Restoring brain cholesterol turnover improves autophagy and has therapeutic potential in mouse models of spinocerebellar ataxia

Abstract

Spinocerebellar ataxias (SCAs) are devastating neurodegenerative disorders for which no curative or preventive therapies are available. Deregulation of brain cholesterol metabolism and impaired brain cholesterol turnover have been associated with several neurodegenerative diseases. SCA3 or Machado-Joseph disease (MJD) is the most prevalent ataxia worldwide. We show that cholesterol 24-hydroxylase (CYP46A1), the key enzyme allowing efflux of brain cholesterol and activating brain cholesterol turnover, is decreased in cerebellar extracts from SCA3 patients and SCA3 mice. We investigated whether reinstating CYP46A1 expression would improve the disease phenotype of SCA3 mouse models. We show that administration of adeno-associated viral vectors encoding CYP46A1 to a lentiviral-based SCA3 mouse model reduces mutant ataxin-3 accumulation, which is a hallmark of SCA3, and preserves neuronal markers. In a transgenic SCA3 model with a severe motor phenotype we confirm that cerebellar delivery of AAVrh10-CYP46A1 is strongly neuroprotective in adult mice with established pathology. CYP46A1 significantly decreases ataxin-3 protein aggregation, alleviates motor impairments and improves SCA3-associated neuropathology. In particular, improvement in Purkinje cell number and reduction of cerebellar atrophy are observed in AAVrh10-CYP46A1-treated mice. Conversely, we show that knocking-down CYP46A1 in normal mouse brain impairs cholesterol metabolism, induces motor deficits and produces strong neurodegeneration with impairment of the endosomal-lysosomal pathway, a phenotype closely resembling that of SCA3. Remarkably, we demonstrate for the first time both in vitro, in a SCA3 cellular model, and in vivo, in mouse brain, that CYP46A1 activates autophagy, which is impaired in SCA3, leading to decreased mutant ataxin-3 deposition. More broadly, we show that the beneficial effect of CYP46A1 is also observed with mutant ataxin-2 aggregates. Altogether, our results confirm a pivotal role for CYP46A1 and brain cholesterol metabolism in neuronal function, pointing to a key contribution of the neuronal cholesterol pathway in mechanisms mediating clearance of aggregate-prone proteins. This study identifies CYP46A1 as a relevant therapeutic target not only for SCA3 but also for other SCAs.

Atxn2-CAG100-KnockIn mouse spinal cord shows progressive TDP43 pathology associated with cholesterol biosynthesis suppression

“…It is crucial to note that also in a mouse model of SCA3 (Machado-Joseph disease), recent global transcriptome profiling demonstrated a significant enrichment of cholesterol biogenesis dysregulations in brainstem, but increased levels of ceramides, di- and triglycerides in blood [204]. Furthermore, for SCA3 it was shown that restoration of brain cholesterol homeostasis has therapeutic potential [131]. Our observation of reduced cholesterol biogenesis in the Atxn2 -CAG100-KIn mouse is easily related with the documented depletion of peripheral fat tissues in SCA2 [121], and with findings of early demyelination in this CAG100-KIN mouse and in SCA2 patients [57, 140, 168].…”

The blood-brain barrier is disrupted in Machado-Joseph disease/spinocerebellar ataxia type 3: evidence from transgenic mice and human post-mortem samples

“…Since MJD is associated with autophagy impairments, this can explain, at least in part, the decrease in claudin-5 oligomers even when there is an increase in the monomer observed in our MJD transgenic model [45,50]. Moreover, based on the fact that TJs are associated with cholesterol-rich lipid domains at the membrane, alterations in claudin-5 oligomerization in MJD might be related to cholesterol, since a deregulation in brain cholesterol metabolism was recently demonstrated in MJD [47]. It would also be relevant to evaluate other claudins, for instance claudin-1 and -25, since they also play a significant role in maintaining paracellular tightness and TJs formation [3].…”

The cholesterol 24-hydroxylase activates autophagy and decreases mutant huntingtin build-up in a neuroblastoma culture model of Huntington’s disease

“…Impaired brain cholesterol metabolism has been broadly associated with neurodegenerative disorders. We and others showed that strategies aiming at restoring cholesterol metabolism using different strategies are beneficial in AD, SCA and HD mouse models [22,24,36,37]. Local synthesis/efflux of cholesterol is essential for the structural regulation of cells and membranes within the brain, being implicated in signal transduction, release of neurotransmitters and membrane trafficking [38].…”

“…Values expressed as mean ± SEM. (a, b, n = 5 independent experiments, two-way ANOVA with Bonferroni's multiple comparisons test, *P < 0.05; ***P < 0.0001; ### P < 0.0001 comparing to LC3 + lacZ; c, n = 3 independent experiments Unpaired Student's t test, ****P < 0.00001) increased the autophagic flux, i.e., augmented the levels of LC3-II and decreased the p62/SQSTM1 levels [36].…”