Local injection of bone morphogenetic protein 7 promotes neuronal regeneration and motor function recovery after acute spinal cord injury

Abstract

After spinal cord injury, the number of glial cells and motor neurons expressing bone morphogenetic protein 7 (BMP7) increases, indicating that upregulation of BMP7 can promote nerve repair. We, therefore, tested whether direct injection of BMP7 into acutely injured rat spinal cord can affect neurological recovery. Allen's impactor was used to create spinal cord injury at T₁₀. The injury site was then injected with 50 ng BMP7 (BMP7 group) or physiological saline (control group) for 7 consecutive days. Electrophysiological examination showed that the amplitude of N1 in motor evoked potentials (MEP) decreased after spinal cord injury. At 8 weeks post-operation, the amplitude of N1 in the BMP7 group was remarkably higher than that at 1 week post-operation and was higher than that of the control group. Basso, Beattie, Bresnahan scale (BBB) scores, hematoxylin-eosin staining, and western blot assay showed that at 1, 2, 4 and 8 weeks post-operation, BBB scores were increased; Nissl body staining was stronger; the number of Nissl-stained bodies was increased; the number of vacuoles gradually decreased; the number of synapses was increased; and the expression of neuronal marker, neurofilament protein 200, was increased in the hind limbs of the BMP7 group compared with the control group. Western blot assay showed that the expression of GFAP protein in BMP7 group and control group did not change significantly and there was no significant difference between the BMP7 and control groups. These data confirmed that local injection of BMP7 can promote neuronal regeneration after spinal cord injury and promote recovery of motor function in rats.

Keywords: Basso; Beattie; Bresnahan scale score; Nissl staining; behavior; glial cells; glial fibrillary acidic protein; motor evoked potential wave; nerve regeneration; neural regeneration; neurofilament protein 200; neurons.

Figure 1

Effects of local injection of BMP7 on MEP waveforms at different time points in each group. (A–C) MEP waveforms of sham operation (A) control (B), and BMP7 groups (C) at 1 week. (D, E) MEP waveforms of control (D) and BMP7 groups (E) at 8 weeks. Abscissa: Recording time (ms); ordinate: nerve voltage (mV); BMP7: bone morphogenetic protein 7; MEP: motor evoked potential.

Figure 2

Effects of local BMP7 injection on injured tissue (hematoxylin-eosin staining). At 1–8 weeks after BMP7 treatment, the Nissl staining was stronger in the BMP7 group compared with the control group, and there were more Nissl bodies in the BMP7 group than in the control group at each corresponding time point. Scale bars: 10 μm. Original magnification, 400×. BMP7: Bone morphogenetic protein 7.

Figure 3

Effects of local BMP7 injection on the expression of NF200 and GFAP at various time points in the control and BMP7 groups. (A) NF200 and GFAP at the injury site at different time points. (B, C) The grayscale ratios of NF200 and GFAP bands relative to β-actin for control and BMP7 groups at different time points. *P < 0.05, vs. control group (mean ± SD, n = 5; one-way analysis of variance and Newman-Keuls multiple comparison test). BMP7: Bone morphogenetic protein 7; NF200: neurofilament protein 200; GFAP: glial fibrillary acidic protein.