Characterization of collagens and proteoglycans at the insertion of the human Achilles tendon

This study provides a unique correlation between a molecular biological and biochemical analysis of the extracellular matrix (ECM) macromolecules in one half of 28 human Achilles tendons with an immunohistochemical study of the other. Both the insertion site and the mid-tendon were studied. The insertion (enthesis) is characterized by three distinctive fibrocartilages, two in the tendon (enthesial and sesamoid) and one on the heel bone (periosteal). Thus, its structure contrasts markedly with the fibrous character of the mid-tendon. RT-PCR analyses were performed on RNA extracted from mid-tendon and from the tendon fibrocartilages to investigate transcription of collagens and proteoglycans. Western blotting was also used to identify and characterize these macromolecules, and immunohistochemistry to localize their distribution. The results demonstrate striking differences in the ECM between the mid-tendon and its insertion. Types I, III, V and VI collagens, decorin, biglycan, fibromodulin and lumican were found in both the mid-tendon and the fibrocartilages, although their precise distribution often differed with site. mRNA for type II collagen was constantly present in the fibrocartilages, but it was only found in the mid-tendon of one specimen. The patterns of distribution for versican and aggrecan mRNA were complimentary - versican mRNA was present in the mid-tendon and absent from the fibrocartilages, while aggrecan mRNA was present in the fibrocartilages and absent from the mid-tendon. The range and distribution of ECM molecules detected in the Achilles tendon reflect the differing forces acting on it - the mid-tendon largely transmits tension and is characterized by molecules typical of fibrous tissues, but the fibrocartilages must also resist compression and thus contain, in addition, molecules typical of cartilage.

Study of aging rat tail collagen using atomic force microscope

Collagen structure of young and old rats was examined by using atomic force microscope (AFM) images. Rat tail tendons of eight and twenty-four month-old Wistar rats were digested enzymatically (pepsin), and allowed to refibrillate for 24 hours at 37 degrees C. The samples were examined using a Nanoscope III (Digital Instruments, Santa Barbara, CA, U.S.A.) with a J scanning head and a 200 microns silicon nitride cantilever. The study was performed in air and without filters. The AFM inspection of refibrillated collagen produced images showing long fibrils with relatively homogeneous heights and widths, characterized by clear banding with a periodic interval (D band) of 67 nm. With respect to collagen extracted from young rats, collagen extracted from old rats revealed fibrils exhibiting the same band interval, but with lower widths and heights. Furthermore, the depth of gap between two overlaps showed a higher mean value in the aged rats. These data are consistent with biochemical reports of collagen modifications during aging; we suggest that post-synthetic reactions might be responsible for this as they interfere with the refibrillation process and also modify the three-dimensional structure of fibrils.

Active oxygen-induced modification alters properties of collagen as a substratum for fibroblasts

Acid-soluble collagen from rat skin was modified by active oxygen in vitro, and properties of the modified collagen as a substratum for fibroblasts were studied. When collagen was treated with ascorbate-copper ion systems, cross-linking and a little degradation occurred rapidly. The cells attached but spread poorly on the modified collagen gel as compared with on the untreated collagen gel. On the other hand, when collagen was treated with H2O2-copper ion systems, only degradation of collagen molecule occurred rapidly. This treatment did not affect the attachment and spreading of the cells on the collagen gel, but when the incubation was continued for a long time, the cells migrated actively and gathered. Thymidine incorporation by the cells was suppressed on both modified collagen gels as compared with that on untreated collagen gel, and the extent of the suppression on the H2O2-copper-treated collagen was larger than that on the ascorbate-copper-treated collagen. These results indicate that the active oxygen-induced cross-linking and degradation significantly alter properties of collagen as a substratum for fibroblasts.

Acceleration of glucose-mediated crosslinking of collagen by free lysine

Crosslinking occurred in collagen when it was incubated with glucose. Free lysine accelerated the crosslinking markedly.