Histochemical studies of the extracellular matrix of human articular cartilage--a review

[Tissue biomechanics: connective tissue characterization : Cluster tissue biomechanics]

The various connective tissues of the body have different functions, which result from their specific structure and composition. The identification of this structure-function relationship is of great importance for various disciplines such as medicine, biology or tissue engineering. Connective tissue consists mainly of an extracellular matrix (ECM) and a limited number of cells. It is extremely adaptable because the activity of the cells remodels the composition and structure of the ECM in order to adapt the mechanical properties (functions) to the new demands (e.g. an increased mechanical stimulus).

Intra-articular administration of extra-virgin olive oil in degenerative osteoarthritis

BACKGROUND

We aimed to analyze the outcomes of intraarticular extra virgin olive oil (EVOO) injection on mechanically induced rabbit knee osteoarthritis (OA) by studying the morphological, histological, and radiological findings.

METHODS

The study was conducted on 32 New Zealand White rabbits. The randomly numbered subjects were divided into two main groups. The rabbits numbered 1 to 16 were selected to be the group to receive EVOO, and the remaining were selected into a control group. Both groups were separated into two subgroups for short-term (five weeks) and long-term (10 weeks) follow-up. Anterior cruciate ligament transection was applied on the left knees of all the rabbits via medial parapatellar arthrotomy to simulate knee instability. Immediately after the surgical procedure, 0.2 cc of EVOO was injected into the knee joint of rabbits numbered 1-16, and the control group received 0.2 cc of sterile saline. On the 14th day, long-term group subjects were administered another dose of 0.2 cc EVOO intraarticularly.

RESULTS

The gross morphological scores of the control group subjects were significantly different from the EVOO group for both short-term (p = 0,055) and long-term (p = 0,041) scores. In parallel, the MRI results of the EVOO subjects were significantly different from the control group for both short-term and long-term follow-up assessment scores (p = 0.017, p = 0.014, respectively). The Mankin scoring results showed that there were statistically significant differences between the EVOO and control group in the comparison of both total scores (p = 0.001 for short-term and p = 0.004 for long-term) and subgroup scoring, including macroscopic appearance, chondrocyte cell number, staining, and Tidemark integrity in both short-term (p = 0.005, p = 0.028, p = 0.001, p = 0.005, respectively) and long-term assessments (p = 0.002, p = 0.014, p < 0.001, p = 0. 200, respectively).

CONCLUSIONS

We have observed promising outcomes of intra-articular application of extra virgin olive oil in the treatment of acute degenerative osteoarthritis in rabbit knees. Due to its potential cartilage restorative and regenerative effects, EVOO, when administered intra-articularly, may be a promising agent to consider for further research in the treatment of OA.

A new insight on copper: Promotion of collagen synthesis and myofiber growth and development in juvenile grass carp (Ctenopharyngodon idella)

Copper (Cu) is a trace element, essential for fish growth. In the current study, in addition to growth performance, we first explored the effects of Cu on collagen synthesis and myofiber growth and development in juvenile grass carp (Ctenopharyngodon idella). A total of 1080 fish (11.16 ± 0.01 g) were randomly divided into 6 treatments (3 replicates per treatment) to receive five doses of organic Cu, which were Cu citrate (CuCit) at 0.99 (basal diet), 2.19, 4.06, 6.15, and 8.07 mg/kg, and one dose of inorganic Cu (CuSO4·5H2O at 3.15 mg/kg), for 9 weeks. The results showed appropriate Cu level (4.06 mg/kg) enhanced growth performance, improved nutritional Cu status, and downregulated Cu-transporting ATPase 1 mRNA levels in the hepatopancreas, intestine, and muscle of juvenile grass carp. Meanwhile, collagen content in fish muscle was increased after Cu intake, which was probably due to the following pathways: (1) activating CTGF/TGF-β1/Smads signaling pathway to regulate collagen transcription; (2) upregulating of La ribonucleoprotein domain family 6 (LARP6) mRNA levels to regulate translation initiation; (3) increasing proline hydroxylase, lysine hydroxylase, and lysine oxidase activities to regulate posttranslational modifications. In addition, optimal Cu group increased myofiber diameters and the frequency of myofibers with diameter >50 μm, which might be associated with upregulation of cyclin B, cyclin D, cyclin E, proliferating cell nuclear antigen, myogenic determining factor (MyoD), myogenic factor 5, myogenin (MyoG), myogenic regulatory factor 4 and myosin heavy chain (MyHC) and downregulation of myostatin mRNA levels, increasing protein levels of MyoD, MyoG and MyHC in fish muscle. Finally, based on percentage weight gain (PWG), serum ceruloplasmin (Cp) activity and collagen content in fish muscle, Cu requirements were determined as 4.74, 4.37 and 4.62 mg/kg diet (CuCit as Cu source) of juvenile grass carp, respectively. Based on PWG and Cp activity, compared to CuSO4·5H2O, the efficacy of CuCit were 131.80% and 115.38%, respectively. Our findings provide new insights into Cu supplementation to promote muscle growth in fish, and help improve the overall productivity of aquaculture.

A guide to preclinical evaluation of hydrogel-based devices for treatment of cartilage lesions

The drive to develop cartilage implants for the treatment of major defects in the musculoskeletal system has resulted in a major research thrust towards developing biomaterial devices for cartilage repair. Investigational devices for the restoration of articular cartilage are considered as significant risk materials by regulatory bodies and therefore proof of efficacy and safety prior to clinical testing represents a critical phase of the multidisciplinary effort to bridge the gap between bench and bedside. To date, review articles have thoroughly covered different scientific facets of cartilage engineering paradigm, but surprisingly, little attention has been given to the preclinical considerations revolving around the validation of a biomaterial implant. Considering hydrogel-based cartilage products as an example, the present review endeavors to provide a summary of the critical prerequisites that such devices should meet for cartilage repair, for successful implantation and subsequent preclinical validation prior to clinical trials. Considerations pertaining to the choice of appropriate animal model, characterization techniques for the quantitative and qualitative outcome measures, as well as concerns with respect to GLP practices are also extensively discussed. This article is not meant to provide a systematic review, but rather to introduce a device validation-based roadmap to the academic investigator, in anticipation of future healthcare commercialization. STATEMENT OF SIGNIFICANCE: There are significant challenges around translation of in vitro cartilage repair strategies to approved therapies. New biomaterial-based devices must undergo exhaustive investigations to ensure their safety and efficacy prior to clinical trials. These considerations are required to be applied from early developmental stages. Although there are numerous research works on cartilage devices and their in vivo evaluations, little attention has been given into the preclinical pathway and the corresponding approval processes. With a focus on hydrogel devices to concretely illustrate the preclinical path, this review paper intends to highlight the various considerations regarding the preclinical validation of hydrogel devices for cartilage repair, from regulatory considerations, to implantation strategies, device performance aspects and characterizations.

Histochemical and Immunohistochemical Methods for the Identification of Proteoglycans

Proteoglycans (PGs) are non-fibrillar extracellular matrix (ECM) molecules composed by a protein core and glycosaminoglycan (GAG) chains. These molecules are present in all tissues playing essential structural, biomechanical, and biological roles. In addition, PGs can regulate cell behavior due to their versatility and ability to interact with other ECM molecules, growth factors, and cells. The distribution of PGs can be evaluated by histochemical and immunohistochemical methods. Histochemical methods aimed to provide a useful overview of the presence and distribution pattern of certain groups of PGs. In contrast, immunohistochemical procedures aimed the identification of highly specific target molecules. In this chapter we described Alcian Blue, Safranin O, and Toluidine Blue histochemical methods for the screening of PGs in tissue sections. Finally, we describe the immunohistochemical procedures for specific identification of PGs (decorin, biglycan, and versican) in formaldehyde-fixed and paraffin-embedded tissues.

3D in-vitro cultures of human bone marrow and Wharton’s jelly derived mesenchymal stromal cells show high chondrogenic potential

In this study, chondrogenic potentials of 3D high-density cultures of Bone Marrow (BM) and Wharton’s Jelly (WJ)-derived mesenchymal stromal cells (MSCs) was investigated by chondrogenesis- and cytokine-related gene expression over a 16-day culture period supplemented with human transforming growth factor (hTGF)-β1 at 10 ng/ml. In BM-MSC 3D models, a marked upregulation of chondrogenesis-related genes, such as SOX9, COL2A1, and ACAN (all p < 0.05) and formation of spherical pellets with structured type II collagen fibers were observed. Similarly, WJ-based high-density culture appeared higher in size and more regular in shape, with a significant overexpression of COL2A1 and ACAN (all p < 0.05) at day 16. Moreover, a similar upregulation trend was documented for IL-6 and IL-10 expression in both BM and WJ 3D systems. In conclusion, MSC-based high-density cultures can be considered a promising in vitro model of cartilage regeneration and tissue engineering. Moreover, our data support the use of WJ-MSCs as a valid alternative for chondrogenic commitment of stem cells in regenerative medicine.

Comparative Assessment of Primary Osteoarthritis Progression Using Conventional Histopathology, Polarized Light Microscopy, and Immunohistochemistry

OBJECTIVE

Evaluation of collagen orientation and arrangement in articular cartilage can improve our understanding of primary osteoarthritis (OA) progression and targeted therapies. Our goal was to determine if polarized light microscopy (PLM) for collagen organization is useful in identifying early primary OA features in comparison to current standard histopathological methods.

DESIGN

Osteochondral specimens from 90 total knee arthroplasty patients with relatively preserved lateral femoral condyle were scored using (1) histological-histochemical grading system (HHGS); (2) Osteoarthritis Research Society International (OARSI); (3) PLM-Changoor system for repair cartilage, scores ranging between 0 (totally disorganized cartilage) and 5 (healthy adult cartilage); and (4) new PLM system for primary OA cartilage with superficial zone PLM (PLM-SZ) and deep zone PLM (PLM-DZ) scores, each ranging between 0 (healthy adult SZ and DZ collagen organization) and 4 (total loss of collagen organization). Serial sections were stained for collagen I and II antibodies. Spearman correlation coefficients (r_s) were determined.

RESULTS

The associations between: (1) PLM-Changoor and HHGS or OARSI were weak (r_s = -0.36) or moderate (r_s = -0.56); (2) PLM-SZ and HHGS or OARSI were moderate (r_s = 0.46 or r_s = 0.53); and (3) PLM-DZ and HHGS or OARSI were poor (r_s = 0.31 or r_s = 0.21), respectively. Specimens exhibiting early and mild OA (HHGS < 5 and OARSI < 8.6) had PLM-SZ and PLM-DZ scores between 0 and 4 and between 0 and 3, respectively, and indicated new histopathological features not currently considered by HHGS/OARSI.

CONCLUSIONS

PLM was effective at identifying early SZ and DZ collagen alterations that were not evident in the traditional scoring systems. Incorporating PLM scores and/or additional HHGS/OARSI features can help improve characterization of early primary OA cartilage.

Contrast-Enhanced Micro-Computed Tomography for 3D Visualization and Quantification of Glycosaminoglycans in Different Cartilage Types

OBJECTIVE

To compare CA4+-enhanced micro-computed tomography (microCT) of bovine articular, meniscal, nasal, and auricular cartilage, each of which possesses a different extracellular matrix (ECM) composition and structure.

DESIGN

The diffusion kinetics of CA4+ in different native cartilage types were assessed over 20 hours. The feasibility of CA4+-enhanced microCT to visualize and quantify glycosaminoglycans (GAGs) in these different tissues was tested using safranin-O staining and 1,9-dimethylmethylene blue assay.

RESULTS

The diffusion kinetics of CA4+ in auricular cartilage are significantly slower compared with all other cartilage types. Total GAG content per volume correlates to microCT attenuation with an R² value of 0.79 for all cartilage types. Three-dimensional contrast-enhanced microCT images of spatial GAG distribution reflect safranin-O staining and highlight the differences in ECM structure, with heterogeneous regions with higher GAG concentrations highlighted by the contrast agent.

CONCLUSIONS

CA4+-enhanced microCT enables assessment of 3-dimensiona distribution and GAG content in different types of cartilage and has promise as an ex vivo diagnostic technique to monitor matrix development in different tissues over time as well as tissue-engineered constructs.

Biomechanical Changes of Repair Tissue after Autologous Chondrocyte Implantation at Long-Term Follow-Up

Objective. This study aims to describe biomechanical maturation process of repair tissue after cartilage repair with autologous chondrocyte implantation (ACI) at long-term follow-up. Design. After ACI, 40 patients underwent altogether 60 arthroscopic biomechanical measurements of the repair tissue at various time points during an up to 11-year follow-up period. Of these patients, 30 patients had full-thickness cartilage lesions and 10 had an osteochondritis dissecans (OCD) defect. The mean lesion area was 6.5 cm² (SD 3.2). A relative indentation stiffness value for each individually measured lesion was calculated as a ratio of repair tissue and surrounding cartilage indentation value to enable interindividual comparison. Results. Repair tissue stiffness improved during approximately 5 years after surgery. Most of the increase in stiffness occurred during the first 2 years. The curvilinear correlation between relative stiffness values and the follow-up time was 0.31 (95% CI 0.07-0.52), P = 0.017. The interindividual variation of the stiffness was high. Lesion properties or demographic factors showed no significant correlation to biomechanical outcome. The overall postoperative average relative stiffness was 0.75 (SD 0.47). Conclusions. Our clinical study describes a biomechanical maturation process of cartilage repair that may continue even longer than expected. A substantial increase in tissue stiffness proceeds for the first two years postoperatively. Minor progression proceeds for even longer. In some repairs, the biomechanical result was equal to native cartilage, suggesting hyaline-type repair. The variation in biomechanical results suggests substantial inconsistency in the structural outcome following ACI.

Optimization and Validation of a Human Ex Vivo Femoral Head Model for Preclinical Cartilage Research and Regenerative Therapies

OBJECTIVE

Articular cartilage is incapable of effective repair following injury or during osteoarthritis. While there have been developments in cartilage repair technologies, there is a need to advance biologically relevant models for preclinical testing of biomaterial and regenerative therapies. This study describes conditions for the effective ex vivo culture of the whole human femoral head.

DESIGN

Fresh, viable femoral heads were obtained from femoral neck fractures and cultured for up to 10 weeks in (a) Dulbecco's modified Eagle's medium (DMEM); (b) DMEM + mixing; (c) DMEM + 10% human serum (HS); (d) DMEM + 10% HS + mixing. The viability, morphology, volume, and density of fluorescently labelled in situ chondrocytes and cartilage surface roughness were assessed by confocal microscopy. Cartilage histology was studied for glycosaminoglycan content using Alcian blue and collagen content using picrosirius red.

RESULTS

Chondrocyte viability remained at >95% in DMEM + 10% HS. In DMEM alone, viability remained high for ~4 weeks and then declined. For the other conditions, superficial zone chondrocyte viability fell to <35% at 10 weeks with deeper zones being relatively unaffected. In DMEM + 10% HS at 10 weeks, the number of chondrocytes possessing cytoplasmic processes increased compared with DMEM (P = 0.017). Alcian blue labeling decreased (P = 0.02) and cartilage thinned (P ≤ 0.05); however, there was no change to surface roughness, chondrocyte density, chondrocyte volume, or picrosirius red labeling (P > 0.05).

CONCLUSIONS

In this ex vivo model, chondrocyte viability was maintained in human femoral heads for up to 10 weeks in culture, a novel finding not previously reported. This human model could prove invaluable for the exploration, development, and assessment of preclinical cartilage repair and regenerative therapies.

3D Cell Culture Systems: Tumor Application, Advantages, and Disadvantages

The traditional two-dimensional (2D) in vitro cell culture system (on a flat support) has long been used in cancer research. However, this system cannot be fully translated into clinical trials to ideally represent physiological conditions. This culture cannot mimic the natural tumor microenvironment due to the lack of cellular communication (cell-cell) and interaction (cell-cell and cell-matrix). To overcome these limitations, three-dimensional (3D) culture systems are increasingly developed in research and have become essential for tumor research, tissue engineering, and basic biology research. 3D culture has received much attention in the field of biomedicine due to its ability to mimic tissue structure and function. The 3D matrix presents a highly dynamic framework where its components are deposited, degraded, or modified to delineate functions and provide a platform where cells attach to perform their specific functions, including adhesion, proliferation, communication, and apoptosis. So far, various types of models belong to this culture: either the culture based on natural or synthetic adherent matrices used to design 3D scaffolds as biomaterials to form a 3D matrix or based on non-adherent and/or matrix-free matrices to form the spheroids. In this review, we first summarize a comparison between 2D and 3D cultures. Then, we focus on the different components of the natural extracellular matrix that can be used as supports in 3D culture. Then we detail different types of natural supports such as matrigel, hydrogels, hard supports, and different synthetic strategies of 3D matrices such as lyophilization, electrospiding, stereolithography, microfluid by citing the advantages and disadvantages of each of them. Finally, we summarize the different methods of generating normal and tumor spheroids, citing their respective advantages and disadvantages in order to obtain an ideal 3D model (matrix) that retains the following characteristics: better biocompatibility, good mechanical properties corresponding to the tumor tissue, degradability, controllable microstructure and chemical components like the tumor tissue, favorable nutrient exchange and easy separation of the cells from the matrix.

Hyalinization as a histomorphological risk predictor in oral pathological lesions

Background

Hyalinization is a process of conversion of stromal connective tissue into a homogeneous, acellular translucent material. Nevertheless, hyalinization could provide insights into the biologic behaviour and prognosis of pathological lesions. Few studies with limited sample size have intended to assess the correlation of hyalinization and biologic behaviour in oral lesions.

Aim

The current review aims to comprehensively appraise the mechanism of hyalinization in pathological oral hyalinizing lesions (OHL) and its clinical implications with emphasis on differential stains employed.

Methods

An electronic search was performed in the PubMed database (from year 2000-2020) using the keywords "special stains in oral hyalinizing lesions", "significance of hyalinization in oral lesions" and "hyalinization and biologic behaviour". Original research articles analyzing the effect of hyalinization on biologic characteristics of the lesion were evaluated in this review. Narrative review articles that provided insights into the mechanism of hyalinization and maturity of collagen fibers were also considered for analysis.

Conclusion

The presence of hyalinization does seem to have a significant effect on the biologic behaviour of pathological lesions. There is substantial scope to further investigate the process of hyalinization on larger samples and its correlation with the aggressive behaviour of OHLs. Special stains and advanced investigations such as immunohistochemistry for stromal markers would define the nature of hyalinized material and validate the correlation.

Clinical significance

The prediction of the biologic behaviour of a lesion established through assessment of hyalinization would prevent unwanted over or under treatment leading to a better prognosis.

Changes in Matrix Components in the Developing Human Meniscus

BACKGROUND

Treatment of meniscal tears is necessary to maintain the long-term health of the knee joint. Morphological elements, particularly vascularity, that play an important role in meniscal healing are known to change during skeletal development.

PURPOSE

To quantitatively evaluate meniscal vascularity, cellularity, collagen, and proteoglycan content by age and location during skeletal development.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Medial and lateral menisci from 14 male and 7 female cadavers aged 1 month to 11 years were collected and evaluated. For each meniscus, histologic and immunohistologic techniques were used to establish the ratio of the area of proteoglycan (safranin O) positivity to the total area (proteoglycan ratio), collagen type I and type II immunostaining positivity, number of blood vessels, and cell density. These features were evaluated over the entire meniscus and also separately in 5 circumferential segments: anterior root, anterior horn, body, posterior horn, and posterior root. Additionally, cell density and number of blood vessels were examined in 3 radial regions: inner, middle, and periphery.

RESULTS

Age was associated with a decrease in meniscal vessel count and cell density, while the proteoglycan ratio increased with skeletal maturity. Differences in vessel counts, cellular density, and proteoglycan ratio in different anatomic segments as well as in the inner, middle, and peripheral regions of the developing menisci were also observed. Collagen immunostaining results were inconsistent and not analyzed.

CONCLUSION

The cellularity and vascularity of the developing meniscus decrease with age and the proteoglycan content increases with age. All of these parameters are influenced by location within the meniscus.

CLINICAL RELEVANCE

Age and location differences in meniscal morphology, particularly in the number of blood vessels, are expected to influence meniscal healing.

Slippery when wet: The free surface of the articular cartilage

The free surface of the articular cartilage must withstand compressive and shearing forces, maintain a low friction coefficient and allow oxygen and metabolites to reach the underlying matrix. In many ways it is critical to the physiology of the whole tissue and its disruption always involves deep pathological alterations and loss of the joint integrity. Being very difficult to image with section-based conventional techniques, it was often described by previous research in conflicting terms or entirely overlooked. High-magnification face-on observations with high resolution scanning electron microscopy and with scanning probe microscopy revealed a very thin, delicate superficial layer rich in glycoconjugates, which may explain the very low friction coefficient of the tissue but which was very easily altered and/or dissolved in the preparation. Beneath this superficial sheet lies a thicker coat of thin, highly uniform, slightly wavy collagen fibrils lying parallel to the surface and mutually interconnected by a huge number of interfibrillar glycosaminoglycan bridges. These bridges and the collagen fibrils form an extended reticular structure able to redistribute tensile and compressive stress across a larger area of the surface and hence a greater volume of tissue.

Mechano-activated biomolecule release in regenerating load-bearing tissue microenvironments

Although mechanical loads are integral for musculoskeletal tissue homeostasis, overloading and traumatic events can result in tissue injury. Conventional drug delivery approaches for musculoskeletal tissue repair employ localized drug injections. However, rapid drug clearance and inadequate synchronization of molecule provision with healing progression render these methods ineffective. To overcome this, a programmable mechanoresponsive drug delivery system was developed that utilizes the mechanical environment of the tissue during rehabilitation (for example, during cartilage repair) to trigger biomolecule provision. For this, a suite of mechanically-activated microcapsules (MAMCs) with different rupture profiles was generated in a single fabrication batch via osmotic annealing of double emulsions. MAMC physical dimensions were found to dictate mechano-activation in 2D and 3D environments and their stability in vitro and in vivo, demonstrating the tunability of this system. In models of cartilage regeneration, MAMCs did not interfere with tissue growth and activated depending on the mechanical properties of the regenerating tissue. Finally, biologically active anti-inflammatory agents were encapsulated and released from MAMCs, which counteracted degradative cues and prevented the loss of matrix in living tissue environments. This unique technology has tremendous potential for implementation across a wide array of musculoskeletal conditions for enhanced repair of load-bearing tissues.

Safranin O without fast green is the best staining method for testing the degradation of macromolecules in a cartilage extracellular matrix for the determination of the postmortem interval

Methods for the determination of the postmortem interval (PMI) include methods that monitor the postmortem changes of cells and molecules in different tissues. The rate of pathological degradation of macromolecules in the extracellular matrix (ECM) of hyaline cartilage could be verified by assessing the intensity of collagen and proteoglycan (PG) staining. In the presented in vitro pilot study, this methodology was used for the first time to determine PMI. The osteochondral samples of three donors were stored at 11 °C and 35 °C and analyzed on day 1, day 12, and day 36 postmortem. The intensity of staining using Masson's trichrome and Sirius red for collagen, and Alcian blue and Safranin O dyes for PG was estimated ten times according to the modified Bern grading scale. Statistical analysis showed that the Safranin O without Fast green method is the most appropriate (raters agreement 0.5541) for up to 36 days postmortem, and that the influence of time is more important (p = 0.023) than the influence of temperature (p = 0.061) on the degradation of the ECM macromolecules. The described method, which is simple and can be performed in any histological laboratory, should be verified in corpore conditions, on a large number of donors, and using an objective method for assessing the intensity of cartilage macromolecule staining for PMI determination.

Histochemical quantification of collagen content in articular cartilage

Background

Articular cartilage (AC) is mainly composed of water, type II collagen, proteoglycans (PGs) and chondrocytes. The amount of PGs in AC is routinely quantified with digital densitometry (DD) from Safranin O-stained sections, but it is unclear whether similar method could be used for collagens.

Objective

The aim of this study was to clarify whether collagens can be quantified from histological AC sections using DD.

Material and methods

Sixteen human AC samples were stained with Masson’s trichrome or Picrosirius red. Optical densities of histological stains were compared to two commonly used collagen parameters (amide I and collagen CH₂ side chain peak at 1338cm^-1) measured using Fourier Transform Infrared (FTIR) spectroscopic imaging.

Results

Optical density of Modified Masson’s trichrome staining, which included enzymatic removal of PGs before staining, correlated significantly with FTIR-derived collagen parameters at almost all depths of cartilage. The other studied staining protocols displayed significant correlations with the reference parameters at only few depth layers.

Conclusions

Based on our findings, modified Masson’s trichrome staining protocol is suitable for quantification of AC collagen content. Enzymatic removal of PGs prior to staining is critical as us allows better staining of the collagen. Further optimization of staining protocols may improve the results in the future studies.

Raman Spectroscopy: Guiding Light for the Extracellular Matrix

The extracellular matrix (ECM) consists of a complex mesh of proteins, glycoproteins, and glycosaminoglycans, and is essential for maintaining the integrity and function of biological tissues. Imaging and biomolecular characterization of the ECM is critical for understanding disease onset and for the development of novel, disease-modifying therapeutics. Recently, there has been a growing interest in the use of Raman spectroscopy to characterize the ECM. Raman spectroscopy is a label-free vibrational technique that offers unique insights into the structure and composition of tissues and cells at the molecular level. This technique can be applied across a broad range of ECM imaging applications, which encompass in vitro, ex vivo, and in vivo analysis. State-of-the-art confocal Raman microscopy imaging now enables label-free assessments of the ECM structure and composition in tissue sections with a remarkably high degree of biomolecular specificity. Further, novel fiber-optic instrumentation has opened up for clinical in vivo ECM diagnostic measurements across a range of tissue systems. A palette of advanced computational methods based on multivariate statistics, spectral unmixing, and machine learning can be applied to Raman data, allowing for the extraction of specific biochemical information of the ECM. Here, we review Raman spectroscopy techniques for ECM characterizations over a variety of exciting applications and tissue systems, including native tissue assessments (bone, cartilage, cardiovascular), regenerative medicine quality assessments, and diagnostics of disease states. We further discuss the challenges in the widespread adoption of Raman spectroscopy in biomedicine. The results of the latest discovery-driven Raman studies are summarized, illustrating the current and potential future applications of Raman spectroscopy in biomedicine.

Simultaneous tractography and elastography imaging of the zone-specific structural and mechanical responses in articular cartilage under compressive loading

We quantified the precise zonal cartilage structural and mechanical responses to unconfined compressive loading by using simultaneous PSOCT based optical tractography and elastography imaging. Twelve bovine knee articular cartilage samples from six animals were imaged under bulk compression from 4% to 20%. The results revealed strong evidence that the conventional radial zone could be divided into two sub-zones with distinct mechanical properties. The "upper" part of the radial zone played a critical role in "absorbing" the mechanical compression. The study also showed that the zonal fiber organization greatly affected the cartilage structural and mechanical responses. A strong correlation was observed between the optical birefringence and logarithm of the Young's modulus. These new results provide useful information for improving mechanical modeling of articular cartilage and developing better cartilage-mimetic biomaterials.

Impact of HOXB7 overexpression on human adipose-derived mesenchymal progenitors

Background

The ex vivo expansion potential of mesenchymal stromal/stem cells (MSC) together with their differentiation and secretion properties makes these cells an attractive tool for transplantation and tissue engineering. Although the use of MSC is currently being tested in a growing number of clinical trials, it is still desirable to identify molecular markers that may help improve their performance both in vitro and after transplantation.

Methods

Recently, HOXB7 was identified as a master player driving the proliferation and differentiation of bone marrow mesenchymal progenitors. In this study, we investigated the effect of HOXB7 overexpression on the ex vivo features of adipose mesenchymal progenitors (AD-MSC).

Results

HOXB7 increased AD-MSC proliferation potential, reduced senescence, and improved chondrogenesis together with a significant increase of basic fibroblast growth factor (bFGF) secretion.

Conclusion

While further investigations and in vivo models shall be applied for better understanding, these data suggest that modulation of HOXB7 may be a strategy for innovative tissue regeneration applications.

In Vitro Screening of Molecularly Engineered Polyethylene Glycol Hydrogels for Cartilage Tissue Engineering using Periosteum-Derived and ATDC5 Cells

The rapidly growing field of tissue engineering and regenerative medicine has brought about an increase in demand for biomaterials that mimic closely the form and function of biological tissues. Therefore, understanding the cellular response to the changes in material composition moves research one step closer to a successful tissue-engineered product. With this in mind, polyethylene glycol (PEG) hydrogels comprised of different concentrations of polymer (2.5%, 4%, 6.5%, or 8% (w/v)); different protease sensitive, peptide cross-linkers (VPMSMRGG or GPQGIWGQ); and the incorporation or lack of a peptide cell adhesion ligand (RGD) were screened for their ability to support in vitro chondrogenesis. Human periosteum-derived cells (hPDCs), a mesenchymal stem cell (MSC)-like primary cell source, and ATDC5 cells, a murine carcinoma-derived chondrogenic cell line, were encapsulated within the various hydrogels to assess the effects of the different formulations on cellular viability, proliferation, and chondrogenic differentiation while receiving exogenous growth factor stimulation via the medium. Through the results of this screening process, the 6.5% (w/v) PEG constructs, cross-linked with the GPQGIWGQ peptide and containing the RGD cell binding molecule, demonstrated an environment that consistently supported cellular viability and proliferation as well as chondrogenic differentiation.

Early changes in the extracellular matrix of the degenerating intervertebral disc, assessed by Fourier transform infrared imaging

OBJECTIVE

Mechanical overloading induces a degenerative cell response in the intervertebral disc. However, early changes in the extracellular matrix (ECM) are challenging to assess with conventional techniques. Fourier Transform Infrared (FTIR) imaging allows visualization and quantification of the ECM. We aim to identify markers for disc degeneration and apply these to investigate early degenerative changes due to overloading and katabolic cell activity.

DESIGN

Three experiments were conducted; Exp 1.: In vivo, lumbar spines of seven goats were operated: one disc was injected with chondroitinase ABC [cABC (mild degeneration)] and compared to the adjacent disc (control) after 24 weeks. Exp 2a: Ex vivo, caprine discs received physiological loading (n = 10) or overloading (n = 10) in a bioreactor. Exp 2b: Cell activity was diminished prior to testing by freeze-thaw cycles, 18 discs were then tested as in Exp 2a. In all experiments, FTIR images (spectral region: 1000-1300 cm^-1) of mid-sagittal slices were analyzed using multivariate curve resolution.

RESULTS

In vivo, FTIR was more sensitive than biochemical and histological analysis in identifying reduced proteoglycan content (P = 0.046) and increased collagen content in degenerated discs (P < 0.01). Notably, FTIR analysis additionally showed disorganization of the ECM, indicated by increased collagen entropy (P = 0.011). Ex vivo, the proteoglycan/collagen ratio decreased due to overloading (P = 0.047) and collagen entropy increased (P = 0.047). Cell activity affected collagen content only (P = 0.044).

CONCLUSION

FTIR imaging allows a more detailed investigation of early disc degeneration than traditional measures. Changes due to mild overloading could be assessed and quantified. Matrix remodeling is the first detectable step towards intervertebral disc degeneration.

Decellularized Cartilage Directs Chondrogenic Differentiation: Creation of a Fracture Callus Mimetic

Complications that arise from impaired fracture healing have considerable socioeconomic implications. Current research in the field of bone tissue engineering predominantly aims to mimic the mature bone tissue microenvironment. This approach, however, may produce implants that are intrinsically unresponsive to the cues present during the initiation of fracture repair. As such, this study describes the development of decellularized xenogeneic hyaline cartilage matrix in an attempt to mimic the initial reparative phase of fracture repair. Three approaches based on vacuum-assisted osmotic shock (Vac-OS), Triton X-100 (Vac-STx), and sodium dodecyl sulfate (Vac-SDS) were investigated. The Vac-OS methodology reduced DNA content below 50 ng/mg of tissue, while retaining 85% of the sulfate glycosaminoglycan content, and as such was selected as the optimal methodology for decellularization. The resultant Vac-OS scaffolds (decellularized extracellular matrix [dcECM]) were also devoid of the immunogenic alpha-Gal epitope. Furthermore, minimal disruption to the structural integrity of the dcECM was demonstrated using differential scanning calorimetry and fluorescence lifetime imaging microscopy. The biological integrity of the dcECM was confirmed by its ability to drive the chondrogenic commitment and differentiation of human chondrocytes and periosteum-derived cells, respectively. Furthermore, histological examination of dcECM constructs implanted in immunocompetent mice revealed a predominantly M2 macrophage-driven regenerative response both at 2 and 8 weeks postimplantation. These findings contrasted with the implanted native costal cartilage that elicited a predominantly M1 macrophage-mediated inflammatory response. This study highlights the capacity of dcECM from the Vac-OS methodology to direct the key biological processes of endochondral ossification, thus potentially recapitulating the callus phase of fracture repair.

Raman spectroscopic imaging for quantification of depth-dependent and local heterogeneities in native and engineered cartilage

Articular cartilage possesses a remarkable, mechanically-robust extracellular matrix (ECM) that is organized and distributed throughout the tissue to resist physiologic strains and provide low friction during articulation. The ability to characterize the make-up and distribution of the cartilage ECM is critical to both understand the process by which articular cartilage undergoes disease-related degeneration and to develop novel tissue repair strategies to restore tissue functionality. However, the ability to quantitatively measure the spatial distribution of cartilage ECM constituents throughout the tissue has remained a major challenge. In this experimental investigation, we assessed the analytical ability of Raman micro-spectroscopic imaging to semi-quantitatively measure the distribution of the major ECM constituents in cartilage tissues. Raman spectroscopic images were acquired of two distinct cartilage tissue types that possess large spatial ECM gradients throughout their depth: native articular cartilage explants and large engineered cartilage tissue constructs. Spectral acquisitions were processed via multivariate curve resolution to decompose the "fingerprint" range spectra (800-1800 cm-1) to the component spectra of GAG, collagen, and water, giving rise to the depth dependent concentration profile of each constituent throughout the tissues. These Raman spectroscopic acquired-profiles exhibited strong agreement with profiles independently acquired via direct biochemical assaying of spatial tissue sections. Further, we harness this spectroscopic technique to evaluate local heterogeneities through the depth of cartilage. This work represents a powerful analytical validation of the accuracy of Raman spectroscopic imaging measurements of the spatial distribution of biochemical components in a biological tissue and shows that it can be used as a valuable tool for quantitatively measuring the distribution and organization of ECM constituents in native and engineered cartilage tissue specimens.

3D histopathological grading of osteochondral tissue using contrast-enhanced micro-computed tomography

OBJECTIVE

Histopathological grading of osteochondral (OC) tissue is widely used in osteoarthritis (OA) research, and it is relatively common in post-surgery in vitro diagnostics. However, relying on thin tissue section, this approach includes a number of limitations, such as: (1) destructiveness, (2) sample processing artefacts, (3) 2D section does not represent spatial 3D structure and composition of the tissue, and (4) the final outcome is subjective. To overcome these limitations, we recently developed a contrast-enhanced μCT (CEμCT) imaging technique to visualize the collagenous extracellular matrix (ECM) of articular cartilage (AC). In the present study, we demonstrate that histopathological scoring of OC tissue from CEμCT is feasible. Moreover, we establish a new, semi-quantitative OA μCT grading system for OC tissue.

RESULTS

Pathological features were clearly visualized in AC and subchondral bone (SB) with μCT and verified with histology, as demonstrated with image atlases. Comparison of histopathological grades (OARSI or severity (0-3)) across the characterization approaches, CEμCT and histology, excellent (0.92, 95% CI = [0.84, 0.96], n = 30) or fair (0.50, 95% CI = [0.16, 0.74], n = 27) intra-class correlations (ICC), respectively. A new μCT grading system was successfully established which achieved an excellent cross-method (μCT vs histology) reader-to-reader intra-class correlation (0.78, 95% CI = [0.58, 0.89], n = 27).

CONCLUSIONS

We demonstrated that histopathological information relevant to OA can reliably be obtained from CEμCT images. This new grading system could be used as a reference for 3D imaging and analysis techniques intended for volumetric evaluation of OA pathology in research and clinical applications.

How best to preserve and reveal the structural intricacies of cartilaginous tissue

No single processing technique is capable of optimally preserving each and all of the structural entities of cartilaginous tissue. Hence, the choice of methodology must necessarily be governed by the nature of the component that is targeted for analysis, for example, fibrillar collagens or proteoglycans within the extracellular matrix, or the chondrocytes themselves. This article affords an insight into the pitfalls that are to be encountered when implementing the available techniques and how best to circumvent them. Adult articular cartilage is taken as a representative pars pro toto of the different bodily types. In mammals, this layer of tissue is a component of the synovial joints, wherein it fulfills crucial and diverse biomechanical functions. The biomechanical functions of articular cartilage have their structural and molecular correlates. During the natural course of postnatal development and after the onset of pathological disease processes, such as osteoarthritis, the tissue undergoes structural changes which are intimately reflected in biomechanical modulations. The fine structural intricacies that subserve the changes in tissue function can be accurately assessed only if they are faithfully preserved at the molecular level. For this reason, a careful consideration of the tissue-processing technique is indispensable. Since, as aforementioned, no single methodological tool is capable of optimally preserving all constituents, the approach must be pre-selected with a targeted structure in view. Guidance in this choice is offered.

Comparison of cartilage histopathology assessment systems on human knee joints at all stages of osteoarthritis development

OBJECTIVE

To compare the MANKIN and OARSI cartilage histopathology assessment systems using human articular cartilage from a large number of donors across the adult age spectrum representing all levels of cartilage degradation.

DESIGN

Human knees (n=125 from 65 donors; age range 23-92) were obtained from tissue banks. All cartilage surfaces were macroscopically graded. Osteochondral slabs representing the entire central regions of both femoral condyles, tibial plateaus, and the patella were processed for histology and Safranin O - Fast Green staining. Slides representing normal, aged, and osteoarthritis (OA) tissue were scanned and electronic images were scored online by five observers. Statistical analysis was performed for inter- and intra-observer variability, reproducibility and reliability.

RESULTS

The inter-observer variability among five observers for the MANKIN system showed a similar good Intra-class correlation coefficient (ICC>0.81) as for the OARSI system (ICC>0.78). Repeat scoring by three of the five readers showed very good agreement (ICC>0.94). Both systems showed a high reproducibility among four of the five readers as indicated by the Spearman's rho value. For the MANKIN system, the surface represented by lesion depth was the parameter where all readers showed an excellent agreement. Other parameters such as cellularity, Safranin O staining intensity and tidemark had greater inter-reader disagreement.

CONCLUSION

Both scoring systems were reliable but appeared too complex and time consuming for assessment of lesion severity, the major parameter determined in standardized scoring systems. To rapidly and reproducibly assess severity of cartilage degradation, we propose to develop a simplified system for lesion volume.

Ultrashort-echo time MR imaging of the patella with bicomponent analysis: correlation with histopathologic and polarized light microscopic findings

PURPOSE

To correlate short and long T2* water fractions, derived from ultrashort-echo time (TE) magnetic resonance (MR) imaging, with semiquantitative histopathologic and polarized light microscopic (PLM) assessment of human cadaveric patellae cartilage.

MATERIALS AND METHODS

Twenty human cadaveric patellae were evaluated by using ultrashort-TE imaging, spin-echo imaging, histopathologic analysis, and PLM, with institutional review board approval. Short and long T2* water components were evaluated for each patella by using bicomponent fitting of ultrashort-TE signal decay. Four to six regions of interest (ROIs) within each patella were chosen for correlation between ultrashort-TE bicomponent analysis, histopathologic grading (Mankin score), and PLM grading (Vaudey score).

RESULTS

Ultrashort-TE imaging with bicomponent analysis showed two distinct water components with a short T2* and a longer T2* in all patellae. ROI analysis showed that the short T2* fraction was correlated significantly with the Mankin (ρ = 0.66, P < .001) and Vaudey (ρ = 0.68, P < .001) scores. The Mankin scores were weakly positively correlated with T2 (ρ = 0.28, P = .13) and short T2* (ρ = 0.24, P = .14) but were negatively correlated with long T2* (ρ = -0.55, P < .01). The Vaudey scores were weakly positively correlated with T2 (ρ = 0.18, P = .16) and short T2* (ρ = 0.22, P = .14) but were negatively correlated with long T2* (ρ = -0.55, P < .01).

CONCLUSION

Short T2* water fraction derived from ultrashort-TE imaging with bicomponent analysis correlates significantly with both the Mankin and Vaudey scores and may serve as a biomarker of cartilage degeneration.

Healing of long-term frozen orthotopic bone allografts is not affected by MHC differences between donor and recipient

BACKGROUND

The use of bone grafting in orthopaedic surgery has increased dramatically in recent years. However, the degree to which immune responses are important for the survival of the allograft is not fully understood. In particular it remains unclear whether differences in the major histocompatibility complex (MHC) influence incorporation of bone allografts and their subsequent biologic performance.

QUESTIONS/PURPOSES

Therefore, we asked whether isolated mismatch for MHC antigens of deep frozen bone allografts in the long-term causes (1) immune reactions, and whether these reactions have any effect on (2) morphologic features of the graft, (3) radiographic graft healing, and (4) graft strength.

METHODS

We used an established orthotopic tibial segment transplantation technique that allows determination of mechanical strength, histologic evaluation, and immune responses. Tibial segments that had been deep-frozen at -80°C for 1 year were transplanted into 24 PVG (RT1 (c)) rats from either 12 syngeneic donors or 12 MHC congenic donors PVG.1U (RT1 (u)). We determined immune responses using an indirect Coombs reaction and determined graft healing radiographically and mechanically after 6 months.

RESULTS

We detected no alloantibody production to graft MHC-I antigens, and found no differences between syngeneic and MHC mismatched grafts in terms of remodeling with host bone, graft healing, and mechanical strength.

CONCLUSIONS

Mismatches for MHC antigens do not seem to play a decisive role in healing of long-term, deep-frozen bone allografts.

The OARSI histopathology initiative - recommendations for histological assessments of osteoarthritis in the rat

OBJECTIVE

During the development of disease-modifying osteoarthritis (OA) drugs, rat models of OA are frequently used for a first assessment of in vivo efficacy. The most efficacious compound in the rat model may then be tested in a larger animal model before entering human trials. The aim of this study was to describe a histologic scoring system for use in different models of OA in rats that allows standardization and comparison of results obtained by different investigators.

METHODS

The experience of the authors with current scoring systems and the range of lesions observed in rat and human OA studies were considered in recommending this common paradigm for rat histologic scoring. Considerations were made for reproducibility and ease of use for new scorers. Additional scoring paradigms may be employed to further identify specific effects of some disease-modifying drugs.

RESULTS

Although the described scoring system is more complex than the modified Mankin scores, which are recommended for some other species, the reliability study showed that it is easily understood and can be reproducibly used, even by inexperienced scorers.

CONCLUSIONS

The scoring paradigm described here has been found to be sufficiently sensitive to discriminate between treatments and to have high reproducibility. Therefore we recommend its use for evaluation of different rat OA models as well as assessment of disease-modifying effects of treatments in these models.

Matrix metalloproteinase 13 loss associated with impaired extracellular matrix remodeling disrupts chondrocyte differentiation by concerted effects on multiple regulatory factors

OBJECTIVE

To link matrix metalloproteinase 13 (MMP-13) activity and extracellular matrix (ECM) remodeling to alterations in regulatory factors leading to a disruption in chondrocyte homeostasis.

METHODS

MMP-13 expression was ablated in primary human chondrocytes by stable retrotransduction of short hairpin RNA. The effects of MMP-13 knockdown on key regulators of chondrocyte differentiation (SOX9, runt-related transcription factor 2 [RUNX-2], and beta-catenin) and angiogenesis (vascular endothelial growth factor [VEGF]) were scored at the protein level (by immunohistochemical or Western blot analysis) and RNA level (by real-time polymerase chain reaction) in high-density monolayer and micromass cultures under mineralizing conditions. Effects on cellular viability in conjunction with chondrocyte progression toward a hypertrophic-like state were assessed in micromass cultures. Alterations in SOX9 subcellular distribution were assessed using confocal microscopy in micromass cultures and also in osteoarthritic cartilage.

RESULTS

Differentiation of control chondrocyte micromasses progressed up to a terminal phase, with calcium deposition in conjunction with reduced cell viability and scant ECM. MMP-13 knockdown impaired ECM remodeling and suppressed differentiation in conjunction with reduced levels of RUNX-2, beta-catenin, and VEGF. MMP-13 levels in vitro and ECM remodeling in vitro and in vivo were linked to changes in SOX9 subcellular localization. SOX9 was largely excluded from the nuclei of chondrocytes with MMP-13-remodeled or -degraded ECM, and exhibited an intranuclear staining pattern in chondrocytes with impaired MMP-13 activity in vitro or with more intact ECM in vivo.

CONCLUSION

MMP-13 loss leads to a breakdown in primary human articular chondrocyte differentiation by altering the expression of multiple regulatory factors.

Evaluation of histological scoring systems for tissue-engineered, repaired and osteoarthritic cartilage

OBJECTIVE

Regeneration of hyaline cartilage has been the focus of an increasing number of research groups around the world. One of the most important outcome measures in evaluation of its success is the histological quality of cartilaginous tissue. Currently, a variety of histological scoring systems is used to describe the quality of osteoarthritic, in vivo repaired or in vitro engineered tissue. This review aims to provide an overview of past and currently used histological scoring systems, in an effort to aid cartilage researchers in choosing adequate and validated cartilage histological scoring systems.

METHODS

Histological scoring systems for analysis of osteoarthritic, tissue engineered and in vivo repaired cartilage were reviewed. The chronological development as well as the validity and practical applicability of the scoring systems is evaluated.

RESULTS

The Histological-Histochemical Grading System (HHGS) or a HHGS-related score is most often used for evaluation of osteoarthritic cartilage, however the Osteoarthritis Research Society International (OARSI) Osteoarthritis Cartilage Histopathology Assessment System seems a valid alternative. The O'Driscoll score and the International Cartilage Repair Society (ICRS) II score may be used for in vivo repaired cartilage. The 'Bern score' seems most adequate for evaluation of in vitro engineered cartilage.

CONCLUSION

A great variety of histological scoring systems exists for analysis of osteoarthritic or normal, in vivo repaired or tissue-engineered cartilage, but only few have been validated. Use of these validated scores may considerably improve exchange of information necessary for advances in the field of cartilage regeneration.

Autologous chondrocyte implantation to repair knee cartilage injury: ultrastructural evaluation at 2 years and long-term follow-up including muscle strength measurements

Autologous chondrocyte implantation (ACI) usually results in improvement in clinical scores. However, long-term isokinetic muscle strength measurements have not been reported. Biopsies from the repair tissue have shown variable proportions of hyaline-like cartilage. In this study, 21 consecutive patients were treated with autologous cartilage implantations in the knee. Mean size of the lesions was 5.5 cm(2). Follow-up arthroscopy with biopsy was performed at 2 years in 19 patients. The biopsies were examined with both light microscopy and transmission electron microscopy (TEM) techniques including immunogold analysis of collagen type 1. Patient function was evaluated with modified 10-point scales of the Cincinnati knee rating system obtained preoperatively and at 1 and 8.1 years. Isokinetic quadriceps and hamstrings muscle strength testing was performed at 1, 2 and 7.4 years. Light microscopy and TEM both showed predominately fibrous cartilage. The immunogold analysis showed a high percentage of collagen type I. At 7.4 years, the total work deficits when compared with the contra-lateral leg for isokinetic extension were 19.1 and 11.4%, and for isokinetic flexion 11.8 and 8.5% for 60 and 240 masculine/s, respectively. Mean pain score improved from 4.3 preoperatively to 6.3 at 1 year (p = 0.031) and 6.6 at 8.1 years (p = 0.013). Overall health condition score improved from 4.1 preoperatively to 6.1 at 1 year (p = 0.004) and 6.5 at 8.1 years (p = 0.008). Three patients later went through revision surgery with other resurfacing techniques and are considered failures. In summary, the formation of fibrous cartilage following ACI was confirmed by TEM with immunogold histochemistry. Although the functional scores were generally good, strength measurements demonstrated that the surgically treated leg remained significantly weaker.

Bone marrow mesenchymal stem cells in a hyaluronan scaffold for treatment of an osteochondral defect in a rabbit model

The purpose of this study was to evaluate the efficiency of using mesenchymal stem cells (MSC) in a hyaluronan scaffold for repair of an osteochondral defect in rabbit knee. Bone marrow was harvested from the posterior iliac crest in 11 New Zealand White rabbits. MSC were isolated and cultured in autologous serum for 28 days and transferred to a hyaluronan scaffold 24 h prior to implantation. A 4 mm diameter and 1.5 mm deep defect was created in the medial femoral condyle of both knees and the scaffold with MSC was implanted in one knee while an empty scaffold was implanted in the contra-lateral knee. After 24 weeks the rabbits were killed and histological sections were subjected to semiquantitative and quantitative evaluation by observers blinded regarding treatment modality. High degree of filling was obtained, but there was no statistically significant difference between the two treatments. However, there was a tendency for a better quality of repair in the MSC treated knees. No hypertrophy was observed by either method. MSC in a hyaluronan scaffold may be a promising treatment approach, but further studies are needed to determine the best combination of scaffold and cells.

Differential requirements for IKKalpha and IKKbeta in the differentiation of primary human osteoarthritic chondrocytes

OBJECTIVE

Osteoarthritic (OA) chondrocytes behave in an intrinsically deregulated manner, characterized by chronic loss of healthy cartilage and inappropriate differentiation to a hypertrophic-like state. IKKalpha and IKKbeta are essential kinases that activate NF-kappaB transcription factors, which in turn regulate cell differentiation and inflammation. This study was undertaken to investigate the differential roles of each IKK in chondrocyte differentiation and hypertrophy.

METHODS

Expression of IKKalpha or IKKbeta was ablated in primary human chondrocytes by retro-transduction of specific short-hairpin RNAs. Micromass cultures designed to reproduce chondrogenesis with progression to the terminal hypertrophic stage were established, and anabolism and remodeling of the extracellular matrix (ECM) were investigated in the micromasses using biochemical, immunohistochemical, and ultrastructural techniques. Cellular parameters of hypertrophy (i.e., proliferation, viability, and size) were also analyzed.

RESULTS

The processes of ECM remodeling and mineralization, both characteristic of terminally differentiated hypertrophic cells, were defective following the loss of IKKalpha or IKKbeta. Silencing of IKKbeta markedly enhanced accumulation of glycosaminoglycan in conjunction with increased SOX9 expression. Ablation of IKKalpha dramatically enhanced type II collagen deposition independent of SOX9 protein levels but in association with suppressed levels of runt-related transcription factor 2. Moreover, IKKalpha-deficient cells retained the phenotype of cells in a pre-hypertrophic-like state, as evidenced by the smaller size and faster proliferation of these cells prior to micromass seeding, along with the enhanced viability of their differentiated micromasses.

CONCLUSION

IKKalpha and IKKbeta exert differential roles in ECM remodeling and endochondral ossification, which are events characteristic of hypertrophic chondrocytes and also complicating factors often found in OA. Because the effects of IKKalpha were more profound and pleotrophic in nature, our observations suggest that exacerbated IKKalpha activity may be responsible, at least in part, for the characteristic abnormal phenotypes of OA chondrocytes.

Visual histological grading system for the evaluation of in vitro-generated neocartilage

Here we present the development of a visual evaluation system for routine assessment of in vitro-engineered cartilaginous tissue. Neocartilage was produced by culturing human articular chondrocytes in pellet culture systems or in a scaffold-free bioreactor system. All engineered tissues were embedded in paraffin and were sectioned and stained with Safranin O-fast green. The evaluation of each sample was broken into 3 categories (uniformity and intensity of Safranin O stain, distance between cells/amount of matrix produced, and cell morphology), and each category had 4 components with a score ranging from 0 to 3. Three observers evaluated each sample, and the new system was independently tested against an objective computer-based histomorphometry system. Pellets were also assessed biochemically for glycosaminoglycan (GAG) content. Pellet histology scores correlated significantly with GAG contents and were in agreement with the computer-based histomorphometry system. This system allows a valid and rapid assessment of in vitro-generated cartilaginous tissue that has a relevant association with objective parameters indicative of cartilage quality.

[Spontaneous and post-therapeutic cartilage repair: evaluation criteria]

Articular cartilage has poor reparative capacities, and once damaged cartilage lesions remain chronic and can lead to osteoarthritis. Over the last decade, several innovative therapies have been introduced to promote the regeneration of articular cartilage while sustaining sufficient mechanical stress and permitting a pain free motion. An important measure of outcome is the morphological characterization of the repair tissue in order to allow for cross-study evaluation. The International Cartilage Repair Society has developed a analogue visual scale to quantify repair tissue, which is described in this paper.

Osteoarthritis cartilage histopathology: grading and staging

OBJECTIVE

Current osteoarthritis (OA) histopathology assessment methods have difficulties in their utility for early disease, as well as their reproducibility and validity. Our objective was to devise a more useful method to assess OA histopathology that would have wide application for clinical and experimental OA assessment and would become recognized as the standard method.

DESIGN

An OARSI Working Group deliberated on principles, standards and features for an OA cartilage pathology assessment system. Using current knowledge of the pathophysiology of OA morphologic features, a proposed system was presented at OARSI 2000. Subsequently, this was widely circulated for comments amongst experts in OA pathology.

RESULTS

An OA cartilage pathology assessment system based on six grades, which reflect depth of the lesion and four stages reflecting extent of OA over the joint surface was developed.

CONCLUSIONS

The OARSI cartilage OA histopathology grading system appears consistent and simple to apply. Further studies are required to confirm the system's utility.

Fourier transform infrared imaging spectroscopic analysis of tissue engineered cartilage: histologic and biochemical correlations

The composition of cartilage is predictive of its in vivo performance. Therefore, the ability to assess its primary macromolecular components, proteoglycan (PG) and collagen, is of great importance. In the current study, we hypothesized that PG content and distribution in tissue engineered cartilage could be determined using Fourier-transform infrared imaging spectroscopy (FT-IRIS). The cartilage was grown from chondrocytes within a hollow fiber bioreactor (HFBR) system previously used extensively to study cartilage development. FT-IRIS analysis showed a gradient of PG content, with the highest content in the center near the nutritive fibers and the lowest near the interior surface of the HFBR. Further, we found significantly greater PG content in the region near culture medium inflow (45.0%) as compared to the outflow region (24.7%) (p<0.001). This difference paralleled the biochemically determined glycosaminoglycan difference of 42.6% versus 27.8%. In addition, FT-IRIS-determined PG content at specific positions within the tissue sections correlated with histologically determined PG content (R=0.73, p=0.007). In summary, FT-IRIS determination of PG correlates with histological determination of PG and yields quantitatively similar results to biochemical determination of glycosaminoglycan in developing cartilage.

Topographic and zonal distribution of tenascin in human articular cartilage from femoral heads: normal versus mild and severe osteoarthritis

OBJECTIVE

The extracellular matrix glycoprotein tenascin (TN) is upregulated in articular cartilage with severe osteoarthritis (OA). This study gives a detailed description of TN expression in areas of articular cartilage from femoral heads with mild OA showing structural lesions and in structurally normal areas of the same femoral heads compared with normal cartilage and cartilage with severe OA.

METHODS

Immunohistochemical evaluation was performed on cryosections stained with antibodies against TN. Sections were selected as follows: from each macroscopically normal femoral head (n=6) a normal central and peripheral biopsy; from each femoral head with macroscopically mild OA (n=8) a central biopsy that showed structural lesions and a peripheral normal biopsy; from each femoral head with severe OA (n=9) a central and a peripheral biopsy with structural lesions. Central biopsies represent load bearing areas, whereas peripheral biopsies are non-load bearing.

RESULTS

Central cartilage with mild OA contains significantly higher levels of TN in the superficial zone than structurally normal, peripheral cartilage from the same femoral heads. Normal cartilage and cartilage with severe OA do not display this topographic variation. Central cartilage with mild OA shows significantly higher levels of TN than normal, central cartilage. Peripheral, normal cartilage with mild OA shows significantly less TN than peripheral cartilage with severe OA.

CONCLUSIONS

In femoral heads with mild OA, TN is accumulated in areas displaying structural damage. This proposes mild OA to be a localized disorder. Extreme caution is necessary for sampling of articular cartilage, especially from joints with mild OA.