Abstract
Objective: The enhancement of multiple functions, including osteogenesis, angiogenesis, and cell recruitment, is required for efficient bone regeneration therapy. Recently, special attention has been focused on the microenvironment of stem cells to facilitate bone regeneration. Herein, we examined the effects of various combinations of hypoxic conditions and osteogenic induction on rat mesenchymal cells, to develop a specific protocol for enhancing the multiple cellular functions beneficial to bone regeneration. Methods: Rat mesenchymal cells, isolated from bone marrow, adipose tissue, and periodontal ligament, were examined. The cells were cultured under varied conditions of O2 tension (hypoxia) and duration and timing of hypoxic exposure, with or without osteogenic induction. Consequently, four different protocols were examined by measuring the gene expression levels of Runx2, Vegfa, and Cxcl12, indicating a capability for osteogenesis, angiogenesis, and cell recruitment, respectively. Finally, the mineralization ability of the rat mesenchymal cells was assessed by quantitating their calcified nodule formation. Results: The simultaneous application of hypoxic exposure and osteogenic induction promoted Vegfa expression in all types of cells, but suppressed Runx2. In contrast, hypoxic preconditioning, followed by osteogenic induction, did not increase the expression of these genes; in fact, Vegfa expression decreased significantly. Among the various protocols, 0.5% O2 exposure for 12 h after osteogenic induction exhibited the largest fold changes of gene expression level, especially of Vegfa. Hypoxic post-conditioning enhanced the formation of calcified nodules in periodontal ligament-derived cells. Conclusion: Short-term hypoxic exposure after osteogenic induction could be used to improve the efficiency of mesenchymal cells for bone regeneration.
Highlights
Mastication, speech, and facial aesthetics are often severely compromised by jaw bone defects caused by trauma, inflammatory disease, and benign or malignant tumors in the oral and maxillofacial region
Hypoxic preconditioning is considered to be beneficial to mesenchymal stem cells (MSCs) to enhance their angiogenic activity and cell induction ability, it is still controversial for bone regeneration therapy because some reports have demonstrated that osteogenic differentiation was accelerated under hypoxia, whereas many others stated that the process was suppressed [16]-[22]
Cells positive for CD29 and CD90, both rat MSC markers [28], numbered 90% or greater in the bone marrow-derived cells (BMDCs), adipose tissue-derived cells (ATDCs), and periodontal ligament-derived cells (PDLDCs) (Figure 2(A) and Figure 2(B)), suggesting that the cells used in the experiments had stem cell characteristics
Summary
Mastication, speech, and facial aesthetics are often severely compromised by jaw bone defects caused by trauma, inflammatory disease, and benign or malignant tumors in the oral and maxillofacial region. Autogenous bone grafting is a standard treatment for jaw bone reconstruction, it may cause donor site morbidity, post-operative complications, healing failure, and insufficient bone volume [2] [3] [4] For overcoming these problems, tissue engineering technology has a lot of potential, providing an alternative treatment option for autogenous bone grafting in jaw bone reconstruction and bone regeneration therapy [5] [6] [7]. Hypoxic preconditioning is considered to be beneficial to MSCs to enhance their angiogenic activity and cell induction ability, it is still controversial for bone regeneration therapy because some reports have demonstrated that osteogenic differentiation was accelerated under hypoxia, whereas many others stated that the process was suppressed [16]-[22]
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