Mechanical Strain Regulates Osteoblast Proliferation Through Ca2+-CaMK-CREB Signal Pathway.

Objective To investigate the effects of mechanical strain on Ca2+-calmodulin dependent kinase (CaMK)-cAMP response element binding protein (CREB) signal pathway and proliferation of osteoblasts.Methods Using a four-point bending device, MC3T3-E1 cells were exposed to mechanical tensile strains of 2500 µs and 5000 µs at 0.5 Hz respectively. The intracellular free Ca2+ ([Ca2+]i) concentration and calmodulin activity were assayed by fluorospectrophotometry, CaMK II ß, CREB, and phosphorylated (activated) CREB (p-CREB) were assessed by Western blot, and cells proliferation was assayed with MTT. Pretreatment with verapamil was carried out to block Ca2+ channel, and inhibitor U73122 was used to inhibit phospholipase C (PLC).Results Mechanical strains of 2500 µs and 5000 µs for 1 to 10 minutes both increased [Ca2+]i level of the cells. The 2500 µs strain, a periodicity of 1 h/d for 3 days, activated calmodulin, elevated protein levels of CaMK II ß and p-CREB, and promoted cells proliferation, which were attenuated by pretreatment of verapamil or U73122. The effects of 5000 µs strain on calmodulin, CaMK II ß, p-CREB and proliferation were contrary to 2500 µs strain.Conclusion The mechanical strain regulates osteoblasts proliferation through Ca2+-CaMK-CREB signal pathway via Ca2+ channel and PLC/IP3 transduction cascades.

Mechanical strain promotes osteoblast ECM formation and improves its osteoinductive potential.

BACKGROUND: The extracellular matrix (ECM) provides a supportive microenvironment for cells, which is suitable as a tissue engineering scaffold. Mechanical stimulus plays a significant role in the fate of osteoblast, suggesting that it regulates ECM formation. Therefore, we investigated the influence of mechanical stimulus on ECM formation and bioactivity. METHODS: Mouse osteoblastic MC3T3-E1 cells were cultured in cell culture dishes and stimulated with mechanical tensile strain. After removing the cells, the ECMs coated on dishes were prepared. The ECM protein and calcium were assayed and MC3T3-E1 cells were re-seeded on the ECM-coated dishes to assess osteoinductive potential of the ECM. RESULTS: The cyclic tensile strain increased collagen, bone morphogenetic protein 2 (BMP-2), BMP-4, and calcium levels in the ECM. Compared with the ECM produced by unstrained osteoblasts, those of mechanically stimulated osteoblasts promoted alkaline phosphatase activity, elevated BMP-2 and osteopontin levels and mRNA levels of runt-related transcriptional factor 2 (Runx2) and osteocalcin (OCN), and increased secreted calcium of the re-seeded MC3T3-E1 cells. CONCLUSION: Mechanical strain promoted ECM production of osteoblasts in vitro, increased BMP-2/4 levels, and improved osteoinductive potential of the ECM. This study provided a novel method to enhance bioactivity of bone ECM in vitro via mechanical strain to osteoblasts.

Differential effects of mechanical strain on osteoclastogenesis and osteoclast-related gene expression in RAW264.7 cells.

Mechanical strain plays a critical role in the formation, proliferation and maturation of bone cells. However, little is known about the direct effects of different magnitudes of mechanical strain on osteoclast differentiation. The aim of the present study was to investigate how the fusion and activation of osteoclasts can be regulated by mechanical strain magnitude using the RAW264.7 mouse monocyte/macrophage cell line as an osteoclast precursor. Mechanical strain (substrate stretching) was applied via a 4-point bending system when RAW cells were treated with macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor-κB (RANK) ligand (RANKL) for an indicated period of time. The numbers of tartrate-resistant acid phosphatase-positive (TRAP+) and apoptotic cells were counted. The expression of TRAP, matrix metalloproteinase-9 (MMP-9), RANK, cathepsin K and carbonic anhydrase II (CAII) was measured by semi-quantitative RT-PCR, and immunocytochemistry staining for RANK was performed. We found that the number of nuclei per osteoclast derived from RAW cells decreased under low magnitude mechanical strain and increased under high magnitude strain within physiological load with an enhanced fusion of TRAP+ osteoclasts, compared to the control with no mechanical strain. The expression of RANK mRNA was downregulated by low magnitude strain and beyond physiological load, while it was upregulated by high magnitude strain within physiological load, correlating with the increased expression of RANK examined by immunocytochemistry, suggesting the mechanical regulation of RANK expression. There was also an increase in the expression of MMP-9 mRNA in the groups subjected to a mechanical strain of 2,000 and 2,500 µÎµ. No significant differences were detected in the expression of TRAP mRNA, cathepsin K and CAII under mechanical strain compared to the control under no strain (0 µÎµ). These findings indicate that low-magnitude strain suppresses osteoclast fusion and activation, while high-magnitude strain within physiological load promotes osteoclast fusion and activation related to a mechanical magnitude-dependent response of RANK expression. These data, therefore, provide a deeper understanding of how different magnitudes of mechanical strains exert their effects on osteoclastogenesis.

Mechanical strain regulates osteoblast proliferation through integrin-mediated ERK activation.

Mechanical strain plays a critical role in the proliferation, differentiation and maturation of bone cells. As mechanical receptor cells, osteoblasts perceive and respond to stress force, such as those associated with compression, strain and shear stress. However, the underlying molecular mechanisms of this process remain unclear. Using a four-point bending device, mouse MC3T3-E1 cells was exposed to mechanical tensile strain. Cell proliferation was determined to be most efficient when stimulated once a day by mechanical strain at a frequency of 0.5 Hz and intensities of 2500 µÎµ with once a day, and a periodicity of 1 h/day for 3 days. The applied mechanical strain resulted in the altered expression of 1992 genes, 41 of which are involved in the mitogen-activated protein kinase (MAPK) signaling pathway. Activation of ERK by mechanical strain promoted cell proliferation and inactivation of ERK by PD98059 suppressed proliferation, confirming that ERK plays an important role in the response to mechanical strain. Furthermore, the membrane-associated receptors integrin ß1 and integrin ß5 were determined to regulate ERK activity and the proliferation of mechanical strain-treated MC3T3-E1 cells in opposite ways. The knockdown of integrin ß1 led to the inhibition of ERK activity and cell proliferation, whereas the knockdown of integrin ß5 led to the enhancement of both processes. This study proposes a novel mechanism by which mechanical strain regulates bone growth and remodeling.

[Cholecystokinin octapeptide augments expression of anti-inflammatory cytokines in mice challenged by lipopolysaccharide].

OBJECTIVE: To observe the effects of cholecystokinin octapeptide (CCK-8) on the expression of anti-inflammatory cytokines interleukin-4 (IL-4) and IL-10 in lipopolysaccharide (LPS) challenged mice. METHODS: Kunming mice were randomly assigned into four groups (each n=7): (1) Intraperitoneal injection of LPS (10 mg/kg), and the times of peak level of IL-4 and IL-6 expression in serum and lung tissue were noted at 0, 2, 4, 6 and 12 hours after challenge. (2) Control group ( intraperitoneal injection of normal saline 0.2 ml). (3) LPS+CCK-8 group ( intraperitoneal injection of CCK-8 60 microg/kg 30 minutes before giving LPS). (4) CCK-8 group (intraperitoneal injection injection CCK-8 60 microg/kg) at different time points. The expressions of IL-4 and IL-10 in the serum and lung tissues were assayed by enzyme linked immunoadsorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: Two hours after LPS challenge, IL-4 and IL-6 were increased significantly in serum and lung tissue. At 4 hours and 6 hours, serum IL-4 and IL-6 reached their peak levels, while in lung tissue they reached their peak levels at 6 hours. Pre-treatment of CCK-8 augmented IL-4 and IL-10 expressions in LPS challenged mice (both P<0.01). But single CCK-8 injection showed no significant effect on IL-4 and IL-10 in serum and lung tissue. CONCLUSION: CCK-8 is involved in the anti-inflammatory response by increasing the expressions of IL-4, IL-10 in LPS challenged mice, and in turn it alleviates the inflammatory response in lung tissue.

[Receptor mechanisms underlying the modulation of lipopolysaccharide-induced nuclear factor-kappaB expression in vascular endothelial cells by cholecystokinin octapeptide].

OBJECTIVE: To elucidate the receptor mechanisms underlying the modulation of lipopolysaccharide (LPS)-induced nuclear factor-kappaB (NF-kappaB) expression in human umbilical vein endothelial cell line ECV-304 cells by cholecystokinin octapeptide (CCK-8). METHODS: Human umbilical vein endothelial cell line ECV-304 cells were stimulated with vehicle, LPS, CCK-8 (10(-9)-10(-7) mol/L), CCK receptor non-specific antagonist proglumide, CCK-A receptor (CCK-AR) specific antagonist CR-1409 or CCK-B receptor (CCK-BR) specific antagonist CR-2945 singularly or in combination. The NF-kappaB p65 protein level was determined by Western blot and immunocytochemistry technique. RESULTS: LPS resulted in an increase in the up-regulatory expression and nuclear translocation of NF-kappaB p65 protein in ECV-304 compared with vehicle stimulation. CCK-8 obviously inhibited LPS-induced the changes in NF-kappaB p65 protein in a dose-dependent manner. The inhibitory effects of CCK-8 on NF-kappaB p65 protein expression were attenuated by proglumide>CR-2945>CR-1409. CONCLUSION: CCK-AR and CCK-BR are involved in the mediation of CCK-8 inhibitive regulation for LPS-induced NF-kappaB protein expression in ECV-04 cells, whereas the effect of CCK-BR are more than that of CCK-R.