Evaluation of developing lesions with a combined approach of Magnetic Resonance Imaging, Magnetic Resonance Elastography and histopathology in an animal model of multiple sclerosis.
Final Report Abstract
This project focused on the evaluation of early inflammatory activity in the brain using magnetic resonance imaging (MRI) and magnetic resonance elastography (MRE). For this, an experimental autoimmune encephalomyelitis (EAE) mouse model was used, which is widely used to study multiple sclerosis (MS). EAE not only shares important histopathological hallmarks of MS, but also reflects dissemination and diversity of the disease. This hinders the analysis of lesion development and progression and also the correlation of structural and functional deficits. Hence, an EAE model, in which lesions can be targeted to specific brain or spinal cord regions would be of great value. Such a targeted lesion development was accomplished previously, but required invasive methods. Therefore, a specific aim of my project was to implement a model of controlled brain lesion development that both reflects EAE pathology and is noninvasive. For this, a local blood brain barrier disruption (BBBD) was induced with focused ultrasound (FUS) in mice after induction of EAE. The hypothesis was that FUS-BBBD increases the likelihood of the occurrence of normal EAE lesions as the influx of inflammatory immune cells into the brain is facilitated by the opened BBB. A MOG-induced active EAE model in C57BL/6 mice was used. As spinal cord lesions are predominant in this model, lesion development within the sonicated parenchyma would be a strong argument for the influence of FUS-BBBD. FUS was performed six, seven and nine days after immunization in subgroups of four animals each to establish the optimal timing for BBBD and in an additional group of four healthy control mice. MRI and MRE data were acquired longitudinally two and three weeks after EAE induction. A subgroup of mice was imaged two days after sonication to study potential early effects. Additionally, BBBD was confirmed in another subset of animals immediately after sonication. It was planned to use a continuous pulse ASL-sequence to evaluate BBBD. However, preliminary tests of this sequence did not yield satisfactory results. A contrast-enhanced T1w sequences was acquired instead, as this is goldstandard for detection of increased BBB permeability. Histopathological analyses comprising conventional staining and immunohistochemistry were performed after the last scan time point. A total of seven EAE animals presented with focal T2w hyperintense signal alterations in the sonicated hemisphere, which corresponded to clusters of activated microglia and macrophages. EAE animals had significantly reduced viscoelasticity, elasticity and viscosity in the sonicated cortex and deep grey matter compared to the contralateral normal tissue. Even though the comparison of lesional biomechanical properties to corresponding normal tissue did not yield significant results, regions with abnormal T2w hyperintensity tended to be softer and less viscous. FUS- BBBD can cause a transient sterile inflammation. However, the observed alterations in T2w signal and biomechanical properties as well as the accumulation of microglia and macrophages followed a different time course and were absent in control animals. Hence, they presumably occurred in the context of EAE in combination with FUS-BBBD and were not exclusively FUS-induced. Interestingly, all MRI, MRE and histopathological conspicuities were most frequent in the group of animals sonicated nine days after immunization. This might be associated with a more advanced peripheral immune response, increasing the likelihood of a promoted CNS inflammation. In conclusion, the findings provide first evidence for a noninvasive controlled lesion development in EAE using FUS-BBBD. Focal activation of microglia/macrophages within the sonicated parenchyma of MOG immunized animals may be interpreted as targeted initial inflammatory activity, which influences the cerebral biomechanical properties and eventually can be identified with conventional MRI. Upon confirmation of these findings in further studies using different EAE models, the model may be of use in research focusing on the correlation of structural and functional deficits or pharmaceutical investigations of drug effects on EAE lesions in different stages.
Publications
- Characterization of glioblastoma in an orthotopic mouse model with magnetic resonance elastography. NMR Biomed.
Katharina Schregel, Navid Nazari, Michal O. Nowicki, Miklos Palotai, Sean E. Lawler, Ralph Sinkus, Paul E. Barbone, Samuel Patz
(See online at https://doi.org/10.1002/nbm.3840)
