[Expression and significance of growth-associated protein 43 in a rat model of intervertebral disc inflammation]

Abstract

Objective: To investigate the expression and significance of growth-associated protein 43 (GAP-43) in the dorsal root ganglion (DRG) and intervertebral disc in the rat model of intervertebral disc inflammation.

Methods: A total of 103 adult male Sprague Dawley rats (weighing, 200-250 g) were randomly divided into the experimental group (n = 48), the control group (n = 48), and the blank control group (n = 7). Fluoro-gold (F-G) as tracer was injected into the L6, 6 intervertebral disc of 3 groups; after 7 days of F-G injection, complete Freund's adjuvant (50 microL) and the same volume of saline were injected in the experimental group (to prepare the model of intervertebral disc inflammation) and the control group, respectively, and the blank control group had no further treatment. After 1, 3, 7, and 14 days, T13-L6 DRG and L5, 6 intervertebral disc of experimental group and control group were harvested to detect the GAP-43 by using fluorescent immunohistochemistry, in situ hybridization, and RT-PCR. The DRG and intervertebral disc of blank control group were also harvested after 8 days of F-G injection.

Results: Fluorescent immunohistochemistry results showed that the number of F-G-labeled GAP-43 immunoreaction (GAP-43-IR) cells of the DRGs in the experimental group was significantly higher than that in the control group (P < 0.05) at 3 days, and no significant difference was found at the other time points (P > 0.05). There was no significant difference in the cross-sectional area of F-G-labeled GAP-43-IR cells between the experimental group and the control group at each time point (P > 0.05). The co-expression of GAP-43 with calcitonin gene-related peptide (CGRP) and isolectin B4 (IB4)-binding glycoprotein exhibited that the expression of CGRP was 91.4% +/- 7.4% in the control group and was 87.6% +/- 7.8% in the experimental group, showing no significant difference between 2 groups (P > 0.05). There was no IB4-binding glycoprotein expression in GAP-43-IR cells of the DRGs in 2 groups. The expressions of GAP-43, CGRP, and IB4-positive nerve fibers in the intervertebral disc exhibited that the GAP-43-IR nerve fibers in the experimental group were significantly more than that in the control group (P < 0.05), but no significant difference was found in the expression of CGRP between 2 groups (P > 0.05); and there was no IB4-binding glycoprotein expression in GAP-43-IR nerve fibers of the intervertebral disc in 2 group. In situ hybridization and RT-PCR detection showed that the positive expression cells ratio of GAP-43 mRNA and the level of GAP-43 mRNA were significantly higher in the experimental group than in the control group at 1 day (P < 0.05), and no significant difference was found at the other time points (P > 0.05).

Conclusion: Intradiscal inflammatory environment may induce the expression of GAP-43, and potentially promote the nerve fiber ingrowth of rat.