The p38 MAPK pathway is essential for skeletogenesis and bone homeostasis in mice
Matthew B. Greenblatt, … , Roger Davis, Laurie H. Glimcher
Matthew B. Greenblatt, … , Roger Davis, Laurie H. Glimcher
Published June 14, 2010
Citation Information: J Clin Invest. 2010;120(7):2457-2473. https://doi.org/10.1172/JCI42285.
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Research Article Bone biology

The p38 MAPK pathway is essential for skeletogenesis and bone homeostasis in mice

Abstract

Nearly every extracellular ligand that has been found to play a role in regulating bone biology acts, at least in part, through MAPK pathways. Nevertheless, much remains to be learned about the contribution of MAPKs to osteoblast biology in vivo. Here we report that the p38 MAPK pathway is required for normal skeletogenesis in mice, as mice with deletion of any of the MAPK pathway member–encoding genes MAPK kinase 3 (Mkk3), Mkk6, p38a, or p38b displayed profoundly reduced bone mass secondary to defective osteoblast differentiation. Among the MAPK kinase kinase (MAP3K) family, we identified TGF-β–activated kinase 1 (TAK1; also known as MAP3K7) as the critical activator upstream of p38 in osteoblasts. Osteoblast-specific deletion of Tak1 resulted in clavicular hypoplasia and delayed fontanelle fusion, a phenotype similar to the cleidocranial dysplasia observed in humans haploinsufficient for the transcription factor runt-related transcription factor 2 (Runx2). Mechanistic analysis revealed that the TAK1–MKK3/6–p38 MAPK axis phosphorylated Runx2, promoting its association with the coactivator CREB-binding protein (CBP), which was required to regulate osteoblast genetic programs. These findings reveal an in vivo function for p38β and establish that MAPK signaling is essential for bone formation in vivo. These results also suggest that selective p38β agonists may represent attractive therapeutic agents to prevent bone loss associated with osteoporosis and aging.

Authors

Matthew B. Greenblatt, Jae-Hyuck Shim, Weiguo Zou, Despina Sitara, Michelle Schweitzer, Dorothy Hu, Sutada Lotinun, Yasuyo Sano, Roland Baron, Jin Mo Park, Simon Arthur, Min Xie, Michael D. Schneider, Bo Zhai, Steven Gygi, Roger Davis, Laurie H. Glimcher

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Figure 8

Mapping the p38 phosphorylated residues in Runx2 and their functional consequences.

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Mapping the p38 phosphorylated residues in Runx2 and their functional co...
(A) Schematic diagram showing Runx2 phosphorylation sites by the p38 MAPK pathway. (B) C3H10T1/2 were transfected with either vector, WT Runx2, or mutant Runx2 constructs harboring the indicated mutations, the OSE2 luciferase reporter, and either vector or p38α and MKK6. Results are expressed as relative luciferase activity normalized by Renilla control. Values are mean + SD. (C) Primary Tak1fl/fl CalvOb were infected with either vector or cre lentivirus together with Myc-Runx2–expressing lentivirus. Nuclear extracts were immunoprecipitated with either IgG or anti-CBP antibodies and protein A agarose and immunoblotted with anti-Myc antibody. Expression of Myc-Runx2 protein was analyzed by immunoblotting with anti-Myc antibody. (D) Human mesenchymal stem cells were infected with lentiviruses encoding Runx2-WT or Runx2-3SA and cultured under osteoblast differentiation conditions. After 6 days, osteoblast differentiation was analyzed by a colorimetric assay (upper) or fast blue staining (lower) for alkaline phosphatase activity. Original magnification, ×25. For the colorimetric assay, Runx2-WT was compared with Runx2-3SA via an unpaired Student’s t test. *P < 0.0005. (E) A schema depicting the TAK1/MKK3/6/p38/RUNX2 axis in osteoblasts.