Muramyl dipeptide enhances osteoclast formation induced by lipopolysaccharide, IL-1 alpha, and TNF-alpha through nucleotide-binding oligomerization domain 2-mediated signaling in osteoblasts.
Muramyl dipeptide (MDP) is the minimal essential structural unit responsible for the immunoadjuvant activity of peptidoglycan. As well as bone-resorbing factors such as 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3) and PGE2, LPS and IL-1alpha stimulate osteoclast formation in mouse cocultures of primary osteoblasts and hemopoietic cells. MDP alone could not induce osteoclast formation in the coculture, but enhanced osteoclast formation induced by LPS, IL-1alpha, or TNF-alpha but not 1alpha,25(OH)2D3 or PGE2. MDP failed to enhance osteoclast formation from osteoclast progenitors induced by receptor activator of NF-kappaB ligand (RANKL) or TNF-alpha. MDP up-regulated RANKL expression in osteoblasts treated with LPS or TNF-alpha but not 1alpha,25(OH)2D3. Osteoblasts expressed mRNA of nucleotide-binding oligomerization domain 2 (Nod2), an intracellular sensor of MDP, in response to LPS, IL-1alpha, or TNF-alpha but not 1alpha,25(OH)2D3. Induction of Nod2 mRNA expression by LPS but not by TNF-alpha in osteoblasts was dependent on TLR4 and MyD88. MDP also enhanced TNF-alpha-induced osteoclast formation in cocultures prepared from Toll/IL-1R domain-containing adapter protein (TIRAP)-deficient mice through the up-regulation of RANKL mRNA expression in osteoblasts, suggesting that TLR2 is not involved in the MDP-induced osteoclast formation. The depletion of intracellular Nod2 by small interfering RNA blocked MDP-induced up-regulation of RANKL mRNA in osteoblasts. LPS and RANKL stimulated the survival of osteoclasts, and this effect was not enhanced by MDP. These results suggest that MDP synergistically enhances osteoclast formation induced by LPS, IL-1alpha, and TNF-alpha through RANKL expression in osteoblasts, and that Nod2-mediated signals are involved in the MDP-induced RANKL expression in osteoblasts.
Yang
Shuhua
S
Department of Oral and Maxillofacial Surgery, Matsumoto Dental University, Shiojiri, Nagano, Japan.
Takahashi
Naoyuki
N
Yamashita
Teruhito
T
Sato
Nobuaki
N
Takahashi
Masahiro
M
Mogi
Makio
M
Uematsu
Takashi
T
Kobayashi
Yasuhiro
Y
Nakamichi
Yuko
Y
Takeda
Kiyoshi
K
Akira
Shizuo
S
Takada
Haruhiko
H
Udagawa
Nobuyuki
N
Furusawa
Kiyofumi
K
D000119:Acetylmuramyl-Alanyl-Isoglutamine / Q000494:pharmacology*; D048868:Adaptor Proteins, Signal Transducing; D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000818:Animals; D000943:Antigens, Differentiation / Q000502:physiology; D002352:Carrier Proteins / Q000096:biosynthesis / Q000502:physiology; D002454:Cell Differentiation / Q000276:immunology*; D002470:Cell Survival / Q000276:immunology; D002478:Cells, Cultured; D018920:Coculture Techniques; D006023:Glycoproteins / Q000096:biosynthesis; D007375:Interleukin-1 / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008297:Male; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000502:physiology; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88; D053473:Nod2 Signaling Adaptor Protein; D010006:Osteoblasts / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D010010:Osteoclasts / Q000166:cytology / Q000276:immunology*; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger / Q000096:biosynthesis; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis; D011971:Receptors, Immunologic / Q000502:physiology; D018124:Receptors, Tumor Necrosis Factor / Q000096:biosynthesis; D015398:Signal Transduction / Q000276:immunology; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D015854:Up-Regulation / Q000276:immunology
D048868:Adaptor Proteins, Signal Transducing; D000276:Adjuvants, Immunologic; D000943:Antigens, Differentiation; D002352:Carrier Proteins; D006023:Glycoproteins; D007375:Interleukin-1; D047908:Intracellular Signaling Peptides and Proteins; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D053473:Nod2 Signaling Adaptor Protein; C495945:Nod2 protein, mouse; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D011971:Receptors, Immunologic; D018124:Receptors, Tumor Necrosis Factor; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; C505687:Tnfrsf11a protein, mouse; C506031:Tnfrsf11b protein, mouse; C505689:Tnfsf11 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D000119:Acetylmuramyl-Alanyl-Isoglutamine