The neuron regrowth is associated with the proliferation of neural precursor cells after leukemia inhibitory factor administration following spinal cord injury in mice

Abstract

Objectives: To explore whether LIF could promote the proliferation of neural precursor cells (NPCs) and to analyze the correlation between increased NPCs and FluoroGold (FG) labeled neurons in mice after spinal cord injury (SCI).

Methods: Motor behavior was assessed using Rotarod and Platform Hang tests; neurons in the corticospinal and rubrospinal systems were labeled with FG, NPCs were immustained with nestin-FITC conjugate. The numbers of FG-labeled neurons and NPCs were estimated, and the correlation between FG-labeled neurons and NPCs was assessed.

Results: Mice in the SCI group showed negligible recovery of locomotor behavior; in contrast, mice in the LIF group showed a statically significant improvement. Both FG-labeled neurons and NPCs were significantly increased in the LIF group compared to the SCI group, and this increase in FG-labeled neurons and NPCs showed a clear association above the lesion level.

Conclusions: LIF could promote locomotive behaviors in mice post-SCI by encouraging the proliferation of NPCs; LIF may in fact be a potential cytokine for the induction of NPCs post-SCI.

Figure 1. Locomotor behavior analysis of mice in the Nor, SCI, LIF and sham groups using the Rotarod and the Platform Hang tests.

Fig. 1A showed a permanent hind limb paralysis in Rotarod analysis in the SCI group. A significant improvement was detected on the Rotarod in the LIF group compared to the SCI group; a statistical difference was found after the fourth day and the maximal response was achieved by the sixth day, despite continuous treatment for 14 days. A similar significant (p<0.05) improvement was observed in the Platform Hang test (Fig. 1B) in LIF group. The locomotor behavior of the Nor and Sham groups was not affected in both Rotarod and Platform Hang tests.

Figure 2. Analysis of FG-labeled neurons in the corticospinal and rubrospinal systems in the Nor, SCI, LIF and Sham groups.

Fig. 2A–D showed the FG-labeled neurons in the corticospinal system in the Nor (2A), SCI (2B), LIF (2C) and Sham (2D) groups. Fig. 2E summarized the number of FG-labeled neurons in the corticospinal system. The number of FG-labeled neurons in the LIF group decreased compared to the Nor group, but increased compared to SCI group. Fig. 2F–I showed the FG-labeled neurons in the rubrospinal system in the Nor (2F), SCI (2G), LIF (2H) and Sham (2I) groups. Fig. 2J showed a similar pattern to that shown in Fig. 2E in the rubrospinal system. * Indicates comparison with the Nor group. # Indicates comparison with the SCI group. Cor: Corticospinal; Rub: Rubrospinal. Bar =  100 µm.

Figure 3. NPCs in spinal cord above and below the lesion level.

Fig. 3A–E showed the NPCs in spinal cord above the lesion level. Fig. 3A–D showed the NPCs above the lesion level in the Nor (3A), SCI (3B), LIF (3C) and Sham (3D) groups. Fig. 3E showed that the number of NPCs above the lesion level in the LIF group increased compared to the SCI group, but they were rare in the Nor and Sham groups. Fig. 3F–J showed the NPCs in the spinal cord below the lesion level. Fig. 3F–I showed the NPCs below the lesion level in the Nor (3F), SCI (3G), LIF (3H) and Sham (3I) groups. Fig. 3J showed the number of NPCs below the lesion level in LIF group increased compared to the SCI group, but they were rare in the Nor and Sham groups. * indicates comparison with the Nor and Sham groups. # Indicates comparison with the SCI group. Bar  = 50 µm.

Figure 4. The correlation between NPCs and FG-labeled neurons.

Fig. 4A–B showed that the number of NPCs above the lesion level, but not below the lesion level (Fig. 4C–D), was positively correlated with the number of FG-labeled neurons in both the corticospinal and rubrospinal systems in the LIF group. There was no any positive correlation detected between the number of NPCs and the number of FG-labeled neurons above (Fig. 4E–F) and below (Fig. 4G–H) the lesion level of spinal cord in both the corticospinal and rubrospinal systems in the SCI group.