Effects of different physical factors on osteogenic differentiation

Whole-body vibration protects against chronic high-altitude hypoxic bone loss by regulating the nitric oxide/HIF-1α axis in osteoblasts

The hypobaric hypoxia environment found at high altitudes imposes various reversible and irreversible detrimental effects on living organisms. Accumulating evidence suggests that hypobaric hypoxia negatively impacts skeleton health by diminishing bone quality and disrupting bone microarchitecture. However, therapeutic strategies to counteract this bone loss remain limited. This study investigates the impact of whole-body vibration (WBV) stimulation on skeletal health of rats continuously exposed to simulated hypobaric hypoxia environment at an altitude of 4500 m for 6 weeks. We found that WBV stimulation at 30 Hz and 0.3 g significantly improved femoral bone mass, microarchitecture, and biomechanical properties in rats exposed to chronic hypobaric hypoxia. Additionally, in vitro studies demonstrated that WBV enhanced osteogenic potential and activity in primary osteoblasts under hypoxia conditions. It also reduced levels of hypoxia-inducible factor 1α (HIF-1α), a key transcription factor involved in cellular response to hypoxia. Conversely, overexpression of HIF-1α significantly inhibited cellular differentiation and osteogenesis in osteoblasts exposed to WBV stimulation under hypoxic conditions. Furthermore, WBV stimulation led to a significant increase in nitric oxide (NO) concentrations in osteoblasts during hypoxic exposure. In vitro experiments showed that blocking of NO synthesis with L-NAME impeded WBV-stimulated osteogenic activity in hypoxia-exposed osteoblasts. In vivo studies demonstrated that inhibiting NO synthesis similarly abolished the positive impact of WBV on bone microarchitecture and biomechanical properties under hypobaric hypoxia. Collectivity, our findings indicate that WBV protects against hypobaric hypoxia-induced bone loss by regulating the NO/HIF-1α axis in osteoblasts, and reveal its clinical potential as a promising non-invasive approach.

Effects of polylactic acid scaffolds with various orientations and diameters on osteogenesis and angiogenesis

Researchers in the field of regenerative medicine have consistently focused on the biomimetic design of engineered bone materials on the basis of the microstructure of natural bone tissue. Additionally, the effects of the micromorphological characteristics of these materials on angiogenesis have garnered increasing attention. In vitro, the orientation and diameter of scaffold materials can exert different effects on osteogenesis and vascularisation. However, more comprehensive investigations, including in vivo studies, are required to confirm the results observed in vitro. Accordingly, in the present study, fibre scaffolds with various orientations and diameters were prepared by electrospinning with polylactic acid. The effects of the micromorphological characteristics of these scaffolds with different orientations and diameters on osteogenesis and vascularisation were systematically studied via in vivo experiments. The scaffolds with aligned micromorphological features positively affected osteogenesis and vascularisation, which indicated that such characteristics could be considered crucial factors when designing materials for bone repair.

Differential effects of structurally different lysophosphatidylethanolamine species on proliferation and differentiation in pre-osteoblast MC3T3-E1 cells

Lysophosphatidylethanolamine (LPE) is a bioactive lipid mediator involved in diverse cellular functions. In this study, we investigated the effects of three LPE species, 1-palmitoyl LPE (16:0 LPE), 1-stearoyl LPE (18:0 LPE), and 1-oleoyl LPE (18:1 LPE) on pre-osteoblast MC3T3-E1 cells. All LPE species stimulated cell proliferation and activated the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) 1/2. MAPK/ERK1/2 activation by 16:0 LPE and 18:1 LPE was inhibited by the Gq/11 inhibitor YM-254890, while activation by 18:0 LPE was blocked by the Gi/o inhibitor pertussis toxin. Intracellular Ca2+ transients were triggered by 16:0 LPE and 18:1 LPE but not by 18:0 LPE, with YM-254890 suppressing these responses. These results suggest that 16:0 and 18:1 LPE act via Gq/11-coupled G protein coupled receptors (GPCRs), and 18:0 LPE acts via Gi/o-coupled GPCRs. Furthermore, receptor desensitization experiments suggested that each LPE acts through distinct GPCRs. Interestingly, 18:0 LPE suppressed osteogenic differentiation, reducing mineralization, alkaline phosphatase activity, and osteogenic gene expression, whereas 16:0 LPE and 18:1 LPE had no such effects. These results suggest the physiological significance of LPEs in bone formation and indicate that different LPE species and their receptors play distinctive roles in this process.

Direct coupled electrical stimulation towards improved osteogenic differentiation of human mesenchymal stem/stromal cells: a comparative study of different protocols

Electrical stimulation (ES) has been described as a promising tool for bone tissue engineering, being known to promote vital cellular processes such as cell proliferation, migration, and differentiation. Despite the high variability of applied protocol parameters, direct coupled electric fields have been successfully applied to promote osteogenic and osteoinductive processes in vitro and in vivo. Our work aims to study the viability, proliferation, and osteogenic differentiation of human bone marrow-derived mesenchymal stem/stromal cells when subjected to five different ES protocols. The protocols were specifically selected to understand the biological effects of different parts of the generated waveform for typical direct-coupled stimuli. In vitro culture studies evidenced variations in cell responses with different electric field magnitudes (numerically predicted) and exposure protocols, mainly regarding tissue mineralization (calcium contents) and osteogenic marker gene expression while maintaining high cell viability and regular morphology. Overall, our results highlight the importance of numerical guided experiments to optimize ES parameters towards improved in vitro osteogenesis protocols.

Vanadium-Doped Mesoporous Bioactive Glass Promotes Osteogenic Differentiation of rBMSCs via the WNT/β-Catenin Signaling Pathway

Pentavalent vanadium [V(V)] has been studied as bioactive ions to improve the bone defect repair; however, its osteogenic promotion mechanism is still not fully understood so far. In this study, a V-doped mesoporous bioactive glass (V-MBG) was prepared, and its effects on osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs) and potential signaling pathways were investigated. The physicochemical characterization revealed that the incorporation of V slightly reduced the specific surface area and increased the mesoporous pore size, and the abundant mesopores of V-MBG were beneficial to the sustained dissolution of V(V) ions as well as calcium, silicon, and phosphorus ions. Cell proliferation results indicated that the high dilution ratio (>16) V-MBG extract markedly promoted the proliferation of rBMSCs compared with the control group and the same dilution ratio MBG extract. Compared with the same dilution ratio MBG extract, diluted V-MBG extracts markedly promoted the secretion of alkaline phosphatase (ALP) and osteocalcin (OCN) protein at day 7 but insignificantly stimulated the runt-related transcription factor 2 (RUNX2) and vascular endothelial growth factor (VEGF) protein synthesis. In depth, the diluted V-MBG extracts remarkably up-regulated the expression of WNT/β-catenin pathway direct target genes, including WNT3a, β-catenin, and AXIN2 genes in contrast to the same dilution ratio MBG extracts, suggesting that the released V(V) ions might promote osteogenic differentiation of rBMSCs via the WNT/β-catenin signaling pathway.

The Role of PEMFs on Bone Healing: An In Vitro Study

Bone responses to pulsed electromagnetic fields (PEMFs) have been extensively studied by using devices that expose bone cells to PEMFs to stimulate extracellular matrix (ECM) synthesis for bone and cartilage repair. The aim of this work was to highlight in which bone healing phase PEMFs exert their action. Specifically, we evaluated the effects of PEMFs both on human adipose mesenchymal stem cells (hASCs) and on primary human osteoblasts (hOBs) by testing gene and protein expression of early bone markers (on hASCs) and the synthesis of late bone-specific proteins (on hOBs) as markers of bone remodeling. Our results indicate that PEMFs seem to exert their action on bone formation, acting on osteogenic precursors (hASCs) and inducing the commitment towards the differentiation pathways, unlike mature and terminally differentiated cells (hOBs), which are known to resist homeostasis perturbation more and seem to be much less responsive than mesenchymal stem cells. Understanding the role of PEMFs on bone regenerative processes provides important details for their clinical application.