TrkA+ Neurons Induce Pathologic Regeneration After Soft Tissue Trauma

IGFBP3 enhances adipose-derived stem cell function in soft tissue injury repair via ITGB1 and ERK pathway activation

Soft tissue injury (STI) is a prevalent condition that requires effective therapeutic approaches. The focus of this investigation was to elucidate the molecular mechanisms linked to the IGFBP3 protein in adipose-derived stem cells (ADSCs) for STI repair, utilizing single-cell multiomics technology and a 3D bioprinting model. Establishment of a mouse-based STI model facilitated the comparison of cellular compositions and communication variances between wounded and normal tissues through single-cell RNA sequencing (scRNA-seq). High-throughput transcriptomics and bioinformatics analysis pinpointed IGFBP3 as a key target in ADSCs related to STI repair. In vitro experiments assessed IGFBP3's effects on ADSCs' epithelial cell differentiation, proliferation, and migration using various assays and lentivirus transfection to manipulate IGFBP3 expression. A 3D bioprinting technique was used to create an ADSCs-IGFBP3 peptide self-assembling hydrogel scaffold, characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, SEM, and TEM. The scaffold's efficacy was validated in an animal model. Results showed nine cell subtypes in both normal and injured tissues, with increased ADSCs in STI tissues exhibiting enhanced connectivity and interactions. RNA-seq analysis confirmed IGFBP3 as crucial for ADSCs and STI. In vitro and 3D bioprinting experiments, along with animal model validation, confirmed IGFBP3's role in STI repair. Upregulation of IGFBP3 in ADSCs promoted epithelial cell differentiation by enhancing ITGB1 expression, activating the ERK pathway to boost cell proliferation and migration. This study highlights IGFBP3's significant role in ADSCs for STI repair, providing potential molecular targets for developing new treatments. The findings offer valuable insights into IGFBP3's mechanisms, aiding in advancing STI therapeutic strategies.

Muscle-guided mapping of post-traumatic heterotopic ossification of the elbow: a novel computed tomography-based study

BACKGROUND

Heterotopic ossification (HO) involves abnormal bone formation in soft tissues near joints, commonly occurring after elbow trauma or surgery, leading to pain and functional limitations. Previous studies have primarily characterized HO distribution based on bony landmarks, lacking a detailed investigation into the characteristics of its distribution in periarticular soft tissue in post-traumatic elbows. This study aimed to (1) develop a muscle-guided classification system using computed tomography (CT) to map HO relative to elbow muscle-tendon units and (2) investigate correlations between HO location and severity.

METHODS

In a retrospective study, 56 patients with HO and elbow stiffness following trauma were analyzed. CT imaging was used to classify HO into 7 categories: Posterior - olecranon tip - triceps brachii; Posteromedial - medial gutter - flexor carpi ulnaris (PM-MG-FCU); Posterolateral - lateral gutter - anconeus; Medial - medial epicondylar - flexor muscles; Lateral - lateral epicondylar - extensor muscles; Anterior - humeroulnar joint - brachialis; and Anterior - humeroradial - supinator. HO severity was graded (1-3) based on CT morphology, and correlations between HO location and severity were assessed.

RESULTS

PM-MG-FCU was the most common HO location (67.9%). Significant correlations were found between HO severity and location, with higher rates of HO in grades 2 and 3, characterized by extensive mature bone formation and bone bridge development occurring in the posterolateral - lateral gutter - anconeus, posterior - olecranon tip - triceps brachii, and PM-MG-FCU.

CONCLUSION

The muscle-guided classification system effectively delineated HO distribution near elbow muscle-tendon units. HO locations surrounding the anconeus, triceps brachii, and flexor carpi ulnaris correlate with higher radiographic severity, providing valuable insights for treatment strategies.

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.

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.

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.

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.

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.