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Fibrogenic Cytokines in Airway Fibrosis
Published in Alastair G. Stewart, AIRWAY WALL REMODELLING in ASTHMA, 2020
Collagens are a family of highly characteristic fibrous proteins sharing a common structure, that is, a rigid triple-stranded helical chain. So far, 11 types of collagen molecules encoded by a group of 20 genes23,24 have been described, each having distinctive structural and metabolic characteristics and different identifiable functions. The predominant are types I, II, III, IV, and V.23,25 Types I, II, and III are the main types of collagen found in connective tissues.23,25,26 Type IV collagen is the main constituent of basement membrane and is thought to be a product of cells resting on it, principally epithelial and endothelial cells.25,26 Type V collagen, the structure of which is still the subject of controversy, is present in laminae and interstitium and smooth muscle.25–27
Eicosanoids and the Uterine Cervix
Published in Murray D. Mitchell, Eicosanoids in Reproduction, 2020
Minamoto et al.6 and Junquiera et al.7 described a reduced concentration of collagen utilizing immunohistochemical and electron-microscopic and polarization techniques (Plate 1*). They found at term that collagen fibers were thinner, more spread out, and disoriented, with a great variation in fiber thickness.7 Minamoto et al.6 also described the presence of type I and lesser amounts of type III collagen, with type IV collagen located only in the basement membrane region. Neither of the histological techniques distinguished between intact and degraded collagen. Measurement of the collagen concentration by hydroxyproline assessment before labor and following delivery has revealed that there is no decrease associated with the process of labor itself, despite continued softening and effacement, increased PG levels, and uterine contractility.3 This result indicates that ground substance changes are important; however, there are methodological limitations in this study as collagen degradation can occur which would not be detected using only hydroxyproline assessment.
The kidneys
Published in C. Simon Herrington, Muir's Textbook of Pathology, 2020
The major genetically determined abnormality of the glomerular basement membrane is Alport's syndrome. This disease usually shows an X-linked pattern of inheritance and is associated with mutation in the type IV collagen genes responsible for encoding the proteins that make up the glomerular basement membrane. Alport's syndrome may present in the first and second decades with proteinuria, haematuria, and progressive renal failure but this may be delayed until later life. Males are often more severely affected than females. The disease is diagnosed by characteristic electron microscopic appearances of the glomerular basement membrane (Figure 14.4), but can also be confirmed by genotyping. It is usually accompanied by high-frequency nerve deafness and sometimes ocular abnormalities.
A Review of Lens Biomechanical Contributions to Presbyopia
Published in Current Eye Research, 2023
The lens capsule plays a critical role in the development of the ocular lens as well as influencing how lens properties change throughout life. Changes to the lens capsule structure can heavily influence lens behavior, especially with regard to accommodation since the lens capsule is the densest and most stiff structure in the ocular lens. It is also the thickest basement membrane in the body.3 Electron microscope analysis revealed that the lens capsule is composed of parallel lamellae which are more tightly packed near the outer surface of the lens. The lamellar structure of the lens capsule appears to disappear with age and the capsule becomes more homogeneous.3 The capsule consists mostly of collagen types I, III, and IV, with collagen IV forming the majority of the basement membrane. Type IV collagen forms a mesh network loosely resembling chicken wire, with crosslinking between the triple helical collagen strands. These cross links are thought to consist largely of 7S domain disulfide cross-link bonds. Collagen IV may also be more flexible than other collagen types like collagen I and II due to having more interruptions between its triple helical segments where crosslinking and molecular binding occurs. Collagen molecules typically interlink through bonding of triple helical domains to form thicker collagen fibrils, and these fibrils can then continue to lace together into thicker rope like fibers or intertwine into a mesh.3
Continuous Curvilinear Capsulorhexis – A Practical Review
Published in Seminars in Ophthalmology, 2022
Several ocular conditions carry predisposition for a more difficult CCC and rhexis runaway due to disturbances in the biomechanical and morphological properties of the lens capsule.41 Intumescent cataracts affect the capsular ultrastructure morphology and advanced cataract can diminish the red reflex, interfering with capsulorhexis.22,41,42 Aniridia is characterized by a thinner and more fragile capsule.41 In patients with Alport syndrome, the defective synthesis of type IV collagen is associated with risk for anterior lenticonus, which is characterized by thinning of the anterior capsular center and capsular fragility.41,43 Increased capsular elasticity with anterior lenticonus is also possible.43 In eyes filled with silicone oil tamponade, the lens capsule might be more rigid.41 In coloboma cataract, the capsular tension is decreased and is sometimes variable secondary to zonular defects.44,45
Enzymatic cross-linking of collagens in organ fibrosis – resolution and assessment
Published in Expert Review of Molecular Diagnostics, 2021
Martin Pehrsson, Joachim Høg Mortensen, Tina Manon-Jensen, Anne-Christine Bay-Jensen, Morten Asser Karsdal, Michael Jonathan Davies
Whereas LHs, LOX(L)s, and TG2 target both fibrillar collagens in the interstitial matrix and basement membrane collagens such as type IV collagen, PXDN is suggested to primarily target type IV collagen. Although the current data on PXDN in organ fibrosis is sparse, studies have linked dysregulated expression of PXDN in pathologies involving fibrotic processes including cancer and organ fibrosis [18,151]. Activation of pulmonary and dermal fibroblasts by transforming growth factor-β1 (TGF-β1) induces extracellular release of PXDN, which was also demonstrated in an in vivo model of renal fibrosis [18]. Furthermore, inhibition of PXDN and eosinophil peroxidase reduced the number of myofibroblasts, and type I collagen content in renal fibrosis [152]. The reduction in type I collagen rather than type IV collagen suggests a reduction in collagen content by processes not directly linked to sulfilimine formation by PXDN. Still, these data suggest a potential involvement of PXDN in fibrosis progression due to its extracellular release by TGF-β1 stimulation of myofibroblast and reduction of α-SMA positive cells following PXDN inhibition. Additionally, knockout of PXDN in mice resulted in a significant reduction in sulfilimine cross-links in the NC1 domain of type IV collagen with a reduction in tissue stiffness [104]. This underlines the ability of PXDN catalyzed cross-linking to influence the stiffness of the BM independent of LOX(L), which could indicate a role for PXDN in cross-linking fibrotic BM.