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Review
. 2020 Jan;38(1):23-35.
doi: 10.1002/jor.24440. Epub 2019 Aug 26.

The "other" 15-40%: The Role of Non-Collagenous Extracellular Matrix Proteins and Minor Collagens in Tendon

Nandaraj Taye  1 , Stylianos Z Karoulias  1 , Dirk Hubmacher  1
Affiliations
Review

The "other" 15-40%: The Role of Non-Collagenous Extracellular Matrix Proteins and Minor Collagens in Tendon

Nandaraj Taye et al. J Orthop Res. 2020 Jan.

Abstract

Extracellular matrix (ECM) determines the physiological function of all tissues, including musculoskeletal tissues. In tendon, ECM provides overall tissue architecture, which is tailored to match the biomechanical requirements of their physiological function, that is, force transmission from muscle to bone. Tendon ECM also constitutes the microenvironment that allows tendon-resident cells to maintain their phenotype and that transmits biomechanical forces from the macro-level to the micro-level. The structure and function of adult tendons is largely determined by the hierarchical organization of collagen type I fibrils. However, non-collagenous ECM proteins such as small leucine-rich proteoglycans (SLRPs), ADAMTS proteases, and cross-linking enzymes play critical roles in collagen fibrillogenesis and guide the hierarchical bundling of collagen fibrils into tendon fascicles. Other non-collagenous ECM proteins such as the less abundant collagens, fibrillins, or elastin, contribute to tendon formation or determine some of their biomechanical properties. The interfascicular matrix or endotenon and the outer layer of tendons, the epi- and paratenon, includes collagens and non-collagenous ECM proteins, but their function is less well understood. The ECM proteins in the epi- and paratenon may provide the appropriate microenvironment to maintain the identity of distinct tendon cell populations that are thought to play a role during repair processes after injury. The aim of this review is to provide an overview of the role of non-collagenous ECM proteins and less abundant collagens in tendon development and homeostasis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:23-35, 2020.

Keywords: elastin; extracellular matrix; pericellular matrix; proteoglycans; tenocyte.

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Figures

Figure 1.
Figure 1.
Tendon composition. Relative quantities of major tendon extracellular matrix (ECM) proteins. Numbers are based on Kjaer, Elliott, Connizzo et al., and Thorpe et al. and references therein.– n.d., not determined.
Figure 2.
Figure 2.
Hierarchical organization of tendon and its extracellular matrix (ECM) compartments. Proteins that play a major role in each of the ECM/pericellular matrix (PCM) compartments in tendon are listed. However, most of the proteins are found in several ECM/PCM compartments and their expression and localization is dynamically regulated during development, growth, and homeostasis and in response to chronic or acute injury. Images on the bottom show (from left to right): Hematoxylin/eosin-stained longitudinal section through mouse Achilles tendon; PCM of murine tenocytes stained for fibronectin (FN, red); electron microscopy image of cross-section through mouse Achilles tendon showing a tenocyte (T) and collagen fibrils (CF).
Figure 3.
Figure 3.
Complexity of the extracellular matrix (ECM)/pericellular matrix (PCM) protein network in tendon tissue. The network of biochemical or proposed functional interactions between ECM/PCM proteins was generated using the String database (https://string-db.org/) which is a curated database that draws information from multiple experimental databases and by text mining. The network was visualized using Cytoscape (https://cytoscape.org/).
See this image and copyright information in PMC

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