Aucubin promotes neurite outgrowth in neural stem cells and axonal regeneration in sciatic nerves

Abstract

Aucubin is an iridoid glycoside with a wide range of biological activities, including anti-inflammatory, anti-microbial, anti-algesic as well as anti-tumor activities. Recently, it has been shown that aucubin prevents neuronal death in the hippocampal CA1 region in rats with diabetic encephalopathy. In addition, it has protective effects on H2O2-induced apoptosis in PC12 cells. We have shown here that aucubin promotes neuronal differentiation and neurite outgrowth in neural stem cells cultured primarily from the rat embryonic hippocampus. We also investigated whether aucubin facilitates axonal elongation in the injured peripheral nervous system. Aucubin promoted lengthening and thickness of axons and re-myelination at 3 weeks after sciatic nerve injury. These results indicate that administration of aucubin improved nerve regeneration in the rat model of sciatic nerve injury, suggesting that aucubin may be a useful therapeutic compound for the human peripheral nervous system after various nerve injuries.

Keywords: aucubin; axonal regeneration; neural stem cell; neurite outgrowth; sciatic nerve.

Fig. 1

Neurite extension and neuronal differentiation promoted by aucubin addition in neural stem cells cultured from the rat embryonic hippocampus. Differentiated neuron were immunostained with mature neuron marker, NeuN and neurites with MAP2 antibodies (green) and nuclei were counterstained with DAPI (blue). Numbers of NeuN positive cells and extention of MAP2 positive neurites were promoted in the presence of ACB (1 to 10 µg/mL, A and B) compared with control (vehicle). Light chain of Neurofilament protein was also increased by addition of aucubin (1 µg/mL C). (D) Quantification of MAP2 positive cells containing neurites in ranges between 0 and 100um. Inlet shows averages of neurites length in vehicle, 1 and 10 µg/mL. Data represents the means±standard error measures. ^**p<0.001 compared with the control, one-way ANOVA.

Fig. 2

Sciatic nerve regeneration improved by administration of aucubin (2.5 mg/kg) in the injured rat sciatic nerves at 3 weeks after sciatic nerve injury (A, at nerve injury site; B, in the middle; C, at the front site of growing axons). Axons were immunostained at the distal stump of the injured sciatic nerve with anti-neurofilament antibodies (green) and Schwann cells with anti-MBP antibodies (red). Inlets show diameter of axons.

Fig. 3

Aucubin promotes axonal regeneration. The diameter of axons (A, B, D) and myelinated axons (A) increased by aucubin treatment in the distal stumps of injured sciatic nerves. At three weeks, there is no myelination observed in vehicle treated nerves (A). Quantification graph of sciatic nerve regeneration shows average of axonal diameter (A) and average diameters of 3 regrowing sites (A, the beginning, B, the middle and C, the front, Fig. 2) (C). Average length of axons in vehicle and aucubin treated animals. Data indicates means±standard error measures. (D) Numbers of growing axons show distribution of axon diameter between 10 and 100 um in 3 regrowing sites ^*p<0.01 and ^**p<0.001 compared with the vehicle injected group, one-way ANOVA.