Different bone growth rates are associated with changes in the expression pattern of types II and X collagens and collagenase 3 in proximal growth plates of the rat tibia

Excess Growth Hormone Triggers Inflammation-Associated Arthropathy, Subchondral Bone Loss, and Arthralgia

Growth hormone (GH) is a key mediator of skeletal growth. In humans, excess GH secretion due to pituitary adenoma, seen in patients with acromegaly, results in severe arthropathies. This study investigated the effects of long-term excess GH on the knee joint tissues. One year-old wild-type (WT) and bovine GH (bGH) transgenic mice were used as a model for excess GH. bGH mice showed increased sensitivity to mechanical and thermal stimuli, compared with WT mice. Micro-computed tomography analyses of the distal femur subchondral bone revealed significant reductions in trabecular thickness and significantly reduced bone mineral density of the tibial subchondral bone-plate associated with increased osteoclast activity in both male and female bGH compared with WT mice. bGH mice showed severe loss of matrix from the articular cartilage, osteophytosis, synovitis, and ectopic chondrogenesis. Articular cartilage loss in the bGH mice was associated with elevated markers of inflammation and chondrocyte hypertrophy. Finally, hyperplasia of synovial cells was associated with increased expression of Ki-67 and diminished p53 levels in the synovium of bGH mice. Unlike the low-grade inflammation seen in primary osteoarthritis, arthropathy caused by excess GH affects all joint tissues and triggers severe inflammatory response. Data from this study suggest that treatment of acromegalic arthropathy should involve inhibition of ectopic chondrogenesis and chondrocyte hypertrophy.

Impact loading intensifies cortical bone (re)modeling and alters longitudinal bone growth of pubertal rats

Physical exercise is important for musculoskeletal development during puberty, which builds bone mass foundation for later in life. However, strenuous levels of training might bring adverse effects to bone health, reducing longitudinal bone growth. Animal models with various levels of physical exercise were largely used to provide knowledge to clinical settings. Experiments from our previous studies applied different levels of mechanical loading on rat tibia during puberty accompanied by weekly in vivo micro-CT scans. In the present article, we apply 3D image registration-based methods to retrospectively analyze part of the previously acquired micro-CT data. Longitudinal bone growth, growth plate thickness, and cortical bone (re)modeling were evaluated from rats' age of 28-77 days. Our results show that impact loading inhibited proximal bone growth throughout puberty. We hypothesize that impact loading might bring different growth alterations to the distal and proximal growth plates. High impact loading might lead to pathological consequence of osteochondrosis and catch-up growth due to growth inhibition. Impact loading also increased cortical bone (re)modeling before and after the peak proximal bone growth period of young rats, of which the latter case might be caused by the shift from modeling to remodeling as the dominant activity toward the end of rat puberty. We confirm that the tibial endosteum is more mechano-sensitive than the periosteum in response to mechanical loading. To our knowledge, this is the first study to follow up bone growth and bone (re)modeling of young rats throughout the entire puberty with a weekly time interval.

Validation of an in vivo micro-CT-based method to quantify longitudinal bone growth of pubertal rats

Bone growth is an essential part of skeletal development during childhood and puberty. Accurately characterizing longitudinal bone growth helps to better understand the determining factors of peak bone mass, which has impacts on bone quality later in life. Animal models were largely used to study longitudinal bone growth. However, the commonly used histology-based method is destructive and unable to follow up the growth curve of live animals in longitudinal experiments. In this study, we validated an in vivo micro-CT-based method against the histology-based method to quantify longitudinal bone growth rates of young rats non-destructively. CD (Sprague Dawley) IGS rats aged 35, 49 and 63 days received the same treatments: two series of repeated in vivo micro-CT scans on their proximal hind limb at a five-day interval, and two calcein injections separated by three days. The longitudinal bone growth rate was quantified by registering time-lapse micro-CT images in 3D, calculating the growth distance on registered images, and dividing the distance by the five-day gap. The growth rate was also evaluated by measuring the 2D distance between consecutive calcein fluorescent bands on microscopic images, divided by the three-day gap. The two methods were both validated independently with reproducible repeated measurements, where the micro-CT-based method showed higher precision. They were also validated against each other with low relative errors and a strong Pearson sample correlation coefficient (0.998), showing a significant (p < 0.0001) linear correlation between paired results. We conclude that the micro-CT-based method can serve as an alternative to the histology-based method for the quantification of longitudinal growth. Thanks to its non-invasive nature and true 3D capability, the micro-CT-based method helps to accommodate in vivo longitudinal animal studies with highly reproducible measurements.

Main and Minor Types of Collagens in the Articular Cartilage: The Role of Collagens in Repair Tissue Evaluation in Chondral Defects

Several collagen subtypes have been identified in hyaline articular cartilage. The main and most abundant collagens are type II, IX and XI collagens. The minor and less abundant collagens are type III, IV, V, VI, X, XII, XIV, XVI, XXII, and XXVII collagens. All these collagens have been found to play a key role in healthy cartilage, regardless of whether they are more or less abundant. Additionally, an exhaustive evaluation of collagen fibrils in a repaired cartilage tissue after a chondral lesion is necessary to determine the quality of the repaired tissue and even whether or not this repaired tissue is considered hyaline cartilage. Therefore, this review aims to describe in depth all the collagen types found in the normal articular cartilage structure, and based on this, establish the parameters that allow one to consider a repaired cartilage tissue as a hyaline cartilage.

Tumor Microenvironmental Competitive Endogenous RNA Network and Immune Cells Act as Robust Prognostic Predictor of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is malignant hematologic tumors with frequent recurrence and cause high mortality. Its fate is determined by abnormal intracellular competitive endogenous RNA (ceRNA) network and extracellular tumor microenvironment (TME). This study aims to build a ceRNA network related to AML TME to explore new prognostic and therapeutic targets. The RNA expression data of AML were obtained from The Cancer Genome Atlas (TCGA) database. First, we used the ESTIMATE algorithm to calculate the immune cells and stromal cells infiltration scores in the TME and found that all scores were highly correlated with AML’s prognostic characteristics. Subsequently, differentially expressed mRNAs and lncRNAs between high and low score groups were identified to construct a TME-related ceRNA network. Further, the Cox-lasso survival model was employed to screen out the hub prognostic ceRNA network composed of two mRNAs (EPB41L3, COL2A1), three miRNAs (hsa-mir-26a-5p, hsa-mir-148b-3p, hsa-mir-148a-3p), and two lncRNAs (CYP1B1-AS1, C9orf106), and construct nomograms. Finally, we used CIBERSORT algorithm and Kaplan-Meier survival analysis to identify the prognostic TME immune cells and found that naive B cells, M2-type macrophages, and helper follicular T cells were related to prognosis, and the hub ceRNAs were highly correlated with immune cell infiltration. This study provided a new perspective to elucidate how TME regulates AML process and put forward the new therapy strategies combining targeting tumor cells with disintegrating TME.

Nondestructive Assessment of Growing Rat Tibial Mechanical Properties Under Three-Point Bending: A Microcomputed Tomography Based Finite Element Study

Microcomputed tomography (micro-CT) based finite element models (FEM) are efficient tools to assess bone mechanical properties. Although they have been developed for different animal models, there is still a lack of data for growing rat long bone models. This study aimed at developing and calibrating voxel-based FEMs using micro-CT scans and experimental data. Twenty-four tibiae were extracted from rats aged 28, 56, and 84 days old (d.o.) (n = 8/group), and their stiffness values were evaluated using three-point bending tests. Prior to testing, tibiae were scanned, reconstructed, and converted into FEM composed of heterogeneous bone properties based on pixel grayscales. Three element material laws (one per group) were calibrated using back-calculation process based on experimental bending data. Two additional specimens per group were used for model verification. The calibrated rigidity-density (E-ρ) relationships were different for each group: E28 = 10,320·ρash3.45; E56 = 43,620·ρash4.41; E84 = 20,090·ρash2.0. Obtained correlations between experimental and FEM stiffness values were 0.43, 0.10, and 0.66 with root-mean-square error (RMSE) of 14.4%, 17.4%, and 15.2% for 28, 56, and 84 d.o. groups, respectively. Prediction errors were less than 13.5% for 28 and 84 d.o. groups but reached 57.1% for the 56 d.o. group. Relationships between bone physical and mechanical properties were found to change during the growth, similarly to bending stiffness values, which increased with bone development. The reduced correlation observed for the 56 d.o. group may be related to the pubescent transition at that age group. These FE models will be useful for investigation of bone behavior in growing rats.

Bone phenotypes in rheumatology - there is more to bone than just bone

Osteoarthritis, rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis, all have one clear common denominator; an altered turnover of bone. However, this may be more complex than a simple change in bone matrix and mineral turnover. While these diseases share a common tissue axis, their manifestations in the area of pathology are highly diverse, ranging from sclerosis to erosion of bone in different regions. The management of these diseases will benefit from a deeper understanding of the local versus systemic effects, the relation to the equilibrium of the bone balance (i.e., bone formation versus bone resorption), and the physiological and pathophysiological phenotypes of the cells involved (e.g., osteoblasts, osteoclasts, osteocytes and chondrocytes). For example, the process of endochondral bone formation in chondrocytes occurs exists during skeletal development and healthy conditions, but also in pathological conditions. This review focuses on the complex molecular and cellular taxonomy of bone in the context of rheumatological diseases that alter bone matrix composition and maintenance, giving rise to different bone turnover phenotypes, and how biomarkers (biochemical markers) can be applied to potentially describe specific bone phenotypic tissue profiles.

The Follistatin-like Protein 1 Pathway Is Important for Maintaining Healthy Articular Cartilage

OBJECTIVE

We sought to determine whether follistatin-like protein 1 (FSTL1), a protein produced by articular chondrocytes, promotes healthy articular cartilage and prevents chondrocytes from undergoing terminal differentiation to hypertrophic cells.

METHODS

In vitro experiments were performed with immortalized human articular chondrocytes. The cells were transduced with a lentivirus encoding human FSTL1 small hairpin RNA or with an adenovirus encoding FSTL1. A quantitative polymerase chain reaction was used for gene expression analysis. Protein expression was assessed by Western blotting. Co-immunoprecipitation was used to identify interacting partners of FSTL1. FSTL1 expression in human articular cartilage was analyzed using confocal microscopy.

RESULTS

Downregulation of FSTL1 expression in transforming growth factor β (TGFβ)-stimulated chondrocyte pellet cultures led to chondrocyte terminal differentiation characterized by poor production of cartilage extracellular matrix and altered expression of genes and proteins involved in cartilage homeostasis, including MMP13, COL10A1, RUNX2, COL2A1, ACAN, Sox9, and phospho-Smad3. We also showed that FSTL1 interacts with TGFβ receptor proteins, Alk1 and endoglin, suggesting a potential mechanism for its effects on chondrocytes. Transduction of chondrocytes with an FSTL1 transgene increased COL2A1 expression, whereas it did not affect MMP13 expression. FSTL1 protein expression was decreased in human osteoarthritic cartilage in situ.

CONCLUSION

Our data suggest that FSTL1 plays an important role in maintaining healthy articular cartilage and the FSTL1 pathway may represent a therapeutic target for degenerative diseases of cartilage.

Use of Computational Modeling to Study Joint Degeneration: A Review

Osteoarthritis (OA), a degenerative joint disease, is the most common chronic condition of the joints, which cannot be prevented effectively. Computational modeling of joint degradation allows to estimate the patient-specific progression of OA, which can aid clinicians to estimate the most suitable time window for surgical intervention in osteoarthritic patients. This paper gives an overview of the different approaches used to model different aspects of joint degeneration, thereby focusing mostly on the knee joint. The paper starts by discussing how OA affects the different components of the joint and how these are accounted for in the models. Subsequently, it discusses the different modeling approaches that can be used to answer questions related to OA etiology, progression and treatment. These models are ordered based on their underlying assumptions and technologies: musculoskeletal models, Finite Element models, (gene) regulatory models, multiscale models and data-driven models (artificial intelligence/machine learning). Finally, it is concluded that in the future, efforts should be made to integrate the different modeling techniques into a more robust computational framework that should not only be efficient to predict OA progression but also easily allow a patient’s individualized risk assessment as screening tool for use in clinical practice.

NF-κB Signaling Pathways in Osteoarthritic Cartilage Destruction

Osteoarthritis (OA) is a type of joint disease associated with wear and tear, inflammation, and aging. Mechanical stress along with synovial inflammation promotes the degradation of the extracellular matrix in the cartilage, leading to the breakdown of joint cartilage. The nuclear factor-kappaB (NF-κB) transcription factor has long been recognized as a disease-contributing factor and, thus, has become a therapeutic target for OA. Because NF-κB is a versatile and multi-functional transcription factor involved in various biological processes, a comprehensive understanding of the functions or regulation of NF-κB in the OA pathology will aid in the development of targeted therapeutic strategies to protect the cartilage from OA damage and reduce the risk of potential side-effects. In this review, we discuss the roles of NF-κB in OA chondrocytes and related signaling pathways, including recent findings, to better understand pathological cartilage remodeling and provide potential therapeutic targets that can interfere with NF-κB signaling for OA treatment.

miR-195 contributes to human osteoarthritis via targeting PTHrP

The dysregulated expression of the osteoarthritis (OA)-related genes in cartilage, such as matrix metalloproteinase 13 (MMP-13) and type X collagen (Col X), facilitates the onset and progression of OA. Reduced parathyroid hormone-related protein (PTHrP) may also accelerate this progression. Furthermore, miRNAs, endogenous regulators of mRNAs, are thought to play key roles in the pathogenesis of OA. In this study, we found that miR-195 levels were significantly upregulated in OA tissue, while PTHrP mRNA/protein expression was substantially downregulated, and there was a negative correlation between miR-195 and PTHrP. Upregulated miR-195 strongly inhibited Aggrecan, type II collagen (Col II) mRNA/protein expression, while it enhanced the expression of MMP-13 and Col X at mRNA/protein level; conversely, downregulated miR-195 significantly increased Col II mRNA/protein expression, while it decreased the expression of MMP-13 and Col X mRNA/protein. Moreover, our study demonstrated that PTHrP is a novel target of miR-195 using dual luciferase reporter assay. Finally, miR-195-mediated changes of Col II and OA-related genes were substantially attenuated by siRNA_PTHrP treatment. These results suggested that miR-195 is involved in the pathogenesis of OA via PTHrP.

Postnatal ex vivo rat model for longitudinal bone growth investigations

BACKGROUND

Chondrocytes in the growth plate (GP) undergo increases in volume during different cascades of cell differentiation during longitudinal bone growth. The volume increase is reported to be the most significant variable in understanding the mechanism of long bone growth.

METHODS

Forty-five postnatal Sprague-Dawley rat pups, 7-15 days old were divided into nine age groups (P7-P15). Five pups were allocated to each group. The rats were sacrificed and tibia and metatarsal bones were harvested. Bone lengths were measured after 0, 24, 48, and 72 hours of ex vivo incubation. Histology of bones was carried out, and GP lengths and chondrocyte densities were determined.

RESULTS

There were significant differences in bone length among the age groups after 0 and 72 hours of incubation. Histological sectioning was possible in metatarsal bone from all age groups, and in tibia from 7- to 13-day-old rats. No significant differences in tibia and metatarsal GP lengths were seen among different age groups at 0 and 72 hours of incubation. Significant differences in chondrocyte densities along the epiphyseal GP of the bones between 0 and 72 hours of incubation were observed in most of the age groups.

CONCLUSION

Ex vivo growth of tibia and metatarsal bones of rats aged 7-15 days old is possible, with percentage growth rates of 23.87 ± 0.80% and 40.38 ± 0.95% measured in tibia and metatarsal bone, respectively. Histological sectioning of bones was carried out without the need for decalcification in P7-P13 tibia and P7-P15 metatarsal bone. Increases in chondrocyte density along the GP influence overall bone elongation.

Diazoxide ameliorates severity of experimental osteoarthritis by activating autophagy via modulation of the osteoarthritis-related biomarkers

Accumulating evidence suggests that autophagy plays a protective role in chondrocytes and prevents cartilage degeneration in osteoarthritis (OA). The objective of this study was to investigate the effect of diazoxide on chondrocyte death and cartilage degeneration and to determine whether these effects are correlated to autophagy in experimental OA. In this study, a cellular OA model was established by stimulating SW1353 cells with interleukin 1β. A rat OA model was generated by transecting the anterior cruciate ligament combined with the resection of the medial menisci, followed by treatment with diazoxide or diazoxide combination with 3-methyladenine. The percentage of viable cells was evaluated using calcein-acetoxymethyl/propidium iodide double staining. The messenger RNA expression levels of collagen type II alpha 1 chain (COL2A1), matrix metalloproteinase 13 (MMP-13), TIMP metallopeptidase inhibitor 1 (TIMP-1), and a disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS5) were determined using quantitative real-time polymerase chain reaction. The cartilage thickness and joint space were evaluated using ultrasound. SW1353 cell degeneration and autophagosomes were observed using transmission electron microscopy. The expression levels of microtubule-associated protein 1 light chain 3 (LC3), beclin-1, P62, COL2A1, and MMP-13 were evaluated using immunofluorescence staining and Western blot analysis. Diazoxide significantly attenuated articular cartilage degeneration and SW1353 cell death in experimental OA. The restoration of autophagy was observed in the diazoxide-treated group. The beneficial effects of diazoxide were markedly blocked by 3-methyladenine. Diazoxide treatment also modulated the expression levels of OA-related biomarkers. These results demonstrated that diazoxide exerted a chondroprotective effect and attenuated cartilage degeneration by restoring autophagy via modulation of OA-related biomarkers in experimental OA. Diazoxide treatment might be a promising therapeutic approach to prevent the development of OA.

Biological effect of hydrolyzed collagen on bone metabolism

Osteoporosis is a chronic and asymptomatic disease characterized by low bone mass and skeletal microarchitectural deterioration, increased risk of fracture, and associated comorbidities most prevalent in the elderly. Due to an increasingly aging population, osteoporosis has become a major health issue requiring innovative disease management. Proteins are important for bone by providing building blocks and by exerting specific regulatory function. This is why adequate protein intake plays a considerable role in both bone development and bone maintenance. More specifically, since an increase in the overall metabolism of collagen can lead to severe dysfunctions and a more fragile bone matrix and because orally administered collagen can be digested in the gut, cross the intestinal barrier, enter the circulation, and become available for metabolic processes in the target tissues, one may speculate that a collagen-enriched diet provides benefits for the skeleton. Collagen-derived products such as gelatin or hydrolyzed collagen (HC) are well acknowledged for their safety from a nutritional point of view; however, what is their impact on bone biology? In this manuscript, we critically review the evidence from literature for an effect of HC on bone tissues in order to determine whether HC may represent a relevant alternative in the design of future nutritional approaches to manage osteoporosis prevention.

The minor collagens in articular cartilage

Articular cartilage is a connective tissue consisting of a specialized extracellular matrix (ECM) that dominates the bulk of its wet and dry weight. Type II collagen and aggrecan are the main ECM proteins in cartilage. However, little attention has been paid to less abundant molecular components, especially minor collagens, including type IV, VI, IX, X, XI, XII, XIII, and XIV, etc. Although accounting for only a small fraction of the mature matrix, these minor collagens not only play essential structural roles in the mechanical properties, organization, and shape of articular cartilage, but also fulfil specific biological functions. Genetic studies of these minor collagens have revealed that they are associated with multiple connective tissue diseases, especially degenerative joint disease. The progressive destruction of cartilage involves the degradation of matrix constituents including these minor collagens. The generation and release of fragmented molecules could generate novel biochemical markers with the capacity to monitor disease progression, facilitate drug development and add to the existing toolbox for in vitro studies, preclinical research and clinical trials.

Anatomical Localization of Cartilage Degradation Markers in a Surgically Induced Rat Osteoarthritis Model

Osteoarthritis (OA) is a degenerative disease characterized by an irreversible loss of articular cartilage. Although surgically induced animal OA models are commonly used in drug efficacy assessment, degradation of type II collagen, an important component of articular cartilage is not routinely evaluated. Here, the medial meniscectomy surgical model (MMT) in Lewis rats was evaluated for proteoglycan loss with toluidine blue staining and collagen degradation with immunohistochemical staining for a collagen cleavage C-neoepitope, using a novel anti-type II collagen neoepitope antigen (TIINE) antibody. Femorotibial joints were collected for histology at 0 (no surgery), 3, 7, 14, 21, 28, 35, and 42 days postsurgery. Following MMT surgery, the medial tibial articular cartilage had proteoglycan matrix loss by day 3 that reached subchondral bone by days 28–42. Femoral cartilage damage occurred by day 14. TIINE staining was present at basal levels in growth plates and articular cartilage of all joints while all MMT-treated animals had increased intensity and area of staining in erosions that colocalized with proteoglycan loss. The MMT model produces a progressive pattern of cartilage damage resembling human OA lesions, making it useful, when evaluated with cartilage biomarkers, for assessing changes in cartilage degradation.

Intra-articular injection of Torin 1 reduces degeneration of articular cartilage in a rabbit osteoarthritis model

Objectives

Recent studies have shown that systemic injection of rapamycin can prevent the development of osteoarthritis (OA)-like changes in human chondrocytes and reduce the severity of experimental OA. However, the systemic injection of rapamycin leads to many side effects. The purpose of this study was to determine the effects of intra-articular injection of Torin 1, which as a specific inhibitor of mTOR which can cause induction of autophagy, is similar to rapamycin, on articular cartilage degeneration in a rabbit osteoarthritis model and to investigate the mechanism of Torin 1’s effects on experimental OA.

Methods

Collagenase (type II) was injected twice into both knees of three-month-old rabbits to induce OA, combined with two intra–articular injections of Torin 1 (400 nM). Degeneration of articular cartilage was evaluated by histology using the Mankin scoring system at eight weeks after injection. Chondrocyte degeneration and autophagosomes were observed by transmission electron microscopy. Matrix metallopeptidase-13 (MMP-13) and vascular endothelial growth factor (VEGF) expression were analysed by quantitative RT-PCR (qPCR).Beclin-1 and light chain 3 (LC3) expression were examined by Western blotting.

Results

Intra-articular injection of Torin 1 significantly reduced degeneration of the articular cartilage after induction of OA. Autophagosomes andBeclin-1 and LC3 expression were increased in the chondrocytes from Torin 1-treated rabbits. Torin 1 treatment also reduced MMP-13 and VEGF expression at eight weeks after collagenase injection.

Conclusion

Our results demonstrate that intra-articular injection of Torin 1 reduces degeneration of articular cartilage in collagenase-induced OA, at least partially by autophagy activation, suggesting a novel therapeutic approach for preventing cartilage degeneration and treating OA.

Cite this article: N-T. Cheng, A. Guo, Y-P. Cui. Intra-articular injection of Torin 1 reduces degeneration of articular cartilage in a rabbit osteoarthritis model. Bone Joint Res 2016;5:218–224. DOI: 10.1302/2046-3758.56.BJR-2015-0001.

Local intra-articular injection of rapamycin delays articular cartilage degeneration in a murine model of osteoarthritis

Introduction

Recent studies have revealed that rapamycin activates autophagy in human chondrocytes preventing the development of osteoarthritis (OA) like changes in vitro, while the systemic injection of rapamycin reduces the severity of experimental osteoarthritis in a murine model of OA in vivo. Since the systemic use of rapamycin is associated with numerous side effects, the goal of the current study was to examine the beneficial effect of local intra-articular injection of rapamycin in a murine model of OA and to elucidate the mechanism of action of rapamycin on articular cartilage.

Methods

Destabilization of the medial meniscus (DMM) was performed on 10-week-old male mice to induce OA. Intra-articular injections of 10 μl of rapamycin (10 μM) were administered twice weekly for 8 weeks. Articular cartilage damage was analyzed by histology using a semi-quantitative scoring system at 8 and 12 weeks after surgery. Mammalian target of rapamycin (mTOR), light chain 3 (LC3), vascular endothelial growth factor (VEGF), collagen, type X alpha 1 (COL10A1), and matrix metallopeptidase 13 (MMP13) expressions were analyzed by immunohistochemistry. VEGF, COL10A1, and MMP13 expressions were further examined via quantitative RT-PCR (qPCR).

Results

Intra-articular injection of rapamycin significantly reduced the severity of articular cartilage degradation at 8 and 12 weeks after DMM surgery. A reduction in mTOR expression and the activation of LC3 (an autophagy marker) in the chondrocytes was observed in the rapamycin treated mice. Rapamycin treatment also reduced VEGF, COL10A1, and MMP13 expressions at 8 and 12 weeks after DMM surgery.

Conclusion

These results demonstrate that the intra-articular injection of rapamycin could reduce mTOR expression, leading to a delay in articular cartilage degradation in our OA murine model. Our observations suggest that local intra-articular injection of rapamycin could represent a potential therapeutic approach to prevent OA.

In vivo dynamic loading reduces bone growth without histomorphometric changes of the growth plate

This in vivo study aimed at investigating the effects of dynamic compression on the growth plate. Rats (28 days old) were divided into three dynamically loaded groups, compared with two groups (control, sham). A device was implanted on the 6th and 8th caudal vertebrae for 15 days. Controls (n = 4) did not undergo surgery. Shams (n = 4) were operated but not loaded. Dynamic groups had sinusoidal compression with a mean value of 0.2 MPa: 1.0 Hz and ± 0.06 MPa (group a, n = 4); 0.1 Hz and ± 0.2 MPa (group b, n = 4); 1.0 Hz and ± 0.14 MPa (group c, n = 3). Growth rates (µm/day) of dynamic groups (a) and (b) were lower than shams (p < 0.01). Growth plate heights, hypertrophic cell heights and proliferative cell counts per column did not change in dynamic (a) and (b) groups compared with shams (p > 0.01). Rats from dynamic group (c) had repeated inflammations damaging tissues; consequently, their analysis was unachievable. Increasing magnitude or frequency leads to growth reduction without histomorphometric changes. However, the combined augmentation of magnitude and frequency alter drastically growth plate integrity. Appropriate loading parameters could be leveraged for developing novel growth modulation implants to treat skeletal deformities.

Bone sialoprotein as a potential key factor implicated in the pathophysiology of osteoarthritis

OBJECTIVE

We previously identified an association between bone sialoprotein (BSP) and osteoarthritic (OA) chondrocyte hypertrophy but the precise role of BSP in ostearthritis (OA) has not been extensively studied. This study aimed to confirm the association between BSP and OA chondrocyte hypertrophy, to define its effect on molecules produced by chondrocytes and to analyse its association with cartilage degradation and vascular density at the osteochondral junction.

METHOD

Human OA chondrocytes were cultivated in order to increase hypertrophic differentiation. The effect of parathyroid hormone-related peptide (PTHrP), interleukin (IL)-1β or tumour necrosis factor (TNF)-α on BSP was analysed by real-time reverse transcription polymerase chain reaction (RT-PCR) and western blot. The effects of BSP on OA chondrocytes production of inflammatory response mediators (IL-6, nitric oxide), major matrix molecule (aggrecan), matrix metalloprotease-3 and angiogenic factors (vascular endothelial growth factor, basic fibroblast growth factor, IL-8, and thrombospondin-1) were investigated. BSP was detected by immunohistochemistry and was associated with cartilage lesions severity and vascular density.

RESULTS

PTHrP significantly decreased BSP, confirming its association with chondrocyte hypertrophy. In presence of IL-1β, BSP stimulated IL-8 synthesis, a pro-angiogenic cytokine but decreased the production of TSP-1, an angiogenesis inhibitor. The presence of BSP-immunoreactive chondrocytes in cartilage was associated with the severity of histological cartilage lesions and with vascular density at the osteochondral junction.

CONCLUSION

This study supports the implication of BSP in the pathology of OA and suggests that it could be a key mediator of the hypertrophic chondrocytes-induced angiogenesis. To control chondrocyte hypertrophic differentiation is promising in the treatment of OA.

Decreased hypertrophic differentiation accompanies enhanced matrix formation in co-cultures of outer meniscus cells with bone marrow mesenchymal stromal cells

Introduction

The main objective of this study was to determine whether meniscus cells from the outer (MCO) and inner (MCI) regions of the meniscus interact similarly to or differently with mesenchymal stromal stem cells (MSCs). Previous study had shown that co-culture of meniscus cells with bone marrow-derived MSCs result in enhanced matrix formation relative to mono-cultures of meniscus cells and MSCs. However, the study did not examine if cells from the different regions of the meniscus interacted similarly to or differently with MSCs.

Methods

Human menisci were harvested from four patients undergoing total knee replacements. Tissue from the outer and inner regions represented pieces taken from one third and two thirds of the radial distance of the meniscus, respectively. Meniscus cells were released from the menisci after collagenase treatment. Bone marrow MSCs were obtained from the iliac crest of two patients after plastic adherence and in vitro culture until passage 2. Primary meniscus cells from the outer (MCO) or inner (MCI) regions of the meniscus were co-cultured with MSCs in three-dimensional (3D) pellet cultures at 1:3 ratio, respectively, for 3 weeks in the presence of serum-free chondrogenic medium containing TGF-β1. Mono-cultures of MCO, MCI and MSCs served as experimental control groups. The tissue formed after 3 weeks was assessed biochemically, histochemically and by quantitative RT-PCR.

Results

Co-culture of inner (MCI) or outer (MCO) meniscus cells with MSCs resulted in neo-tissue with increased (up to 2.2-fold) proteoglycan (GAG) matrix content relative to tissues formed from mono-cultures of MSCs, MCI and MCO. Co-cultures of MCI or MCO with MSCs produced the same amount of matrix in the tissue formed. However, the expression level of aggrecan was highest in mono-cultures of MSCs but similar in the other four groups. The DNA content of the tissues from co-cultured cells was not statistically different from tissues formed from mono-cultures of MSCs, MCI and MCO. The expression of collagen I (COL1A2) mRNA increased in co-cultured cells relative to mono-cultures of MCO and MCI but not compared to MSC mono-cultures. Collagen II (COL2A1) mRNA expression increased significantly in co-cultures of both MCO and MCI with MSCs compared to their own controls (mono-cultures of MCO and MCI respectively) but only the co-cultures of MCO:MSCs were significantly increased compared to MSC control mono-cultures. Increased collagen II protein expression was visible by collagen II immuno-histochemistry. The mRNA expression level of Sox9 was similar in all pellet cultures. The expression of collagen × (COL10A1) mRNA was 2-fold higher in co-cultures of MCI:MSCs relative to co-cultures of MCO:MSCs. Additionally, other hypertrophic genes, MMP-13 and Indian Hedgehog (IHh), were highly expressed by 4-fold and 18-fold, respectively, in co-cultures of MCI:MSCs relative to co-cultures of MCO:MSCs.

Conclusions

Co-culture of primary MCI or MCO with MSCs resulted in enhanced matrix formation. MCI and MCO increased matrix formation similarly after co-culture with MSCs. However, MCO was more potent than MCI in suppressing hypertrophic differentiation of MSCs. These findings suggest that meniscus cells from the outer-vascular regions of the meniscus can be supplemented with MSCs in order to engineer functional grafts to reconstruct inner-avascular meniscus.

Structured three-dimensional co-culture of mesenchymal stem cells with meniscus cells promotes meniscal phenotype without hypertrophy

Menisci play a crucial role in weight distribution, load bearing, shock absorption, lubrication, and nutrition of articular cartilage within the knee joint. Damage to the meniscus typically does not heal spontaneously due to its partial avascular nature. Partial or complete meniscectomy is a common clinical treatment of the defective meniscus. However, this procedure ultimately leads to osteoarthritis due to increased mechanical stress to the articular cartilage. Meniscus tissue engineering offers a promising solution for partial or complete meniscus deficiency. Mesenchymal stem cells (MSC) have the potential to differentiate into meniscal fibrochondrocyte as well as deliver trophic effects to the differentiated cells. This study tested the feasibility of using MSC co-cultured with mature meniscal cells (MC) for meniscus tissue engineering. Structured cell pellets were created using MC and MSC at varying ratios (100:0, 75:25, 50:50, 25:75, and 0:100) and cultured with or without transforming growth factor-beta 3 supplemented chondrogenic media for 21 days. The meniscal and hypertrophic gene expression, gross appearance and structure of the pellets, meniscus extracellular matrix (ECM), histology and immunohistochemistry of proteoglycan and collagen were evaluated. Co-culture of MC with MSC at 75:25 demonstrated highest levels of collagen type I and glycosaminoglycans (GAG) production, as well as the lowest levels of hypertrophic genes, such as COL10A1 and MMP13. All co-culture conditions showed better meniscus ECM production and hypertrophic inhibition as compared to MSC culture alone. The collagen fiber bundles observed in the co-cultures are important to produce heterogenic ECM structure of meniscus. In conclusion, co-culturing MC and MSC is a feasible and efficient approach to engineer meniscus tissue with enhanced ECM production without hypertrophy.

Chondrocyte hypertrophy and osteoarthritis: role in initiation and progression of cartilage degeneration?

OBJECTIVE

To review the literature on the role and regulation of chondrocyte terminal differentiation (hypertrophy-like changes) in osteoarthritis (OA) and to integrate this in a conceptual model of primary OA development.

METHODS

Papers investigating chondrocyte terminal differentiation in human OA cartilage and experimental models of OA were recapitulated and discussed. Focus has been on the occurrence of hypertrophy-like changes in chondrocytes and the factors described to play a role in regulation of chondrocyte hypertrophy-like changes in OA.

RESULTS

Chondrocyte hypertrophy-like changes are reported in both human OA and experimental OA models by most investigators. These changes play a crucial part in the OA disease process by protease-mediated cartilage degradation. We propose that altered chondrocyte behavior and concomitant cartilage degradation result in a disease-amplifying loop, leading to a mixture of disease stages and cellular responses within an OA joint.

CONCLUSION

Chondrocyte hypertrophy-like changes play a role in early and late stage OA. Since not all cells in an OA joint are synchronized, inhibition of hypertrophy-like changes might be a therapeutic target to slow down further OA progression.

In vivo dynamic bone growth modulation is less detrimental but as effective as static growth modulation

Longitudinal bone growth, which occurs in growth plates, has important implications in pediatric orthopedics. Mechanical loads are essential to normal bone growth, but excessive loads can lead to progressive deformities. In order to compare the effects of in vivo static and dynamic loading on bone growth rate and growth plate histomorphometry, a finely controlled, normalized and equivalent compression was applied for a period of two weeks on the seventh caudal vertebra (Cd7) of rats during their pubertal growth spurt. The load was sustained (0.2MPa, 0.0Hz) in the static group and sinusoidally oscillating (0.2MPa±30%, 0.1Hz) in the dynamic group. Control and sham (operated but no load applied) groups were also studied. Cd7 growth rate was statistically reduced by 19% (p<0.001) for both static and dynamic groups when compared to the sham group. Loading effects on growth plate histomorphometry were greater in the static than dynamic groups with significant reductions (p<0.001) observed for growth plate thickness, proliferative chondrocyte number per column and hypertrophic chondrocyte height in the static group when compared to the sham group. Significant differences (p<0.01) were also found between static and dynamic groups for growth plate thickness and proliferative chondrocyte number per column while the difference nearly reached significance (p=0.014) for hypertrophic chondrocyte height. This in vivo study shows that static and dynamic loading are equally effective in modulating bone growth of rat caudal vertebrae. However, dynamic loading causes less detrimental effects on growth plate histomorphometry compared to static loading. This knowledge is greatly relevant for the improvement and/or development of new minimally invasive approaches, which are based on the local modulation of bone growth, to correct several progressive musculoskeletal deformities.

Growth plate explants respond differently to in vitro static and dynamic loadings

This study aimed at investigating the effects of static and dynamic compression applied on growth plate explants using matched compressive strains. Growth plate explants from 4-week-old swine ulnae were submitted to in vitro static (10% strain) or dynamic (oscillating between 7% and 13% at 0.1 Hz) unconfined compression for 48 h. The total growth plate height, the combined proliferative and hypertrophic thickness and the resulting ratio between these two thicknesses were evaluated. Standard immunohistochemistry was used to analyze the protein expression of key components of the extracellular matrix: aggrecan, type II collagen, type X collagen, and MMP13. In the statically loaded samples, the columnar organization of the cells was preserved but with slight columns deviation from the growth axis. Decreases in all histomorphological parameters were important and a notable loss of aggrecan, type II and type X collagens expressions was denoted. In the dynamically loaded samples, a severe loss of columnar arrangement was observed in the proliferative and hypertrophic zones. However, dynamic compressive loads preserved the proliferative and hypertrophic zones ratio and contributed to the synthesis of aggrecan and type II collagen in the extracellular matrix. The exact response of the growth plate to mechanical stresses along with optimal loading parameters could help improve the current treatment approaches or develop new treatment approaches for the underlying progressive musculoskeletal deformities.

Expression of Runx2 and type X collagen in vertebral growth plate of patients with adolescent idiopathic scoliosis

The different expression of type X collagen and Runx2 between the convex and concave side of vertebral growth plate in scoliosis may help to improve our understanding of the role that growth plate tissue play in the development or progression of idiopathic scoliosis. In this investigation, there were significant differences of the total expression of type X collagen, Runx2 protein, and Runx2 mRNA between convex side and concave side growth plates of the apex vertebrae (p < 0.05). The total expression of type X collagen in the concave side growth plates of the lower end vertebrae was higher than that in the same side growth plates of apex (p < 0.05). The total expression of Runx2 in the concave side growth plates in the upper and lower end vertebrae were higher than that in the concave side growth plates of apex (p < 0.05). The expression of type X collagen, Runx2, and Runx2 mRNA, the cell density of type X collagen and Runx2 positive chondrocytes, and histological changes between convex side and concave side of the vertebral growth plate indicated that the vertebral growth plate was affected by mechanical forces, which was a secondary change and could contribute to progression of adolescent idiopathic scoliosis.

Growth plate mechanics and mechanobiology. A survey of present understanding

The longitudinal growth of long bones occurs in growth plates where chondrocytes synthesize cartilage that is subsequently ossified. Altered growth and subsequent deformity resulting from abnormal mechanical loading is often referred to as mechanical modulation of bone growth. This phenomenon has key implications in the progression of infant and juvenile musculoskeletal deformities, such as adolescent idiopathic scoliosis, hyperkyphosis, genu varus/valgus and tibia vara/valga, as well as neuromuscular diseases. Clinical management of these deformities is often directed at modifying the mechanical environment of affected bones. However, there is limited quantitative and physiological understanding of how bone growth is regulated in response to mechanical loading. This review of published work addresses the state of knowledge concerning key questions about mechanisms underlying biomechanical modulation of bone growth. The longitudinal growth of bones is apparently controlled by modifying the numbers of growth plate chondrocytes in the proliferative zone, their rate of proliferation, the amount of chondrocytic hypertrophy and the controlled synthesis and degradation of matrix throughout the growth plate. These variables may be modulated to produce a change in growth rate in the presence of sustained or cyclic mechanical load. Tissue and cellular deformations involved in the transduction of mechanical stimuli depend on the growth plate tissue material properties that are highly anisotropic, time-dependent, and that differ in different zones of the growth plate and with developmental stages. There is little information about the effects of time-varying changes in volume, water content, osmolarity of matrix, etc. on differentiation, maturation and metabolic activity of chondrocytes. Also, the effects of shear forces and torsion on the growth plate are incompletely characterized. Future work on growth plate mechanobiology should distinguish between changes in the regulation of bone growth resulting from different processes, such as direct stimulation of the cell nuclei, physico-chemical stimuli, mechanical degradation of matrix or cellular components and possible alterations of local blood supply.

Skeletal unloading induces a full-thickness patellar cartilage defect with increase of urinary collagen II CTx degradation marker in growing rats

Mechanical stress plays an important role in tissue morphogenesis and extracellular matrix metabolism. However, little is known about the effects of reduced loading without restriction of joint motion on the patella. We investigated the effects of long-term skeletal unloading on patellar cartilage and subchondral bone and systemic collagen II metabolism. Nine-week-old male F344/N rats (n=128) were randomly divided into two groups: caged control (C) and tail suspended (TS). Hindlimbs of the TS rats were subjected to unloading for up to 12 weeks. Sequential changes in the patellar cartilage and subchondral bone were analyzed macroscopically, by pathological findings and histomorphologically. All animals received double tidemark fluorochrome labeling prior to sacrifice. Glycosaminoglycan (GAG) content in patellar cartilage, cross-linked C-telopeptide of type II collagen (CTx-II) in 24-h urine and type II procollagen-C-peptide (pCol-II-C) in sera were also measured by DMB assay, ELISA and EIA, respectively. In the TS group, GAG content was significantly reduced only during the first 3 weeks. No further significant decrease was found. Alkaline phosphatase (ALP) activity was increased, especially at the deep zone. Tidemark mineral apposition rate (MAR) was temporally increased, which resulted in an increase in the ratio of calcified cartilage to the entire cartilage. In the medial part, in addition, thickness of the entire cartilage was decreased by temporal acceleration of subchondral ossification advancement and, in the medial margin, a full-thickness cartilage defect was revealed in 88.6% of TS rats. However, the remaining articular surface was free from fibrillation. While urinary CTx-II was significantly increased during the experimental periods, serum pCol-II-C was significantly decreased at the early phase. There were significant correlations between the urinary CTx-II levels and tidemark MAR. Our results provided evidence that skeletal unloading increased ALP activity at the deep zone and temporally accelerated tidemark advancement associated with a decrease in proteoglycan content. In addition, skeletal unloading temporally accelerated subchondral ossification advancement in the medial part of the patella and finally induced a full-thickness patellar cartilage defect without any fibrillation at the remaining articular surface by additional subchondral bone modeling and possible retarded cartilage growth, which was through a different mechanism than overloading.

Effects of in vivo static compressive loading on aggrecan and type II and X collagens in the rat growth plate extracellular matrix

Mechanical loads are essential to normal bone growth, but excessive loads can lead to progressive deformities. In addition, growth plate extracellular matrix remodelling is essential to regulate the normal longitudinal bone growth process and to ensure physiological bone mineralization. In order to investigate the effects of static compression on growth plate extracellular matrix using an in vivo animal model, a loading device was used to precisely apply a compressive stress of 0.2 MPa for two weeks on the seventh caudal vertebra (Cd7) of rats during the pubertal growth spurt. Control, sham and loaded groups were studied. Growth modulation was quantified based on calcein labelling, and three matrix components (type II and X collagens, and aggrecan) were assessed using immunohistochemistry/safranin-O staining. As well, extracellular matrix components and enzymes (MMP-3 and -13, ADAMTS-4 and -5) were studied by qRT-PCR. Loading reduced Cd7 growth by 29% (p<0.05) and 15% (p=0.07) when compared to controls and shams respectively. No significant change could be observed in the mRNA expression of collagens and the proteolytic enzyme MMP-13. However, MMP-3 was significantly increased in the loaded group as compared to the control group (p<0.05). No change was observed in aggrecan and ADAMTS-4 and -5 expression. Low immunostaining for type II and X collagens was observed in 83% of the loaded rats as compared to the control rats. This in vivo study shows that, during pubertal growth spurt, two-week static compression reduced caudal vertebrae growth rates; this mechanical growth modulation occurred with decreased type II and X collagen proteins in the growth plate.

Analyses of early events during chondrogenic repair in rat full-thickness articular cartilage defects

In this study we investigated the cellular events that occur during the onset of chondrogenic differentiation during the repair of full-thickness defects of articular cartilage. The V-shaped full-thickness cartilage defects (width 0.7 or 1.5 mm; depth 0.8 mm; length 4 mm) were created in the femoral patellar groove of rats using a custom-built twin-blade device. The time course of the repair response in these cartilage defects was examined using a semi-quantitative histological grading scale. Cartilaginous repair responses failed to occur in the larger 1.5 mm defects, which was covered only by fibrous scar tissue. In contrast, hyaline-like articular cartilage was regenerated concomitantly with the repair of the subchondral bone by 4 weeks in smaller 0.7 mm width defects. Cells in the reparative regions were then characterized by immunohistochemistry and in situ hybridization. Undifferentiated mesenchymal cells migrate into the defects and fill the cavities within 4 days of their creation. The expression of PCNA, N-cadherin, and PTH/PTHrP receptors was induced in cells at the center of the defects, where type II collagen-positive polygonal-shaped cells also begin to appear at day 7. Marrow-derived mesenchymal cells acquire higher levels of proliferative activity in induced cartilage cavities after their initial migration and filling of the smaller 0.7 mm defects. During the regenerative repair of articular cartilage in the rat, there is a distinctive step that appears to be analogous to the precartilaginous condensation that is pivotal during chondrogenesis in development.

A novel fusionless vertebral physeal device inducing spinal growth modulation for the correction of spinal deformities

Current fusionless scoliosis surgical techniques span the intervertebral disc. This alters the spine stiffness, disc pressure equilibrium and possibly may lead to disc degeneration. A new fusionless physeal device was developed that locally modulates vertebral growth by compressing the physeal ring, while maintaining maximum segmental spinal mobility without spanning the intervertebral disc. This study's objective was to test the feasibility of the device on a small animal model by inducing a scoliotic deformity (inverse approach) while analyzing the growth modifications. This study was conducted on caudal vertebrae of 21 rats (26-day-old) divided into 3 groups: (1) "experimental" (n = 11) with 4 instrumented vertebrae, (2) sham (n = 5) and (3) control (n = 5). Radiographs were taken at regular intervals during the 7-week experimental period. Tissues were embedded in methyl metacrylate (MMA), prepared by the cutting/grinding method, and then stained (Toluidine blue). The discs physiological alterations were qualitatively assessed and classified by inspection of the histological sections. A mean maximum Cobb angle of 30 masculine (+/-6 masculine) and a mean maximum vertebral wedge angle of 10 masculine (+/-3 masculine) were obtained between the 23rd and 35th day postoperative in the subgroup that underwent a long-term response from the device. The sham group underwent no growth alterations when compared to the control group. Descriptive histological analyses of the operated segments showed that 69% had no alterations to the intervertebral disc. This study presents experimental evidence that the device induces a significant and controlled wedging of the vertebrae while maintaining regular flexibility. In most discs, there were no visible morphological alterations induced. Further analysis of the discs and testing of this device on a larger animal is recommended with the long-term objective of developing an early treatment of progressive idiopathic scoliosis.

Passage and reversal effects on gene expression of bovine meniscal fibrochondrocytes

The knee meniscus contains a mixed population of cells that exhibit fibroblastic as well as chondrocytic characteristics. Tissue engineering studies and future therapies for the meniscus require a large population of cells that are seeded on scaffolds. To achieve this, monolayer expansion is often used as a technique to increase cell number. However, the phenotype of these cells may be significantly different from that of the primary population. The objective of this study was to investigate changes in meniscal fibrochondrocytes at the gene expression level over four passages using quantitative real-time reverse transcriptase polymerase chain reaction. Cells from the inner two-thirds of bovine medial menisci were used. Four extracellular matrix (ECM) molecules, commonly found in the meniscus, were investigated, namely collagen I, collagen II, aggrecan and cartilage oligomeric matrix protein (COMP). In addition, primary and passaged meniscus fibrochondrocytes were placed on surfaces coated with collagen I or aggrecan protein to investigate whether any gene expression changes resulting from passage could be reversed. Collagen I expression was found to increase with the number of passages, whereas collagen II and COMP expression decreased. Collagen I and aggrecan surface coatings were shown to downregulate and upregulate collagen I and COMP expression levels, respectively, in passaged cells. However, decreases in collagen II expression could not be reversed by either protein coating. These results indicate that although monolayer expansion results in significant changes in gene expression in meniscal fibrochondrocytes, protein coatings may be used to regain the primary cell expression of several ECM molecules.

In situ localization of gelatinolytic activity during development and resorption of Meckel's cartilage in mice

Degradation of Meckel's cartilage in the middle portion is accompanied by hypertrophy and death of chondrocytes, calcification of the cartilaginous matrix, and chondroclastic resorption. We hypothesize that the gelatinolytic activity of matrix metalloproteinases (MMPs) largely contributes to the degradation of extracellular matrix (ECM) in the process. The activity in Meckel's cartilage of mouse mandibular arches at embryonic days 14-16 (E14-E16) was examined by a combination of in situ zymography (ISZ), using quenched fluorescent dye-labeled gelatin as a substrate, with CTT (a selective inhibitor of MMP-2 and -9) or with EDTA (a general MMP inhibitor). On E14 and E15, ISZ showed fluorescence in the perichondrium, in the intercellular septa between chondrocytes, and in the nucleus of chondrocytes. CTT attenuated fluorescence, and EDTA eliminated it. On E16, calcified cartilaginous matrix showed intense fluorescence, and dot-like fluorescence was observed in as-yet uncalcified intercellular septa, even after CTT treatment. EDTA inhibited fluorescence, but unexpectedly intense fluorescence was found in the cytoplasm of hypertrophic chondrocytes facing the resorption front. MMP-2, -9, and -13 immunoreactivity was detected in the perichondrium and chondrocytes of Meckel's cartilage. These findings suggest that MMPs and other proteinases capable of degrading gelatin play an integral role in the development, calcification, and resorption of Meckel's cartilage through ECM reconstitution.

Catch-up growth follows an abnormal pattern in experimental renal insufficiency and growth hormone treatment normalizes it

The primary goal of this study was to determine if the ability to undergo catch-up growth following a transient injury is preserved in an experimental model of moderate chronic renal failure (CRF) and the effect of growth hormone (GH) administration on such phenomenon. Young rats were subtotally nephrectomized (days 0 and 4) (Nx). From days 11 to 13, food intake was restricted in subgroups of Nx and control (C) rats (NxR and CR). After refeeding, subgroups of NxR and CR rats received GH from days 14 to 20 (NxRGH and CRGH). Rats were killed on days 14 (C, CR, Nx, NxR), 17 and 21 (C, CR, CRGH, Nx, NxR, NxRGH), and 36 (C, CR, Nx, NxR). Longitudinal growth rate was measured by osseous front advance in the proximal tibiae. With refeeding, growth rate of CR, NxR, and NXrGH rats became significantly greater than that of C, indicating catch-up growth. This occurred later and with lower growth rate in NxR than in CR rats, whereas the characteristics of catch-up growth in CR and NxRGH animals were similar. Changes in growth rate were associated with modifications in the morphology and proliferative activity of growth cartilage. We conclude that catch-up growth occurs in renal insufficiency but follows a different pattern from that observed with normal renal function. GH treatment normalizes the pattern of catch-up growth in CRF. Changes in growth velocity are associated to modifications in the structure and dynamics of growth cartilage.

Bone morphogenetic protein 3 expression pattern in rat condylar cartilage, femoral cartilage and mandibular fracture callus

Mandibular condylar cartilage differs from primary cartilage in morphological organization of the chondrocytes and in responses to biomechanical stress and humoral factors. For the first time, we describe the expression of Bmp3 mRNA in relation to types I, II and X collagen mRNA (as determined by in situ hybridization) in chondrocytes of the rat mandibular condylar cartilage, femoral articular cartilage, femoral growth plate cartilage, and temporal cartilage, which transiently appeared in the reparative response stage of mandibular ramus fracture healing. In all cartilages evaluated, Bmp3 was expressed in proliferating chondrocytes that expressed type I collagen in condylar cartilage, articular cartilage, and temporal cartilage appearing during fracture healing. Bmp3 was also found in hypertrophic chondrocytes that expressed type X collagen mRNA in all cartilages evaluated. Furthermore, in remodeling bone, Bmp3 mRNA was strongly expressed in active osteoblast cells in periosteal reaction layers formed after fracture. These findings suggest that Bmp3 expression in a special layer of typical articular cartilage may be regulated by mechanical stress stimulation. We also found that Bmp3 was expressed in the periosteal layers of the bone segments near the fracture site during fracture healing.

Transient disturbance in physeal morphology is associated with long-term effects of nitrogen-containing bisphosphonates in growing rabbits

Bisphosphonates have clinical benefit in children with severe osteogenesis imperfecta or osteoporosis and potential benefit in children with Perthes disease or undergoing distraction osteogenesis. However, there is concern about the effects of bisphosphonates on the physis and bone length. In 44 growing rabbits, zoledronic acid caused a transient disruption of physeal morphology, retention of cartilaginous matrix in trabeculae and cortical bone of the metaphysis, and a minor decrement in tibial bone length at maturity.

INTRODUCTION

Data from growing animal models suggest that bisphosphonates cause retention of longitudinal cartilaginous septa at the chondro-osseous junction, extension of trabeculae to the metaphyseal-diaphyseal junction, and varying dose-dependent effects on longitudinal growth. However, there is a lack of data regarding effects of intermittent use of nitrogen-containing bisphosphonates on the physis and on tibial length in models reaching maturity.

MATERIALS AND METHODS

Contralateral tibias of juvenile rabbits were examined after right tibial distraction osteogenesis from two previous studies. Animals were randomized to receive 0.1 mg/kg zoledronic acid (ZA) IV at 8 weeks of age (ZA*1) or 8 and 10 weeks of age (ZA*2) or saline. Body mass was analyzed from 5 to 44 weeks of age; tibial length and proximal physeal-metaphyseal histology and histomorphometry were analyzed at 8-52 weeks of age.

RESULTS

Tibial length was 3% less at 14 weeks of age in the ZA*2-treated versus saline group (p<0.05) in both studies, and this difference persisted at maturity in the long-term study group (26 weeks of age, p<0.05). Total body mass gain from 5 to 26 weeks of age was 14% less in ZA*2-treated than saline animals (p<0.05). Rate of weight gain from 8 to 10 weeks of age was 76% less in ZA*2 compared with saline animals (p<0.05). Radiographs showed radiodense lines in the metaphyses of ZA-treated bones, corresponding to the number of doses. Histologically, lines resulting from the first dose of ZA contained longitudinal cartilaginous matrix cores surrounded by bone, whereas those from the second dose contained spherical cores of matrix caused by transient disruption of physeal morphology after the first dose of ZA. Resorption of these lines at later times was radiographically and histologically evident, but remnants of cartilaginous matrix remained in the cortical bone of ZA-treated animals.

CONCLUSIONS

ZA treatment within the final 13.5% of the rabbit tibial growth period caused a transient disruption in physeal morphology and resorption associated with retention of cartilaginous matrix and coinciding with a persistent 3% decrement in tibial length. Disruption of physeal morphology and potential loss of bone length should be considered when administering nitrogen-containing bisphosphonates to children before closure of the major physes.

The role of collagen in bone structure: An image processing approach

Bone collagen structure in normal and pathological tissues is illustrated using techniques of thin section transmission electron microscopy and computer-assisted analysis. The normal bone collagen types, fibril architecture and diameter are described. In pathological tissue, deviations from normal fine structure are reflected in abnormal arrangements of collagen fibrils and abnormalities in fibril diameter. Computer analyses of normal fibril positive staining patterns are presented in order to provide a basis for comparing such patterns with pathological ones.

Integrin alpha1beta1 mediates collagen induction of MMP-13 expression in MC615 chondrocytes

During endochondral ossification, type I collagen is synthesized by osteoblasts together with some hypertrophic chondrocytes. Type I collagen has also been reported to be progressively synthesized in degenerative joints. Because Matrix Metalloproteinase-13 (MMP-13) plays an active role in remodeling cartilage in fetal development and osteoarthritic cartilage, we investigated whether type I collagen could activate MMP-13 expression in chondrocytes. We used a well-established chondrocytic cell line (MC615) and we found that MMP-13 expression was induced in MC615 cells cultured in type I collagen gel. We also found that alpha1beta1 integrin, a major collagen receptor, was expressed by MC615 cells and we further assessed the role of alpha1beta1 integrin in conducting MMP-13 expression. Induction of MMP-13 expression by collagen was potently and synergistically inhibited by blocking antibodies against alpha1 and beta1 integrin subunits, indicating that alpha1beta1 integrin mediates the MMP-13-inducing cellular signal generated by three-dimensional type I collagen. We also determined that activities of tyrosine kinase and ERK and JNK MAP kinases were required for this collagen-induced MMP-13 expression. Interestingly, bone morphogenetic protein (BMP)-2 opposed this induction, an effect that may be related to a role of BMP-2 in the maintenance of cartilage matrix.

Expression patterns of matrix metalloproteinases and vascular endothelial growth factor during epiphyseal ossification

In situ hybridization studies allowed for the localization of three MMPs and the angiogenic factor VEGF during secondary ossification. MMPs were widely expressed during ossification of the secondary center, whereas expression of VEGF was restricted to later stages.

INTRODUCTION

The spatiotemporal expression patterns of the matrix metalloproteinases gelatinase-B (MMP-9), collagenase-3 (MMP-13), and membrane-type 1 metalloproteinase (MMP-14) and the angiogenic peptide vascular endothelial growth factor (VEGF) were studied during development of the proximal epiphysis of the rat tibia.

MATERIALS AND METHODS

Cell expression was analyzed by in situ hybridization. Studies on osteoclastic activity, matrix mineralization, cell proliferation, and vascular progression were also performed.

RESULTS

MMP-9, MMP-13, and MMP-14 were expressed in discrete perichondrial cells that gave way to sites of intrachondral canal formation. High expression levels for the three MMPs were found at the blind ends of advancing intrachondral canals and at the expanding borders of the marrow space. Signals for MMP-9 and MMP-13 were in close proximity but did not overlap, whereas MMP-14 was expressed in both MMP-9+ and MMP-13+ cells. VEGF was not expressed during formation of intrachondral vascular canals but was observed in hypertrophic chondrocytes during formation of the bone marrow cavity.

CONCLUSIONS

Expression of MMPs and VEGF are constant events during development of the secondary ossification center. We propose that MMPs are involved in targeting proteolytic activity during epiphyseal development. VEGF is not expressed during early formation of vascular canals, but it may have a role in the formation of the bone marrow cavity.

Morphometric changes in the epiphyseal plate of the growing and young adult male rat after long-term salmon calcitonin administration

The function of the epiphyseal plate is related to the differentiation and maturation of the chondrocytes, especially of the hypertrophic zone. Salmon calcitonin exerts a positive effect on chondrocytes of different types of cartilage, e.g., articular cartilage, osteochondral callus formation, and the epiphyseal plate. In the present study, the effect of long-term daily salmon calcitonin treatment upon epiphyseal plate function was examined in 80 male Wistar rats aged 12 weeks at the beginning of the experiment. A daily dose of 6 IU of salmon calcitonin enhanced the number of the chondrocytes of the hypertrophic zone of the upper tibial epiphyseal plate, increased the mean thickness of the epiphyseal plate, and accelerated the longitudinal growth of long bones. It was found that the peripheral growth of the epiphyseal plate was delayed after calcitonin treatment in comparison with the placebo-treated animals. The most effective period for calcitonin treatment on epiphyseal plate function seems to be the late accelerated period of growth, i.e., puberty. In conclusion, long-term salmon calcitonin treatment has a beneficial effect on longitudinal skeletal growth and this effect remains throughout the adult life of the animal. Salmon calcitonin does not enlarge the surface of the epiphyseal plate.

Bone Formation: Biological Aspects and Modelling Problems

In this work we succintly review the main features of bone formation in vertebrates. Out of the many aspects of this exceedingly complex process, some particular stages are selected for which mathematical modelling appears as both feasible and desirable. In this way, a number of open questions are formulated whose study seems to require interaction among mathematical analysis and biological experimentation.

Static compressive loading reduces the mRNA expression of type II and X collagen in rat growth-plate chondrocytes during postnatal growth

The mechanisms by which chondrocytes modulate longitudinal bone growth are not well understood. This in vitro study investigated the effects of loading on the mRNA expression pattern of key molecular components of the growth-plate related to the extracellular matrix (type II and type X collagen) and the PTH-PTHrP feedback loop. Short-term static compressive loading was applied to rat proximal tibial growth-plate explants. Four age groups at specific developmental stages were investigated. The spatial variation in the mRNA expression was compared among loaded explants, their contralateral sham controls, and uncultured growth plates from normal animals. Basic cell metabolism (18S rRNA) was unaffected by load. Results indicated a narrower spatial distribution of mRNA expression of type II collagen throughout the growth plate; similarly, a narrowed distribution of expression of type X collagen was noted in the lower hypertrophic zone of the growth-plate. This suggests that mechanical compression influences chondrocytes of the hypertrophic zone to alter their expression of specific genes encoding proteins of the extracellular matrix, while PTH-PTHrP receptor mRNA, a regulatory protein, remained unaffected by loading. The effects of compression were similar at the different stages of growth, suggesting that additional factors may be involved in the clinical progression of skeletal deformities observed during growth spurts. Although this study was done in vitro and limited to static loading, it furthers our understanding of growth-plate mechanobiology as a first step toward providing a scientific rationale for treating progressive musculoskeletal deformities.

ACTH enhances chondrogenesis in multipotential progenitor cells and matrix production in chondrocytes

The association of melanocortin peptide overproduction with enhanced linear growth prompted the current investigation of adrenocorticotropin hormone (ACTH) effects on multipotential chondroprogenitor populations and committed chondrocytes in culture. Two multipotential progenitor populations, rat bone marrow stromal cells (BMSC) and the clonal multipotential cell line RCJ3.1, and two committed chondrocyte populations, resting chondrocytes (RC) isolated from the rib of young rats and the chondrocyte restricted cell line RCJ3.1C5.18 (C5.18), were cultured in differentiation medium plus or minus ACTH. Alcian blue stain was used to quantitate proteoglycan matrix production in all populations treated with a range of ACTH concentrations. Changes in proliferation due to ACTH treatment of all cell types were measured using 3H-thymidine incorporation. Differences in matrix production of ACTH-treated and -untreated RC and C5.18 cells were determined using 3H-proline incorporation. Relative transcript expression of the chondrocyte matrix proteins collagen type II (COLL II) and aggrecan (AGR) in treated and untreated cells was analyzed by Northern blot. Collagen type X (COLL X), a marker of hypertrophic differentiation, was measured in committed chondrocytic populations. Western analysis was used to detect the melanocortin-3 receptor (MC3-R), which was a suspected mediator of the ACTH signal. Matrix deposition was dose-dependently increased by ACTH in all cell populations as measured by alcian blue stain. ACTH treatment increased proliferation in multipotential progenitor populations (BMSC and RCJ3.1) while proliferation was decreased in committed chondrocyte populations (RC and C5.18). Total protein and total cell-associated collagen production were significantly increased by ACTH treatment in committed populations. Relative COLL II and AGR transcript expressions were significantly increased in both the RC- and C5.18-committed population and very significantly increased in the progenitor populations. Additionally, collagen type X expression was detected earlier and in greater abundance in ACTH-treated committed chondrocyte populations. Finally, the melanocortin-3 receptor was detected in all examined cell types by Western blot. These data show that ACTH promotes the development of the chondrocyte phenotype from multipotential mesenchymal progenitor populations and increases matrix production and differentiation of committed chondrocytes. These findings, together with the detection of the MC3-R in all of these cell types, indicate a role for the melanocortin system in chondrogenesis.

Connective tissue growth factor mRNA expression pattern in cartilages is associated with their type I collagen expression

Connective tissue growth factor (CTGF) has been identified as a secretory protein encoded by an immediate early gene and is a member of the CCN family. In vitro CTGF directly regulates the proliferation and differentiation of chondrocytes; however, a previous study showed that it was localized only in the hypertrophic chondrocytes in the costal cartilages of E 18 mouse embryos. We described the expression of CTGF mRNA and protein in chondrocytes of different types of cartilages, including femoral growth plate cartilage, costal cartilage, femoral articular cartilage, mandibular condylar cartilage, and cartilage formed during the healing of mandibular ramus fractures revealed by in situ hybridization and immunohistochemistry. To characterize the CTGF-expressing cells, we also analyzed the distribution of the type I, type II, and type X collagen mRNA expression. Among these different types of cartilages we found distinct patterns of CTGF mRNA and protein expression. Growth plate cartilage and the costal cartilage showed localization of CTGF mRNA and protein in the hypertrophic chondrocytes that expressed type X collagen mRNA with less expression in proliferating chondrocytes that expressed type II collagen mRNA, whereas it was also expressed in the proliferating chondrocytes that expressed type I collagen mRNA in the condylar cartilage, the articular cartilage, and the cartilage appearing during fracture healing. In contrast, the growth plate cartilages or the costal cartilages were negative for type I collagen and showed sparse expression of CTGF mRNA in the proliferating chondrocytes. We found for the first time that CTGF mRNA could be differentially expressed in five different types of cartilage associated with those expressing type I collagen. Moreover, the spatial distribution of CTGF mRNA in the cartilages with type I collagen mRNA suggested its roles in the early differentiation, as well as in the proliferation and the terminal differentiation, of those cartilages.

Broad-spectrum matrix metalloproteinase inhibitor marimastat-induced musculoskeletal side effects in rats

OBJECTIVE

To characterize the clinical and histopathologic changes in a rat model of broad-spectrum matrix metalloproteinase (MMP)-induced musculoskeletal syndrome (MSS), and to facilitate research into the causes and treatments of MSS in humans.

METHODS

Male Lewis rats weighing 150-180 gm were administered 10-30 mg of the broad-spectrum MMP inhibitor marimastat over a 2-week period via surgically implanted subcutaneous osmotic pumps. The animals were monitored and scored for the onset and severity of MSS, using clinical and histologic parameters.

RESULTS

Marimastat-treated rats exhibited various clinical signs, including compromised ability to rest on their hind feet, high-stepping gait, reluctance or inability to move, and hind paw swelling. Histologically, marimastat-treated rat joints were characterized by soft tissue and bone changes, such as increased epiphyseal growth plate, synovial hyperplasia, and increased cellularity in the joint capsule and extracapsular ligaments. The severity of MSS, as judged by clinical criteria (2 blinded observers using 3 clinical parameters), paw volume, and histologic score, was nearly identical. The observed changes were indistinguishable from those reported for primate models and mimic MSS in humans.

CONCLUSION

This simple and sensitive model of MSS is an attractive alternative for studying the pathology of MSS.

Distinct phases of coordinated early and late gene expression in growth plate chondrocytes in relationship to cell proliferation, matrix assembly, remodeling, and cell differentiation

Although much has been learned about growth plate development and chondrocyte gene expression during cellular maturation and matrix remodeling in the mouse, there has been a limited study of the interrelationships of gene expression between proteinases, growth factors, and other regulatory molecules in the mouse and in other species. Here we use RT-PCR of sequential transverse sections to examine the expression profiles of genes involved in chondrocyte growth, differentiation, matrix assembly, remodeling, and mineralization in the bovine proximal tibial growth plate. Specifically, we studied the expression of genes encoding COL2A1 and COL10A1, the latter a marker of cellular hypertrophy, the matrix metalloproteinases (MMP), MMP-13 and MMP-9, as well as the transcriptional factors, Sox9 and Cbfa1, the growth factors basic fibroblast growth factor (bFGF), parathyroid hormone-related peptide (PTHrP), transforming growth factor (TGF)beta1, and beta2, Indian hedgehog (Ihh), and the matrix protein osteocalcin. These were analyzed in relationship to cell division defined by cyclin B2 expression. Two peaks of gene expression activity were observed. One was transient, limited, and located immediately before and at the onset of cyclin B2 expression in the early proliferative zone. The other was generally much more pronounced and was located in the early hypertrophic zone. The upregulation of expression of COL2A1, its transcriptional activator Sox9, osteocalcin, MMP-13, and TGFbeta2 was observed immediately before and at the onset of cyclin B2 expression and also in the hypertrophic zones. The upregulation of COL10A1, Cbfa1, MMP-9, TGFbeta-1, and Ihh gene expression was associated exclusively with the terminal differentiation of chondrocytes at the time of mineral formation in the extracellular matrix. In contrast, bFGF and PTHrP expression was observed in association with the onset of cyclin B2 expression and hypertrophy. This initial cluster of gene expression associated predominantly with matrix assembly and onset of cell proliferation is therefore characterized by expression of regulatory molecules distinct from those involved at hypertrophy. Together these results identify separate phases of coordinated gene expression associated with the development of the physis in endochondral bone formation.