Assessing recovery from neurodegeneration in spinocerebellar ataxia 1: Comparison of in vivo magnetic resonance spectroscopy with motor testing, gene expression and histology

Abstract

Suppression of transgene expression in a conditional transgenic mouse model of spinocerebellar ataxia 1 (SCA1) reverses the Purkinje cell pathology and motor dysfunction that are hallmarks of SCA1. We previously showed that cerebellar neurochemical levels measured by magnetic resonance spectroscopy (MRS) correlate with progression of pathology and clinical status of patients and that abnormal neurochemical levels normalize upon suppression of transgene expression, indicating their potential as robust surrogate markers of treatment effects. Here we investigated the relative sensitivities of MRS, histology, transgene expression and motor behavioral testing to disease reversal in conditional SCA1 mice. Transgene expression was suppressed by doxycycline administration and treated and untreated mice were assessed by MRS at 9.4tesla before and after treatment and with an accelerating Rotarod, histology and quantitative polymerase chain reaction (qPCR) for ataxin-1 transgene expression following doxycycline treatment. The MRS-measured N-acetylaspartate-to-myo-inositol ratio (NAA/Ins) correlated significantly with the molecular layer (ML) thickness and transgene expression. NAA/Ins, ML thickness and transgene expression were highly significantly different between the treated vs. untreated groups (p<0.0001), while the Rotarod assessment showed a trend for treatment effect. MRS, qPCR and histology had high sensitivity/specificity to distinguish treated from untreated mice, all with areas under the curve (AUC)=0.97–0.98 in receiver operating characteristic (ROC) analyses, while Rotarod had significantly lower sensitivity and specificity (AUC=0.72). Therefore, MRS accurately reflects the extent of recovery from neurodegeneration with sensitivity similar to invasive measures, further validating its potential as a surrogate marker in pre-clinical and clinical treatment trials.