On the distribution of intranuclear and cytoplasmic aggregates in the brainstem of patients with spinocerebellar ataxia type 2 and 3

Abstract

The polyglutamine (polyQ) diseases are a group of genetically and clinically heterogeneous neurodegenerative diseases, characterized by the expansion of polyQ sequences in unrelated disease proteins, which form different types of neuronal aggregates. The aim of this study was to characterize the aggregation pathology in the brainstem of spinocerebellar ataxia type 2 (SCA2) and 3 (SCA3) patients. For good recognition of neurodegeneration and rare aggregates, we employed 100 µm PEG embedded brainstem sections, which were immunostained with the 1C2 antibody, targeted at polyQ expansions, or with an antibody against p62, a reliable marker of protein aggregates. Brainstem areas were scored semiquantitatively for neurodegeneration, severity of granular cytoplasmic staining (GCS) and frequency of neuronal nuclear inclusions (NNI). SCA2 and SCA3 tissue exhibited the same aggregate types and similar staining patterns. Several brainstem areas showed statistically significant differences between disease groups, whereby SCA2 showed more severe GCS and SCA3 showed more numerous NNI. We observed a positive correlation between GCS severity and neurodegeneration in SCA2 and SCA3 and an inverse correlation between the frequency of NNI and neurodegeneration in SCA3. Although their respective disease proteins are unrelated, SCA2 and SCA3 showed the same aggregate types. Apparently, the polyQ sequence alone is sufficient as a driver of protein aggregation. This is then modified by protein context and intrinsic properties of neuronal populations. The severity of GCS was the best predictor of neurodegeneration in both disorders, while the inverse correlation of neurodegeneration and NNI in SCA3 tissue implies a protective role of these aggregates.

Oligonucleotide therapy mitigates disease in spinocerebellar ataxia type 3 mice

“…Previous studies have shown that p62 localizes to protein aggregates in many neurodegenerative diseases including SCA3 and may play a protective role in autophagic clearance of polyglutamine disease proteins. 28,29,41,42 By immunoblot analysis, diencephalic and cerebellar p62 expression levels did not differ across vehicle-treated WT, vehicle-treated Q84/Q84, or ASO-5-treated mice (see Fig 7C, E, F, H). We did, however, observe small, nuclear p62-positive puncta in the pons of Q84/Q84 vehicle-treated mice at 16 weeks of age, which were nearly absent in vehicle-treated WT or ASO-5-treated Q84/Q84 mice (see Fig 7B).…”

“…pons, olivary nuclei, vestibular nuclei, cranial nerve nuclei), we focused our biochemical analysis on diencephalic tissue 3,28,29 . By immunoblot analysis, ASO-5 significantly reduced diencephalic mutATXN3 expression in a dose-dependent manner, though all doses showed efficacy (p<0.05) (Fig 1B and 1C).…”

“…Employing immunofluorescence with an anti-ASO antibody, we assessed ASO-5 delivery and retention in the pons and DCN (Fig 2H), two subcortical regions known to undergo significant neuronal loss in post-mortem SCA3 patient brains 3,28,29 . Fourteen weeks after injection, ASO levels in the pons and DCN were equal to or greater than that of surrounding brain structures, confirming that these key disease-affected regions are readily targetable.…”

“…Previous studies have shown that p62 localizes to protein aggregates in many neurodegenerative diseases including SCA3 and may play a protective role in autophagic clearance of polyglutamine disease proteins 28,29,41,42 . By immunoblot analysis, diencephalic (Fig 7C and 7E) and cerebellar (Fig 7F and 7H) p62 expression levels did not differ across vehicle-treated WT, vehicle-treated Q84/Q84, or ASO-5 treated mice.…”

Chaperones in Polyglutamine Aggregation: Beyond the Q-Stretch

“…Furthermore, we will not go into the discussion on the toxicity of aggregation. For instance, it is still unclear whether the presence of aggregates contributes to SCA2 pathology (Huynh et al, 2000), even though aggregates are found in affected brain areas (Pang et al, 2002; Seidel et al, 2016). Finally, we will highlight the role of chaperones in the aggregation process and include only studies that provide insight in direct interaction of chaperones with the polyQ proteins.…”