Age-related changes in the synthesis and mRNA expression of decorin and aggrecan in human meniscus and articular cartilage

Lyme Disease Surveillance and Epidemiology in the United States: A Historical Perspective

In the 40 years since Steere and colleagues first described Lyme disease, the illness has increased in incidence and distribution to become the most common vector-borne disease in the United States. Public health officials have developed, implemented, and revised surveillance systems to describe and monitor the condition. Much has been learned about the epidemiology of the illness, despite practical and logistical constraints that have encumbered the collection and interpretation of surveillance data. Future development of automated data collection from electronic health records as a source of surveillance and clinical information will address practical challenges and help answer ongoing questions about complications and persistent symptoms. Robust surveillance will be essential to monitor the effectiveness and safety of future vaccines and other preventive measures.

Age-dependent changes in collagen crosslinks reduce the mechanical toughness of human meniscus

The mechanical resilience of the knee meniscus is provided by a group of structural proteins in the extracellular matrix. Aging can alter the quantity and molecular structure of these proteins making the meniscus more susceptible to debilitating tears. In this study, we determined the effect of aging on the quantity of structural proteins and collagen crosslinks in human lateral meniscus, and examined whether the quantity of these molecules was predictive of tensile toughness (area under the stress-strain curve). Two age groups were tested: a young group under 40 and an older group over 65 years old. Using mass spectrometry, we quantified the abundance of proteins and collagen crosslinks in meniscal tissue that was adjacent to the dumbbell-shaped specimens used to measure uniaxial tensile toughness parallel or perpendicular to the circumferential fiber orientation. We found that the enzymatic collagen crosslink deoxypyridinoline had a significant positive correlation with toughness, and reductions in the quantity of this crosslink with aging were associated with a loss of toughness in the ground substance and fibers. The non-enzymatic collagen crosslink carboxymethyl-lysine increased in quantity with aging, and these increases corresponded to reductions in ground substance toughness. For the collagenous (Types I, II, IV, VI, VIII) and non-collagenous structural proteins (elastin, decorin, biglycan, prolargin) analyzed in this study, only the quantity of collagen VIII was predictive of toughness. This study provides valuable insights on the structure-function relationships of the human meniscus, and how aging causes structural adaptations that weaken the tissue's mechanical integrity.

Advanced glycation end-product accumulation differs by location and sex in aged osteoarthritic human menisci

OBJECTIVE

There is a clear link between increasing age and meniscus degeneration, leading to increased injury, osteoarthritis (OA) progression, and often total knee replacement. Advanced glycation end-products (AGEs) are non-enzymatic crosslinks and adducts that accumulate in collagen with age, altering tissue mechanics and cell function, ultimately leading to increased injury and inflammation. AGEs, both fluorescent and non-fluorescent, play a central role in age-related degradation of tissues throughout the body; however, little is known about their role in meniscus degeneration. The objective of this study was to characterize changes in aged OA menisci, specifically evaluating zonal AGE accumulation, to gain a better understanding of changes that may lead to age-related meniscal degeneration.

METHOD

Deidentified human menisci (N = 48, 52-84 years old) were obtained from subjects undergoing total knee replacement. Changes in extracellular matrix (ECM) were assessed by gross morphology, confocal analysis, and biochemical assays. Deoxyribonucleic acid (DNA), glycosaminoglycan (GAG), collagen, and AGE accumulation were compared with patient age, zonal region, and patient sex.

RESULTS

There were minimal changes in DNA, GAG, and collagen concentration with age or zone. However, collagen fraying and AGEs increased with age, with more AGEs accumulating in the meniscal horns compared to the central body and in male menisci compared to females.

CONCLUSIONS

Overall, this work provides greater insights into regional changes that occur in human menisci with age and OA. These results suggest AGEs may play a role in the degeneration of the meniscus, with AGEs being a possible target to reduce age-related tears, degeneration, and OA progression.

The role of SLRPs and large aggregating proteoglycans in collagen fibrillogenesis, extracellular matrix assembly, and mechanical function of fibrocartilage

PURPOSE

Proteoglycans, especially small leucine rich proteoglycans (SLRPs), play major roles in facilitating the development and regulation of collagen fibers and other extracellular matrix components. However, their roles in fibrocartilage have not been widely reviewed. Here, we discuss both SLRP and large aggregating proteoglycan's roles in collagen fibrillogenesis and extracellular matrix assembly in fibrocartilage tissues such as the meniscus, annulus fibrosus (AF), and TMJ disc. We also discuss their expression levels throughout development, aging and degeneration, as well as repair.

METHODS

A review of literature discussing proteoglycans and collagen fibrillogenesis in fibrocartilage was conducted and data from these manuscripts were analyzed and grouped to discuss trends throughout the tissue's architectural zones and developmental stage.

RESULTS

The spatial collagen architecture of these fibrocartilaginous tissues is reflected in the distribution of proteoglycans expressed, suggesting that each proteoglycan plays an important role in the type of architecture presented and associated mechanical function.

CONCLUSION

The unique structure-function relationship of fibrocartilage makes the varied architectures throughout the tissues imperative for their success and understanding the functions of these proteoglycans in developing and maintaining the fiber structure could inform future work in fibrocartilage replacement using tissue engineered constructs.

Meniscus Matrix Structural and Biomechanical Evaluation: Age-Dependent Properties in a Swine Model

The analysis of the morphological, structural, biochemical, and mechanical changes of the Extracellular Matrix (ECM), which occur during meniscus development, represents the goal of the present study. Medial fully developed menisci (FD, 9-month-old pigs), partially developed menisci (PD, 1-month-old piglets), and not developed menisci (ND, from stillbirths) were collected. Cellularity and glycosaminoglycans (GAGs) deposition were evaluated by ELISA, while Collagen 1 and aggrecan were investigated by immunohistochemistry and Western blot analyses in order to be compared to the biomechanical properties of traction and compression tensile forces, respectively. Cellularity decreased from ND to FD and GAGs showed the opposite trend (p < 0.01 both). Collagen 1 decreased from ND to FD, as well as the ability to resist to tensile traction forces (p < 0.01), while aggrecan showed the opposite trend, in accordance with the biomechanics: compression test showed that FD meniscus greatly resists to deformation (p < 0.01). This study demonstrated that in swine meniscus, clear morphological and biomechanical changes follow the meniscal maturation and specialization during growth, starting with an immature pattern (ND) to the mature organized meniscus of the FD, and they could be useful to understand the behavior of this structure in the light of its tissue bioengineering.

Mediation of Cartilage Matrix Degeneration and Fibrillation by Decorin in Post-traumatic Osteoarthritis

OBJECTIVE

To elucidate the role of decorin, a small leucine-rich proteoglycan, in the degradation of cartilage matrix during the progression of post-traumatic osteoarthritis (OA).

METHODS

Three-month-old decorin-null (Dcn^-/- ) and inducible decorin-knockout (Dcn^{i KO} ) mice were subjected to surgical destabilization of the medial meniscus (DMM) to induce post-traumatic OA. The OA phenotype that resulted was evaluated by assessing joint morphology and sulfated glycosaminoglycan (sGAG) staining via histological analysis (n = 6 mice per group), surface collagen fibril nanostructure via scanning electron microscopy (n = 4 mice per group), tissue modulus via atomic force microscopy-nanoindentation (n = 5 or more mice per group) and subchondral bone structure via micro-computed tomography (n = 5 mice per group). Femoral head cartilage explants from wild-type and Dcn^-/- mice were stimulated with the inflammatory cytokine interleukin-1β (IL-1β) in vitro (n = 6 mice per group). The resulting chondrocyte response to IL-1β and release of sGAGs were quantified.

RESULTS

In both Dcn^-/- and Dcn^{i KO} mice, the absence of decorin resulted in accelerated sGAG loss and formation of highly aligned collagen fibrils on the cartilage surface relative to the control (P < 0.05). Also, Dcn^-/- mice developed more salient osteophytes, illustrating more severe OA. In cartilage explants treated with IL-1β, loss of decorin did not alter the expression of either anabolic or catabolic genes. However, a greater proportion of sGAGs was released to the media from Dcn^-/- mouse explants, in both live and devitalized conditions (P < 0.05).

CONCLUSION

In post-traumatic OA, decorin delays the loss of fragmented aggrecan and fibrillation of cartilage surface, and thus, plays a protective role in ameliorating cartilage degeneration.

Identification of Pivotal Genes and Pathways in Osteoarthritic Degenerative Meniscal Lesions via Bioinformatics Analysis of the GSE52042 Dataset

Background

To better understand the process of osteoarthritic degenerative meniscal lesions (DMLs) formation, this study analyzed the dataset GSE52042 using bioinformatics methods to identify the pivotal genes and pathways related to osteoarthritic DMLs.

Material/Methods

The GSE52042 dataset, comprising diseased meniscus samples and healthier meniscus samples, was downloaded and the differentially-expressed genes (DEGs) were extracted. The reactome pathways assessment and functional analysis were performed using the “ClusterProfiler” package and “ReactomePA” package of Bioconductor. The protein–protein interaction network was constructed, followed by the extraction of hub genes and modules.

Results

A set of 154 common DEGs, including 64 upregulated DEGs and 90 downregulated DEGs, were obtained. GO analysis suggested that the DEGs primarily participated in positive regulation of the mitotic cell cycle and extracellular matrix organization. Reactome pathway analysis showed that the DEGs were predominantly enriched in TP53, which regulates transcription of genes involved in G2 cell cycle arrest and extracellular matrix organization. The top 10 hub genes were TYMS, AURKA, CENPN, NUSAP1, CENPM, TPX2, CDK1, UBE2C, BIRC5, and CCNB1. The genes in the 2 modules were primarily associated with M Phase and keratan sulfate degradation.

Conclusions

A series of pivotal genes and reactome pathways were identified elucidate the molecular mechanisms involved in the formation of osteoarthritic DMLs and to discover potential therapeutic targets.

Mountain ultramarathon results in temporary meniscus extrusion in healthy athletes

PURPOSE

In recent literature medial meniscus extrusion (MME) was demonstrated as an age, BMI and load dependent physiological phenomenon in healthy knees. The aim of the present study was to evaluate the influence of mountain ultramarathon running on the medial meniscus extrusion (MME) in healthy athletes.

METHODS

Healthy athletes of the 2017 Gore-Tex® Transalpine run (seven stages with in total 270.5 km and 16453 m altitude) with asymptomatic knee, and no history of knee injuries or surgeries were included. All athletes underwent standard knee examination, MRI to exclude further knee pathologies and ultrasound imaging (USI) for measurement of MME before the competition. Extrusion in USI was determined in supine position (unloaded) and in standing position with full weight bearing and 20° of flexion (loaded). After the 1st, 3rd, and 7th stage ultrasound measurements were repeated directly after the competition. For evaluation of recovery, ultrasound measurement of MME was repeated 2 weeks after the race. Difference between ultrasound measurements of MME was assessed by unpaired t-test with significance set at p < 0.05.

RESULTS

Eighteen athletes (mean age 37.4 ± 8.3 years, 5 females, 13 males) were included in the study. The mean USI MME before the race was 1.9 mm ± 0.3 mm in supine position and 2.4 mm ± 0.4 mm under full weight bearing. During the race the mean MME increased significantly compared to baseline measurements. After 7th stage the mean MME in supine position was 2.7 mm ± 0.7 mm and 3.1 mm ± 0.6 mm under full weight bearing. After 2 weeks of recovery medial meniscus demonstrated a complete reversibility of the extrusion to normal (N.S).

CONCLUSION

Medial meniscus extrusion observed under extreme loads generated by a mountain ultramarathon is a temporary and reversible phenomenon in healthy athletes. This suggests, that the meniscus has viscoelastic capacities showing short-term adaptions to high loads, which are completely reversible over time. For clinical practice assessment of the MME by ultrasound might be favorable compared to MRI due to the ability of dynamic evaluation and the easy access. Furthermore, load should be taken in account when assessing the MME and the current cut-off value of 3 mm for meniscus pathologies should be reconsidered.

LEVEL OF EVIDENCE

IV.

The Importance of the Knee Joint Meniscal Fibrocartilages as Stabilizing Weight Bearing Structures Providing Global Protection to Human Knee-Joint Tissues

The aim of this study was to review aspects of the pathobiology of the meniscus in health and disease and show how degeneration of the meniscus can contribute to deleterious changes in other knee joint components. The menisci, distinctive semilunar weight bearing fibrocartilages, provide knee joint stability, co-ordinating functional contributions from articular cartilage, ligaments/tendons, synovium, subchondral bone and infra-patellar fat pad during knee joint articulation. The meniscus contains metabolically active cell populations responsive to growth factors, chemokines and inflammatory cytokines such as interleukin-1 and tumour necrosis factor-alpha, resulting in the synthesis of matrix metalloproteases and A Disintegrin and Metalloprotease with ThromboSpondin type 1 repeats (ADAMTS)-4 and 5 which can degrade structural glycoproteins and proteoglycans leading to function-limiting changes in meniscal and other knee joint tissues. Such degradative changes are hall-marks of osteoarthritis (OA). No drugs are currently approved that change the natural course of OA and translate to long-term, clinically relevant benefits. For any pharmaceutical therapeutic intervention in OA to be effective, disease modifying drugs will have to be developed which actively modulate the many different cell types present in the knee to provide a global therapeutic. Many individual and combinatorial approaches are being developed to treat or replace degenerate menisci using 3D printing, bioscaffolds and hydrogel delivery systems for therapeutic drugs, growth factors and replacement progenitor cell populations recognising the central role the menisci play in knee joint health.

Connective Tissue and Age-Related Diseases

We begin this chapter by describing normal characteristics of several pertinent connective tissue components, and some of the basic changes they undergo with ageing. These alterations are not necessarily tied to any specific disease or disorders, but rather an essential part of the normal ageing process. The general features of age-induced changes, such as skin wrinkles, in selected organs with high content of connective or soft tissues are discussed in the next part of the chapter. This is followed by a section dealing with age-related changes in specific diseases that fall into at least two categories. The first category encompasses common diseases with high prevalence among mostly ageing populations where both genetic and environmental factors play roles. They include but may not be limited to atherosclerosis and coronary heart disease, type II diabetes, osteopenia and osteoporosis, osteoarthritis, tendon dysfunction and injury, age-related disorders of spine and joints. Disorders where genetics plays the primary role in pathogenesis and progression include certain types of progeria, such as Werner syndrome and Hutchinson-Gilford progeria belong to the second category discussed in this chapter. These disorders are characterized by accelerated signs and symptoms of ageing. Other hereditary diseases or syndromes that arise from mutations of genes encoding for components of connective tissue and are less common than diseases included in the first group will be discussed briefly as well, though they may not be directly associated with ageing, but their connective tissue undergoes some changes compatible with ageing. Marfan and Ehlers-Danlos syndromes are primary examples of such disorders. We will probe the role of specific components of connective tissue and extracellular matrix if not in each of the diseases, then at least in the main representatives of these disorders.

Differential protein expression in human knee articular cartilage and medial meniscus using two different proteomic methods: a pilot analysis

Background

Proteomics is an emerging field in the study of joint disease. Our two aims with this pilot analysis were to compare healthy human knee articular cartilage with meniscus, two tissues both known to become affected in the osteoarthritic disease process, and to compare two mass spectrometry (MS)-based methods: data-dependent acquisition (DDA) and data-independent acquisition (DIA).

Methods

Healthy knee articular cartilage taken from the medial tibial condyle and medial meniscus samples taken from the body region were obtained from three adult forensic medicine cases. Proteins were extracted from tissue pieces and prepared for MS analysis. Each sample was subjected to liquid chromatography (LC)-MS/MS analysis using an Orbitrap mass spectrometer, and run in both DDA and DIA mode. Linear mixed effects models were used for statistical analysis.

Results

A total of 653 proteins were identified in the DDA analysis, of which the majority was present in both tissue types. Only proteins with quantitation information in both tissues (n = 90) were selected for more detailed analysis, of which the majority did not statistically significantly differ in abundance between the two tissue types, in either of the MS analyses. However, 21 proteins were statistically significantly different (p < 0.05) between meniscus and cartilage in the DIA analysis. Out of these, 11 proteins were also significantly different in the DDA analysis. Aggrecan core protein was the most abundant protein in articular cartilage and significantly differed between the two tissues in both methods. The corresponding protein in meniscus was serum albumin. Dermatopontin exhibited the highest meniscus vs articular cartilage ratio among the statistically significant proteins. The DIA method led to narrower confidence intervals for the abundance differences between the two tissue types than DDA.

Conclusions

Although articular cartilage and meniscus had similar proteomic composition, we detected several differences by MS. Between the two analyses, DIA yielded more precise estimates and more statistically significant different proteins than DDA, and had no missing values, which makes it preferable for future LC-MS/MS analyses.

Electronic supplementary material

The online version of this article (10.1186/s12891-018-2346-6) contains supplementary material, which is available to authorized users.

Role of the Inflammation-Autophagy-Senescence Integrative Network in Osteoarthritis

Osteoarthritis is the most common musculoskeletal disease causing chronic disability in adults. Studying cartilage aging, chondrocyte senescence, inflammation, and autophagy mechanisms have identified promising targets and pathways with clinical translatability potential. In this review, we highlight the most recent mechanistic and therapeutic preclinical models of aging with particular relevance in the context of articular cartilage and OA. Evidence supporting the role of metabolism, nuclear receptors and transcription factors, cell senescence, and circadian rhythms in the development of musculoskeletal system degeneration assure further translational efforts. This information might be useful not only to propose hypothesis and advanced models to study the molecular mechanisms underlying joint degeneration, but also to translate our knowledge into novel disease-modifying therapies for OA.

Human Knee Meniscus Regeneration Strategies: a Review on Recent Advances

PURPOSE OF REVIEW

Lack of vascularity in the human knee meniscus often leads to surgical removal (total or partial meniscectomy) in the case of severe meniscal damage. However, complete recovery is in question after such removal as the meniscus plays an important role in knee stability. Thus, meniscus tissue regeneration strategies are of intense research interest in recent years.

RECENT FINDINGS

The structural complexity and inhomogeneity of the meniscus have been addressed with processing technologies for precisely controlled three dimensional (3D) complex porous scaffold architectures, the use of biomolecules and nanomaterials. The regeneration and replacement of the total meniscus have been studied by the orthopedic and scientific communities via successful pre-clinical trials towards mimicking the biomechanical properties of the human knee meniscus. Researchers have attempted different regeneration strategies which contribute to in vitro regeneration and are capable of repairing meniscal tears to some extent. This review discusses the present state of the art of these meniscus tissue engineering aspects.

Differential tissue specific, temporal and spatial expression patterns of the Aggrecan gene is modulated by independent enhancer elements

The transcriptional mechanism through which chondrocytes control the spatial and temporal composition of the cartilage tissue has remained largely elusive. The central aim of this study was to identify whether transcriptional enhancers played a role in the organisation of the chondrocytes in cartilaginous tissue. We focused on the Aggrecan gene (Acan) as it is essential for the normal structure and function of cartilage and it is expressed developmentally in different stages of chondrocyte maturation. Using transgenic reporter studies in mice we identified four elements, two of which showed individual chondrocyte developmental stage specificity. In particular, one enhancer (-80) distinguishes itself from the others by being predominantly active in adult cartilage. Furthermore, the -62 element uniquely drove reporter activity in early chondrocytes. The remaining chondrocyte specific enhancers, +28 and -30, showed no preference to chondrocyte type. The transcription factor SOX9 interacted with all the enhancers in vitro and mutation of SOX9 binding sites in one of the enhancers (-30) resulted in a loss of its chondrocyte specificity and ectopic enhancer reporter activity. Thus, the Acan enhancers orchestrate the precise spatiotemporal expression of this gene in cartilage types at different stages of development and adulthood.

Age-related changes in the knee meniscus

BACKGROUND

Aging is the most prominent risk factor for the development of osteoarthritis (OA), which affects knees and causes major health burdens. Meniscal dysfunction mostly based on degeneration contributes to the development and progression of knee OA. Meniscal degeneration is caused by various extrinsic factors, such as repetitive trauma or leg malalignment, while meniscal aging is considered as internal changes, such as molecular or cellular changes. Little is known about age-related changes in the meniscus. Therefore, this review aimed to summarize and clarify the understanding of the aged meniscus.

METHODS

There are few articles about natural aging in the meniscus, because most reports only demonstrate the effects of OA on the meniscus. We searched PubMed (1948 to November 2016) to identify and summarize all English-language articles evaluating natural aging in the meniscus.

RESULTS

There is evidence of compositional change in the meniscus with aging, involving cells, collagens, and proteoglycans. In addition, as recent reports on the natural aging of cartilage have indicated, senescence of the meniscal cells may also lead to disruption of meniscal cells and tissue homeostasis. Due to the low turnover rate of collagen, accumulation of advanced glycation end-products largely contributes to tissue stiffness and vulnerability, and finally results in degenerative changes or tears. Furthermore, environmental factors such as joint fluid secreted by inflamed synovium could also contribute to meniscal tissue deterioration.

CONCLUSIONS

Age-related changes induce meniscal tissue vulnerability and finally lead to meniscal dysfunction.

The nutrition of the human meniscus: A computational analysis investigating the effect of vascular recession on tissue homeostasis

The meniscus is essential to the functioning of the knee, offering load support, congruency, lubrication, and protection to the underlying cartilage. Meniscus degeneration affects ∼35% of the population, and potentially leads to knee osteoarthritis. The etiology of meniscal degeneration remains to be elucidated, although many factors have been considered. However, the role of nutritional supply to meniscus cells in the pathogenesis of meniscus degeneration has been so far overlooked. Nutrients are delivered to meniscal cells through the surrounding synovial fluid and the blood vessels present in the outer region of the meniscus. During maturation, vascularization progressively recedes up to the outer 10% of the tissue, leaving the majority avascular. It has been hypothesized that vascular recession might significantly reduce the nutrient supply to cells, thus contributing to meniscus degeneration. The objective of this study was to evaluate the effect of vascular recession on nutrient levels available to meniscus cells. This was done by developing a novel computational model for meniscus homeostasis based on mixture theory. It was found that transvascular transport of nutrients in the vascularized region of the meniscus contributes to more than 40% of the glucose content in the core of the tissue. However, vascular recession does not significantly alter nutrient levels in the meniscus, reducing at most 5% of the nutrient content in the central portion of the tissue. Therefore, our analysis suggests that reduced vascularity is not likely a primary initiating source in tissue degeneration. However, it does feasibly play a key role in inability for self-repair, as seen clinically.

The biology of meniscal pathology in osteoarthritis and its contribution to joint disease: beyond simple mechanics

The meniscal cartilages in the knee function to improve congruity of the medial and lateral femoro-tibial joints and play critical roles in load distribution and joint stability. Meniscal tears of various configurations are one of the most common conditions of the knee and are associated with an increased risk of developing osteoarthritis (OA). While this risk has been largely attributed to loss of the biomechanical functions of the menisci, there is accumulating evidence suggesting that other aspects of meniscal biology may play a role in determining the long-term consequences of meniscal damage for joint health. In this narrative review, we examine the existing literature and present some new data implicating synthesis and secretion of enzymes and other pro-catabolic mediators by injured and degenerate menisci, contributing to the pathological change in other knee joint tissues in OA.

A Porcine Animal Model for Early Meniscal Degeneration - Analysis of Histology, Gene Expression and Magnetic Resonance Imaging Six Months after Resection of the Anterior Cruciate Ligament

BACKGROUND/OBJECTIVE

The menisci of the mammalian knee joint balance the incongruence between femoral condyle and tibial plateau and thus menisci absorb and distribute high loads. Degeneration processes of the menisci lead to pain syndromes in the knee joint. The origin of such degenerative processes on meniscal tissue is rarely understood and may be described best as an imbalance of anabolic and catabolic metabolism. A standardized animal model of meniscal degeneration is needed for further studies. The aim of the current study was to develop a porcine animal model with early meniscal degeneration.

MATERIAL AND METHODS

Resection of the anterior cruciate ligament (ACLR) was performed on the left knee joints of eight Göttingen minipigs. A sham operation was carried out on the right knee joint. The grade of degeneration was determined 26 weeks after the operation using histology and magnetic resonance imaging (MRI). Furthermore, the expression of 14 genes which code for extracellular matrix proteins, catabolic matrix metalloproteinases and inflammation mediators were analyzed.

RESULTS

Degenerative changes were detected by a histological analysis of the medial meniscus after ACLR. These changes were not detected by MRI. In terms of their gene expression profile, these degenerated medial menisci showed a significantly increased expression of COL1A1.

CONCLUSION

This paper describes a new animal model for early secondary meniscal degeneration in the Göttingen minipig. Histopathological evidence of the degenerative changes could be described. This early degenerative changes could not be seen by NMR imaging.

Quantitative tracking of passage and 3D culture effects on chondrocyte and fibrochondrocyte gene expression

Success in cartilage and fibrocartilage tissue engineering relies heavily on using an appropriate cell source. Many different cell sources have been identified, including primary and stem cells, along with experimental strategies to obtain the required number of cells or to induce chondrogenesis. However, no definitive method exists to quantitatively evaluate the similarity of the resulting cell phenotypes to those of the native cells between candidate strategies. In this study, we develop an integrative approach to enable such evaluations by deriving, from gene expression profiles, two quantitative metrics representing the nearest location within the range of native cell phenotypes and the deviation from it. As an example application to evaluating potential cell sources for cartilage or meniscus tissue engineering, we examine phenotypic changes of juvenile and adult articular chondrocytes and fibrochondrocytes across multiple passages and subsequent 3D culture. A substantial change was observed in cell phenotype due to the isolation process itself, followed by a clear progression toward the outer meniscal cell phenotype with passage. The new metrics also indicated that 3D culture moderately reduced the passage-induced deviation from the native meniscal phenotypes for juvenile chondrocytes and adult fibrochondrocytes, which was not obvious through examination of individual gene expressions. However, brief 3D culture alone did not move any of the cells towards an inner meniscal phenotype, the most relevant target for meniscal tissue engineering. This integrative approach of examining and combining multiple gene expressions can be used to evaluate various other tissue-engineering strategies to direct cells toward the desired phenotype. Copyright © 2015 John Wiley & Sons, Ltd.

Transcriptome analysis of injured human meniscus reveals a distinct phenotype of meniscus degeneration with aging

OBJECTIVE

Meniscus tears are associated with a heightened risk of osteoarthritis. This study aimed to advance our understanding of the metabolic state of injured human meniscus at the time of arthroscopic partial meniscectomy through transcriptome-wide analysis of gene expression in relation to the patient's age and degree of cartilage chondrosis.

METHODS

The degree of chondrosis of knee cartilage was recorded at the time of meniscectomy in symptomatic patients without radiographic osteoarthritis. RNA preparations from resected menisci (n = 12) were subjected to transcriptome-wide microarray and QuantiGene Plex analyses. Variations in the relative changes in gene expression with age and chondrosis were analyzed, and integrated biologic processes were investigated computationally.

RESULTS

We identified a set of genes in torn menisci that were differentially expressed with age and chondrosis. There were 866 genes that were differentially regulated (≥1.5-fold difference and P < 0.05) with age and 49 with chondrosis. In older patients, genes associated with cartilage and skeletal development and extracellular matrix synthesis were repressed, while those involved in immune response, inflammation, cell cycle, and cellular proliferation were stimulated. With chondrosis, genes representing cell catabolism (cAMP catabolic process) and tissue and endothelial cell development were repressed, and those involved in T cell differentiation and apoptosis were elevated.

CONCLUSION

Differences in age-related gene expression suggest that in older adults, meniscal cells might dedifferentiate and initiate a proliferative phenotype. Conversely, meniscal cells in younger patients appear to respond to injury, but they maintain the differentiated phenotype. Definitive molecular signatures identified in damaged meniscus could be segregated largely with age and, to a lesser extent, with chondrosis.

Platelet-rich plasma can replace fetal bovine serum in human meniscus cell cultures

Concerns over fetal bovine serum (FBS) limit the clinical application of cultured tissue-engineered constructs. Therefore, we investigated if platelet-rich plasma (PRP) can fully replace FBS for meniscus tissue engineering purposes. Human PRP and platelet-poor plasma (PPP) were isolated from three healthy adult donors. Human meniscal fibrochondrocytes (MFCs) were isolated from resected tissue after a partial meniscectomy on a young patient. Passage-4 MFCs were cultured in monolayer for 24 h, and 3 and 7 days. Six different culture media were used containing different amounts of either PRP or PPP and compared to a medium containing 10% FBS. dsDNA was quantified, and gene expression levels of collagen types I and II and aggrecan were measured at different time points with quantitative polymerase chain reaction in the cultured MFCs. After 7 days, the dsDNA quantity was significantly higher in MFCs cultured in 10% and 20% PRP compared to the other PRP and PPP conditions, but equal to 10% FBS. Collagen type I expression was lower in MFCs cultured with medium containing 5% PRP, 10% and 20% PPP compared to FBS. When medium with 10% PRP or 20% PRP was used, expressions were not significantly different from medium containing 10% FBS. Collagen type II expression was absent in all medium conditions. Aggrecan expression did not show differences between the different media used. However, after 7 days a higher aggrecan expression was measured in most culture conditions, except for 5% PRP, which was similar compared to FBS. Statistical significance was found between donors at various time points in DNA quantification and gene expression, but the same donors were not statistically different in all conditions. At 7 days cell cultured with 10% PRP and 20% PRP showed a higher density, with large areas of clusters, compared to other conditions. In an MFC culture medium, FBS can be replaced by 10% PRP or 20% PRP without altering proliferation and gene expression of human MFCs.

T2 values of posterior horns of knee menisci in asymptomatic subjects

Purpose

The magnetic resonance (MR) T2 value of cartilage is a reliable indicator of tissue properties and therefore may be used as an objective diagnostic tool in early meniscal degeneration. The purpose of this study was to investigate age, gender, location, and zonal differences in MR T2 value of the posterior horns of knee menisci in asymptomatic subjects.

Methods

Sixty asymptomatic volunteers (30 men and 30 women) were enrolled and divided into three different age groups: 20–34, 35–49 and 50–70 years. The inclusion criteria were BMI<30 kg/cm²_, normalized Western Ontario and McMaster Universities (WOMAC) pain score of zero, and no evidence of meniscal and ligamentous abnormalities on routine knee MR imaging. The T2 values were measured on images acquired with a T2-weighted fat-suppressed turbo spin-echo sequence at 3T.

Results

The mean T2 values in both medial and lateral menisci for the 20–34, 35–49, and 50–70 age groups were 9.94 msec±0.94, 10.73 msec±1.55, and 12.36 msec±2.27, respectively, for women and 9.17 msec±0.74, 9.64 msec±0.67, and 10.95 msec±1.33, respectively, for men. The T2 values were significantly higher in the 50–70 age group than the 20–34 age group (P<0.001) and in women than in men (P = 0.001, 0.004, and 0.049 for each respective age group). T2 values were significantly higher in medial menisci than in lateral menisci only in women age 50–70 (3.33 msec, P = 0.006) and in the white zone and red/white zone of the 50–70 and 35–49 age groups than that of the 20–34 age group (2.47, 1.02; 2.77, 1.16 msec, respectively, all P<0.01).

Conclusion

The MR T2 values of the posterior meniscal horns increase with increasing age in women and are higher in women than in men. The age-related rise of T2 values appears to be more severe in medial menisci than in lateral menisci. Differences exist in the white zone and red/white zone.

[Histopathological degeneration score of fibrous cartilage. Low- and high-grade meniscal degeneration]

Although histopathology of meniscal degeneration plays an important role, no criteria to assess severity of the degeneration are available to date. Our aim was to create a histopathological scoring system for meniscal degeneration with good interobserver variability, taking matrix degradation and cellularity in meniscal tissue into consideration. Degeneration is classified as follows: grade 1 (low), grade 2 (intermediate), grade 3 (high). The pattern of NITEGE deposits (G1 fragment of aggrecan) was assessed immunohistochemically (n=38) and compared with the grades of degeneration. In 48% of the patients with grade 2 or 3 degeneration extracellular NITEGE deposits (specificity 100%) were found, whereas grade 1 patients showed no deposits. Extracellular NITEGE deposits correlated positively with the grade of degeneration. In all, 30 cases (10 per grade) were assessed by three pathologists (A, B, C). Grading conformity was 70% for grade 1, 66% for grade 2 and 100% for grade 3. Cohen's Kappa coefficient was 0.6--0.7 between pairs of observers. Combining grade 1 and 2 to low-grade degeneration, compared to a grade-3 high-grade degeneration achieved Kappa coefficients of between 0.93 and 1.0. This reproducible degeneration score for fibrous cartilage could form the basis for the standardized assessment of meniscal degeneration.

[Meniscal degeneration score and NITEGE expression : immunohistochemical detection of NITEGE in advanced meniscal degeneration]

BACKGROUND

Meniscal degeneration (MD) is a structural change of fibrous cartilage that is common in orthopaedic diagnostics and relevant for health insurance matters. So far, there has been neither a standardised scoring system nor an immunohistochemical marker for MD.

MATERIAL AND METHOD

In this retrospective trial, the meniscal tissue of 60 patients was assessed immunohistochemically for NITEGE (G1 fragment of the proteoglycan aggrecan) expression. NITEGE expression was correlated with defined grades of MD: little (grade 0/1), medium (grade 2), or severe (grade 3).

RESULTS

Detection of extracellular NITEGE deposits in grade 2 or 3 MD had a positive predictive value and specificity of 100%, whereas no deposits were found in grade 0/1 MD. Sensitivity in advanced MD was 55%. Detection of extracellular NITEGE correlated positively with the grade of degeneration, as did patient age and the grade of degeneration. The patient age of those with grade 0/1 MD was significantly lower than for grade 3 (p<0.0001).

CONCLUSION

The thoroughly defined degeneration score (grade 1 - grade 3 MD) is suitable to assess the severity of degeneration. Extracellular NITEGE deposits can be regarded as an immunohistochemical marker for advanced (grades 2 and 3) MD.

Chondrocytes and meniscal fibrochondrocytes differentially process aggrecan during de novo extracellular matrix assembly

Aggrecan is an extracellular matrix molecule that contributes to the mechanical properties of articular cartilage and meniscal fibrocartilage, but the abundance and processing of aggrecan in these tissues are different. The objective of this study was to compare patterns of aggrecan processing by chondrocytes and meniscal fibrochondrocytes in tissue explants and cell-agarose constructs. The effects of transforming growth factor-beta 1 (TGF-beta1) stimulation on aggrecan deposition and processing were examined, and construct mechanical properties were measured. Fibrochondrocytes synthesized and retained less proteoglycans than did chondrocytes in tissue explants and agarose constructs. In chondrocyte constructs, TGF-beta1 induced the accumulation of a 120-kDa aggrecan species previously detected in mature bovine cartilage. Fibrochondrocyte-seeded constructs contained high-molecular-weight aggrecan but lacked aggrecanase-generated fragments found in native, immature meniscus. In addition, reflecting the lesser matrix accumulation, fibrochondrocyte constructs had significantly lower compression moduli than did chondrocyte constructs. These cell type-specific differences in aggrecan synthesis, retention, and processing may have implications for the development of functional engineered tissue grafts.

Synovial fluid level of aggrecan ARGS fragments is a more sensitive marker of joint disease than glycosaminoglycan or aggrecan levels: a cross-sectional study

INTRODUCTION

Aggrecanase cleavage at the 392Glu-393Ala bond in the interglobular domain (IGD) of aggrecan, releasing N-terminal 393ARGS fragments, is an early key event in arthritis and joint injuries. Here, we use a quantitative immunoassay of aggrecan ARGS neoepitope fragments in human synovial fluid to determine if this cleavage-site specific method better identifies joint pathology than previously available less specific aggrecan assays.

METHODS

Synovial fluid (SF) from 26 people with healthy knees (reference) and 269 patients were analyzed in a cross-sectional study. Patient groups were acute inflammatory arthritis, acute knee injury, chronic knee injury and knee osteoarthritis (OA). Aggrecan ARGS fragments were assayed by ELISA using the monoclonal antibody OA-1. Total aggrecan content was analyzed by an ELISA using the monoclonal antibody 1-F21, and sulfated glycosaminoglycan by Alcian blue precipitation.

RESULTS

Aggrecan ARGS fragment concentrations in all groups differed from the reference group (P < 0.001). The acute inflammatory arthritis group had the highest median level, 177-fold greater than that of the reference group. Median levels (in pmol ARGS/ml SF) were: reference 0.5, acute inflammatory arthritis 88.5, acute knee injury 53.9, chronic knee injury 0.5 and OA 4.6. In contrast, aggrecan and sulfated glycosaminoglycan concentrations varied much less between groups, and only acute inflammatory arthritis and acute knee injury were found to have a two-fold increase in median levels compared to the reference.

CONCLUSIONS

Levels of aggrecan ARGS fragments in human synovial fluid are increased in human arthritis, OA and after knee injury, likely reflecting an enhanced cleavage at the 392Glu-393Ala bond in the IGD by aggrecanase. An assay that specifically quantified these fragments better distinguished samples from joints with pathology than assays monitoring aggrecan or glycosaminoglycan concentrations. The newly developed ARGS fragment assay can be used to monitor aggrecanase activity in human joint disease and experimental models.

Western blot quantification of aggrecan fragments in human synovial fluid indicates differences in fragment patterns between joint diseases

OBJECTIVE

To develop a Western blot method for quantification of multiple aggrecan fragments in human synovial fluids (SFs).

METHOD

SF aggrecan fragments were prepared from knee healthy (reference), knee injury and arthritis subjects by CsCl gradient centrifugations collecting D1 fractions. Samples were analyzed by Western blot, using antibodies against the N-terminal epitope ARGS and the G3 domain, and fragments were quantified using a digital luminescence image analyzer.

RESULTS

The method had a coefficients of variation of 10-30%, and a high correlation (r(S)=0.86) with a corresponding enzyme-linked immunosorbent assay (ELISA). The SFs from reference, knee injured and arthritic subjects contained two major ARGS fragments, ARGS-SELE and ARGS-CS1, and three major G3 fragments (GRGT-G3, GLGS-G3 and AGEG-G3). Compared to the reference, the acute arthritis and acute joint injury groups had a 30-fold elevated concentration of ARGS fragments, and both groups had a higher proportion of the aggrecan in joint fluid as ARGS fragments compared to the other groups. The reference and chronic injury groups had an excess of ARGS-CS1 fragments over ARGS-SELE fragments, while subjects with acute arthritis or osteoarthritis had a more even distribution between these fragments.

CONCLUSIONS

We have developed a novel Western blot quantification method for quantification of SF aggrecan fragments which can differentiate fragments of different sizes sharing the same epitope. The anti-ARGS and anti-G3 quantitative Western blots provided information important for a better understanding of the proteolytic pathways in aggrecan breakdown, information that discriminates between different joint diseases, and may aid in identification of new biomarkers.

Fragmentation of decorin, biglycan, lumican and keratocan is elevated in degenerate human meniscus, knee and hip articular cartilages compared with age-matched macroscopically normal and control tissues

Introduction

The small leucine-rich proteoglycans (SLRPs) modulate tissue organization, cellular proliferation, matrix adhesion, growth factor and cytokine responses, and sterically protect the surface of collagen type I and II fibrils from proteolysis. Catabolism of SLRPs has important consequences for the integrity of articular cartilage and meniscus by interfering with their tissue homeostatic functions.

Methods

SLRPs were dissociatively extracted from articular cartilage from total knee and hip replacements, menisci from total knee replacements, macroscopically normal and fibrillated knee articular cartilage from mature age-matched donors, and normal young articular cartilage. The tissue extracts were digested with chondroitinase ABC and keratanase-I before identification of SLRP core protein species by Western blotting using antibodies to the carboxyl-termini of the SLRPs.

Results

Multiple core-protein species were detected for all of the SLRPs (except fibromodulin) in the degenerate osteoarthritic articular cartilage and menisci. Fibromodulin had markedly less fragments detected with the carboxyl-terminal antibody compared with other SLRPs. There were fewer SLRP catabolites in osteoarthritic hip than in knee articular cartilage. Fragmentation of all SLRPs in normal age-matched, nonfibrillated knee articular cartilage was less than in fibrillated articular cartilage from the same knee joint or total knee replacement articular cartilage specimens of similar age. There was little fragmentation of SLRPs in normal control knee articular cartilage. Only decorin exhibited a consistent increase in fragmentation in menisci in association with osteoarthritis. There were no fragments of decorin, biglycan, lumican, or keratocan that were unique to any tissue. A single fibromodulin fragment was detected in osteoarthritic articular cartilage but not meniscus. All SLRPs showed a modest age-related increase in fragmentation in knee articular and meniscal cartilage but not in other tissues.

Conclusion

Enhanced fragmentation of SLRPs is evident in degenerate articular cartilage and meniscus. Specific decorin and fibromodulin core protein fragments in degenerate meniscus and/or human articular cartilage may be of value as biomarkers of disease. Once the enzymes responsible for their generation have been identified, further research may identify them as therapeutic targets.

Kinetic analysis of the polymerization and depolymerization of β2-microglobulin-related amyloid fibrils in vitro

beta(2)-Microglobulin-related (Abeta(2)M) amyloidosis is a serious complication in patients on long-term dialysis, and partial unfolding of beta(2)-microglobulin (beta(2)-m) is believed to be prerequisite to its assembly into Abeta(2)M amyloid fibrils. Many kinds of amyloid-associated molecules (e.g., apolipoprotein E (apoE), glycosaminoglycans (GAGs), proteoglycans (PGs)) may contribute to the development of Abeta(2)M amyloidosis. The formation of Abeta(2)M amyloid fibrils in vitro was first observed at low pH (2.0-3.0). Very recently, low concentrations of 2,2,2-trifluoroethanol (TFE) and the sub-micellar concentration of sodium dodecyl sulfate, a model for anionic phospholipids, have been reported to cause the extension of Abeta(2)M amyloid fibrils at a neutral pH, inducing partial unfolding of beta(2)-m and stabilization of the fibrils. Moreover, apoE, GAGs and PGs were found to stabilize Abeta(2)M amyloid fibrils at a neutral pH, forming a stable complex with the fibrils. Some GAGs, especially heparin enhanced the fibril extension in the presence of TFE at a neutral pH. Some PGs, especially biglycan also induced the polymerization of acid-denatured beta(2)-m. These findings are consistent with the hypothesis that in vivo, specific molecules that affect the conformation and stability of beta(2)-m and amyloid fibrils will have significant effects on the deposition of Abeta(2)M amyloid fibrils.

Comparative spatial and temporal localisation of perlecan, aggrecan and type I, II and IV collagen in the ovine meniscus: an ageing study

This is the first study to immunolocalise perlecan in meniscal tissues and to demonstrate how its localisation varied with ageing relative to aggrecan and type I, II and IV collagen. Perlecan was present in the middle and inner meniscal zones where it was expressed by cells of an oval or rounded morphology. Unlike the other components visualised in this study, perlecan was strongly cell associated and its levels fell significantly with age onset and cell number decline. The peripheral outer meniscal zones displayed very little perlecan staining other than in small blood vessels. Picrosirius red staining viewed under polarised light strongly delineated complex arrangements of slender discrete randomly oriented collagen fibre bundles as well as transverse, thick, strongly oriented, collagen tie bundles in the middle and outer meniscal zones. The collagen fibres demarcated areas of the meniscus which were rich in anionic toluidine blue positive proteoglycans; immunolocalisations confirmed the presence of aggrecan and perlecan. When meniscal sections were examined macroscopically, type II collagen localisation in the inner meniscal zone was readily evident in the 2- to 7-day-old specimens; this became more disperse in the older meniscal specimens. Type I collagen had a widespread distribution in all meniscal zones at all time points. Type IV collagen was strongly associated with blood vessels in the 2- to 7-day-old meniscal specimens but was virtually undetectable at the later time points (>7 month).

Systemic hypoxia alters gene expression levels of structural proteins and growth factors in knee joint cartilage

We investigated the effects of short- (8- and 24-h) and long-term (3 weeks) exposure to systemic normobaric hypoxia (13%) on the gene expression level of structural proteins and growth factors in knee joint cartilage of rabbits. Collagen type Ia2, II, and Va1, TGF-beta1, and b-FGF were upregulated after short-term hypoxia in both menisci, but not in articular cartilage. In contrast, long-term hypoxia downregulated gene expression level of collagens, aggrecan, and growth factors in articular cartilage and meniscal fibrocartilage. Interestingly, gene expression levels of non-collagenous proteins biglycan, decorin, and versican were not affected by short-term or by long-term hypoxia in knee joint cartilage. The present study suggests that changes in oxygen level differentially affect gene expression levels of growth factors, collagens, and non-collagenous proteins in normal knee joint cartilage in rabbits.

Age-related changes in muscles and joints

Aging muscle and joint changes can have a tremendous impact on the functionality of elderly people with and without disabilities. Studies in animal models have shown some potentially beneficial interventions (eg, gene therapy). Further research is needed to ascertain their benefits in humans. A better understanding of mechanisms by which skeletal muscle and joint changes take place in a geriatric population will be helpful to find reasonable ways to prevent age-related change and improve disability. Although some agents have been reported to have significant positive effects, further studies are needed to determine long-term side effects. More information is needed with respect to the changes in muscles and joints in various disabilities.

Molecular interactions in the formation and deposition of beta2-microglobulin-related amyloid fibrils

In beta2-microglobulin-related (A beta2M) amyloidosis, a serious complication in patients on long-term dialysis, partial unfolding of beta2-microglobulin (beta2-m) is believed to be prerequisite to its assembly into A beta2M amyloid fibrils. Many kinds of amyloid-associated molecules, (e.g., apolipoprotein E (apoE), glycosaminoglycans (GAGs), proteoglycans (PGs)) may contribute to the development of A beta2M amyloidosis. In 1990s, the formation of A beta2M amyloid fibrils in vitro was first observed at low pH (2.0-3.0). Very recently, low concentrations of 2,2,2-trifluoroethanol (TFE) and the sub-micellar concentration of sodium dodecyl sulfate, a model for anionic phospholipids, have been reported to cause the extension of A beta2M amyloid fibrils at a neutral pH, inducing partial unfolding of beta2-m and stabilization of the fibrils. Moreover, apoE, GAGs, and PGs were found to stabilize A beta2M amyloid fibrils at a neutral pH, forming a stable complex with the fibrils. Some GAGs, especially heparin, enhanced the fibril extension in the presence of TFE at a neutral pH. Some PGs, especially biglycan also induced the polymerization of acid-denatured beta2-m. These findings are consistent with the hypothesis that in vivo, specific molecules that affect the conformation and stability of beta2-m and amyloid fibrils will have significant effects on the deposition of A beta2M amyloid fibrils.

The concentration, gene expression, and spatial distribution of aggrecan in canine articular cartilage, meniscus, and anterior and posterior cruciate ligaments: a new molecular distinction between hyaline cartilage and fibrocartilage in the knee joint

The concentration, spatial distribution, and gene expression of aggrecan in meniscus, articular cartilage, and the anterior and posterior cruciate ligaments (ACL and PCL) was determined in the knee joints of five mature dogs. An anti-serum against peptide sequences specific to the G1 domain of aggrecan was employed in competitive-inhibition ELISA of guanidine HCl extracts and immunofluorescence microscopy. Gene expression was determined by Taqman real-time PCR. The concentration of aggrecan in articular cartilage (240.1 +/- 32 nMol/g dry weight) was higher than that in meniscus (medial meniscus: 33.4 +/- 4.3 nMol/g) and ligaments (ACL: 6.8 +/- 0.9 nMol/g). Aggrecan was more concentrated in the inner than the outer zone of the meniscus. Aggrecan in meniscus showed an organized, spatial network, in contrast to its diffuse distribution in articular cartilage. Thus, differences in the concentration, gene expression, and spatial distribution of aggrecan constitute another molecular distinction between hyaline cartilage and fibrocartilage of the knee.

Glycosaminoglycan and proteoglycan inhibit the depolymerization of beta2-microglobulin amyloid fibrils in vitro

BACKGROUND

Although several kinds of evidence suggest that glycosaminoglycans (GAGs) and proteoglycans (PGs) may contribute to the development of beta2-microglobulin-related (Abeta2m) amyloidosis, the precise roles of these molecules for the development of Abeta2m amyloidosis are poorly understood.

METHODS

We investigated the effects of GAGs and PGs on the depolymerization of Abeta2m amyloid fibrils at a neutral pH, as well as on the formation of the fibrils at an acidic pH in vitro, using fluorescence spectroscopy with thioflavin T and electron microscopy.

RESULTS

Depolymerization of Abeta2m amyloid fibrils at pH 7.5 at 37 degrees C was inhibited dose-dependently by the presence of some GAGs (heparin, dermatan sulfate, or heparan sulfate) or PGs (biglycan, decorin, or keratan sulfate proteoglycan). Electron microscopy revealed that a significant amount of Abeta2m amyloid fibrils remained in the reaction mixture with some lateral aggregation. Second, when monomeric beta2m was incubated with aggrecan, biglycan, decorin, or heparin at pH 2.5 at 37 degrees C for up to 21 days, the thioflavin T fluorescence increased depending on dose and time. Electron microscopy revealed the formation of rigid and straight fibrils similar to Abeta2m amyloid fibrils in beta2m incubated with biglycan for 21 days.

CONCLUSION

These results suggest that some GAGs and PGs could enhance the deposition of Abeta2m amyloid fibrils in vivo, possibly by binding directly to the surface of the fibrils and stabilizing the conformation of beta2m in the fibrils, as well as by acting as a scaffold for the polymerization of beta2m into the fibrils.