Suture compression induced bone resorption with intensified MMP-1 and 13 expressions

Compressive force-induced autophagy in periodontal ligament cells downregulates osteoclastogenesis during tooth movement

BACKGROUND

Autophagy has recently emerged as a protective mechanism in response to compressive force and an important process in maintenance of bone homeostasis. It appears to be involved in the degradation of osteoclasts, osteoblasts, and osteocytes. The aim of this study was to investigate the role of compressive force-induced autophagy in periodontal ligament (PDL) cells in regulating osteoclastogenesis of orthodontic tooth movement (OTM).

METHODS

An OTM model and compressive force on PDL cells were employed to investigate the expression of autophagy markers in vivo and in vitro, respectively. Autophagosomes and autolysosomes were observed in PDL cells by transmission electron microscope (TEM) and autophagy LC3 double labelling. 3-Methyladenine (3-MA) and rapamycin were respectively used to inhibit and promote autophagy, and the effect of autophagy on osteoclastogenesis was explored via microcomputed tomography, hematoxylin and eosin (H&E) staining, histochemistry of titrate-resistant acid phosphatase, and real-time polymerase chain reaction (RT-PCR) in vivo. Receptor activator of nuclear factor-kappa B ligand/osteoprotegerin (RANKL/OPG) was investigated by RT-PCR and ELISA in vitro.

RESULTS

Orthodontic force-induced autophagy was prominent on the pressured side of PDL tissues. Administration of 3-MA downregulated bone density and upregulated osteoclasts, while rapamycin had reverse results in OTM. The autophagy activity increased initially then decreased in PDL cells during compressive force application and responded to light force. In PDL cells, administration of 3-MA upregulated while rapamycin downregulated the RANKL/OPG ratio.

CONCLUSION

Autophagy is activated by compressive force in PDL cells. Besides, it could modulate OTM by negatively regulating osteoclastogenesis and keep bone homeostasis via RANKL/OPG signaling.

Effects of continuous and intermittent parathyroid hormone administration on midpalatal suture expansion in rats

OBJECTIVES

The aim of this study was to investigate the effects of continuous parathyroid hormone (cPTH) and intermittent parathyroid hormone (iPTH) on bone formation and bone resorption in midpalatal suture during maxillary expansion.

METHODS

Forty-eight male SD rats were randomly divided into four groups (n = 12 each), including the control, the expansion (E), the E + cPTH, and the E + iPTH. A thermosensitive controlled-release hydrogel was synthesized for cPTH administration. All animals were sacrificed after seven days. Microcomputed tomography, histochemical staining and real-time PCR were used to investigate the bone remodeling of midpalatal suture. Serum chemistry was adopted to evaluate the systemic condition of experimental animals.

RESULTS

The suture width was increased by the expansion, and further elevated by cPTH and iPTH administration. Both regimes improved bone volume fraction and trabecular thickness of suture bone region. Moreover, both cPTH and iPTH decreased SOST expression and enhanced the expression of β-catenin and Col-I. cPTH increased RANKL expression, inhibited OPG expression, and resulted in an increment of osteoclasts, while iPTH had no influence on osteoclastogenesis. The serum calcium concentration was enhanced by PTH administration.

CONCLUSION

Both cPTH and iPTH promote midpalatal suture expansion by enhancing bone formation, probably via SOST downregulation and the resulting β-catenin activation. Our results demonstrated that PTH administration may have potential to be an adjunctive approach for maxillary expansion treatment.

The role of physical forces in osteoclastogenesis

The movements of life at every level from organs, tissues, cells to sub-cells, are all conducted in certain physical environments. In the human body, skeletal tissue among all connective tissues is influenced the most by physical forces. Studying the biological behavior of bone cells under different physical environments is helpful in further understanding bone homeostasis and metabolism. Among all bone cells, osteoclast (OC) and OC steered bone remodeling is one of the key points in bone metabolism. In the past few decades, people's understanding of OC was mostly limited to its involvement of bone resorption under physiological and pathological conditions. However, more and more studies started to focus on how physical forces affect the formation and differentiation of OC. This review tries to illustrate the knowledge up to date about how osteoclastogenesis is regulated by physical forces through direct and indirect ways, including fluid shear force, compressive force, and microgravity. The direct way describes the straightforward effects produced by different forces in osteoclastogenesis, whereas the indirect way describes the effects of different forces in osteoclastogenesis through regulation of other bone cells when a certain force is applied. Molecular mechanisms were analyzed and reviewed in both direct and indirect regulation by different forces. Finally, we discussed the status quo and tendency of related research, as well as other unresolved issues, and some future prospects.

Effects of lactoferrin on bone resorption of midpalatal suture during rapid expansion in rats

INTRODUCTION

The aim of this study was to investigate the effect of lactoferrin (LF) on bone resorption of rats' midpalatal sutures during rapid palatal expansion.

METHODS

Sixty male 5-week-old Wistar rats were randomly divided into 3 groups: expansion only (EO), expansion plus LF (E + LF), and sham device (control).

RESULTS

Microcomputed tomography showed that the bone volume/tissue volume ratio and the relative bone mineral density of the suture bone were significantly increased in the E + LF group compared with the EO group. Histochemical staining suggested that the activity of osteoblast-like cells and the amount of new bone formation were stimulated in the E + LF group whereas the activity of osteoclasts showed no obvious difference between groups. On the other hand, the immunohistochemical and the real-time polymerase chain reaction results showed that the expressions of receptor activator of nuclear factor kappa B ligand and osteoprotegerin had no significant difference between the EO and E + LF groups.

CONCLUSIONS

These findings demonstrated that LF could stimulate bone volume and bone density in midpalatal sutures during the suture remodeling process under tensile force. However, this enhancement effect was not caused by the reduction of bone resorption.

Direct influence of titanium and zirconia particles on the morphology and functionality of mature human osteoclasts

Within the last ten years of biomedical implants, the focus is increasingly on bioceramics, specifically on zirconia (ZrO₂ ). Hence, we analyzed the impact of ZrO₂ particles in comparison to titanium particles on mature human osteoclasts (OCs) as little is known about the direct effect of wear particles on mature OCs and their role in the osteolytic process during aseptic endoprosthesis loosening. Changes in cell morphology and functionality of OCs incubated with particles in different concentrations were investigated in vitro. OCs tend to be enlarged after three days of cultivation with both types of particles, especially with high concentrations of ZrO₂ , suggesting increased cell fusion. Further, we identified significantly increased expression of OC specific and bone matrix related genes: VNR, RANK, TRAP, and CTSK pointing on a direct stimulatory particle effect on the functionality of mature OCs. In completion, we quantified the bone resorption activity of particle treated mature OCs but could not detect a significant difference in bone resorption compared to OCs cultivated without particles. However, we could identify significantly higher gene expression of MMP-1 in particle treated OCs compared to untreated control OCs after three days of incubation. We also detected an impaired production of the tissue inhibitor of metalloproteinase, especially for OCs treated with high ZrO₂ concentrations. In conclusion, our in vitro data show that abrasion particles could have a direct influence on mature OCs and therefore could promote increased OC-mediated bone resorption during aseptic loosening of total joint replacements. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2608-2615, 2017.

Testicular Dnmt3 expression and global DNA methylation are down-regulated by gonadotropin releasing hormones in the ricefield eel Monopterus albus

In vertebrates, DNA methyltransferase 3 (Dnmt3) homologues are responsible for de novo DNA methylation and play important roles in germ cell development. In the present study, four dnmt3 genes, dnmt3aa, dnmt3ab, dnmt3ba and dnmt3bb.1, were identified in ricefield eels. Real-time quantitative PCR analysis showed that all four dnmt3 mRNAs were detected broadly in tissues examined, with testicular expression at relatively high levels. In the testis, immunostaining for all four Dnmt3 forms was mainly localized to spermatocytes, which also contained highly methylated DNA. All three forms of Gonadotropin-releasing hormone (Gnrh) in the ricefield eel were shown to decrease the expression of dnmt3 genes in the in vitro incubated testicular fragments through cAMP and IP₃/Ca²⁺ pathways. Moreover, in vivo treatment of male fish with three forms of Gnrh decreased significantly the testicular Dnmt3 expression at both mRNA and protein levels, and the global DNA methylation levels. These results suggest that the expression of Dnmt3 and global DNA methylation in the testis of ricefield eels are potentially down-regulated by Gnrh, and reveal a novel regulatory mechanism of testicular Dnmt3 expression in vertebrates.

Epithelium-Derived Wnt Ligands Are Essential for Maintenance of Underlying Digit Bone

Clinically, many nail disorders accompany bone deformities, but whether the two defects are causally related is under debate. To investigate the potential interactions between the two tissue types, we analyzed epithelial-specific β-catenin-deficient mice, in which nail differentiation is abrogated. These mice showed regression of not only the nail plate but also of the underlying digit bone. Characterization of these bone defects revealed active bone resorption, which is suppressed by Wnt activation in osteoblast and osteoclast precursors. Furthermore, we found that Wntless expression, essential for Wnt ligand secretion, was lacking in the β-catenin-deficient nail epithelium and that genetic deletion of Wntless (Wls) in the nail epithelium led to the lack of Wnt activation in osteoblast and osteoclast precursors and subsequently led to defective regression of the underlying digit bone. Together, these data show that epithelial Wnt ligands can ultimately regulate Wnt signaling in osteoblast and osteoclast precursors, known to regulate bone homeostasis. These results reveal a critical role for the nail epithelium on the digit bone during homeostatic regeneration and show that Wnt/β-catenin signaling is critical for this interaction.

Xanthan gum inhibits cartilage degradation by down-regulating matrix metalloproteinase-1 and -3 expressions in experimental osteoarthritis

We previously reported that intra-articular injection of xanthan gum protected the joint cartilage and reduced osteoarthritis progression. In this study, the effects of xanthan gum on chondrocytes apoptosis were evaluated using the labeling assay, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay, to determine the protein expression of matrix metalloproteinase-1, 3, and tissue inhibitors of metalloproteinase-1 using immunohistochemistry and Western blot assay in cartilage of papain-induced rabbit osteoarthritis model. Compared to the negative control group, intra-articular injection of xanthan gum, once every 2 weeks for 5 weeks significantly inhibited chondrocytes apoptosis and matrix metalloproteinase-1 and -3 protein expression levels and also enhanced the tissue inhibitors of metalloproteinase-1 production in cartilage. No significant differences between the xanthan gum-treated group and the sodium hyaluronate-treated group (intra-articular injection of sodium hyaluronate only once a week for 5 weeks) were observed.