Antitumor necrotic factor agent promotes BMP-2-induced ectopic bone formation

Single-cell RNA-seq analysis reveals that immune cells induce human nucleus pulposus ossification and degeneration

Background and aims

Determining the transcriptomes and molecular mechanism underlying human degenerative nucleus pulposus (NP) is of critical importance for treating intervertebral disc degeneration (IDD). Here, we aimed to elucidate the detailed molecular mechanism of NP ossification and IDD using single-cell RNA sequencing.

Methods

Single-cell RNA-seq and bioinformatic analysis were performed to identify NP cell populations with gene signatures, biological processes and pathways, and subpopulation analysis, RNA velocity analysis, and cell-to-cell communication analysis were performed in four IDD patients. We also verified the effects of immune cells on NP ossification using cultured NP cells and a well-established rat IDD model.

Results

We identified five cell populations with gene expression profiles in degenerative NP at single-cell resolution. GO database analysis showed that degenerative NP-associated genes were mainly enriched in extracellular matrix organization, immune response, and ossification. Gene set enrichment analysis showed that rheumatoid arthritis signaling, antigen processing and presentation signaling were activated in the blood cell cluster. We revealed that stromal cells, which are progenitor cells, differentiated toward an ossification phenotype and delineated interactions between immune cells (macrophages and T cells) and stromal cells. Immune factors such as TNF-α, CD74 and CCL-3 promoted the differentiation of stromal cells toward an ossification phenotype in vitro. Blocking TNF-α with a specific inhibitor successfully reversed NP ossification and modified NP morphology in vivo.

Conclusion

Our study revealed an increase in macrophages and T cells in degenerative NP, which induced stromal cell differentiation toward an ossification phenotype, and contributed to the identification of a novel therapeutic target to delay IDD.

What do we know about bone morphogenetic proteins and osteochondroprogenitors in inflammatory conditions?

Osteochondroprogenitors are crucial for embryonic bone development and postnatal processes such as bone repair in response to fracture injury, and their dysfunction may contribute to insufficient repair of structural damage in inflammatory arthritides. In the fracture healing, the early inflammatory phase is crucial for normal callus development and new bone formation. This process involves a complex interplay of many molecules and cell types, responsible for recruitment, expansion and differentiation of osteochondroprogenitor populations. In inflammatory arthritides, inflammation induces bone resorption and causes insufficient bone formation, which leads to local and systemic bone loss. While bone loss is a predominant feature in rheumatoid arthritis, inflammation also induces pathologic bone formation at enthesial sites in seronegative spondyloarthropathies. Bone morphogenetic proteins (BMP) are involved in cell proliferation, differentiation and apoptosis, and have fundamental roles in maintenance of postnatal bone homeostasis. They are crucial regulators of the osteochondroprogenitor pool and drive their proliferation, differentiation, and lifespan during bone regeneration. In this review, we summarize the effects of inflammation on osteochondroprogenitor populations during fracture repair and in inflammatory arthritides, with special focus on inflammation-mediated modulation of BMP signaling. We also present data in which we describe a population of murine synovial osteochondroprogenitor cells, which are reduced in arthritis, and characterize their expression of genes involved in regulation of bone homeostasis, emphasizing the up-regulation of BMP pathways in early progenitor subset. Based on the presented data, it may be concluded that during an inflammatory response, innate immune cells induce osteochondroprogenitors by providing signals for their recruitment, by producing BMPs and other osteogenic factors for paracrine effects, and by secreting inflammatory cytokines that may positively regulate osteogenic pathways. On the other hand, inflammatory cells may secrete cytokines that interfere with osteogenic pathways, proapoptotic factors that reduce the pool of osteochondroprogenitor cells, as well as BMP and Wnt antagonists. The net effect is strongly context-dependent and influenced by the local milieu of cells, cytokines, and growth factors. Further elucidation of the interplay between inflammatory signals and BMP-mediated bone formation may provide valuable tools for therapeutic targeting.

The Influence of Adalimumab and Cyclosporine A on the Expression Profile of the Genes Related to TGFβ Signaling Pathways in Keratinocyte Cells Treated with Lipopolysaccharide A

BACKGROUND

In the treatment of moderate to severe psoriasis, cyclosporine A (CsA) conventional therapy is used and biological, anti-cytokine treatment using, for example, anti-TNF drug-adalimumab.

AIM

This study aimed at investigating the effect of CsA and adalimumab on the profile of mRNAs and protein expression associated with transforming growth factor β (TGFβ) pathways in human keratinocyte (HaCaT) culture previously exposed to lipopolysaccharide (LPS).

MATERIALS AND METHODS

HaCaT culture was exposed to 1 ng/ml LPS for 8 hours+8 μg/ml adalimumab for 2, 8, and 24 hours or 1 ng/ml LPS for 8 hours+100 ng/ml CsA for 2, 8, and 24 hours and compared to the control culture. Sulphorodamine B cytotoxicity assay was performed. The expression profile of mRNA related to TGFβ paths was indicated by microarray and RTqPCR analyses. The ELISA test was used to analyze changes on the proteome level. Statistical analysis consisted of ANOVA analysis and the post hoc Tukey test (p < 0.05).

RESULTS

The cytotoxicity test showed that LPS, adalimumab, and cyclosporine in the concentration used in this experiment did not have any cytotoxicity effect on HaCaT cells. The largest fold changes (FC) in expression in (∣FC | >4.00) was determined for TGFβ1-3, TGFβRI-III, SKIL, SMURF2, SMAD3, BMP2, BMP6, JAK2, UBE2D1, SKP2, EDN1, and PRKAR2B (p < 0.05). In addition, on the protein level, the direct changes observed at mRNA were the same.

CONCLUSION

Analysis of the microarray expression profile of genes associated with TGFβ signaling pathways has demonstrated the potential of cyclosporin A and adalimumab to induce changes in their transcriptional activity. The anti-TNF drug seems to affect TGFβ cascades to a greater extent than cyclosporin A. The obtained results suggest that the regularity of taking the drug is important for the efficacy of psoriasis therapy.

The Bone Building Blues: Self-hardening copper-doped calcium phosphate cement and its in vitro assessment against mammalian cells and bacteria

A blue calcium phosphate cement with optimal self-hardening properties was synthesized by doping whitlockite (β-TCP) with copper ions. The mechanism and the kinetics of the cement solidification process were studied using energy dispersive X-ray diffraction and it was found out that hardening was accompanied by the phase transition from TCP to brushite. Reduced lattice parameters in all crystallographic directions resulting from the rather low (1:180) substitution rate of copper for calcium was consistent with the higher ionic radius of the latter. The lower cationic hydration resulting from the partial Ca→Cu substitution facilitated the release of constitutive hydroxyls and lowered the energy of formation of TCP from the apatite precursor at elevated temperatures. Addition of copper thus effectively inhibited the formation of apatite as the secondary phase. The copper-doped cement exhibited an antibacterial effect, though exclusively against Gram-negative bacteria, including E. coli, P. aeruginosa and S. enteritidis. This antibacterial effect was due to copper ions, as demonstrated by an almost negligible antibacterial effect of the pure, copper-free cement. Also, the antibacterial activity of the copper-containing cement was significantly higher than that of its precursor powder. Since there was no significant difference between the kinetics of the release of copper from the precursor TCP powder and from the final, brushite phase of the hardened cement, this has suggested that the antibacterial effect was not solely due to copper ions, but due to the synergy between cationic copper and a particular phase and aggregation state of calcium phosphate. Though inhibitory to bacteria, the copper-doped cement increased the viability of human glial E297 cells, murine osteoblastic K7M2 cells and especially human primary lung fibroblasts. That this effect was also due to copper ions was evidenced by the null effect on viability increase exhibited by the copper-free cements. The difference in the mechanism of protection of dehydratases in prokaryotes and eukaryotes was used as a rationale for explaining the hereby evidenced selectivity in biological response. It presents the basis for the consideration of copper as a dually effective ion when synergized with calcium phosphates: toxic for bacteria and beneficial for the healthy cells.

Calcium Phosphate as a Key Material for Socially Responsible Tissue Engineering

Socially responsible technologies are designed while taking into consideration the socioeconomic, geopolitical and environmental limitations of regions in which they will be implemented. In the medical context, this involves making therapeutic platforms more accessible and affordable to patients in poor regions of the world wherein a given disease is endemic. This often necessitates going against the reigning trend of making therapeutic nanoparticles ever more structurally complex and expensive. However, studies aimed at simplifying materials and formulations while maintaining the functionality and therapeutic response of their more complex counterparts seldom provoke a significant interest in the scientific community. In this review we demonstrate that such compositional simplifications are meaningful when it comes to the design of a solution for osteomyelitis, a disease that is in its natural, non-postoperative form particularly prevalent in the underdeveloped parts of the world wherein poverty, poor sanitary conditions, and chronically compromised defense lines of the immune system are the norm. We show that calcium phosphate nanoparticles, which are inexpensive to make, could be chemically designed to possess the same functionality as a hypothetic mixture additionally composed of: (a) a bone growth factor; (b) an antibiotic for prophylactic or anti-infective purposes; (c) a bisphosphonate as an antiresorptive compound; (d) a viral vector to enable the intracellular delivery of therapeutics; (e) a luminescent dye; (f) a radiographic component; (g) an imaging contrast agent; (h) a magnetic domain; and (i) polymers as viscous components enabling the injectability of the material and acting as carriers for the sustained release of a drug. In particular, calcium phosphates could: (a) produce tunable drug release profiles; (b) take the form of viscous and injectable, self-setting pastes; (c) be naturally osteo-inductive and inhibitory for osteoclastogenesis; (d) intracellularly deliver bioactive compounds; (e) accommodate an array of functional ions; (f) be processed into macroporous constructs for tissue engineering; and (g) be naturally antimicrobial. All in all, we see in calcium phosphates the presence of a protean nature whose therapeutic potentials have been barely tapped into.

When 1+1>2: Nanostructured composites for hard tissue engineering applications

Multicomponent, synergistic and multifunctional nanostructures have taken over the spotlight in the realm of biomedical nanotechnologies. The most prospective materials for bone regeneration today are almost exclusively composites comprising two or more components that compensate for the shortcomings of each one of them alone. This is quite natural in view of the fact that all hard tissues in the human body, except perhaps the tooth enamel, are composite nanostructures. This review article highlights some of the most prospective breakthroughs made in this research direction, with the hard tissues in main focus being those comprising bone, tooth cementum, dentin and enamel. The major obstacles to creating collagen/apatite composites modeled after the structure of bone are mentioned, including the immunogenicity of xenogeneic collagen and continuously failing attempts to replicate the biomineralization process in vitro. Composites comprising a polymeric component and calcium phosphate are discussed in light of their ability to emulate the soft/hard composite structure of bone. Hard tissue engineering composites created using hard material components other than calcium phosphates, including silica, metals and several types of nanotubes, are also discoursed on, alongside additional components deliverable using these materials, such as cells, growth factors, peptides, antibiotics, antiresorptive and anabolic agents, pharmacokinetic conjugates and various cell-specific targeting moieties. It is concluded that a variety of hard tissue structures in the body necessitates a similar variety of biomaterials for their regeneration. The ongoing development of nanocomposites for bone restoration will result in smart, theranostic materials, capable of acting therapeutically in direct feedback with the outcome of in situ disease monitoring at the cellular and subcellular scales. Progress in this research direction is expected to take us to the next generation of biomaterials, designed with the purpose of fulfilling Daedalus' dream - not restoring the tissues, but rather augmenting them.

Effects of aging on osteogenic response and heterotopic ossification following burn injury in mice

Heterotopic ossification (HO) is a common and debilitating complication of burns, traumatic brain injuries, and musculoskeletal trauma and surgery. Although the exact mechanism of ectopic bone formation is unknown, mesenchymal stem cells (MSCs) capable of osteogenic differentiation are known to play an essential role. Interestingly, the prevalence of HO in the elderly population is low despite the high overall occurrence of musculoskeletal injury and orthopedic procedures. We hypothesized that a lower osteogenicity of MSCs would be associated with blunted HO formation in old compared with young mice. In vitro osteogenic differentiation of adipose-derived MSCs from old (18-20 months) and young (6-8 weeks) C57/BL6 mice was assessed, with or without preceding burn injury. In vivo studies were then performed using an Achilles tenotomy with concurrent burn injury HO model. HO formation was quantified using μCT scans, Raman spectroscopy, and histology. MSCs from young mice had more in vitro bone formation, upregulation of bone formation pathways, and higher activation of Smad and nuclear factor kappa B (NF-κB) signaling following burn injury. This effect was absent or blunted in cells from old mice. In young mice, burn injury significantly increased HO formation, NF-κB activation, and osteoclast activity at the tenotomy site. This blunted, reactive osteogenic response in old mice follows trends seen clinically and may be related to differences in the ability to mount acute inflammatory responses. This unique characterization of HO and MSC osteogenic differentiation following inflammatory insult establishes differences between age populations and suggests potential pathways that could be targeted in the future with therapeutics.

Multiple roles of tumor necrosis factor-alpha in fracture healing

This review presents a summary of basic science evidence examining the influence of tumor necrosis factor-alpha (TNF-α) on secondary fracture healing. Multiple studies suggest that TNF-α, in combination with the host reservoir of peri-fracture mesenchymal stem cells, is a main determinant in the success of bone healing. Disease states associated with poor bone healing commonly have inappropriate TNF-α responses, which likely contributes to the higher incidence of delayed and nonunions in these patient populations. Appreciation of TNF-α in fracture healing may lead to new therapies to augment recovery and reduce the incidence of complications.

Different effects of indomethacin on healing of shaft and metaphyseal fractures

BACKGROUND AND PURPOSE

NSAIDs are commonly used in the clinic, and there is a general perception that this does not influence healing in common types of human fractures. Still, NSAIDs impair fracture healing dramatically in animal models. These models mainly pertain to fractures of cortical bone in shafts, whereas patients more often have corticocancellous fractures in metaphyses. We therefore tested the hypothesis that the effect of an NSAID is different in shaft healing and metaphyseal healing.

METHODS

26 mice were given an osteotomy of their left femur with an intramedullary nail. 13 received injections of indomethacin, 1 mg/kg twice daily. After 17 days of healing, the femurs were analyzed with 3-point bending and microCT. 24 other mice had holes drilled in both proximal tibias, to mimic a stable metaphyseal injury. A screw was inserted in the right tibial hole only. After 7 days of indomethacin injections or control injections, screw fixation was measured with mechanical pull-out testing and the side without a screw was analyzed with microCT.

RESULTS

In the shaft model, indomethacin led to a 35% decrease in force at failure (95% CI: 14-54). Callus size was reduced to a similar degree, as seen by microCT. Metaphyseal healing was less affected by indomethacin, as no effect on pull-out force could be seen (95% CI: -27 to 17) and there was only a small drop in new bone volume inside the drill hole. The difference in the relative effect of indomethacin between the 2 models was statistically significant (p = 0.006).

INTERPRETATION

Indomethacin had a minimal effect on stable metaphyseal fractures, but greatly impaired healing of unstable shaft fractures. This could explain some of the differences found between animal models and clinical experience.

The role of PGRN in musculoskeletal development and disease

Progranulin (PGRN) is a growth factor that has been implicated in wound healing, inflammation, infection, tumorigenesis, and is most known for its neuroprotective and proliferative properties in neurodegenerative disease. This pleiotropic growth factor has been found to be a key player and regulator of a diverse spectrum of multi-systemic functions. Its critical anti-inflammatory role in rheumatoid arthritis and other inflammatory disease models has allowed for the propulsion of research to establish its significance in musculoskeletal diseases, including inflammatory conditions involving bone and cartilage pathology. In this review, we aim to elaborate on the emerging role of PGRN in the musculoskeletal system, reviewing its particular mechanisms described in various musculoskeletal diseases, with special focus on osteoarthritis and inflammatory joint disease patho-mechanisms and potential therapeutic applications of PGRN and its derivatives in these and other musculoskeletal diseases.

Bone formation induced by BMP-2 in human osteosarcoma cells

Our previous studies demonstrated that BMP-2 inhibits the tumorigenicity of cancer stem cells identified as cells with high aldehyde dehydrogenase activity (ALDH ^br cells) from the human osteosarcoma cell line OS99-1. We further investigated whether BMP-2 is capable of inducing bone formation in OS99-1 cells. Flow cytometry sorting was used to isolate tumorigenic ALDH ^br and non-tumorigenic ALDH ^lo cells. qRT-PCR was used to quantify the gene expression. A xenograft model was used to verify the bone formation in vivo . There was significantly higher mRNA expression of BMPR1B and BMPR2 in ALDH ^lo cells compared with that in ALDH ^br cells and the BMPR1B expression in ALDH ^lo cells was ∼8-fold higher compared to that in ALDH ^br cells. BMP-2 was also found to induce higher transcription of osteogenic markers Runx-2, Osterix (Osx), alkaline phosphatase (ALP) and collagen type I in ALDH ^lo cells compared to ALDH ^br cells, which were mediated by the canonical Smad signaling pathway. In vivo , BMP-2 was identified to induce bone formation in both ALDH ^br and ALDH ^lo cells. All animals receiving 1×10 ⁴ ALDH ^lo cells treated with 30 μ g of BMP-2 per animal showed bone formation within 1–2 weeks after injection in mice. Bone formation induced by BMP-2 in ALDH ^lo cells showed significantly more bone mineral content compared to that in ALDH ^br cells. BMP-2 induces bone formation in heterogeneous osteosarcoma cells and BMP-2 may have a promising therapeutic role for treating human osteosarcoma by inducing differentiation along an osteogenic pathway.

The promotion of bone healing by progranulin, a downstream molecule of BMP-2, through interacting with TNF/TNFR signaling

Endochondral ossification plays a key role in the bone healing process, which requires normal cartilage callus formation. Progranulin (PGRN) growth factor is known to enhance chondrocyte differentiation and endochondral ossification during development, yet whether PGRN also plays a role in bone regeneration remains unknown. In this study we established surgically-induced bone defect and ectopic bone formation models based on genetically-modified mice. Thereafter, the bone healing process of those mice was analyzed through radiological assays including X-ray and micro CT, and morphological analysis including histology and immunohistochemistry. PGRN deficiency delayed bone healing, while recombinant PGRN enhanced bone regeneration. Moreover, PGRN was required for BMP-2 induction of osteoblastogenesis and ectopic bone formation. Furthermore, the role of PGRN in bone repair was mediated, at least in part, through interacting with TNF-α signaling pathway. PGRN-mediated bone formation depends on TNFR2 but not TNFR1, as PGRN promoted bone regeneration in deficiency of TNFR1 but lost such effect in TNFR2 deficient mice. PGRN blocked TNF-α-induced inflammatory osteoclastogenesis and protected BMP-2-mediated ectopic bone formation in TNF-α transgenic mice. Collectively, PGRN acts as a critical mediator of the bone healing process by constituting an interplay network with BMP-2 and TNF-α signaling, and this represents a potential molecular target for treatment of fractures, especially under inflammatory conditions.

Studies of bone morphogenetic protein-based surgical repair

Over the past several decades, recombinant human bone morphogenetic proteins (rhBMPs) have been the most extensively studied and widely used osteoinductive agents for clinical bone repair. Since rhBMP-2 and rhBMP-7 were cleared by the U.S. Food and Drug Administration for certain clinical uses, millions of patients worldwide have been treated with rhBMPs for various musculoskeletal disorders. Current clinical applications include treatment of long bone fracture non-unions, spinal surgeries, and oral maxillofacial surgeries. Considering the growing number of recent publications related to clincal research of rhBMPs, there exists enormous promise for these proteins to be used in bone regenerative medicine. The authors take this opportunity to review the rhBMP literature paying specific attention to the current applications of rhBMPs in bone repair and spine surgery. The prospective future of rhBMPs delivered in combination with tissue engineered scaffolds is also reviewed.

Altered bone biology in psoriatic arthritis

Psoriatic arthritis (PsA) is characterized by focal bone erosions mediated by osteoclasts at the bone-pannus junction. The bulk of research over the past decade has centered on mechanisms that underlie osteoclastogenesis along with new insights into osteoimmunology; however, recent advances that focus on steps that lead to new bone formation are beginning to emerge. New revelations about bone formation may have direct relevance to PsA given the presence of enthesophytes, syndesmophytes, and bony ankylosis frequently observed in patients with this disorder. In this review, we discuss current developments in the pathogenesis of new bone formation, novel imaging approaches to study bone remodeling and highlight innovative approaches to study the effect of inflammation on bone. Lastly, we discuss promising therapies that target joint inflammation and osteitis with the potential to mediate pathologic bone formation.

Etanercept does not impair healing in rat models of tendon or metaphyseal bone injury

BACKGROUND AND PURPOSE

Should blockade of TNF-α be avoided after orthopedic surgery? Healing of injuries in soft tissues and bone starts with a brief inflammatory phase. Modulation of inflammatory signaling might therefore interfere with healing. For example, Cox inhibitors impair healing in animal models of tendon, ligament, and bone injury, as well as in fracture patients. TNF-α is expressed locally at increased levels during early healing of these tissues. We therefore investigated whether blocking of TNF-α with etanercept influences the healing process in established rat models of injury of tendons and metaphyseal bone.

METHODS

Rats were injected with etanercept, 3.5 mg/kg 3 times a week. Healing of transected Achilles tendons and bone healing around screws implanted in the tibial metaphysis were estimated by mechanical testing. Tendons were allowed to heal either with or without mechanical loading. Ectopic bone induction following intramuscular BMP-2 implants has previously been shown to be stimulated by etanercept in rodents. This was now tested as a positive control.

RESULTS

Tendon peak force after 10 days was not significantly influenced by etanercept. Changes exceeding 29% could be excluded with 95% confidence. Likewise, screw pull-out force was not significantly influenced. More than 25% decrease or 18% increase could be excluded with 95% confidence. However, etanercept treatment increased the amount of bone induced by intramuscular BMP-2 implants, as estimated by blind histological scoring.

INTERPRETATION

Etanercept does not appear to impair tendon or metaphyseal bone healing to any substantial degree.

Brief review of models of ectopic bone formation

Ectopic bone formation is a unique biologic entity--distinct from other areas of skeletal biology. Animal research models of ectopic bone formation most often employ rodent models and have unique advantages over orthotopic (bone) environments, including a relative lack of bone cytokine stimulation and cell-to-cell interaction with endogenous (host) bone-forming cells. This allows for relatively controlled in vivo experimental bone formation. A wide variety of ectopic locations have been used for experimentation, including subcutaneous, intramuscular, and kidney capsule transplantation. The method, benefits and detractions of each method are summarized in the following review. Briefly, subcutaneous implantation is the simplest method. However, the most pertinent concern is the relative paucity of bone formation in comparison to other models. Intramuscular implantation is also widely used and relatively simple, however intramuscular implants are exposed to skeletal muscle satellite progenitor cells. Thus, distinguishing host from donor osteogenesis becomes challenging without cell-tracking studies. The kidney capsule (perirenal or renal capsule) method is less widely used and more technically challenging. It allows for supraphysiologic blood and nutrient resource, promoting robust bone growth. In summary, ectopic bone models are extremely useful in the evaluation of bone-forming stem cells, new osteoinductive biomaterials, and growth factors; an appropriate choice of model, however, will greatly increase experimental success.

Inflammation and uncoupling as mechanisms of periodontal bone loss

Periodontal disease is characterized by both inflammation and bone loss. Advances in research in both these areas have led to a new appreciation of not only each field but also the intimate relationship between inflammation and bone loss. This relationship has resulted in a new field of science called osteoimmunology and provides a context for better understanding the pathogenesis of periodontal disease. In this review, we discuss several aspects of the immuno-inflammatory host response that ultimately results in loss of alveolar bone. A proposal is made that periodontal inflammation not only stimulates osteoclastogenesis but also interferes with the uncoupling of bone formation and bone resorption, consistent with a pathologic process. Furthermore, arguments based on experimental animal models suggest a critical role of the spatial and temporal aspects of inflammation in the periodontium. A review of these findings leads to a new paradigm to help explain more fully the impact of inflammation on alveolar bone in periodontal disease so that it includes the effects of inflammation on uncoupling of bone formation from resorption.