MRI evaluation of axonal reorganization after bone marrow stromal cell treatment of traumatic brain injury

We treated traumatic brain injury (TBI) with human bone marrow stromal cells (hMSCs) and evaluated the effect of treatment on white matter reorganization using MRI. We subjected male Wistar rats (n = 17) to controlled cortical impact and either withheld treatment (controls; n = 9) or inserted collagen scaffolds containing hMSCs (n = 8). Six weeks later, the rats were sacrificed and MRI revealed selective migration of grafted neural progenitor cells towards the white matter reorganized boundary of the TBI-induced lesion. Histology confirmed that the white matter had been reorganized, associated with increased fractional anisotropy (FA; p < 0.01) in the recovery regions relative to the injured core region in both treated and control groups. Treatment with hMSCs increased FA in the recovery regions, lowered T(2) in the core region, decreased lesion volume and improved functional recovery relative to untreated controls. Immunoreactive staining showed axonal projections emanating from neurons and extruding from the corpus callosum into the ipsilateral cortex at the boundary of the lesion. Fiber tracking (FT) maps derived from diffusion tensor imaging confirmed the immunohistological data and provided information on axonal rewiring. The apparent kurtosis coefficient (AKC) detected additional axonal remodeling regions with crossing axons, confirmed by immunohistological staining, compared with FA. Our data demonstrate that AKC, FA, FT and T(2) can be used to evaluate treatment-induced white matter recovery, which may facilitate restorative therapy in patients with TBI.