abstract

Spinocerebellar ataxia type 3 (SCA3/MJD) is caused by CAG expansion mutation resulting in a long polyQ domain in mutant ataxin-3. The mutant protein is a special type of protease, deubiquitinase, which may indicate its prominent impact on the regulation of cellular proteins levels and activity. Yet, the global model picture of SCA3 disease progression on the protein level, molecular pathways in the brain, and neurons, is largely unknown. Here, we investigated the molecular SCA3 mechanism using an interdisciplinary research paradigm combining behavioral and molecular aspects of SCA3 in the knock-in ki91 model. We used the behavior, brain magnetic resonance imaging (MRI) and brain tissue examination to correlate the disease stages with brain proteomics, precise axonal proteomics, neuronal energy recordings, and labeling of vesicles. We have demonstrated that altered metabolic and mitochondrial proteins in the brain and the lack of weight gain in Ki91 SCA3/MJD mice is reflected by the failure of energy metabolism recorded in neonatal SCA3 cerebellar neurons. We have determined that further, during disease progression, proteins responsible for metabolism, cytoskeletal architecture, vesicular, and axonal transport are disturbed, revealing axons as one of the essential cell compartments in SCA3 pathogenesis. Therefore we focus on SCA3 pathogenesis in axonal and somatodendritic compartments revealing highly increased axonal localization of protein synthesis machinery, including ribosomes, translation factors, and RNA binding proteins, while the level of proteins responsible for cellular transport and mitochondria was decreased. We demonstrate the accumulation of axonal vesicles in neonatal SCA3 cerebellar neurons and increased phosphorylation of SMI-312 positive adult cerebellar axons, which indicate axonal dysfunction in SCA3. In summary, the SCA3 disease mechanism is based on the broad influence of mutant ataxin-3 on the neuronal proteome. Processes central in our SCA3 model include disturbed localization of proteins between axonal and somatodendritic compartment, early neuronal energy deficit, altered neuronal cytoskeletal structure, an overabundance of various components of protein synthesis machinery in axons.

Mitochondrial Dysfunction in Spinocerebellar Ataxia Type 3 Is Linked to VDAC1 Deubiquitination

“…Recently, proteomics revealed a wide range of metabolic and mitochondrial dysregulated proteins in an SCA3 knockin mouse model in early pathogenesis. In line with the described protein dysregulation, these mice demonstrated reduced oxygen consumption rates and failed to gain weight, which points to an important defect in mitochondrial function and energy metabolism early in SCA3 pathogenesis [ 22 ]. Importantly, SCA3 patients also show a decreased BMI, which is inversely correlated with the expanded CAG repeat length [ 38 ] and could be a predictor of disease progression, as shown in a Chinese SCA3 cohort [ 39 ].…”

“…Additionally, mass spectrometry analyses revealed new mitochondrial proteins as potential interaction partners of ataxin-3 under normal and also disease conditions [ 20 ]. Proteome analyses of an SCA3 knockin mouse model demonstrated energy metabolism and dysfunctional expression of mitochondrial proteins as an early event in the pathogenesis [ 22 ]. Therapeutically, vitamin B6 supplementation in an SCA3 Drosophila model resulted in mitochondrial protection of polyQ-induced cellular toxicity [ 23 ].…”

From psychiatry to neurology: Psychedelics as prospective therapeutics for neurodegenerative disorders

“…Another protein necessary for BDNF signal transduction to the nucleus is Pea15, which is also down-regulated in SCA3 mice (Wiatr, Marczak, Pérot, et al, 2021). Silencing of Pea15 results in inhibition of BDNF retrograde signaling (Ammar et al, 2015).…”

“…Psychedelics have also been shown to reduce oxidative stress, which is a significant issue in neurodegenerative disorders. Several oxidative stress biomarkers are elevated in models of neurodegenerative disorders (Fan et al, 2019;Hueso et al, 2020;Wiatr, Marczak, Pérot, et al, 2021). Other anti-oxidative proteins, which play an essential role in reducing oxidative stress by breaking down ROS (Gstp1, Sod2, Fth1), are down-regulated in the SCA3 model (Wang et al, 2015;Wiatr et al, 2019Wiatr et al, , 2021.…”

“…Several oxidative stress biomarkers are elevated in models of neurodegenerative disorders (Fan et al, 2019;Hueso et al, 2020;Wiatr, Marczak, Pérot, et al, 2021). Other anti-oxidative proteins, which play an essential role in reducing oxidative stress by breaking down ROS (Gstp1, Sod2, Fth1), are down-regulated in the SCA3 model (Wang et al, 2015;Wiatr et al, 2019Wiatr et al, , 2021. Moreover, Txn downregulation in SCA3 mice might increase the vulnerability of neurons to ROS (Sewastianik et al, 2016;Wiatr, Marczak, Pérot, et al, 2021).…”