Effect of olfactory ensheathing cells transplantation on polarization of M2 macrophages and its significance in rats with spinal cord contusion at acute phase

Objective To observe the regulatory effect of olfactory ensheathing cells (OECs) on polarization of M2 macrophages after acute contusion of spinal cords in rats, and explore the mechanism of OECs transplantation in promoting repair of spinal cord injury. Methods The primary OECs were isolated and cultured for transplantation. The T10 spinal cords of SD rats were exposed and impacted by impact stick (10 g) dropping vertically from a height of 25 mm with a NYU-II impactor. Twenty-four rats with contusion of spinal cord immediately after injury were randomly divided into DMEM/F12 control group and OECs transplantation group according a random number table. DMEM/F12 culture medium or OECs suspension (3×104/μL, 1 μL×3 times) was implanted into the injured spinal cords. At one to 9 weeks after injury, Basso Beattie Bresnahan (BBB) scale was used to evaluate the motor functions in rats. At one week after injury, M2 macrophages and Nogo-A positive cells were labeled by immunofluorescence staining; the expressions of interleukin (IL)-4 and IL-6 were detected by Western blotting. At 9 weeks after injury, the pathological changes of injured spinal cords were observed by HE staining. Results One and 9 weeks after injury, BBB scores in OECs transplantation group were significantly higher than those in control group at each time point after injury (P<0.05). One week after injury, the number of M2 macrophages in OECs transplantation group was significantly larger than that in control group (3.24%±0.56% vs. 0.63%±0.21%), and the number of Nogo-A positive cells was significantly smaller and fluorescence intensity was significantly lower in OECs transplantation group than those in control group ([43±24] field vs. ([207±88]/field; 0.042±0.006 vs. 0.062±0.011, P<0.05); the IL-4 protein level was significantly higher and the IL-6 protein level was significantly lower in OECs transplantation group than those in the control group (0.717±0.152 vs. 0.183±0.063; 0.550±0.124 vs. 1.060±0.209; P<0.05). Nine weeks after injury, the cytoplasmic cavity area in OECs transplantation group ([1.511±0.581] mm2) was significantly lower than that in control group [2.939±0.823] mm2, P<0.05). Conclusion OECs transplantation may promote macrophages polarizing to subtype M2, improve the microenvironment of inflammation, reduce Nogo-A secretion, thus promote the structure and spinal cord function recovery. Key words: Olfactory ensheathing cell; Spinal cord injury; M2 macrophage; Cell polarization; Nogo-A; Cell transplantation