In vivo monitoring of recovery from neurodegeneration in conditional transgenic SCA1 mice

Abstract

Reliable and objective markers of neuronal function and pathology that can directly assess the effects of neuroprotective treatments in the brain are urgently needed for clinical trials in neurodegenerative diseases. Here we assessed the sensitivity of high field proton magnetic resonance spectroscopy (1H MRS) to monitor reversal of neurodegeneration by taking advantage of a well characterized conditional mouse model of spinocerebellar ataxia type 1 (SCA1), where the cerebellar pathology and ataxic phenotype are reversible by doxycycline administration. Transgene expression was suppressed by feeding the mice with chow that contains doxycycline from 6 – 12 weeks of age in an early stage group and from 12 – 24 weeks in a mid-stage group. Cerebellar neurochemical profiles of treated and untreated conditional mice were measured at 9.4 tesla (T) before and after treatment and compared to those of wild type (WT) controls, as well as to histology measures (molecular layer thickness in the primary fissure and a global pathological severity score). Concentrations of N-acetylaspartate (NAA) and myo-inositol in the treated mice trended towards normalization to WT levels in both the early and mid-stage groups. The NAA-to-myo-inositol ratio was significantly different between the treated vs. untreated SCA1 mice and demonstrated partial reversal to WT values both at early and mid-stage, consistent with the histological measures. Taurine and total creatine levels were completely normalized in early and mid-stage treatment groups, respectively. The MRS markers were a more sensitive measure of treatment response than the histological measures from the same volume-of-interest in the early stage group. NAA, myo-inositol and taurine levels were significantly correlated with the histology measures in data combined from all groups. These data demonstrate that MRS markers reliably detect rescue from neuronal pathology and imply that the neurochemical levels measured by MRS accurately reflect treatment efficacy. Therefore this study presents an important step in validating MRS biomarkers as potential surrogate markers to evaluate therapeutics in pre-clinical and clinical trials in SCA1.

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

“…Only male mice were studied to obviate the need to control for the phase of estrous cycle in female mice (a requirement difficult to reconcile with scanner time availability) and because gender was not shown to influence neurochemical levels in prior MRS studies (Nagae-Poetscher et al, 2004; Pouwels and Frahm, 1998). In addition, exclusion of female mice from the analysis had not changed the findings in our prior study (Öz et al, 2011b). …”

“…All tTA mice were also treated with doxycycline from 12 to 24 weeks to account for potential effects of the doxycycline treatment on the neurochemical profiles. Note that our prior study indicated that doxycycline treatment alone does not significantly alter the neurochemical profile in WT mice (Öz et al, 2011b). All mice were scanned at 9.4 tesla (T) before treatment began at 12 weeks and after treatment ended at 24 weeks.…”

“…Remarkably, the same neurochemicals, namely N -acetylaspartate (NAA), myo -inositol (Ins) and glutamate, also distinguished patients with SCA1 from controls and correlated with scores on a standardized ataxia rating scale (Öz et al, 2010a). We further showed that abnormal neurochemical levels reverse towards wild-type (WT) levels upon suppression of transgene expression in a conditional SCA1 [ 82Q ] line (Öz et al, 2011b) and that early neurochemical changes are detectable even in the absence of overt pathology in a knock-in model of SCA1 (Emir et al, 2013). Together these data demonstrated the potential of MRS-measured neurochemical levels as robust biomarkers of progressive neurodegeneration and its reversal in SCA1.…”

RNAi prevents and reverses phenotypes induced by mutant human ataxin‐1

“…4,16 In earlier studies by Orr and colleagues, mutant ataxin-1 was completely eliminated and aggregates resolved quickly with recovery of cerebellar pathology. 4 Our results are similar but contrasting in important ways.…”

“…11 These data have been recapitulated in transgenic SCA1 mice 12 and were reversed in a conditional mouse model of SCA1. 16 NAA reduction usually precedes neuronal loss, and is used as a marker of neuronal dysfunction. 24 In this work, NAA levels were modestly reduced in control treated SCA1 mice at 20 weeks of age, a time prior to significant PC loss.…”