Altered fracture callus formation in chondromodulin-I deficient mice

A Narrative Review of the Roles of Chondromodulin-I (Cnmd) in Adult Cartilage Tissue

Articular cartilage is crucial for joint function but its avascularity limits intrinsic repair, leading to conditions like osteoarthritis (OA). Chondromodulin-I (Cnmd) has emerged as a key molecule in cartilage biology, with potential implications for OA therapy. Cnmd is primarily expressed in cartilage and plays an important role in chondrocyte proliferation, cartilage homeostasis, and the blocking of angiogenesis. In vivo and in vitro studies on Cnmd, also suggest an involvement in bone repair and in delaying OA progression. Its downregulation correlates with OA severity, indicating its potential as a therapeutic target. Further research is needed to fully understand the mode of action of Cnmd and its beneficial implications for managing OA. This comprehensive review aims to elucidate the molecular characteristics of Cnmd, from its expression pattern, role in cartilage maintenance, callus formation during bone repair and association with OA.

Chondromodulin is necessary for cartilage callus distraction in mice

Chondromodulin (Cnmd) is a glycoprotein known to stimulate chondrocyte growth. We examined in this study the expression and functional role of Cnmd during distraction osteogenesis that is modulated by mechanical forces. The right tibiae of the mice were separated by osteotomy and subjected to slow progressive distraction using an external fixator. In situ hybridization and immunohistochemical analyses of the lengthened segment revealed that Cnmd mRNA and its protein in wild-type mice were localized in the cartilage callus, which was initially generated in the lag phase and was lengthened gradually during the distraction phase. In Cnmd null (Cnmd-/-) mice, less cartilage callus was observed, and the distraction gap was filled by fibrous tissues. Additionally, radiological and histological investigations demonstrated delayed bone consolidation and remodeling of the lengthened segment in Cnmd-/- mice. Eventually, Cnmd deficiency caused a one-week delay in the peak expression of VEGF, MMP2, and MMP9 genes and the subsequent angiogenesis and osteoclastogenesis. We conclude that Cnmd is necessary for cartilage callus distraction.

Neuron-to-vessel signaling is a required feature of aberrant stem cell commitment after soft tissue trauma

The functional interdependence of nerves and blood vessels is a well-established concept during tissue morphogenesis, yet the role of neurovascular coupling in proper and aberrant tissue repair is an emerging field of interest. Here, we sought to define the regulatory relationship of peripheral nerves on vasculature in a severe extremity trauma model in mice, which results in aberrant cell fate and heterotopic ossification (HO). First, a high spatial degree of neurovascular congruency was observed to exist within extremity injury associated heterotopic ossification. Vascular and perivascular cells demonstrate characteristic responses to injury, as assessed by single cell RNA sequencing. This vascular response to injury was blunted in neurectomized mice, including a decrease in endothelial proliferation and type H vessel formation, and a downregulation of key transcriptional networks associated with angiogenesis. Independent mechanisms to chemically or genetically inhibit axonal ingrowth led to similar deficits in HO site angiogenesis, a reduction in type H vessels, and heterotopic bone formation. Finally, a combination of single cell transcriptomic approaches within the dorsal root ganglia identified key neural-derived angiogenic paracrine factors that may mediate neuron-to-vascular signaling in HO. These data provide further understanding of nerve-to-vessel crosstalk in traumatized soft tissues, which may reflect a key determinant of mesenchymal progenitor cell fate after injury.

Analysis of the Progeny of Sibling Matings Reveals Regulatory Variation Impacting the Transcriptome of Immune Cells in Commercial Chickens

There is increasing recognition that the underlying genetic variation contributing to complex traits influences transcriptional regulation and can be detected at a population level as expression quantitative trait loci. At the level of an individual, allelic variation in transcriptional regulation of individual genes can be detected by measuring allele-specific expression in RNAseq data. We reasoned that extreme variants in gene expression could be identified by analysis of inbred progeny with shared grandparents. Commercial chickens have been intensively selected for production traits. Selection is associated with large blocks of linkage disequilibrium with considerable potential for co-selection of closely linked "hitch-hiker alleles" affecting traits unrelated to the feature being selected, such as immune function, with potential impact on the productivity and welfare of the animals. To test this hypothesis that there is extreme allelic variation in immune-associated genes we sequenced a founder population of commercial broiler and layer birds. These birds clearly segregated genetically based upon breed type. Each genome contained numerous candidate null mutations, protein-coding variants predicted to be deleterious and extensive non-coding polymorphism. We mated selected broiler-layer pairs then generated cohorts of F2 birds by sibling mating of the F1 generation. Despite the predicted prevalence of deleterious coding variation in the genomic sequence of the founders, clear detrimental impacts of inbreeding on survival and post-hatch development were detected in only one F2 sibship of 15. There was no effect on circulating leukocyte populations in hatchlings. In selected F2 sibships we performed RNAseq analysis of the spleen and isolated bone marrow-derived macrophages (with and without lipopolysaccharide stimulation). The results confirm the predicted emergence of very large differences in expression of individual genes and sets of genes. Network analysis of the results identified clusters of co-expressed genes that vary between individuals and suggested the existence of trans-acting variation in the expression in macrophages of the interferon response factor family that distinguishes the parental broiler and layer birds and influences the global response to lipopolysaccharide. This study shows that the impact of inbreeding on immune cell gene expression can be substantial at the transcriptional level, and potentially opens a route to accelerate selection using specific alleles known to be associated with desirable expression levels.

Chondromodulin-1 in health, osteoarthritis, cancer, and heart disease

The human chondromodulin-1 (Chm-1, Chm-I, CNMD, or Lect1) gene encodes a 334 amino acid type II transmembrane glycoprotein protein with characteristics of a furin cleavage site and a putative glycosylation site. Chm-1 is expressed most predominantly in healthy and developing avascular cartilage, and healthy cardiac valves. Chm-1 plays a vital role during endochondral ossification by the regulation of angiogenesis. The anti-angiogenic and chondrogenic properties of Chm-1 are attributed to its role in tissue development, homeostasis, repair and regeneration, and disease prevention. Chm-1 promotes chondrocyte differentiation, and is regulated by versatile transcription factors, such as Sox9, Sp3, YY1, p300, Pax1, and Nkx3.2. Decreased expression of Chm-1 is implicated in the onset and progression of osteoarthritis and infective endocarditis. Chm-1 appears to attenuate osteoarthritis progression by inhibiting catabolic activity, and to mediate anti-inflammatory effects. In this review, we present the molecular structure and expression profiling of Chm-1. In addition, we bring a summary to the potential role of Chm-1 in cartilage development and homeostasis, osteoarthritis onset and progression, and to the pathogenic role of Chm-1 in infective endocarditis and cancers. To date, knowledge of the Chm-1 receptor, cellular signalling, and the molecular mechanisms of Chm-1 is rudimentary. Advancing our understanding the role of Chm-1 and its mechanisms of action will pave the way for the development of Chm-1 as a therapeutic target for the treatment of diseases, such as osteoarthritis, infective endocarditis, and cancer, and for potential tissue regenerative bioengineering applications.

Meniscus, articular cartilage and nucleus pulposus: a comparative review of cartilage-like tissues in anatomy, development and function

The degradation of cartilage in the human body is impacted by aging, disease, genetic predisposition and continued insults resulting from daily activity. The burden of cartilage defects (osteoarthritis, rheumatoid arthritis, intervertebral disc damage, knee replacement surgeries, etc.) is daunting in light of substantial economic and social stresses. This review strives to broaden the scope of regenerative medicine and tissue engineering approaches used for cartilage repair by comparing and contrasting the anatomical and functional nature of the meniscus, articular cartilage (AC) and nucleus pulposus (NP). Many review papers have provided detailed evaluations of these cartilages and cartilage-like tissues individually but none have comprehensively examined the parallels and inconsistencies in signaling, genetic expression and extracellular matrix composition between tissues. For the first time, this review outlines the importance of understanding these three tissues as unique entities, providing a comparative analysis of anatomy, ultrastructure, biochemistry and function for each tissue. This novel approach highlights the similarities and differences between tissues, progressing research toward an understanding of what defines each tissue as distinctive. The goal of this paper is to provide researchers with the fundamental knowledge to correctly engineer the meniscus, AC and NP without inadvertently developing the wrong tissue function or biochemistry.

Chondromodulin-1 ameliorates osteoarthritis progression by inhibiting HIF-2α activity

OBJECTIVES

Hypoxia is known to stabilize hypoxia-inducible factor (HIF) and initiate angiogenic signaling cascade. However, cartilage living in hypoxia environment can maintain avascularity. It is well known that abrogation of avascularity is related to cartilage degradation in osteoarthritis (OA). The aims of present study were to investigate the role of chondromodulin-1 (ChM-1), an endogenously anti-angiogenic protein in cartilage, during chondrocyte maturation and OA progression, as well as to explore the molecular mechanisms underlying the function of ChM-1 with a focus on HIF-2α pathway.

METHODS

Angiogenic-related markers were evaluated in OA cartilage and different stages of chondrocyte differentiation. Chondrocytes transfected with ChM-1 lentivirus or siRNA was treated with tumor necrosis factor (TNF-α) to investigate the role of ChM-1 in chondrocyte hypertrophic changes. In vivo study was conducted by using a surgical induced OA rat model with intra-articular injection of lentivirus ChM-1 (LV-ChM-1) or mock lentivirus (LV-GFP) control. Transcriptional activity of HIF-2α was determined by chromatin immunoprecipitation (ChIP) assay to unveil the mechanisms of ChM-1.

RESULTS

Majority angiogenic factors increased in severe OA cartilage, while anti-angiogenic factors including ChM-1 decreased. ChM-1 expression was strongly related with chondrocyte differentiation and chondrogenesis in vitro. ChM-1 overexpression protected chondrocytes from TNF-α induced hypertrophy, and intra-articular injection of LV-ChM-1 delayed OA progression. ChM-1 delayed HIF-2α nuclear translocation at early time-points and decreased transcriptional activity of HIF-2α on collagen type Х α1 (COL10A1), vascular endothelial growth factor A (VEGFA) and matrix metallopeptidase-13 (MMP-13).

CONCLUSIONS

ChM-1 maintains cartilage homeostasis by inhibiting HIF-2α induced catabolic activity and regulation of ChM-1 in cartilage may be a promising therapeutic strategy for OA.

The N-terminal cleavage of chondromodulin-I in growth-plate cartilage at the hypertrophic and calcified zones during bone development

Chondromodulin-I (ChM-I) is a 20-25 kDa anti-angiogenic glycoprotein in cartilage matrix. In the present study, we identified a novel 14-kDa species of ChM-I by immunoblotting, and purified it by immunoprecipitation with a newly raised monoclonal antibody against ChM-I. The N-terminal amino acid sequencing indicated that it was an N-terminal truncated form of ChM-I generated by the proteolytic cleavage at Asp37-Asp38. This 14-kDa ChM-I was shown by the modified Boyden chamber assay to have very little inhibitory activity on the VEGF-A-induced migration of vascular endothelial cells in contrast to the intact 20-25 kDa form of ChM-I (ID50 = 8 nM). Immunohistochemistry suggested that 20-25 kDa ChM-I was exclusively localized in the avascular zones, i.e. the resting, proliferating, and prehypertrophic zones, of the cartilaginous molds of developing long bone, whereas the 14-kDa form of ChM-I was found in hypertrophic and calcified zones. Immunoblotting demonstrated that mature growth-plate chondrocytes isolated from rat costal cartilage actively secrete ChM-I almost exclusively as the intact 20-25 kDa form into the medium in primary culture. Taken together, our results suggest that intact 20-25 kDa ChM-I is stored as a component of extracellular matrix in the avascular cartilage zones, but it is inactivated by a single N-terminal proteolytic cleavage in the hypertrophic zone of growth-plate cartilage.

FOXO3A regulation by miRNA-29a Controls chondrogenic differentiation of mesenchymal stem cells and cartilage formation

Skeletal development and cartilage formation require stringent regulation of gene expression for mesenchymal stem cells (MSCs) to progress through stages of differentiation. Since microRNAs (miRNAs) regulate biological processes, the objective of the present study was to identify novel miRNAs involved in the modulation of chondrogenesis. We performed miRNA profiling and identify miR-29a as being one of the most down-regulated miRNAs during the chondrogenesis. Using chromatin immunoprecipitation, we showed that SOX9 down-regulates its transcription. Moreover, the over-expression of miR-29a strongly inhibited the expression of chondrocyte-specific markers during in vitro chondrogenic differentiation of MSCs. We identified FOXO3A as a direct target of miR-29a and showed a down- and up-regulation of FOXO3a protein levels after transfection of, respectively, premiR- and antagomiR-29a oligonucleotides. Finally, we showed that using the siRNA or premiR approach, chondrogenic differentiation was inhibited to a similar extent. Together, we demonstrate that the down-regulation of miR-29a, concomitantly with FOXO3A up-regulation, is essential for the differentiation of MSCs into chondrocytes and in vivo cartilage/bone formation. The delivery of miRNAs that modulate MSC chondrogenesis may be applicable for cartilage regeneration and deserves further investigation.

Fracture non-union: Can biomarkers predict outcome?

Delayed bone healing and non-union occurs in approximately 10-15% of long bone fractures. Both pathologies may result in prolonged period of pain, disability and repetitive operative interventions. Despite intense investigations and progress done in understanding the pathophysiologic processes governing bone healing, the diagnostic tools have not been altered. The clinical findings and radiographic features remain the two important landmarks of diagnosing non-union and even when the diagnosis is established there is debate on the ideal timing and mode of intervention. Emerging evidence suggest that there are certain molecules and genes that can serve as predictors of potentially unsuccessful fracture union. This article summarises the current evidence on the available 'bio-markers'to predict fracture non-union.

Antiangiogenic and anticancer molecules in cartilage

Cartilage is one of the very few naturally occurring avascular tissues where lack of angiogenesis is the guiding principle for its structure and function. This has attracted investigators who have sought to understand the biochemical basis for its avascular nature, hypothesising that it could be used in designing therapies for treating cancer and related malignancies in humans through antiangiogenic applications. Cartilage encompasses primarily a specialised extracellular matrix synthesised by chondrocytes that is both complex and unique as a result of the myriad molecules of which it is composed. Of these components, a few such as thrombospondin-1, chondromodulin-1, the type XVIII-derived endostatin, SPARC (secreted protein acidic and rich in cysteine) and the type II collagen-derived N-terminal propeptide (PIIBNP) have demonstrated antiangiogenic or antitumour properties in vitro and in vivo preclinical trials that involve several complicated mechanisms that are not completely understood. Thrombospondin-1, endostatin and the shark-cartilage-derived Neovastat preparation have also been investigated in human clinical trials to treat several different kinds of cancers, where, despite the tremendous success seen in preclinical trials, these molecules are yet to show success as anticancer agents. This review summarises the current state-of-the-art antiangiogenic characterisation of these molecules, highlights their most promising aspects and evaluates the future of these molecules in antiangiogenic applications.

Long bone fracture repair in mice harboring GFP reporters for cells within the osteoblastic lineage

GFP reporter mice previously developed to assess levels of osteoblast differentiation were employed in a tibial long bone fracture model using a histological method that preserves fluorescent signals in non-decalcified sections of bone. Two reporters, based on Col1A1 (Col3.6GFPcyan) and osteocalcin (OcGFPtpz) promoter fragments, were bred into the same mice to reflect an early and late stage of osteoblast differentiation. Three observations were apparent from this examination. First, the osteoprogenitor cells that arise from the flanking periosteum proliferate and progress to fill the fracture zone. These cells differentiate to osteoblasts, chondrocytes, to from the outer cortical shell. Second, the hypertrophic chondrocytes are dispersed and the cartilage matrix mineralized by the advancing Col3.6+ osteoblasts. The endochondral matrix is removed by the following osteoclasts. Third, a new cortical shell develops over the cartilage core and undergoes a remodeling process of bone formation on the inner surface and resorption on the outer surface. The original fractured cortex undergoes resorption as the outer cortical shell remodels inward to become the new diaphyseal bone. The fluorescent microscopy and GFP reporter mice used in this study provide a powerful tool for appreciating the molecular and cellular processes that control these fundamental steps in fracture repair, and may provide a basis for understanding fracture nonunion.

Fixation compliance in a mouse osteotomy model induces two different processes of bone healing but does not lead to delayed union

Delayed unions are a problematic complication of fracture healing whose pathophysiology is not well understood. Advanced molecular biology methods available with mice would be advantageous for investigation. In humans, decreased fixation rigidity and poor reduction are generally associated with delayed unions. In this study, these two factors were combined to observe their effect on bone healing in mice. Two plates with locking screws, one with 14 the bending stiffness of the other, were used to stabilize a 0.45mm gap osteotomy. muCT, radiographs, 4pt-bending tests and histological analysis demonstrated that the different plate types led to two different healing pathways. The less flexible bridging plate induced only intramembranous ossification whereas the more flexible bridging plate induced a mixture of endochondral and intramembranous ossification. However, the different plates led to a delay in healing of only 3-5 days in the period between 14 and 21 post-operative days. In mice, considerable fixation flexibility is necessary to induce secondary bone healing similar to that which occurs in humans, but this was not sufficient to induce a substantial delay in bone healing as would be expected in humans.