Multi-parametric MRI at 14T for muscular dystrophy mice treated with AAV vector-mediated gene therapy

Abstract

The objective of this study was to investigate the efficacy of using quantitativemagnetic resonance imaging (MRI) as a non-invasive tool for the monitoring of gene therapy formuscular dystrophy. The clinical investigations for this family of diseases often involve surgical biopsy which limits the amount of information that can be obtained due to the invasive nature of the procedure. Thus, other non-invasive tools may provide more opportunities for disease assessment and treatment responses. In order to explore this, dystrophic mdx 4cv mice were systemically treated with a recombinant adeno-associated viral (AAV) vector containing a codonoptimized micro-dystrophin gene. Multi-parametricMRI of T2, magnetization transfer, and diffusion effects alongside 3-D volumemeasurements were then utilized to monitor disease/ treatment progression. Mice were imaged at 10 weeks of age for pre-treatment, then again post-treatment at 8, 16, and 24 week time points. The efficacy of treatment was assessed by physiological assays for improvements in function and quantification of expression. Tissues from the hindlimbs were collected for histological analysis after the final time point for comparison withMRI results. We found that introduction of themicro-dystrophin gene restored some aspects of normal muscle histology and pathology such as decreased necrosis and resistance to contraction-induced injury. T2 relaxation values showed percentage decreases across all muscle types measured (tibialis anterior, gastrocnemius, and soleus) when treated groups were compared to untreated groups. Additionally, the differences between groups were statistically significant for the tibialis anterior as well. The diffusionmeasurements showed a wider range of percentage changes and less statistical significance while the magnetization transfer effect measurements showed minimal change.MR images displayed hyper-intense regions of muscle that correlated with muscle pathology in histological sections. T2 relaxation, alongside diffusion and magnetization transfer effects provides useful data towards the goal of non-invasively monitoring the treatment of muscular dystrophy.