Chronic sciatic nerve compression induces fibrosis in dorsal root ganglia

Abstract

In the present study, pathological alterations in neurons of the dorsal root ganglia (DRG) were investigated in a rat model of chronic sciatic nerve compression. The rat model of chronic sciatic nerve compression was established by placing a 1 cm Silastic tube around the right sciatic nerve. Histological examination was performed via Masson's trichrome staining. DRG injury was assessed using Fluoro Ruby (FR) or Fluoro Gold (FG). The expression levels of target genes were examined using reverse transcription‑quantitative polymerase chain reaction, western blot and immunohistochemical analyses. At 3 weeks post‑compression, collagen fiber accumulation was observed in the ipsilateral area and, at 8 weeks, excessive collagen formation with muscle atrophy was observed. The collagen volume fraction gradually and significantly increased following sciatic nerve compression. In the model rats, the numbers of FR‑labeled DRG neurons were significantly higher, relative to the sham‑operated group, however, the numbers of FG‑labeled neurons were similar. In the ipsilateral DRG neurons of the model group, the levels of transforming growth factor‑β1 (TGF‑β1) and connective tissue growth factor (CTGF) were elevated and, surrounding the neurons, the levels of collagen type I were increased, compared with those in the contralateral DRG. In the ipsilateral DRG, chronic nerve compression was associated with significantly higher levels of phosphorylated (p)‑extracellular signal‑regulated kinase 1/2, and significantly lower levels of p‑c‑Jun N‑terminal kinase and p‑p38, compared with those in the contralateral DRGs. Chronic sciatic nerve compression likely induced DRG pathology by upregulating the expression levels of TGF‑β1, CTGF and collagen type I, with involvement of the mitogen‑activated protein kinase signaling pathway.

Figure 1

Muscle fiber changes in rats with chronic sciatic nerve compression. The rats were subjected to sciatic nerve compression for 0, 3 or 8 weeks. (A) Muscles stained with Masson's trichrome. Representative images show collagen fiber and muscle formation. Scale bar=50 µm. (B) Gastrocnemius muscle fiber CSA in different groups. (C) Percentage of gastrocnemius muscle fiber CVF in different groups. Data are presented as the mean ± standard deviation. ^*P<0.05 and ^**P<0.01 compared with the control (0 weeks). CSA, cross-sectional area; CVF, collagen volume fraction.

Figure 2

Retrograde fluorescent tracing of DRG neurons. Tissues from rats in the sham control and chronic sciatic nerve compression groups were labeled with FR and FG. (A) FR (red) and FG (blue) labeling of DRG neurons. Scale bar=200 µm. (B) Numbers of FR- and FG-positive neurons per field. Data are presented as the mean ± standard deviation. ^*P<0.05, compared with the sham control group. DRG, dorsal root ganglion; FR, Fluoro Ruby; FG, Fluoro Gold.

Figure 3

mRNA and protein levels of TGF-β1, CTGF and collagen type I in DRG neurons. (A) mRNA levels of target genes in contralateral and ipsilateral DRG neurons were examined using reverse transcription-quantitative polymerase chain reaction 3 weeks following surgery (n=4). (B) Protein levels of target genes were evaluated using western blotting. Representative results are shown. (C) Relative protein levels were calculated (n=3). (D) Levels and distribution of target proteins were examined using immunohistochemistry. Nuclei were counterstained with DAPI (n=10). Magnification, ×200. Data are presented as the mean ± standard deviation. ^*P<0.05, compared with the contralateral DRG. TGF-β1, transforming growth factor-β1; CTGF, connective tissue growth factor; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; DRG, dorsal root ganglion; Con, contralateral; Ips, ipsilateral.

Figure 4

Involvement of the mitogen-activated protein kinase signaling pathway in chronic sciatic nerve compression-induced DRG injury. (A) Levels of p-ERK, p-p38 and p-JNK in the ipsilateral and contralateral DRGs following chronic nerve compression. Representative results are shown. (B) Relative protein expression levels were calculated. Data are presented as the mean ± standard deviation. ^*P<0.05 compared with contralateral DRG (n=3). ERK, extracellular signal-regulated kinase; JNK, c-Jun N-terminal kinase; p-, phosphorylated; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; DRG, dorsal root ganglion;Con, contralateral; Ips, ipsilateral.