Expression of matrix metalloproteinase-2 inosteoarthritic fibrocartilage from humanmandibular condyle

Akira Tanaka1

Shuichi Kawashiri1

Shigehiro Kumagai1

Shigeyuki Takatsuka1

Masayoshi Narinobou2

Kiyomasa Nakagawa1

Shigenori Tanaka3

1Department of Oral and MaxillofacialSurgery, School of Medicine, KanazawaUniversity2Department of Oral and MaxillofacialSurgery, Noto General Hospital and3Second Department of Anatomy, School ofMedicine, Kanazawa University, Ishikawa,Japan

Correspondence to:A. TanakaDepartment of Oral and Maxillofacial Surgery,School of Medicine, Kanazawa University,13–1 Takara-machi Kanazawa city, 920–8640,Ishikawa, Japan

Accepted for publication October 21, 1999

Copyright C Munksgaard 2000J Oral Pathol Med . ISSN 0904-2512

Printed in Denmark . All rights reserved

314

Abstract: Matrix metalloproteinase (MMP)-2 is expressed in os-teoarthritic cartilage and synovial fluid and is thought to be in-volved in the degradation of cartilage extracellular matrix. How-ever, MMP-2 expression and osteoarthritic changes in internalderangement of the temporomandibular joint are unknown. Inthe present study, we have examined the histological relation-ship between osteoarthritic changes on articular cartilage withor without articular disc perforation, and MMP-2 expression, in85 mandibular condyles from cadavers. The expression andtissue immunolocalization of MMP-2 in fibrocartilages fromthese condyles was examined histochemically. The Mankingrade of histological criteria for specimens with disc perforationwas significantly higher than that of specimens without perfor-ation. MMP-2 immunostaining was positive in the cytoplasm ofchondrocytes and in their surrounding matrix. There was a lin-ear correlation between MMP-2-positive cell rates and Mankingrade. Our data suggest that MMP-2 plays an important role infibrocartilage degradation in internal derangement of the tem-poromandibular joint.

Key words: degenerative changes; disc perforation; fibrocarti-lage; matrix metalloproteinases; temporomandibular joint

J Oral Pathol Med 2000: 29: 314–20

Osteoarthritis (OA) is the most common joint disease in humans and

is characterized by degenerative changes due to a gradual loss of

extracellular cartilage matrix. In the temporomandibular joint (TMJ),

the degenerative changes are similar to those in other synovial joints.

Clinically, a relationship has been postulated between these degener-

ative changes and internal derangement symptoms (e.g., disc dis-

placement) (1, 2). Hitherto, in only a few basic studies has human ma-

terial been employed to examine this relationship histopathologically.

The lack of basic data is considered a crucial drawback, since the cur-

rently accepted treatments for temporomandibular joint disorder

(TMD) are mainly conservative procedures, including occlusal appli-

ances for relaxation, occlusal adjustment and drug prescription. On

the other hand, the indications for surgical treatment have tended to

become narrower due to improvements in arthroscopic surgery. As a

Expression of MMP-2 in fibrocartilage

result, clinical samples from TMD patients are limited to the aspir-

ation of synovial fluid and resection of the articular disc in severe

cases. Therefore, previous studies have not focused on the patholog-

ical changes in the human mandibular condyle, and it has been diffi-

cult to understand its pathological status. Although there have been

several reports on experimental disc injury (3, 4), the question re-

mains whether pathologic changes due to abrupt violent disc trauma

in animals are different from the ‘‘natural’’ process in human TMD (5).

Accordingly, the relationship between signs of internal derangement

and the severity of osteoarthritic changes must be examined in hu-

man material.

Matrix metalloproteinases (MMPs) are known to play a major

role in the destruction of extracellular matrix (ECM) among classes

of proteinases. MMPs belong to the family of Zn2π metalloprotein-

ases and can be classified into subgroups composed of interstitial

collagenases, gelatinases, stromelysins, membrane-type (MT)-

MMPs, and other MMPs, including matrilysin, metalloelastase, and

enamelysin. Apart from MT-MMPs and stromelysin-3 (MMP-11),

MMPs are secreted as pro-forms from various cells and degrade

ECM when activated in the extracellular component. MMP-2 and

MMP-9 are gelatinases with a wide range of substrate specificity,

including gelatin, collagen types IV, V, VII, XI, link protein, aggre-

can and fibronectin. Following clarification of the pro-MMP-2 acti-

vation system by MT-MMP-1 (6), the important role of MMP-2 in

degradation of cartilage in joint diseases such as OA has been rec-

ognized (7). High levels of MMP-2 have been detected in synovial

fluid and chondrocyte culture derived from knee or hip OA (7, 8).

Recently, it was reported that MMP-2 was detected in synovial fluid

from OA cases and internal derangement of the TMJ (9). However,

the immunolocalization of MMP-2 has not yet been clarified histo-

pathologically in TMJ tissues and the detailed mechanism of pro-

gressive fibrocartilage destruction is still unclear. Therefore, the

present study investigated the immunohistochemical distribution of

MMP-2 in cartilage of the human mandibular condyle.

Material and methods

Samples and gross anatomy

This study was based on the evaluation of 85 mandibular condyles

and their articular discs (43 from men and 42 from women). These

were removed from 51 cadavers (25 men, 26 women; mean age 79.7

years; age range 62–95 years) pledged voluntarily during their life-

time for the purposes of medical education and research to the De-

partment of Anatomy at Kanazawa University School of Medicine.

The cadavers were fixed with formalin solution infused via the fem-

315J Oral Pathol Med 29: 314–20

oral artery within 72 h after death. Data regarding TMJ symptoms

before death were not available. All condyles were transected at the

condylar neck and removed separately from the temporal compo-

nent with attached articular discs. Each disc was cut at its medial

and lateral mandibular attachment and isolated for macroscopical

assessment of perforation. Deviation in form of the articular surface

of discs and condyles was recorded for each joint. Deviation in form

was defined as local irregularity of the articular surface, including

pits, depressions, progressive remodeling (i.e., protuberances), rough

surfaces or indentations.

Histology

The 85 condyles were cut into 5-mm thick slices at the central part of

the condyles, including the anterior, superior, and posterior portions,

along the sagittal plane for histological observation. The slices were

embedded in paraffin wax after decalcification with 0.5 M EDTA (pH

7.5). Four-micron thick paraffin sections were mounted on silane-

coated slides and stained with hematoxylin and eosin (H&E) or with

toluidine blue (pH 4.1) as a special stain for acid proteoglycans. Sec-

tions were evaluated in the antero-superior portion by a histological-

histochemical grading technique (Mankin grade) (10), which is based

on four items – i.e., structure, cells, staining reduction of cartilage ma-

trix and tidemark integrity (Table 1).

Immunohistochemistry

Four-micron thick sections were treated by clear masking with

0.1% trypsin for 40 min. The immunoreaction was performed by

Table 1. Histological-histochemical grading [Mankin et al. (7)]

Grade

I. StructureNormal 0Surface irregularities 1Pannus and surface irregularities 2Clefts to transitional zone 3Clefts to radial zone 4Clefts to calcified zone 5Complete disorganization 6

II. CellsNormal 0Diffuse hypercellularity 1Cloning 2Hypocellularity 3

III. Safranin-O (toluidine blue) stainingNormal 0Slight reduction 1Moderate reduction 2Severe reduction 3No dye noted 4

IV. Tidemark integrityIntact 0Crossed by blood vessels 1

Tanaka et al.

Fig. 1. Macroscopic overview of human mandibular condyles. A) Normalappearance of a condyle (82 years, male) showing an elliptical shape withsmooth articular surface. B) Advanced osteoarthritic appearance of condyle(89 years, female) showing a depressed surface (arrow) and partially exposedsubchondral bone (arrowheads).

the catalyzed signal amplification (CSA) method (CSA kit, DAKO,

Carpinteria, CA, USA). Thereafter, sections were rinsed three times

in 50 mM Tris-HCl (pH 7.6) (DAKO) containing 0.3 M NaCl and

0.1% Tween 20 (Bio-Rad Laboratories, Hercules, CA, USA) for 5

min. They were then treated with 3% hydrogen peroxide for 5

min to block endogenous peroxidase. Endogenous biotin was rou-

tinely blocked by sequential application of avidin and biotin in

the Biotin blocking system (DAKO). Nonspecific proteins were

blocked by 0.25% casein for 5 min. The sections were reacted

with monoclonal antibody specific to human MMP-2 (0.25 mg/ml,

clone 42–5D11, Fuji Chemical Co., Toyama, Japan) overnight. As

a negative control, normal mouse serum was used in place of the

primary antibodies. After secondary reaction with biotinylated

rabbit anti-mouse immunoglobulins for 15 min, sections were incu-

bated with streptavidin-biotin complex. Biotinyltyramide was used

316 J Oral Pathol Med 29: 314–20

to amplify the chromogen reactivity, and peroxidase-conjugated

streptavidin was reacted with the biotin. The immunoreaction was

developed with 3, 3ø diaminobenzidine (Wako Pure Chemical In-

dustries, Ltd, Osaka, Japan). All sections were counterstained with

hematoxylin and observed by light microscopy. Microscopic obser-

vation was performed in four fields of view at ¿50 magnification

in the middle portions of the sections. Immunostained chondro-

cytes were counted to calculate the percentage of MMP-2-positive

cells (positive cell rate).

Statistical analysis

The macroscopic incidence of disc perforation and deformity be-

tween men and women was compared using the chi-squared test

(PÆ0.05). The mean∫SD for Mankin grade and the positive cell

rate were calculated and compared for disc-perforated and non-per-

forated specimens using Student’s paired t-test (PÆ0.05). Simple lin-

ear regression analysis and Spearman rank correlation were used

to compare data between the MMP-2-positive cell rate and Mankin

grade at P50.0001.

Results

Macroscopically (Fig. 1A & B), noticeable deformities of the condy-

lar surfaces were observed in 59 of 85 TMJs (69.4%). Disc perfor-

ations were observed in 11 TMJs (12.9%), in which all condylar

articular surfaces showed obvious deformities adjoining the perfor-

ated area. However, in the remaining 48 TMJs (56.5%) with deform-

ities, the articular discs were not perforated. In the macroscopically

normal condyles, 26 TMJs (30.6%) with a smooth articular surface

showed no disc perforations. Disc perforation in women (9/42 TMJs)

was significantly more frequent than in men (2/43 TMJs) (PÆ0.05).

However, the frequency of deformity of the articular surfaces be-

tween men and women was not significantly different.

Microscopically, the condyles varied in their histological appear-

ance, ranging from a normal structure to cracking, fibrillation, and

eburnation of the subchondral bone. The distribution of Mankin

grades ranged from 2 to 14 (mean∫SD; 8.85∫3.54). There was no

significant relationship between age and Mankin grades but grades

in women (10.3∫3.4) were significantly higher than in men (8.8∫3.5)

(PÆ0.01). The grades of condyles with disc perforation (11.3∫3.1)

were significantly higher than those of non-perforated specimens

(7.0∫3.1) (PÆ0.05).

Normal articular cartilage was composed of four zones (Fig.

2A). A superficial zone contained only a few chondrocytes and

Expression of MMP-2 in fibrocartilage

fibrous tissue, in which collagen fibers were parallel to the articu-

lar surface. Just below this zone was a transitional zone with

rounded chondrocytes. Below this was a radial zone characterized

by collagen fibers predominantly oriented perpendicular to the ar-

ticular surface. Finally, a basophilic tidemark demarcation line

was observed on top of a calcified zone of mineralized cartilage.

Subchondral cortical bone was in contact with the calcified zone

lined with the above cartilage. Immunohistochemical staining was

absent from condyles with an almost normal structure (Fig. 2A).

In osteoarthritic condyles, immunohistochemical staining for

MMP-2 was localized in the cytoplasm and the pericellular matrix

of chondrocytes of the radial zone. In condyles with early os-

teoarthritic changes (Fig. 2B&C), the transitional zone was absent

and weak immunoreactivity appeared in areas of the cracked and

fissured radial zone. Furthermore, several positive cells which

showed granuliform reactivity in the cytoplasm were visible at

the site of cracking or fissuring in the radial zone. In condyles

showing moderate osteoarthritic changes (Fig. 2D), the superficial

and transitional zones were frequently lost and the exposed radial

zone displayed a rough surface due to collagen fibrillation. The

cytoplasm of chondrocytes lying close to the surface, as well as

the fibrillated ECM, were strongly labeled. In condyles with severe

osteoarthritic changes (Fig. 2E & F), the cartilage zone was almost

completely lost, while the exposed subchondral bone showed ebur-

nation and an intensive immunoreaction on the bone surface. In

the remaining cracked and partially desquamated fibrocartilage,

vascular granulo-fibrous repair tissue was frequently observed to

have invaded from the bone marrow. Chondrocytes in the remain-

ing cartilage zone showed a high proportion of positive cells. In

higher grades (grades 13 & 14), the articular surface showed com-

plete loss of fibrocartilage. Immunostaining was considered to be

specific to MMP-2 because immunoreactivity was not observed in

the negative controls. Statistically, a linear correlation was demon-

strated between the positive cell rate and the Mankin grades with

a correlation coefficient of 0.85 from 2 to 12 (PÆ0.001) (Fig. 3). A

direct positive correlation between MMP-2 and Mankin grade was

shown by Spearman rank correlation (r50.86). The positive cell

rate for disc-perforated specimens was significantly higher than

for non-perforated specimens (PÆ0.05).

Discussion

Intense expression of MMP-2 has been described in cancer tissue,

inflammatory tissue, pulmonary emphysema, arterial disease, and

joint disease such as rheumatoid arthritis (RA) and OA. However,

317J Oral Pathol Med 29: 314–20

in association with OA the correlation between MMP-2 and carti-

lage destruction has not previously been evaluated, because MMP-

2 is also detected in samples of normal synovial fluid (11). Re-

cently, it has been verified that MMP-2 has an indirect effect on

matrix degradation. First, the collagenolytic activity of MT-MMP-

1 on type I collagen is synergistically increased in the presence

of MMP-2 (12). Second, MMP-13, which possesses high degrada-

tion activity against type II collagen and aggrecan of the cartilage

matrix, is also activated by MMP-2 (13). Since articular cartilage

in the mandibular condyle is composed of fibrocartilage with a

collagen matrix that is almost entirely composed of type I and II

collagen (14), the role of MMP-2 associated with cartilage matrix

degradation is thought to be important. Our data suggest that

MMP-2 is strongly correlated with fibrocartilage matrix degrada-

tion.

Chondrocytes, synoviocytes and inflammatory cells infiltrating

the synovial membrane have been reported to represent MMP-pro-

ducing cells. MMP-2 staining in the matrix may not be what is

secreted from the chondrocytes themselves, because once the integ-

rity of the articular surface of the cartilage is lost, exogenous MMP-

2 produced by synoviocytes and inflammatory cells may penetrate

the fibrocartilage and accelerate degradation (15). However, the posi-

tive immunoreaction in chondrocytes seen in this study provides

evidence that the chondrocytes themselves produce MMP-2. Like-

wise, MMP-1, -3, -7, -8, -9, -13 and MT-MMP-1 have been demon-

strated to be produced by chondrocytes in a previous histological

and histochemical study (16). The authors suggest in this study

that interactions between the individual MMP species form several

complex cascades.

Our recent data indicate that activated MMP-2 is detectable in

synovial fluid from patients with unreduced anterior disc displace-

ment (unpublished data). Since MMP-2 is activated on the cell sur-

face by MT-MMP-1 (7), it is suggested that MMP-2 plays a major

role in cartilage matrix degradation of the pericellular space around

the chondrocytes of fibrocartilage.

The activation of MMPs is regulated by four types of tissue

inhibitors of matrix metalloproteinases (TIMP-1, -2, -3, -4); an imbal-

ance between MMPs and TIMPs induces ECM degradation. There-

fore, the molecular quantity of MMPs will exceed TIMPs in areas

of local degradation (17). However, although MMP-2 is specifically

complexed with TIMP-2, it has been postulated that the activation

is accelerated by low doses of TIMP-2, though it is suppressed by

high doses in vitro (18).

Both general and local factors are involved in the inititation and

progression of OA in TMJ. Aging and gender-related factors influ-

ence general connective tissue metabolism (19–21), such as ECM

remodeling (22). Ishibashi et al. (23) reported that with advancing

Tanaka et al.

Fig. 2. Immunostaining for MMP-2. A) Mandibular condyle consists of articular fibrocartilage and subchondral bone (SB). The articular fibrocartilage isseparated into four zones: superficial zone (SZ), transitional zone (TZ), radial zone (RZ) and calcified zone (CZ). No immunoreactivity was seen in almostnormal condyles (grade 2). (Original magnification ¿50) B) Chondrocytes (arrowheads) close to a cracked radial zone are immunostained in an earlyosteoarthritic condyle (grade 6). (Original magnification ¿50) C) At higher magnification than in panel B, the cytoplasm in chondrocytes (arrowheads) showgranuliform reactivity. (Original magnification ¿200) D) Superficial chondrocytes (arrowheads) in and around the matrix in a fibrillated surface are immuno-stained in a moderate osteoarthritic condyle (grade 10). (Original magnification ¿50) E) An exposed bone surface in a severely osteoarthritic condyle (grade12) shows eburnation (arrow) and the remaining chondrocytes (arrowheads) in the cracked radial zone are almost completely immunostained. (Originalmagnification ¿25) F) At higher magnification than in panel E, matrix around the chondrocytes is seen to be positively stained. (Original magnification¿200) (A–F: Hematoxylin counterstain)

318 J Oral Pathol Med 29: 314–20

Expression of MMP-2 in fibrocartilage

Fig. 3. Linear correlation of MMP-2 immunostaining with Mankin grade (r50.86).

age the cellular components of TMJ cartilage may play a critical

role in the development of degenerative changes. They found that

fibrocartilage is reduced to a few chondrocytes with weak express-

ion of ECM after the seventh decade, suggesting limited capacity

for morphological and histological repair of damage induced by

functiomal stress (23). In our study, it was not possible to identify

a direct relationship between TMJ symptoms and age-dependent

histopathological changes because data was not available from the

medical history. However, according to our histopathological data,

aging hardly appears to impact on the severity of OA, as we failed

to show a significant relationship between age and Mankin grades

(unpublished data). With regard to gender, Widmalm et al. (24) re-

ported, on the basis of an autopsy study, that gender did not have

an influence on development of morphologic changes in the TMJ.

In our study, the frequency of macroscopic deformity did not sig-

nificantly differ according to gender, whereas the microscopic de-

gree of deformity in women was greater than in men (PÆ0.01).

Thus, gender may affect the progression of degenerative changes

in the TMJ.

Local factors depend to a large extent upon the anatomical

characteristics of the TMJ, which include the position of the articu-

lar disc between the mandibular fossa and the condyle, and the

condylar pathways during mastication. As disc position was not

examined in this study, its relationship with deformation could not

be evaluated. Because a relationship between degenerative changes

and disc perforation is obviously recognized in the present study, it

319J Oral Pathol Med 29: 314–20

is suggested that a local mechanical overstress eventually leads to

disc perforation and induces cartilage matrix degradation. A recent

experimental study (25) using a disc perforation model in rabbits

also demonstrated that disc perforation contributes to irreversible

degenerative changes on the articular surface. The authors specu-

late that the pathological changes following disc displacement are

due to the same etiology.

Cartilage degradation occurs as a result of extrinsic and intrinsic

factors. Dijkgraaf et al. found that degenerative changes in articular

cartilage in OA are mainly intrinsic degradation, differing from RA

which shows extrinsic degradation by proliferation of inflamed

synovium (15). In addition, chronic mechanical stress may induce

metabolic abnormalities of chondrocytes in articular cartilage, re-

sulting in degradation of matrix exceeding its synthesis.

The degree to which degenerative changes can be alleviated by

current conservative treatment has not been established. Hitherto,

little scientific proof is available regarding the ability of a repo-

sitioning or stabilizing occlusal appliance effectively to slow down

or reverse degenerative changes that are evident on radiographs.

Therefore, a new biochemical marker reflecting pathological status

is necessary for the diagnosis of OA involving the TMJ. From our

study, it is suggested that the frequency of MMP-2 expression in

fibrocartilage is associated with progression of pathological os-

teoarthritic changes in the mandibular condyle. Since activated

MMP-2 infiltrates the synovial fluid, it can be utilized as a new

marker for diagnosing OA.

Tanaka et al.

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Acknowledgement

We gratefully thank Professor Etsuhide Yamamoto (Department of Oral andMaxillofacial Surgery, School of Medicine, Kanazawa University) for helpfulsuggestions and support in this study.