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A Simple Pit Assay Protocol to Visualize and Quantify Osteoclastic Resorption In Vitro
Published on: June 16, 2022
[Bone destruction caused by osteoclasts]
Teruhito Yamashita1, Naoyuki Takahashi, Shuhua Yang
1Matsumoto Dental University, Institute for Oral Science.
Abstract:
Lipopolysaccharide (LPS) and muramyl dipeptide (MDP) are components of bacterial cell walls that cause innate immune responses and inflammation. Toll-like receptor 4 (TLR4) is a receptor for LPS and transduces signals through myeloid differentiation factor 88 (MyD88), which plays essential roles in the TLR/interleukin (IL)-1R signaling and activates MAP/ERK kinase (MEK)/ERK pathway to induce receptor activator of NF-kappaB ligand (RANKL) expression in osteoblasts. Osteoblasts express nucleotide oligomerization domain (NOD)2, an intracellular sensor for MDP, in response to LPS, IL-1 and TNF. NOD2 binds receptor-interacting protein (RIP2), a serine/threonine kinase which transduces NF-kappaB signaling. MDP synergistically enhances osteoclast formation induced by LPS, IL-1 and TNF through RANK ligand up-regulation in osteoblasts. TLR4 and NOD2 recognize bacterial components on cell surfaces and inside cells, respectively, and these signals up-regulate RANKL expression in osteoblasts, which results in enhancing osteoclast formation and function.
Insights
Bacterial components lipopolysaccharide (LPS) and muramyl dipeptide (MDP) activate innate immunity via Toll-like receptor 4 (TLR4) and nucleotide oligomerization domain 2 (NOD2). These pathways enhance osteoclast formation by up-regulating RANKL in osteoblasts.
Area of Science:
- Immunology
- Cell Biology
- Bone Biology
Context:
- Lipopolysaccharide (LPS) and muramyl dipeptide (MDP) are bacterial cell wall components triggering innate immune responses and inflammation.
- Toll-like receptor 4 (TLR4) and nucleotide oligomerization domain 2 (NOD2) are key pattern recognition receptors involved in sensing these bacterial products.
Purpose:
- To elucidate the signaling pathways initiated by LPS and MDP in osteoblasts.
- To investigate the role of TLR4 and NOD2 in regulating osteoclastogenesis.
- To understand how bacterial components influence bone remodeling.
Summary:
- LPS binds TLR4, activating MyD88 and the MEK/ERK pathway, leading to RANKL expression in osteoblasts.
- MDP binds NOD2, activating RIP2 and NF-kappaB signaling.
- Both LPS and MDP synergistically enhance osteoclast formation through RANKL upregulation, linking bacterial recognition to bone resorption.
Impact:
- This study reveals a critical link between bacterial sensing by osteoblasts and the regulation of bone remodeling.
- Understanding these pathways could inform therapeutic strategies for inflammatory bone diseases.
- Highlights the dual role of osteoblasts as immune sensors and regulators of bone homeostasis.
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