Age-related changes in gene expression patterns of matrix metalloproteinases and their collagenous substrates in mandibular condylar cartilage in rats

Abstract

Matrix metalloproteinases (MMPs) have been implicated in physiological cartilage matrix remodelling as well as in pathological and invasive extracellular matrix remodelling of tissue. Age-related changes in the gene expression patterns of MMPs in mandibular condylar cartilages (MCCs) were analysed. We examined the gene expression patterns of Mmp-8 and -13 and their substrates, Col1a1, Col2a1 and Col10a1, in MCC of growing and ageing rats. Temporomandibular joints of male Wistar rats aged 4, 8, 16 and 32 weeks were subjected to in situ hybridization analysis. Histologically, MMCs showed characteristics of growth plate cartilage at ages 4 and 8 weeks, and more closely resembled articular cartilage thereafter. Mmp-8 was expressed in the cells in all cartilaginous cell layers at ages 4 and 8 weeks, and then was localized only in the mature cells at ages 16 and 32 weeks. Whereas Mmp-13 expression was limited to the lowermost hypertrophic chondrocytes in the growth stage, mature chondrocytes instead of hypertrophic chondrocytes expressed Mmp-13 in adult non-hypertrophic MCC. Because Mmp-8 and -13 expression overlapped with Col2a1 and Col10a1, chondrocytes could play a pivotal role in degradation as well as production of the cartilaginous matrix in MCC.

Fig. 1

Sagittal sections of MCC and tibial articular cartilage stained by H&E. A, B, C and D are MCC at 4, 8, 16 and 32 weeks of age, respectively. Fi: fibrous layer, Pr: proliferative cell layer, Tr: transitional cell layer, Ma: mature cell layer, Hy: hypertrophic cell layer, Er: erosion zone, Re: resting cell layer. Scale bar = 100 µm; original magnification: ×40.

Fig. 2

The results of in situ hybridization (ISH) in sagittal sections of MCC. The expression patterns of Col1a1 mRNA are shown in A–D. E–H show the signals of Col2a1 mRNA, and I–L show the expression patterns of Col10a1 mRNA. A, E and I are 4 weeks of age; B, F and J are 8 weeks of age MCC; C, G and K are 16 weeks of age; D, H and L are 32 weeks of age. The arrows indicate the positive ISH signals. Fi: fibrous layer, Pr: proliferative cell layer, Tr: transitional cell layer, Ma: mature cell layer, Hy: hypertrophic cell layer, Er: erosion zone. Scale bar = 100 µm; original magnification: ×20.

Fig. 3

The expression patterns of Mmp-8 mRNA (A–D) and Mmp-13 mRNA (E–H) in MCC. A and E are 4 weeks of age; B and F are 8 weeks of age; C and G are 16 weeks of age; D and H are 32 weeks of age. The arrows indicate the positive signals of in situ hybridization. Fi: fibrous layer, Pr: proliferative cell layer, Tr: transitional cell layer, Ma: mature cell layer, Hy: hypertrophic cell layer, Er: erosion zone. Scale bar = 100 µm; original magnification: ×40.

Fig. 4

The results of in situ hybridization using sense DIG-labelled riboprobes for negative control experiments from 16-week-old MCC. No positive signal of Col1a1 sense riboprobe was observed in A; Col2a1 sense riboprobe in B; Col10a1 sense riboprobe in C; Mmp-8 sense riboprobe in D; Mmp-13 sense riboprobe in E. Scale bar = 200 µm; original magnification: ×20.