title: Bone morphogenic protein (BMP) signaling up-regulates neutral sphingomyelinase 2 to suppress chondrocyte maturation via the Akt protein signaling pathway as a negative feedback mechanism.
abstract: Although bone morphogenic protein (BMP) signaling promotes chondrogenesis, it is not clear whether BMP-induced chondrocyte maturation is cell-autonomously terminated. Loss of function of Smpd3 in mice results in an increase in mature hypertrophic chondrocytes. Here, we report that in chondrocytes the Runx2-dependent expression of Smpd3 was increased by BMP-2 stimulation. Neutral sphingomyelinase 2 (nSMase2), encoded by the Smpd3 gene, was detected both in prehypertrophic and hypertrophic chondrocytes of mouse embryo bone cartilage. An siRNA for Smpd3, as well as the nSMase inhibitor GW4869, significantly enhanced BMP-2-induced differentiation and maturation of chondrocytes. Conversely, overexpression of Smpd3 or C2-ceramide, which mimics the function of nSMase2, inhibited chondrogenesis. Upon induction of Smpd3 siRNA or GW4869, phosphorylation of both Akt and S6 proteins was increased. The accelerated chondrogenesis induced by Smpd3 silencing was negated by application of the Akt inhibitor MK2206 or the mammalian target of rapamycin inhibitor rapamycin. Importantly, in mouse bone culture, GW4869 treatment significantly promoted BMP-2-induced hypertrophic maturation and calcification of chondrocytes, which subsequently was eliminated by C2-ceramide. Smpd3 knockdown decreased the apoptosis of terminally matured ATDC5 chondrocytes, probably as a result of decreased ceramide production. In addition, we found that expression of hyaluronan synthase 2 (Has2) was elevated by a loss of Smpd3, which was restored by MK2206. Indeed, expression of Has2 protein decreased in nSMase2-positive hypertrophic chondrocytes in the bones of mouse embryos. Our data suggest that the Smpd3/nSMase2-ceramide-Akt signaling axis negatively regulates BMP-induced chondrocyte maturation and Has2 expression to control the rate of endochondral ossification as a negative feedback mechanism.
authors: From the Departments of Medical Joint Materials and.
authors: Hironori
authors: H
authors: Kakoi
authors: Shingo
authors: S
authors: Maeda
authors: Naohiro
authors: N
authors: Shinohara
authors: Kanehiro
authors: K
authors: Matsuyama
authors: Katsuyuki
authors: K
authors: Imamura
authors: Ichiro
authors: I
authors: Kawamura
authors: Satoshi
authors: S
authors: Nagano
authors: Takao
authors: T
authors: Setoguchi
authors: Masahiro
authors: M
authors: Yokouchi
authors: Yasuhiro
authors: Y
authors: Ishidou
authors: Setsuro
authors: S
authors: Komiya
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism*; D050659:Core Binding Factor Alpha 1 Subunit / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D008810:Mice, Inbred C57BL; D009924:Organ Culture Techniques; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034622:RNA Interference; D015398:Signal Transduction; D013108:Sphingomyelin Phosphodiesterase / Q000235:genetics* / Q000378:metabolism
chemical_list: D055396:Bone Morphogenetic Protein 2; D050659:Core Binding Factor Alpha 1 Subunit; D051057:Proto-Oncogene Proteins c-akt; C491483:Smpd3 protein, mouse; D013108:Sphingomyelin Phosphodiesterase
keywords: Akt; Bone Morphogenetic Protein (BMP); Ceramide; Chondrogenesis; Hyaluronan Synthase 2; Sphingomyelin Phosphodiesterase 3; Sphingomyelinase