What is Spasticity?
Valerie L. Stevenson, Louise Jarrett in Spasticity Management, 2016
The stiffness of bundles of muscle fibres (including their surrounding connective tissue/extracellular matrix) in people with spasticity is higher than normal.82 As changes in isolated muscle fibre stiffness are not seen, this implies that the greater stiffness is caused by an increase in connective tissue content, the major component of which is collagen. In keeping with this, increased collagen and laminin (also components of the extracellular matrix) have been found in spastic muscles82,91 (Figure 1.15). Collagen is a triple-helical structure that, when aggregated into fibrils, has high tensile strength and limited elasticity. An increase in connective tissue content is therefore probably the main reason for an increase in the passive stiffness of muscle in many people. It is unknown whether there is also a change in the structure of connective tissue; for example, in the number of cross-links between collagen fibrils.
Articular Cartilage
Manoj Ramachandran, Tom Nunn in Basic Orthopaedic Sciences, 2018
Collagen synthesis takes place in stages both within and outside the chondrocyte (see Chapter 8). Polypeptide chains are formed and modified following messenger ribonucleic acid (mRNA) translation within the rough endoplasmic reticulum. The signal peptide is cleaved, lysine and proline residues are hydroxylated and hydroxylysine residues are glycosylated. N-linked sugars are added to the terminal portion, and the modified polypeptide chains form triplehelical molecules. Disulphide bonds between and within the chains define the shape of the molecule. In the Golgi apparatus, the resultant procollagen is packed into secretory granules and released into the extracellular matrix via microtubules. Outside the cell, the terminal ends of procollagen uncoil and are cleaved to form tropocollagen fibrils. These molecules combine via the cross-linkage of lysine and hydroxylysine residues. The resulting fibrils aggregate to form collagen fibres. See Chapter 8 for further structural detail on collagen.
Introduction and Review of Biological Background
Luke R. Bucci in Nutrition Applied to Injury Rehabilitation and Sports Medicine, 2020
The major component, 70 to 90% by weight, of connective tissues is collagen. Collagen is the most abundant protein in the human body, making up about 30% of total proteins. Collagen is 6% of human total body weight. Because of its prevalence and importance, collagen studies have accumulated into many recent reviews. Collagen provides tensile strength and structural rigidity to tissues. Collagen protein is actually a layered buildup of polypeptide chains intertwined and cross-linked in exact manner to form physically large fibrils and fibers. Collagen is a prime example of using the submicroscopic to form macroscopic structures. At least 15 distinct forms of collagen are known,100,103 as listed in Table 2. Types I and III are found primarily in skin, bone, tendons, ligaments, and blood vessel walls, whereas Type II is the predominant collagen in cartilage. Types IV and VII are associated with basement membranes. Types V and VI are associated with cell surfaces and other collagen fibers. Types IX to XII are minor types found in cartilage. Collagen exhibits long half-lives in tissues, ranging from weeks to months to years, depending upon the tissue.
Comparison of Surgically Excised Premacular Membranes in Eyes with Macular Pucker and Proliferative Vitreoretinopathy
Published in Current Eye Research, 2019
Stefanie R. Guenther, Ricarda G. Schumann, Felix Hagenau, Armin Wolf, Siegfried G. Priglinger, Denise Vogt
In eyes with iMP, myofibroblasts were identified as the predominant cell type located in multi-layered cell proliferation (Figure 2C). Myofibroblasts are characterized by their aggregates of 5–7-nm subplasmalemmal cytoplasmatic filaments with fusiform densities, few rough endoplasmatic reticula and long cell fibers with contractile properties. Due to their cell fibers with contractile forces, the ILM was mostly seen folded. Besides, fibroblasts and hyalocytes were found very frequently. Fibroblasts are distinguished by their abundant rough endoplasmatic reticulum, prominent golgi complex and a fusiform shape of the cell body and nucleus. Hyalocytes are identified by their lobulated cell nuclei, intracellular vacuoles, vesicles and mitochondria as well as long cell fibers. Native vitreous collagen was frequently embedded as a continuous layer between the premacular cells and the ILM. It is characterized by a regular arrangement of fibrils with a collagen fibril diameter of less than 16 nm. Newly formed collagen, presented with irregular fibril arrangement and fibril diameter of more than 16 nm, was often seen, too. Fibrous long spacing collagen, identified by a periodicity of approximately 100 nm (Figure 2D), was occasionally documented in eyes with iMP, but exclusively embedded in native vitreous collagen.
Proteomic exploration of cystathionine β-synthase deficiency: implications for the clinic
Published in Expert Review of Proteomics, 2020
Collagen is a major structural protein component of connective tissues (e.g., skin, tendons, bone), which accounts for 25 to 35% of the total protein weight in mammals [93]. Normal function of collagenous fibers depends on inter-chain crosslinks, which stabilize triple helical structures [94]. Crosslinking is initiated by the oxidation of specific lysine and hydroxylysine residues to the aldehydes allysine and hydroxyallysine, respectively. The enzymatic oxidation reactions are catalyzed by lysine oxidase (LOX) [95,96]. Spontaneous chemical reactions between the allysine/hydroxyallysine residues and the ε-amino group of lysine residue afford a Schiff-base adduct, which converts to a stable pyridinoline crosslink [97]. Each triple-helical collagen unit contains one to two crosslinks. The fibril-forming type I, II, and III collagens have four cross-linking sites: one in each of the short non-helical ends, called telopeptides, and two in the triple-helical region, close to the N- and C-terminal ends of collagen molecules. The pyridinoline crosslinks, which occur in collagens of cartilage, bone, and skeletal tissues, provide the stability and tensile strength to collagen fibrils, which is important for the mechanical function of connective tissues [93,94].
Coll2-1 and Coll2-1NO2 as exemplars of collagen extracellular matrix turnover – biomarkers to facilitate the treatment of osteoarthritis?
Published in Expert Review of Molecular Diagnostics, 2019
Ali Mobasheri, Cecile Lambert, Yves Henrotin
Collagens are the most abundant proteins in mammals [13]. They represent one of the best examples of an evolutionarily conserved, structurally related but genetically distinct family of proteins. There are at least 28 types of collagen, but 80–90% of the collagen in the human body consists of structural types I, II, and III. Interestingly, a recent systemic review highlighted that 13 collagens are found in the chondrocyte secretome and that type II collagen is the major one [14]. The fibrillar collagens are the main structural proteins in vertebrates [15]. Fibrillar collagen proteins are abundant in connective tissues including cartilage, intervertebral disk, bone, and tendon [16]. In humans, fibrillar collagen proteins are intimately linked to numerous musculoskeletal diseases, such as osteoporosis, OA, osteogenesis imperfecta and achondroplasia [17,18].