Acceleration in the rate of CNS remyelination in lysolecithin-induced demyelination

Abstract

One important therapeutic goal during CNS injury from trauma or demyelinating diseases such as multiple sclerosis is to develop methods to promote remyelination. We tested the hypothesis that spontaneous remyelination in the toxic nonimmune model of lysolecithin-induced demyelination can be enhanced by manipulating the inflammatory response. In PBS-treated SJL/J mice, the number of remyelinating axons per square millimeter of lesion area increased significantly 3 and 5 weeks after lysolecithin injection in the spinal cord. However, methylprednisolone or a monoclonal antibody (mAb), SCH94.03, developed for its ability to promote remyelination in the Theiler's virus murine model of demyelination, further increased the number of remyelinating axons per lesion area at 3 weeks by a factor of 2.6 and 1.9, respectively, but did not increase the ratio of myelin sheath thickness to axon diameter or the number of cells incorporating tritiated thymidine in the lesion. After 3 weeks, the number of remyelinating axons in the methylprednisolone or mAb SCH94.03 treatment groups was similar to the spontaneous remyelination in the 5 week PBS control-treated group, indicating that these treatments promoted remyelination by increasing its rate rather than its extent. To address a mechanism for promoting remyelination, through an effect on scavenger function, we assessed morphometrically the number of macrophages in lesions after methylprednisolone and mAb SCH94.03 treatment. Methylprednisolone reduced the number of macrophages, but SCH94.03 did not, although both enhanced remyelination. This study supports the hypothesis that even in toxic nonprimary immune demyelination, manipulating the inflammatory response is a benefit in myelin repair.

Fig. 1.

Demonstration of the methodology for determining lesion area measurements. A, Lysolecithin lesion from a PBS-treated control mouse 3 weeks after lysolecithin injection.B, Area in blue shows the normal white matter surrounding lesion that was used to discriminate lesion.C, Area in red demonstrates the area used in calculating the total lesion area.

Fig. 2.

Demonstration of the methodology for macrophage enumeration. A, Region of macrophage infiltration that does not allow for distinction of individual cells. B, Region of macrophages from A discriminated to calculate total macrophage area. C, Region where individual macrophages can be distinguished. D, Region discriminated from C used to calculate individual size of macrophages. Note examples of axons remyelinated by Schwann cells (arrows).

Fig. 3.

Spinal cord sections from SJL/J mice injected with lysolecithin and treated with A, PBS control;B, methylprednisolone; C, mAb 94.03; orD, polyclonal Ig directed against spinal cord homogenate (SCH/Ig). Treatment was begun on day 0 (methylprednisolone) or day 7 (PBS control, mAb 94.03 or SCH/Ig) and continued until day 21 at time of kill. Note focal area of demyelination with dense macrophage infiltration with minimal remyelination in the mouse treated with PBS control (A). In contrast, there is oligodendrocyte remyelination, characterized by abnormally thin myelin sheath relative to axon diameter, and Schwann cell remyelination in mice treated with methylprednisolone (B), mAb SCH94.03 (C) or SCH/Ig (D). The number of remyelinated axons from sections such as these are shown in Tables 1 and 2 (× 750).

Fig. 4.

Relative myelin sheath thickness as a function of axon diameter in axons remyelinated by oligodendrocytes at 2, 3 or 5 weeks in PBS-treated SJL/J mice injected with lysolecithin.

Fig. 5.

Number of proliferating cells per mm² of lesion in PBS-treated groups and treatment groups at 3 weeks after lysolecithin injection (data expressed as proliferating cells per square millimeter of lesion + SEM).n, Number of mice studied.

Fig. 6.

Number of macrophages per lesion area in treatment groups (data expressed as macrophages per square millimeter of lesion + SEM). n, Number of mice studied. Data marked by * denote statistical significance by Dunnett’s multiple comparison procedure with the PBS-treated group serving as the control.