Decreased BMP2 signal in GIT1 knockout mice slows bone healing.

Endochondral ossification, an important stage of fracture healing, is regulated by a variety of signaling pathways. Transforming growth factor ß (TGFß) superfamily plays important roles and comprises TGFßs, bone morphogenetic proteins (BMPs), and growth differentiation factors. TGFßs primarily regulate cartilage formation and endochondral ossification. BMP2 shows diverse efficacy, from the formation of skeleton and extraskeletal organs to the osteogenesis and remodeling of bone. G-protein-coupled receptor kinase 2-interacting protein-1 (GIT1), a shuttle protein in osteoblasts, facilitates fracture healing by promoting bone formation and increasing the secretion of vascular endothelial growth factor. Our study examined whether GIT1 regulates fracture healing through the BMP2 signaling pathway and/or through the TGFß signaling pathway. GIT1 knockout (KO) mice exhibited delayed fracture healing, chondrocyte accumulation in the fracture area, and reduced staining intensity of phosphorylated Smad1/5/8 (pSmad1/5/8) and Runx2. Endochondral mineralization diminished while the staining intensity of phosphorylated Smad2/3 (pSmad2/3) showed no significant change. Bone marrow mesenchymal stem cells extracted from GIT1 KO mice showed a decline of pSmad1/5/8 levels and of pSmad1/5/8 translocated into the cell nucleus after BMP2 stimulus. We detected no significant change in the pSmad2/3 level after TGFß1 stimulus. Data obtained from reporter gene analysis of C3H10T1/2 cells cultured in vitro confirmed these findings. GIT1-siRNA inhibited transcription in the cell nucleus via pSmad1/5/8 after BMP2 stimulus but had no significant effect on transcription via pSmad2/3 after TGFß1 stimulus. Our results indicate that GIT1 regulates Smad1/5/8 phosphorylation and mediates BMP2 regulation of Runx2 expression, thus affecting endochondral ossification at the fracture site.

IGF-1 regulation of type II collagen and MMP-13 expression in rat endplate chondrocytes via distinct signaling pathways.

OBJECTIVE: Abnormal maturation and ossification of the endplate chondrocytes play a central role in the pathogenesis of degenerative disorders of the cervical spine. It is widely held that insulin like growth factor-1 (IGF-1) stimulates chondrocyte proliferation and inhibits chondrocyte terminal differentiation both in vitro and in vivo. However, the mechanism underlying such regulation is not fully understood. The present study aimed to determine the role of IGF-1 on the mRNA expression of collagen type II, alpha 1 (Col2a1) and matrix metallopeptidase 13 (MMP-13) in rat endplate chondrocytes. The possible pathways that transduce IGF-1 effects such as phosphatidylinositol-3 (PI-3)-kinase (PI3K) and mitogen activated protein kinase (MAPK) were also investigated in these cells. METHODS: Cultured endplate chondrocytes harvested from rat cervical spines were treated with IGF-1 (100ng/ml), and the changes in Col2a1 and MMP-13 mRNA were monitored with real-time polymerase chain reaction (PCR). MMP-13 activity was also assayed. Activation of signaling proteins was evaluated by western blot analysis. Cells were also treated with pharmacological agents that block PI3K and MAPK signaling pathways. RESULTS: IGF-1 increased Col2a1 mRNA expression in rat endplate chondrocytes in a time- and dose-dependent manner. IGF-1 treatment resulted in a fourfold increase of Col2a1 mRNA with the effect maximizing at 24h. In contrast, IGF-1 treatment for 24h caused a roughly 50% reduction in MMP-13 mRNA. Similar effects were seen on the protein levels of type II collagen (col2) and MMP-13. Consistent with these results, IGF-1 also repressed MMP-13 activity. IGF-1 activated both the PI3K and the extracellular signal-regulated kinase (ERK) pathways as evidenced by phosphorylation of either Akt or ERK1/2 (respectively). The PI3K inhibitor Wartmannin significantly inhibited the IGF-1 effect on Col2a1 mRNA expression but did not affect IGF-1-induced repression of MMP-13 expression. In contrast, the ERK/MAPK inhibitor PD98059 significantly inhibited the effect of IGF-1 on MMP-13 mRNA repression and enhanced IGF-1-induced Col2a1 mRNA expression. CONCLUSIONS: In rat endplate chondrocytes the PI3K pathway mainly transduces IGF-1 effect on col2 expression while the ERK pathway mediates IGF-1 effect on MMP-13 expression.

Putative signaling action of amelogenin utilizes the Wnt/beta-catenin pathway.

BACKGROUND AND OBJECTIVE: While it has long been known that amelogenin is essential for the proper development of enamel, its role has generally been seen as structural in nature. However, our new data implicate this protein in the regulation of cell signaling pathways in periodontal ligament cells and osteoblasts. In this article we report the successful purification of a recombinant mouse amelogenin protein and demonstrate that it has signaling activity in isolated mouse calvarial cells and human periodontal ligament cells. MATERIAL AND METHODS: To determine the regulatory function of canonical Wnt signaling by amelogenin, we used TOPGAL transgenic mice. These mice express a beta-galactosidase transgene under the control of a LEF/TCF and beta-catenin-inducible promoter. To investigate in greater detail the molecular mechanisms involved in the beta-catenin signaling pathway, isolated osteoblasts and periodontal ligament cells were exposed to full-length recombinant mouse amelogenin and were evaluated for phenotypic changes and beta-catenin signaling using a TOPFLASH construct and the LacZ reporter gene. RESULTS: In these in vitro models, we showed that amelogenin can activate beta-catenin signaling. CONCLUSION: Using the TOPGAL transgenic mouse we showed that amelogenin expression in vivo is localized mainly around the root, the periodontal ligament and the alveolar bone.

The in vivo effect of lipopolysaccharide on the spontaneous release of transmitter from motor nerve terminals.

1. The in vivo effect of E. coli lipopolysaccharide (LPS) on the spontaneous release of transmitter was studied in the isolated phrenic nerve-diaphragm preparation of the mouse. 2. The resting membrane potential was decreased and frequency of miniature endplate potentials (m.e.p.ps) was increased by treatment with LPS. 3. Pretreatment of diaphragms with ouabain markedly increased the frequency of m.e.p.ps in control group but not in the LPS group. 4. When mice were treated with polymyxin B (a LPS neutralizer), pentoxifylline (an inhibitor of tumor necrosis factor-alpha formation) and NG-nitro-L-arginine (an inhibitor of nitric oxide (NO) synthase) the effects of LPS were reversed. 5. These results suggest that LPS increases the spontaneous transmitter release through, at least in part, the pathways of tumour necrosis factor-alpha and NO followed by an inhibition of the Na(+)-pump activity in the endplate area.

The in vivo effect of lipopolysaccharide on Na+,K(+)-ATPase catalytic (alpha) subunit isoforms in rat sciatic nerve.

The Na+,K(+)-ATPase catalytic (alpha) subunit in sciatic nerve of lipopolysaccharide (endotoxin, LPS)-treated rat was investigated. Using Western blot to determine subunit isoform polypeptide levels in rat sciatic nerve, we found a substantial reduction in alpha 1 polypeptide, but not that of alpha 2 and alpha 3 polypeptides, after the administration of LPS. Moreover, when rats were treated with polymyxin B (a LPS neutralizer) and NG-nitro-L-arginine (an inhibitor of nitric oxide (NO) synthase), the effects of LPS were reversed. These results implicate a specific marked deficit in alpha 1 subunit isoform of Na+,K(+)-ATPase in the pathogenesis of neuropathy during endotoxemia, through, at least in part, the L-arginine/NO pathway.

Changes in lymphocyte single strand breakage and liver function of workers exposed to vinyl chloride monomer.

Vinyl chloride monomer (VCM) is a suspected human carcinogen. Its metabolite, chloroethylene epoxide, is able to alkylate the DNA molecule and to produce single strand breakage (SSB). A total of 244 workers from 4 polyvinyl chloride (PVC) manufacturing factories were recruited to assess the SSB of their peripheral lymphocyte DNA. The method of alkaline unwinding and hydroxyapatite chromatography was used to detect and calculate frequencies of SSB. In addition, hepatitis B and C markers and the liver function of the workers were also examined. The worker's cumulative exposures to VCM were retrospectively constructed from the current monitoring data and each worker's job history. Multiple linear regression models were constructed to predict the worker's level of SSB and liver functions based on various exposure indices and variables, such as age, sex, smoking, drinking, and hepatitis markers. The results showed that current smoking and drinking status, and the presence of VCM exposures on the previous day were 3 major determinants of the level of SSB. Among the liver function tests, only gamma-glutamyl transpeptidase (GGT) was associated with current VCM exposures. In contrast, aspartate aminotransferase (AST), alkaline phosphatase (ALP) and alanine aminotransferase (ALT) were mainly affected by the presence of hepatitis B surface antigen (HBsAg) or anti-hepatitis C virus (anti-HCV). We conclude that GGT should be considered to be included in the regular health screening of VCM workers, and that the SSB method may not be suitable for long-term monitoring of cumulative exposure because of the quick DNA repair mechanism in humans.