Background/Aims: Osteoporosis is a progressive bone disease characterized by a decrease in bone mass and density, which results in an increased risk of fractures. Mesenchymal stem cells (MSCs) are progenitor cells that can differentiate into osteoblasts, osteocytes and adipocytes in bone and fat formation. A reduction in the differentiation of MSCs into osteoblasts contributes to the impaired bone formation observed in osteoporosis. MicroRNAs (miRNAs) play a regulatory role in osteogenesis and MSC differentiation. MiR-27a has been reported to be down-regulated in the development of osteoporosis and during adipogenic differentiation. Methods: In this study, a miRNA microarray analysis was used to investigate expression profiles of miRNA in the serum of osteoporotic patients and healthy controls and this data was validated by quantitative real-time PCR (qRT-PCR). MSCs isolated from human and mice with miR-27a inhibition or overexpression were induced to differentiate into osteoblasts or adipocytes. TargetScan and PicTar were used to predict the target gene of miR-27a. The mRNA or protein levels of several specific proteins in MSCs were detected using qRT-PCR or western blot analysis. Ovariectomized mice were used as in vivo model of human postmenopausal osteoporosis for bone mineral density measurement, micro-CT analysis and histomorphometric analysis. Results: Here, we analyzed the role of miR-27a in bone metabolism. Microarray analysis indicated that miR-27a expression was significantly reduced in osteoporotic patients. Analysis on MSCs derived from patients with osteoporosis indicated that osteoblastogenesis was reduced, whereas adipogenesis was increased. MSCs that had undergone osteoblast induction showed a significant increase in miR-27a expression, whereas cells that had undergone adipocyte induction showed a significant decrease in miR-27a expression, indicating that miR-27a was essential for MSC differentiation. We demonstrated that myocyte enhancer factor 2 c (Mef2c), a transcription factor, was the direct target of miR-27a using a dual luciferase assay. An inverse relationship between miR-27a expression and Mef2c expression in osteoporotic patients was shown. Silencing of miR-27a decreased bone formation, confirming the role of miR-27a in bone formation in vivo. Conclusion: In summary, miR-27a was essential for the shift of MSCs from osteogenic differentiation to adipogenic differentiation in osteoporosis by targeting Mef2c.

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Faced with the serious pollution caused by the viscose method (use of CS 2 ), a primarily industrialized trial via a "green" wet-spinning process based on dissolution of cellulose in NaOH/urea aqueous solution precooled to -12.5 °C was performed. In a dissolution tank of 1000 L capacity, the cellulose could be dissolved completely in the NaOH/urea system within 5 min, and cellulose fibers were spun successfully from the transparent dope. A 15:10 H 2 SO 4 /Na 2 SO 4 aqueous solution was adopted as the first coagulants in the bath, and a 5 wt % H 2 SO 4 aqueous solution was used as the second coagulant to fabricate new regenerated cellulose fibers. There was no evaporation of any chemical agent during dissolution and regeneration. The structure of the fibers was characterized with scanning electron microscope, wide-angle X-ray diffraction, 13 C NMR, and tensile testing. The cellulose fibers exhibited a bright surface and a circular section, and their tensile strength reached 1.63-1.97 cN/dtex, which is close to commercial viscose fiber, although the drawing orientation in the production process was not performed. Therefore, we created a novel and simple approach combining a nonpolluting, low-cost, and quick process for the production of cellulose fibers, which was important for environmental conservation.

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The infiltration of adipocytes in osteoporotic patients' bone marrow suggests an important regulatory function of bone marrow fat on the development of aged bone. Therefore, we have examined the effects of adipocytes derived from bone mesenchymal stem cell (MSC) on osteoblast differentiation using two different co-culture modes (direct mode and indirect mode). Alkaline phosphatase (ALP)-positive areas and mineralized areas of MSC-derived osteoblasts decrease similarly in the two co-culture modes as the amount of MSC-derived adipocytes increases, suggesting that the crosstalk between adipocytes and osteoblasts may be mainly through secretory factors in the medium. To further understand the molecular mechanisms, both mRNA and protein expressions in osteoblasts in the lower layer of the indirect mode were analyzed, leading to identification of 12 differential genes/proteins. Among them, S100A6 and calreticulin are possibly related to bone formation. S100A6 was down-regulated and calreticulin was up-regulated as MSC-derived adipocytes increased. Similarly, differential expression of these proteins was also observed in bone tissue slides from young (1-month-old) and old (6-month-old) mice. The expression level of β-catenin in osteoblasts of bone tissues was lower in 6-month-old mice compared to 1-month-old mice. Total TGF-β analyzed with antibody-based protein microarray and active TGF-β analyzed with ELISA in the co-cultured cell medium increased consistently as the amount of adipocytes increased. Taken together, our results suggest that MSC-derived adipocytes may regulate osteoblast differentiation in the aged bone through TGF-β-mediated canonical Wnt signaling.

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