BACKGROUND:The effects of advanced glycation end products (AGEs) on osteoclast-induced bone resorption is controversial and the underlying mechanisms remain unclear. Most of the studies indicate that AGEs can enhance bone resorption, while some othersshowthe opposite effects.
OBJECTIVE:To investigate the effects of AGEs on osteoclast-induced inorganicmatrixdissolution and organic componentdegradation and the underlying mechanisms.
METHODS:RAW 264.7 cels were induced to generate osteoclasts,and AGEs (50-400 μg/mL) or control-bovine serum albumin (100 μg/mL) was added since the beginning of the induction. The effect of AGEs on bone resorption was evaluated by analyzing the area of resorption pits on the Osteo Assay Surface plates and the expression of cathepsin K. Furthermore, the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cels, nuclei per osteoclasts and the expression of integrinανβ3were detected.
RESULTS AND CONCLUSION:The area of resorption pits and expression of cathepsin K in AGEs groups were significantly decreased compared withthecontrol group, and this inhibiting effect became more obvious with the increase of AGEs concentration. TRAP staining also showed that number of TRAP-positivemultinucleated celsand nuclei per osteoclast were significantly reduced in an AGE dose-dependent manner. Quantitative PCR revealed that the expression of integrin ανβ3decreased significantly with the extension of AGEs incubation time. These data indicate that AGEs can exert inhibitory effects on organic and inorganicmatrixdegradation induced by osteoclasts. The underlying mechanism may be involved in the inhibitory effects of AGEs on directed differentiation and cel fusion of osteoclast precursor cels, and migration and adhension of osteoclasts.

OBJECTIVE: To investigate the role of N-methyl-D-aspartate receptor(NMDAR)/cyclic adenosine monophosphate(cAMP)/protein kinase A(PKA) signaling pathways in regulating 2-chloroethanol-induced aquaporin-4(AQP4) expression in astrocytes(AS). METHODS: i) AS in logarithmic growth phase were treated with 2-chloroethanol at the doses of 0.0, 7.5, 15.0 and 30.0 mmol/L for 12 hours, and the cells were collected for detection. ii) The AS in logarithmic growth phase were divided into blank control group, inhibitor control group, 2-chloroethanol group, and inhibitor intervention group. The inhibitor included dizocilpine(MK-801) and N-(2-[p-bromocinnamylamino-]ethyl)-5-isoquinolinesulfonamide(H89). The blank control group did not receive any treatment. The inhibitor control group was treated with a concentration of 10.0 μmmol/L MK-801 or 15.0 μmmol/L H89. The MK-801 intervention group was pretreated with MK-801 at a concentration of 10.0 μmmol/L for 30 minutes. The H89 intervention group was pretreated with H89 at a concentration of 15.0 μmmol/L for 1 hour. After the intervention, the AS in 2-chloroethanol group and MK-801, H89 intervention group were stimulated with 2-chloroethanol at a dose of 30.0 mmol/L for 12 hours. iii) The AS in each group were collected and used for Western blotting and real-time fluorescence quantitative polymerase chain reaction analysis to detect the protein and mRNA expression of AQP4, NMDAR receptor main subunit(NR1), NMDAR receptor 2 B subunit(NR2 B) and calmodulin dependent protein kinaseⅡ(CaMKⅡ). The Western blotting was adopted to detect the expression of phosphorylase-CaMKⅡ(p-CaMKⅡ) and PKA. Colorimetric method was used to detect the concentration of calcium(Ca~(2+)) in AS. The enzyme-linked adsorption test was used to measure adenylate cyclase(AC) activity and cAMP levels. RESULTS: i) The relative expression of protein and mRNA of AQP4, NR1 and NR2 B, PKA at protein level and CaMKⅡ at mRNA level, and the ratio of p-CaMKⅡ/CaMKⅡ protein, the concentration of Ca~(2+), AC activity and cAMP level in 30.0 mmol/L group were higher then those of 0.0 mmol/L group in AS(P<0.05). The relative protein expression of PKA and the concentration of Ca~(2+) increased with the increase of 2-chloroethanol(P<0.05). ii) The relative protein expression of AQP4 and the concentration of Ca~(2+) in the 2-chloroethanol group were higher than that of the blank control group and MK-801 control group(P<0.05). The relative protein expression of AQP4 and the concentration of Ca~(2+) in MK-801 intervention group were lower than that in 2-chloroethanol group(P<0.05). The relative protein expression of AQP4 and PKA in 2-chloroethanol group were higher than that of the blank control group and H89 control group(P<0.05). The relative protein expression of AQP4 and PKA in H89 intervention group was lower than that in 2-chloroethanol group(P<0.05). CONCLUSION: The 2-chloroethanol timulation induces the expression of AQP4 by activating NMDAR/cAMP/PKA signaling pathway in AS.