NGF-TrkA signaling dictates neural ingrowth and aberrant osteochondral differentiation after soft tissue trauma

Involvement of Nerve Growth Factor in the Reparative Reaction to Osteonecrotic Lesions

The reparative zone in femoral head osteonecrosis is pivotal for repair; however, the repair response mechanism remains poorly understood. Although neurotrophic nerve growth factor significantly contributes to bone formation in fatigue fractures and ectopic ossification, the relationship between nerve growth factor and the repair response to osteonecrosis remains unexplored. We aimed to elucidate the role of nerve growth factor in osteonecrosis repair. Twenty-seven wholly resected femoral heads diagnosed with Japanese Investigation Committee Stage 3 femoral head osteonecrosis, excluding those with severe collapse, were analyzed. Histopathological diagnosis confirmed the presence of necrotic, reparative, and viable zones in all examined femoral heads. Quantitative evaluation of immunohistological staining, including nerve growth factor, vascular endothelial growth factor, osteocalcin, CD31, and TUBB3, was conducted in each zone. Additionally, micro-computed tomography was used to measure the trabecular bone microstructure in the reparative zone. Nerve growth factor expression was detected in all 27 femoral heads with osteonecrosis, exhibiting a significantly higher prevalence in the reparative zone than in other regions (p < 0.0001). Nerve growth factor was predominantly distributed on the necrotic side within the reparative zone, rather than the viable side. In the reparative zone, nerve growth factor expression was positively correlated with bone formation parameters derived from micro-computed tomography images. Vascular endothelial growth factor, osteocalcin, CD31(+) vascular endothelial cells, and TUBB3(+) nerve cells also significantly increased in the reparative zone. In conclusion, nerve growth factor expression was consistent across all femoral heads with osteonecrosis and may play a role in reparative reaction to osteonecrotic lesions.

Nociceptive neurons promote gastric tumour progression via a CGRP-RAMP1 axis

Cancer cells have been shown to exploit neurons to modulate their survival and growth, including through the establishment of neural circuits within the central nervous system1-3. Here we report a distinct pattern of cancer-nerve interactions between the peripheral nervous system and gastric cancer. In multiple mouse models of gastric cancer, nociceptive nerves demonstrated the greatest degree of nerve expansion in an NGF-dependent manner. Neural tracing identified CGRP+ peptidergic neurons as the primary gastric sensory neurons. Three-dimensional co-culture models showed that sensory neurons directly connect with gastric cancer spheroids. Chemogenetic activation of sensory neurons induced the release of calcium into the cytoplasm of cancer cells, promoting tumour growth and metastasis. Pharmacological ablation of sensory neurons or treatment with CGRP inhibitors suppressed tumour growth and extended survival. Depolarization of gastric tumour membranes through in vivo optogenetic activation led to enhanced calcium flux in jugular nucleus complex and CGRP release, defining a cancer cell-peptidergic neuronal circuit. Together, these findings establish the functional connectivity between cancer and sensory neurons, identifying this pathway as a potential therapeutic target.

A lubcan cross-linked polyethylene glycol dimethyl ether hydrogel for hyaluronic acid replacement as soft tissue engineering fillers

The structure of soft tissues is often destroyed by injury and aging. Injectable fillers eliminate the need for surgery and enhance repair. Hyaluronic acid-based hydrogels are commonly employed for their effectiveness and biocompatibility. However, hyaluronidase breaks them down quickly. Lubcan, a naturally sourced microbial extracellular polysaccharide, has demonstrated significant water absorption and retention capabilities, as well as lubricating properties comparable to those of hyaluronic acid. In this study, a novel injectable and implantable hydrogel was created from lubcan by adding polyethylene glycol diglycidyl ether as a cross-linking agent. Lubcan hydrogels exhibit exceptional thermal stability, favorable swelling behavior, in vitro degradation, compressive strength, injectability, and rheological properties, all while preserving the integrity of their three-dimensional porous structure. In vitro tests indicated that the lubcan hydrogel was non-cytotoxic, did not adhere to blood cells, and exhibited good hemocompatibility. Compared to the subcutaneous injection of commercially available hyaluronic acid hydrogels, lubcan hydrogels demonstrated superior integrity, persistence, and a softer texture in Balb/c mice after 16 weeks. At the same time, lubcan hydrogel is non-toxic to organs, does not affect blood biochemical test values, and is non-immunogenic in mice. These findings suggest that lubcan hydrogel may be a promising new superficial soft tissue filler.

Selective promotion of sensory innervation-mediated immunoregulation for tissue repair

Sensory innervation triggers the regenerative response after injury. However, dysfunction and impairment of sensory nerves, accompanied by excessive inflammation impede tissue regeneration. Consequently, specific induction of sensory innervation to mediate immunoregulation becomes a promising therapeutic approach. Herein, we developed a cell/drug-free strategy to selectively boost endogenous sensory innervation to harness immune responses for promoting tissue rehabilitation. Specifically, a dual-functional phage was constructed with a sensory nerve-homing peptide and a β-subunit of nerve growth factor (β-NGF)-binding peptide. These double-displayed phages captured endogenic β-NGF and localized to sensory nerves to promote sensory innervation. Furthermore, regarding bone regeneration, phage-loaded hydrogels achieved rapid sensory nerve ingrowth in bone defect areas. Mechanistically, sensory neurotization facilitated M2 polarization of macrophages through the Sema3A/XIAP/PAX6 pathway, thus decreasing the M1/M2 ratio to induce the dissipation of local inflammation. Collectively, these findings highlight the essential role of sensory innervation in manipulating inflammation and provide a conceptual framework based on neuroimmune interactions for promoting tissue regeneration.

Heterotopic ossification: Current developments and emerging potential therapies

ABSTRACT

This review aimed to provide a comprehensive analysis of the etiology, epidemiology, pathology, and conventional treatment of heterotopic ossification (HO), especially emerging potential therapies. HO is the process of ectopic bone formation at non-skeletal sites. HO can be subdivided into two major forms, acquired and hereditary, with acquired HO predominating. Hereditary HO is a rare and life-threatening genetic disorder, but both acquired and hereditary form can cause severe complications, such as peripheral nerve entrapment, pressure ulcers, and disability if joint ankylosis develops, which heavily contributes to a reduced quality of life. Modalities have been proposed to treat HO, but none have emerged as the gold standard. Surgical excision remains the only effective modality; however, the optimal timing is controversial and may cause HO recurrence. Recently, potential therapeutic strategies have emerged that focus on the signaling pathways involved in HO, and small molecule inhibitors have been shown to be promising. Moreover, additional specific targets, such as small interfering RNAs (siRNAs) and non-coding RNAs, could be used to effectively block HO or develop combinatorial therapies for HO.

Neuroregulation during Bone Formation and Regeneration: Mechanisms and Strategies

The skeleton is highly innervated by numerous nerve fibers. These nerve fibers, in addition to transmitting information within the bone and mediating bone sensations, play a crucial role in regulating bone tissue formation and regeneration. Traditional bone tissue engineering (BTE) often fails to achieve satisfactory outcomes when dealing with large-scale bone defects, which is frequently related to the lack of effective reconstruction of the neurovascular network. In recent years, increasing research has revealed the critical role of nerves in bone metabolism. Nerve fibers regulate bone cells through neurotransmitters, neuropeptides, and peripheral glial cells. Furthermore, nerves also coordinate with the vascular and immune systems to jointly construct a microenvironment favorable for bone regeneration. As a signaling driver of bone formation, neuroregulation spans the entire process of bone physiological activities from the embryonic formation to postmaturity remodeling and repair. However, there is currently a lack of comprehensive summaries of these regulatory mechanisms. Therefore, this review sketches out the function of nerves during bone formation and regeneration. Then, we elaborate on the mechanisms of neurovascular coupling and neuromodulation of bone immunity. Finally, we discuss several novel strategies for neuro-bone tissue engineering (NBTE) based on neuroregulation of bone, focusing on the coordinated regeneration of nerve and bone tissue.

The Hedgehog-GLI1 Pathway Regulates Osteogenic Differentiation of Human Cervical Posterior Longitudinal Ligament Cells by BMP Signalling Pathway

Cervical ossification of the posterior longitudinal ligament (OPLL) is an ectopic ossification disorder characterised by endochondral ossification. Its aetiology remains to be fully elucidated. This study aimed to clarify its pathogenesis through RNA sequencing of primary cells cultured from patients without cervical OPLL (control, PLL) and patients with cervical OPLL (disease, OPLL). We revealed for the first time the role of GLI1 within OPLL cells. Functional experiments indicated that GLI1, acting as a pivotal mediator between the upstream Hedgehog pathway and downstream BMP pathway, influences the pathogenesis of OPLL. The positive/negative effects on osteogenic differentiation following activation/inhibition of the Hedgehog pathway can be rescued by manipulating GLI1 expression. Overexpression of GLI1 activates BMP signalling, enhancing osteogenic capacity in PLL cells, while GLI1 knockdown suppresses BMP signal transduction, attenuating osteogenic differentiation in OPLL cells. Our findings highlight the significant role of the canonical Hedgehog signalling pathway and its interaction with the BMP pathway in the pathogenesis of OPLL.

A novel treatment strategy with hyperbaric oxygen of chronic osteomyelitis and pseudoarthrosis in a child with congenital hereditary sensory and autonomic neuropathy type 4 congenital insensitivity to pain with anhidrosis syndrome: a case report

BACKGROUND

Congenital insensitivity to pain with anhidrosis is a rare but devastating hereditary disease. Congenital insensitivity to pain with anhidrosis is caused by a mutation in the neurotrophic receptor tyrosine kinase 1 gene (NRTK1). The condition is characterized by multiple injuries, recurrent infections, and mental retardation.

CASE PRESENTATION

A 7-year-old Kurdish female patient, with a known case of congenital insensitivity to pain with anhidrosis, presented with a left tibial fracture, complicated by incorrect healing, osteomyelitis, and pseudoarthrosis spanning over a number of years. The osteomyelitis and pseudoarthrosis eventually healed after treatment with a combination of a long course of antibiotics, CERAMENT with gentamicin, and 40 sessions of hyperbaric oxygen treatment at 2.4 bar, 113 minutes with two air breaks. This is the first reported case of using hyperbaric oxygen treatment in children with congenital insensitivity to pain with anhidrosis. We discuss potential mechanistic explanations of the association between healing and hyperbaric oxygen treatment.

CONCLUSION

Hyperbaric oxygen treatment may be considered in other cases of complicated infections or treatment-resistant pseudoarthrosis in patients with this rare disease.

Heterotopic Ossification Is Associated with Painful Neuromas in Transtibial Amputees Undergoing Surgical Treatment of Symptomatic Neuromas

BACKGROUND

A relationship between nerve and osseous regeneration has been described. During the surgical treatment of symptomatic neuroma in transtibial amputees, the authors have found that heterotopic ossification (HO) depicted on preoperative radiographs appeared to be associated with the location of symptomatic neuromas in both the peroneal and tibial nerve distributions.

METHODS

Data were collected for transtibial amputees who underwent surgical management of symptomatic neuroma and were prospectively enrolled from 2018 through 2023. Preoperative radiographs were assessed for the presence of HO located at the distal fibula and tibia. The presence of a peroneal or tibial neuroma was based on findings contained within the operative reports. Pain levels were measured on a numeric rating scale (0 to 10).

RESULTS

Sixty-five limbs of 62 amputees were included. Peroneal neuroma and presence of fibular HO ( P = 0.001) and tibial neuroma and presence of tibial HO ( P = 0.038) demonstrated an association. The odds of having a symptomatic peroneal neuroma with fibular HO present were greater than the odds of a symptomatic peroneal neuroma when fibular HO was absent (OR, 9.3 [95% CI, 1.9 to -45.6]; P = 0.006). Preoperative pain scores were significantly higher for all patients with HO ( P < 0.001), those with fibular HO ( P < 0.001), and those with tibial HO ( P < 0.001), compared with patients without HO.

CONCLUSIONS

In patients with symptomatic neuromas, preoperative pain was worse when HO was present in the transtibial amputee's residual limb. Further research on the neuroma-HO complex in symptomatic amputees is required.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, III.

Exploring the role of peripheral nerves in trauma-induced heterotopic ossification

Recent studies have linked pain and the resultant nociception-induced neural inflammation (NINI) to trauma-induced heterotopic ossification (THO). It is postulated that nociception at the injury site stimulates the transient receptor potential vanilloid-1 (the transient receptor potential cation channel subfamily V member 1) receptors on sensory nerves within the injured tissues resulting in the expression of neuroinflammatory peptides, substance P (SP), and calcitonin gene-related peptide (CGRP). Additionally, BMP-2 released from fractured bones and soft tissue injury also selectively activates TRVP1 receptors, resulting in the release of SP and CGRP and causing neuroinflammation and degranulation of mast cells causing the breakdown the blood-nerve barrier (BNB), leading to release of neural crest derived progenitor cells (NCDPCs) into the injured tissue. Parallel to this process BMP-2 initiates the NCDPCs toward osteogenic differentiation. CGRP has direct osteogenic effects on osteoprogenitor cells/mesenchymal stem cells, by activating BMP-2 via canonical Wnt/β-catenin signaling and cAMP-cAMP-response element binding protein signaling. BMP-2 binds to TGF-βRI and activates TGF-β-activated kinase 1 (TAK1) leading to phosphorylation of SMAD1/5/8, which binds to the co-activator SMAD4 and translocates to the nucleus to serve as transcription factor for BMP responsive genes critical in osteogenesis such as Runx2 and others. Thus, NINI phenotypes, and specifically CGRP induction, play a crucial role in THO initiation and progression through the activation of the BMP pathway, breakdown of the BNB, leading to the escape of NCDPCs, and the osteogenic differentiation of the latter.

Mast cell activation by NGF drives the formation of trauma-induced heterotopic ossification

Soft tissue trauma can cause immune system disturbance and neuropathological invasion, resulting in heterotopic ossification (HO) due to aberrant chondrogenic differentiation of mesenchymal stem cells (MSCs). However, the molecular mechanisms behind the interaction between the immune and nervous systems in promoting HO pathogenesis are unclear. In this study, we found that mast cell-specific deletion attenuated localized tissue inflammation, with marked inhibition of HO endochondral osteogenesis. Likewise, blockage of nerve growth factor (NGF) receptor, known as tropomyosin receptor kinase A (TrkA), led to similar attenuations in tissue inflammation and HO. Moreover, while NGF/TrkA signaling did not directly affect MSCs chondrogenic differentiation, it modulated mast cell activation in traumatic soft tissue. Mechanistically, lipid A in LPS binding to TrkA enhanced NGF-induced TrkA phosphorylation, synergistically stimulating mast cells to release neurotrophin-3 (NT3), thereby promoting MSC chondrogenic differentiation in situ. Finally, analysis of single-cell datasets and human pathological specimens confirmed the important role of mast cell-mediated neuroinflammation in HO pathogenesis. In conclusion, NGF regulates mast cells in soft tissue trauma and drives HO progression via paracrine NT3. Targeted early inhibition of mast cells holds substantial promise for treating traumatic HO.

Upregulation of NGF/TrkA-Related Proteins in Dorsal Root Ganglion of Paclitaxel-Induced Peripheral Neuropathy Animal Model

Background

Paclitaxel (PTX) can induce chemotherapy-induced peripheral neuropathy (CIPN) as a side effect. The aim of this study was to understand the neurochemical changes induced by NGF/TrkA signaling in PTX-induced neuropathic pain.

Methods

The PTX-induced CIPN mouse model was evaluated using nerve conduction velocity (NCV) and behavioral tests. Protein expression in mouse DRG was observed by Western blotting and immunohistochemistry. Nerve growth factor (NGF), IL-6, and IL-1β mRNA levels were determined using qRT-PCR by isolating total RNA from whole blood.

Results

PTX showed low amplitude and high latency values in NCV in mice, and induced cold allodynia and thermal hyperalgesia in behavioral assessment. Activating transcription factor 3 (ATF3) and MAPK pathway related proteins (ERK1/2), tropomyosin receptor kinase A (TrkA), calcitonin gene related peptide (CGRP) and transient receptor potential vanilloid 1 (TRPV1) were upregulated 7th and 14th days after 2 mg/kg and 10 mg/kg of PTX administration. Protein kinase C (PKC) was upregulated 7th days after 10 mg/kg PTX treatment and 14th days after 2 mg/kg and 10 mg/kg PTX administration. NGF, IL-6, and IL-1β fold change values also showed a time- and dose-dependent increase.

Conclusion

Taken together, our findings may improve our understanding of the nociceptive symptoms associated with PTX-induced neuropathic pain and lead to the development of new treatments for peripheral neuropathy.

A bilayer hydrogel mimicking the periosteum-bone structure for innervated bone regeneration

In bone tissue, nerves are primarily located in the periosteum and play an indispensable role in bone defect repair. However, most bone tissue engineering approaches ignored the reconstruction of the nerve network. Herein, we aimed to develop a bilayer hydrogel simulating periosteum-bone structure to induce innervated bone regeneration. The bottom "bone" layer consisted of gelatin methacryloyl (GelMA), poly(ethylene glycol) diacrylate (PEGDA), and nano-hydroxyapatite (nHA), whereas the upper "periosteum" layer consisted of GelMA, sodium alginate (SA) and MgCl2. The mechanical properties of the upper and bottom hydrogels were designed to be suitable for neurogenesis and osteogenesis, respectively. Besides, Mg2+ from the "periosteum" layer released at the early stage (within 7 d), which aligned with the optimal time window for nerve regeneration and osteogenic related neuropeptide release. Simultaneously, the prevention of long-term Mg2+ release (after 7 d) could avoid osteogenic inhibition caused by prolonged Mg2+ exposure. Additionally, the incorporation of nHA in the bottom "bone" layer supported the long-term osteogenesis due to its osteoconductivity and slow degradation. In vitro biological experiments revealed that the bilayer hydrogel (GS@Mg/GP@nHA) promoted neurite growth and calcitonin gene-related peptide (CGRP) expression in rat dorsal root ganglion (DRG) neurons, as well as the osteogenesis of rat bone-derived mesenchymal stem cells (BMSCs). Moreover, the in vivo experiments demonstrated that the GS@Mg/GP@nHA hydrogel efficiently promoted nerve network reconstruction and bone regeneration of rat calvarial bone defects. Altogether, the bilayer hydrogel GS@Mg/GP@nHA could promote innervated bone regeneration, providing new insights for biomaterial design for bone tissue engineering.

Sensory nerve EP4 facilitates heterotopic ossification by regulating angiogenesis-coupled bone formation

Objective

Heterotopic ossification (HO) refers to the abnormal development of bone in soft tissue rather than within bone itself. Previous research has shown that sensory nerve prostaglandin E2 receptor 4 (EP4) signaling not only governs pain perception but also influences bone formation. However, the relationship between sensory nerve EP4 and the pathogenesis of HO in the Achilles tendon remains unclear. This study aims to investigate this relationship and the underlying mechanisms.

Methods

We generated sensory nerve EP4-specific knockout mice, with the genotype of Avil-CreEP4fl/fl, was propagated. Transcriptome sequencing and bioinformatics analysis techniques were used to identify the potential molecular pathways involving with sensory nerve EP4. Additionally, a neurectomy mouse model was created by transecting the sciatic nerve transection, to examine the effects and mechanisms of peripheral innervation on HO in vivo. Micro-CT, immunofluorescence (IF), Hematoxylin and Eosin (H&E) Staining, Safranin O-Fast Green staining and western blotting were used to analyze changes in cellular and tissue components.

Results

We here observed an increase in sensory nerve EP4 and H-type vessels during the pathogenesis of HO in both human subjects and mice. Proximal neurectomy through sciatic nerve transection or the targeted knockout of EP4 in sensory nerves hindered angiogenesis-dependent bone formation and the development of HO at the traumatic site of the Achilles tendon. Furthermore, we identified the Efnb2 (Ephrin-B2)/Dll4 (Delta-like ligand 4) axis as a potential downstream element influenced by sensory nerve EP4 in the regulation of HO. Notably, administration of an EP4 inhibitor demonstrated the ability to alleviate HO. Based on these findings, sensory nerve EP4 emerges as an innovative and promising approach for managing HO.

Conclusion

Our findings demonstrate that the sensory nerve EP4 promotes ectopic bone formation by modulating angiogenesis-associated osteogenesis during HO.

The translational potential of this article

Our results provide a mechanistic rationale for targeting sensory nerve EP4 as a promising candidate for HO therapy.

Pharmacologic or genetic targeting of peripheral nerves prevents peri-articular traumatic heterotopic ossification

Heterotopic ossification (HO) is a pathological process that commonly arises following severe polytrauma, characterized by the anomalous differentiation of mesenchymal progenitor cells and resulting in the formation of ectopic bone in non-skeletal tissues. This abnormal bone growth contributes to pain and reduced mobility, especially when adjacent to a joint. Our prior observations suggested an essential role of NGF (Nerve Growth Factor)-responsive TrkA (Tropomyosin Receptor Kinase A)-expressing peripheral nerves in regulating abnormal osteochondral differentiation following tendon injury. Here, we utilized a recently developed mouse model of hip arthroplasty-induced HO to further validate the role of peripheral nerve regulation of traumatic HO. Nerve ingrowth was either modulated using a knockin transgenic animals with point mutation in TrkA, or local treatment with an FDA-approved formulation of long acting Bupivacaine which prevents peripheral nerve growth. Results demonstrate exuberant sensory and sympathetic nerve growth within the peri-articular HO site, and that both methods to reduce local innervation significantly reduced heterotopic bone formation. TrkA inhibition led to a 34% reduction in bone volume, while bupivacaine treatment resulted in a 50% decrease. Mechanistically, alterations in TGFβ and FGF signaling activation accompanied both methods of local denervation, and a shift in macrophages from M1 to M2 phenotypes was observed. In sum, these studies reinforce the observations that peripheral nerves play a role in the etiopathogenesis of HO, and that targeting local nerves represents a potential therapeutic approach for disease prevention.

Predictive Neuromarker Patterns for Calcification Metaplasia in Early Tendon Healing

Unsuccessful tendon healing leads to fibrosis and occasionally calcification. In these metaplastic drifts, the mouse AT preclinical injury model represents a robust experimental setting for studying tendon calcifications. Previously, calcium deposits were found in about 30% of tendons after 28 days post-injury. Although a neuromediated healing process has previously been documented, the expression patterns of NF200, NGF, NPY, GAL, and CGRP in mouse AT and their roles in metaplastic calcific repair remain to be explored. This study included a spatiotemporal analysis of these neuromarkers during the inflammatory phase (7 days p.i.) and the proliferative/early-remodelling phase (28 days p.i.). While the inflammatory phase is characterised by NF200 and CGRP upregulation, in the 28 days p.i., the non-calcified tendons (n = 16/24) showed overall NGF, NPY, GAL, and CGRP upregulation (compared to 7 days post-injury) and a return of NF200 expression to values similar to pre-injury. Presenting a different picture, in calcified tendons (n = 8), NF200 persisted at high levels, while NGF and NPY significantly increased, resulting in a higher NPY/CGRP ratio. Therefore, high levels of NF200 and imbalance between vasoconstrictive (NPY) and vasodilatory (CGRP) neuromarkers may be indicative of calcification. Tendon cells contributed to the synthesis of neuromarkers, suggesting that their neuro-autocrine/paracrine role is exerted by coordinating growth factors, cytokines, and neuropeptides. These findings offer insights into the neurobiological mechanisms of early tendon healing and identify new neuromarker profiles predictive of tendon healing outcomes.

Angiogenesis in heterotopic ossification: From mechanisms to clinical significance

Heterotopic ossification (HO) refers to the formation of pathologic bone in nonskeletal tissues (including muscles, tendons or other soft tissues). HO typically occurs after a severe injury and can occur in any part of the body. HO lesions are highly vascularized. Angiogenesis, which is the formation of new blood vessels, plays an important role in the pathophysiology of HO. Surgical resection is considered an effective treatment for HO. However, it is difficult to completely remove new vessels, which can lead to the recurrence of HO and is often accompanied by significant problems such as intraoperative hemorrhage, demonstrating the important role of angiogenesis in HO. Here, we broadly summarize the current understanding of how angiogenesis contributes to HO; in particular, we focus on new insights into the cellular and signaling mechanisms underlying HO angiogenesis. We also review the development and current challenges associated with antiangiogenic therapy for HO.

Multilevel neurium-mimetic individualized graft via additive manufacturing for efficient tissue repair

Complicated peripheral nerve injuries or defects, especially at branching sites, remain a prominent clinical challenge after the application of different treatment strategies. Current nerve grafts fail to match the expected shape and size for delicate and precise branched nerve repair on a case-by-case basis, and there is a lack of geometrical and microscale regenerative navigation. In this study, we develop a sugar painting-inspired individualized multilevel epi-/peri-/endoneurium-mimetic device (SpinMed) to customize natural cues, featuring a selectively protective outer sheath and an instructive core, to support rapid vascular reconstruction and consequent efficient neurite extension along the defect area. The biomimetic perineurium dictates host-guest crosslinking in which new vessels secrete multimerin 1 binding to the fibroin filler surface as an anchor, contributing to the biological endoneurium that promotes Schwann cell homing and remyelination. SpinMed implantation into rat sciatic nerve defects yields a satisfactory outcome in terms of structural reconstruction, with sensory and locomotive function restoration. We further customize SpinMed grafts based on anatomy and digital imaging, achieving rapid repair of the nerve trunk and branches superior to that achieved by autografts and decellularized grafts in a specific beagle nerve defect model, with reliable biosafety. Overall, this intelligent art-inspired biomimetic design offers a facile way to customize sophisticated high-performance nerve grafts and holds great potential for application in translational regenerative medicine.

The Role of Neuromodulation and Potential Mechanism in Regulating Heterotopic Ossification

Heterotopic ossification (HO) is a pathological process characterized by the aberrant formation of bone in muscles and soft tissues. It is commonly triggered by traumatic brain injury, spinal cord injury, and burns. Despite a wide range of evidence underscoring the significance of neurogenic signals in proper bone remodeling, a clear understanding of HO induced by nerve injury remains rudimentary. Recent studies suggest that injury to the nervous system can activate various signaling pathways, such as TGF-β, leading to neurogenic HO through the release of neurotrophins. These pathophysiological changes lay a robust groundwork for the prevention and treatment of HO. In this review, we collected evidence to elucidate the mechanisms underlying the pathogenesis of HO related to nerve injury, aiming to enhance our understanding of how neurological repair processes can culminate in HO.

From inflammation to bone formation: the intricate role of neutrophils in skeletal muscle injury and traumatic heterotopic ossification

Neutrophils are emerging as an important player in skeletal muscle injury and repair. Neutrophils accumulate in injured tissue, thus releasing inflammatory factors, proteases and neutrophil extracellular traps (NETs) to clear muscle debris and pathogens when skeletal muscle is damaged. During the process of muscle repair, neutrophils can promote self-renewal and angiogenesis in satellite cells. When neutrophils are abnormally overactivated, neutrophils cause collagen deposition, functional impairment of satellite cells, and damage to the skeletal muscle vascular endothelium. Heterotopic ossification (HO) refers to abnormal bone formation in soft tissue. Skeletal muscle injury is one of the main causes of traumatic HO (tHO). Neutrophils play a pivotal role in activating BMPs and TGF-β signals, thus promoting the differentiation of mesenchymal stem cells and progenitor cells into osteoblasts or osteoclasts to facilitate HO. Furthermore, NETs are specifically localized at the site of HO, thereby accelerating the formation of HO. Additionally, the overactivation of neutrophils contributes to the disruption of immune homeostasis to trigger HO. An understanding of the diverse roles of neutrophils will not only provide more information on the pathogenesis of skeletal muscle injury for repair and HO but also provides a foundation for the development of more efficacious treatment modalities for HO.

Promotion of perineural invasion of cholangiocarcinoma by Schwann cells via nerve growth factor

Background

Cholangiocarcinoma (CCA), a highly lethal tumor of the hepatobiliary system originating from bile duct epithelium, can be divided into the intrahepatic, hilar, and extrahepatic types. Due to its insidious onset and atypical early clinical symptoms, the overall prognosis is poor. One of the important factors contributing to the poor prognosis of CCA is the occurrence of perineural invasion (PNI), but the specific mechanisms regarding how it contributes to the occurrence of PNI are still unclear. The main purpose of this study is to explore the molecular mechanism leading to the occurrence of PNI and provide new ideas for clinical treatment.

Methods

CCA cell lines and Schwann cells (SCs) were stimulated to observe the changes in cell behavior. SCs cocultured with tumor supernatant and SCs cultured in normal medium were subjected to transcriptome sequencing to screen the significantly upregulated genes. Following this, the two types of tumor cells were cultured with SC supernatant, and the changes in behavior of the tumor cells were observed. Nonobese diabetic-severe combined immunodeficiency disease (NOD-SCID) mice were injected with cell suspension supplemented with nerve growth factor (NGF) via the sciatic nerve. Four weeks later, the mice were euthanized and the tumor sections were removed and stained.

Results

Nerve invasion by tumor cells was common in CCA tissues. SCs were observed in tumor tissues, and the number of SCs in tumor tissues and the degree of PNI were much higher than were those in normal tissues or tissues without PNI. The overall survival time was shorter in patients with CCA with PNI than in patients without PNI. SCs were enriched in CCA tissues, indicating the presence of PNI and associated with poor prognosis in CCA patients. CCA was found to promote NGF secretion from SCs in vitro. After the addition of exogenous NGF in CCA cell culture medium, the proliferation activity and migration ability of CCA cells were significantly increased, suggesting that SCs can promote the proliferation and migration of CCA through the secretion of NGF. NGF, in turn, was observed to promote epithelial-mesenchymal transition in CCA through tropomyosin receptor kinase A (TrkA), thus promoting its progression. Tumor growth in mice shows that NGF can promote PNI in CCA.

Conclusions

In CCA, tumor cells can promote the secretion of NGF by SCs, which promotes the progression of CCA and PNI by binding to its high-affinity receptor TrkA, leading to poor prognosis.

TrkA + sensory neurons regulate osteosarcoma proliferation and vascularization to promote disease progression

Bone pain is a presenting feature of bone cancers such as osteosarcoma (OS), relayed by skeletal-innervating peripheral afferent neurons. Potential functions of tumor-associated sensory neurons in bone cancers beyond pain sensation are unknown. To uncover neural regulatory functions, a chemical-genetic approach in mice with a knock-in allele for TrkA was used to functionally perturb sensory nerve innervation during OS growth and disease progression. TrkA inhibition in transgenic mice led to significant reductions in sarcoma-associated sensory innervation and vascularization, tumor growth and metastasis, and prolonged overall survival. Single-cell transcriptomics revealed that sarcoma denervation was associated with phenotypic alterations in both OS tumor cells and cells within the tumor microenvironment, and with reduced calcitonin gene-related peptide (CGRP) and vascular endothelial growth factor (VEGF) signaling. Multimodal and multi-omics analyses of human OS bone samples and human dorsal root ganglia neurons further implicated peripheral innervation and neurotrophin signaling in OS tumor biology. In order to curb tumor-associated axonal ingrowth, we next leveraged FDA-approved bupivacaine liposomes leading to significant reductions in sarcoma growth, vascularity, as well as alleviation of pain. In sum, TrkA-expressing peripheral neurons positively regulate key aspects of OS progression and sensory neural inhibition appears to disrupt calcitonin receptor signaling (CALCR) and VEGF signaling within the sarcoma microenvironment leading to significantly reduced tumor growth and improved survival. These data suggest that interventions to prevent pathological innervation of osteosarcoma represent a novel adjunctive therapy to improve clinical outcomes and survival.

Vegfc-expressing cells form heterotopic bone after musculoskeletal injury

Heterotopic ossification (HO) is a challenging condition that occurs after musculoskeletal injury and is characterized by the formation of bone in non-skeletal tissues. While the effect of HO on blood vessels is well established, little is known about its impact on lymphatic vessels. Here, we use a mouse model of traumatic HO to investigate the relationship between HO and lymphatic vessels. We show that injury triggers lymphangiogenesis at the injury site, which is associated with elevated vascular endothelial growth factor C (VEGF-C) levels. Through single-cell transcriptomic analyses, we identify mesenchymal progenitor cells and tenocytes as sources of Vegfc. We demonstrate by lineage tracing that Vegfc-expressing cells undergo osteochondral differentiation and contribute to the formation of HO. Last, we show that Vegfc haploinsufficiency results in a nearly 50% reduction in lymphangiogenesis and HO formation. These findings shed light on the complex mechanisms underlying HO formation and its impact on lymphatic vessels.

Strategies for Treating Traumatic Neuromas with Tissue-Engineered Materials

Neuroma, a pathological response to peripheral nerve injury, refers to the abnormal growth of nerve tissue characterized by disorganized axonal proliferation. Commonly occurring after nerve injuries, surgeries, or amputations, this condition leads to the formation of painful nodular structures. Traditional treatment options include surgical excision and pharmacological management, aiming to alleviate symptoms. However, these approaches often offer temporary relief without addressing the underlying regenerative challenges, necessitating the exploration of advanced strategies such as tissue-engineered materials for more comprehensive and effective solutions. In this study, we discussed the etiology, molecular mechanisms, and histological morphology of traumatic neuromas after peripheral nerve injury. Subsequently, we summarized and analyzed current nonsurgical and surgical treatment options, along with their advantages and disadvantages. Additionally, we emphasized recent advancements in treating traumatic neuromas with tissue-engineered material strategies. By integrating biomaterials, growth factors, cell-based approaches, and electrical stimulation, tissue engineering offers a comprehensive solution surpassing mere symptomatic relief, striving for the structural and functional restoration of damaged nerves. In conclusion, the utilization of tissue-engineered materials has the potential to significantly reduce the risk of neuroma recurrence after surgical treatment.

Nerve growth factor receptor limits inflammation to promote remodeling and repair of osteoarthritic joints

Osteoarthritis (OA) is a painful, incurable disease affecting over 500 million people. Recent clinical trials of the nerve growth factor (NGF) inhibitors in OA patients have suggested adverse effects of NGF inhibition on joint structure. Here we report that nerve growth factor receptor (NGFR) is upregulated in skeletal cells during OA and plays an essential role in the remodeling and repair of osteoarthritic joints. Specifically, NGFR is expressed in osteochondral cells but not in skeletal progenitor cells and induced by TNFα to attenuate NF-κB activation, maintaining proper BMP-SMAD1 signaling and suppressing RANKL expression in mice. NGFR deficiency hyper-activates NF-κB in murine osteoarthritic joints, which impairs bone formation and enhances bone resorption as exemplified by a reduction in subchondral bone and osteophytes. In human OA cartilage, NGFR is also negatively associated with NF-κB activation. Together, this study suggests a role of NGFR in limiting inflammation for repair of diseased skeletal tissues.

Intersections of Fibrodysplasia Ossificans Progressiva and Traumatic Heterotopic Ossification

Heterotopic ossification (HO) is a debilitating pathology where ectopic bone develops in areas of soft tissue. HO can develop as a consequence of traumatic insult or as a result of dysregulated osteogenic signaling, as in the case of the orphan disease fibrodysplasia ossificans progressiva (FOP). Traumatic HO (tHO) formation is mediated by the complex interplay of signaling between progenitor, inflammatory, and nerve cells, among others, making it a challenging process to understand. Research into the pathogenesis of genetically mediated HO (gHO) in FOP has established a pathway involving uninhibited activin-like kinase 2 receptor (ALK2) signaling that leads to downstream osteogenesis. Current methods of diagnosis and treatment lag behind pre-mature HO detection and progressive HO accumulation, resulting in irreversible decreases in range of motion and chronic pain for patients. As such, it is necessary to draw on advancements made in the study of tHO and gHO to better diagnose, comprehend, prevent, and treat both.

Nociceptive neurons interact directly with gastric cancer cells via a CGRP/Ramp1 axis to promote tumor progression

Cancer cells have been shown to exploit neurons to modulate their survival and growth, including through establishment of neural circuits within the central nervous system (CNS) 1-3 . Here, we report a distinct pattern of cancer-nerve interactions between the peripheral nervous system (PNS) and gastric cancer (GC). In multiple GC mouse models, nociceptive nerves demonstrated the greatest degree of nerve expansion in an NGF-dependent manner. Neural tracing identified CGRP+ peptidergic neurons as the primary gastric sensory neurons. Three-dimensional co-culture models showed that sensory neurons directly connect with gastric cancer spheroids through synapse-like structures. Chemogenetic activation of sensory neurons induced the release of calcium into the cytoplasm of cancer cells, promoting tumor growth and metastasis. Pharmacological ablation of sensory neurons or treatment with CGRP inhibitors suppressed tumor growth and extended survival. Depolarization of gastric tumor membranes through in vivo optogenetic activation led to enhanced calcium flux in nodose ganglia and CGRP release, defining a cancer cell-peptidergic neuronal circuit. Together, these findings establish the functional connectivity between cancer and sensory neurons, identifying this pathway as a potential therapeutic target.

Biology and pathophysiology of symptomatic neuromas

ABSTRACT

Neuromas are a substantial cause of morbidity and reduction in quality of life. This is not only caused by a disruption in motor and sensory function from the underlying nerve injury but also by the debilitating effects of neuropathic pain resulting from symptomatic neuromas. A wide range of surgical and therapeutic modalities have been introduced to mitigate this pain. Nevertheless, no single treatment option has been successful in completely resolving the associated constellation of symptoms. While certain novel surgical techniques have shown promising results in reducing neuroma-derived and phantom limb pain, their effectiveness and the exact mechanism behind their pain-relieving capacities have not yet been defined. Furthermore, surgery has inherent risks, may not be suitable for many patients, and may yet still fail to relieve pain. Therefore, there remains a great clinical need for additional therapeutic modalities to further improve treatment for patients with devastating injuries that lead to symptomatic neuromas. However, the molecular mechanisms and genetic contributions behind the regulatory programs that drive neuroma formation-as well as the resulting neuropathic pain-remain incompletely understood. Here, we review the histopathological features of symptomatic neuromas, our current understanding of the mechanisms that favor neuroma formation, and the putative contributory signals and regulatory programs that facilitate somatic pain, including neurotrophic factors, neuroinflammatory peptides, cytokines, along with transient receptor potential, and ionotropic channels that suggest possible approaches and innovations to identify novel clinical therapeutics.

Immunohistochemical phenotype of sensory neurons associated with sympathetic plexuses in the trigeminal ganglia of adult nerve growth factor transgenic mice

Following peripheral nerve injury, postganglionic sympathetic axons sprout into the affected sensory ganglia and form perineuronal sympathetic plexuses with somata of sensory neurons. This sympathosensory coupling contributes to the onset and persistence of injury-induced chronic pain. We have documented the presence of similar sympathetic plexuses in the trigeminal ganglia of adult mice that ectopically overexpress nerve growth factor (NGF), in the absence of nerve injury. In this study, we sought to further define the phenotype(s) of these trigeminal sensory neurons having sympathetic plexuses in our transgenic mice. Using quantitative immunofluorescence staining analyses, we show that the invading sympathetic axons specifically target sensory somata immunopositive for several biomarkers: NGF high-affinity receptor tyrosine kinase A (trkA), calcitonin gene-related peptide (CGRP), neurofilament heavy chain (NFH), and P2X purinoceptor 3 (P2X3). Based on these phenotypic characteristics, the majority of the sensory somata surrounded by sympathetic plexuses are likely to be NGF-responsive nociceptors (i.e., trkA expressing) that are peptidergic (i.e., CGRP expressing), myelinated (i.e., NFH expressing), and ATP sensitive (i.e., P2X3 expressing). Our data also show that very few sympathetic plexuses surround sensory somata expressing other nociceptive (pain) biomarkers, including substance P and acid-sensing ion channel 3. No sympathetic plexuses are associated with sensory somata that display isolectin B4 binding. Though the cellular mechanisms that trigger the formation of sympathetic plexus (with and without nerve injury) remain unknown, our new observations yield an unexpected specificity with which invading sympathetic axons appear to target a precise subtype of nociceptors. This selectivity likely contributes to pain development and maintenance associated with sympathosensory coupling.

Sema3A secreted by sensory nerve induces bone formation under mechanical loads

Bone formation and deposition are initiated by sensory nerve infiltration in adaptive bone remodeling. Here, we focused on the role of Semaphorin 3A (Sema3A), expressed by sensory nerves, in mechanical loads-induced bone formation and nerve withdrawal using orthodontic tooth movement (OTM) model. Firstly, bone formation was activated after the 3rd day of OTM, coinciding with a decrease in sensory nerves and an increase in pain threshold. Sema3A, rather than nerve growth factor (NGF), highly expressed in both trigeminal ganglion and the axons of periodontal ligament following the 3rd day of OTM. Moreover, in vitro mechanical loads upregulated Sema3A in neurons instead of in human periodontal ligament cells (hPDLCs) within 24 hours. Furthermore, exogenous Sema3A restored the suppressed alveolar bone formation and the osteogenic differentiation of hPDLCs induced by mechanical overload. Mechanistically, Sema3A prevented overstretching of F-actin induced by mechanical overload through ROCK2 pathway, maintaining mitochondrial dynamics as mitochondrial fusion. Therefore, Sema3A exhibits dual therapeutic effects in mechanical loads-induced bone formation, both as a pain-sensitive analgesic and a positive regulator for bone formation.

Nerve Growth Factor Receptor Limits Inflammation to Promote Remodeling and Repair of Osteoarthritic Joints

Osteoarthritis (OA) is a painful, incurable disease affecting over 500 million people. The need for relieving OA pain is paramount but inadequately addressed, partly due to limited understandings of how pain signaling regulates non-neural tissues. Here we report that nerve growth factor receptor (NGFR) is upregulated in skeletal cells during OA and plays an essential role in the remodeling and repair of osteoarthritic joints. Specifically, NGFR is expressed in osteochondral cells but not in skeletal progenitor cells and induced by TNFα to attenuate NF-κB activation, maintaining proper BMP-SMAD1 signaling and suppressing RANKL expression. NGFR deficiency hyper-activates NF-κB in murine osteoarthritic joints, which impairs bone formation and enhances bone resorption as exemplified by a reduction in subchondral bone and osteophytes. In human OA cartilage, NGFR is also negatively associated with NF-κB activation. Together, this study uncovers a role of NGFR in limiting inflammation for repair of diseased skeletal tissues.

TrkA-mediated sensory innervation of injured mouse tendon supports tendon sheath progenitor cell expansion and tendon repair

Peripheral neurons terminate at the surface of tendons partly to relay nociceptive pain signals; however, the role of peripheral nerves in tendon injury and repair remains unclear. Here, we show that after Achilles tendon injury in mice, there is new nerve growth near tendon cells that express nerve growth factor (NGF). Conditional deletion of the Ngf gene in either myeloid or mesenchymal mouse cells limited both innervation and tendon repair. Similarly, inhibition of the NGF receptor tropomyosin receptor kinase A (TrkA) abrogated tendon healing in mouse tendon injury. Sural nerve transection blocked the postinjury increase in tendon sensory innervation and the expansion of tendon sheath progenitor cells (TSPCs) expressing tubulin polymerization promoting protein family member 3. Single cell and spatial transcriptomics revealed that disruption of sensory innervation resulted in dysregulated inflammatory signaling and transforming growth factor-β (TGFβ) signaling in injured mouse tendon. Culture of mouse TSPCs with conditioned medium from dorsal root ganglia neuron further supported a role for neuronal mediators and TGFβ signaling in TSPC proliferation. Transcriptomic and histologic analyses of injured human tendon biopsy samples supported a role for innervation and TGFβ signaling in human tendon regeneration. Last, treating mice after tendon injury systemically with a small-molecule partial agonist of TrkA increased neurovascular response, TGFβ signaling, TSPC expansion, and tendon tissue repair. Although further studies should investigate the potential effects of denervation on mechanical loading of tendon, our results suggest that peripheral innervation is critical for the regenerative response after acute tendon injury.

Neutrophil and NETosis Modulation in Traumatic Heterotopic Ossification

OBJECTIVE

To characterize the role of neutrophil extracellular traps (NETs) in heterotopic ossification (HO) formation and progression and to use mechanical and pharmacological methods to decrease NETosis and mitigate HO formation.

BACKGROUND

Traumatic HO is the aberrant osteochondral differentiation of mesenchymal progenitor cells after traumatic injury, burns, or surgery. While the innate immune response has been shown to be necessary for HO formation, the specific immune cell phenotype and function remain unknown. Neutrophils, one of the earliest immune cells to respond after HO-inducing injuries, can extrude DNA, forming highly inflammatory NETs. We hypothesized that neutrophils and NETs would be diagnostic biomarkers and therapeutic targets for the detection and mitigation of HO.

METHODS

C57BL6J mice underwent burn/tenotomy (a well-established mouse model of HO) or a non-HO-forming sham injury. These mice were either (1) ambulated ad libitum, (2) ambulated ad libitum with daily intraperitoneal hydroxychloroquine, ODN-2088 (both known to affect NETosis pathways), or control injections, or (3) had the injured hind limb immobilized. Single-cell analysis was performed to analyze neutrophils, NETosis, and downstream signaling after the HO-forming injury. Immunofluorescence microscopy was used to visualize NETosis at the HO site and neutrophils were identified using flow cytometry. Serum and cell lysates from HO sites were analyzed using enzyme-linked immunosorbent assay for myeloperoxidase-DNA and ELA2-DNA complexes to identify NETosis. Micro-computerized tomography was performed on all groups to analyze the HO volume.

RESULTS

Molecular and transcriptional analyses revealed the presence of NETs within the HO injury site, which peaked in the early phases after injury. These NETs were highly restricted to the HO site, with gene signatures derived from both in vitro NET induction and clinical neutrophil characterizations showing a high degree of NET "priming" at the site of injury, but not in neutrophils in the blood or bone marrow. Cell-cell communication analyses revealed that this localized NET formation coincided with high levels of toll-like receptor signaling specific to neutrophils at the injury site. Reducing the overall neutrophil abundance within the injury site, either pharmacologically through treatment with hydroxychloroquine, the toll-like receptor 9 inhibitor OPN-2088, or mechanical treatment with limb offloading, results in the mitigation of HO formation.

CONCLUSIONS

These data provide a further understanding of the ability of neutrophils to form NETs at the injury site, clarify the role of neutrophils in HO, and identify potential diagnostic and therapeutic targets for HO mitigation.

Itaconate-producing neutrophils regulate local and systemic inflammation following trauma

Modulation of the immune response to initiate and halt the inflammatory process occurs both at the site of injury as well as systemically. Due to the evolving role of cellular metabolism in regulating cell fate and function, tendon injuries that undergo normal and aberrant repair were evaluated by metabolic profiling to determine its impact on healing outcomes. Metabolomics revealed an increasing abundance of the immunomodulatory metabolite itaconate within the injury site. Subsequent single-cell RNA-Seq and molecular and metabolomic validation identified a highly mature neutrophil subtype, not macrophages, as the primary producers of itaconate following trauma. These mature itaconate-producing neutrophils were highly inflammatory, producing cytokines that promote local injury fibrosis before cycling back to the bone marrow. In the bone marrow, itaconate was shown to alter hematopoiesis, skewing progenitor cells down myeloid lineages, thereby regulating systemic inflammation. Therapeutically, exogenous itaconate was found to reduce injury-site inflammation, promoting tenogenic differentiation and impairing aberrant vascularization with disease-ameliorating effects. These results present an intriguing role for cycling neutrophils as a sensor of inflammation induced by injury - potentially regulating immune cell production in the bone marrow through delivery of endogenously produced itaconate - and demonstrate a therapeutic potential for exogenous itaconate following tendon injury.

Role of the Peripheral Nervous System in Skeletal Development and Regeneration: Controversies and Clinical Implications

PURPOSE OF REVIEW

This review examines the diverse functional relationships that exist between the peripheral nervous system (PNS) and bone, including key advances over the past century that inform our efforts to translate these discoveries for skeletal repair.

RECENT FINDINGS

The innervation of the bone during development, homeostasis, and regeneration is highly patterned. Consistent with this, there have been nearly 100 studies over the past century that have used denervation approaches to isolate the effects of the different branches of the PNS on the bone. Overall, a common theme of balance emerges whereby an orchestration of both local and systemic neural functions must align to promote optimal skeletal repair while limiting negative consequences such as pain. An improved understanding of the functional bidirectional pathways linking the PNS and bone has important implications for skeletal development and regeneration. Clinical advances over the next century will necessitate a rigorous identification of the mechanisms underlying these effects that is cautious not to oversimplify the in vivo condition in diverse states of health and disease.

Unveiling the Neural Environment in Cancer: Exploring the Role of Neural Circuit Players and Potential Therapeutic Strategies

The regulation of the immune environment within the tumor microenvironment has provided new opportunities for cancer treatment. However, an important microenvironment surrounding cancer that is often overlooked despite its significance in cancer progression is the neural environment surrounding the tumor. The release of neurotrophic factors from cancer cells is implicated in cancer growth and metastasis by facilitating the infiltration of nerve cells into the tumor microenvironment. This nerve-tumor interplay can elicit cancer cell proliferation, migration, and invasion in response to neurotransmitters. Moreover, it is possible that cancer cells could establish a network resembling that of neurons, allowing them to communicate with one another through neurotransmitters. The expression levels of players in the neural circuits of cancers could serve as potential biomarkers for cancer aggressiveness. Notably, the upregulation of certain players in the neural circuit has been linked to poor prognosis in specific cancer types such as breast cancer, pancreatic cancer, basal cell carcinoma, and stomach cancer. Targeting these players with inhibitors holds great potential for reducing the morbidity and mortality of these carcinomas. However, the efficacy of anti-neurogenic agents in cancer therapy remains underexplored, and further research is necessary to evaluate their effectiveness as a novel approach for cancer treatment. This review summarizes the current knowledge on the role of players in the neural circuits of cancers and the potential of anti-neurogenic agents for cancer therapy.

Tppp3+ synovial/tendon sheath progenitor cells contribute to heterotopic bone after trauma

Heterotopic ossification (HO) is a pathological process resulting in aberrant bone formation and often involves synovial lined tissues. During this process, mesenchymal progenitor cells undergo endochondral ossification. Nonetheless, the specific cell phenotypes and mechanisms driving this process are not well understood, in part due to the high degree of heterogeneity of the progenitor cells involved. Here, using a combination of lineage tracing and single-cell RNA sequencing (scRNA-seq), we investigated the extent to which synovial/tendon sheath progenitor cells contribute to heterotopic bone formation. For this purpose, Tppp3 (tubulin polymerization-promoting protein family member 3)-inducible reporter mice were used in combination with either Scx (Scleraxis) or Pdgfra (platelet derived growth factor receptor alpha) reporter mice. Both tendon injury- and arthroplasty-induced mouse experimental HO models were utilized. ScRNA-seq of tendon-associated traumatic HO suggested that Tppp3 is an early progenitor cell marker for either tendon or osteochondral cells. Upon HO induction, Tppp3 reporter+ cells expanded in number and partially contributed to cartilage and bone formation in either tendon- or joint-associated HO. In double reporter animals, both Pdgfra+Tppp3+ and Pdgfra+Tppp3- progenitor cells gave rise to HO-associated cartilage. Finally, analysis of human samples showed a substantial population of TPPP3-expressing cells overlapping with osteogenic markers in areas of heterotopic bone. Overall, these data demonstrate that synovial/tendon sheath progenitor cells undergo aberrant osteochondral differentiation and contribute to HO after trauma.

Platelet-rich plasma in the pathologic processes of tendinopathy: a review of basic science studies

Tendinopathy is a medical condition that includes a spectrum of inflammatory and degenerative tendon changes caused by traumatic or overuse injuries. The pathological mechanism of tendinopathy has not been well defined, and no ideal treatment is currently available. Platelet-rich plasma (PRP) is an autologous whole blood derivative containing a variety of cytokines and other protein components. Various basic studies have found that PRP has the therapeutic potential to promote cell proliferation and differentiation, regulate angiogenesis, increase extracellular matrix synthesis, and modulate inflammation in degenerative tendons. Therefore, PRP has been widely used as a promising therapeutic agent for tendinopathy. However, controversies exist over the optimal treatment regimen and efficacy of PRP for tendinopathy. This review focuses on the specific molecular and cellular mechanisms by which PRP manipulates tendon healing to better understand how PRP affects tendinopathy and explore the reason for the differences in clinical trial outcomes. This article has also pointed out the future direction of basic research and clinical application of PRP in the treatment of tendinopathy, which will play a guiding role in the design of PRP treatment protocols for tendinopathy.

Engineered Sensory Nerve Guides Self-Adaptive Bone Healing via NGF-TrkA Signaling Pathway

The upstream role of sensory innervation during bone homeostasis is widely underestimated in bone repairing strategies. Herein, a neuromodulation approach is proposed to orchestrate bone defect healing by constructing engineered sensory nerves (eSN) in situ to leverage the adaptation feature of SN during tissue formation. NGF liberated from ECM-constructed eSN effectively promotes sensory neuron differentiation and enhances CGRP secretion, which lead to improved RAOECs mobility and osteogenic differentiation of BMSC. In turn, such eSN effectively drives ossification in vivo via NGF-TrkA signaling pathway, which substantially accelerates critical size bone defect healing. More importantly, eSN also adaptively suppresses excessive bone formation and promotes bone remodeling by activating osteoclasts via CGRP-dependent mechanism when combined with BMP-2 delivery, which ingeniously alleviates side effects of BMP-2. In sum, this eSN approach offers a valuable avenue to harness the adaptive role of neural system to optimize bone homeostasis under various clinical scenario.

Denervation during mandibular distraction osteogenesis results in impaired bone formation

Mandibular distraction osteogenesis (DO) is mediated by skeletal stem cells (SSCs) in mice, which enact bone regeneration via neural crest re-activation. As peripheral nerves are essential to progenitor function during development and in response to injury, we questioned if denervation impairs mandibular DO. C57Bl6 mice were divided into two groups: DO with a segmental defect in the inferior alveolar nerve (IAN) at the time of mandibular osteotomy ("DO Den") and DO with IAN intact ("DO Inn"). DO Den demonstrated significantly reduced histological and radiological osteogenesis relative to DO Inn. Denervation preceding DO results in reduced SSC amplification and osteogenic potential in mice. Single cell RNA sequencing analysis revealed that there was a predominance of innervated SSCs in clusters dominated by pathways related to bone formation. A rare human patient specimen was also analyzed and suggested that histological, radiological, and transcriptional alterations seen in mouse DO may be conserved in the setting of denervated human mandible distraction. Fibromodulin (FMOD) transcriptional and protein expression were reduced in denervated relative to innervated mouse and human mandible regenerate. Finally, when exogenous FMOD was added to DO-Den and DO-Inn SSCs undergoing in vitro osteogenic differentiation, the osteogenic potential of DO-Den SSCs was increased in comparison to control untreated DO-Den SSCs, modeling the superior osteogenic potential of DO-Inn SSCs.

Nerves within bone and their application in tissue engineering of bone regeneration

Nerves within bone play an irreplaceable role in promoting bone regeneration. Crosstalk between the nerve system and bone has arisen to the attention of researchers in the field of basic medicine, clinical medicine, and biomaterials science. Successful bone regeneration relies on the appropriate participation of neural system components including nerve fibers, signaling molecules, and neural-related cells. Furthermore, more about the mechanisms through which nerves took part in bone regeneration and how these mechanisms could be integrated into tissue engineering scaffolds were under exploration. In the present review, we aimed to systematically elaborate on the structural and functional interrelationship between the nerve system and bone. In particular, peripheral nerves interact with the bone through innervated axons, multiple neurotrophins, and bone resident cells. Also, we aimed to summarize research that took advantage of the neuro-osteogenic network to design tissue engineering scaffolds for bone repair.

Sensory nerve niche regulates mesenchymal stem cell homeostasis via FGF/mTOR/autophagy axis

Mesenchymal stem cells (MSCs) reside in microenvironments, referred to as niches, which provide structural support and molecular signals. Sensory nerves are niche components in the homeostasis of tissues such as skin, bone marrow and hematopoietic system. However, how the sensory nerve affects the behavior of MSCs remains largely unknown. Here we show that the sensory nerve is vital for mesenchymal tissue homeostasis and maintenance of MSCs in the continuously growing adult mouse incisor. Loss of sensory innervation leads to mesenchymal disorder and a decrease in MSCs. Mechanistically, FGF1 from the sensory nerve directly acts on MSCs by binding to FGFR1 and activates the mTOR/autophagy axis to sustain MSCs. Modulation of mTOR/autophagy restores the MSCs and rescues the mesenchymal tissue disorder of Fgfr1 mutant mice. Collectively, our study provides insights into the role of sensory nerves in the regulation of MSC homeostasis and the mechanism governing it.

The interplay between the nerves and skeleton: a 30-year bibliometric analysis

Background

The mechanisms and effects of the interplay between the nerves and skeleton remain a popular research topic. This study aimed to analyze and evaluate publications on nerve-bone interactions using bibliometrics and to identify the state of the art of current research, hotspots, and future directions.

Methods

This study included 1989 articles and reviews from the Web of Science Core Collection (WoSCC) published from January 1, 1991, to June 22, 2022. The Bibliometrix package of R 4.2.0 (The R Foundation for Statistical Computing, Vienna, Austria) was used to analyze basic information about the publications, including the annual number of publications, institution analysis, author influence analysis, journal analysis, and the national cooperation network. We also used CiteSpace 5.8.R3 for bibliometric analysis, including co-occurrence, co-citation, and cluster analysis.

Results

We discovered a significant increase in the number of articles on nerve-bone interactions published over the last 10 years. The most active country and institution were the United States and the University of Minnesota, respectively. In terms of journals and cocited journals, Bone was ranked highest with respect to the number of publications, while Journal of Bone and Mineral Research was ranked highest among cited journals. Wang Lei was the author with the most publications, and Bjurholm A was the most cited author. The analysis of references and keywords revealed that the impact of nerve- and neuromodulation-related factors on stem cell differentiation was a persistently hot topic. Osteoarthritis, neuropeptide Y, and osteoclastogenic process are likely to be the next era of research hotspots. The neurovascular crosstalk within bone has received great attention, especially in skeletal diseases, which may provide potential targets for future treatments.

Conclusions

We used a bibliometric method to provide an efficient, objective, and comprehensive assessment of existing research about the interplay between the skeletal and nervous systems and to accurately identify hotspots and research frontiers, providing valuable information for future research.

Biological and Mechanical Factors and Epigenetic Regulation Involved in Tendon Healing

Tendons are an important part of the musculoskeletal system. Connecting muscles to bones, tendons convert force into movement. Tendon injury can be acute or chronic. Noticeably, tendon healing requires a long time span and includes inflammation, proliferation, and remodeling processes. The mismatch between endogenous and exogenous healing may lead to adhesion causing further negative effects. Management of tendon injuries and complications such as subsequent adhesion formation are still challenges for clinicians. Due to numerous factors, tendon healing is a complex process. This review introduces the role of various biological and mechanical factors and epigenetic regulation processes involved in tendon healing.

Hallmarks of peripheral nerve function in bone regeneration

Skeletal tissue is highly innervated. Although different types of nerves have been recently identified in the bone, the crosstalk between bone and nerves remains unclear. In this review, we outline the role of the peripheral nervous system (PNS) in bone regeneration following injury. We first introduce the conserved role of nerves in tissue regeneration in species ranging from amphibians to mammals. We then present the distribution of the PNS in the skeletal system under physiological conditions, fractures, or regeneration. Furthermore, we summarize the ways in which the PNS communicates with bone-lineage cells, the vasculature, and immune cells in the bone microenvironment. Based on this comprehensive and timely review, we conclude that the PNS regulates bone regeneration through neuropeptides or neurotransmitters and cells in the peripheral nerves. An in-depth understanding of the roles of peripheral nerves in bone regeneration will inform the development of new strategies based on bone-nerve crosstalk in promoting bone repair and regeneration.

Bioactive semaphorin 3A promotes sequential formation of sensory nerve and type H vessels during in situ osteogenesis

Introduction: Sensory nerves and vessels are critical for skeletal development and regeneration, but crosstalk between neurovascular network and mineralization are not clear. The aim of this study was to explore neurovascular changes and identify bioactive regulators during in situ osteogenesis. Method: In situ osteogenesis model was performed in male rats following Achilles tenotomy. At 3, 6 and 9 weeks after surgery, mineralization, blood vessels, sensory innervation, and bioactive regulators expression were evaluated via micro-computed tomography, immunofluorescent staining, histology and reverse transcriptase-polymerase chain reaction analyses. Result: In the process of in situ osteogenesis, the mineral density increased with time, and the locations of minerals, nerves and blood vessels were highly correlated at each time point. The highest density of sensory nerve was observed in the experimental group at the 3rd week, and then gradually decreased with time, but still higher than that in the sham control group. Among many regulatory factors, semaphorin 3A (Sema3A) was highly expressed in experimental model and its expression was temporally sequential and spatially correlated sensory nerve. Conclusion: The present study showes that during in situ osteogenesis, innervation and angiogenesis are highly correlated, and Sema3A is associated with the position and expression of the sensory nerve.

Role of protein phosphorylation in cell signaling, disease, and the intervention therapy

Protein phosphorylation is an important post-transcriptional modification involving an extremely wide range of intracellular signaling transduction pathways, making it an important therapeutic target for disease intervention. At present, numerous drugs targeting protein phosphorylation have been developed for the treatment of various diseases including malignant tumors, neurological diseases, infectious diseases, and immune diseases. In this review article, we analyzed 303 small-molecule protein phosphorylation kinase inhibitors (PKIs) registered and participated in clinical research obtained in a database named Protein Kinase Inhibitor Database (PKIDB), including 68 drugs approved by the Food and Drug Administration of the United States. Based on previous classifications of kinases, we divided these human protein phosphorylation kinases into eight groups and nearly 50 families, and delineated their main regulatory pathways, upstream and downstream targets. These groups include: protein kinase A, G, and C (AGC) and receptor guanylate cyclase (RGC) group, calmodulin-dependent protein kinase (CaMK) group, CMGC [Cyclin-dependent kinases (CDKs), Mitogen-activated protein kinases (MAPKs), Glycogen synthase kinases (GSKs), and Cdc2-like kinases (CLKs)] group, sterile (STE)-MAPKs group, tyrosine kinases (TK) group, tyrosine kinase-like (TKL) group, atypical group, and other groups. Different groups and families of inhibitors stimulate or inhibit others, forming an intricate molecular signaling regulatory network. This review takes newly developed new PKIs as breakthrough point, aiming to clarify the regulatory network and relationship of each pathway, as well as their roles in disease intervention, and provide a direction for future drug development.

Neurovascular coupling in bone regeneration

The mammalian skeletal system is densely innervated by both neural and vascular networks. Peripheral nerves in the skeleton include sensory and sympathetic nerves. The crosstalk between skeletal and neural tissues is critical for skeletal development and regeneration. The cellular processes of osteogenesis and angiogenesis are coupled in both physiological and pathophysiological contexts. The cellular and molecular regulation of osteogenesis and angiogenesis have yet to be fully defined. This review will provide a detailed characterization of the regulatory role of nerves and blood vessels during bone regeneration. Furthermore, given the importance of the spatial relationship between nerves and blood vessels in bone, we discuss neurovascular coupling during physiological and pathological bone formation. A better understanding of the interactions between nerves and blood vessels will inform future novel therapeutic neural and vascular targeting for clinical bone repair and regeneration.

TrkA+ Neurons Induce Pathologic Regeneration After Soft Tissue Trauma

Heterotopic ossification (HO) is a dynamic, complex pathologic process that often occurs after severe polytrauma trauma, resulting in an abnormal mesenchymal stem cell differentiation leading to ectopic bone growth in soft-tissues including tendons, ligaments, and muscles. The abnormal bone structure and location induce pain and loss of mobility. Recently, we observed that NGF (Nerve growth factor)-responsive TrkA (Tropomyosin receptor kinase A)-expressing nerves invade sites of soft-tissue trauma, and this is a necessary feature for heterotopic bone formation at sites of injury. Here, we assayed the effects of the partial TrkA agonist Gambogic amide (GA) in peritendinous heterotopic bone after extremity trauma. Mice underwent HO induction using the burn/tenotomy model with or without systemic treatment with GA, followed by an examination of the injury site via radiographic imaging, histology, and immunohistochemistry. Single-cell RNA Sequencing confirmed an increase in neurotrophin signaling activity after HO-inducing extremity trauma. Next, TrkA agonism led to injury site hyper-innervation, more brisk expression of cartilage antigens within the injured tendon, and a shift from FGF to TGFβ signaling activity among injury site cells. Nine weeks after injury, this culminated in higher overall levels of heterotopic bone among GA-treated animals. In summary, these studies further link injury site hyper-innervation with increased vascular ingrowth and ultimately heterotopic bone after trauma. In the future, modulation of TrkA signaling may represent a potent means to prevent the trauma-induced heterotopic bone formation and improve tissue regeneration.