Implication of receptor activator of NF-κB ligand in Wnt/β-catenin pathway promoting osteoblast-like cell differentiation

Lactobacillus Plantarum HFY15 Helps Prevent Retinoic Acid-Induced Secondary Osteoporosis in Wistar Rats

A rat model of secondary osteoporosis was constructed using retinoic acid as an inducer, and the genes, proteins, and bone mass of the rats were analyzed. qPCR detection of the Wnt/β-catenin and OPG/RANK/RANKL signaling pathway-related gene expression levels showed that Lactobacillus plantarum HFY15 played a positive role in regulating both pathways. HFY15 significantly increased β-catenin, Lrp5, Lrp6, Wnt10b, OPG, RANKL, and Runx2 expression and downregulated DKK1, RANK, CTSK, TRACP, and ALP expression. Enzyme-linked immunosorbent assays further confirmed the qPCR results. Tartrate-resistant acid phosphatase staining showed that HFY15 slowed retinoic acid-induced osteoclast formation. Microcomputed tomography showed that HFY15 reduced trabecular separation and increased the percent bone volume, trabecular numbers, trabecular thickness, and bone mineral density in the rats in vivo. These findings indicate that HFY15 may help prevent retinoic acid-induced secondary osteoporosis in vivo.

Catalpol Promotes the Proliferation and Differentiation of Osteoblasts Induced by High Glucose by Inhibiting KDM7A

INTRODUCTION

The protective effect of catalpol on diabetic osteoporosis (DOP) and its mechanism remain unclear. This study aimed to explore whether catalpol enhanced the proliferation and differentiation of MC3T3 cells induced by high glucose by inhibiting the expression of KDM7A.

METHODS

MC3T3 cells were induced by high glucose (HG) and treated with different concentrations of catalpol. The proliferation and mineralization abilities of MC3T3-E1 cells were determined by CCK-8 assay and Alizarin Red Staining, respectively. The expression of differentiation-related osteogenic proteins, KDM7A and related proteins of Wnt/β-catenin signaling pathway was analyzed by Western blot analysis. The alkaline phosphatase (ALP) activity was detected by ALP assay kits.

RESULTS

MC3T3-E1 cells induced by high glucose showed decreased proliferation and mineralization abilities and decreased ALP activity, which were all reversed by the treatment of catalpol. High glucose induction inhibited the expression of KDM7A, Total-β-catenin, Nuclear-β-catenin and p-GSK3β, which was reversed by the treatment of catalpol. And KDM7A interference up-regulated the expression of Total-β-catenin, Nuclear-β-catenin and p-GSK3β, which was down-regulated by KDM7A overexpression. Furthermore, the proliferation and mineralization abilities and ALP activity were improved when treated with KDM7A interference and decreased when treated with KDM7A overexpression. However, SKL2001 could improve the proliferation and mineralization abilities and ALP activity of MC3T3-E1 cells.

DISCUSSION

Catalpol promotes the proliferation and differentiation of osteoblasts induced by high glucose by regulating the Wnt/β-catenin signaling pathway through KDM7A.

Angiotensin II prevents calcification in vascular smooth muscle cells by enhancing magnesium influx

BACKGROUND

Vascular calcification (VC) is highly prevalent in patients with chronic kidney disease (CKD). Low magnesium levels are associated with VC, and recent in vitro studies confirm a protective role of magnesium, which is mediated by its entry into the VSMCs through the Transient Receptor Potential Melastatin 7 (TRPM7) channel. The role of Angiotensin II (Ang II) on VC is still unclear. As Ang II is able to stimulate TRPM7 activity, we hypothesize that it might prevent VC. Thus, the aim of this study was to dissect the direct effect of Ang II on VC.

MATERIALS AND METHODS

We worked with a model of high phosphate (HP)-induced calcification in human aortic smooth muscle cells, which resembles the CKD-related VC.

RESULTS

Addition of Ang II to cells growing in HP decreased calcification, which was associated with the upregulation of the osteogenic factors BMP2, Runx2/Cbfa1, Osterix and ALP. A reduction of magnesium entry into the HP-calcifying cells was found. The treatment with Ang II avoided this reduction, which was reversed by the cotreatment with the TRPM7-inhibitor 2-APB. The protective effect of Ang II was related to AT1R-induced ERK1/2 MAPKinase activation. HP-induced calcification was also associated with the upregulation of the canonical Wnt/beta-catenin pathway, while its downregulation was related to attenuation of calcification by Ang II.

CONCLUSION

As hypothesized, Ang II prevented phosphate-induced calcification in VSMCs, which appears mediated by the increase of magnesium influx and by the activation of the ERK1/2 and the inhibition of the canonical Wnt/beta-catenin signalling pathways.

Osteoprotegerin inhibits calcification of vascular smooth muscle cell via down regulation of the Notch1-RBP-Jκ/Msx2 signaling pathway

Objective

Vascular calcification is a common pathobiological process which occurs among the elder population and in patients with diabetes and chronic kidney disease. Osteoprotegerin, a secreted glycoprotein that regulates bone mass, has recently emerged as an important regulator of the development of vascular calcification. However, the mechanism is not fully understood. The purpose of this study is to explore novel signaling mechanisms of osteoprotegerin in the osteoblastic differentiation in rat aortic vascular smooth muscle cells (VSMCs).

Methods and Results

VSMCs were isolated from thoracic aorta of Sprague Dawley rats. Osteoblastic differentiation of VSMCs was induced by an osteogenic medium. We confirmed by Von Kossa staining and direct cellular calcium measurement that mineralization was significantly increased in VSMCs cultured in osteogenic medium; consistent with an enhanced alkaline phosphatase activity. This osteoblastic differentiation in VSMCs was significantly reduced by the addition of osteoprotegerin in a dose responsive manner. Moreover, we identified, by real-time qPCR and western blotting, that expression of Notch1 and RBP-Jκ were significantly up-regulated in VSMCs cultured in osteogenic medium at both the mRNA and protein levels, these effects were dose-dependently abolished by the treatment of osteoprotegerin. Furthermore, we identified that Msx2, a downstream target of the Notch1/RBP-Jκ signaling, was markedly down-regulated by the treatment of osteoprotegerin.

Conclusion

Osteoprotegerin inhibits vascular calcification through the down regulation of the Notch1-RBP-Jκ signaling pathway.

Review of Signaling Pathways Governing MSC Osteogenic and Adipogenic Differentiation

Mesenchymal stem cells (MSC) are multipotent cells, functioning as precursors to a variety of cell types including adipocytes, osteoblasts, and chondrocytes. Between osteogenic and adipogenic lineage commitment and differentiation, a theoretical inverse relationship exists, such that differentiation towards an osteoblast phenotype occurs at the expense of an adipocytic phenotype. This balance is regulated by numerous, intersecting signaling pathways that converge on the regulation of two main transcription factors: peroxisome proliferator-activated receptor- γ (PPAR γ ) and Runt-related transcription factor 2 (Runx2). These two transcription factors, PPAR γ and Runx2, are generally regarded as the master regulators of adipogenesis and osteogenesis. This review will summarize signaling pathways that govern MSC fate towards osteogenic or adipocytic differentiation. A number of signaling pathways follow the inverse balance between osteogenic and adipogenic differentiation and are generally proosteogenic/antiadipogenic stimuli. These include β -catenin dependent Wnt signaling, Hedgehog signaling, and NELL-1 signaling. However, other signaling pathways exhibit more context-dependent effects on adipogenic and osteogenic differentiation. These include bone morphogenic protein (BMP) signaling and insulin growth factor (IGF) signaling, which display both proosteogenic and proadipogenic effects. In summary, understanding those factors that govern osteogenic versus adipogenic MSC differentiation has significant implications in diverse areas of human health, from obesity to osteoporosis to regenerative medicine.