In vitro culture of enzymatically isolated chondrons: a possible model for the initiation of osteoarthritis

Osteoarthritis as a disease of the cartilage pericellular matrix

Osteoarthritis is a painful joint disease characterized by progressive degeneration of the articular cartilage as well as associated changes to the subchondral bone, synovium, and surrounding joint tissues. While the effects of osteoarthritis on the cartilage extracellular matrix (ECM) have been well recognized, it is now becoming apparent that in many cases, the onset of the disease may be initially reflected in the matrix region immediately surrounding the chondrocytes, termed the pericellular matrix (PCM). Growing evidence suggests that the PCM - which along with the enclosed chondrocytes are termed the "chondron" - acts as a critical transducer or "filter" of biochemical and biomechanical signals for the chondrocyte, serving to help regulate the homeostatic balance of chondrocyte metabolic activity in response to environmental signals. Indeed, it appears that alterations in PCM properties and cell-matrix interactions, secondary to genetic, epigenetic, metabolic, or biomechanical stimuli, could in fact serve as initiating or progressive factors for osteoarthritis. Here, we discuss recent advances in the understanding of the role of the PCM, with an emphasis on the reciprocity of changes that occur in this matrix region with disease, as well as how alterations in PCM properties could serve as a driver of ECM-based diseases such as osteoarthritis. Further study of the structure, function, and composition of the PCM in normal and diseased conditions may provide new insights into the understanding of the pathogenesis of osteoarthritis, and presumably new therapeutic approaches for this disease.

Age-Correlated Phenotypic Alterations in Cells Isolated From Human Degenerated Intervertebral Discs With Contained Hernias

STUDY DESIGN

Human intervertebral disc (hIVD) cells were isolated from 41 surgically excised samples and assessed for their phenotypic alterations with age.

OBJECTIVE

Toward the design of novel anti-aging strategies to overcome degenerative disc disease (DDD), we investigated age-correlated phenotypic alterations that occur on primary hIVD cells.

SUMMARY OF BACKGROUND DATA

Although regenerative medicine holds great hope, much is still to be unveiled on IVD cell biology and its intrinsic signaling pathways, which can lead the way to successful therapies for IDD. A greater focus on age-related phenotypic changes at the cell level would contribute to establish more effective anti-aging/degeneration targets.

METHODS

The study was subdivided in four main steps: i) optimization of primary cells isolation technique; ii) high-throughput cell morphology analysis, by imaging flow cytometry (FC) and subsequent validation by histological analysis; iii) analysis of progenitor cell surface markers expression, by conventional FC; and iv) statistical analysis and correlation of cells morphology and phenotype with donor age.

RESULTS

Three subsets of cells were identified on the basis of their diameter: small cell (SC), large cell (LC), and super LC (SLC). The frequency of SCs decreased nearly 50% with age, whereas that of LCs increased nearly 30%. Interestingly, the increased cells size was due to an enlargement of the pericellular matrix (PCM). Moreover, the expression pattern for CD90 and CD73 was a reflexion of age, where older individuals show reduced frequencies of positive cells for those markers. Nevertheless, the elevated percentages of primary positive cells for the mesenchymal stem cells (MSCs) marker CD146 found, even in some older donors, refreshed hope for the hypothetical activation of the self-renewal potential of the IVD.

CONCLUSION

These findings highlight the remarkable morphological alterations that occur on hIVD cells with aging and degeneration, while reinforcing previous reports on the gradual disappearance of an endogenous progenitor cell population.

LEVEL OF EVIDENCE

N/A.

Human osteoarthritic chondrons outnumber patient- and joint-matched chondrocytes in hydrogel culture-Future application in autologous cell-based OA cartilage repair?

Autologous chondrocyte implantation (ACI) is used in 34-60% for osteoarthritic (OA) cartilage defects, although ACI is neither recommended nor designed for OA. Envisioning a hydrogel-based ACI for OA that uses chondrons instead of classically used chondrocytes, we hypothesized that human OA chondrons may outperform OA chondrocytes. We compared patient- and joint surface-matched human OA chondrons with OA chondrocytes cultured for the first time in a hydrogel, using a self-assembling peptide system. We determined yield, viability, cell numbers, mRNA expression, GAPDH mRNA enzyme activity, Collagen II synthesis (CPII) and degradation (C2C), and sulfated glycosaminoglycan. Ex vivo, mRNA expression was comparable. Over time, significant differences in survival led to 3.4-fold higher OA chondron numbers in hydrogels after 2 weeks (p = .002). Significantly, more enzymatically active GAPDH protein indicated higher metabolic activity. The number of cultures that expressed mRNA for Collagen Types I and VI, COMP, aggrecan, VEGF, TGF-β1, and FGF-2 (but not Collagen Types II and X) was different, resulting in a 3.5-fold higher number of expression-positive OA chondron cultures (p < .05). Measuring CPII and C2C per hydrogel, OA chondron hydrogels synthesized more than they degraded Collagen Type II, the opposite was true for OA chondrocytes. Per cell, OA chondrons but not OA chondrocytes displayed more synthesis than degradation. Thus, OA chondrons displayed superior biosynthesis and mRNA expression of tissue engineering and phenotype-relevant genes. Moreover, human OA chondrons displayed a significant survival advantage in hydrogel culture, whose presence, drastic extent, and timescale was novel and is clinically significant. Collectively, these data highlight the high potential of human OA chondrons for OA ACI, as they would outnumber and, thus, surpass OA chondrocytes.

Chondrons and the pericellular matrix of chondrocytes

In cartilage, chondrocytes are embedded within an abundant extracellular matrix (ECM). A typical chondron consists of a chondrocyte and the immediate surrounding pericellular matrix (PCM). The PCM has a patent structure, defined molecular composition, and unique physical properties that support the chondrocyte. Given this spatial position, the PCM is pivotal in mediating communication between chondrocytes and the ECM and, thus, plays a critical role in cartilage homeostasis. The biological function and mechanical properties of the PCM have been extensively studied, mostly in the form of chondrons. This review intends to summarize recent progress in chondron and chondrocyte PCM research, with emphasis on the re-establishment of the PCM by isolated chondrocytes or mesenchymal stem cells during chondrogenic differentiation, and the effects of the PCM on cartilage tissue formation.

Induction of protoporphyrin IX in patient-derived synoviocytes, cartilage explants and chondrons after application of 5-aminolevulinic acid or its methyl ester

OBJECTIVE

To compare the accumulation of protoporphyrin IX between synoviocytes of patients with rheumatoid arthritis (RA) or osteoarthritis (OA) and cartilage explants (CE) as well as chondrons of patients with OA after the application of 5-aminolevulinic acid (ALA) or its methyl ester (ALA-Me).

MATERIALS AND METHODS

Samples of synovial and cartilage tissues were obtained from joint replacement surgeries. The accumulation of PpIX was determined by measuring fluorescence spectra from 2 × 10(5) synoviocytes or chondrons suspended in a glass tube or directly from CE surface after 2, 4, 8 and 24h of incubation with ALA or ALA-Me.

RESULTS

No differences were found between the average fluorescence intensity values of PpIX in synoviocytes of patients with RA and OA. These values were non-significantly higher after incubation with ALA in comparison with ALA-Me at almost all time points. The average fluorescence intensity of PpIX in CE and chondrons was about ten times lower than in synoviocytes. The presence of preparation of hyaluronic acid (HA) significantly enhanced PpIX induction in chondrons versus treatment only with ALA.

CONCLUSIONS

A potential for the selective synovial sensitization with endogenous PpIX in comparison with cartilage tissue has been demonstrated in vitro after application of ALA or ALA-Me.

Human osteoarthritic chondrocytes exposed to extremely low-frequency electromagnetic fields (ELF) and therapeutic application of musically modulated electromagnetic fields (TAMMEF) systems: a comparative study

Osteoarthritis (OA) is the most common joint disease, characterized by matrix degradation and changes in chondrocyte morphology and metabolism. Literature reported that electromagnetic fields (EMFs) can produce benefits in OA patients, even if EMFs mechanism of action is debated. Human osteoarthritic chondrocytes isolated from femoral heads were cultured in vitro in bidimensional (2-D) flasks and in three-dimensional (3-D) alginate beads to mimic closely cartilage environment in vivo. Cells were exposed 30 min/day for 2 weeks to extremely low-frequency electromagnetic field (ELF) with fixed frequency (100 Hz) and to therapeutic application of musically modulated electromagnetic field (TAMMEF) with variable frequencies, intensities, and waveforms. Cell viability was measured at days 7 and 14, while healthy-cell density, heavily vacuolized (hv) cell density, and cluster density were measured by light microscopy only for 3-D cultures after treatments. Cell morphology was observed for 2-D and 3-D cultures by transmission electron microscopy (TEM). Chondrocyte exposure to TAMMEF enhances cell viability at days 7 and 14 compared to ELF. Light microscopy analysis showed that TAMMEF enhances healthy-cell density, reduces hv-cell density and clustering, compared to ELF. Furthermore, TEM analysis showed different morphology for 2-D (fibroblast-like) and 3-D (rounded shape) cultures, confirming light microscopy results. In conclusion, EMFs are effective and safe for OA chondrocytes. TAMMEF can positively interfere with OA chondrocytes representing an innovative non-pharmacological approach to treat OA.

A proteomic approach for identification and localization of the pericellular components of chondrocytes

Although the pericellular matrix (PCM) plays a central role in the communication between chondrocytes and extracellular matrix, its composition is largely unknown. In this study, the PCM was investigated with a proteomic approach using chondrons, which are enzymatically isolated constructs including the chondrocyte and its surrounding PCM. Chondrons and chondrocytes alone were isolated from human articular cartilage. Proteins extracted from chondrons and chondrocytes were used for two-dimensional electrophoresis. Protein spots were quantitatively compared between chondron and chondrocyte gels. Cellular proteins, which had similar density between chondron and chondrocyte gels, did not proceed for analysis. Since chondrons only differ from chondrocytes in association of the PCM, protein spots in the chondron gels that had higher quantity than that in the chondrocyte gels were selected as candidates of the PCM components and processed for mass spectrometry. Among 15 identified peptides, several were fragments of the three type VI collagen chains (α-1, α-2, and α-3). Other identified PCM proteins included triosephosphate isomerase, transforming growth factor-β induced protein, peroxiredoxin-4, ADAM (A disintegrin and metalloproteinases) 28, and latent-transforming growth factor beta-binding protein-2. These PCM components were verified with immunohisto(cyto)chemistry for localization in the PCM region of articular cartilage. The abundance of type VI collagen in the PCM emphasizes its importance to the microenvironment of chondrocytes. Several proteins were localized in the PCM of chondrocytes for the first time and that warrants further investigation for their functions in cartilage biology.

The protective role of the pericellular matrix in chondrocyte apoptosis

INTRODUCTION

This study was designed to quantify the role of the pericellular matrix (PCM) in chondrocyte apoptosis using chondrons, which are a cartilage functional unit including a chondrocyte and its associated PCM.

METHODS

Chondrocytes and chondrons were enzymatically isolated from human articular cartilage and exposed to monosodium iodoacetate (MIA) and staurosporine for apoptosis induction. Chondrons were defined by the presence of type VI collagen, a basic component of the PCM. Apoptosis of chondrocytes and chondrons was measured with annexin V binding by flow cytometry and verified with terminal dUTP nick end-labeling staining. In a separate experiment, isolated chondrocytes were treated with soluble type VI collagen, before or after apoptosis induction with MIA, and cell death was measured by the activity of LDH and terminal dUTP nick end-labeling staining.

RESULTS

Chondrocytes treated with MIA incurred 27% cell death, compared with 12% in chondrons. On treating with MIA, 9% of chondrocytes underwent apoptosis, compared with only 1.6% of chondrons. Similarly, staurosporine induced 13% apoptosis in chondrocytes, whereas it was 3% in chondrons. Preincubation of type VI collagen effectively prevented chondrocytes from MIA-induced cell death. After apoptosis was induced with MIA, however, treatment with type VI collagen failed to rescue chondrocytes from death.

CONCLUSION

The PCM, a native microenvironment of chondrocytes, protects chondrocytes from apoptosis. Type VI collagen is a functional component of the PCM that contributes to the survival of chondrocytes.

Abnormal human chondrocyte morphology is related to increased levels of cell-associated IL-1β and disruption to pericellular collagen type VI

Early osteoarthritis (OA) is poorly understood, but abnormal chondrocyte morphology might be important. We studied IL-1β and pericellular collagen type VI in morphologically normal and abnormal chondrocytes. In situ chondrocytes within explants from nondegenerate (grade 0/1) areas of human tibial plateaus (n = 21) were fluorescently labeled and visualized [2-photon laser scanning microscopy (2PLSM)]. Normal chondrocytes exhibited a "smooth" membrane surface, whereas abnormal cells were defined as demonstrating ≥1 cytoplasmic process. Abnormal chondrocytes were further classified by number and average length of cytoplasmic processes/cell. IL-1β or collagen type VI associated with single chondrocytes were visualized by fluorescence immuno-histochemistry and confocal laser scanning microscopy (CLSM). Fluorescence was quantified as the number of positive voxels (i.e., 3D pixels with fluorescence above baseline)/cell. IL-1β-associated fluorescence increased between normal and all abnormal cells in the superficial (99.7 ± 29.8 [11 (72)] vs. 784 ± 382 [15 (132)]; p = 0.04, positive voxels/cell) and deep zones (66.5 ± 29.4 [9 (64)] vs. 795 ± 224 [9 (56)]; p = 0.006). There was a correlation (r(2) = 0.988) between the number of processes/cell (0-5) and IL-1β, and an increase particularly with short processes (≤5 µm; p = 0.022). Collagen type VI coverage and thickness decreased (p < 0.001 and p = 0.005, respectively) with development of processes. Abnormal chondrocytes in macroscopically nondegenerate cartilage demonstrated a marked increase in IL-1β and loss of pericellular type VI collagen, changes that could lead to cartilage degeneration.

Primary cilia in osteoarthritic chondrocytes: from chondrons to clusters

Osteoarthritis (OA) is a common joint disease characterized by articular cartilage degeneration. The etiology of OA is unknown. Because several previous studies have shown that primary cilia play critical roles in joint development, this study examined the incidence and morphology of primary cilia in chondrocytes during joint degeneration in a naturally occurring bovine model of OA. Primary cilia were detected using antibodies to acetylated alpha-tubulin in normal cartilage as well as in mild and severe OA tissue. In normal cartilage, cilia number and length were lowest in the superficial zone and increased with distance from the articular surface. In OA tissue, the incidence and length of cilia increased at the eroding articulating surface, resulting in an overall increased proportion of cilia. This is the first study to show that primary cilia are present on chondrocytes throughout OA progression and that the overall percentage of ciliated cells within the degenerating cartilage increases with OA severity.

Glycosaminoglycans in the pericellular matrix of chondrons and chondrocytes

This is the first study to quantitate and profile the glycosaminoglycan (GAG) composition of the pericellular matrix (PCM) of chondrons and chondrocytes using the highly sensitive technique; fluorophore-assisted carbohydrate electrophoresis (FACE). Bovine articular chondrocytes and chondrons were isolated enzymatically. High cell yield and viability were obtained for both preparations. Chondrons had strong immunofluorescent labeling for keratan sulphate and chondroitin-6 sulphate but no labeling for hyaluronan. We compared the immunofluorescent data with FACE. The quantities of total keratan sulphate were determined to be 0.013 +/- 0.002 pg cell(-1) and 0.032 +/- 0.003 pg cell(-1) in the chondrocyte and chondron preparations, respectively. Four internal keratan sulphate sugars were detected (gal beta 1,4glcNAc6S, gal6S beta 1,4glcNAc6S, glcNAc beta 1,3gal and glcNAc6S beta 1,3gal) for both preparations but they were present at significantly higher concentrations in chondron preparations (P < 0.01). Total chondroitin sulphate (CS) was determined to be 0.054 +/- 0.004 pg cell(-1) and 0.077 +/- 0.005 pg cell(-1) for chondrocyte and chondron preparations, respectively. Unsulphated CS disaccharide levels were similar but chondrons had significantly more chondroitin-4 sulphated disaccharides and chondroitin-6 sulphated disaccharides (P < 0.05). Hyaluronan acid was present at low concentrations (0.010 +/- 0.001 pg cell(-1)) in both chondrocytes and chondrons. In this study, enzyme digestion coupled with FACE separation revealed new information about the differences in GAGs from isolated chondrocyte and chondron preparations. Further investigation of the differences in GAGs from chondrocytes and chondrons from different zones of articular cartilage may be useful for tissue engineering approaches.

Methodological models for in vitro amplification and maintenance of human articular chondrocytes from elderly patients

Articular cartilage defects, an exceedingly common problem closely correlated with advancing age, is characterized by lack of spontaneous resolution because of the limited regenerative capacity of adult articular chondrocytes. Medical and surgical therapies yield unsatisfactory short-lasting results. Recently, cultured autologous chondrocytes have been proposed as a source to promote repair of deep cartilage defects. Despite encouraging preliminary results, this approach is not yet routinely applicable in clinical practice, but for young patients. One critical points is the isolation and ex vivo expansion of large enough number of differentiated articular chondrocytes. In general, human articular chondrocytes grown in monolayer cultures tend to undergo dedifferentiation. This reversible process produces morphological changes by which cells acquire fibroblast-like features, loosing typical functional characteristics, such as the ability to synthesize type II collagen. The aim of this study was to isolate human articular chondrocytes from elderly patients and to carefully characterize their morphological, proliferative, and differentiative features. Cells were morphologically analyzed by optic and transmission electron microscopy (TEM). Production of periodic acid-schiff (PAS)-positive cellular products and of type II collagen mRNA was monitored at different cellular passages. Typical chondrocytic characteristics were also studied in a suspension culture system with cells encapsulated in alginate-polylysine-alginate (APA) membranes. Results showed that human articular chondrocytes can be expanded in monolayers for several passages, and then microencapsulated, retaining their morphological and functional characteristics. The results obtained could contribute to optimize expansion and redifferentiation sequences for applying cartilage tissue engineering in the elderly patients.