Mechanical Stretching of Mouse Calvarial Osteoblasts In Vitro Models Changes in MMP-2 and MMP-9 Expression at the Bone-Implant Interface

Hexokinase 2-mediated glycolysis promotes receptor activator of NF-κB ligand expression in Porphyromonas gingivalis lipopolysaccharide-treated osteoblasts

BACKGROUND

Glucose metabolism plays a pivotal role in sustaining the inflammatory response to microbial stimulation by providing sufficient energy in immune cells. The main purpose of our study was to explore whether hexokinase 2 (HK2)-mediated glycolysis affected the expression of receptor activator of NF-κB Ligand (RANKL) in Porphyromonas gingivalis lipopolysaccharide (P. gingivalis-LPS)-treated osteoblasts and evaluate the potential involvement of the AKT/PI3K pathway activation during HK2-mediated glycolysis.

METHODS

Primary mice osteoblasts were treated with P. gingivalis-LPS, whereas the HK2 inhibitor (Lonidamine, LND) and small interference RNA were used to restrain HK2 expression. Conditioned medium from osteoblasts was utilized for culturing osteoclast precursors. The mRNA and protein levels of genes involved in glycolysis and bone metabolism including RANKL and osteoprotegerin (OPG) were detected by real-time PCR and western blotting. HK2 and lactate levels were detected by ELISA. Tartrate-resistant acid phosphatase (TRAP) staining was utilized to assess osteoclast formation. The involvement of the AKT/PI3K pathway in osteoblasts was explored by Western blotting.

RESULTS

P. gingivalis-LPS enhanced HK2 expression along with rising glycolysis in osteoblasts. LND and HK2-knockdown decreased RANKL expression and the RANKL/OPG ratio in osteoblasts, leading to less osteoclast formation from osteoclast precursors as evidenced by TRAP staining, while the osteogenic potential and proliferation of osteoblasts were not affected by HK2-knockdown. Moreover, P. gingivalis-LPS activated the AKT/PI3K pathway, which could regulate HK2 and RANKL expression in osteoblasts.

CONCLUSIONS

HK2-mediated glycolysis promoted RANKL in osteoblasts and enhanced osteoclast differentiation. Targeting glycolysis may provide novel therapeutic methods for reducing alveolar bone loss.

Physical Activity and Bone Vascularization: A Way to Explore in Bone Repair Context?

Physical activity is widely recognized as a biotherapy by WHO in the fight and prevention of bone diseases such as osteoporosis. It reduces the risk of disabling fractures associated with many comorbidities, and whose repair is a major public health and economic issue. Bone tissue is a dynamic supportive tissue that reshapes itself according to the mechanical stresses to which it is exposed. Physical exercise is recognized as a key factor for bone health. However, the effects of exercise on bone quality depend on exercise protocols, duration, intensity, and frequency. Today, the effects of different exercise modalities on capillary bone vascularization, bone blood flow, and bone angiogenesis remain poorly understood and unclear. As vascularization is an integral part of bone repair process, the analysis of the preventive and/or curative effects of physical exercise is currently very undeveloped. Angiogenesis–osteogenesis coupling may constitute a new way for understanding the role of physical activity, especially in fracturing or in the integration of bone biomaterials. Thus, this review aimed to clarify the link between physical activities, vascularization, and bone repair.

Role of Oxygen Supply in Macrophages in a Model of Simulated Orthodontic Tooth Movement

Apart from periodontal ligament fibroblasts, immune cells like macrophages also play an important mediating role in orthodontic tooth movement (OTM). Upon orthodontic force application to malpositioned teeth, macrophages in the periodontal ligament get exposed to both mechanical strain and hypoxic conditions (via a compression of blood vessels). In this study, we assessed the relative impact of orthodontically induced mechanical strain and hypoxic conditions on macrophages for the mediation and regulation of OTM. Macrophages were stimulated with physiological orthodontic compressive forces of 2 g/cm² for 4 h and 24 h on gas-impermeable or gas-permeable cell culture plates under normoxic or hypoxic cell culture conditions. We quantified expression of genes involved in inflammation (Tnf, Il-6, and Cox-2), extracellular remodelling (Mmp-9), and angiogenesis (Vegf) by RT-qPCR. Furthermore, we analysed HIF-1α, prostaglandin-E2, and VEGF protein expression via immunoblotting or ELISA. Mechanical strain and oxygen supply both differentially affected expression of genes and proteins involved in inflammation and angiogenesis. In this context, we found that HIF-1α protein levels were elevated by combined mechanical strain and hypoxic conditions, whereas gas-permeable plates providing sufficient oxygen supply prevented HIF-1α stabilization at the protein level after pressure application on macrophages. Our results thus indicate that macrophages involved in the mediation of OTM are affected by and respond differently to hypoxic conditions and mechanical compressive strain, which occur concomitantly during OTM, than periodontal ligament fibroblasts (PDLF), thus indicating different roles of these cells in the regulation of OTM at the cellular-molecular level. We further observed that contrary to PDLF HIF-1α stabilization in macrophages is rather induced via the decreased oxygen supply associated with OTM than via mechanotransduction by mechanical strain.

The Effect of Exercise on the Prevention of Osteoporosis and Bone Angiogenesis

Physical activity or appropriate exercise prevents the development of osteoporosis. However, the exact mechanism remains unclear although it is well accepted that exercise or mechanical loading regulates the hormones, cytokines, signaling pathways, and noncoding RNAs in bone. Accumulating evidence has shown that bone is a highly vascularized tissue, and dysregulation of vasculature is associated with many bone diseases such as osteoporosis or osteoarthritis. In addition, exercise or mechanical loading regulates bone vascularization in bone microenvironment via the modulation of angiogenic mediators, which play a crucial role in maintaining skeletal health. This review discusses the effects of exercise and its underlying mechanisms for osteoporosis prevention, as well as an angiogenic and osteogenic coupling in response to exercise.

Genistein induces adipogenic differentiation in human bone marrow mesenchymal stem cells and suppresses their osteogenic potential by upregulating PPARγ

Genistein is a soy isoflavone that exists in the form of an aglycone. It is the primary active component in soy isoflavone and has a number of biological activities (anti-inflammatory and anti-oxidative). However, the specific effect of genistein on human bone marrow mesenchymal stem cells (BMSCs) remains unclear. In the present study, the mechanism underlying the effect of genistein on the suppression of BMSC adipogenic differentiation and the enhancement of osteogenic potential was investigated using an MTT assay. It was observed that genistein significantly increased BMSC cell proliferation in a time- and dose-dependent manner (P<0.01). In addition, reverse transcription-quantitative polymerase chain reaction revealed that genistein significantly inhibited the expression of runt-related transcription factor 2 (Runx2), type I collagen (Col I) and osteocalcin (OC; P<0.01). Furthermore, 20 µm genistein significantly inhibited the activity of alkaline phosphatase (ALP) and increased the activity of triglycerides (TGs) increased (P<0.01) as determined by an enzyme-linked immunosorbent assay. Finally, western blotting revealed that BMSC pretreatment with 20 µm genistein significantly increased peroxisome proliferator-activated receptor γ (PPARγ) protein expression (P<0.01). This suggests that the downregulation of PPARγ may significantly reduce the effect of genistein on cell proliferation, suppress the expression of Runx2, Col I and OC mRNA, and reduce ALP and promote TG activity in BMSCs. Thus, the results of the present study conclude that genistein induces adipogenic differentiation in human BMSCs and suppresses their osteogenic potential by upregulating the expression of PPARγ. In conclusion, genistein may be a promising candidate drug for treatment against osteogenesis.