Establishment of cocultures of osteoblasts, Schwann cells, and neurons towards a tissue-engineered approach for orofacial reconstruction

Schwann cells promote prevascularization and osteogenesis of tissue-engineered bone via bone marrow mesenchymal stem cell-derived endothelial cells

Background

Tissue-engineered bone grafts (TEBGs) that undergo vascularization and neurotization evolve into functioning bone tissue. Previously, we verified that implanting sensory nerve tracts into TEBGs promoted osteogenesis. However, the precise mechanisms and interaction between seed cells were not explored. In this study, we hypothesized that neurotization may influence the osteogenesis of TEBGs through vascularization.

Methods

We cultured rat Schwann cells (SCs), aortic endothelial cells (AECs), and bone marrow-derived mesenchymal stem cells (BM-MSCs) and then obtained BM-MSC-derived induced endothelial cells (IECs) and induced osteoblasts (IOBs). IECs and AECs were cultured in an SC-conditioned medium (SC-CM) to assess proliferation, migration, capillary-like tube formation, and angiogenesis, and the vascular endothelial growth factor (VEGF) levels in the supernatants were detected. We established an indirect coculture model to detect the expression of nestin and VEGF receptors in IECs and tissue inhibitor of metalloproteinase (TIMP)-2 in SCs. Then, SCs, IECs, and IOBs were labeled and loaded into a β-tricalcium phosphate scaffold to induce prevascularization, and the scaffold was implanted into a 6-mm-long defect of rat femurs. Three groups were set up according to the loaded cells: I, SCs, and IECs (coculture for 3 days) plus IOBs; II, IECs (culture for 3 days) plus IOBs; III, IOBs. Nestin and TIMP-2 expression and osteogenesis of TEBGs were evaluated at 12 weeks post-implantation through histological and radiological assessments.

Results

We found that SC-CM promoted IEC proliferation, migration, capillary-like tube formation, and angiogenesis, but no similar effects were observed for AECs. IECs expressed nestin extensively, while AECs barely expressed nestin, and SC-CM promoted the VEGF secretion of IECs. In the coculture model, SCs promoted nestin and VEGF receptor expression in IECs, and IECs inhibited TIMP-2 expression in SCs. The promotion of prevascularized TEBGs by SCs and IECs in group I augmented new bone formation at 6 and 12 weeks. Nestin expression was higher in group I than in the other groups, while TIMP-2 expression was lower at 12 weeks.

Conclusions

This study demonstrated that SCs can promote TEBG osteogenesis via IECs and further revealed the related specific characteristics of IECs, providing preliminary cytological evidence for neurotization of TEBGs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02433-3.

Dorsal root ganglion neurons promote proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells

Preliminary animal experiments have confirmed that sensory nerve fibers promote osteoblast differentiation, but motor nerve fibers have no promotion effect. Whether sensory neurons promote the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells remains unclear. No results at the cellular level have been reported. In this study, dorsal root ganglion neurons (sensory neurons) from Sprague-Dawley fetal rats were co-cultured with bone marrow mesenchymal stem cells transfected with green fluorescent protein 3 weeks after osteogenic differentiation in vitro, while osteoblasts derived from bone marrow mesenchymal stem cells served as the control group. The rat dorsal root ganglion neurons promoted the proliferation of bone marrow mesenchymal stem cell-derived osteoblasts at 3 and 5 days of co-culture, as observed by fluorescence microscopy. The levels of mRNAs for osteogenic differentiation-related factors (including alkaline phosphatase, osteocalcin, osteopontin and bone morphogenetic protein 2) in the co-culture group were higher than those in the control group, as detected by real-time quantitative PCR. Our findings indicate that dorsal root ganglion neurons promote the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells, which provides a theoretical basis for in vitro experiments aimed at constructing tissue-engineered bone.

Sensory neurons and osteoblasts: close partners in a microfluidic platform

We presented a microfluidic-based coculture system as a new tool to be explored for modeling biological processes and pharmacological screening concerning peripheral tissues innervation.

Isolation and culture of Schwann cells

Primarily cultured Schwann cells are essential for the investigation of molecular mechanisms regulating proliferation, survival, differentiation, and myelination of Schwann cell and for the development of efficient transplantation for regeneration of injured spinal cord or peripheral nervous system. Here we describe a basic protocol for isolation and purification of primary Schwann cell from neonatal rat or mouse and discuss some modifications adapted to the culturing from adult nerves and optional methods for Schwann cell enrichment.

Culturing of glial and neuronal cells on polysialic acid

Although peripheral nerves exhibit regeneration capacities after transection injuries, the success of nerve repair depends crucially on the length of the gap. In addition to autologous nerve grafting as the conventional neurosurgical treatment to overcome long gaps, alternative strategies are needed. Numerous experimental studies have been undertaken to find the optimal material for production of artificial prostheses, which can be introduced as conduits between the nerve stumps. The current study follows the aim to establish polysialic acid (polySia), a homopolymer of alpha2,8-linked sialic acid residues, as a novel, biocompatible, and bioresorbable material for nerve tissue engineering. As a first step towards this goal, protocols for efficient coating of cell culture dishes with soluble polySia were established. In addition, primary nerve cells which are candidates for reconstructive therapies, including neonatal and adult Schwann cells, neural progenitor cells, spinal ganglionic neurons and motoneurons were cultured on polySia substrates. Cultures were evaluated with regard to cell survival and cell proliferation capacities. polySia turned out to be stable under cell culture conditions, and induced degradable and degradation products had no negative effects on cell cultures. Furthermore, polySia revealed its compatibility for several cell types derived from rat embryonic, postnatal and adult nervous tissue when used as a substrate.