Endogenous CCN family member WISP1 inhibits trauma-induced heterotopic ossification

Sustained notch signaling inhibition with a gamma-secretase inhibitor prevents traumatic heterotopic ossification

Background

Traumatic heterotopic ossification (THO) is a devastating sequela following traumatic injuries and orthopedic surgeries. To date, the exact molecular mechanism of THO formation is still unclear, which hinders the development of effective treatments. The process of THO formation is believed to recapitulate a series of spatiotemporal cellular and signaling events that occur during skeletal development. The Notch signaling pathway is a critical genetic regulator in embryological bone development and fracture healing. However, few data are available concerning whether Notch signaling regulates THO development and maturation.

Methods

We firstly detected the expressions of Notch target genes in both mouse and human THO samples with quantitative RT-PCR and immunohistochemistry (IHC). Then, tissue-resident mesenchymal progenitor cells (TMPCs) were isolated, and the abilities of the proliferation and osteogenic and chondrogenic differentiation of TMPCs were examined under the intervention of the gamma-secretase inhibitor-DAPT at different time points. Finally, DAPT was also administrated in THO mice by burn and Achilles tenotomy injury, and ectopic cartilage and bone formation were monitored by histology and micro-CT.

Results

Several Notch target genes were upregulated in both mouse and human THO tissues. Sustained Notch signaling inhibition by DAPT reduced proliferation, osteogenic and chondrogenic differentiation of TMPCs in a time-dependent manner. Moreover, DAPT administration within 3 weeks could inhibit ectopic cartilage and bone formation in a mouse THO model without affecting the total body bone mass.

Conclusions

The Notch signaling serves as an important therapeutic target during THO formation. And sustained gamma-secretase inhibition by DAPT has great potential in repressing chondrogenic and osteogenic differentiation of TMPCs, as well as inhibited ectopic cartilage and bone formation in vivo.

The translational potential of this article

Sustained Notch inhibition via systemic DAPT (or other similar gamma-secretase inhibitors) administration has promising clinical utility for inhibiting THO formation, providing new insight into THO prophylaxis and treatment.

A Novel Burn / Synovectomy Mouse Model for Temporomandibular Joint Osteoarthritis

Temporomandibular Disorders (TMDs) is present in 33% of the U.S. population. Currently available animal models do not faithfully simulate the native disease progression of TMJ OA. The initiation of TMJ OA requires both local trauma and systemic inflammation. In this study, we present a novel mouse model which reproduces these two conditions. This is achieved by a procedure involving both synovectomy (local trauma) and a distant burn injury (systemic inflammation). Its efficacy at inducing TMJ OA was assessed with histomorphology and radiographic evaluation at 1,3, and 9 weeks after the procedure. We found that burn/synovectomy mice demonstrated significantly more degenerative changes in TMJ than uninjured control mice or synovotomy mice. The observed histology in burn/synoectomy mice mimicked native TMJ OA disease progression in a faithful manner. This animal model is invaluable in future research of the mechanism and risk factors of TMJ OA.

Differential pericyte marker expression in craniofacial benign and malignant vascular tumors

BACKGROUND

Vascular anomalies and tumors are common in the head, neck, and craniofacial areas and are associated with abnormalities in the angiomatous architecture. However, the etiology and molecular basis for the pathogenesis of most vascular lesions are still unknown. Pericytes are mural cells that surround endothelial cells. Besides angiogenesis and other physiological functions, pericytes play an important role in vascularized tissue repair and as resident mesenchymal stem/progenitor cells. Perivascular cells demonstrate a distinct immunohistochemical profile, including expression of alpha-smooth muscle actin (α-SMA), CD146, CD105, and PDGFRβ, without endothelial differentiation (absence of CD31 and CD34 immunoreactivity). These pericyte markers have been shown to be expressed in soft tissue hemangiomas. However, they have not been fully examined in intraosseous hemangiomas.

METHODS

In this study, we compared mesenchymal stem cell (MSC) expression of CD146 and α-SMA markers in pericytes from hemangiomas from different tissues and malignant vascular tumors.

RESULTS

The results demonstrated an increased expression of pericyte markers in perivascular cells of benign hemangiomas, especially intraosseous hemangiomas and a significantly reduced expression of pericyte markers in malignant angiosarcomas.

CONCLUSION

The evidence provides insight into the function of pericytes in vascular tumors and suggests their role in vascular tumor disease types.

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.

Single-cell RNA sequencing in orthopedic research

Although previous RNA sequencing methods have been widely used in orthopedic research and have provided ideas for therapeutic strategies, the specific mechanisms of some orthopedic disorders, including osteoarthritis, lumbar disc herniation, rheumatoid arthritis, fractures, tendon injuries, spinal cord injury, heterotopic ossification, and osteosarcoma, require further elucidation. The emergence of the single-cell RNA sequencing (scRNA-seq) technique has introduced a new era of research on these topics, as this method provides information regarding cellular heterogeneity, new cell subtypes, functions of novel subclusters, potential molecular mechanisms, cell-fate transitions, and cell‒cell interactions that are involved in the development of orthopedic diseases. Here, we summarize the cell subpopulations, genes, and underlying mechanisms involved in the development of orthopedic diseases identified by scRNA-seq, improving our understanding of the pathology of these diseases and providing new insights into therapeutic approaches.

Early diagnosis of heterotopic ossification with a NIR fluorescent probe by targeting type II collagen

Heterotopic ossification (HO) is a devastating sequela in which the pathologic extracellular matrix of the cartilage and bone forms abnormally in soft tissues following traumatic injuries or orthopaedic surgeries. Early treatment is essential for inhibiting the progression of HO but is currently limited by the absence of sensitive and specific early diagnosis. Herein, this study exploits the enrichment of type II collagen (Col2a1) in the HO cartilage formation stage towards developing a near-infrared (NIR) probe for early HO diagnosis, namely WL-808 by conjugating a Col2a1-binding peptide (WYRGRL) and a cyanine dye (IR-808). WL-808 exhibits high specificity for targeting the cartilage in vitro and in vivo with no apparent cytotoxicity. The NIR signal of WL-808 can be detected in the HO cartilage lesions as early as 1 week after injury when micro-CT cannot show any ectopic bone formation. Moreover, the probe is rarely distributed in the normal knee articular cartilage in vivo via the intravenous administration method. Taken together, WL-808 demonstrates great potential in early HO diagnosis under NIR imaging, facilitating early HO prophylaxis and treatment in the clinic.

Myeloid CCN3 protects against aortic valve calcification

BACKGROUND

Cellular communication network factor 3 (CCN3) has been implicated in the regulation of osteoblast differentiation. However, it is not known if CCN3 can regulate valvular calcification. While macrophages have been shown to regulate valvular calcification, the molecular and cellular mechanisms of this process remain poorly understood. In the present study, we investigated the role of macrophage-derived CCN3 in the progression of calcific aortic valve disease.

METHODS

Myeloid-specific knockout of CCN3 (Mye-CCN3-KO) and control mice were subjected to a single tail intravenous injection of AAV encoding mutant mPCSK9 (rAAV8/D377Y-mPCSK9) to induce hyperlipidemia. AAV-injected mice were then fed a high fat diet for 40 weeks. At the conclusion of high fat diet feeding, tissues were harvested and subjected to histologic and pathologic analyses. In vitro, bone marrow-derived macrophages (BMDM) were obtained from Mye-CCN3-KO and control mice and the expression of bone morphogenic protein signaling related gene were verified via quantitative real-time PCR and Western blotting. The BMDM conditioned medium was cocultured with human valvular intersititial cells which was artificially induced calcification to test the effect of the conditioned medium via Western blotting and Alizarin red staining.

RESULTS

Echocardiography revealed that both male and female Mye-CCN3-KO mice displayed compromised aortic valvular function accompanied by exacerbated valve thickness and cardiac dysfunction. Histologically, Alizarin-Red staining revealed a marked increase in aortic valve calcification in Mye-CCN3-KO mice when compared to the controls. In vitro, CCN3 deficiency augmented BMP2 production and secretion from bone marrow-derived macrophages. In addition, human valvular interstitial cells cultured with conditioned media from CCN3-deficient BMDMs resulted in exaggerated pro-calcifying gene expression and the consequent calcification.

CONCLUSION

Our data uncovered a novel role of myeloid CCN3 in the regulation of aortic valve calcification. Modulation of BMP2 production and secretion in macrophages might serve as a key mechanism for macrophage-derived CCN3's anti-calcification function in the development of CAVD. Video Abstract.

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.

Contemporary perspectives on heterotopic ossification

Heterotopic ossification (HO) is the formation of ectopic bone that is primarily genetically driven (fibrodysplasia ossificans progressiva [FOP]) or acquired in the setting of trauma (tHO). HO has undergone intense investigation, especially over the last 50 years, as awareness has increased around improving clinical technologies and incidence, such as with ongoing wartime conflicts. Current treatments for tHO and FOP remain prophylactic and include NSAIDs and glucocorticoids, respectively, whereas other proposed therapeutic modalities exhibit prohibitive risk profiles. Contemporary studies have elucidated mechanisms behind tHO and FOP and have described new distinct niches independent of inflammation that regulate ectopic bone formation. These investigations have propagated a paradigm shift in the approach to treatment and management of a historically difficult surgical problem, with ongoing clinical trials and promising new targets.

Sustained local ionic homeostatic imbalance caused by calcification modulates inflammation to trigger heterotopic ossification

Heterotopic ossification (HO) is a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues. Despite being a frequent complication of orthopedic and trauma surgery, brain and spinal injury, the etiology of HO is poorly understood. The aim of this study is to evaluate the hypothesis that a sustained local ionic homeostatic imbalance (SLIHI) created by mineral formation during tissue calcification modulates inflammation to trigger HO. This evaluation also considers the role SLIHI could play for the design of cell-free, drug-free osteoinductive bone graft substitutes. The evaluation contains five main sections. The first section defines relevant concepts in the context of HO and provides a summary of proposed causes of HO. The second section starts with a detailed analysis of the occurrence and involvement of calcification in HO. It is followed by an explanation of the causes of calcification and its consequences. This allows to speculate on the potential chemical modulators of inflammation and triggers of HO. The end of this second section is devoted to in vitro mineralization tests used to predict the ectopic potential of materials. The third section reviews the biological cascade of events occurring during pathological and material-induced HO, and attempts to propose a quantitative timeline of HO formation. The fourth section looks at potential ways to control HO formation, either acting on SLIHI or on inflammation. Chemical, physical, and drug-based approaches are considered. Finally, the evaluation finishes with a critical assessment of the definition of osteoinduction. STATEMENT OF SIGNIFICANCE: The ability to regenerate bone in a spatially controlled and reproducible manner is an essential prerequisite for the treatment of large bone defects. As such, understanding the mechanism leading to heterotopic ossification (HO), a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues, would be very useful. Unfortunately, the mechanism(s) behind HO is(are) poorly understood. The present study reviews the literature on HO and based on it, proposes that HO can be caused by a combination of inflammation and calcification. This mechanism helps to better understand current strategies to prevent and treat HO. It also shows new opportunities to improve the treatment of bone defects in orthopedic and dental procedures.

When the Nervous System Turns Skeletal Muscles into Bones: How to Solve the Conundrum of Neurogenic Heterotopic Ossification

PURPOSE OF REVIEW

Neurogenic heterotopic ossification (NHO) is the abnormal formation of extra-skeletal bones in periarticular muscles after damage to the central nervous system (CNS) such as spinal cord injury (SCI), traumatic brain injury (TBI), stroke, or cerebral anoxia. The purpose of this review is to summarize recent developments in the understanding of NHO pathophysiology and pathogenesis. Recent animal models of NHO and recent findings investigating the communication between CNS injury, tissue inflammation, and upcoming NHO therapeutics are discussed.

RECENT FINDINGS

Animal models of NHO following TBI or SCI have shown that NHO requires the combined effects of a severe CNS injury and soft tissue damage, in particular muscular inflammation and the infiltration of macrophages into damaged muscles plays a key role. In the context of a CNS injury, the inflammatory response to soft tissue damage is exaggerated and persistent with excessive signaling via substance P-, oncostatin M-, and TGF-β1-mediated pathways. This review provides an overview of the known animal models and mechanisms of NHO and current therapeutic interventions for NHO patients. While some of the inflammatory mechanisms leading to NHO are common with other forms of traumatic and genetic heterotopic ossifications (HO), NHOs uniquely involve systemic changes in response to CNS injury. Future research into these CNS-mediated mechanisms is likely to reveal new targetable pathways to prevent NHO development in patients.