Tendons Macromolecules | Sciences Dissertations

Contents

  • 1 Chapter One
  • 2 Literature Review
  • 3 1.0 Introduction
  • 4 1.1 Synovial Joint
  • 5 1.1.1 Articular Cartilage
  • 6 1.1.2 Joint Capsule and Ligament
  • 7 1.1.3 Synovial Membrane
  • 8 1.1.4 Tendon
  • 9 1.1.5 Tendon Extracellular Matrix
  • 10 1.1.6 Tendon cells
  • 11 Tendon Extracellular Matrix Macromolecules
  • 12 1.2.1 Collagens
  • 13 1.2.1.1 Type I Collagen
  • 14 1.2.1.2 Type II Collagen
  • 15 1.2.1.3 Type III Collagen
  • 16 1.2.1.4 Type IV Collagen
  • 17 1.2.1.5 Type V Collagen
  • 18 1.2.1.6 Type VI Collagen
  • 19 1.2.1.7 Type IX Collagen
  • 20 1.2.1.8 Type X Collagen
  • 21 1.2.1.9 Type XI Collagen
  • 22 1.2.1.10 Type XII Collagen
  • 23 1.2.1.11Type XIV Collagen
  • 24 1.2.2 Proteoglycans
  • 25 1.2.2.1 Small Leucine-Rich Repeat Proteoglycans (SLRPs)
  • 26 1.2.2.2 Decorin
  • 27 1.2.2.3 Biglycan
  • 28 1.2.2.4 Fibromodulin
  • 29 1.2.2.5 Lumican
  • 30 1.2.3 Large Aggregating Proteoglycans
  • 31 1.2.3.1 Aggrecan
  • 32 1.2.3.2 Versican
  • 33 1.2.4 Glycosaminoglycans (GAGs)
  • 34 1.2.4.1 Hyaluronan
  • 35 1.2.4.2 Chondroitin Sulphate
  • 36 1.2.4.3 Dermatan Sulphate
  • 37 1.2.4.4 Keratan Sulphate
  • 38 1.2.4.5 Heparin and Heparan Sulphate
  • 39 1.2.5 Non-Collagenous Proteins
  • 40 1.2.5.1 Elastin
  • 41 1.2.5.2 Link Protein
  • 42 1.2.5.3 Tenascin-C
  • 43 1.2.5.4 Cartilage Oligomeric Matrix Protein (COMP)
  • 44 1.2.5.5 Other Non-Collagenous Proteins
  • 45 1.2.6 Collagen Synthesis
  • 46 1.2.7 Proteoglycan Synthesis
  • 47 1.2.8 Hyaluronan Synthesis
  • 48 1.3 Variation in the Structural Composition of the Tendon Extracellular Matrix
  • 49 1.4 Proteinases of the Tendon Extracellular Matrix
  • 50 1.4.1 Metalloproteinases (Metzincins)
  • 51 1.4.2 Matrix Metalloproteinases (Matrixins)
  • 52 1.4.3 MMP Inhibition
  • 53 1.4.4 Reprolysins
  • 54 1.4.5 A Disintergrin and Metalloproteinases with Thrombospondin Motifs (ADAMTS)
  • 55 1.4.6 Collagen Catabolism
  • 56 1.4.7 Proteoglycan Catabolism
  • 57 1.4.8 Hyaluronan Catabolism
  • 58 1.5 Overuse Tendinopathy
  • 59 1.5.1 Predisposing Factors
  • 60 1.5.2 Changes in Collagen Content in Overuse Tendinopathy and Other Pathological Conditions
  • 61 1.5.3 Changes in Proteoglycan and GAG Content in Overuse Tendinopathy and Other Pathological Conditions
  • 62 1.5.4 Changes in the Non-Collagenous Proteins in Overuse Tendinopathy and Other Pathological Conditions
  • 63 1.5.5 Changes in MMPs and TIMPs in Overuse Tendinopathy and Other Pathological Conditions
  • 64 1.5.6 Changes in ADAM and ADAMTS in Overuse Tendinopathy
  • 65 1.5.7 Other Changes in Overuse Tendinopathy
  • 66 Tendon Healing
  • 67 1.7 Aims of this Study

Chapter One

Literature Review

1.0 Introduction

Tendons are dynamic structures; their extracellular matrices are continuously being synthesised and broken down over the course of an individual’s lifetime. The macromolecules, namely collagen, proteoglycans, hyaluronan and the non-collagenous proteins form the extracellular matrix of tendons. In normal tendon exists a fine balance between the synthesis and degradation of these macromolecules resulting in a strong healthy tendon.

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It is evident that damage to tendons, such as in overuse tendinopathy results in changes to the levels and types of macromolecules present in tendon with decreased levels of collagen and increased levels of proteoglycans, hyaluronan and non-collagenous proteins, causing a weakened tendon that is prone to rupture. These degenerative features have thus far been partially characterised. By identifying the levels and various types of macromolecules present in normal tendons and tendons exhibiting overuse tendinopathy an understanding of the basis of the condition can be determined and possible ways of preventing or ameliorating tendon degeneration can be considered. The terms overuse tendinopathy and pathological tendon will be used interchangeably throughout this study. This literature review will attempt to define and characterise the structural and functional properties of tendon and will discuss the current literature regarding the levels, types, synthesis and catabolism of macromolecules present in the extracellular matrix of tendons and also attempt to define and characterise the pathological aspects of overuse tendinopathies. Chapter Two of this thesis will dictate the materials and methodology used in these studies. Chapters Three, Four and Five will present the results of this thesis. Finally, chapter Six will include the discussion and discuss any limitations and future considerations.

1.1 Synovial Joint

Joints are articulations found between adjacent parts of bone that allow controlled frictionless movement (for review see; Mankin & Radin, 1997). In the human body there are three different types of joints and these are grouped according to the type of movement they make. They include the freely movable joints (synovial joints; i.e., most joints of the extremities such as the knee joint), slightly movable (cartilaginous joints; i.e., the vertebrae and ribs) and those that are immovable (fibrous joints; i.e., the skull). The majority of the joints found in the human body are synovial joints (for review see; Mankin & Radin, 1997). There are six different types of synovial joints including the ball-and-socket joints, hinge joints, saddle joint, pivot joint, gliding joints and condyloid joints. A synovial joint contains a joint cavity that is enclosed by a fibrous capsule linking the adjoining bones. This joint capsule is lined by a synovial membrane that secretes a lubricating and nutritious fluid called synovial fluid that is rich in albumin and hyaluronan. The surface of each bone is typically covered with articular hyaline cartilage or in some circumstances fibrocartilage. In addition, the joint capsule is supported by accessory structures such as tendons and ligaments, which provide stability to the synovial joint (Sledge et al., 2001).

1.1.1 Articular Cartilage

Articular cartilage covers the adjoining ends of bones in joints and has a white colour (for review see; Mankin & Radin, 1997). It is a tissue that is devoid of blood and nerves and provides a wear resistant surface with low frictional properties for the joint and attains its nutrients via diffusion from the synovium into the synovial fluid (for review see; Mankin & Radin, 1997). Furthermore, articular cartilage is resilient and flexible. This allows articular cartilage to withstand large compressive and tensile forces as well as allowing it to distribute load on subchondral bone during joint loading (Kempson, 1980) even though it is only a few millimetres thick (Hardingham, 1998). Its biomechanical properties are dependent on the structural composition of the extracellular matrix, which is comprised of water (70-80%), collagens (predominantly Type II collagen), proteoglycans (predominantly aggrecan) and non-collagenous proteins (Kuettner et al., 1991; Poole, 1997). The predominant cell type present in articular cartilage is called the chondrocyte. These cells are responsible for the maintenance, synthesis and degradation of all the extracellular matrix components (Kuettner et al., 1991; Buckwalter & Mankin, 1998). Mature articular cartilage can be divided up into four zones including the superficial (tangential) zone, the middle (transitional) zone, the deep (radial) zone and the zone of calcified cartilage (Huber et al., 2000). The organisation and composition as well as mechanical properties of the extracellular matrix varies within these zones. The deeper zones have high proteoglycan levels and low cellularity whereas the more superficial zones contain low proteoglycan levels and increased cellularity (Aydelotte et al., 1988; Buckwalter & Mankin, 1998).

1.1.2 Joint Capsule and Ligament

The joint capsule is a fibrous connective tissue that is attached to the skeletal parts of a joint beyond their articular surfaces. The principal function of the joint capsule is to seal the joint space and to supply stability by limiting movement (for review see; Mankin & Radin, 1997). Most joint capsules are strengthened by ligaments. Ligaments act together with the joint capsule and the peri-articular muscles to provide stability to the joint preventing excessive movements. They permit free movements when lax, but can stop unwanted movements when tight by virtue of their high tensile strength. Occasionally joint capsules are strengthened by tendons, such as the extensor tendon in the finger joint. The joint capsule and ligaments proceed to hold the bones together and to guide and limit joint movements. Ligaments attach one bone with another bone and have a limited vascular and neural supply which enable them to repair relatively well after damage (Bray et al., 1990). The knee joint is a good example of different types of ligaments. The medial collateral ligament fuses with the joint capsule, and the cruciate ligaments and the lateral collateral ligament, which are both completely independent of the joint capsule.

1.1.3 Synovial Membrane

The synovial membrane (synovium) lines the non-articular surfaces of a joint such as the joint capsule and ligaments, and is responsible for secreting and absorbing synovial fluid, which contains hyaluronan (Mason et al., 1999). Synovial fluid lubricates the joint and provides at least partly for the nutrition of articular cartilage, invertebral discs and menisci. The synovial extracellular matrix acts as a scaffolding to support synoviocytes and plays an important role in cell migration and differentiation. It is mostly composed of collagen particularly Type III collagen, with smaller amounts of proteoglycans such as decorin and biglycan (Mason et al., 1999), non-collagenous proteins such as fibronectin, elastin and lamina, hyaluronic acid as well as lipids, serum proteins and electrolytes (Hirohata & Kobayashi, 1964). The synovial membrane has only been detected in vertebrate animals (Henderson & Edwards, 1987). Furthermore, synovial tissue is not arranged into discrete layers, but rather represents a continuum from surface to deep zones. The extracellular matrix of the synovial membrane varies in composition from its surface to its deep zones (Hirohata & Kobayashi, 1964).

1.1.4 Tendon

Tendons are dense fibrous connective tissues found between muscles and bones (for review see; Benjamin & Ralphs, 1997). The primary role of tendon is to absorb and transmit force generated by muscle to the bone to provide movement at a joint. In addition tendons operate as a buffer by absorbing forces to limit muscle damage. Each individual muscle has two tendons, one that is proximal and the other distal. The attachment of the proximal tendon of a muscle to bone is called a muscle origin and that of the distal tendon an insertion. A normal tendon has a bright white colour and a fibroelastic texture and enables resistance to mechanical forces. Tendons come in many shapes and this is most likely due to their function, they can be round or oval in cross section or they can come in the form of flattened sheets, fan shaped, ribbon shaped or cylindrical in shape (for review see; Benjamin & Ralphs, 1997). In a muscle like the quadriceps which creates strong forces the tendons are short and broad, while those that are involved in more delicate movements like the finger flexors, long and thin tendons are present (Kannus, 2000). Tendons are arranged in a hierarchical fashion (see Figure 1.1). A group of collagen fibres form a primary fibre bundle or subfascicle; this is the basic unit of tendon. A group of subfascicles form secondary bundles or fascicles, which form tertiary bundles constituting the tendon as a whole. The primary, secondary and tertiary bundles are encased in a thin connective tissue reticulum called the endotenon (Elliott, 1965; Kastelic et al., 1978; Rowe, 1985). The endotenon carries blood vessels, nerves and lymphatics to deeper areas of the tendon (Elliott, 1965; Hess et al., 1989). The whole tendon is surrounded by an epitenon, which is a dense fibrillar network of collagen (Jozsa et al., 1991). The epitenon is contiguous with the endotenon and like the endotenon is rich in blood vessels, nerves and lymphatics (Hess et al., 1989). Many tendons are surrounded by a connective tissue called the paratenon. Paratenon allows free movement of the tendon against the surrounding tissues (Schatzker & Branemark, 1969; Hess et al., 1989). The myotendinous junction is the site of union with a muscle, and the osteotendinous junction is the site of union with a bone (Kannus, 2000). In tendon, blood vessels represent between 1-2% of the entire extracellular matrix (Lang, 1960; Lang, 1963). Some blood vessels may originate from the perimysium at the musculotendinous junction and blood vessels from the osteotendinous junction (Schatzker & Branemark, 1969; Carr & Norris, 1989; Clark et al., 2000). At rest, rabbit tendons have been shown to have blood flow of around one-third that of muscle, and it is known that blood flow in tendon increases with exercise and during healing in animals (Backman et al., 1991). The oxygen consumption of tendons is 7.5 times lower than that of skeletal muscles (Vailas et al., 1978).

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