Lithium chloride reinforces the effect of chondroitinase ABC on promoting axonal regeneration of rubrospinal neurons after spinal cord injury

Abstract

In the injured spinal cord, enzymatic degradation of chondroitin sulfate proteoglycans (CSPGs) promotes axonal regeneration of neurons across the lesion scar. We examined whether chondroitinase ABC (ChABC) promote the axonal regeneration of rubrospinal tract (RST) neurons after spinal cord injury. We also assessed the effect of a GSK-3ƒÒ inhibitor, lithium chloride (LiCl), on the regeneration of axotomized RST neurons. Adult rats received a unilateral hemisection at the seventh cervical spinal cord segment (C7) followed by different treatments. Four weeks after the lesion, regeneration of RST axons across the lesion scar was examined by injection of Fluoro-Gold at spinal segment T2. The recovery of motor function was studied on a test of forelimb usage. Injured RST axons did not regenerate spontaneously after spinal cord injury. Intraperitoneal injection of LiCl alone did not promote the axonal regeneration of RST neurons. Administration of ChABC at the lesion site promoted the regeneration of RST axons by 20%. Combined treatment of LiCl together with ChABC significantly increased the regeneration of RST axons to 42%. Animals receiving the combined treatment used both forelimbs together more often than animals received sham or single treatment. Immunoblotting and immunohistochemical analysis demonstrated that LiCl induced the expression of inactive GSK-3ƒÒ as well as the upregulation of Bcl-2 in RST neurons after spinal cord injury. These results suggest that LiCl inhibits GSK-3ƒÒ and reinforces the regeneration-promoting function of ChABC through a Bcl-2 dependent mechanism. Combined use of LiCl together with ChABC could be a novel therapeutic approach for spinal cord injury. Supported by Hong Kong Research Grants Council