Paracrine and endocrine actions of bone-the functions of secretory proteins from osteoblasts, osteocytes, and osteoclasts

Micro-Nanofibrillar Polycaprolactone Scaffolds as Translatable Osteoconductive Grafts for the Treatment of Musculoskeletal Defects without Infection

The treatment of musculoskeletal defects is currently limited by the tissue-regenerative materials available to orthopedic surgeons: autologous bone grafts only have a finite amount of harvestable material within a given patient, while allografts are prone to severe immunological complications and host rejection. With this motivation, the production of poly(ε-caprolactone) (PCL) scaffolds as synthetic, biomimetic biomaterials was investigated, with a specific focus on potential orthopedic translation. PCL scaffolds were produced through three different fabrication techniques: electrospinning (ES), rotary jet spinning (RJS), and airbrush (AB). ES and RJS were observed to produce microfibrillar scaffolds, while all AB products were nanofibrous. Osteoblast viability, within the PCL scaffolds, and the osteogenic phenotype were assessed in vitro through a combination of adherence, metabolic activity, proliferation, gene expression, alkaline phosphatase bioactivity, and calcium deposition assays. While the polymeric scaffolds induced slight reductions in initial osteoblast adhesion and metabolic activity, seeded cells were able to proliferate and demonstrate the bone formation phenotype. AB products demonstrated reduced bacterial surface colonization when inoculated with both Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacterial strains, in comparison to the microfibrous ES and RJS products, without any small-molecule antibiotics, antimicrobial peptides, or reactive nanomaterials included during scaffold synthesis.

Correlations between serum concentration of three bone-derived factors and obesity and visceral fat accumulation in a cohort of middle aged men and women

BACKGROUND

The aim of this study was to investigate the interrelationships between three bone-derived factors [serum osteocalcin (OCN), fibroblast growth factor (FGF) 23, and neutrophil gelatinase-associated lipocalin (NGAL) levels] and body fat content and distribution, in order to reveal the potential endocrine function of bone in the development of obesity.

METHODS

We recruited 1179 people (aged 59.5 ± 6.2 years) from communities in Shanghai. Serum OCN levels were determined using an electrochemiluminescence immunoassay. Serum FGF23 and NGAL levels were determined using a sandwich enzyme-linked immunosorbent assay. The abdominal fat distribution, including visceral fat area (VFA), was assessed by magnetic resonance imaging. Visceral obesity was defined as a VFA ≥ 80 cm².

RESULTS

Serum OCN levels were inversely correlated with body fat parameters, while FGF23 and NGAL were positively correlated (P < 0.05). After adjusting for confounders, waist circumference (W) and VFA had a closer relationship with serum OCN, FGF23, and NGAL levels than body mass index (BMI) and body fat percentage (fat%, all P < 0.05). The risk of visceral obesity significantly increased with higher FGF23 and/or NGAL levels, as well as with reduced OCN levels (all P < 0.05). In addition, serum OCN, FGF23, and NGAL levels were independently associated with visceral obesity (all P < 0.01). The relationships persisted among subjects with normal glucose tolerance or subjects with hyperglycaemia (both P < 0.05).

CONCLUSIONS

Compared to the indicators of overall adiposity such as BMI or fat%, visceral adiposity indicators (W or VFA) were more closely related to serum OCN, FGF23 and NGAL levels. There was no interaction among the relationship of three bone-derived factors with visceral obesity, which revealed the independent relationship of endocrine function of skeleton with body fat.

[Bone and metabolism]

Bone is now considered as a particular endocrine organ. Its endocrine function is not yet fully understood and has been the subject of several conferences at the European Society of Endocrinology Congress 2018. Bone regulates phosphate metabolism by secreting fibroblast growth factor 23; it also regulates glucose metabolism via osteocalcin and energy metabolism, thanks to lipocalin 2, a new hormone acting on the brain. In addition, the incidence of diabetes continues to grow, and its impact on bone has been demonstrated, with an increased risk of fractures regardless the type of diabetes. The mechanism of bone fragility in this disease is not fully known but it involves a decrease in bone turnover and bone demineralization. Recent findings on the role of bone on glucose and mineral metabolism could open therapeutic perspectives, especially for the treatment of diabetes or obesity.

Nanostructured titanium regulates osseointegration via influencing macrophage polarization in the osteogenic environment

Introduction

Fabricating nanostructured surface topography represents the mainstream approach to induce osteogenesis for the next-generation bone implant. In the past, the bone implant was designed to minimize host repulsive reactions in order to acquire biocompatibility. However, increasing reports indicate that the absence of an appropriate immune response cannot acquire adequate osseointegration after implantation in vivo.

Materials and methods

We prepared different topographies on the surface of titanium (Ti) specimens by grinding, etching and anodizing, and they were marked as polished specimen (P), specimen with nanotubes (NTs) in small diameters (NT-30) and specimen with NTs in large diameters (NT-100). We evaluated the ability of different topographies of the specimen to induce osteogenic differentiation of mice bone marrow mesenchymal stem cells (BMSCs) in vitro and to induce osseointegration in vivo. Furthermore, we investigated the effect of different topographies on the polarization and secretion of macrophages, and the effect of macrophage polarization on topography-induced osteogenic differentiation of mice BMSCs. Finally, we verified the effect of macrophage polarization on topography-induced osseointegration in vivo by using Cre*RBP-J^fl/fl mice in which classically activated macrophage was restrained.

Results

The osteogenic differentiation of mice BMSCs induced by specimen with different topographies was NT-100>NT-30>P, while the osseointegration induced by specimen with different topographies in vivo was NT-30>NT-100>P. In addition, specimen of NT-30 could induce more macrophages to M2 polarization, while specimen of P and NT-100 could induce more macrophages to M1 polarization. When co-culture mice BMSCs and macrophages on specimen with different topographies, the osteogenic differentiation of mice BMSCs was NT-30>NT-100≥P. The osseointegration induced by NT-100 in Cre*RBP-J^fl/fl mice was much better than that of wild type mice.

Conclusion

It is suggested that the intrinsic immunomodulatory effects of nanomaterials are not only crucial to evaluate the in vivo biocompatibility but also required to determine the final osseointegration. To clarify the immune response and osseointegration may be beneficial for the designation and optimization of the bone implant.

Early effects of parathyroid hormone on vascularized bone regeneration and implant osseointegration in aged rats

The decreased bone mass and impaired osteogenesis capacities that occur with aging may influence the outcome of dental implants. Parathyroid hormone (PTH) (1-34) is an anabolic agent for the treatment of osteoporosis. However, little is known about its effects and mechanisms on vascularized bone regeneration and implant osseointegration in aging. In current study, we adopted both in vivo and in vitro approaches to explore the mechanisms of early actions of PTH (1-34) on the angiogenic and osteogenic microenvironment to enhance implant osseointegration in aged rats. Daily subcutaneous injections of 30 μg/kg PTH (1-34) were given to female rats aged 20 months beginning on next day of implantation and lasting for 5 weeks. Radiological and histological analysis confirmed that PTH (1-34) improved new bone formation, angiogenesis and implant osseointegration in aged rats in the early stage. The osteogenic potential of aged bone mesenchymal stem cells (BMSCs) was enhanced, while their adipogenesis capacity was attenuated. Furthermore, PTH (1-34) was shown to promote angiogenesis directly via endothelial cell migration and blood vessel formation in vitro. Meanwhile, PTH (1-34) stimulated more osteoclasts participation in bone remodeling by secreting angiogenic and osteogenic growth factors to induce early vascularization and stimulate the migration or differentiation of BMSCs indirectly. Together, these results demonstrate mechanistic insight into how PTH (1-34) regulates the angiogenic and osteogenic microenvironment to result in more active bone remodeling and new bone formation, making it an excellent potential therapeutic agent for rapid vascularized bone regeneration and implant osseointegration in the aged population.