Inhibition of osteogenesis surrounding the titanium implant by CGRP deficiency

Neural regulation of mesenchymal stem cells in craniofacial bone: development, homeostasis and repair

Mesenchymal stem cells endow various functions, including proliferation, multipotency, migration, etc. Craniofacial bones originate from the cranial neural crest and are developed mainly through intramembranous ossification, which are different from long bones. There are varied mesenchymal stem cells existing in the craniofacial bone, including Gli1 + cells, Axin2 + cells, Prx1 + cells, etc. Nerves distributed in craniofacial area are also derived from the neural crest, and the trigeminal nerve is the major sensory nerve in craniofacial area. The nerves and the skeleton are tightly linked spatially, and the skeleton is broadly innervated by sensory and sympathetic nerves, which also participate in bone development, homeostasis and healing process. In this review, we summarize mesenchymal stem cells located in craniofacial bone or, to be more specific, in jaws, temporomandibular joint and cranial sutures. Then we discuss the research advance concerning neural regulation of mesenchymal stem cells in craniofacial bone, mainly focused on development, homeostasis and repair. Discovery of neural regulation of mesenchymal stem cells may assist in treatment in the craniofacial bone diseases or injuries.

Micro Computed Tomography and Immunohistochemistry Analysis of Dental Implant Osseointegration in Animal Experimental Model: A Scoping Review

Osseointegration is a complex process that involves the interaction of dental implants, bone, and the immune system. Preclinical testing was carried out to develop a better understanding of the mechanism. Micro-computed tomography (micro-CT) imaging techniques and immunohistochemistry are excellent tools for this objective as both enable quantitative assessment of bone microarchitecture and intercellular interaction. An extensive literature search was conducted using the databases PubMed, Science Direct, Wiley Online, Proquest and Ebscohost from January 2011 to January 2021. Among the publications retrieved, the rat model was the most frequently used experimental protocol, with the tibia being the most frequently implanted site. The region of interest demonstrates a high degree of homogeneity as measured by trabecula but varies in size and shape. The most frequently mentioned micro-CT bone parameter and immunohistochemistry bone markers were bone volume per total volume (BV/TV) and runt-related transcription factors (RUNX). Animal models, micro-CT analysis methods, and immunohistochemistry biomarkers yielded a variety of results in the studies. Understanding bone architecture and the remodeling process will aid in the selection of a viable model for a specific research topic.

The role of sensory and sympathetic nerves in craniofacial bone regeneration

Multiple factors regulate the regeneration of craniofacial bone defects. The nervous system is recognized as one of the critical regulators of bone mass, thereby suggesting a role for neuronal pathways in bone regeneration. However, in the context of craniofacial bone regeneration, little is known about the interplay between the nervous system and craniofacial bone. Sensory and sympathetic nerves interact with the bone through their neuropeptides, neurotransmitters, proteins, peptides, and amino acid derivates. The neuron-derived factors, such as semaphorin 3A (SEMA3A), substance P (SP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), and vasoactive intestinal peptide (VIP), possess a remarkable role in craniofacial regeneration. This review summarizes the roles of these factors and recently published factors such as secretoneurin (SN) and spexin (SPX) in the osteoblast and osteoclast differentiation, bone metabolism, growth, remodeling and discusses the novel application of nerve-based craniofacial bone regeneration. Moreover, the review will facilitate understanding the mechanism of action and provide potential treatment direction for the craniofacial bone defect.

Nervous System-Driven Osseointegration

Implants are essential therapeutic tools for treating bone fractures and joint replacements. Despite the in-depth study of osseointegration for more than fifty years, poor osseointegration caused by aseptic loosening remains one of the leading causes of late implant failures. Osseointegration is a highly sophisticated and spatiotemporal process in vivo involving the immune response, angiogenesis, and osteogenesis. It has been unraveled that the nervous system plays a pivotal role in skeletal health via manipulating neurotrophins, neuropeptides, and nerve cells. Herein, the research related to nervous system-driven osseointegration was systematically analyzed and reviewed, aiming to demonstrate the prominent role of neuromodulation in osseointegration. Additionally, it is indicated that the implant design considering the role of neuromodulation might be a promising way to prevent aseptic loosening.

CGRP regulates the dysfunction of peri-implant angiogenesis and osseointegration in streptozotocin-induced diabetic rats

Diabetes is a chronic systematic disease which results in neuropathy and dysfunctional bone metabolism and microcirculation. Calcitonin gene related peptide (CGRP) is an important neuropeptide that is involved in bone formation and vascular response. This study aimed to elucidate the role of CGRP in diabetic peri-implant angiogenesis and osteogenesis, which is yet to be reported. In vivo, we injected streptozotocin into SD rats to establish an experimental diabetes model. We then implanted 1 mm × 5 mm Ti implants into rat tibiae and injected lentivirus into the bone marrow cavity to overexpress or silence the peri-implant CGRP expression. We also applied overexpression lentivirus and silencing short hair RNA (shRNA) in rat bone marrow mesenchymal stem cells (BMSCs) to investigate the biological effects of CGRP in vitro. Through the investigation of diabetic neurons, blood, and peri-implant bone, we could observe that diabetes led to decreased synthesis and expression of CGRP, and high CGRP expression were only seen in peri-implant tissues in the early-to-middle phase of diabetic bone integration. Microfil perfusion followed by micro-CT analysis showed that the overexpression of CGRP enhanced peri-implant angiogenesis via increased vessel volume and thickness. Regarding osteogenesis, CGRP was found to improve the impaired osseointegration, as observed through micro-CT reconstruction and H&E staining. Similarly, overCGRP alleviated the hyperglycemia-triggered decrease in mineralization, and rescued ALP activity and the mRNA and protein expression of VEGF-A, ALP, and OPN. CGRP also attenuated the high glucose-induced production of reactive oxygen species (ROS). Our results demonstrate the potential promotive role of CGRP in early-to-middle phase of osseointegration, as CGRP could regulate the diabetes-induced dysfunctions in peri-implant angiogenesis and osseointegration. Our study provides a new insight into the diabetic peri-implant vasculature and the potential positive effect of CGRP on diabetic peri-implant vessels and bone.

Targeting Local Osteogenic and Ancillary Cells by Mechanobiologically Optimized Magnesium Scaffolds for Orbital Bone Reconstruction in Canines

Large-sized orbital bone defects have serious consequences that destroy orbital integrity and result in maxillofacial deformities and vision loss. The treatment of orbital bone defects is currently palliative and not reparative, suggesting an urgent demand for biomaterials that regenerate orbital bones. In this study, via alloying, extrusion and surface modification, we developed mechanobiologically optimized magnesium (Mg) scaffolds (Ca-P-coated Mg-Zn-Gd scaffolds, referred to as Ca-P-Mg) for the orthotopic reconstruction of large-sized orbital bone defects. At 6 months after transplanting the scaffolds to a clinically relevant canine large animal model, large-sized defects were successfully bridged by an abundance of new bone with normal mechanical properties that corresponded to gradual degradation of the implants. The osteogenic and ancillary cells, including vascular endothelial cells and trigeminal neurons, played important roles in this process. The scaffolds robustly enhanced bone marrow mesenchymal stem cell (BMSC) osteogenic differentiation. In addition, the increased angiogenesis including increased ratio of the specific endothelial subtype CD31^hi endomucin^hi (CD31^hiEmcn^hi) endothelial cells can facilitate osteogenesis. Furthermore, the scaffolds trigger trigeminal neurons via transient receptor potential vanilloid subtype 1 (Trpv1) to produce the neuropeptide calcitonin gene-related peptide (CGRP), which promotes angiogenesis and osteogenesis. Overall, our investigations revealed the efficacy of Ca-P-Mg scaffolds in healing orbital bone defects and warrant further exploration of these scaffolds for clinical applications.

Injectable colloidal hydrogel with mesoporous silica nanoparticles for sustained co-release of microRNA-222 and aspirin to achieve innervated bone regeneration in rat mandibular defects

Nerve fibers and vessels play important roles in bone formation, and inadequate innervation in the bone defect area can delay the regeneration process. However, there are few studies aiming to promote innervation to engineer bone formation. Here, we report the development of an injectable thermoresponsive mesoporous silica nanoparticle (MSN)-embedded core-shell structured poly(ethylene glycol)-b-poly(lactic-co-glycolic acid)-b-poly(N-isopropylacrylamide) (PEG-PLGA-PNIPAM) hydrogel for localized and long-term co-delivery of microRNA-222 and aspirin (ASP) (miR222/MSN/ASP hydrogel). ASP was found to stimulate bone formation as previously reported, and miR222 induced human bone mesenchymal stem cell differentiation into neural-like cells through Wnt/β-catenin/Nemo-like kinase signaling. In a rat mandibular bone defect, injection of the co-delivered MSN hydrogel resulted in neurogenesis and enhanced bone formation, indicating that the present injectable miR222- and ASP-co-delivering colloidal hydrogel is a promising material for innervated bone tissue engineering.