Chondrocyte apoptosis increases with age in the articular cartilage of adult animals

Time dependence of changes of two cartilage layers in anterior cruciate ligament insertion after resection on chondrocyte apoptosis and decrease in glycosaminoglycan

Background

The purpose of this study is to clarify the differences in time-dependent histological changes (chondrocyte apoptosis and glycosaminoglycan (GAG) layer thickness decrease) between uncalcified fibrocartilage (UF) and calcified fibrocartilage (CF) layers at the anterior cruciate ligament (ACL) insertion after ACL resection of rabbits.

Methods

Forty male Japanese white rabbits underwent ACL substance resection in the right knee (resection group) and same operation without resection in the left knee (sham group). Animals were sacrificed 1, 2, 4 and 6 weeks after surgery.

Results

In the UF layer, the apoptosis rate in the resection group was significantly higher than that in the sham group at 1 and 2 weeks. The GAG layer thicknesses of the UF layer in the resection group at 1, 2, 4 and 6 weeks were lower than those in the sham group. In the CF layer, the apoptosis rate in the resection group was significantly higher than that in the sham group at 2 and 4 weeks. The GAG layer thickness of the CF layer in the resection group was lower than that in the sham group only at 6 weeks.

Conclusion

The increase in chondrocyte apoptosis rate preceded the decrease in GAG layer thickness in both layers. In the UF layer, the increase in chondrocyte apoptosis rate and the decrease in GAG layer thickness preceded those in the CF layer. Using a surviving ligament and minimizing a debridement of ACL remnant during ACL reconstruction may be important to maintain cartilage layers of ACL insertion. An injured ACL should be repaired before degenerative changes of the insertion occur.

Altered senescence, apoptosis, and DNA damage response in a mutant p53 model of accelerated aging

The tumor suppressors p16(INK4a) and p53 have been implicated as contributors to age-associated stem cell decline. Key functions of p53 are the induction of cell cycle arrest, senescence, or apoptosis in response to DNA damage. Here, we examine senescence, apoptosis, and DNA damage responses in a mouse accelerated aging model that exhibits increased p53 activity, the p53(+/m) mouse. Aged tissues of p53(+/m) mice display higher percentages of senescent cells (as determined by senescence-associated beta-galactosidase staining and p16(INK4a) and p21 accumulation) compared to aged tissues from p53(+/+) mice. Surprisingly, despite having enhanced p53 activity, p53(+/m) lymphoid tissues exhibit reduced apoptotic activity in response to ionizing radiation compared to p53(+/+) tissues. Ionizing radiation treatment of p53(+/m) tissues also induces higher and prolonged levels of senescence markers p16(INK4a) and p21, suggesting that in p53(+/m) tissues the p53 stress response is enhanced and is shifted away from apoptosis toward senescence. One potential mechanism for accelerated aging in the p53(+/m) mouse is a failure to remove damaged or dysfunctional cells (including stem and progenitor cells) through apoptosis. The increased accumulation of dysfunctional and senescent cells may contribute to reduced tissue regeneration, tissue atrophy, and some of the accelerated aging phenotypes in p53(+/m) mice.

Aging and osteoarthritis: the role of chondrocyte senescence and aging changes in the cartilage matrix

OBJECTIVE

Age-related changes in multiple components of the musculoskeletal system may contribute to the well established link between aging and osteoarthritis (OA). This review focused on potential mechanisms by which age-related changes in the articular cartilage could contribute to the development of OA.

METHODS

The peer-reviewed literature published prior to February 2009 in the PubMed database was searched using pre-defined search criteria. Articles, selected for their relevance to aging and articular chondrocytes or cartilage, were summarized.

RESULTS

Articular chondrocytes exhibit an age-related decline in proliferative and synthetic capacity while maintaining the ability to produce pro-inflammatory mediators and matrix degrading enzymes. These findings are characteristic of the senescent secretory phenotype and are most likely a consequence of extrinsic stress-induced senescence driven by oxidative stress rather than intrinsic replicative senescence. Extracellular matrix changes with aging also contribute to the propensity to develop OA and include the accumulation of proteins modified by non-enzymatic glycation.

CONCLUSION

The effects of aging on chondrocytes and their matrix result in a tissue that is less able to maintain homeostasis when stressed, resulting in breakdown and loss of the articular cartilage, a hallmark of OA. A better understanding of the basic mechanisms underlying senescence and how the process may be modified could provide novel ways to slow the development of OA.

A comparison of primary and passaged chondrocytes for use in engineering the temporomandibular joint

OBJECTIVE

This study examines the tissue engineering potential of passaged (P3) and primary (P0) articular chondrocytes (ACs) and costal chondrocytes (CCs) from skeletally mature goats for use in the temporomandibular joint (TMJ).

DESIGN

These four cell types were assembled into scaffoldless tissue engineered constructs and cultured for 4 wks. The constructs were then tested for cell, collagen, and glycosaminoglycan (GAG) content with biochemical assays, and collagen types I and II with enzyme-linked immunosorbent assays. Constructs were also tested under tension and compression to determine biomechanical properties.

RESULTS

Both primary and passaged CC constructs had greater GAG/wet weight than AC constructs. Primary AC constructs had significantly less total collagen and contained no collagen type I. AC P3 constructs had the largest collagen I/collagen II ratio, which was also greater in passaged CC constructs relative to primary groups. Primary AC constructs were not mechanically testable, whereas passaged AC and CC constructs had significantly greater tensile properties than primary CC constructs.

CONCLUSIONS

Primary CCs are considerably better than primary ACs and have potential use in tissue engineering when larger quantities of collagen type II are desired. The poor performance of the ACs, in this study, which contradicts the results seen with previous studies using immature bovine ACs, may thus be attributed to the animals' maturity. However, CC P3 cells appear particularly well suited for tissue engineering fibrocartilage of the TMJ due to the high quantity of collagen and GAG, and tensile and compressive mechanical properties.

RGD peptide-induced cell death of chondrocytes and synovial cells

BACKGROUND

Small peptides including the Arg-Gly-Asp (RGD) motif have been used in studies on cell-extracellular matrix (ECM) attachment due to their ability to disturb integrin-mediated attachment on the cell surface. As another biological action of RGD peptides, several reports have shown that RGD peptides are incorporated into cytoplasm and induce apoptosis by direct activation of caspase-3. This study evaluated the effect of RGD peptides on chondrocytes and synovial cells and studied the involvement of caspases.

METHODS

Chondrocytes and synovial cells were isolated and cultured from the knee joints of New Zealand White rabbits. Cells were incubated in serum-free medium with peptides (RGD, RGDS, GRGDSP, GRGDNP, RGES), and the survival rates were evaluated. The rate of apoptotic cells was measured by flow cytometry in cells treated with RGDS, GRGDSP, and RGES. Caspase-3, -8 and -9 activity was measured in cells treated with RGDS and GRGDSP. Osteochondral explants harvested from rabbits were also incubated with RGD peptides (RGDS, GRGDSP, and GRGDNP), and the survival rate of chondrocytes was evaluated.

RESULTS

The survival rate of cultured chondrocytes was significantly decreased in the GRGDSP- and GRGDNP-treated groups. The survival rate of synovial cells was significantly decreased with four of the RGD peptides (RGD, RGDS, GRGDSP, and GRGDNP) at 5 mM, and in the RGDS- and GRGDSP-treated groups at 1 mM. Flow cytometric assay revealed increases of apoptotic chondrocytes with GRGDSP and increases of apoptotic synovial cells with RGDS and GRGDSP. Caspase-3 was activated in chondrocytes treated with GRGDSP and it was also activated in synovial cells treated with RGDS and GRGDSP. Caspases-8 and -9 were not activated in chondrocytes or in synovial cells. The survival rate of chondrocytes in explants decreased in the superficial layer with all three RGD peptides (RGDS, GRGDSP, and GRGDNP) and in the middle layer with GRGDSP.

CONCLUSIONS

RGD peptides induced apoptosis in cultured chondrocytes as well as in cells in cartilage explants and synovial cells, presumably through direct activation of caspase-3.

Determining the influence of telomere dysfunction and DNA damage on stem and progenitor cell aging: what markers can we use?

The decline in organ maintenance and function is one of the major problems limiting quality of life during aging. The accumulation of telomere dysfunction and DNA damage appears to be one of the underlying causes. Uncapping of chromosome ends in response to critical telomere shortening limits the proliferative capacity of human cells by activation of DNA damage checkpoints inducing senescence or apoptosis. Telomere shortening occurs in the vast majority of human tissues during aging and in chronic diseases that increase the rate of cell turnover. There is emerging evidence that telomere shortening can limit the maintenance and function of adult stem cells -- a cell type of utmost importance for organ maintenance and regeneration. In mouse models, telomere dysfunction leads to a depletion of adult stem cell compartments suggesting that stem cells are very sensitive to DNA damage. Both the rarity of stem and progenitor cells in adult organs and their removal in response to damage make it difficult to assess the impact of telomere dysfunction and DNA damage on stem and progenitor cell aging. Such approaches require the development of sensitive biomarkers recognizing low levels of telomere dysfunction and DNA damage in stem and progenitor cells. Here, we review experimental data on the prevalence of telomere dysfunction and DNA damage during aging and its possible impact on stem and progenitor cell aging.

Influência do exercício na indução da apoptose e necrose das células do líquido sinovial de eqüinos atletas

Examinaram-se os efeitos do estresse mecânico na resposta inflamatória e adaptativa dos tecidos articulares de cavalos atletas. O líquido sinovial foi colhido das articulações metacarpofalangeanas de eqüinos atletas antes, 3, 6 e 24 horas após o exercício, assim como de um grupo controle (cavalos não exercitados). A porcentagem de apoptose/necrose, o TNF-a e a PGE2 foram determinados pelo ensaio de AnexinaV/Iodeto de Propídeo, bioensaio (L929) e ELISA, respectivamente. Os resultados mostraram que a contagem total de células nucleadas foi sempre menor no grupo controle em relação ao grupo atleta (P<0,05). Observaram-se aumentos na porcentagem de células em apoptose (P<0,05) e necrose (P<0,05), concentração de PGE2 (P<0,05) e proteína sinovial (P<0,05), e diminuição da concentração de TNF-a (P<0,05) após 3 horas do término do exercício. O grupo atleta apresentou grau moderado de inflamação articular após o exercício intenso. Esta resposta dos tecidos articulares frente ao insulto mecânico do exercício, com maior intensidade às 3 horas após término da atividade esportiva e retornando à normalidade 24 horas após, revela a capacidade da adaptação articular ao estresse físico, em eqüinos atletas.

Morphology, mechanisms and pathology of musculoskeletal ageing

In general terms, the recognized alterations in circulating humoral factors (hormones, cytokines, growth factors) that occur in ageing, coupled with innate cellular senescence exaggerated by the slow turnover of many connective tissue cell populations and the age-associated alterations in matrix molecule cross-linking, predispose the elderly to altered connective tissue biology. These changes can be profound, leading to poor mobility, altered ability to withstand cold, weakness and an increased risk of falls, fractures and age-associated 'degenerative' diseases, such as osteoarthritis and osteoporosis. As understanding of the causes of altered connective tissue function with age increases, it is becoming clearer that many of the predisposing factors (growth hormone, cytokines, load/life style) are potential targets for improving quality of life in the elderly.

Chondrocyte apoptosis and decrease of glycosaminoglycan in cranial cruciate ligament insertion after resection in rabbits

We examined time-dependent histological changes of the calcified fibrocartilage area in a tibial cranial cruciate ligament (CCL) insertion after ligament resection in rabbits. The animals were divided into two groups: those undergoing CCL substance resection in the right stifle (resected group) and those receiving the same operation without CCL resection in the left stifle (sham operated group). Five animals were euthanized with deep anaesthesia at four time periods (1, 2, 4 and 6 weeks), and Haematoxylin-eosin and Safranin-O stainings and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) staining were performed. The average percentage of TUNEL-positive chondrocytes and the average thickness of the glycosaminoglycan (GAG)-stained area in the calcified fibrocartilage area were measured. Two and 4 weeks after the surgery, the average percentages of TUNEL-positive chondrocytes in the resected group (23.8 +/- 10.3% and 15.9 +/- 6.7%, respectively) were significantly higher than those in the sham operated group (8.9 +/- 3.8% and 7.4 +/- 1.6%, P<0.05, respectively). Six weeks after the surgery, the average thickness of the GAG-stained area in the resected group (7.7 +/- 13. 5 microm) was significantly smaller than that in the sham operated group (69.4 +/- 39.9 microm, P<0.05). Our results suggest that the average percentage of TUNEL-positive chondrocytes became a peak in 2 weeks and that histological changes occurred in 6 weeks. The chondrocyte apoptosis can induce decrease of GAG-stained area after resection of CCL. Therefore, chondrocyte apoptosis in the calcified cartilage area in the CCL tibial insertion might lead to histological changes.

Histological changes and apoptosis of cartilage layer in human anterior cruciate ligament tibial insertion after rupture

The purpose of this study is to investigate the histological changes and apoptosis of cartilaginous layers in human anterior cruciate ligament (ACL) tibial insertion at different time periods after rupture. By using a core reamer, 35 tibial insertions of ruptured ACLs were obtained during primary ACL reconstructions (number of days after injury: 19-206 days). A histological examination was performed and a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) staining assay was carried out to detect apoptosis. The average thickness of the cartilage layer, the glycosaminoglycan-stained area and the number of chondrocytes per millimeter decreased with time. The percentage average of TUNEL-positive chondrocytes was 42.0 +/- 16.2. The histological degenerative changes of the cartilage layer in the ruptured ACL tibial insertion progressed with time, especially in the first 2 months. Moreover, chondrocyte apoptosis continued from 19 to 206 days after rupture. The results may help elucidate the etiology of the histological changes of the insertion, and may help in devising optimal treatment protocols for ACL injuries if apoptosis is controlled. Moreover, we consider that using a surviving ligament and minimizing a debridement of ACL remnant during ACL reconstruction may be important for ACL reconstruction to maintain cartilage layers in ACL insertions.

Role of apoptotic and matrix-degrading genes in articular cartilage and meniscus of mature and aged rabbits during development of osteoarthritis

OBJECTIVE

To determine expression patterns of apoptotic and matrix-degrading genes during aging and development of osteoarthritis (OA), using a rabbit model of induced OA.

METHODS

Six mature and 6 aged rabbits underwent anterior cruciate ligament transection and were killed 4 and 8 weeks after surgery, respectively, to create early-grade and advanced-grade OA. RNA from articular cartilage and menisci was examined for expression of the genes caspase 8, Fas, Fas ligand, p53, aggrecanase, matrix metalloproteinase 1 (MMP-1), and MMP-3. A second cohort of animals that had undergone no intervention in the joint was also killed. Parametric data were analyzed with analysis of variance and Student's t-tests, while nonparametric data were assessed with the Mann-Whitney U test.

RESULTS

Expression levels of Fas, caspase 8, FasL, and MMP-1 were significantly higher (>100%) in aged cartilage compared with mature cartilage (P < 0.05). After induction of OA, expression of apoptotic genes in aged rabbits remained high, while significant up-regulation of Fas and caspase 8 (nearly 150% increase) was observed in mature rabbits (P < 0.05). No significant up-regulation of these genes was observed in the menisci of aged or mature rabbits prior to or after induction of OA. Development of OA occurred more rapidly in aged cartilage compared with mature cartilage (P < 0.05).

CONCLUSION

Differential expression of apoptotic and matrix-degrading genes occurs in aged compared with mature cartilage, both at baseline and during development of OA. This may be responsible for faster degradation of aged cartilage and its predisposition for developing OA.

Caspase-2 deficiency enhances aging-related traits in mice

Alteration of apoptotic activity has been observed in a number of tissues in aging mammals, but it remains unclear whether and/or how apoptosis may affect aging. Caspase-2 is a member of the cysteine protease family that plays a critical role in apoptosis. To understand the impact of compromised apoptosis function on mammalian aging, we conducted a comparative study on caspase-2 deficient mice and their wild-type littermates with a specific focus on the aging-related traits at advanced ages. We found that caspase-2 deficiency enhanced a number of traits commonly seen in premature aging animals. Loss of caspase-2 was associated with shortened maximum lifespan, impaired hair growth, increased bone loss, and reduced body fat content. In addition, we found that the livers of caspase-2 deficient mice had higher levels of oxidized proteins than those of age-matched wild-type mice, suggesting that caspase-2 deficiency compromised the animal's ability to clear oxidatively damaged cells. Collectively, these results suggest that caspase-2 deficiency affects aging in the mice. This study thus demonstrates for the first time that disruption of a key apoptotic gene has a significant impact on aging.

Variation in articular cartilage in rats between 3 and 32 months old. A histomorphometric and scanning electron microscopy study

In this study we assess the thickness, the cellular density, the cell sizes and the collagen of the three superficial cartilage zones and the morphology of the articular surface of the femoral trochlea in rats with 3, 12 and 32 months of age. The cartilage was studied using light microscopy and scanning electron microscopy. The quantitative results are expressed as means +/- SEM. The data were compared statistically (P < 0.05). Both the thickness and the cellular density significantly diminish with age, in the three cartilage zones studied. The reduction of cellular density is more pronounced in the superficial and intermediate zones of the cartilage (zones I and II, respectively). In zone III (deep zone), the cellular density declines only as from 12 months of age. The area of the chondrocytes diminishes in the superficial and deep zones, but only as from 12 months old. In the intermediate zone, there is no chondrocyte hypotrophy with age. The types of collagen in the zones of the cartilage change with age. In the superficial zone, the collagen type I predominates at 3 months of age while the collagen type II predominates at 12 and 32 months of age. In the intermediate and deep zones, the collagen type I that predominates at 3 months of age is substituted by the collagen type III at 12 and 32 months of age. The articular surface in the 3-month-old rats is relatively smooth, presenting few undulations. In 12-month-old animal cartilages, few fissures and craters are found. In the 32-month-old animals, it was observed a higher number of this kind of degenerative changes and with a more severe look.

Chondrocyte apoptosis and posttraumatic arthrosis

Apoptosis, or programmed cell death, plays an important role in many normal and pathologic conditions. This article has been designed to introduce the concept of chondrocyte apoptosis and how it may contribute to posttraumatic arthrosis following articular injury. Available means of assessing chondrocyte apoptosis are presented, in addition to the findings of in vitro and in vivo studies of cartilage injury. Unfortunately, despite active research in this area, the exact contribution chondrocyte apoptosis makes following joint injury to the development of posttraumatic arthrosis is unknown.

Chondrolysis after continuous intra-articular bupivacaine infusion: an experimental model investigating chondrotoxicity in the rabbit shoulder

PURPOSE

Postoperative pain pumps are increasingly used to deliver a continuous infusion of local anesthetic into the surgical wound or the joint. Recently, there have been concerns that the use of such devices may be associated with chondrotoxicity and even cases of chondrolysis in the shoulder. An experimental model is presented that investigates potential chondrotoxic effects of a continuous intra-articular infusion of bupivacaine in the rabbit shoulder.

METHODS

We divided 30 rabbits into 3 groups that received continuous infusions of either saline solution, bupivacaine, or bupivacaine with epinephrine into the glenohumeral joint over a period of 48 hours. Animals were killed after 1 week, and osteochondral and synovial samples from the glenohumeral joint underwent analyses with confocal microscopy for live/dead cell assay, metabolic sulfate uptake assessment, and conventional histologic analysis.

RESULTS

Infusion of bupivacaine with epinephrine and without epinephrine decreased sulfate uptake by 56% (P = .009) and 50% (P = .02), respectively, when compared with saline solution; cell viability decreased by 20% (P = .08) and 32% (P = .02), respectively. Histologic analysis yielded significantly worse scores for bupivacaine infusion with epinephrine (P = .004) and without epinephrine (P = .02). The results for bupivacaine with or without epinephrine were not significantly different.

CONCLUSIONS

Continuous intra-articular infusion of bupivacaine with and without epinephrine led to significant histopathologic and metabolic changes in articular cartilage.

CLINICAL RELEVANCE

Bupivacaine showed profound chondrotoxic effects in an experimental model that closely followed the current clinical application of postoperative pain pumps. The results caution against the use of such devices in applications for smaller joints with minimal clearance or dilution as a result of hematoma, where continuous exposure of cartilage to bupivacaine is expected.

Developing a research agenda in biogerontology: physiological systems

The Biology of Aging Program (BAP) at the National Institute on Aging supports research in many areas, including processes of cell senescence and apoptosis, genetic influences on aging, and how aging leads to tissue dysfunction. Several approaches to research on aging physiological systems are described, along with BAP programmatic efforts to enhance and support that research. Understanding the relation between aging and tissue dysfunction has led to new insights into how health can be improved for aged individuals.

CHONDROCYTE APOPTOSIS IN RESPONSE TO DISLOCATION OF THE HIP IN THE RAT MODEL

BACKGROUND

Joint dislocation is a traumatic event that can lead to osteoarthritis. The purpose of this paper is to study cartilage changes following prolonged joint dislocation for 1, 2 or 8 h.

METHODS

Sprague-Dawley rats (n = 27) were used in this study. Surgical dislocation of the hip under anaesthesia was carried out on the animals. The joints remained dislocated for 1, 2 or 8 h. The joints were subsequently harvested and terminal deoxnucleotidyl transferase-mediated dUTP nick-end labelling testing was carried out to show chondrocyte apoptosis in the femoral head and acetabulum. Using this test, the apoptotic index, which is the proportion of apoptotic chondrocytes to total number of chondrocytes, was calculated. A comparison of apoptotic indices was made among the three groups.

RESULTS

The mean apoptotic indices for the femoral head for the 1-, 2- and 8-h groups were 0.065 +/- 0.025, 0.162 +/- 0.031 and 0.201 +/- 0.030, respectively. There was a significant difference (P < 0.05) in the mean apoptotic indices between each of the three groups. For the acetabulum, the mean apoptotic indices were 0.046 +/- 0.012, 0.051 +/- 0.023 and 0.057 +/- 0.031 for the 1-, 2- and 8-h groups, respectively. There was no significant difference (P > 0.05) between each of the three groups.

CONCLUSIONS

Dislocation of a joint causes chondrocyte apoptosis. There is a progressive increase in the apoptotic index with prolonged dislocation of the rat hip.

Hydrostatic pressure induces apoptosis of chondrocytes cultured in alginate beads

The purpose of this study was to investigate the influence of hydrostatic pressure (HP) on apoptosis and expression of heat-shock protein 70 (HSP70) in chondrocytes cultured in alginate beads. Chondrocytes were isolated from the articular cartilage of rabbit joints and seeded in alginate beads. The beads in Group A were cultured for less than 24 h after being embedded with the chondrocytes, while those in Group B were cultured for 2 weeks. Both groups were exposed to HP of 10 or 50 MPa for 12 or 24 h. The beads in Groups A and B that were not exposed to HP were regarded as controls. Apoptotic cells induced by exposure to HP were quantified using the TUNEL method. Immunohistochemical analysis for HSP70 and in situ TUNEL analysis were also performed. Apoptotic chondrocytes were not observed in the control cells under atmospheric pressure, whereas apoptosis was observed in the beads in Group A, and the number of apoptotic cells increased as the duration and magnitude of HP increased. On the other hand, we observed no significant population of apoptotic cells in the beads in Group B. Chondrocytes expressing HSP70 were not TUNEL positive in the histological analysis. Excessively strong HP could evoke apoptosis when the extracellular matrix did not accumulate around the chondrocytes. HSP70 expression was related to occurrence of apoptosis that resulted from HP. These findings suggest a mechanism for the pathogenesis of cartilage degeneration in osteoarthritis.

Distribution of tenascin-C and tenascin-X, apoptotic and proliferating cells in postnatal soft-diet rat temporomandibular joint (TMJ)

We immunohistochemically examined the relationship between the distribution of extracellular matrix glycoproteins (tenascin-C and tenascin-X), apoptotic cells, and proliferating cells to determine the effect of a soft diet in the rat temporomandibular joint (TMJ) over a period of 4 weeks from 21 days of age. Using confocal Laser scanning microscopy, strong expression of tenascin-C and tenascin-X was found in the soft-diet group, mainly from the proliferative layer to the cartilage layer of the condyle, and posterior and anterior regions of the disk, in contrast to that of the control group, which was fed a hard diet. The number of proliferating cells in the soft-diet group was lower than that in the control group and was especially low in the calcified zone and proliferative cell layer of the sagittal section of the TMJ. The apoptotic cells were found mainly in the endochondral ossification layer of the condyle. On day 28 in the soft-diet group, they were also highly concentrated in endochondral ossification layer of the anterior condyle beneath the disk. A few apoptotic cells were observed in the synovial membrane and the disk. These distributions reflect the process of replication in the TMJ in accordance with the feeding of a soft diet.

Potential predictive markers for proliferative capacity of cultured human articular chondrocytes: PCNA and p21

The purpose of this study was to investigate age-related changes in the proliferative ability of human articular chondrocytes in culture. In addition, the possible markers for the proliferative capacity of chondrocytes were examined. Chondrocytes obtained from human articular cartilages of young (under 40 years) or old (over 60 years) individuals were expanded until their growth was arrested. The number of cells and the type II collagen phenotype were determined together with the expression levels of proliferating cell nuclear antigen (PCNA) and p21(WAF1/CIP) along with the passages of cultured chondrocytes. The results showed that young chondrocytes had higher proliferative capacity and viability than old chondrocytes. The growth arrest and the cessation in the expression of type II collagen were accompanied by down-regulation of PCNA and up-regulation of p21(WAF1/CIP) levels in both young and old chondrocytes. Notably, the expression levels of PCNA and p21(WAF1/CIP) along with the passages were correlated inversely to each other and showed distinct patterns between young and old chondrocytes. These results suggest that senescence of human articular chondrocytes leads to the decrease in the proliferative capacity and phenotypic stability. In addition, PCNA and p21 could be molecular markers that represent the status of these age-related properties of human articular chondrocytes in vitro.

Increased chondrocyte apoptosis in growth plates from children with slipped capital femoral epiphysis

Ultrastructural studies of slipped capital femoral epiphysis (SCFE) growth plates have shown diminished cellularity and marked distortion of the architecture in the proliferative and hypertrophic zones. Chondrocyte degeneration and death were noted at all levels of the hypertrophic and proliferative zones, suggesting an accelerated disturbance in the life-to-death cycle of the chondrocytes. The current study examines the mechanism responsible for the diminished cell number and whether increased programmed cell death (apoptosis) or necrosis was operative. Proximal femoral growth plates from patients with SCFE (three patients) were prepared and sectioned for histochemistry, in situ detection of apoptosis, and immunohistochemistry. The results showed that the diminished cell number is due to an abnormal frequency and distribution of chondrocytes undergoing apoptosis. Although it is unclear whether the increased apoptosis is occurring early or late in the disease, it is highly likely that it is directly linked to pathogenesis.

Apoptosis in the supraspinatus tendon with stage II subacromial impingement

The purpose of this study was to investigate the histopathology, including apoptosis, in the supraspinatus tendon with stage II subacromial impingement. Samples from the critical zone of the supraspinatus tendon were obtained from 5 patients with subacromial impingement syndrome and 10 autopsy cases without shoulder diseases as controls. Three-micrometer-thick sections were cut and stained with hematoxylin-eosin (H-E) for routine histologic examination. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) method and single-stranded deoxyribonucleic acid (ssDNA) assay in which the frequency of the apoptotic cells was expressed by the apoptotic index. Control supraspinatus tendons showed normal morphology, whereas supraspinatus tendons from shoulders with impingement showed significant mucoid degeneration. Correspondingly, few apoptotic cells were observed in control tendons, whereas a large number of apoptotic cells were observed in the degenerative area of tendons from impingement shoulders. The apoptotic indices were significantly higher in the impingement shoulders (ssDNA, 18.84% +/- 1.75%; TUNEL, 24.92% +/- 2.79%) than in the control shoulders (ssDNA, 5.22% +/- 1.30%; TUNEL, 7.01% +/- 1.05%) (P = .04 for ssDNA and P = .017 for TUNEL). Mechanical impingement seems to cause tendon degeneration and apoptosis of the tendon cells in the supraspinatus tendon in stage II impingement.

Multiple Signals Induce Endoplasmic Reticulum Stress in Both Primary and Immortalized Chondrocytes Resulting in Loss of Differentiation, Impaired Cell Growth, and Apoptosis

The endoplasmic reticulum is the site of synthesis and folding of secretory proteins and is sensitive to changes in the internal and external environment of the cell. Both physiological and pathological conditions may perturb the function of the endoplasmic reticulum, resulting in endoplasmic reticulum stress. The chondrocyte is the only resident cell found in cartilage and is responsible for synthesis and turnover of the abundant extracellular matrix and may be sensitive to endoplasmic reticulum stress. Here we report that glucose withdrawal, tunicamycin, and thapsigargin induce up-regulation of GADD153 and caspase-12, two markers of endoplasmic reticulum stress, in both primary chondrocytes and a chondrocyte cell line. Other agents such as interleukin-1beta or tumor necrosis factor alpha induced a minimal or no induction of GADD153, respectively. The endoplasmic reticulum stress resulted in decreased chondrocyte growth based on cell counts, up-regulation of p21, and decreased PCNA expression. In addition, perturbation of endoplasmic reticulum function resulted in decreased accumulation of an Alcian Blue positive matrix by chondrocytes and decreased expression of type II collagen at the protein level. Further, quantitative real-time PCR was used to demonstrate a down-regulation of steady state mRNA levels coding for aggrecan, collagen II, and link protein in chondrocytes exposed to endoplasmic reticulum stress-inducing conditions. Ultimately, endoplasmic reticulum stress resulted in chondrocyte apoptosis, as evidenced by DNA fragmentation and annexin V staining. These findings have potentially important implications regarding consequences of endoplasmic reticulum stress in cartilage biology.

A Morphometric Study of Age-Related Changes in Adult Human Epiglottis Using Quantitative Digital Analysis of Cartilage Calcification

The epiglottis plays an important role in deglutition in humans. The present study investigated age-related changes in the epiglottis using macroscopic and microscopic measurements. Epiglottic specimens from 281 Japanese adult cadavers (177 males, 104 females) were obtained. Specimens were divided into three groups according to age: group I: 20-39 years old (32 males, 26 females), group II: 50-69 years old (82 males, 36 females), and group III: 80-98 years old (63 males, 42 females). Width, height, and thickness were measured macroscopically. To evaluate the degree of calcium deposition, the calcium volume in digitalized von Kossa-stained sections was assessed using a quantitative analysis. An elemental analysis of the area detected with von Kossa staining was done using energy-dispersive X-ray fluorescence spectrometer (EDX). Measurements of the thickness and cell density in the superficial and deep layers of epiglottic cartilage were performed in horizontal histological sections. No significant differences in macroscopic width or height were found across the age groups in either sex. A series of three measurements in males was significantly larger than in females (p<0.05). The volume of the calcium deposit area was greater in males than in females (p<0.05) and was significantly increased in group III in males (p<0.05). The lower level of the epiglottic cartilage showed a greater calcium deposit area than the upper level. In the scanning image by line and surface analysis using EDX, the calcium deposit areas detected with von Kossa staining indicated a close association of calcium and phosphorus ions. The mean Ca/P molar ratio in the calcium deposit area was 1.32+/-0.12. Microscopic cartilage thickness increased significantly with age (p<0.05), and was greater in males than in females (p<0.05). Cartilage cell density in the superficial cartilage layer was higher than in the deep layer and was decreased in group III (p<0.05). Cartilage cell density was lower in males compared to females. Diameter of chondrocytes significantly increased in group III (p<0.05) and was larger in males than in females in group III (p<0.05). Epiglottic cartilage exhibited marked sex-related differences and progression of calcification with age. Calcification of epiglottic cartilage in elderly individuals may affect movement patterns in deglutition.

Vulnerability to ROS-induced cell death in ageing articular cartilage: the role of antioxidant enzyme activity

OBJECTIVES

To test the hypothesis that age-related loss of chondrocytes in cartilage is associated with impaired reactive oxygen species (ROS) homeostasis resulting from reduced antioxidant defence.

METHODS

Cell numbers: The total number of chondrocytes in the articular cartilage of the femoral head of young, mature and old rats was estimated using an unbiased stereological method. ROS quantification: Fluorescence intensity in chondrocytes was quantified using the oxygen free radical sensing probe dihydrorhodamine 123 (DHR 123), confocal laser scanning microscopy and densitometric image analysis. In order to delineate the reactive species, explants were pre-treated with N-acetylcysteine (NAC) or N(G)-nitro-l-arginine methyl ester (l-NAME) prior to ROS quantification. Induction of intracellular ROS: Explants were incubated in the redox-cycling drug menadione after which they underwent ROS quantification and cell-viability assay. Antioxidant enzyme activity: The activity of catalase, superoxide dismutase (SOD) and glutathione peroxidase (GPX) was measured.

RESULTS

Chondrocyte numbers: A significant and progressive loss of chondrocytes was observed with ageing. Cellular ROS levels: A significant age-related increase in cellular ROS-induced fluorescence was demonstrated. NAC significantly reduced ROS levels in old chondrocytes only. Induction of intracellular ROS: Menadione increased cellular ROS levels dose-dependently in young and old chondrocytes, with a greater effect in the latter. Old chondrocytes were more vulnerable to menadione-induced cytotoxicity. Antioxidant enzymes: Catalase activity declined significantly in aged cartilage whilst SOD and GPX activities were unaltered.

CONCLUSIONS

Substantial loss of chondrocytes occurs in rat articular cartilage which may result from increased vulnerability to elevated intracellular ROS levels, consequent upon a decline in antioxidant defence.

Bcl-2 positively regulates Sox9-dependent chondrocyte gene expression by suppressing the MEK-ERK1/2 signaling pathway

Bcl-2 is an anti-apoptotic protein that has recently been shown to regulate other cellular functions. We previously reported that Bcl-2 regulates chondrocyte matrix gene expression, independent of its anti-apoptotic function. Here, we further investigate this novel function of Bcl-2 and examine three intracellular signaling pathways likely to be associated with this function. The present study demonstrates that the activity of Sox9, a master transcription factor that regulates the gene expression of chondrocyte matrix proteins, is suppressed by Bcl-2 small interference RNA in the presence of caspase inhibitors. This effect was attenuated by prior exposure of chondrocytes to an adenoviral vector expressing sense Bcl-2. In addition, the down-regulation of Bcl-2, Sox9, and chondrocyte-specific gene expression by serum withdrawal in primary chondrocytes was reversed by expressing Bcl-2. Inhibition of the protein kinase C alpha and NFkappaB pathways had no effect on the maintenance of Sox9-dependent gene expression by Bcl-2. In contrast, whereas the MEK-ERK1/2 pathway negatively regulated the differentiated phenotype in wild type chondrocytes, inhibition of this pathway reversed the loss of differentiation markers and fibroblastic phenotype in Bcl-2-deficient chondrocytes. In conclusion, the present study identifies a specific signaling pathway, namely, MEK-ERK1/2, that is downstream of Bcl-2 in the regulation of Sox9-dependent chondrocyte gene expression and phenotype.

Effect of tissue maturity on cell viability in load-injured articular cartilage explants

OBJECTIVE

During joint maturation, articular cartilage undergoes compositional, structural, and biomechanical changes, which could affect how the chondrocytes within the cartilage matrix respond to load-induced injury. The objective of this study was to determine the effects of tissue maturity on chondrocyte viability when explanted cartilage was subjected to load-induced injury.

DESIGN

Cartilage explants from immature (4-8-week-old) and mature (1.5-2-year-old) bovine humeral heads were cyclically loaded at 0.5 hertz in confined compression with a stress of 1 or 5 megapascals for 0.5, 1, 3, 6 and 16 h. Cell death was assessed at 0, 24 and 48 h after load removal using cell viability dyes and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. The organization of pericellular matrix (PCM), biochemical composition and biomechanical properties of the cartilage were also determined.

RESULTS

For the immature and mature cartilage, cell death began at the articular surface and increased in depth with loading time up to 6h. No increase of cell death was found after load removal for up to 48 h. In both groups, cell death increased at a faster rate with the increase of stress level. The depth of cell death in the immature cartilage was greater than the mature cartilage, despite the immature cartilage having a higher bulk aggregate modulus. A less organized PCM in immature cartilage was found as indicated by the weak staining of type VI collagen.

CONCLUSION

Cells in the mature cartilage are less vulnerable to load-induced injury than those in immature cartilage.

Aging bone and cartilage: cross-cutting issues

Aging is a major risk factor for osteoarthritis and osteoporosis. Yet, these are not necessary outcomes of aging, and the relationship between age-related changes in bone and cartilage and development of disease is not clear. There are some well-described cellular changes associated with aging in multiple tissues that appear to be fundamental to the decline in function of cartilage and bone. A better understanding of age-related changes in cells and tissues is necessary to mitigate or, hopefully, avoid loss of bone and cartilage with aging. In addition, a better understanding of the dynamics of tissue maintenance in vivo is critical to developing tissue replacement and repair therapies. The role of stem cells in this process, and why tissues are not well maintained with advancing age, are frontiers for future aging research.

Apoptosis in osteoarthritis

Many studies have shown that apoptotic cell death occurs at an increased rate in osteoarthritic cartilage. Whichever type of cell death takes places in articular cartilage, it is important to prevent, because it is detrimental to articular cartilage maintenance. Thus, it is important to characterize events going on during cellular degeneration in more detail. Overall, physicians have reached a reasonable level of understanding of the extent of cell death occurring in the disease process, but they are still at an early stage in the understanding of the mechanisms underlying this process and the means of intervening in this facet of cartilage destruction.

Regulation of retinoic acid distribution is required for proximodistal patterning and outgrowth of the developing mouse limb

Exogenous retinoic acid (RA) induces marked effects on limb patterning, but the precise role of endogenous RA in this process has remained unknown. We have studied the role of RA in mouse limb development by focusing on CYP26B1, a cytochrome P450 enzyme that inactivates RA. Cyp26b1 was shown to be expressed in the distal region of the developing limb bud, and mice that lack CYP26B1 exhibited severe limb malformation (meromelia). The lack of CYP26B1 resulted in spreading of the RA signal toward the distal end of the developing limb and induced proximodistal patterning defects characterized by expansion of proximal identity and restriction of distal identity. CYP26B1 deficiency also induced pronounced apoptosis in the developing limb and delayed chondrocyte maturation. Wild-type embryos exposed to excess RA phenocopied the limb defects of Cyp26b1(-/-) mice. These observations suggest that RA acts as a morphogen to determine proximodistal identity, and that CYP26B1 prevents apoptosis and promotes chondrocyte maturation, in the developing limb.

Hydrostatic pressure induces apoptosis in human chondrocytes from osteoarthritic cartilage through up-regulation of tumor necrosis factor-alpha, inducible nitric oxide synthase, p53, c-myc, and bax-alpha, and suppression of bcl-2

Hydrostatic pressure (HP) is thought to increase within cartilage extracellular matrix as a consequence of fluid flow inhibition. The biosynthetic response of human articular chondrocytes to HP in vitro varies with the load magnitude, load frequency, as well as duration of loading. We found that continuous cyclic HP (5 MegaPascals (MPa) for 4 h; 1 Hz frequency) induced apoptosis in human chondrocytes derived from osteoarthritic cartilage in vitro as evidenced by reduced chondrocyte viability which was independent of initial cell densities ranging from 8.1 x 10(4) to 1.3 x 10(6) cells ml(-1). HP resulted in internucleosomal DNA fragmentation, activation of caspase-3, and cleavage of poly-ADP-ribose polymerase (PARP). At the molecular level, induction of apoptosis by HP was characterized by up-regulation of p53, c-myc, and bax-alpha after 4 h with concomitant down-regulation of bcl-2 after 2 h at 5 MPa as measured by RT-PCR. In contrast, beta-actin expression was unchanged. Real-time quantitative RT-PCR confirmed a HP-induced (5 MPa) 1.3-2.6 log-fold decrease in bcl-2 mRNA copy number after 2 and 4 h, respectively, and a significant increase (1.9-2.5 log-fold) in tumor necrosis factor-alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) mRNA copy number after 2 and 4 h, respectively. The up-regulation of p53 and c-myc, and the down-regulation of bcl-2 caused by HP were confirmed at the protein level by Western blotting. These results indicated that HP is a strong inducer of apoptosis in osteoarthritic human chondrocytes in vitro.

Biology of Fibrocartilage Cells

Fibrocartilage is an avascular tissue that is best documented in menisci, intervertebral discs, tendons, ligaments, and the temporomandibular joint. Several of these sites are of particular interest to those in the emerging field of tissue engineering. Fibrocartilage cells frequently resemble chondrocytes in having prominent rough endoplasmic reticulum, many glycogen granules, and lipid droplets, and intermediate filaments together with and actin stress fibers that help to determine cell organization in the intervertebral disc. Fibrocartilage cells can synthesize a variety of matrix molecules including collagens, proteoglycans, and noncollagenous proteins. All the fibrillar collagens (types I, II, III, V, and XI) have been reported, together with FACIT (types IX and XII) and network-forming collagens (types VI and X). The proteoglycans include large, aggregating types (aggrecan and versican) and small, leucine-rich types (decorin, biglycan, lumican, and fibromodulin). Less attention has been paid to noncollagenous proteins, although tenascin-C expression may be modulated by mechanical strain. As in hyaline cartilage, matrix metalloproteinases are important in matrix turnover and fibrocartilage cells are capable of apoptosis.

Increased apoptosis in human osteoarthritic cartilage corresponds to reduced cell density and expression of caspase-3

OBJECTIVE

Chondrocyte apoptosis has been described in both human and experimentally induced osteoarthritis (OA), but its importance in the etiopathogenesis of OA is uncertain. The aims of this study were to determine the rate of chondrocyte apoptosis using different methods, and to investigate the relationship between this process and cartilage cellularity, expression of proapoptotic molecules, and expression of antiapoptotic molecules in articular cartilage obtained from patients with OA and from nonarthritic controls.

METHODS

We examined the extent of apoptosis in OA and nonarthritic control cartilage using expression of caspase-3, an enzyme that mediates the final stage of cell death by apoptosis, as well as the TUNEL method. We used immunohistochemistry to analyze the expression of a panel of proapoptotic and antiapoptotic molecules that regulate apoptosis in articular cartilage, in order to determine whether the rate of apoptosis is associated with the expression of these molecules.

RESULTS

The median (range) percentage of TUNEL-positive chondrocytes in knee OA cartilage (n = 10 specimens), hip OA cartilage (n = 9), and control cartilage (n = 7) was 3.11 (1.67-3.67), 1.86 (1.22-2.89), and 0.39 (0.00-1.78), respectively. When all cartilage samples were pooled, apoptosis showed a strong inverse correlation with cellularity (r = -0.74, P < 0.0001). The percentage (range) of cells expressing caspase-3 in the 3 groups was 15.70 (7.40-20.50), 15.77 (7.42-20.5), and 7.40 (5.90-8.00), respectively. One-way analysis of variance showed that the differences between groups for both TUNEL-positive cells and expression of caspase-3 were statistically significant (P < 0.0001). There was a significant positive correlation between TUNEL-positive cells and expression of caspase-3 (r = 0.654, P< 0.01).

CONCLUSION

The data suggest that apoptosis is increased, on average, 2-4-fold in OA cartilage. Considering that OA develops over many years, such an increase in the rate of apoptosis in the articular cartilage could play an important role in the disease process.

Age-related expression patterns of Bag-1 and Bcl-2 in growth plate and articular chondrocytes

Aging cartilage displays increased chondrocyte apoptosis and decreased responsiveness of chondrocytes to growth factors. The molecular mechanisms responsible for these changes have not been identified. Bag-1 is a Bcl-2-binding protein that promotes cell survival, interacts with a diverse group of cellular proteins, and may integrate multiple pathways involved in controlling cell survival, growth, and phenotype. Bcl-2 is important for maintaining chondrocyte phenotype and delaying terminal differentiation and apoptosis of chondrocytes. Comparatively little is known about the role of Bag-1 in cartilage. Here we show that both growth plate and articular chondrocytes in the mouse express the Bag-1 protein. In the growth plate, Bag-1 expression is prominent in the late proliferative and prehypertrophic chondrocytes, displaying a pattern similar to what has been reported for Bcl-2. Further, the expression of both Bcl-2 and Bag-1 declines with age in the articular cartilage. Growth assays demonstrate that knocking down Bag-1 expression causes a decrease in growth rate. These results suggest that Bag-1 is involved in the regulation of chondrocyte phenotype and cartilage aging.

Increased oxidative stress with aging reduces chondrocyte survival: Correlation with intracellular glutathione levels

OBJECTIVE

To examine the role of oxidative stress in mediating cell death in chondrocytes isolated from the articular cartilage of young and old adult human tissue donors.

METHODS

Cell death induced by the oxidant SIN-1 was evaluated in the alginate bead culture system using fluorescent probes to assess membrane integrity. Generation of peroxynitrite by the decomposition of SIN-1 was confirmed by positive immunostaining of treated cells for 3-nitrotyrosine. Determinations of oxidized glutathione (GSSG) and reduced glutathione (GSH) were performed in monolayer cultures using an enzyme- recycling assay. Cells were depleted of intracellular glutathione either by the addition of DL-buthionine-(S,R)-sulfoximine or by removal of L-cystine from the culture media. The activity of cellular antioxidant enzymes was determined spectrophotometrically by the decay of substrate from the reaction mixture.

RESULTS

More chondrocytes (>2-fold) from old donors (>/=50 years) died after exposure to 1 mM SIN-1 relative to those derived from young donors (18-49 years). Although autocrine production of insulin-like growth factor 1 (IGF-1) promotes chondrocyte survival, pretreatment with IGF-1 could not prevent the cell death induced by SIN-1 exposure. Cells isolated from old donors had a higher ratio of GSSG to GSH. Glutathione reductase is the principal enzyme involved in the regeneration of GSH from GSSG. Treatment of chondrocytes with SIN-1 to induce oxidative stress in vitro resulted in the decreased activity of glutathione reductase and thioredoxin reductase, but not catalase. Cells depleted of intracellular glutathione were more susceptible to cell death induced by SIN-1.

CONCLUSION

These results provide evidence that increased oxidative stress with aging makes chondrocytes more susceptible to oxidant-mediated cell death through the dysregulation of the glutathione antioxidant system. This may represent an important contributing factor to the development of osteoarthritis in older adults.

Ageing–apoptosis relation in murine spleen

Relatively few studies have been published with regard to modification of apoptosis in normal tissues as a function of ageing. The majority of these studies demonstrated an increase in programmed cell death (PCD) with age. However, opposite results, namely loss of apoptotic control with age, have also been reported. In the present study, we examined proliferation and apoptotic cell death in spleens of C57/BL mice of different ages. A tendency towards decrease in cell proliferative capacity was seen with age. By contrast, apoptosis was increased in spleens from aged animals. Moreover, the proliferative cell/apoptotic cell ratio decreased in function of age. Ladder type DNA degradation was much more pronounced in DNA derived from splenocytes of old mice. These results were supported by a decrease of Bcl-2 and an increase in Fas receptor expression as well as by increased activation of caspases 8, 3 and 9 in splenocytes from aged animals. In addition, cell surface molecular markers recognizable by macrophages in apoptotic cells, namely decreased sialic acid concomitant with increased unmasking of galactose residues, were more pronounced on splenocytes from old mice than on those from young animals. In addition to the experimental evidence which supports a role of apoptotic cell death in ageing, a series of theoretical reasoning, which could also favor this possibility, are discussed.

Accelerated, aging-dependent development of osteoarthritis in alpha1 integrin-deficient mice

OBJECTIVE

Cell-matrix interactions regulate chondrocyte differentiation and survival. The alpha1beta1 integrin is a major collagen receptor that is expressed on chondrocytes. Mice with targeted inactivation of the integrin alpha1 gene (alpha1-KO mice) provide a model that can be used to address the role of cell-matrix interactions in cartilage homeostasis and osteoarthritis (OA) pathogenesis.

METHODS

Knee joints from alpha1-KO and wild-type (WT) BALB/c mice were harvested at ages 4-15 months. Knee joint sections were examined for inflammation, cartilage degradation, and loss of glycosaminoglycans (by Safranin O staining). Immunohistochemistry was performed to detect the distribution of alpha1 integrin, matrix metalloproteinases (MMPs), and chondrocyte apoptosis.

RESULTS

In WT mice, the alpha1 integrin subunit was detected in hypertrophic chondrocytes in the growth plate and in a subpopulation of cells in the deep zone of articular cartilage. There was a marked increase in alpha1-positive chondrocytes in the superficial and upper mid-zones in OA-affected areas in joints from old WT mice. The alpha1-KO mice showed more severe cartilage degradation, glycosaminoglycan depletion, and synovial hyperplasia as compared with the WT mice. MMP-2 and MMP-3 expression was increased in the OA-affected areas. In cartilage from alpha1-KO mice, the cellularity was reduced and the frequency of apoptotic cells was increased. These results suggest that the alpha1 integrin subunit is involved in the early remodeling process in OA cartilage.

CONCLUSION

Deficiency in the alpha1 integrin subunit is associated with an earlier deregulation of cartilage homeostasis and an accelerated, aging-dependent development of OA.

Induction of chondrocyte apoptosis following impact load

OBJECTIVE

To investigate the presence and extent of chondrocyte apoptosis following impact load of articular cartilage in an in vivo model.

DESIGN

An in vivo animal model, using a pendulum device and New Zealand White rabbits, was designed to study the effects of impact load on the development of chondrocyte apoptosis. Animals were placed into either a High Impact group or a Low Impact group, and the right medial femoral condyle was impacted with a single impact load. A sham operation was performed on the left limb, and this cartilage served as the control.

SETTING

Academic medical center.

PARTICIPANTS

New Zealand White rabbits (3 months).

INTERVENTION

Impact load to the right medial femoral condyle.

MAIN OUTCOME MEASURES

Three different methods were used to assess the presence and extent of chondrocyte apoptosis: 1) light microscopy (hematoxylin and eosin and terminal dUTP nick end labeling staining); 2) transmission electron microscopy; and 3) fluorescent microscopy with Hoechst 33342 staining. Secondary outcome measures included determination of the magnitude of impact force and time to peak force.

RESULTS

Light microscopy demonstrated chondrocytes with changes consistent with apoptosis including condensed nuclei, deep eosinophilic cytoplasmic staining, and vacuolization within the impacted specimens. Terminal dUTP nick end labeling staining-stained specimens had a high degree of positively stained cells (60%) in both injured and uninjured specimens. Transmission electron microscopy of the impacted specimens demonstrated numerous chondrocytes with changes characteristic of apoptosis, including nuclear and cellular fragmentation, volume shrinkage, and cytoplasmic vacuolization. Eleven percent of the cells in the High Impact group had changes consistent with apoptosis, versus 3% for the low impact group and <1% for the sham specimens. The High Impact group received a statistically significant greater stress than the Low Impact group. Impact group (P < 0.05), and the average time to peak force was 0.021 seconds for each impact group.

CONCLUSIONS

The current data strongly indicate that in vivo chondrocyte apoptosis can be stimulated by the application of a single, rapid impact load and that the extent of chondrocyte apoptosis is related to the amount of load applied. The contribution chondrocyte apoptosis makes to the development of posttraumatic arthritis following joint injury or intra-articular fracture still remains to be determined.

Functional differences between growth plate apoptotic bodies and matrix vesicles

Mineralization often occurs in areas of apoptotic changes. Our findings indicate that physiological mineralization is mediated by matrix vesicles. These matrix vesicles use mechanisms to induce mineralization that are different from the mechanisms used by apoptotic bodies released from apoptotic cells. Therefore, different therapeutic approaches must be chosen to inhibit pathological mineralization depending on the mechanism of mineralization (matrix vesicles versus apoptotic bodies).

INTRODUCTION

Physiological mineralization in growth plate cartilage is restricted to regions of terminally differentiated and apoptotic chondrocytes. Pathological mineralization of tissues also often occurs in areas of apoptosis. We addressed the question of whether apoptotic changes control mineralization events or whether both events are regulated independently.

METHODS

To induce mineralization, we treated growth plate chondrocytes with retinoic acid (RA); apoptosis in these cells was induced by treatment with staurosporine, anti-Fas, or TNFalpha. The degrees of mineralization and apoptosis were determined, and the structure and function of matrix vesicles and apoptotic bodies were compared.

RESULTS

Release of matrix vesicles and mineralization in vivo in the growth plate occurs earlier than do apoptotic changes. To determine the functional relationship between apoptotic bodies and matrix vesicles, growth plate chondrocytes were treated with RA to induce matrix vesicle release and with staurosporine to induce release of apoptotic bodies. After 3 days, approximately 90% of staurosporine-treated chondrocytes were apoptotic, whereas only 2-4% of RA-treated cells showed apoptotic changes. RA- and staurosporine-treated chondrocyte cultures were mineralized after 3 days. Matrix vesicles isolated from RA-treated cultures and apoptotic bodies isolated from staurosporine-treated cultures were associated with calcium and phosphate. However, matrix vesicles were bigger than apoptotic bodies. Furthermore, matrix vesicles but not apoptotic bodies contained alkaline phosphatase and Ca2+ channel-forming annexins II, V, and VI. Consequently, matrix vesicles but not apoptotic bodies were able to take up Ca2+ and form the first mineral phase inside their lumen. Mineralization of RA-treated cultures was inhibited by antibodies specific for annexin V but not mineralization of staurosporine-treated cultures.

CONCLUSION

Physiological mineralization of growth plate chondrocytes is initiated by specialized matrix vesicles and requires alkaline phosphatase and annexins. In contrast, mineral formation mediated by apoptotic bodies occurs by a default mechanism and does not require alkaline phosphatase and annexins.

Increased Expression of the Huntingtin Interacting Protein-1 Gene in Cells From Hutchinson Gilford Syndrome (Progeria) Patients and Aged Donors

Hutchinson Gilford syndrome (progeria [PG]) is a human disease associated with accelerated aging. To elucidate the acceleration mechanism, we first tried to transform a PG-derived cell line by infection of a recombinant adenovirus expressing HPV (human papilloma virus)-E6 and HPV-E7 genes. The transfected PG cells had a greater number of population doublings (PD) (>80), faster doubling time, and less staining of senescence-associated ss-galactosidase than the nontransfected PG cells. The transfected cells also showed markedly more detectable telomerase activity than the nontransformed cells. The expression levels of the genes in the E6-transduced and E7-transduced cell line were then compared with those of the nontransfected cell line using an mRNA differential display method, following reverse-transcriptase polymerase chain reaction analysis. Expression of huntingtin interacting protein-1 (HIP-1) gene was found to be increased not only in PG cells but also in fibroblast cells from aged healthy donors. Thus, HIP-1 might be a molecular assistant in the pathogenesis of the cellular senescent process in the human cells tested.

Apoptosis and the loss of chondrocyte survival signals contribute to articular cartilage degradation in osteoarthritis

Apoptotic death of articular chondrocytes has been implicated in the pathogenesis of osteoarthritis (OA). Apoptotic pathways in chondrocytes are multi-faceted, although some cascades appear to play a greater in vivo role than others. Various catabolic processes are linked to apoptosis in OA cartilage, contributing to the reduction in cartilage integrity. Recent studies suggest that beta1-integrin mediated cell-matrix interactions provide survival signals for chondrocytes. The loss of such interactions and the inability to respond to IGF-1 stimulation may be partly responsible for the hypocellularity and matrix degradation that characterises OA. Here we have reviewed the literature in this area of cartilage cell biology in an effort to consolidate the existing information into a plausible hypothesis regarding the involvement of apoptosis in the pathogenesis of OA. Understanding of the interactions that promote chondrocyte apoptosis and cartilage hypocellularity is essential for developing appropriately targeted therapies for inhibition of chondrocyte apoptosis and the treatment of OA.

Coordinate down-regulation of cartilage matrix gene expression in Bcl-2 deficient chondrocytes is associated with decreased SOX9 expression and decreased mRNA stability

The anti-apoptotic protein Bcl-2 has been shown to function in roles unrelated to apoptosis in a variety of cell types. We have previously reported that loss of Bcl-2 expression alters chondrocyte morphology and modulates aggrecan expression via an apoptosis-independent pathway. Here we show that Bcl-2 is required for chondrocytes to maintain expression of a variety of cartilage-specific matrix proteins. Using quantitative, real-time PCR, we demonstrate that Bcl-2-deficient chondrocytes coordinately down-regulate genes coding for hyaline cartilage matrix proteins including collagen II, collagen IX, aggrecan, and link protein. The decrease in steady-state level of these mRNA transcripts results, in part, from decreased mRNA stability in Bcl-2-deficient chondrocytes. Transcriptional regulation is also likely involved because chondrocytes with decreased Bcl-2 levels show decreased expression of SOX9, a transcription factor necessary for expressing the major cartilage matrix proteins. In contrast, chondrocytes constitutively expressing Bcl-2 have a stable phenotype when subjected to loss of serum factor signaling. These cells maintain high levels of SOX9, as well as the SOX9 targets collagen II and aggrecan. These results suggest that Bcl-2 is involved in a pathway important for maintaining a stable chondrocyte phenotype.

Articular cartilage degradation and de-differentiation of chondrocytes by the systemic administration of retinyl acetate-ectopic production of osteoblast stimulating factor-1 by chondrocytes in mice

OBJECTIVE

Vitamin A derivatives are widely used therapeutic agents for the treatment of dermatological and rheumatological disorders. Long-standing administration of these drugs, in turn, causes skeletal changes including ossification of ligaments, premature fusion of epiphyses and abnormalities of modeling. Recent in vitro experiments have further suggested that retinoid treatment of cultured chondrocytes may cause apoptotic cell death. The present study aims to address detailed cartilage changes associated with in vivo administration of vitamin A derivatives.

METHODS

Retinyl acetate was administrated to experimental mice, C3H-Heston, for more than 12 months. Modified morphometry on the articular cartilage and fluorescent labeling of the subchondral bone were carried out to address the changes in the articular cartilage and subchondral bone. In order to address the detailed chondrocytes phenotypes, electron microscopy was carried out. Since findings of these studies suggested that biological properties of the cartilage matrix might be altered, the present study also immunolocalized functional matrix molecules, type I collagen and osteoblast-stimulating factor-1 (OSF-1).

RESULTS

Histomorphometry demonstrated that retinoid administration lead to progressive atrophy of the articular cartilage with concomitant proliferation of subchondral bone. Furthermore, detailed light and electron microscopy suggested that the subchondral bone proliferates into the degenerating cartilage. The affected articular cartilage also resembled that of osteoarthritis in terms of ectopic type I collagen production. Furthermore, the affected articular cartilage produced a developmentally regulated matrix molecule, osteoblast-stimulating factor-1 (OSF-1) that is normally expressed in both the fetal cartilage and the epiphyseal growth plate cartilage but not in the articular cartilage.

CONCLUSION

The present results indicate that the systemic retinoid administration may alter the biological properties of the articular cartilage.

Age-related changes in cartilage endogenous osteogenic protein-1 (OP-1)

Articular cartilage has a poor reparative capacity. This feature is exacerbated with aging and during degenerative joint conditions, contributing to loss of motion and impairment of quality of life. This study focused on osteogenic protein-1 (OP-1) and its ability to serve as a repair-stimulating factor in articular cartilage. The purpose of this work was to develop a quantitative method for the assessment of the content of OP-1 protein in extracts from human articular cartilage and to investigate the changes in OP-1 mRNA expression and protein levels with aging of normal adult cartilage. Full thickness cartilage was dissected from femoral condyles of donors with no history of joint disease within 24 h of death. Levels of OP-1 mRNA expression were measured by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) method; concentration of OP-1 protein was detected by new sandwich enzyme-linked immunosorbent assay (ELISA); qualitative changes in OP-1 forms were evaluated by Western blots with various anti-OP-1 antibodies. The sensitivity of the ELISA method allowed the detection of picogram quantities of OP-1 in cartilage extracts. We found that (1) concentration of OP-1 in normal cartilage is within the range of biological activity of OP-1 in vitro; and (2) during aging of human adult, articular cartilage, levels of OP-1 protein and message are dramatically reduced (more than 4-fold; p<0.02). The major qualitative changes affected primarily mature OP-1. The results of the current study suggest the possibility that OP-1 may be critical for chondrocytes to maintain their normal homeostasis and could also serve as a repair factor during joint disease or aging.

Apoptosis in rotator cuff tendonopathy

The aim of this study was to investigate the involvement of apoptosis (programmed cell death) in the pathogenesis of rotator cuff disorders. The edges of torn supraspinatus rotator cuff tendons were collected from patients with rotator cuff tear (n = 25). Samples of the intra-articular portion of subscapularis tendons were collected from patients without rotator cuff tear as control (n = 6). To minimize individual variance, we also collected six pairs of supraspinatus tendon and subscapularis tendon from six patients with rotator cuff tears. Apoptosis was detected by in situ DNA end labelling assay and DNA laddering assay. Immunohistochemical staining was performed to identify cells undergoing apoptosis. Control subscapularis tendon had normal morphology. Tendon from torn supraspinatus rotator cuff showed significant mucoid degeneration. Within the areas of degeneration, there were large numbers of apoptotic cells. The percentage of apoptotic cells in the degenerative rotator cuff (34%) was significantly higher than that in controls (13%) (p < 0.001). The excessive apoptosis detected in degenerative rotator cuff tissue was confirmed by DNA laddering assays. This is the first report of excessive apoptosis in degenerating rotator cuff tendon. Cells undergoing apoptosis in rotator cuff were mainly fibroblast-like cells. These finding indicate that apoptosis may play an important role in the pathogenesis of rotator cuff degeneration.