Background: Low intensity pulsed ultrasound (LIPUS) is a mechanical stimulus clinically used to promote bone fracture healing. Results: LIPUS suppresses adipogenesis and promotes osteogenesis of mesenchyme stem/progenitor cell lines by inhibiting PPAR␥2 through ROCK-Cot/Tpl2-MEK-ERK pathway. Conclusion: LIPUS influences multilineage differentiation of mesenchymal stem and progenitor cells. Significance: LIPUS may be a new clinical approach to chronic bone metabolic disorders, including osteoporosis.

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Edited by Masayuki MiyasakaKeywords: Macrophage Chemokine LPS Cot/Tpl2 ERK a b s t r a c t LPS signaling is mediated through MyD88-dependent and -independent pathways, activating NF-jB, MAP kinases and IRF3. Cot/Tpl2 is an essential upstream kinase in LPS-mediated activation of ERKs. Here we explore the roles of MyD88 and Cot/Tpl2 in LPS-induced chemokine expression by studying myd88 À/À and cot/tpl2 À/À macrophages. Among the nine LPS-responsive chemokines examined, mRNA induction of ccl5, cxcl10, and cxcl13 is mediated through the MyD88-independent pathway. Notably, Cot/Tpl2-ERK signaling axis exerts negative effects on the expression of these three chemokines. In contrast, LPS-induced gene expression of ccl2, ccl7, cxcl2, cxcl3, ccl8, and cxcl9 is mediated in the MyD88-dependent manner. The Cot/Tpl2-ERK axis promotes the expression of the first four and inhibits the expression of the latter two. Thus, LPS induces expression of multiple chemokines through various signaling pathways in macrophages.

Chemokines are a family of cytokines inducing cell migration and inflammation. Recent reports have implicated the roles of chemokines in cell differentiation. However, little is known about the functional roles of chemokines in adipocytes. Here, we explored gene expression levels of chemokines and chemokine receptors during adipogenic differentiation. We have found that two chemokines, chemokine (C-X-C motif) ligand 3 (CXCL3) and CXCL13, as well as CXC chemokine receptor 2 (CXCR2), a CXCL3 receptor, are highly expressed in mature adipocytes. When 3T3-L1 cells and ST2 cells were induced to differentiate, both the number of lipid droplets and the expression levels of adipogenic markers were significantly promoted by the addition of CXCL3, but not CXCL13. Conversely, gene knockdown of either CXCL3 or CXCR2 by specific siRNA effectively inhibited the course of adipogenic differentiation. CXCL3 treatment of 3T3-L1 cells significantly induced the phosphorylation of ERK and c-jun N-terminal kinase (JNK). Furthermore, CXCL3-induced CCAAT-enhancer binding protein (C/EBP)β and δ expression was suppressed by both ERK and JNK-specific inhibitors. Furthermore, chromatin immunoprecipitation assay revealed functional binding of PPARγ2 within the cxcl3 promoter region. Taken together, these results have indicated that CXCL3 is a novel adipokine that facilitates adipogenesis in an autocrine and/or a paracrine manner through induction of c/ebpb and c/ebpd.

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Bone morphogenetic protein (BMP)9 has been reported to be the most potent BMP to induce bone formation. However, the details of BMP9‐transduced intracellular signaling remain ambiguous. Here, we have investigated signal transduction mechanisms of BMP9 in comparison to BMP2, another potent inducer of bone formation, in osteoblasts. In a mouse osteoblast cell line, BMP9 induced higher mRNA levels of alkaline phosphatase (ALP) and runt‐related transcription factor 2 (Runx2) than BMP2 within 2 h. Unlike BMP2, BMP9 induced rapid phosphorylation of glycogen synthase kinase 3‐β (GSK3‐β) and protein kinase B (Akt) and increased the cellular protein content of β‐catenin. BMP9 moderately increased mRNA levels of several canonical Wingless‐related integration site to lower degrees than BMP2. Furthermore, BMP9‐induced GSK3‐β phosphorylation was not inhibited by pretreatment with actinomycin D, cycloheximide, or Brefeldin A, indicating it is independent of Wnt protein secretion. BMP9‐induced GSK3‐β phosphorylation was abrogated by Akt or class I PI3K‐specific inhibitors. Moreover, inactivation of GSK3‐β by LiCl did not further promote ALP and Runx2 mRNA induction by BMP9 as significantly as that by BMP2. Notably, BMP9‐induced GSK3‐β phosphorylation was inhibited by small interfering RNA against endoglin and GIPC PDZ domain‐containing family, member 1. Taken together, our present findings have indicated that BMP9 directly activates GSK3β‐β‐catenin signaling pathway through class I PI3K‐Akt Axis in osteoblasts, which may be essential for the potent osteoinductive activity of BMP9.—Eiraku, N., Chiba, N., Nakamura, T., Amir, M. S., Seong, C.‐H., Ohnishi, T., Kusuyama, J., Noguchi, K., Matsuguchi, T. BMP9 directly induces rapid GSK3‐β phosphorylation in a Wnt‐independent manner through class I PI3K‐Akt axis in osteoblasts. FASEB J. 33, 12124‐12134 (2019). http://www.fasebj.org

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