Abstract
The sympathetic nervous system regulates bone formation and resorption under physiological conditions. However, it is still unclear how the sympathetic nerves affect stem cell migration and differentiation in bone regeneration. Distraction osteogenesis is an ideal model of bone regeneration due to its special nature as a self-engineering tissue. In this study, a rat model of mandibular distraction osteogenesis with transection of cervical sympathetic trunk was used to demonstrate that sympathetic denervation can deplete norepinephrine (NE) in distraction-induced bone callus, down-regulate β3-adrenergic receptor (adrb3) in bone marrow mesenchymal stem cells (MSCs), and promote MSC migration from perivascular regions to bone-forming units. An in vitro Transwell assay was here used to demonstrate that NE can inhibit stroma-derived factor-1 (SDF-1)-induced MSC migration and expression of the migration-related gene matrix metalloproteinase-2 (MMP-2) and downregulate that of the anti-migration gene tissue inhibitor of metalloproteinase-3 (TIMP-3). Knockdown of adrb3 using siRNA abolishes inhibition of MSC migration. An in vitro osteogenic assay was used to show that NE can inhibit the formation of MSC bone nodules and expression of the osteogenic marker genes alkaline phosphatase (ALP), osteocalcin (OCN), and runt-related transcription factor-2 (RUNX2), but knockdown of adrb3 by siRNA can abolish such inhibition of the osteogenic differentiation of MSCs. It is here concluded that sympathetic denervation-induced MSC mobilization in rat mandibular distraction osteogenesis is associated with inhibition of MSC migration and osteogenic differentiation by NE/adrb3 in vitro. These findings may facilitate understanding of the relationship of MSC mobilization and sympathetic nervous system across a wide spectrum of tissue regeneration processes.
Highlights
Current bone regeneration methods are still unable to satisfactorily correct large bone deformities and defects
NE has been demonstrated to stimulate osteoclast formation, thereby enhancing bone resorption [19]. It remains unclear whether NE regulates mesenchymal stem cells (MSCs) mobilization in bone regeneration processes, such as Distraction osteogenesis (DO)
Because perivascular regions contribute to a critical stem cell niche for bone marrow MSCs, and because the sympathetic nervous system has been shown to thoroughly innervate the skeletal system along blood vessels [12,13,14,15,16,17,18], it was here determined whether bone marrow MSCs resided along sympathetic nerves in the normal rat mandible
Summary
Current bone regeneration methods are still unable to satisfactorily correct large bone deformities and defects This is largely because of poor understanding of stem cell mechanisms. DO induces the formation of new bone along gradual distraction stress at the broken ends of bone It is an ideal model of bone regeneration because of its special nature as a selfengineering tissue. It has been demonstrated that MSCs are a subset of perivascular cells and reside in particular microenvironments called niches These control MSC survival, proliferation, self-renewal, and differentiation [9,10,11,12,13,14,15]. In order to differentiate into osteoblasts, MSCs must migrate from their niches to bone-forming sites For this reason, MSC mobilization is prerequisite to the bone formation in DO
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