p38 Mitogen-Activated Protein Kinase Is Involved in Interleukin-6 Secretion from Human Ligamentum Flavum-Derived Cells Stimulated by Tumor Necrosis Factor-α

Transforming Growth Factor-β Induces Interleukin-6 Secretion from Human Ligamentum Flavum-Derived Cells through Partial Activation of p38 and p44/42 Mitogen-Activated Protein Kinases

STUDY DESIGN

This experimental study was performed using human ligamentum flavum-derived cells (HFCs).

PURPOSE

To investigate the intracellular signaling mechanism of interleukin-6 (IL-6) secretion in transforming growth factor-β (TGF- β)-stimulated HFCs.

OVERVIEW OF LITERATURE

Lumbar spinal stenosis (LSS) is a prevalent disease among the elderly, characterized by debilitating pain in the lower extremities. Although the number of patients with LSS has increased in recent years, the underlying pathomechanism remains unclear. Clinical examinations typically rely on magnetic resonance imaging to diagnose patients, revealing ligamentum flavum hypertrophy. Some studies have suggested an association between ligamentum flavum hypertrophy and inflammation/fibrosis, and expression of TGF-β and IL-6 has been observed in surgically obtained ligamentum flavum samples. However, direct evidence linking TGF-β and IL-6 expression in HFCs is lacking.

METHODS

HFCs were obtained from patients with LSS who had undergone decompression surgery. The cells were stimulated with TGF-β and pretreated with either the p38 mitogen-activated protein (MAP) kinase inhibitor SB203580 or the p44/42 MAP kinase inhibitor FR180204. IL-6 secretion in the cell culture medium and IL-6 messenger RNA (mRNA) expression levels were analyzed using an enzyme-linked immunoassay and real-time polymerase chain reaction, respectively.

RESULTS

TGF-β administration resulted in a dose- and time-dependent stimulation of IL-6 release. Treatment with SB203580 and FR180204 markedly suppressed TGF-β-induced IL-6 secretion from HFCs. Moreover, these inhibitors suppressed IL-6 mRNA expression in response to TGF-β stimulation.

CONCLUSIONS

Our findings indicate that TGF-β induces IL-6 protein secretion and gene expression in HFCs through the activation of p38 or p44/42 MAP kinases. These results suggest a potential association between IL-6-mediated inflammatory response and tissue hypertrophy in LSS, and we provide insights into molecular targets for therapeutic interventions targeting LSS-related inflammation through our analysis of the MAP kinase pathway using HFCs.

Administration of N-Acetylcysteine to Regress the Fibrogenic and Proinflammatory Effects of Oxidative Stress in Hypertrophic Ligamentum Flavum Cells

Ligamentum flavum hypertrophy (LFH) is a major cause of lumbar spinal stenosis (LSS). In hypertrophic ligamentum flavum (LF) cells, oxidative stress activates intracellular signaling and induces the expression of inflammatory and fibrotic markers. This study explored whether healthy and hypertrophic LF cells respond differently to oxidative stress, via examining the levels of phosphorylated p38 (p-p38), inducible nitric oxide synthase (iNOS), and α-smooth muscle actin (α-SMA). Furthermore, the efficacy of N-acetylcysteine (NAC), an antioxidant, in reversing the fibrogenic and proinflammatory effects of oxidative stress in hypertrophic LF cells was investigated by assessing the expression levels of p-p38, p-p65, iNOS, TGF-β, α-SMA, vimentin, and collagen I under H2O2 treatment with or without NAC. Under oxidative stress, p-p38 increased significantly in both hypertrophic and healthy LF cells, and iNOS was elevated in only the hypertrophic LF cells. This revealed that oxidative stress negatively affected both hypertrophic and healthy LF cells, with the hypertrophic LF cells exhibiting more active inflammation than did the healthy cells. After H2O2 treatment, p-p38, p-p65, iNOS, TGF-β, vimentin, and collagen I increased significantly, and NAC administration reversed the effects of oxidative stress. These results can form the basis of a novel therapeutic treatment for LFH using antioxidants.