Bone marrow stromal cells promote skilled motor recovery and enhance contralesional axonal connections after ischemic stroke in adult mice

Abstract

Background and purpose: We tested the effect of bone marrow stromal cells (BMSCs) on neuronal remodeling of the corticospinal tract originating from the contralesional cortex in mice subjected to unilateral pyramidotomy (PT) followed by middle cerebral artery occlusion (MCAO).

Methods: Adult mice with transgenic yellow fluorescent protein labeling in the corticospinal tract were subjected to right hemispheric PT and right permanent or sham MCAO. One day later, the mice were treated intravenously with BMSCs or phosphate-buffered saline. A Foot-Fault test and a single pellet-reaching test were performed before surgery, 3 days after MCAO, and weekly thereafter. Pseudorabies virus-614-monomeric red fluorescent protein was injected into the left forelimb flexor muscles 28 days after surgery (4 days before euthanasia). The brain and cervical cord were processed for fluorescent microscopy to detect red fluorescent protein and yellow fluorescent protein labeling, respectively.

Results: Significant functional improvements were evident in PT-MCAO mice treated with BMSCs (n=9) compared with phosphate-buffered saline-treated mice (n=9, P<0.05), but not in mice with PT-sham MCAO treated with either phosphate-buffered saline (n=9) or BMSCs (n=10). Furthermore, in PT-MCAO mice, both corticospinal tract axonal density in the denervated side of the cervical gray matter and red fluorescent protein-labeled pyramidal neurons in the left intact cortex were significantly increased compared with PT-sham MCAO mice (P<0.05). BMSCs significantly enhanced both corticospinal tract density and red fluorescent protein labeling in PT-MCAO mice (P<0.05) only. The behavioral outcome was highly correlated with corticospinal tract density and red fluorescent protein labeling.

Conclusions: BMSCs amplify stroke-induced contralesional neuronal remodeling, which contributes to motor recovery after stroke.

Figure 1

Line graphs show the temporal profile of left forepaw behavioral deficit and recovery after right PT followed by sham-MCAo or right MCAo with and without BMSC treatment, respectively, measured by the Foot-Fault test (A) and the single pellet reaching test (B). The left forepaw motor disability progressively decreased with time in all mice; while mice subjected to PT followed by MCAo were more seriously impaired in the Foot-Fault test, they exhibited more complete recovery. BMSC treatment significantly promoted the functional recovery in PT-MCAo mice.

Figure 2

Single layer confocal images show CST axons in the gray matter of the cervical cord in CST-YFP mice subjected to PT followed by Sham MCAo with PBS (A) or BMSC (B) treatment, and MCAo with PBS (C) or BMSC (D) treatment. Broken lines in A to D indicate the midline of the spinal cord. Note that in the cervical gray matter in PT-MCAo mice, the number of axons crossing the midline into the denervated left side from the right intact side was evident in both PBS and BMSC treated groups. Quantitative analysis of the percentage of CST axons in the denervated side to the contralateral side (E) demonstrated that BMSC treatment significantly increased axonal density in PT-MCAo mice but not in PT-sham MCAo mice. A scheme of the corticospinal projections and the lesion sites is shown in F. A rectangle field in the central area of the spinal gray matter indicates the position of the photomicrographs appearing in A to D. cc: central canal. Scale bar=50 μm.

Figure 3

Data point graphs of correlations between neural remodeling and behavioral recovery. The behavioral outcome assessed by both Foot-Fault test and single pellet reaching test were highly correlated with the CST axonal density in the denervated side of the spinal cord and numbers of PRV-positive pyramidal neurons in the left contralesional cortex.