Investigation of causal relationships between cortical structure and osteoporosis using two-sample Mendelian randomization.

The mutual interaction between bone characteristics and brain had been reported previously, yet whether the cortical structure has any relevance to osteoporosis is questionable. Therefore, we applied a two-sample bidirectional Mendelian randomization analysis to investigate this relationship. We utilized the bone mineral density measurements of femoral neck (n = 32,735) and lumbar spine (n = 28,498) and data on osteoporosis (7300 cases and 358,014 controls). The global surficial area and thickness and 34 specific functional regions of 51,665 patients were screened by magnetic resonance imaging. For the primary estimate, we utilized the inverse-variance weighted method. The Mendelian randomization-Egger intercept test, MR-PRESSO, Cochran's Q test, and "leave-one-out" sensitivity analysis were conducted to assess heterogeneity and pleiotropy. We observed suggestive associations between decreased thickness in the precentral region (OR = 0.034, P = 0.003) and increased chance of having osteoporosis. The results also revealed suggestive causality of decreased bone mineral density in femoral neck to declined total cortical surface area (ß = 1400.230 mm2, P = 0.003), as well as the vulnerability to osteoporosis and reduced thickness in the Parstriangularis region (ß = -0.006 mm, P = 0.002). Our study supports that the brain and skeleton exhibit bidirectional crosstalk, indicating the presence of a mutual brain-bone interaction.

Visualization of GLUT1 Trafficking in Live Cancer Cells by the Use of a Dual-Fluorescence Reporter.

Glucose metabolism is an essential process for energy production and cell survival for both normal and abnormal cellular metabolism. Several glucose transporter/solute carrier 2A (GLUT/SLC2A) superfamily members, including glucose transporter 1 (GLUT1), have been shown to mediate the cellular uptake of glucose in diverse cell types. GLUT1-mediated glucose uptake is a transient and rapid process; thus, the real-time monitoring of GLUT1 trafficking is pivotal for a better understanding of GLUT1 expression and GLUT1-dependent glucose uptake. In the present study, we established a rapid and effective method to visualize the trafficking of GLUT1 between the plasma membrane (PM) and endolysosomal system in live cells using an mCherry-EGFP-GLUT1 tandem fluorescence tracing system. We found that GLUT1 localized at the PM exhibited both red (mCherry) and green (EGFP) fluorescence (yellow when overlapping). However, a significant increase in red punctate fluorescence (mCherry is resistant to acidic pH), but not green fluorescence (EGFP is quenched by acidic pH), was observed upon glucose deprivation, indicating that the mCherry-EGFP-GLUT1 functional protein was trafficked to the acidic endolysosomal system. Besides, we were able to calculate the relative ratio of mCherry to EGFP by quantification of the translocation coefficient, which can be used as a readout for GLUT1 internalization and subsequent lysosomal degradation. Two mutants, mCherry-EGFP-GLUT1-S226D and mCherry-EGFP-GLUT1-ΔC4, were also constructed, which indirectly confirmed the specificity of mCherry-EGFP-GLUT1 for monitoring GLUT1 trafficking. By using a series of endosomal (Rab5, Rab7, and Rab11) and lysosomal markers, we were able to define a model of GLUT1 trafficking in live cells in which upon glucose deprivation, GLUT1 dissociates from the PM and experiences a pH gradient from 6.8-6.1 in the early endosomes to 6.0-4.8 in the late endosomes and finally pH 4.5 in lysosomes, which is appropriate for degradation. In addition, our proof-of-concept study indicated that the pmCherry-EGFP-GLUT1 tracing system can accurately reflect endogenous changes in GLUT1 in response to treatment with the small molecule, andrographolide. Since targeting GLUT1 expression and GLUT1-dependent glucose metabolism is a promising therapeutic strategy for diverse types of cancers and certain other glucose addiction diseases, our study herein indicates that pmCherry-EGFP-GLUT1 can be utilized as a biosensor for GLUT1-dependent functional studies and potential small molecule screening.

Transcriptional regulation of Runx2 by HSP90 controls osteosarcoma apoptosis via the AKT/GSK-3ß/ß-catenin signaling.

Osteosarcoma (OS) is the most malignant primary bone tumor in children and adolescents with limited treatment options and poor prognosis. Recently, aberrant expression of Runx2 has been found in OS, thereby contributing to the development, and progression of OS. However, the upstream signaling molecules that regulate its expression in OS remain largely unknown. In the present study, we first confirmed that the inhibition of HSP90 with 17-AAG caused significant apoptosis of OS cells via a caspase-3-dependent mechanism, and that inhibition or knockdown of HSP90 by 17-AAG or siRNAs significantly suppressed mRNA and protein expression of Runx2. Furthermore, we provided evidence that Runx2 was transcriptionally regulated by HSP90 when using MG132 and CHX chase assay. We also demonstrated that ß-catenin was overexpressed in OS tissue, and that knockdown of ß-catenin induced pronounced apoptosis of OS cells in the presence or absence of 17-AAG. Interestingly, this phenomenon was accompanied with a significant reduction of Runx2 and Cyclin D1 expression, indicating an essential role of Runx2/Cyclin D1 in 17-AAG-induced cells apoptosis. Moreover, we demonstrated that the apoptosis of OS cells induced by 17-AAG did require the involvement of the AKT/GSK-3ß/ß-catenin signaling pathway by using pharmacological inhibitor GSK-3ß (LiCl) or siGSK-3ß. Our findings reveal a novel mechanism that Runx2 is transcriptionally regulated by HSP90 via the AKT/GSK-3ß/ß-catenin signaling pathway, and by which leads to apoptosis of OS cells.

Andrographolide Induces Cell Cycle Arrest and Apoptosis of Chondrosarcoma by Targeting TCF-1/SOX9 Axis.

Chondrosarcoma is the second most malignant bone tumor with poor prognosis and limited treatment options. Thus, development of more effective treatments has become urgent. Recently, natural compounds derived from medicinal plants have emerged as promising therapeutic options via targeting multiple key cellular molecules. Andrographolide (Andro) is such a compound, which has previously been shown to induce cell cycle arrest and apoptosis in several human cancers. However, the molecular mechanism through which Andro exerts its anti-cancer effect on chondrosarcoma remains to be elucidated. In the present study, we showed that Andro-induced G2/M cell cycle arrest of chondrosarcoma by fine-tuning the expressions of several cell cycle regulators such as p21, p27, and Cyclins, and that prolonged treatment of cells with Andro caused pronounced cell apoptosis. Remarkably, we found that SOX9 was highly expressed in poor-differentiated chondrosarcoma, and that knockdown of SOX9 suppressed chondrosarcoma cell growth. Further, our results showed that Andro dose-dependently down-regulated SOX9 expression in chondrosarcoma cells. Concomitantly, an inhibition of T cell factor 1 (TCF-1) mRNA expression and an enhancement of TCF-1 protein degradation by Andro were observed. In contrast, the expression and subcellular localization of ß-catenin were not altered upon the treatment of Andro, suggesting that ß-catenin might not function as the primary target of Andro. Additionally, we provided evidence that there was a mutual regulation between TCF-1 and SOX9 in chondrosarcoma cells. In conclusion, these results highlight the potential therapeutic effects of Andro in treatment of chondrosarcoma via targeting the TCF-1/SOX9 axis. J. Cell. Biochem. 118: 4575-4586, 2017. © 2017 Wiley Periodicals, Inc.

MiRNA-140 is a negative feedback regulator of MMP-13 in IL-1ß-stimulated human articular chondrocyte C28/I2 cells.

OBJECTIVE: Osteoarthritis is a degenerative joint disease, in which matrix metalloproteinase (MMP)-13 plays an important role. This study aimed to investigate miRNA-140-mediated negative regulation of MMP-13 expression in interleukin-1ß (IL-1ß)-stimulated human cartilage cells. METHODS: The human cartilage cell line C28/I2 was cultured in the presence of IL-1ß to mimic an osteoarthritic environment. Expression of miRNA-140 and MMP-13 was analyzed after 48 h by real-time RT-PCR and western blot analyses. MiRNA-140 mediated regulation of MMP-13 expression was analyzed by luciferase reporter assays and anti-miRNA-140 oligonucleotide transfection. Furthermore, miRNA-140 and MMP-13 expression was analyzed following DHMEQ treatment. RESULTS: Expression of miRNA-140 and MMP-13 was elevated in IL-1ß-stimulated C28/I2 cells. Bioinformatic prediction showed that the 3'-UTR of MMP-13 mRNA contained a potential binding miRNA-140 site and luciferase mRNA fused with 3'-UTR of MMP-13 mRNA was shown to be repressed by miRNA-140 in reporter assays. Expression of MMP-13 was elevated in IL-1ß-stimulated C28/I2 cells following anti-miRNA-140 oligonucleotide transfection. NF-κB activity was inhibited in DHMEQ treated IL-1ß-stimulated C28/I2 cells and was associated with decreased miRNA-140 and MMP-13 expression. CONCLUSION: Expression of miRNA-140 and MMP-13 was induced by IL-1ß. Expression of miRNA-140 inhibited MMP-13 in C28/I2 cells. Expression of miRNA-140 and MMP-13 was shown to be NF-κB-dependent.

Apigenin accelerates lipopolysaccharide induced apoptosis in mesenchymal stem cells through suppressing vitamin D receptor expression.

BACKGROUND: Transplantation of mensenchymal stem cells (MSCs) has been proposed as a promising way for tissue engineering. However, the application of MSCs for transplantation will undergo apoptosis due to the extremely harsh microenvironment such as excessive inflammation. Apigenin (API) has been reported to protect cells against inflammatory damage and cell death by exhibiting anti-inflammatory and anti-oxidative capacity. Here we investigated the modulatory effects of API in lipopolysaccharide (LPS)-mediated inflammation and apoptosis of MSCs, and further defined the underlying mechanism. METHODS: Effects of different concentrations of API (0, 5, 10, 20, 40 and 80 µmol/L) for 24 hours, and LPS (0, 0.5 and 5.0 µg/ml) for 6 hours and 24 hours on MSCs viability were assayed by MTT. Based on this, MSCs were pretreated with different concentrations of API (0 - 40 µmol/L) at the indicated times (6, 12 and 24 hours) followed by exposure to 5 µg/ml LPS for 24 hours. MTT, phase-contrast microscopy, annexinV/propidium iodide (PI) double stain flow cytometry (FCM) and Hoechst staining were applied to explore the effects of API on MSCs induced by 5 µg/ml LPS for 24 hours. In addition, reverse-transcription polymerase chain reaction (RT-PCR) was applied to detect the mRNA expression of pro-inflammatory factors including cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), nuclear factor-kappa B (NF-κB), pro-apoptotic gene caspase-3, Bad, and anti-apoptotic gene Bcl-2. Moreover, AutoDock software was used to imitate the docking score of API and vitamin D receptor (VDR). In parallel, Western blotting and RT-PCR were used to investigate protein and mRNA expression of VDR. RESULTS: MSCs stimulated with LPS 5 µg/ml for 24 hours was used as a model of apoptosis induced by over inflammatory stimulus. API (0 - 40 µmol/L) had non-toxic effect on MSCs; however, it could decrease mRNA expression of COX-2, iNOS and NF-κB at different time points in MSCs induced by LPS, except for API at the concentration of 5 µmol/L. RESULTS: from phase-contrast microscopy, MTT, Hoechst staining and AnnexinV/PI double stain FCM demonstrated that with the increasing concentrations of API and extension of administrating time, significant morphological changes of MSCs occurred, viability of cells was strongly inhibited, and meanwhile, apoptosis of LPS-administrated MSCs was exacerbated, compared with LPS individual group. In addition, API promoted caspase-3, Bad mRNA expression and inhibited Bcl-2 mRNA expression in a time-dependent and concentration- dependent manner. Further study found that pro-apoptosis effect of API was related to suppress VDR expression. CONCLUSIONS: API could inhibit the expression of inducible inflammatory factors, therefore exert the strong anti-inflammatory function. However, API could not protect MSC apoptosis induced by LPS but amplified the apoptosis. The apoptosis is related to Bad/Bcl-2 increasing and caspase-3 activation, which is mediated through suppressing VDR expression.