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Dioscorin isolated from Dioscorea alata activates TLR4-signaling pathways and induces cytokine expression in
Shu-Ling Fu1, Ya-Hui Hsu, Pei-Yeh Lee
1Institute of Traditional Medicine, National Yang-Ming University, 155, Sec.2, Li-Nong St., Taipei 11221, Taiwan. slfu@ym.edu.tw
Abstract:
The Toll-like receptor 4 (TLR4)-signaling pathway is crucial for activating both innate and adaptive immunity. TLR4 is a promising molecular target for immune-modulating drugs, and TLR4 agonists are of therapeutic potential for treating immune diseases and cancers. Several medicinal herb-derived components have recently been reported to act via TLR4-dependent pathways, suggesting that medicinal plants are potential resources for identifying TLR4 activators. We have applied a screening procedure to systematically identify herbal constituents that activate TLR4. To exclude possible LPS contamination in these plant-derived components, a LPS inhibitor, polymyxin B, was added during screening. One of the plant components we identified from the screening was dioscorin, the glycoprotein isolated from Dioscorea alata. It induced TLR4-downstream cytokine expression in bone marrow cells isolated from TLR4-functional C3H/HeN mice but not from TLR4-defective C3H/HeJ mice. Dioscorin also stimulated multiple signaling molecules (NF-kappaB, ERK, JNK, and p38) and induced the expression of cytokines (TNF-alpha, IL-1beta, and IL-6) in murine RAW 264.7 macrophages. Furthermore, the ERK, p38, JNK, and NF-kappaB-mediated pathways are all involved in dioscorin-mediated TNF-alpha production. In summary, our results demonstrate that dioscorin is a novel TLR4 activator and induces macrophage activation via typical TLR4-signaling pathways.
Insights
Dioscorin, a plant component, activates Toll-like receptor 4 (TLR4) signaling, a key pathway in immunity. This discovery highlights medicinal plants as sources for novel immune-modulating compounds like dioscorin.
Area of Science:
- Immunology
- Pharmacology
- Natural Products
Background:
- Toll-like receptor 4 (TLR4) signaling is vital for innate and adaptive immunity.
- TLR4 is a therapeutic target for immune diseases and cancers.
- Medicinal plants may yield TLR4 activators.
Purpose of the Study:
- To systematically screen herbal constituents for TLR4 activation.
- To identify novel TLR4 activators from medicinal plants.
- To investigate the mechanism of action of identified compounds.
Main Methods:
- Screening of herbal constituents using TLR4-dependent assays.
- Inclusion of polymyxin B to rule out LPS contamination.
- Analysis of cytokine expression and signaling pathways in immune cells.
Main Results:
- Dioscorin, from Dioscorea alata, was identified as a TLR4 activator.
- Dioscorin induced TLR4-downstream cytokine expression in mouse bone marrow cells.
- Dioscorin activated NF-kappaB, ERK, JNK, and p38 signaling pathways in macrophages, leading to cytokine production.
Conclusions:
- Dioscorin is a novel Toll-like receptor 4 activator.
- Dioscorin induces macrophage activation through TLR4-dependent signaling pathways.
- Medicinal plants are a valuable source for discovering immunomodulatory compounds.
