Purpose: Majority of the previous studies compared lumbar spinal stenosis (LSS) and lumbar disc herniation (LDH) patients for analyses of LFH. However, the separation of normal/hypertrophied LF has often been ambiguous and the severity of hypertrophic activity differed. Here, we present a novel analysis scheme for LFH in which myofibroblast is proposed as a major etiological factor for LFH study.
Methods: Seventy-one LF patient tissue samples were used for this study. Initially, mRNA levels of the samples were assessed by qRT-PCR: angiopoietin-like protein-2 (ANGPTL2), transforming growth factor-beta1 (TGF-β1), vascular endothelial growth factor (VEGF), interleukin-6, collagen-1, 3, 4, 5, and 11, and elastin. Myofibroblasts were detected by immune stain using α-smooth muscle actin (αSMA) as a marker. To study the myofibroblast in TGF-β pathway, LF tissues were analyzed for protein levels of αSMA/TGF-β1 by Western blot. In addition, from LF cells cultured with exogenous TGF-β1 conditioned medium, expression of αSMA/collagen-1 was assessed and the cell morphology was identified.
Results: The comparative analysis of mRNA expression levels (LSS vs LDH) failed to show significant differences in TGF-β1 (p = 0.08); however, we found a significant positive correlation among ANGPTL2, VEGF, TGF-β1, and collagen-1 and 3, which represent common trends in hypertrophic activity (p < 0.05). We detected myofibroblast in the patient samples by αSMA staining, and the protein levels of αSMA were positively correlated with TGF-β1. In LF cell culture, exogenous TGF-β1 upregulated αSMA/collagen-1 mRNA levels and facilitated trans-differentiation to myofibroblast.
Conclusions: We conclude that the transition of fibroblast to myofibroblasts via TGF-β pathway is a key linker between inflammation and fibrosis in LFH mechanism.
Keywords: Alpha-smooth muscle actin; Hypertrophy; Ligamentum flavum; Myofibroblasts; Transforming growth factor beta1.